EPA-HQ-OPPT-2009-0156-0029

United States Environmental Protection Agency Prevention, Pesticides and Toxic Substances (7101) EPA 712–C–98–223 August 1998 Health Effects Test Guidelines O ppt 关于艾滋病ppt课件精益管理ppt下载地图下载ppt可编辑假如ppt教学课件下载triz基础知识ppt S 870.5375 In Vitro Mammalian Chromosome Aberration Test i INTRODUCTION This guideline is one of a series of test guidelines that have been developed by the Office of Prevention, Pesticides and Toxic Substances, United States Environmental Protection Agency for use in the testing of pesticides and toxic substances, and the development of test data that must be submitted to the Agency for review under Federal regulations. The Office of Prevention, Pesticides and Toxic Substances (OPPTS) has developed this guideline through a process of harmonization that blended the testing guidance and requirements that existed in the Office of Pollution Prevention and Toxics (OPPT) and appeared in Title 40, Chapter I, Subchapter R of the Code of Federal Regulations (CFR), the Office of Pesticide Programs (OPP) which appeared in publications of the National Technical Information Service (NTIS) and the guidelines pub- lished by the Organization for Economic Cooperation and Development (OECD). The purpose of harmonizing these guidelines into a single set of OPPTS guidelines is to minimize variations among the testing procedures that must be performed to meet the data requirements of the U. S. Environ- mental Protection Agency under the Toxic Substances Control Act (15 U.S.C. 2601) and the Federal Insecticide, Fungicide and Rodenticide Act (7 U.S.C. 136, et seq.). Final Guideline Release: This guideline is available from the U.S. Government Printing Office, Washington, DC 20402 on disks or paper copies: call (202) 512–0132. This guideline is also available electronically in PDF (portable document format) from EPA’s World Wide Web site (http://www.epa.gov/epahome/research.htm) under the heading ‘‘Research- ers and Scientists/Test Methods and Guidelines/OPPTS Harmonized Test Guidelines.’’ 1 OPPTS 870.5375 In vitro mammalian chromosome aberration test. (a) Scope—(1) Applicability. This guideline is intended to meet test- ing requirements of both the Federal Insecticide, Fungicide, and Rodenticide Act (FIFRA) (7 U.S.C. 136, et seq.) and the Toxic Substances Control Act (TSCA) (15 U.S.C. 2601). (2) Background. The source materials used in developing this har- monized OPPTS test guideline are OPPT 40 CFR 798.5375 In vitro mam- malian cytogenetics and OECD 473, In Vitro Mammalian Chromosome Aberration Test. (b) Purpose. (1) The purpose of the in vitro chromosome aberration test is to identify agents that cause structural chromosome aberrations in cultured mammalian cells (see paragraphs (i)(1), (i)(2), and (i)(3) of this guideline). Structural aberrations may be of two types, chromosome or chromatid. With the majority of chemical mutagens, induced aberrations are of the chromatid type, but chromosome-type aberrations also occur. An increase in polyploidy may indicate that a chemical has the potential to induce numerical aberrations. However, this guideline is not designed to measure numerical aberrations and is not routinely used for that pur- pose. Chromosome mutations and related events are the cause of many human genetic diseases and there is substantial evidence that chromosome mutations and related events causing alterations in oncogenes and tumour- suppressor genes of somatic cells are involved in cancer induction in hu- mans and experimental animals. (2) The in vitro chromosome aberration test may employ cultures of established cell lines, cell strains or primary cell cultures. The cells used are selected on the basis of growth ability in culture, stability of the karyotype, chromosome number, chromosome diversity, and spontaneous frequency of chromosome aberrations. (c) Definitions. The definitions in section 3 of TSCA and in 40 CFR Part 792—Good Laboratory Practice Standards (GLP) apply to this test guideline. The following definitions also apply to this test guideline. Chromatid-type aberration is structural chromosome damage ex- pressed as breakage of single chromatids or breakage and reunion between chromatids. Chromosome-type aberration is structural chromosome damage ex- pressed as breakage, or breakage and reunion, of both chromatids at an identical site. Endoreduplication is a process in which after an S period of DNA replication, the nucleus does not go into mitosis but starts another S period. The result is chromosomes with 4, 8, 16,...chromatids. 