Inosine exerts dopaminergic neuroprotective effects via mitigation of NLRP3 inflammasome activation

Neuroinflammation plays a crucial role in the pathogenesis of Parkinson's disease (PD). Transformation of pro-interleukin (IL)-1β into a mature IL-1β via active inflammasome may be related to the progression of PD. Therefore, the modification of inflammasome activity may be a potential therapeutic strategy for PD. Inosine has been shown to exert anti-inflammatory effects in various disease models. In this study, we evaluated inosine's inhibitory effects on the microglial NLRP3 inflammasome, which may be related to the dopaminergic neuroprotective effects of inosine. Inosine suppresses lipopolysaccharides (LPS)-induced NLRP3 inflammasome activation in BV-2 microglial cells dose dependently. When SH-SY5Y cells were treated with conditioned medium from BV-2 cells treated with LPS and inosine, an NLRP3 inhibitor, or a caspase-1 inhibitor, the viability of SH-SY5Y cells was reduced indicating that LPS-induced microglial inflammasome activation could contribute to neuronal death. Inosine's modulatory effect on NLRP3 inflammasome activity appears to rely on the adenosine A_2A and A₃ receptors activation, as A_2A or A₃ receptor antagonists reversed the amelioration of NLRP3 activation by inosine. In addition, inosine treatment attenuated intracellular and mitochondrial ROS production mediated by LPS and this effect might be related to attenuation of NLRP3 inflammasome activity, as the antioxidant, N-acetyl cysteine ameliorated LPS-induced activation of the inflammasome. Finally, we assessed the inosine's neuroprotective effects via inflammasome activity modulation in mice receiving an intranigral injection of LPS. Immunohistochemical analysis revealed that LPS caused a significant loss of nigral dopaminergic neurons, which was mitigated by inosine treatment. LPS increased NLRP3 expression in IBA1-positive microglial cells, which was attenuated by inosine injection. These findings indicate that inosine can rescue neurons from LPS-induced injury by ameliorating NLRP3 inflammasome activity. Therefore, inosine could be applied as an intervention for neuroinflammatory diseases such as Parkinson's disease.