UV B-irradiation enhances the racemization and isomerizaiton of aspartyl residues and production of Nε-carboxymethyl lysine (CML) in keratin of skin.

UV-B irradiation is one of the risk factors in age-related diseases. We have reported that biologically uncommon D-ß-Asp residues accumulate in proteins from sun-exposed elderly human skin. A previous study also reported that carboxymethyl lysine (CML; one of the advanced glycation end products (AGEs)) which is produced by the oxidation of glucose and peroxidation of lipid, also increases upon UV B irradiation. The formation of D-ß-Asp and CML were reported as the alteration of proteins in UV B irradiated skin, independently. In this study, in order to clarify the relationship between the formation of D-ß-Asp and CML, immunohistochemical analysis using anti-D-ß-Asp containing peptide antibodies and anti-CML antibodies was performed in UV B irradiated mice. Immunohistochemical analyses clearly indicated that an anti-D-ß-Asp containing peptide antibody and anti-CML antibody reacted at a common area in UV B irradiated skin. Western blot analyses of the proteins isolated from UV B irradiated skin demonstrated that proteins of 50-70 kDa were immunoreactive towards antibodies for both D-ß-Asp containing peptide and CML. These proteins were identified by proteomic analysis as members of the keratin families including keratin-1, keratin-6B, keratin-10, and keratin-14.

Phototransformations of advanced glycation end products in the human eye lens due to ultraviolet A light irradiation.

Previous studies from this laboratory have shown that ultraviolet A (UVA) light can bleach the yellow advanced glycation end products (AGEs) of aged and cataractous human lenses. The AGEs OP-lysine and argpyrimidine are two UVA-absorbing posttranslational modifications that are abundant in the eye lens. The purpose of this study was to outline the changes in these two AGEs due to UVA irradiation. The changes of OP-lysine, OP-phenethylamine (a phenethylamine analogue of OP-lysine), and argpyrimidine due to irradiation with UVA light in the presence or absence of air and ascorbic acid were followed by different spectral methods. Aged human lenses were similarly irradiated in artificial aqueous humor. The amounts of OP-lysine in the irradiated lenses and in the corresponding dark controls were determined by HPLC. Both OP-lysine and argpyrimidine decreased 20% when irradiated with UVA light in the absence of ascorbic acid. Under the same conditions, OP-lysine was bleached 80% in the presence of ascorbic acid during irradiation experiments. In contrast, argpyrimidine UVA light bleaching was not affected by the presence of ascorbic acid. Interestingly the major product of OP-phenethylamine after UVA irradiation in the presence of ascorbic acid was phenethylamine, which indicates that the entire heterocycle of this AGE was cleaved and the initial amino group was restored. Some AGEs in the human eye lens can be transformed by UVA light.