The malondialdehyde-derived fluorophore DHP-lysine is a potent sensitizer of UVA-induced photooxidative stress in human skin cells

Light-driven electron and energy transfer involving non-DNA skin chromophores as endogenous photosensitizers induces oxidative stress in UVA-exposed human skin a process relevant to photoaging and photocarcinogenesis Malondialdehyde is an electrophilic dicarbonyl-species derived from membrane lipid peroxidation Here we present experimental evidence suggesting that the malondialdehyde-derived protein epitope dihydropyridine (DHP)-lysine is a potent endogenous UVA-photosensitizer of human skin cells Immunohistochemical analysis revealed the abundant occurrence of malondialdehyde-derived and DHP-lysine epitopes in human skin Using the chemically protected dihydropyridine-derivative (2S)-Boc-2-amino-6-(3 5-diformyl-4-methyl-4H-pyridin-1-yl)-hexanoic acid-t-butylester as a model of peptide-bound DHP-lysine photodynamic inhibition of proliferation and induction of cell death were observed in human skin Hs27 fibroblasts as well as primary and HaCaT keratinocytes exposed to the combined action of UVA and DHP-lysine DHP-lysine photosensitization induced intracellular oxidative stress p38 MAPkinase activation and upregulation of heme oxygenase-1 expression Consistent with UVA-driven ROS formation from DHP-lysine formation of superoxide hydrogen peroxide and singlet oxygen was detected in chemical assays but little protection was achieved using SOD or catalase during cellular photosensitization In contrast inclusion of NaN3 completely abolished DHP-photosensitization Taken together these data demonstrate photodynamic activity of DHP-lysine and support the hypothesis that malondialdehyde-derived protein-epitopes may function as endogenous sensitizers of UVA-induced oxidative stress in human skin (C) 2010 Elsevier B V All rights reserved