Solar radiation exposure of dihydrobiopterin and biopterin in aqueous solution

ADRIANA IPIÑA; CAROLINA CASTAÑO; CAROLINA LORENTE; ANDRÉS H. THOMAS

Cordoba

Congreso; 16th International Congress on Photobiology; 2014

International Union of Photobiology

Dihydrobiopterin (H2Bip) and Biopterin (Bip) accumulate in the skin of patients suffering from vitiligo, which lack of melanin involves a deficient protection against UV radiation. H2Bip and Bip undergo photooxidation upon UV radiation and the former acts as a photosensitizer of biomolecules. This work, analyze the photochemical reactions of these compounds exposed to sunlight under outdoor conditions. H2Bip and Bip in aqueous solutions were exposed in a plataform at La Plata city (34.90ºS, 57.92ºW) from near Spring equinox to Summer solstice and the spectral solar irradiance was recorded with a high-resolution spectrometer. The photochemical reactions were followed by HPLC and UV-Vis spectrophotometry. Upon sun exposure, excitation of H2Bip leads to the formation of dimers and to its oxidation to Bip, which, in turn, is photooxidized into 6-formylpterin (Fop). Further excitation induces the oxidation of Fop to 6-carboxypterin, which is much more photostable than Bip and Fop and then it is accumulated in the solution. Rates of reactant consumption were determined under different environmental conditions and the corresponding quantum yields were calculated. We have demonstrated that solar radiation causes significant oxidation of the pterin derivatives investigated within a few minutes, even in cloudy days. Finally, the biological implications of our the results are discussed.