Increased serum osteoprotegerin values in long-lived subjects: different effects of inflammation and bone metabolism.

Aim: To evaluate serum osteoprotegerin (OPG) concentrations in relation to age-dependent changes in serum markers of bone metabolism and systemic inflammation.
Methods: Two-hundred and eighty-three healthy subjects were evaluated for plasma estimated creatinine clearance (Cr-clearance), C-reactive protein (CRP), bone alkaline phosphatase, C-telopeptides of type-1 collagen (CrossLaps), nuclear factor-kappaB ligand (RANKL) and OPG concentrations.
Results: In adult subjects (82 cases aged between 27 and 64 years) serum OPG concentrations were significantly and independently correlated with RANKL and Cr-clearance (R(2): 0.29), but not with CRP and biochemical markers of bone metabolism. In old subjects who were between 65 and 84 years of age (52 cases) serum OPG concentrations were significantly higher as compared with the adult subjects and correlated independently and significantly with serum RANKL, Cr-clearance and CrossLaps values (R(2): 0.63). The highest OPG values were found in the long-lived subjects (149 cases with ages between 85 and 110 years) who also showed increased serum CrossLaps and CRP concentrations as compared with the younger subjects. However, in the long-lived subjects serum OPG concentrations were significantly and independently correlated with Cr-clearance and CRP (R(2): 0.45) but not with CrossLaps values.
Conclusions: These data would suggest that different factors might be responsible for the age-dependent enhancement of OPG production. Bone metabolism would seem to be the most important factor influencing serum OPG concentrations in old subjects under 85 years of age, whereas in long-lived subjects the circulating values of this cytokine seem to be mainly correlated with serum CRP which could be a marker of inflammation and cardiovascular risk.