title: Characterization of cutaneous phototoxicity induced by topical alpha-terthienyl and ultraviolet A radiation.
abstract: Alpha-terthienyl (alpha-T), a phototoxic thiophene compound isolated from marigolds (Tagetes species), affects cell membranes and does not appear to induce cytogenetic damage. This study was undertaken to investigate topical delivery of alpha-T and characterize its cutaneous phototoxicity in combination with long-wave UV radiation (UVA) in comparison with locally (intradermal) administered alpha-T. Percutaneous penetration (PC) of 0.1% and 1% alpha-T in a 3% Azone gel vehicle was studied in guinea pig skin in vitro and quantitated by UV fluorescence microscopy. Dose-dependent PC of epidermis, adnexae, and superficial dermis was demonstrated in vitro. Alpha-terthienyl (0.1% and 1%) in this vehicle was applied topically in vivo and irradiated with 30 J/cm2 UVA at intervals of 10 min-24 h. Maximum sensitization was achieved with irradiation 1 h following drug application. The clinical response was dose-dependent consisting of erythema, edema, crusting, erosion, and inhibition of hair growth and was observed 72 h to 7 days postirradiation. A comparable dose-dependent phototoxic response was observed when 5-500 micrograms alpha-T were injected intradermally and irradiated with UVA. These results indicated that low-dose topical alpha-T in a nonirritating vehicle can rapidly produce cutaneous photosensitization. Topical alpha-T/UVA may provide a selective and safer alternative approach for the photochemotherapy of psoriasis and other cutaneous diseases.
mesh_terms: D000284:Administration, Oral; D000818:Animals; D005260:Female; D006168:Guinea Pigs; D007271:Injections, Intradermal; D010787:Photosensitivity Disorders / Q000209:etiology*; D013876:Thiophenes / Q000008:administration & dosage / Q000009:adverse effects*; D014466:Ultraviolet Rays / Q000009:adverse effects*
chemical_list: D013876:Thiophenes; C019101:alpha-terthienyl