SIRT1 and cancer

In the past we've had some discussion of the histone deacetylase (HDAC) enzyme SIRT1 and other related sirtuin proteins, especially with respect to their possible relationship with longevity. (See here, for example.)

Much of the focus has been on the HDAC properties of SIRT1 that can switch off various genes. But there have also been findings of more direct relations between SIRT1 and cancer. Some indicate that sirtuins, including SIRT1, may help suppress cancer in certain circumstances, while others suggest it may actually help promote cancer. We'll have to save a general discussion of this relationship for later.

But now we have some research that shows how SIRT1 is directly involved, and has a beneficial effect, in an important pathway that's quite relevant to breast cancer.

The background is that the BRCA1 gene (short for breast-cancer-associated gene 1) is a tumor suppressor gene that, when mutated, may lose its ability to suppress tumors. Defective BRCA1 is sometimes inherited, which helps explain familial tendencies to breast cancer.

So what does BRCA1 normally do to suppress tumors? Well, apparently it maintains expression of SIRT1, which in turn inhibits the expression of another protein, called Survivin. The latter is an inhibitor of programmed cell death (apoptosis), and therefore, when it is active, helps protect cancer cells, which might otherwise be killed by the immune system, chemotherapy, or radiation.

In a nutshell: defective BRCA1 leads to insufficient SIRT1, which leads to an inadequate ability to kill cancer cells.

New Findings May Improve Treatment Of Inherited Breast Cancer (10/9//08)

About 8% of breast cancer cases are caused by mutations in tumor suppressor genes, such as breast cancer associated gene-1 (BRCA1). BRCA1 is the most frequently mutated tumor suppressor gene found in inherited breast cancers and BRCA1 mutation carriers have a 50-80% risk of developing breast cancer by age 70. "Although work with animal models of BRCA1 mutation has provided some insight into the many biological processes linked with BRCA1, very little is known about the downstream mediators of BRCA1 function in tumor suppression," says lead study author Dr. Chu-Xia Deng from the Genetics of Development and Diseases Branch at the National Institutes of Health.

Dr. Deng and colleagues were interested in investigating the relationship among BRCA1, SIRT1 and Survivin. SIRT1 is a protein and histone deacetylase involved in numerous critical cell processes including metabolism, DNA repair and programmed cell death, known as apoptosis. Although SIRT1 has been implicated in tumorigenesis, no concrete role in cancer initiation or progression has been identified. Survivin is an apoptosis inhibitor that is dramatically elevated in many types of tumors. Research has suggested that Survivin may serve to maintain the tumor and promote growth.

The researchers found that BRCA1 functioned as a tumor suppressor by maintaining SIRT1 expression, which in turn inhibited Survivin expression. When BRCA1 was not functioning properly, SIRT levels decreased and Survivin levels increased, allowing BRCA1-deficient cells to overcome apoptosis and undergo malignant transformation.

This leads one to ask whether there are other ways that SIRT1 activation could be maintained when BRCA1 is defective. Fans of resveratrol will observe that this is something that resveratrol can do. And so the researchers gave it a try:

They went on to show that the compound resveratrol strongly inhibited BRCA1-mutant tumor growth in cultured cells and animal models. ... In the current paper, resveratrol enhanced SIRT1 activity, this leading to reduced Survivin expression and subsequent apoptosis of BRCA1 deficient cancer cells.

Ironically, previous research had indicated circumstances in which SIRT1 might promote growth of other types of cancers. It might, for instance, inhibit expression of other tumor-suppressor genes.

Another news account goes into this a little more:

Gene thought to promote tumor growth has opposite role in a kind of breast cancer (10/9/08)

These results were surprising in light of previous reports showing that high levels of SIRT1 enhance growth of other types of tumors. It now appears that SIRT1 can enhance or inhibit tumor growth — it all depends on the context, says Deng. ...

The researchers also found that a red wine chemical called resveratrol, recently touted as a powerful antiaging compound, was effective in combating BRCA1-associated tumor formation specifically.

How resveratrol is able to do this is unclear. “The work in this case is that SIRT1 has an antitumor effect, and this paper provides mechanistic insights into that,” comments Pere Puigserver, a Harvard biologist who studies SIRT1. But the resveratrol data should be taken with caution, he notes. While this new research clearly shows the direct relationship between BRCA1 and SIRT1, the direct link between resveratrol and SIRT1 is more difficult to demonstrate.

Nonetheless, molecular details of BRCA1-related breast cancer are emerging, and this new data places SIRT1 squarely inside the complex web of molecules that impact tumor growth.

One of the main reasons that sirtuins are suspected of having cancer-promoting properties in some circumstances is that they may inhibit the highly important p53 tumor suppressor gene. (P53, when functioning properly, promotes cell apoptosis when DNA defects are detected during cell division.) In just one example of many, here's research from earlier this year that suggests a tumor-promoting property of sirtuins:

Switching on cancer killer gene (5/8/08)

Scottish scientists have discovered how to control a major anti-tumour gene that could lead to more effective chemotherapy. According to a report in the Cancer Cell Journal, research conducted by the Universities of St Andrews and Dundee may eventually lead to the development of new cancer drugs.

The gene, called p53 and known as "the guardian of the genome", is damaged or switched off in most cancers. But the resrchers found that they could reboot it using two new biological compounds called "tenovins".

In a laboratory study, the academics found that these compounds could kick-start p53 by turning off enzymes called sirtuins. Sirtuins act like genetic switches and keep p53 under control, ensuring that the cells stay alive.

Other news accounts of this research: here, here.

Tags: cancer, BRCA1, SIRT1, sirtuin, p53, resveratrol

Resveratrol and cancer

I suppose some readers here may be getting tired of the news flow on resveratrol. The substance may not actually live up to all the hype. But it surely does seem to have quite a variety of beneficial properties. (Most recent previous note is here.) The latest thing resveratrol seems to do is help reduce cancer risk – and a specific mechanism of action has been identified:

Cancer Preventive Properties Identified In Resveratrol, Found In Red Wine, Red Grapes (7/7/08)

Early laboratory research has shown that resveratrol, a common dietary supplement, suppresses the abnormal cell formation that leads to most types of breast cancer, suggesting a potential role for the agent in breast cancer prevention. Resveratrol is a natural substance found in red wine and red grapes. It is sold in extract form as a dietary supplement at most major drug stores.

"Resveratrol has the ability to prevent the first step that occurs when estrogen starts the process that leads to cancer by blocking the formation of the estrogen DNA adducts. We believe that this could stop the whole progression that leads to breast cancer down the road," said Eleanor G. Rogan, Ph.D., a professor in the Eppley Institute for Research in Cancer and Allied Diseases at the University of Nebraska Medical Center.

The reason that estrogen plays a role in breast cancer is that it has a tendency to bind to DNA. (That's what "DNA adduct" refers to.) This binding can damage the DNA, and plausibly may interfere with the expression of genes needed for protection against cancer. Resveratrol seems to interfere with adduct formation:

The formation of breast cancer is a multi-step process which differs depending on type of disease, a patient's genetic makeup and other factors. However, scientists know that many breast cancers are fueled by increased estrogen, which collects and reacts with DNA molecules to form adducts. Rogan and colleagues found that resveratrol was able to suppress the formation of these DNA adducts. ...

Rogan said resveratrol works by inducing an enzyme called quinone reductase, which reduces the estrogen metabolite back to inactive form. By making estrogen inactive, resveratrol decreases the associated risk.

Tags: resveratrol, cancer

Resveratrol is getting rather confusing

Here, have another glass of this great Cabernet...

But hold on about jumping to conclusions. The resveratrol story keeps getting more complicated, according to the most recent research. This is in addition to what we just discussed here.

To begin with, there is additional confirmation that resveratrol does confer health benefits – at least in mice. However – and this is a major qualification – the research did not indicate there was a general extension of longevity in the mice.

Furthermore, the way that the research was announced introduced further confusion. In one press release (from the publisher, Cell Press, of Cell Metabolism) we have:

Red wine ingredient wards off effects of age on heart, bones, eyes and muscle (7/3/08)

Large doses of a red wine ingredient can ward off many of the vagaries of aging in mice who begin taking it at midlife, according to a new report published online on July 3rd in Cell Metabolism, a Cell Press publication. Those health improvements of the chemical known as resveratrol—including cardiovascular benefits, greater motor coordination, reduced cataracts and better bone density—come without necessarily extending the animals' lifespan.

Sinclair and de Cabo's team further show evidence that resveratrol mimics the beneficial effects of eating fewer calories. In mice, they found that resveratrol induces gene activity patterns in multiple tissues that parallel those induced by dietary restriction and every-other-day feeding.

