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Evaluation of the 50% inhibitory concentration (IC50) of acetylsalicylic acid, ferrous sulfate, amitriptyline, methanol, isopropanol and ethylene glycol was done on human cancer cells cultured in in vitro conditions. Three different in vitro assays were used in this study: the plating efficiency test, the microprotein test and the neutral red uptake test. Obtained results were evaluated by statistical methods. All used methods seem to be useful for screening a cytotoxic potential of the tested chemicals. The knowledge of cytotoxic effects of frequently used chemicals on mammalian cells is important not only for necessary in vitro genotoxicity and carcinogenicity studies but also for assessing the toxicity of chemicals to find out possible hazards to the human health. Results presented in this paper underline the usefulness of the wider methodological approach for the comparison of the different endpoints as well as a necessity for selection of a battery of in vitro cytotoxicity tests allowing to estimate the possible harmful effects of xenobiotics.

Mutagenicity of N-cyclohexylthiophthalimide (Duslin P) was tested first by the Ames test in the bacteria, Salmonella typhimurium. The negative results of the Ames test suggested that this compound does not induce mutations in the genome of S. typhimurium under the conditions used. To estimate the cytotoxicity of Duslin P to human cells, we measured cellular DNA and protein as well as cell proliferation, i.e., the mitotic index of treated and control cells. The genotoxic effects were assayed by two biochemical methods developed for detection of single-strand breaks of DNA in mammalian cells, i.e., by the alkaline single cell gel electrophoresis (comet assay) and by the DNA unwinding method, respectively. The DNA unwinding method showed that this compound did not induce DNA damage at concentrations < 7 micrograms/ml. Alkaline single cell gel electrophoresis revealed approximately double the level of DNA damage (in comparison to untreated control DNA) at a concentration of 2 micrograms/ml, which reduced proliferation to approximately 30%, and triple the level of DNA damage at higher concentrations (6 and 7 micrograms/ml), which inhibited completely both DNA synthesis and proteosynthesis. Cells with moderately damaged DNA were more common than cells with heavily damaged DNA. Parallel experiments with the strong mutagen and carcinogen MNNG showed that MNNG induced in cells a high level of DNA damage at concentrations which did not reduce the mitotic index or proteosynthesis, while DNA synthesis inhibited only partially. After treatment with MNNG, cells with heavily damaged DNA were more common than cells with moderately damaged DNA. Duslin P-treated VH10 cells were also tested cytogenetically, confirming that Duslin P induced neither chromosomal aberrations nor aneuploidy. We conclude that Duslin P has no mutagenic effect on bacteria, does not induce chromosomal aberrations and CREST positive or CREST negative micronuclei in human cells and induces only a small increase of DNA damage in human cells which is consistent with DNA fragmentation due to cell death.

Apoptosis is genetically programmed cell death, an irreversible process of cell senescence with characteristic features (cell shrinkage, chromatin condensation, DNA fragmentation, apoptotic bodies) different from necrosis. Several effective in vitro methods for qualitative and quantitative detection of apoptotic events have been developed. Chromatin degradation, reductions in cell volume and other apoptosis-associated changes in cell morphology and physiology can be quickly analysed by multiparametric flow cytometry (FC) using small numbers of intact cells. One further method used for morphological determination of apoptotic changes is the fluorescent microscopic technique (FM) based on labeling of cells with fluorochromes acridine orange and ethidium bromide. In our experiments FC was used for determination of DNA changes in HeLa cells based on staining of DNA by fluorochrome propidium iodide (PI). Among the tested chemicals (paracetamol and sodium fluoride) apoptotic process could only be detected in paracetamol-treated cells. Apoptosis was induced mainly in cells treated with paracetamol (concentration range 4-5 mg/ml) for 8 h and following incubation for 18 h in fresh medium without paracetamol. The results obtained by the FM method correlated with the results obtained by FC.

Apoptosis is a programmed form of cell death which occurs in response to specific stimuli. It is distinguished from necrotic or accidental cell death by unique events, including the degradation of chromatin and a loss of cellular volume. In contrast to necrotic cell death, cell membrane integrity and mitochondrial function are thought to be maintained until the apoptotic process is well advanced. One of the novel assays for detecting apoptosis is flow cytometry. In our experiments, we used a flow cytometric assay to detect DNA changes in a human cell line (HeLa) exposed to paracetamol, by measuring propidium iodide binding. We were able to detect the apoptotic process in cells exposed to paracetamol. Apoptosis did not correlate with cytotoxicity, and was only found in samples exposed to 4-5mg/ml paracetamol for 8 hours in minimum essential medium and incubated in fresh medium without paracetamol for 14-19 hours. The greatest effect was noted 18 hours after paracetamol exposure. These results were confirmed by studying cell morphology and chromatin condensation by fluorescent microscopy with the fluorochromes acridine orange and ethidium bromide. Our results support the hypothesis that, in cultured cells, apoptosis is induced by a relatively narrow range of chemical concentrations which are known to inhibit the cell cycle, and that apoptosis and inhibition of cell proliferation coincide to some degree., (1999 FRAME.)

The mutagenic activity of sodium fluoride at reduced pH was studied in the V79/HGPRT system. Statistical analysis of the results of mutagenicity testing suggests that, despite its high toxicity, sodium fluoride has no mutagenic effects at reduced pH on hamster V79 cells. Short-term treatment of cells with sodium fluoride at reduced pH inhibits growth activity of cells as well as synthesis of pulse-labeled nascent DNA and cumulative RNA synthesis and proteosynthesis. From the results of this study we suggest that an acid environment which supports formation of hydrogen fluoride increases toxic but not mutagenic potencies of sodium fluoride.

To study the genotoxic activity of Decemtione (Imidan), this substance was subjected to a series of tests. After preliminary cytotoxicity testing, the capacity of Decemtione to damage human DNA was determined by alkaline elution of DNA and DNA unwinding. Both tests gave positive results, suggesting that Decemtione was able to induce single-strand breaks in DNA. This capacity was higher in the absence and lower in the presence of the S9 fraction. The potential mutagenicity of Decemtione was followed on the basis of its ability to induce resistance to 6-thioguanine in V79 hamster cells. Unlike the induction of single-strand breaks, Decemtione showed, in the absence of the metabolic activation system, a very weak mutagenic effect, which was, however, significantly higher in the presence of the S9 fraction. The ability of the substance to transform diploid cells under in vitro conditions was followed on the basis of morphological transformation of Syrian hamster embryo cells. The results showed that Decemtione, like positive carcinogenes, induced a significant elevation in morphologically transformed colonies of embryo cells. The results suggest a carcinogenic potential of this organophosphate insecticide.