Preconditioning protects endothelium by preventing ET-1-induced activation of NADPH oxidase and xanthine oxidase in post-ischemic heart.
The hypothesis was tested that endothelin-1 (ET-1)-induced superoxide (O(2)(-)) generation mediates post-ischemic coronary endothelial injury, that ischemic preconditioning (IPC) affords endothelial protection by preventing post-ischemic ET-1, and thus O(2)(-), generation, and that opening of the mitochondrial ATP-dependent potassium channel (mK(ATP)) triggers the mechanism of IPC. Furthermore, the study was aimed at identifying the source of O(2)(-) mediating the endothelial injury. Langendorff-perfused guinea-pig hearts were subjected either to 30 min ischemia/35 min reperfusion (IR) or were preconditioned prior to IR with three cycles of either 5 min ischemia/5 min reperfusion or 5 min infusion/5 min washout of mK(ATP) opener diazoxide (0.5 mM). Coronary flow responses to acetylcholine (ACh) served as a measure of endothelium-dependent vascular function. Myocardial outflow of ET-1 and O(2)(-) and functional recoveries were followed during reperfusion. NADPH oxidase and xanthine oxidase (XO) activities were measured in cardiac homogenates. IR augmented ET-1 and O(2)(-) outflow and impaired ACh response. All these effects were attenuated or prevented by IPC and diazoxide, and 5-hydroxydecanoate (a selective mK(ATP) blocker) abolished the effects of IPC and diazoxide. Superoxide dismutase and tezosentan (a mixed ET-1-receptor antagonist) mimicked the effects of IPC, although they had no effect on the ET-1 generation. IR augmented also the activity of NADPH oxidase and XO. Apocynin treatment, that resulted in NADPH oxidase inhibition, prevented XO activation and O(2)(-) generation in IR hearts. The inhibition of XO, either by allopurinol or feeding the animals with tungsten-enriched chow, prevented post-ischemic O(2)(-) generation, although these interventions had no effect on the NADPH activity. In addition, the post-ischemic activation of NADPH oxidase and XO, and O(2)(-) generation were prevented by IPC, tezosentan, thenoyltrifluoroacetone (mitochondrial complex II inhibitor), and tempol (cell-membrane permeable O(2)(-) scavenger). In guinea-pig heart: (i) ET-1-induced O(2)(-) generation mediates post-ischemic endothelial dysfunction; (ii) IPC and diazoxide afford endothelial protection by attenuating the ET-1, and thus O(2)(-) generation, and the mK(ATP) opening triggers the protection; (iii) the NADPH oxidase maintains the activity of XO, and the XO-derived O(2)(-) mediates the endothelial injury, and (iv) ET-1 and O(2)(-) (probably of mitochondrial origin) are upstream activators of the NADPH oxidase-XO cascade, and IPC prevents the cascade activation and the endothelial dysfunction by preventing the ET-1 generation.
Duda
Monika
M
Department of Clinical Physiology, Postgraduate Medical School, Marymoncka 99, 01-813 Warsaw, Poland.
Konior
Anna
A
Klemenska
Emilia
E
Beresewicz
Andrzej
A
D000818:Animals; D019332:Endothelin-1 / Q000037:antagonists & inhibitors / Q000378:metabolism*; D004730:Endothelium, Vascular / Q000201:enzymology / Q000293:injuries / Q000473:pathology; D004789:Enzyme Activation / Q000187:drug effects; D004791:Enzyme Inhibitors / Q000494:pharmacology; D006168:Guinea Pigs; D019157:Ischemic Preconditioning, Myocardial; D008929:Mitochondria, Heart / Q000201:enzymology / Q000473:pathology; D017202:Myocardial Ischemia / Q000201:enzymology* / Q000473:pathology; D009206:Myocardium / Q000201:enzymology* / Q000473:pathology; D019255:NADPH Oxidases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D013481:Superoxides / Q000378:metabolism; D014969:Xanthine Oxidase / Q000037:antagonists & inhibitors / Q000378:metabolism*
D019332:Endothelin-1; D004791:Enzyme Inhibitors; D013481:Superoxides; D014969:Xanthine Oxidase; D019255:NADPH Oxidases