But in another press release, from NIH's National Institute on Aging, we find:

Resveratrol found to improve health, but not longevity in aging mice on standard diet (7/3/08)

Scientists have found that the compound resveratrol slows age-related deterioration and functional decline of mice on a standard diet, but does not increase longevity when started at middle age. This study, conducted and supported in part by the National Institute on Aging (NIA), part of the National Institutes of Health, is a follow-up to 2006 findings that resveratrol improves health and longevity of overweight, aged mice. The report confirms previous results suggesting the compound, found naturally in foods like grapes and nuts, may mimic, in mice, some of the effects of dietary or calorie restriction, the most effective and reproducible way found to date to alleviate age-associated disease in mammals.

The findings, published July 3, 2008, in Cell Metabolism, may increase interest in resveratrol as a possible intervention for age-related declines, said NIA scientists. The authors emphasized, however, that their findings are based on research in mice, not in humans, and have no immediate and direct application to people, whose health is influenced by a variety of factors beyond those which may be represented in the animal models.

Keep in mind, this is all about the same research. Clearly, there are some differences of spin being offered here. The second announcement seems to be closer to what was actually found, as can be seen from the abstract of the actual journal article:

Resveratrol Delays Age-Related Deterioration and Mimics Transcriptional Aspects of Dietary Restriction without Extending Life Span

A small molecule that safely mimics the ability of dietary restriction (DR) to delay age-related diseases in laboratory animals is greatly sought after. We and others have shown that resveratrol mimics effects of DR in lower organisms. In mice, we find that resveratrol induces gene expression patterns in multiple tissues that parallel those induced by DR and every-other-day feeding. Moreover, resveratrol-fed elderly mice show a marked reduction in signs of aging, including reduced albuminuria, decreased inflammation, and apoptosis in the vascular endothelium, increased aortic elasticity, greater motor coordination, reduced cataract formation, and preserved bone mineral density. However, mice fed a standard diet did not live longer when treated with resveratrol beginning at 12 months of age. Our findings indicate that resveratrol treatment has a range of beneficial effects in mice but does not increase the longevity of ad libitum-fed animals when started midlife.

(Aside: in discussions like this you will often see the terms "longevity" and "lifespan" used almost interchangably. Properly speaking, "longevity" is usually the better term, as it refers to average length of life, a statistical property, while "lifespan" refers to maximum potential length of life. For the most part, the distinction can be glossed over, though it isn't entirely unimportant.)

Confused yet? Let me try to boil this down a little. This is just my interpretation, but the conclusions I see are these:

1. Resveratrol fed to middle-aged mice can have health benefits, such as cardiovascular benefits, greater motor coordination, reduced cataracts and better bone density.
   
2. The health benefits and gene transcriptional changes resulting from resveratrol in the diet are similar to, though not quite the same as, those resulting from calorie restriction alone.
   
3. Resveratrol in the diet did not increase longevity of mice on normal diets, even though calorie restriction by itself has been shown to increase longevity (in mice), while resveratrol does increase longevity of mice on high-calorie diets.
   
4. In mice on high-calorie diets where resveratrol increased both health factors and longevity, the improvement occurred without decreasing actual body weight.
   
5. This research on mice may not be predictive of the effects that might be seen in similar experiments (which have not yet been done) on humans.
   

Putting this even more succinctly, in mice adding resveratrol to the diet slows down some undesirable side-effects of aging, but does not appear to actually increase longevity, whereas calorie restriction does slow aging and increase longevity somewhat. All bets are still off as to what effects resveratrol may have in humans.

How could it be that resveratrol had all these health benefits, but didn't increase longevity? The logical conclusion would be that resveratrol has little effect on conditions that usually cause mice to die. In particular, mice usually die of cancer, and resveratrol doesn't have much benefit in that regard, though calorie restriction does.

There might actually be good news for humans in this – if resveratrol did benefit cardiovascular health in humans, that would be great, since cardiovascular disease is the largest cause of human mortality. (Cancer's a big cause too, just not as big.)

In spite of the ambiguities, this is a very significant piece of research, in part because of the large team of experienced scientists – such as David Sinclair – who participated. Here are some additional news reports on the research:

• Resveratrol helps hearts in mice, but doesn’t reproduce all the benefits of low-calorie diets (7/3/08)
  
• Wine chemical improves health but not longevity (7/3/08)
  
• Fountain of youth? Red wine gives up secrets (7/3/08)
  

But wait. We're not done yet. There are additional complications, as some of these other reports point out. For one thing, it isn't at all clear how resveratrol is beneficial at a molecular level. (And it's just as unclear why calorie restriction is beneficial – which might be different in some ways from the reasons applicable to resveratrol.) It is known that resveratrol has antioxidant and anti-inflammatory properties. Both of those are positives.

However, resveratrol also seems to activate the sirtuin protein Sirt1. There's quite a bit of research – in model organisms like nematodes, yeast, fruit flies, and rodents – that shows sirtuins have beneficial properties of their own. In particular, sirtuins do increase longevity, as does calorie restriction, in the model organisms, even if the molecular mechanisms aren't quite the same. (This is more evidence that the beneficial effects of resveratrol are not largely due to sirtuin activation.)

Regarding Sirt1 specifically, there have been at least two other recent research results published. The results are mixed. In some ways Sirt1 is shown to be beneficial, while in at least one way, it may be harmful. To the extent that resveratrol does serve to activate Sirt1, is may have the same helpful or harmful properties.

Here's the bad news, first:

Life-extending Protein Can Also Have Damaging Effects On Brain Cells (7/1/08)

Proteins widely believed to protect against aging can actually cause oxidative damage in mammalian brain cells, according to a new report in the July Cell Metabolism, a publication of Cell Press. The findings suggest that the proteins can have both proaging and protective functions, depending on the circumstances, the researchers said.

"Sirtuins are very important proteins," said Valter Longo of the University of Southern California, Los Angeles. "Overexpression can protect in some cases, and in other cases, it may do the opposite. It has to do with the fact that they do so many things." ...

SirT1, the mammalian version of yeast Sir2, controls numerous physiological processes including glucose metabolism, DNA repair, and cell death, the researchers added. In mammalian cells, SirT1 also controls several stress-response factors.

Now, the researchers show that cultured rat neurons treated with a SirT1 inhibitor more often survived treatment with oxidative stress-inducing chemicals. They further show evidence to explain the mechanism responsible for that effect.

They also found lower oxidative stress levels in the brains of mice without SirT1. However, those SirT1 knockout mice didn't live as long as normal mice do on either a normal or a calorie-restricted diet.

In brief: lowering Sirt1 levels helps cells withstand oxidative stress, while higher levels make cells more vulnerable to oxidative stress. Nevertheless, mice without Sirt1 at all live shorter lives. Confusing, no?

This research, which was published in the same issue of Cell Metabolism as the de Cabo-Sinclair study, went on to investigate in more detail what Sirt1 inhibition was doing. Here's the research abstract to explain:

SirT1 Inhibition Reduces IGF-I/IRS-2/Ras/ERK1/2 Signaling and Protects Neurons

Sirtuins are known to protect cells and extend life span, but our previous studies indicated that S. cerevisiae Sir2 can also increase stress sensitivity and limit life-span extension. Here we provide evidence for a role of the mammalian Sir2 ortholog SirT1 in the sensitization of neurons to oxidative damage. SirT1 inhibition increased acetylation and decreased phosphorylation of IRS-2; it also reduced activation of the Ras/ERK1/2 pathway, suggesting that SirT1 may enhance IGF-I signaling in part by deacetylating IRS-2. Either the inhibition of SirT1 or of Ras/ERK1/2 was associated with resistance to oxidative damage. Markers of oxidized proteins and lipids were reduced in the brain of old SirT1-deficient mice, but the life span of the homozygote knockout mice was reduced under both normal and calorie-restricted conditions. These results are consistent with findings in S. cerevisiae and other model systems, suggesting that mammalian sirtuins can play both protective and proaging roles.

(Technical aside: Note, in particular, the conjectured effect of Sirt1 on IGF-1 signaling. Sirt1 promotes phosphorylation of IRS2, the "Insulin receptor substrate 2", which enhances IGF-1 signaling, and this makes cells more vulnerable to oxidative stress. Conversely, inhibition of Sirt1 reduces cell vulnerability. (We discussed many properties of IGF-1, including relations to calorie restriction and longevity, here.))

