United States Prevention, Pesticides EPA712-C-98-235
Environmental Protection and Toxic Substances August 1998
Agency (7101)
&EPA Health Effects Test
Guidelines
OPPTS 870.5915
In Vivo Sister Chromatid
Exchange Assay
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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
(7U.S.C. I36,etseq.).
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."
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OPPTS 870.5915 In vivo sister chromatid exchange assay.
(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 798.5915 In vivo sister
chromatid exchange assay and OPP 84-2 Mutagenicity Testing (Pesticide
Assessment Guidelines, Subdivision F—Hazard Evaluation; Human and
Domestic Animals) EPA report 540/09-82-025, 1982.
(b) Purpose. The sister chromatid exchange (SCE) assay detects the
ability of a chemical to enhance the exchange of DNA between two sister
chromatids of a duplicating chromosome. The test may be performed in
vitro using cultured mammalian cells or in vivo using nonmammalian or
mammalian tissues. The most commonly used assays employ bone marrow
or lymphocytes from mammalian species such as mice, rats, or hamsters.
Human lymphocytes may also be used.
(c) Definition. 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 definition also applies to this test guideline.
Sister chromatid exchanges are reciprocal interchanges of the two
chromatid arms within a single chromosome. These exchanges are visual-
ized during the metaphase portion of the cell cycle and presumably require
enzymatic incision, translocation and ligation of at least two DNA helices.
(d) Test method—(1) Principle. Animals are exposed to test sub-
stance by appropriate routes followed by administration of
bromodeoxyuridine (BrdU). A spindle inhibitor (e.g., colchicine or
Colcemid®) is administered prior to sacrifice. After sacrifice, tissue is ob-
tained and metaphase preparations made, stained, and scored for SCE.
(2) Description. The method described here employs bone marrow
of laboratory rodents exposed to test chemicals. After treatment with test
chemical, animals are further treated with BrdU and, prior to sacrifice,
with a spindle inhibitor (e.g., colchicine or Colcemid®) to arrest cells in
c-metaphase. After sacrifice, chromosome preparations from bone marrow
cells are made, stained, and scored for SCE.
(3) Animal selection—(i) Species and strain. Any appropriate mam-
malian species may be used. Examples of commonly used rodent species
include mice, rats, and hamsters.
(ii) Age. Healthy, young adult animals should be used.
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(iii) Number and sex. At least five female and five male animals
per experimental and control group should be used. The use of a single
sex or different number of animals should be justified.
(iv) Assignment to groups. Animals should be randomized and as-
signed to treatment and control groups.
(4) Control groups—(i) Concurrent controls. Current positive and
negative (vehicle) controls should be included in the assay.
(ii) Positive controls. A compound know to produce SCE in vivo
should be employed as the positive control.
(5) Test chemicals—(i) Vehicle. When possible, test chemicals
should be dissolved in isotonic saline or distilled water. Water insoluble
chemicals may be dissolved or suspended in appropriate vehicles. The ve-
hicle used should neither interfere with the test compound nor produce
toxic effects. Fresh preparations of the test compound should be employed.
(ii) Dose levels. For an initial assessment, one dose of the test sub-
stance may be used, the dose being the maximum tolerated dose or that
producing some indication of toxicity as evidenced by animal morbidity
(including death) or target cell toxicity. The LDso is a suitable guide. Addi-
tional dose levels may be used. For determination of dose-response, at
least three dose levels should be used.
(iii) Route of administration. The usual routes of administration are
IP or oral. Other routes may be appropriate.
(iv) Treatment schedule. In general, test substances should be ad-
ministered only once. However, based upon toxicological information a
repeated treatment schedule may be employed.
(e) Test performance—(1) Treatment. Animals should be treated
with test chemical followed by administration of BrdU. BrdU may be ad-
ministered by multiple IP injections, by continuous tail vein infusion or
by subcutaneous implantation of tablets. Animals should be treated with
a spindle inhibitor (e.g., colchicine or Colcemid®) 2 hours prior to sac-
rifice. After sacrifice, bone marrow should be extracted and slides made
and prepared for SCE evaluation.
(2) Staining method. Staining of slides to reveal SCEs can be per-
formed according to any of several protocols. However, the fluorescence
plus Giemsa method is recommended.
(3) Number of cells scored. The number of cells to be analyzed per
animal should be based upon the number of animals used, the negative
control frequency, the predetermined sensitivity and the power chosen for
the test. Slides should be coded before microscopic analysis.
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(f) Data and report—(1) Treatment of results. Data should be pre-
sented in tabular form, providing scores for both the number of SCE for
each metaphase and the number of SCE per chromosome for each meta-
phase. Differences among animals within each group should be considered
before making comparisons between treated and control groups.
(2) Statistical evaluation. Data should be evaluated by appropriate
statistical methods.
(3) Interpretation of results, (i) There are several criteria for deter-
mining a positive result, one of which is a statistically significant dose-
related increase in the number of SCE. Another criterion may be based
upon detection of a reproducible and statistically significant positive re-
sponse for at least one of the test points.
(ii) A test substance which does not produce either a statistically sig-
nificant dose-related increase in the number of SCE or a statistically sig-
nificant and reproducible positive response at any one of the test points
is considered not to induce rearrangements of DNA segments in this sys-
tem.
(iii) Both biological and statistical significance should be considered
in the evaluation.
(4) Test evaluation, (i) Positive results in the in vivo SCE
assayindicate that under the test conditions the test substance induces re-
ciprocal interchanges in the bone marrow of the test species.
(ii) Negative results indicate that under the test conditions the test
substance does not induce reciprocal interchanges in the bone marrow of
the test species.
(5) Test report. In addition to the reporting recommendations as
specified under 40 CFR part 792, subpart J, the following specific informa-
tion should be reported:
(i) Species, strain, age, weight, number, and sex of animals in each
treatment and control group.
(ii) Test chemical vehicle, dose level used, rationale for dose selec-
tion, toxicity data, negative and positive controls.
(iii) Route and schedule of administration of both test chemical and
BrdU.
(iv) Identity of spindle inhibitor, its concentration and duration of
treatment.
(v) Time of sacrifice after administration of BrdU.
(vi) Details of the protocol used for slide preparation.
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(vii) Criteria for scoring SCE.
(viii) Dose-response relationship, if applicable.
(g) References. The following references should be consulted for ad-
ditional background material on this test guideline.
(1) Allen, J.W. et al. Bromodeoxyuridine tablet methodology for in
vivo studies of DNA synthesis. Somatic Cell Genetics 4:393-405 (1978).
(2) Allen, J.W. et al. Simplified technique for in vivo analysis of
sister chromatid exchanges using 5-bromodeoxyuridine tablets. Cyto-
genetics Cell Genetics 18:231-237 (1977).
(3) Latt, S.A. et al. Sister chromatid exchanges: A report of the U.S.
EPA Gene-Tox Program. Mutation Research 87:17-62 (1981).
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