Reduction of cutaneous photosensitivity by application of ointment containing ferrous or cobaltous ions concomitant with the use of topical protoporphyrin IX precursors

Abstract

5-Aminolevulinic acid (ALA) or its methyl ester mediated photodynamic therapy (PDT) is the most widely practiced form of PDT in dermatology. One of the advantages of topical PDT is that undesirable photosensitization lasts only for 24-48 h. However, patients are still sensitive in the areas where the cream has been applied, and are advised to avoid exposure to the sun and other light sources for at least 40 h after ALA-PDT. Therefore, the main aim of this work is to improve post-treatment procedures for increasing patient's comfort. The present study was carried out to investigate clearance of protoporphyrin IX (PpIX) in the presence of metal ions in the cream applied on healthy skin of mice in vivo. The photosensitizer PpIX was induced in normal mouse skin by topical application of ALA. Fluorescence spectroscopy was used to study porphyrin kinetics. Topical application of ferrous, cobalt or zinc sulphate significantly diminished the fluorescence of PpIX in mouse skin. These results show that the clearance kinetics of PpIX observed after exogenous application of ALA are determined by the conversion of PpIX into haem, and not by the clearance of PpIX from the body. Application of a vehicle containing ferrous or cobalt sulphate after PDT might be an approach in clinical practice for the reduction of cutaneous photosensitivity and elimination of undesirable photoreactions in skin and lesions.