Uric Acid as a Photosensitizer in the Reaction of Deoxyribonucleosides with UV Light of Wavelength Longer than 300 nm : Identification of Products from 2'-Deoxycytidine

Suzuki Toshinori, Ozawa-Tamura Atsuko, Takeuchi Miyu, Sasabe Yuriko

doi:10.1248/cpb.c21-00501

<p>DNA reacts directly with UV light with a wavelength shorter than 300 nm. Although ground surface sunlight includes little of this short-wavelength UV light due to its almost complete absorption by the atmosphere, sunlight is the primary cause of skin cancer. Photosensitization by endogenous substances must therefore be involved in skin cancer development mechanisms. Uric acid is the final metabolic product of purines in humans, and is present at relatively high concentrations in cells and fluids. When a neutral mixed solution of 2′-deoxycytidine, 2′-deoxyguanosine, thymidine, and 2′-deoxyadenosine was irradiated with UV light with a wavelength longer than 300 nm in the presence of uric acid, all the nucleosides were consumed in a uric acid dose-dependent manner. These reactions were inhibited by the addition of radical scavengers, ethanol and sodium azide. Two products from 2′-deoxycytidine were isolated and identified as N⁴-hydroxy-2′-deoxycytidine and N⁴,5-cyclic amide-2′-deoxycytidine, formed by cycloaddition of an amide group from uric acid. A ¹⁵N-labeled uric acid, uric acid-1,3-¹⁵N₂, having two ¹⁴N and two ¹⁵N atoms per molecule, produced N⁴,5-cyclic amide-2′-deoxycytidine containing both ¹⁴N and ¹⁵N atoms from uric acid-1,3-¹⁵N₂. Singlet oxygen, hydroxyl radical, peroxynitrous acid, hypochlorous acid, and hypobromous acid generated neither N⁴-hydroxy-2′-deoxycytidine nor N⁴,5-cyclic amide-2′-deoxycytidine in the presence of uric acid. These results indicate that uric acid is a photosensitizer for the reaction of nucleosides by UV light with a wavelength longer than 300 nm, and that an unidentified radical derived from uric acid with a delocalized unpaired electron may be generated.</p>

Uric Acid as a Photosensitizer in the Reaction of Deoxyribonucleosides with UV Light of Wavelength Longer than 300 nm : Identification of Products from 2'-Deoxycytidine

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