Catalase contents in cells determine sensitivity to the apoptosis inducer gallic acid

Gallic acid (3,4,5-trihydroxybenzoic acid, GA) is known to induce apoptosis in cancer cells at lower IC50 values compared with values for normal cells . Apoptosis is inhibited completely by the addition of conditioned medium f rom cultured hepatocytes, whereas it is not prevented by conditioned media from tumor cells. We therefore studied the reason for the different respons e to GA-induced apoposis. GA-induced dRLh-84 cell death was completely abol ished by the addition of peroxisome or cytosol as well as conditioned mediu m from primary cultured rat hepatocyte. As GA-induced cell death is known t o be mediated by reactive oxygen species (ROS) and intracellular Ca2+ we de termined the type of ROS generated by GA and found that GA generated hydrog en peroxide in culture medium. The addition of hydrogen peroxide generated by GA induced cell death in dRLh-84 cells. These results suggest that GA-in duced cell death is mediated by hydrogen peroxide. On the other hand, the i nhibitory activity of hepatocyte medium on GA-induced cell death was comple tely abolished by anti-catalase antibody. When the amount of catalase antig en was determined by Western blotting analysis, conditioned medium and the cytoplasm of hepatocytes contained high concentrations of catalase. Conditi oned media from various tumor cell lines did not contain catalase, and the cytoplasm contained only low levels of catalase. These results show that GA -sensitive cells, including various tumor cells, produce only small amounts of catalase and secreted little enzyme into media, suggesting a lack of pr otective machinery against GA. In contrast, GA-insensitive cells, including hepatocytes, produce large amounts of catalase and release it in medium, r esulting in the development of insensitivity to GA. In conclusion, catalase contents in cells determine different sensitivity to GA.