2-methylbutyraldehyde

Carcinogenicity

Administrative data

Endpoint:

carcinogenicity: inhalation

Type of information:

migrated information: read-across from supporting substance (structural analogue or surrogate)

Adequacy of study:

supporting study

Study period:

1990-08-16 to 1992-08-19

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

other: GLP guideline study

Cross-reference

Reason / purpose for cross-reference:

reference to other study

Data source

Reference

Reference 1

Reference Type:

study report

Title:

Unnamed

Year:

1999

Reference 2

Reference Type:

publication

Title:

Unnamed

Year:

1998

Reference 3

Reference Type:

other: study report abstract

Title:

Unnamed

Year:

1999

Materials and methods

Test guideline

Qualifier:

equivalent or similar to guideline

Guideline:

OECD Guideline 453 (Combined Chronic Toxicity / Carcinogenicity Studies)

Deviations:

yes

Remarks:

only comprehensive pathohistology: focused on non-neoplastic and neoplastic lesions

GLP compliance:

yes

Test material

Test material information

Constituent 1

Reference substance name:

Isobutyraldehyde

EC Number:

201-149-6

EC Name:

Isobutyraldehyde

Cas Number:

78-84-2

IUPAC Name:

2-methylpropanal

Details on test material:

- Analytical purity: approx. 98 %
- Impurities (identity and concentrations): Isobutyic acid approx. 1.4 %
- Lot/batch No.: E080289
-Supplier: Texas Eastman Chemicals

Test animals

Species:

rat

Strain:

Fischer 344

Sex:

male/female

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Source: Simonsen Laboratories (Gilroy, CA)
- Age at study initiation: 6 weeks
- Weight at study initiation:
- Fasting period before study: none
- Housing: 1 animal per cage
- Diet: ad libitum, except during exposure
- Water: ad libitum
- Acclimation period: 13 days


ENVIRONMENTAL CONDITIONS
- Temperature (°C): 20.4 - 21.8
- Humidity (%): 43 - 66
- Air changes (per hr): 12 - 15
- Photoperiod (hrs dark / hrs light): 12 / 12

IN-LIFE DATES: From: To:

Administration / exposure

Route of administration:

inhalation: vapour

Type of inhalation exposure (if applicable):

whole body

Vehicle:

other: air

Details on exposure:

GENERATION OF TEST ATMOSPHERE / CHAMBER DESCRIPTION
- The vapor for the 13-week studies was generated by bubbling nitrogen gas through a column of the liquid maintained at a constant temperature in a water bath.
- Exposure apparatus:
Inhalation chambers of the Rochester design were used in the 2-year studies. The total volume for each chamber was 2.3 m3. The chamber ventilation system provided 12 to 15 charcoal- and HEPA-filtered air changes per hour, and the internal design of the chamber afforded equal exposure to each animal. This flow rate was sufficient to maintain proper temperature and humidity, provide a uniform and reproducible test atmosphere, and remove ammonia.

TEST ATMOSPHERE
- Brief description of analytical method used:
The chamber concentrations of isobutyraldehyde in the 2-years studies were monitored 4x/h using an 8-port stream-select valve with two on-line gaschromatographs (HP Model 5840).
Calibration of the gas chromatograph monitoring the exposure chamber was achieved by independent quantitative analysis of grab samples collected with bubblers containing dimethylformamide and an internal standard. Additionally, the gas chromatograph was calibrated by a comparison of grab samples and gravimetrically prepared standards with an offline gas chromatograph. The off-line gas chromatograph was calibrated with gravimetrically prepared standards of isobutyraldehyde in dimethylformamide.

Particulate matter:
A particle detector (Type CN, Gardner Associates) was used with and without animals to ensure that isobutyraldehyde vapour was produced and not aerosol. No particle counts above the minimum resolvable level (approximately 200 particles/cm ) were detected.


