Caloric Restriction and Healthy Life Span: Frail Phenotype of Nonhuman Primates in the Wisconsin National Primate Research Center Caloric Restriction Study.

Calorie restriction without malnutrition increases longevity and delays the onset of age-associated disorders in multiple species. Recently, greater emphasis has been placed on healthy life span and preventing frailty than on longevity. Here, we show the beneficial effect of long-term calorie restriction on frailty in later life in a nonhuman primate. Frail phenotypes were evaluated using metabolic and physical activity data and defined using the Fried index. Shrinking was defined as unintentional weight loss of greater than 5% of body weight. Weakness was indicated by decline in high intensity spontaneous physical activity. Poor endurance or exhaustion was indicated by a reduction in energy efficiency of movements. Slowness was indicated by physical activity counts in the morning. Low physical activity level was measured by total energy expenditure using doubly labeled water divided by sleeping metabolic rate. Weakness, poor endurance, slowness, and low physical activity level were significantly higher in control compared with calorie restriction (p < .05) as was total incidence of frailty (p < .001). In conclusion, we established a novel set of measurable criteria of frailty in nonhuman primates, and using these criteria, showed that calorie restriction reduces the incidence of frailty and increases healthy life span in nonhuman primates.

Identification of tissue-specific transcriptional markers of caloric restriction in the mouse and their use to evaluate caloric restriction mimetics.

Caloric restriction (CR) without malnutrition has been shown to retard several aspects of the aging process and to extend lifespan in different species. There is strong interest in the identification of CR mimetics (CRMs), compounds that mimic the beneficial effects of CR on lifespan and healthspan without restriction of energy intake. Identification of CRMs in mammals is currently inefficient due to the lack of screening tools. We have performed whole-genome transcriptional profiling of CR in seven mouse strains (C3H/HeJ, CBA/J, DBA/2J, B6C3F1/J, 129S1/SvImJ, C57BL/6J, and BALB/cJ) in white adipose tissue (WAT), gastrocnemius muscle, heart, and brain neocortex. This analysis has identified tissue-specific panels of genes that change in expression in multiple mouse strains with CR. We validated a subset of genes with qPCR and used these to evaluate the potential CRMs bezafibrate, pioglitazone, metformin, resveratrol, quercetin, 2,4-dinitrophenol, and L-carnitine when fed to C57BL/6J 2-month-old mice for 3 months. Compounds were also evaluated for their ability to modulate previously characterized biomarkers of CR, including mitochondrial enzymes citrate synthase and SIRT3, plasma inflammatory cytokines TNF-α and IFN-γ, glycated hemoglobin (HbA1c) levels and adipocyte size. Pioglitazone, a PPAR-γ agonist, and L-carnitine, an amino acid involved in lipid metabolism, displayed the strongest effects on both the novel transcriptional markers of CR and the additional CR biomarkers tested. Our findings provide panels of tissue-specific transcriptional markers of CR that can be used to identify novel CRMs, and also represent the first comparative molecular analysis of several potential CRMs in multiple tissues in mammals.

Effects of calorie restriction on the lifespan and healthspan of POLG mitochondrial mutator mice.

Mitochondrial DNA (mtDNA) mutations are thought to have a causative role in age-related pathologies. We have shown previously that mitochondrial mutator mice (PolgD257A/D257A), harboring a proofreading-deficient version of the mtDNA polymerase gamma (POLG), accumulate mtDNA mutations in multiple tissues and display several features of accelerated aging. Calorie restriction (CR) is known to delay the onset of age-related diseases and to extend the lifespan of a variety of species, including rodents. In the current study we investigated the effects of CR on the lifespan and healthspan of mitochondrial mutator mice. Long-term CR did not increase the median or maximum lifespan of PolgD257A/D257A mice. Furthermore, CR did not reduce mtDNA deletions in the heart and muscle, accelerated sarcopenia, testicular atrophy, nor improve the alterations in cardiac parameters that are present in aged mitochondrial mutator mice. Therefore, our findings suggest that accumulation of mtDNA mutations may interfere with the beneficial action of CR in aging retardation.

