2-Oxazolidinone, 3-ethenyl-5-methyl-

Developmental toxicity / teratogenicity

Administrative data

Endpoint:

developmental toxicity

Type of information:

experimental study

Adequacy of study:

key study

Study period:

26 Mar 2019 - 04 Feb 2020

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Data source

Reference

Reference Type:

study report

Title:

Unnamed

Year:

2020

Report date:

2020

Materials and methods

Test guideline

Test guideline 1

Qualifier:

according to guideline

Guideline:

OECD Guideline 414 (Prenatal Developmental Toxicity Study)

Version / remarks:

25 Jun 2018

Test guideline 2

Qualifier:

according to guideline

Guideline:

EPA OPPTS 870.3700 (Prenatal Developmental Toxicity Study)

Version / remarks:

Aug 1998

GLP compliance:

yes

Limit test:

no

Test material

Test material information

Constituent 1

Reference substance name:

3-ethenyl-5-methyl-1,3-oxazolidin-2-one

EC Number:

809-852-5

Cas Number:

3395-98-0

Molecular formula:

C6H9NO2

IUPAC Name:

3-ethenyl-5-methyl-1,3-oxazolidin-2-one

Specific details on test material used for the study:

Name of test substance: 5-Methyl-3-vinyloxazolidin-2-on
Test substance No.: 14/0031-4
Batch No.: Z019-2018
CAS No.: 3395-98-0
Purity: 99.4area-%(GC,DB-1) 96.3area-%(GC,DB-WAX) 96.5 area-% (GC, CP-Sil 19S8)
Content: 95.9 g/100 g (1H-NMR)
ldentity: Confirmed
Homogeneity: Given
Expiry date: 09 Feb 2020
Storage stability: The stability of the test substance under storage
conditions over the test period was guaranteed by the
Sponsor, and the Sponsor holds this responsibility.
Storage conditions: Room temperature
Physical state/appearance: Liquid, yellow

Test animals

Species:

rat

Strain:

Wistar

Details on test animals or test system and environmental conditions:

Species: rat
Strain: Crl:Wl(Han)
Source: Charles River Laboratories, Research Models and Services, Germany GmbH
Reason for species selection:
The Crl:WI(Han) strain was selected since extensive historical control data is available from
the test facility for Wistar rats. This specific strain has been proven to be sensitive to
substances with a teratogenic potential.

Sex: Female
Age at study initiation: 10-12 weeks
Weight at study initiation: 168.6 - 228.8 g.
Type of cage: Polycarbonate cages type III
No. of animals per cage: 1
Enrichment: Wooden gnawing blocks
Nesting material: Cellulose wadding was offered toward the end of gestation
Bedding: Dust-free wooden bedding


ENVIRONMENTAL CONDITIONS
Temperature 20-24°C
Relative humidity 45-65%,
15 air changes per hour
Illumination period: 12/12
Type of cage: Polycarbonate cages type III
No. of animals per cage: 1
Diet: ad libitum
Water ad libitum

Acclimatization period: From GD 0 (day of supply) to the beginning of administration (GD 6),

Administration / exposure

Route of administration:

oral: gavage

Vehicle:

corn oil

Details on exposure:

PREPARATION OF DOSING SOLUTIONS:
The test substance preparations were prepared at the beginning of the administration period
and thereafter at intervals, which took into account the period of established stability. The
preparations were kept at room temperature.
For the test substance preparations, the specific amount of test substance was weighed,
topped up with corn oil in a graduated flask and intensely mixed with a magnetic stirrer until it
was completely dissolved.

VEHICLE
- Amount of vehicle (if gavage): 4 mL/kg bw/d

Analytical verification of doses or concentrations:

yes

Details on analytical verification of doses or concentrations:

Analytical verifications of the stability of the test substance in corn oil over a period of 7 days
at room temperature had been verified prior to the start of the study in a similar batch.
All determined concentrations were in the range of 90 % - 110 % of the nominal concentration.

