Effect of chronic caloric restriction on the circadian regulation of physiological and behavioral variables in old male B6C3F1 mice

In the land of not-unhappiness: On the state-of-the-art of targeting aging and age-related diseases by biomedical research

The concept of the Land of Not-Unhappiness refers to the potential achievement of eliminating the pathologies of the aging process. To inform of how close we are to settling in the land, we summarize and review the achievements of research on anti-aging interventions over the last hundred years with a specific focus on strategies that slow down metabolism, compensate for aging-related losses, and target a broad range of age-related diseases. We critically evaluate the existing interventions labeled as "anti-aging," such as calorie restriction, exercise, stem cell administration, and senolytics, to provide a down-to-earth evaluation of their current applicability in counteracting aging. Throughout the text, we have maintained a light tone to make it accessible to non-experts in biogerontology, and provide a broad overview for those considering conducting studies, research, or seeking to understand the scientific basis of anti-aging medicine.

Costs of exploratory behavior: the energy trade-off hypothesis and the allocation model tested under caloric restriction

In order to maintain the energy balance, animals often exhibit several physiological adjustments when subjected to a decrease in resource availability. Specifically, some rodents show increases in behavioral activity in response to food restriction; a response regarded as a paradox because it would imply an investment in locomotor activity, despite the lack of trophic resources. Here, we aim to explore the possible existence of trade-offs between metabolic variables and behavioral responses when rodents are faced to stochastic deprivation of food and caloric restriction. Adult BALB/c mice were acclimatized for four weeks to four food treatments: two caloric regimens (ad libitum and 60% restriction) and two periodicities (continuous and stochastic). In these mice, we analyzed: exploratory behavior and home-cage behavior, basal metabolic rate, citrate synthase and cytochrome oxidase c enzyme activity (in liver and skeletal muscle), body temperature and non-shivering thermogenesis. Our results support the model of allocation, which indicates commitments between metabolic rates and exploratory behavior, in a caloric restricted environment. Specifically, we identify the role of thermogenesis as a pivotal budget item, modulating the reallocation of energy between behavior and basal metabolic rate. We conclude that brown adipose tissue and liver play a key role in the development of paradoxical responses when facing decreased dietary availability.

Methionine Restriction Extends Lifespan in Progeroid Mice and Alters Lipid and Bile Acid Metabolism

Dietary intervention constitutes a feasible approach for modulating metabolism and improving the health span and lifespan. Methionine restriction (MR) delays the appearance of age-related diseases and increases longevity in normal mice. However, the effect of MR on premature aging remains to be elucidated. Here, we describe that MR extends lifespan in two different mouse models of Hutchinson-Gilford progeria syndrome (HGPS) by reversing the transcriptome alterations in inflammation and DNA-damage response genes present in this condition. Further, MR improves the lipid profile and changes bile acid levels and conjugation, both in wild-type and in progeroid mice. Notably, treatment with cholic acid improves the health span and lifespan in vivo. These results suggest the existence of a metabolic pathway involved in the longevity extension achieved by MR and support the possibility of dietary interventions for treating progeria.

Dominance rank and the presence of sexually receptive females predict feces-measured body temperature in male chimpanzees

Quantifying the costs of mating is key for understanding life-history trade-offs. As a reflection of metabolic rate, body temperature is one metric for assaying these costs. However, conventional methods for measuring body temperature are invasive and unsuitable for the study of free-living populations of endangered species, including great apes. A promising proxy for body temperature is fecal temperature, the internal temperature of fecal deposits shortly following defecation. We validated this method with humans, finding that maximum fecal temperature is a reliable proxy for rectal temperature. We then applied this method to wild chimpanzees (Pan troglodytes schweinfurthii) at Ngogo, Kibale National Park, Uganda. We collected and analyzed 101 fecal temperature measurements from 43 adult chimpanzees (male: N = 28; female: N = 15). Chimpanzee fecal temperature ranged from 33.4 to 38.9 °C, with a mean of 35.8 °C. Although fecal temperature was not predicted by sex, age, or ambient temperature, male fecal temperature was 1.1 °C higher on days when sexually receptive females were present and was positively correlated with male dominance rank. Post hoc analyses showed that overall copulation rates, but not aggression rates, were positively correlated with fecal temperature, suggesting that sexual physiology and behavior best explain mating-related temperature variation. Together, these results indicate fecal temperature is a reliable proxy for core body temperature in large-bodied mammals, captures metabolic costs associated with male mating behavior, and represents a valuable noninvasive tool for biological field research.

Flipping the Metabolic Switch: Understanding and Applying the Health Benefits of Fasting

OBJECTIVE

Intermittent fasting (IF) is a term used to describe a variety of eating patterns in which no or few calories are consumed for time periods that can range from 12 hours to several days, on a recurring basis. This review is focused on the physiological responses of major organ systems, including the musculoskeletal system, to the onset of the metabolic switch: the point of negative energy balance at which liver glycogen stores are depleted and fatty acids are mobilized (typically beyond 12 hours after cessation of food intake).

RESULTS AND CONCLUSIONS

Emerging findings suggest that the metabolic switch from glucose to fatty acid-derived ketones represents an evolutionarily conserved trigger point that shifts metabolism from lipid/cholesterol synthesis and fat storage to mobilization of fat through fatty acid oxidation and fatty acid-derived ketones, which serve to preserve muscle mass and function. Thus, IF regimens that induce the metabolic switch have the potential to improve body composition in overweight individuals. Moreover, IF regimens also induce the coordinated activation of signaling pathways that optimize physiological function, enhance performance, and slow aging and disease processes. Future randomized controlled IF trials should use biomarkers of the metabolic switch (e.g., plasma ketone levels) as a measure of compliance and of the magnitude of negative energy balance during the fasting period.

Intermittent metabolic switching, neuroplasticity and brain health

During evolution, individuals whose brains and bodies functioned well in a fasted state were successful in acquiring food, enabling their survival and reproduction. With fasting and extended exercise, liver glycogen stores are depleted and ketones are produced from adipose-cell-derived fatty acids. This metabolic switch in cellular fuel source is accompanied by cellular and molecular adaptations of neural networks in the brain that enhance their functionality and bolster their resistance to stress, injury and disease. Here, we consider how intermittent metabolic switching, repeating cycles of a metabolic challenge that induces ketosis (fasting and/or exercise) followed by a recovery period (eating, resting and sleeping), may optimize brain function and resilience throughout the lifespan, with a focus on the neuronal circuits involved in cognition and mood. Such metabolic switching impacts multiple signalling pathways that promote neuroplasticity and resistance of the brain to injury and disease.

Nutrition modulation of human aging: The calorie restriction paradigm

Globally, the aging population is growing rapidly, creating an urgent need to attenuate age-related health conditions, including metabolic disease and disability. A promising strategy for healthy aging based on consistently positive results from studies with a variety of species, including non-human primates (NHP), is calorie restriction (CR), or the restriction of energy intake while maintaining intake of essential nutrients. The burgeoning evidence for this approach in humans is reviewed and the major study to date to address this question, CALERIE (Comprehensive Assessment of the Long-term Effects of Reducing Intake of Energy), is described. CALERIE findings indicate the feasibility of CR in non-obese humans, confirm observations in NHP, and are consistent with improvements in disease risk reduction and potential anti-aging effects. Finally, the mechanisms of CR in humans are reviewed which sums up the fact that evolutionarily conserved mechanisms mediate the anti-aging effects of CR. Overall, the prospect for further research in both NHP and humans is highly encouraging.

