Hypocaloric diet and its mimetics in anti-aging medicine

For thousands of years, humanity has been tirelessly searching for the “elixir of youth,” but only the last decades, marked by revolutionary discoveries in biology and medicine, have brought us very close to this goal. At the same time, it should be recognized that most of the technologies for increasing maximum life expectancy and slowing down primary aging, studied and proposed by fundamental gerontology and anti-aging medicine, are still controversial. Perhaps today, the only generally accepted effective way among experts to increase maximum life expectancy is to limit the caloric content of the diet while compulsorily replenishing the deficiency of essential nutrients. It is the hypocaloric diet / caloric restriction (from the Latin restrictio - “restriction”) and the so-called mimetics (substances that imitate the effect of other substances) of the hypocaloric diet as ways to maintain health, slow down aging and increase life expectancy that will be discussed in this article.

Molecular biological effects of a hypocaloric diet

Since 1935 McCay et al. first demonstrated in rats that hypocaloric diet/calorie restriction slows primary aging and increases maximum lifespan by approximately 20–50%, there have been hundreds of studies documenting similar effects in yeast, fruit flies, worms, fish, mice and rats.

The molecular biological effects of caloric restriction have been studied quite well experimentally. It has been established that, among other things, a hypocaloric diet affects the primary link of life - gene expression, which explains its such a significant effect on the aging process. However, there are a number of equally important results that are not related to modification of gene activity. Below are the main molecular biological effects of a hypocaloric diet that are currently known:

• multidirectional influence on genes that control cell repair and death - the sirtuin family (Sirt) and others;
• reducing the formation of free radicals;
• reduction of protein glycation processes;
• reducing protein damage and accelerating its elimination;
• changes in the activity of enzymes that control protein metabolism;
• modification of the activity of chaperones (heat shock proteins) - molecules that restore damaged proteins;
• modulation of apoptosis processes (programmed cell death);
• reducing damage and improving DNA repair;
• reduction of systemic inflammation;
• reducing glycolysis by increasing insulin sensitivity.

In turn, these biological mechanisms determine the following clinical effects:

• optimization of hormone secretion (especially those whose levels decrease with age - DHEA, growth hormone, etc.);
• reduction of fat mass (including omental fat with a simultaneous increase in muscle mass);
• positive effect on cardiovascular system, including reduction of heart rate, blood pressure, improvement of lipid profile;
• improving tissue sensitivity to insulin and reducing glucose levels;
• increased protein synthesis;
• reduction of oxidative stress;
• decrease in body temperature and energy expenditure;
• stimulation of growth factors, including BDNF (nerve growth factor);
• improved brain function, including memory, cognitive function and mood.

Testing the hypothesis on primates

For now, it seems unlikely that the effect of a hypocaloric diet on maximum human lifespan will ever be completely determined. However, it is entirely possible to answer a similar question in a study conducted on humans' closest relatives, the primates. Since 1989, the United States has been studying the effect of a hypocaloric diet on the aging process in rhesus monkeys. Over the next 15 to 20 years, this research is expected to definitively establish whether calorie restriction increases maximum lifespan in primates. Even if we take into account that rhesus macaques are not considered great apes, it is clear that the data from these studies can be extrapolated to humans with much greater justification than the data from studies on rodents and smaller animals.

Until 2008, researchers could only report intermediate results of their work, but even then they looked encouraging. In macaques, a hypocaloric diet has been reported to induce metabolic and physical changes associated with an increase in maximum lifespan in previous experiments in other animals. In particular, calorie restriction protects against the development of insulin resistance and type II diabetes mellitus, reduces risk factors for atherosclerosis, reduces the level of triiodothyronine (T3), the level of general metabolism and body temperature, the severity of oxidative stress, the concentration of an important mitogenic agent - insulin-like growth factor I (IGF- 1) - and pro-inflammatory interleukin-6 (IL-6), and also slows down the aging of the immune system.

