Unscheduled DNA Synthesis in Human Skin After In Vitro Ultraviolet-Excimer Laser Ablation

DNA damage repaired by the excision repair system and measured as unscheduled DNA synthesis (UDS) was assessed in freshly excised human skin after 193 and 248 nm ultraviolet (UV)-excimer laser ablative incisions. Laser irradiation at 248 nm induced DNA damage throughout a zone of cells surrounding the ablated and heat-damaged area. In contrast, with 193 nm irradiation UDS was not detected in cells adjacent to the ablated area, even though DNA strongly absorbs this wavelength. Our results suggest that the lack of UDS after 193 nm irradiation is due to: (1) "shielding" of DNA by the cellular interstitium, membrane, and cytoplasm, (2) DNA damage that is not repaired by excision repair, or (3) thermal effects that either temporarily or permanently inhibit the excision repair processes.