Eugenol

Developmental toxicity / teratogenicity

Administrative data

Endpoint:

developmental toxicity

Type of information:

migrated information: read-across from supporting substance (structural analogue or surrogate)

Adequacy of study:

key study

Study period:

June 16, 1998 to August 18, 1998

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: Study design is considered to follow OECD guideline Test Guideline No 414 (2001). The study was fully reliable (Klimisch score = 1), however the reliability score was lowered to 2 which is the maximum score for read-across.

Cross-reference

Reason / purpose for cross-reference:

reference to other study

Data source

Reference

Reference Type:

study report

Title:

Unnamed

Year:

1999

Materials and methods

Test guideline

Qualifier:

equivalent or similar to guideline

Guideline:

OECD Guideline 414 (Prenatal Developmental Toxicity Study)

Deviations:

no

GLP compliance:

yes

Limit test:

no

Test material

Test material information

Constituent 1

Reference substance name:

Isoeugenol

EC Number:

202-590-7

EC Name:

Isoeugenol

Cas Number:

97-54-1

Molecular formula:

C10H12O2

IUPAC Name:

2-methoxy-4-prop-1-en-1-ylphenol

Details on test material:

- Name of test material (as cited in study report): Isoeugenol
- Analytical purity: 97.9%
- Lot/batch No.: 46928

Test animals

Species:

rat

Strain:

Crj: CD(SD)

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Source: Charles River Laboratories, Inc.
- Age at study initiation: Not reported
- Weight at study initiation: 232-275 g on gestational day 0
- Fasting period before study: Not reported
- Housing: Sani-Chip hardwood cage litter
- Diet (e.g. ad libitum): Purina Certified Roden Chow ad libitum
- Water (e.g. ad libitum): ad libitum
- Acclimation period: 10 days

ENVIRONMENTAL CONDITIONS
- Temperature (°C): 21.5-23.3
- Humidity (%): 39.8-59.9
- Air changes (per hr): Not reported environmental conditions monitored and controlled by computer
- Photoperiod (hrs dark / hrs light): 12/12

IN-LIFE DATES: Not reported

Administration / exposure

Route of administration:

oral: gavage

Type of inhalation exposure (if applicable):

other: not applicable

Vehicle:

corn oil

Details on exposure:

PREPARATION OF DOSING SOLUTIONS:

VEHICLE
- Justification for use and choice of vehicle (if other than water): Not reported
- Concentration in vehicle: Not reported
- Amount of vehicle (if gavage): 5 ml/kg (administered dose volume)

Analytical verification of doses or concentrations:

no

Details on mating procedure:

- Impregnation procedure: cohoused
- If cohoused:
- M/F ratio per cage: 1/1
- Length of cohabitation: overnight
- After ... days of unsuccessful pairing replacement of first male by another male with proven fertility: not reported
- Further matings after two unsuccessful attempts: not reported
- Verification of same strain and source of both sexes: yes
- Proof of pregnancy:sperm found in vaginal lavage referred to as day 0 of pregnancy
- Any other deviations from standard protocol: not reported

Duration of treatment / exposure:

Day 6 through day 19 of gestation

Frequency of treatment:

Daily

Duration of test:

13 days

Doses / concentrations

Doses / concentrations 1

Remarks:

Doses / Concentrations:
250 mg/kg bw/day
Basis:
actual ingested

Doses / concentrations 2

Remarks:

Doses / Concentrations:
500 mg/kg bw/day
Basis:
actual ingested

Doses / concentrations 3

Remarks:

Doses / Concentrations:
1000 mg/kg bw/day
Basis:
actual ingested

No. of animals per sex per dose:

25 pregnant females/group

Control animals:

yes, concurrent vehicle

Details on study design:

- Dose selection rationale: based on screening study

Examinations

Maternal examinations:

CAGE SIDE OBSERVATIONS: Yes
- Time schedule: daily

DETAILED CLINICAL OBSERVATIONS: Yes
- Time schedule: daily at dosing, and at 0.5 and 2 hours after dosing

BODY WEIGHT: Yes
- Time schedule for examinations: Gestational Day 0, 6 through 19, 20 and immediately following termination at day 20

FOOD CONSUMPTION: Yes
- Time schedule for examinations: Gestational Day 0, 6, 9, 12, 15, 18, 19, and 20

WATER CONSUMPTION: Yes
- Time schedule for examinations: Gestational Day 0, 6, 9, 12, 15, 18, 19, and 20

POST-MORTEM EXAMINATIONS: Yes
- Sacrifice on gestation day #20
- Organs examined: liver, gravid uterus, thoracic and abdominal cavities

Ovaries and uterine content:

The ovaries and uterine content was examined after termination: Yes
Examinations included:
- Gravid uterus weight: Yes
- Number of corpora lutea: Yes
- Number of implantations: Yes
- Number of early resorptions: Yes
- Number of late resorptions: Yes
- Other: number of dead and live fetuses

Fetal examinations:

- External examinations: Yes: all live fetuses
- Soft tissue examinations: Yes: half per litter
- Skeletal examinations: Yes: all per litter
- Head examinations: Yes: half per litter

