Circulating levels of cytokines that modulate bone resorption: Effects of age and menopause in women

Interleukin 1αa (IL‐1α), interleukin 1β (IL‐1β), and interleukin 6 (IL‐6) are cytokines with potent bone‐resorbing effects; some of these biologic effects are opposed by interleukin‐1 receptor antagonist (IL‐1ra). In vitro and animal model studies suggest that these cytokines are paracrine mediators of the increased bone resorption associated with estrogen deficiency, and increases in their production also could contribute to age‐related bone loss. Therefore, we measured serum concentrations of these cytokines in 80 normal women who were 24‐87 years old. IL‐6 concentration correlated highly with age (p > 0.001) and increased three‐fold during life. However, multiple‐regression analysis showed no significant correlation between serum IL‐6 levels and menopausal status, serum estradiol concentration, or markers for bone turnover (serum bone alkaline phosphatase, osteocalcin, carboxyl‐terminal telopeptide of type I collagen, or 24 h urinary free pyridinoline excretion). Serum IL‐1α, IL‐1β, or IL‐1ra level did not change with age and, by multiple‐regression analysis, did not correlate with markers of bone turnover, except IL‐1ra weakly with ICTP. We found no relationship between bone‐resorbing cytokines and ovarian function. Although the large age‐related increase in serum IL‐6 concentration could contribute to age‐related bone loss, the lack of correlation with markers for bone turnover argues against this. However, based on the strong evidence in experimental animals that these cytokines are involved in estrogen action on bone, further studies in humans are warranted.