The role of IL-6 and osteoprotegerin in bone metabolism in patients with Graves' disease.

Abstract

Increased bone turnover is a hallmark of hyperthyroidism. The underlying factors of how thyroid hormones affect bone cells are still under the spotlight. Previous studies indicated serum osteoprotegerin (OPG), receptor activator of NF-kB ligand (RANKL), and interleukin-6 (IL-6) as mediators of the effect of thyroid hormones on bone metabolism. Ultimately, the present research aimed to examine the association of IL-6 with OPG and RANKL in patients with hyperthyroidism. We carried out this study with 39 newly diagnosed and untreated Graves' patients and 43 healthy controls. In addition to routine tests, we measured serum OPG, RANKL, and IL-6 levels. Mean age and sex distribution were similar in both groups. The hyperthyroid group had significantly higher OPG (p = 0.002) and IL-6 (p < 0.001) levels, but RANKL levels were significantly lower in this group (p < 0.001). We found OPG not to correlate with free T4 and T3, while it had a moderate and negative correlation with thyrotropin (TSH) (r = -0.372, p = 0.001). IL-6 had no correlation with OPG but positively correlated with free T4 (r = 0.445, p < 0.001) and free T3 (r = 0.326, p = 0.035). It also negatively correlated with RANKL (r = -0.247, p = 0.033). Maintaining skeletal development and integrity is partially regulated by a normal balance of thyroid hormones. We concluded that increases in serum OPG and IL-6 levels accompanied hyperthyroidism. However, excessive levels of the hormones might cause drops in serum RANKL levels. Our results suggested that OPG, RANKL, and IL-6 might be involved in the cross-talking among immunity, thyroid function, and bone metabolism in the case of hyperthyroidism.