Inhibitory effect of physiological concentrations of cortisol but not estradiol on interleukin (IL)-6 production by human osteoblast-like cell lines with different constitutive IL-6 expression

Estrogen deficiency and glucocorticoid excess are two well-known conditions that account for osteoporosis. Interleukin (IL)-6 plays an important role in bone resorption; both estrogens and glucocorticoids are credited with an inhibitory effect on osteoblast production of IL-6. The aim of the study was to investigate whether endogenous hormones, which lead to opposite changes in bone mass, have a common inhibitory effect upon constitutive and inducible IL-6 production by human osteoblast-like cells. We used two human osteosarcoma cell lines (MG-63 and Saos-2) with a different degree of differentiation and constitutive production of IL-6 [2587 +/- 536 (mean SE) and 3.65 +/- 0.06 pg/10(6) cells, respectively]. We examined the effects of physiological and supraphysiological concentrations of 17 beta -estradiol (E-2) and cortisol on basal and IL-1 beta -induced IL-6 release in the medium. In all experimental conditions, cellular estrogen receptors (ERs) and glucocorticoid receptors (GRs) were measured by binding assay. Both MG-63 and Saos-2 cell lines had measurable GRs (106 300 +/- 24 996 and 18 100 +/- 3215 binding sites/cell, respectively) and ERs (2197 +/- 377 and 1261 +/- 66.5 binding sites/cell, respectively). In MG-63 cells, cortisol treatment for 20 h decreased both basal and IL- I P-induced IL-6 release in a dose-dependent manner; in Saos-2 cells the same effect was apparent for IL-1 beta -induced release. Mifepristone (RU-486) did function as partial agonist and antagonist of cortisol. At variance with cortisol, E-2 did not exert any effect on IL-6 secretion. Treatment with 1,25(OH)(2)D-3 increased by 100-200% ER concentrations, but did not change ineffectiveness of E-2 in modifying IL-6 production; furthermore, when E-2 was combined with cortisol, there was no additive effect on cortisol-induced inhibition. The dissociation between glucocorticoid and estrogen effects observed in these human cell lines is a sufficiently robust phenomenon to raise questions about the pathogenetic role of IL-6 in osteoporosis associated with estrogen deficiency. Conversely inhibition of osteoblast production of IL-6 may offer an explanation why bone resorption is not the dominant factor in the pathogenesis of glucocorticoid-induced osteoporosis. (C) 2001 Academic Press.