Department of Biosciences at Novum, Karolinska Institute, Huddinge, Sweden

Correspondence: Dr Kari Hemminki, Department of Biosciences at Novum, Karolinska Institute, 141 57 Huddinge, Sweden. Email: kari.hemminki@cnt.ki.se

Received 27 June 2000; Revised 30 March 2001; Accepted 2 April 2001.

Abstract

Cyclobutane thymidine dimer (T=T) is the major DNA photoproduct formed in human skin after solar radiation. We have developed a ³²P-postlabeling method suitable for quantitating T=T in human urine with a detection limit of about 0.5 fmol per 10 l urine. The method was used in the present study to measure the daily T=T urinary level of two volunteers over a 15 d period, including frequent sun exposures ranging from 0 to 5 h daily. T=T was not detected before or immediately (4 h) after the initial sun exposure but was first observed in urine samples collected 18 h after the initial exposure. Thereafter, urinary T=T levels gradually increased up to a peak reached about 3 d after the maximum sun exposure. The levels decreased during the following days but were still detectable 8 d after the last sun exposure. About 70–75% decrease in excreted T=T was observed after 8 d. The T=T levels measured in urine were lower but in the same order of magnitude as the levels expected after a theoretical calculation based on previous published results and reasonable assumptions. This study shows the occurrence of cyclobutane thymidine dimers in human urine after skin exposure to solar radiation.