Isoprene

Repeated dose toxicity: inhalation

Administrative data

Endpoint:

sub-chronic toxicity: inhalation

Type of information:

experimental study

Adequacy of study:

key study

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

other: GLP, guideline study, published in peer reviewed literature, fully adequate for assessment

Data source

Reference

Reference 1

Reference Type:

publication

Title:

Unnamed

Year:

1995

Reference 2

Reference Type:

publication

Title:

Isoprene, An Endogenous Hydrocarbon And Industrial Chemical, Induces Multiple Organ Neoplasia In Rodents After 26 Weeks Of Inhalation Exposure

Author:

Melnick RL et al

Year:

1994

Bibliographic source:

Cancer Res., Vol. 54, pp. 5333-5339.

Materials and methods

Test guideline

Qualifier:

equivalent or similar to guideline

Guideline:

OECD Guideline 413 (Subchronic Inhalation Toxicity: 90-Day Study)

GLP compliance:

yes

Limit test:

no

Test material

Test material information

Constituent 1

Reference substance name:

Isoprene

EC Number:

201-143-3

EC Name:

Isoprene

Cas Number:

78-79-5

Molecular formula:

C5H8

IUPAC Name:

2-methylbuta-1,3-diene

Details on test material:

purity > 99%.

Test animals

Species:

rat

Strain:

Fischer 344

Sex:

male/female

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Source: Taconic Farms, Germantown, NY, USA
- Age at study initiation: At least 6 weeks
- Housing: Individually in wire mesh cages
- Diet: NIH-07 diet ad libitum except during the exposure periods
- Water ad libitum
- Acclimation period: 11-13 days

ENVIRONMENTAL CONDITIONS
- Temperature: 75±3°C
- Humidity: 55 ± 15%
- Air changes: 15 per hr
- Photoperiod (hrs dark / hrs light): no data

IN-LIFE DATES: no data

Administration / exposure

Route of administration:

inhalation

Type of inhalation exposure:

whole body

Vehicle:

other: air

Details on inhalation exposure:

GENERATION OF TEST ATMOSPHERE / CHAMBER DESCRIPTION
- Stainless steel Hazelton 2000 chambers (total volume 2.3 m3)
- Exposure apparatus: Vapours were generated in a Buchi Rotavapor system at 50°C
- Chamber concentrations of isoprene were regulated by adjusting metering valves into the exposure chamber
- The daily mean concentrations of isoprene was 99-100% of target concentration

Analytical verification of doses or concentrations:

yes

Details on analytical verification of doses or concentrations:

Concentrations in the chambers were measured continuously during the exposures with a Hewlett-Packard gas chromatograph equipped with a flame ionization detector.
t90 (time to reach 90% of target concentration) was approximately 12 mins.

Duration of treatment / exposure:

6 hours/day for 13 weeks

Frequency of treatment:

5 days/week for 13 weeks

Doses / concentrations

Doses / concentrations 1

Remarks:

Doses / Concentrations:
0, 70, 220, 700, 2200, or 7000 ppm
Basis:
nominal conc.

Doses / concentrations 2

Remarks:

Doses / Concentrations:
0, 195, 613, 1950, 6129 and 19,503 mg/m3
Basis:
nominal conc.

No. of animals per sex per dose:

10

Control animals:

yes

Details on study design:

Post-exposure period: not applicable

Examinations

Observations and examinations performed and frequency:

BODYWEIGHTS / CLINICAL OBSERVATIONS
- Weekly

HAEMATOLOGY: Yes, Blood samples were collected for clinical pathology evaluations on days 4, 24 and at study termination
- Blood samples collected from supraorbital sinus of CO2 anaesthetised animals
- The following parameters were measured:
erythrocyte, leukocyte, and platelet counts, haemoglobin concentration, haematocrit, reticulocyte count, mean cell volume, mean cell haemoglobin and leukocyte differential counts

CLINICAL CHEMISTRY: Yes, Blood samples were collected for clinical pathology evaluations on days 4, 24 and at study termination
- Blood samples collected from supraorbital sinus of CO2 anaesthetised animals
- The following parameters were measured:
urea nitrogen, creatinine, alanine aminotransferase, glutamate dehydrogenase and sorbitol dehydrogenase

URINALYSIS: Yes, All animals in study week 12
- Urinalysis of overnight urine samples. The following parameters were measured: glucose, creatinine, alkaline phosphatase and aspartate aminotransferase concentrations

Sacrifice and pathology:

GROSS PATHOLOGY: Yes. Complete necropsies were performed on all animals.

