Estimation of cytotoxicity to HEP-G2 cells of 255 environmental pollutants and water using QSAR (Quantitative Structure-Activity Relationship)

Statistical treatment of cytotoxicity in Ames bacterial reverse mutation assays can provide additional structure–activity relationship information

The bacterial reverse mutation assay, that is, the Ames test, measures mutations that reverse the inactivation of a gene involved in the synthesis of either histidine in Salmonella bacteria or tryptophan in Escherichia coli. The classic dose–response curve of an Ames assay plots number of reverse mutations (“revertants”) on the y-axis versus dose of the test chemical on the x-axis. Frequently, the dose–response curve resembles a parabola with a linear initial slope resulting from the accumulation of mutations, which transitions to a downward curvature resulting from cell killing (cytotoxicity) at increasingly higher doses of the test chemical. For regulatory purposes, a positive Ames test is usually considered as induction of twice the number of reverse mutations above background levels. For research purposes, the potency of the mutagenic response can be calculated from measuring the initial slope of the mutagenic response. This initial slope can be calculated in a manner that disentangles the downward pull on the initial slope value provided by the initiation of cytotoxicity. For a dose–response curve resembling a parabola, both the initial positive slope representing mutagenicity and the secondary negative slope representing cytotoxicity can be calculated from the same dose–response curve. The Ames test is the most commonly conducted genotoxicity assay. When a series of molecular congeners are assayed in the Ames test for mutagenicity, additional consideration of the cytotoxicity can provide important structure–activity relationship information.

Prediction of genotoxicity of various environmental pollutants by artificial neural network simulation

In order to evaluate human carcinogenic risks, genotoxicity data such as animal cancer bioassay are often not available. In this study, to assess the relevance of indicator of carcinogenic risks, we used the "molecular diversity approach" to estimate the genotoxicity based upon Salmonella genotoxicity test using the umu test and systemic toxicity data of the 82 environmental chemicals predicted by neural network simulation. The 82 environmental chemicals were randomly selected for this study according to the production and usage in Japan. Even in this challenging trial for QSTR (Quantitative Structure Toxicity Relationship) study, approaches using artificial neural networks can account for about 94% of the variation in the genotoxicity results derived by the umu-test.

Rapid activated sludge respiration inhibition test performed by CO2 producing rate using a carbon dioxide sensor

The rapid activated sludge inhibition test (rapid ASRI) is one of the promising bioassays to evaluate environmental risk to the ecosystem caused by various pollutants. To improve the sensitivity and stability of ASRI, the CO2 producing rate (CPR) using a carbon dioxide gas sensor was employed to examine the respiration activity of activated sludge and to compare it to that by the conventional activated sludge respiration inhibition test using oxygen uptake rate (OUR) by EC50 values derived from dose response curve. Detection of respiratory activity based on CPR has higher reliability and sensitivity than that of OUR. It should be noted that the sensitivity of CPR for evaluating toxicity is sufficiently high in terms of derived dose response curve of some model environmental pollutants and the resultant EC50 values.