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Vitamin D Inhibits ROS, ICAM‐1, and Monocyte Adhesion in High Glucose and Acetoacetate Treated Endothelial Cells by Upregulating GSH

The incidence of developing microvascular dysfunction is significantly higher in type 1 diabetic (T1D) patients. Monocyte adhesion to the endothelium plays a central role in the progression of endothelial dysfunction. This study examines whether vitamin D (VD) supplementation is beneficial in preventing endothelial dysfunction in diabetes. Human umbilical vein endothelial cells (HUVEC) were treated with 1, 25‐(OH)2‐D3 (0‐25 nM, 24 h) and later exposed to the ketone body acetoacetate (AA, 4 mM) or high glucose (HG, 25 mM) for 24 h. Treatment with AA or HG causes an increase in ROS, ICAM‐1 expression, and monocyte adhesion, along with a decrease in GSH levels in HUVEC. VD supplementation (25 nM) significantly lowered ROS (41%, p<0.05), ICAM‐1 (73%, p=0.05) and monocyte adhesion (37.5%, p=0.05) in AA treated HUVEC. VD had a similar beneficial effect on HG treated cells. Interestingly, we also saw an upregulation in GSH levels following treatment with VD. We hypothesize that the beneficial effect of VD is mediated by the upregulation of GSH. Glutamyl cysteine ligase (GCLC) catalyzes GSH biosynthesis. Knocking down GCLC using siRNA reduced GSH levels as well as abolished the beneficial effect of VD on ketone‐ or HG‐induced ROS, ICAM‐1, and monocyte adhesion. This suggests that VD mediates its beneficial effects via the upregulation of GCLC. This study provides the biochemical mechanism through which VD can lower ROS, ICAM‐1 expression, monocyte–endothelial adhesion, and thereby lower the risk of endothelial dysfunction in diabetes.