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Toxicological information

Developmental toxicity / teratogenicity

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Administrative data

Endpoint:
developmental toxicity
Type of information:
experimental study
Adequacy of study:
key study
Study period:
not reported
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
other: Study conducted to GLP in accordance with generally accepted scientific principles, possibly with incomplete reporting or methodological deficiencies, which do not affect the quality of the relevant results.

Data source

Reference
Reference Type:
publication
Title:
Maternal and Fetal Toxicity of Dimethyltin in Rats.
Author:
Noda, T.
Year:
2001
Bibliographic source:
Journal of Health Science, 47(6) 544-551

Materials and methods

Test guideline
Qualifier:
equivalent or similar to
Guideline:
OECD Guideline 414 (Prenatal Developmental Toxicity Study)
Deviations:
yes
Principles of method if other than guideline:
The method followed the basic general outline of OECD Guideline 414, however there were several deviations.
The most notable of these were:
-Dosing occurred in the period of organogenesis (days 7 – 17 of gestation)
-Group size was below that recommended in the guideline (Study I, 5 groups of 10; Study II, 8 groups of 8 – 11)
GLP compliance:
not specified
Limit test:
no

Test material

Reference
Name:
Unnamed
Type:
Constituent
Test material form:
solid: crystalline

Test animals

Species:
rat
Strain:
Wistar
Details on test animals and environmental conditions:
TEST ANIMALS
- Source: CLEA Japan Inc. (Tokyo, Japan)
- Age at study initiation: 3 months
- Housing: Animals were individually housed.
- Diet (e.g. ad libitum): ad libitum. Fed commercial laboratory chow (NMF; Oriental Yeast Co., Ltd. Tokyo, Japan)
- Water (e.g. ad libitum): ad libitum tap water.

ENVIRONMENTAL CONDITIONS
- Temperature (°C): 23 ± 2°C
- Humidity (%):60 ± 20% relative
- Photoperiod (hrs dark / hrs light): Constant day/night cycle (lights on from 7:00 to 19:00 hr)

Administration / exposure

Route of administration:
oral: gavage
Vehicle:
other: saline
Analytical verification of doses or concentrations:
no
Details on mating procedure:
A female rat was paired overnight with a male of the same age and the day on which sperm was observed in the vaginal smears was designated as day 0 of gestation.
Duration of treatment / exposure:
Two teratological studies were performed. In the first (Study I), DMTC was administered to pregnant animals during the organogenetic phase of gestation (days 7-17 of gestation). DMTC was administered to pregnant females t 0, 5, 10, 15 or 20 mg/kg/day on days 7-17 of gestation. The volume of vehicle was held constant at 2 mL/kg based on maternal body weight.

In the second teratological study (Study II), DMTC was administered to pregnant animals at 0, 20 or 40 mg/ kg/day for two to three consecutive days at one of four different periods of gestation (gestational days 7-9, 10-12, 13-15 and 16-17). The group treated with DMTC at 20 mg/kg/day on days 16-17 was not tested. Control animals were administered an appropriate volume of vehicle without DMTC on days 10-12 of gestation.
Duration of test:
20 days
Doses / concentrationsopen allclose all
Remarks:
Doses / Concentrations:
0, 5, 10, 15, 20 mg/kg/day
Basis:
actual ingested
Study I
Remarks:
Doses / Concentrations:
0, 20, 40 mg/kg/day
Basis:
actual ingested
Study II
No. of animals per sex per dose:
Study I: Mated females were randomly assigned to five groups of ten rats each.
Study II: Mated females were randomly assigned to eight groups of 8-11 rats each.
Control animals:
yes, concurrent vehicle
Details on study design:
All procedures were substantially the same in the two teratological studies. Animals were randomly assigned to test groups.

Examinations

Maternal examinations:
Maternal body weight and food intake were measured daily. Pregnant females were observed daily for clinical signs of toxicity and were sacrificed by overdose of ether anesthesia on day 20 of gestation. Maternal thymus and brain weights, and the gravid uteri weights (only in study II) were also recorded.
Ovaries and uterine content:
The position and the number of living fetuses and implantation loss in the uterus, and the number of corpora lutea, were recorded. Uteri with total resorption were isolated and stained with 10% ammonium sulfide to determine the total number of implantations.
Fetal examinations:
The living fetuses were examined for their sex and external malformations, and were then weighed. Half of the living fetuses in each litter were fixed with 95% ethanol and processed for staining of the skeleton by the alizarin red S dye method. These preparations were examined for skeletal abnormalities. The other half of each litter was fixed in Bouin's solution and examined for visceral abnormalities according to the method of Wilson.
Statistics:
Data on the number of dams with living fetuses and with total resorption and the number of malformed fetuses were analysed by Fisher's exact test. Other data were analysed by Dunnett's multiple comparison method) in a parametric or non-parametric manner. The litter was used as the statistical unit for calculation of fetal values.

