Apocyanin, a microglial NADPH oxidase inhibitor prevents dopaminergic neuronal degeneration in lipopolysaccharide induced Parkinson's disease model

Abstract

Microglia-associated inflammatory processes have been strongly implicated in the development and progression of Parkinson’s disease (PD). Specifically, microglia are activated in response to lipopolysaccharide (LPS) and become chronic source of cytokines and reactive oxygen species (ROS) production. Nicotinamide adenine dinucleotide phosphate (NADPH) oxidase complex is responsible for extracellular as well as intracellular production of ROS by microglia and its expression is upregulated in PD. Therefore, targeting NADPH oxidase complex activation using an NADPH oxidase inhibitor, i.e., apocyanin seems to be an effective approach. The aim of present study was to investigate the neuroprotective effects of apocyanin in a LPS-induced PD model. LPS (5 μg) was injected intranigral and apocyanin was administered daily at a dose of 10 mg/kg b.wt (i.p.) during the experiment. LPS when injected into the substantia nigra (SN) reproduced the characteristic hallmark features of PD in rats. It elicited an inflammatory response characterized by glial cell activation (Iba-1, GFAP). Furthermore, LPS upregulated the gene expression of nuclear factor-κB (NFκB), iNOS, and gp91PHOX and resulted in an elevated total ROS production as well as NADPH oxidase activity. Subsequently, this resulted in dopaminergic loss as depicted by decreased tyrosine hydroxylase (TH) expression with substantial loss in neurotransmitter dopamine and its metabolites, whereas treatment with apocyanin significantly reduced the number of glial fibrillary acidic protein (GFAP) and Iba-1-positive cells in LPS-treated animals. It also mitigated microglial activation-induced inflammatory response and elevation in NADPH oxidase activity, thus reducing the extracellular as well as intracellular ROS production. The present study indicated that targeting NADPH oxidase can inhibit microglial activation and reduce a broad spectrum of toxic factors generation (i.e., cytokines, ROS, and reactive nitrogen species [RNS]), thus offering a hope in halting the progression of PD.