Registration Dossier

Administrative data

Endpoint:
developmental toxicity
Type of information:
migrated information: read-across from supporting substance (structural analogue or surrogate)
Adequacy of study:
key study
Reliability:
2 (reliable with restrictions)

Data source

Reference
Reference Type:
publication
Title:
Unnamed
Year:
2006

Materials and methods

Test guideline
Qualifier:
according to
Guideline:
OECD Guideline 414 (Prenatal Developmental Toxicity Study)
Deviations:
no
GLP compliance:
not specified
Remarks:
GLP conduct expected
Limit test:
no

Test material

Reference
Name:
Unnamed
Type:
Constituent
Test material form:
solid: particulate/powder
Remarks:
migrated information: powder
Details on test material:
DBHCB
Lot: 05004IX3
Purity: 99.9%
Storage in the dark at room temperature

Test animals

Species:
rat
Strain:
Crj: CD(SD)
Details on test animals and environmental conditions:
Animals were reared with a basal diet (CE-2; Clea Co.,Ltd., Tokyo, Japan), water was provided ad libitum, and the animals were maintained in an air-conditioned room at 21.6–22.2°C, with a relative humidity of 45–58%, a 12-h light/dark cycle, and ventilation with 15 air changes/hour

Administration / exposure

Route of administration:
oral: gavage
Vehicle:
other: gum arabicum
Analytical verification of doses or concentrations:
yes
Details on analytical verification of doses or concentrations:
purity and stability of the chemical were verified by analysis before the study
Details on mating procedure:
Virgin female rats were mated overnight with male rats. The day when the sperm and/or vaginal plug was found to be day 0 of pregnancy. The copulated females, weighing 245–314 g, 11 weeks old, were distributed on a random basis into 4 groups of 20 rats each and housed individually.
Duration of treatment / exposure:
The rats were acclimatized to the laboratory for 1 week prior to the start of the experiment.Pregnant rats were euthanized by exsanguination under
ether anesthesia on day 20 of pregnancy.
Frequency of treatment:
once daily
Duration of test:
20 days
Doses / concentrations
Remarks:
Doses / Concentrations:
0 (control), 62.5, 250, or 1000 mg/kg
Basis:
nominal conc.
No. of animals per sex per dose:
20
Control animals:
yes, concurrent vehicle

Examinations

Maternal examinations:
All females were observed daily during the preadministration period and twice a day (before administration and 1 to 2 h after administration) during the administration period for clinical signs of toxicity. Maternal body weight was recorded on days 0, 5, 8, 11, 14, 17, 19, and 20 of pregnancy. Feed consumption was recorded on days 0–1, 5–6, 8–9, 11–12, 14–15, 17–18, and 19–20 of pregnancy
Ovaries and uterine content:
The pregnant rats were euthanized by exsanguination under ether anesthesia on day 20 of pregnancy. The peritoneal cavity was opened, and the uterus and ovaries were removed from the maternal body and weighed. The numbers of corpora lutea, implantation sites, and live and dead fetuses and resorptions were counted.
Fetal examinations:
The live fetuses were removed from the uterus and sexed, weighed, and inspected for external malformations and malformations within the oral cavity. Approximately one-half of the live fetuses in each litter were randomly selected, fixed in alcohol, stained with alizarin red S (Dawson, 1926), and examined for skeletal anomalies. The remaining live fetuses in each litter were fixed in Bouin’s solution. Their heads were subjected to free-hand razor-blade sectioning (Wilson, 1973), and the thoracic areas were subjected to microdissecting (Nishimura, 1974) to reveal internal abnormalities.
Statistics:
Bartlett's and Dunnett’s tests or Fisher's exact test
Indices:
yes

Results and discussion

Results: maternal animals

Maternal developmental toxicity

Details on maternal toxic effects:
Maternal toxic effects:no effects

Effect levels (maternal animals)

Dose descriptor:
NOAEL
Effect level:
1 000 mg/kg bw/day (nominal)
Based on:
test mat.
Basis for effect level:
other: maternal toxicity

Results (fetuses)

Details on embryotoxic / teratogenic effects:
Embryotoxic / teratogenic effects:no effects

Effect levels (fetuses)

Dose descriptor:
NOAEL
Effect level:
1 000 mg/kg bw/day (nominal)
Based on:
test mat.
Basis for effect level:
other: embryotoxicity

Fetal abnormalities

Abnormalities:
not specified

Overall developmental toxicity

Developmental effects observed:
not specified

Any other information on results incl. tables

The number of implantations was slightly reduced, and incidence of preimplantation loss was slightly increased in the high-dosage group, a finding associated with the tendency for reduced maternal body weight gain during the administration period, with an increase in maternal body weight gain after completion of the administration period. These differences were probably associated with

the variability in litter sizes in the high-dosage group and unrelated to the administration of the test chemical. No significant changes in any maternal parameters were noted, even at 1000 mg/kg. No significant changes in embryonic/fetal survival or growth parameters were found, even at 1000 mg/kg. These findings indicate that DBHCB is not toxic to maternal animals, embryonic/fetal survival, or fetal growth when administered during the time of implantation to the term of pregnancy.

Morphological examinations in the fetuses of exposed mothers revealed no fetuses with external malformations. However, some fetuses with skeletal and/or internal variations were found in all groups. The variations observed in the current study are of the types that occur spontaneously among the control rat fetuses (Kameyama et al., 1980; Morita et al., 1987; Nakatsuka et al., 1997;

Barnett et al., 2000). A skeletal variation (i.e., full supernumerary ribs) has been described as a warning sign of possible teratogenicity and is known to occur in the presence of perturbation of maternal homeostatis. All other variations, short supernumerary ribs, sternebral variations, and bilobed centra of the vertebral column, are frequent variations, which were considered to be normal findings.

Applicant's summary and conclusion