- Samples taken from breathing zone: no

Analytical verification of doses or concentrations:

yes

Details on analytical verification of doses or concentrations:

The times for the chamber concentrations to build up to 90% of the final exposure concentrations (T90) and to decay to 10% of the exposure concentrations (T10) were measured in the 2-year studies with and without animals present in the chambers. At a chamber airflow rate of 15 air changes per hour, the theoretical value for both T90 and T 10 is approximately 12 to 13 minutes; the T90 value chosen for all studies was 12 minutes. The uniformity of isobutyraldehyde concentrations in the exposure chambers was measured.
Uniformity of exposure concentrations in all chambers was acceptable. The persistence of isobutyraldehyde in the 2,000 ppm exposure chamber after shutting off the system was monitored during the 2-year studies, with and without animals present. The concentration of isobutyraldehyde in the exposure chambers fell to less than 1% of the beginning concentration within less than 30 minutes in all cases.

Duration of treatment / exposure:

105 weeks

Frequency of treatment:

5 days/week, 6 h/day

Post exposure period:

none

Doses / concentrations

Remarks:

Doses / Concentrations:
0, 500, 1000 or 2000 ppm (1.5, 3, and 6 mg/L)
Basis:
nominal conc.
confirmed by regular analysis

No. of animals per sex per dose:

50

Control animals:

yes, concurrent no treatment

Details on study design:

- Dose selection rationale: based on 90-d study (see NTP 1999a)
- Rationale for animal assignment (if not random):
- Rationale for selecting satellite groups:
- Post-exposure recovery period in satellite groups:
- Section schedule rationale (if not random):

Examinations

Observations and examinations performed and frequency:

CAGE SIDE OBSERVATIONS: Yes
- Time schedule: 2x/d

DETAILED CLINICAL OBSERVATIONS: Yes
- Time schedule: recorded at 4-weeks intervals until week 91 and every two weeks thereafter.

BODY WEIGHT: Yes
- Time schedule for examinations: initially, weekly for 12 weeks, monthly therafter until week 91 and then every two weeks and end of the study.


FOOD CONSUMPTION:
- Food consumption for each animal determined and mean daily diet consumption calculated as g food/kg body weight/day: No data


FOOD EFFICIENCY:
- Body weight gain in kg/food consumption in kg per unit time X 100 calculated as time-weighted averages from the consumption and body weight gain data: No data


WATER CONSUMPTION: No data

OPHTHALMOSCOPIC EXAMINATION: No


HAEMATOLOGY: No


CLINICAL CHEMISTRY: No


URINALYSIS: No


NEUROBEHAVIOURAL EXAMINATION: No


OTHER:

Sacrifice and pathology:

GROSS PATHOLOGY: Yes (Appendices A - D)
HISTOPATHOLOGY: Yes (Appendices A - D)

Statistics:

The probability of survival was estimated by the product-limit procedure of Kaplan and Meier (1958). The primary statistical method used for the evaluation of tumor incidence was logistic regression analysis (Dinse and Lagakos, 1983; Dinse and Haseman, 1986; McKnight and Crowley, 1984). Additional methods used included the life table test (Cox, 1972; Tarone, 1975), appropriate for rapidly lethal neoplasms, and the Fisher exact test and the Cochran-Armitage trend test (Armitage, 1971; Gart et aL, 1979). Tests of significance included pairwise comparisons of each exposed group with controls and a test for an overall dose-related trend. (see NTP 1999, p. 25).

Results and discussion

Results of examinations

Details on results:

Survival and Body Weight:
No differences in survival rates between exposed and chamber control rats were found. The mean body weights of male and female rats were generally similar to those of the chamber controls throughout the study.

Clinical signs: No clinical findings that could be attributed to isobutyraldehyde exposure were observed.

Pathology Findings:
No increase in neoplasm incidences that could be attributed to exposure to isobutyraldehyde was observed in male or female rats.
However three primary nasal neoplasms were observed in male and female rats exposed to isobutyraldehyde. One polypoid adenoma was present in the anterior nose section of a male rat exposed to 1000 ppm, one adenoma of the vomeronasal organ was noted in a 2000 ppm male, and an undifferentiated malignant neoplasm, classified as a sarcoma (mesenchymal origin), was present in the most posterior section of the nose in a 500 ppm (NTP 1999, Tab. 7).

