In Vitro Study of Biosynthesis of Protoporphyrin IX Induced By δ-Aminolevulinic Acid in Normal and Cancerous Cells of the Human Cervix

Abstract

Background δ-Aminolevulinic acid (ALA) is recognized as the starter in the biosynthesis of the heme group, the structural basis of cytochromes, chlorophylls, biliary pigments, and other porphyrins. It is the first intermediary in the biosynthesis of protoporphyrin IX (PpIX), and of the heme group. PpIX is present in low concentration in normal cells, and in high concentration in tumor cells. Methods The accumulation of protoporphyrin IX (PpIX) induced by δ-aminolevulinic 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 intra- and extracellular accumulation of PpIX in both HeLa and NHCE cells was 300 μg of ALA/mL, and for CaLo cells, 150 μg/mL. The viability of HeLa, CaLo, and NHCE cells exposed to ALA measured 81, 98, and 84%, respectively. 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 exposure to optimal concentrations of ALA. After the maximum level of PpIX accumulation was reached, there was a gradual decrease until there was only a small quantity. A statistically significant difference ( p <0.0001) was found in 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 and CaLo cells, 1:5. Conclusions These results are important for determining the usefulness of the sensitizer (PpIX).