The Tyrosine Phosphatase Inhibitor Bis(Maltolato)- Oxovanadium Attenuates Myocardial Reperfusion Injury by Opening ATP-Sensitive Potassium Channels David A. Liem, Coen C. Gho, Ben C. Gho, Shahla Kazim, Olivier C. Manintveld, Pieter D. Verdouw, and Dirk J. Duncker Experimental Cardiology, Thoraxcenter, Cardiovascular Research School (COEUR), Erasmus MC, University Medical Center Rotterdam, Rotterdam, The Netherlands (D.A.L., B.C.G., S.K., O.C.M., P.D.V., D.J.D.); and GHO Pharma, Maastricht, The Netherlands (C.C.G., S.K.) Received November 5, 2003; accepted February 25, 2004 ABSTRACT Vanadate has been shown to inhibit tyrosine phosphatase, leading to an increased tyrosine phosphorylation state. The latter has been demonstrated to be involved in the signal trans- duction pathway of ischemic preconditioning, the most potent endogenous mechanism to limit myocardial infarct size. Fur- thermore, there is evidence that phosphatase inhibition may be cardioprotective when given late after the onset of ischemia, but the mechanism of protection is unknown. We tested the hypothesis that the organic vanadate compound bis(maltolato)- oxovanadium (BMOV) limits myocardial infarct size by attenu- ating reperfusion injury and investigated the underlying mech- anism. Myocardial infarction was produced in 112 anesthetized rats by a 60-min coronary artery occlusion, and infarct size was determined histochemically after 180 min of reperfusion. Intra- venous infusion of BMOV in doses of 3.3, 7.5, and 15 mg/kg i.v. decreased infarct size dose-dependently from 70  2% of the area at risk in vehicle-treated rats down to 41  5% (P  0.05 versus control), when administered before occlusion. Adminis- tration of the low dose just before reperfusion was ineffective, but administration of the higher doses was equally cardiopro- tective as compared with administration before occlusion. The cardioprotection by BMOV was abolished by the tyrosine ki- nase inhibitor genistein and by the ATP-sensitive potassium (K + ATP ) channel blocker glibenclamide but was not affected by the ganglion blocker hexamethonium. We conclude that BMOV afforded significant cardioprotection principally by limiting reperfusion injury. The mode of action appears to be by open- ing of cardiac K + ATP channels via increased tyrosine phosphor- ylation. An increase in tyrosine residue phosphorylation via in- creased tyrosine kinase activity has been implicated in the signal transduction pathway of cardioprotection by ischemic preconditioning (Przyklenk and Kloner, 1998; Vahlhaus et al., 1998; Fryer et al., 1999), which is the most potent endog- enous mechanism to limit myocardial infarct size. There is evidence that increased tyrosine residue phosphorylation, produced by a shift in the balance between tyrosine kinase and tyrosine phosphatase, increases white blood cell survival by inhibiting apoptosis (Bergamaschi et al., 1993; LaVoie and Witorsch, 1995; Brown et al., 1996). Vanadate enhances ty- rosine residue phosphorylation by inhibition of tyrosine phos- phatase (Simons, 1979; Palmer et al., 1996), suggesting that vanadate may be of therapeutic benefit in myocardial infarc- tion, which may involve both apoptosis and necrosis (Kajs- tura et al., 1996; Weiss et al., 2003). In support of this concept, Armstrong et al. (1998) reported that serine threo- nine phosphatase inhibitors are highly effective in protecting isolated cardiomyocytes subjected to ischemia (without reperfusion), even when administered late (75 min) after onset of ischemia, suggesting that vanadate may not require administration before the onset of ischemia and might also act against reperfusion injury. However, to date, in vivo studies on the cardioprotective effects of tyrosine phospha- tase inhibitors are lacking. The mechanism by which tyrosine phosphatase inhibitors exert their cardioprotective effects is incompletely under- stood. However, since K + ATP channels have been reported to be downstream targets of tyrosine kinase in the signaling This study was supported by a grant from the Netherlands Heart Founda- tion (NHS99.143), a grant from GHO Pharma, and the Netherlands Heart Foundation (Established Investigator Stipend no. 2000T038 to D.J.D.). Article, publication date, and citation information can be found at http://jpet.aspetjournals.org. DOI: 10.1124/jpet.103.062547. ABBREVIATIONS: K + ATP , ATP-sensitive potassium; BMOV, bis(maltolato)-oxovanadium; CAO, coronary artery occlusion; PBS, phosphate- buffered saline; ANOVA, analysis of variance. 0022-3565/04/3093-1256 –1262$20.00 THE JOURNAL OF PHARMACOLOGY AND EXPERIMENTAL THERAPEUTICS Vol. 309, No. 3 Copyright © 2004 by The American Society for Pharmacology and Experimental Therapeutics 62547/1151728 JPET 309:1256–1262, 2004 Printed in U.S.A. 1256