Age-Related Differences in the Gut Microbiome of Rhesus Macaques.

Aging is a multifactorial process characterized by progressive changes in gut physiology and the intestinal mucosal immune system. These changes, along with alterations in lifestyle, diet, nutrition, inflammation and immune function alter both composition and stability of the gut microbiota. Given the impact of environmental influences on the gut microbiota, animal models are particularly useful in this field. To understand the relationship between the gut microbiota and aging in nonhuman primates, we collected fecal samples from 20 male and 20 female rhesus macaques (Macaca mulatta), across the natural macaque age range, for 16S rRNA gene analyses. Operational taxonomic units were then grouped together to summarize taxon abundance at different hierarchical levels of classification and alpha- and beta-diversity were calculated. There were no age or sex differences in alpha diversity. At the phylum level, relative abundance of Proteobacteria and Firmicutes and Firmicutes to Bacteriodetes ratio were different between age groups though significance disappeared after correction for multiple comparisons. At the class level, relative abundance of Firmicutes_Bacilli decreased and Proteobacteria_Alphaproteobacteria and Proteobacteria_Betaproteobacteria increased with each successively older group. Only differences in Firmicutes_Bacilli remained significant after correction for multiple comparisons. No sex differences were identified in relative abundances after correction for multiple comparisons. Our results are not surprising given the known impact of environmental factors on the gut microbiota.

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.

Glucoregulatory function in adult rhesus macaques (Macaca mulatta) undergoing treatment with medroxyprogesterone acetate for endometriosis.

Endometriosis affects a large percentage of the rhesus macaques (Macaca mulatta) at our institution. When the disease is diagnosed in macaques on long-term research protocols, the treatment of choice in our facility is monthly administration of medroxyprogesterone acetate (MPA) to decrease estrogen release and subsequently diminish clinical signs associated with the disease. Because hormonal fluctuations associated with the normal menstrual cycle are known to affect parameters of glucoregulatory function in rhesus macaques, we evaluated the effect of MPA treatment on glucoregulatory function cross-sectionally in 6 animals and longitudinally in 4 animals with endometriosis. Our hypothesis was that monthly administration of MPA for the treatment of endometriosis would negatively affect glucoregulatory function in rhesus macaques. We found that adult female rhesus macaques on MPA therapy for 1.4 to 36.1 mo had lower insulin sensitivity than did age- and weight-matched healthy control animals. In addition, glucoregulatory function was reduced after MPA treatment as compared with pretreatment levels in a group of 4 macaques. These data suggest that glucoregulatory function should be considered when endometriosis treatment is planned for rhesus macaques.

Metabolizable energy intake during long-term calorie restriction in rhesus monkeys.

Calorie restriction (CR) is a dietary intervention shown to increase maximum life-span. The aim of this study was to compare the metabolizable energy of the pelleted semi-purified diet with estimated energy intake from food weight. Energy density of diet, urine and feces were measured by bomb calorimetry in rhesus monkeys (23-29 years old) on CR (CR, n=11) and control (C, n=9). Food moisture was measured to be 2-fold higher (9+/-1%) than indicated on the label (approximately 5%). The measured gross energy of diet was 4.4 kcal/g dry weight of CR and 4.5 kcal/g dry weight of C diets. In a two-day trial, food intake (mean+/-SD) was 112+/-20 g and 136+/-26 g of dry mass/d in the CR and C monkeys, respectively (p=0.003). The fraction of the diet absorbed (CR=0.91; C=0.95) was different (p<0.001) between CR and C monkeys. Using these coefficients, the metabolizable energy intake averaged over 6 months was 450+/-53 and 534+/-97 kcal/d in CR and C monkeys, respectively (Diff=16%; p=0.03). These values were compared with energy expenditure (EE), as measured annually by indirect calorimetry (490+/-61 kcal/d in CR and 532+/-62 kcal/d in C monkeys). Adjusted for changes in body composition (2+/-10 kcal/d in CR and -7+/-12 kcal/d in C), energy balance was not different from zero in CR (-42+/-42 kcal/d) and C (9+/-61 kcal/d) monkeys. Use of diet weight is a reasonable estimate of the level of CR when food waste is assessed.

