Hydroquinone

Developmental toxicity / teratogenicity

Administrative data

Endpoint:

developmental toxicity

Type of information:

experimental study

Adequacy of study:

key study

Study period:

01.03.1988 - 18.04.1988

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

other: Guideline study

Data source

Reference

Reference 1

Reference Type:

publication

Title:

A study of developmental toxicity of hydroquinone in the rabbit

Author:

Murphy SJ, Schroeder RE, Blacker AM, Krasavage WJ & English JC

Year:

1992

Bibliographic source:

Fundam Appl Toxicol 19, 214 - 221

Reference 2

Reference Type:

study report

Title:

Unnamed

Year:

1988

Report date:

1988

Reference 3

Reference Type:

study report

Title:

Unnamed

Year:

1989

Report date:

1989

Materials and methods

Test guideline

Qualifier:

according to guideline

Guideline:

EPA OTS 798.4900 (Prenatal Developmental Toxicity Study)

Deviations:

no

GLP compliance:

yes

Test material

Test material information

Constituent 1

Reference substance name:

Hydroquinone

EC Number:

204-617-8

EC Name:

Hydroquinone

Cas Number:

123-31-9

Molecular formula:

C6H6O2

IUPAC Name:

hydroquinone

Details on test material:

Physical state: white crystalline powder
Purity: 100 %
Supplier: Eastman Co., Kingsport
LOT: 71541
The purity was determined using gas chromatography/flame ionization detection. Structure confirmation was made using gas chromatography/mass spectrometry.

Test animals

Species:

rabbit

Strain:

New Zealand White

Details on test animals or test system and environmental conditions:

4 – 5 month-old nulliparous female NZW rabbits were obtained from Hazleton Research Products, Inc. (Denver) and allowed to acclimate to laboratory conditions for approximately 6 weeks. They were maintained in animal rooms controlled for lighting (12 hr light/day), temperature (18.4 degrees C) and relative humidity (50 +/- 20 %) and were supplied Purina High-Fiber Rabbit Chow 5325 and water ad lib.
The body weight range of animals at the time of initial dosing for the range-finding study was 3244 - 4561 g.
For the definitive study, initial body weights ranged from 3385 - 4949 g.
Animals were housed individually in stainless-steel wire-mesh hanging cages except during breeding.

Administration / exposure

Route of administration:

oral: gavage

Vehicle:

water

Analytical verification of doses or concentrations:

yes

Details on analytical verification of doses or concentrations:

Dosing solutions were prepared fresh daily and solution concentrations were verified once a week using liquid chromatography. Representative dosing solutions were found to be stable at room temperature for at least 6 hr.
In the definitive study, mean nominal values were 100 +/- 2.01, 103 +/- 2.69 and 105 +/- 3.39 % of targeted concentrations for the low-, mid-, and high-dose groups, respectively.

Details on mating procedure:

The day on which evidence of mating with two proven breeder males was observed was defined as day 0 of gestation. Females that mated with males from a pool of proven breeders were assigned to groups in a way that equalized Day 0 mean group body wts.

Duration of treatment / exposure:

gestation days 6 - 18

Frequency of treatment:

once daily

Duration of test:

caesarean section on gestation day 30

Doses / concentrations

Remarks:

Doses / Concentrations:
0, 25, 75 or 150 mg/kg bw
Basis:
nominal conc.

No. of animals per sex per dose:

18 mated females

Control animals:

yes, concurrent vehicle

Details on study design:

The dose selection was based on a range finding study.

Range-finding study:
In the range-finding study, groups of five mated females were administered degassed, distilled water (vehicle control) or HQ in degassed, distilled water at doses of 50, 100. 200, 300, or 400 mg/kg/d (dose volume of 10 ml/kg body wt) by gavage on days 6 - 18 of gestation. A group treated with 500 mg HQ/kg was terminated on gestation day 6 because two animals died immediately after being given the first dose.

Definite study:
Groups of 18 mated females were administered 0, 25, 75, or 150 mg/kg/d in degassed, distilled water (in a dose volume of 8 ml/kg bw) by gavage on days 6-18 of gestation.

