Zn Supplement-Antagonized Cadmium-Induced Cytotoxicity in Macrophages In Vitro: Involvement of Cadmium Bioaccumulation and Metallothioneins Regulation

Cadmium (Cd) is a toxic metal leading to multiple forms of organ damage. Zinc (Zn) was reported as a potential antagonist against Cd toxicity. The present study investigates the antagonistic effect of Zn (20 μM) on Cd (20 or 50 μM) cytotoxicity in macrophages in vitro. The results shows that Cd exposure caused dose-dependent morphologic and ultrastructural alterations in RAW 264.7 macrophages. Zn supplement significantly inhibited Cd cytotoxicity in RAW 264.7 or HD-11 macrophages by mitigating cell apoptosis, excessive ROS output, and mitochondrial membrane depolarization. Notably, Zn supplement for 12 h remarkably prevented intracellular Cd2+ accumulation in 20 μM (95.99 ± 9.93 vs 29.64 ± 5.08 ng/106 cells; P = 0.0008) or 50 μM Cd (179.78 ± 28.66 vs 141.62 ± 22.15 ng/106 cells; P = 0.003) exposed RAW 264.7 cells. Further investigation found that Cd promoted metallothioneins (MTs) and metal regulatory transcription factor 1 (MTF-1) expression in RAW 264.7 macrophages. Twenty μM Zn supplement dramatically enhanced MTs and MTF-1 levels in Cd-exposed RAW 264.7 macrophages. Intracellular Zn2+ chelation or MTF-1 gene silencing inhibited MTs synthesis in Cd-exposed RAW 264.7 macrophages, which was accompanied by the declined expression of MTF-1, indicating that regulation of Zn on MTs was partially achieved by MTF-1 mobilization. In conclusion, this study demonstrates the antagonism of Zn against Cd cytotoxicity in macrophages and reveals its antagonistic mechanism by preventing Cd2+ bioaccumulation and promoting MTs expression.