Attenuation of UVA-induced damage to human keratinocytes by silymarin

BACKGROUND: UV radiation from sunlight is a potent environmental risk factor in skin cancer pathogenesis. UVA is the major portion of UV light reaching the earth surface ( approximately 95%) and it is reported to lead to benign and malignant tumor formation. UVA-mediated cellular damage occurs primarily through the release of reactive oxygen species (ROS) and it is responsible for inflammation, immunosuppression, photoaging and photocarcinogenesis. OBJECTIVE: The aim of our study was to investigate the potency of silymarin, the polyphenol fraction from the seeds of Silybum marianum, to modulate UVA-induced oxidative damage to human keratinocytes. METHODS: Skin epidermal cell line HaCaT, extensively used for studying the influence of UV radiation, was chosen as an experimental model. Silymarin's effect on UVA-disrupted cell viability, proliferation, mitochondrial function, and intracellular ATP and GSH level was measured. Furthermore, silymarin's potency to reduce UVA-induced ROS generation, membrane lipid peroxidation, caspase-3 activation and DNA damage was monitored. RESULTS: Treatment of irradiated HaCaT (20 J/cm(2)) with silymarin (0.7-34 mg/l; 4h) resulted in concentration-dependent diminution of UVA-caused oxidative stress on all studied parameters. Silymarin application extensively reduced GSH depletion and ROS production as well as lipid peroxidation in irradiated cells. Formation of UVA-induced DNA single strand breaks and caspase-3 activity was also significantly decreased by silymarin. CONCLUSION: The results suggest that silymarin may be beneficial in the treatment of UVA-induced skin oxidative injury and inflammation. However, further studies especially whose using human systems are needed to determine efficacy of silymarin in vivo.