Epigenetic alterations in the suprachiasmatic nucleus and hippocampus contribute to age-related cognitive decline

Circadian rhythm dysfunction and cognitive decline, specifically memory loss, frequently accompany natural aging. Circadian rhythms and memory are intertwined, as circadian rhythms influence memory formation and recall in young and old rodents. Although, the precise relationship between circadian rhythms and memory is still largely unknown, it is hypothesized that circadian rhythm disruption, which occurs during aging, contributes to age-associated cognitive decline, specifically memory loss. While there are a variety of mechanisms that could mediate this effect, changes in the epigenome that occur during aging has been proposed as a potential candidate. Interestingly, epigenetic mechanisms, such as DNA methylation and sirtuin1 (SIRT1) are necessary for both circadian rhythms and memory. During aging, similar alterations of epigenetic mechanisms occur in the suprachiasmatic nucleus (SCN) and hippocampus, which are necessary for circadian rhythm generation and memory, respectively. Recently, circadian rhythms have been linked to epigenetic function in the hippocampus, as some of these epigenetic mechanisms oscillate in the hippocampus and are disrupted by clock gene deletion. The current paper will review how circadian rhythms and memory change with age, and will suggest how epigenetic changes in these processes might contribute to age-related cognitive decline.

Caloric restriction in lean and obese strains of laboratory rat: effects on body composition, metabolism, growth and overall health

NEW FINDINGS

What is the central question of this study? How do lean and obese rats respond physiologically to caloric restriction? What is the main finding and its importance? Obese rats show marked benefits compared with lean animals. Reduced body fat is associated with improved longevity with caloric restriction (CR) in rodents. Little is known regarding effects of CR in genetically lean versus obese strains. Long-Evans (LE) and Brown Norway (BN) rats make an ideal comparison for a CR study because the percentage body fat of young adult LE rats is double that of BN rats. Male LE and BN rats were either fed ad libitum (AL) or were calorically restricted to 80 or 90% of their AL weight. The percentages of fat, lean and fluid mass were measured non-invasively at 2- to 4-week intervals. Metabolic rate and respiratory quotient were measured after 3, 6, 9 and 12 months of CR. Overall health was scored monthly. The percentage of fat of the LE strain decreased with CR, whereas the percentage of fat of the BN strain remained above the AL group for several months. The percentage of lean mass increased above the AL for both strains subjected to CR. The percentage of fluid was unaffected by CR. The average metabolic rate over 22 h of the BN rats subjected to CR was reduced, whereas that of LE rats was increased slightly above the AL group. The respiratory quotient of BN rats was decreased with CR. Overall health of the CR LE group was significantly improved compared with that of the AL group, whereas health of the CR BN rats was impaired compared with the AL group. Overall, the lean BN and obese LE strains differ markedly in fat utilization and metabolic response to prolonged CR. There appears to be little benefit of CR in the lean strain.

Behavioral mechanisms underlying nicotine reinforcement

Cigarette smoking is the leading cause of preventable deaths worldwide, and nicotine, the primary psychoactive constituent in tobacco, drives sustained use. The behavioral actions of nicotine are complex and extend well beyond the actions of the drug as a primary reinforcer. Stimuli that are consistently paired with nicotine can, through associative learning, take on reinforcing properties as conditioned stimuli. These conditioned stimuli can then impact the rate and probability of behavior and even function as conditioning reinforcers that maintain behavior in the absence of nicotine. Nicotine can also act as a conditioned stimulus (CS), predicting the delivery of other reinforcers, which may allow nicotine to acquire value as a conditioned reinforcer. These associative effects, establishing non-nicotine stimuli as conditioned stimuli with discriminative stimulus and conditioned reinforcing properties as well as establishing nicotine as a CS, are predicted by basic conditioning principles. However, nicotine can also act non-associatively. Nicotine directly enhances the reinforcing efficacy of other reinforcing stimuli in the environment, an effect that does not require a temporal or predictive relationship between nicotine and either the stimulus or the behavior. Hence, the reinforcing actions of nicotine stem both from the primary reinforcing actions of the drug (and the subsequent associative learning effects) as well as the reinforcement enhancement action of nicotine which is non-associative in nature. Gaining a better understanding of how nicotine impacts behavior will allow for maximally effective tobacco control efforts aimed at reducing the harm associated with tobacco use by reducing and/or treating its addictiveness.

Links between thermoregulation and aging in endotherms and ectotherms

While the link between thermoregulation and aging is generally accepted, much further research, reflection, and debate is required to elucidate the physiological and molecular pathways that generate the observed thermal-induced changes in lifespan. Our aim in this review is to present, discuss, and scrutinize the thermoregulatory mechanisms that are implicated in the aging process in endotherms and ectotherms. Our analysis demonstrates that low body temperature benefits lifespan in both endothermic and ectothermic organisms. Research in endotherms has delved deeper into the physiological and molecular mechanisms linking body temperature and longevity. While research in ectotherms has been steadily increasing during the past decades, further mechanistic work is required in order to fully elucidate the underlying phenomena. What is abundantly clear is that both endotherms and ectotherms have a specific temperature zone at which they function optimally. This zone is defended through both physiological and behavioral means and plays a major role on organismal senescence. That low body temperature may be beneficial for lifespan is contrary to conventional medical theory where reduced body temperature is usually considered as a sign of underlying pathology. Regardless, this phenomenon has been targeted by scientists with the expectation that advancements may compress morbidity, as well as lower disease and mortality risk. The available evidence suggests that lowered body temperature may prolong life span, yet finding the key to temperature regulation remains the problem. While we are still far from a complete understanding of the mechanisms linking body temperature and longevity, we are getting closer.

The influence of shc proteins on the whole body energetic response to calorie restriction initiated in 3-month-old mice

There is increasing evidence that Shc proteins play a role in energy metabolism, and we have previously reported that knockdown of Shc proteins influences the energetic response to acute (3 days) calorie restriction (CR) in 18-month-old mice. Whether Shc proteins play a role in the metabolic response to CR in younger mice has yet to be elucidated. Hence, we sought to determine the impact of 3 days and longer term (2 months) CR on energy expenditure (EE) and respiratory quotient (RQ) in 3 month-old Shc knockout (ShcKO) and wild-type (WT) mice. ShcKO mice decreased (P < 0.001) EE normalized for body weight (EE_BW) by 3 days of CR, while no such change was observed in WT animals. However, both ShcKO and WT mice decreased (P < 0.001) EE_BW at 2 months of CR and there were no differences in body weight between the ShcKO and WT mice at either 3 days or 2 months of CR. Consistent with increased fatty acid oxidation, only ShcKO mice maintained decreased (P < 0.001) 24 h RQ through 2 months of CR, suggesting that they were able to maintain increased fatty acid oxidation for a longer period of time than WT mice. These results indicate that Shc proteins may contribute to some of the acute energetic responses to CR.

