title: Potent inhibition of aldehyde dehydrogenase-2 by diphenyleneiodonium: focus on nitroglycerin bioactivation.
abstract: Aldehyde dehydrogenase-2 (ALDH2) catalyzes vascular bioactivation of the antianginal drug nitroglycerin (GTN) to yield nitric oxide (NO) or a related species that activates soluble guanylate cyclase (sGC), resulting in cGMP-mediated vasodilation. Accordingly, established ALDH2 inhibitors attenuate GTN-induced vasorelaxation in vitro and in vivo. However, the ALDH2 hypothesis has not been reconciled with early studies demonstrating potent inhibition of the GTN response by diphenyleneiodonium (DPI), a widely used inhibitor of flavoproteins, in particular NADPH oxidases. We addressed this issue and investigated the effects of DPI on GTN-induced relaxation of rat aortic rings and the function of purified ALDH2. DPI (0.3 µM) inhibited the high affinity component of aortic relaxation to GTN without affecting the response to NO, indicating that the drug interfered with GTN bioactivation. Denitration and bioactivation of 1-2 µM GTN, assayed as 1,2-glycerol dinitrate formation and activation of purified sGC, respectively, were inhibited by DPI with a half-maximally active concentration of about 0.2 µM in a GTN-competitive manner. Molecular modeling indicated that DPI binds to the catalytic site of ALDH2, and this was confirmed by experiments showing substrate-competitive inhibition of the dehydrogenase and esterase activities of the enzyme. Our data identify ALDH2 as highly sensitive target of DPI and explain inhibition of GTN-induced relaxation by this drug observed previously. In addition, the data provide new evidence for the essential role of ALDH2 in GTN bioactivation and may have implications to other fields of ALDH2 research, such as hepatic ethanol metabolism and cardiac ischemia/reperfusion injury.
authors.affiliation: Department of Pharmacology and Toxicology, Karl-Franzens-Universität Graz, Austria.
authors.forename: Regina
authors.initials: R
authors.lastname: Neubauer
authors.forename: Andrea
authors.initials: A
authors.lastname: Neubauer
authors.forename: Gerald
authors.initials: G
authors.lastname: Wölkart
authors.forename: Christine
authors.initials: C
authors.lastname: Schwarzenegger
authors.forename: Barbara
authors.initials: B
authors.lastname: Lang
authors.forename: Kurt
authors.initials: K
authors.lastname: Schmidt
authors.forename: Michael
authors.initials: M
authors.lastname: Russwurm
authors.forename: Doris
authors.initials: D
authors.lastname: Koesling
authors.forename: Antonius C F
authors.initials: AC
authors.lastname: Gorren
authors.forename: Astrid
authors.initials: A
authors.lastname: Schrammel
authors.forename: Bernd
authors.initials: B
authors.lastname: Mayer
mesh_terms: D000444:Aldehyde Dehydrogenase / Q000037:antagonists & inhibitors* / Q000737:chemistry; D000071396:Aldehyde Dehydrogenase, Mitochondrial; D000818:Animals; D001013:Aorta, Thoracic / Q000187:drug effects / Q000502:physiology; D020134:Catalytic Domain; D042783:Endothelial Cells / Q000187:drug effects / Q000201:enzymology; D005260:Female; D006801:Humans; D066298:In Vitro Techniques; D008297:Male; D024101:Mitochondrial Proteins / Q000037:antagonists & inhibitors*; D062105:Molecular Docking Simulation; D009131:Muscle, Smooth, Vascular / Q000187:drug effects / Q000502:physiology; D005996:Nitroglycerin / Q000378:metabolism*; D009861:Onium Compounds / Q000494:pharmacology*; D011485:Protein Binding; D051381:Rats; D017207:Rats, Sprague-Dawley; D013552:Swine; D014664:Vasodilation / Q000187:drug effects; D014665:Vasodilator Agents / Q000378:metabolism*
chemical_list: D024101:Mitochondrial Proteins; D009861:Onium Compounds; D014665:Vasodilator Agents; C007517:diphenyleneiodonium; C096127:ALDH2 protein, human; D000444:Aldehyde Dehydrogenase; D000071396:Aldehyde Dehydrogenase, Mitochondrial; C505112:Aldh2 protein, rat; D005996:Nitroglycerin