Genetic toxicity assessment: employing the best science for human safety evaluation. Part II: Performances of the in vitro micronucleus test compared to the mouse lymphoma assay and the in vitro chromosome aberration assay

Genotoxicity and mutagenicity evaluation of isoquercitrin-γ-cyclodextrin molecular inclusion complex using Ames test and a combined micronucleus and comet assay in rats

Flavonoids such as quercetin and its glucosides, especially isoquercitrin are well known as anti-inflammatory, anti-allergic, and anti-carcinogenic, etc. The safety of isoquercitrin formulations needs to be established prior to their use in functional food applications. The mutagenicity and genotoxicity of the IQC-γCD inclusion complex were assessed with three standard assays of the bacterial reverse mutation assay (Ames test) and using a combined in-vivo micronucleus and comet assay under the Organisation for Economic Co-operation and Development (OECD) guidelines. In combined rat bone marrow micronucleus and rat liver comet assay performed in male Sprague Dawley (SD) rats, the various doses of IQC-γCD inclusion complex (max. 2000 mg/kg bw) and positive controls ethyl methanesulfonate (EMS) and mitomycin C (MMC), respectively, and negative control (vehicle) were administrated. The results of the Salmonella typhimurium mutagenicity assay (strains TA100, TA1535, WP2uvrA, TA98, and TA1537) after exposure to the IQC-γCD inclusion complex with the absence and presence of the metabolic activation system (S9 fraction from rat liver) revealed a weakly positive response but with no biologically relevant mutagenicity at the conditions examined according to recommended regulatory guidelines. The combined micronucleus and comet assay results reveal that the IQC-γCD inclusion complex did not induce in-vivo genotoxic potential or indication of any oxidative DNA damage in rat liver tissues. Altogether, considering the results of the study, it is unlikely that the consumption of IQC-γCD inclusion complex as food or supplement would present any concern for humans regarding the mutagenicity and genotoxicity.

Antigenotoxic effects of a polyherbal drug septilin against the genotoxicity of cyclophosphamide in mice

Septilin (Spt) is a polyherbal drug formulation from Himalaya Drug Company, consisting of extracts from different medicinal plants and minerals. In the traditional system of medicine, septilin is being used as immunomodulatory, antioxidant and anti-inflammatory agent. In the present study, the protective effects of septilin against the genotoxicity of cyclophosphamide (CP) a widely used alkylating anticancer drug was evaluated by using in vivo micronucleus (MN) and sperm shape abnormality assays in Swiss albino mice. CP administered intraperitoneally at a dose of 50 mg/kg b.w. was used as positive mutagen. Different doses of septilin viz., 125, 250 and 500 mg/kg b.w. was orally administered for 5 consecutive days. CP was administered intraperitoneally on 5th day. MN and sperm preparations were made after 24 h and 35 days respectively. CP induced significant MN in both bone marrow and peripheral blood cells and also a high frequency of abnormal sperms. In septilin supplemented animals, no significant induction of MN and abnormal sperms was recorded. In septilin supplemented groups, a dose dependent significant decrease in CP induced clastogenicity was observed. Thus the current in vivo study revealed the antigenotoxic effects of septilin against CP induced damage, in both somatic and germ cells of Swiss albino mice.

Mutagenicity testing for chemical risk assessment: update of the WHO/IPCS Harmonized Scheme

Since the publication of the International Programme on Chemical Safety (IPCS) Harmonized Scheme for Mutagenicity Testing, there have been a number of publications addressing test strategies for mutagenicity. Safety assessments of substances with regard to genotoxicity are generally based on a combination of tests to assess effects on three major end points of genetic damage associated with human disease: gene mutation, clastogenicity and aneuploidy. It is now clear from the results of international collaborative studies and the large databases that are currently available for the assays evaluated that no single assay can detect all genotoxic substances. The World Health Organization therefore decided to update the IPCS Harmonized Scheme for Mutagenicity Testing as part of the IPCS project on the Harmonization of Approaches to the Assessment of Risk from Exposure to Chemicals. The approach presented in this paper focuses on the identification of mutagens and genotoxic carcinogens. Selection of appropriate in vitro and in vivo tests as well as a strategy for germ cell testing are described.

