Protective effects of a herbal extract combination of Bupleurum falcatum, Paeonia suffruticosa, and Angelica dahurica against MPTP-induced neurotoxicity via regulation of nuclear receptor-related 1 protein.

Parkinson's disease (PD) is one of the progressive neurodegenerative diseases of whose condition is characterized by dopaminergic neuronal cell loss and dysfunction in the substantia nigra pars compacta (SNpc) and the striatum. Recent studies have demonstrated that the nuclear receptor-related 1 protein (Nurr1) is critical of dopaminergic phenotype induction in mesencephalic dopaminergic neurons. Further, Nurr1 engages in synthesizing and storing dopamine through regulating levels of tyrosine hydroxylase (TH), dopamine transporter (DAT) and vesicular monoamine transporter 2 (VMAT2). The aim of this study was to investigate the protective effects of a herbal extract combination, consisting of Bupleurum falcatum, Paeonia suffruticosa, and Angelica dahurica (MABH), on 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced PD-like symptoms and to elucidate possible mechanisms of action focusing on Nurr1. In a subacute mouse model of MPTP-induced PD, MABH treatment resulted in recovery from movement impairments. MABH prevented dopamine depletion and protected against dopaminergic neuronal degradation induced by MPTP. Additionally, MABH increased Nurr1 expression in the SNpc of mice. To evaluate the effects of MABH on Nurr1 expression, we measured the protein levels of Nurr1 and its regulating factors using Western blot analysis in PC12 cells. MABH treatment induced the phosphorylation of extracellular signal-regulated kinase protein via increasing the protein expression levels of Nurr1 and ultimately the levels of TH, VMAT2, and DAT. These results indicate that MABH has protective effects on dopaminergic neurons in a mouse model of PD by regulating Nurr1.