Effects of additives on reaction of nucleosides with UV light in presence of uric acid and salicylic acid

Abstract

Recently, we reported that uric acid and salicylic acid are photosensitizers of the reaction of nucleosides with UV light via radical formation and energy transfer, respectively. In the present study, effects of 45 biologically relevant compounds on nucleoside reactions photosensitized by uric acid and salicylic acid were examined. When a mixed solution of 2'-deoxycytidine, 2'-deoxyguanosine, thymidine, and 2'-deoxyadenosine with uric acid was irradiated with UV light of a wavelength longer than 300 nm, all the nucleosides decreased. The addition of antioxidants suppressed the consumption of nucleosides. When the UV reaction of nucleosides was conducted with salicylic acid, thymidine decreased almost exclusively. Several antioxidants such as ascorbates, thiols, catecholamines, trans-2-hexen-1-ol, penicillin G, and NaHSO₃ enhanced the consumption of thymidine, although the other antioxidants suppressed it. The results suggest that antioxidants may be beneficial to protect against DNA damage by photosensitization via radical formation, but that several of them may be detrimental as they facilitate DNA damage by photo-sensitization via energy transfer.

Keywords: antioxidant; nucleoside; photosensitizer; salicylic acid; uric acid.

Fig. 1.

A UV transmittance spectrum of the longpass filter for wavelengths ranging from 200 to 400 nm. The percentage transmittance (%) was measured by a spectrophotometer at room temperature.

Fig. 2.

UV absorption spectra from 200 to 400 nm of the 16 compounds used as additives, which showed an absorbance value larger than 0.01 (a.u.) at wavelengths ranging from 300–800 nm. UV spectra were measured by a spectrophotometer for 1 mM additives in 100 mM potassium phosphate buffer of pH 7.4 at room temperature.

Fig. 3.

Schemes for possible roles of the antioxidants in the reaction of nucleosides with UV irradiation in the presence of uric acid and salicylic acid.