25R-Inokosterone from Achyranthes bidentata Ameliorates Parkinson’s Disease Pathology Predominantly via Nrf2/HO-1 Activation with Coordinated MAOB/GSK-3β Expression Downregulation: An In Vitro and In Silico Study

Neurological disorders, particularly Parkinson’s disease (PD), represent a pressing global health challenge with limited disease-modifying therapies. While Achyranthes bidentata exhibits neuroprotective potential, its bioactive constituents against PD remain poorly characterized. This study integrated phytochemical isolation and in silico target prediction to identify eight compounds from A. bidentata, followed by neuroprotective evaluation in 1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-challenged SH-SY5Y cells. Among these, 25R-inokosterone significantly downregulated Monoamine oxidase B (MAOB) and Glycogen synthase kinase-3β (GSK-3β) expression and showed superior neuroprotection compared to β-ecdysterone. It markedly restored mitochondrial membrane potential, suppressed Bcl-2-associated X protein (Bax)/ Cysteinyl aspartate specific proteinase 3 (caspase-3) apoptotic signaling, and alleviated oxidative stress. Mechanistically, Nuclear factor erythroid 2-related factor 2 (Nrf2)/ Heme oxygenase 1 (HO-1) activation was the dominant and indispensable mechanism for neuroprotection, while MAOB/GSK-3β expression downregulation served as an upstream synergistic regulatory event, as evidenced by the abolition of neuroprotection following Nrf2 knockdown in SH-SY5Y cells. These findings identify 25R-inokosterone as a promising multi-target natural lead for PD, which exerts antioxidant and anti-apoptotic effects predominantly by activating Nrf2, accompanied by the upstream modulation of MAOB/GSK-3β expression.