Role of oxidative stress in high glucose-induced decreased expression of Gi proteins and adenylyl cyclase signaling in vascular smooth muscle cells

Li Y, Descorbeth M, Anand-Srivastava MB. Role of oxidative stress in high glucose-induced decreased expression of Gi proteins and adenylyl cyclase signaling in vascular smooth muscle cells. Am J Physiol Heart Circ Physiol 294: H2845–H2854, 2008. First published April 25, 2008; doi:10.1152/ajpheart.91422.2007.—We have recently shown that aorta from streptozotocin (STZ)-induced diabetic rats and A10 vascular smooth muscle cells (VSMCs) exposed to high glucose exhibited decreased levels of inhibitory guanine nucleotide regulatory protein (Gi) proteins. In the present studies, we investigated the implication of oxidative stress in the hyperglycemia/diabetes-induced decreased expression of the Gi protein and adenylyl cyclase signaling in VSMCs by using antioxidants. The levels of Gi proteins were significantly decreased in A10 VSMCs exposed to high glucose and in aortic VSMCs from STZ-diabetic rats compared with control cells and were restored to control levels by antioxidants. In addition, Mntetralis(benzoic acid porphyrin) and uric acid, scavengers of peroxynitrite, and N-nitro-L-arginine methyl ester, an inhibitor of nitric oxide synthase but not catalase, also restored the high glucose-induced decreased expression of Gi proteins to the control levels in A10 VSMCs. Furthermore, the enhanced production of superoxide anion (O2 ) and increased activity of NADPH oxidase in these cells were also restored to control levels by diphenyleneiodonium, an inhibitor of NADPH oxidase. In addition, the diminished inhibition of adenylyl cyclase activity by inhibitory hormones and forskolin-stimulated adenylyl cyclase activity by low concentrations of GTP S as well as the enhanced stimulation of adenylyl cyclase by stimulatory agonists in hyperglycemic cells were restored to control levels by antioxidant treatments. These results suggest that high glucose-induced decreased levels of Gi proteins and associated signaling in A10 VSMCs may be attributed to the enhanced oxidative stress due to augmented levels of peroxynitrite and not to H2O2.