DNA Repair in Skin of Lupus Erythematosus Following In Vivo Exposure to Ultraviolet Radiation

The in vivo repair of pyrimidine dimers induced in the DNA of skin of 9 patients diagnosed as systemic or discoid lupus erythematosus (LE) was measured. A small area of the buttock was exposed to radiation emitted from a Burdick UV-800 sunlamp. The number of pyrimidine dimers was measured by incubating the epidermal skin DNA with UV-specific endonuclease and sedimenting the DNA through alkaline sucrose gradients. The initial number of dimers induced following sunlamp exposure was 7.6 ± 1.8 per 108 daltons DNA. The level of photorepair was measured by illuminating an area of the skin with > 450-nm radiation immediately following sunlamp exposure. We found that 56.5 ± 9.5% of the dimers are photorepaired with 5 min of illumination. Excision repair was measured in an area of the skin covered for 2 and 24 h postirradiation. Approximately 44 and 81% of the dimers induced immediately following sunlamp exposure were removed at these respective times. These observations in LE are similar to those observed in the skin of normal individuals.