Details on mating procedure:

The animals were paired by the breeder (“time-mated”); the day of evidence of mating
(= detection of vaginal plug/sperm) was referred to as GD 0. The animals arrived on the same
day (GD 0) at the experimental laboratory. The following day was designated as “GD 1”. The
animals were acclimated to the laboratory conditions between start of the study (beginning of
the experimental phase) and first administration (GD 6).

Duration of treatment / exposure:

GD 6 to GD19

Frequency of treatment:

once a day

Duration of test:

On GD 20, blood samples were obtained in a randomized order from all females
by retrobulbar venous puncture. After blood sampling all surviving dams were
sacrificed and examined
The fetuses were removed from the uterus and investigated.

Doses / concentrations

Doses / concentrations 1

Dose / conc.:

15 mg/kg bw/day

Doses / concentrations 2

Dose / conc.:

50 mg/kg bw/day

Doses / concentrations 3

Dose / conc.:

150 mg/kg bw/day

No. of animals per sex per dose:

25

Control animals:

yes, concurrent vehicle

Examinations

Maternal examinations:

CAGE SIDE OBSERVATIONS: Yes / No / No data
- A cage-side examination was conducted at least once daily before and after treatment period
(GD 0-5 and 20). During treatment period (GD 6-19) all rats were checked daily for any signs
of morbidity, pertinent behavioral changes and/or signs of overt toxicity before administration
as well as within 2 hours and between 2 and 5 hours after administration.

Mortality
A check was made twice a day on working days or once a day on Saturdays, Sundays or on
public holidays (GD 0-20).

BODY WEIGHT: Yes
- Time schedule for examinations: All animals were weighed on GD 0, 1, 3, 6, 8, 10, 13, 15, 17, 19
and 20. The body weight change of the animals was calculated based on the obtained results.
Corrected (net) body weight gain
Furthermore, the corrected body weight gain was calculated after terminal sacrifice (terminal
body weight on GD 20 minus weight of the unopened uterus minus body weight on GD 6).

FOOD CONSUMPTION AND COMPOUND INTAKE: Yes
The consumption of food was recorded for the intervals GD 0-1, 1-3, 3-6, 6-8, 8-10, 10-13,
13-15, 15-17, 17-19 and 19-20.

WATER CONSUMPTION AND COMPOUND INTAKE: Yes
The consumption of water was recorded for the intervals GD 0-1, 1-3, 3-6, 6-8, 8-10, 10-13,
13-15, 15-17, 17-19 and 19-20.

POST-MORTEM EXAMINATIONS: Yes
- Sacrifice on gestation day 20
- Organs weights: thyroid glands (with parathyroid glands), spleen
- Histopathology: thyroid glands

OTHER:
- Clinical pathology
- Haematology: leukocyte count (WBC), erythrocyte count (RBC), hemoglobin (HCT),
hematocrit (HCT), mean corpuscular volume (MCV), mean corpuscular hemoglobin (MCH),
mean corpuscular hemoglobin concentration (MCHC), platelet count (PLT), differential blood
count, reticulocytes (RET),

- Clinical chemistry:
Enzyme: alanine aminotransferase (ALT), aspartate aminotransferase (AST), Alkaline
phosphate (ALP), γ-Glutamyltransferase (GGT),
- Blood chemistry parameter:
inorganic phosphate (INP), calcium (Ca), urea (UREA), creatine (CREA), glucose (GLUC), total bilirubin (TBIL),
total protein (TPROT), albumin (ALB), globulins (GLOB), triglycerides (TRIG), cholesterol (CHOL).

- Thyroid hormones:
Total triiodothyronine (T3), Total thyroxine (T4), Thyroid stimulating hormone (TSH)

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: Dead fetuses (hypoxemic fetuses which did not breathe spontaneously after the
uterus had been opened)

Fetal examinations:

- External examinations: Yes:
At necropsy each fetus was weighed, sexed, and external tissues and all orifices were
examined macroscopically. The sex was determined by observing the distance between the
anus and the base of the genitalia.
Furthermore, the viability of the fetuses and the condition of placentas, umbilical cords, fetal
membranes, and fluids were examined. The placentas were weighed and their individual weights
were recorded.
The anogenital distance (defined as the distance from the center of the anal opening to the
base of the genital tubercle) measurements were conducted, using a measuring ocular, on all
liveborn fetuses.
After these examinations, approximately one half of the fetuses per dam were eviscerated,
skinned and fixed in ethanol; the other half was placed in Harrison’s fluid for fixation.

