Prevention of ornithine decarboxylase induction in Ehrlich ascites, tumor cells by tea polyphenols

Green tea extract and some components of green tea are known to inhibit carcinogenesis. However, the mechanisms by which green tea extract exerts its anticarcinogenic effect are not yet clearly understood. We have examined the effect of tea polyphenols on polyamine metabolism and the mechanism of its antitumor activity in Ehrlich ascites tumor cells, Ornithine decarboxylase (ODC) activity was measured by estimating the release-of (CO2)-C-14 from L[1-C-14] ornithine, The amount of ODC mRNA was measured by Northern-blot analysis, The polyphenols decreased DNA synthesis and cell viability in a dose-dependent manner, The increase in ODC activity caused by changing the medium was inhibited by adding tea polyphenols, The inhibition of the enzyme was dependent on the structure of tea polyphenols. (-)-epigallocatechin and (-)- epigallocatechin gallate were effective,, but(+)-catechin, (-)-epicatechin and (-)-epicatechin gallate did not inhibit ODC; induction, suggesting that pyrogallol-type catechins inhibit the enzymic activity of ODC whereas catechol-type catechins are less inhibitory, ODC was : not inhibited by tea polyphenols when they were added to the Culture medium 2h after a change to fresh medium. Incubating the cells for 4h with tea polyphenols then washing them out did not recover ODC activity. The ODC mRNA level in the cells treated with green tea extract was comparable to that in the control cells, These results confirm that green tea extract inhibits ODC induction dose-dependently in Ehrlich ascites tumor cells and that the inhibition of its induction was dependent on the structure of the tea polyphenols, We found that the tea polyphenols caused a marked decrease in ODC activity with no detectable effect on ODC mRNA levels in the cells, suggesting that tea polyphenols inhibit ODC induction at the post-transcriptional level.