2 Gap is an achromatic lesion smaller than the width of one chromatid, and with minimum misalignment of the chromatid(s). Mitotic index is the ratio of cells in metaphase divided by the total number of cells observed in a population of cells; an indication of the degree of proliferation of that population. Numerical aberration is a change in the number of chromosomes from the normal number characteristic of the cells utilized. Polyploidy is a multiple of the haploid chromosome number (n) other than the diploid number (i.e., 3n, 4n, and so on). Structural aberration is a change in chromosome structure detectable by microscopic examination of the metaphase stage of cell division, ob- served as deletions and fragments, intrachanges, and interchanges. (d) Initial considerations. (1) Tests conducted in vitro generally re- quire the use of an exogenous source of metabolic activation. This meta- bolic activation system cannot mimic entirely the mammalian in vivo con- ditions. Care should be taken to avoid conditions which would lead to positive results which do not reflect intrinsic mutagenicity and may arise from changes in pH, osmolality, or high levels of cytotoxicity (see para- graphs (i)(4) and (i)(5) of this guideline). (2) This test is used to screen for possible mammalian mutagens and carcinogens. Many compounds that are positive in this test are mammalian carcinogens; however, there is not a perfect correlation between this test and carcinogenicity. Correlation is dependent on chemical class and there is increasing evidence that there are carcinogens that are not detected by this test because they appear to act through mechanisms other than direct DNA damage. (e) Principle of the test method. Cell cultures are exposed to the test substance both with and without metabolic activation. At predeter- mined intervals after exposure of cell cultures to the test substance, they are treated with a metaphase-arresting substance (e.g., Colcemid or col- chicine), harvested, stained, and metaphase cells are analysed microscopi- cally for the presence of chromosome aberrations. (f) Description of the method—(1) Preparations—(i) Cells. A vari- ety of cell lines, strains, or primary cell cultures, including human cells, may be used (e.g., Chinese hamster fibroblasts, human, or other mamma- lian peripheral blood lymphocytes). (ii) Media and culture conditions. Appropriate culture media, and incubation conditions (culture vessels, CO2 concentration, temperature and humidity) should be used in maintaining cultures. Established cell lines and strains should be checked routinely for stability in the modal chro- mosome number and the absence of Mycoplasma contamination and 3 should not be used if contaminated. The normal cell-cycle time for the cells and culture conditions used should be known. (iii) Preparation of cultures—(A) Established cell lines and strains. Cells are propagated from stock cultures, seeded in culture me- dium at a density such that the cultures will not reach confluency before the time of harvest, and incubated at 37 °C. (B) Lymphocytes. Whole blood treated with an anti-coagulant (e.g., heparin) or separated lymphocytes obtained from healthy subjects are added to culture medium containing a mitogen (e.g., phytohemagglutinin) and incubated at 37 °C. (iv) Metabolic activation. Cells should be exposed to the test sub- stance both in the presence and absence of an appropriate metabolic activa- tion system. The most commonly used system is a co-factor-supplemented post-mitochondrial fraction (S9) prepared from the livers of rodents treated with enzyme-inducing agents such as Aroclor 1254 (see paragraphs (i)(6), (i)(7), (8)(i), and (i)(9) of this guideline), or a mixture of phenobarbitone and β-naphthoflavone (see paragraphs (i)(10), (i)(11), and (i)(12) of this guideline). The post-mitochondrial fraction is usually used at concentra- tions in the range from 1-10 percent v/v in the final test medium. The condition of a metabolic activation system may depend upon the class of chemical being tested. In some cases, it may be appropriate to utilize more than one concentration of post-mitochondrial fraction. A number of devel- opments, including the construction of genetically engineered cell lines expressing specific activating enzymes, may provide the potential for en- dogenous activation. The choice of the cell lines used should be scientif- ically justified (e.g., by the relevance of the cytochrome P450 isoenzyme for the metabolism of the test substance). (v) Test substance/preparation. Solid test substances should be dis- solved or suspended in appropriate solvents or vehicles and diluted, if ap- propriate, prior to treatment of the cells. Liquid test substances may be added directly to the test systems and/or diluted prior to treatment. Fresh preparations of the test substance should be employed unless stability data demonstrate the acceptability of storage. (2) Test conditions—(i) Solvent/vehicle. The solvent/vehicle should not be suspected of chemical reaction with the test substance and should be compatible with the survival of the cells and the S9 activity. If other than well-known solvent/vehicles are used, their inclusion should be sup- ported by data indicating their compatibility. It is recommended that wher- ever possible, the use of an aqueous solvent/vehicle be considered first. When testing water-unstable substances, the organic solvents used should be free of water. Water can be removed by adding a molecular sieve. 