Caloric restriction improves health and survival of rhesus monkeys.

Caloric restriction (CR) without malnutrition extends lifespan and delays the onset of age-related disorders in most species but its impact in nonhuman primates has been controversial. In the late 1980s two parallel studies were initiated to determine the effect of CR in rhesus monkeys. The University of Wisconsin study reported a significant positive impact of CR on survival, but the National Institute on Aging study detected no significant survival effect. Here we present a direct comparison of longitudinal data from both studies including survival, bodyweight, food intake, fasting glucose levels and age-related morbidity. We describe differences in study design that could contribute to differences in outcomes, and we report species specificity in the impact of CR in terms of optimal onset and diet. Taken together these data confirm that health benefits of CR are conserved in monkeys and suggest that CR mechanisms are likely translatable to human health.

Hyperinsulinemia/diabetes, hearing, and aging in the University of Wisconsin calorie restriction monkeys.

The purpose of this study was to determine the effects of hyperinsulinemia/Type 2 diabetes mellitus (HI-T2DM) on hearing impairment using rhesus monkeys to obtain control over diet and lifestyle factors that confound human studies. The study is a retrospective evaluation of rhesus monkeys from the Wisconsin National Primate Research Center (WNPRC) study on caloric restriction and aging. The research questions were the following: 1. Is HI-T2DM related to hearing impairment? 2. If so, what is the site of lesion in the auditory system? and 3. What physiological factors affect the risk of hearing loss in HI-T2DM? Three groups of eight monkeys each were matched by sex and age; the caloric restricted (CR) monkeys had a reduced risk of diabetes, the normal control (NL) group had a normal risk, and the hyperinsulinemia/diabetes (HI-D) group had already developed HI-T2DM. Auditory testing included distortion product otoacoustic emissions (DPOAEs) with f2 frequencies from 2211 to 8837 Hz and auditory brainstem responses (ABRs) obtained with clicks and tone bursts (8, 16, and 32 kHz). DPOAEs had signal-to-noise ratios 8-17 dB larger in the NL group than in the HI-D and CR groups, signifying that cochlear function was best in the NL group. ABR thresholds were 5-8 dB better in the NL group than in the HI-D group, although no significant differences across the groups were evident for the thresholds, latencies, interwave intervals, or amplitudes. Correlations were significant for quadratic relations between body mass index (BMI) and DPOAE, with largest DPOAEs for animals in the middle of the BMI range. ABR thresholds elicited with 16 and 32 kHz signals were significantly correlated, positively with BMI and HbA1c, and negatively with KG (glucose tolerance), SI (insulin sensitivity index) and DI (disposition index). These findings suggest that the hearing loss associated with HI-T2DM is predominantly cochlear, and auditory structures underlying the higher frequencies are at risk with HI-T2DM. Loss of auditory function begins in the hyperinsulinemia, pre-diabetic state.

A conserved transcriptional signature of delayed aging and reduced disease vulnerability is partially mediated by SIRT3.

Aging is the most significant risk factor for a range of diseases, including many cancers, neurodegeneration, cardiovascular disease, and diabetes. Caloric restriction (CR) without malnutrition delays aging in diverse species, and therefore offers unique insights into age-related disease vulnerability. Previous studies suggest that there are shared mechanisms of disease resistance associated with delayed aging, however quantitative support is lacking. We therefore sought to identify a common response to CR in diverse tissues and species and determine whether this signature would reflect health status independent of aging. We analyzed gene expression datasets from eight tissues of mice subjected to CR and identified a common transcriptional signature that includes functional categories of mitochondrial energy metabolism, inflammation and ribosomal structure. This signature is detected in flies, rats, and rhesus monkeys on CR, indicating aspects of CR that are evolutionarily conserved. Detection of the signature in mouse genetic models of slowed aging indicates that it is not unique to CR but rather a common aspect of extended longevity. Mice lacking the NAD-dependent deacetylase SIRT3 fail to induce mitochondrial and anti-inflammatory elements of the signature in response to CR, suggesting a potential mechanism involving SIRT3. The inverse of this transcriptional signature is detected with consumption of a high fat diet, obesity and metabolic disease, and is reversed in response to interventions that decrease disease risk. We propose that this evolutionarily conserved, tissue-independent, transcriptional signature of delayed aging and reduced disease vulnerability is a promising target for developing therapies for age-related diseases.

