Endothelin B receptor agonist, IRL-1620, enhances angiogenesis and neurogenesis following cerebral ischemia in rats

Endothelin B receptor agonist, IRL-1620, has been shown in previous studies, conducted in our lab, to provide significant neuroprotection at both 24h and 1 week following permanent cerebral ischemia. It is possible that IRL-1620 may be neuroprotective due to angiogenesis and neurogenesis. However, the effect of IRL-1620 on neurovascular remodeling following cerebral ischemia has not been established. The present study was conducted to determine the effect of IRL-1620 [Suc-[Glu9,Ala11,15]-Endothelin-1(8-12)] on astrocytes, neurons, and vascular endothelial cells after induction of cerebral ischemia. Male Sprague-Dawley rats undergoing permanent middle cerebral artery occlusion (MCAO) received three intravenous injections of either vehicle or IRL-1620 at 2, 4, and 6h post occlusion. At 24h post occlusion, IRL-1620 treatment preserved neuronal numbers in the cortex, striatum and subventricular zone (SVZ) of the ischemic rat brain, while simultaneously enhancing the number of blood vessels labeled with vascular endothelial growth factor (VEGF) compared to vehicle treatment. By 1 week following MCAO, VEGF-positive vessels/30 µm brain slice in the IRL-1620 group numbered 11.33±2.13 versus 4.19±0.79 in the vehicle group (P<0.01). Additionally, animals receiving IRL-1620 displayed increased number of proliferating cells (P<0.0001) and cells positively staining for nerve growth factor (NGF; P<0.0001) in the infarcted brain. VEGF and NGF protein expression significantly increased at 1 week post MCAO in the infarcted hemisphere of IRL-1620 treated rats as compared to sham (P<0.01). Pretreatment with BQ788 blocked the effects of IRL-1620, thus confirming the role of ETB receptors in the neurovascular remodeling actions of IRL-1620. Results of the present study indicate that IRL-1620, administered on the day of infarct, is neuroprotective and enhances angiogenic and neurogenic remodeling following cerebral ischemia.