Mori M, Kobayashi H, Katsumura Y, Furihata C
Life Science Research Center, Shiseido Co., Ltd., 2-12-1 Fukuura, Kanazawa-ku, Yokohama-shi, Kanagawa 236-8643, Japan.
J Toxicol Sci. 2001 Feb;26(1):1-8. doi: 10.2131/jts.26.1.
Induction of unscheduled DNA synthesis (UDS) by 8-methoxypsoralen (8-MOP) plus ultraviolet A (UV-A) (PUVA) was investigated in the epidermis of female hairless mice by means of an in vivo--in vitro assay using a liquid scintillation counting method. Groups of three to five 8-week-old female hairless mice had 8-MOP applied once onto two areas of the back after stripping of the stratum corneum with adhesive tape to enhance skin penetration, and were irradiated with UV-A. Skin samples were taken and cultured in a medium containing [3H]thymidine with or without hydroxyurea (HU) for 2 hr. DNA of the epidermis was extracted, and the incorporation of [3H]thymidine into DNA and the DNA content were determined with a liquid scintillation counter and a fluorescence spectrophotometer, respectively. Induction of UDS was judged in terms of the UDS index [(the ratio of DNA synthesis in the presence of HU to that in its absence) x 100]. In a time-course study, the UDS index was increased at 1, 2 and 24 hr after 1 x 10(5) J/m2 UV-A irradiation with 0.001% 8-MOP, reaching the maximum level at 24 hr. In a dose-response study, it was significantly increased at the dose of 1 x 10(5) J/m2 of UV-A at 24 hr with 0.001% 8-MOP, but showed no significant change at the doses of 0.5 x 10(5), 2 x 10(5) and 4 x 10(5) J/m2. In a further study on the effect of varying the dose of 8-MOP, the UDS index was significantly increased at 0.001 and 0.002% 8-MOP at 24 hr after 1 x 10(5) J/m2 UV-A irradiation, reaching the maximum level with 0.002% 8-MOP. The increase of the UDS index in these studies was less than 3-fold. These results show that PUVA causes a small induction of UDS, which might be due to slow DNA excision repair over a long period.
采用液体闪烁计数法，通过体内 - 体外试验，研究了8 - 甲氧基补骨脂素（8 - MOP）加紫外线A（UV - A）（PUVA）对雌性无毛小鼠表皮中非常规DNA合成（UDS）的诱导作用。将三到五只8周龄的雌性无毛小鼠分为一组，用胶带剥去角质层以增强皮肤渗透性后，在背部的两个区域涂抹一次8 - MOP，然后用UV - A照射。采集皮肤样本，在含有[³H]胸腺嘧啶核苷的培养基中培养2小时，添加或不添加羟基脲（HU）。提取表皮DNA，分别用液体闪烁计数器和荧光分光光度计测定[³H]胸腺嘧啶核苷掺入DNA的情况和DNA含量。根据UDS指数[（存在HU时的DNA合成率与不存在HU时的DNA合成率之比）×100]来判断UDS的诱导情况。在一项时间进程研究中，用0.001% 8 - MOP进行1×10⁵ J/m² UV - A照射后1、2和24小时，UDS指数升高，在24小时达到最高水平。在一项剂量反应研究中，24小时时，0.001% 8 - MOP存在下，UV - A剂量为1×10⁵ J/m²时UDS指数显著升高，但在0.5×10⁵、2×10⁵和4×10⁵ J/m²剂量下无显著变化。在进一步研究8 - MOP剂量变化的影响时，1×10⁵ J/m² UV - A照射后24小时，0.001%和0.002% 8 - MOP时UDS指数显著升高，0.002% 8 - MOP时达到最高水平。这些研究中UDS指数的升高小于3倍。这些结果表明，PUVA引起UDS的诱导作用较小，这可能是由于长时间的DNA切除修复缓慢所致。
