pH-Dependent formation of 5-aminolaevulinic acid-induced protoporphyrin IX in fibrosarcoma cells

pH-Dependent variations in the fluorescence intensity of 5-aminolaevulinic acid-induced 5-aminolaevulinic acid protoporphyrin IX (PP IX) were compared with the cell viability following light irradiation. The fluorescence intensity was determined by flow cytometry and the cell activity was investigated by a colorimetric 3-(4,5-dimethylthiazol-2-yl) -2,5-diphenyltetrazolium bromide (MTT) assay 24 h after photodynamic treatment. The results obtained by fluorescence measurements clearly showed that pH values of the incubation medium containing (5-ALA) below and above pH 7.4 led to a significant decrease in the fluorescence intensity. The viability of cells incubated with 0.6 mM 5-ALA in a medium at pH 6.0 was unaffected on exposure to light at lambda = 635 nm up to 15 J cm(-2). However, cells incubated at pH 7.3 (with the other treatment parameters the same) were nearly completely destroyed. In addition, depletion of intracellular PP IX was faster in physiological medium than in acidic medium. (C) 1997 Elsevier Science S.A.