As you recall, Sirt1 is what's called a histone deacetylase (HDAC) enzyme. (Some discussion here.) As such, one of the main properties of Sirt1 is that it can silence a bunch of genes at the same time, by removing acetyl groups from the histones to which the genes are normally bound. Clearly, that is why Sirt1 affects many diverse processes, and why it can be risky to mess with.

That's the cautionary news on Sirt1. But again on the positive side of the ledger for Sirt1 (and hence perhaps resveratrol also), there is one more study that did not receive as much media attention. The study, was published July 3 in the Proceedings of the National Academy of Sciences. Its authors included Matthias Tschöp and Paul Pfluger.

Here's the abstract (via BioInfoBank):

Sirt1 protects against high-fat diet-induced metabolic damage

Here, we report that mice with moderate overexpression of Sirt1 under the control of its natural promoter exhibit fat mass gain similar to wild-type controls when exposed to a high-fat diet. Higher energy expenditure appears to be compensated by a parallel increase in food intake. Interestingly, transgenic Sirt1 mice under a high-fat diet show lower lipid-induced inflammation along with better glucose tolerance, and are almost entirely protected from hepatic steatosis. We present data indicating that such beneficial effects of Sirt1 are due to at least two mechanisms: induction of antioxidant proteins MnSOD and Nrf1, possibly via stimulation of PGC1-α, and lower activation of proinflammatory cytokines, such as TNF-α and IL-6, via down-modulation of NF-κB activity. Together, these results provide direct proof of the protective potential of Sirt1 against the metabolic consequences of chronic exposure to a high-fat diet.

From this news story already mentioned, here's a little more explanation:

Increasing levels of the mouse sirtuin, SirT1, prevents mice from developing heart problems and fatty livers even when they are fed high-fat diets, researchers at the University of Cincinnati College of Medicine and the Spanish National Cancer Research Center in Madrid reported June 30 in Proceedings of the National Academy of Sciences. These mice with higher levels of SirT1 eat more but also burn more calories than do mice with normal levels of the enzyme.

If you haven't had enough punishment yet, here's a more detailed report on all the research already discussed, and a bit more:

SIRT1, Resveratrol and More: Moving Closer to Anti-aging Elixir? (7/8/08)

One of the additional bits is this:

Working independently and publishing 4 June in PLoS ONE, researchers led by Tomas Prolla at the University of Wisconsin, Madison, report similar results in their microarray analysis comparing transcription profiles induced by CR and resveratrol. First author Jamie Barger and colleagues fed mice from middle age (14 months) to old age (30 months) a control diet, CR diet, or resveratrol-supplemented control diet. The researchers report a “striking transcriptional overlap” of CR and resveratrol (99.7 percent of gene expression changes correlating by direction) in heart, skeletal muscle, and brain (neocortex), and show that both regimens prevent age-related cardiac problems.

And here's the journal article, in full, being referred to:

A Low Dose of Dietary Resveratrol Partially Mimics Caloric Restriction and Retards Aging Parameters in Mice (6/4/08) - also here

Resveratrol in high doses has been shown to extend lifespan in some studies in invertebrates and to prevent early mortality in mice fed a high-fat diet. We fed mice from middle age (14-months) to old age (30-months) either a control diet, a low dose of resveratrol (4.9 mg kg⁻¹ day⁻¹), or a calorie restricted (CR) diet and examined genome-wide transcriptional profiles. We report a striking transcriptional overlap of CR and resveratrol in heart, skeletal muscle and brain. Both dietary interventions inhibit gene expression profiles associated with cardiac and skeletal muscle aging, and prevent age-related cardiac dysfunction. Dietary resveratrol also mimics the effects of CR in insulin mediated glucose uptake in muscle. Gene expression profiling suggests that both CR and resveratrol may retard some aspects of aging through alterations in chromatin structure and transcription. Resveratrol, at doses that can be readily achieved in humans, fulfills the definition of a dietary compound that mimics some aspects of CR.

If that sounds a bit familiar, it's because not only does it parallel the research reported by Sinclair and de Cabo discussed above, but in fact we're already written about it here, as it was described in this press release.

To summarize this whole thing, resveratrol has benefits for both general health and longevity. The benefits are similar to, but not quite the same as, those of either sirtuins or calorie restriction. Further, sirtuins, and hence resveratrol, may also have detrimental side effects. A lot more research, which must eventually include human studies, is needed.

There have also been a couple of other recent reports on completely different possible mechanisms to explain the benefits of calorie restriction, but we'll save those for another time.

Additional reading:

The Ongoing Saga of Sirtuins and Aging – overview in Cell Metabolism of the research by Li, et al (sub rqd)

Tags: resveratrol, sirtuins, aging, longevity, calorie restriction, biogerontology

More resveratrol hoopla

Resveratrol is in the news. Again.

My last major note about resveratrol is here, way back last September. How time flies. I also mentioned it more briefly here, in May, in connection with cancer. (Where its effect may involve facilitating apoptosis of tumor cells.)

But resveratrol's now back in the news again, so I guess it's time for an update.

As you recall, resveratrol seems to have a number of properties that confer health benefits. For example, it is thought to be an antioxidant, an anti-inflammatory, and perhaps to activate sirtuin enzymes, which may help produce an effect similar to calorie restriction.

The big question is whether you can get the benefits from the amount of the stuff you can get in a dose of reasonable size, for a reasonable price, and without having to drink gallons of wine per day (not a great idea).

Now we have recent reports of two more research results dealing with resveratrol. One suggests a benefit in countering obesity, and the other concerns anti-aging properties that mimic calorie restriction.

Here's the finding on obesity, the relation to which of resveratrol I cannot recall having heard bandied about before:

Red Wine's Resveratrol May Help Battle Obesity (6/16/08)

Resveratrol, a compound present in grapes and red wine, reduces the number of fat cells and may one day be used to treat or prevent obesity, according to a new study.

Past research found that resveratrol protected laboratory mice that were fed a high-calorie diet from the health problems of obesity, by mimicking the effects of calorie restriction. Researchers at the University of Ulm in Germany wanted to know if resveratrol could mimic the effects of calorie restriction in human fat cells by changing their size or function. The German team used a strain of human fat cell precursors, called preadipocytes. In the body, these cells develop into mature fat cells. ...

In the cell-based study, they found that resveratrol inhibited the pre-fat cells from increasing and prevented them from converting into mature fat cells. Also, resveratrol hindered fat storage.

One would certainly expect effects like that, if they can be reproduced in living humans, to be helpful in countering obesity. But there were two other beneficial effects as well:

[R]esveratrol reduced production of certain cytokines (interleukins 6 and 8), substances that may be linked to the development of obesity-related disorders, such as diabetes and clogged coronary arteries. Also, resveratrol stimulated formation of a protein known to decrease the risk of heart attack. Obesity decreases this substance, called adiponectin.

We've discussed both of these subjects before: IL-6 and inflammation were discussed here, while adiponectin was discussed here and here.

But the intriguing connections don't even stop there. Another report on the same research suggests that the effects related to fat cells may be mediated through sirtuin proteins:

Red wine component resveratrol might fight obesity, lab tests show (6/16/08)

Resveratrol’s mechanism of action is not entirely clear, but the compound seems to activate at least one member of a family of proteins called sirtuins. While also poorly understood, some sirtuins show up in fat cells.

Previous work showed that low levels of sirtuins allowed fat cells to add fats and to proliferate freely from nascent to mature stages, a recipe for weight gain. Conversely, that work also showed that an increase in sirtuins — in that case the compound Sirt2 — kept stem cells from maturing into full-fledged fat cells and inhibited mature fat cells from filling with fats.

In the new study, resveratrol’s good effects failed to emerge in either nascent or mature fat cells engineered to lack a sirtuin called Sirt1, Wabitsch said.

As potential therapeutics, “the sirtuins are a new class in the armamentarium of diabetes and pre-diabetes management,” says Henry Anhalt, a pediatric endocrinologist at Animas Corp. in West Chester, Pa., who wasn’t involved in this study. Sirtuins seem to curb the risk of obesity, cardiovascular disease and inflammation, all of which have been correlated with development of diabetes and its complications. The finding that resveratrol seems to work through a sirtuin (Sirt1) opens up new research opportunities, he says.

As previously noted, I've had a lot to say about sirtuins, which you can refer to here.

The second recent study, which appeared about two weeks before the one just discussed, involved experiments with mice that explicitly compared the effects of resveratrol and calorie restriction:

Substance In Red Wine, Resveratrol, Found To Keep Hearts Young (6/4/08)

[T]he researchers report that low doses of resveratrol in the diet of middle-aged mice has a widespread influence on the genetic levers of aging and may confer special protection on the heart.

