2,6-dimethylheptan-4-one

Developmental toxicity / teratogenicity

Administrative data

Endpoint:

developmental toxicity

Type of information:

read-across based on grouping of substances (category approach)

Adequacy of study:

key study

Study period:

1984

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Justification for type of information:

Please refer to Category Document

Data source

Reference

Reference 1

Reference Type:

study report

Title:

Unnamed

Year:

1984

Report date:

1984

Reference 2

Reference Type:

publication

Title:

Developmental toxicity evaluation of inhaled methyl isobutyl ketone in Fischer 344 rats and CD-1 mice

Author:

Tyl RW, France KA, Fisher LC, Pritts IM, Tyler TR, Phillips RD and Moran EJ

Year:

1987

Bibliographic source:

Fundam Appl Toxicol, 8, 310–327

Materials and methods

Test guideline

Qualifier:

according to guideline

Guideline:

OECD Guideline 414 (Prenatal Developmental Toxicity Study)

Version / remarks:

Previous guideline with exposure to test material from GD 6-15

Deviations:

no

GLP compliance:

yes

Limit test:

no

Test material

Test material information

Constituent 1

Reference substance name:

4-methylpentan-2-one

EC Number:

203-550-1

EC Name:

4-methylpentan-2-one

Cas Number:

108-10-1

Molecular formula:

C6H12O

IUPAC Name:

4-methylpentan-2-one

Specific details on test material used for the study:

- Name of test material (as cited in study report): MIBK
- Analytical purity: 99.5%
- Lot/batch No.: UN1245

Test animals

Species:

rat

Strain:

Fischer 344

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Source: Hilltop Lab Animals, Inc., Scottdale, PA
- Age at study initiation: not reported
- Weight at study initiation: not reported
- Housing: individual
- Diet (e.g. ad libitum): Standard rodent chow ad libitum, except during exposure
- Water (e.g. ad libitum): ad libitum, except during exposure
-Acclimation: 2 week quarantine period

ENVIRONMENTAL CONDITIONS
- Temperature (°C): 24-25°C
- Humidity (%): 44-50%
- Photoperiod (hrs dark / hrs light): 12/12


IN-LIFE DATES: Not reported

Administration / exposure

Route of administration:

inhalation: vapour

Type of inhalation exposure (if applicable):

whole body

Vehicle:

unchanged (no vehicle)

Details on exposure:

GENERATION OF TEST ATMOSPHERE / CHAMBER DESCRIPTION
- Exposure apparatus: glass and stainless steel inhalation chamber
- Method of holding animals in test chamber: in cage
- Temperature, humidity, pressure in air chamber: not reported
- Airflow : 1000 L/minute
- Treatment of exhaust air: chamber atmospheres containing MIBK were filtered before leaving an exhaust stack


TEST ATMOSPHERE
- Brief description of analytical method used: Each chamber atmosphere was analyzed for MIBK approximately once every hour during each 6-hour exposure. Daily nominal concentrations (an estimated concentration calculated from the amount of test material delivered and the chamber airflow during the exposure period) were also calculated for each chamber.

Analytical verification of doses or concentrations:

yes

Details on analytical verification of doses or concentrations:

MIBK concentration was checked approximately 10 times during each exposure, and verified using a gas chromatograph equipped with a flame ionization detector.

Details on mating procedure:

- Impregnation procedure: cohoused
- If cohoused:
- M/F ratio per cage: 1:1
- Length of cohabitation: 4 days
- Further matings after two unsuccessful attempts: no
- Verification of same strain and source of both sexes: yes
- Proof of pregnancy: vaginal plug referred to as day 0 of pregnancy

Duration of treatment / exposure:

Rats were exposed to MIBK (or vehicle) on gestational days 6 through 15.

Frequency of treatment:

Exposures were 6 hours/day, for 10 consecutive days

Duration of test:

25 days

Doses / concentrations

Doses / concentrations 1

Dose / conc.:

0 ppm

Doses / concentrations 2

Dose / conc.:

300 ppm (analytical)

Remarks:

1229 mg/m3

Doses / concentrations 3

Dose / conc.:

1 000 ppm (analytical)

Remarks:

4106 mg/m3

Doses / concentrations 4

Dose / conc.:

3 000 ppm (analytical)

Remarks:

12292 mg/m3

No. of animals per sex per dose:

35

Control animals:

yes, sham-exposed

Details on study design:

- Dose selection rationale: based on results of a previous range finding study
- Rationale for animal assignment (if not random): random

Examinations

Maternal examinations:

CAGE SIDE OBSERVATIONS: Yes
- Time schedule: daily

DETAILED CLINICAL OBSERVATIONS: Yes
- Time schedule: daily

BODY WEIGHT: Yes
- Time schedule for examinations: gestational days 0, 6, 9, 12, 15, 18, and 21.