In July 2009, the journal Science published the results of a 20-year study conducted by a group of scientists from the University of Wisconsin (Madison). By 2009, most of the 76 rhesus macaques in both groups had reached old age (25 years or older; the known maximum lifespan is about 40 years), and researchers were able to talk about the long-term effect of caloric restriction on at least secondary aging in primates. It turned out that three times more individuals died from diseases associated with aging (cardiovascular diseases, cancer, diabetes, brain atrophy) in the control group than in the experimental group (14 out of 38 versus 5 out of 38). The number of cardiovascular diseases and malignant tumors in the experimental group was 2 times less. In the control group, 5 cases of type II diabetes mellitus and 11 cases of impaired glucose tolerance/insulin resistance were registered, while not a single such case was identified in the caloric restriction group. It is noteworthy that on a hypocaloric diet, the monkeys lost fat mass while maintaining muscle mass. It was also found that calorie restriction helped preserve brain volume, especially in the areas responsible for cognitive and motor activity. And finally, in the experimental group the monkeys looked incomparably more intact (young) by all standards.

According to the research team and other experts, the results obtained now (albeit with reservations) can be extrapolated to humans, since monkeys are susceptible to the same chronic age-related diseases as people: obesity, metabolic syndrome, diabetes, degenerative changes in the brain. The main causes of death in them, as in humans, are cardiovascular diseases and cancer. Of course, in order to draw final conclusions, it will be necessary to wait until the last macaque dies, and this may take another 15–20 years, but it is already clear that the hypocaloric diet works. And even if it does not live up to expectations in terms of increasing maximum life expectancy, the data obtained to date about its powerful preventive effect already provide a compelling basis for testing this method in humans.

Caloric restriction: studies on volunteers

Since a direct study of the effect of calorie restriction on human life expectancy is impossible, scientists currently have to rely on surrogate criteria. There are 3 possible approaches:

• in the first, they focus on the appearance in humans of adaptive reactions and other changes (genetic, metabolic, hormonal, etc.), similar to those that were previously discovered in animals and were reliably associated with the prevention of primary aging / increase in maximum life expectancy;
• the second approach involves assessing the signs of secondary aging, that is, primarily age-related diseases, most often leading to death;
• The third approach measures physiological parameters that inevitably deteriorate progressively with age—the so-called biomarkers of aging.

Of course, all three criteria are closely interrelated, and their joint assessment is the most appropriate and reliable.

Currently, information about the effect of a hypocaloric diet on humans comes from two main sources, including:

• a large multicenter project CALERIE (Comprehensive Assessment of Long-Term Effects of Reducing Calorie Intake), initiated by the US National Institute of Aging in 2002, which combined the efforts of three research centers: Tufts University (Boston, Massachusetts), Pennington Biomedical Research Center (Baton Rouge, Louisiana) and Washington University (St. Louis, Missouri);
• Caloric Restriction Society, whose members voluntarily follow a hypocaloric diet in the hope that they can achieve the same beneficial effects that have been demonstrated in animal models.

It should be noted that for all three categories of surrogate markers described above, the observed effects are very positive and encouraging.

Calerie

The Pennington Biomedical Research Center's phase 1 CALERIE study (25% calorie reduction over 6 months in overweight men and women aged 25–50 years) noted:

• reduction of body weight by 10% due to adipose tissue (including intrahepatic fat deposits);
• a significant decrease in body temperature, daily energy expenditure, and triiodothyronine (T3) levels;
• decreased fasting insulin levels and improved insulin sensitivity.

Very similar data were obtained in the first phase of CALERIE and at Washington University (20% reduction in calories over 6 months in overweight men and women aged 50–60 years).

The phase 2 CALERIE study, which also included all three centers, included healthy men and women aged 25–45 years with a body mass index of 22 to 28 kg/m2. This phase, which lasted 2 years and ended in April 2012, implied a reduction in calorie intake by 25%.

