Association between serum OPG/s rankl system and leptin with aging in male rats

ABSTRACT

Increasing evidences have suggested the association between serum leptin and bone formation. Osteoprotegerin [OPG], an osteoblast derived regulator of bone resorption and formation binds with soluble receptor activator of nuclear factor Kappa beta ligand [sRANKL] on osteoclast surface -which binds to its cognate receptor RANK on the osteoclast precursor. Thus, OPG/RANKL/RANK system controls the balance in bone formation and resorption. This study is designed to evaluate whether the OPG/sRANKL system and leptin levels are modified with aging and how they are related to bone and aortic changes. Three groups of rats were selected according to age, 4 months old [Group I], 12 months old [Group II] and 24 months old [Group III]. Serum levels of OPG, sRANKL, leptin, calcium and phosphorus [in sera and aortic extracts] were determined. Histopathological examination of rat femur and aorta from each group was also done. ANOVA test revealed significant difference between the three groups. The aged group [Group III] had higher calcium levels in sera and aortic extracts, serum phosphorus, serum sRANKL, leptin with increased sRANKL/OPG ratio. However OPG was significantly decreased in the same group in comparison to the other 2 groups. A significant negative correlation between serum OPG and sRANKL/OPG ratio [r = -0.879, p < 0.001] and body weight [r = -0.763, p < 0.01] and positive correlation between leptin and sRANKL/OPG ratio [r = 0.734, p < 0.01] and Ca aortic extract [r = 0.844, p < 0.01]. The disruption of OPG/sRANKL system and leptin with old age due to deficient OPG, high serum sRANKL and leptin resistance would represent a link between arterial calcification and bone resorption that are mostly present in the elderly