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Downregulation of NADPH oxidase, antioxidant enzymes, and inflammatory markers in the heart of streptozotocin-induced diabetic rats by N-acetyl-L-cysteine

¹Faculty of Pharmaceutical Sciences, Division of Pharmacology, University of British Columbia, Vancouver, British Columbia, Canada; and ²Department of Endocrinology, Second Hospital, Shanxi Medical University, Taiyuan, Shanxi, People's Republic of China

Submitted 16 December 2005 ; accepted in final form 20 November 2006

We investigated the effect of N-acetyl-L-cysteine (NAC) on the expression of nicotinamide adenine dinucleotide phosphate (NADPH) oxidase, antioxidant enzymes, and inflammatory markers in diabetic rat hearts. Metabolic parameters, free 15-F_2t-isoprostane level, protein expression of NADPH oxidase, superoxide dismutase (SOD), heme oxygenase (HO-1), interleukin-6 (IL-6), and cyclooxygenase-2 (COX-2) were analyzed in control and streptozotocin-induced diabetic rats treated with or without NAC in drinking water for 8 wk. The cardiac protein expression of p67^phox and p22^phox was increased in diabetic rats, accompanied by increased NADPH-dependent superoxide production. As a compensatory response to the increased NADPH oxidase, the protein expression of Cu-Zn-SOD and HO-1 and the total SOD activity were also increased in diabetic rat hearts. Consequently, cardiac free 15-F_2t-isoprostane, an index of oxidative stress, was increased in diabetic rats, indicating that the production of reactive oxygen species becomes excessive in diabetic rat hearts. Cardiac inflammatory markers IL-6 and COX-2 were also increased in diabetic rats. NAC treatment prevented the increased expression of p22^phox and translocation of p67^phox to the membrane in diabetic rat hearts. Subsequently, the levels of cardiac free 15-F_2t-isoprostane, HO-1, Cu-Zn-SOD, total SOD, IL-6, and COX-2 in diabetic rats were decreased by NAC. Consequently, cardiac hypertrophy was attenuated in diabetic rats treated with NAC. The protective effects of NAC on diabetic rat hearts may be attributable to its protection of hearts against oxidative damage induced by the increased NADPH oxidase and to its reduction in cardiac inflammatory mediators IL-6 and COX-2.

oxidative stress; streptozotocin-induced diabetes; nicotinamide adenine dinucleotide phosphate oxidase

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