Examinations

Maternal examinations:

Range-finding study:
During gestation, animals were observed twice daily for obvious toxicological effects and/or mortality.
Body weights were recorded on GD 0, 6, 12, 18, 24, and 30.
Feed consumption was recorded on GD 3. 6, 7, 8, 9. 10, 12, 15, 18, 24, and 29.
Test animals were given a detailed physical evaluation on GD 0, 6, 9, 12, 15, 18, 24, and 30. Animals that delivered prematurely were euthanized that same day and given a gross post-mortem examination. Surviving females were euthanized on GD 30 and were given a gross post-mortem evaluation.

Definitive study:
During the treatment period, animals were observed twice daily for signs of pharmacologic or toxicological effects and mortality.
Body weights were recorded on GD 0. 6, 9, 12, 16, 18, 24, and 30.
Feed consumption was recorded daily (GDs 1- 29).
Test animals were given a detailed physical evaluation on GDs 0, 6-19, 24, and 30. On GD 30, each female was euthanized, given a gross post-mortem evaluation and liver and kidney weights were recorded.

Ovaries and uterine content:

Range-finding study:
The intact gravid uterus was removed and weighed, corpora lutea were counted on each ovary, and uterine implantations were identified as live, dead, or resorbed foetuses. When no implants were grossly apparent, the uterus was stained with ammonium sulphide. If no foci were visualized post-staining, the female was considered to be not pregnant.

Definite study:
Examination of corpora lutea/uterine implantation data. Animals that delivered prematurely were euthanized on the day such evidence was observed. Uteri of seemingly non-pregnant females were stained as described above.

Fetal examinations:

Range-finding study:
All live and dead foetuses were removed from the uterus, weighed and given a gross external examination.

Definite study:
Foetuses recovered on GD 30 were weighed and evaluated for external and visceral malformations/variations. Subsequently all foetuses were processed for staining of the skeletal structures with alizarin red S and evaluated for skeletal malformation/variations.

Statistics:

Data from the range-finding study were not analyzed statistically because group sizes were small. Data from the definitive study were analyzed as follows. The equality of means was evaluated using a one-way analysis of variance (ANOVA) technique, followed by a multiple-comparison procedure, when appropriate. Bartlett's test was performed to determine if groups had equal variances. If the variances were equal, parametric procedures were used; if not, nonparametric procedures were used. A one-way ANOVA, using the F distribution to assess the significance level, was followed by Dunnett's test if significant differences (p <= 0.05) among the means were indicated. If nonparametric methods were required, the Kruskal-Wallis test was used; if significant differences were indicated, Dunn's summed rank test was performed to determine which treatment groups differed from the control group. Methods for analyzing trends were also utilized, i.e., standard regression analysis was used for parametric evaluations and Jonckheere's test for monotonic trend was used for nonparametric evaluations. Incidence data from treatment versus control groups (pregnancy rates, the percentage of foetuses with malformations, the percentage of litters containing malformed foetuses, and ossification variations) were analyzed using standard X2 analysis. This analysis was followed by a 2 X 2 Fisher exact test, using the Bonferroni inequality correction to ensure the stated significance level was corrected for multiple comparisons. Armitage's test was performed to determine if there was a linear dose-response.

Indices:

females mated, pregnant (%), pregnancies aborted, premature births, litters with viable foetuses, corpora lutea/dam, implantations/dam, pre-implantation loss, live foetuses/litter, resorptions/litter, resorptions/implants, foetal body weights, sex ratio

Results and discussion

Results: maternal animals

Maternal developmental toxicity

Details on maternal toxic effects:

Maternal toxic effects:yes. Remark: >= 75 mg/kg/d: decreased feed consumption and/or body weights

Effect levels (maternal animals)

1

Dose descriptor:

NOEL

Effect level:

25 mg/kg bw/day

Basis for effect level:

other: maternal toxicity

2

Dose descriptor:

NOEL

Effect level:

75 mg/kg bw/day

Basis for effect level:

other: developmental toxicity

Results (fetuses)

Details on embryotoxic / teratogenic effects:

