Effects of Selective NADPH Oxidase Inhibitors on Real-Time Blood Nitric Oxide and Hydrogen Peroxide Release in Acute Hyperglycemia

摘要

Hyperglycemia (blood glucose > 5.5 mM) has been definitively linked to the development of vascular and neurologic complications in diabetic patients. Moreover, even in non-diabetic subjects, acute hyperglycemia during oral glucose tolerance tests or postprandially can temporarily induce vascular endothelial dysfunction, which is characterized by decreased endothelium-derived nitric oxide (NO) release and increased reactive oxygen species (ROS): superoxide (SO) and hydrogen peroxide (H2O2). Vascular NO is produced by endothelial NO synthase (eNOS) and plays critical roles in maintaining blood flow and suppressing inflammatory and coagulant vascular signals. It has been proposed that hyperglycemia induces eNOS enzymatic uncoupling resulting in SO production instead of NO leading to oxidative stress. Our lab has established an acute hyperglycemia animal model to monitor blood NO and H2O2 levels via free radical microsensors in real-time. We found that acute hyperglycemia had significantly higher blood H2O2 and lower blood NO levels compared to euglycemia [1]. However, the initial or trigger source of oxidative stress under acute hyperglycemic conditions is still unclear. One strong candidate is non-phagocytic nicotinamide adenine dinucleotide phosphate (NADPH) oxidase a multi-subunit enzyme that catalyzes SO production (see Figure 1), is widely distributed in various cells types, normally participates in various signaling pathways and has been shown to be activated following protein kinase C activation in chronic hyperglycemia [2,3]. To better understand the role of NADPH oxidase in acute hyperglycemia induced vascular dysfunction, two NADPH oxidase inhibitors, gp91 ds-tat (RKKRRQRRR-CSTRIRRQL-amide, MW=2452 g/mol, 1.2 mg/kg, Genemed Synthesis Inc., San Antonio, TX) and apocynin (MW=166 g/mol, Sigma Chemicals), were tested to determine whether they will increase NO and reduce H2O2 blood levels under acute hyperglycemic conditions.