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Toxicological information

Toxicity to reproduction

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Administrative data

Endpoint:
screening for reproductive / developmental toxicity
Remarks:
other: Combined repeat dose study with reproduction/developmental toxicity screening
Type of information:
migrated information: read-across based on grouping of substances (category approach)
Adequacy of study:
key study
Study period:
No data
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
other: This study was classified as reliable with restriction because although it is a GLP guideline study, a study report in English was not available for data verification. However, this study is peer reviewed and considered sufficient for this endpoint.

Data source

Reference
Reference Type:
study report
Title:
Unnamed
Year:
2006
Report Date:
2006

Materials and methods

Test guideline
Qualifier:
according to
Guideline:
OECD Guideline 422 (Combined Repeated Dose Toxicity Study with the Reproduction / Developmental Toxicity Screening Test)
Deviations:
yes
Remarks:
The histopathological examination of the reproductive organs was only performed on 5 animals/sex of the control and top dose.
GLP compliance:
yes
Limit test:
no

Test material

Reference
Name:
Unnamed
Type:
Constituent
Details on test material:
Test substance: 2-methyl-2-propanethiol
Purity 99.0-99.9%
Lot No. 200501-001

Test animals

Species:
rat
Strain:
Sprague-Dawley
Sex:
male/female
Details on test animals and environmental conditions:
TEST ANIMALS
- Source: no data
- Age at study initiation: no data
- Weight at study initiation: 272.2-325.1 g for males, 188.1-235-9 g for females
- Housing:no data
- Diet (e.g. ad libitum): no data
- Water (e.g. ad libitum):no data
- Acclimation period:no data

ENVIRONMENTAL CONDITIONS
- Temperature (°C): 21-27
- Humidity (%): 35-75
- Air changes (per hr): no data
- Photoperiod (hrs dark / hrs light): 12-12

Administration / exposure

Route of administration:
oral: gavage
Vehicle:
corn oil
Analytical verification of doses or concentrations:
yes
Details on analytical verification of doses or concentrations:
no details available
Duration of treatment / exposure:
Exposure period: Males: 42 days; Females: 42-53 days from 14 days before mating to day 4 of lactation
Premating exposure period (males): 2 weeks
Premating exposure period (females): 2 weeks
Duration of test: 10, 50, 200 mg/kg bw/day
Frequency of treatment:
Once daily
Doses / concentrations
Remarks:
Doses / Concentrations:
10, 50, 200 mg/kg bw/day
Basis:

No. of animals per sex per dose:
Males: 12
Females: 17 for control and top dose, 12 for low and mid doses
Control animals:
yes, concurrent vehicle

Examinations

Parental animals: Observations and examinations:
CAGE SIDE OBSERVATIONS: Yes
General condition was observed 2 or 3 times a day throughout the administration period

DETAILED CLINICAL OBSERVATIONS: Yes
Detailed clinical observation was carried out once a week in all animals throughout the administration period. In pregnant females, it was carried out on days 7, 14, and 20 of gestation and on day 4 of lactation. Sensory reaction test, grip strength, and motor activity were examined at 6 weeks of administration in males and on day 4 of lactation in pregnant females.

BODY WEIGHT: Yes
Body weights were measured on days 1 (before dosing), 4, 8, 11, 15, 18, 22, 25, 30, 32, 36, 39, and 42 of administration for males, For females, body weight was measured on days 1 (before dosing), 4, 8, 11, 15, 18, 22, 25, 30, 32, 36, 39, and 42 of administration, except for pregnant females for whom it was measured on days 0, 7, 14, and 20 of gestation and days 0 and 4 of lactation. Further, it was measured at necropsy in both sexes.

FOOD CONSUMPTION :
Food consumption was measured on days 1 (before dosing), 4, 8, 11, 15, 30, 32, 36, 39, and 42 of administration for males. For females, food consumption was measured on days 1 (before dosing), 4, 8, 11, 15, 30, 32, 36, 39, and 42 of administration, except for pregnant females for whom it was measured on days 1, 7, 14, and 20 of gestation and days 1 and 4 of lactation

WATER CONSUMPTION : No
Estrous cyclicity (parental animals):
yes
Sperm parameters (parental animals):
No
Litter observations:
STANDARDISATION OF LITTERS
Performed on day 4 postpartum: no

PARAMETERS EXAMINED
The following parameters were examined in F1 offspring:
number and sex of pups, stillbirths, live births, postnatal mortality, presence of gross anomalies, weight gain

GROSS EXAMINATION OF DEAD PUPS:
yes, for external and internal abnormalities; possible cause of death was not determined for pups born or found dead.
Postmortem examinations (parental animals):
SACRIFICE
Necropsy was carried out at the day following the end of the administration and recovery periods

GROSS NECROPSY
- Gross necropsy consisted of external and internal examinations including the cervical, thoracic, and abdominal viscera.
- The testis and epididymis of all males were weighed.

