Assignment on Genotoxicity

Basic of Mutation, Genotoxicity studies (Ames Test in vitro and in vivo Micronucleus and Chromosomal aberrations studies)

1. INTRODUCTION
Mutationisabroadtermcoveringawholerangeof
changestotheinformationalmolecule,DNA(madeup
ofthefournucleotides:thepurines,adenineand
guanine,andthepyrimidines,thymineandcytosine)
packagedintochromosomes,ofanorganismfromgene
changestomodificationsofthenumberandstructure
ofchromosomes
Pointmutationsarechangestothesequenceof
nucleotidesandmayinvolvethesubstitutionof
individualbases

2. …continued
MutationsinvolvingthelossorgainofDNAmayrange
fromasinglebasepairchange,calledaframeshift
mutation,tomanybases, calleddeletionor
duplications,ortowholechromosomechangescalled
aneuploidy
Allthesetypesofchangeareproducedspontaneously
duringthelifecycleoflivingorganismsandmayalso
beproducedbyexposuretosomechemicalswhich
interactwiththeDNA(adductformation)andto
ionizingradiationandnonionizingradiationsuchas
ultravioletlight.Suchchemicalandphysicalagents
areclassifiedasmutagensorgenotoxins

3. …continued
NotalltheDNAinacellcarriescodedinformationfor
proteinsynthesis.Someofitisnoncodingandis
importantforchromosomestructure
Theeffectofamutationwilldependupontheposition
ofthemutationwithintheDNAandthelocationand
activityoftheparticulargeneinwhichthemutation
hasbeeninduced

4. …continued
AllchemicalsthatproduceDNAdamageleadingto
mutationorcanceraredescribedasgenotoxic
Themutationsinsomaticcellsarenotonlyinvolvedin
thecarcinogenesisprocessbutalsoplayaroleinthe
pathogenesisofotherchronicdegenerativediseases,
suchasatherosclerosisandheartdiseases,which
aretheleadingcausesofdeathinthehuman
population

5. …continued
Basicallyonecandistinguishthreeclassesof
geneticalterations:
1.Chromosomal aberrations,whicharestructural
alterationsofchromosomes
2. Gene mutations, which are changes in the genetic
code
3.Genome mutations,whichinvolvechangesin
chromosomenumbers

6. …continued
Genotoxicitydescribesthepropertyofchemical
agentsthatdamagesthegeneticinformation
withinacellcausingmutations,whichmayleadto
cancer
Thealterationcanhavedirectorindirecteffects
ontheDNA:theinductionofmutationsanddirect
DNAdamageleadingtomutations

7. …continued
Thepermanent,heritablechangescaneffecteither
somaticcellsoftheorganismorgermcellstobe
passedontofuturegenerations
Cellspreventexpressionofthegenotoxicmutation
byeitherDNArepairorapoptosis;however,the
damagemaynotalwaysbefixedleadingto
mutagenesis

8. …continued
If the mutation occurs in a germ cell the effect is
heritable
There is no effect on the exposed person; rather
the effect is passed on to future generations
If the mutation occurs in a somatic cell, it can cause
altered cell growth (e.g. cancer) or cell death (e.g.
teratogenesis) in the exposed person

9. …continued
Genotoxicitystudieswithtransgenicanimalsare
moreappropriateassaytechniquestodetermine
thetoxicityofatestsubstance
Genotoxicitytestingisused toassess
submicroscopicchangesinthebasesequenceof
DNA,chromosomal aberrationsandstructural
aberrationsinDNA includingduplications,
insertions,inversionsandtranslocations

10. …continued
Certaintypesofmutationsresultincarcinogenesis
andsothedeterminationofthegenotoxicityis
essentialinthedrugdevelopmentprocess
Oneofthebestwaystominimizetheeffectof
mutagensandcarcinogensistoidentifythe
anticlastogens/antimutagensanddesmutagensin
ourdietsandincreasingtheiruse
Allmutagensaregenotoxic,howevernotall
genotoxicsubstancesaremutagenic

11. MECHANISM
Thegenotoxicsubstancesinducedamagetothe
geneticmaterialinthecellsthroughinteractions
withtheDNAsequenceandstructure
Forexample,thetransitionmetalchromium
interactswithDNAinitshigh-valentoxidationstate
sotoincurDNAlesionsleadingtocarcinogenesis
ThemetastableoxidationstateCr(V)isachieved
throughreductiveactivation

