2,4,4-trimethylpentene

Toxicity to reproduction

Administrative data

Endpoint:

screening for reproductive / developmental toxicity

Remarks:

based on test type (migrated information)

Type of information:

experimental study

Adequacy of study:

key study

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

other: GLP compliant, guideline study, available as unpublished report, no restrictions, fully adequate for assessment

Cross-reference

Cross-reference 1

Reason / purpose for cross-reference:

reference to same study

Cross-reference 2

Reason / purpose for cross-reference:

reference to other study

Data source

Reference

Reference Type:

study report

Title:

Unnamed

Year:

1997

Report date:

1997

Materials and methods

Test guideline

Qualifier:

according to guideline

Guideline:

OECD Guideline 421 (Reproduction / Developmental Toxicity Screening Test)

Deviations:

not specified

GLP compliance:

yes (incl. QA statement)

Test material

Test material information

Constituent 1

Reference substance name:

2,4,4-trimethylpentene

EC Number:

246-690-9

EC Name:

2,4,4-trimethylpentene

Cas Number:

25167-70-8

Molecular formula:

C8H16

IUPAC Name:

2,4,4-trimethylpent-1-ene

Constituent 2

Reference substance name:

25167-70-8       

IUPAC Name:

25167-70-8       

Details on test material:

- Name of test material (as cited in study report): 2,4,4-trimethylpentene (also known as diisobutylene and diisobutene)
- Physical state: clear, colourless liquid
- Analytical purity: 95.19%
- Lot/batch No.: Batch No. 2 (a 50:50 mixture of two original batches of 2,4,4-trimethylpentene - the details of which are as follows: Batch No. R11 supplied by Shell and Batch No. 155833 supplied by Erdolchemie).
- Expiration date of the lot/batch: 29 April 1997
- Storage condition of test material: Under nitrogen, protected from light, in a cool store.

Test animals

Species:

rat

Strain:

other: CD (Sprague-Dawley origin)

Sex:

male/female

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Source: Charles River (UK) Limited, Margate, Kent, England
- Age at study initiation: 11-12 weeks
- Weight at study initiation: 352-401 g (males); 229-262 g (females)
- Housing: Stainless steel or high density polypropylene cages. Five animals of the same sex/cage pre-mating; 1 male:1 female for pairing; females housed individually during gestation and lactation.
- Diet: pelleted rodent diet (LAD 1 SQC, from Special Diets Services Limited, Witham, Essex, England) ad libitum
- Water: Tap water ad libitum
- Acclimation period: 12 days
- Bedding: Lignocel 3/4 wood flakes (RS Biotech, Finedon, Northamptonshire, UK) during the littering phase

ENVIRONMENTAL CONDITIONS
- Temperature: 19.5-21.5°C
- Humidity: 49-74%
- Air changes: Approximately 15/hr
- Photoperiod: 12 hrs dark / 12 hrs light

IN-LIFE DATES: From: 24 June 1996 To: 9 August 1996

Administration / exposure

Route of administration:

oral: gavage

Vehicle:

maize oil

Details on exposure:

PREPARATION OF DOSING SOLUTIONS:
- The formulation for the high dosage group (Group 4) was prepared by mixing the test material with maize oil. The formulations for the other treated groups were prepared by serial dilution of the Group 4 formulation.
All efforts were taken to minimise vaporisation of the test material during the formulation procedure.

VEHICLE
- Concentration in vehicle: Prepared at the appropriate concentration in maize oil to permit administration at a constant volume-dosage of 5 mL/kg.

Details on mating procedure:

- Impregnation procedure: co-housed
- M/F ratio per cage: 1:1
- Length of cohabitation: 6 days
- Verification of same strain and source of both sexes: yes
- Proof of pregnancy: vaginal plug and/or sperm in vaginal smear; referred to as day 0 of pregnancy
- Any other deviations from standard protocol: Males and females paired on the fifteenth day of treatment.

Analytical verification of doses or concentrations:

yes

Details on analytical verification of doses or concentrations:

Homogeneity, stability and achieved concentrations of the formulations were measured throughout the study.

Duration of treatment / exposure:

Dosing was for 15 days before pairing. Treatment was continued throughout mating, gestation and lactation to Day 3 of lactation for females and to termination after approximately six weeks of treatment for males.

Frequency of treatment:

Daily

Details on study schedule:

The animals were dosed for 15 days before pairing and throughout the study until termination. Males had received between 44 and 46 dose administrations, and females between 40 and 45 dose administrations. Females were not dosed if parturition was in progress.

Doses / concentrations

Remarks:

Doses / Concentrations:
100, 300 or 1000
Basis:
analytical conc.
mg/kg bw/day

No. of animals per sex per dose:

10

Control animals:

yes, concurrent vehicle

Details on study design:

- Dose selection rationale: Based on the results of a preliminary seven-day toxicity study performed at these laboratories in which no evidence of toxicity was apparent at dosages up to and including 1000 mg/kg bw/day.

