Gadusol protects tryptophan from photosensitized oxidation by pterin

DALILA ELISABET ORALLO; CAROLINA LORENTE; MARIA FLORENCIA FANGIO; CHURIO, MARIA SANDRA

Villa Carlos Paz

Encuentro; XIII Encuentro Latinoamericano de Fotoquímica y Fotobiología; 2017

Pterins (Ptr) are heterocyclic compounds present in biological systems. They are consideredphotosensitizers that, under UV-A radiation, degrade DNA, proteins and their components. Thus, the study of defense mechanisms against these reactive species through the action of natural protective compounds has concentrated important attention. The mechanisms may imply: (i) inhibition of the formation of Ptr in excited state; (ii) deactivation of the excited states of Ptr; (iii) elimination of the reactive oxygen species (ROS) generated in theenvironment. Previously, the behavior of Ptr in the presence of the essentialamino acid tryptophan (Trp) has beenstudied. The predominantphotooxidation pathway of Trp is anelectron transfer process from theamino acid to the Ptr triplet excitedstate.[1]Gadusol is a natural antioxidant that has been found to be associated withproteins in ocular lenses and in the skin of fish.[2] It has been established that itsanionic form (gadusolate, Gad) is very efficient at neutralizing ROS anddeactivating triplet excited states of sensitizers.[3-4] Therefore, it is interesting to study the effect of Gad on the oxidation mechanisms of amino acids in the presence of Ptr.Gad was obtained from Pseudopercis semifasciata roes, according to the procedure reported by Plack et al. [5] and adapted by Arbeloa et al..[3] Aereated aqueous solutions (pH 6.5) containing Trp, Gad and Ptr were irradiated at 350 ± 5 nm in a quartz cell of 1 cm optical path, at room temperature. Control experiments with solutions containing only Trp and Ptr, or Gad and Ptr, were carried out under the same conditions. The progress of the reaction was monitored by HPLC with UV detection at 282 nm. Both Trp and Gad concentrations decrease as a function of the irradiation time, whereas the Ptr concentration does not change within the analyzed period (60 min). In the presence of Ptr and Gad, the concentration of Trp drops around 20% but, in the absence of Gad, the amino acid dissapears faster (ca. 61%). However, in deareated solutions containing Ptr and Gad no significant changes were observed in the absorption after irradiation for more than 180 min. This behavior is similar to that found for Trp-Ptr solutions in the absence of O2, indicating that Ptr photosensitizes the oxidation of Trp in the presence of O2.[1] Ours results suggest that Gad protectsTrp from the photosensitized oxidation by Ptr. Therefore, further studies should be directed to explore potential applications of this marine metabolite in the treatment of skin disorders where Ptr is pathologically accumulated.[1] A. H. Thomas, M. P. Serrano, V. Rahal, P. Vicendo, C. Claparols, E. Oliveros, C. Lorente, Free Rad. Biol. Med.2013, 63, 467.[2] W. M. Bandaranayake. Nat. Prod. Rep. 1998, 15, 159.[3] E. M. Arbeloa, M. J. Uez, S. G. Bertolotti, M. S. Churio, Food Chemistry. 2010, 119, 586.[4] E. M. Arbeloa, S. G. Bertolotti, M. S. Churio. Photochem. Photobiol. Sci. 2011, 10, 133.[5] P. A. Plack, N. W. Fraser, P. T. Grant, C. Middleton, A. I. Mitchell, R. H. Thomson, Biochem. J. 1981, 199, 741.