The PXR Agonist Rhynchophylline Improves Experimental Parkinson’s Disease And Relative Mechanisms

Objective:Rhynchophylline(Rhy)is a monoamine indole alkaloid naturaly ocurring in the traditional Chinese medicine Uncaria rhynchophylla(Fam.Rubiaceae.).Rhy has beneficial effects on lowing the excitability of cerebral cortex,lowing blood pressure,anti-inflammation,antispasmodic,promoting sleep,and so on.This study aims to investigate whether Rhy can improve Parkinsonian-like behavior of locomotor deficits and gait disorders,and exert neuroprotective effect through activating the pregnane X receptor(PXR)-mediated detoxification system in experimental Parkinson’s disease(PD)model,based on the previous work that Rhy was identified as an agonist of PXR.This study may provide a novel idea for treating and preventing the progression of PD.Methods:1.To further investigate whether Rhy increase the transicriptional activity of mutant PXR through luciferase reporter gene assay based on our lab previous study.2.The effect of Rhy on 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine(MPTP)/6-hydroxydopamine(6-OHDA)-induced PD mice:These PD mice induced by intraperitoneally injecting with MPTP and unilaterally delivering 6-OHDA to substantia nigra pars compacta(SNpc),were orally administrated with Rhy.The pole test,open field test,balance beam test,gait analysis,and real-time locomotion measurement were used to assess the effect of Rhy on locomotory behavior and gait disorders of PD mice.Immunostaining was used to measure the expression of tyrosine hydroxylase(TH)in striatum and SNpc of PD mice.The CYP450 m RNA expression was measured by real-time PCR.3.The effect of Rhy on the metabolism of 1-methyl-4-phenylridinium ion(MPP~+)in brain tissue:The mice were treated with Rhy or MPTP,perfused and separated the brain in 1,2,4 hours after oral administration.The brain was used to measure the concentration of Rhy and MPP~+by UPLC-MS/MS.4.The effect of Rhy on model of C.elegans:Locomotion measurement in6-OHDA-exposured N2 and UA57 strain,and ageing-related UA57 strain.Dopamine neurons degeneration assay in 6-OHDA-exposured and ageing-related UA57 strain.α-synuclein accumulation assay in NL5901 strain.Results:1.Rhy increased the transcriptional activity of PXR,which was abrogated by mutant M247A,W299R,M425A,M425Q,suggesting that Rhy could activate PXR and it was possible that Rhy binds these sites.2.Rhy improved the Parkinsonian-like behavior of slow movement,locomotion activity,gait parameters and balance ability in MPTP/6-OHDA-induced PD mice.Rhy protected TH-positive neurons in striatum and SNpc from degeneration in PD mice.Rhy also regulated the P450 expression in striatum of PD mice.3.Rhy and MPP~+were attenuated in the brain tissue,but further investigation is need to confirm whether Rhy can promote the metabolism and excretion of MPP~+from brain.4.Rhy improved the locomotory deficit behavior in 6-OHDA-exposed N2 and UA57,also in ageing-UA57 strain.Rhy also alleviated the degeneration of dopamine neuron in UA57 strain induced by 6-OHDA and senesence.Meanwhile,Rhy mitigatedα-synuclein accumulation in NL5901 strain.Conclusion:Rhy could improve the Parkinsonian-like behavior locomotory deficits and gait disorders in MPTP/6-OHDA-induced PD mice and in C.elegans induced by6-OHDA-exposure and ageing.Mechanisticly,rhy may exert the neuroprotective effects through the activation of PXR-mediated the expression of CYP450.Whether Rhy could accelerate detoxification in the brain needs to be further studied.