Bazedoxifene Ameliorates Homocysteine-Induced Apoptosis and Accumulation of Advanced Glycation End Products by Reducing Oxidative Stress in MC3T3-E1 Cells

Elevated plasma homocysteine (Hcy) level increases the risk of osteoporotic fracture by deteriorating bone quality. However, little is known about the effects of Hcy on osteoblast and collagen cross-links. This study aimed to investigate whether Hcy induces apoptosis of osteoblastic MC3T3-E1 cells as well as affects enzymatic and nonenzymatic collagen cross-links and to determine the effects of bazedoxifene, a selective estrogen receptor modulator, on the Hcy-induced apoptosis and deterioration of collagen cross-links in the cells. Hcy treatments (300 μM, 3 mM, and 10 mM) increased intracellular reactive oxygen species (ROS) production in a dose-dependent manner. Propidium iodide staining showed that 3 and 10 mM Hcy induced apoptosis of MC3T3-E1 cells. Moreover, the activities of caspases-8, 9, and 3 were increased by 3 mM Hcy. The detrimental effects of 3 mM Hcy on apoptosis and ROS production were partly reversed by bazedoxifene and 17β estradiol. In addition, real-time PCR, immunostaining and Western blot showed that 300 μM Hcy decreased the expression of lysyl oxidase (Lox). Furthermore, 300 μM Hcy increased extracellular accumulation of pentosidine, an advanced glycation end product. Treatment with bazedoxifene ameliorated Hcy-induced suppression of Lox expression and increase in pentosidine accumulation. These findings suggest that high-dose Hcy induces apoptosis of osteoblasts by increasing oxidative stress, and low-dose Hcy decreases enzymatic collagen cross-links and increases pentosidine accumulation, resulting in the deterioration of bone quality. Bazedoxifene treatment effectively prevents the Hcy-induced detrimental reactions of osteoblasts. Thus, bazedoxifene may be a potent therapeutic drug for preventing Hcy-induced bone fragility.