Neuroprotective effects of chitosan nanoparticle-loaded orientin in a 6-OHDA-induced Parkinson's disease experimental model in rats

Purpose: The present study investigated the neuroprotective effects of orientin, a natural flavonoid with antioxidant and anti-inflammatory properties, loaded into chitosan nanoparticles (CNPs-Orientin) in a unilateral 6-hydroxydopamine (6-OHDA)-induced rat model of Parkinson's disease. The study further evaluated behavioral performance, histopathological alterations, tyrosine hydroxylase (TH) immunoreactivity, oxidative stress, inflammatory cytokines, and apoptosis- and survival-related signaling proteins. Materials and methods: Seventy-two male Sprague-Dawley rats (220–260 g) were randomly assigned into nine experimental groups (n = 8/group): Control, Orientin, CNPs, CNPs-Orientin, 6-OHDA, 6-OHDA + L-DOPA, 6-OHDA + Orientin, 6-OHDA + CNPs, and 6-OHDA + CNPs-Orientin. Parkinsonism was induced by unilateral stereotaxic injection of 6-OHDA into the substantia nigra pars compacta. Drug treatments were initiated after lesion induction and continued for 14 consecutive days. Behavioral, histopathological, immunohistochemical, biochemical, and Western blot analyses were subsequently performed. Results: 6-OHDA administration caused marked motor impairment, neuronal degeneration, reduced TH immunoreactivity, increased α-synuclein and Beclin-1 immunoreactivity, increased oxidative stress, elevated inflammatory cytokines, increased apoptosis-related protein expression, and suppression of antioxidant defense mechanisms. Treatment with CNPs-Orientin significantly improved behavioral performance, preserved TH-positive neurons, reduced α-synuclein-positive cell density and Beclin-1-positive DAB area, reduced neuronal degeneration, decreased MDA, TNF-α, IL-1β, IFN-γ, NF-κB, and Caspase-3 levels, while restoring SOD, GSH, Bcl-2, PI3K, Akt, and mTOR protein expression. Overall, CNPs-Orientin produced greater neuroprotective effects than free orientin alone. Conclusion: Chitosan nanoparticle-mediated delivery substantially enhanced the neuroprotective efficacy of the natural flavonoid orientin against 6-OHDA-induced dopaminergic neurodegeneration. The observed protective effects were associated with reduced oxidative stress, inflammation, apoptosis, and changes in PI3K/Akt/mTOR-related protein expression.