Thermoregulatory, cardiovascular, and metabolic responses to mild caloric restriction in the Brown Norway rat

Caloric restriction (CR) has been demonstrated to prolong the life span of a variety of species. CR-induced reduction in core temperature (Tc) is considered a key mechanism responsible for prolonging life span in rodents; however, little is known about the regulation of CR-induced hypothermia as a function of the circadian cycle. We assessed how mild CR that resulted in a 10% reduction in body weight affected the 24 h patterns of Tc as well as heart rate (HR) and motor activity (MA) of the Brown Norway rat. Telemetered rats were allowed to feed for 20 weeks ad libitum (AL) or given a CR diet. Tc, HR, and MA of CR rats exhibited nocturnal reductions and diurnal elevations, opposite to that of AL rats. The effects of CR appeared to peak at ∼4 weeks. Metabolic rate (MR) and respiratory exchange ratio (RER) were measured overnight after 18 weeks of CR. MR and RER were elevated markedly at the time of feeding in CR rats and then declined during the night. We found that the pattern of Tc was altered with CR, characterized by elimination of high nocturnal Tc's typically observed in AL animals. In terms of mechanisms to prolong life span in CR animals, we suggest that the shift in the pattern of Tc during CR (i.e., elimination of high Tc's) may be as critical as the overall mean reduction in Tc. Future studies should address how the time of feeding may affect the thermoregulatory response in calorically restricted rats.

Decreased body weight and hepatic steatosis with altered fatty acid ethanolamide metabolism in aged L-Fabp -/- mice

The tissue-specific sources and regulated production of physiological signals that modulate food intake are incompletely understood. Previous work showed that L-Fabp(-/-) mice are protected against obesity and hepatic steatosis induced by a high-fat diet, findings at odds with an apparent obesity phenotype in a distinct line of aged L-Fabp(-/-) mice. Here we show that the lean phenotype in L-Fabp(-/-) mice is recapitulated in aged, chow-fed mice and correlates with alterations in hepatic, but not intestinal, fatty acid amide metabolism. L-Fabp(-/-) mice exhibited short-term changes in feeding behavior with decreased food intake, which was associated with reduced abundance of key signaling fatty acid ethanolamides, including oleoylethanolamide (OEA, an agonist of PPARα) and anandamide (AEA, an agonist of cannabinoid receptors), in the liver. These reductions were associated with increased expression and activity of hepatic fatty acid amide hydrolase-1, the enzyme that degrades both OEA and AEA. Moreover, L-Fabp(-/-) mice demonstrated attenuated responses to OEA administration, which was completely reversed with an enhanced response after administration of a nonhydrolyzable OEA analog. These findings demonstrate a role for L-Fabp in attenuating obesity and hepatic steatosis, and they suggest that hepatic fatty acid amide metabolism is altered in L-Fabp(-/-) mice.

Long-term restricted feeding alters circadian expression and reduces the level of inflammatory and disease markers

The circadian clock in peripheral tissues can be entrained by restricted feeding (RF), a regimen that restricts the duration of food availability with no calorie restriction (CR). However, it is not known whether RF can delay the occurrence of age-associated changes similar to CR. We measured circadian expression of clock genes, disease marker genes, metabolic factors and inflammatory and allergy markers in mouse serum, liver, jejunum and white adipose tissue (WAT) after long-term RF of 4 months. We found that circadian rhythmicity is more robust and is phase advanced in most of the genes and proteins tested under RF. In addition, average daily levels of some disease and inflammatory markers were reduced under RF, including liver Il-6 mRNA, tumour necrosis factor (TNF)-α and nuclear factor κB (NF-κB) protein; jejunum Arginase, Afp, Gadd45β, Il-1α and Il-1β mRNA, and interleukin (IL)-6 and TNF-α protein and WAT Il-6, Il-1β, Tnfα and Nfκb mRNA. In contrast, the anti-inflammatory cytokine Il-10 mRNA increased in the liver and jejunum. Our results suggest that RF may share some benefits with those of CR. As RF is a less harsh regimen to follow than CR, the data suggest it could be proposed for individuals seeking to improve their health.

Long-term calorie restriction, but not endurance exercise, lowers core body temperature in humans

Reduction of body temperature has been proposed to contribute to the increased lifespan in calorie restricted animals and mice overexpressing the uncoupling protein-2 in hypocretin neurons. However, nothing is known regarding the long-term effects of calorie restriction (CR) with adequate nutrition on body temperature in humans. In this study, 24-hour core body temperature was measured every minute by using ingested telemetric capsules in 24 men and women (mean age 53.7±9.4 yrs) consuming a CR diet for an average of 6 years, 24 age- and sex-matched sedentary (WD) and 24 body fat-matched exercise-trained (EX) volunteers, who were eating Western diets. The CR and EX groups were significantly leaner than the WD group. Energy intake was lower in the CR group (1769±348 kcal/d) than in the WD (2302±668 kcal/d) and EX (2798±760 kcal/d) groups (P<0.0001). Mean 24-hour, day-time and night-time core body temperatures were all significantly lower in the CR group than in the WD and EX groups (P≤0.01). Long-term CR with adequate nutrition in lean and weight-stable healthy humans is associated with a sustained reduction in core body temperature, similar to that found in CR rodents and monkeys. This adaptation is likely due to CR itself, rather than to leanness, and may be involved in slowing the rate of aging.

Effect of calorie restriction on the free-living physical activity levels of nonobese humans: results of three randomized trials

The objective of this study was to evaluate the influence of calorie restriction (CR) on free-living physical activity levels among humans. Data were from three CALERIE phase I site-specific protocols. Participants were nonobese (body mass index = 23.5-29.9 kg/m² adults randomly assigned to 25% CR, low-calorie diet (LCD, 890 kcal/day supplement diet until 15% weight loss, then weight maintenance), or control at Pennington Biomedical Research Center (PBRC); 30% or 10% CR at Tufts University; and 20% CR or control at Washington University School of Medicine (WUSM). Activity was measured at months 0, 3, and 6 (PBRC) and at months 0, 3, 6, 9, and 12 (WUSM and Tufts). Total daily energy expenditure (TEE) by doubly labeled water and resting metabolic rate (RMR) were used to compute activity energy expenditure: AEE = TEE - RMR - 0.1 * TEE. Accelerometry and 7-day recall categorized activities by intensity. At Tufts, the 10% and 30% CR groups experienced significant decreases in AEE at months 6, 9, and 12. At month 6, a larger decrease in AEE was observed in the CR than the control group at WUSM. At months 3 and 6, larger decreases in AEE were observed in the CR and LCD groups than the control group at PBRC. Accelerometry and 7-day PAR did not consistently detect changes in activity categories. CR-associated changes in AEE were variable but, generally, reduced the energy deficit, which would reduce the expected rate of weight loss. Accelerometry and recall did not consistently explain reduced AEE, suggesting that increased muscle efficiency and/or decreased fidgeting accounted for decreased AEE. Inaccuracy of accelerometry and recall also likely negatively affected sensitivity.