Specifically, the researchers found that low doses of resveratrol mimic the effects of what is known as caloric restriction - diets with 20-30 percent fewer calories than a typical diet - that in numerous studies has been shown to extend lifespan and blunt the effects of aging.

This research sharpens results that have previously been found, and also shows that the required dose of resveratrol may not be unreasonable:

Previous research has shown that resveratrol in high doses extends lifespan in invertebrates and prevents early mortality in mice given a high-fat diet. The new study, conducted by researchers from academia and industry, extends those findings, showing that resveratrol in low doses and beginning in middle age can elicit many of the same benefits as a reduced-calorie diet.

"Resveratrol is active in much lower doses than previously thought and mimics a significant fraction of the profile of caloric restriction at the gene expression level," says Tomas Prolla, a UW-Madison professor of genetics and a senior author of the new report.

Another way this research differs from earlier work is that it looks specifically at the expression of genes known to be affected by aging in several important tissue types:

The group explored the influence of the agent on heart, muscle and brain by looking for changes in gene expression in those tissues. As animals age, gene expression in the different tissues of the body changes as genes are switched on and off.

In the new study - which compared the genetic crosstalk of animals on a restricted diet with those fed small doses of resveratrol - the similarities were remarkable, explains lead author Jamie Barger of Madison-based LifeGen Technologies. In the heart, for example, there are at least 1,029 genes whose functions change with age, and the organ's function is known to diminish with age. In animals on a restricted diet, 90 percent of those heart genes experienced altered gene expression profiles, while low doses of resveratrol thwarted age-related change in 92 percent. The new findings, say the study's authors, were associated with prevention of the decline in heart function associated with aging.

Another report stresses the overlap between the effects of calorie restriction and of resveratrol:

Red wine compound seen protecting heart from aging (6/4/08)

Using a method that permits simultaneous analysis of thousands of genes at the same time, the researchers found a huge overlap in the genes whose activity were changed by resveratrol and caloric restriction.

They looked at the heart, brain and muscles, and said that the effect of resveratrol was strongest in the heart but did prevent some aging-related changes in the other tissues.

A similar news release on this research mentions an upcoming Phase I human clinical trial that will study the effects of resveratrol on older humans:

Substance in red wine found to keep hearts young (6/5/08)

Resveratrol is currently sold over-the-counter as a nutritional supplement with supposed anti-cancer, anti-viral, anti-inflammatory and anti-aging benefits, although few scientific studies have verified these claims in humans. That may soon change: Researchers at the University of Florida hope to explore the effects of resveratrol on older people in a phase 1 clinical trial, set to begin this summer.

The study will assess the supplement's effects on memory, physical performance, inflammation and oxidative damage.

It also calls attention to the possible longevity-promoting effects of resveratrol on the mitochondria of cells:

Mitochondria, the tiny power plants that keep a cell functioning, are especially vulnerable to the oxidative damage that accumulates during the aging process.

"In animal studies, (resveratrol) seems to promote mitochondrial health," said Todd Manini, also a principal investigator of the upcoming trial and an assistant professor of aging and geriatrics in the UF College of Medicine. "Mitochondria are everywhere: They're in the brain, in the muscle, the liver. So it could have kind of a global impact on many different organ systems."

New York Times science writer Nicholas Wade (who, in earlier articles, had questioned the necessary dosage of resveratrol, see here) has a cautionary article that puts this research into context of other work on resveratrol and sirtuins. Among other points, he notes that there is still plenty of room to question whether resveratrol, or something similar, will actually have health benefits in humans, for example:

New Hints Seen That Red Wine May Slow Aging (6/4/08)

Dr. Auwerx, who used doses almost 100 times greater in his treadmill experiments, expressed reservations about the new result. “I would be really cautious, as we never saw significant effects with such low amounts,” he said Tuesday in an e-mail message.

Another researcher in the sirtuin field, Dr. Matthew Kaeberlein of the University of Washington in Seattle, said, “There’s no way of knowing from this data, or from the prior work, if something similar would happen in humans at either low or high doses.”

More news reports about this:

• Red Wine Compound Helps Heart, May Slow Aging (6/5/08)
  
• Study boosts wine chemical hopes (6/4/08)
  

Update, 7/16/08: There's more recent news about resveratrol here.

Further reading:

A Low Dose of Dietary Resveratrol Partially Mimics Caloric Restriction and Retards Aging Parameters in Mice – abstract and complete technical article describing the mouse study

Low-dose resveratrol as a calorie restriction mimetic – 6/12/08 blog post with further comments on the mouse study and associated issues

Tags: resveratrol, sirtuins, aging, longevity, calorie restriction

Resveratrol and cancer

Resveratrol is not a very new story these days. (For some earlier news, see here.) It is primarily known as an anti-oxidant and activator of sirtuins, but it has also been found to have specific anti-cancer properties, at least for pancreatic cancer:

Mounting Evidence Shows Red Wine Antioxidant Kills Cancer (3/25/08)

Rochester researchers showed for the first time that a natural antioxidant found in grape skins and red wine can help destroy pancreatic cancer cells by reaching to the cell's core energy source, or mitochondria, and crippling its function.

The new study also showed that when the pancreatic cancer cells were doubly assaulted -- pre-treated with the antioxidant, resveratrol, and irradiated -- the combination induced a type of cell death called apoptosis, an important goal of cancer therapy.

The fact that resveratrol has effects on the mitochondria of cancer cells is particularly interesting, since mitochondria are known to play an important role in apoptosis. One of the main ways cancer therapies such as radiation and chemotherapy kill cancer cells is by inducing apoptosis. However, advanced cancers develop ways of evading apoptosis. (See here.) If resveratrol independently interferes with the function of the mitochondria in cancer cells, that would be helpful.

In fact, the research indicated several relevant effects of resveratrol:

Laboratory experiments showed that resveratrol:

• Reduced the function of proteins in the pancreatic cancer cell membranes that are responsible for pumping chemotherapy out of the cell, making the cells chemo-sensitive.
• Triggered the production of reactive oxygen species (ROS), which are substances circulating in the human body that have been implicated in a number of diseases: when ROS is increased, cells burn out and die.
• Caused apoptosis, which is likely the result of increased ROS.
• Depolarized the mitochondrial membranes, which indicates a decrease in the cell's potential to function. Radiation alone does not injure the mitochondrial membrane as much.

More: Red wine compound may kill pancreatic cancer cells (4/14/08)

In related news, it may be worth noting that the biotech company called Sirtris, which has been developing enhanced therapeutic forms of resveratrol, recently entered into an agreement to be acquired by the pharmaceutical company GlaxoSmithKline. (See here, here, here.) This shows that the therapeutic potential of resveratrol, and other sirtuins – at least at this early stage – looks promising.


Tags: resveratrol, sirtuins, cancer

Wnt signaling

We've discussed Wnt signaling a couple of times before, here, and here.

Wnt refers to a family of proteins now numbering perhaps 20 or more, which have been found in a wide range of multicellular animals, from fruit flies, to fish, to mice and humans. Wnt proteins carry messages between cells, and are especially important in embryogenesis. They are known to play a large role in the control of stem cells and regeneration of body parts (in species where this occurs). In mammals, including humans, Wnt signaling, when it malfunctions, also seems to be involved in many types of cancer, degenerative diseases of aging, and other aging-related problems such as insulin resistance. It may be possible to ameliorate a number of these disease conditions once we have a better understanding of the details of Wnt signaling.

The "Wnt signaling pathway" refers to a sequence of proteins that, in the presence of earlier members of the pathway, change in behavior to affect proteins later in the pathway. The pathway begin when a Wnt protein (secreted by a nearby cell) binds to a cell surface protein, such as the whimsically-named Frizzled. Various other proteins in the pathway then interact, and eventually result in the build-up of a protein called β-catenin, which enters the cell nucleus, where it combines with various transcription factors to affect gene expression.

The name "Wnt" originates from the realization that two genes discovered earlier were homologous – the "wingless" gene in fruit flies (which, when mutated, yields flies without wings), and the Int genes found in mouse tumors.

Although Wnt genes and proteins have now been studied for nearly 20 years, the pace of discovery continues to increase. This is because of the large number of very interesting processes heavily influenced by Wnt signaling – from proliferation and differentiation of stem cells to embryonic development, regeneration of body parts, cancer, and degenerative diseases of aging.

The following summaries of research reports from just the past half year or so will give a buffet-style sample of Wnt-related investigations.

