The Chinese herbal formula Liuwei dihuang protects dopaminergic neurons against Parkinson's toxin through enhancing antioxidative defense and preventing apoptotic death

Abstract

Liuwei dihuang (LWDH), a widely used traditional Chinese medicine (TCM), has been employed as an anti-aging prescription to improve declined function. Parkinson's disease (PD) is a common adult-onset neurodegenerative disorder characterized by the degeneration of dopaminergic nigrostriatal neurons with complex pathological mechanisms, including oxidative stress. Increasing evidence indicate that TCM has the potential to be neuroprotective drugs because of their antioxidant characteristics. The aim of this study is to investigate the mechanisms of LWDH-mediated protection in Parkinson's toxin-induced dopaminergic neurodegeneration by evaluating water extract of LWDH (LWDH-WE) in 1-methyl-4-phenylpyridinium (MPP(+))-treated primary mesencephalic neurons and 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-treated C57BL/6 mice. In the present study, chemical profiling and quantitative analysis of LWDH-WE were revealed using 3D-HPLC technique, and were confirmed by the data of three batches of LWDH-WE. In primary mesencephalic neuronal cultures, LWDH-WE decreased MPP(+)-induced loss of tyrosine hydroxylase (TH)-positive neurons and increase of Annexin V-positive neurons. LWDH-WE reduced MPP(+)-induced oxidative damage via increasing antioxidant defense (SOD, GSH), decreasing ROS production, and down-regulating NADPH oxidases (Nox2 and Nox4). Also, LWDH-WE inhibited neuronal apoptosis by improving mitochondrial membrane potential, increasing antiapoptotic protein Bcl-2 expression, and down-regulating apoptotic signaling (Bax, cytochrome c, cleaved-caspase-3) in MPP(+)-treated neurons. In MPTP-treated C57BL/6 mice, LWDH-WE attenuated TH-positive neuronal loss in substantia nigra pars compacta (SNpc), and improved locomotor activity of mice. In conclusion, the present results reveal that LWDH-WE possesses protection on dopaminergic neurons through enhancing antioxidant defense and decreasing apoptotic death, suggesting the potential benefits of LWDH-WE for PD treatment.

Keywords: 1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine; Dopaminergic neurons; Liuwei dihuang; Neuroprotection; Traditional Chinese medicine.