Assessment of the Cytotoxicity of Peptide Modifications of Doxorubicin on Tetrahymena pyriformis.

The cytotoxicity of doxorubicin (Dox) and its peptide modifications Z-Gly-Pro-Dox and Boc-Gly-Pro-Dox were studied. Tetrahymena pyriformis was used as a test system, which made it possible, due to the short life cycle and high reproduction rate of ciliates, to trace their response to the effects of toxicants over several generations. It was found that peptide modification of the Dox molecule markedly reduces its cytotoxic and cytostatic effect. The Z-Gly-Pro-Dox modification has less cytotoxic and cytostatic effect compared to Boc-Gly-Pro-Dox. When determining the ability of drugs (at a concentration of 100 µM) to prevent bacterial contamination of samples, it was shown that the smallest degree of overgrowth was recorded in the presence of Dox (OD600nm 81.1). Boc-Gly-Pro-Dox also had a bacteriostatic effect, though less pronounced (OD600nm 93.8). The degree of overgrowth in the presence of Z-Gly-Pro-Dox was close to that of distilled water. The results obtained on ciliates did not contradict the data obtained in similar studies on mice.

Modelling quantitative structure activity-activity relationships (QSAARs): auto-pass-pass, a new approach to fill data gaps in environmental risk assessment under the REACH regulation.

Reviewing the toxicological literature for over the past decades, the key elements of QSAR modelling have been the mechanisms of toxic action and chemical classes. As a result, it is often hard to design an acceptable single model for a particular endpoint without clustering compounds. The main aim here was to develop a Pass-Pass Quantitative Structure-Activity-Activity Relationship (PP QSAAR) model for direct prediction of the toxicity of a larger set of compounds, combing the application of an already predicted model for another species, and molecular descriptors. We investigated a large acute toxicity data set of five aquatic organisms, fish, Daphnia magna, and algae from the VEGA-Hub, as well as Tetrahymena pyriformis and Vibrio fischeri. The statistical quality of the models encouraged us to consider this alternative for the prediction of toxicity using interspecies extrapolation QSAAR models without regard to the toxicity mechanism or chemical class. In the case of algae, the use of activity values from a second species did not improve the models. This can be attributed to the weak interspecies relationships, due to different aquatic toxicity mechanisms in species.

Chlorination and bromination of 1,3-diphenylguanidine and 1,3-di-o-tolylguanidine: Kinetics, transformation products and toxicity assessment.

This works investigates the chlorination and bromination of two rubber and polymer related chemicals, which have emerged as relevant water contaminants, i.e. 1,3-di-o-tolylguanidine (DTG) and 1,3-diphenylguanidine (DPG). Kinetic constants at different pH values were obtained and modelled, taking into account the pKa values of DTG/DPG and HClO, showing that the maximum reaction rate (kapp > 104 M-1 s-1) is obtained at pH values 8.8 for DPG and 9.1 for DTG. Bromination is also very fast, although unlike chlorination, deviation from the model was observed at neutral pH, which was attributed to formation of metastable transformation product (TP). A total of 35 TPs, corresponding to halogenation, hydroxylation, formation of monophenylguanidine derivatives and cyclization reactions, were tentatively identified. Furthermore it was found that chloroform can be formed up to a 25% molar yield, while dichloroacetonitrile was formed into less than a 3% yield. Several ecotoxicological endpoints were predicted by quantitative structure-activity relationship models (QSAR) for the TPs, some of which were predicted to be more toxic than DPG/DTG. Also a chlorinated solution investigated by a Vibrio Fisheri acute toxicity test, confirmed that toxicity increases with chlorination.

In silico prediction of toxicity of phenols to Tetrahymena pyriformis by using genetic algorithm and decision tree-based modeling approach.

