[Cytokines of bone turnover in postmenopause and old age]

The aim of the study was the assessment of the influence of cytokines on bone ageing by measuring their level in serum and their secretion in vitro by monocytes from women of different age.

The levels of cytokines in 34 postmenopausal subjects and 14 old subjects were compared to those measured in 13 cycling subjects who were considered as control group. Subjects suffering from diseases inducing secondary osteoporosis, subjects taking medications that affect bone metabolism and alcohol- or tobacco-consumers were excluded from the study. The levels in serum of (i) the bone stimulating peptide insulin-like growth factor-I (IGF-I), (ii) the inhibitor of bone resorption interferon-gamma (IFN gamma), (iii) the stimulators of bone resorption interleukin-1 beta (IL-1 beta) tumor necrosis factor alpha (TNF alpha) and interleukin 6 (IL-6) were evaluated by immunoassay. IL-1 beta, TNF alpha and IL-6 secreted by monocytes (MO) cultured in vitro from peripheral blood of the same subjects were measured, too. Bacterial endotoxin (LPS) was used as stimulator for cytokine secretion by monocytes.

Unlike IFN gamma, which was unaltered, circulating IGF-I level was found significantly diminished in postmenopausal and old subjects compared to control group. Among stimulators of bone resorption, IL-6 was greatly increased in postmenopausal and old subjects, while TNF alpha was reduced in postmenopausal group. In the supernatants of unstimulated monocytes the level of IL-1 beta was consistently decreased in old subjects; TNF alpha was found to be decreased in postmenopausal and old subjects. The stimulation index (SI), calculated as the ratio between the level of cytokines secreted by LPS-stimulated MO and the level of cytokines secreted by unstimulated MO, was found to be significantly increased for IL-1 beta and TNF alpha in postmenopausal subjects vs control group. In the old subjects the SI for IL-6 was enhanced.

The data collected suggest that the measurement of cytokines in serum and supernatants from monocytes may give a picture of the mechanisms regulating bone aging.