Apocynin restores endothelial dysfunction in streptozotocin diabetic rats through regulation of nitric oxide synthase and NADPH oxidase expressions.
OBJECTIVE
Increased production of reactive oxygen species (ROS) in the diabetic vasculature results in the impairment of nitric oxide (NO)-mediated relaxations leading to impaired endothelium-dependent vasodilation. An important source of ROS is nicotinamide adenine dinucleotide phosphate (NADPH) oxidase, and the inhibition of this enzyme is an active area of interest. This study aimed to investigate the effects of apocynin, an NADPH oxidase inhibitor, on endothelial dysfunction and on the expression of NO synthase (NOS) and NADPH oxidase in thoracic aorta of diabetic rats.


METHODS
Streptozotocin (STZ)-diabetic rats received apocynin (16 mg/kg per day) for 4 weeks. Endothelium-dependent and -independent relaxations were determined in thoracic aortic rings. Western blotting and RT-PCR analysis were performed for NOSs and NADPH oxidase in the aortic tissue.


RESULTS
Acetylcholine-induced relaxations and l-NAME-induced contractions were decreased in diabetic aorta. The decrease in acetylcholine and l-NAME responses were prevented by apocynin treatment without a significant change in plasma glucose levels. Endothelial NOS (eNOS) protein and mRNA expression exhibited significant decrease in diabetes, while protein and/or mRNA expressions of inducible NOS (iNOS) as well as p22(phox) and gp91(phox) subunits of NADPH oxidase were increased, and these alterations were markedly prevented by apocynin treatment.


CONCLUSIONS
NADPH oxidase expression is increased in diabetic rat aorta. NADPH oxidase-mediated oxidative stress is accompanied by the decreased eNOS and increased iNOS expressions, contributing to endothelial dysfunction. Apocynin effectively prevents the increased NADPH oxidase expression in diabetic aorta and restores the alterations in NOS expression, blocking the vicious cycle leading to diabetes-associated endothelial dysfunction.
Olukman
Murat
M
Department of Pharmacology and Clinical Pharmacology, Faculty of Medicine, Ege University, Bornova, İzmir, Turkey.
Orhan
Cahide Elif
CE
Celenk
Fatma Gül
FG
Ulker
Sibel
S
D000098:Acetophenones / Q000008:administration & dosage*; D000109:Acetylcholine / Q000494:pharmacology; D000818:Animals; D001013:Aorta, Thoracic / Q000187:drug effects / Q000201:enzymology / Q000503:physiopathology; D003921:Diabetes Mellitus, Experimental / Q000201:enzymology / Q000503:physiopathology*; D004730:Endothelium, Vascular / Q000187:drug effects / Q000503:physiopathology*; D004791:Enzyme Inhibitors / Q000008:administration & dosage*; D015971:Gene Expression Regulation, Enzymologic / Q000187:drug effects; D008297:Male; D019255:NADPH Oxidases / Q000037:antagonists & inhibitors / Q000235:genetics*; D019331:NG-Nitroarginine Methyl Ester / Q000494:pharmacology; D019001:Nitric Oxide Synthase / Q000235:genetics*; D012333:RNA, Messenger / Q000032:analysis; D051381:Rats; D017208:Rats, Wistar; D020133:Reverse Transcriptase Polymerase Chain Reaction; D014664:Vasodilation / Q000187:drug effects
D000098:Acetophenones; D004791:Enzyme Inhibitors; D012333:RNA, Messenger; C056165:acetovanillone; D019001:Nitric Oxide Synthase; D019255:NADPH Oxidases; D000109:Acetylcholine; D019331:NG-Nitroarginine Methyl Ester