- Soft tissue examinations: Yes:
The fetuses fixed in Harrison’s fluid were examined for any visceral findings according to the
method of BARROW and TAYLOR. After this examination these fetuses were discarded.

- Skeletal examinations: Yes:
The skeletons of the fetuses fixed in ethanol were stained according to a modified method of
KIMMEL and TRAMMELL. Thereafter, the skeletons of these fetuses were examined under a
stereomicroscope. After this examination the stained fetal skeletons were retained individually.

Statistics:

Statistic of clinical, necropsy and fetal examinations
Simultaneous comparison of all dose groups with the control group using the DUNNETT-test
(two-sided) for the hypothesis of equal means was used for the following parameters:
Water consumption, food consumption, body weight, body weight change, corrected body weight
gain (net maternal body weight change), carcass weight, weight of unopened uterus, number of
corpora lutea, number of implantations, number of resorptions, number of live fetuses, proportions
of preimplantation loss, prop ortions of postimplantation loss, proportions of resorptions, proportion
of live fetuses in each litter, lit ter mean fetal body weight, litter mean placental weight, anogenital
distance, anogenital index

Pairwise comparison of each dose group with the control group using FISHER'S EXACT test
(one-sided) for the hypothesis of equal proportions was used for the following parameters:
Female mortality, females pregnant at terminal sacrifice, number of litters with fetal findings

Pairwise comparison of each dose group with the control group using the WILCOXON-test (onesided)
for the hypothesis of equal medians was used for the following parameters:
Proportions of fetuses with malformations, variations and/or unclassified observations in each litter.

Statistics of pathology

Weight parameters;
Non-parametric one-way analysis using KRUSKAL-WALLIS H test (two-sided). If the resulting p-value
was equal or less than 0.05, a pairwise comparison of each dose group with the control group was
performed using WILCOXON-test (two-sided) for the equal medians.

Indices:

Conception rate, pre-implantation loss, post-implantation loss,
Anogenital index

Results and discussion

Results: maternal animals

General toxicity (maternal animals)

Clinical signs:

effects observed, non-treatment-related

Description (incidence and severity):

Piloerection after treatment occurred in females of test groups 2 and 3 (50 and 150 mg/kg
bw/d) from GD 6-14: in two mid-dose and six high-dose females, this finding was recorded
within the 2-hour examination interval, in 16 mid-dose and 25 high-dose females even afterwards
(>2h<5h after treatment).
Reduced attention after treatment was also recorded in females of test groups 2 and 3 from
GD 6-11: in three mid-dose and nine high-dose females, this finding was recorded within the
2-hour examination interval, in 13 mid-dose and 22 high-dose females even afterwards
(>2h<5h after treatment).
Both above mentioned unspecific clinical findings were most likely induced by the treatment
with the test substance but were not assessed as adverse per se.
One mid-dose female (50 mg/kg bw/d) had an abdominal body position after treatment on GD 6
(within the 2-hour examination interval). Since only one dam was affected without relation to
dose, it was assessed as incidental.
Furthermore, most females (23 out of 25) of the high-dose group and 6 females of the middose
group showed transient salivation during the treatment period. Salivation occurred in the
respective animals within the 2-hour examination interval after treatment (i.e. 0-2h) and was
initially observed on GD 6 (150 mg/kg bw/d) or GD 12 (50 mg/kg bw/d). Salivation occurred
most probably due to the bad taste of the test substance, was assessed to be a local effect
and, therefore, considered as not adverse.
No clinical signs or changes of general behavior, which may be attributed to the test substance,
were detected in any female of test group 1 (15 mg/kg bw/d)..