Results and discussion

Results: maternal animals

Maternal developmental toxicity

Details on maternal toxic effects:
Maternal toxic effects:yes

Details on maternal toxic effects:
STUDY I
Oral treatment of pregnant rats with DMTC during the organogenetic phase of gestation (days 7-17 of gestation) caused reduction in the maternal body weight gain in a dose dependent manner. Significantly reduced body weight gain was observed in pregnant rats treated with DMTC at 15 or 20 mg/kg/day in late gestation. Maternal food in-take was significantly reduced by DMTC-treatment at 20 mg/kg/day, but no other statistically significant differences in maternal food intake were present.

Oral administration of DMTC at 20 mg/kg/day resulted in the death of two pregnant rats, one died on day 18 of gestation and another died on day 19 of gestation. These deaths were considered to be DMTC treatment related because the animals exhibited severe clinical signs of toxicity (piloerection, ataxia, perinasal and periocular staining, vaginal bleeding, tremor and convulsion) for about four days prior to their deaths. No gross pathological changes were noted upon necropsy in the organs of the dead dams. No other mortalities were observed in either the control or DMTC-treatment groups.

Perinasal and periocular staining, piloerection and ataxia were observed in all the pregnant rats administered DMTC at 20 mg/kg/day mainly after day 15 of gestation. In addition to these clinical signs of toxicity, vaginal bleeding, tremor and convulsion were observed in three pregnant animals other than two dead pregnant rats in the late stage of gestation. No clinical signs of toxicity were observed in the other groups. Maternal thymus weights were reduced in a dose-dependent manner with significance at 15 and 20 mg/kg/day on day 20 of gestation. Maternal brain weight was unaffected in any group.

Total resorption was observed in one of eight living pregnant rats at 20 mg/kg/day. This same rat also exhibited vaginal bleeding, tremor and convulsion in the late stage of gestation. Mean body weight in living fetuses of both sexes decreased in a dose-dependent manner with significance at 15 and 20 mg/ kg/day. No significant differences were noted in the number of corpora lutea, implants and living fetuses, and the incidence of post-implantation loss and sex ratio.

STUDY II
Oral gavage administration of DMTC at 40 mg/ kg/day to pregnant rats on days 10-12 of gestation caused significant reductions of maternal body weight gain on days 13, 16 and 17 of gestation and reduction of food intake on the consecutive days of gestation after day 12 of gestation. No significant reduction in maternal body weight gain was observed in other treatment period groups, in spite of the reduced food intake caused by the treatment. There were no significant differences in general behaviour among the groups including controls.

Maternal thymus weights and adjusted body weight gain were reduced significantly in the group treated with DMTC at 20 mg/kg/day on days 10-12 of gestation and in every treatment period groups at 40 mg/kg/day. Gravid uterus and maternal brain weights were unaffected at either dose level in any treatment period group. Total resorption was observed in one of 10 dams in the group treated with DMTC at 40 mg/kg/day on days 7-9 of gestation. In this group, mean fetal body weight of the females was reduced. No significant differences were noted in the number of corpora lutea, implants and living fetuses and incidence of postimplantation loss, sex ratio and male fetal body weight at either close level in any treatment period group.

Effect levels (maternal animals)

open allclose all
Dose descriptor:
NOAEL
Effect level:
10 mg/kg bw/day (actual dose received)
Based on:
test mat.
Basis for effect level:
other: maternal toxicity
Dose descriptor:
NOAEL
Effect level:
10 mg/kg bw/day (actual dose received)
Based on:
test mat.
Basis for effect level:
other: other:

Results (fetuses)

Details on embryotoxic / teratogenic effects:
Embryotoxic / teratogenic effects:yes

Details on embryotoxic / teratogenic effects:
STUDY I
The incidence of external malformations increased in fetuses from dams exposed to DMTC at 20 mg/kg/day from days 7-17 of gestation. There were 21 fetuses with cleft palate from five of seven pregnant rats with living fetuses on day 20 of gestation. In addition to cleft palate, one fetus was associated with general edema and pes varus and one with general edema. There were two fetuses with omphalocele from one dam exposed to DMTC at 15/mg/day, but the incidence was not statistically significant. No other external malformations were observed in either the control or DMTC-treatment groups.

No significant difference was observed in the incidence of skeletal malformations and skeletal variations. No significant difference was observed in the incidence of visceral malformations, however the number of visceral variation, dilation of the renal pelvis, was significantly increased at 20 mg/kg/day.

STUDY II
The incidence of external, skeletal and visceral malformations did not significantly increase at either close in any treatment period group. No cleft palate were found in any fetus treated with DMTC at 20 or 40 mg/kg/day on two to three consecutive days at one of four different treatment periods of gestation. The numbers of fetuses with skeletal variation and visceral variation increased significantly at 40 mg/kg/day in some treatment periods. Numbers of fetuses with cervical ribs increased in the groups treated with DMTC on days 7-9 or 13-15 of gestation. Numbers of fetuses with splitting of first cervical vertebral arches and with kinked ureter increased in the group treated with DMTC on days 7-9 and 16-17 of gestation, respectively.

