Photosensitizing activity of advanced glycation endproducts on tryptophan, glucose 6-phosphate dehydrogenase, human serum albumin and ascorbic acid evaluated at low oxygen pressure.
A comparative study of the photosensitizing activity of advanced glycation endproducts (AGEs) prepared by incubating glucose (Glc), threose (Threo) and ascorbate (AH-) in the presence of lysine (Lys) was performed. Photochemical activity was evaluated under low oxygen pressure with the aim to simulate the conditions of the eye lens. AGE-sensitized tryptophan and AH- photodecomposition and glucose 6-phosphate dehydrogenase inactivation were studied. In all systems, glucose-derived AGEs showed the highest photosensitizing efficiency, followed by ascorbate and threose. The presence of different sensitizers in glycation products mixtures was investigated. For this purpose, Trp decomposition quantum yields were determined at 344 and 367 nm. The values obtained at 344 nm are between three and six times higher than those observed at 367 nm, confirming the presence of at least two compounds with different photosensitizing activities in the mixtures. The chemiluminescence associated with the AGE-mediated oxidation of free Trp and Trp residues in human serum albumin was also studied, and a good correlation between the emission of light and the extent of Trp decomposition was found. In conclusion, it is demonstrated that glucose derived AGEs, which can be formed in vivo in the eye lens of diabetic patients and are accumulated in elderly lenses, have a higher photosensitizing efficiency, at low oxygen pressure, than those arising from ascorbate and threose. This high efficiency is especially significant when proteins are employed as photochemical targets, indicating that protein-sensitizer interaction and the local environment around the sensitizers play an important role.
Fuentealba
Denis
D
Departamento de Química Física, Facultad de Química, Pontificia Universidad Católica de Chile, Santiago, Chile.
Galvez
Manuel
M
Alarcón
Emilio
E
Lissi
Eduardo
E
Silva
Eduardo
E
D001205:Ascorbic Acid / Q000528:radiation effects*; D005954:Glucosephosphate Dehydrogenase / Q000528:radiation effects*; D017127:Glycation End Products, Advanced / Q000494:pharmacology*; D006801:Humans; D007908:Lens, Crystalline; D008954:Models, Biological; D010100:Oxygen; D017319:Photosensitizing Agents / Q000494:pharmacology*; D012709:Serum Albumin / Q000528:radiation effects*; D014364:Tryptophan / Q000528:radiation effects*; D014466:Ultraviolet Rays
D017127:Glycation End Products, Advanced; D017319:Photosensitizing Agents; D012709:Serum Albumin; D014364:Tryptophan; D005954:Glucosephosphate Dehydrogenase; D001205:Ascorbic Acid; D010100:Oxygen