Mortality:

no mortality observed

Body weight and weight changes:

effects observed, treatment-related

Description (incidence and severity):

From GD 8 onwards until scheduled sacrifice on GD 20 the mean body weights of the highdose
dams (150 mg/kg bw/d) were lower in comparison to the concurrent control group,
attaining statistical significance during GD 10-13 (up to -5 %). The mean body weight gain of
the high-dose dams (150 mg/kg bw/d) was statistically significantly decreased during GD 6-10
showing a body weight loss during GD 6-8 (-1.4 g vs. 4.4 g in control). If calculated for the
entire treatment (GD 6-19), the mean body weight gain was 11% below the concurrent control
values (attaining statistical significance). Together with the reduction in water and food
consumption, these effects are assessed as treatment-related and adverse.
In test group 2 (50 mg/kg bw/d) the mean body weight values were below those of the
concurrent control group but without attaining statistical significance. The average body weight
gain was statistically significantly decreased on GD 6-8 (1.9 g vs. 4.4 g in control) and during
the entire treatment period (GD 6-19: 74.2 g vs. 82 g in control). This was assessed as
treatment-related.
The mean body weights and the average body weight gain of the low-dose dams (15 mg/kg
bw/d) were generally comparable to the concurrent control group throughout the entire study
period.

Food consumption and compound intake (if feeding study):

effects observed, treatment-related

Description (incidence and severity):

Consistently to the reduction in water consumption, the mean food consumption
of the high- and mid-dose dams (150 and 50 mg/kg bw/d) was statistically significantly
reduced during GD 6-13 (test group 3: up to 35%; test group 2: up to 16% below control) but
recovered afterwards. Nevertheless, if calculated for the entire treatment period (GD 6-19), the
high- and mid-dose dams consumed about 13% and 7% less food than the controls, respectively,
showing no statistical significance. The reduction in both test groups was assessed as
treatment-related.
The mean food consumption of the low-dose dams (15 mg/kg bw/d) was generally comparable
to the concurrent control group throughout the entire study period.

Corrected (net) body weight gain
The corrected body weight gain (terminal body weight on GD 20 minus weight of the unopened
uterus minus body weight on GD 6) was statistically significantly lower in test groups 3 (about
27% below the concurrent control value) and 2 (about 15% below control).
The corrected body weight gain of test group 1 (15 mg/kg bw/d) revealed no difference of any
biological relevance to the corresponding control group. Moreover, mean carcass weights of
test groups 1-3 were not adversely affected.

Food efficiency:

not examined

Water consumption and compound intake (if drinking water study):

effects observed, treatment-related

Description (incidence and severity):

The mean water consumption of the dams was statistically significantly reduced during GD
6-10, respectively, in test groups 2 (50 mg/kg bw/d - up to 17% below control) and 3 (150 mg/kg
bw/d - up to 24% below control). Afterwards, the mean values of both test groups recovered
and even exceeded the control values towards the end of the study (attaining statistical
significance in test group 3 on GD 17-19). Furthermore, if calculated for the entire treatment
period (GD 6-19), the mid and high-dose dams consumed an amount of water that was
comparable to the control (26.5 g / 28.2 g versus 27.8 g in control). The transient reduction in
water consumption in both test groups in the beginning of administration was assessed as
treatment-related.
The mean water consumption of the dams in test group 1 (15 mg/kg bw/d) was comparable to
the concurrent control group throughout the entire study period.
The statistically significantly decreased water consumption value in test group 2 on GD 1-3
(pretreatment period) was assessed as incidental.