Fasting-induced reductions in cardiovascular and metabolic variables occur sooner in obese versus lean mice

It is not uncommon for laboratory animals to be fasted prior to experimentation. Fasting evokes marked reductions in heart rate (HR), blood pressure (BP), heat production and oxygen consumption (VO(2)) in rodents. Mice with diet-induced obesity exhibit elevated HR and BP, and lower VO(2) and heat production in the fed condition versus their lean counterparts. It is unknown whether body composition alters the tempo of response to fasting. We tested the hypothesis that cardiovascular and metabolic responses to fasting are delayed in obese versus lean male C57BL/6J mice. In the fed condition, mice that consumed high-fat (HF, 45% fat) chow for 98 ± 5 days had elevated (P < 0.05) body fat percentage (DEXA), serum leptin (ELISA), HR and BP (72-h biotelemetry), and lower (P < 0.05) heat production and VO(2) (72-h metabolic chamber) versus animals that consumed standard chow (CON, 10% fat; n = 16 per group). HR, BP, VO(2), heat production and serum leptin decreased (all P < 0.05) in response to a 16-h fast (16:00-08:00 h) in both groups. Although the overall fold changes in cardiovascular and metabolic parameters were similar in magnitude among animals, fasting-induced reductions in cardiovascular and metabolic variables occurred ∼4 and ∼7 h earlier (P < 0.05), respectively, in HF versus CON mice. These findings indicate that while metabolic and cardiovascular stress evoked by a 16-h fast at 22°C is not different between HF and CON mice, fasting-induced responses occur sooner in obese animals.

Food anticipation in Bmal1-/- and AAV-Bmal1 rescued mice: a reply to Fuller et al

Evidence that circadian food-anticipatory activity and temperature rhythms are absent in Bmal1 knockout mice and rescued by restoration of Bmal1 expression selectively in the dorsomedial hypothalamus was published in 2008 by Fuller et al and critiqued in 2009 by Mistlberger et al. Fuller et al have responded to the critique with new information. Here we update our critique in the light of this new information. We also identify and correct factual and conceptual errors in the Fuller et al response. We conclude that the original results of Fuller et al remain inconclusive and fail to clarify the role of Bmal1 or the dorsomedial hypothalamus in the generation of food-entrainable rhythms in mice.

Effect of acute and chronic caloric restriction and metabolic glucoprivation on spontaneous physical activity in obesity-prone and obesity-resistant rats

Caloric restriction (CR) and metabolic glucoprivation affect spontaneous physical activity (SPA), but it's unknown whether these treatments similarly affect SPA in selectively bred obesity-prone (OP) and -resistant (OR) rats. OR rats have greater basal SPA and are more responsive to treatments that modulate SPA, such as orexin A administration. We hypothesized that OR rats would be more sensitive to other treatments modulating SPA. To test this, continuous 24-h SPA was measured before and during acute (24 h) and chronic (8 wk) CR in OR, OP, and Sprague-Dawley rats. Pharmacological glucoprivation was produced by injection of 2-deoxyglucose (2-DG), and SPA was measured 5 h postinjection. Acute CR increased SPA in all groups; however, the effect was dependent on the index of SPA and time interval during the 24-h time period. In contrast to OR rats, chronic CR increased distance traveled, ambulatory episodes, and time spent in ambulation and stereotypy during the time interval preceding anticipation of food in OP and Sprague-Dawley rats. Although the effects of 2-DG treatment on SPA were minimal, OR rats had significantly greater SPA than OP and Sprague-Dawley rats independent of treatment. That chronic CR failed to result in significant changes in SPA in OR rats suggests that these rats may be especially unresponsive to treatments modulating feeding. This insensitivity coupled with elevated basal SPA levels may in part mediate phenotypic traits of lean rats.

Influence of calorie restriction on measures of age-related cognitive decline: role of increased physical activity

Controversy exists as to whether lifelong 40% calorie restriction (CR) enhances, has no effect on, or disrupts cognitive function during aging. Here, we report the effects of CR versus ad-lib feeding on cognitive function in male Brown Norway x Fisher344 rats across a range of ages (8-38 months), using two tasks that are differentially sensitive to age-related cognitive decline: object recognition and Morris water maze (MWM). All ages performed equally in object recognition, whereas, as a group, CR rats were impaired. In contrast, there was an age-related impairment in the MWM that was attenuated by CR as measured by time in proximity with and latency to reach the platform. Distance to the platform, a more sensitive measure, was not affected by CR. Finally, CR resulted in an overall increase in physical activity, one of several behavioral confounders to consider in the interpretation of cognitive outcomes in both tasks.

Effect of calorie restriction on resting metabolic rate and spontaneous physical activity

OBJECTIVE

It is unclear if resting metabolic rate (RMR) and spontaneous physical activity (SPA) decrease in weight-reduced non-obese participants. Additionally, it is unknown if changes in SPA, measured in a respiratory chamber, reflect changes in free-living physical activity level (PAL).

RESEARCH METHODS AND PROCEDURES

Participants (N = 48) were randomized into 4 groups for 6 months: calorie restriction (CR, 25% restriction), CR plus structured exercise (CR+EX, 12.5% restriction plus 12.5% increased energy expenditure via exercise), low-calorie diet (LCD, 890 kcal/d supplement diet until 15% weight loss, then weight maintenance), and control (weight maintenance). Measurements were collected at baseline, Month 3, and Month 6. Body composition and RMR were measured by DXA and indirect calorimetry, respectively. Two measures of SPA were collected in a respiratory chamber (percent of time active and kcal/d). Free-living PAL (PAL = total daily energy expenditure by doubly labeled water/RMR) was also measured. Regression equations at baseline were used to adjust RMR for fat-free mass and SPA (kcal/d) for body weight.

RESULTS

Adjusted RMR decreased at Month 3 in the CR group and at Month 6 in the CR+EX and LCD groups. Neither measure of SPA decreased significantly in any group. PAL decreased at Month 3 in the CR and LCD groups, but not in the CR+EX group, who engaged in structured exercise. Changes in SPA in the chamber and free-living PAL were not related.

DISCUSSION

Body weight is defended in non-obese participants during modest caloric restriction, evidenced by metabolic adaptation of RMR and reduced energy expenditure through physical activity.

Hormonal regulation of longevity in mammals

Multiple biological and environmental factors impact the life span of an organism. The endocrine system is a highly integrated physiological system in mammals that regulates metabolism, growth, reproduction, and response to stress, among other functions. As such, this pervasive entity has a major influence on aging and longevity. The growth hormone, insulin-like growth factor-1 and insulin pathways have been at the forefront of hormonal control of aging research in the last few years. Other hormones, including those from the thyroid and reproductive system have also been studied in terms of life span regulation. The relevance of these hormones to human longevity remains to be established, however the evidence from other species including yeast, nematodes, and flies suggest that evolutionarily well-conserved mechanisms are at play and the endocrine system is a key determinant.

