Analysis of negative historical control group data from the in vitro micronucleus assay using TK6 cells.

The recent revisions of the Organisation for Economic Co-operation and Development (OECD) genetic toxicology test guidelines emphasize the importance of historical negative controls both for data quality and interpretation. The goal of a HESI Genetic Toxicology Technical Committee (GTTC) workgroup was to collect data from participating laboratories and to conduct a statistical analysis to understand and publish the range of values that are normally seen in experienced laboratories using TK6 cells to conduct the in vitro micronucleus assay. Data from negative control samples from in vitro micronucleus assays using TK6 cells from 13 laboratories were collected using a standard collection form. Although in some cases statistically significant differences can be seen within laboratories for different test conditions, they were very small. The mean incidence of micronucleated cells/1000 cells ranged from 3.2/1000 to 13.8/1000. These almost four-fold differences in micronucleus levels cannot be explained by differences in scoring method, presence or absence of exogenous metabolic activation (S9), length of treatment, presence or absence of cytochalasin B or different solvents used as vehicles. The range of means from the four laboratories using flow cytometry methods (3.7-fold: 3.5-12.9 micronucleated cells/1000 cells) was similar to that from the nine laboratories using other scoring methods (4.3-fold: 3.2-13.8 micronucleated cells/1000 cells). No laboratory could be identified as an outlier or as showing unacceptably high variability. Quality Control (QC) methods applied to analyse the intra-laboratory variability showed that there was evidence of inter-experimental variability greater than would be expected by chance (i.e. over-dispersion). However, in general, this was low. This study demonstrates the value of QC methods in helping to analyse the reproducibility of results, building up a 'normal' range of values, and as an aid to identify variability within a laboratory in order to implement processes to maintain and improve uniformity

Comparative evaluation of the in vitro micronucleus test and the alkaline single cell gel electrophoresis assay for the detection of DNA damaging agents: Genotoxic effects of cobalt powder, tungsten carbide and cobalt-tungsten carbide

Although it is well known that micronuclei may arise from either DNA breakage leading to acentric chromosome fragments or from chromosome/chromatid lagging in anaphase, the ratio between the amount of DNA breakage induced and the frequency of micronuclei expressed in the following interphase is unclear. With the development of the alkaline single cell gel electrophoresis assay, which measures single strand and/or double strand breaks in a cell by cell approach, it is now possible to address this question at the cellular level. We therefore compared the genotoxic potential of pure cobalt powder (Co) and a cobalt-containing alloy, cobalt-tungsten carbide (WC-Co), involved in specific lung disorders, in parallel with the alkaline single cell gel electrophoresis (SCGE) assay (comet assay) and the cytokinesis-blocked micronucleus (MN) test, both carried out in vitro on isolated human leukocytes. The comet assay indicated that the WC-Co mixture produced a higher level of DNA damage than Co alone; WC alone was not able to induce a dose-dependent DNA breakage effect as was seen for Co and WC-Co. Results from the MN test confirmed these observations. It was clear that the clastogenic property of Co-containing dust is significantly enhanced when the Co metal is mixed with WC and suggested that their physicochemical characteristics may act as one of the important parameters responsible for the increased incidence of lung cancers observed in the population of hard metal workers. In agreement with data obtained in the same laboratory on liposoluble chemicals (PCBs and chlorinated aliphatic hydrocarbons) and from the literature, the results indicate that both the comet assay and the micronucleus test were able to detect differences in the genotoxic potential of the compounds studied. Although the micronucleus test seemed to be less sensitive to assess a synergistic DNA damaging potential of the mixture involved, it detects chromosomal aberrations (chromosome/genome mutations) and not just repairable DNA breakage or alkali-labile sites. Combination of the comet assay and the in vitro MN test might therefore be recommended for genotoxins to understand the mechanisms underlying mutagenicity and to assess the lowest efficient dose.SCOPUS: ar.jinfo:eu-repo/semantics/publishe

Identification of clastogenic and/or aneugenic events during the preneoplastic stages of experimental rat hepatocarcinogenesis by fluorescence in situ hybridization