Carbohydrate Regulates Stem Cell Potency (2/1/08)

Embryonic stem cells are characterized by an ability to continually self-renew, but also to give rise to any adult cell type. Stem cell renewal is driven by several external signaling proteins and growth factors, including Wnt, FGF (fibroblast growth factor), and BMP (bone morphogenetic protein). In particular, Wnt signaling stimulates β-catenin to produce the transcription factor Nanog, which maintains pluripotency. However, the ability of these proteins to attach to stem cell surface proteins in order to induce a response seems to depend on the presence of a carbohydrate molecule called heparan sulfate (HS). Stem cells were found to reproduce less frequently but differentiate more frequently in proportion to experimental inhibition of HS production.

Beta-catenin Gradient Linked To Process Of Somite Formation (12/27/07)

In a developing vertebrate embryo somites are masses of a type of tissue (mesoderm) that will eventually develop into such adult tissue types as skeletal muscle and vertebrae. This research on mouse embryos demonstrates the importance of β-catenin as the principal mediator of the Wnt-signaling pathway, in the process of somite formation. In particular, there is a gradient in levels of β-catenin found in cells of the presomitic mesoderm (PSM), and this gradient is critical in regulating mesoderm maturation. This leads to the development of the characteristic vertebral column in embryos of vertebrate animals.

Certain Diseases, Birth Defects May Be Linked To Failure Of Protein Recycling System (12/20/07)

The Wnt signaling protein, like other proteins, is produced in the nuclei of certain cells, and it must be transported to the cell surface, so it can be secreted into the extracellular environment to regulate the growth of tissues during (and after) embryonic development. Another protein, called Wntless (Wls), acts as a cargo container for Wnt, and plays a key role in the transport process. Another protein, called Vps35, which makes up an important part of the "retromer complex", is responsible for moving empty Wls molecules (like freight cars) to where they are needed in the cell. But mutated Vps35 proteins can fail to perform their function, and consequently lead to the failure to transport Wnt out of the cell where it has been produced.

Grape Powder Blocks Genes Linked To Colon Cancer (11/14/07)

Previous research has found that the Wnt signaling pathway is linked to more than 85 percent of sporadic (i. e. not caused by a hereditary defect) colon cancers. Additionally, in vitro studies have shown that resveratrol is capable of blocking the Wnt pathway. The present research showed that in some colon cancer patients who consumed grape powder (which contains resveratrol and possibly other active ingredients), Wnt signaling in biopsied colon tissue was significantly reduced.

Odd protein interaction guides development of olfactory system (10/29/07)

The olfactory system of fruit flies has been shown to develop abnormally when the signaling protein Wnt5 is absent. However, if large amounts of Wnt5 but no Wnt5 receptors called "derailed" are present, development is even more abnormal. Specifically, structures called glomeruli in fruit fly antennal lobes (which are analogous to human olfactory bulbs) grow abnormally when Wnt5 is absent. But if Wnt5 is present in large amounts and there are no derailed receptors, malformed glomeruli develop in locations where they should not be.

Cilia: Small Organelles, Big Decisions (10/3/07)

Research into the development of zebra fish (a favorite of developmental biologists) has shown that organelles called cilia in the cells of developing embryos play a large role in the transduction of Wnt signaling proteins that guide the development process. By blocking the production of three proteins used by cilia, researchers were able to disrupt proper balances in the interpretation of Wnt signals, resulting in developmental defects.

New Insights into the Control of Stem Cells: Keeping the Right Balance (9/15/07)

The Wnt signaling pathway plays a crucial role in embryonic development, cell growth (proliferation), and maturation of cells into specialized cells (differentiation). It is also an important regulator of stem cells. An interaction between Wnt signaling and tyrosine kinases enables the proliferating cells to mature into specialized (differentiated) cells. Normally this interaction strikes a proper balance between proliferation and differentiation. Cancers, such as breast and colon cancer, result when the interaction gets unbalanced. In 90% of human cancers the tumor suppressor APC (adenomatous polypolis coli), one of the core components of the Wnt pathway, is deregulated. This results in excessive amounts of β-catenin, which triggers the onset of breast and colon cancer when it gets into the cell nucleus and affects gene expression.

Reactivating A Critical Gene Lost In Kidney Cancer Reduces Tumor Growth (8/15/07)

Studies of an important tumor-suppressor protein, sFRP-1 (secreted frizzled-related protein 1), in clear cell renal cell carcinoma, the most common type of kidney cancer, may reveal a means to defeat the cancer. sFRP-1 was found to control 13 tumor-promoting genes along the Wnt signaling pathway, which has been linked to a number of cancers, especially colon cancer. Several close relatives of sFRP-1 are also known to affect at least 20 Wnt-related proteins, and up-regulation of members of the sFRP-1 family may be an effective way to control cancers linked to Wnt signaling. In one experiment, increasing sFRP-1 expression in human renal cancer cells was effective, and Wnt regulated oncogenes, such as c-myc, were suppressed compared to untreated cells.

Why Aging Muscles Heal Poorly (8/9/07)

Stem cells normally found in muscle tissue are responsible for repair to muscles damaged by injury or age-related degeneration. But in aged muscle tissue, stem cells tend to produce scar-tissue cells called fibroblasts, instead of normal muscle cells (myoblasts). The overproduction of fibroblasts is a condition known as fibrosis. New research shows that it isn't the age of the muscle stem cells that is the problem, but rather the age of the cellular environment itself, including blood supply to the tissue. The malfunction appears to be a problem with Wnt signaling in the aged environment rather than with the actual stem cells. Muscle stem cells from young mice exhibited the same problems when exposed to an enviroment from older animals.

Related research found that Wnt signaling increased, with detrimental effect, due to age-related deficiency of a hormone called klotho. Klotho seems to inhibit Wnt signaling, and also has some control over insulin sensitivity. However, production of klotho seems to decline with age, possibly leading to age-related problems such as cancer, arterial disease, and insulin resistance.

Not A Relay Race, But A Team Game: New Model For Signal Transduction In Cells (6/27/07)

Details of the inner workings of the Wnt signal transduction process have remained incomplete, but are gradually coming into focus. Member of the Wnt family of proteins may dock with a variety of cell-surface proteins, including LRP6 (low density lipoprotein receptor-related protein 6) and members of the family of G protein-coupled receptors known as Frizzled. After the docking, a signaling cascade is triggered that transmits molecular messages via the cytoplasm to the nucleus. This research shows that the first step after docking involves large protein complexes formed from proteins already known to be part of the signaling pathway, such as phosphorylated LRP6, axin, and Dishevelled (Dvl).

Further reading:

The Wnt Homepage

Regeneration for Repair's Sake

The answer is blowing in the Wnt

Miller on Wnt and Klotho

A hazy shade of Wnt

Tags: Wnt, embryogenesis, stem cells, signal transduction, cancer, developmental biology, aging

Sirtuin news

Back in November we had a series of posts about sirtuin proteins. This included an overview, with a particular focus on the relevance to calorie restriction and longevity, especially in light of recent research announcements at the time. This was followed by a couple of posts (here, here) on background history.

Now is a good time to return to that thread and continue the discussion of sirtuins, because of additional related research announcements, including especially this:

Sirtris Announces Positive Results with Proprietary Version of Resveratrol, SRT501, in a Phase 1b Type 2 Diabetes Clinical Study (1/7/08)

Sirtris Pharmaceuticals, Inc. ... announced today that the Company's first product to enter the clinic, SRT501, was found to be safe and well-tolerated, and was found to significantly lower glucose in an oral glucose tolerance test conducted as part of a 28 day Phase 1b clinical study in patients with Type 2 Diabetes.

This 28-day Phase 1b study was designed to assess the safety, tolerability and pharmacokinetics of once-daily, orally administered doses of either 2.5 g or 5 g of SRT501 in patients with Type 2 Diabetes who were naive to other diabetes drug treatments. Both doses of SRT501 were found to be safe and well-tolerated, and pharmacokinetics, a measure of drug levels in the blood, were identical at days one and 28, suggesting no drug accumulation. There were no serious adverse events and no dose-related adverse events. Importantly, SRT501 showed a statistically significant improvement in an oral glucose tolerance test on day 28 at two hours and a trend towards lower fasting plasma glucose levels.

SRT501 is also being tested in patients with Type 2 Diabetes in a Phase 1b BID (twice daily administration) study and in a Phase 2a study in combination with metformin, the current first-line therapy for Type 2 Diabetes. SIRT1 is the founding member of the human sirtuin family of enzymes which control the aging process. Specifically, SRT501 acts by increasing mitochondrial activity and therefore is targeted to address metabolic diseases, such as Type 2 Diabetes.

