Photodynamic properties of Sn-protoporphyrin: clinical investigations and phototesting in human subjects.
Emtestam L, Angelin B, Berglund L, Drummond GS, Kappas A.
Pure synthetic metalloporphyrins have been developed for experimental and clinical use as inhibitors of heme oxygenase, the rate limiting enzyme in the catabolism of heme to bilirubin. Tin (Sn)-protoporphyrin is one such compound, which potently suppresses bilirubin production and thus jaundice in animals and man. We have previously reported that this metalloporphyrin in conjunction with UVA might be useful as a treatment for psoriasis. To assess the photodynamic properties of Sn-protoporphyrin, 31 subjects were investigated with regard to photosensitivity. In all subjects, phototesting using UVB, UVA, and visible light as well as photopatch testing was performed. Our investigations revealed that 16 of the 31 individuals treated with Sn-protoporphyrin developed a mild photosensitivity, mainly erythema of the hands and face, and in some cases a mild conjunctivitis. The duration of this sensitivity, which in no case caused discomfort, was dose-dependent and ranged from several weeks to 1-3 months. After administration of Sn-protoporphyrin, lower thresholds were found for both UVA and visible light, but the sensitivity for UVB was normal and photopatch tests were negative. In summary, the photosensitivity observed during Sn-protoporphyrin administration was of limited duration and magnitude and did not occur in all subjects. Thus, the combination of photoactive synthetic metalloporphyrins and artificial light might prove to be useful as a regimen for the treatment of skin disease.