A growing body of evidence from human and animal cancer cytogenetics studies indicates that aneuploidy is an important chromosome change in carcinogenesis. To understand the role of this genetic phenomenon during the first steps of an experimental cancer model, molecular and cellular techniques were combined. A sequential cytogenetic study of a modified Solt-Farber liver cancer model in the rat was performed to identify the importance of chromosome versus genome mutations. Male Wistar rats were initiated with diethylnitrosamine (DENA), followed by a 2-acetylaminofluorene exposure to select resistant hepatocytes. Chronic phenobarbital (PB) treatment was used to induce promotion. Cell proliferation was induced by a necrogenic dose of CCl4, administered during the selection period (Gerlans protocol) or 3 days before hepatocyte isolation (experimental protocol). In order to discriminate between genetic events causing chromosome breakage (clastogenic) and those that induce chromosome loss (aneugenic), isolated micronucleated hepatocytes (MNH) were analysed for the presence of a centromere in the micronucleus (MN). Non-radioactive in situ hybridization with a rat centromere satellite 1 DNA probe was applied. Our results show that the majority of the observed genetic changes, expressed as MN during different preneoplastic stages, were of clastogenic origin. However, the number of induced aneugenic hepatocytes increased markedly during the promotion period of the Gerlans protocol (~7-fold above control) and during PB exposure in the experimental protocol (~4-fold above control). Additionally, these stages were also characterized by an increased level of MN expression (20.3 < ?MNH < 32.8), in comparison with the initiation stage after DENA exposure (13.5 < ?MNH < 17.1). Although it is not yet clear if these genetic alterations have a causative nature in neoplastic liver transformation, the use of interphase cytogenetics certainly might lead to a better understanding of the genomic changes which occur during experimental hepatocarcinogenesis.SCOPUS: ar.jinfo:eu-repo/semantics/publishe

The mucosal toxicity of different benzalkonium chloride analogues evaluated with an alternative test using slugs

Purpose. The objective of this study was to evaluate the mucosal toxicity of different benzalkonium chloride (BAC) analogues using slugs as the alternative test organism. Methods. The effect of different BAC analogues on the mucosal tissue of slugs was determined from the protein, lactate dehydrogenase, and alkaline phosphatase released from the foot mucosa after treatment. Additionally, mucus production and reduction in body weight of the slugs were measured. The eye irritation potency of the molecules was evaluated with the Bovine Corneal Opacity and Permeability (BCOP) assay. The antimicrobial activity of the different BAC analogues was also assessed. Results. All BAC analogues induced severe damage to the mucosal epithelium of the slugs, and the irritation increased with decreasing alkyl chain length: BAC-C16 BAC-C12. The BAC-C14 exhibited higher activity than the BAG-mix. Conclusions. The toxicity and activity of BAG analogues depend on the alkyl chain length. The use of BAC-C14 as a conservative agent in pharmaceutical preparations instead of the BAG-mix should be considered

Flow cytometric analysis of micronuclei in mammalian cell cultures: past, present and future.

The relative simplicity of the in vitro micronucleus (MNvit) endpoint has made it amenable to several automated scoring approaches. Flow cytometry is one such scoring platform that has been successfully employed. This review describes the origins of the MNvit assay, as well as the evolution and properties of flow cytometry-based scoring systems. While the current state-of-the-art methods acquire micronucleus (MN) frequency data very efficiently, it is becoming clear that they also endow the assay with high information content. For instance, simultaneous with MN frequency determinations, several additional endpoints are acquired that provide insights into cytotoxicity, cell cycle perturbations and, in the event of MN induction, information about genotoxic mode of action. This review concludes with a discussion regarding data gaps and also recommendations for additional work that is needed to more fully realise the potential of flow cytometric MNvit scoring

Hepatotoxicity Screening on In Vitro Models and the Role of 'Omics

The liver is one of the five most common target organs of toxicity, both during acute and chronic (repeated dose) toxicity, not only for drugs but also for cosmetic ingredients. Chemical entities can trigger liver damage in humans, and hepatotoxicity is the leading cause of withdrawal of drugs from the market, accounting for 40% of withdrawals worldwide. It has been estimated that only 50% of human liver toxicities could be predicted using animal models, and there is a clear need for accurately predictive toxicity and safety testing methods. Hepatocellular injury can manifest in a number of ways, including hepatitis, steatosis, cirrhosis, inflammation, phospholipidosis, and cholestasis. Cholestasis and steatosis are among the most prominent and well-documented types of liver injury and are the focus of this chapter. Furthermore, attention is also paid to necrosis, a mode of cell death that is observed in most of the aforementioned types of hepatocellular injury

Are zebrafish larvae suitable for assessing the hepatotoxicity potential of drug candidates?