Ophthalmological findings:

not examined

Haematological findings:

effects observed, non-treatment-related

Description (incidence and severity):

At the end of gestation in dams of test groups 2 and 3 (50 and 150 mg/kg bw/d), platelet counts
were significantly increased and the means were above the historical control range (platelets
706-940 Giga/L). However, medians of platelet counts were not dose-dependently increased
and the means in test groups 2 and 3 were around 10 % higher compared to the study control
mean. The platelet counts in the study controls were already in the upper part of the historical
control range. Therefore, the increase of platelet counts in dams of test groups 2 and 3 are
regarded as incidental and not treatment-related.
In dams of test group 3 (150 mg/kg bw/d), total white blood cell (WBC) as well as absolute
neutrophil and monocyte counts were significantly increased. Neutrophil and monocyte counts
were already significantly higher in dams of test group 2 (50 mg/kg bw/d) compared to controls.
However, all means were within historical control ranges (WBC 4.47-6.50 Giga/L, absolute
neutrophils 1.62-2.25 Giga/L, absolute monocytes 0.10-0.18 Giga/L). Therefore, these
alterations were regarded as incidental and not treatment-related.

Clinical biochemistry findings:

effects observed, treatment-related

Description (incidence and severity):

At the end of gestation in dams of test groups 2 and 3 (50 and 150 mg/kg bw/d), cholesterol
and triglyceride values were statistically significantly increased. These alterations were regarded
as treatment-related and adverse.
Additionally, in rats of test groups 2 and 3 total protein, albumin and globulin values were significantly
decreased. However, lower total protein and albumin levels in test group 2 and lower
globulin levels in test groups 2 and 3 were within historical control ranges (total protein 56.50-
63.03 g/L; albumin 30.64-36.31 g/L; globulins 23.64-28.97 g/L). Therefore, total protein and
albumin increases in dams of test group 3 were regarded as treatment-related and adverse,
whereas lower total protein and albumin levels in rats of test groups 2 and 3 as well as decreased
globulin levels in dams of test groups 2 and 3 were regarded as treatment-related but
non-adverse because these alterations were marginal.
In dams of test group 3 (150 mg/kg bw/d) alkaline phosphatase (ALP) activities and creatinine
values were slightly but significantly decreased. Lower ALP values are probably due to slightly
lower carcass weights of the dams in this test group, resulting secondarily in lower activities of
bone ALP isoenzymes. This correlates with decreased creatinine values as consequence of
lower skeletal muscle mass in these individuals. Creatinine mean in dams of test group 3 was
within, that of ALP below the historical control range (creatinine 24.0-33.6 μmol/L; ALP 0.88-
1.48 μkat/L). Therefore, the creatinine and ALP decrease were regarded as treatment-related
but non-adverse per se.

Thyroid hormones
In dams of test groups 2 and 3 (50 and 150 mg/kg bw/d), T3 values were significantly decreased
and in dams of test groups 1, 2 and 3 (15, 50 and 150 mg/kg bw/d), TSH values were increased
(in test group 2 not statistically significantly). T4 values were not changed in any test group.
Regarding the preliminary historical control ranges, T3 values in this study were above the
range in any test group including the controls, whereas T4 values and TSH values apart from
the low TSH mean in the control group were within the historical control range (T3 0.65-0.81
nmol/L; T4 25.01-42.00 nmol/L; TSH 5.52-7.55 μg/L). No thyroid weight changes and only minimal
follicular hypertrophy/hyperplasia of the thyroid follicular epithelium and minimal altered
colloid in the thyroid follicles of only a few dams in test group 3 were observed. Therefore,
statistically lower T3 levels and higher TSH values in dosed dams including sporadic, minimal
histopathologic findings in the thyroids of test group 3 were regarded as non-adverse if at all
treatment-related.

Urinalysis findings:

not examined

Behaviour (functional findings):

not examined

Immunological findings:

not examined

Organ weight findings including organ / body weight ratios:

no effects observed

Description (incidence and severity):

Organ weights:
All mean absolute and relative weight parameters did not show significant differences when
compared to the control group 0.
Weight of the placentae:
The mean placental weights of the low-, mid- and high-dose groups were comparable to the
corresponding control group.

Gross pathological findings:

no effects observed

Description (incidence and severity):

Regarding pathology, there were neither treatment-related organ weight changes nor gross
lesions.

