A novel neuroregenerative approach using ET(B) receptor agonist, IRL-1620, to treat CNS disorders.

Endothelin B (ET(B)) receptors present in abundance the central nervous system (CNS) have been shown to have significant implications in its development and neurogenesis. We have targeted ET(B) receptors stimulation using a highly specific agonist, IRL-1620, to treat CNS disorders. In a rat model of cerebral ischemia intravenous administration IRL-1620 significantly reduced infarct volume and improved neurological and motor functions compared to control. This improvement, in part, is due to an increase in neuroregeneration. We also investigated the role of IRL-1620 in animal models of Alzheimer's disease (AD). IRL-1620 improved learning and memory, reduced oxidative stress and increased VEGF and NGF in Abeta treated rats. IRL-1620 also improved learning and memory in an aged APP/PS1 transgenic mouse model of AD. These promising findings prompted us to initiate human studies. Successful chemistry, manufacturing and control along with mice, rat and dog toxicological studies led to completion of a human Phase I study in healthy volunteers. We found that a dose of 0.6 microg/kg of IRL-1620 can be safely administered, three times every four hours, without any adverse effect. A Phase II clinical study with IRL-1620 has been initiated in patients with cerebral ischemia and mild to moderate AD.

Alterations in endothelin receptors following hemorrhage and resuscitation by centhaquin.

Endothelin-1 (ET-1) acts on ET(A) and ET(B) receptors and has been implicated in hemorrhagic shock (shock). We determined effect of shock and resuscitation by hypertonic saline (saline) or centhaquin on ET(A) and ET(B) receptor expression. Rats were anesthetized, a pressure catheter was placed in the left femoral artery; blood was withdrawn from the right femoral artery to bring mean arterial pressure (MAP) to 35 mm Hg for 30 min, resuscitation was performed and 90 min later sacrificed to collect samples for biochemical estimations. Resuscitation with centhaquin decreased blood lactate and increased MAP. Protein levels of ET(A) or ET(B) receptor were unaltered in the brain, heart, lung and liver following shock or resuscitation. In the abdominal aorta, shock produced an increase (140 %) in ET(A) expression which was attenuated by saline and centhaquin; ET(B) expression was unaltered following shock but was increased (79 %) by centhaquin. In renal medulla, ET(A) expression was unaltered following shock, but was decreased (-61 %) by centhaquin; shock produced a decrease (-34 %) in ET(B) expression which was completely attenuated by centhaquin and not saline. Shock induced changes in ET(A) and ET(B) receptors in the aorta and renal medulla are reversed by centhaquin and may be contributing to its efficacy.

Synthesis and characterization of centhaquin and its citrate salt and a comparative evaluation of their cardiovascular actions.

Centhaquin is a compound that produces hypotension and bradycardia in higher doses and resuscitation in lower doses. It is water insoluble, and is unsuitable for intravenous use. We prepared the citrate salt of centhaquin and evaluated its cardiovascular efficacy vs. centhaquin. Centhaquin citrate was prepared and characterized; its purity was determined by HPLC. Mean arterial pressure (MAP), heart rate (HR), pulse pressure (PP), cardiac output (CO), stroke volume (SV) and stroke work (SW) following intravenous administration of centhaquin and the citrate (0.05, 0.15 and 0.45 mg.kg(-1)) were determined in anaesthetized male Sprague-Dawley rats. Centhaquin citrate was 99.8% pure and water soluble. Centhaquin (0.05, 0.15 and 0.45 mg.kg(-1)) produced a maximal decrease in MAP of 15.6, 25.2 and 28.1%, respectively; while centhaquin citrate produced a greater (p<0.001) decrease of 35.7, 47.1 and 54.3%, respectively. The decrease in PP and HR produced by the citrate was greater than centhaquin (p<0.001). At 0.45 mg.kg(-1) centhaquin produced a maximal decrease of 20.9% (p<0.01) in CO, while centhaquin citrate produced a decrease of 42.1% (p<0.001). Reduction in SV (p<0.01) and SW (p<0.001) produced by centhaquin citrate were greater than centhaquin. Centhaquin citrate has greater cardiovascular activity compared to centhaquin.

Repeated administration of centhaquin to pregnant rats did not affect postnatal development and expression of endothelin receptors in the brain, heart or kidney of pups.

The effect of repeated administration of centhaquin to pregnant rats on postnatal development, and expression of ETA and ETB receptors was determined. Pregnant rats were treated daily with either saline or centhaquin for 2 weeks. Male rat pups were sacrificed on day 1, 7, 14 and 28 of birth. Brain, kidney and heart were removed to study the expression of ETA and ETB receptor protein levels. Body weight of pregnant rats increased steadily in both vehicle and centhaquin groups. Expression of ETA receptors in the heart and kidney was similar in vehicle and centhaquin treated postpartum rats, but was significantly increased in the brain of centhaquin treated postpartum rats. No change in expression of ETB receptors was observed. In postnatal rats, mean body weight and weights of the brain, kidney and heart increased proportionally with advancing age and were similar in vehicle and centhaquin groups. The expression of ETA receptors in the brain, heart and kidneys was similar in vehicle and centhaquin groups. ETB receptor expression significantly (p<0.001) decreased by 72% and 70% on day 28 compared to rats of age 1, 7 and 14 days in control and centhaquin groups, respectively. Centhaquin treated rats showed similar expression of ETA and ETB receptors compared to vehicle treatment. This study suggests that repeated administration of centhaquin was well tolerated by pregnant rats that gave birth to normal pups. Centhaquin did not affect postnatal development of rats and had similar expression of ETA and ETB receptors compared to control pups.