UVA-1 phototherapy, used in the management of psoriasis, atopic dermatitis and fibrosing skin disorders has been reported to mediate part of its therapeutic benefit via aryl hydrocarbon receptor (AHR) signalling. Accessibility to therapy remains limited and a cost-effective topical preparation permissive of UVA-1 transmission at therapeutic doses whilst offering photoprotection in the UVB and UVA-2 spectra and activity at the AHR would represent a notable therapeutic advance. The amino acid L-tryptophan absorbs maximally at 280 nm with absorbance falling rapidly to 310 nm potentially providing photoprotection in the UVB spectrum. In addition, this amino acid is photo-oxidized to 6-formylindolo3,2-b carbazole (FICZ), a potent endogenous ligand of the AHR and is thus a potential candidate for inclusion. Lecithin absorbs UV light in a broad band from 200 to 380 nm with peak absorbance at 235, 271 and 355 nm and has potential as a biodegradable and ecofriendly sunscreen with an efficacy equivalent to traditional sunscreens. A proof-of-concept study was performed to assess whether a topical solution of L-tryptophan formulated to favour the generation of FICZ on photoactivation demonstrated activity at the aryl hydrocarbon receptor (AHR) as assessed by the intensity of cytochrome P450 1A2 staining. Ten participants applied a trial agent consisting of 2% L-tryptophan, 30% sunflower lecithin, 3% polyvinyl alcohol, 20% ethanol, pH 5.8 followed by 36 sessions of progressively graduated sun exposure increasing to a total of 20 J/cm 2 as determined by UV integrator over a period 12 weeks. At the end of the trial, biopsies were taken from treated sites and assessed by the intensity of cytochrome P450 1A2 staining. Photo protected skin from the buttock was used as a control. An average baseline value of 53 488 923 units was obtained at the control site and 972 214 294 at the treatment site supporting the concept that this preparation displays activity at the AHR.
Rowland Noakes (Sun,) studied this question.