Studies on the action of nystatin on cultured rat myocardial cells and cell membranes, isolated rat hearts, and intact rats.

The action of nystatin, a polyene antibiotic, was studied in rat myocardial cells, isolated rat hearts, and intact rats. Myocardial cells responded to 10 and 25 micrograms nystatin/ml with arrhythmias that could be minimized by elevated concentrations of K+ and Mg2+ or reversed by washing the cells. Similarly, the isolated heart responded to 100 micrograms nystatin/ml with arrhythmias that could be tempered by addition of elevated concentrations of K+ and Mg2+. The i.v. injection of the drug caused heart failure in intact animals at the 4-mg/kg dose level. At the subcellular level, nystatin made the myocardial cell membranes more rigid, as measured by electron spin resonance spectrometry. These findings indicate a parallel between physiocochemical changes caused by nystatin in the myocardial cell membrane and the biological changes caused by this drug in myocardial cells, isolated heart, and heart of the intact animal.

Recommended protocols based on a survey of current practice in genotoxicity testing laboratories: I. Unscheduled DNA synthesis assay in rat hepatocyte cultures.

A protocol based primarily on current laboratory practices in the performance of the unscheduled DNA synthesis (UDS) assay with primary rat hepatocyte cultures has been developed. These guidelines were developed using tabulated responses to a detailed questionnaire completed by North American and European governmental, university and contract laboratories involved with the UDS test. This report identifies those modifications to previously described methodologies which are used on a regular basis and also serves to clarify confusing or inconsistent practices. Although this protocol pertains specifically to the use of primary rat hepatocyte cultures, it can be modified to incorporate other types of cells in which certain aspects remain the same.

Framework for validation and implementation of in vitro toxicity tests.

The development and application of in vitro alternatives designed to reduce or replace the use of animals, or to lessen the distress and discomfort of laboratory animals, is a rapidly developing trend in toxicology. However, at present there is no formal administrative process to organize, coordinate, or evaluate validation activities. A framework capable of fostering the validation of new methods is essential for the effective transfer of new technologic developments from the research laboratory into practical use. This committee has identified four essential validation resources: chemical bank(s), cell and tissue banks, a data bank, and reference laboratories. The creation of a Scientific Advisory Board composed of experts in the various aspects and endpoints of toxicity testing, and representing the academic, industrial, and regulatory communities, is recommended. Test validation acceptance is contingent on broad buy-in by disparate groups in the scientific community--academics, industry, and government. This is best achieved by early and frequent communication among parties and agreement on common goals. It is hoped that the creation of a validation infrastructure composed of the elements described in this report will facilitate scientific acceptance and utilization of alternative methodologies and speed implementation of replacement, reduction, and refinement alternatives in toxicity testing.

Evaluation of purified 4-deoxynivalenol (vomitoxin) for unscheduled DNA synthesis in the primary rat hepatocyte-DNA repair assay.

Primary cultures of rat hepatocytes were used to determine unscheduled DNA synthesis (UDS) and cytotoxicity of purified 4-deoxynivalenol (vomitoxin), a trichothecene mycotoxin produced on cereal grains by fungi of the genus Fusarium. Nontoxic and toxic doses of deoxynivalenol, 0.1 to 1000 micrograms/ml, did not significantly increase UDS as measured by net grains per nucleus, net grains per nuclear area or percentage of cells incorporating greater than or equal to 5, 6, 10 or 20 grains per nucleus. Evidence of cytotoxicity, manifested as a reduction in cell number in autoradiographs, pyknotic nuclei or vacuolated cytoplasm, was observed in hepatocytes treated with deoxynivalenol concentrations of 5 micrograms/ml and above. These findings suggest that the cellular toxicity of deoxynivalenol may not be mediated by a DNA-damaging event in cultured hepatocytes. An increased percentage of large-sized nuclei was also found to be associated with toxic doses of deoxynivalenol as well as 2-acetylaminofluorene used as the positive control.

Influence of Mycoplasma arginini infection on the induction of aryl hydrocarbon hydroxylase by TCDD in rat hepatoma cell cultures.

Mycoplasma arginini was eliminated from a rat hepatoma cell line (H-4-II-E) by plating at low cell density and treatment with chlortetracycline (250 micrograms/ml), kanamycin (250 micrograms/ml), tylosin (100 micrograms/ml), 3% M. arginini antiserum and 5% fresh guinea-pig serum. The induction of AHH activity in the cell culture was measured in response to increasing concentrations of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). The ED50 values (estimated doses that produce 50% maximum enzyme induction) were calculated to be 0.256, 0.452 and 0.344 pmol TCDD/plate for original, mycoplasma-free and reinfected cells, respectively. Although the absence of M. arginini in the rat hepatoma cell line makes the cells slightly less responsive to AHH induction by TCDD, this decrease does not detract from the use of the method to screen food extracts and environmental samples for the presence of certain toxic planar organic compounds.

Evaluation of drug and chemical toxicity with cell culture systems.

Approaches to the evaluation of drug and other chemical toxicity with mammalian cell culture systems are designed to enhance the predictability of animal models. Identification of toxic agents by in vitro screening tests and studies of mechanisms through which chemicals induce critical lesions at the cellular and subcellular levels help to make those predictions sooner and perhaps single out those target sites and chemicals of most concern.

