Humulus japonicus Prevents Dopaminergic Neuron Death in 6-Hydroxydopamine-Induced Models of Parkinson's Disease.

Humulus japonicus (HJ), popularly known as Japanese hops, is a traditional herbal medicine widely used for the treatment of pulmonary disease, skin disease, and hypertension in Korea. HJ exerts scavenging effects against reactive oxygen species (ROS), such as superoxide radical, hydroxyl radical, and hydrogen peroxide. Moreover, dysfunction and damage of mitochondria elicited by ROS are of critical importance in the pathogenesis of Parkinson's disease (PD). The present study aimed to examine neuroprotective potential of extracts of HJ using in vitro and in vivo 6-hydroxydopamine (6-OHDA) models. SH-SY5Y cells were cultured to explore the mechanisms for the neuroprotective effect of HJ in vitro. Unilateral 6-OHDA-induced mouse model of PD was established to investigate the neuroprotective effect of HJ on dopaminergic neurons in substantia nigra pars compacta (SNc) and striatum in vivo. Methanol extract of HJ (HJM) significantly attenuated cytotoxicity and the mitochondrial apoptosis pathway caused by 6-OHDA in SH-SY5Y cells. In addition, HJM significantly increased glutathione levels and decreased phosphorylation of ERK1/2 in SH-SY5Y cells exposed to 6-OHDA. In the in vivo study, the administration of methanol or ethanol extract of HJ improved the motor dysfunction and notably reduced dopaminergic cell death and fiber loss in the SNc and striatum caused by 6-OHDA. Our findings demonstrate that HJ may have therapeutic potential to protect dopaminergic neuron degeneration in Parkinson's disease.