Time kinetics of cyclobutane pyrimidine dimer formation by narrowband and broadband UVB irradiation

Abstract

BackgroundMaximum cyclobutane pyrimidine dimer (CPD) formation in the skin induced by ultraviolet B (UVB) irradiation is thought to occur within a few minutes and is immediately decreased by the DNA repair system. ObjectiveWe evaluated the time course and differential effects of narrowband (NB-UVB) and broadband (BB-UVB) UVB on CPD formation. MethodsWe investigated CPD formation at various time-points in vivo, from 3 min to 72 h, after UVB irradiation using 2 mouse strains, C57BL/6 J and BALB/c. The backs of the mice were shaved and irradiated with NB-UVB or BB-UVB. Skin specimens were obtained and stained with anti-CPD antibody. Positive signals in the epidermis were measured using ImageJ. DNA was extracted from the isolated epidermis and subjected to quantitative CPD analysis by enzyme-linked immunosorbent assay (ELISA). ResultsCPDs induced by UVB irradiation (1 minimum erythemal dose) in epidermal skin were detected in the nucleus. Although the CPD levels increased immediately after irradiation (3 min), the highest level was detected at 1 h and the increase lasted 24–48 h after irradiation. BB-UVB tended to induce greater CPD levels than NB-UVB in both mouse strains. The ELISA showed similar results. ConclusionsCPDs were induced immediately after UV irradiation, with the maximum level observed 1 h after irradiation. BB-UVB irradiation tended to induce greater levels of CPD formation. In addition to the direct effects of UVB, the presence of CPDs in hair follicles, which were not irradiated by UVB, suggests that reactive oxygen species are also involved in CPD formation in the skin.