POST-MORTEM EXAMINATIONS: Yes
- Sacrifice on gestation day 21
- Organs examined: The gravid uteri, ovaries (including corpora lutea), cervices, vagina, and peritoneal and thoracic cavities were examined grossly. Ovarian corpora lutea of pregnancy were counted. Maternal liver, kidney and gravid uterine weights were determined.

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

Fetal examinations:

- External examinations: Yes: all per litter
- Soft tissue examinations: Yes: half per litter
- Skeletal examinations: Yes: half per litter
- Head examinations: Yes: half per litter

Statistics:

Results of quantitative continuous variables were compared to the control group using Levene’s test for equal variances, ANOVA, and t-tests with Bonferroni probabilities. Non-parametric data were analyzed using the Kruskal-Wallis test and the Mann-Whitney U-test. Incidence data were compared using Fischer’s exact test. For all tests, a 2-tailed limit of 0.05 was used as the criterion for significance.

Indices:

no

Historical control data:

none

Results and discussion

Results: maternal animals

General toxicity (maternal animals)

Clinical signs:

effects observed, treatment-related

Description (incidence and severity):

In the top dose group (3000ppm) the following clinical signs were noted during the exposure period: coordination loss, hindlimb weakness, paresis, irregular gait, hypoactivity, ataxia, unkempt fur, negative tail or toe pinch, piloerection, lacrimation, or red perioral encrustation.

Mortality:

no mortality observed

Body weight and weight changes:

effects observed, treatment-related

Description (incidence and severity):

Maternal mean body weight and weight gain were significantly decreased in rats exposed to 3000 ppm during the exposure period, but they had recovered to control levels by the day of sacrifice.

Food consumption and compound intake (if feeding study):

effects observed, treatment-related

Description (incidence and severity):

Food consumption was significantly decreased in rats exposed to 3000ppm during the exposure period, but recovered to control levels by the day of sacrifice.

Food efficiency:

no effects observed

Ophthalmological findings:

no effects observed

Haematological findings:

no effects observed

Clinical biochemistry findings:

no effects observed

Urinalysis findings:

no effects observed

Behaviour (functional findings):

effects observed, treatment-related

Description (incidence and severity):

In the high dose, the following were observed during exposure: coordination loss, hindlimb weakness, paresis, irregular gait, hypoactivity, ataxia, unkempt fur,

Immunological findings:

not examined

Maternal developmental toxicity

Details on maternal toxic effects:

Maternal toxic effects:yes

Details on maternal toxic effects:
maternal toxicity was indicated by mortality, clinical signs and elevated absolute and relative liver weight at 3000 ppm.

Effect levels (maternal animals)

Key result

Dose descriptor:

NOAEL

Effect level:

1 000 ppm

Based on:

test mat.

Basis for effect level:

other: maternal toxicity

Results (fetuses)

Details on embryotoxic / teratogenic effects:

Embryotoxic / teratogenic effects:yes

Details on embryotoxic / teratogenic effects:
Fetal toxicity was indicated by reduced fetal body weight at 3000 ppm in rats, an increase in fetal deaths at 3000 ppm and by the increased incidence of poorly ossified or unossified skeletal elements observed in rat fetuses at 3000 ppm.

Effect levels (fetuses)

1

Dose descriptor:

NOAEL

Effect level:

1 000 ppm

Based on:

test mat.

Sex:

male/female

Basis for effect level:

other: fetotoxicity

2

Dose descriptor:

NOAEL

Effect level:

3 000 ppm

Based on:

test mat.

Sex:

male/female

Basis for effect level:

other: teratogenicity

Fetal abnormalities

Abnormalities:

not specified

Overall developmental toxicity

Key result

Developmental effects observed:

yes

Lowest effective dose / conc.:

3 000 ppm (analytical)

Treatment related:

yes

Relation to maternal toxicity:

developmental effects as a secondary non-specific consequence of maternal toxicity effects

Dose response relationship:

not specified

Relevant for humans:

no

Any other information on results incl. tables

Parameter	0 ppm	300 ppm	1000 ppm	3000 ppm
Number of dams removed from study at sacrifice (not required)	6	5	4	0
Number of early deliveries	0	0	0	0
Number of aborted fetuses	0	0	0	0
Number of dead dams	0	0	0	0
% non-pregnant at sacrifice	13.8	13.3	19.4	34.3
Number of litters examined	25	26	25	23
Corpora lutea	12.40 ± 1.04	12.46 ± 1.42	12.44 ± 1.39	12.44 ± 1.41
Total implants	9.92 ± 3.43	11.12 ± 2.61	10.88 ± 2.47	11.04 ± 2.32
Percent pre-implantation loss	20.04 ± 26.48	11.23 ± 18.41	13.44 ± 16.76	11.19 ± 16.24
Live fetuses per litter	9.48 ± 3.28	10.77 ± 2.63	10.60 ± 2.52	10.65 ± 2.21
Non-viable implants per litter	0.44± 0.71	0.35± 0.69	0.28± 0.68	0.39± 0.58

