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.