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Toxicological information

Developmental toxicity / teratogenicity

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Administrative data

Endpoint:
developmental toxicity
Type of information:
migrated information: read-across based on grouping of substances (category approach)
Adequacy of study:
key study
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
other: Test procedure according to national standards.

Data source

Reference
Reference Type:
publication
Title:
Unnamed
Year:
2005

Materials and methods

Test guideline
Qualifier:
according to
Guideline:
other: EPA OPPTS 870.6300 (Developmental Neurotoxicity)
GLP compliance:
not specified
Limit test:
no

Test material

Reference
Name:
Unnamed
Type:
Constituent
Type:
Constituent
Details on test material:
- Name of test material (as cited in study report): Monomethyl tin
- Molecular formula (if other than submission substance): CH3Cl3Sn
- Molecular weight (if other than submission substance): 240.8 g/mol
- Smiles notation (if other than submission substance): CL[Sn](CL)(CL)C
- Physical state: liquid
- Analytical purity: 97%

Test animals

Species:
rat
Strain:
Sprague-Dawley
Details on test animals and environmental conditions:
TEST ANIMALS
- Source: Charles River, Raleigh, North Carolina, USA
- Age at study initiation: 53-54 days old
- Weight at study initiation:
- Fasting period before study: not reported
- Housing: AAALAC-International accredited rooms
- Diet (e.g. ad libitum): ad libitum; Purina Rodent Chow 5001; Purina Rodent Chow 5008 following breeding.
- Water (e.g. ad libitum): ad libitum
- Acclimation period: yes; time period not reported


ENVIRONMENTAL CONDITIONS
- Temperature (°C): 19-21 deg C
- Humidity (%): 40-60%
- Air changes (per hr): not reported
- Photoperiod (hrs dark / hrs light): Experiment 1 reverse 12 hour light / 12 hour dark- lights on at 1200h; Experiment 2 lights on at 0600 h


IN-LIFE DATES: From: not reported To:

Administration / exposure

Route of administration:
oral: drinking water
Vehicle:
water
Details on exposure:
PREPARATION OF DOSING SOLUTIONS: dissolved in distilled/deionied water


DIET PREPARATION not applicable



VEHICLE
- Justification for use and choice of vehicle (if other than water): water
- Concentration in vehicle: 10, 50, 245, 500 ppm
- Amount of vehicle (if gavage): not applicable
Analytical verification of doses or concentrations:
yes
Details on analytical verification of doses or concentrations:
The stock solution and solutions of the low and high test concentrations were sampled daily for 5 days in water bottles under conditions of the anial exposure. Analysis were determined using ion chromatography (IC) with inductively coupled plasma mass spectometer (ICP-MS). In addition, total tin levels were measured using inductively coupled plasma optical emission spectrometer (ICP-OES).
Details on mating procedure:
- Impregnation procedure: purchased timed pregnant- Experiment 2 / cohoused- Experiment 1
- If cohoused:
- M/F ratio per cage: 1/2- late stage proestrus
- Length of cohabitation: late in the afternoon and removed the next day
- 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: Experiment 2 sperm in vaginal smear referred to as day 0 of pregnancy
- Any other deviations from standard protocol: none
Duration of treatment / exposure:
Experiment 1: 2 weeks prior to breeding, and through gestation and lactation
Experiment 2: gestation day 6 through gestation and lactation
Frequency of treatment:
in drinking water
Duration of test:
Experiment 1: until weaning at postnatal day 21
Experiment 2: until weaning
Doses / concentrationsopen allclose all
Remarks:
Doses / Concentrations:
10, 50, 245 ppm
Basis:
nominal in water
Experiment 1
Remarks:
Doses / Concentrations:
500 ppm
Basis:
nominal in water
Experiment 2
No. of animals per sex per dose:
Experiment 1: 30 females
Experiment 2: 35 females
Control animals:
yes, concurrent no treatment
Details on study design:
- Dose selection rationale: doses were chosen for Experiment 1 to match and extend those used in a previously published study
- Rationale for animal assignment (if not random): randomly housed in pairs upon arrival; then rearranged and paired according to synchronized estrous cycles

Examinations

Maternal examinations:
Reproductive parameters

BODY WEIGHT: Yes
- Time schedule for examinations: not reported

WATER CONSUMPTION AND COMPOUND INTAKE (if drinking water study): Yes
- Time schedule for examinations: not reported


Ovaries and uterine content:
Not reported
Fetal examinations:
Runway learning test, motor activity, Morris water maze, neuropathology, neurochemical assessment and brain weight, body weights,
Statistics:
Continuous data (e.g. body weight, water intake, activity counts, etc.) were analyed using a general linear model ANOVA (SAS, Cary, North Carolina, USA). Extinction in the runway test was analyzed with a survival model for censored data (SAS), and count data (e.g. number of pups learning, pregnancy rate) were compared usinf Fisher's exact test (SAS). When the same rat was used in repeated tests (e.g. repeated motor activity testing, body weights over time), the analyses included time as a repeated factor. For apoptosis data, all brain region values were compared to their respective controls, and arcsine transformed prior statistical analyses. Following a significant overall analysis, Dunnett's t-test was used to compare dose groups with the control. In all cases resulting probability values <0.05 were considered significant.
Indices:
no data
Historical control data:
not provided

Results and discussion

Results: maternal animals

Maternal developmental toxicity

Details on maternal toxic effects:
Maternal toxic effects:yes

Details on maternal toxic effects:
Experiment 1: Fluid intake increased somewhat during gestation (about 30–40%), and was much higher (more than double) during lactation. There were, however, no differences in fluid intake across treatment groups at any time during the study. Likewise, there were no treatment-related differences in body weight throughout exposure

Experiment 2: There was a significant depression of fluid intake across almost all days of treatment; Despite the lowered intake, body weight was not different in the treated group.