Calorie Restriction Society

Even more interesting information was obtained from a study of volunteers from the Caloric Restriction Society. This work was carried out by the same group of scientists from Washington University that is involved in the CALERIE project. Scientists' attention has been focused on risk factors for atherosclerosis. The study compared members of the Caloric Restriction Society aged 50 ± 10 years who had been on a hypocaloric diet (1,112–1,958 kcal/day) for about 6 years with age- and sex-matched healthy volunteers on a so-called typical American diet ( 1,976–3,537 kcal/day). Thus, the caloric restriction of the diet was about 30%, as in most laboratory studies conducted previously.

In the calorie restriction group, the same significant differences from the control group were revealed as in other studies, namely: lower BMI and percentage of body fat, more favorable lipid profile, lower fasting glucose and insulin levels, lower levels of markers systemic inflammation – C-reactive protein and tumor necrosis factor α (TNF-α). Triiodothyronine (T3) levels were also significantly lower in the calorie restriction group and were in the lower normal range. Similar dynamics were noted for one of the growth factors, transforming growth factor β1 (TGF β1). Comparative data are summarized in Table 1.

Table 1. Comparative characteristics of risk factors for atherosclerosis in the experimental and control groups. Hypocaloric diet versus Western diet (source: Holloszy J., Fontana L. Caloric Restriction in Humans // Exp Gerontol. – 2007, August; 42(8):709–712)

An interesting finding was lower blood pressure than in the comparison group, approximately 100/60 mm Hg. Art. Interested by this fact, the researchers asked the subjects' family doctors for information about their health status before starting the diet. Based on these data, it became possible not only to compare the current indicators in the experimental and control groups, but also to retrospectively assess the dynamics of indicators within the experimental group itself. The data are presented in Table 2. It can be seen that after just a year of the hypocaloric diet there was a very noticeable decrease in blood pressure. It has long been proven that lower blood pressure determines a lower level of cardiovascular mortality and longer life expectancy in humans.

Table 2. Dynamics of risk factors for atherosclerosis in members of the Caloric Restriction Society (source: Holloszy J., Fontana L. Caloric Restriction in Humans // Exp Gerontol. – 2007, August; 42(8):709–712)

However, the most impressive data were obtained during an instrumental study: in the caloric restriction group, the thickness of the intima-media complex of the carotid arteries was 40% less, and the index of diastolic function (the most important marker of biological aging, reflecting fibrosis and loss of elasticity of the left ventricle) was “16 years lower.” “younger” than the actual age of the subjects. Other studies of caloric restriction have also noted “rejuvenation” of the myocardium and skeletal muscle associated with an increase in the number and improvement of the function of energy-producing mitochondria.

Together with favorable metabolic changes, instrumental data clearly confirm the pronounced preventive effect of a long-term hypocaloric diet on the development of cardiovascular diseases. It is especially gratifying that similar dynamics of cardiac markers were observed in experiments on rodents, which ultimately experienced an increase in maximum life expectancy.

Hypocaloric mimetics - alternative methods of life extension

So, it is obvious that a hypocaloric diet works for humans. Therefore, even if someone is unlucky with the set of genes for longevity, the scenario laid down by nature can still be corrected, and, it seems, quite significantly. However, looking at this issue with a grain of realism, we have to admit that even if the prolonging effect of the diet had already been proven, there would be few who would want to experience a constant feeling of hunger throughout most of their lives, albeit longer. The idea of dietary restriction is quite unpleasant for most people in the modern world, that is, caloric restriction cannot be considered as a method for mass application. These obvious disadvantages of the “hypocaloric lifestyle” are pushing scientists to look for alternative methods to prolong life and improve health.

The good news is that 70 years of research into caloric restriction have not been in vain. Focusing on already known genetic, metabolic, clinical and other markers, scientists were able to discover many substances that reproduce the positive effects of a hypocaloric diet without actually using it. This seems surprising, but such a phenomenon is really possible: to get all the benefits of a hypocaloric diet, you don’t need to starve yourself - just take a “magic pill”. At least this will be the case in the near future.

