Astaxanthin-Loaded Silver Nanoparticles Mitigate 6-OHDA-Induced Parkinson's via ER Stress and PI3K/Akt/mTOR Signaling

Parkinson's disease (PD) is characterized by progressive dopaminergic neuronal loss, with oxidative stress and neuroinflammation as critical pathological mechanisms. The blood-brain barrier presents a significant challenge for therapeutic delivery, while current treatments provide only symptomatic relief without halting disease progression. This study investigated the neuroprotective effects of astaxanthin-loaded citrate-coated silver nanoparticles (AST-AgNPs), leveraging their potent antioxidant properties, anti-inflammatory capacity, and enhanced blood-brain barrier penetration. In vitro cytotoxicity analyses were performed using 6-hydroxydopamine (6-OHDA)-induced SH-SY5Y neuroblastoma cells, while in vivo experiments utilized a unilateral 6-OHDA-induced rat model. Following 14 days of treatment, comprehensive evaluations included behavioral assessments, biochemical analyses (MDA, GSH, SOD, TNF-α, IL-1β, IFN-γ), histopathology, immunohistochemistry (BrdU, tyrosine hydroxylase), and molecular analyses. Western blot measured CHOP, IRE1, ATF6, p-AKT, total AKT, caspase-3, and cleaved caspase-3, while RT-PCR quantified caspase-3, Bcl-2, Bax, PI3K, mTOR, Akt, CREB, and NF-κB-p65 expression. AST-AgNP treatment significantly ameliorated motor dysfunction, reduced neuroinflammation (TNF-α, IL-1β), improved oxidative stress parameters (MDA, GSH, SOD), and preserved dopaminergic neurons (all p < 0.05). Western blot revealed significant downregulation of ER stress markers (CHOP, IRE1, ATF6) and cleaved caspase-3, while restoring p-AKT and total AKT levels (p < 0.05). RT-PCR demonstrated decreased pro-apoptotic gene expression (caspase-3, NF-κB-p65) and increased anti-apoptotic Bcl-2 expression (p < 0.05). These findings demonstrate that AST-AgNPs provide neuroprotection through simultaneous modulation of ER stress and PI3K/Akt/mTOR pathways, representing a novel dual-pathway therapeutic strategy for PD addressing multiple pathological mechanisms through enhanced nanoparticle-mediated delivery.