Fetal abnormalities

Abnormalities:
not specified

Overall developmental toxicity

Developmental effects observed:
not specified

Any other information on results incl. tables

Table 1. Effects of DMTC on Maternal Thymus and Brain Weights on Day 20 of Gestation

 

Saline

2 mL/kg

DMTC (mg/kg)

5

10

15

20

Body wt. (g)

 

Thymus wt. (mg)

 

Brain wt. (g)

333 ± 26.7

 

169 ± 37.5

 

 

1.75 ± 0.02

334 ± 21.9

 

190 ± 32.6

 

 

1.72 ± 0.05

321 ± 21.0

 

168 ± 26.8

 

 

1.71 ± 0.07

315 ± 9.2

 

151 ± 13.6*

 

 

1.76 ± 0.04

252 ± 41.1**

 

45 ± 21.7**

 

 1.68 ± 0.04

Pregnant rats were treated orally with DMTC on days 7-17 of gestation. These weights were recorded on day 20 of gestation. Values are mean ± S.D. *Significantly different from control, p < 0.05. **Significantly different from control, p < 0.01.

 

 

Table 2. Effects of DMTC Exposed to Pregnant Rats on Two or Three Consecutive Days at One of Four Different Treatment Periods of Gestation, on Maternal Brain, Thymus, Gravid Uterus Weights and Adjusted Body Weight Gain at the Day 20 of Gestation

 

Saline

days 10-12 2 mL/kg

DMTC (mg/kg)

days 7-9

days 10-12

days 13-15

days 16-17

20

40

20

40

20

40

40

Body wt. (g)

 

Brain wt. (g)

 

Thymus wt. (mg)

 

Body weight gain (g)

 

Gravid uterus wt. (g)

 

Adjusted body weight gaina(g)

338 ± 19.7

 

1.79 ± 0.08

 

253 ± 45.1

 

112 ± 21.6

 

 

65 ± 20.0

 

 

 47 ± 7.0

330 ± 23.2

 

1.79 ± 0.04

 

220 ± 22.7

 

110 ± 12.5

 

 

69 ± 10.2

 

 

 40 ± 7.4

330 ± 47.4

 

1.80 ± 0.05

 

208 ± 37.6*

 

110 ± 13.1

 

 

75 ± 11.7

 

 

 35 ± 6.0**

325 ± 23.1

 

1.79 ± 0.04

 

207 ± 39.9*

 

107 ± 18.0

 

 

72 ± 11.1

 

 

 35 ± 9.6*

312 ± 22.7

 

1.76 ± 0.06

 

190 ± 36.9**

 

95 ± 17.8

 

 

66 ± 19.7

 

 

 30 ± 9.2**

331 ± 12.7

 

1.75 ± 0.06

 

217 ± 15.3

 

111 ± 9.0

 

 

69 ± 4.5

 

 

 42 ± 6.5

325 ± 14.8

 

1.79 ± 0.05

 

182 ± 32.7**

 

103 ± 12.4

 

 

71 ± 8.6

 

 

 33 ± 6.6**

340 ± 23.4

 

1.80 ± 0.05

 

172 ± 45.1**

 

102 ± 22.6

 

 

71 ± 15.6

 

 

 31 ± 13.3**

Pregnant rats were sacrificed on day 20 of gestation. Values are the mean ± S.D. of 8-11 animals per group. a(Body weight gain from day 0 to 20 of gestation) - (gravid uterus weight). *Significantly different from control, p < 0.05. **Significantly different from control, p < 0.01.

 

Applicant's summary and conclusion

Conclusions:
Under the conditions of the study, the NOAEL for maternal toxictiy and foetal toxicity was determined to be 10 mg/kg bw/day.
Executive summary:

The maternal and fetal toxicity of dimethyltin chloride (DMTC) was examined in two teratological studies in pregnant Wistar rats. In one study, the animals were treated by oral gavage with DMTC at doses of 0, 5, 10, 15, or 20 mg/kg/day on gestational days 7-17. In the second study, animals were treated by oral gavage at doses of 0, 20 or 40 mg/kg/day DMTC on two or three consecutive days at one of four different periods of gestation (gestational days 7-9, 10-12, 13-15 or 16-17). Caesarean sections were performed on day 20 of gestation in both studies. In the first study, vaginal bleeding, tremor and convulsions were observed in animals treated at 20 mg/kg/day after day 15 of gestation. Of ten dams treated with 20 mg/kg/day DMTC, two died and one exhibited total resorption. While a increase in the incidence of cleft palate was found in the fetuses of animals treated with 20 mg/kg/day DMTC, the dams so treated exhibited severe clinical signs of toxicity. Animals treated in the second study with doses of 20 or 40 mg/kg/day at one of four periods of gestation had a reduction in the adjusted body weight gain but not in gravid uterus weight and did not show any evidence of teratogenic effect at either dose and period tested. These studies suggest that DMTC did not produce teratogenic effects at dose levels where no maternal toxicity was observed. It was suggested that under the conditions of the first study, since no signs of maternal or fetal toxicity could be detected up 10 mg/kg/day DMTC, this dose was chosen to represent the no-observed-adverse-effect level (NOAEL).