Risk assessment of chemicals is an important issue in environmental protection; however, there is a huge lack of experimental data for a large number of end-points. The experimental determination of toxicity of chemicals involves high costs and time-consuming process. In silico tools such as quantitative structure-toxicity relationship (QSTR) models, which are constructed on the basis of computational molecular descriptors, can predict missing data for toxic end-points for existing or even not yet synthesized chemicals. Phenol derivatives are known to be aquatic pollutants. With this background, we aimed to develop an accurate and reliable QSTR model for the prediction of toxicity of 206 phenols to Tetrahymena pyriformis. A multiple linear regression (MLR)-based QSTR was obtained using a powerful descriptor selection tool named Memorized_ACO algorithm. Statistical parameters of the model were 0.72 and 0.68 for Rtraining2 and Rtest2, respectively. To develop a high-quality QSTR model, classification and regression tree (CART) was employed. Two approaches were considered: (1) phenols were classified into different modes of action using CART and (2) the phenols in the training set were partitioned to several subsets by a tree in such a manner that in each subset, a high-quality MLR could be developed. For the first approach, the statistical parameters of the resultant QSTR model were improved to 0.83 and 0.75 for Rtraining2 and Rtest2, respectively. Genetic algorithm was employed in the second approach to obtain an optimal tree, and it was shown that the final QSTR model provided excellent prediction accuracy for the training and test sets (Rtraining2 and Rtest2 were 0.91 and 0.93, respectively). The mean absolute error for the test set was computed as 0.1615.

Prediction of Aquatic Toxicity of Benzene Derivatives to Tetrahymena pyriformis According to OECD Principles.

BACKGROUND: Many QSAR studies have been developed to predict acute toxicity over several biomarkers like Pimephales promelas, Daphnia magna and Tetrahymena pyriformis. Regardless of the progress made in this field there are still some gaps to be resolved such as the prediction of aquatic toxicity over the protozoan T. pyriformis still lack a QSAR study focused in accomplish the OECD principles. METHODS: Atom-based quadratic indices are used to obtain quantitative structure-activity relationship (QSAR) models for the prediction of aquatic toxicity. Our models agree with the principles required by the OECD for QSAR models to regulatory purposes. The database employed consists of 392 substituted benzenes with toxicity values measured in T. pyriformis (defined endpoint), was divided using cluster analysis in two series (training and test sets). RESULTS: We obtain (with an unambiguous algorithm) two good multiple linear regression models for non-stochastic (R2=0.807 and s=0.334) and stochastic (R2=0.817 and s=0.321), quadratic indices. The models were internally validated using leave-one-out, bootstrapping as well as Y-scrambling experiments. We also perform an external validation using the test set, achieving values of R2 pred values of 0.754 and 0.760, showing that our models have appropriate measures of goodness- of-fit, robustness and predictivity. Moreover, we define a domain of applicability for our best models. CONCLUSION: The achieved results demonstrated that, the atom-based quadratic indices could provide an attractive alternative to the experiments currently used for determining toxicity, which are costly and time-consuming.

Building up a QSAR model for toxicity toward Tetrahymena pyriformis by the Monte Carlo method: A case of benzene derivatives.

Data on toxicity toward Tetrahymena pyriformis is indicator of applicability of a substance in ecologic and pharmaceutical aspects. Quantitative structure-activity relationships (QSARs) between the molecular structure of benzene derivatives and toxicity toward T. pyriformis (expressed as the negative logarithms of the population growth inhibition dose, mmol/L) are established. The available data were randomly distributed three times into the visible training and calibration sets, and invisible validation sets. The statistical characteristics for the validation set are the following: r(2)=0.8179 and s=0.338 (first distribution); r(2)=0.8682 and s=0.341 (second distribution); r(2)=0.8435 and s=0.323 (third distribution). These models are built up using only information on the molecular structure: no data on physicochemical parameters, 3D features of the molecular structure and quantum mechanics descriptors are involved in the modeling process.

Formation of categories from structure-activity relationships to allow read-across for risk assessment: toxicity of alpha,beta-unsaturated carbonyl compounds.

alpha,beta-Unsaturated carbonyl compounds are common environmental pollutants that are able to interact with proteins, enzymes, and DNA through various mechanisms. As such, they are able to stimulate a range of environmental toxicities and adverse health effects. In this study, a "category" of alpha,beta-unsaturated carbonyl compounds (aldehydes and ketones), assumed to act by a common mechanism of action (Michael type addition), was formed. This toxicologically and mechanistically important category was formed on the premise of structure-activity relationships. The acute aquatic toxicities to Tetrahymena pyriformis of compounds within the category were obtained in an effort to develop approaches for (qualitative) read-across. In addition, Salmonella typhimurium (strain TA100) mutagenicity data were analyzed to establish the structural differences between mutagenic and nonmutagenic compounds. These structural differences were compared with the structural characteristics of molecules associated with acute aquatic toxicity in excess of narcosis as well as other end points, for example, skin sensitization. The results indicate that a category can be formed that allows structural information and boundaries to be elucidated. This knowledge will guide future toxicity prediction within this category and assist in the development of category formation.