"This is the first time that a small molecule targeting sirtuins, the genes which control the aging process, has shown efficacy in a disease of aging," said Peter Elliott, Ph.D., Senior Vice President of Development at Sirtris.

OK, this is obviously a self-promotional PR piece from the drug developer. In particular, sirtuins aren't "the genes which control the aging process", merely some of them. However, if the claims hold up under further testing, especially the one stated in the last paragraph, this is an important validation of much prior research into the effect of sirtuins on longevity as a result of action in various cellular pathways. Our previous discussions reviewed some of this research conducted on model organisms like yeast and the nematode C. elegans.

More information: Resveratrol-like drug works in humans-Sirtris (1/7/08), Sirtris Anti-Aging Drug Generates Buzz, But May Already Be Old News (1/8/08)

This drug, SRT501, has been in human clinical trials for about a year and a half already. The initial trial (called "Phase 1") involved 85 healthy volunteers and began in June 2006 (see here). Results from that trial were reported in October 2006 (see here) and demonstrated that the drug was reasonably safe and well-tolerated.

SRT501 is a small molecule drug that achieves its effects by activating the mammalian SIRT1 NAD-dependent deacetylase enzyme, which has been investigated extensively for a decade (as discussed here). The drug is essentially just a proprietary formulation of resveratrol, the well-known component of red wine that has been shown to have lifespan-extending and anti-diabetes properties in several model organisms. (See here for an extended discussion, including reports of important research announced in late 2006.) SRT501, however, is a much more practical way to take advantage of resveratrol, compared to consumption of red wine, where hundreds or thousands of bottles of wine would be needed to achieve the same effect.

Perhaps the most important result shown by this newly reported result is that SRT501 actually seems to provide measurable beneficial effects of improved glucose tolerance and reduced blood glucose levels for humans with diabetes.

SIRT1 activators which are apparently much more powerful than SRT501 are under active investigation at Sirtris and in the laboratory of Sirtris co-founder David Sinclair. This has been documented in research that was published last November:

Sirtris unveils promising, novel SIRT1 activators for treating diseases of aging (11/28/07)

In November 2006, Sirtris scientists and Sirtris co-founder, Prof. David Sinclair from Harvard Medical School, published consecutive papers in the journals Cell and Nature showing that resveratrol, a SIRT1 activator found in red wine, could reduce the impact of a high fat diet, increase stamina two fold and significantly extend lifespan of mice. Unfortunately, it was estimated that a person would need to drink 1000 bottles of red wine to obtain an equivalent dose of resveratrol. Now, scientists at Sirtris have developed SIRT1 activating molecules that are chemically distinct from resveratrol and are 1000 times more potent.

"The new drug candidates represent a significant milestone because they are the first molecules that have been designed to act on genes that control the aging process. For this reason, we feel they have considerable potential to treat diseases of aging such as Type 2 Diabetes," said Christoph Westphal, M.D., Ph.D., Chief Executive Officer and Vice Chair of Sirtris Pharmaceuticals. "The breakthrough in potency we have achieved with the novel chemical entities (NCEs) means that we can obtain the health benefits of resveratrol with a considerably lower dose."

Here's a useful professional assessment of these results: Sirtuin activators as anti-diabetes drugs, and beyond (11/29/07) More: Sirtris Drug May Slow Aging, Create 'Armstrong' Cells (11/28/07)

Additional information:

Gene Believed To Promote Long Life Linked To Cholesterol Flushing (10/12/07)

Research conducted in part by sirtuin-research pioneer Leonard Guarente has established one mechanism through which SIRT1 provides health and longevity benefits. The mechanism promotes flushing harmful buildups of cholesterol in macrophage cells of the immune systems of mice. This mechanism could explain part of the health benefits of SIRT1-activators such as resveratrol and calorie restriction.

Red Wine Ingredient -- Resveratrol -- Fights Diabetes In Mice (10/4/07)

Chinese researchers have reported that relatively low doses of resveratrol can improve insulin sensitivity in mouse cells, and they believe this effect is due to SIRT1 activation by resveratrol. Additionally, the researchers found that SIRT1 levels are reduced in insulin-resistant cells, and that increased SIRT1 activity improved insulin sensitivity

Sirtris Pharmaceuticals – Treating Disease by Modulating Sirtuins

This is a brief overview of Sirtris Pharmaceuticals drug development focus.

Tags: resveratrol, sirtuins, aging, longevity, calorie restriction, SIRT1, Sirtris, SRT501, diabetes

Sirtuin proteins

What's a sirtuin protein? Perhaps this will jog your memory. Not quite two months ago I wrote about resveratrol – the trace ingredient in red wine that may (or may not) have longevity-extending effects. See the article for plenty of details, but there are a few summary points to repeat here.

First, resveratrol may not occur in sufficiently high concentrations in red wine to offer practical health benefits to humans. Second, there are other compounds in red wine (and red or purple grape skins) which may play a larger role than resveratrol in the reported health benefits of red wine. Third, it is suspected that some of the health benefits observed in experiments with mice fed diets having high concentrations of resveratrol may be a result of its activation of a gene that produces the enzyme called SIRT1, which is a "sirtuin" protein. But, fourth, the observed health benefits of resveratrol may also be due to other effects. In summary, that situation with red wine and resveratrol is still not very clear.

However, it's specifically the sirtuin protein SIRT1 (and some closely related variants) we're interested in here, for reasons we'll get to in a moment. But to set the stage a little further, SIRT1 itself (and related proteins) has been of interest to biologists for over ten years because SIRT1 and its relatives appear to affect the longevity (usually in a positive way) of individuals belonging to several diverse eukaryotic species, ranging from yeast and nematodes to mammals. And this effect seems to be closely related to the observed beneficial effects on longevity of calorie restriction – effects that have been observed for many decades.

There's a little history behind the name of the protein SIRT1. It begins with certain proteins, which were observed in yeast, and which seemed to have something to do with the longevity of yeast cells. There were several of these proteins, which were called Silent Information Regulators. Three of them, in particular, known as SIR2, SIR3, and SIR4, seemed to be implicated in the longevity effect, although they are not structurally similar. Ultimately SIR2 proved to be the most important, and remarkably, a gene in the nematode Caenorhabditis elegans turned out not only to be a close analogue of SIR2 but also to have similar longevity-enhancing effects.

Because of their interesting effects, such proteins became known as "sirtuins" (get it?). It turns out that there are at least seven similar human proteins, named SIRT1 through SIRT7. Of these, it is SIRT1 that has (for good reason) attracted the most attention. It is an enzyme, in particular a histone deacetylase enzyme. Such enzymes are able to efficiently silence the expression of a variety of genes, so they are involved in a wide diversity of biological processes, as I've written about before. (And as I hope to write much more about.)

There are all sorts of interesting things to note about the human sirtuins, but the most notable recent finding, which is very relevant to calorie restriction and was announced at almost the same time as my resveratrol post, is this:

Eat Less To Live Longer: Calorie Restriction Linked To Long Healthy Lives (9/26/07)

Now, reporting in the September 21 issue of the journal Cell, researchers from Harvard Medical School, in collaboration with scientists from Cornell Medical School and the National Institutes of Health, have discovered two genes in mammalian cells that act as gatekeepers for cellular longevity. When cells experience certain kinds of stress, such as caloric restriction, these genes rev up and help protect cells from diseases of aging.

"We've reason to believe now that these two genes may be potential drug targets for diseases associated with aging," says David Sinclair, associate professor of pathology at Harvard Medical School and senior author on the paper.

The new genes that Sinclair's group have discovered, in collaboration with Anthony Sauve of Cornell Medical School and Rafael de Cabo of NIH, are called SIRT3 and SIRT4. They are members of a larger class of genes called sirtuins. (Another gene belonging to this family, SIRT1, was shown last year to also have a powerful impact on longevity when stimulated by the red-wine molecule resveratrol.)

David Sinclair, of course, has been heavily involved in research on SIRT1 and resveratrol, as discussed here. He is also co-founder of Sirtris Pharmaceuticals, which is investigating drugs that target sirtuins. Sinclair is a former student of Leonard Guarente, who is also very prominent in sirtuin research, and who had a great deal to do with investigation of the analogous proteins in yeast and nematodes.

One of the most interesting things about the longevity-enhancing effects of sirtuin proteins in yeast and nematodes is that they seem to achieve their effects by rather different means. In yeast, one cause of aging is the formation of "ribosomal DNA circles", and SIR2 (under appropriate conditions) can inhibit this. In C. elegans, on the other hand, the biological effect that retards aging is the inhibition of "insulin signaling". So what is it that SIRT3 and SIRT4 do in the cells of humans (and other mammals)?

