THE RELATIVE UV SENSITIZER ACTIVITY OF PURIFIED ADVANCED GLYCATION ENDPRODUCTS

The oxidation products of ascorbic acid react with lens proteins to fo rm advanced glycation endproducts (AGE) that are capable of generating reactive oxygen species when irradiated with UVA light, L-Threose, th e most active of these oxidation products, was reacted with N-acetyl l ysine and six AGE peaks were isolated by RP-HPLC. Each peak exhibited fluorescence and generated superoxide anion and singlet oxygen in resp onse to UV light, Solutions of these AGE peaks (50 mu g/mL) generated 5-10 nmol/mL of superoxide anion during a 30 min irradiation, This act ivity was 100-fold less than the superoxide anion generated by kynuren ic acid and 400-fold less than riboflavin. Ultraviolet irradiation gen erated from 1.2 to 2.7 pmol/mL of singlet oxygen with the purified thr eose AGE compounds, This activity was similar to that seen with other purified AGE compounds (pentosidine, LM-1 and Ac-FTP) and with kynuren ine and 3-OH kynurenine. This considerable singlet oxygen formation, h owever, was still 40-fold less than that obtained with kynurenic acid and 100-fold less than riboflavin under the same irradiation condition s. In spite of this lower sensitizer efficiency, the purified AGE gene rated 20-60-fold more singlet oxygen on a weight basis than either cru de ascorbic acid glycated proteins or a preparation of water-insoluble proteins from aged normal human lenses, On a molar basis, therefore, AGE could account for the sensitizer activity in these protein prepara tions if they represented less than 1% of the total amino acids.