ORGAN WEIGHTS: Yes. Brain, heart, right kidney, liver, lung, spleen, right testis, and thymus were weighed prior to fixation.

HISTOPATHOLOGY: Yes. Tissue samples, preserved in 10% neutral buffered formalin, were embedded in paraffin, sectioned, and stained with haematoxylin and eosin. -Tissues examined: gross lesions and tissue masses, adrenal glands, brain, oesophagus, femur and marrow, heart, small intestine, large intestine, kidneys, larynx, liver, lungs, lymph nodes (bronchial, mediastinal, mandibular, and mesenteric), mammary gland with adjacent skin, nasal cavity and turbinates, ovaries, pancreas, parathyroid glands, pituitary gland, preputial gland, prostate gland, salivary glands, spinal cord, and sciatic nerve, spleen, forestomach, glandular stomach, testes with epididymis and seminal vesicle, thymus, thyroid gland, trachea, urinary bladder, and uterus.

Statistics:

Analysis of survival and incidence of neoplastic and nonneoplastic lesions was performed. Clinical chemistry, haematology, and urine data were analyzed by nonparametric methods (Shirley (1977) or Dunn (1964)).

Results and discussion

Results of examinations

Clinical signs:

no effects observed

Mortality:

no mortality observed

Body weight and weight changes:

no effects observed

Food consumption and compound intake (if feeding study):

not specified

Food efficiency:

not specified

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

not specified

Ophthalmological findings:

not specified

Haematological findings:

no effects observed

Clinical biochemistry findings:

no effects observed

Urinalysis findings:

no effects observed

Behaviour (functional findings):

no effects observed

Organ weight findings including organ / body weight ratios:

no effects observed

Gross pathological findings:

no effects observed

Histopathological findings: non-neoplastic:

no effects observed

Histopathological findings: neoplastic:

no effects observed

Details on results:

Following 13 week inhalation exposure to 7000 ppm (19,503 mg/mg3) isoprene, no treatment-related effects were observed in rats.

Effect levels

1

Key result

Dose descriptor:

NOAEC

Effect level:

19 503 mg/m³ air (nominal)

Sex:

male/female

Basis for effect level:

other: Based on lack of toxicological effects in rats exposed up to 7000 ppm (19,503 mg/m3) isoprene for 13 weeks.

2

Dose descriptor:

LOAEC

Effect level:

> 19 503 mg/m³ air (nominal)

Sex:

male/female

Basis for effect level:

other: Based on lack of toxicological effects in rats exposed up to 7000 ppm (19,503 mg/m3) isoprene for 13 weeks.

Target system / organ toxicity

Critical effects observed:

not specified

Applicant's summary and conclusion

Conclusions:

No toxicological effects were evident in rats exposed up to 7000 ppm (19,503 mg/m3) isoprene for 13 weeks.

Executive summary:

In a sub-chronic inhalation toxicity study, Fischer 344 rats (10/sex/concentration) were exposed via whole body inhalation to vapours of isoprene at concentrations of 0, 70, 220, 700, 2200, or 7000 ppm (0, 195, 613, 1950, 6129 and 19,503 mg/m³) 6 hours/day, 5 days per week for a period of 13 weeks.

No toxicological effects were evident in rats exposed up to 7000 ppm (19,503 mg/m³) isoprene for 13 weeks.

The NOAEC was determined to be 19,503 mg/m³.