12. …continued
Theresearchersperformedanexperimenttostudy
theinteractionbetweenDNAwiththecarcinogenic
chromiumbyusingaCr(V)-Salencomplexatthe
specificoxidationstate
Theinteractionwasspecifictotheguanine
nucleotideinthegeneticsequence
InordertonarrowtheinteractionbetweentheCr(V)-
Salencomplexwiththeguaninebase,the
researchersmodifiedthebasesto8-oxo-Gsotohave
sitespecificoxidation

13. …continued
Thereactionbetweenthetwomoleculescaused
DNAlesions;thetwolesionsobservedatthe
modifiedbasesitewereguanidinohydantoinand
spiroiminodihydantoin
Tofurtheranalyzethesiteoflesion,itwasobserved
thatpolymerasestoppedatthesiteandadenine
wasinappropriatelyincorporatedintotheDNA
sequenceoppositeofthe8-oxo-Gbase

14. …continued
Therefore,theselesionspredominatelycontain
GTtransversions
High-valentchromiumisseentoactasa
carcinogenasresearchersfoundthat“the
mechanism of damageandbaseoxidation
productsfortheinteractionbetweenhigh-valent
chromiumandDNA……relevant toinvivoformation
ofDNAdamageleadingtocancerinchromate-
exposedhumanpopulations”

15. …continued
Whenonepurinenucleotideisreplacedbyanother
purineorapyrimidinebyapyrimidine,itiscalleda
transitionmutation
Whenapurineisreplacedbypyrimidineorvice
versa,themutationiscalledatransversion

16. …continued
Anotherexampleofagenotoxicsubstancecausing
DNAdamagearepyrrolizidinealkaloids(PAs)
Thesesubstancesarefoundmainlyinplantspecies
andarepoisonoustoanimals,includinghumans;
abouthalfofthemhavebeenidentifiedas
genotoxicandmanyastumorigenic

17. …continued
Theresearchersconcludedfromtestingthatwhen
metabolicallyactivated,“PAsproduceDNA
adducts,DNAcross-linking,DNAbreaks,sister
chromatidexchange,micronuclei,chromosomal
aberrations,genemutationsandchromosome
mutationsinvivoandinvitro
Thepyrrolizidinealkaloidsaremutagenicinvivo
andinvitroand,therefore,responsibleforthe
carcinogenesisprominentlyintheliver

18. How to m easure genotoxicity
BIOMARKERS OF EXPOSURE
BIOMARKERS OF EFFECT
BIOMARKERS OF SUSCEPTIBILITY
BIOMARKERS OF GENETIC DAMAGE

19. BIOMARKERS OF EXPOSURE
Biomarkersofexposurearethosethatindicate
exposureoftheorganismtothechemicals,butdo
notgiveinformationofthedegreeofadverseeffect
thatthischangecauses
Biomarkersofexposureeasilyindicatethe
presenceofaxenobioticsubstanceorits
metabolitesmaybemeasuredwithincompartment
ofanorganismintheabsenceofanyadverseeffect

20. …continued
Theapplicationofthisistopredictthedose
receivedbyanindividualwhichcanthenberelated
tochangesresultinginadiseasestate
Theyalsoprovideveryusefulinformationonthe
effectsoftoxicantswithtime

21. …CONTINUED
They are most widely used because they can
provide information on the route, pathway and
sometimes, even the source of exposure

22. Biomarkers of exposure to
carcinogens
Itisoneofthemostimportantbiomarkerswhich
involvesdetectingtheabilityofxenobioticsor
carcinogenstoformadductswithDNAorprotein
DNAadductsarethechemicalspeciesboundto
DNA
DNAadductsmayberelatedtocarcinogenesis
whichcanbemeasuredbyvarioussensitive
methodslikeTLCorHPLC,MS,RIAandELISA

23. …continued
Mostofthecarcinogensareelectrophilicinnature
which may react with nucleoplilic
biomacromolecules(DNA)toformadducts
Theseadductscanbedetectedbytotalhydrolysis
oftheproteintoalkylatedaminoacids(histidine,
cysteineadducts)
Itishelpfultodetectcarcinogens.Thepresenceof
adductscanalsobedetectedbythecreationof
pointmutation

24. Biomarkers of effects
Effectsoftoxicagentsthatcanbedetectedby
variousassays
Cytogenetic Biomarkers
Chromosomal aberrations
Micronucleus (MN)
Biochemical Biomarkers
Comet assay
Oxidative stress assays
Ames test

