title: Insulin-induced generation of reactive oxygen species and uncoupling of nitric oxide synthase underlie the cerebrovascular insulin resistance in obese rats.
abstract: Hyperinsulinemia accompanying insulin resistance (IR) is an independent risk factor for stroke. The objective is to examine the cerebrovascular actions of insulin in Zucker obese (ZO) rats with IR and Zucker lean (ZL) control rats. Diameter measurements of cerebral arteries showed diminished insulin-induced vasodilation in ZO compared with ZL. Endothelial denudation revealed vasoconstriction to insulin that was greater in ZO compared with ZL. Nonspecific inhibition of nitric oxide synthase (NOS) paradoxically improved vasodilation in ZO. Scavenging of reactive oxygen species (ROS), supplementation of tetrahydrobiopterin (BH(4)) precursor, and inhibition of neuronal NOS or NADPH oxidase or cyclooxygenase (COX) improved insulin-induced vasodilation in ZO. Immunoblot experiments revealed that insulin-induced phosphorylation of Akt, endothelial NOS, and expression of GTP cyclohydrolase-I (GTP-CH) were diminished, but phosphorylation of PKC and ERK was enhanced in ZO arteries. Fluorescence studies showed increased ROS in ZO arteries in response to insulin that was sensitive to NOS inhibition and BH(4) supplementation. Thus, a vicious cycle of abnormal insulin-induced ROS generation instigating NOS uncoupling leading to further ROS production underlies the cerebrovascular IR in ZO rats. In addition, decreased bioavailability and impaired synthesis of BH(4) by GTP-CH induced by insulin promoted NOS uncoupling.
authors.affiliation: Department of Pharmacology, Tulane University School of Medicine, 1430 Tulane Avenue, New Orleans, LA 70112, USA. pkatakam@tulane.edu
authors.forename: Prasad V G
authors.initials: PV
authors.lastname: Katakam
authors.forename: James A
authors.initials: JA
authors.lastname: Snipes
authors.forename: Mesia M
authors.initials: MM
authors.lastname: Steed
authors.forename: David W
authors.initials: DW
authors.lastname: Busija
mesh_terms: D000818:Animals; D001708:Biopterins / Q000031:analogs & derivatives / Q000494:pharmacology; D002536:Cerebral Arteries / Q000378:metabolism / Q000503:physiopathology; D002560:Cerebrovascular Circulation / Q000187:drug effects*; D006136:GTP Cyclohydrolase; D015971:Gene Expression Regulation, Enzymologic / Q000187:drug effects; D007004:Hypoglycemic Agents / Q000378:metabolism / Q000494:pharmacology*; D007328:Insulin / Q000378:metabolism / Q000494:pharmacology*; D007333:Insulin Resistance; D019255:NADPH Oxidases / Q000378:metabolism; D009569:Nitric Oxide / Q000378:metabolism*; D052248:Nitric Oxide Synthase Type I / Q000037:antagonists & inhibitors / Q000378:metabolism*; D010766:Phosphorylation / Q000187:drug effects; D011451:Prostaglandin-Endoperoxide Synthases / Q000378:metabolism; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D011924:Rats, Zucker; D017382:Reactive Oxygen Species / Q000378:metabolism*; D014664:Vasodilation / Q000187:drug effects
chemical_list: D007004:Hypoglycemic Agents; D007328:Insulin; D017382:Reactive Oxygen Species; D001708:Biopterins; D009569:Nitric Oxide; D052248:Nitric Oxide Synthase Type I; C496322:Nos1 protein, rat; D011451:Prostaglandin-Endoperoxide Synthases; D019255:NADPH Oxidases; D051057:Proto-Oncogene Proteins c-akt; D006136:GTP Cyclohydrolase; C003402:sapropterin