In this paper, the newly discovered role of SIRT3 and SIRT4 drives home something scientists have suspected for a long time: mitochondria are vital for sustaining the health and longevity of a cell.

Mitochondria, a kind of cellular organ that lives in the cytoplasm, are often considered to be the cell's battery packs. When mitochondria stability starts to wane, energy is drained out of the cell, and its days are numbered. In this paper, Sinclair and his collaborators discovered that SIRT3 and SIRT4 play a vital role in a longevity network that maintains the vitality of mitochondria and keeps cells healthy when they would otherwise die.

When cells undergo caloric restriction, signals sent in through the membrane activate a gene called NAMPT. As levels of NAMPT ramp up, a small molecule called NAD begins to amass in the mitochondria. This, in turn, causes the activity of enzymes created by the SIRT3 and SIRT4 genes--enzymes that live in the mitochondria--to increase as well. As a result, the mitochondria grow stronger, energy-output increases, and the cell's aging process slows down significantly.

Other news stories on this research:

• Researchers Pinpoint Link Between Caloric Restriction and Longevity (9/20/07)
  
• New Clue To Why Eating Fewer Calories Can Help You Live Longer (9/21/07)
  
• Eat (Less) to Live (Longer) (9/20/07)
  
• U.S. study finds potential new ways to fight aging (9/20/07)
  

Tags: resveratrol, sirtuins, aging, longevity, calorie restriction, caloric restriction, SIRT1

Resveratrol

Resveratrol, of course, is somewhat famous as the substance in red wine that is widely believed to be able to retard aging and promote longevity. There are various hypotheses as to how it might do this, and several may turn out to be correct, as they are not mutually exclusive. There is experimental evidence supporting several of these hypotheses.

Ironically, however, it may be that the amount of resveratrol available in red wine is not sufficient to account for the experimentally supported effects, and there may be other substances in red wine that account for whatever anti-aging properties red wine may have.

Among the properties of resveratrol that might explain an ability to promote longevity are its antioxidant characteristics or other abilities to impede cancer. Resveratrol also has anti-inflammatory properties. Yet another hypothesis is that resveratrol is able to stimulate sirtuin proteins. These proteins are hypothesized to promote longevity, and they may also explain the known longevity-enhancing effects of calorie restriction.

I plan to write about both sirtuins and calorie restriction soon, but right now let's just focus on resveratrol. The most recent news about resveratrol concerns its anti-cancer properties:

Red Wine Compound Shown To Prevent Prostate Cancer

Researchers at the University of Alabama at Birmingham (UAB) have found that nutrients in red wine may help reduce the risk of developing prostate cancer.

The study involved male mice that were fed a plant compound found in red wine called resveratrol, which has shown anti-oxidant and anti-cancer properties. Other sources of resveratrol in the diet include grapes, raspberries, peanuts and blueberries.

The magnitude of the observed effect was substantial:

In the study resveratrol-fed mice showed an 87 percent reduction in their risk of developing prostate tumors that contained the worst kind of cancer-staging diagnosis. The mice that proved to have the highest cancer-protection effect earned it after seven months of consuming resveratrol in a powdered formula mixed with their food.

Other mice in the study, those fed resveratrol but still developed a less-serious form of prostate cancer, were 48 percent more likely to have their tumor growth halted or slowed when compared to mice who did not consume the compound, the UAB research team said.

Unfortunately, the amount of resveratrol (in proportion to body weight) the mice received to achieve these effects would not be very practical for humans to get from wine:

The amounts used in the UAB mice studies were the equivalent of one person consuming one bottle of red wine per day, which is not advisable. Since drinking alcohol in excessive amounts can have harmful health effects, doctors generally recommend moderate red wine consumption, which is an average of two drinks a day for men and one drink a day for women.

Actually, the amounts used are the equivalent of far more than one bottle of wine per day – see further discussion on this below.

Unfortunately, too, this research doesn't address various questions we'd really like answers to. Does resveratrol have a similar effect with other cancers? What is the mechanism by which resveratrol affects cancer?

Here's a blog post at Futurepundit with more on this research, and in particular some suggestions about connection with sirtuins: Resveratrol Reduces Prostate Cancer In Mice

Let's now go back a little way in time, to November 2006, when resveratrol made a big splash with apparent longevity-enhancing effects of a different kind.

Red Wine Molecule Extends Lifespan Of Fat Mice Lives By Reversing Obesity-Related Gene Pathways (11/2/06)

Researchers have used a single compound to increase the lifespan of obese mice, and found that the drug reversed nearly all of the changes in gene expression patterns found in mice on high calorie diets--some of which are associated with diabetes, heart disease, and other significant diseases related to obesity. The research, led by investigators at Harvard Medical School and the National Institute on Aging, is the first time that the small molecule resveratrol has been shown to offer survival benefits in a mammal.

Importantly, one of the other principal investigators in this research is David Sinclair, who has been one of the main researchers studying sirtuins (see references in the Futurepundit post mentioned above), has done previous work with resveratrol (in non-mammals), and whose research has also been somewhat controversial. Some relevant background:

Resveratrol is found in red wines and produced by a variety of plants when put under stress. It was first discovered to have an anti-aging properties by Sinclair, other HMS researchers, and their colleagues in 2003 and reported in Nature. The 2003 study showed that yeast treated with resveratrol lived 60 percent longer. Since 2003, resveratrol has been shown to extend the lifespan of worms and flies by nearly 30 percent, and fish by almost 60 percent. It has also been shown to protect against Huntington's disease in two different animal models (worms and mice).

Here's what the researchers say about the sirtuin connection:

Investigators identified resveratrol while looking for compounds that activate Sir2, an enzyme linked to lifespan extension in yeast and other lower organisms. For the last 70 years, scientists have been able to increase the lifespan of a variety of species by reducing their normal food consumption by 30 to 40 percent - a diet known as calorie restriction. Through this research, scientists identified Sir2 as a key contributor to life extension. Without Sir2, for example, fruit flies see none of the benefits from either calorie restriction or treatment by resveratrol. The mammalian version of the Sir2 gene is SIRT1, which has the same enzymatic activity as Sir2, but modifies a wider variety of molecules throughout cells. Indicators in this study show that resveratrol might also be activating SIRT1 in mice, as well as other known longevity pathways.

The experiments divided their mice into three categories: standard diet (SD), high-calorie diet (HC), and high-calorie diet with resveratrol (HCR). Among other findings, there were some which looked specifically at standard indicators of diabetes.

In humans, high calorie diets can increase glucose and insulin levels leading to diabetes, cardiovascular disease, and non-alcoholic fatty liver disease. In the HC fed mice, researchers found biomarkers that might predict diabetes, including increased levels of insulin, glucose and insulin-like growth factor-1 (IGF-1). Conversely, the HCR fed group had significantly lower levels of these markers, paralleling the SD group. For example, a standard diabetes glucose test on the HCR fed group found considerably higher insulin sensitivity, meaning the HCR group had a lower disposition toward diabetes than the HC fed group. Lower insulin levels also predict increased lifespan in mice.

All-in-all, this appears to be a pretty comprehensive piece of research. However, there are a couple of flies in the ointment. Most importantly, as with the prostate cancer research reported above, the mice received rather high doses of resveratrol – much higher, even, in Sinclair's study. The following article by Nicholas Wade explains it pretty well:

Yes, Red Wine Holds Answer. Check Dosage. (11/2/06)

The mice were fed a hefty dose of resveratrol, 24 milligrams per kilogram of body weight. Red wine has about 1.5 to 3 milligrams of resveratrol per liter, so a 150-lb person would need to drink 750 to 1,500 bottles of red wine a day to get such a dose.

Dr. Richard Hodes, director of the National Institute on Aging, which helped support the study, also said that people should wait for the results of safety testing. Substances that are safe and beneficial in small doses, like vitamins, sometimes prove to be harmful when taken in high doses, Dr. Hodes said.

One person who is not following this prudent advice, however, is Dr. Sinclair, the chief author of the study. He has long been taking resveratrol, though at a dose of only five milligrams per kilogram. Mice given that amount in a second feeding trial have shown similar, but less pronounced, results as those on the 24-milligram-a-day dose, he said.

So Sinclair is taking about one fifth the dose as his mice – still something like the equivalent of 150 to 300 bottles of wine per day. It's probably a good idea not to expect that drinking even a bottle a day will provide any significant protection against diabetes. The recognized fact that there does appear to be some health benefit to people who consume moderate amounts of wine must therefore be due either to other effects of resveratrol (anti-oxidant, anti-inflammatory, for example), or else to other substances in wine.

