1,25(OH) 2 Vitamin D Inhibits Foam Cell Formation and Suppresses Macrophage Cholesterol Uptake in Patients With Type 2 Diabetes Mellitus

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Abstract
Background— Cardiovascular disease is the leading cause of death among those with diabetes mellitus. Vitamin D deficiency is associated with an increased risk of cardiovascular disease in this population. To determine the mechanism by which vitamin D deficiency mediates accelerated cardiovascular disease in patients with diabetes mellitus, we investigated the effects of active vitamin D on macrophage cholesterol deposition. Methods and Results— We obtained macrophages from 76 obese, diabetic, hypertensive patients with vitamin D deficiency (25-hydroxyvitamin D 3 [1,25(OH) 2 D 3 ] –supplemented media and exposed to modified low-density lipoprotein cholesterol. 1,25(OH) 2 D 3 suppressed foam cell formation by reducing acetylated or oxidized low-density lipoprotein cholesterol uptake in diabetic subjects only. Conversely, deletion of the vitamin D receptor in macrophages from diabetic patients accelerated foam cell formation induced by modified LDL. 1,25(OH) 2 D 3 downregulation of c-Jun N-terminal kinase activation reduced peroxisome proliferated–activated receptor-γ expression, suppressed CD36 expression, and prevented oxidized low-density lipoprotein–derived cholesterol uptake. In addition, 1,25(OH) 2 D 3 suppression of macrophage endoplasmic reticulum stress improved insulin signaling, downregulated SR-A1 expression, and prevented oxidized and acetylated low-density lipoprotein–derived cholesterol uptake. Conclusion— These results identify reduced vitamin D receptor signaling as a potential mechanism underlying increased foam cell formation and accelerated cardiovascular disease in diabetic subjects.