Statistics:

SAS software

Results and discussion

Results: maternal animals

Maternal developmental toxicity

Details on maternal toxic effects:

Maternal toxic effects:yes

Details on maternal toxic effects:
Compared to control, findings included lower maternal body weight (4.6%, 11.6%, and 9.9% lower at dose levels of 250, 500, and 1,000 mg/kg body weight/day, respectively) when measured on GD 20 and statistically significant and dose-dependent lower gestation body weight gain (13.6%, 22.6%, and 30.5% lower at dose levels of 250, 500, and 1,000 mg/kg body weight/day, respectively) when measured over GD 0 to 20 . Other notable changes included clinical signs of piloerection and sedation at 500 and 1,000 mg/kg body weight/day, and lower gravid uterine weight (statistically significant values of 8.54% and 10.5% at 500 and 1,000 mg/kg body weight/day, respectively) and lower maternal relative food intake (statistically significant values of 15.3% at 1,000 mg/kg body weight/day). There were no treatment-related group mean differences for the following reproductive parameters: number of corpora lutea per dam, number of implantation sites per dam, percent preimplatation loss per dam, percent preimplantation loss per litter, resorptions, late foetal deaths, average litter size, and percentage of male foetuses per litter

Effect levels (maternal animals)

1

Dose descriptor:

LOAEL

Effect level:

250 mg/kg bw/day (actual dose received)

Based on:

test mat.

Basis for effect level:

other: maternal toxicity

2

Dose descriptor:

NOAEL

Effect level:

500 mg/kg bw/day (actual dose received)

Based on:

test mat.

Basis for effect level:

other: developmental toxicity

3

Dose descriptor:

LOAEL

Effect level:

1 000 mg/kg bw/day (actual dose received)

Based on:

test mat.

Basis for effect level:

other: developmental toxicity

Results (fetuses)

Details on embryotoxic / teratogenic effects:

Embryotoxic / teratogenic effects:yes

Details on embryotoxic / teratogenic effects:
The only developmental effect noted was a 7 to 9% decrease in body weight in high-dose foetuses when compared with control group. There were no statistically significant differences among groups for the incidences of foetal malformations (i.e., total, external, or skeletal); however, the incidence of skeletal variations (i.e., unossified sternebrae) was significantly increased in high-dose foetuses. Incidental occurrences of visceral malformations were noted in one mid-dose and one high-dose foetus; however, these did not occur in a dose-related manner and were therefore considered not to be relate to the test article; these variations included enlarged lateral ventricle, enlarged nasal sinus, agenesis of the innominate artery, and distended ureter.

Effect levels (fetuses)

Dose descriptor:

NOAEL

Effect level:

500 mg/kg bw/day (nominal)

Based on:

test mat.

Sex:

male/female

Basis for effect level:

other: based on intra-uterine growth retardations mildly delayed skeletal ossification observed at 1000 mg/kg bw/day. However, this finding is likely secondary to maternal toxicity and not indicative of a teratogenic effect.

Fetal abnormalities

Abnormalities:

not specified

Overall developmental toxicity

Developmental effects observed:

not specified

Applicant's summary and conclusion

Conclusions:

LOAEL maternal toxicity = 250 mg/kg bw/day, based on dose-dependent reduced body weight gain.
NOAEL developmental toxicity = 500 mg/ kg bw/day, based on intra-uterine growth retardations mildly delayed skeletal ossification observed at 1000 mg/kg bw/day. However, this finding is likely secondary to maternal toxicity and not indicative of a teratogenic effect.

Executive summary:

A read-across strategy is used for the endpoint of developmental toxicity, with justification provided below.

Justification for Read-Across

The use of isoeugenol (CAS No. 97-54-1) as a structural surrogate for eugenol (CAS No. 97-53-0) is justified on the basis of structural similarity; both substances are 2-methoxy-4-propenylphenol isomers, whose chemical structures are identical except for the position of the double bond in the propenyl substituent. The difference in the position of the double bond is expected to exert little or no effect on the physical-chemical properties of the two substances with respect to biological activity, and their absorption and distribution profiles are therefore also expected to be essentially identical. Based on data from studies in rats, the pharmacokinetic profiles of isoeugenol and eugenol appear to be similar; the major route of elimination of these compounds isviathe urine and the major metabolites are glucuronic acid and sulphate conjugates.

Summary of Study

The teratogenic potential of isoeugenol was evaluated in a key oral embryo-foetal developmental study; administration of the isoeugenol to CD rats on Gestation Days (GD) 6 to 19 at dose levels up to 1,000 mg/kg body weight/day resulted in a number of test article-related maternal effects beginning at the low dose level (including, but not limited to, decreases in maternal body weight and body weight gain and significant decreases in gravid uterine weight and maternal relative food intake at the higher dose levels). A significant increase in the incidence of skeletal variations (i.e., unossified sternebrae) was noted in high-dose foetuses; however, this finding is likely secondary to maternal toxicity and not indicative of a teratogenic effect.