Sarcopenia is the age-related loss of skeletal muscle mass and function. Dietary restriction (DR) is the only known intervention that reduces the effects of age on muscle mass loss; however, nearly all studies have been conducted on rodent species. The purpose of this study is to monitor the effects of DR on age-related changes in muscle mass and muscle fibers, in the same rhesus monkeys over time.
Thirty male rhesus macaques, 8-14 years of age, were assigned to the study in 1989. Following a 3-month baseline period, animals were equally randomized to Control or DR and food allotments in DR animals were reduced by 10% per month for 3 months to achieve a 30% restriction. Beginning in year 1, animals underwent annual dual-energy x-ray absorptiometry (DXA) scanning and skeletal muscle mass was estimated. DXA estimates for Control monkeys over the past 13 years showed muscle mass changes with age, with a significant decrease between years 9 and 13 of the study. DR monkeys, over the same period of time, showed no significant changes in muscle mass.
Every three years, beginning in year six of the study, biopsies were obtained from the vastus lateralis (VL) to monitor changes in muscle fibers with age. Biopsies were sectioned (200, 10µ thick sections) and stained for electron transport system (ETS) enzymatic activities to detect age- and diet-related changes in mitochondria. Biopsies obtained from Control animals six and nine years after initiation of the study, exhibited few ETS abnormalities. In the 12-year Control samples (20-26 year old animals) there were significantly more fibers with ETS enzyme abnormalities. No ETS abnormalities were found in the 6-year biopsy samples from DR monkeys and very few ETS abnormalities were detected in the 12-year DR biopsies.
To this point in our study, DR monkeys showed no change in muscle mass over time, where Control muscle mass estimates decrease with age. Although ETS abnormalities increase with age in monkey VL, DR monkeys present significantly fewer ETS abnormalities than Control. These longitudinal studies are ongoing, but already provide valuable insight into early sarcopenic changes with age and the effects of adult on-set dietary restriction.