Photo-induced inhibitory effect of titanium dioxide nanoparticles on a human epidermal squamous cell carcinoma cell line A431

Abstract

Objective To evaluate the inhibitory effect of photocatalytic titanium dioxide （TiO2）on the growth of a human epidermal squamous cell carcinoma cell line A431 and its mechanism. Methods Cultured A431 cells were classified into various groups to remain untreated （blank control group）, be treated with different concentrations （100, 200, 300, 400, 500, 600 mg/L） of TiO2 nanoparticles alone or in combination with ultraviolet （UV, main wavelength 253.7 nm, power 30 W, distance 30 cm, exposure duration 15 min） irradiation. After additional culture for different durations, methyl thiazolyl tetrazolium （MTY） assay was performed to evaluate cell growth, annexin V-fluorescein isothiocyanate/propidium iodide （PI） double staining to observe cell apoptosis, and Rho123 staining to determine mitochondrial transmembrane potential. Statistical analysis was earried out using SPSS 13.0 software. Analysis of variance （AOV）, t test and Student-NewmanKeuls （SNK） test were performed to assess the differences in these parameters between these groups. Results The growth of A431 cells was inhibited by pretreatment with TiO2 nanoparticles followed by UV irradiation, and the inhibitory effect was enhanced as the dose of TiO2 nanoparticles increased. As AOV and SNK test showed, there were significant differences in the growth inhibition rate among A431 cells treated with different concentrations of TiO2 nanoparticles at the three time points （24, 48 and 72 hours） after UV irradiation （n = 6, F = 21.54, 77.56, 20.27, respectively, all P 〈 0.05）. No statistical inhibition was observed in the growth of A431 cells treated with TiO2 nanopartieles alone compared with untreated A431 cells （all P 〉 0.05）. Photocatalytie TiO2 nanoparticles also induced the apoptosis but decreased the mitochondrial transmembrane potential in A431 cells. In detail, theapoptosis rate was 8.86% ± 0.22%, 11.72% ± 0.29% and 31.24% ± 0.78% in A431 cells treated with Ti02 nanoparticles of 100, 200, 400 mg/L followed by UV irradiation, respectively, compared to 2.69% ± 0.28% in the blank control group （n = 3, F = 256.61, P 〈 0.05）. Decreased mitochondrial transmembrane potential （expressed as total fluorescence intensity） was observed in A431 cells treated with Ti02 nanoparticles of 100, 200, 400 mg/L followed by UV irradiation compared with blank control group （758.48 ± 15.42, 676.60 ± 14.35, 557.71 ± 13.12 vs. 2943.65 ± 70.26, F = 208.57, P 〈 0.05, n = 3）, and SNK test also revealed statistical differences between these groups. Conclusions Ti02 nanoparticles combined with UV can inhibit the growth of but induce the apoptosis in A431 cells, which may be associated with the reduction in mitoehondrial transmembrane potential in A431 cells, while Ti02 nanoparticles alone show no inhibitory effect on the growth of A431 cells. Key words: Carcinoma, squamous cell; Nanocomposites; Cell line, tumor; Ultraviolet rays; Apoptosis; Membrane potential, mitochondrial