EGCG inhibits Cd2+-induced apoptosis through scavenging ROS rather than chelating Cd2+ in HL-7702 cells

Context and objective: Epigallocatechin-3-gallat (EGCG), the major catechin in green tea, shows a potential protective effect against heavy metal toxicity to humans. Apoptosis is one of the key events in cadmium (Cd²⁺)-induced cytotoxicity. Nevertheless, the study of EGCG on Cd²⁺-induced apoptosis is rarely reported. The objective of this study was to clarify the effect and detailed mechanism of EGCG on Cd²⁺-induced apoptosis.

Methods: Normal human liver cells (HL-7702) were treated with Cd²⁺ for 21?h, and then co-treated with EGCG for 3?h. Cell viability, apoptosis, intracellular reactive oxygen species (ROS), malondialdehyde (MDA), mitochondrial membrane potential (MMP) and caspase-3 activity were detected. On the other hand, the chelation of Cd²⁺ with EGCG was tested by UV-Vis spectroscopy analysis and Nuclear Magnetic Resonance (¹H NMR) spectroscopy under neutral condition (pH 7.2).

Results and conclusion: Cd²⁺ significantly decreased the cell viability and induced apoptosis in HL-7702 cells. Conversely, EGCG co-treatment resulted in significant inhibition of Cd²⁺-induced reduction of cell viability and apoptosis, implying a rescue effect of EGCG against Cd²⁺ poisoning. The protective effect most likely arises from scavenging ROS and maintaining redox homeostasis, as the generation of intracellular ROS and MDA is significantly reduced by EGCG, which further prevents MMP collapse and suppresses caspase-3 activity. However, no evidence is observed for the chelation of EGCG with Cd²⁺ under neutral condition. Therefore, a clear conclusion from this work can be made that EGCG could inhibit Cd²⁺-induced apoptosis by acting as a ROS scavenger rather than a metal chelating agent.