An in vitro toxicity testing strategy for the classification and labelling of chemicals according to their potential acute lethal potency

Modernizing persistence-bioaccumulation-toxicity (PBT) assessment with high throughput animal-free methods

The assessment of persistence (P), bioaccumulation (B), and toxicity (T) of a chemical is a crucial first step at ensuring chemical safety and is a cornerstone of the European Union's chemicals regulation REACH (Registration, Evaluation, Authorization, and Restriction of Chemicals). Existing methods for PBT assessment are overly complex and cumbersome, have produced incorrect conclusions, and rely heavily on animal-intensive testing. We explore how new-approach methodologies (NAMs) can overcome the limitations of current PBT assessment. We propose two innovative hazard indicators, termed cumulative toxicity equivalents (CTE) and persistent toxicity equivalents (PTE). Together they are intended to replace existing PBT indicators and can also accommodate the emerging concept of PMT (where M stands for mobility). The proposed "toxicity equivalents" can be measured with high throughput in vitro bioassays. CTE refers to the toxic effects measured directly in any given sample, including single chemicals, substitution products, or mixtures. PTE is the equivalent measure of cumulative toxicity equivalents measured after simulated environmental degradation of the sample. With an appropriate panel of animal-free or alternative in vitro bioassays, CTE and PTE comprise key environmental and human health hazard indicators. CTE and PTE do not require analytical identification of transformation products and mixture components but instead prompt two key questions: is the chemical or mixture toxic, and is this toxicity persistent or can it be attenuated by environmental degradation? Taken together, the proposed hazard indicators CTE and PTE have the potential to integrate P, B/M and T assessment into one high-throughput experimental workflow that sidesteps the need for analytical measurements and will support the Chemicals Strategy for Sustainability of the European Union.

Inclusion of Physicochemical Data in Quantitative Comparisons of In Vitro and In Vivo Toxic Potencies

In order to evaluate the relevance of in vitro test systems for acute toxicity assessment, quantitative comparisons of in vitro and in vivo potency data have to be performed. The potency of chemicals to cells in vitro is usually characterised by nominal effective concentrations (e.g. EC50 values). Often, the only available in vivo data are acute lethal body doses (e.g. LD50 values). To enable a reasonable quantitative in vitro–in vivo comparison to be made, a formula has been developed to permit the conversion of EC50 values into “effective model body doses, ED50 values”. This formula takes into account the lipophilicity of the compounds and the very different relationships between the volumes of the lipid and water compartments in vitro and in vivo. The suitability of this approach is evaluated with results obtained for the first 30 MEIC chemicals.

Immunotoxicity in Ascidians: Antifouling Compounds Alternative to Organotins—V. the Case of Dichlofluanid

Dichlofluanid has long been employed as a fungicide in agriculture and has been massively introduced in antifouling paints for boat hulls over the last two decades. One of the most important toxic effects of antifoulants is represented by immunosuppression in marine invertebrates, which can be analysed in vitro with a number of short-term toxicity assays on haemocytes. Among bioindicators, the colonial ascidian Botryllus schlosseri is a useful candidate; it is a filter-feeding organism living in the water-sediment interface that is found worldwide and is sensitive to antifouling xenobiotics. Dichlofluanid adversely affects both immunocyte lines (phagocyte and cytotoxic lines) after exposure to sublethal concentrations. At 0.05 μM (16.65 μg/L), dichlofluanid induced haemocyte apoptosis and cell shrinkage with a decrease in both motility and phagocytosis. At the lowest concentration (0.01 μM, 3.33 μg/L), inhibition of pivotal enzymatic activities of phagocytes and cytotoxic cells occurred. At the highest concentration (0.1 μM, 33.3 μg/L), dichlofluanid increased glutathione oxidation, leading to stress conditions. The effects of dichlofluanid on immune defence responses are similar to those of organometal-based antifoulants (i.e., organotin compounds and zinc pyrithione), and its use in coastal areas requires attention.

The tenth anniversary of the Björn Ekwall memorial foundation

The Björn Ekwall Memorial Foundation (BEMF) was initiated by the Scandinavian Society for Cell Toxicology in 2001, to honour the memory of Dr Björn Ekwall (1940-2000) and to establish a prize, the Björn Ekwall Memorial Award. The prize is awarded to scientists who have significantly contributed to the field of cell toxicology, and whose work is contributing toward the replacement of animal experiments by alternative toxicity tests. Over the past 10 years, the Björn Ekwall Memorial Award has been presented annually. Björn Ekwall, an outstanding Swedish cell toxicologist, was one of the pioneers in the development and application of alternative methods to animal tests in toxicology. All his scientific work was devoted to in vitro toxicology, and in particular, to the use of cultured human cells for the screening of toxic chemicals. In the middle of the 1980s, he initiated the international Multicentre Evaluation of In Vitro Cytotoxicity (MEIC) project, to evaluate the usefulness of in vitro tests for the estimation of human acute systemic toxicity. To prove his "basal cytotoxicity concept", he established the MEMO database, in which data on the acutely toxic human blood concentrations of drugs and chemicals were collated from the literature and from clinical studies. He also initiated another project, Evaluation-Guided Development of In Vitro Toxicity and Toxicokinetic Tests (EDIT). The ideas from the EDIT project, together with those from the MEIC project, became the basis for today's international EU projects, e.g. ACuteTox, Sens-it-iv and ReProTect. In this article, 10 years after the start of the BEMF, the scientific achievements of each of the award winners in the field of in vitro toxicology are presented, together with a brief synopsis of their careers.

