Cytotoxicity and mutagenicity of vapor-phase pollutants in rat lung epithelial cells and Chinese hamster ovary cells grown on collagen gels

Value and limitation of in vitro bioassays to support the application of the threshold of toxicological concern to prioritise unidentified chemicals in food contact materials

Some of the chemicals in materials used for packaging food may leak into the food, resulting in human exposure. These include so-called Non-intentionally Added Substances (NIAS), many of them being unidentified and toxicologically uncharacterized. This raises the question of how to address their safety. An approach consisting of identification and toxicologically testing all of them appears neither feasible nor necessary. Instead, it has been proposed to use the threshold of toxicological concern (TTC) Cramer class III to prioritise unknown NIAS on which further safety investigations should focus. Use of the Cramer class III TTC for this purpose would be appropriate if amongst others sufficient evidence were available that the unknown chemicals were not acetylcholinesterase inhibitors or direct DNA-reactive mutagens. While knowledge of the material and analytical chemistry may efficiently address the first concern, the second could not be addressed in this way. An alternative would be use of a bioassay capable of detecting DNA-reactive mutagens at very low levels. No fully satisfactory bioassay was identified. The Ames test appeared the most suitable since it specifically detects DNA-reactive mutagens and the limit of biological detection of highly potent genotoxic carcinogens is low. It is proposed that for a specific migrate, the evidence for absence of mutagenicity based on the Ames test, together with analytical chemistry and information on packaging manufacture could allow application of the Cramer class III TTC to prioritise unknown NIAS. Recommendations, as well as research proposals, have been developed on sample preparation and bioassay improvement with the ultimate aim of improving limits of biological detection of mutagens. Although research is still necessary, the proposed approach should bring significant benefits over the current practices used for safety evaluation of food contact materials.

Cell and tissue-based in vitro models for improving the development of oral inhalation drug products

The interplay of costs and ethics has increased the need for adequate models mimicking the human in vivo situation drastically. An adequate model has the ability to generate data which are predictive for a certain aspect of the human response, for example for the bioavailability. This review highlights how in vitro models can enrich pulmonary drug delivery research with more detailed insights in cellular and non-cellular barriers, allowing for faster improvements and significant innovations of inhalation drug products. Risk assessment in inhalation toxicology and aerosol medicines and related important guidelines (e.g. OECD, EMA) are mentioned as a fundament for the described methods. Principle decisions to find a suitable in vitro tool for the question being asked are discussed to support the individual selection. Depending on the cellular and non-cellular barrier, exemplary in vitro tools are described with their ability to reflect a certain part of the in vivo lung situation. The review closes with a short summary of more complex systems as well as their advantages and limitations.

Integrated Decision-tree Testing Strategies for Acute Systemic Toxicity and Toxicokinetics with Respect to the Requirements of the EU REACH Legislation

Liverpool John Moores University and FRAME conducted a joint research project, sponsored by Defra, on the status of alternatives to animal testing with regard to the European Union REACH (Registration, Evaluation and Authorisation of Chemicals) system for the safety testing and risk assessment of chemicals. The project covered all the main toxicity endpoints associated with REACH. This paper focuses on the use of alternative (non-animal) methods (both in vitro and in silico) for acute systemic toxicity and toxicokinetic testing. The paper reviews in vitro tests based on basal cytotoxicity and target organ toxicity, along with QSAR models and expert systems available for this endpoint. The use of PBPK modelling for the prediction of ADME properties is also discussed. These tests are then incorporated into a decision-tree style, integrated testing strategy, which also includes the use of refined in vivo acute toxicity tests, as a last resort. The implementation of the strategy is intended to minimise the use of animals in the testing of acute systemic toxicity and toxicokinetics, whilst satisfying the scientific and logistical demands of the EU REACH legislation.

