Adipocyte Reactive Oxygen Species Production

SUN, XIAOCUN AND MICHAEL B. ZEMEL. 1 ,25Dihydroxyvitamin D3 modulation of adipocyte reactive oxygen species production. Obesity. 2007;15:1944–1953. Objective: We have previously shown 1 ,25-dihydroxyvitamin D3 [1 ,25-(OH)2D3] to inhibit mitochondrial uncoupling protein 2 (UCP2) expression in adipocytes and that in vivo suppression of calcitriol levels with calcium-rich diets increases UCP2 expression. Because UCP2 plays a significant role in the clearance of reactive oxygen species (ROS), we studied the effect of calcitriol on ROS production and ROS-induced adipocyte proliferation. Research Methods and Procedures: ROS production in human and murine adipocytes was stimulated by high glucose (30 mM) or H2O2 (100 nM). Results: Both approaches resulted in increased ROS production by 27% to 100% (p 0.05) and increased cell proliferation by 15% to 39% (p 0.03). These effects were augmented by the addition of mitochondrial uncoupling inhibitor guanosine 5 -diphosphate (GDP; 100 M) or 1 ,25-(OH)2D3 (10 nM) and attenuated by UCP2 overexpression, suggesting that inhibition of mitochondrial uncoupling suppresses clearance of ROS and increases adipocyte proliferation. The addition of tocopherol (1 M) inhibited cell proliferation in adipocytes treated with either H2O2 or high glucose, indicating that ROS plays a major role in the regulation of cell proliferation in adipocytes. Moreover, stimulation of ROS with high glucose and H2O2 resulted in a 2to 5-fold increase in adipocyte intracellular calcium ([Ca ]i; p 0.001), and calcium channel antagonism (nifedipine, 10 M) suppressed ROS induced calcium influx and cell proliferation, indicating that [Ca ]i may also regulate ROS production and exert a mitogenic effect in adipocytes. Discussion: These data support a role of 1 ,25-(OH)2D3, UCP2, and [Ca ]i in the regulation of adipocyte ROS production.