Critical assessment of QSAR models of environmental toxicity against Tetrahymena pyriformis: focusing on applicability domain and overfitting by variable selection.

The estimation of the accuracy of predictions is a critical problem in QSAR modeling. The "distance to model" can be defined as a metric that defines the similarity between the training set molecules and the test set compound for the given property in the context of a specific model. It could be expressed in many different ways, e.g., using Tanimoto coefficient, leverage, correlation in space of models, etc. In this paper we have used mixtures of Gaussian distributions as well as statistical tests to evaluate six types of distances to models with respect to their ability to discriminate compounds with small and large prediction errors. The analysis was performed for twelve QSAR models of aqueous toxicity against T. pyriformis obtained with different machine-learning methods and various types of descriptors. The distances to model based on standard deviation of predicted toxicity calculated from the ensemble of models afforded the best results. This distance also successfully discriminated molecules with low and large prediction errors for a mechanism-based model developed using log P and the Maximum Acceptor Superdelocalizability descriptors. Thus, the distance to model metric could also be used to augment mechanistic QSAR models by estimating their prediction errors. Moreover, the accuracy of prediction is mainly determined by the training set data distribution in the chemistry and activity spaces but not by QSAR approaches used to develop the models. We have shown that incorrect validation of a model may result in the wrong estimation of its performance and suggested how this problem could be circumvented. The toxicity of 3182 and 48774 molecules from the EPA High Production Volume (HPV) Challenge Program and EINECS (European chemical Substances Information System), respectively, was predicted, and the accuracy of prediction was estimated. The developed models are available online at http://www.qspr.org site.

Toxicity assessment of the herbicides sulcotrione and mesotrione toward two reference environmental microorganisms: Tetrahymena pyriformis and Vibrio fischeri.

The potential toxicity of sulcotrione (2-[2-chloro-4-(methylsulfonyl)benzoyl]-1,3-cyclohexanedione) and mesotrione (2-[4-(methylsulfonyl)-2-nitrobenzoyl]-1,3-cyclohexanedione), two selective triketonic herbicides, was assessed using representative environmental microorganisms frequently used in ecotoxicology: the eukaryote Tetrahymena pyriformis and the prokaryote Vibrio fischeri. The aims were also to evaluate the toxicity of different known degradation products, to compare the toxicity of these herbicides with that of atrazine, and to assess the toxicity of the commercial herbicidal products Mikado and Callisto. Toxicity assays involved the Microtox test, the T. pyriformis population growth impairment test, and the T. pyriformis nonspecific esterase activity test. For each compound, we report original data (IC(50) values) on nontarget cells frequently used in ecotoxicology. Analytical standards sulcotrione and mesotrione showed no toxic effect on T. pyriformis population growth but a toxic influence was observed on nonspecific esterase activities of this microorganism and on metabolism of V. fischeri. Most of the degradation products studied and the two commercial formulations showed a greater toxicity than the parent molecules. Compared with the effect of atrazine, the toxicity of these triketonic herbicides was less than in T. pyriformis and greater than or the same as in V. fischeri. Additional work is needed to obtain a more accurate picture of the environmental impact of these herbicides. It will be necessary in future experiments to study the ecosystemic levels (aquatic and soil compartments) and to assess the potential toxicity of the newly discovered degradation products and of the additives accompanying the active ingredient in the commercial herbicidal formulations.

Involvement of Tetrahymena pyriformis and selected fungi in the elimination of anthracene, and toxicity assessment of the biotransformation products.

Anthracene (AC) is a non-mutagenic and non-carcinogenic, low-molecular-weight polycyclic aromatic hydrocarbon present in the environment. Its toxicity can be dramatically increased after solar-light exposure. Biotransformation capacities of AC by Tetrahymena pyriformis and a selection of eight micromycetes were studied, and the ability of these microorganisms to detoxify the polluted ecosystems was assessed. We showed that T. pyriformis was able to accumulate high amounts of AC without any transformation. In contrast, the fungi Cunninghamella elegans, Absidia fusca, Absidia cylindrospora, Rhodotorula glutinis, and Aspergillus terreus were able to transform AC with a high efficiency. Cytotoxicity assays conducted on HeLa cells and T. pyriformis showed that crude extract from A. fusca culture medium obtained after AC biotransformation was not toxic. For A. fusca and A. cylindrospora, 1-4 dihydroxyanthraquinone was shown to be the major product during the biotransformation process. This compound seemed to be a dead-end metabolite at least for the Absidia strains. The cytotoxicity of 1-4 dihydroxyanthraquinone was higher than that of AC to T. pyriformis but lower to HeLa cells. On the whole our results showed that the microorganisms studied were all able to decontaminate an AC-polluted ecosystem, either by accumulating or transforming the compound. A possible detoxification process resulting from AC biotransformation can be considered only using the human cell model.

