Carbonylated proteins exposed to UVA and to blue light generate reactive oxygen species through a type I photosensitizing reaction.

BACKGROUND

Carbonylated proteins (CPs) are generated by the reaction of basic amino acid residues in proteins with aldehyde compounds produced during lipid peroxidation. CPs in the stratum corneum (SC) impact skin conditions such as skin moisture functions including water content and transepidermal water loss (TEWL). In addition, CPs can be frequently seen in the SC from sun-exposed sites compared with sun-protected sites.

OBJECTIVE

The aim of this study was to reveal whether CPs could be a generation source of reactive oxygen species (ROS) in the SC following exposure to ultraviolet (UV) radiation and to identify the type of ROS and its generation mechanism.

METHODS

ROS generation was detected using a methyl cypridina luciferin analog (MCLA) chemiluminescence system and an ESR spin-trapping method. CPs in porcine SC, in a keratin film and in bovine serum albumin (BSA) were prepared by reaction with acrolein. Levels of protein carbonylation were quantified by detecting aldehyde residues.

RESULTS

CP levels in the SC were increased in a UVA energy-dependent manner. That result suggested that a source of ROS generation existed in the SC initiated and produced the carbonylation of SC proteins. Carbonylated BSA and carbonylated porcine SC sheets exhibited fluorescence spectra at an excitation wavelength of 430nm and an emission wavelength of 520nm. Irradiation of the SC with UVA increased protein carbonylation and the amount of autofluorescence in the SC. ROS generation in the SC caused by UVA and by short-wavelength visible light (blue light, 400-470nm) was detected by the MCLA chemiluminescence system. Artificially carbonylated porcine SCs and keratin films had increases of chemiluminescence intensity after exposure to both light sources as well. The addition of superoxide dismutase to the MCLA system completely abolished the incremental chemiluminescence intensity after both UVA and blue light exposure of the SC. In addition, acrolein-treated BSA gave ESR signals like hydroxyl radicals (OH) converted from superoxide anion radicals (O) during irradiation with a xenon arc lamp containing UVA and visible light. From the sum of these results, we consider that CPs are produced from O initially generated from exposure to UVA and blue light.

CONCLUSION

CPs are excited by absorbing sunlight, particularly UVA and blue light, and result in the generation of O through a CPs progress new protein carbonylation in stratum corneum through ROS generation. photosensitizing reaction. Further, the results suggest that the O produces CPs in the SC through lipid peroxidation in the sebum, and finally affects skin conditions including color and moisture functions.