Caloric restriction reduces age-related and all-cause mortality in rhesus monkeys.

Caloric restriction (CR) without malnutrition increases longevity and delays the onset of age-associated disorders in short-lived species, from unicellular organisms to laboratory mice and rats. The value of CR as a tool to understand human ageing relies on translatability of CR's effects in primates. Here we show that CR significantly improves age-related and all-cause survival in monkeys on a long-term ~30% restricted diet since young adulthood. These data contrast with observations in the 2012 NIA intramural study report, where a difference in survival was not detected between control-fed and CR monkeys. A comparison of body weight of control animals from both studies with each other, and against data collected in a multi-centred relational database of primate ageing, suggests that the NIA control monkeys were effectively undergoing CR. Our data indicate that the benefits of CR on ageing are conserved in primates.

Effect of age and calorie restriction on corpus callosal integrity in rhesus macaques: a fiber tractography study.

The rhesus macaque exhibits age-related brain changes similar to humans, making an excellent model of normal aging. Calorie restriction is a dietary intervention that reduces age-related comorbidities in short-lived animals, and its effects are still under study in rhesus macaques. Here, using deterministic fiber tracking method, we examined the effects of age and calorie restriction on a diffusion tensor imaging measure of white matter integrity, fractional anisotropy (FA), within white matter tracks traversing the anterior (genu) and posterior (splenium) corpus callosum in rhesus monkeys. Our results show: (1) a significant inverse relationship between age and mean FA of tracks traversing the genu and splenium; (2) higher mean FA of the splenium tracks as compared to that of genu tracks across groups; and (3) no significant diet effect on mean track FA through either location. These results are congruent with the age-related decline in white matter integrity reported in humans and monkeys, and the anterior-to-posterior gradient in white matter vulnerability to normal aging in humans. Further studies are warranted to critically evaluate the effect of calorie restriction on brain aging in this unique cohort of elderly primates.

Long-term calorie restriction decreases metabolic cost of movement and prevents decrease of physical activity during aging in rhesus monkeys.

BACKGROUND: Short-term (<1 year) calorie restriction (CR) has been reported to decrease physical activity and metabolic rate in humans and non-human primate models; however, studies examining the very long-term (>10 year) effect of CR on these parameters are lacking. OBJECTIVE: The objective of this study was to examine metabolic and behavioral adaptations to long-term CR longitudinally in rhesus macaques. DESIGN: Eighteen (10 male, 8 female) control (C) and 24 (14 male, 10 female) age matched CR rhesus monkeys between 19.6 and 31.9 years old were examined after 13 and 18 years of moderate adult-onset CR. Energy expenditure (EE) was examined by doubly labeled water (DLW; TEE) and respiratory chamber (24 h EE). Physical activity was assessed both by metabolic equivalent (MET) in a respiratory chamber and by an accelerometer. Metabolic cost of movements during 24 h was also calculated. Age and fat-free mass were included as covariates. RESULTS: Adjusted total and 24 h EE were not different between C and CR. Sleeping metabolic rate was significantly lower, and physical activity level was higher in CR than in C independent from the CR-induced changes in body composition. The duration of physical activity above 1.6 METs was significantly higher in CR than in C, and CR had significantly higher accelerometer activity counts than C. Metabolic cost of movements during 24 h was significantly lower in CR than in C. The accelerometer activity counts were significantly decreased after seven years in C animals, but not in CR animals. CONCLUSIONS: The results suggest that long-term CR decreases basal metabolic rate, but maintains higher physical activity with lower metabolic cost of movements compared with C.

