Relationship of protoporphyrin IX synthesis to photodynamic effects by 5-aminolaevulinic acid and its esters on various cell lines derived from the skin

Background  5-Aminolaevulinic acid (ALA) and its esters act as precursors to the fluorescent photosensitizer protoporphyrin IX (PpIX) in photodynamic therapy (PDT). There is little information about how ALA and its esters induce PpIX synthesis and photodynamic effects in cell lines derived from the skin.
Objectives  We compared the amount of PpIX synthesis induced by ALA and its esters in skin cell lines, and evaluated the relationship of PpIX synthesis to photodynamic effects by ALA and its esters in vitro .
Methods  Four cell lines, including human epidermal keratinocytes (HEK), human dermal fibroblast (hF), A431, and TXM13 were used. Cell survival was evaluated by the MTT assay. Fluorescence spectroscopy was used to measure the amount of PpIX synthesis induced by ALA and its esters. Flow cytometry measured cell death induced by ALA- and its esters-mediated PDT.
Results  ALA and its esters were not toxic at concentrations lower than 2 mmol L⁻¹ in all cell lines. PpIX synthesis was dose-dependent at low doses (0·01–0·1 mmol L⁻¹), and ALA esters were more effective than ALA. Cell death occurred from necrosis rather than apoptosis just after light irradiation illumination on both ALA and its esters-treated cells. Cell death related more to PpIX synthesis than the irradiation light dose.
Conclusions  PpIX production by ALA and its esters was induced on both normal and malignant cell lines derived from the skin, and cell death of PDT responses is closely related to the amount of PpIX synthesis rather than to the irradiation dose.