Sildenafil protects neuronal cells from mitochondrial toxicity induced by β-amyloid peptide via ATP-sensitive K+ channels

To understand the molecular mechanisms underlying the beneficial effects of sildenafil in animal models of neurological disorders, we investigated the effects of sildenafil on the mitochondrial toxicity induced by β-amyloid (Aβ) peptide. Treatment of HT-22 hippocampal neuronal cells with Aβ25∼35 results in increased mitochondrial Ca2+ load, which is subsequently suppressed by sildenafil as well as by diazoxide, a selective opener of the ATP-sensitive K+ channels (KATP). However, the suppressive effects of sildenafil and diazoxide are significantly attenuated by 5-hydroxydecanoic acid (5-HD), a KATP inhibitor. The increased mitochondrial Ca2+ overload is accompanied by decrease in the intracellular ATP concentration, increase in intracellular ROS generation, occurrence of mitochondrial permeability transition, and activation of caspase-9 and cell death. Exposure to sildenafil inhibited the mitochondria-associated changes and cell death induced by Aβ. However, the inhibitory effects of sildenafil are abolished or weakened in the presence of 5-HD, suggesting that opening of the mitochondrial KATP is required for sildenafil to exert these effects. Taken together, these results indicate that at the mitochondrial levels, sildenafil plays a protective role towards neuronal cell in an environment rich in Aβ, and exerts its effects via the mitochondrial KATP channels-dependent mechanisms.