We are talking about substances that can activate “longevity genes”, block inflammation, optimize fat and carbohydrate metabolism, slow down the development of atherosclerosis and cancer, etc. Moreover, all these effects can be caused by just one of them. These substances are called “mimetics (that is, imitators) of a hypocaloric diet.” They are now seen as some of the most promising agents in the anti-aging medicine armamentarium. The identified hypocaloric mimetics belong to different types of substances - drugs, endogenous hormones, vitamins and vitamin-like substances - but most are found among compounds of plant origin.

Let us briefly consider the most interesting and promising hypocaloric mimetics.

Resveratrol

It is a natural phytoalexin secreted by some plants as a protective compound against parasites such as bacteria or fungi, and also in response to non-specific stress - ultraviolet radiation, drought, etc. Resveratrol is found in the largest quantities in the skins of dark-colored grapes. It is found in smaller quantities in Japanese knotweed (Polygonum cuspidatum) (a popular industrial source of resveratrol), peanuts, raspberries, blueberries, pomegranate, hops, pistachios, dark chocolate, etc.

Resveratrol is perhaps the best known of the natural hypocaloric mimetics, although previously it was more often talked about only as a means of preventing cardiovascular diseases in the context of the so-called French paradox. It turned out that the potential of this polyphenol is much greater. In various in vitro and in vivo experiments, resveratrol has demonstrated numerous geroprotective and preventive effects:

• cardioprotective:
  • suppresses the expression of cell adhesion molecules and proliferation of smooth muscle cells in the vascular wall;
  • stimulates the activity of endothelial NO synthase (eNOS);
  • reduces platelet aggregation;
  • reduces the oxidation of LDL cholesterol;
• oncoprotective:
  • resveratrol affects all three stages of carcinogenesis – initiation, promotion and progression;
  • modulates the expression of key pro-inflammatory molecules - the transcription factor NF-kB and cyclooxygenases (COX);
  • inhibits the isoform of cytochrome P450 - 1A1, the hyperactivity of which leads to the formation of more aggressive/carcinogenic intermediates from weak carcinogens (for example, non-pyrenes, polyaromatic hydrocarbons, etc.);
  • modulates the activity of key genes/proteins that control the cell cycle and tumor growth, including p53, cyclins A, B1 and cyclin-dependent kinases 1 and 2;
  • induces apoptosis of atypical cells;
  • suppresses neoangiogenesis;
  • is a powerful antioxidant;
  • convincing effects in vivo were obtained for those localizations in which direct contact of resveratrol and the surface involved in the tumor process was possible (skin, gastrointestinal tract);
• antidiabetic:
  • hypoglycemic and hypolipidemic effect; reduction of polyphagia, polydipsia and weight in experimentally induced diabetes in rats;
  • in humans, demonstrated glucose reduction in two phases (Ib and IIa) in clinical studies conducted by Sirtis Pharmaceuticals;
• neuroprotective:
  • significantly reduces the formation of degenerative lesions in the brain of animals (amyloid in Alzheimer's disease, etc.);
  • in mice – in the hypothalamus (–90%), in the striatum (–89%), in the medial cortex (–48%);
  • the effect has been demonstrated in several studies in animal models;
  • possible mechanism – antioxidant + chelation (binding) of copper ions;
  • researchers suggest the possible effectiveness of resveratrol in humans in preventing the formation of amyloid plaques.

In the list of identified “longevity genes,” one of the most active and universal are the so-called sirtuins (Sir – silent information regulator). It has been established that activation of sirtuins is one of the main mechanisms determining the effectiveness of caloric restriction. In mammals, Sirt1 is a major modulator of mechanisms controlling glucose homeostasis, insulin sensitivity, endothelial function, mitochondrial number and function, tumor growth, and other important factors associated with lifespan.

Resveratrol is the most effective sirtuin activator known today.

