Mark A. Lane

Intermittent fasting dissociates beneficial effects of dietary restriction on glucose metabolism and neuronal resistance to injury from calorie intake

Dietary restriction has been shown to have several health benefits including increased insulin sensitivity, stress resistance, reduced morbidity, and increased life span. The mechanism remains unknown, but the need for a long-term reduction in caloric intake to achieve these benefits has been assumed. We report that when C57BL/6 mice are maintained on an intermittent fasting (alternate-day fasting) dietary-restriction regimen their overall food intake is not decreased and their body weight is maintained. Nevertheless, intermittent fasting resulted in beneficial effects that met or exceeded those of caloric restriction including reduced serum glucose and insulin levels and increased resistance of neurons in the brain to excitotoxic stress. Intermittent fasting therefore has beneficial effects on glucose regulation and neuronal resistance to injury in these mice that are independent of caloric intake.

Calorie restriction mimetics: an emerging research field.

When considering all possible aging interventions evaluated to date, it is clear that calorie restriction (CR) remains the most robust. Studies in numerous species have demonstrated that reduction of calories 30–50% below ad libitum levels of a nutritious diet can increase lifespan, reduce the incidence and delay the onset of age‐related diseases, improve stress resistance, and decelerate functional decline. A current major focus of this research area is whether this nutritional intervention is relevant to human aging. Evidence emerging from studies in rhesus monkeys suggests that their response to CR parallels that observed in rodents. To assess CR effects in humans, clinical trials have been initiated. However, even if results from these studies could eventually substantiate CR as an effective pro‐longevity strategy for humans, the utility of this intervention would be hampered because of the degree and length of restriction required. As an alternative strategy, new research has focused on the development of ‘CR mimetics’. The objective of this strategy is to identify compounds that mimic CR effects by targeting metabolic and stress response pathways affected by CR, but without actually restricting caloric intake. For example, drugs that inhibit glycolysis (2‐deoxyglucose), enhance insulin action (metformin), or affect stress signaling pathways (resveratrol), are being assessed as CR mimetics (CRM). Promising results have emerged from initial studies regarding physiological responses which resemble those observed in CR (e.g. reduced body temperature and plasma insulin) as well as protection against neurotoxicity (e.g. enhanced dopamine action and up‐regulated neurotrophic factors). Ultimately, lifespan analyses in addition to expanded toxicity studies must be accomplished to fully assess the potential of any CRM. Nonetheless, this strategy clearly offers a very promising and expanding research endeavor.

Caloric restriction increases neurotrophic factor levels and attenuates neurochemical and behavioral deficits in a primate model of Parkinson's disease

We report that a low-calorie diet can lessen the severity of neurochemical deficits and motor dysfunction in a primate model of Parkinsons disease. Adult male rhesus monkeys were maintained for 6 months on a reduced-calorie diet [30% caloric restriction (CR)] or an ad libitum control diet after which they were subjected to treatment with a neurotoxin to produce a hemiparkinson condition. After neurotoxin treatment, CR monkeys exhibited significantly higher levels of locomotor activity compared with control monkeys as well as higher levels of dopamine (DA) and DA metabolites in the striatal region. Increased survival of DA neurons in the substantia nigra and improved manual dexterity were noted but did not reach statistical significance. Levels of glial cell line-derived neurotrophic factor, which is known to promote the survival of DA neurons, were increased significantly in the caudate nucleus of CR monkeys, suggesting a role for glial cell line-derived neurotrophic factor in the anti-Parkinsons disease effect of the low-calorie diet.

Calorie restriction in rhesus monkeys

Calorie restriction (CR) extends lifespan and reduces the incidence and age of onset of age-related disease in several animal models. To determine if this nutritional intervention has similar actions in a long-lived primate species, the National Institute on Aging (NIA) initiated a study in 1987 to investigate the effects of a 30% CR in male and female rhesus macaques (Macaca mulatta) of a broad age range. We have observed physiological effects of CR that parallel rodent studies and may be predictive of an increased lifespan. Specifically, results from the NIA study have demonstrated that CR decreases body weight and fat mass, improves glucoregulatory function, decreases blood pressure and blood lipids, and decreases body temperature. Juvenile males exhibited delayed skeletal and sexual maturation. Adult bone mass was not affected by CR in females nor were several reproductive hormones or menstrual cycling. CR attenuated the age-associated decline in both dehydroepiandrosterone (DHEA) and melatonin in males. Although 81% of the monkeys in the study are still alive, preliminary evidence suggests that CR will have beneficial effects on morbidity and mortality. We are now preparing a battery of measures to provide a thorough and relevant analysis of the effectiveness of CR at delaying the onset of age-related disease and maintaining function later into life.

Caloric Restriction in Primates and Relevance to Humans

Abstract: Dietary caloric restriction (CR) is the only intervention conclusively and reproducibly shown to slow aging and maintain health and vitality in mammals. Although this paradigm has been known for over 60 years, its precise biological mechanisms and applicability to humans remain unknown. We began addressing the latter question in 1987 with the first controlled study of CR in primates (rhesus and squirrel monkeys, which are evolutionarily much closer to humans than the rodents most frequently employed in CR studies). To date, our results strongly suggest that the same beneficial “antiaging” and/or “antidisease” effects observed in CR rodents also occur in primates. These include lower plasma insulin levels and greater sensitivity; lower body temperatures; reduced cholesterol, triglycerides, blood pressure, and arterial stiffness; elevated HDL; and slower age‐related decline in circulating levels of DHEAS. Collectively, these biomarkers suggest that CR primates will be less likely to incur diabetes, cardiovascular problems, and other age‐related diseases and may in fact be aging more slowly than fully fed counterparts.

