Aryl Hydrocarbon Receptor Activity in Patients Receiving Narrowband UVB Therapy

Narrowband UVB is used by dermatologists to treat atopic dermatitis and psoriasis. Although multimodal in its mechanism of action, the photo-oxidation of L-tryptophan to 6-formylindolo [3,2-b] carbazole, a potent Aryl Hydrocarbon Receptor (AHR) agonist, is proposed to play a role. This study aimed to assess AHR induction in patients treated with Narrowband UVB (NBUVB). 10 patients undergoing NBUVB therapy for psoriasis and atopic dermatitis had biopsies taken from a treatment site, with photo-protected buttock skin used as the control. Fitzpatrick skin types were one to three. Ages ranged from 29 to 82, with a median age of 63. The sex ratio was 4:6 (M: F). NBUVB was introduced at a commencing dose of 100 mJ with 20% increments three times weekly. Following 36 sessions of therapy, 4 mm punch biopsies were taken. Cytochrome P450 1A2 (CYP1A2) immunohistochemistry was used as a marker for AHR activity. Analysis was via Aperio Imagescope using Positive Pixel Count v9. Values for total intensity/mm2 were used to assess enzyme activity. A value of 45395360 was obtained at the control site and 5060956 at the treatment site with a p value of 0.12, which, although a positive result, fails to reach statistical significance. The interpretation of these results is complicated by the fact that FICZ is active at femtomolar concentrations, and a demonstration of a statistically significant effect on AHR induction via immunohistochemistry may be difficult.