E1A-3Y1 CELL-SPECIFIC TOXICITY OF TEA POLYPHENOLS AND THEIR KILLING MECHANISM

To screen carcinostatic components in foodstuffs, the toxicity of tea polyphenols was compared between rat 3Y1 diploid fibroblasts and a variety of their virally transformed cells. Among tea polyphenols tested, epigallocatechin gallate killed 3Y1 cells transformed by E1A gene of human adenovirus type 12 (E1A-3Y1 cells) at a 100 times lower concentration than the parental 3Y1 cells. Epigallocatechin gallate also exerted a strong E1A-3Y1 cell-specific toxicity, while epicatechin and epicatechin gallate did not. When the activity of three antioxidant enzymes was compared between 3Y1 and its transformants, catalase activity was markedly low in the latter, especially in E1A-3Y1 cells, and the substrate of the enzyme, hydrogen peroxide, exerted a toxicity specific to this cell line. Then the inhibitory activities of various chemicals on E1A-3Y1 cell-specific toxicity of phospholipids or catechol were examined. Among lipoxygenase inhibitors, all of the polyphenolic compounds inhibited the toxicity of phospholipids, but not a nonpolyphenolic inhibitor (clofibrate). Two phospholipase A,inhibitors (dexamethasone and quinacrine) did not inhibit the toxicity. These results indicate that the triphenol structure of the B ring is essential for the E1A-3Y1 cell-specific toxicity of tea polyphenols, and that the decrease in catalase activity is partially responsible for the higher sensitivity of E1A-3Y1 cells against the polyphenols. The inhibitory effect of polyphenolic lipoxygenase inhibitors is ascribed at least in part to their antioxidant activities.