Roles of Superoxide, Peroxynitrite, and Protein Kinase C in the Development of Tolerance to Nitroglycerin

• Published in: The Journal of pharmacology and experimental therapeutics 2004-01, Vol.308 (1), p.289-299
• Main Authors: Abou-Mohamed, G., Johnson, J.A., Jin, L., El-Remessy, A.B., Do, K., Kaesemeyer, W.H., Caldwell, R.B., Caldwell, R.W.
• Format: Article
• Language: English
• Subjects: Animals; Cattle; Cells, Cultured; Cyclic GMP - metabolism; Drug Tolerance; Enzyme Activation; Nitroglycerin - adverse effects; Peroxynitrous Acid - metabolism; Protein Kinase C - metabolism; Rats; Rats, Sprague-Dawley; Superoxides - metabolism
• ISSN: 0022-3565; 1521-0103
• DOI: 10.1124/jpet.103.056119

A current hypothesis states that tolerance to nitroglycerin (GTN) involves increased formation of superoxide (▪). Studies showing that inhibitors of protein kinase C (PKC) prevent tolerance to GTN suggest the involvement of PKC activation, which can also increase ▪. We examined the roles of ▪, peroxynitrite (ONOO-), and PKC activation in GTN tolerance. Pre-exposure of rat aortic rings to GTN (5 × 10-4 M) for 2 h caused tolerance to the vasodilating effect of GTN, as evidenced by a substantial rightward shift of GTN concentration-relaxation curves. This shift was reduced by treatment of the rings with the antioxidants uric acid, vitamin C, or tempol or the PKC inhibitor chelerythrine. We also found that ▪ generation via xanthine/xanthine oxidase in the bath induced tolerance to GTN. However, responses to nitroprusside were not affected. In vivo tolerance produced in rats by 3-day i.v. infusion of GTN was also almost completely prevented by coinfusion of tempol. In bovine aortic endothelial cells (EC), addition of GTN produced a marked increase in tyrosine nitrosylation, indicating increased ONOO- formation. This action was blocked by prior treatment with uric acid, superoxide dismutase, NG-nitro-l-arginine methyl ester, or chelerythrine. We also demonstrated that GTN translocates the α- and ϵPKC isoforms in EC. However, PKCζ was not affected by GTN treatment. In conclusion, tolerance to GTN involves enhanced production of ▪ and ONOO- and activation of NO synthase. Furthermore, sustained activation of α- and ϵPKC isozymes in EC by GTN may play a role in development of tolerance.