1α,25‐Dihydroxyvitamin D 3 Modulation of Adipocyte Reactive Oxygen Species Production

Objective: We have previously shown 1α,25‐dihydroxyvitamin D 3 [1α,25‐(OH) 2 D 3 ] 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 H 2 O 2 (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 μM) or 1α,25‐(OH) 2 D 3 (10 nM) and attenuated by UCP2 overexpression, suggesting that inhibition of mitochondrial uncoupling suppresses clearance of ROS and increases adipocyte proliferation. The addition of α ± tocopherol (1 μM) inhibited cell proliferation in adipocytes treated with either H 2 O 2 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 H 2 O 2 resulted in a 2‐ to 5‐fold increase in adipocyte intracellular calcium ([Ca 2+ ]i; p < 0.001), and calcium channel antagonism (nifedipine, 10 μM) suppressed ROS induced calcium influx and cell proliferation, indicating that [Ca 2+ ]i may also regulate ROS production and exert a mitogenic effect in adipocytes. Discussion: These data support a role of 1α,25‐(OH) 2 D 3 , UCP2, and [Ca 2+ ]i in the regulation of adipocyte ROS production.