A shift in energy metabolism anticipates the onset of sarcopenia in rhesus monkeys.

Age-associated skeletal muscle mass loss curtails quality of life and may contribute to defects in metabolic homeostasis in older persons. The onset of sarcopenia occurs in middle age in rhesus macaques although the trigger has yet to be identified. Here, we show that a shift in metabolism occurs in advance of the onset of sarcopenia in rhesus vastus lateralis. Multiphoton laser-scanning microscopy detects a shift in the kinetics of photon emission from autofluorescent metabolic cofactors NADH and FAD. Lifetime of both fluorophores is shortened at mid-age, and this is observed in both free and bound constituent pools. Levels of FAD and free NADH are increased and the NAD/NADH redox ratio is lower. Concomitant with this, expression of fiber-type myosin isoforms is altered resulting in a shift in fiber-type distribution, activity of cytochrome c oxidase involved in mitochondrial oxidative phosphorylation is significantly lower, and the subcellular organization of mitochondria in oxidative fibers is compromised. A regulatory switch involving the transcriptional coactivator PGC-1α directs metabolic fuel utilization and governs the expression of structural proteins. Age did not significantly impact total levels of PGC-1α; however, its subcellular localization was disrupted, suggesting that PGC-1α activities may be compromised. Consistent with this, intracellular lipid storage is altered and there is shift to larger lipid droplet size that likely reflects a decline in lipid turnover or a loss in efficiency of lipid metabolism. We suggest that changes in energy metabolism contribute directly to skeletal muscle aging in rhesus monkeys.

Calorie restriction attenuates astrogliosis but not amyloid plaque load in aged rhesus macaques: a preliminary quantitative imaging study.

While moderate calorie restriction (CR) in the absence of malnutrition has been consistently shown to have a systemic, beneficial effect against aging in several animals models, its effect on the brain microstructure in a non-human primate model remains to be studied using post-mortem histopathologic techniques. In the present study, we investigated differences in expression levels of glial fibrillary acid protein (GFAP) and ß-amyloid plaque load in the hippocampus and the adjacent cortical areas of 7 Control (ad libitum)-fed and 6 CR male rhesus macaques using immunostaining methods. CR monkeys expressed significantly lower levels (∼30% on average) of GFAP than Controls in the CA region of the hippocampus and entorhinal cortex, suggesting a protective effect of CR in limiting astrogliosis. These results recapitulate the neuroprotective effects of CR seen in shorter-lived animal models. There was a significant positive association between age and average amyloid plaque pathology in these animals, but there was no significant difference in amyloid plaque distribution between the two groups. Two of the seven Control animals (28.6%) and one of the six CR animal (16.7%) did not express any amyloid plaques, five of seven Controls (71.4%) and four of six CR animals (66.7%) expressed minimal to moderate amyloid pathology, and one of six CR animals (16.7%) expressed severe amyloid pathology. That CR affects levels of GFAP expression but not amyloid plaque load provides some insight into the means by which CR is beneficial at the microstructural level, potentially by offsetting the increased load of oxidatively damaged proteins, in this non-human primate model of aging. The present study is a preliminary post-mortem histological analysis of the effects of CR on brain health, and further studies using molecular and biochemical techniques are warranted to elucidate underlying mechanisms.

Transcriptomics and Metabonomics Identify Essential Metabolic Signatures in Calorie Restriction (CR) Regulation across Multiple Mouse Strains.