Assessment of the potential toxicity of herbicides and their degradation products to nontarget cells using two microorganisms, the bacteria Vibrio fischeri and the ciliate Tetrahymena pyriformis.

The potential toxicity of several herbicides-alachlor, diuron and its photo and biotransformation products, glyphosate and its metabolite aminomethyl phosphonic acid (AMPA)-to nontarget cells was assessed using two microorganisms frequently used in ecotoxicology, Vibrio fischeri and Tetrahymena pyriformis. Toxicity assays involved the Microtox test, the T. pyriformis population growth impairment test employing three different processes (flasks, tubes, microplates), and the T. pyriformis nonspecific esterase activities test. Several IC(50) or EC(50) values are reported for each molecule. Alachlor exerted a toxic effect on the two nontarget cells used. The results for diuron and its photo and biotransformation products indicated that most of the metabolites presented nontarget toxicity higher than that of diuron. Glyphosate and AMPA had a less negative effect on T. pyriformis than on V. fischeri. Nevertheless, in all cases, glyphosate was found to be more toxic than AMPA. Comparison analysis of the sensitivity of the different tests showed that, in general, tests using the eukaryotic cell (T. pyriformis) were more sensitive than test using the prokaryotic cell (V. fischeri), and that a population growth criterion is more sensitive than an enzymatic criterion. The three different processes that could be used to evaluate effects on population growth rate were equally sensitive for the herbicides tested. A significant correlation between toxicity data and the hydrophobicity of the chemicals could only be established with the growth population test. This study demonstrates that it is essential to assess the toxicity of the metabolites formed to complete a more comprehensive study of the environmental impact of a polluting agent.

A combined QSAR and partial order ranking approach to risk assessment.

QSAR generated data appear as an attractive alternative to experimental data as foreseen in the proposed new chemicals legislation REACH. A preliminary risk assessment for the aquatic environment can be based on few factors, i.e. the octanol-water partition coefficient (Kow), the vapour pressure (VP) and the potential biodegradability of the compound in combination with the predicted no-effect concentration (PNEC) and the actual tonnage in which the substance is produced. Application of partial order ranking, allowing simultaneous inclusion of several parameters leads to a mutual prioritisation of the investigated substances, the prioritisation possibly being further analysed through the concept of linear extensions and average ranks. The ranking uses endpoint values (log Kow and log VP) derived from strictly linear 'noise-deficient' QSAR models as input parameters. Biodegradation estimates were adopted from the BioWin module of the EPI Suite. The population growth impairment of Tetrahymena pyriformis was used as a surrogate for fish lethality.

Cytotoxicity assessment of gliotoxin and penicillic acid in Tetrahymena pyriformis.

Various studies have documented the associations between mold exposure and effects on health. Mycotoxins, which occur in spores and mold fragments, can be involved in processes that have pathological effects, such as adynamia of the immune system, recurrent infections of the respiratory tract, or asthma. Using Tetrahymena pyriformis, a single-cell organism well established as a suitable model for human respiratory epithelium-cell functionalities, we investigated dose-response relationships of the mycotoxins gliotoxin and penicillic acid. Our study focused on the viability (cell count, MTT assay), energy levels (adenosine-5'-triphosphate content), energy-providing processes (MTT reduction per cell), and cell respiration (oxygen consumption). Both mycotoxins acted as cytotoxins in a dose-dependent manner. Gliotoxin had a stronger inhibitory effect (EC50 0.38 microM) than did penicillic acid (EC50 343.19 microM). The energy-providing processes were not inhibited or were only weakly inhibited under the influence of gliotoxin, whereas penicillic acid caused stimulation of the physiological parameters. Summarizing the results, it is clear that the two investigated mycotoxins must have different modes of action. They are not only different in the strength of their toxic effects but also in a variety of physiological aspects. In addition, T. pyriformis showed differences in its ability to overcome the negative effects of particular mycotoxin exposures.

