Osteoarthritic changes in the macaque spine with age: their use on the U.S. National Institute of Aging (NIA) caloric restriction study.

L. Newell-Morris, P.A. Kramer, P. Simkin, Y. Hamda, H. Prossinger and D.K.Ingram.

Studies on small laboratory animals have shown since 1935 that caloric restriction (CR) extends life span. Whether or not CR has the same effect on long-lived taxa, e.g., the human species, is not known. As the requisite research is not possible on human subjects, the rhesus macaque monkey, a proven biomedical model, has been the subject of a long-term CR project. Initiated in 1987 by the National Institute of Aging (NIA), a total of 120 animals evenly divided by sex and age group (range 0.7- 22.9 yrs) was enrolled over 5 years, and assigned to CR or control (CON) group. Animals are single-caged under standard husbandry, with the exception of diet; CR animals receive 30% fewer calories daily than do CON. This study explores the effects of CR on body mass (BM) and spinal osteoarthritis (OA). CR significantly decreased median BM in both sexes enrolled on the study pre-adult (p<. 001, Kolmogorov-Smirow test). Male BM was more depressed (~ 80% of CON) over a 12- 14 yr interval, than was female BM (~ 90% of CON). Sexual selection theory offers an explanation for the preservation of female bodily resources. Given the difficulty of determining life span, the question becomes whether or not CR slows the rate of aging. Spinal OA is used as a biomarker for rate of aging. Change over 4 years among animals enrolled pre-adult was assessed from radiographs, using an average score (OST) over 12 thoracolumbar vertebrae. Males show significantly faster progression of OA than do females (a OST = 0.109 and 0.052, respectively, linear regression with repeated measures). Gompertz parameters from another rhesus sample show that males initiate OA earlier and reach a higher score at older ages than do females. This pattern replicates an earlier ontogenetic pattern typical of primates, and may account for the unexplained “maleness” risk factor for OA. OA among CR males enrolled pre-adult may not be progressing as rapidly as CON, but further longitudinal data are needed to confirm the trend.