Protective Role of L-Cysteine Against High Glucose Induces G6PD-Deficiency and Endothelial Dysfunction

African Americans have high incidences of diabetes and cardiovascular disease, and glucose-6-phosphate dehydrogenase (G6PD) deficiency. G6PD supplies NADPH, which recycles GSSG to GSH. Clinical studies demonstrate that lower blood GSH/G6PD correlate with excess oxidative stress with vascular inflammation markers which contribute to the development of complications in diabetic patients. However, the contribution of high glucose (HG) on G6PD deficiency to endothelial activation/dysfunction and monocyte recruitment, a forerunner of atherosclerosis, remains unknown. G6PD-normal and G6PD-deficient HUVEC and monocytic cells were silenced with control or G6PD siRNA (100nM) for 24 h, followed by exposure with normal glucose (5.5mM) or HG (25mM) or glutathione precursor L-Cysteine (LC; 300µM) in basal medium for 6 h. HG reduced the G6PD mRNA and its activity along with GSH in both G6PD-normal and G6PD-deficient endothelial and monocytic cells. Conversely, mRNA levels of iNOS, NOX4, and its activity were significantly upregulated but eNOS and nitrate levels were remarkably decreased under HG treated G6PD-deficient cells compared to G6PD-normal cells. The expression of cell adhesion molecules (CAMs) ICAM-1 and VCAM-1 mRNA levels significantly increased in HG-treated G6PD-deficient cells compared to G6PD-normal cells. Elevated MCP-1 was found in G6PD-deficient cells under HG conditions. Enhanced adherence of monocytes to HUVEC was observed in HG-treated G6PD-deficient cells (15.13%; p<0.005) compared to control cells (10%; ns). LC supplementation significantly increased the G6PD activity, GSH, and decreased CAMs reduced adherence to control level. These findings demonstrate that high glucose induces and fuels a GSH/G6PD-deficient phenotype to impair endothelial function; LC supplementation improves vascular reactivity by restoring GSH/G6PD levels.