[High-speed biological assessment of raw materials from hydrobionts].

The paper shows it's possible to use the high-speed biological assay using the infusoria Tetrahymena pyriformis to estimate the nutritive value of hydrobionts. Biotesting in the assessment of the quality of raw materials from sea hydrobionts provided an integral index of physiological action on the indicator organism of all the muscular tissue components of hydrobionts as a response signal.

Cytotoxicity assessment of three therapeutic agents, cyclosporin-A, cisplatin and doxorubicin, with the ciliated protozoan Tetrahymena pyriformis.

Cyclosporin-A, a drug possessing potent immunosuppressive properties, is used to prevent allograft rejection. Cisplatin and doxorubicin are two of the pharmaceutical drugs most widely used in cancer chemotherapy. In this study, the cytotoxicological impact of these three therapeutic agents was determined using bioassays performed with a unicellular eukaryote, the ciliated protozoan Tetrahymena pyriformis. For this purpose we used the population growth impairment test and the non-specific esterase activities test. We also examined some morphological effects. The results show that these three agents are toxic towards T. pyriformis. A concentration-dependent inhibitory effect on the cell proliferation rate of T. pyriformis populations was found for the three drugs. The IC(50) values were, respectively, 42.03+/-4.64, 124.37+/-7.47 and 74.62+/-6.12 microM for cyclosporin-A, cisplatin and doxorubicin. Non-specific esterase activities were also modified compared with untreated cells. The IC(50) values were, respectively, 88.32+/-8.35 and 44.61+/-3.33 microM for cisplatin and doxorubicin. Exposure of T. pyriformis to these drugs caused the prompt appearance of digestive vacuoles concentrating particulate elements. This phenomenon was more pronounced at higher concentrations. We also observed deformed cells with cisplatin. T. pyriformis bioassays can offer an alternative in vitro method to cell cultures for the risk assessment of potentially toxic drugs.

Assessment of mutagenicity and toxicity of different-size fractions of air particulates from La Plata, Argentina, and Leipzig, Germany.

Airborne particulates, especially fine particles and bound chemical compounds, are a potential mediator of adverse health effects. In this study an analysis was done of the concentration and size distribution of air particulate matter, the content of bound polycyclic aromatic hydrocarbons (PAHs), and the biological effects of organic extracts from different fractions of dust that had been influenced by urban and industrial emissions from the regions of La Plata, Argentina, and Leipzig, Germany, along with samples from control areas. Air particulate matter was sampled in summer and winter in each region using a high-volume sampler with a six-stage cascade impactor, classifying dust in six size fractions from 10-microm particles to those less than 0.49 microm in size. Organic extracts of dust were tested for mutagenicity (Ames test, Salmonella typhimurium TA98 strain, S9+) and cytotoxicity (Tetrahymena pyriformis test system, growth rate, cell respiration). The content of PAHs was analyzed by high-performance liquid chromatography (HPLC) with diode array and fluorescence detection. Mutagenic and cytotoxic effects were found to be associated with very fine (<0.49 microm) and fine (<1.5 microm) particle-bound compounds, corresponding to a higher content of PAHs. The mutagenic potency (revertants/m(3)) associated with particles less than 0.49 microm from urban areas of La Plata was about 1 order of magnitude higher than in particles in the range of 3.0 to 0.49 microm. Fine fractions from sites with an industrial burden were also found to exhibit high mutagenic potency. A similar tendency was observed in cytotoxicity tests with T. pyriformis. This cell system proved to be very sensitive to toxicants in tested dust fractions. The observed biological effects were found to be correlated significantly with concentrations of total PAH, carcinogenic PAHs, and benzo[a]pyrene.

Development of quantitative structure-activity relationships for the toxicity of aromatic compounds to Tetrahymena pyriformis: comparative assessment of the methodologies.

