Introduction
Exposure of skin to solar ultraviolet radiation (UVR) induces the formation of thymidine dimers in DNA, serving as a biomarker for UVR exposure. Traditional analysis methods, like 32P-postlabeling, have been replaced by simpler LC-MS/MS techniques (1,2).
Aims
In this study, the impact of dose-delivery and exposed area on thymidine dimer excretion was investigated. Part 1 sought to determine if the administration of UVR dose influences thymidine dimer excretion by comparing the excretion after a single dose of 3 standard erythema doses (SED) with three doses of 1 SED given on consecutive days. Part 2 aimed to assess how the excretion of thymidine dimers is affected by the amount of clothing worn during exposure to 2 SED on 3 consecutive days.
Methods
Volunteers (n=16, part 1), (n=30, part 2) were exposed to UV6 tubes emitting 66% UVA and 34% UVB radiation. Morning urine samples were collected daily up to 8 days post-exposure and analyzed using LC-MS/MS. In Part 1, all volunteers were full body exposed. In Part 2, volunteers were divided into three groups with approximately 75%, 60%, or 45% exposed body surface area. Pigmentation and erythema values were measured using skin reflectance.
Results and Discussion
In Part 1 significantly higher levels of thymidine dimers were found in the group receiving a single dose of 3 SED compared to those receiving three doses of 1 SED (median 4325 ng vs. 730 ng, p=0.001). In Part 2, significant correlations were observed between thymidine dimers in urine and body surface area exposed (r2=0.20, p=0.012), as well as thymidine dimers and change in erythema (r2=0.38, p=0.00026).
Conclusion
In conclusion, receiving a single high dose of UVR results in higher thymidine dimer excretion compared to multiple lower doses. Additionally, there is a correlation between body surface area and excreted thymidine dimers in urine.