Lifelong alpha-tocopherol supplementation increases the median life span of C57BL/6 mice in the cold but has only minor effects on oxidative damage.

The effects of dietary antioxidant supplementation on oxidative stress and life span are confused. We maintained C57BL/6 mice at 7 +/- 2 degrees C and supplemented their diet with alpha-tocopherol from 4 months of age. Supplementation significantly increased (p = 0.042) median life span by 15% (785 days, n = 44) relative to unsupplemented controls (682 days, n = 43) and also increased maximum life span (oldest 10%, p = 0.028). No sex or sex by treatment interaction effects were observed on life span, with treatment having no effect on resting or daily metabolic rate. Lymphocyte and hepatocyte oxidative DNA damage and hepatic lipid peroxidation were unaffected by supplementation, but hepatic oxidative DNA damage increased with age. Using a cDNA macroarray, genes associated with xenobiotic metabolism were significantly upregulated in the livers of female mice at 6 months of age (2 months supplementation). At 22 months of age (18 months supplementation) this response had largely abated, but various genes linked to the p21 signaling pathway were upregulated at this time. We suggest that alpha-tocopherol may initially be metabolized as a xenobiotic, potentially explaining why previous studies observe a life span extension generally when lifelong supplementation is initiated early in life. The absence of any significant effect on oxidative damage suggests that the life span extension observed was not mediated via any antioxidant properties of alpha-tocopherol. We propose that the life span extension observed following alpha-tocopherol supplementation may be mediated via upregulation of cytochrome p450 genes after 2 months of supplementation and/or upregulation of p21 signaling genes after 18 months of supplementation. However, these signaling pathways now require further investigation to establish their exact role in life span extension following alpha-tocopherol supplementation.

Calorie-restricted mice that gorge show less ability to compensate for reduced energy intake.

Caloric restriction in mice can trigger gorging behaviour, which is characterized by periods of excessive food ingestion in a short time. Animals that gorge are thought to have a reduced metabolism compared to those that nibble their food over a longer period and might therefore be more able to compensate for reduced energy intake. We examined whether mice that gorged showed less weigh loss during restriction. We placed female mice (n=60) on a restriction of 75% of their ad libitum food intake (FI) for 22 days. FI and body mass (BM) were measured at 1, 2 and 24 h after food provision. Ten controls remained feeding ad lib and we selected the 10 strongest gorgers and 10 strongest non-gorgers for comparison. Mice had BM, FI, resting metabolic rate (RMR), body composition, body temperature, daily energy expenditure (DEE) and circulating levels of the regulatory hormones leptin and ghrelin measured. Gorgers had a significantly lower BM at the end of restriction than non-gorgers or controls, indicating that they were less able to compensate for the reduced energy. Both groups of restricted mice had reduced RMR, however reduced activity was only used as an energy saving mechanism in non-gorgers. Gorging mice had a significantly lower level of circulating leptin than controls and non-gorgers but no differences in ghrelin levels. Gorging mice were, in fact, less able to compensate for reduced energy intake, as they reduced RMR by a similar extent as non-gorgers, but did not reduce activity compared to non-gorgers on the same restriction level. The reduced leptin levels may drive the gorging behaviour.

Life-long vitamin C supplementation in combination with cold exposure does not affect oxidative damage or lifespan in mice, but decreases expression of antioxidant protection genes.

