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Aminolaevulinic acid (ALA) induced porphyrin biosynthesis and the resulting in vitro phototoxicity have been determined in both SV40 transformed Swiss mouse 3T3 fibroblasts and PtK2 epithelial cells. Both cell lines respond to the addition of exogenous ALA, producing porphyrin linearly with ALA concentrations up to 0.3 mM. Notably the only accumulating porphyrin detected by HPLC was PpIX. Although the levels of PpIX are both dependent on the time and concentration used, the final intracellular porphyrin concentration is dictated by the presence of serum. When ALA is added in medium containing 10% new born calf serum, 90 - 95% of the induced porphyrin appears in the incubation medium. In the absence of serum, the intracellular PpIX levels are maintained and only under these conditions can successful in vitro PDT be performed. Gel permeation chromatography has indicated that the afflux of PpIX is promoted by the low density and high density lipoproteins, with an unknown protein (mw < 66000) contributing significantly to the effect seen. It appears that this protein is present at very low concentrations in both foetal and new born calf serum.
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