Homocysteine (Hcy) at elevated levels is a putative risk factor for many cardiovascular disorders including atherosclerosis. In the present study, we investigated the effect of Hcy on the expression of cyclooxygenase (COX)-2 in murine macrophages and the mechanisms involved. Hcy increased the expression of COX-2 mRNA and protein in dose- and time-dependent manners, but did not affect COX-1 expression. Hcy-induced COX-2 expression was attenuated not only by the calcium chelators, EGTA and BAPTA-AM, but also by an antioxidant, N-acetylcysteine. Calcium chelators also attenuated Hcy-induced reactive oxygen species (ROS) production in macrophages, indicating that Hcy-induced COX-2 expression might be mediated through ROS generated by calcium-dependent signaling pathways. In another series of experiments, Hcy increased the intracellular concentration of calcium in a dose-dependent manner, which was attenuated by MK-801, an N-methyl-D-aspartate (NMDA) receptor inhibitor, but not by bicuculline, a gamma-aminobutyric acid receptor inhibitor. Molecular inhibition of NMDA receptor using small interfering RNA also attenuated Hcy-induced increases in intracellular calcium. Furthermore, both ROS production and Hcy-induced COX-2 expression were also inhibited by MK-801 as well as by molecular inhibition of NMDA receptor. Taken together, these findings suggest that Hcy enhances COX-2 expression in murine macrophages by ROS generated via NMDA receptor-mediated calcium signaling pathways.

Denosumab is a humanized monoclonal antibody targeting the receptor activator of nuclear factor kappa-B ligand (RANKL). Denosumab is an effective treatment for osteoporosis but can cause hypocalcemia. We present a case of denosumab-induced hypocalcemia in a patient with hyperthyroidism with a high bone turnover state. A 48-year-old postmenopausal woman was diagnosed with hyperthyroidism and osteoporosis and received antithyroid drugs (propylthiouracil 200 mg/day) and denosumab. After 2 months of taking medication, the patient complained of numbness and tingling in the hands and feet and was diagnosed with hypocalcemia (calcium, 5.8 mg/dL; ionized calcium, 0.83 mmol/L). Alfacalcidol (0.5 μg/day) and calcium carbonate (3000 mg/day) were prescribed. Subsequently, the patient’s symptoms improved, and her serum calcium level normalized. The risk of denosumab-induced hypocalcemia may be increased in patients with diseases related to high bone turnover, such as hyperthyroidism; therefore, caution is needed.