Neuropathological findings:

not examined

Histopathological findings: non-neoplastic:

effects observed, treatment-related

Description (incidence and severity):

In test group 3, histopathology revealed in the thyroid glands a minimal increase in the
incidence of follicular hypertrophy/hyperplasia (5 out of 24) and a minimal increase in the incidence
and grading of altered colloid (3 out of 24, minimal to slight). Since these small changes
in the dams of test group 3 were not consistent with the individual T3 and TSH values changes,
they were assumed to be most likely treatment-related but not adverse.

All other findings occurred either individually or were biologically equally distributed over control
and treatment groups. They were considered to be incidental or spontaneous in origin and
without any relation to treatment.

Histopathological findings: neoplastic:

no effects observed

Other effects:

no effects observed

Maternal developmental toxicity

Number of abortions:

no effects observed

Pre- and post-implantation loss:

no effects observed

Total litter losses by resorption:

no effects observed

Early or late resorptions:

no effects observed

Dead fetuses:

no effects observed

Changes in pregnancy duration:

no effects observed

Changes in number of pregnant:

no effects observed

Details on maternal toxic effects:

weights:
The mean gravid uterus weights of the animals of test groups 1-3 (15, 50 and 150 mg/kg bw/d)
were not influenced by the test substance. The differences between these groups and the
control group revealed no dose-dependency and were assessed to be without biological
relevance.


Reproduction data
The conception rate reached 96% in the test groups 0, 1 and 3 (0, 15 and 150 mg/kg bw/d)
and 100 % in test group 2 (50 mg/kg bw/d). With these rates, a sufficient number of pregnant
females were available for the purpose of this study.
There were no test substance-related and/or biologically relevant differences between the test
groups 0-3 in conception rate, in the mean number of corpora lutea and implantation sites or
in the values calculated for the pre- and post-implantation losses, the number of resorptions
and viable fetuses. All observed differences are considered to reflect the normal range of
fluctuations for animals of this strain and age.

Effect levels (maternal animals)

Dose descriptor:

NOAEL

Effect level:

15 mg/kg bw/day

Based on:

test mat.

Basis for effect level:

body weight and weight gain

clinical biochemistry

food consumption and compound intake

water consumption and compound intake

Results (fetuses)

Fetal body weight changes:

effects observed, treatment-related

Description (incidence and severity):

The mean fetal weights of test groups 2 and 3 (50 and 150 mg/kg bw/d) were statistically significantly reduced (about 6% and 8% below control - both sexes combined). However, the mean values (3.4 and 3.3 g in test groups 2 and 3, respectively) were close to the mean value of the historical control (HCD, mean: 3.6 g, cf. “Attached background material”). These rather marginal decreases in mean fetal weight were in presence of maternal toxicity and assessed as consequence of that. They were not considered to be an independent effect per se and were, therefore, not assessed as a selective adverse effect.

Reduction in number of live offspring:

not examined

Changes in sex ratio:

no effects observed

Description (incidence and severity):

The sex distribution of the fetuses in test groups 1-3 (15, 50 and 150 mg/kg bw/d) was
comparable to the control fetuses.

Changes in postnatal survival:

not examined

External malformations:

effects observed, non-treatment-related

Description (incidence and severity):

Fetal external malformations
One control fetus had an external malformation (anasarca) associated with multiple skeletal
malformations. This is considered to be an incidental finding.
Fetal external variations
No external variations were recorded.
Fetal external unclassified observations
One unclassified external observation was recorded. Placentae fused were seen in one litter,
each, in test groups 1-3 (15, 50 and 150 mg/kg bw/d). This finding was not considered
biologically relevant, since it was a single event in the respective test group and can be found
in the historical control data (cf. "Attached background material").

Skeletal malformations:

effects observed, non-treatment-related

Description (incidence and severity):

Fetal skeletal malformations
Skeletal malformations were detected in two fetuses of the control group One female fetus
had multiple skeletal
malformations affecting the sternum, skull, cervical/thoracic vertebral column and ribs
compared with an additional external malformation. One male fetus ha a fused cervical arch,
Since the findings were single events recorded exclusively in the control group, they are
considered to be spontaneous in origin and not treatment-related.

