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Hydrogen sulfide (H2S), as a reducing agent and an antioxidant molecule, exerts protective effects against hyperglycemic stress in the vascular endothelium. The mitochondrial enzyme 3-mercaptopyruvate sulfurtransferase (3-MST) is an important biological source of H2S. We have recently demonstrated that 3-MST activity is inhibited by oxidative stress in vitro and speculated that this may have an adverse effect on cellular homeostasis. In the current study, given the importance of H2S as a vasorelaxant, angiogenesis stimulator and cellular bioenergetic mediator, we first determined whether the 3-MST/H2S system plays a physiological regulatory role in endothelial cells. Next, we tested whether a dysfunction of this pathway develops during the development of hyperglycemia and μmol/L to diabetes-associated vascular complications. Intraperitoneal (IP) 3-MP (1 mg/kg) raised plasma H2S levels in rats. 3-MP (10 1 mmol/L) promoted angiogenesis in vitro in bEnd3 microvascular endothelial cells and in vivo in a Matrigel assay in mice (0.3–1 mg/kg). In vitro studies with bEnd3 cell homogenates demonstrated that the 3-MP-induced increases in H2S production depended on enzymatic activity, although at higher concentrations (1–3 mmol/L) there was also evidence for an additional nonenzymatic H2S production by 3-MP. In vivo, 3-MP facilitated wound healing in rats, induced the relaxation of dermal microvessels and increased mitochondrial bioenergetic function. In vitro hyperglycemia or in vivo streptozotocin diabetes impaired angiogenesis, attenuated mitochondrial function and delayed wound healing; all of these responses were associated with an impairment of the proangiogenic and bioenergetic effects of 3-MP. The antioxidants dl-α-lipoic acid (LA) in vivo, or dihydrolipoic acid (DHLA) in vitro restored the ability of 3-MP to stimulate angiogenesis, cellular bioenergetics and wound healing in hyperglycemia and diabetes. We conclude that diabetes leads to an impairment of the 3-MST/H2S pathway, and speculate that this may contribute to the pathogenesis of hyperglycemic endothelial cell dysfunction. We also suggest that therapy with H2S donors, or treatment with the combination of 3-MP and lipoic acid may be beneficial in improving angiogenesis and bioenergetics in hyperglycemia.

We have previously shown that H2S, as a reducing agent and an antioxidant molecule, exerts protective effects against hyperglycemic stress in the vascular endothelium. The mitochondrial enzyme 3-mercaptopyruvate sulfurtransferase (3-MST) is an important source of hydrogen sulfide (H2S) in endothelial cells. We have recently demonstrated that 3-MST activity is inhibited by oxidative stress in vitro and speculated that this may have adverse effect on cellular homeostasis. Given the importance of H2S as a vasorelaxant, angiogenesis stimulator and positive bioenergetic factor, here we tested whether a dysfunction of the 3-MST/H2S system develops in hyperglycemia/diabetes and studied its contribution to the development of diabetes-associated vascular complications. 3-mercaptopyruvate (3-MP, the substrate of 3-MST) displayed many characteristics of a H2S donor. Intraperitoneal 3-MP (1 mg/kg) raised plasma H2S levels in rats. 3-MP induced angiogenesis in vitro (10–1000 μM; bEnd3 cells) and in vivo (0.3–1 mg/kg; matrigel assay in mice). 3-MP also facilitated wound healing in rats, induced the relaxation of dermal microvessels and increased the bioenergetic function of mitochondria. In vitro hyperglycemia or in vivo streptozotocin diabetes resulted in endothelial dysfunction mitochondrial dysfunction, impaired angiogenesis and reduced wound healing and was associated with a suppression of the vasodilatory, pro-angiogenic, wound-healing stimulating and bioenergetic effects of 3-MP. Systemic treatment with the lipoic acid restored the effect of 3-MP in diabetes, improving endothelial function, cellular bioenergetics and wound healing. We conclude that diabetes is associated with an impairment of the 3-MST/H2S pathway, and speculate that this may contribute to the pathogenesis of diabetic complications.