title: Dissociation between superoxide accumulation and nitroglycerin-induced tolerance.
abstract: We hypothesize that superoxide (O(2)(*-)) accumulation is not a crucial causative factor in inducing nitroglycerin (NTG) tolerance. In LLC-PK1 cells, pre-exposure to NTG resulted in increased O(2)(*-) accumulation and reduced cGMP response to NTG versus vehicle control. O(2)(*-) stimulated by NTG was reduced by oxypurinol (100 microM), a xanthine oxidase inhibitor. Exposure to angiotensin II (Ang II) increased O(2)(*-) but did not reduce cGMP response. The O(2)(*-) scavenger tiron reduced Ang II-induced O(2)(*-) production but did not increase NTG-stimulated cGMP production. Using p47(phox-/-) and gp91(phox-/-) mice versus their respective wild-type controls (WT), we showed that aorta from mice null of these critical NADPH oxidase subunits exhibited similar vascular tolerance after NTG dosing (20 mg/kg s.c., t.i.d. for 3 days), as indicated by their ex vivo pEC(50) and cGMP accumulation upon NTG challenge. In vitro aorta O(2)(*-) production was enhanced by NTG incubation in both p47(phox) null and WT mice. Pre-exposure of isolated mice aorta to 100 microM NTG for 1 h resulted in vascular tolerance toward NTG and increased O(2)(*-) accumulation. Oxypurinol (1 mM) reduced O(2)(*-) but did not attenuate vascular tolerance. These results suggest that O(2)(*-) does not initiate either in vitro and in vivo NTG tolerance, and that the p47(phox) and gp91(phox) subunits of NADPH oxidase are not critically required. Increased O(2)(*-) accumulation may be an effect, rather than an initiating cause, of NTG tolerance.
authors.affiliation: Department of Pharmaceutical Sciences, School of Pharmacy and Pharmaceutical Sciences, University at Buffalo, Buffalo, NY 14260-1200, USA.
authors.forename: Pei-Suen
authors.initials: PS
authors.lastname: Tsou
authors.forename: Vamsi
authors.initials: V
authors.lastname: Addanki
authors.forename: Ho-Leung
authors.initials: HL
authors.lastname: Fung
mesh_terms: D000804:Angiotensin II / Q000494:pharmacology; D000818:Animals; D001011:Aorta / Q000187:drug effects / Q000502:physiology; D006152:Cyclic GMP / Q000378:metabolism; D004361:Drug Tolerance; D018374:LLC-PK1 Cells; D008562:Membrane Glycoproteins / Q000502:physiology; D051379:Mice; D008810:Mice, Inbred C57BL; D000074662:NADPH Oxidase 2; D019255:NADPH Oxidases / Q000502:physiology; D005996:Nitroglycerin / Q000494:pharmacology*; D013481:Superoxides / Q000378:metabolism*; D014664:Vasodilation / Q000187:drug effects
chemical_list: D008562:Membrane Glycoproteins; D013481:Superoxides; D000804:Angiotensin II; C488842:Cybb protein, mouse; D000074662:NADPH Oxidase 2; D019255:NADPH Oxidases; C060505:neutrophil cytosolic factor 1; D005996:Nitroglycerin; D006152:Cyclic GMP