Calorie restriction (CR) has long been used to study lifespan effects and oppose the development of a broad array of age-related biological and pathological changes (increase healthspan). Yet, a comprehensive comparison of the metabolic phenotype across different genetic backgrounds to identify common metabolic markers affected by CR is still lacking. Using a system biology approach comprising metabonomics and liver transcriptomics we revealed the effect of CR across multiple mouse strains (129S1/SvlmJ, C57BL6/J, C3H/HeJ, CBA/J, DBA/2J, JC3F1/J). Oligonucleotide microarrays identified 76 genes as differentially expressed in all six strains confirmed. These genes were subjected to quantitative RT-PCR analysis in the C57BL/6J mouse strain, and a CR-induced change expression was confirmed for 14 genes. To fully depict the metabolic pathways affected by CR and complement the changes observed through differential gene expression, the metabolome of C57BL6/J was further characterized in liver tissues, urine and plasma levels using a combination or targeted mass spectrometry and proton nuclear magnetic resonance spectroscopy. Overall, our integrated approach commonly confirms that energy metabolism, stress response, lipids regulators and the insulin/IGF-1 are key determinants factors involved in CR regulation.

Circulating factors induced by caloric restriction in the nonhuman primate Macaca mulatta activate angiogenic processes in endothelial cells.

Moderate caloric restriction (CR) without malnutrition increases healthspan in virtually every species studied, including nonhuman primates. In mice, CR exerts significant microvascular protective effects resulting in increased microvascular density in the heart and the brain, which likely contribute to enhanced tolerance to ischemia and improved cardiac performance and cognitive function. Yet, the underlying mechanisms by which CR confer microvascular protection remain elusive. To test the hypothesis that circulating factors triggered by CR regulate endothelial angiogenic capacity, we treated cultured human endothelial cells with sera derived from Macaca mulatta on long-term (over 10 years) CR. Cells treated with sera derived from ad-libitum-fed control monkeys served as controls. We found that factors present in CR sera upregulate vascular endothelial growth factor (VEGF) signaling and stimulate angiogenic processes, including endothelial cell proliferation and formation of capillary-like structures. Treatment with CR sera also tended to increase cellular migration (measured by a wound-healing assay using electric cell-substrate impedance sensing [ECIS] technology) and adhesion to collagen. Collectively, we find that circulating factors induced by CR promote endothelial angiogenic processes, suggesting that increased angiogenesis may be a potential mechanism by which CR improves cardiac function and prevents vascular cognitive impairment.

Brain volumetric and microstructural correlates of executive and motor performance in aged rhesus monkeys.

The aged rhesus macaque exhibits brain atrophy and behavioral deficits similar to normal aging in humans. Here we studied the association between cognitive and motor performance and anatomic and microstructural brain integrity measured with 3T magnetic resonance imaging in aged monkeys. About half of these animals were maintained on moderate calorie restriction (CR), the only intervention shown to delay the aging process in lower animals. T1-weighted anatomic and diffusion tensor images were used to obtain gray matter (GM) volume and fractional anisotropy (FA) and mean diffusivity (MD), respectively. We tested the extent to which brain health indexed by GM volume, FA, and MD were related to executive and motor function, and determined the effect of the dietary intervention on this relationship. We hypothesized that fewer errors on the executive function test and faster motor response times would be correlated with higher volume, higher FA, and lower MD in frontal areas that mediate executive function, and in motor, premotor, subcortical, and cerebellar areas underlying goal-directed motor behaviors. Higher error percentage on a cognitive conceptual shift task was significantly associated with lower GM volume in frontal and parietal cortices, and lower FA in major association fiber bundles. Similarly, slower performance time on the motor task was significantly correlated with lower volumetric measures in cortical, subcortical, and cerebellar areas and decreased FA in several major association fiber bundles. Notably, performance during the acquisition phase of the hardest level of the motor task was significantly associated with anterior mesial temporal lobe volume. Finally, these brain-behavior correlations for the motor task were attenuated in CR animals compared to controls, indicating a potential protective effect of the dietary intervention.

A calorie-restricted diet decreases brain iron accumulation and preserves motor performance in old rhesus monkeys.