In 2003, a group of scientists from Harvard Medical School reported that resveratrol activates sirtuins in the yeast Saccharomyces cerevisiae, which in turn stabilizes DNA, prevents the formation of abnormal DNA replications and increases the life cycle of the yeast by 70%! Later, a similar effect of resveratrol was demonstrated on the flatworm Caenorhabditis elegans, fruit flies and the short-lived fish Nothobranchius furzeri. In other words, by activating sirtuins, in these experiments, resveratrol made it possible to reproduce many of the effects of a hypocaloric diet and increase maximum life expectancy.

Very interesting data were later obtained by the same group from Harvard. Middle-aged mice were put on a high-calorie diet. Their diet was supplemented with hydrogenated coconut oil, which provided 60% of the total energy value of the food, while they consumed an average of 30% more calories than mice on a regular diet. (It should be emphasized that with age, even on a normal diet, many mice develop obesity and diabetes.) Some mice on a high-calorie diet simultaneously received resveratrol, others did not. Mice fed only the high-calorie diet quickly developed obesity, which was accompanied by a high rate of early mortality, while the group that received concomitant resveratrol did not show a greater tendency to become obese than usual. Moreover, even the survival rate was comparable to the control group, although there was no positive effect of resveratrol on the levels of free fatty acids and cholesterol, that is, they were significantly higher in the experimental group. However, parametric gene analysis revealed that resveratrol counteracted the negative effects of a high-calorie diet in 144 of 153 areas. Many of the identified molecular effects caused by resveratrol were identical to those of a hypocaloric diet. Based on the data obtained, the authors concluded that the use of resveratrol and similar compounds may be a new effective approach in the treatment of obesity-associated diseases and other “diseases of aging.”

Alas, further research showed that resveratrol had a number of beneficial effects when used in elderly mice, but did not increase the lifespan of ad libitum-fed mice that began receiving resveratrol in midlife. Research led by the National Institute on Aging's Interventions Testing Program tested three different doses of resveratrol in young mice, including a dose 8 times higher than the Harvard study described above. Unfortunately, convincing data on an increase in maximum life expectancy were also not obtained in these studies. At a superficial level, it may seem that attempts to prove the geroprotective effect of resveratrol have failed. However, it is still very early to put an end to this issue, since resveratrol has demonstrated convincing effectiveness not only in vitro, but also in vivo, too many times.

When interpreting the data from the studies described, it should be borne in mind that regular resveratrol has very poor bioavailability. In both rats and humans, no more than 5% of unchanged resveratrol from a dose taken per os enters the systemic circulation. This is due to the fact that most of orally ingested resveratrol is very quickly metabolized (conjugated) by intestinal and liver enzymes to form glucuronides and sulfates, which apparently do not have pharmacological activity. Only trace amounts (less than 5 ng/ml) of free resveratrol are detected in the blood after oral administration of 25 mg. Therefore, now we can increasingly find indications of the need to use transmucosal (for example, sublingual or chewable) resveratrol delivery systems, the bioavailability of which is many times greater. After holding 50 ml of a 50% aqueous-alcohol solution containing only 1 mg of resveratrol in the mouth for just 1 minute, after 2 minutes the concentration of its free form in the blood was 37 ng/ml. On the other hand, after drinking 600 ml of red wine (about 2 mg of resveratrol) by five men, unchanged resveratrol was detected in only two of them, and then only in trace amounts - 2.5 ng/ml.

Therefore, when distinguishing between the issues of bioavailability and potential activity of resveratrol as such, no one has any real reason to discount or ignore the data previously obtained in numerous studies. Perhaps resolving the issue of bioavailability in higher mammals or uncovering another, as yet unobvious, phenomenon will eliminate the existing contradictions and give a new impetus to the effective use of resveratrol or its derivatives in preventive and anti-aging medicine. For example, the proprietary oral form of resveratrol SRT-501, developed by Sirtis Pharmaceuticals, provides plasma concentrations of free resveratrol 5-8 times higher than conventional forms. According to scientists, this concentration is quite enough to obtain the effects described in experiments on animals and in vitro. Sirtis Pharmaceuticals also has two more potent and selective Sirt1 gene/protein activators in development, SRT2104 and SRT2379, which have already been included in several pilot clinical trials.

