Complementary antioxidant function of caffeine and green tea polyphenols in normal human skin fibroblasts

The study of free radicals is particularly relevant in the context of human skin carcinogenesis and photoaging because of these oxidants' ability to induce DNA mutations and produce lipid peroxidation byproducts, including 4-hydroxy-2-nonenal (HNE). Therefore, it is important to identify and evaluate agents with the ability to modulate intracellular free radicals and HNE. The purpose of this research is to investigate the ability of antioxidants green tea polyphenols (GTPs) and caffeine, alone and in combination, to modulate the hydrogen peroxide (H2O2)-induced upregulation of reactive oxygen species (ROS) free radicals and HNE in normal human skin fibroblast WS-1 cells in vitro. GTPs and caffeine were selected for evaluation because these compounds have demonstrated antioxidative properties in various skin models. Furthermore, GTPs and caffeine share a close natural botanical association as caffeine is present in green tea, as well. Hydrogen peroxide is a well-known generator of free radicals that is produced during endogenous and UV-induced oxidation processes in human skin and was used to upregulate ROS and HNE in normal human fibroblast WS-1 cells. Using a flow cytometry-based assay, the results demonstrate that at 0.001% concentration, green tea polyphenols alone, and in combination with 0.1 mM caffeine, inhibited the upregulation of H2O2-generated free radicals and HNE in human skin fibroblasts in vitro. Caffeine alone demonstrated limited anti-oxidant properties.