Young A R, Potten C S, Chadwick C A, Murphy G M, Cohen A J
Photobiology Unit, Institute of Dermatology, St. Thomas's Hospital, London, UK.
Pigment Cell Res. 1988;1(5):350-4. doi: 10.1111/j.1600-0749.1988.tb00131.x.
Previously untanned buttock skin of 4 volunteers (skin type II; tan with difficulty as they sunburn easily) was treated with various sunscreen preparations and solar--simulated radiation (SSR) or SSR alone for 2 weeks. One week later, the treatment sites were challenged with a DNA-damaging dose of SSR--twice the minimal erythema dose (2 MED). Skin biopsy samples were assayed for the levels of unscheduled DNA synthesis (a measure of DNA damage), melanin distribution, and skin thickening. 5-Methoxypsoralen-containing sunscreen preparations plus SSR or SSR alone induced melanogenesis and increased the stratum corneum thickness, but only the former regimen afforded a high degree of protection against subsequent SSR-induced DNA damage. 5-Methoxypsoralen-free sunscreen preparations plus SSR induced negligible tanning, skin thickening, and photoprotection. These findings are relevant to the risk-benefit analysis of sunscreen preparations, especially in skin type II, as they provide evidence that a 5-methoxypsoralen-induced tan is protective against the DNA-damaging effects of solar UV radiation, and thus has the potential to reduce the carcinogenic risk of exposure to such radiation.
4名志愿者（皮肤类型为II型，容易晒伤，难以晒黑）先前未晒黑的臀部皮肤分别用各种防晒制剂处理，并接受太阳模拟辐射（SSR）或仅接受SSR照射，为期2周。一周后，对处理部位给予双倍最小红斑量（2MED）的DNA损伤剂量的SSR照射。对皮肤活检样本进行非定时DNA合成水平（一种DNA损伤的测量指标）、黑色素分布和皮肤增厚情况的检测。含5-甲氧基补骨脂素的防晒制剂加SSR或仅加SSR均可诱导黑色素生成并增加角质层厚度，但只有前一种方案能高度保护皮肤免受随后SSR诱导的DNA损伤。不含5-甲氧基补骨脂素的防晒制剂加SSR诱导的晒黑、皮肤增厚和光保护作用可忽略不计。这些发现与防晒制剂的风险效益分析相关，特别是对于II型皮肤，因为它们提供了证据表明5-甲氧基补骨脂素诱导的晒黑可保护皮肤免受太阳紫外线辐射的DNA损伤作用，因此有可能降低暴露于此类辐射的致癌风险。
