Rosmarinic Acid Protects Skin Keratinocytes from Particulate Matter 2.5-Induced Apoptosis

Background: The exposure of the human skin to particulate matter 2.5 (PM_2.5) results in adverse health outcomes, such as skin aging, wrinkle formation, pigment spots, and atopic dermatitis. It has previously been shown that rosmarinic acid (RA) can protect keratinocytes from ultraviolet B radiation by enhancing cellular antioxidant systems and reducing oxidative damage; however, its protective action against the adverse effects of PM_2.5 on skin cells remains unclear. Therefore, in this study, we explored the mechanism underlying the protective effects of RA against PM_2.5-mediated oxidative stress in HaCaT keratinocytes. Methods: HaCaT keratinocytes were pretreated with RA and exposed to PM_2.5. Thereafter, reactive oxygen species (ROS) production, protein carbonylation, lipid peroxidation, DNA damage, and cellular apoptosis were investigated using various methods, including confocal microscopy, western blot analysis, and flow cytometry. Results: RA significantly inhibited PM_2.5-induced lipid peroxidation, protein carbonylation, DNA damage, increases in intracellular Ca²⁺ level, and mitochondrial depolarization. It also significantly attenuated PM_2.5-induced apoptosis by downregulating Bcl-2-associated X, cleaved caspase-9, and cleaved caspase-3 protein levels, while upregulating B-cell lymphoma 2 protein level. Further, our results indicated that PM_2.5-induced apoptosis was associated with the activation of the mitogen-activated protein kinase (MAPK) signaling pathway and that MAPK inhibitors as well as RA exhibited protective effects against PM_2.5-induced apoptosis. Conclusion: RA protected HaCaT cells from PM_2.5-induced apoptosis by lowering oxidative stress.