Generation of hydrogen peroxide primarily contributes to the induction of Fe(II)-dependent apoptosis in Jurkat cells by (-)-epigallocatechin gallate

Although (-)-epigallocatechin gallate (EGCG) has been reported to induce apoptosis in a variety of tumor cells, detailed mechanisms remain to be explored. In the present study, we investigated the antitumor mechanism of EGCG by using human T-cell acute lymphoblastic leukemia Jurkat cells. We focused on the involvement of reactive oxygen species, as we found previously that EGCG caused apoptotic cell death in osteoclastic cells due mainly to promotion of the reduction of Fe(III) to Fe(II) to trigger Fenton reaction, which affords hydroxyl radical from hydrogen peroxide [H2O2 + Fe(II) --> (OH)-O-. + OH- + Fe(III)]. EGCG (12.5-50 muM) decreased the viability of Jurkat cells and caused concomitant increase in cellular caspase-3 activity. Catalase and the Fe(II)-chelating reagent o-phenanthroline suppressed the EGCG effects, indicating involvements of both H2O2 and Fe(II) in the mechanism. Unexpectedly, epicatechin gallate (ECG), which has Fe(III)-reducing potency comparable with EGCG, failed to decrease the viability of Jurkat cells, while epigallocatechin (EGC), which has low capacity to reduce Fe(III), showed cytotoxic effects similar to EGCG. These results suggest that, unlike in osteoclastic cells, a mechanism other than Fe(III) reduction plays a role in catechin-mediated Jurkat cell death. We found that EGCG causes an elevation of H2O2 levels in Jurkat cell culture, in cell-free culture medium and sodium phosphate buffer. Catechins with a higher ability to produce H2O2 were more cytotoxic to Jurkat cells. Hydrogen peroxide itself exerted Fe(II)-dependent cytotoxicity. Amongst tumor and normal cell lines tested, cells exhibiting lower H2O2-eliminating activity were more sensitive to EGCG. From these findings, we propose the mechanism that make catechins cytotoxic in certain tumor cells is due to their ability to produce H2O2 and that the resulting increase in H2O2 levels triggers Fe(II)-dependent formation of highly toxic hydroxyl radical, which in turn induces apoptotic cell death.