How does ascorbate improve endothelial dysfunction? - A computational analysis.

Low levels of ascorbate (Asc) are observed in cardiovascular and neurovascular diseases. Asc has therapeutic potential for the treatment of endothelial dysfunction, which is characterized by a reduction in nitric oxide (NO) bioavailability and increased oxidative stress in the vasculature. However, the potential mechanisms remain poorly understood for the Asc mitigation of endothelial dysfunction. In this study, we developed an endothelial cell based computational model integrating endothelial cell nitric oxide synthase (eNOS) biochemical pathway with downstream reactions and interactions of oxidative stress, tetrahydrobiopterin (BH) synthesis and biopterin ratio ([BH]/[TBP]), Asc and glutathione (GSH). We quantitatively analyzed three Asc mediated mechanisms that are reported to improve/maintain endothelial cell function. The mechanisms include the reduction of •BH to BH, direct scavenging of superoxide (O) and peroxynitrite (ONOO) and increasing eNOS activity. The model predicted that Asc at 0.1-100 μM concentrations improved endothelial cell NO production, total biopterin and biopterin ratio in a dose dependent manner and the extent of cellular oxidative stress. Asc increased BH availability and restored eNOS coupling under oxidative stress conditions. Asc at concentrations of 1-10 mM reduced O and ONOO levels and could act as an antioxidant. We predicted that glutathione peroxidase and peroxiredoxin in combination with GSH and Asc can restore eNOS coupling and NO production under oxidative stress conditions. Asc supplementation may be used as an effective therapeutic strategy when BH levels are depleted. This study provides detailed understanding of the mechanism responsible and the optimal cellular Asc levels for improvement in endothelial dysfunction.