Protective Effect Of Urantide On Myocardial Ischemia Or Reperfusion Injury And Its Mechanism

UrotensinⅡ(U-Ⅱ)is an 11 amino acid cyclic peptide which was first isolated from the fish spinal cord, and recently cloned in several mammalian species, including humans. Ames (1999) found the specific human receptor of urotensinⅡ, now referred to as UT receptor. Many studies have shown that U-Ⅱmay play an important role in cardiovascular regulation. As we know now, U-Ⅱis the most potent vasoconstrictor and is even more potent than endothelin-1 (ET-1). Growing evidence suggests that the U-Ⅱ/UT system may be a novel therapeutic target for cardiovascular disease.Urantide is derived from hU-Ⅱ, whose structure is [Pen5, DTrp7, Orn8]hU-Ⅱ(4–11). The present results of many studies show that urantide is actually the most potent UT receptor antagonist at rat UT receptors, being 50- to 100-fold more potent than any other compound described thus far. At the same time, urantide is a high selective and competitive antagonist in the rat isolated aorta bioassay: one of the most reliable and responsive bioassays for studying hU-Ⅱ-mediated effects. It is worth noting that urantide also shows a comparable high affinity for human UT receptors . As a potent vasoconstrictor, U-Ⅱcould also constrict coronary artery, therefore decreased myocardial blood flow. We presumed that urantide, as a UT receptor antagonist, probably could antagonize this effect, thus play a protective role on myocardial ischemia. So we designed the following experiments.Part I The protective effects of urantide on experimental myocardial ischemia model1,Protective effect of urantide on acute myocardial ischemia injury induced by isoproterenol in miceAcute myocardial ischemia episodes and typical ischemia ECG developed after subcutaneous injection (sc) of Iso. The results revealed that urantide in the range of 3～30μg·kg-1 iv markedly inhibited Iso-induced raise of the ST segment of ECG;10 and 30μg·kg-1 significantly reduced the increases of MDA content and LDH activity in myocardial supertant and blood serum,remarkably raised the activity of NOS and the content of NO.Urantide (10 and 30μg·kg-1) also significantly ameliorated myocardial ischemic injury.2,Protective effect of urantide on myocardial ischemia induced by pituitrin in miceTo explore the protective effects of urantide on experimental acute myocardial ischemia induced by pituitrin (Pit) in mice, 6 IU·kg-1 Pit was given through intraveneous injection. Results demonstrated the administration of urantide 3～30μg·kg-1 markedly inhibited Pit-induced raise of the ST and T segment of ECG;30μg·kg-1 significantly reduced the increases of MDA content and LDH activity in myocardial mitochondria and blood serum,remarkably raised the activity of SOD. 10μg·kg-1 urantide could also reduced the increases of MDA content. At the same time, urantide (10 and 30μg·kg-1) significantly ameliorated myocardial ischemic injury.3,The effects and mechanism of urantide on myocardial infarction induced by ligating left anterior descending coronary artery in ratsAfter ligating left anterior descending coronary artery in rats, MDA content and LDH activity in blood serum increased significantly, while NO content and NOS activity decreased sharply. Urantide (10, 30μg/kg) markedly inhibited the elevation of MDA content and LDH activity, and inhibited the decline of NO content and NOS activity, at the same time decreased I/R-induced IS/AAR. With the intravenous administration of urantide, the morphological injury induced by I/R was highly improved. Except for this, urantide (10, 30μg/kg) up-regulated the expression of p-ERK and eNOS protein, but down-regulated the I/R induced expression of iNOS and p-JNK.Part II The protective effects and mechanism of urantide on cultured neonatal rat cardiomyocytes with anoxia and reoxygenation cultured neonatal rat cardiomyocytes, an anoxia/reoxygenation (A/R) model was established. Cellular injury was evaluated by measuring cell viability, the release of CK,LDH and MDA. The results showed that on the A/R model of myocardial cells, 10-6～10-9 mol·L-1 urantide could evidently inhibit the increases of cTnI content and CK activity, reduce the rise of intracellular Ca2+ concentration.10-6～10-7mol·L-1 urantide increased the viability of myocardial cells injured by A/R and cut down LDH activity and MDA content in the cell culture medium.The examination of flow cytometer method and Hochest 33258 staining also showed that urantide in range of 10-6～10-9 mol·L-1 had significant inhibitory effect on A/R-induced cardiomyocytes apoptosis.Conclusions: Our findings indicate that urantide has a protective effect against myocardial ischemia or I/R injury in rats and mouse. The protective mechanism may related with anti-oxidation, inhibiting the cardiomyocytes apoptosis, lowing the cardiomyocytes calcium overload and augmenting the synthesis of NO.