Examinations

Parental animals: Observations and examinations:

CAGE SIDE OBSERVATIONS: Yes
- Time schedule: At least twice daily

DETAILED CLINICAL OBSERVATIONS: Yes
- Time schedule: Daily during weeks 1-2, weekly during weeks 3-6

BODY WEIGHT: Yes
- Time schedule for examinations: Males were weighed on the day that treatment commenced, at weekly intervals thereafter, and before termination. Females were weighed on the day that treatment commenced, at weekly intervals until mating was detected, on Days 0, 7, 14 and 20 of gestation and on Days I and 4 of lactation.

FOOD CONSUMPTION : Yes
- Food consumption (by cage) determined until pairing and mean weekly diet consumption calculated as g food/kg body weight/day: Yes
- Food consumption for females was also recorded for the periods Days 0-3, 4-6, 7-10, 11-13, 14-16 and 17-19 of gestation and for the period Days 1-3 of lactation.

POST-MORTEM EXAMINATIONS: Yes

Oestrous cyclicity (parental animals):

- Vaginal smears were taken for ten days before pairing from all females and examined to establish the regularity and duration of the oestrous cycle.

Litter observations:

PARAMETERS EXAMINED
- The following parameters were examined in offspring at approximately 24 hours after birth (day 1): number and sex of pups (live and dead), individual bodyweight (live offspring only), sex ratio, individual observations.

GROSS EXAMINATION OF DEAD PUPS:
- yes, for external and internal abnormalities.

Postmortem examinations (parental animals):

SACRIFICE
- Male animals: All surviving animals killed after successful littering of the parental females (after approximately 6 weeks of treatment)
- Maternal animals: All surviving animals killed on Day 4 of lactation

GROSS PATHOLOGY
- Gross necropsy consisted of external and internal examinations including a detailed examination of the cranial, thoracic, abdominal and pelvic cavities and their viscera
- The external and cut surfaces of the organs and tissues were examined before or after weighing, as appropriate
- The number of corpora lutea and uterine implantation sites were recorded in all females
- Abnormalities, interactions and changes were noted and representative tissue samples preserved in fixative

HISTOPATHOLOGY / ORGAN WEIGHTS
- Organs examined histopathologically: all abnormalities, epididymides, kidneys, liver, ovaries, testes
- Organs stored: prostate, seminal vesicles, uterus, cervix and vagina
- Organs weighed: epididymides, kidneys, liver, ovaries, prostate, seminal vesicles, testes, uterus and cervix

Postmortem examinations (offspring):

SACRIFICE
- Killed on Day 4 of age

GROSS NECROPSY
- Gross necropsy consisted of external and internal examinations

HISTOPATHOLOGY
- Specimens of abnormal tissues indicated were retained

Statistics:

Absolute bodyweights at the start of each phase, bodyweight gains, food consumption values and litter sizes were assessed by one-way analysis of variance. Whenever this was found to be significant, a Student's 't'-test was used. For organ weights, homogeneity of variance was automatically tested using Bartlett's test. Whenever this was found to be statistically significant a Behrens-Fisher test was used to perform pair-wise comparisons, otherwise a Dunnett's test was used. Inter-group differences in offspring survival, sex ratio and macroscopic pathology and histopathology were assessed, on indication, using Fisher's Exact test.

Reproductive indices:

- Mating performance and fertility
- Pre-coital interval
- Gestation length
- Group mean litter size

Offspring viability indices:

- Survival indices: pre-implantation survival index; post-implantation survival index; live birth index; viability index.

Results and discussion

Results: P0 (first parental generation)

General toxicity (P0)

Clinical signs:

effects observed, treatment-related

Body weight and weight changes:

no effects observed

Food consumption and compound intake (if feeding study):

no effects observed

Organ weight findings including organ / body weight ratios:

effects observed, treatment-related

Histopathological findings: non-neoplastic:

effects observed, treatment-related

Other effects:

not examined

Reproductive function / performance (P0)

Reproductive function: oestrous cycle:

no effects observed

Reproductive function: sperm measures:

not examined

Reproductive performance:

no effects observed

Details on results (P0)

CLINICAL SIGNS AND MORTALITY (PARENTAL ANIMALS)
One female receiving 2,4,4-Trimethyl pentene at 1000 mg/kg bw/day was killed in extremis on Day 2 of lactation due to signs including under-active behaviour, hunched posture, piloerection, slow respiration, brown-coloured urine and brown perigenital staining. In the absence of any similar signs or findings in other females on this study, it was considered that the death of this animal was incidental.
At 1000 mg/kg bw/day, animals showed transient salivation after dose administration. Single occurrences of transient salivation after dosing were observed for three males receiving 300 mg/kg bw/day and for one male receiving 100 mg/kg bw/day. At 1000 mg/kg bw/day, a number of animals showed brown staining on the dorsal and ventral body surfaces. In males this sign was first evident in Week 2 whilst in females it was generally first observed in Week 4.

ORGAN WEIGHTS (PARENTAL ANIMALS)
The absolute and bodyweight-relative weights of reproductive organs were similar in all groups and not affected by treatment. The absolute and bodyweight-relative weights of the liver and kidneys were high, when compared with the Controls, for males that received 300 or 1000 mg/kg bw/day and for females that received 1000 mg/kg bw/day.

