Longevity Genes and Caloric restrictionJuly 2006
By Xi Zhao-Wilson, PhD, and Paul C. Watkins
Caloric Restriction Extends Maximum Life Span
While the SIR2 story is a fascinating one, it is highly likely that other longevity genes operate in mice and other mammals, including humans. What we have learned so far is that restricting calorie intake (while maintaining good nutrition) extends life span in yeast, worms, flies, mice, rats, dogs, and probably monkeys. It is the only intervention proven to extend maximum life span in these species by slowing or reversing normal aging. What is needed now is to translate this research from animals to humans. Scientists are pushing forward by studying the effects of caloric restriction in humans and identifying changes in gene expression associated with the life span-extending effects of caloric restriction.
The National Institutes of Health is funding controlled clinical studies to determine whether the health benefits associated with caloric restriction apply to humans. These studies are beginning to generate important results showing that caloric restriction positively affects biomarkers of longevity while improving heart health and function. Although reducing calorie intake appears to benefit humans, it is unlikely that a severe calorie-restricted diet would be widely adopted. The Life Extension Foundation and its affiliates are attempting to develop a substitute for caloric restriction—that is, a therapeutic intervention that will produce the health and longevity effects of caloric restriction, without forgoing normal food intake.
Results of Clinical Caloric-Restriction Studies
More than 70 years after caloric restriction was shown to work in rodents, emerging scientific evidence suggests that caloric restriction produces health benefits in humans as well.9
In 2002, the National Institutes of Health began funding studies to determine whether the effects of caloric restriction apply to humans. Three centers were chosen to conduct these studies: the Washington University in St. Louis School of Medicine, the Pennington Biomedical Research Center in Baton Rouge, and the Jean Mayer USDA Human Nutrition Research Center on Aging at Tufts University in Boston. The first two groups have now published their results, and it is clear that if you eat less, you will be healthier. These results also support the Life Extension Foundation’s strategy to fund research to develop therapies that can induce the healthy effects produced by caloric restriction.
The group at Washington University focused on caloric restriction’s effects on the heart. Their studies show that caloric restriction has a “powerful protective effect against atherosclerosis” and appears to prevent primary aging in the heart.10,11 In this study, a group of men and women, averaging 50 years of age, ate a calorie-restricted diet (1,112-1,958 calories per day) for an average of six years. They were compared to a control group that ate a typical American diet (1,976-3,537 calories per day). The calorie-restricted group showed no evidence of risk factors for atherosclerosis. Their total cholesterol and LDL levels were lower than those of the controls, as were their glucose, insulin, C-reactive protein (a marker for inflammation), and triglyceride levels. The artery-protective lipoprotein HDL was also higher in the calorie-restricted group than in the controls.10 In fact, these middle-aged adults had the same triglyceride levels normally found in the top fifth percentile of healthy 20-year-olds. The calorie-restricted group also had a 40% reduction in carotid arterial wall thickness compared to the controls, and no evidence of atherosclerotic plaque formation.
The same research group also evaluated heart function in the calorie-restricted subjects. A decline in cardiac performance, as measured by diastolic function, is a primary marker of aging. The study found that in calorie-restricted individuals, diastolic function resembled that found in adults about 15 years younger in age. Because the subjects had been on the restricted diet for an average of six years, the researchers concluded that caloric restriction may even have a rejuvenating effect on human health.11 One lesson learned from this study is that even if you are not lucky enough to have inherited the “good” longevity genes that allow some individuals to live beyond 100 years, you can still implement strategies to ensure a longer, healthier life.
While the Washington University researchers studied people who had chosen a calorie-restricted diet themselves, the Pennington group has just published the first randomized, controlled clinical study of caloric restriction.12 Overweight but non-obese men and women (as determined by a body mass index of 25-30) who were fed a diet reduced in calories by 25% were compared to a control group for a period of six months. This study was designed to measure caloric restriction’s effects on biomarkers that have been associated with longevity, oxidative stress, and how individuals adapt to changes in metabolism. Although the study was intended as a pilot for a two-year study to begin later in 2006, its results to date have already been called “striking.”
Like mice and monkeys, the calorie-restricted human subjects had decreased fasting insulin levels and body temperature, indicating improvements in two biomarkers of longevity. These results support the hypothesis that caloric restriction attenuates the human aging process. Calorie-restricted subjects also adapted their metabolism to the reduction in calories by decreasing the amount of energy they expended, an effect that extended beyond what could be explained by a loss of body weight. In addition, the calorie-restricted group exhibited reduced DNA damage. Reactive oxygen species, which are byproducts of energy metabolism, are known to attack DNA, lipids, and proteins. This reduction in DNA damage links the decreased oxidative stress induced by caloric restriction to the oxidative stress theory, a popular theory that connects damage caused by reactive oxygen species over time to the onset of diseases like cancer, as well as to aging itself.
These studies provide evidence that caloric restriction works in humans as well as in animals, and offer clues as to how it might work. Now that accumulating evidence suggests that caloric restriction may slow aging and protect against age-related diseases in humans, does this mean that animal studies will have less to contribute? No. In fact, the opposite is true. Now that we have evidence that caloric restriction benefits humans, we can employ animal studies to investigate the intricate interrelationships between genes, molecular pathways involved in the pathology of chronic diseases and aging, and the physiological changes induced by caloric restriction. Using this strategy, the Life Extension Foundation will continue to support scientific research by BioMarker to find interventions that exert the same beneficial effects as caloric restriction.
