5-Aminolevulinic acid induced lipid peroxidation after light exposure on human colon carcinoma cells and effects of α-tocopherol treatment

This work relates to studies on modes of phototoxicity by protoporphyrin (PpIX) after incubation of 5-aminolevulinic acid (5-ALA) on cultured cells. Lipid peroxidation in the 5-ALA incubated primary adenocarcinoma cells from the rectosigmoid colon (WiDr cells) was determined by measurement of protein-associated thiobarbituric acid reactive substances (TBARS). TBARS were increased 2-fold in cells treated with 2 mM 5-ALA for 3.5 h in serum enriched medium. After illumination of 5-ALA incubated cells, TBARS were formed in a light dose dependent manner. TBARS analysis were compared with high-performance liquid chromatography (HPLC) analysis of malondialdehyde, and results indicate that 90% of the thiobarbituric reactive substances were due to malondialdehyde. Pretreating WiDr cells with α-tocopherol for 48 h inhibits the cytotoxic effect of 5-ALA and increases 5-fold the light dose needed to kill 50% of the cells. Pretreatment with α-tocopherol shows a considerable decrease (about 80%) on TBARS formation after illumination. The cellular content of α-tocopherol was determined by HPLC and found to be 15.3 pmol/106 cells.