27. Comet assay
DetectDNAdamagei.esinglestrandbreaks(SSBs)
DamagedDNAmigratemoretowardanodeforming
cometappearance
LengthoftailisproportionaltoextentofDNA
damage
Wholebloodorharvestedlymphocytes

29. Oxidative stress mark ers
Oxidative stress is oxidative modification of
biological components like nucleic acids, proteins,
lipids by reactive oxygen species
Reactive oxygen species include free radicals and
peroxides
Binding of reactive oxygen species leads to
damage
Reactive oxygen species are formed during
metabolism of genotoxic agents

32. Biomarkers of adverse eff ects
Itisveryimportanttorelatethedegreeofchange
ofbiologicalresponseduetotheadverseeffectof
toxicants
Forexample,whenanorganismisexposed
sufficientlytotheenvironmentalpollutants,they
maycausedamagetoDNA
Thesepollutantsarespecificgenotoxiceffects,
especiallytheincreaseofcarcinogenesis,rather
thaneffectsonthereproductiveprocess

33. Biomarkers of susceptibility
Theyhaveanimportantroleinassessingindivdual
differencesinsusceptibilitiestotheimpactsof
chemicals,physicalorinfectiousagents
Forexample,thepeoplewithglucose- ß-phosphate
dehydrogenasedeficiencyaremoresusceptibleto
developanaemiauponexposuretoaromaticamines
Manyxenobioticcompoundsinhibittheactivitiesof
theimmunesystemandthusincreasethe
susceptibilitytoinfectiousagents,parasitesand
cancer

34. …continued
Higheraffinitytoarylhydrocarbonreceptor(AHR)
mayincreasetheriskofdevelopingcancer
Thepeoplewithhighmetabolizersofdebrisoquine
haveanincreasedriskoflungcancer

35. Biomarkers of genetic damage
Biomarkersofgeneticdamageareusedtoassess
thedamagecausedtoDNAadductsmaybe
mechanisticallyrelatedtocarcinogenesis,theuse
ofgeneticmarkershasbecomeintriguingfor
molecularepidemiologists
Thegeneticmarkersincludethealterationsin
chromosomal structuresuchasrestriction
fragmentlengthpolymorphism(RFLPs),lossof
heterozygosityandtranslocationmarkers

36. …continued
TheinteractionofaxenobioticwithDNAand
consequentmutationinvolvedifferentstagessuchas:
Formation of DNA adduct
Modification of DNA such as strand breakage
Alteration of gene function

37. Ames assay
PURPOSE/RATIONALE :
Thebacterial
reversemutationtest(Amestest)investigatesthe
abilityofchemicalsanddrugstoinducereverse
(back)mutationsinbacteria,whichinvolvesbase
pairsubstitutions,additionsand/ordeletions
(frameshiftmutations)ofoneorafewDNAbase
pairs

38. …continued
Thebacterialstrainsusedinthetestsystemhave
mutationsingenescodingforenzymesrequired
forthebiosynthesisoftheaminoacidshistidine
(Salmonellatyphimurium) and tryptophan
(Escherichiacoli)
Anextensivedatabaseexistsbasedontheuseof
thistest,andithasbeenfoundthatcompounds
producingapositiveresultinthebacterialreverse
mutationtesthaveahighpotencytoinduce
cancerinanimalstudies

39. Ames test

40. Procedure
The commonly used strains for S. typhimurium are
TA100 and TA1535 (base pair substitution), TA98
and TA1537 (frame shift mutations) and TA102 for
cross-link mutations
The preferred strain of E. coli to detect base pair
substitution mutations is WP2

41. …continued
Bacteria of an overnight nutrient broth culture are
mixed with the test compound or solvent (as a
negative control), S9- mix or buffer, and molten top
agar and poured into a petri dish containing a layer
of minimal agar
After incubation for approximately 48 h at approx.
37˚ C in the dark, colonies (representing the
number of revertants) are counted by hand or an
automatic colony counter

42. …continued
The method can be modified by including a
preincubation step or by using a higher amount of
S9-mix in the test system
Preincubation would involve incubating the test
compound, S9- mix or buffer, and bacteria for a
short period before pouring this mixture onto plates
of minimal agar

43. According to the current ICH S2R Guideline, one
experiment is sufficient to determine the mutagenic
potential
The assay can be conducted as plate or
preincubation assay