Caloric restriction (CR) reduces the pathological effects of aging and extends the lifespan in many species, including nonhuman primates, although the effect on the brain is less well characterized. We used two common indicators of aging, motor performance speed and brain iron deposition measured in vivo using magnetic resonance imaging, to determine the potential effect of CR on elderly rhesus macaques eating restricted (n=24, 13 males, 11 females) and standard (n=17, 8 males, 9 females) diets. Both the CR and control monkeys showed age-related increases in iron concentrations in globus pallidus (GP) and substantia nigra (SN), although the CR group had significantly less iron deposition in the GP, SN, red nucleus, and temporal cortex. A Diet X Age interaction revealed that CR modified age-related brain changes, evidenced as attenuation in the rate of iron accumulation in basal ganglia and parietal, temporal, and perirhinal cortex. Additionally, control monkeys had significantly slower fine motor performance on the Movement Assessment Panel, which was negatively correlated with iron accumulation in left SN and parietal lobe, although CR animals did not show this relationship. Our observations suggest that the CR-induced benefit of reduced iron deposition and preserved motor function may indicate neural protection similar to effects described previously in aging rodent and primate species.

Calorie restriction reduces the influence of glucoregulatory dysfunction on regional brain volume in aged rhesus monkeys.

Insulin signaling dysregulation is related to neural atrophy in hippocampus and other areas affected by neurovascular and neurodegenerative disorders. It is not known if long-term calorie restriction (CR) can ameliorate this relationship through improved insulin signaling or if such an effect might influence task learning and performance. To model this hypothesis, magnetic resonance imaging was conducted on 27 CR and 17 control rhesus monkeys aged 19-31 years from a longitudinal study. Voxel-based regression analyses were used to associate insulin sensitivity with brain volume and microstructure cross-sectionally. Monkey motor assessment panel (mMAP) performance was used as a measure of task performance. CR improved glucoregulation parameters and related indices. Higher insulin sensitivity predicted more gray matter in parietal and frontal cortices across groups. An insulin sensitivity × dietary condition interaction indicated that CR animals had more gray matter in hippocampus and other areas per unit increase relative to controls, suggesting a beneficial effect. Finally, bilateral hippocampal volume adjusted by insulin sensitivity, but not volume itself, was significantly associated with mMAP learning and performance. These results suggest that CR improves glucose regulation and may positively influence specific brain regions and at least motor task performance. Additional studies are warranted to validate these relationships.

The caloric restriction paradigm: implications for healthy human aging.

Underlying the importance of research on the biology of aging is the fact that many nations face the demographic reality of a rapidly aging populace and the looming healthcare challenges that it brings. This reality is a result of aging itself being the most significant risk factor for a range of the most prevalent diseases, including many cancers, cardiovascular disease, and diabetes. Accordingly, interventions are sorely needed that would be able to delay or prevent diseases and disorders associated with the aging process and thereby increase the period of time that aging individuals are in good health (the health-span). Caloric restriction (CR) has emerged as a model of major interest as it is widely agreed that CR is the most potent environmental intervention that delays the onset of aging and extends life span in diverse experimental organisms. A better understanding of the mechanisms by which CR delays aging will reveal new insights into the aging process and the underlying causes of disease vulnerability with age. These novel insights will allow the development of novel treatments and preventive measures for age-associated diseases and disorders.

Cellular adaptation contributes to calorie restriction-induced preservation of skeletal muscle in aged rhesus monkeys.