HISTOPATHOLOGY / ORGAN WEIGHTS
The testis, epididymis, prostate, and seminal vesicles of 5 males at 0 and 200 mg/kg bw/day were microscopically examined at the end of the administration period. Further, the ovary, uterus, and vagina of 5 females at 0 and 200 mg/kg bw/day were microscopically examined at the end of the administration period.
Postmortem examinations (offspring):
SACRIFICE
- The F1 offspring were sacrificed at 5 days of age.
- These animals were subjected to postmortem macroscopic examination for gross abnormalities.
Statistics:
Statistical methods: X2 test was used for mating index, males and females fertility indices, gestation index, and delivery index were used. Wilcoxon Rank Sum Test Method for implantation index, death birth index, live birth index, and viability index on day 4 were used.
Reproductive indices:
Estrous cycle, number of copulated, number of pregnant females, mating length, mating index (# of pairs with successful copulation/# of pairs mating × 100), males or females fertility indices (# of pregnant animals/#of animals with successful mating×100), number of females with live pups, gestational length, number of corpora lutea, number of implantations, number of pups delivered, number of live pups delivered, gestation index (# of females with live pups/# of pregnant females × 100), implantation index (# of implants/# of corpora lutea × 100), delivery index (# of pups born/# of implants × 100), death birth index (number of stillborns/number of litter × 100), were determined.
Offspring viability indices:
Sex ratio, live birth index (# of live pups born/# of pups born × 100), and viability index on day 4 (# of live pups on postnatal day (PND) 4 /# of live pups born × 100) were determined.

Results and discussion

Results: P0 (first parental animals)

General toxicity (P0)

Clinical signs:
no effects observed
Body weight and weight changes:
effects observed, treatment-related
Food consumption and compound intake (if feeding study):
effects observed, treatment-related
Organ weight findings including organ / body weight ratios:
effects observed, treatment-related
Gross pathological findings:
no effects observed
Histopathological findings: non-neoplastic:
no effects observed
Other effects:
not examined

Reproductive function / performance (P0)

Reproductive function: estrous cycle:
no effects observed
Reproductive function: sperm measures:
not examined
Reproductive performance:
no effects observed

Details on results (P0)

BODY WEIGHT AND FOOD CONSUMPTION (PARENTAL ANIMALS)
A low body weight value was observed in both sexes at 200 mg/kg bw/day throughout the administration period. During the recovery period, a lower body weight was observed in females, but their body weight gains throughout the recovery period were similar to those of the control group.

A low food consumption value or a tendency toward a low value was observed in males at 200 mg/kg bw/day on days 4 and 15 of administration and in females at 200 mg/kg bw/day throughout the administration period. During the recovery period, females exhibited lower food consumption on day 1 of the recovery period, but food consumption after day 4 of the recovery period was similar to the control group. A decrease in food consumption was observed in females at 10mg/kg on day 15 of the administration period. However, it was not observed at 50mg/kg and not considered to be a dose-related effect.

ORGAN WEIGHTS (PARENTAL ANIMALS)
There were increases in relative weights of the testes and epididymides in males at 200 mg/kg. However, absolute weights of these organs were not changed, and no histopathological changes were observed in these organs. These changes were considered to be due to decreases in body weights.
Increases in absolute and relative weights of the epididymides were observed at 50mg/kg, but these changes were not considered to be dose related effects because these effects were not observed at 200 mg/kg bw/day.

Effect levels (P0)

open allclose all
Dose descriptor:
NOAEL
Remarks:
General toxicity
Effect level:
>= 200 mg/kg bw/day
Based on:
test mat.
Sex:
male/female
Basis for effect level:
other: No adverse effects.
Dose descriptor:
NOAEL
Remarks:
reproductive toxicity
Effect level:
>= 200 mg/kg bw/day (actual dose received)
Based on:
test mat.
Sex:
male/female
Basis for effect level:
other: No adverse effects observed.