Pterostilbene

One possible solution to the problem of bioavailability/efficacy of resveratrol may be the use of its derivatives, which have similar biological activity in vitro, but greater bioavailability/bioactivity in vivo. An example is another natural phytoalexin, pterostilbene. It is found in the highest concentrations in blueberries and, again, dark-colored grapes (by the way, it is possible that the French paradox is actually explained not so much by resveratrol as by pterostilbene; no one has studied this issue yet).

Pterostilbene is a methylated derivative of resveratrol: two of the three hydroxyl groups of resveratrol are replaced by methyl groups in pterostilbene. This modification makes it less susceptible to metabolic transformation/inactivation when passing through enzymatic conjugation systems in the intestines and liver. Pterostilbene also has greater lipophilicity, which improves its passage through the lipid bilayer of the membrane into the cell, which, in turn, provides it with better tissue distribution and a longer half-life: about 14 minutes for resveratrol and about 105 minutes for pterostilbene.

In fact, after a 2-week saturation period, effective blood concentrations of pterostilbene after the last dose were maintained for 24 hours. Thus, pterostilbene has greater metabolic stability and duration of effect than resvetrol.

Research on pterostilbene began much later than resveratrol, and therefore a comparable amount of information has not yet been accumulated. However, available data give every reason to believe that, according to similar criteria, pterostilbene is a more effective substance than resveartrol. For example, it has been shown that, unlike resveratrol and two other related stilbenes - piceatannol and trimethoxystilbene - pterostilbene is a potent agonist of PPARα - a receptor involved in the regulation of carbohydrate and fat metabolism (a target for antidiabetic drugs of the glitazone group and lipid-lowering fibrates). In an in vitro experiment in hepatocyte culture, pterostilbene turned out to be an even more effective agonist of this receptor than the pharmacological lipid-lowering agent ciprofibrate.

Also, unlike resveratrol, pterostilbene demonstrated distinct lipid-lowering and hypoglycemic activity in a three-week rodent study (Table 3).

Table 3. The effect of pterostilbene on the level of glucose and major blood lipids in hamsters. A single dose per day of 25 mg/kg/day for 3 weeks (source: Rimando et al. Pterostilbene, a new agonist for the peroxisome proliferator-activated receptor alpha-isoform, lowers plasma lipoproteins and cholesterol in hypercholesterolemic hamsters // J Agric Food Chem. 2005; 53: 3403)

In a model of diabetes in rats, by the end of the sixth week of the study, pterostilbene demonstrated a greater hypoglycemic effect compared to the reference drug metformin, and at a dose more than an order of magnitude lower: a decrease in glucose levels from 279.58 ± 22.66 to 121.50 ± 10.84 mg/dL for pterostilbene at a dose of 40 mg/kg/day versus a decrease from 288.49 ± 24.52 to 40.89 ± 12.09 mg/dL for metformin at a dose of 500 mg/kg/day!

Pterostilbene demonstrates the most pronounced antioxidant and anti-inflammatory effect of all stilbenes tested! Interestingly, a synergistic antioxidant effect was observed when pterostilbene and resveratrol were used together. It has also been suggested that pterostilbene improves the pharmacodynamics and pharmacokinetics of resveratrol by reducing its level of conjugation (i.e. increasing bioavailability) and increasing its half-life in the body. Based on this phenomenon, currently most serious manufacturers of dietary supplements produce only combined and not single preparations of resveratrol.

Literature:

• Andrey Gostry, general practitioner, candidate of medical sciences, International Institute of Integral Preventive and Anti-Aging Medicine PreventAge (Russia - USA)