UVC-Protective Activity of Lemongrass Among 12 Fat-soluble Herbal Extracts: Rapid Decay Due to Cytotoxicity.

Abstract

The COVID-19 pandemic led to the rapid spread of the use of ultraviolet C (UVC) sterilizers in many public facilities. Considering the harmful effects of prolonged exposure to UVC, manufacturing of safe skin care products is an important countermeasure. In continuation of our recent study of water-soluble herbal extracts, the present study aimed at searching for anti-UVC components from fat-soluble herbal extracts. Human dermal fibroblast and melanoma cells were exposed to UVC (1.193 W/m2) for 3 min. Viable cell number was determined by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay. Cell-cycle analysis was performed using a cell sorter. UVC-protective activity was quantified by the selective index (SI), i.e., the ratio of the 50% cytotoxic concentration for unirradiated cells to the concentration that restored viability of UVC-treated cells by 50%. Only lemongrass extract, among 12 fat-soluble herbal extracts, showed significant anti-UVC activity, comparable to that of lignified materials and tannins, but exceeding that of N-acetyl-L-cysteine and resveratrol. Lemongrass extract was highly cytotoxic, producing a subG1 cell population. During prolonged incubation in culture medium, the anti-UVC activity of lemongrass extract, sodium ascorbate and vanillic acid declined with an approximate half-life of <0.7, 5.4-21.6, and 27.8-87.0 h, respectively. Removal of cytotoxic principle(s) from lemongrass extract is crucial to producing long-lasting UVC-protective effects.