UVB damage onset and progression 24 h post exposure in human-derived skin cells.

The focus of this research was on UVB radiation (280-320 nm) responsible for cellular changes in skin of acute and chronically exposed individuals. This study investigated the acute cellular damages triggered by UVB exposure of cultured human fibroblasts and keratinocyte cells immediately and 24 h post exposure in order to understand damage onset and progression. The study evaluated a number of cellular parameters including mitochondria, lysosomes, cell membrane, DNA damages as well as pro and anti-apoptotic protein expression levels. Cellular organelle damages were assessed by a battery of in vitro toxicological assays using MTS and Neutral red cytotoxicity assays. Cell membrane damages were also assessed by measuring lactate dehydrogenase (LDH) enzyme leakage from UVB exposed cells. Lastly DNA damages was assessed using the comet assay while protein expression was evaluated using Western Blot. In this study we reported in all our assay systems (MTS, NR and LDH) that cellular damages were UVB dose dependent with damages amplified 24 h post exposure. Our results also indicated that incubation of exposed cells for a period of 24 h increased the sensitivity of the assay systems used. The increased sensitivity in detecting early cytotoxic damages was manifested though organelle damage measurement at very low doses which were not manifested immediately post exposure. The data also indicated that HaCaT cells were most sensitive in detecting UVB triggered damages immediately and 24 h post exposure using the MTS assay. We also established upregulation and downregulation of various apoptotic proteins at various time points post exposure. The presented data clearly indicated the need for a comprehensive assessment of UVB damages 4 and 24 h post exposure due to the different assay sensitivities in addition to various signaling mechanisms activated at different time points post exposure.