Generation and characterization of sodium-dicarboxylate cotransporter-deficient mice

The sodium-dependent dicarboxylate cotransporter (NaDC1) has a proposed function of reabsorbing various Krebs cycle intermediates in the kidney and the small intestine. Since Krebs cycle intermediates have been suggested to be important for renal cell survival and recovery after hypoxia and reoxygenation, the transporter may play a role in the recovery of the kidney. Additionally, mutations in the transporter homolog in Drosophila led to fly longevity which was thought to be similar to that induced by caloric restriction (CR). To clarify the role of the sodium dicarboxylate cotransporter in vivo we generated cotransporter-deficient mice. These knockout mice excreted significantly higher amounts of various Krebs cycle intermediates in their urine; thus confirming the proposed function to reabsorb these metabolic intermediates in the kidney. No other phenotypic change was identified in these mice, however. Transporter deficiency did not affect renal function under normal physiological conditions, nor did it have an effect on renal damage and recovery from ischemic injury. Additionally, the absence of the transporter did not lead to metabolic or physiological changes associated with CR. Our results suggest that although the sodium dicarboxylate cotransporter is involved in regulating levels of various Krebs cycle intermediates in the kidney, impaired uptake of these intermediates does not significantly affect renal function under normal or ischemic stress.

Calorie restriction in nonhuman primates: assessing effects on brain and behavioral aging

Dietary caloric restriction (CR) is the only intervention repeatedly demonstrated to retard the onset and incidence of age-related diseases, maintain function, and extend both lifespan and health span in mammals, including brain and behavioral function. In 70 years of study, such beneficial effects have been demonstrated in rodents and lower animals. Recent results emerging from ongoing studies of CR in humans and nonhuman primates suggest that many of the same anti-disease and anti-aging benefits observed in rodent studies may be applicable to long-lived species. Results of studies in rhesus monkeys indicate that CR animals (30% less than controls) are healthier than fully-fed counterparts based on reduced incidence of various diseases, exhibit significantly better indices of predisposition to disease and may be aging at a slower rate based on analysis of selected indices of aging. The current review discusses approaches taken in studies of rhesus monkeys to analyze age-related changes in brain and behavioral function and the impact of CR on these changes. Approaches include analyses of gross and fine locomotor performance as well as brain imaging. In a related study it was observed that short-term CR (6 months) in adult rhesus monkeys can provide protection against a neurotoxic insult. Increasing interest in the CR paradigm will expand its role in demonstrating how nutrition can modulate the rate of aging and the mechanisms responsible for this modulation.

Caloric restriction and melatonin substitution: Effects on murine circadian parameters

Aging effects have been reported in endocrine, metabolic and behavioral circadian rhythms. The effects of age on the circadian system have been investigated primarily in rats and hamsters and only seldom in mice. Our aim was to assess the effects of two common "anti-aging" treatments, namely caloric restriction (CR) and melatonin substitution, on the circadian system of mice. Animals were subjected to phase delays of the light-dark cycle and constant darkness (DD). The most pronounced change in the murine circadian system was the length of the endogenous period, tau, which increased with age regardless of treatment. CR had diverse effects e.g., enabling a more rapid phase shift response while concomitantly leading to a fragmented circadian phenotype with considerable activity during the rest (light) phase. Melatonin enforced the adaptation to the light/dark cycle, thus facilitating a rapid re-entrainment to phase delayed lighting conditions. Interestingly, the melatonin-substituted animals displayed an increase in locomotor activity under constant darkness and in 50% of all cases a biphasic (split) activity pattern. These results contribute to the phenotypic evaluation of two very different approaches to intervene in the age-related degeneration of the mammalian circadian system. As both CR and melatonin have negative and positive effects on the behavioral expression of clock function (i.e., fragmentation of rhythms vs. faster re-entrainment), their usefulness in managing age-related circadian disorders may be limited.

Mild energy restriction alters mouse–nematode transmission dynamics in free-running indoor arenas

Energy restriction reduces Heligmosomoides polygyrus (Dujardin, 1845) (Nematoda) infection by reducing transmission-related behaviours but prolongs parasite survival by suppressing immune responses in individually housed mice. To determine the relative importance of these two processes in accumulation of worms in mouse populations, 10 female CD1 mice were housed in each of eight indoor arenas with ad libitum access to either an energy-sufficient (ES) diet or an energy-restricted (ER) diet with 20% less metabolizable energy (four arenas per diet). After 3 weeks, H. polygyrus transmission was initiated by introducing larvae onto damp peat trays. Mice adapted to the ER diet through increased food intake and nesting and reduced overall activity; after 6 weeks, nutritional and immunological measures were comparable between diet groups. With continuing exposure to parasite larvae, mice in both ER and ES arenas developed resistance to the incoming larvae; however, mice in the ER arenas accumulated lower worm burdens than mice in the ES arenas despite their increased contact with peat. We suggest that the comparable immunocompetence of mice in the ER and ES arenas enabled the ER mice exposed to higher transmission rates to more rapidly reject the parasites, leading to lower final worm numbers, a pattern frequently observed in other helminth infections.

αMUPA mice: a transgenic model for longevity induced by caloric restriction

Caloric restriction (CR) is currently the only therapeutic intervention known to attenuate aging in mammals, but the underlying mechanisms of this phenomenon are still poorly understood. To get more insight into these mechanisms, we took advantage of the alphaMUPA transgenic mice that previously were reported to spontaneously eat less and live longer compared with their wild-type control mice. Currently, two transgenic lines that eat less are available, thus implicating the transgenic enzyme, i.e. the urokinase-type plasminogen activator (uPA), in causing the reduced appetite. This phenotypic change could have resulted from the ectopic transgenic expression that we detected in the adult alphaMUPA brain, or alternatively, from a transgenic interference in brain development. Here, we have summarized similarities and differences so far found between alphaMUPA and calorically restricted mice. Recently, we noted several changes in the alphaMUPA liver, at the mitochondrial and cellular level, which consistently pointed to an enhanced capacity to induce apoptosis. In addition, alphaMUPA mice showed a reduced level of serum IGF-1 and a reduced incidence of spontaneously occurring or carcinogen-induced tumors in several tissues. In contrast, alphaMUPA did not differ from wild type mice in the levels of low molecular weight antioxidants when compared in several tissues at a young or an old age. Overall, the alphaMUPA model suggests that fine-tuning of the threshold for apoptosis, possibly linked in part to modulation of serum IGF-1 and mitochondrial functions, could play a role in the attenuation of aging in calorically restricted mice.