Integrated decision-tree testing strategies for acute systemic toxicity and toxicokinetics with respect to the requirements of the EU REACH legislation

Liverpool John Moores University and FRAME conducted a joint research project, sponsored by Defra, on the status of alternatives to animal testing with regard to the European Union REACH (Registration, Evaluation and Authorisation of Chemicals) system for the safety testing and risk assessment of chemicals. The project covered all the main toxicity endpoints associated with REACH. This paper focuses on the use of alternative (non-animal) methods (both in vitro and in silico) for acute systemic toxicity and toxicokinetic testing. The paper reviews in vitro tests based on basal cytotoxicity and target organ toxicity, along with QSAR models and expert systems available for this endpoint. The use of PBPK modelling for the prediction of ADME properties is also discussed. These tests are then incorporated into a decision-tree style, integrated testing strategy, which also includes the use of refined in vivo acute toxicity tests, as a last resort. The implementation of the strategy is intended to minimise the use of animals in the testing of acute systemic toxicity and toxicokinetics, whilst satisfying the scientific and logistical demands of the EU REACH legislation.

Enhanced sodium absorption in middle ear epithelial cells cultured at air-liquid interface

CONCLUSION

As we demonstrated previously that transcription of alpha-ENaC was correlated with oxygen tension in the culture medium, this study suggests that the increase in alpha-ENaC expression observed under ALI conditions may result from greater oxygenation of ME cells.

OBJECTIVE

The physiology of the middle ear (ME) is primarily concerned with keeping the cavities fluid-free, to allow transmission of sound vibrations from the eardrum to the inner ear. ME epithelial cells are thought to play a key role in this process as they actively absorb sodium and water in order to clear any excess fluid present in the cavities.

MATERIAL AND METHODS

As an air-liquid interface (ALI) model has been shown to improve differentiation and enhance sodium absorption in other respiratory epithelia, we established an ALI model for ME cells.

RESULTS

ME cells cultured under ALI conditions exhibited a fourfold increase in sodium absorption, which was not related to either a metabolic effect or to enhanced morphological differentiation, but instead to an increase in expression of the alpha-subunit of the epithelial sodium channel (alpha-ENaC).

A review and analysis of the Chinese hamster ovary/hypoxanthine guanine phosphoribosyl transferase assay to determine the mutagenicity of chemical agents. A report of phase III of the U.S. Environmental Protection Agency Gene-Tox Program

Published literature on the Chinese hamster ovary cell/hypoxanthine guanine phosphoribosyl transferase (CHO/HGPRT) assay from mid-1979 through June 1986 was reviewed and evaluated. Data from the papers considered acceptable include test results on 121 chemicals belonging to 25 chemical classes. A total of 87 chemicals were evaluated positive, 3 negative, and 31 inconclusive. Mutagenicity data on 49 of the 121 chemicals evaluated could also be compared with in vivo animal carcinogenicity data. 40 of the 43 reported animal carcinogens were considered mutagenic. Caprolactam, the only definitive noncarcinogen in the group of 49, was not mutagenic. The CHO/HGPRT assay was concluded to be an appropriate assay system for use in the screening of chemicals for genotoxicity.

An in vitro lung epithelial cell system for evaluating the potential toxicity of inhalable materials

Assays have been developed using a lung epithelial cell strain, LEC, for evaluating the cytotoxicity and genotoxicity of gases, vapours, particles and fibres. LEC was derived from an adult male Fischer 344 rat and was cultured continuously in vitro for over 60 passages. The cells had an epithelial morphology, a near-diploid modal chromosome number of 43-44, and properties of untransformed cells. Lamellar inclusion bodies were found in the cytoplasm, suggesting that LEC originated from the type II alveolar cells. The ability to LEC to metabolize xenobiotics was demonstrated by the formation of polar metabolites from benzo[a]pyrene, the induction of gene mutation by promutagens in a metabolically incompetent cell line (Chinese hamster ovary cells) after co-cultivation with LEC, and the induction of sister chromatid exchange in LEC by promutagens. LEC will grow on collagen gel in the absence of an overlying medium, thereby constituting an in vitro exposure system closely resembling lung epithelium in vivo. The cytotoxic potential of inhalable agents, including nitrogen dioxide, phenol vapours, formaldehyde, automobile exhaust, titanium dioxide and chrysotile and crocidolite forms of asbestos was studied. The in vitro cytotoxicity appeared to correlate well with the known in vivo pulmonary toxicity of the substances studied. Using chromosomal-aberration induction as an endpoint, chrysotile asbestos was found to be genotoxic to LEC. Our results suggest that LEC may be a useful in vitro system for the evaluation of the toxic potential of inhalable materials.