BioMarker’s Visionary Mission
BioMarker’s mission is to understand how longevity genes that confer long life span and protection against age-related diseases are altered by interventions designed to mimic the effects of caloric restriction and other models of life-span extension, such as Ames dwarf mice. BioMarker employs gene-expression profiling—using DNA “chips” or microarrays—to observe how nearly 40,000 markers for all the genes that make up the basic blueprint for a mouse respond to caloric restriction or various candidate caloric-restriction mimetics—that is, agents that reproduce the beneficial effects of caloric restriction. The sophisticated instrumentation, technology, and current approaches that BioMarker employs were described in a previous article published in Life Extension (“Life Extension’s Visionary Plan to Conquer Aging and Death,” January 2006).13
Genes that respond to caloric restriction in various organs and tissues of an animal model (a long-lived hybrid mouse) are first identified in controlled studies. These patterns are then used to identify pharmaceutical compounds, molecules, foods, dietary supplements, and botanical extracts that reproduce, to a significant degree, the same gene-expression patterns produced by caloric restriction. Candidate caloric-restriction mimetics are then subjected to functional testing using various biochemical and biological assays. Final confirmation of caloric-restriction mimetics will require testing in humans, and BioMarker is already planning such studies.
While studies are now demonstrating caloric restriction’s benefits for heart health in humans, BioMarker scientists recently identified how heart genes respond to caloric restriction in an animal model.14 This study showed that caloric restriction’s key beneficial effects act rapidly to change the way the heart functions, enhancing its contractility and energy production. Animals on lifelong caloric restriction have hearts that have reduced perivascular collagen deposition in the left ventricle and smaller cardiac muscle cells, resembling the hearts of much younger animals. Gene-expression studies have shown that eight weeks of caloric restriction reproduced nearly 20% of the total gene-expression changes found in long-term calorie-restricted animals. These genes are likely responsible for caloric restriction’s cardioprotective effects.
Another important study recently showed that the animal model we use is capable of detecting compounds that exhibit caloric-restriction mimetic activity.15 A number of drugs commonly used to treat diabetes were screened using this model. We discovered that metformin, an off-patent drug that is a first-line therapy for overweight people with type II diabetes, reproduced gene-expression changes in the liver that are very similar to those produced by long-term caloric restriction. Eight weeks of metformin treatment produced gene-expression changes that were even more similar to those induced by long-term caloric restriction than did eight weeks of caloric restriction. These results validate our screening model and provide valuable information about how to identify and develop caloric-restriction mimetics in the future.
Combating Aging and Brain Disease
Now that BioMarker scientists have developed a screening model for caloric-restriction mimetics and have identified key genes that are involved in the response to caloric restriction by the heart and liver, they are now looking into caloric restriction’s effects on brain health. Neurodegenerative diseases such as Alzheimer’s and Parkinson’s, as well as age-related cognitive decline, are all major targets of pharmaceutical industry research. Caloric restriction’s neuroprotective effects, as demonstrated in animal models, are profound and likely to be produced in humans as well. Scientists are studying the brain using the same approach used to evaluate caloric restriction-responsive genes in the heart and liver, but with a twist.
Rather than subject the entire brain to gene-expression analysis, a new technology allows for examination of specific regions of the brain. The Arcturus Laser Capture Microdissection (LCM) and Laser Cutting System connects a microscope to a UV laser. Thin frozen sections of the brain can be viewed through the microscope, and the system can be programmed to “harvest” cells from specific brain regions. Our studies are focusing on the hippocampus, which is involved in spatial learning and memory, and is one of the first regions of the brain to suffer damage from Alzheimer’s disease.
The LCM has been used to collect specific hippocampal neurons for RNA preparation (ribonucleic acid, which is involved in transmitting genetic expression) prior to subjecting the material to gene-expression profile analysis. Figures 1 and 2 show stained hippocampal neurons before and after harvesting with the LCM. BioMarker scientists hope to identify specific brain genes that respond to caloric restriction, and to use this information in developing caloric-restriction mimetics that will ward off disabling neurodegenerative diseases and enable our brains to remain healthy and youthful in advancing age.
We are living in a time of rapid technological advances. Longevity genes identified in yeast, worms, flies, and mice are directly relevant to humans. The powerful health and longevity benefits of caloric restriction in animals are now being demonstrated in humans. Scientists are actively pursuing intervention strategies based on the caloric-restriction model. The Life Extension Foundation has been a pioneer in funding research and charting the course for one of the most important scientific endeavors of all time: the search to understand how genes determine human life span, and how we can manipulate these genes to live longer, healthier lives.
Humans seeking to slow aging and reduce degenerative disease risk may consider reducing food intake and ingesting 20-40 mg of resveratrol and 250-850 mg of metformin each day. These doses are based on studies conducted at BioMarker as well as analysis of the most current scientific literature.
Caution: Those suffering from malnutrition should not attempt to restrict their calorie intake. Likewise, people who have medical conditions such as hypoglycemia, or liver or kidney disorders, should not take the prescription drug metformin. Always consult your physician before taking any prescription drug or nutritional supplement.
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