Quantification of DNA Repair Products in the Urine After Ultraviolet Radiation of the Skin

Purpose of the experiment The investigators know that DNA damage is formed in the skin by sun exposure of the thymine-dimer type. Many of these injuries are repaired and excreted through the urine.

The purpose of the study is to quantify DNA damage in the urine after ultraviolet (UV) irradiation of the skin in healthy subjects. The investigators would like to investigate which day after two different irradiation regimens the highest secretion of thymine dimers occurs. If the investigators establish such a test system, it will be possible to test potential photoprotective substances or potential photocarcinogenic substances.

Method of the experiment, design, and examination procedures The subjects (n = 16-20) are recruited by a post on Bispebjerg's hospital website. Based on this, subjects are divided into 2 groups of 8-10 people. Group 1 is irradiated 3 times with 1 standard erythema dose (SED). 1 SED corresponds to approx. 10 minutes sun around 13 pm on a good Danish summer day. Group 2 is irradiated once with 3 SED, which corresponds to approx. 30 minutes around 13 pm on a good Danish summer day. The irradiation is carried out on day 1 for group 2 and days 1, 2 and 3 for group 1.

Subjects are irradiated in a full-body UV cabin (Waldmann, Willing-Schwenningen, Germany) with 26 F85 / 100W UV6 tubes (290-350 nm, broad-spectrum). 13 seconds of illumination, equivalent to 1 SED. The subjects are standing in the cabin and have a screen on so that their eyes and face are not exposed to radiation. When irradiated, the subjects must only wear underwear, which for men are underpants/boxer shorts, while for women it is bras and panties. The experiment is performed between October and March, to avoid that the subjects do not simultaneously receive UV radiation from the sun and thus form DNA damage.

Subjects must collect morning urine in dispensed containers and must store it in their own freezer until the final visit. Morning urine (2x 50 mL) is collected before irradiation, called day 1, and even until day 8 after the last exposure, ie. day 10 for group 1 and day 8 for group 2. Before the first exposure, pigment and redness are measured on the subjects. Pigment and redness measurements are performed on the back, chest, and shoulder.