CROSS-LINKING OF COLLAGEN BY SINGLET OXYGEN GENERATED WITH UV-A

Singlet oxygen (O-1(2)), a highly reactive and toxic intermediate, may play a role in photo-induced aging, We examined singlet oxygen genera tion from hematoporphyrin (HP) with UV-A, by monitoring the emission a t 1268 nm corresponding to O-1(2)-->O-3(2). Singlet oxygen was formed HP-dose-dependently in this system, We then investigated the reaction of singlet oxygen generated by UV-A irradiation with collagen, which i s related to skin elasticity and softness, Collagen from skin was rapi dly and dose-dependently cross-linked by singlet oxygen, The reaction was inhibited by NaN3, a selective quencher of singlet oxygen, In cont rast, SOD (superoxide dismutase) and mannitol had no effect, These res ults suggested that cross-linking of collagen was caused by W-A-genera ted singlet oxygen, not by any other reactive oxygen species. Compared with another multisubunit protein, alcohol dehydrogenase, collagen wa s cross-linked much more efficiently, Further, the finding that semica rbazide inhibited cross-linking of collagen showed that cross-links we re formed between photooxidized histidyl residues and amino groups, Si nglet oxygen generated by UV-A irradiation may contribute to cross-lin king of collagen in the process of skin photoaging.