It is possible that dietary supplements containing more concentrated resveratrol might help, but probably not any currently on the market, as Wade notes:

Many companies sell the substance, along with claims that rivals’ preparations are inactive. One such company, Longevinex, sells an extract of red wine and knotweed that contains an unspecified amount of resveratrol. But each capsule is equivalent to “5 to 15 5-ounce glasses of the best red wine,” the company’s Web site asserts.

A couple of other problems are that the longevity-enhancing effects of resveratrol – or even calorie restriction, for that matter – have not yet been demonstrated in human trials, and that the lack of human trials also leaves open the question of possible harmful side-effects at high dosage, given the other properties of resveratrol (anti-oxidant, anti-inflammatory).

And if all that weren't enough to worry about, the connection between resveratrol and sirtuins is still not clearly demonstrated to general scientific satisfaction. As Wade writes,

“It hasn’t really been clearly shown, the way a biochemist would want to see it, that resveratrol can activate sirtuin,” said Matt Kaeberlein, a former student of Dr. Guarente’s who does research at the University of Washington in Seattle. Sirtuin is the protein produced by the SIRT-1 gene.

Dr. Sinclair said experiments at Sirtris had essentially wrapped up this point. But they have not yet been published, so under the rules of scientific debate he cannot use them to support his position. In his Nature article he therefore has to concede that “Whether resveratrol acts directly or indirectly through Sir-2 in vivo is currently a subject of debate.

Sinclair is working with a start-up biotech company (Sirtris Pharmaceuticals) that is developing pills containing resveratrol and similar molecules for eventual use in humans. But it almost always takes 5 to 10 years to guide a new drug – which must show measurable beneficial effects for specific diseases as well as safety – through clinical trials in humans, in order to gain approval from the FDA.

Other reports on this research: here, here, here, here, here, and here.

Results of this study were followed closely by those of another study, which apparently was funded by Sirtris:

Red wine compound boosts athletic endurance (11/16/06)

High doses of a compound found naturally in grape skins and red wine can improve muscle endurance in mice, and the compound also keeps them slim, a new study shows. ...

Johan Auwerx at the Institute of Genetics and Molecular and Cell Biology in Illkirch, France, and colleagues placed mice on a high-fat diet. Half of those mice received daily amounts of up to 400 milligrams of resveratrol per kilogram of body weight. ...

After three weeks, the mice on the resveratrol supplements weighed only about 20% more than mice on a standard diet. But those on the high-fat diet that did not receive the supplement weighed 60% more than the control mice. The resveratrol also improved the rodents endurance in fitness tests, and seemed to have no toxic side effects.

Mice on the high-fat diet that also took resveratrol were able to run twice as far on a treadmill as those on the same diet but without the supplement, even after the animals’ weight differences were taken into account.

Note that the dose of 400 mg per kg of body weight is about 17 times as much as was used in Sinclair's study. One has to wonder whether these dosage levels have been reported correctly. It would seem to make more sense to use similar dosages so that similar studies of this sort would be more comparable to each other.

Another report on this research suggests a possible explanation for the results:

A Second Pour of Good News About Substance in Red Wine (11/17/06)

Additional experiments on the animals' cells indicate the substance works by increasing the activity of an enzyme known as SIRT1, boosting the number and activity of structures inside cells called mitochondria, the researchers said. Mitochondria are like power plants inside cells, burning fat and providing energy. They tend to get revved up by exercise, and deteriorate with age.

Mice fed resveratrol had more muscle tissue resembling that of a trained athlete, sharply increasing their endurance. They could run twice as far before collapsing as mice that did not receive the substance.

The researchers in this study also had something to say about the connection with sirtuins in humans:

In addition to the mouse experiments, the researchers also produced evidence supporting the theory that SIRT1 plays a key role in longevity in humans in an accompanying analysis of 123 Finnish adults. The subjects born with certain variations of the SIRT1 gene had faster metabolisms, naturally burning energy more efficiently, indicating the same pathway works in humans, too.

According to a third report, Sirtris has actually (as of last November) begun phase 1 clinical trials in humans of their more potent formulation of resveratrol:

Red Wine Compound Could Boost Endurance (11/17/06)

But if you think that drinking more wine or taking resveratrol supplements might turn you into a super-athlete, think again, said Sirtris CEO Dr. Christoph Westphal.

"Native resveratrol from red wine or nutraceuticals cannot reach therapeutic levels in man," he said. "You would need to drink hundreds of glasses of red wine or take hundreds of nutraceutical pills in a day to get a therapeutic dose."

According to Westphal, the company has completed two phase 1 studies with 85 human volunteers of an improved formulation of resveratrol which reaches therapeutic levels in man and is safe.

In addition, Sirtris has started giving diabetic patients its resveratrol compound in a 28-day phase 1 trial to test the safety of the drug and to see how it affects glucose levels.

Another report on this study: here.

Just about 10 days later additional cold water was thrown on the notion that resveratrol in red wine is responsible for the apparent benefits of wine drinking for cardiovascular health. Whatever virtues resveratrol may actually have, there simply isn't enough of it in wine to make a difference. Instead, other substances in wine are more likely to deserve the credit:

Forget Resveratrol, Tannins Key to Heart Health from Wine (11/29/06)

Resveratrol, a molecule found in the skin of red grapes, among other places, has been found to have a host of health effects, most recently prolonging the life spans of obese mice. But the natural wonder drug does not play a role in the beneficial effects of wine drinking, according to research published in the November 28 issue of Nature. "There are some fascinating effects of resveratrol in animal systems," notes plant biochemist Alan Crozier of the University of Glasgow. "To get similar doses into humans through red wine, you would have to consume more than 1,000 liters of red wine a day."

... Using the endothelial cells that line human artery walls, the researchers tested which compounds in wine had the greatest effect. The tests showed that flavonoids called oligomeric procyanidins--essentially condensed tannins, the compounds that impart bitterness to young reds--suppressed production of the peptide responsible for hardening arteries. Such procyanidins can make up as much as 50 percent of the bioactive compounds in a given wine, the researchers observed. "Resveratrol," Crozier notes, "is available at one one-hundredth or one one-thousandth of the levels of procyanidin." Corder adds: "The role of resveratrol in the health benefits of wine has been popularized without any scientific evidence to support it, given the amounts needed for these actions are approximately 1,000-fold greater than could be achieved by wine consumption."

Other reports of this research: here, here.

Unfortunately, some people have perhaps gone off the deep end where resveratrol is concerned. In spite of the tiny amount of it that's actually in red wine, some folks have actually invested their time in charting that amount in different wines and spinning fantasies about adding information on resveratrol content to wine labels:

Resveratrol Content Varies Among Red Wines (4/20/07)

“The long-term aim is for people to be able to go along to the supermarket and to be able to know at a glance the levels of resveratrol contained in the wines they are choosing,” said Dr Hoffman.

Such information, if ever provided, will serve no other purpose than (wine merchants hope) sell more wine, but otherwise be next to useless.

However, one should not conclude that resveratrol has been over-hyped and is nothing but one of the latest "neutraceutical" scams. The problem is that it's a natural substance that hasn't been specifically optimized as a therapeutic drug – especially while in the form of just one biologically active trace ingredient in wine.

Many researchers, including David Sinclair, are hard at work to find a better form or chemical analogue of resveratrol. Sirtris Pharmaceuticals is also working hard to that end. The following article from January of this year profiles the company and its CEO. The profile is mostly from a business perspective, but there's a lot about resveratrol itself in it, so it's worth reading, despite its length:

Can red wine help you live forever? (1/19/07)

[I]f [Sirtris] succeeds, its medicines may retard the onset or progression of a whole slew of age-related diseases, from diabetes to Alzheimer's to cancer. The drugs may also have an extremely provocative side effect: They might extend life span. You have to go back to the advent of antibiotics in the first half of the 20th century to find such broad therapeutic potential.

There's much more to say about Sirtris and about the related scientific issues of calorie restriction and sirtuin proteins. But that will have to wait for later.

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Further information:

Via Eye on DNA I see some new research by David Sinclair and others has just been reported, dealing with calorie restriction: New Clue To Why Eating Fewer Calories Can Help You Live Longer.

There's a lot of information on resveratrol, as well as the related topic of sirtuins, at the Ouroboros blog. In fact, the whole blog is about the biology of aging. For resveratrol see here, and for sirtuins see here.

Tags: resveratrol, sirtuins, aging, longevity, diabetes, cancer, calorie restriction, caloric restriction