Toxicity QSAR of substituted benzenes to yeast Saccharomyces cerevisiae

QSAR study using acute toxicity of Daphnia magna and Hyalella azteca through exposure to polycyclic aromatic hydrocarbons (PAHs)

Polycyclic aromatic hydrocarbons are organic chemicals consisting of a small number of benzene rings. PAHs are exposed to the environment by events such as Crude oil spills, even though they are substances present in the environment. Exposure of PAHs to the environment will affect not only the environment, but also the living organisms and the ecosystem as a whole. The effects of PAHs vary widely depending on the type of PAHs and have been studied for a long time. However, there are only 16 kinds of PAHs defined by US EPA, and there are more kinds of PAHs present in the environment. Therefore, it is time- and space-limited to judge the toxicity of all kinds of PAHs by evaluating them. In all cases, the tendency of research is shifting toward predicting toxicity evaluation through modeling rather than the direction of toxicity evaluation. In this study, we constructed a quantitative structure-activity relationship (QSAR) model, one of the molecular structure activation models, and predicted the correlation between the toxicity value and the logKow value of PAHs. Basically, as the logKow value increases, the median effective concentration (EC50) tends to decrease. Compared with the previous studies, Hyalella azteca showed this tendency, but Daphnia magna showed different results when exposed to Naphthalene. The RMSE(Root Mean Square Error) values of Daphnia magna and Hyalella azteca were 6.0049 and 5.9980, respectively, when the QSAR model was constructed using the toxicity data for PAHs. We confirmed the validity of the QSAR model in this study by comparing the results of exposing Daphnia magna to PAHs and the ECOSAR data, one of the existing models. The R² value was found to be 0.9356. This study suggests that it may be helpful to predict the toxicity evaluation and to prepare countermeasures for accidents such as Crude oil spill. It is thought that if more data base is created by using additional types of PAHs and species in the same way as this study in the future, it will help to construct the modeling.

Effects of gas pressurization with ethylene on the ultrastructure of the yeast Saccharomyces cerevisiae

We investigated ultrastructural changes in the yeast Saccharomyces cerevisiae when exposed to compressed ethylene gas. Transmission electron microscopy (TEM) revealed that intracellular organelles in yeast cells treated with compressed ethylene at up to 0.640 MPa (6.4 atm), especially the nuclear and plasma membranes, were seriously damaged.

Structure–activity relationships for halobenzene induced cytotoxicity in rat and human hepatoctyes

Halobenzenes are ubiquitous environmental contaminants, which are hepatotoxic in both rodents and humans. The molecular mechanism of halobenzene hepatotoxicity was investigated using Quantitative structure-activity relationships (QSAR) and accelerated cytotoxicity mechanism screening (ACMS) techniques in rat and human hepatocytes. The usefulness of isolated hepatocytes for prediciting in vivo xenobiotic toxicity was reassessed by correlating the LC(50) of 12 halobenzene congeners in phenobarbital (PB) induced rat hepatocytes in vitro determined by ACMS to the hepatotoxicities reported in vivo in PB-induced male Sprague-Dawely (SD) rats. A high correlation (r(2)=0.90) confirmed the application of hepatocytes as a "gold standard" for toxicity testing in vitro. QSARs were derived to determine the physico-chemcial variables that govern halobenzene toxicity in PB-induced rat, normal rat and human hepatocytes. We found that toxicity in normal rat and normal human hepatocytes both strongly correlate with hydrophobicity (logP), ease of oxidation (E(HOMO), energy of the highest molecular orbital) and on the asymmetric charge distribution according to arrangement of halogen substituents (dipole moment, mu). This suggests that halobenzene interaction with cytochrome P450 for oxidation is the metabolic activating path for toxicity and is similar in both species. In PB-induced rat hepatocytes the QSAR derivation is changed, where halobenzene toxicity strongly correlates to logP and dipole moment, but not E(HOMO). The changed QSAR suggests that oxidation is no longer the rate-limiting step in the cytotoxic mechanism when CYP2B/3A levels are increased, confirming CYP450 oxidation as the metabolic activating step under normal conditions.

The combined toxic effects of nonpolar narcotic chemicals to Pseudokirchneriella subcapitata

This paper presents the toxicity data of 10 nonpolar narcotic chemicals on Pseudokirchneriella subcapitata (green algae) assessed by a new algal toxicity testing technique conducted under air-tight environment. Based on DO production, median effective concentration (EC50) varies from 1.73 mg/L (1-octanol) to 8,040 mg/L (2-propanol). The endpoint of algal growth rate reveals similar sensitivity as that from DO production. Compared to literature data, Pseudokirchneriella subcapitata and Nitrosomonas are apparently more sensitive to nonpolar narcotics than other organisms such as minnow, daphnia, and Tetrahymena pyriformis. Furthermore, good correlations between toxic effects observed from Pseudokirchneriella subcapitata and other aquatic organisms were found. Hence, algal toxicity test can be considered as a surrogate test for estimating the toxicity of nonpolar chemicals to fathead minnow, Microtox, activated sludge, Daphina magna, and Tetrahymena pyriformis. The combined effects of 13 binary mixtures of nonpolar chemicals were investigated using both additive-index method and isobologram analysis. Overall speaking, the joint actions between these chemicals are strictly additive. Model analyses indicate that these compounds act on identical reaction sites or receptors, which verify that these chemicals are of the same toxicity mechanism (narcosis).