Gadusol protects tryptophan from photosensitized oxidation by pterin

DALILA E. ORALLO; FLORENCIA FANGIO; M. SANDRA CHURIO; CAROLINA LORENTE

Villa Carlos Paz , Córdoba, Argentina.

Congreso; XIII Encuentro Latinoamericano de Fotoquímica y Fotobiología (XIII ELAFOT); 2017

ELAFOT

Pterins (Ptr) are heterocycliccompounds present in biological systems. They are considered photosensitizers that, under UV-Aradiation, degradated DNA, proteins and their components. Thus, the study ofdefense mechanisms against these reactive species through the action of naturalprotective compounds has concentrated important attention. The mechanisms may imply:(i) inhibition of the formation of Ptr in excited state; (ii) deactivation of theexcited states of Ptr; (iii) elimination of the reactive oxygen species (ROS)generated in the environment. Previously, the behavior of Ptr in the presenceof the essential amino acid tryptophan (Trp) has been studied. The predominant photooxidation pathway of Trp is an electron transferprocess from the amino acid to the Ptr triplet excited state.[1]Gadusol is a natural antioxidantthat has been found to be associated with proteins in ocular lenses and in theskin of fish.[2] It has been established that its anionic form (gadusolate, Gad)is very efficient at neutralizing ROS and deactivating triplet excited statesof sensitizers.[3-4] Therefore, it is interesting to study the effect of Gad onthe 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, Gadand Ptr were irradiated at 350 ± 5 nm in a quartz cell of 1 cm of optical path,at room temperature. Control experiments with solutions containing only Trp andPtr, or Gad and Ptr, were carried out under the same conditions. The progressof the reaction was monitored by HPLC with UV detection 282 nm. It was observed that both Trp and Gad concentrationsdecrease as a function of the irradiation time, whereas the Ptr concentrationdoes not change within the analyzed period (60 min). Inpresence of Ptr and Gad, the concentration of Trp decreases around 20% but, inthe absence of Gad, the amino acid dissapears faster (ca. 61%). However, in deareated solutions containing Ptr and Gad nosignificant changes were observed in the absorption after irradiation for morethan 180 min. This behavior is similar to that found for Trp-Ptr solutions in theabsence of O2, indicating that Ptr photosensitizes the oxidation ofTrp in the presence of O2.[1]Accordingly, ours results suggest that Gad protects Trp from thephotosensitized oxidation by Ptr. Therefore, further studies should be directedto explore potential applications of this marine metabolite in the treatment ofskin disorders where Ptr are 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.