Health benefits of late-onset metformin treatment every other week in mice

Characteristics of mice on intermittent metformin treatment. a Protocol design. Male mice (108 week-old) were fed a standard diet (SD) without (n？=？68) or with 1% metformin in the diet every-other week (EOW, n？=？64) or for two consecutive weeks each month (2WM, n？=？67) for 24 weeks. At the indicated time points (weeks), body composition (NMR), metabolic assessment (RER), and physical performance tests (PPT) were performed on non-fasted animals, whereas blood glucose and lactate levels were measured in 6-h fasted mice. Sac, sacrifice of a subset of animals for tissue collection and analysis (SD, n？=？10; EOW, n？=？6; 2WM, n？=？6). b Kaplan–Meier survival curve for the three experimental groups of mice (SD, EOW, 2WM). No extension of maximal lifespan was observed. c Body weight profile over the lifespan. Data include all live animals at each time point. Inset, Body weight at the initiation (0) and after 10 weeks of treatment (10) (SD, n？=？68(0) and 64(10); EOW, n？=？64(0) and 58(10); 2WM, n？=？67(0) and 57(10)). #p？<？0.05 compared to t？=？0; *p？<？0.05 compared to SD at t？=？10 weeks. d Body temperature. e Food consumption. f Average daily food consumption per mouse. g The data shown in panel f was segregated by whether mice were on metformin treatment or returned to SD without metformin. h Correlations between % body fat (upper panel) or lean-to-fat ratio (lower panel) and time of death (n？=？12 in each group) (upper, F？=？22.27; dFn, dFd (1, 35); P？<？0.0001); lower, (F？=？11.1; dFn, dFd (1, 35); P？<？0.002). i–j Mice were subjected to metabolic assessment after 17 weeks of treatment (SD, n？=？11; EOW on metformin, n？=？6; EOW off metformin, n？=？6; 2WM on metformin, n？=？9; 2WM off metformin, n？=？3): i Respiratory exchange ratio (RER) values over the course of 48？h; j RER values shown in panel i were segregated based on the light and dark periods of the L12:D12 cycle; k Latency to fall from wire hang was measured after 16 weeks of treatment (SD, n？=？47; EOW on metformin, n？=？12; EOW off metformin, n？=？7; 2WM on metformin, n？=？0; 2WM off metformin, n？=？22) before (upper panel) and after (lower panel) correction for body weight. l, m At 13–16 weeks of treatment, mice were fasted for 6？h (SD, n？=？8–10; EOW, n？=？9–10; 2WM, n？=？9–10) and circulating levels of l glucose and m lactate were measured. n–r The following analyses were carried out at 17 weeks of treatment in fed mice (SD, n？=？10; EOW, n？=？6; 2WM, n？=？6): n blood glucose; o serum insulin levels; p HOMA-IR index; q blood lactate; r Serum levels of leptin. s Correlation between circulating levels of leptin and amount