GROSS PATHOLOGY (PARENTAL ANIMALS)
After approximately six weeks of treatment (Day 4 of lactation for females), all males and four females that received 1000 mg/kg/day had swollen livers or liver lobes. Two males that received 1000 mg/kg bw/day also had large kidneys. No remarkable findings were apparent at dosages up to 300 mg/kg bw/day.

HISTOPATHOLOGY (PARENTAL ANIMALS)
Treatment-related findings were confined to the kidneys of males. Basophilic cortical tubules were seen in all treated groups whilst proteinaceous casts and interstitial inflammatory cells were seen only at 300 or 1000 mg/kg bw/day. The severity of the basophilic cortical tubular changes was greater in males given 300 or 1000 mg/kg bw/day than in those given 100 mg/kg bw/day. Centriacinar fatty vacuolation was recorded in the livers of two females given 1000 mg/kg bw/day (one of these animals was an early decedent). This distribution of fat in the liver is more commonly associated with hepatotoxicity than periacinar vacuolation, but is considered equivocal in this instance.

Effect levels (P0)

Dose descriptor:

LOAEL

Effect level:

100 mg/kg bw/day (nominal)

Sex:

male/female

Basis for effect level:

other: kidney enlargement (histopath: basophilic cortical tubular changes). Liver enlargement (histopath equivocal)

Results: F1 generation

General toxicity (F1)

Clinical signs:

no effects observed

Mortality / viability:

no mortality observed

Body weight and weight changes:

no effects observed

Sexual maturation:

not examined

Organ weight findings including organ / body weight ratios:

not examined

Gross pathological findings:

no effects observed

Histopathological findings:

no effects observed

Details on results (F1)

VIABILITY (OFFSPRING)
At 1000 mg/kg bw/day, one litter showed low offspring survival and the offspring were under-active, cold, unfed and all showed bodyweight loss. This was considered to have resulted from the flooding of the cage overnight on Days 2-3 of lactation, and therefore was not associated with parental treatment with 2,4,4-trimethyl pentene.

GROSS PATHOLOGY (OFFSPRING)
For the majority of offspring dying prematurely the necropsy findings observed were due to a lack of milk in the stomach.

Effect levels (F1)

Dose descriptor:

NOAEL

Generation:

F1

Effect level:

1 000 mg/kg bw/day (nominal)

Sex:

male/female

Basis for effect level:

other: no treatment-related effects reported

Overall reproductive toxicity

Reproductive effects observed:

not specified

Any other information on results incl. tables

The absolute and bodyweight-relative weights of the liver and kidneys were high, when compared with the controls, for males that received 300 or 1000 mg/kg bw/day and for females that received 1000 mg/kg bw/day.

In the absence of any associated histopathological change, the increase in liver weight was considered to represent increased metabolism, as an adaptive response to the administration of a xenobiotic. Due to the effects on the kidneys at dosages of 100 mg/kg bw/day and higher, a parental no-observed-effect level (NOEL) was not demonstrated as part of this study.

Intergroup comparison of mean liver and kidney weight (g) relative to bodyweight

 

Dose level of 2,4,4-Trimethylpentene
	Males				Females
	0	100	300	1000	0	100	300	1000 #
Liver	4.10	4.17	4.72*	6.65**	5.44	5.34	5.53	6.83**
Kidney	0.758	0.794	0.918**	0.981**	0.723	0.794*	0.745	0.845

# 9 animals (10 in other groups)

*p<0.05 **p<0.01

 

At dosages up to 1000 mg/kg/day, there were no effects on mating performance and fertility, or the birth and subsequent growth and survival of offspring to Day 4 of age. A parental dosage of 1000 mg/kg/day was therefore considered to be the no-observed-effect level (NOEL) for the offspring.

Applicant's summary and conclusion

Conclusions:

The reproductive no-observed-effect level (NOEL) was 1000 mg/kg bw/day. Due to the effects on the kidneys at dosages of 100 mg/kg bw/day and higher, a parental no-observed-effect level (NOEL) was not demonstrated.

Executive summary:

Groups of 10 males and 10 female CD rats were dosed orally with solutions of 2,4,4 -trimethylpentene in maize oil at dose levels of 0, 100, 300 or 1000 mg/kg/day in a combined reproductive toxicity / developmental toxicity screening test. Oral administration of 2,4,4-Trimethyl pentene at dosages of up to 1000 mg/kg bw/day was without adverse effect on the general condition or reproductive performance of male and female rats, or on the growth and viability of their offspring up to Day 4 of age. The dosage of 1000 mg/kg bw/day was therefore considered to represent the no-observed-effect level (NOEL) for these reproductive parameters. Due to the effects on the kidneys at dosages of 100 mg/kg bw/day and higher, a parental no-observed-effect level (NOEL) was not demonstrated as part of this study. Subsequent immunohistochemical investigations of alpha-2u-Globulin in kidneys has been reported.