Unlocking the neuroprotective potential of <i>Citrus japonica</i> peel oil: Gas chromatography-mass spectrometry analysis and anti-Parkinsonian activity in a paraquat rat model

Citrus japonica, commonly known as Kumquat, is an economically and pharmacologically important citrus fruit, indigenous to Asia-Pacific and South Asia. The current work seeks to investigate the neuroprotective potential of the essential oil extracted from C. japonica fruit’s peel in a paraquat (PQT)-induced dopaminergic neurodegeneration rat model, as well as the chemical profiling by using gas chromatography-mass spectrometry (GC/MS) analysis. The Parkinson’s disease (PD) rat model was prepared by administering PQT at 5-day intervals of 10 mg/kg i.p. for 3 weeks. Animals were divided into healthy (received normal saline), PD control, standard treated (L-dopa 100 mg/kg + carbidopa 25 mg/kg), and CJ 50 and 100 (received 50 μL and 100 μL C. japonica peel oil). Behavioral studies were performed before biochemical, neurochemical, histopathological, and gene expression analysis. The GC/MS analysis identified seven volatile chemical compounds, predominated by D-limonene (98.17%), followed by β-pinene (0.68%), α-terpineol (0.40%), germacrene D (0.36%), α-pinene (0.17%), terpinen-4-ol (0.15%) and γ-terpinene (0.07%). The behavioral study indicated that C. japonica peel oil treatment significantly improved the motor and cognitive impairments as well as the neuromuscular coordination. Biochemical study indicated a decrease in the oxidative burden; improved hematological, liver, and renal profiles; an increase in the acetylcholinesterase level; and upregulation of the mRNA expression of IL-1α, IL-1β, TNF-α, α–synuclein, and amyloid beta precursor protein. Current findings indicate that this oil mitigates motor and nonmotor PD-aasociated symptoms, reduces oxidatiev stress, and regulates the mRNA expression of pathological genes. Consequently, it is proposed that C. japonica oil may be used as a novel disease-modifying therapeutic remedy in the treatment of PD.