Table 2          Offspring outcomes

Parameter	0 ppm	300 ppm	1000 ppm	3000 ppm
Body weight (per litter; g)	4.46 ± 0.22	4.33 ± 0.12*	4.39 ± 0.14	4.18 ± 0.13*
Body weight (per litter; males; g)	4.59 ± 0.21	4.46 ± 0.13*	4.54 ± 0.14	4.32 ± 0.14*
Body weight (per litter; females; g)	4.34 ± 0.23	4.20 ± 0.13*	4.25 ± 0.15	4.04 ± 0.15*
External malformations (% of fetuses)	0.4	0.4	0.0	0.0
Visceral malformations (% of fetuses)	0.8	1.4	0.0	0.0
Skeletal malformations (% of fetuses)	0.9	0.0	0.0	0.0
Total malformations (% of fetuses)	1.3	1.1	0.0	0.0
Percent live fetuses	96.11± 5.97	96.96± 6.29	97.47± 6.18	96.72± 4.83
Sex ratio (% males)	44.6± 18.5	49.5± 13.9	46.4± 14.5	47.8± 14.5

Applicant's summary and conclusion

Conclusions:

Exposure of Fischer 344 rats to MIBK by inhalation, on GD 6 to 15, resulted in maternal (evidenced by the observation of reductions in body weight and food consumption, increased clinical signs of toxicity, increased kidney weights, in the 3000 ppm group relative to the control) and fetal (evidenced by observation of reduced fetal body weight in the 300 and 3000 ppm groups relative to the control, and retarded ossification in the 3000 ppm group relative to the control) toxicity; however, no evidence of teratogenicity was observed. 

Executive summary:

Developmental and maternal toxicity were evaluated in groups of 35 pregnant Fischer 344 rats exposed by inhalation to 0, 300, 1000, or 3000 ppm (0, 1229, 4106, 12,292 mg/m3) MIBK for 6 hrs/day on gestation days 6 through 15. Animals were sacrificed on gestation day 21. Dams were evaluated for exposure-related changes in clinical signs, body weight, food consumption, organ weights (kidney, liver, and gravid uterus), and reproductive parameters; fetuses were evaluated for exposure-related changes in body weight and viability, and for external, skeletal, and thoracic and peritoneal visceral alterations. Maternal mean body weight, weight gain, and food consumption were significantly decreased in rats exposed to 12,292 mg/m3(but not to 4106 mg/m3or lower ) during the exposure period, but they had recovered to control levels by the day of sacrifice. Maternal clinical signs observed in rats included coordination loss, hindlimb weakness, paresis, irregular gait, hypoactivity, ataxia, unkempt fur, negative tail or toe pinch, piloerection, lacrimation, or red perioral encrustation. These clinical signs were observed only during the exposure period and only at 12,292 mg/m3. No exposure-related deaths occurred in the rat exposure groups. Statistical analyses by the authors were per dam or per litter. No exposure-related effects were observed in rats with respect to numbers of corpora lutea, total implants, percent implantation loss, live fetuses per litter, nonviable implants per litter, percent live fetuses, and sex ratio. Fetal body weights (litter weight, male weight per litter, and female weight per litter) were significantly reduced in rats exposed to 1229 (the mean by 3%) and 12,292 mg/m3 (the mean by 6%) but not to 4106 mg/m3. The authors indicated that the reduction in rat fetal body weight was confounded by a skewed distribution of litter size, whereby higher doses had very small litters and smaller litters had varied mean weights across dose, while lower-dosed dams appeared to have larger litters and larger litters showed a dose-dependence in mean weight. There was no statistically significant increase in the number of rat fetuses per litter. The authors decided the reductions in rat fetal body weight was not treatment-related. No exposure-related change in the incidence of malformations of any type were observed in rat fetuses. The number of litters with observations indicating retarded skeletal ossification was significantly increased to various degrees in rats at 12,292 mg/m3 relative to controls for a variety of skeletal endpoints, with scattered increases in litters with retarded ossification at lower exposure levels that were not considered by the authors to be exposure-related. 4106 mg/m3 was considered to be the NOEL for both maternal animals and offspring.