Fetal skelatal variations
For all test groups, skeletal variations of different bone structures were observed, with or
without effects on corresponding cartilages. The observed skeletal variations were related to
several parts of fetal skeletons and appeared in the majority of cases without a relation to dose.
The overall affected fetuses/litter incidences of skeletal variations were statistically significantly
increased in the high-dose group (150 mg/kg bw/d).
However, the incidence in test group 3 was well within the historical control range (cf. "Attached background material"), whereas the
incidence of the control was at the lower end of the range. Therefore, it was not assessed as
treatment-related and adverse.
Skeletal variations with statistically significant differences between the control and any
treated group were: (expressed as mean percentage of affected fetuses/litter
Supraoccipital holes in test group 2 (50mg/kg) 2.3; Incomplete ossification of supraoccipital;
unchanged cartilage test group3 (150mg/kg) 27.0; Incomplete ossification of temporal 2.7
and Bipartite ossification of sternebra, unchanged cartilage 2.0 in test group 1 (15 mg/kg)
Concerning the statistically significant findings, no dose dependency was observed and/or all
values were clearly inside the historical control range (cf. "Attached background material"), thus, an association to the test substance
and a toxicological relevance is not assumed.

Fetal skeletal unclassified cartilage observations
Additionally, some isolated cartilage findings without impact on the respective bony structures,
which were designated as unclassified cartilage observations, occurred in all test groups.
The observed unclassified cartilage findings were related to the skull, the ribs and
the sternum and did not show any relation to the dose. The incidence of ‘branched rib cartilage’
was statistically significantly increased in the mid- and high-dose groups (test groups 1-3:
1.4% / 2.4%* / 1.9%* affected fetuses per litter versus 0.0% in control) but was well within the
historical control range (HCD of affected fetuses per litter: 1.4% [0.0 - 7.0]). Therefore, it was
not assessed as treatment-related. The overall incidences of skeletal unclassified cartilage
observations in the substance-treated groups did not differ significantly from the concurrent
control group.

Finally, fetal examinations revealed that there is no effect of the compound on the respective
morphological structures up to 150 mg/kg bw/d.

Visceral malformations:

effects observed, non-treatment-related

Description (incidence and severity):

Fetal soft tissue malformations
No soft tissue malformations were recorded.

Fetal soft tissue variations
Two soft tissue variations were detected, i.e. dilated renal pelvis and dilated ureter, both in test
groups 0-3. The incidences of these variations were neither statistically significantly different
from control nor dose-dependent and therefore, not considered biologically relevant.

Fetal soft tissue unclassified observations:
No soft tissue unclassified observations were recorded.

Other effects:

no effects observed

Description (incidence and severity):

Anogenital distance/anogenital index
The anogenital distance and anogenital index of all male and female fetuses in the test groups
1-3 was comparable to the concurrent control values.

Effect levels (fetuses)

Key result

Dose descriptor:

NOAEL

Effect level:

150 mg/kg bw/day

Based on:

test mat.

Sex:

male/female

Basis for effect level:

other: no adverse treatment-related effects observed

Fetal abnormalities

Key result

Abnormalities:

no effects observed

Overall developmental toxicity

Key result

Developmental effects observed:

no

Treatment related:

no

Applicant's summary and conclusion

Conclusions:

Under the conditions of this prenatal developmental toxicity study, the oral administration of 5- Methyl-3-vinyloxazolidin-2-on to pregnant Wistar rats from implantation to one day prior to the expected day of parturition (GD 6-19) caused evidence of systemic maternal toxicity, such as a reduction of water and food consumption, a decrease in (corrected) body weight gain and changes in clinical pathology parameters in mid- and high-dose dams (50 and 150 mg/kg bw/d).
In conclusion, the no observed adverse effect level (NOAEL) for maternal toxicity is the low-dose of 15 mg/kg bw/d and for prenatal developmental
toxicity the high dose of 150 mg/kg bw/d. Under the conditions of this study the test item is not teratogenic.