Cerebral ischemia induces oxidative injury and increases the intracellular calcium ion concentration to activate several calcium-dependent proteases such as calpains. Calpain activation leads to various necrotic and apoptotic processes. Calpeptin is a potent, cell-permeable calpain inhibitor. As a strong antioxidant and free radical scavenger, melatonin shows beneficial effect in rodent models of focal cerebral ischemia when given prior to ischemia or reperfusion. This study was focused on the neuroprotective effects of melatonin and/or calpeptin given after onset of reperfusion. For this purpose, right-sided middle cerebral artery occlusion (MCAO) for 90 minutes followed by 24 or 72 hours of reperfusion was performed in male Sprague Dawley rats, then, melatonin 50 or 150 µg/kg, calpeptin 10, 15 or 50 µg/kg or a combination of melatonin 50 µg/kg plus calpeptin 15 or 50 µg/kg were injected via an intracerebroventricular route at 15 minutes after onset of reperfusion. Melatonin or calpeptin tended to reduce the relative infarct volume and significantly decreased the neurological deficit at 24 hours. The combination achieved a greater protection than each of them alone. Melatonin, calpeptin or the combination all decreased Fluoro-Jade B (FJB)+ degenerative neurons and cleaved/total caspase-3 ratio at 24 hours. These treatments did not significantly impact the density of surviving neurons and ED-1+ macrophage/activated microglia. At the 72-hour-reperfusion, melatonin or the combination decreased the relative infarct volume and neurological deficit. Nevertheless, only the combination reduced FJB+ degenerating neurons at 72 hours. In conclusion, a combination of melatonin and calpeptin exerted synergistic protection against post-reperfusion injury in a rat MCAO stroke model.
Reduction of infarct volume and mortality by thrombolysis in a rat embolic stroke model.