Registration Dossier

Administrative data

Endpoint:
in vivo mammalian somatic cell study: cytogenicity / erythrocyte micronucleus
Remarks:
Type of genotoxicity: chromosome aberration
Type of information:
experimental study
Adequacy of study:
key study
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
other: Well documented publication which meets basic scientific principles

Data source

Reference
Reference Type:
publication
Title:
The in vivo effect of 2,6-xylidine on induction of micronuclei in mouse bone marrow cells
Author:
Parton JW, et al.
Year:
1988
Bibliographic source:
Mutat. Res. 206, 281-283

Materials and methods

Test guideline
Qualifier:
no guideline followed
Principles of method if other than guideline:
The ability of 2 .6-xylidine to produce chromosome breakage and/or spindle malformation in vivo was evaluated by an assessment of the capacity of the compound to induce micronuclei in bone marrow polychromatic erythrocytes.
GLP compliance:
no
Type of assay:
micronucleus assay

Test material

Reference
Name:
Unnamed
Type:
Constituent
Details on test material:
- Name of test material (as cited in study report): 2,6-xylidine
- Aldrich Chemical Co.. Milwaukee, WI
- no further data

Test animals

Species:
mouse
Strain:
ICR
Sex:
male
Details on test animals and environmental conditions:
TEST ANIMALS
- Source: Harlan - Sprague-Dawley, Indianapolis IN
- Weight at study initiation: 28-32 g
- Assigned to test groups randomly: yes
- Fasting period before study: none
- Housing: groups of 5
- Diet Purma pelleted rodent chow (No . 5002) ad libitum
- Water ad libitum
- Acclimation period: 7 days


ENVIRONMENTAL CONDITIONS
- Temperature (°F): 72
- Humidity (%): 40
- Photoperiod (hrs dark / hrs light): 12/12

Administration / exposure

Route of administration:
oral: gavage
Vehicle:
- Vehicle(s)/solvent(s) used: 10 % acacia
Details on exposure:
PREPARATION OF DOSING SOLUTIONS: 2,6-xylidine was diluted in 10 % acacia
Duration of treatment / exposure:
not applicable due to single oral application
Frequency of treatment:
single treatment
Post exposure period:
72 hours
Doses / concentrations
Remarks:
Doses / Concentrations:
87.5, 175, or 350 mg/kg
Basis:
actual ingested
No. of animals per sex per dose:
5 animals
Control animals:
yes
Positive control(s):
cyclophosphamide;
- Route of administration: oral (gavage)
- Doses / concentrations: 100 mg/kg

Examinations

Tissues and cell types examined:
Bone marrow
Details of tissue and slide preparation:
CRITERIA FOR DOSE SELECTION:
highest dose represents 50 % of the oral LD50

TREATMENT AND SAMPLING TIMES:
24, 48, 72 hours

Results and discussion

Test results
Sex:
male
Genotoxicity:
negative
Toxicity:
no effects
Vehicle controls validity:
valid
Negative controls validity:
not examined
Positive controls validity:
valid
Additional information on results:
The oral administration of up to 350 mg/kg of 2,6-xylidine did not result in the induction of micronuclei in bone marrow of male ICR mice either at 24, 48 or 72 h after dosing. Furthermore, no decrease in the PCE/NCE ratio observed in any animal treated with the test article. In contrast, the administration of 100 mg/kg cyclophosphamide produced a significant induction of micronucleated PCE and confirmed sensitivity of the system for the identification of genotoxins.

Any other information on results incl. tables

 

Treatment (mg/kg)

Harvest time (h)

PCE/NCE ratio

MPCE/1000 PCE

350

24

0.9 ± 0.1

1.6 ± 1.5

48

1.1 ± 0.4

2.2 ± 0.8

72

1.1 ± 0.4

1.2 ± 1.3

175

24

0.9 ± 0.5

1.2 ± 1.1

48

1.1 ± 0.2

0.8 ± 1.1

72

1.5 ± 0.2

1.3 ± 1.0

87.5

24

1.0 ± 0.3

0.8 ± 1.1

48

1.0 ± 0.1

1.2 ± 0.8

72

1.0 ± 0.6

1.3 ± 1.3

control

24

1.0 ± 0.2

1.4 ± 0.9

48

1.0 ± 0.0

1.0 ± 0.7

72

1.3 ± 0.4

0.8 ± 1.1

100 cyclophosphamide

24

1.0 ± 0.5

46.2 ± 10.7

48

severe bone marrow toxicity

72

severe bone marrow

 

The negative results obtained in this study are in contrast to the positive findings for the in vitro induction of SCE and chromosome aberrations reported by other authors. Such discordant cytogenetic observations are not unprecedented. In vitro systems do not duplicate the possible detoxification, distribution and excretion mechanisms that exist in vivo which can prevent chemicals from reaching a target population, in this case the bone marrow . The absence of an effect on the PCE/NCE ratio in suggests that 2,6-xylidine or an active metabolite may not have been present in bone marrow in sufficient concentration to induce micronuclei. On the other hand, the high dose in this was equivalent to 50% of the LD50 and this should have been more than adequate to evaluate the intrinsic genotoxic potential of the test compound.

 

 

Applicant's summary and conclusion