Formation of 8‐hydroxy‐2′‐deoxyguanosine in the DNA of cultured human keratinocytes by clinically used doses of narrowband and broadband ultraviolet B and psoralen plus ultraviolet A

Psoralen plus ultraviolet A (PUVA) and narrowband ultraviolet B (UVB) are widely used in skin disease phototherapy. Recently, the efficacy of UVB therapy has been greatly improved by narrowband UVB, compared to conventional broadband UVB. The objectives of the current study were to evaluate the influence of UVB‐induced and PUVA‐induced oxidative stress on cultured keratinocytes. We analyzed 8‐hydroxy‐2′‐deoxyguanosine (8‐OH‐dG) in human keratinocytes (HaCaT cell line) using a high‐performance liquid chromatography system equipped with an electrochemical detector. Non‐irradiated human keratinocytes contained a baseline of 1.48 ± 0.22 (mean ± SD) 8‐OH‐dG per 10 6 deoxyguanosine (dG) residues in cellular DNA, which increased linearly with higher doses of UVB. When their abilities to induce 8‐OH‐dG were compared to each other, based on the minimal erythemal and therapeutically used doses, by irradiating them with broadband UVB at 100 mJ/cm 2 , the amount of 8‐OH‐dG increased to 3.42 ± 0.46 residues per 10 6 dG, while a narrowband UVB treatment at 1000 mJ/cm 2 , with biological effects comparable to those elicited by 100 mJ/cm 2 broadband UVB, increased it to 2.06 ± 0.31 residues per 10 6 dG. PUVA treatment, with 100 ng/mL 8‐methoxypsoralen and 5000 mJ/cm 2 UVA, increased the 8‐OH‐dG level to 4.52 ± 0.42 residues per 10 6 dG. When HaCaT cells treated with 2000 mJ/cm 2 narrowband UVB were cultured and the amount of 8‐OH‐dG was monitored in the living cells, 65.6% of the residues were repaired 24 h after treatment. Our study provides a warning that   widely used narrowband UVB and PUVA induce cellular oxidative DNA damage at the therapeutically used doses, although to a lesser degree than broadband UVB with the same clinically effective dose. ( Cancer Sci 2006; 97: 99  – 105)