Avermectin A1a, 25-cyclohexyl-5-O-demethyl-25-de(1-methylpropyl)-

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:

experimental study

Adequacy of study:

key study

Study period:

August 1990

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

other: Study run to a method comparable with current guidelines and to GLP .

Data source

Reference

Reference Type:

study report

Title:

Unnamed

Year:

1991

Report date:

1991

Materials and methods

Test guideline

Qualifier:

according to guideline

Guideline:

other: Schlegel and MacGregor, (Mutation Res. 104:367-369, 1982), MacGregor et al., (Ibid. 189: 103-112, 1987) and Heddle et al., (Ibid 123:61-118, 1983)

Deviations:

no

GLP compliance:

yes

Type of assay:

micronucleus assay

Test material

Test material information

Constituent 1

Reference substance name:

(1'R,2S,4'S,5S,6R,8'R,10'E,12'S,13'S,14'E,16'E,20'R,21'R,24'S)-6-cyclohexyl-21',24'-dihydroxy-12'-{[(2R,4S,5S,6S)-5-{[(2S,4S,5S,6S)-5-hydroxy-4-methoxy-6-methyloxan-2-yl]oxy}-4-methoxy-6-methyloxan-2-yl]oxy}-5,11',13',22'-tetramethyl-5,6-dihydro-3',7',19'-trioxaspiro[pyran-2,6'-tetracyclo[15.6.1.1⁴,⁸.0²⁰,²⁴]pentacosane]-10',14',16',22'-tetraen-2'-one

EC Number:

601-490-4

Cas Number:

117704-25-3

Molecular formula:

C50H74O14

IUPAC Name:

(1'R,2S,4'S,5S,6R,8'R,10'E,12'S,13'S,14'E,16'E,20'R,21'R,24'S)-6-cyclohexyl-21',24'-dihydroxy-12'-{[(2R,4S,5S,6S)-5-{[(2S,4S,5S,6S)-5-hydroxy-4-methoxy-6-methyloxan-2-yl]oxy}-4-methoxy-6-methyloxan-2-yl]oxy}-5,11',13',22'-tetramethyl-5,6-dihydro-3',7',19'-trioxaspiro[pyran-2,6'-tetracyclo[15.6.1.1⁴,⁸.0²⁰,²⁴]pentacosane]-10',14',16',22'-tetraen-2'-one

Test material form:

solid: particulate/powder

Remarks:

migrated information: powder

Details on test material:

Batch No.: 15497-237-1
Purity: Not specified

Test animals

Species:

mouse

Strain:

CD-1

Sex:

male/female

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Source:
- Age at study initiation:
- Weight at study initiation: 30±5 grams
- Assigned to test groups randomly: yes
- Fasting period before study:
- Housing:
- Diet (e.g. ad libitum): ad libitum
- Water (e.g. ad libitum): ad libitum
- Acclimation period:

ENVIRONMENTAL CONDITIONS
- Temperature (°C):
- Humidity (%):
- Air changes (per hr):
- Photoperiod (hrs dark / hrs light):

IN-LIFE DATES: From: To:

Administration / exposure

Route of administration:

oral: gavage

Vehicle:

- Vehicle(s)/solvent(s) used: distill water containing 5% methylcellulose
- Justification for choice of solvent/vehicle:
- Concentration of test material in vehicle:
- Amount of vehicle (if gavage or dermal):0.3 mL/30 g
- Type and concentration of dispersant aid (if powder):
- Lot/batch no. (if required):
- Purity:

Duration of treatment / exposure:

three days

Frequency of treatment:

once per day

Post exposure period:

24 hours

Doses / concentrations

Remarks:

Doses / Concentrations:
500, 1000 and 2000 mg/kg/day
Basis:
actual ingested

No. of animals per sex per dose:

5

Control animals:

yes, concurrent vehicle

Positive control(s):

Mitomycin C
- Route of administration: i.p. adminstration
- Doses / concentrations: 0.5 mg/kg/day

Examinations

Tissues and cell types examined:

For each preparation, 1000 PCEs (polychromatic erythrocyte) were scored for presence of micronuclei. Also, the ratio of PCE to NCE (normochromatic erythrocytes) in 200 erythrocytes was determined as an index of cytotoxicity.

Details of tissue and slide preparation:

Twenty-four hours after the final treatment, mice were sacrificed by cervical dislocation and swears were made from the bone marrow of the femora from each mouse. At least two slides were prepared. Slides were fixed in absolute methanol within one hour of collection and were then coded hy independent technician. Immediately prior to scoring, slides were stained 1-3 minutes in acridine orange (0.125 mg/mL) in phosphate buffer, rinsed in buffer and coverslips were mounted in the buffer.

Evaluation criteria:

A positive response is defined as a substantial, dose-related and reproducible elevation in the number of micronucleated PCEs in the treated animals. Where a positive response is indicated, statistical analysis can be conducted using a one-tailed trend test and also a pairwise comparison of the results for each treatment group with the concurrent negative control (Margolin et al., A general purpose statistical analysis program for the micronucleus assay-working document. ILS Committee for the Development of a Software Program for the Micronucleus Assay, 1990).

Statistics:

None stated

Results and discussion

Test results

Sex:

male/female

Genotoxicity:

negative

Toxicity:

yes

Remarks:

Drug-associated reduction in the percent of PCEs

Vehicle controls validity:

valid

Positive controls validity:

valid

Additional information on results:

The frequencies of MNPCE at all dose levels of test substance are within the acceptable historical negative control limits. Positive controls showed a significant elevation in micronucleated PCEs in accordance with historical control data. Negative controls showed expected results. There was evidence of drug-related bone marrow toxicity as indicated by a dose-related decrease in percent PCEs. There was no substantial increase in micronucleated PCEs. The test substance produced a dose-related decrease in the percentage of PCEs indicating drug-related toxicity.

Applicant's summary and conclusion

Conclusions:

Interpretation of results (migrated information): negative
These studies demonstrate that the test subsance does not induce micronuclei in PCEs in bone marrow in male or female mice. Drug-associated reduction in the percent of PCEs in both sexes confirms that the dose level used were at or near the maximum tolerated dose.