44. EVALUATION
To evaluate the result of a test compound, the
number of revertant colonies has to be determined
for each concentration used in the test system as
well as for the negative (solvent or untreated) and
positive control
Bacterial toxicity is expressed as a thinning of the
bacterial lawn or in a reduction in the number of
colonies compared to the negative control

45. …continued
Bacterial toxicity and precipitation should be taken
into consideration when assessing the mutagenicity
of a substance
The following criteria should be met to consider a
bacterial reverse mutation test as valid

46. …continued
The number of revertant colonies on both negative
(solvent or untreated) control plates should be in a
historical control range described in literature or
determined in the laboratory
The positive control should induce a significant
increase in the number of revertant colonies

47. …continued
At least five dose levels for the test article are
analyzable (i.e., number of revertant colonies can
be determined), for each strain in each
experimental condition
The highest dose level fulfills the rational for the
highest dose level selection

48. Critical assessment of the method
The advantages of the bacterial reverse mutation
test are the ease with which it can be performed,
the short amount of time required and the low cost.
The test should be regarded as the first test in the
GLP testing strategy for the detection of a
genotoxic potential of a test compound. The test is
as well required as part of the nonclinical testing
strategy before the start of phase I in the clinical
development

49. …continued
The number of revertant colonies exceeds the
upper value of the range of the historical negative
control data
If the test substance does not achieve either of
the above criteria, it is not considered as showing
evidence of mutagenic activity in this system

50. In vitro
The purpose of in vitro testing is to determine
whether a substrate, product, or environmental
factor induces genetic damage
One technique is cytogenetic assays using different
mammalian cells
The types of aberrations detected in cells affected
by a genotoxic substance are chromosome gaps,
chromosome breaks, chromatid deletions,
fragmentation, translocation, complex
rearrangements, and many more

51. …continued
The clastogenic or aneugenic effects from the
genotoxic damage will cause an increase in
frequency of structural or numerical aberrations of
the genetic material
This is similar to the micronucleus test and
chromosome aberration assay, which detect
structural and numerical chromosomal aberrations
in mammalian cells

52. …continued
Gene mutations are commonly point mutations,
these point mutations include base substitutions,
deletions, frame- shifts, and rearrangements
Also, chromosomes' integrity may be altered
through chromosome

53. …continued
The specific type of damage is determined by the
size of the colonies, distinguishing between genetic
mutations (mutagens) and chromosomal
aberrations (clastogens)

54. Chromosome aberration test
The chromosome aberration test (CAT) measures the
occurrence of chromosome aberrations generally in
bone marrow or peripheral blood cells
In the CAT the mitosis is arrested in the metaphase stage
with a mitotic inhibitor (colchicine)
Metaphase preparations are examined for chromosome
breaks and/or chromosomal rearrangements
The number of cells with chromosomal breaks is a
measure for clastogenicity of chemicals for this test

55. Purpose/Rationale
This in vitro cytogenetic test is a clastogenicity test
system for the detection of chromosomal
aberrations in cultured mammalian cells or primary
cultures
Chromosomal aberrations may be either structural
or numerical

56. …continued
Structural aberrations are of two types:
Chromosome –type aberrations are induced when
a compound acts in the G
1phase of the cell cycle
Chromatid –type aberrations are induced when a
chemical acts in the S and G
2phase of the cell cycle

57. …continued
Numerical aberrations are changes in the number
of chromosomes of the normal number
characteristic of the animals utilized
The best estimate of aberration frequency is the
first cell division after the start of treatment

59. Procedur e
In this test, cultured cells are seeded onto slides
and the cells, which have been treated with and
without metabolic activation for a short –time
period (e.g., 3 h)
Where negative or equivocal results are obtained,
an independent experiment is conducted in which
cells are treated for long –time period (e.g., 20 h) in
the absence of metabolic activation alone and then
sampled and examined for chromosome analysis

60. …continued
Colcemidis added to each culture 2 h before
sampling in order to arrest cell division
Chromosome preparations are made, fixed, stained
and examined

61. …continued
However, if clearly positive results are obtained in
the first experiment, those from the second assay
are not examined
If equivocal or negative results are obtained in the
first experiment, modifications to the testing
procedure are included in order to clarify the result

62. Evaluation
The set of chromosomes is examined for
completeness and the various chromosomal
aberrations are assessed and classified
The metaphases are examined for the following
aberrations : chromatidgap, chromosome gap,
chromatidbreak, chromosome break, chromatid
acentricfragment, chromosome acentric fragment,
chromatiddeletion, chromosome deletion, chromatid
exchanges including intrachanges, chromosomes
exchanges including intrachanges, dicentrics,
pulverization and ring formation