Induction of enzyme activity in cell culture: a rapid screen for detection of planar polychlorinated organic compounds.

Induction of aryl hydrocarbon hydroxylase (AHH) activity in rat hepatoma cell line serves as a simple and rapid method to detect minute (pg) amounts of certain classes of compounds, e.g., dibenzo-p-dioxins, dibenzofurans, and biphenyls. This method may provide a quick screen for such substances in extracts from foods prior to chemical identification. AHH activity is measured by conversion of benzo[a]pyrene (BP) to 3-hydroxy BP in homogenized cell extracts from control and treated cultures and is reported as pmol product formed/mg protein/min. Substances screened by this method include polyhalogenated analogs of dibenzo-p-dioxin (24 compounds), dibenzofuran (11 compounds), biphenyl (7 compounds), and extracts from several food sources. Response of the most reactive compound, 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) was used to prepare a standard curve, and the AHH activity induced by mole doses of test substance is reported as an ED50 response (the estimated dose needed to produce 50% maximum enzyme induction). The AHH activity induced by food extracts is equated to the standard curve and reported as TCDD equivalents. A potent ED50 response in cell culture appears to correlate well with known toxic responses in other mammalian and avian systems for certain test substances. This correlation suggests that the cell culture enzyme induction method is a useful model for screening food extracts that are suspected to be contaminated with polychlorinated planar substances. A collaborative study would demonstrate the reproducibility of the method.

Screening of fresh water fish extracts for enzyme-inducing substances by an aryl hydrocarbon hydroxylase induction bioassay technique.

A sensitive biological test to detect the presence of certain contaminants, such as highly toxic halogenated dioxins, dibenzofurans, and biphenyls in foods, was applied to extracts of fresh water fish that had been prepared by a food extraction-cleanup procedure developed by the Food and Drug Administration for pesticides and industrial chemicals. Aryl hydrocarbon hydroxylase (AHH) activity in a rat hepatoma cell line was used as the biological detection system for residues that induce enzyme activity. The induction of AHH activity by the extracts was compared with a standard AHH-induction curve for the most active compound known, 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), and results were computed as TCDD equivalents. Several dilutions of fish extracts were used to produce AHH-induction curves from which an optimal dose-response range was determined and used to estimate TCDD equivalents. Cleaned-up extracts of fish obtained from different water bodies in the United States were examined for AHH activity. The samples which had low levels of polyhalogenated contaminants produced low biological activity, while a higher activity was obtained from fish that contained higher levels of polyhalogenated contaminants. The results suggest that the fish extracts can be screened for AHH inducers before chemical analysis.

Induction of aryl hydrocarbon hydroxylase activity in cell cultures by aroclors, residues from yusho oil samples, and polychlorinated biphenyl residues from fish samples.

Four Aroclor reference materials, cleaned-up extracts of 2 yusho rice oil samples, and cleaned-up extracts of 3 fish samples containing polychlorinated biphenyl (PCB) residues were tested for their ability to induce aryl hydrocarbon hydroxylase (AHH) activity in a rat hepatoma cell line. Before the AHH bioassay, the samples were fractionated by a Florisil column chromatographic method. All samples contained about 1000 micrograms PCBs before Florisil column chromatography. The first Florisil eluate contains about 95% of the PCBs in a typical Aroclor, and the second contains the more polar or adsorbent PCB congeners. In this study, the first eluate for all samples produced no quantifiable AHH activity. The second Florisil eluates of both Aroclors 1242 and 1248 induced AHH activity, whereas these eluates of both Aroclors 1254 and 1260 did not. This difference may be due to the presence in Aroclors 1242 and 1248 of 3,3',4,4'-tetrachlorobiphenyl, which has not been detected in Aroclors 1254 and 1260. The second Florisil eluates of the fish samples induced somewhat less AHH activity than did Aroclor 1242 or 1248. The second Florisil eluates of the PCB residues from yusho rice oil samples induced significantly greater AHH activity than these eluates of either Aroclor 1242 or 1248, perhaps because yusho rice oil contains a greater amount of polychlorinated dibenzofurans than PCB commercial mixtures on a PCB equivalent basis.

Report of the Validation and Technology Transfer Committee of the Johns Hopkins Center for Alternatives to Animal Testing. Framework for validation and implementation of in vitro toxicity tests.

The development and application of in vitro alternatives designed to reduce or replace the use of animals, or to lessen the distress and discomfort of laboratory animals, is a rapidly developing trend in toxicology. However, at present there is no formal administrative process to organize, coordinate, or evaluate validation activities. A framework capable of fostering the validation of new methods is essential for the effective transfer of new technological developments from the research laboratory into practical use. This committee has identified four essential validation resources: chemical bank(s), cell and tissue banks, a data bank, and reference laboratories. The creation of a Scientific Advisory Board composed of experts in the various aspects and endpoints of toxicity testing, and representing the academic, industrial and regulatory communities, is recommended. Test validation acceptance is contingent upon broad buy-in by disparate groups in the scientific community-academics, industry and government. This is best achieved by early and frequent communication among parties and agreement upon common goals. It is hoped that the creation of a validation infrastructure composed of the elements described in this report will facilitate scientific acceptance and utilization of alternative methodologies and speed implementation of replacement, reduction and refinement alternatives in toxicity testing.