Azathioprine treatment photosensitizes human skin to ultraviolet A radiation.

Centre for Cutaneous Research and Department of Dermatology, Institute of Cell and Molecular Science, Barts and The London, Queen Mary School of Medicine and Dentistry, 4 Newark Street, London, E1 2AT, UK. conalperrett@hotmail.com

BACKGROUND: Azathioprine is used to treat a variety of conditions and to prevent graft rejection in organ transplant recipients (OTRs). OBJECTIVES: To investigate clinically our previous finding that azathioprine metabolites interact with ultraviolet (UV) A radiation to form promutagenic oxidative DNA damage and to determine whether this may be causal or contributory to the development of excess skin cancers post-transplantation. METHODS: The clinical corollary of these data were investigated. Five patients were recruited and the minimal erythema dose (MED) for UVB, UVA and solar-simulated radiation (SSR) was determined for each person before, and at least 12 weeks after, starting azathioprine therapy. RESULTS: In all five patients azathioprine treatment was associated with an increased UVA and SSR sensitivity of the skin and a significant reduction in MEDs for UVA and SSR. We found no change in UVB-induced erythema or MED. In addition, we found that DNA from the skin of patients on azathioprine contains 6-thioguanine (6-TG). CONCLUSIONS: Our findings confirm the presence of DNA 6-TG in the skin of those taking therapeutic doses of azathioprine and provide support for the hypothesis that DNA damage occurs when DNA 6-TG interacts with UVA, resulting in abnormal cutaneous photosensitivity.

PMID: 18489587 [PubMed - indexed for MEDLINE]