Biomonitoring of complex occupational exposures to carcinogens: the case of sewage workers in Paris

Background

Sewage workers provide an essential service in the protection of public and environmental health. However, they are exposed to varied mixtures of chemicals; some are known or suspected to be genotoxics or carcinogens. Thus, trying to relate adverse outcomes to single toxicant is inappropriate. We aim to investigate if sewage workers are at increased carcinogenic risk as evaluated by biomarkers of exposure and early biological effects.

Methods/design

This cross sectional study will compare exposed sewage workers to non-exposed office workers. Both are voluntaries from Paris municipality, males, aged (20–60) years, non-smokers since at least six months, with no history of chronic or recent illness, and have similar socioeconomic status. After at least 3 days of consecutive work, blood sample and a 24-hour urine will be collected. A caffeine test will be performed, by administering coffee and collecting urines three hours after. Subjects will fill in self-administered questionnaires; one covering the professional and lifestyle habits while the a second one is alimentary. The blood sample will be used to assess DNA adducts in peripheral lymphocytes. The 24-hour urine to assess urinary 8-oxo-7, 8-dihydro-2'-deoxy-Guanosine (8-oxo-dG), and the in vitro genotoxicity tests (comet and micronucleus) using HeLa S3 or HepG2 cells. In parallel, occupational air sampling will be conducted for some Polycyclic Aromatic Hydrocarbons and Volatile Organic Compounds. A weekly sampling chronology at the offices of occupational medicine in Paris city during the regular medical visits will be followed. This protocol has been accepted by the French Est III Ethical Comitee with the number 2007-A00685-48.

Discussion

Biomarkers of exposure and of early biological effects may help overcome the limitations of environmental exposure assessment in very complex occupational or environmental settings.

Interlaboratory evaluation of a flow cytometric, high content in vitro micronucleus assay

An international, multi-lab trial was conducted to evaluate a flow cytometry-based method for scoring micronuclei in mouse lymphoma L5178Y cells [S.L. Avlasevich, S.M. Bryce, S.E. Cairns, S.D. Dertinger, In vitro micronucleus scoring by flow cytometry: differential staining of micronuclei versus apoptotic and necrotic chromatin enhances assay reliability, Environ. Mol. Mutagen. 47 (2006) 56-66]. A reference laboratory investigated the potential of six chemicals to induce micronuclei -- the genotoxicants mitomycin C (MMC), etoposide (ETOPO), and vinblastine (VB), and the non-genotoxicants sucrose (SUC), staurosporine (STS), and dexamethasone (DEX). The latter two non-genotoxicants were selected as extreme challenges to the assay because of their potent apoptogenic activity. Three collaborating laboratories were supplied with prototype In Vitro MicroFlow kits, and each was assigned one genotoxicant and one non-genotoxicant. Cells were treated continuously for 24h over a range of concentrations up to 5 mg/ml, or overtly cytotoxic concentrations. Micronuclei were scored via standard microscopy and flow cytometry. In addition to enumerating micronucleus frequencies, a cytotoxicity measurement that is simultaneously acquired with the flow cytometric micronucleus scoring procedure was evaluated (Flow-NBR). With this method, latex particles served as counting beads, and facilitated relative survival measurements that exclude the presence of dead/dying cells. For comparison purposes, additional cytotoxicity endpoints were measured, including several that are based on cell number, and others that reflect compromised membrane integrity, including dye permeability and/or phospholipid distribution. Key findings for this set of compounds include the following: (1) significant discrepancies in top concentration selection were found when cytotoxicity measurements were based on different methods, with the Flow-NBR approach tending to be the most sensitive, (2) both microscopy- and flow cytometry-based scoring methods detected concentration-dependent micronucleus formation for the three genotoxic agents studied, with good agreement between the reference laboratory and the collaborating laboratories, and (3) whereas flow cytometric analyses showed no significant increases for the non-genotoxicants when top concentration selection was based on Flow-NBR, significantly elevated micronucleus frequencies were observed for concentrations that were chosen based on less-sensitive cytotoxicity assays. Collectively, these results indicate that rapid assessment of genotoxicity can be accomplished with a relatively simple flow cytometric technique, and that the scoring system is transferable across laboratories. Furthermore, a concurrent assessment of cytotoxicity, Flow-NBR, may help reduce the occurrence of irrelevant positive results, as it may represent a more appropriate means for choosing top concentration levels. Finally, the data presented herein reinforce concerns about the manner in which cytotoxicity limits are described in guidance documents, since these recommendations tend to cite fixed cut-off values without reference to methodology.