Cytoprotective effect of bioactive sea buckthorn extract on paraquat-exposed A549 cells via induction of Nrf2 and its downstream genes.

The extract of sea buckthorn (SBT) [Hippophae rhamnoides L. (Elaeagnaceae)], is used as a food supplement and traditional medicine in numerous countries. This study investigated the protective effects of the functional extract of SBT against paraquat (PQ)-induced toxicity via antioxidant mechanisms in A549 cells. The methanol extract of SBT (25-200 µg/ml) was used to protect cells against PQ (200 µM)-induced cell death. A viability assay was conducted using 3-(4,5-dimethylthioazol-2-ly)-2,5-diphenyltetrazolium bromide and lactate dehydrogenase (LDH). Total intracellular reactive oxygen species (ROS) were measured and plotted. For validation of the SBT-induced expression of nuclear factor-E2-related factor 2 (Nrf2) and its target genes, western blot analysis and qPCR were performed. The present study showed that pretreatment of A549 cells with SBT extract significantly attenuated PQ (200 µM)-induced cellular toxicity. The maximum cytoprotective effect was identified using 200 µg/ml SBT extract; it began 24 h following exposure and was sustained up to 120 h (P<0.05). SBT extract significantly reduced LDH activity by 35.63% and ROS levels by 30.90% (P<0.05). Pretreatment with SBT extract activated Nrf2 mRNA and protein expression and its nuclear translocation. The SBT extract effectively induced Nrf2 target genes, such as NAD(P)H dehydrogenase quinone 1, glutathione peroxidase 1, glutathione reductase and catalase following treatment with PQ. Based on these results, it was hypothesized that SBT extract may be used as a potential therapeutic agent for the treatment of various oxidative stress-related diseases.