Antioxidant activity of thunbergia laurifolia lindl. Ethanolic extract in keratinocytes

Abstract

Fine particulate matter (PM2.5) can cause skin damage through the induction of oxidative stress in epidermis. Antioxidants help counteract with cellular oxidant species and maintain cell homeostasis. This study aims to examine the protective effect of Thunbergia laurifolia lindl. ethanolic extract on PM2.5-mediated oxidative stress in epidermal keratinocytes. High-performance liquid chromatography with diode array detection was conducted for quantitative analysis of rosmarinic acid content in the extract. Cell viability was detected by the 3-(4,5-Dimethylthiazol-2-yl)-2,5-Diphenyltetrazolium Bromide assay. Intracellular ROS was monitored using 2’,7’-Dichlorodihydrofluorescein diacetate. Proteins related to p62-Keap1-Nrf2 signaling pathway were examined by western blot analysis. Expressions of Nrf2 and p62 were further determined by immunofluorescence. PM2.5 treatment at non-cytotoxic concentration could remarkably induce reactive oxygen species (ROS) production within 6 h. The co-treatment of the extract and PM2.5 for 6 h dramatically inhibited excess ROS production induced by PM2.5. In addition, the extract enhanced cellular defense of keratinocytes, by increasing the levels of p62, Nrf2 and SOD1 proteins. The extract stabilizes Nrf2 and p62 expressions, while suppresses Keap1 expression. The T. laurifolia extract is promising natural antioxidants against oxidative stress induced by PM2.5 in keratinocytes.