Abstract
The risk of exposure to environmental UV such as sunlight has been one of the public greatest concerns because of its potent genotoxic hazard for the skin. The risk for human skin is currently estimated mainly by an empirical index of erythema, which is specifically detectable on UV-exposed skin. The erythema-based assessment has been useful for protection against UV, but cannot provide any quantitative prediction of the future effects of UV exposure because erythema induction is a threshold event that does not correlate linearly with the UV dose. To solve the problem, quantifiable indices which correlate more directly with the UV genotoxicity should have been introduced. For such indices, we adopted mutation, which has a direct correlation with the UV genotoxicity. Importantly, we utilized it from two aspects based on the analysis of mutation induction kinetics in the UV-exposed skin. The two indices of mutation are mutagenicity (the initial increment of mutant frequency) and mutation induction suppression (MIS), a skin-specific protective response to UV found in our previous study. With these indices, we determined a set of action spectra of UV genotoxicity and developed a UV risk estimation system for the skin. Based on the system, we actually estimated mutant frequencies (MFs) induced in the skin after one-hour exposure to the sunlight at noon on a clear summer day in Japan, using data on the spectral solar UV intensities, which are measured regularly by Japan Meteorological Agency and available online (http://www.woudc.org). The predicted MFs were found to become more reliable and accurate by the introduction of the MIS index and to show a good agreement with the observed values we directly measured before. (This study was carried out under the NIBB Cooperative Research Programs for the Okazaki Large Spectrograph, 10-501.)