Target system / organ toxicity (P0)

Critical effects observed:
no

Results: F1 generation

General toxicity (F1)

Clinical signs:
not examined
Mortality / viability:
no mortality observed
Body weight and weight changes:
effects observed, treatment-related
Sexual maturation:
not examined
Organ weight findings including organ / body weight ratios:
not examined
Gross pathological findings:
not specified
Histopathological findings:
not examined

Details on results (F1)

BODY WEIGHT (OFFSPRING)
Decreases in body weight of live pups on PND 4 were observed in both sexes at 200 mg/kg bw/day.

Effect levels (F1)

Dose descriptor:
NOAEL
Generation:
F1
Effect level:
50 mg/kg bw/day (actual dose received)
Based on:
test mat.
Sex:
male/female
Basis for effect level:
body weight and weight gain

Target system / organ toxicity (F1)

Critical effects observed:
no

Overall reproductive toxicity

Reproductive effects observed:
not specified

Any other information on results incl. tables

Reproductive performance of rats
Dose (mg/kg bw/day)
0
10
50
200
Number of females eximaned
12
12
12
12
Count of estrus
3.67(0.78)
3.92(0.29)
3.83(0.58)
3.83(0.39)
Estrus cycle
3.97(0.10)
4.00(0.00)
4.03(0.10)
4.00(0.00)
No. of pairs mating
12
12
12
12
No. of pairs with successful mating
12
12
12
12
No. of pregnant females
12
12
12
11
Duration of mating
2.75(1.42)
3.33(2.84)
3.58(3.18)
3.36(1.80)
Fertility index (%)
100
100
100
91.67

Terminal delivery of F0 dams

Dose (mg/kg bw/day)
0
10
50
200
No. of females with live pups
12
12
12
11
Gestational length (day)
22.08(0.29)
22.50(0.52)
22.33(0.65)
22.18(0.40)
# of corpora lutea
15.08(2.11)
14.58(2.61)
15.67(2.15)
15.36(1.96)
# of implantation sites
14.25(1.76)
13.42(3.00)
14.92(2.75)
14.45(3.00)
# of pups delivered
13.75(1.82)
13.08(3.34)
14.08(3.20)
13.64(2.77)
Sex ratio (male/female)
0.83
1.20
0.92
0.88
# of live pups on day 4
13.75(1.82)
13.00(3.28)
13.75(3.11)
13.64(2.77)
Viability index on day 4
98.79
98.08
 96.97
99.33
Body weight of live newborns (g)
    Male Day 0
6.4(0.5)
6.9(0.6)
6.7(0.7)
6.2(0.2)
    Male Day 4
10.3(0.8)
10.3(2.2)
10.0(2.4)
8.6(0.9)**
    Female Day 0
6.1(0.6)
6.4(0.6)
6.3(0.6)
5.9(0.2)
    Female Day 4
9.8(0.9)
9.8(2.0)
 9.5(2.4)
8.2(0.9)**
Number with external anomalies
0
0
0
1
(exencephaly
open eyelid
protruding tongue)

**: P<0.01

Applicant's summary and conclusion

Conclusions:
In a combined repeated dose/reproductive/developmental toxicity screening test (OECD 422), conducted in compliance with GLP, the test substance had no effects on any reproductive parameters, including fertility (MHLW, 2006). Therefore the NOAEL for reproductive toxicity was considered to be ≥ 200 mg/kg bw/day. The NOAEL for parental toxicity was also ≥ 200 mg/kg bw/day.
Executive summary:

In a combined repeated dose/reproductive/developmental toxicity screening test (OECD 422), groups of male and female Sprague-Dawley rats (12-17/sex/dose) were administered 2 -methylpropane-2 -thiol in corn oil by gavage at 0, 10, 50 or 200 mg/kg bw/day daily for 42-53 days (MHLW, 2006). The animals were dosed daily for 2 weeks prior to mating, during mating and gestation, and the females were dosed for 4 days post-partum after which the adult females and their pups were terminated. 

There were no treatment-related effects at any dose on reproductive and developmental parameters including mating index, fertility index, duration of gestation, gestation index, total number of pups born, live birth index, number of pups alive and viability index on day 4 of lactation or sex ratio. Decreases in body weight of live pups on PND 4 were observed in both sexes at 200 mg/kg bw/day. All reproductive organs from adult animals were normal during gross pathology and microscopic evaluations. Therefore the NOAEL for parental and reproductive performance was 200 mg/kg bw/day.

This study was classified as reliable with restriction because although it is a GLP guideline study, a study report in English was not available for data verification. However, this study is peer reviewed and considered sufficient for this endpoint.