4 (ii) Exposure concentrations. (A) Among the criteria to be consid- ered when determining the highest concentration are cytotoxicity, solu- bility in the test system, and changes in pH or osmolality. (B) Cytotoxicity should be determined with and without metabolic activation in the main experiment using an appropriate indication of cell integrity and growth, such as degree of confluency, viable cell counts, or mitotic index. It may be useful to determine cytotoxicity and solubility in a preliminary experiment. (C) At least three analyzable concentrations should be used. Where cytotoxicity occurs, these concentrations should cover a range from the maximum to little or no toxicity; this will usually mean that the concentra- tions should be separated by no more than a factor between 2 and √10. At the time of harvesting, the highest concentration should show a signifi- cant reduction in degree of confluency, cell count or mitotic index, (all greater than 50 percent). The mitotic index is only an indirect measure of cytotoxic/cytostatic effects and depends on the time after treatment. However, the mitotic index is acceptable for suspension cultures in which other toxicity measurements may be cumbersome and impractical. Infor- mation on cell-cycle kinetics, such as average generation time (AGT), could be used as supplementary information. AGT, however, is an overall average that does not always reveal the existence of delayed subpopula- tions, and even slight increases in average generation time can be associ- ated with very substantial delay in the time of optimal yield of aberrations. For relatively non-cytotoxic compounds the maximum concentration should be 5 µg/ml, 5mg/ml, or 0.01M, whichever is the lowest. (D) For relatively insoluble substances that are not toxic at concentra- tions lower than the insoluble concentration, the highest dose used should be a concentration above the limit of solubility in the final culture medium at the end of the treatment period. In some cases (e.g., when toxicity oc- curs only at higher than the lowest insoluble concentration) it is advisable to test at more than one concentration with visible precipitation. It may be useful to assess solubility at the beginning and the end of the treatment, as solubility can change during the course of exposure in the test system due to presence of cells, S9, serum etc. Insolubility can be detected by using the unaided eye. The precipitate should not interfere with the scor- ing. (iii) Controls. (A) Concurrent positive and negative (solvent or vehi- cle) controls both with and without metabolic activation should be included in each experiment. When metabolic activation is used, the positive control chemical should be the one that requires activation to give a mutagenic response. (B) Positive controls should employ a known clastogen at exposure levels expected to give a reproducible and detectable increase over back- 5 ground which demonstrates the sensitivity of the test system. Positive con- trol concentrations should be chosen so that the effects are clear but do not immediately reveal the identity of the coded slides to the reader. Exam- ples of positive-control substances include: Metabolic activation condition Chemical CAS number Absence of exogenous metabolic activation Methyl methanesulfonate ............ [66–27–3] Ethyl methanesulfonate .............. [62–50–0] Ethylnitrosourea .......................... [759–73–9] Mitomycin C ................................ [50–07–7] 4-Nitroquinoline-N-Oxide ............ [56–57–5] Presence of exogenous metabolic activation Benzo(a)pyrene .......................... [50–32–8] Cyclophosphamide ..................... (monohydrate) ............................. [50–18–0] ([6055–19–2]) (C) Other appropriate positive control substances may be used. The use of chemical class-related positive-control chemicals may be consid- ered, when available. (D) Negative controls, consisting of solvent or vehicle alone in the treatment medium, and treated in the same way as the treatment cultures, should be included for every harvest time. In addition, untreated controls should also be used unless there are historical-control data demonstrating that no deleterious or mutagenic effects are induced by the chosen solvent. (g) Procedure—(1) Treatment with test substance. (i) Proliferating cells are treated with the test substance in the presence and absence of a metabolic-activation system. Treatment of lymphocytes should com- mence at about 48 hours after mitogenic stimulation. (ii) Duplicate cultures should be used at each concentration, and are strongly recommended for negative/solvent control cultures. Where mini- mal variation between duplicate cultures can be demonstrated (see para- graphs (i)(13) and (i)(14) of this guideline), from historical data, it may be acceptable for single cultures to be used at each concentration. (iii) Gaseous