Embryotoxic / teratogenic effects:no effects

Fetal abnormalities

Abnormalities:

not specified

Overall developmental toxicity

Developmental effects observed:

not specified

Any other information on results incl. tables

Maternal observations:

Survival of control and treated females was comparable and no animals died. There were no adverse effects evident from physical observation data. Mean body weight of dams dosed with 150 mg/kg/d was significantly reduced on GD 18, these animals also exhibited a significantly greater weight loss over GDs 6 - 18 when compared with controls. Feed consumption was significantly reduced on GDs 7 - 15 and on GD 18. Body weight data for mid-dose dams were comparable with controls, but feed consumption was significantly reduced on GDs 12 and 13 . At 25 mg/kg/d no treatment-related changes in body weights or feed consumption were observed. Data for reproductive parameters including percentage pregnant and number of dams delivering prematurely were comparable in all groups. At necropsy, no adverse treatment-related effect was evident on inspection of liver or kidney weight data or gross post-mortem examination data.

Foetal observations:

Mean foetal body weights (by sex and as a composite of both sexes) were comparable between control and treated groups. The ratios of viable male/female foetuses per group were also comparable. Statistically significant differences between groups were not found for the incidences of external malformations both on a per foetus and a per litter basis. Limb flexure defects were seen in one foetus each from the low- and mid-dose groups. In the high-dose group, two foetuses from a single litter did not have eye bulges and at necropsy were found to have small eyes (micropthalmia). The incidences of foetuses/litters with visceral malformations were comparable in all groups. The most frequently seen visceral malformation was absence of the gallbladder (there was no dose-response relationship and the mean historical control incidence was 0.5 % (range: 0.0 - 9.5 %)). In the low-dose group, one foetus had a defect in the lobulation of the left lung. In the high-dose group, a total of three foetuses from two litters exhibited micropthalmia.

The incidences of foetuses with visceral variations were comparable in the control and mid-dose groups, but were higher than the controls in the low- and high-dose groups. The difference for the low-dose group was statistically significant. The most prominent visceral variation was an absence of the postcaval lobe of the lung (in the absence of a dose-response relationship and because other types of variations appeared with similar frequency in all groups, the occurrence of this variation was not considered to be indicative of a treatment-related response).

The incidence of skeletal malformations did not differ statistically between control or treated groups on either a per foetus or per litter basis. The most frequently seen skeletal malformation was angulated arch of the hyoid (incidence: 2.7, 0.7, 0 and 7.2 % at 0, 25, 75 or 150 mg/kg bw; mean historical control incidence was 1.7 % (0.0 to 3.7 %)). The incidence of fused sternebrae was higher in the control group than in any of the treated groups. In the control and high-dose groups, the incidence of foetuses with skeletal malformations exclusive of angulated hyoid arch and fused sternebrae was 0.9 and 4.8 %, respectively, the predominant malformation involved rib defects. No adverse effect of treatment was evident from ossification variation data.

Applicant's summary and conclusion

Conclusions:

This study gave no indication for a potential developmental or reproductive hazard of hydroquinone.

Executive summary:

In a guideline study performed according to EPA OTS 798.4900, hydroquinone was administered to pregnant NZW rabbits (18 mated per dose group) in an aqueous solution at doses of 0, 25, 75, or 150 mg/kg/d by gavage on gestation days 6 to 18. Caesarean sections were performed on gestation day 30. Doses of >= 75 mg/kg/d adversely affected feed consumption and/or body weights of dams during the treatment period. However, at these doses no treatment-related clinical effects and no changes in liver and kidney weights, premature delivery incidence, and caesarean sectioning data were noted. For the dams the NOEL was 25 mg/kg/d. In offspring the dosing with 150 mg/kg/d caused no significant changes in total incidences of external, visceral, and skeletal findings, but there were some slightly increases (statistically not significant when compared with controls) in the incidences of ocular and minor skeletal malformations (micropthalmia, vertebral/rib defects, angulated hyoid arch) on both a per foetus and a per litter basis. These findings were only seen in the presence of maternal toxicity. The NOEL for developmental toxicity was 75 mg/kg/day.