Zinc ions can inhibit the proliferation of tumor cells and induce the apoptosis of cancer cells and commonly used in the topical treatment of conjunctivitis and trachoma. However, the effect of zinc ions on proliferation of human lens epithelial cells (LECs) is still unclear.

The purpose of the present study was to investigate the effect of ZnCl₂ on human LECs proliferation and its mechanism.

Human LECs strains, HLEB-3 cells, were routinely cultured and passaged. Different concentrations of ZnCl₂ was added into the medium to make the final concentrations to 5, 10, 20, 40 and 80 mg/L for 24, 48 and 72 hours, and the cultured cells without ZnCl₂ were as the control group. Viability of the cells was detected by MTT assay; the mitochondrial membrane potential (ΔΨm) was measured using the JC-1 assay kit; the proportion of the cells in different cycles was detected using flow cytometry; meanwhile, the expressions of bcl-2 gene and bcl-2 protein were assayed by real-time quantitative PCR (RT-qPCR) and enzyme-linked immunosorbent assay (ELISA) technique, respectively.

Cultured cells showed polygon-like with the tight arrangement in the control group. However, the number of the cells was obviously decreased with the irregular shape and disorder arrangement in different concentrations of ZnCl₂ groups. The viability of the cells was significantly reduced with the increase of ZnCl₂ concentrations and the lapse of active time (F_{concentrations}=173.949, P=0.000; F_time=16.997, P=0.000). The strong orange fluorescence in cellular membrane was seen in the control group, but the orange fluorescence was gradually weakened and green fluorescence was gradually enhanced with the increase of concentrations of ZnCl₂. The cell proportions in S phase and G₂/M phase were significantly raised and those in the G₀/G₁ phase were declined in different concentrations of ZnCl₂ groups in comparison with the control group (S phase: F=15.594, P=0.000; G₂/M phase: F=12.792, P=0.000; G₀/G₁ phase: F=43.366, P=0.000). The mean relative expression levels of bcl-2 mRNA in the cells were 1.00±0.00 in the control group, which were significantly higher than 0.32±0.13, 0.07±0.03, 0.14±0.05, 0.01±0.00 and 0.12±0.06 in the 5, 10, 20, 40 and 80 mg/L ZnCl₂ groups (all at P<0.01). The expressing levels of bcl-2 protein in the cells were (138.57±32.80) pg/mg, which were significantly higher than (79.20±5.70), (79.95±6.21), (61.02±10.74), (72.05±11.61) and (55.97±10.53) pg/mg in the 5, 10, 20, 40 and 80 mg/L ZnCl₂ groups (all at P<0.01).

ZnCl₂ can arrest the HLEB-3 cells in G₂/M phase and therefore suppresses the proliferation of HLEB-3 cells probably by reducing the ΔΨm and down-regulating the expression of bcl-2.

Zinc ion; Lens; Epithelial cell; Bcl-2 gene; Cell proliferation