63. …continued
Metaphases including five or more break events are
scored as multiple aberrant
The quantity of cells is determined by counting the
number of cells

64. …continued
For each experiment the results from the dose
groups is compared with those of the control group
and the positive control at each sampling time
The assay is considered valid if both of the
following criteria are met:
The solvent control data are within the laboratory’ s
normal control range for the number of cells
carrying structural chromosomal aberrations

65. …continued
The positive controls induce increases in the
number of cells carrying structure aberrations
which are statistically significant and within the
laboratory’s normal range
A test substance is classified as non- clastogenicif
either of the following is met:

66. …continued
The number of induced structural chromosome
aberrations in all evaluated dose groups is in the
range of our historical control data
No significant increase of the number of structural
chromosome aberrations is observed

67. …continued
A test substance is classified as clastogenic if
both the following are met:
The number of induced structural chromosome
aberrations is not in the range of our historical
control data
Either a concentration –related or a significant
increase of the number of structural chromosome
aberrations is observed

68. Micronucleus test
Micronucleus is also the name given to the small
nucleus that forms whenever a chromosome or a
fragment of a chromosome is not incorporated into
one of the daughter nuclei during cell division

69. …continued
In people and many other mammals, which do not
have nuclei in their red blood cells, the micronuclei
are removed rapidly by the spleen
Hence high frequencies of micronuclei in human
peripheral blood indicate a ruptured or absent
spleen

70. Purpose/Rationale
The purpose is to evaluate the potential of
compounds to induce micronuclei (formation of
small membrane- bound DNA fragments) in
different cell lines or primarily cultures, with and
without metabolic activation by S9 liver
homogenate

71. …continued
The test system allows to discriminate between a
clastogenic and aneugenic potential of a test
compound by using an immunochemical labeling of
the kinetochoresor staining the DNA fragments
with FISH (fluorescence in situ hybridization)
technique

73. Procedur e
The cells are treated with the test article in 96- well
microplates for a short treatment period with
metabolic activation (e.g., 3 h) and for a long
treatment period without metabolic activation (e.g.,
24 h) and harvested 24 h (recovery time) after the
end of the treatment
Cells are then fixed and stained

74. …continued
The cytotoxicityof the test compound is evaluated
by the relative cell growth, expressed as a
percentage of the negative control
Duplicated cultures should be performed at each
dose level

75. Evaluation
Structural/numerical chromosome damage is
evaluated by the increase in the number of
micronucleated cells, scored out of 1000 cells in
three analyzable concentrations. The compound is
considered positive if either:
The increase of micronucleated cells is statistically
significant compared to the negative (solvent or
untreated) control, or

76. Criticalassessmentofthemethod
The micronucleus test in vitro is easy and rapid to
perform, inexpensive and needs much less test
compound compared to the mammalian
chromosome aberration test
In addition no detailed training of the personnel for
the light microscopical evaluation of the slides is
necessary

77. …continued
In fact, it is currently the only in vitro test which
allows the differentiation between a clastogenic or
aneugenic effect and is becoming ever more
important in the genotoxictesting strategy
As the evaluation of micronuclei is much easier and
less time consuming, this assay will replace the
chromosome aberration assay in vitro in the future

78. In vivo
The purpose for in vivo testing is to determine the
potential of DNA damage that can affect
chromosomal structure or disturb the mitotic
apparatus that changes chromosome number; the
factors that could influence the genotoxicityare
ADME and DNA repair
It can also detect genotoxicagents missed in in
vitro tests.

79. Chromosome aberration test
Purpose/Rationale :
It is especially relevant
for assessing the mutagenic hazard while taking
into consideration factors like in vivo metabolism,
pharmacokinetics and DNA repair processes,
although these may vary among species and among
tissues

80. …continued
In addition, the assay can be used for the detection
of compounds that induce polyploidy
An increase in the number of polyploidy cells may
indicate that a compound has the potential to
induce numerical aberrations

81. …continued
The induction of structural chromosome
aberrations is classified in two ways, chromosome
or chromatidaberrations
The majority of induced aberrations are of the
chromatid-type, but chromosome- type aberrations
also occur

