Epoxyeicosatrienoic acids in cardioprotection: ischemic versus reperfusion injury.

Cytochrome P-450 (CYP) epoxygenases and their arachidonic acid (AA) metabolites, the epoxyeicosatrienoic acids (EETs), have been shown to produce increases in postischemic function via ATP-sensitive potassium channels (K(ATP)); however, the direct effects of EETs on infarct size (IS) have not been investigated. We demonstrate that two major regioisomers of CYP epoxygenases, 11,12-EET and 14,15-EET, significantly reduced IS in dogs compared to control (22.1 +/- 1.8%), whether administered 15 min before 60 min of coronary occlusion (6.4 +/- 1.9%, 11,12-EET; and 8.4 +/- 2.4%, 14.15-EET) or 5 min before 3 h of reperfusion (8.8 +/- 2.1%, 11,12-EET; and 9.7 +/- 1.4%, 14,15-EET). Pretreatment with the epoxide hydrolase metabolite of 14,15-EET, 14,15-dihydroxyeicosatrienoic acid, had no effect. The protective effect of 11,12-EET was abolished (24.3 +/- 4.6%) by the K(ATP) channel antagonist glibenclamide. Furthermore, one 5-min period of ischemic preconditioning (IPC) reduced IS to a similar extent (8.7 +/- 2.8%) to that observed with the EETs. The selective CYP epoxygenase inhibitor, N-methylsulfonyl-6-(2-propargyloxyphenyl)hexanamide (MS-PPOH), did not block the effect of IPC. However, administration of MS-PPOH concomitantly with N-methylsulfonyl-12,12-dibromododec-11-enanide (DDMS), a selective inhibitor of endogenous CYP omega-hydroxylases, abolished the reduction in myocardial IS expressed as a percentage of area at risk (IS/AAR) produced by DDMS (4.6 +/- 1.2%, DDMS; and 22.2 +/- 3.4%, MS-PPOH + DDMS). These data suggest that 11,12-EET and 14,15-EET produce reductions in IS/AAR primarily at reperfusion. Conversely, inhibition of CYP epoxygenases and endogenous EET formation by MS-PPOH, in the presence of the CYP omega-hydroxylase inhibitor DDMS blocked cardioprotection, which suggests that endogenous EETs are important for the beneficial effects observed when CYP omega-hydroxylases are inhibited. Finally, the protective effects of EETs are mediated by cardiac K(ATP) channels.

Effects of selective inhibition of cytochrome P-450 omega-hydroxylases and ischemic preconditioning in myocardial protection.

Cytochrome P-450 (CYP) omega-hydroxylases and their arachidonic acid (AA) metabolite, 20-hydroxyeicosatetraenoic acid (20-HETE), produce a detrimental effect on ischemia-reperfusion injury in canine hearts, and the inhibition of CYP omega-hydroxylases markedly reduces myocardial infarct size expressed as a percentage of the area at risk (IS/AAR, %). In this study, we demonstrated that a specific CYP omega-hydroxylase inhibitor, N-methylsulfonyl-12,12-dibromododec-11-enamide (DDMS), markedly reduced 20-HETE production during ischemia-reperfusion and reduced myocardial infarct size compared with control [19.5 +/- 1.0% (control), 9.6 +/- 1.5% (0.40 mg/kg DDMS), 4.0 +/- 2.0% (0.81 mg/kg DDMS), P < 0.01]. In addition, 20-hydroxyeicosa-6(Z),15(Z)-dienoic acid (20-HEDE, a putative 20-HETE antagonist) significantly reduced myocardial infarct size from control [10.3 +/- 1.3% (0.032 mg/kg 20-HEDE) and 5.9 +/- 1.9% (0.064 mg/kg 20-HEDE), P < 0.05]. We further demonstrated that one 5-min period of ischemic preconditioning (IPC) reduced infarct size to a similar extent as that observed with the high doses of DDMS and 20-HEDE, and the higher dose of DDMS given simultaneously with IPC augmented the infarct size reduction [9.9 +/- 2.8% (IPC) to 2.5 +/- 1.4% (0.81 mg/kg DDMS), P < 0.05] to a greater degree than that observed with either treatment alone. These results suggest an important negative role for endogenous CYP omega-hydroxylases and their product, 20-HETE, to exacerbate myocardial injury in canine myocardium. Furthermore, for the first time, this study demonstrates that the effect of IPC and the inhibition of CYP omega-hydroxylase synthesis (DDMS) or its actions (20-HEDE) may have additive effects in protecting the canine heart from ischemia-reperfusion injury.

Inhibition of cytochrome P450omega-hydroxylase: a novel endogenous cardioprotective pathway.

Cytochrome P450s (CYP) and their arachidonic acid (AA) metabolites have important roles in regulating vascular tone, but their function and specific pathways involved in modulating myocardial ischemia-reperfusion injury have not been clearly established. Thus, we characterized the effects of several selective CYPomega-hydroxylase inhibitors and a CYPomega-hydroxylase metabolite of AA, 20-hydroxyeicosatetraenoic acid (20-HETE), on the extent of ischemia-reperfusion injury in canine hearts. During 60 minutes of ischemia and particularly after 3 hours of reperfusion, 20-HETE was produced at high concentrations. A nonspecific CYP inhibitor, miconazole, and 2 specific CYPomega-hydroxylase inhibitors, 17-octadecanoic acid (17-ODYA) and N-methylsulfonyl-12,12-dibromododec-11-enamide (DDMS), markedly inhibited 20-HETE production during ischemia-reperfusion and produced a profound reduction in myocardial infarct size (expressed as a percent of the area at risk) (19.6+/-1.7% [control], 8.4+/-2.5% [0.96 mg/kg miconazole], 5.9+/-2.2% [0.28 mg/kg 17-ODYA], and 10.8+/-1.8% [0.40 mg/kg DDMS], P<0.05, respectively). Conversely, exogenous 20-HETE administration significantly increased infarct size (26.9+/-1.9%, P<0.05). Several CYPomega-hydroxylase isoforms, which are known to produce 20-HETE such as CYP4A1, CYP4A2, and CYP4F, were demonstrated to be present in canine heart tissue and their activity was markedly inhibited by incubation with 17-ODYA. These results indicate an important endogenous role for CYPomega-hydroxylases and in particular their product, 20-HETE, in exacerbating myocardial injury in canine myocardium. The full text of this article is available online at http://circres.ahajournals.org.