LBX98

Genetic toxicity: in vivo

Administrative data

Endpoint:

in vivo mammalian somatic cell study: cytogenicity / erythrocyte micronucleus

Remarks:

Type of genotoxicity: chromosome aberration

Type of information:

read-across based on grouping of substances (category approach)

Adequacy of study:

weight of evidence

Justification for type of information:

No data are available for the target substance. Studies of genotoxicity in vitro with the individual (o-, m- and p-) cresol isomers report negative results in Ames tests and mammalian cell mutation assays and positive results in studies of chromosomal aberration in vitro. Studies of genotoxicity in vivo report negative results. Studies of genotoxicity in vitro with xylenol (mixed isomers) report negative results in Ames tests and mammalian cell mutation assays and positive results in studies of chromosomal aberration in vitro. Studies of genotoxicity in vivo report negative results for 3,5-, 2,4- and 2,6-xylenol. Based on the consistent response seen for the source substances, it can be concluded that the target substance is also not genotoxic.

Materials and methods

Test guideline

Test guideline 1

Qualifier:

according to guideline

Guideline:

OECD Guideline 474 (Mammalian Erythrocyte Micronucleus Test)

Test guideline 2

Qualifier:

according to guideline

Guideline:

EU Method B.12 (Mutagenicity - In Vivo Mammalian Erythrocyte Micronucleus Test)

GLP compliance:

yes

Type of assay:

micronucleus assay

Test material

Test material information

Constituent 1

Reference substance name:

Reaction mass of 2,4-xylenol and 2,5-xylenol

EC Number:

905-287-4

Cas Number:

1638758-52-7

Molecular formula:

(CH3)2C6H3OH

IUPAC Name:

Reaction mass of 2,4-xylenol and 2,5-xylenol

Test material form:

solid: bulk

Test animals

Species:

mouse

Strain:

NMRI

Sex:

male/female

Administration / exposure

Route of administration:

oral: gavage

Duration of treatment / exposure:

Single oral administration

Frequency of treatment:

Single oral administration

Post exposure period:

24 and 48 hours

Doses / concentrations

Remarks:

Doses / Concentrations:375, 750 and 1500 mg/kg (24 hr) and 1500 mg/kg (48 hr)Basis:no data

No. of animals per sex per dose:

5 animals/dose/sex

Control animals:

yes, concurrent vehicle

Examinations

Tissues and cell types examined:

Polychromatic erthyrocyte (PCE) examined for the presence of micornulcueiPCE and noromchromatic erthyrocytes (NCE) counted as a measure of toxiciy

Results and discussion

Test results

Sex:

male/female

Genotoxicity:

negative

Toxicity:

yes

Remarks:

Clincial signs of toxicity, with mortality

Vehicle controls validity:

valid

Positive controls validity:

valid

Any other information on results incl. tables

Table 1: Male and female combined data - 24hr time point

Dose (mg/kg)	PCE	NCE	Total	%PCE	MN PCE
0	20000	7942	27944	39.7	1.5
75	20000	7225	27228	36.1	1.0
750	20000	6986	26991	34.9	0.7
1500	20000	8175	28182	40.2	1.0
CPA 20	10000	4610	14612	46.1	11.6**
VIN 0.15	10000	4721	14721	47.2	60.9**

CPA - cyclophosphamide

VIN - Vincristine

** p<0.01

Table 2: Male and female combined data - 48hr time point

Dose (mg/kg)	PCE	NCE	Total	%PCE	MN PCE
0	20000	7968	27968	39.8	0.8
1500	16000	9474	25484	59.2	0.8

Applicant's summary and conclusion

Conclusions:

Interpretation of results (migrated information): negativeIt is concluded that 3,5 xylenol did not induce micronuclei in the polychromatic erthrocytes of the bone marrow following sampling at 24 and 48 hours post dosing of both male and female rats when tested at a dose of 1500 mg/kg (deemed a maximum tolerated dose) under the conditions of the assay described.

Executive summary:

In a bone marrow micronucleus assay using NMRI mice, a single oral gavage of 3,5-xylenol was administered to groups of male and female animals, employing a dose volume of 10 mL/kg. Doses were selected from a pilot toxicity study doses of 1500 and 1750 mg/kg/bw were administered. Mortality was observed in at 1750mg/kg and evident signs of toxicity were observed at 1500mg/kg. The MTD was therefore deemed to be 1500 mg/kg.

 

Negative control groups were treated with vehicle only (olive oil) and positive control groups were treated with the clastogen, cyclophosphamide (CPA, 20 mg/kg bw) or the aneugen, vincristine (0.15 mg/kg). Mouse bone marrow was sampled at 24 and 48 hours after dosing for the vehicle and 3,5 xylenol dosed groups. A single sampling time of 24 hours after dosing was used for both positive control groups. Slides of bone marrow cells were prepared from five animals/sex/time point for each group and scored for the occurrence of micronucleated polychromatic erythrocytes (MN PCE) and PCE/total erythrocyte ratios.

 

Deaths (1 male and 1 female) at 1500mg/kg, 48 hr sample point were observed. Clinical signs of toxicity included irregular breathing (375mg/kg). squatting posture (750mg/kg) and piloerection and squatting (1500mg/kg). There were no marked decreases in mean PCE/total erythrocyte ratio observed for any of the 3,5 xylenol treated groups compared to the vehicle control group for either time point.

 

Analysis of the mean MN PCE group data indicated that there was no statistically significant increases MN PCE frequency compared to concurrent control values for either sex. Indiviudaul animal and group mean MN PCE frequencies were consistent with both the concurrent vehicle control values and the historical control. Positive control treatment induced the appropriate response. 

 

Formulation analysis confirmed the suitability of the doses prepared.

 

It is concluded that 3,5 xylenol did not induce micronuclei in the polychromatic erthrocytes of the bone marrow following sampling at 24 and 48 hours post dosing of both male and female rats when tested at a dose of 1500 mg/kg (deemed a maximum tolerated dose) under the conditions of the assay described.

The above results are suitable to be used for read across for Reaction mass of 2,4-xylenol and 2,5-xylenol, due to the category being based on structural similarity and comparable physicochemical properties, leading to similar (eco)toxicological properties.