A mechanism of paraquat toxicity involving nitric oxide synthase.
Paraquat (PQ) is a well described pneumotoxicant that produces toxicity by redox cycling with cellular diaphorases, thereby elevating intracellular levels of superoxide (O-(2)). NO synthase (NOS) has been shown to participate in PQ-induced lung injury. Current theory holds that NO reacts with O-(2) generated by PQ to produce the toxin peroxynitrite. We asked whether NOS might alternatively function as a PQ diaphorase and reexamined the question of whether NO/O-(2) reactions were toxic or protective. Here, we show that: (i) neuronal NOS has PQ diaphorase activity that inversely correlates with NO formation; (ii) PQ-induced endothelial cell toxicity is attenuated by inhibitors of NOS that prevent NADPH oxidation, but is not attenuated by those that do not; (iii) PQ inhibits endothelium-derived, but not NO-induced, relaxations of aortic rings; and (iv) PQ-induced cytotoxicity is potentiated in cytokine-activated macrophages in a manner that correlates with its ability to block NO formation. These data indicate that NOS is a PQ diaphorase and that toxicity of such redox-active compounds involves a loss of NO-related activity.
Day
B J
BJ
Department of Medicine, National Jewish Medical and Research Center, School of Pharmacy, University of Colorado Health Sciences Center, Denver, CO 80206, USA. DAYB@njc.org
Patel
M
M
Calavetta
L
L
Chang
L Y
LY
Stamler
J S
JS
D000818:Animals; D002460:Cell Line; D002470:Cell Survival / Q000187:drug effects; D004730:Endothelium, Vascular / Q000166:cytology / Q000187:drug effects / Q000502:physiology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D066298:In Vitro Techniques; D008264:Macrophages / Q000166:cytology / Q000187:drug effects; D008297:Male; D009247:NADH, NADPH Oxidoreductases / Q000378:metabolism; D009569:Nitric Oxide / Q000494:pharmacology; D019001:Nitric Oxide Synthase / Q000037:antagonists & inhibitors / Q000378:metabolism*; D052248:Nitric Oxide Synthase Type I; D010269:Paraquat / Q000633:toxicity*; D011817:Rabbits
D004791:Enzyme Inhibitors; D009569:Nitric Oxide; D019001:Nitric Oxide Synthase; D052248:Nitric Oxide Synthase Type I; D009247:NADH, NADPH Oxidoreductases; C085915:paraquat diaphorase; D010269:Paraquat