Synergistic phototoxic effects of glycolic acid in a human keratinocyte cell line (HaCaT)

Abstract

Background Glycolic acid (GA) has been widely used in cosmetic agents and superficial chemical peeling in recent years. It has long been concerned that UV irradiation would enhance the photosensitivity of GA on human skin. Therefore, it is mandatory to explore the biologic effects of concomitant exposure of GA and UV irradiation in human keratinocytes. Objective The aim of the study is to explore the effects of concomitant exposure of GA and UVB in a human keratinocyte cell line (HaCaT). Methods We used HaCaT to investigate the effects of GA (5mM), UVB (50mJ/cm(2)), and co-treatment with GA and UVB (GA+UVB) in human keratinocytes. We used a phase contrast microscope to observe morphological changes of the cells, and employed flow cytometry to detect cell viability, cell cycle, and mitochondrial membrane potential (MMP), and intracellular reactive oxygen species (ROS) levels. Cell damage was detected by DAPI stain, and Western blot was used to detect the activities of apoptosis- related and cycle checkpoint-related proteins such as Bax, Bcl-2, caspases-3, -4, -9, Endo G, AIF, and p21, p27, p53, cdk2, cyclin E, cyclin A. Results We found that either GA or UVB alone had inhibitory effect on cell proliferation, and co-treatment with GA and UVB had synergistic anti-proliferative effect. GA alone did not affect the cell cycle, and UVB induced HaCaT cells accumulated at S phase, and co-treatment with GA and UVB arrested cells at S phase more prominently. Moreover, all the treatment with GA, UVB, and GA+UVB in HaCaT cells induced apoptosis. We further demonstrated that GA had synergistic apoptotic effect in human keratinocytes. GA and UVB both had effects on the decline of MMP and increase of ROS release, and GA had synergistic increase in the level of ROS in UVB-treated HaCaT cells. Besides, co-treatment with GA and UVB had synergistic effect on apoptosis through the over-expressions of Bax, p21, p53, caspases-3, -4, -9, Endo G and AIF, and confocal microscopy disclosed translocation of AIF and Endo G from cytoplasm to the nucleus. Therefore, apoptosis induced by co-treatment by GA+UVB was initiated and executed by multiple pathways including mitochondria- and ER-dependent, and caspase-dependent and caspase-independent pathways. Conclusion We demonstrated that GA, UVB, GA+UVB inhibited proliferation and induced apoptosis in HaCaT cells. The mechanisms of apoptosis induced by co-treatment of GA and UVB involve multiple pathways. The synergistic photo-toxicity may be related to cell cycle arrest and apoptosis in UVB-treated HaCaT cells. These results highlight the potential adverse effects of GA-containing cosmetic agents on human skin.