Eribis peptide 94 reduces infarct size in rat hearts via activation of centrally located µ opioid receptors.

Eribis peptide 94 (EP 94) is a novel enkephalin derivative that binds with high potency to µ and δ opioid receptors with less affinity for the κ opioid receptor. This compound has recently been shown to produce an acute reduction in myocardial infarct size in the anesthetized pig and rat partially via an endothelial nitric oxide synthase and KATP channel-dependent mechanism. EP 94 also was found to produce a chronic reduction in infarct size 24 hours postdrug administration via the upregulation of inducible nitric oxide synthase in rats. Despite these findings, no data have emerged in which the opioid receptor subtype responsible for cardioprotection has been identified and the site of action, heart, other peripheral organs, or the central nervous system, has not been addressed. In the current study, EP 94, was administered in 2 divided doses (0.5 µg/kg, intravenously) at 5 and 10 minutes into the ischemic period, and the opioid antagonists were administered 10 minutes before the onset of the 30-minute ischemic period. The selective antagonists used were the µ receptor antagonist CTOP (D-Phe-Cys-Tyr-D-Trp-Orn-Thr-Pen-Thr-NH2), the δ receptor antagonists naltrindole and BNTX (7-benzylidenenaltrexone), and the κ receptor antagonist nor-BNI (norbinaltorphimine). Surprisingly, only CTOP completely blocked the cardioprotective effect of EP 94, whereas naltrindole, BNTX, and nor-BNI had modest but nonsignificant effects. Because there is controversial evidence suggesting that µ receptors may be absent in the adult rat myocardium, it was hypothesized that the protective effect of EP 94 may be mediated by an action outside the heart, perhaps in the central nervous system. To test this hypothesis, rats were pretreated with the nonselective opioid antagonist, naloxone hydrochloride, which penetrates the blood-brain barrier or naloxone methiodide, the quaternary salt of naloxone hydrochloride, which does not penetrate the blood-brain barrier before EP 94 administration. In support of a central nervous system site of action for EP 94, naloxone hydrochloride completely blocked its cardioprotective effect, whereas naloxone methiodide had no effect. These results suggest that EP 94 reduces infarct size (expressed as a percent of the area at risk) in the rat primarily via activation of central µ opioid receptors.

Acute and chronic cardioprotection by the enkephalin analogue, Eribis peptide 94, is mediated via activation of nitric oxide synthase and adenosine triphosphate-regulated potassium channels.

BACKGROUND/AIMS: Eribis peptide 94 (EP 94) is a new enkephalin derivative which potently binds to the µ- and δ-opioid receptor. In this study, we determined the effects of EP 94 and potential mechanism(s) involved in cardioprotection of the rat heart. METHODS AND RESULTS: An acute (5 and10 min into ischemia) and a chronic (24 h prior to ischemia) EP 94 administration produced a similar 30-40% reduction in infarct size/area at risk and the effects were blocked by the K(ATP) channel antagonists, HMR 1098 and 5-HD. The cardioprotective effects were blocked by a nonselective nitric oxide synthase (NOS) inhibitor (L-NAME) following acute administration and by a selective iNOS inhibitor (1400W) following chronic administration. CONCLUSION: These results suggest that EP 94 may have potential for the treatment of ischemic heart disease via a nitric oxide (NO)-K(ATP)-mediated mechanism.

Dose-dependent cardioprotection of enkephalin analogue Eribis peptide 94 and cardiac expression of opioid receptors in a porcine model of ischaemia and reperfusion.

Opioids confer cardioprotection after myocardial ischaemia and reperfusion. The primary aim of the present study was to evaluate the cardioprotective effect of different doses of enkephalin analogue Eribis peptide 94 (EP 94) in a porcine model of ischaemia and reperfusion. A secondary aim was to analyse the impact of ischaemia and reperfusion on the expression of opioid receptor subtypes in the porcine heart. Thirty-four anesthetised pigs underwent 40 min of balloon occlusion of the left anterior descending coronary artery followed by four hours of reperfusion. Pigs were given either vehicle (0.9% NaCl) or one of four doses of EP 94 (0.2, 1, 5 or 25 ug/kg at each administration, respectively), intravenously after 26, 33 and 40 min of ischaemia. Hearts were stained to quantify area at risk and infarct size. mRNA and protein expressions of the opioid receptor subtypes were detected with RT-PCR, immunoblotting and immunohistochemistry in the control and ischaemic/reperfused areas. There was a significant dose-response relationship between higher doses of EP 94 and reduced infarct size. Expression of κ- and δ-opioid receptors was detected at both mRNA and protein levels. In ischaemic/reperfused areas, an increased expression of mRNA for both receptors was observed, whereas only protein expression for the δ subtype was up-regulated. The µ-opioid receptor was not detected.

Opioid receptor agonist Eribis peptide 94 reduces infarct size in different porcine models for myocardial ischaemia and reperfusion.

Eribis peptide 94 (EP 94) is a novel enkephalin analog, thought to interact with the µ- and δ-opioid receptors. The purpose of the present study was to examine the cardioprotective potential of EP 94 in two clinically relevant porcine models of myocardial ischaemia and reperfusion, and to investigate if such an effect is associated with an increased expression of endothelial nitric oxide synthase (eNOS). Forty-one anesthetized pigs underwent 40min of coronary occlusion followed by 4h of reperfusion. In Protocol I, balloon occlusion of the left anterior descending artery was performed with concurrent intravenous administration of (A) vehicle (n=7), (B) EP 94 (1ug/kg) after 5, 12, 19 and 26min of ischaemia (n=4) or (C) EP 94 (1ug/kg) after 26, 33, 40min of ischaemia (n=6). In Protocol II, open-chest pigs were administered (D) vehicle (n=6) or (E) 0.2ug/kg/min of EP 94 (n=6) through an intracoronary infusion into the jeopardized myocardium, started after 30min of ischaemia and maintained for 15min. The hearts were stained and the protein content of eNOS measured. EP 94 reduces infarct size when administered both early and late during ischaemia compared with vehicle (infarct size group A 61.6±2%, group B 50.2±3% and group C 49.2±2%, respectively, P<0.05), as well as when infused intracoronary (infarct size group D 82.2±3.9% and group E 61.2±2.5% respectively, P<0.01). Phosphorylated eNOS Ser(1177) in relation to total eNOS was significantly increased in the group administered EP 94, indicating activation of nitric oxide production.