Oxidative stress is suggested to be central to the ageing process, with endogenous antioxidant defence and repair mechanisms in place to minimize damage. Theoretically, supplementation with exogenous antioxidants might support the endogenous antioxidant system, thereby reducing oxidative damage, ageing-related functional decline and prolonging life- and health-span. Yet supplementation trials with antioxidants in animal models have had minimal success. Human epidemiological data are similarly unimpressive, leading some to question whether vitamin C, for example, might have pro-oxidant properties in vivo. We supplemented cold exposed (7+/-2 degrees C) female C57BL/6 mice over their lifespan with vitamin C (ascorbyl-2-polyphosphate), widely advocated and self administered to reduce oxidative stress, retard ageing and increase healthy lifespan. No effect on mean or maximum lifespan following vitamin C treatment or any significant impact on body mass, or on parameters of energy metabolism was observed. Moreover, no differences in hepatocyte and lymphocyte DNA oxidative damage or hepatic lipid peroxidation was seen between supplemented and control mice. Using a DNA macroarray specific for oxidative stress-related genes, we found that after 18 months of supplementation, mice exhibited a significantly reduced expression of several genes in the liver linked to free-radical scavenging, including Mn-superoxide dismutase. We confirmed these effects by Northern blotting and found additional down-regulation of glutathione peroxidase (not present on macroarray) in the vitamin C treated group. We suggest that high dietary doses of vitamin C are ineffective at prolonging lifespan in mice because any positive benefits derived as an antioxidant are offset by compensatory reductions in endogenous protection mechanisms, leading to no net reduction in accumulated oxidative damage.

Factors influencing variation in basal metabolic rate include fat-free mass, fat mass, age, and circulating thyroxine but not sex, circulating leptin, or triiodothyronine.

BACKGROUND: Basal metabolic rate (BMR) is the largest component of daily energy demand in Western societies. Previous studies indicated that BMR is highly variable, but the cause of this variation is disputed. All studies agree that variation in fat-free mass (FFM) plays a major role, but effects of fat mass (FM), age, sex, and the hormones leptin, triiodothyrionine (T3), and thyroxine (T4) remain uncertain. OBJECTIVE: We partitioned the variance in BMR into within- and between-subject effects and explored the roles of FFM, FM, bone mineral content, sex, age, and circulating concentrations of plasma leptin, T3, and T4. DESIGN: This was a cross-sectional study of 150 white adults from northeast Scotland, United Kingdom. RESULTS: Only 2% of the observed variability in BMR was attributable to within-subject effects, of which 0.5% was analytic error. Of the remaining variance, which reflected between-subject effects, 63% was explained by FFM, 6% by FM, and 2% by age. The effects of sex and bone mineral content were not significant (P > 0.05). Twenty-six percent of the variance remained unexplained. This variation was not associated with concentrations of circulating leptin or T3. T4 was not significant in women but explained 25% of the residual variance in men. CONCLUSIONS: Our data confirm that both FFM and FM are significant contributors to BMR. When the effect of FM on BMR is removed, any association with leptin concentrations disappears, which suggests that previous links between circulating leptin concentrations and BMR occurred only because of inadequate control for the effects of FM.

Energy expenditure of calorically restricted rats is higher than predicted from their altered body composition.

Debate exists over the impact of caloric restriction (CR) on the level of energy expenditure. At the whole animal level, CR decreases metabolic rates but in parallel body mass also declines. The question arises whether the reduction in metabolism is greater, smaller or not different from the expectation based on body mass change alone. Answers to this question depend on how metabolic rate is normalized and it has recently been suggested that this issue can only be resolved through detailed morphological investigation. Added to this issue is the problem of how appropriate the resting energy expenditure is to characterize metabolic events relating to aging phenomena. We measured the daily energy demands of young and old rats under ad libitum (AD) food intake or 40% CR, using the doubly labeled water (DLW) method and made detailed morphological examination of individuals, including 21 different body components. Whole body energy demands of CR rats were lower than AD rats, but the extent of this difference was much less than expected from the degree of caloric restriction, consistent with other studies using the DLW method on CR animals. Using multiple regression and multivariate data reduction methods we built two empirical predictive models of the association between daily energy demands and body composition using the ad lib animals. We then predicted the expected energy expenditures of the CR animals based on their altered morphology and compared these predictions to the observed daily energy demands. Independent of how we constructed the prediction, young and old rats under CR expended 30 and 50% more energy, respectively, than the prediction from their altered body composition. This effect is consistent with recent intra-specific observations of positive associations between energy metabolism and lifespan and theoretical ideas about mechanisms underpinning the relationship between oxygen consumption and reactive oxygen species production in mitochondria.