Influences of calorie restriction and age on energy expenditure in the rhesus monkey.

Caloric restriction (CR) is known to retard the aging process, and a marker of aging is decreased energy expenditure (EE). To assess longitudinal effects of CR on EE in rhesus monkeys (Macaca mulatta), data from 41 males (M) and 26 females (F) subjected to 9 or 15 yr of CR were studied. EE and body composition of monkeys 11-28 yr of age were measured using indirect calorimetry and dual X-ray absorptiometry. Total EE (24-h EE) was divided into daytime (day EE), nighttime (night EE), and daytime minus nighttime (D - N EE). M calorie-restricted monkeys showed a lower 24-h EE (means +/- SD = 568 +/- 96 kcal/day, P < 0.0001) than controls (C; 630 +/- 129 kcal/day). Calorie-restricted M had a lower night EE (difference = 36 kcal P < 0.0001) compared with C M, but after adjusting for FFM and FM, night EE was not different between calorie-restricted and C males (P = 0.72). The 24-h EE decreased with age (13 kcal decrease/yr, P < 0.0001), but there was no difference between CR and C. Adjusted for FFM and FM, D - N EE decreased with age (9 kcal/yr, P < 0.0001), with no interaction with age (P = 0.72). The F were compared with age-matched M selected from the male cohort. F had a lower 24-h EE (496 +/- 84 kcal/day) than M (636 +/- 139 kcal/day) (P < 0.0001). Adjusting for FFM and FM, night EE was lower in F compared with M (difference = 18 kcal, P = 0.077). Night EE did not differ between calorie-restricted and C younger monkeys after adjusting for FFM and FM. In conclusion, CR did not alter the age-related decrease in EE with CR.

Reference body composition in adult rhesus monkeys: glucoregulatory and anthropometric indices.

Rhesus monkeys have been used as models to study obesity and disease. The aim of this study was to define body mass indices for underweight and obesity in rhesus monkeys. Longitudinal data collected over 8-14 years from 40 male and 26 female rhesus monkeys were analyzed. Body weight, insulin sensitivity index, and disposition index were regressed against percent body fat (%BF). A minimal %BF beyond which further loss of body weight resulted in loss of lean mass was determined to be 11.5% in older males, 8% in adult females, and 9% in younger adult males. Insulin sensitivity index and disposition index reached minimum values at 23% fat in older males, 18% in adult females, and 21% in younger adult males, indicating obesity. The estimated reference range for %BF was 9%-23% in male and 8%-18% in female monkeys, corresponding to body mass indices of 32-44 kg/m(2) for male and 27-35 kg/m(2) for female monkeys.

Insulin resistance and impaired insulin secretion in prenatally androgenized male rhesus monkeys.

Polycystic ovary syndrome (PCOS) is a familial disease. Affected males harbor some of the metabolic deficits seen in affected females. The prenatally androgenized (PA) female rhesus monkey, an animal model for PCOS, manifests glucoregulatory and reproductive abnormalities similar to those seen in PCOS women. The purpose of this study was to determine whether exposure of fetal male rhesus monkeys to testosterone excess would induce glucoregulatory and reproductive deficits. Seven adult PA males and seven matched controls underwent somatometric measurements, sex steroid analysis, and a frequently sampled i.v. glucose tolerance test. Body measurements were similar in the two groups, although arm circumference was greater in control compared with PA males (P < 0.01). There were no differences in neonatal weight or serum levels of sex steroids between the two male groups. Measures of insulin sensitivity and pancreatic beta-cell compensation (disposition index) were clearly diminished in PA compared with control males [insulin sensitivity: PA, mean 0.8 (95% confidence interval, 0.11, 5.82); controls, 3.06 (1.51, 6.19) x 10(-4)/min/microU/ml; P < 0.05; disposition index: PA, 226.38 (69.54, 383.22); controls, 509.21/min (306.52, 711.89); P < 0.02]. PA males do not exhibit elevated androgens during adulthood, suggesting that insulin resistance and impaired pancreatic beta-cell function may result from fetal reprogramming of key metabolic tissues.