Systemic photodynamic therapy with aminolevulinic acid induces apoptosis in lesional T lymphocytes of psoriatic plaques

Photodynamic therapy (PDT) is a recently approved treatment modality that involves the sequential administration of a photosensitizer or its precursor and light to generate singlet oxygen for treating diseased tissue. The use of topical aminolevulinic acid (ALA) and blue light for nonhypertrophic actinic keratoses currently represents the only approved dermatologic application for PDT in the U.S.A. ALA is a photosensitizer precursor that is metabolized by cells into protoporphyrin IX (PpIX), which can be subsequently activated by visible light. PDT with topical ALA has been shown to improve psoriasis, but post-treatment hyperpigmentation as well as inconsistent clinical responses despite repeated PDT sessions have limited the development of this treatment approach for psoriasis. Furthermore the use of topical PDT photosensitizers becomes somewhat impractical for treating larger body surface areas in patients with extensive psoriasis. We have recently shown that oral administration of ALA induces preferential accumulation of PpIX in psoriatic plaques. The objectives of this study were to evaluate the effects of PDT with blue light on psoriatic plaques after systemic ALA administration as well as to determine whether systemic ALA-PDT induces apoptosis in lesional T lymphocytes. It has been suggested that induction of apoptosis in lesional T lymphocytes may be indicative of longer remission time following treatment of psoriasis.