Drug-induced liver injury (DILI) is poorly predicted by single-cell-based assays, probably because of the lack of physiological interactions with other cells within the liver. An intact whole liver system such as one present in zebrafish larvae could provide added value in a screening strategy for DILI; however, the possible occurrence of other organ toxicities and the immature larval stage of the zebrafish might complicate accurate and fast analysis. We investigated whether expression analysis of liver-specific fatty acid binding protein 10a (lfabp10a) was an appropriate endpoint for assessing hepatotoxic effects in zebrafish larvae. It was found that expression analysis of lfabp10a was a valid marker, as after treatment with hepatotoxicants, dose-response curves could be obtained and statistically significant abnormal lfabp10 expression levels correlated with hepatocellular histopathological changes in the liver. However, toxicity in other vital organs such as the heart could impact liver outgrowth and thus had to be assessed concurrently. Whether zebrafish larvae were suitable for assessing human relevant drug-induced hepatotoxicity was assessed with hepatotoxicants and non-hepatotoxicants that have been marketed for human use and classified according to their mechanism of toxicity. The zebrafish larva showed promising predictivity towards a number of mechanisms and was capable of distinguishing between hepatotoxic and non-hepatotoxic chemical analogues, thus implying its applicability as a potential screening model for DILI. Copyright © 2015 John Wiley & Sons, Ltd.status: publishe

Hepatotoxicity Screening on In Vitro Models and the Role of 'Omics

The liver is one of the five most common target organs of toxicity, both during acute and chronic (repeated dose) toxicity, not only for drugs but also for cosmetic ingredients. Chemical entities can trigger liver damage in humans, and hepatotoxicity is the leading cause of withdrawal of drugs from the market, accounting for 40% of withdrawals worldwide. It has been estimated that only 50% of human liver toxicities could be predicted using animal models, and there is a clear need for accurately predictive toxicity and safety testing methods. Hepatocellular injury can manifest in a number of ways, including hepatitis, steatosis, cirrhosis, inflammation, phospholipidosis, and cholestasis. Cholestasis and steatosis are among the most prominent and well-documented types of liver injury and are the focus of this chapter. Furthermore, attention is also paid to necrosis, a mode of cell death that is observed in most of the aforementioned types of hepatocellular injury.</p

Optimizing drug discovery by Investigative Toxicology: Current and future trends – Report of CAAT-ITL Forum Think Tank

Investigative Toxicology describes the de-risking, and mechanistic elucidation of effects that supports critical early safety related decision making in the pharmaceutical industry. While the individual tasks and organizational set-up of these functions differ from company to company, it has become evident that the value of these activities do not only lie in screening assays, which precede the regulatory activities, but also in the contribution of an enhanced understanding of the mechanism of toxicity. In fact, this shifts pharmaceutical toxicology from a purely descriptive to an evidence-based mechanistic discipline. In addition, the high costs and the rather low throughput of the GLP (Good Laboratory Practice) in vivo studies, as well as increasing demands for adhering to the 3Rs (Replacement, Reduction and Refinement) principals, has increased the push for new innovative approaches. A key aspect is therefore the translation of in vitro to in vivo mechanistic data. Outside of the boundaries of regulatory toxicology with its GLP in vivo studies, Investigative Toxicology has the flexibility to embrace new technologies, though there is often a perception that non-GLP /not fully validated assays might compromise the pivotal studies and endanger the approval process. Consequently, standards of harmonization and validation as developed for the GLP studies are implicitly also demanded for the new technologies. A group of 14 European-based Investigative Toxicology leaders from the pharmaceutical industry (AstraZeneca, Bayer, Boehringer Ingelheim, GSK, Janssen, Lundbeck, Merck, Novartis, Novo Nordisk, Orion Pharma, Roche, Sanofi, Servier and UCB-Biopharma) founded the Investigative Toxicology Leaders Forum (ITLF). The goal of Investigative Toxicology, and therefore of improved preclinical decision making, coincides with the notion of an animal-free safety testing environment. Currently, too many compounds are ruled out by animal models during the preclinical phase, without knowledge of how the compounds would behave in humans, i.e. the false-positive rate of animal studies cannot be assessed. Progress in Investigative Toxicology could lead to humanized in vitro test systems and thus pave the way towards medicines less residing on animal use. For this reason, the ITLF collaborated with the Centre for Alternatives to Animal Testing Europe (CAAT-Europe) to organize an "Investigative Toxicology Think-Tank". This event also aimed to enhance the interaction with experts from academia and regulatory bodies in the field