UV-irradiation depletes antioxidants and causes oxidative damage in a model of human skin

Abstract

The degree to which antioxidant loss occurs in human skin after UV irradiation is unknown, as is the cascade of events that might occur. We have, therefore, evaluated a tissue culture model of human skin for its usefulness for studying oxidative injury by UV-irradiation. Human skin equivalents, a tissue culture model, were irradiated using a full solar UV spectrum (UVA and UVB, 280-400 nm) (0 to 16.8 J/cm2, 0-12 minimal erythemal dose, MED), then incubated from 1 to 24 h. Ubiquinol was the most UV-light sensitive antioxidant and was depleted by 2.1 J/cm2 (1.5 MED, p < .004); ubiquinone decreased with 4.2 J/cm2 (3 MED, p < .0007). A linear decrease in alpha-tocopherol occurred--approximately 1.7 pmol tocopherol/cm2 surface were destroyed per J/cm2 UV-light. Urate was depleted by irradiation with 8.4 J/cm2 (6 MED), while ascorbate was depleted by 16.8 J/cm2 (12 MED). Cellular protein carbonyls and lactic dehydrogenase (LDH) leakage into the medium were only increased at 1 h incubation following exposure to 16.8 J/cm2 (12 MED). At 24 h incubation, PGE2 was increased in the medium of cells exposed to UV-irradiation at 0.35 J/cm2 (0.25 MED) compared with sham-exposed cells (p < .04); higher UV exposures lead to significant increases in both PGE2 (p < .001) and LDH (p < .001) in the medium. In conclusion, human skin equivalents respond to suberythemal levels of UV-irradiation by increasing production of PGE2; higher levels of UV-irradiation (at least 1 MED) were needed to deplete cellular antioxidants and induce immediately detectable oxidative damage.