The effects of temperature reduction on gene expression and oxidative stress in skeletal muscle from adult zebrafish

Longevity is inversely proportional to ambient temperature in ectothermic organisms such as fish. However, the mechanism by which reducing temperature over a physiological range increases life span is not known and available data are derived primarily from invertebrates. With a rodent-like longevity and abundant biological resources, the zebrafish is an ideal vertebrate ectothermic model in which to investigate this phenomenon. As an initial approach, the effects of a year-long 10 degrees C reduction in water temperature on global gene expression in tail skeletal muscle from adult zebrafish were determined using an oligonucleotide microarray representing 15,512 genes. Expression levels for approximately 600 genes were up-regulated by 1.7-fold or greater by the reduction in temperature, while a similar number of transcripts were down regulated by more than 1.7-fold. Using gene ontology (GO) classifications for molecular function, two functional groups, "oxygen and reactive oxygen species metabolism" and "response to oxidative stress," were found to be overrepresented among up-regulated genes. Transcripts levels for the genes in these two categories were increased by temperature reduction (TR). However, temperature reduction did not suppress lipid peroxidation potential, protein carbonyl content, or 8-oxoguanine level. Additional studies will be required to further delineate the role of altered gene expression and oxidative stress on the longevity-promoting effects of temperature reduction.

The effects of different levels of dietary restriction on non-neoplastic diseases in male Sprague-Dawley rats

BACKGROUND AND AIMS

The primary purpose of the present study was to investigate the effects of 10, 25, and 40% dietary restriction (DR) on non-neoplastic diseases in rodents at 58 and 110 weeks of age, and to determine whether low-level DR (10 and 25%) can increase the survival rate and decrease variability in chronic bioassay studies.

METHODS

Male Sprague-Dawley (SD) rats (NCTR colony) were divided into four nutritional groups, consisting of an ad libitum (AL) group with unlimited access to the NIH-31 diet, and three dietary restricted (DR) groups given the NIH-31 diet reduced in amount by 10, 25, and 40%.

RESULTS

At 110 weeks of age, the incidence of cardiomyopathy was 95, 75, 45, and 15% for AL and 10, 25, and 40% DR rats, respectively; the incidence of nephropathy was 55, 20, 15, and 0% for AL and 10, 25, and 40% DR rats, respectively. The severity of chronic heart and kidney diseases was significantly reduced in all DR rat groups, with significant DR-dependent linear trends for these diseases. Moreover, DR prevented the progression of skin irritation to foot ulcers, and reduced the age-related degeneration in the adrenal, lacrimal, and thymus glands, and the liver.

CONCLUSIONS

These results clearly indicate that even low DR levels were effective in preventing or slowing the progression of these non-neoplastic diseases.

Energy deficiency alters behaviours involved in transmission ofHeligmosomoides polygyrus(Nematoda) in mice

Independent studies have shown that animal behaviour is affected by nutritional deficiency and that host behaviour influences parasite transmission. The objectives of this study were to determine whether energy deficiency alters the behaviour profile of mice and the rate of exposure of mice to naturally acquired Heligmosomoides polygyrus (Nematoda) larvae. Outbred CF-1 and CD-1 female mice were fed either a control or an energy-deficient (65% of control) diet for 7 days, after which time, the mice fed the deficient diet had consumed signficantly less energy, had lower rectal temperatures, and lower masses (CD-1 mice only) compared with control mice. On day 7, mice were placed individually in natural transmission arenas containing damp peat moss and parasite larvae for 6 h, during which time, each mouse was observed 60 times and her behaviour recorded. All mice were then returned to standard caging and fed the energy-sufficient diets to eliminate confounding effects of energy deficiency on the host immune response over the following 8 days. At necropsy, parasite numbers were significantly lower in the energy-deficient mice of both strains. The behaviour profile differed significantly between diet groups and between strains; deficient mice of both strains groomed less and dug in the peat substrate less than control mice. The frequency of grooming was positively correlated with worm burden in both strains, the frequency of mouthing the peat moss and of sleeping were positively associated with worm burden in CD-1 mice, and the frequency of standing and walking low was positively associated with worm burden in CF-1 mice. These results indicate that grooming and contact with the peat moss are important behaviours in transmission of H. polygyrus, that energy deficiency causes a decrease in the frequency of these behaviours, and that these behavioural changes may contribute to reduced parasite transmission in mice fed the energy-restricted diet.

Cardiovascular responses to caloric restriction and thermoneutrality in C57BL/6J mice

We utilized variations in caloric availability and ambient temperature (T(a)) to examine interrelationships between energy expenditure and cardiovascular function in mice. Male C57BL/6J mice (n = 6) were implanted with telemetry devices and housed in metabolic chambers for measurement of mean arterial pressure (MAP), heart rate (HR), O(2) consumption (VO(2)), and locomotor activity. Fasting (T(a) = 23 degrees C), initiated at the onset of the dark phase, resulted in large and transient depressions in MAP, HR, VO(2), and locomotor activity that occurred during hours 6-17, which suggests torporlike episodes. Food restriction (14 days, 60% of baseline intake) at T(a) = 23 degrees C resulted in progressive reductions in MAP and HR across days that were coupled with an increasing occurrence of episodic torporlike reductions in HR (<300 beats/min) and VO(2) (<1.0 ml/min). Exposure to thermoneutrality (T(a) = 30 degrees C, n = 6) reduced baseline light-period MAP (-14 +/- 2 mmHg) and HR (-184 +/- 12 beats/min). Caloric restriction at thermoneutrality produced further reductions in MAP and HR, but indications of torporlike episodes were absent. The results reveal that mice exhibit robust cardiovascular responses to both acute and chronic negative energy balance. Furthermore, we conclude that T(a) is a very important consideration when assessing cardiovascular function in mice.

Effect of the AIN-93M purified diet and dietary restriction on survival in Sprague-Dawley rats: implications for chronic studies

Survival, growth and dietary intake (DI) variables were monitored in a chronic 114-wk study in which male Sprague-Dawley rats [n = 120; National Center for Toxicological Research (NCTR) colony] consumed the AIN-93M purified diet ad libitum (AL), or an amount reduced by 31% of total AL intake inclusive of all macro- and micronutrients. The main objectives were to ascertain the survival characteristics of rats fed the AIN-93M diet and to determine whether dietary restriction (DR) increases longevity of rats fed this casein-based diet compared with the use of mixed-protein sources of the NIH-31 cereal-based diet in an earlier study. Body, liver, brain, the brain/body ratio, spleen, thymus and kidney weights, body length and body density were decreased (P < 0.05) by DR, whereas testis weight and skull length were not altered by DR. Significant age effects at 58 and 114 wk were found for body, brain, the brain/body ratio, liver and testis weights, and body density. Survival rates for the AL and 31% DR groups were 43.3 and 57.5%, respectively. Survival curves were not significantly different. The survival rate for AL rats fed the AIN-93M diet was not different from that of AL rats fed the NIH-31 diet (43.3 and 51.7%, respectively). However, the survival rate for 31% DR rats fed the AIN-93M diet was significantly lower than 25% DR rats fed the NIH-31 diet (57.5 and 87.5%, respectively) although both groups had similar body weights and energy intake at various ages. Nutritional components in the NIH-31 diet that are missing and/or reduced in the AIN-93M diet may interact with DR to increase 114-wk survival. Although the survivability, growth and anatomical results of this study suggest that the AIN-93M diet is suitable for chronic rodent studies, additional studies such as comprehensive histopathologic and physiologic investigations must be undertaken to complete the evaluation process.

