• Inhibition of UV radiation-induced DNA damage by a 5-methoxypsoralen tan in human skin.

      Young, A R; Potten, Christopher S; Chadwick, Caroline A; Murphy, G M; Cohen, A J; Photobiology Unit, Institute of Dermatology, St. Thomas's Hospital, London, UK. (1988)
      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.
    • Photoprotection and 5-MOP photochemoprotection from UVR-induced DNA damage in humans: the role of skin type.

      Young, A R; Potten, Christopher S; Chadwick, Caroline A; Murphy, G M; Hawk, J L; Cohen, A J; Photobiology Department, United Medical School, Guy's Hospital, London, U.K. (1991-11)
      Sites on previously unexposed buttock skin in 18 subjects (skin types I-V) were treated daily for 2 weeks with suberythemogenic doses of solar-simulated radiation (SSR) alone, SSR plus a UVB sunscreen, and SSR plus the same sunscreen with 5-methoxypsoralen at 30 ppm. The three sites of treatment (designated SSR, SSR/S, and SSR/S/5-MOP), and a control site that received no SSR or topical treatment, were challenged with 2MED SSR 1 week after the treatment had ceased. Biopsy samples, taken within 15 min after the challenge dose, were assessed for unscheduled DNA synthesis (UDS, interpreted as a measure of DNA damage), melanin deposition, and stratum corneum thickening. Within a given skin type, when compared with controls, the significant increase in either pigmentation or stratum corneum thickening was similar for SSR and SSR/S/5-MOP. SSR/S inhibited these endpoints. Compared with controls, UDS was significantly reduced in skin types III-V by SSR and in all skin types by SSR/S/5-MOP. SSR/S elicited no effect apart from minimal reductions in skin types IV and V. Thus, the increases in pigmentation and stratum corneum thickening seen in all skin types with SSR and SSR/S/5-MOP were accompanied by reduced UDS in all skin types with SSR/S/5-MOP but only in skin types III-V with SSR. These findings suggest that, although induced pigmentation and stratum corneum thickening may account in part for the reduction of UDS, qualitative differences in induced pigmentation may exist in skin types I-II between SSR and SSR/S/5-MOP treatments. The findings can also be interpreted to indicate that SSR/S/5-MOP treatment can afford protection against DNA damage from subsequent exposure to solar ultraviolet radiation. Risk-benefit considerations on the use of sunscreens with and without 5-MOP are discussed and the conclusion is drawn that the judicious use of 5-MOP sunscreens, particularly in skin types I-II, affords an alternative option to those seeking a suntan.