or volatile substances should be tested by appropriate methods, such as in sealed culture vessels (see paragraphs (i)(15) and (i)(16) of this guideline). (2) Culture harvest time. In the first experiment, cells should be exposed to the test substance both with and without metabolic activation for 3–6 hours, and sampled at a time equivalent to about 1.5 normal cell- cycle length after the beginning of treatment (see paragraph (i)(12) of this guideline). If this protocol gives negative results both with and without activation, an additional experiment without activation should be done, with continuous treatment until sampling at a time equivalent to about 1.5 normal cell-cycle lengths. Certain chemicals may be more readily de- tected by treatment/sampling times longer than 1.5 cycle lengths. Negative results with metabolic activation need to be confirmed on a case-by-case 6 basis. In those cases where confirmation of negative results is not consid- ered necessary, justification should be provided. (3) Chromosome preparation. Cell cultures should be treated with Colcemid or colchicine usually for 1 to 3 hours prior to harvesting. Each cell culture should be harvested and processed separately for the prepara- tion of chromosomes. Chromosome preparation involves hypotonic treat- ment of the cells, fixation and staining. (4) Analysis. (i) All slides, including those of positive and negative controls, should be independently coded before microscopic analysis. Since fixation procedures often result in the breakage of a proportion of meta- phase cells with loss of chromosomes, the cells scored should therefore contain a number of centromeres equal to the modal number ±2 for all cell types. At least 200 well-spread metaphases should be scored per con- centration and control equally divided amongst the duplicates, if applica- ble. This number can be reduced when high numbers of aberrations are observed. (ii) Though the purpose of the test is to detect structural chromosome aberrations, it is important to record polyploidy and endoreduplication when these events are seen. (h) Data and reporting—(1) Treatment of results. (i) The experi- mental unit is the cell, and therefore the percentage of cells with structural chromosome aberration(s) should be evaluated. Different types of struc- tural chromosome aberrations should be listed with their numbers and fre- quencies for experimental and control cultures. Gaps are recorded sepa- rately and reported but generally not included in the total aberration fre- quency. (ii) Concurrent measures of cytotoxicity for all treated and negative control cultures in the main aberration experiment(s) should also be re- corded. (iii) Individual culture data should be provided. Additionally, all data should be summarized in tabular form. (iv) There is no requirement for verification of a clear positive re- sponse. Equivocal results should be clarified by further testing preferably using modification of experimental conditions. The need to confirm nega- tive results has been discussed in paragraph (g)(2) of this guideline. Modi- fication of study parameters to extend the range of conditions assessed should be considered in follow-up experiments. Study parameters that might be modified include the concentration spacing and the metabolic activation conditions. (2) Evaluation and interpretation of results. (i) There are several criteria for determining a positive result, such as a concentration-related 7 increase or a reproducible increase in the number of cells with chro- mosome aberrations. Biological relevance of the results should be consid- ered first. Statistical methods may be used as an aid in evaluating the test results (see paragraphs (i)(3) and (i)(13) of this guideline). Statistical significance should not be the only determining factor for a positive re- sponse. (ii) An increase in the number of polyploid cells may indicate that the test substance has the potential to inhibit mitotic processes and to in- duce numerical chromosome aberrations. An increase in the number of cells with endoreduplicated chromosomes may indicate that the test sub- stance has the potential to inhibit cell-cycle progression (see paragraphs (i)(17) and (i)(18) of this guideline). (iii) A test substance for which the results do not meet the criteria in paragraphs (h)(2)(i) and (h)(2)(ii) of this guideline is considered non- mutagenic in this system. (iv) Although most experiments will give clearly positive or negative results, in rare cases the data set will preclude making a definite judgement about the activity of the test substance. Results may remain equivocal or questionable regardless of the number of times the experiment is repeated. (v) Positive results from the in vitro chromosome aberration test indi- cate that the test substance induces structural chromosome aberrations in cultured mammalian somatic cells. Negative results indicate that, under the test conditions, the test substance d