Keynote: mechanisms of senescence--complificationists versus simplificationists

It strikes me that among our relatively small community of gerontologists concerned with genetic approaches to our science, there is somewhat of a dichotomization. On the one hand, there are those of us, like myself, who tend to be dour 'complificationists'. Journalists talk to us, but are usually disappointed by the encounter. We are perhaps too impressed with the enormous diversity of genetic modulations of human senescence and with our interpretations of the implications of the evolutionary biological theory of senescence, namely that senescent phenotypes per se are non-adaptive, non-determinative, subject to stochastic events as well as highly polygenic modulations, with resulting wide variability in mechanisms of senescence among and within species. Quite happily, however, there are wonderful optimists among us. They seem to be convinced that there are likely to be a rather small number of major gene effects for a few major mechanisms. They include most Saccharomyces cerevisiae and Caenorhabditis elegans geneticists, some Drosophila melanogaster geneticists, and some mouse geneticists. They also include caloric restriction enthusiasts. Let's call these colleagues 'simplificationists'. Journalists and friends generally find them to be delightful companions. Where does the truth lie? Perhaps the truth lies somewhere between these two extremes and is largely dependent upon the organisms and the range of environments being investigated.

Reduced levels of thyroid hormones, insulin, and glucose, and lower body core temperature in the growth hormone receptor/binding protein knockout mouse

The mechanisms that are responsible for the extension of lifespan in the mouse with targeted disruption (knockout [KO]) of the growth hormone (GH) receptor/binding protein (GHR-KO) are unknown. However, in the long-living Ames dwarf mouse, blood glucose and body core temperature (Tco) are consistently lower than in normal mice. In addition, insulin levels are reduced and corticosterone levels are elevated in male dwarfs. These functional alterations, similar to those seen in animals under caloric restriction, have not been proven to be causally related to the extension of lifespan, but they do provide some insight into what traits may be necessary for long life. Therefore, to investigate which of these parameters are similarly affected in two genetically unrelated, yet similarly long-living mouse models, we measured Tco, thyroid hormones (triiodothyronine [T3] and thyroxine [T4]), and insulin, in addition to morning and afternoon levels of glucose and corticosterone, in young adult male and/or female GHR-KO mice and their normal siblings. Tco in GHR-KO mice was numerically reduced throughout the 24-hr period; however, these differences were only significant 4 hr prior to lights-off (14:00 hr), immediately after lights-off (18:00 hr), and during the 3 hr preceding lights on (03:00 to 06:00 hr). GHR-KO mice had significantly reduced levels of T3 and T4, while the ratio of these hormones was similar to that in normal mice. Insulin levels in GHR-KO mice were lower than in normal mice; levels in male GHR-KO mice were below the detectable limits of the assay used. Glucose levels in GHR-KO mice (male and females) were lower than in normal mice in measurements taken in both morning and afternoon; however, these differences arose from consistent reductions in males, as morning glucose levels in GHR-KO females were similar to those of normal mice. Corticosterone levels measured in blood plasma collected under basal (nonstressed) conditions showed sex-related alterations. Basal corticosterone levels in female GHR-KO mice were similar to normal females, while those in male GHR-KO mice were higher than in normal males in the afternoon. Corticosterone levels in stressed GHR-KO females were similar to those measured in stressed normal females. These data show that the long-living GHR-KO mouse shares a reduction in glucose, insulin, thyroid hormones, and Tco with the Ames dwarf mouse. Reductions in these parameters may be important to the underlying mechanisms of delayed aging in these animals.

Effects of dietary restriction on insulin resistance in obese mice

In many cases, development of insulin resistance has been linked to obesity and may contribute to mechanism of aging. The role of diet, irrespective of degree of obesity, in modulating insulin resistance and development of age degeneration disease remains uncertain. Lowered blood glucose levels are commonly associated with diet restriction (DR), which is an intervention shown to successfully retard aging and age associated disease. The effects of DR on blood glucose and insulin resistance were measured in yellow obese (A(vy)/A), lean black (a/a) mice and in another common inbred strain (B6C3F1) (at three different ages). The yellow obese mice become diabetic as a result of an insulin receptor defect which is not clearly understood. Insulin responses and radioinsulin binding were assayed in yellow obese and lean black mice fed either ad libitum (AL) or DR diets (YAL, BAL, YDR and YAL, respectively) at four different circadian intervals. The B6C3F1 controls were fed either AL (CAL) or DR (CDR) and measures were made at six circadian stages and three different ages. Within 23 days, DR produced a significant loss in body weight and a time-dependent 22-55% reduction in basal blood glucose levels in the yellow obese mice. Additionally, exogenous insulin produced circadian stage dependent (at the time of food intake) reductions in blood glucose in the YDR animals that were not present in YAL animals. (125)I-Insulin binding in liver was increased nearly 2-fold in YDR and BDR mice during the time of day that animals were active and eating. (125)I-Insulin binding was two-fold-higher in CDR mice at 4, 12 and >24 months of age. Binding decreased as a function of age in both the CAL and CDR animals. However, even in the >24 month group the CDR animals were found to have levels of binding that were as high as those found in younger CAL liver. The mechanism of action appears to be through resolution of insulin resistance by modulating an insulin receptor defect.

Increased effective activity of rat liver catalase by dietary restriction

While dietary restriction (DR) increases maximum life span in many animal species, the mechanisms by which this is achieved remain unclear. One possibility is that DR may act in part to reduce free radical levels by retarding age-related declines in rat liver catalase activity. We measured liver cytosolic catalase activity at various times of day in 9-12 month old male (BN X F344)F1 rats fed ad libitum (AL) or subjected to a 30% DR from 14 weeks of age. Catalase activity (expressed as μmol·min(-1)·g liver(-1)) in both diet groups reached minimums at 0600 h but activity was 26% higher in DR as compared to AL rats. This traditional expression of catalase activity did not significantly differ between diet groups at other times of day. One must be careful in the interpretation of such data, however, since catalase is rapidly inactivated by its substrate (H2O2), thus displaying abnormal enzyme kinetics. In order to avoid this difficulty we evaluated the time period during which the reaction remained linear and multiplied it by its activity to yield the effective catalase activity. Using this method we found a significant increase in catalase activity in DR animals at several H2O2 concentrations during the light span. At 1800 h (the beginning of the dark span when the controls initiated peak food intake), fewer and smaller dietary differences were observed and no dietary effects were observed at 2400 h. These data suggest that DR reduces the rate of accumulation of inactive catalase and may contribute to an increased capacity in DR animals to remove free radicals.

