In vitro study of biosynthesis of protoporphyrin IX induced by delta-aminolevulinic acid in normal and cancerous cells of the human cervix

Back:ground. delta-Aminolevulinic acid (ALA) is recognized as the starter i n the biosynthesis of the heme group, the structural basis of cytochromes, chlorophylls, biliary pigments, and other porphyrins. It is the first inter mediary in the biosynthesis of protoporphyrin IX (PpIX), and of the heme gr oup. PpIX is present in low concentration in normal cells, and in high conc entration in tumor cells. Methods. The accumulation of protoporphyrin IX (PpIX) induced by delta-amin olevulinic acid (ALA) was tested in two cervico-uterine cancer cell lines ( HeLa and CaLo), and in normal human cervical epithelial (NHCE) cells. Results. The optimal concentration of ALA that induced maximum levels of in tra- and extracellular accumulation of PpIX in both HeLa and NHCE cells was 300 mu g of ALA/mL, and for CaLo cells, 150 mu g/mL. The viability of HeLa , CaLo, and NHCE cells exposed to ALA measured 81, 98, and 84%, respectivel y. The optimal time for accumulation of PpIX, both intra- and extracellular , was 4 h for HeLa and NHCE cells and 5 h for CaLo cells per 24 h of exposu re to optimal concentrations of ALA. After the maximum level of PpIX accumu lation was reached, there was a gradual decrease until there was only a sma ll quantity. A statistically significant difference (p <0.0001) was found i n the accumulation of PpIX, depending on the concentrations of ALA used as well as between cervical cancer cell lines and NHCE cells (p <0.0001). The concentration ratio of PpIX for NHCE and HeLa cells was 1:7, and for NHCE a nd CaLo cells, 1:5. Conclusions. These results are important for determining the usefulness of the sensitizer (PpIX). (C) 1999 IMSS. Published by Elsevier Science Inc.