Effects of cadmium exposure on NRF2 signaling pathway in HepG2 cells

Objective To explore the effects of cadmium exposure on nuclear factor erythroid 2-related factor 2 (NRF2) signaling pathway in HepG2 cells.Methods The HepG2 cells were treated with cadmium chloride (CdCl₂) at dosages of 0,1,2.5,5,10,25,50,100,and 200 μmol/L for 24 hours and then the viability of the cells was measured with 3-(4,5-dimethylthiazol-2-yl)-5(3-carboxymethonyphenol)-2-(4-sulfophenyl)-2H-tetrazolium (MTS);the cells were treated with CdCl₂ (1,2,5,10,and 20 μmol/L) for 6 hours and the protein levels of NRF2 were determined with Western blot;the cells were treated with 10 μmol/L CdCl₂ for 2,4,6,12,and 24 hours and the mRNA levels of Nrf2 downstream genes glutamate-cysteine ligase catalitic subunit (GCLC),glutamate cysteine ligase modifier (GCLM),heme oxygenase 1 (HO1),and aldo-keto reductase family 1 member (AKR1C1) were determined with reverse transcriptase quantitative polymerase chain reaction (RT-qPCR);the cells were treated with 1,2,5,10,and 20 μmol/L CdCl₂ for 6 hours and the mRNA levels of Nrf2 downstream genes GCLC,GCLM,HO1,and AKR1C1 were determined by RT-qPCR.Results The cell viability significantly decreased with the increased concentration of CdCl₂ in HepG2 cells (P<0.05).Compared to that (0.60±0.01) of the control group,the expression levels of NRF2 protein significantly increased (0.65±0.01,1.37±0.04,1.94±0.05,2.24±0.07,and 2.22±0.05 in the cells with 1,2,5,10 and 20 μmol/L cadmium exposure (P<0.05 for all).Compared with those of the control group,the mRNA levels of NRF2 downstream genes of GCLC,GCLM,HO1,and AKR1C1 significantly increased (45.76±7.04,114.21±5.23,59.52±1.50,and 674.13±27.12) in the cells with 6 hours' cadmium exposure (P<0.05 for all).Compared with those of the control group,the mRNA levels of NRF2 downstream genes of GCLC and GCLM significantly increased (24.77±2.16 and 29.93±0.67) in the cells treated with 5 μmol/L cadmium,and those of HO1 and AKR1C1 also increased significantly (28.55±2.02 and 186.32±12.63) in the cells treated with 2 μmol/L cadmium (all P<0.05).Conclusion Cadmium exposure can activate NRF2 signaling pathway in HepG2 cell line.