Aging: What causes it? What slows it?

First experiments: Osborne, Mendel, Ferry 1917

First scientific experiment suggesting that caloric restriction could extend lifespan During experiments on nutrition, selected rats were fed a calorie restricted diet ("stunted") over various period of time. Normally-fed rats mortality rate (91 rats total): –17 (19%) < 1yr. –48 (53%) < 2 yrs. –26 (29%) > 2 yrs.

Four calorie restricted females More than 2/3 of stock rats die within 2 yrs. All 4 stunted females lived longer than 2 years. All four were breeding at a time when rats are typically in menopause. They produced from 3 to 6 litters; all as vigorous as offspring from younger mothers. Sample size (4 rats) was insufficient to give a statistically significant demonstration.

Osborne knew he couldn’t make any firm conclusions from an experiment with only four rats. But he thought the observation was interesting and published it in the journal Science (which Thomas Edison had founded a few years earlier). In that Science article Osborne said, “it appears as if the preliminary stunting period lengthened the total span of their life.” That same year, J. Northrop showed that he could extend the lifespan of fruit flies when he restricted their food intake during the larval stage.

Caloric restriction results replicated in other species

Spider life span Normal diet average: 50 days; maximum: 100 days Caloric restriction average: 90 days; maximum: 139 days

Single cell organism lifespan Normal diet average: 7 days; maximum: 14 days Caloric restriction average: 13 days; maximum: 25 days

Guppy life span Normal diet average: 33 months; maximum: 54 months Caloric restriction average: 46 months; maximum: 59 months

Rat lifespan Normal diet average: 23 months; maximum: 33 months Caloric restriction average: 33 months; maximum: 47 months

Calorie Restriction in Rhesus Monkeys Mattison, Lane, Roth, Ingram

Methods Typical average life span of rhesus macaques estimated at 25 years. In 1987 National Institute on Aging began study of 30% CR in male and female rhesus macaques of 1-17 years of age. Range of ages allowed assessment of CR on various age groups. Number of animals was eventually 60 of each sex.

CR effect on rhesus lifespan and disease Preliminary mortality data are not yet statistically significant, but indicate that mortality to date is lower in CR animals (15%) than in controls (24%). The CR group has lower incidence of chronic diseases including cancer, cardiovascular disease, diabetes, endometriosis, fibrosis, amyloidosis, ulcers, cataracts and kidney failure.

CR lowers abdominal fat

Biomarkers A biomarker for aging is a measurement that predicts survival. Could help to reduce cost and time involved in evaluation of anti-aging interventions. There is debate over what constitutes a marker and how it should be evaluated. That aside, the following are some candidates.

Body temperature CR over 6 years reduced colonic body temperature about 0.5 Celsius. This agrees with rodent studies. Is consistent across age range of 7-13 years. Additional test using implanted thermometers using radio telemetry for 24 hr monitoring. Temperature decreased as food intake reduced. At 30% restriction, temp was significantly (p<0.003) lower than controls group. Circadian patterns were maintained.

CR lowers body temperature

DHEA Precursor of testosterone and estrogen. Elevated DHEA associated with protection function in aging diseases, diabetes, heart disease and cancer. Peak levels in humans occur at about 20 years of age in men and women. In 792 normal rhesus monkeys, DHEA levels dropped 90% from infancy to 3 years followed by an average decline of 4.2% per yr

DHEA steroid normally declines with age

DHEA down 3% in CR males vs 30% for controls

Reproduction Juveniles: Reproductive maturation delayed in prepubescent monkeys on CR early in life. Adult males: Testosterone level changes delayed by at least one year. Adult females: Little difference in CR vs non-CR monkeys.

Blood sugar, insulin CR monkeys able to regulate glucose better than controls. Lower fasting glucose and insulin levels after 3 years. During intravenous glucose tolerance tests, max glucose level in CR less than in Control. Possible that CR increases insulin sensitivity and may postpone type II diabetes.

CR may alter basic mechanism of fuel use. Short term CR reduced fasting and peak insulin level prior to changes in adiposity. CR induced changes in lean (<22% fat) monkeys. Suggests CR affects insulin levels independent of body weight and fat levels.

Activity Monitored locomotor activity and basic behavior patterns in males after 6 yrs of CR. Used ultra-sonic motion detectors and video. Found daily activities and behaviors typical for captive primates. CR males displayed more pacing, gross movement and less passivity than control. CR female juveniles (6-8yrs) less active than control.

Biomarkers of caloric restriction may predict longevity in humans Roth, G. S., et al

Caloric restriction (CR) slows aging and maintains health and function in a diverse array of species ranging from worms and flies to rodents.

Rhesus monkey data showed that two highly-reproducible biomarkers of CR in rodents, reduced body temperature and reduced plasma insulin, also occur in CR rhesus monkeys. Serum DHEAS levels decline in aging monkeys and humans. CR also slows the rate of decline of DHEAS in CR monkeys.

Do body temperature, plasma insulin, and DHEAS predict human longevity?

Methods The authors studied data from the Baltimore Longitudinal Study of Aging in Male Humans (BLSA). Obtained records of subjects’ body temperature, plasma insulin, and DHEAS, Divided the subjects into those in the upper half or those in the lower half of measurements of each biomarker. Compared survival of men in each group.

Results Significant longer survival in men with lower body temperature, lower plasma insulin, and higher DHEAS (Figure 1) (p < 0.05). The environmental or genetic factors that cause CR-like effects on body temperature, plasma insulin, and DHEAS in these men appear to be related to longevity. Suggest that the same mechanisms that control aging in animals are likely at work in humans, and that modifying these mechanisms may extend lifespan in humans.

Demography of Dietary Restriction and Death in Drosophila Mair, Goymer, Pletcher, Partridge

Mortality rate: the probability of dying in any given interval, given the animal is alive at the start of the interval Hypothesis: CR begun at any stage of life reduces the mortality rate to that of animals on lifetime CR

Methods Four groups of flies: –CR for life –Fully fed for life –Fully fed, then switched to CR –CR, then switched to fully fed

Mortality in fully-fed switched to CR

Mortality in CR to switched fully-fed

Results Two days after starting CR for the first time, and at various ages, fully fed flies are no more likely to die than flies of the same age who have experienced long-term CR. Switching from CR to fully fed resulted in rapid increase of mortality levels. CR animals who switch to fully-fed have the same mortality rate as long-term fully fed flies.

Conclusion It doesn’t matter when CR is started. Switching to CR late in life reduces mortality to the same rate as long-term CR.

Gene Expression Profiling of Aging Using DNA Microarrays Weindruch, Kayo, Lee, Prolla

DNA microarrays A tool that lets us measure biological age on a tissue specific basis. Allow evaluation of interventions at the molecular level. Allow study of 10,000 genes within a single experimental set-up.

Gene expression in old vs young mouse (muscle sample)

Methods mice 30 months old housed individually fed non purified diet and acidified water AL for 1week, then split into 2 groups Control mice fed 84kcal/week, about 20% less than standard diet –necessary to avoid obesity and maintain motor activity CR mice fed 62kcal/week –food enriched with protein, vitamins and minerals to match Control diet for nutrition

Results 6347 genes surveyed 58 (0.9%) displayed greater than 2-fold increase in gene expression 55 (0.9%) displayed greater then 2-fold decrease in expression

Gene groups affected Stress responses (including compensatory response to increased free radicals) Motor neuron genes Metabolism genes