High levels of glucocorticoids are believed to alter bone remodeling by decreasing bone formation and increasing bone resorption. It has been suggested that different cytokines, like interleukin-6 (IL-6) and interleukin-1 (IL-1), are involved in bone resorption by activating immature osteoclasts, and some studies indicate that IL-6 promotes bone formation by a mitogenic effect on osteoblasts. The aim of the present investigation was to study whether cortisol regulates the expression of IL-6 and IL-1 beta in human osteoblast-like cells. A high dose of cortisol (10(-7)M) decreased, as expected, the C-terminal propeptide of type I collagen released into the culture medium. The IL-6 mRNA levels and IL-6 protein released into the culture medium were also decreased by cortisol in a dose-dependent manner. The maximum effect was seen at 1 microM cortisol (mRNA 23.1 +/- 7.9% of control culture; protein 28.2 +/- 8.3% of control culture). The decrease in IL-6 mRNA levels was apparent 4 h after the addition of cortisol and was still present 20 h later. The decrease in IL-6 protein released into the culture medium was seen 20 h later than the decrease in IL-6 mRNA levels. The production of IL-1 beta protein released into the culture medium was decreased in a dose-dependent manner after the addition of cortisol with a maximum effect at 1 microM. The effect of cortisol on IL-1 beta protein released into the culture medium was seen 16 h after the addition of cortisol. To summarize, cortisol decreases the expression of IL-6 as well as IL-1 beta in human osteoblast-like cells.
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