Experiment 1: Despite the timed breeding, pregnancy rate was very low with only 44 of 120 (37%) rats delivering litters (10, 11, 11, and 12 litters for control, 10, 50, and 245 ppm, respectively). We typically find that most of our Sprague–Dawley rats deliver within a 24 h period which we specify as PND 0. In the present study, however, 11 of the 44 (25%) rats delivered later than that time window. Necropsy of all non-pregnant rats revealed resorptions in only two control rats and one rat from the lowdose group. Incidence of pregnancy, late delivery, and resorptions were not statistically different across treatment groups.

Experiment 2: All of the timed-pregnant females in the control group delivered, but two in the MMT group did not. These rats were not evaluated for implantation sites. All of the deliveries occurred when expected. In the MMT group, one litter consisted of all females and was not used, and another litter was killed by the dam shortly after birth.

Effect levels (maternal animals)

open allclose all
Dose descriptor:
NOAEL
Remarks:
Experiment 1
Effect level:
245 ppm (nominal)
Basis for effect level:
other: developmental toxicity
Dose descriptor:
NOAEL
Remarks:
Experiment 2
Effect level:
500 ppm (nominal)
Basis for effect level:
other: developmental toxicity

Results (fetuses)

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

Details on embryotoxic / teratogenic effects:
Experiment 2: Body weight changes during the lactation period showed a significant dose-by-sex interaction, but step-down analyses showed that on 1 day only (PND 11), male and female pups in the control group were different by about 4 g; this was considered to be within biological variability. There were no treatment effects on body weight after weaning.

Experiment 2: Fewer pups were able to learn the different paradigm used in the second study. One control and five treated pups did not meet the criterion of having at least one latency less than 100 s during acquisition; however, this difference did not attain statistical significance (Fisher’s exact p = 0.067). Furthermore, one pup in each group did not extinguish within the 10 trials.

Experiment 1: Total motor activity counts during 30-min sessions were lowest at PND 13 (means ranging from 20.3 to 31.2), and increased over PND 17 (means 46.5 to 72.7) and 21 (means 98.7 to 120.3). Analysis of the within-session activity (in 5 min intervals) showed no habituation during the session at PNDs 13 and 17. By PND 21, habituation was evident. There were no group differences on any of these measures.

Experiment 1: There was a marginal effect on brain weight, although the overall dose effect at p < 0.07 did not reach the criterion for statistical significance. There was no interaction of treatment and age, and collapsed across ages, the high dose group showed a 5% decrease in weight.

Experiment 1: No histological alterations were observed in the brains of MMT-treated offspring killed on PND 1, 12, or 22. There were, however, changes in the brains of the offspring evaluated as adults. The cerebral cortical lesion was characterized by 2–4 mm diameter, round vacuoles of varying size, in the gray matter neuropil, localized to the region of the orbital cortex. Furthermore, the focal location of the lesion was very similar across animals, supporting the conclusion of a treatment-related effect. Myelin was not affected. Two of eight (25%) adult high-dose offspring had vacuolation scored as ‘‘slight/mild’’ (‘2’), whereas one of seven (14%) of the mid-dose group, and three of ten (30%) lowdose rats, had similar vacuolation scored as ‘‘minimal’’ (‘1’). There were no such findings in control rats. These adult rats had been tested previously in the Morris water maze. Review of the water maze data for the rats showing vacuolation revealed that their performance was not different from the unaffected rats. Thus, no within-individual correlations between vacuolation and behavioral performance could be made.

Fetal abnormalities

Abnormalities:
not specified

Overall developmental toxicity

Developmental effects observed:
not specified

Applicant's summary and conclusion

Executive summary:

The objective of these studies was to replicate an earlier publication and further define the dose response characteristics of monomethylitn following perinatal exposure. In Experiment 1, female Sprague-Dawley rats were exposed via drinking water to the test substance (0, 10, 50, 245 ppm; equivalent to 1 -1.8 mg/kg bw/day, 5.3 -10.6 mg/kg bw/day, and 23.3 -41.6 mg/kg bw/day respectively) before mating and throughout gestation and lactation (until weaning at postnatal day [PND] 21). Behavioral assessments of the offspring included: a runway test (PND 11) in which the rat pups learned to negotiate a runway for dy suckling reward; motor activity habituation (PNDs 13, 17 and 21); learning in the Morris water maze (as adults). Other endpoints in the offspring included measures of apoptosis (DNA fragmentation) at PND 22 and as adults, as well as brain weights and neuropathological evaluation at PND 2, 12, 22 and as adults. There were no effects on any measure of growth, development, cognitive function or apoptosis following exposure to the test substance. There was a trend towards decreased brain weight in the high dose group. In addition, there was vacuolation of the neuropil in a focal area of the cerebral cortex of the adult offspring in all dose groups (1 -3 rats per treatment group).

In Experiment 2, pregnant rats were exposed from gestational day 6 until weaning to 500 ppm in drinking water (equivalent to 55.8 -94.3 mg/kg bw/day). The offspring behavioral assessments again included the runway task (PND 11), motor activity habituation (PND 17), and Morris water maze (as adults). In this second study, exposed females consumed significantly less water than the controls throughout both gestation and lactation, although neither dam nor pup weights were affected. As in experiment 1, exposure did not alter pup runway performance, motor activity, or cognitive function. These results indicate that perinatal exposure to the test substance, even at concentrations which decrease fluid intake, does not result in significant neurobehavioral or cognitive deficits. While mild histological lesions were observed in the brain of adult offspring, the biological significance of this restricted finding in unclear.