Singlet oxygen generation by UVA light exposure of endogenous photosensitizers

¹ Department of Dermatology, University of Regensburg
² Institute of Physics, University of Regensburg
³ Institute of Organic Chemistry, University of Regensburg

^* To whom correspondence should be addressed. E-mail: baeumler.wolfgang{at}klinik.uni-regensburg.de.

Submitted on January 31, 2006
Revised on April 3, 2006
Accepted on 17 May 2006

	Abstract

UVA light (320 - 400 nm) has been shown to produce deleterious biological effects in tissue due to the generation of singlet oxygen by substances like flavins or urocanic acid. Riboflavin, Flavin Mononucleotide (FMN), Flavin Adenine Dinucleotide (FAD), -Nicotinamide Adenine Dinucleotide (NAD), and -Nicotinamide Adenine Dinucleotide Phosphate (NADP), urocanic acid or cholesterol in solution were excited at 355 nm. Singlet oxygen was directly detected by time resolved measurement of its luminescence at 1270 nm. NAD, NADP and Cholesterol showed no luminescence signal possibly due to the very low absorption coefficient at 355 nm. Singlet oxygen luminescence of urocanic acid was clearly detected but the signal was too week to quantify a quantum yield. The quantum yield of singlet oxygen was precisely determined for Riboflavin ( = 0.54 ± 0.07), FMN ( = 0.51 ± 0.07) and FAD ( = 0.07 ± 0.02). In aerated solution, Riboflavin and FMN generate more singlet oxygen than exogenous photosensitizers such as Photofrin, which are applied in photodynamic therapy to kill cancer cells. With decreasing oxygen concentration, the quantum yield of singlet oxygen generation decreased, which must be considered when assessing the role of singlet oxygen at low oxygen concentrations (inside tissue).

Key Words: flavins, oxygen concentration, quantum yield, urocanic acid