We have previously shown that a 30% reduced calorie intake diet delayed the onset of muscle mass loss in adult monkeys between ~16 and ~22 years of age and prevented multiple cellular phenotypes of aging. In the present study we show the impact of long term (~17 years) calorie restriction (CR) on muscle aging in very old monkeys (27-33 yrs) compared to age-matched Control monkeys fed ad libitum, and describe these data in the context of the whole longitudinal study. Muscle mass was preserved in very old calorie restricted (CR) monkeys compared to age-matched Controls. Immunohistochemical analysis revealed an age-associated increase in the proportion of Type I fibers in the VL from Control animals that was prevented with CR. The cross sectional area (CSA) of Type II fibers was reduced in old CR animals compared to earlier time points (16-22 years of age); however, the total loss in CSA was only 15% in CR animals compared to 36% in old Controls at ~27 years of age. Atrophy was not detected in Type I fibers from either group. Notably, Type I fiber CSA was ~1.6 fold greater in VL from CR animals compared to Control animals at ~27 years of age. The frequency of VL muscle fibers with defects in mitochondrial electron transport system enzymes (ETS(ab)), the absence of cytochrome c oxidase and hyper-reactive succinate dehydrogenase, were identical between Control and CR. We describe changes in ETS(ab) fiber CSA and determined that CR fibers respond differently to the challenge of mitochondrial deficiency. Fiber counts of intact rectus femoris muscles revealed that muscle fiber density was preserved in old CR animals. We suggest that muscle fibers from CR animals are better poised to endure and adapt to changes in muscle mass than those of Control animals.

Calorie restriction reduces psychological stress reactivity and its association with brain volume and microstructure in aged rhesus monkeys.

BACKGROUND: Heightened stress reactivity is associated with hippocampal atrophy, age-related cognitive deficits, and increased risk for Alzheimer's disease. This temperament predisposition may aggravate age-associated brain pathology or be reflective of it. This association may be mediated through repeated activation of the stress hormone axis over time. Dietary interventions, such as calorie restriction (CR), affect stress biology and may moderate the pathogenic relationship between stress reactivity and brain in limbic and prefrontal regions. METHODS: Rhesus monkeys (Macaca mulatta) aged 19-31 years consumed either a standard diet (N=18) or were maintained on 30% CR relative to baseline intake (N=26) for 13-19 years. Behavior was rated in both normative and aversive contexts. Urinary cortisol was collected. Animals underwent magnetic resonance imaging and diffusion tensor imaging (DTI) to acquire volumetric and tissue microstructure data respectively. Voxel-wise statistics regressed a global stress reactivity factor, cortisol, and their interaction on brain indices across and between dietary groups. RESULTS: CR significantly reduced stress reactivity during aversive contexts without affecting activity, orientation, or attention behavior. Stress reactivity was associated with less volume and tissue density in areas important for emotional regulation and the endocrine axis including prefrontal cortices, hippocampus, amygdala, and hypothalamus. CR reduced these relationships. A Cortisol by Stress Reactivity voxel-wise interaction indicated that only monkeys with high stress reactivity and high basal cortisol demonstrated lower brain volume and tissue density in prefrontal cortices, hippocampus, and amygdala. CONCLUSIONS: High stress reactivity predicted lower volume and microstructural tissue density in regions involved in emotional processing and modulation. A CR diet reduced stress reactivity and regional associations with neural modalities. High levels of cortisol appear to mediate some of these relationships.

Skeletal effects of long-term caloric restriction in rhesus monkeys.

Age-related bone loss is well established in humans and is known to occur in nonhuman primates. There is little information, however, on the effect of dietary interventions, such as caloric restriction (CR), on age-related bone loss. This study examined the effects of long-term, moderate CR on skeletal parameters in rhesus monkeys. Thirty adult male rhesus monkeys were subjected to either a restricted (R, n = 15) or control (C, n = 15) diet for 20 years and examined throughout for body composition and biochemical markers of bone turnover. Total body, spine, and radius bone mass and density were assessed by dual-energy X-ray absorptiometry. Assessment of biochemical markers of bone turnover included circulating serum levels of osteocalcin, carboxyterminal telopeptide of type I collagen, cross-linked aminoterminal telopeptide of type I collagen, parathyroid hormone, and 25(OH)vitamin D. Overall, we found that bone mass and density declined over time with generally higher levels in C compared to R animals. Circulating serum markers of bone turnover were not different between C and R with nonsignficant diet-by-time interactions. We believe the lower bone mass in R animals reflects the smaller body size and not pathological osteopenia.