The broad objective of this program is to explore the vasodilative potential of rhEPO and its non-erythropoietic derivatives and to perform preclinical animal experiments on different models of arterial hypertension to elucidate their mechanism of action and to evaluate their potential for translation into clinical practice in humans. I. Acute hemodynamic effects of EPO. Activation of nitric oxide (NO) signaling is considered, at least partially, as a mechanistic basis for EPO-induced cardioprotection. Surprisingly, hemodynamic response subsequent to NO activation after EPO administration had never been reported. Objectives of this study were to evaluate the acute hemodynamic and cardiovascular responses to EPO administration, to confirm their NO genesis, and to test the hypothesis that EPO-induced cardioprotection is mediated through cardiovascular changes related to NO activation. In Experiment 1 after 3000 U/kg of rhEPO was administered intravenously to Wistar rats, arterial blood pressure, monitored via indwelling catheter, progressively declined, starting almost immediately until leveling off 90 minutes after injection at 20% below control level. In Experiment 2 the 25% reduction of mean blood pressure, compared to control group, was observed 2 hrs after intravenous injection of either 3000 or 150 U/kg of rhEPO. Detailed pressure volume loop analyses of cardiac performance (Experiment 3) 2 hrs after intravenous injection of human or rat recombinant EPO (3000U/kg) revealed a significant reduction of systolic function (PRSW was 33% less than control). Reduction of arterial blood pressure and systolic cardiac function in response to rhEPO were blocked in rats pretreated with a non-selective inhibitor of nitric oxide synthase (L-NAME). In Experiment 4 24 hrs after a permanent ligation of a coronary artery myocardial infarction (MI) measured 263.5% of left ventricle in untreated rats. MI in rats treated with 3000 U/kg of rhEPO immediately after coronary ligation was 56% smaller. Pretreatment with L-NAME did not attenuate the beneficial effect of rhEPO on MI size, while MI size in rats treated with L-NAME alone did not differ from control. Therefore, a single injection of rhEPO resulted in a significant, NO-mediated reduction of systemic blood pressure and corresponding reduction of cardiac systolic function. However, EPO-induced protection of myocardium from ischemic damage is not associated with NO activation or NO-mediated hemodynamic responses. II. Antihypertensive properties of non-erythropoietic derivatives of EPO A small peptide, Helix B Surface Peptide (HBSP), also known as ARA290, was synthesized by Araim Parmaceutical on the basis of EPO molecule and does not activate EPO receptors. This peptide was tested in different experimental models and while it proved to possess strong tissue protective properties did not induce blood cell production. Recently we demonstrated that HBSP have similar potency to rhEPO for increasing the reactive oxygen species (ROS) threshold for induction of the mitochondrial permeability transition by 40% and thus protecting cardiac myocytes from ischemic stress. In the rat model of MI induced by a permanent ligation of coronary artery we also demonstrated the equal potency of single administration of EPO and HBSP for 50% reduction of resulting MI. In that experimental model the anti-apoptotic and anti-inflammatory potentials of HBSP were equal to those of rhEPO. In the first experiment we administered a single intravenous dose of 60 mcg of HBSP (ARA290) to a normotensive rat, while monitoring its arterial blood pressure via catheter inserted into the aorta. We observed that systolic and diastolic blood pressures started to fall reduced during the first several minutes following drug administration. The reduction of blood pressure was about 20% of baseline and lasted for about 2 hrs. The effect was similar to the effect of rhEPO that we previously reported. The Dahl salt sensitive rat is a well-known and widely used experimental animal model of salt sensitive hypertension. We placed two groups of salt sensitive rats on the high salt diet. One of the high salt groups was treated with HBSP via osmotic pump implanted into the abdominal cavity, while another high salt group remained untreated. Arterial blood pressure was measured weekly using tail cuff technique. Another group of Dahl rats remained on a normal, low salt diet and served as a control. The treatment continued for 9 weeks. The starting dose of HBSP was 1 mg/kg/day, but with animals'growth it gradually was reduced to 0.4 mg/kg. During 9 weeks arterial blood pressure of low-salt diet rats increased slightly with growth (systolic blood pressure increased by 12%). At the same time, arterial blood pressure in rats on the high salt diet, as expected in this model, increased dramatically, reaching 200 mmHg. The arterial blood pressure of animals on high salt diet treated with HBSP remained at the level of low salt animals, i.e., remained normal. The sonographic and histological comparison of the effects of high salt diet and treatment on cardiac and kidney remodeling and function are being conducted. Experiments assessing the effects on HBSP on different experimental animal models of hypertension (spontaneously hypertensive rats and renal mass reduction model) are being initiated.
| Ahmet, Ismayil; Lakatta, Edward G; Talan, Mark I (2012) Acute hemodynamic effects of erythropoietin do not mediate its cardioprotective properties. Biol Open 1:1049-53 |