Activity measures in rhesus monkeys on long-term calorie restriction

Calorie restriction (CR), undernutrition without malnutrition, extends the mean and maximal lifespan of several ecologically diverse species. Rodents on CR demonstrate increased activity measured as spontaneous locomotion, wheel running, open field behavior or movement. Activity measures were recorded from 19 male rhesus monkeys (Macaca mulatta) as either controls (C) which were fed a nutritious diet to approximate ad libitum levels, or as experimentals (E) which were fed 30% less than age- and weight-matched controls. Within each diet group, some monkeys (n = 10) began CR at 2.3 years of age (range 2.2-2.4 yrs, J Group) while another group (n = 9) began CR at approximately 4.6 years of age (range 4-5.25, A group). Beginning about 6 years after initiation of the study, behavioral activity was measured via ultrasonic motion detectors and recorded on videotape. Diurnal and circadian activity was clearly discernible. Peaks in activity were associated with mealtime and colony husbandry. Compared to Group A, Group J monkeys exhibited higher overall activity as measured by sensors, and also significantly more circling. Compared to AC monkeys, group AE monkeys demonstrated higher rates of gross motor behavior, pacing, stereotypies and grooming. The increases in motor activity observed in one group of monkeys were consistent with results obtained from rodent studies of CR and aging. CR did not significantly inhibit or negatively influence the display of behavior of rhesus monkeys in the laboratory environment. We report here, for the first time, increases in activity due to CR in a model other than the rodent.

Trichloroethylene cancer risk: simplified calculation of PBPK-based MCLs for cytotoxic end points

Cancer risk assessments for trichloroethylene (TCE) based on linear extrapolation from bioassay results are questionable in light of new data on TCE's likely mechanism of action involving induced cytotoxicity, for which a threshold-type dose-response model may be more appropriate. Previous studies have shown that if a genotoxic mechanism for TCE is assumed, algebraic methods can considerably simplify the use of physiologically based pharmacokinetic (PBPK) models to estimate virtually safe environmental concentrations for humans based on rodent cancer-bioassay data. We show here how such methods can be extended to the case in which TCE is assumed to induce cancer via cytotoxicity, to estimate environmentally safe concentrations based on rodent toxicity data. These methods can be substituted for the numerical methods typically used to calculate PBPK-effective doses when these are defined as peak concentrations. We selected liver and kidney as plausible target tissues, based on an analysis of rodent TCE-bioassay data and on a review of related data bearing on mechanism. Tumor patterns in rodent bioassays are shown to be consistent with our estimates of PBPK-based, effective cytotoxic doses to mice and rats used in these studies. When used with a margin of exposure of 1000, our method yielded maximum concentration levels for TCE of 16 ppb (87 micrograms/m3) for TCE in air respired 24 hr/day, 700 ppb (3.8 mg/m3) for TCE in air respired for relatively brief daily periods (e.g., 0.5 hr while showering/bathing), and 210 micrograms/liter for TCE in drinking water assuming a daily 2-liter ingestion. Cytotoxic effective doses were also estimated for occupational respiratory exposures. These estimates indicate that the current OSHA permissible exposure limit for TCE would produce metabolite concentrations that exceed an acute no observed adverse effect level for hepatotoxicity in mice. On this basis, the OSHA TCE limit is not expected to be protective.

Beyond the rodent model: Calorie restriction in rhesus monkeys

Lifespan extension and reduction of age-related disease by calorie restriction (CR) are among the most consistent findings in gerontological research. The well known effects of CR have been demonstrated many times in rodents and other short-lived species. However, effects of CR on aging in longer-lived species, more closely related to humans, were unknown until recently. Studies of CR and aging using nonhuman primates (rhesus monkeys) were begun several years ago at the National Institute on Aging, the University of Wisconsin-Madison, and the University of Maryland. These studies are beginning to yield useful data regarding the effects of this nutritional intervention in primates. Several studies from these ongoing investigations have shown that rhesus monkeys on CR exhibit physiological responses to CR that parallel findings in rodents. In addition, several potential biomarkers of aging are being evaluated and preliminary findings suggest the possibility that CR in rhesus monkeys could slow the rate of aging and reduce age-related disease, specifically diabetes and cardiovascular disease. It will be several years before conclusive proof that CR slows aging and extends life span in primates is established, however, results from these exciting studies suggest the possibility that the anti-aging effects of CR reported in rodents also occur in longer-lived species such as nonhuman primates, strenghtening the possibility that this nutritional intervention will also prove beneficial in longer-lived species, including humans.

Calorie restriction lowers body temperature in rhesus monkeys, consistent with a postulated anti-aging mechanism in rodents

Many studies of caloric restriction (CR) in rodents and lower animals indicate that this nutritional manipulation retards aging processes, as evidenced by increased longevity, reduced pathology, and maintenance of physiological function in a more youthful state. The anti-aging effects of CR are believed to relate, at least in part, to changes in energy metabolism. We are attempting to determine whether similar effects occur in response to CR in nonhuman primates. Core (rectal) body temperature decreased progressively with age from 2 to 30 years in rhesus monkeys fed ad lib (controls) and is reduced by approximately 0.5 degrees C in age-matched monkeys subjected to 6 years of a 30% reduction in caloric intake. A short-term (1 month) 30% restriction of 2.5-year-old monkeys lowered subcutaneous body temperature by 1.0 degrees C. Indirect calorimetry showed that 24-hr energy expenditure was reduced by approximately 24% during short-term CR. The temporal association between reduced body temperature and energy expenditure suggests that reductions in body temperature relate to the induction of an energy conservation mechanism during CR. These reductions in body temperature and energy expenditure are consistent with findings in rodent studies in which aging rate was retarded by CR, now strengthening the possibility that CR may exert beneficial effects in primates analogous to those observed in rodents.

Calories, fat, fibers, and cellular proliferation in Swiss Webster mice

Increased cellular proliferation has been associated with the enhanced expression of several key stages in carcinogenesis. A standard protocol was used to investigate the effect of specific dietary regimens on cellular proliferation. Young adult Swiss Webster mice were fed for 30 days with modified AIN-76A semi-purified diets designed to illustrate the effects of the levels of dietary or calorie restriction, different fibers and bulking agents, and different fats on cellular proliferation. Female mice were used for the restriction and fat studies, males for the fiber and bulking agent studies. Vaginal smears were taken from females from treatment day 15, and the mice killed 2 days following the first estrus following 30 days feeding; males were killed on the 30th day. One hour before death, mice were injected ip with 0.25 micro Ci/g 3[H]-thymidine. Slides were prepared for radioautography and histopathology. Both dietary and calorie restriction led to reduced 3[H]-thymidine labeling indices in each of the seven tissues studied, the mammary gland being the most severely affected. Different fibers and bulking agents, in specific cases, reduced labeling in the duodenum but not to a consistent statistically significant extent in the colon or colo-rectal region. In the duodenum, oat bran and oat gum were the most effective while wood cellulose (alphacel) had no effect. Investigations on the effects of different fats is continuing. High levels of lard, menhaden oil, or cod liver oil as the fat component of the AIN-76A diet, led to much higher levels of labeled cells in the mammary gland or colo-rectal region than did fat components rich in vegetable oils. The labeling indices appeared to be inversely correlated with the level of linoleic acid in the diet, a presumption that has been confirmed by investigating a series of diets containing different levels of this acid. Anti-oxidants were not used in any of these fat-modified diets. The overall results obtained in these studies clearly indicate the utility of cellular proliferation studies in investigating the effects of dietary modifications.