Calorie Restriction in Primates: Will It Work and How Will We Know?

Dietary caloric restriction is the most robust and reproducible means of slowing aging and extending lifespan and healthspan in short‐lived mammals and lower organisms. Numerous aspects of this paradigm have been investigated in laboratories around the world since its inception more than 60 years ago. However, two questions about calorie restriction remain unanswered to this day: (1) By what mechanism does it work? and (2) Will it work in humans? This review will focus on the latter with particular emphasis on evaluation criteria, current studies in primate models, available data, and plans for actual human caloric restriction interventions.

Development of Calorie Restriction Mimetics as a Prolongevity Strategy

Abstract: By applying calorie restriction (CR) at 30‐50% below ad libitum levels, studies in numerous species have reported increased life span, reduced incidence and delayed onset of age‐related diseases, improved stress resistance, and decelerated functional decline. Whether this nutritional intervention is relevant to human aging remains to be determined; however, evidence emerging from CR studies in nonhuman primates suggests that response to CR in primates parallels that observed in rodents. To evaluate CR effects in humans, clinical trials have been initiated. Even if evidence could substantiate CR as an effective antiaging strategy for humans, application of this intervention would be problematic due to the degree and length of restriction required. To meet this challenge for potential application of CR, new research to create “caloric restriction mimetics” has emerged. This strategy focuses on identifying compounds that mimic CR effects by targeting metabolic and stress response pathways affected by CR, but without actually restricting caloric intake. Microarray studies show that gene expression profiles of key enzymes in glucose (energy) handling pathways are modified by CR. Drugs that inhibit glycolysis (2‐deoxyglucose) or enhance insulin action (metformin) are being assessed as CR mimetics. Promising results have emerged from initial studies regarding physiological responses indicative of CR (reduced body temperature and plasma insulin) as well as protection against neurotoxicity, enhanced dopamine action, and upregulated brain‐derived neurotrophic factor. Further life span analyses in addition to expanded toxicity studies must be completed to assess the potential of any CR mimetic, but this strategy now appears to offer a very promising and expanding research field.

Delay of T cell senescence by caloric restriction in aged long-lived nonhuman primates

Caloric restriction (CR) has long been known to increase median and maximal lifespans and to decreases mortality and morbidity in short-lived animal models, likely by altering fundamental biological processes that regulate aging and longevity. In rodents, CR was reported to delay the aging of the immune system (immune senescence), which is believed to be largely responsible for a dramatic increase in age-related susceptibility to infectious diseases. However, it is unclear whether CR can exert similar effects in long-lived organisms. Previous studies involving 2- to 4-year CR treatment of long-lived primates failed to find a CR effect or reported effects on the immune system opposite to those seen in CR-treated rodents. Here we show that long-term CR delays the adverse effects of aging on nonhuman primate T cells. CR effected a marked improvement in the maintenance and/or production of naïve T cells and the consequent preservation of T cell receptor repertoire diversity. Furthermore, CR also improved T cell function and reduced production of inflammatory cytokines by memory T cells. Our results provide evidence that CR can delay immune senescence in nonhuman primates, potentially contributing to an extended lifespan by reducing susceptibility to infectious disease.

Circulating adiponectin levels increase in rats on caloric restriction: the potential for insulin sensitization.

Caloric restriction (CR) has a well-known insulin sensitizing effect in vivo. Although this effect has been confirmed in rodents and primates for many years, its precise molecular mechanisms remain unknown. Here we show a significant increase in plasma adiponectin and a decrease in blood glucose, plasma triglyceride and insulin levels in rats maintained on CR diet for 2, 10, 15, and 20 months. Long-term CR rats exhibited significantly higher insulin-stimulated insulin receptor tyrosine phosphorylation and lower PTP-1B activity both in liver and skeletal muscle than those observed in rats fed ad libitum (AL). In addition, the triglyceride levels in these tissues were significantly lower in long-term CR animals. Interestingly, concentrations of plasma adiponectin in long-term CR rats were associated with increased expression of the transcription factor mRNAs for the peroxisome proliferator-activated receptor (PPAR)alpha, gamma and delta, but decreased expression for SREBP-1c, resulting in a concerted modulation in the expression of key transcription target genes involved in fatty acid oxidation and energy combustion in liver. Taken together, our findings suggest an important role for adiponectin in the beneficial effects of long-term CR.

Calorie restriction attenuates Alzheimer's disease type brain amyloidosis in Squirrel monkeys (Saimiri sciureus)

Recent studies from our laboratories and others suggest that calorie restriction (CR) may benefit Alzheimers disease (AD) by preventing amyloid-beta (Abeta) neuropathology in the mouse models of AD. Moreover, we found that promotion of the NAD+-dependent SIRT1 mediated deacetylase activity, a key regulator in CR extension of life span, may be a mechanism by which CR influences AD-type neuropathology. In this study we continued to explore the role of CR in AD-type brain amyloidosis in Squirrel monkeys (Saimiri sciureus). Monkeys were maintained on the normal and CR diets throughout the entire lifespan until they died of natural causes. We found that 30% CR resulted in reduced contents of Abeta1-40 and Abeta1-42 peptides in the temporal cortex of Squirrel monkeys, relative to control (CON) fed monkeys. The decreased contents of cortical Abeta peptide inversely correlated with SIRT1 protein concentrations in the same brain region; no detectable change in total full-length amyloid-beta protein precursor (AbetaPP) level was found. Most interestingly, we found that 30% CR resulted in a select elevation of alpha- but not beta- or gamma- secretase activity which coincided with decreased ROCK1 protein content in the same brain region, relative to CON group. Collectively, the study suggests that investigation of the role of CR in non-human primates may provide a valuable approach for further clarifying the role of CR in AD.