Chemical modification of 5-hydroxytryptophan photoinduced by endogenous sensitizers present in skin

FARÍAS, JESUÁN J.; LIZONDO-ARANDA, PALOMA; SERRANO, MARIANA P.; LHIAUBET-VALLET, VIRGINIE; THOMAS, ANDRÉS H.; DANTOLA, MARIA LAURA

Maresias

Congreso; XV Encuentro Latinoamericano de Fotoquímica y Fotobiología (XV ELAFOT)-1st LatASP meeting; 2023

ELAFOT-LatASP

Vitiligo is a skin disorder characterized by the acquired loss of constitutional pigmentation, manifested as white patches, the accumulation of millimolar concentration of hydrogen peroxide (H2O2) and micromolar concentration of aromatic pterins (Pt). It has been reported that in patients with vitiligo many enzymes are deactivated and epidermal albumin levels are affected by H2O2-mediated oxidation, since several amino acid residues are oxidized. Pterins, a family of heterocyclic compounds, are present in biological systems playing different functions. In aqueous solutions and under UV-A excitation, Pt can fluoresce, produce reactive oxygen species and, photosensitize chemical modification of biomolecules through both type I and type II mechanisms [1]. 5-OH-Trp, a common oxidation product of tryptophan which has been suggested as potential endogenous antioxidants [2], is present in the skin of vitiligo sufferers [3].With this background, the photosensitization of 5-OH-Trp by Pt is an interesting model to investigate the oxidative damage of human skin, triggered by electromagnetic radiation. By combining different analytical techniques, we could establish that 5-OH-Trp can be damaged by Pt through a photosensitized process which is initiated by an electron transfer from the 5-OH-Trp to the Pt triplet excited state. In air-equilibrated aqueous solution three products were identified, two of which correspond to 5-OH-Trp dimers, while the other is a product in which the 5-OH-Trp has incorporated an oxygen atom generating a dione. No consumption of Pt was observed. However, in the absence of O2, further free-radical reactions lead to the reduction of the photosensitizer. 5-OH-Trp dimers were the only products detected. The generation of this kind of products in proteins may have relevant biomedical implications.[1] Lorente, C., et al., J. Photochem. Photobiol. 7 : 100045 (2021).[2] Jovanovic, S., et. al., Biochim. Biophys. Acta. 1008: 39 (1989).[3] Rokos, H., et. al., J. Raman Spectrosc. 39: 1214 (2008).