82. Procedur e
Rodents (rat, mice, chinesehamster) are routinely
used in this test
Although chromosome aberrrations can be
detected in various tissues, the most common
methodologies are available for investigations of
bone marrow, peripheral blood and female and
male germ cells

83. Bone marrow is the normally used target tissue in
this test, since it is a highly vascularized tissue, and
it contains a population of rapidly cycling cells that
can be readily isolated and processed
Each treated and control group must include at
least five animals that can be analyzed per sex

84. …continued
Test substances are preferably administered as a
single treatment; however, repeated treatment up to
28 days could also be performed
If a single treatment is used two sample times (12-
18 h and 36- 44 h) should be used for bone marrow

85. …continued
Prior to sacrifice (3- 5 h), animals are treated with a
metaphase- arresting agent (e.g., colchicine)
Chromosome preparations are then made from the
respective tissues and stained with an appropriate
method
For a better discrimination of the chromosomes and
to detect translocations, the FISH technology can
be used

86. …continued
Metaphase cells are microscopically analyzed for
the occurrence of structural and numerical
chromosome aberrations

87. Evaluation
At least 100 metaphase plates per animal should be
scored per animal based on the use of at least five
animals per gender per treatment group
To describe the toxicity in the target organ, the
mitotic index is determined in at least 1000
nucleated cells per animal

88. …continued
However, for the detection of polyploidy at least 22
metaphase cells should be scored
For a discussion of the result of the chromosome
aberration assay the following parameters need to
be considered: (a) comparison of the data from the
treatment group versus concurrent negative control
data and historical control data (b) statistical
analysis of the experimental data using trend
analysis or pair-wise comparison (treatment group
versus control)

89. Critical assessment of the method
There are compounds for which standard in vivo
tests do not provide additional useful information
This is particularly true for compounds for which
data from studies on toxicokineticsor
pharmacokinetics indicate that they are not
systemically absorbed and therefore are not
available for the target tissues

90. …continued
Examples of such compounds are some
radioimaging agents, aluminum-based antacids,
and some dermally applied pharmaceuticals
In those cases other tests systems should be
considered to be more relevant

91. Micronucleus test
Purpose/Rationale:
During erythropoiesis ,
nuclei are expelled during the formation of
polychromatic erythrocytes while micronuclei are
retained in the cells. This fact is used for the
detection of micronuclei

92. …continued
A significant increase in the number of
micronucleated polychromatic erythrocytes is
usually considered as indicative of structural
and/or numerical chromosome damage caused by
exposure to a clastogenic and/or aneugenic
substance

93. …continued
The identification of the presence or absence of a
kinetochoreor centromericDNA in the micronuclei
is needed to discriminate a clastogenic effect from
an aneugenic effect

94. Procedur e
The bone marrow of rodents (rat and mice) is
routinely used in this test since polychromatic
erythrocytes are produced in that tissue, it is a
highly vascularized tissue and it contains a
population of rapidly cycling cells that can be
readily isolated and processed
Each treated and control group must include at
least five analyzable animals per sex

95. …continued
Test substances could be administered as a single
treatment . Repeated treatment up to 28 days could
is also possible
If a single treatment is used the sampling time
should be between 24 and 48 h. If repeated
treatment is used, the sampling time is 24 h after
the last treatment

96. …continued
Bone marrow cells are usually obtained from the
femurs or tibias immediately following sacrifice
Usually, cells are removed from femurs or tibias in a
suitable medium such as fetal serum, and are
prepared and stained using established methods
DNA specific stains (e.g., acridine orange) are
preferred instead of conventional stains like
Giemsa

97. Evaluation
The proportion of immature among total (immature
+ mature) erythrocytes as measure for target organ
toxicity is determined for each animal by counting a
total of at least 200 erythrocytes for bone marrow
and 1000 erythrocytes for peripheral blood
At least 2000 immature erythrocytes per animal are
scored for the incidence of micronucleated
immature erythrocytes to determine the
clastogenic/aneugenicpotential of the test
compound

98. references
Vogel Gerhard Hans, “Drug Discovery and Evaluation:
Safety and Pharmacokinetic Assays, published by
Springer, New York, 2006, page no. 829 – 839
Gupta K P, “Essential concepts in toxicology”, published
by PharmaMedpress, page no 139- 144
PaniB, “Textbook of toxicology”, published by I.k
International publishing house pvt.Ltd, page no 11.1-
11.6
Parry M J, Parry M E, “Textbook of genetic toxicology”,
Published by springerpublication, page no 21-34,69-70