Cylindrospermopsin (CYN), a cyanotoxin produced by certain freshwater cyanobacteria, causes human intoxications and animal mortalities. CYN is a potent inhibitor of protein- and glutathione-synthesis. Preliminary evidence for in vivo tumor initiation has been found in mice but the mechanism remains unclear. Several in vitro and in vivo studies demonstrate that CYN is genotoxic and requires metabolic activation. In the present study, the genotoxicity of CYN was assessed in human hepatocyte and enterocyte cell lines, which are models for CYN target organs. The cytokinesis-block micronucleus assay was conducted on liver-derived HepaRG cells and colon-derived Caco-2 cells. Each cell-type was exposed to CYN in both the differentiated and the undifferentiated states, and both with and without the cytochrome P450 inhibitor, ketoconazole, to determine the involvement of metabolism in CYN genotoxicity. CYN increased the frequency of micronuclei in binucleated cells (MNBNC) in both Caco-2 and HepaRG cells. Moreover, ketoconazole reduced both the genotoxicity and cytotoxicity caused by CYN. Our results confirm the involvement of metabolic activation of CYN in mediating its toxicity and suggest that CYN is progenotoxic.
Genetic toxicity information is critical for the safety assessment of all xenobiotics. In the absence of carcinogenicity data, genetic toxicity studies may be used to draw conclusions about the carcinogenicity potential of chemicals. However, current in vitro assays have many limitations as they produce a high rate of irrelevant positive data and possible false negative data due to the weakness of the in vitro models used. Based on the knowledge that the majority of human genotoxic carcinogens require metabolic activation to become genotoxic, it is necessary to develop in vitro cell models that mimic human liver metabolism to replace the use of liver S9 fraction, which, though helpful for predicting the potential carcinogenicity of chemicals in rodents, is questionable in humans. We therefore investigate whether the recently described human hepatoma HepaRG cells, which express the major characteristics of liver functions similarly to primary human hepatocytes, could be a suitable model for human genotoxicity assessment. We determine the performance of comet and micronucleus assays in HepaRG cells to predict in vivo genotoxins based on the list of compounds published by European Centre for the Validation of Alternative Methods (ECVAM). Twenty compounds were tested in HepaRG cells with comet and micronucleus assays over a 24-h period. The specificity, the sensitivity, and the accuracy of the two tests were determined. We found that the comet assay had higher specificity (100%) than the micronucleus (MN) test (80%), whereas the latter was far more sensitive (73%) than the former (44%), resulting nonetheless in an accuracy of 72% for the comet assay and 75% for the MN test. Taken together, our data suggest that the HepaRG cell line can be of use in genetic toxicology and that efforts to develop competent human liver cell models should be increased.
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