DNA Damage in UV-irradiated Human Skinin Vivo: Automated Direct Measurement by Image Analysis (Thymine Dimers) Compared with Indirect Measurement (Unscheduled DNA Synthesis) and Protection by 5-methoxypsoralen

Abstract

The incidence of the various types of skin cancer in the general population has been increasing at an annual rate of 2-8% over the past 2 decades. In spite of considerable media coverage on the risk of skin cancer the acquisition of a suntan is still very popular. Thus the UV exposures required for tanning pose a serious carcinogenic risk, particularly to individuals who tan poorly. On the other hand, the presence of natural skin pigment, or the ability to tan easily can protect the skin against some of the harmful effects of subsequent UV exposures (Kollias et al. 1991). We have recently shown (Young et al. 1991) in human volunteers, using an indirect measurement of DNA damage (unscheduled DNA synthesis (UDS) detected by autoradiography), that a tan induced by UV in the presence of a UVB sunscreen (Parsol MCX) preparation containing 5-methoxypsoralen (5-MOP) is more effective at protecting the skin against a subsequent DNA-damaging challenge dose of UV than a tan induced by UV alone, particularly in individuals who tan poorly. No such protection was seen with the same sunscreen lacking 5-MOP. 5-MOP is an ingredient in natural citrus oils and in many other plants. Here we show the same pattern of protective action when measuring, for the first time, DNA damage directly using a monoclonal antibody to thymine dimers (a major category of DNA lesion induced by UV radiation) on fixed human skin sections and automated image analysis. There is a good correlation between UV exposure dose and the levels of thymine dimers in epidermal nuclei. The levels of thymine dimers (measured as absorption by the mean integrated optical density (IOD)) also correlated well with the levels of UDS (grains per nucleus). These findings are of importance in the comparative risk-benefit assessment of sunscreens with and without 5-MOP. The techniques described have applications for measuring other DNA lesions following UV and other exposures.

Geographic distribution of environmental factors influencing human skin coloration

“…Previous researchers proposed that maximum UVR, average UVR, or temporal patterns of UVR dose are related to incidents of sunburning. Radiation-induced damage is known to cause cancer (melanoma and basal-and squamous-cell carcinoma; Buzzell, 1993;Kollias et al, 1991;Longstreth et al, 1998;Potten et al, 1993;Zihlman and Cohn, 1988) and to damage sweat glands (Daniels, 1964;Pandolf et al, 1992). Both UVB and long-wave UVR (UVA) can cause deleterious effects in the skin, with those from UVA being mediated by reactive oxygen species (Cleaver and Mitchell, 2000;Roberts, 1977) This led to formulation of the hypothesis that reduced skin reflectance is mediated directly by exposure to UVR through reduced reproductive fitness.…”

Prospects for chemoprevention of cancer

“…In skin tumourigenesis models, ultraviolet radiation acts as a complete carcinogen [125]. Ultraviolet exposure of normal skin can cause DNA thymine dimers, or single strand breaks, which may result in permanent mutations maintained through DNA replication [126‐128]. In this model, the promotion from initiated cells into a preneoplastic state may take 10 years or longer.…”

Quantitation and Visualization of Ultraviolet‐Induced DNA Damage Using Specific Antibodies: Application to Pigment Cell Biology

“…We can visualize and measure CPDs and 6-4PPs in human or murine skin after irradiation with biologically relevant, suberythematous doses, for example 12.5-25 mJ/cm 2 UV-B or 0.5-1 MED solar-simulated radiation using this laser cytometric method. Potten et al (44) and Young et al (55) developed a similar method using TDM-1 and 64M-2 antibodies and immunohistochemistry with similar sensitivity. The sensitivity of this quantitative laser cytometric method is comparable to that of qualitative immunofluorescence with a polyclonal antibody to pyrimidine dimers (31).…”