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.

The improvement of in vitro cytotoxicity testing for the assessment of acute toxicity in fish

The use of fish cell line cytotoxicity tests as alternatives to acute lethality tests with fish is hampered by the clearly lower sensitivity of the fish cell line tests. Recently, it has been shown that this is not a unique feature of fish cells. In fact, the sensitivity of mammalian and human cell lines toward the cytotoxic actions of chemicals, in general, is comparable to that of fish cell lines. Reviewing some of our recent investigations, the objective of this paper is to show that the sensitivity of in vitro cytotoxicity testing and the correspondence between in vitro cytotoxic and acute fish toxic concentrations (LC50) can be increased, if: a) inhibition of cell growth instead of cell death is used as the endpoint; and b) the bioavailable free cytotoxic concentration (ECu50) of chemicals in vitro, instead of the nominal cytotoxic concentration (EC50), is used as the measure of cytotoxic potency. Based on these results, a pragmatic in vitro testing strategy for estimating the minimal aquatic toxic potency of chemicals is proposed.

Acute oral toxicity

The purposes of acute toxicity testing are to obtain information on the biologic activity of a chemical and gain insight into its mechanism of action. The information on acute systemic toxicity generated by the test is used in hazard identification and risk management in the context of production, handling, and use of chemicals. The LD50 value, defined as the statistically derived dose that, when administered in an acute toxicity test, is expected to cause death in 50% of the treated animals in a given period, is currently the basis for toxicologic classification of chemicals. For a classical LD50 study, laboratory mice and rats are the species typically selected. Often both sexes must be used for regulatory purposes. When oral administration is combined with parenteral, information on the bioavailability of the tested compound is obtained. The result of the extensive discussions on the significance of the LD50 value and the concomitant development of alternative procedures is that authorities today do not usually demand classical LD50 tests involving a large number of animals. The limit test, the fixed-dose procedure, the toxic class method, and the up-and-down methods all represent simplified alternatives using only a few animals. Efforts have also been made to develop in vitro systems; e.g., it has been suggested that acute systemic toxicity can be broken down into a number of biokinetic, cellular, and molecular elements, each of which can be identified and quantified in appropriate models. The various elements may then be used in different combinations to model large numbers of toxic events to predict hazard and classify compounds.

FRAME Recommendations for the Application of the Three Rs to the Regulatory Toxicity Testing of Food Additives

Direct food additives are tested for genotoxicity, acute and subchronic toxicity, carcinogenicity and teratogenicity. International guidelines differ in the types of tests required, the duration of the tests, the species of animals to be used, the number of animals recommended and the method of housing experimental animals. This lack of harmonisation is wasteful in terms of animal use and creates additional and, perhaps, unnecessary work for the food industry. In addition, unlike other chemicals, food additives pose a special problem for toxicity testing due to repeated low-dose, life-time human exposure, which is difficult to model in animal studies. In an assessment of the extent to which the Three Rs (reduction, refinement and replacement) can be applied to food additive toxicity testing, it was concluded that differences in regulatory requirements and testing protocols can be improved in both the short term and longer term. Suggestions for improvements to existing alternative approaches for food toxicity testing are made.

The Evaluation of Pesticide Ingredients and Formulations In Vitro and Correlations with In Vivo Data

Pesticides are often insoluble directly in aqueous solvents, but can be dissolved/suspended in surfactant-uased formulations. Both surfactants and pesticides can induce irritation. Since a single in vitro assay has proved inadequate for evaluating the toxicity of a chemical and its ability to cause an irritant response, a combination of assays was employed to examine the potential toxicities of two pesticide formulations. The surfactant-based vehicles had toxicities that reflected their surfactant concentration. The formulation containing 5% permethrin required a more concentrated vehicle than was needed to dissolve 0.1% cypermethrin. In vitro, the ID50 dose (i.e. the dose which inhibited the increase in total cellular protein by 50%) was 576μg/ml for the permethrin formulation and 1080μg/ml for the cypermethrin formulation. This corresponded closely to the ID50 values for the vehicles alone (464μg/ml and 1230μg/ml, respectively). When tested at high concentrations on confluent cells over a 1-minute exposure period to mimic potential exposure of the eye, the more concentrated vehicle, Lanosol 50 ME, was 4–6 times more toxic than Siege II. Technical grade permethrin and cypermethrin had low toxicities in each of the in vitro tests employed. Taken together, these results reflected the in vivo profiles available.

Comparative Cell Toxicology: The Basis for In Vitro Toxicity Testing

If “cell toxicology” is defined as the discipline aimed at studying the general principles of chemical interference with cellular structures and/or functions, then “comparative cell toxicology” may be defined as the study of the variety of responses to xenobiotics using: (a) different endpoints within one cell type; (b) cell types from different tissues from one species; and (c) homologous cell types from different species. If the full potential of in vitro models for toxicity testing is to be realised and the scientific basis for hazard assessment improved, then comparative cell toxicological approaches have to be developed further. In the present paper, an approach using different in vitro systems is described. The approach is aimed at the assessment of the basic toxicological characteristics of chemicals.