Interactions Of EGCG And Zn²⁺ Or Cd²⁺ And Their Biological Behavior In Prostate Cancer PC-3 Cell

Zinc ion is indispensable to human health, and plays an important role in the occurrence of many diseases caused by the absence or excess of their intake. Cadmium is a kind of toxic metal to the human body and an inducer to cancers or tumors. However, previous papers reported that high doses of Cd²⁺, corresponding to acute exposure, could give rise to necrosis or apoptosis to the cells. As investigated before, the mortality caused by prostate cancer has been stood the second place among all diseases to be taken place in the human body. Also, from past reports total Zn²⁺ levels in the prostate are 10 times higher than in other soft tissues, and the ability of Zn²⁺ to be accumulated in the prostate is disappeared during prostate carcinogenesis. Practically, the metabolisms of Zn²⁺ and Cd²⁺ are in a balance in normal prostate glands. Moreover, if their balance was disturbed prostate diseases would be occurred. Depending on the epidemiology, cell scanning experiments in vitro and animal tests in vivo, it was primarily confirmed that EGCG could act as the prevention from prostate cancer. Meantime, the bioactivity of EGCG was significantly affected by metal ions. But so far, it has not been elucidated clearly about the interactions between Zn or Cd²⁺ and EGCG, and their behavior showed in androgen-insensitive human prostate tumor cells (PC-3) yet.In the present dissertation, effects of EGCG, Zn²⁺ and Cd²⁺ on the growth of PC-3 cells were investigated. The results showed that EGCG, Zn²⁺ and Cd²⁺ brought the changes of PC-3 cells morphologically, and the effects of Zn²⁺ and Cd²⁺ in the presence of EGCG were decreased. The proliferation of PC-3 cells was suppressed by EGCG, Zn²⁺ and Cd²⁺ in a dose-dependent manner. 80μmol/L Zn²⁺ could induce apoptosis to PC-3 cells, and 20μmol/L Cd²⁺ could give rise to their necrosis, but, addition of 80μmol/L EGCG could not cause their apoptosis. Also, EGCG, Zn²⁺ or Cd²⁺ could lead to a decrease in membrane fluidity of PC-3 cells as evidenced by a decrease in U/S. Some published papers suggested that the possible reasons for the biological behavior of EGCG against human cancer cells were due to the formation of complexes of EGCG with metal ions. In fact, whether complex of EGCG with Zn²⁺ was a main functional component against prostate cancer was not clear up to now. The objective of this investigation was to explore mechanism of interactions of EGCG with Zn²⁺ or Cd²⁺in the enhancement of Zn²⁺ or Cd²⁺ to inhibition of EGCG against PC-3 cells. MTT assay demonstrated that Zn²⁺ or Cd²⁺ increased the effects of EGCG against PC-3 cells, but their complexes decreased these kinds of effects obviously. From chemiluminescence tests, the free radical scavenging rate of mixture of EGCG and Zn²⁺ or Cd²⁺ was significantly different from the treatment with EGCG alone at 40, 80, 160μmol/L, but the free radical scavenging rate of Zn-EGCG or Cd-EGCG complex was not significantly different from EGCG except for Zn-EGCG complex at 160μmol/L. HPLC was employed to detect and quantify EGCG content in PC-3 cells. The results of HPLC analysis showed that Zn²⁺ and Cd²⁺ enhanced permeatability of EGCG to cytoplasm membrane, but Zn-EGCG or Cd-EGCG complex did not. Thus, we postulated that complex of EGCG with Zn²⁺ or Cd²⁺ was not able to the main functional component in coexisting system of EGCG with Zn²⁺ or Cd²⁺, which inhibited the growth of PC-3 cells.In order to explore the mechanism of EGCG, Zn²⁺ and Cd²⁺ against PC-3 cells, we chose the best exposure period (24h) and optimal concentration to investigate the effects of EGCG, Zn²⁺, Cd²⁺ and EGCG in the presence of Zn²⁺ or Cd²⁺ on the function of mitochondria involved ROS of PC-3 cells. The results indicated that EGCG, Zn²⁺ and Cd²⁺ could interact directly with mitochondria and induce PC-3 cells death through the mitochondria-mediated apoptotic pathway. ROS might be responsible for the EGCG- and Cd²⁺-mediated induction of apoptosis. EGCG, Zn²⁺ and Cd²⁺ could trigger oxidative stress of PC-3 cells to produce ROS, decrease membrane fluidity and destroy biomolecules.