The purpose of this study was to develop quantitative structure-activity relationships (QSARs) for the toxicity of 268 aromatic compounds in the Tetrahymena pyriformis growth inhibition assay. The QSARs were developed using the response-surface (or two-parameter) approach, which was also modified using linear free-energy parameters to account for outliers. Subsequently, the data set was analyzed using partial least-squares (PLS). The results of the modeling using different methodologies were compared to the use of a Bayesian regularized neural network (BRANN) trained on the same data. Both response surface approaches, and PLS explained between 75 and 80% of the variance in the data; BRANN gave a higher statistical fit. In terms of the transparency of the approaches, the response surface clearly provides the simplest and easiest to use QSAR, it is readily interpreted in terms of mechanism of toxic action. PLS and BRANN are respectively less transparent. The use of atomistic and fragment-based indexes as descriptors in QSARs is assessed also, these are found not to be as useful as whole molecule parameters for the prediction of toxicity for molecules outside of the training set. The relative merits of the different approaches to the development of QSARs are described.

Use of the ciliated protozoan Tetrahymena pyriformis for the assessment of toxicity and quantitative structure--activity relationships of xenobiotics: comparison with the Microtox test.

Cytotoxicity and quantitative structure-activity relationships of 13 inorganic and 21 organic substances were determined using three bioassays performed on the ciliated protozoan Tetrahymena pyriformis and the luminescent bacterium Vibrio fischeri. The best concordance of toxicity results was observed between the T. pyriformis FDA--esterase activity and population growth inhibition tests for the organic compounds. The sensitivity of these two assays is compared with that of the Microtox test. The T. pyriformis FDA test showed a high sensitivity is most cases. The aim of the current research was to determine whether the relative toxicity of metal ions and organic molecules, with these three bioassays, was predictable using three ion characteristics and hydrophobicity, respectively. For metal ions, the variable that best modeled the toxicity data obtained with the two T. pyriformis tests was the softness index [sigma(p), i.e., (coordinate bond energy of the metal fluoride--coordinate bond energy of the metal iodide)/(coordinate bond energy of the metal fluoride)]. No correlation was found with the Microtox test. For organic compounds, a significant correlation was observed between the hydrophobicity coefficient and the toxicity data. This correlation is closer with the two tests using Tetrahymena.

Assessment of toxicity and mutagenicity in air particulate matter from an urban industrial area in the coast of the Rio de la Plata.

Chemical characterization and effects assessment of semivolatile organic compounds in organic extracts from air particulate matter from the region of the greater La Plata area was undertaken. Effects covered the study of mutagenicity with the Ames test (Salmonella typhimurium TA100 and TA98 strains with metabolic activation by S9) and cytotoxicity using the Tetrahymena pyriformis test system (growth rate, cell volume, and cell respiration). Chemical analysis of organic extracts was done using gas chromatography. Results demonstrate the presence of polycyclic aromatic hydrocarbons (PAH) in the matrix, high mutagenicity, and cytotoxicity. A higher mutagenic activity detected with TA98 and TA100 strains is associated with an increment of total PAH and total five or six ring PAH content, respectively. Linked with it, a PAH dependent toxicity on Tetrahymena pyriformis has been observed. This cell system proved to be very sensitive. From the results obtained with the cell respiration assay with T. pyriformis it appears that uncoupling agents are present in the samples. The results of this study indicate that air particulate matter from the Rio de La Plata area contains significant genotoxic and cytotoxic activity probably due to the presence of PAHs.

Assessment of chloroaniline toxicity by the submitochondrial particle assay.

The effects on mitochondrial respiration of 15 chloroanilines were recorded by using the in vitro response of submitochondrial particles (SMP) from beef heart mitochondria. The bioassay procedure for SMP is based on the process of reverse electron transfer, which can be negatively affected by inhibitors of electron transport, by uncouplers, and by chemicals that impair membrane integrity. The EC50 values, determined for the tested chloroanilines, indicate a general tendency of increasing toxicity with increasing chlorine substitution. In order to validate the results obtained and to evaluate the capability of the SMP assay to reproduce the toxic effects of the examined compounds on different freshwater species, the EC50 values were compared with literature data from other biological assays regarding both in vitro systems and whole organisms. A good correlation was found in particular with two widely used testing systems, the Microtox and the Tetrahymena assays. In addition, quantitative structure-activity relationships (QSARs) were established between the EC50 values and various molecular descriptors for hydrophobic, steric, and electronic interactions. The results obtained were utilized to elucidate the mechanism of toxic action of chloroanilines, which are commonly reported to act by the polar narcosis mode of action. Moreover, they confirmed that the SMP assay can be a useful tool for studying the toxicity of chemicals that act nonspecifically by impairing membrane structure and functions.