Cytotoxicity and genotoxicity of versicolorins and 5-methoxysterigmatocystin in A549 cells

Aspergillus versicolor and A. flavus are primary colonizers in damp dwellings, and they produce sterigmatocystin (ST) and aflatoxin B1 (AFB(1)), respectively. These hepatotoxic and carcinogenic mycotoxins and their precursors and derivates possess a furofuran ring, which has proven responsible for their toxicity. The aim of this study was to investigate the cytotoxicity and genotoxicity of versicolorin A (VER A) and versicolorin B (VER B), as the furofuran precursors of aflatoxins and ST, and of 5-methoxysterigmatocystin (5-MET-ST), a methoxy derivative of ST, in human adenocarcinoma lung cells A549. The IC50 values of the tested compounds were obtained by the cell proliferation MTT test as follows: 109 +/- A 3.5 mu M (VER A), 172 +/- A 4 mu M (VER B) and 181 +/- A 2.6 mu M (5-MET-ST). The comet assay and micronucleus test were used to assess their genotoxic potential after 24 h of treatment with concentrations corresponding to A1/2 and A1/4 IC50 in comparison with AFB(1) and ST, applied in concentrations corresponding to A1/2 IC50, as previously determined in A549 cells. DNA damage parameters assessed by the comet assay were tail length, tail intensity and tail moment, while the level of DNA damage in the micronucleus test was evaluated by the number of formed micronuclei (MN), nuclear buds (NB) and nucleoplasmic bridges (NPB) in 1,000 binucleated cells. Considering the three comet parameters, all applied toxins exerted significant DNA damage compared to the control, while ST and VER B produced the highest DNA damage. All toxins provoked a statistically significant increase in MN, and a slightly decreased formation of NB and NPB. AFB(1), ST and 20 mu M VER A showed a statistically significant increase in all three micronucleus parameters compared to the control, and the highest increase in the number of MN occurred in cells treated with 50 mu M VER A. The differences between results obtained by the micronucleus test and comet assay could be explained by the fact that the micronucleus detects irreversible DNA damage, which is usually correlated with the previously determined cytotoxic potential of the AFB(1) precursors.