Seven in silico models have been used to assess the prediction accuracy of chemical compound carcinogenicity. More than 1500 compounds with experimental values have been used to evaluate the models. Here we review the application of these models for toxicity prediction and their advantages and disadvantages, discussing the different approaches underlying the models and their main critical points. Some models have fewer false negatives while others are better at avoiding false positives. Since carcinogenicity is typically evaluated using a series of studies, identification of a strategy using one, or preferably a battery of in silico models, could reduce the number of animal studies needed.
Literature data on Chromium show that trivalent chromium has low acute and long term toxicity whilst hexavalent chromium is acutely toxic and produces long term effects on hematological parameters and liver. Continuous exposure to high concentrations of hexavalent chromium in drinking water results in intestinal tumors in mice but not rats. However, evidence of the carcinogenic potential of chromium has been demonstrated in rats but not consistently in mice. Cr (III) organic complexes (chromium picolinate) did not show evident adverse effects after repeated oral exposure. Both in vitro and in vivo data show that trivalent chromium is not genotoxic whilst hexavalent chromium is genotoxic. Chromium has been shown to affect sperm, estrous cycle and fetal development. Human toxicity data reveals mixed results but there is some evidence that hexavalent chromium can increase the risk of cancer. Data on Nickel show that nickel soluble compounds (nickel sulphate, nickel chloride or nickel nitrate) have acute and long term toxicity and produce oxidative stress and long term effects on liver. Less soluble compounds (nickel sulfides or nickel oxides) are less toxic. Nickel shows genotoxic effects both in vitro and in vivo. Only a limited number of studies on carcinogenic effects after oral exposure to nickel compounds are available. These studies showed no neoplastic effects in rats after oral administration. Nickel has been shown to affect sperm, live litter size and post-implantation loss. Teratogenic effects are reported on Amphibian embryos. Nickel can affect neurodifferentiation, the T-cell system and suppress the activity of natural killer cells. Human data reveals that nickel is excreted in the urine following oral exposure and that this increases with increasing age. There is some evidence that nickel might promote oral cancer etiology but no clear evidence that nickel can increase the risk of respiratory cancer.
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