Roles of endothelial nitric oxide synthase (eNOS) and mitochondrial permeability transition pore (MPTP) in epoxyeicosatrienoic acid (EET)-induced cardioprotection against infarction in intact rat hearts

Abstract

We previously demonstrated that 11,12 and 14,15-epoxeicosatrienoic acids (EETs) produce cardioprotection against ischemia-reperfusion injury in dogs and rats. Several signaling mechanisms have been implicated in the cardioprotective actions of the EETs; however, their mechanisms remain largely elusive. Since nitric oxide (NO) plays a significant role in cardioprotection and EETs have been demonstrated to induce NO production in various tissues, we hypothesized that NO is involved in mediating the EET actions in cardioprotection. To test this hypothesis, we used an in vivo rat model of infarction in which intact rat hearts were subjected to 30-min occlusion of the left coronary artery and 2-hr reperfusion. 11,12-EET or 14,15-EET (2.5 mg/kg) administered 10 min prior to the occlusion reduced infarct size, expressed as a percentage of the AAR (IS/AAR), from 63.9±0.8% (control) to 45.3±1.2% and 45.5±1.7%, respectively. A nonselective nitric oxide synthase (NOS) inhibitor, L-NAME (1.0 mg/kg) or a selective endothelial NOS inhibitor, L-NIO (0.30 mg/kg) alone did not affect IS/AAR but they completely abolished the cardioprotective effects of the EETs. On the other hand, a selective neuronal NOS inhibitor, nNOS I (0.03 mg/kg) and a selective inducible NOS inhibitor, 1400W (0.10 mg/kg) did not affect IS/AAR or block the cardioprotective effects of the EETs. Administration of 11,12-EET (2.5 mg/kg) to the rats also transiently increased the plasma NO concentration. 14,15-EET (10 μM) induced the phosphorylation of eNOS (Ser1177) as well as a transient increase of NO production in rat cardiomyoblast cell line (H9c2 cells). When 11,12-EET or 14,15-EET were administered at 5 min prior to reperfusion, infarct size was also reduced to 42.8±2.2% and 42.6±1.9%, respectively. Interestingly, L-NAME (1.0 mg/kg) and a mitochondrial KATP channel blocker, 5-HD (10 mg/kg) did not abolish while a sarcolemmal KATP channel blocker, HMR 1098 (6.0 mg/kg) and a mitochondrial permeability transition pore (MPTP) opener, atractyloside (5.0 mg/kg) completely abolished the cardioprotection produced by the EETs. 14,15-EET (1.5 mg/kg) with an inhibitor of MPTP opening, cyclosporin A (CsA, 1.0 mg/kg) produced a greater reduction of infarct size than their individual administration. Conversely, an EET antagonist 14,15-epoxyeicosa-5(Z)-enoic acid (14,15-EEZE, 2.5 mg/kg) completely abolished the cardioprotective effects of CsA, suggesting a role of MPTP in mediating the EET actions. Taken together, these results suggest that the cardioprotective effects of the EETs in an acute ischemia-reperfusion model are mediated by distinct mediators depending on the time of EET administration. The cardioprotective effects of EETs administered prior to ischemia were regulated by the activation of eNOS and increased NO production, while sarc KATP channels and MPTP were involved in the beneficial effects of the EETs when administered just prior to reperfusion.

Remote Limb Ischaemic Postconditioning Protects Against Myocardial Ischaemia/Reperfusion Injury in Mice: Activation of JAK/STAT3-Mediated Nrf2-Antioxidant Signalling

“…Although the downstream protective targets activated by STAT3 have not been systematically investigated, some research has reported that phosphorylation of STAT3 can activate downstream protective substrates, including Akt, eNOS, and GSK3β [18, 40]. STAT3, Akt and eNOS have been shown to inhibit opening of the mPTP during reperfusion [41-43], which can maintain mitochondrial membrane integrity and inhibit the activation of the mitochondrial apoptosis pathway. In our study, we indeed observed that RIPostC increased Akt and eNOS Ser1177 phosphorylation and that pretreatment with the JAK/STAT3 inhibitor AG490 attenuated the phosphorylation of STAT3 as well as the phosphorylation of Akt and eNOS.…”

The Pharmacology of the Cytochrome P450 Epoxygenase/Soluble Epoxide Hydrolase Axis in the Vasculature and Cardiovascular Disease

“…On the whole, EET-induced activation of K ATP channels seems to be cardioprotective and EETs can regulate cardiac electrophysiology and prevent the increase in intracellular Ca 2+ that is generally associated with ischemia-reperfusion injury (Batchu et al, 2012a). More recently, the cardioprotective effect of EETs administered prior to ischemia was attributed to the activation of the eNOS and increased NO production, whereas K ATP channel activation and the mitochondrial permeability transition pore were involved in the beneficial effects of the EETs when administered just prior to reperfusion (Gross et al, 2013). The actions of EETs in other organs, such as insulin secretion in pancreatic islets, may also be linked to K ATP channel activation (Sharoyko et al, 2007).…”

Ophiopogonin D Reduces Myocardial Ischemia-Reperfusion Injury via Upregulating CYP2J3/EETs in Rats

“…For a more detailed mechanistic analysis, further studies using cell experiments in vitro are needed. The notion that EETs activate eNOS via phosphorylation is supported by previous studies in a number of biological systems [5,35,36]. MI/R injury is reduced in mice overexpressing eNOS, suggesting cardioprotection by eNOS [37][38][39].…”