Non-neoplastic lesions related to isobutyraldehyde exposure were limited to the nose and consisted of squamous metaplasia of the respiratory epithelium, degeneration of the olfactory epithelium, and suppurative inflammation. Incidences of minimal to mild squamous metaplasia in 1000 and 2000 ppm males (10/49 and 44/50, respectively) and females (9/49 and 44/50, respectively) and in 500 ppm females (11/50) were significantly greater than those in the chamber controls (1/50, 1/49). Minimal to mild degeneration of the olfactory epithelium occurred in the 2000 ppm males and females (44/50 and 45/50, respectively, vs. no occurrences in controls). Incidences of suppurative inflammation (rhinitis) in both sexes exposed to 2000 ppm were increased (15/50 and 11/50, respectively) compared to controls (5/50 and 2/49).

Effect levels

1

Dose descriptor:

NOAEC

Effect level:

2 000 ppm

Sex:

male/female

Basis for effect level:

other: overall effects Histopathology: local (nasopharyngeal) and other tissue and organ tumours

Remarks on result:

other: Effect type: carcinogenicity (migrated information)

2

Dose descriptor:

NOAEC

Effect level:

< 500 ppm

Sex:

female

Basis for effect level:

other: overall effects Histopathology: Incidences of minimal to mild squamous metaplasia in 500 ppm females (11/50) were significantly greater than those in the chamber controls (1/50, 1/49).

Remarks on result:

other: Effect type: toxicity (migrated information)

3

Dose descriptor:

LOAEC

Effect level:

500 ppm

Sex:

female

Basis for effect level:

other: overall effects Histopathology: Incidences of minimal to mild squamous metaplasia in 500 ppm females (11/50) were significantly greater than those in the chamber controls (1/50, 1/49).

Remarks on result:

other: Effect type: toxicity (migrated information)

4

Dose descriptor:

NOAEC

Effect level:

2 000 ppm

Basis for effect level:

other: overall effects Survival; body weight; organ weights; histology (systemic effects)

Remarks on result:

other: Effect type: toxicity (migrated information)

Any other information on results incl. tables

NTP 1999 (excerpt Table 7): see below Attached Background Material

[Doc name: NTP1999_Tab7_rat-carcinogenicity]

_________________________________________________________________________________

Summary of the 2-Year Carcinogenesis and Genetic Toxicology Studies of Isobutyraldehyde

	Male F344/N Rats	Female F344/N Rats
Concentrations in air	Chamber control, 500, 1,000, or 2,000 ppm	Chamber control, 500, 1,000, or 2,000 ppm
Body weights	Exposed groups similar to chamber control groups	Exposed groups similar to chamber control groups
Survival rates	12/50, 15/50, 11/50, 10/50	27/50, 24/50, 24/50, 32/50
Nonneoplastic effects	Nose: respiratory epithelium squamous metaplasia (1/50, 1/49, 10/49, 44/50); suppurative inflammation (5/50, 3/49, 6/49, 15/50); olfactory epithelium degeneration (0/50, 0/49, 3/49, 44/50);	Nose: respiratory epithelium squamous metaplasia (1/49, 11/50, 9/49, 44/50); suppurative inflammation (2/49, 3/50, 5/49, 11/50); olfactory epithelium degeneration (0/49, 0/50, 2/49, 45/50);
Neoplastic effects	None	None
Level of evidence of carcinogenic activity	No evidence	No evidence

(from NTP1999 TR-472 Abstract-Summary)

Applicant's summary and conclusion

Conclusions:

Isobutanal was not cancerogenic in rats after long-term inhalation. The NTP peer review panel concluded: no evidence of carcinogenity in rats and mice.

Executive summary:

In a 2-years oncogenicity study, male and female Fischer 344 rats were exposed to 1.5, 3 and 6 mg/L isobutanal (measured) 5 d/wk and 6 h/d. There were no significant increases in the incidences of any tumour type that may have been related to the treatment. In particular, no tumours of the respiratory tract were observed. Local adverse effects were produced: Incidences of minimal to mild squamous metaplasia in 1000 and 2000 ppm males (10/49 and 44/50, respectively) and females (9/49 and 44/50, respectively) and in 500 ppm females (11/50) were significantly greater than those in the chamber controls (1/50, 1/49).

No local NOAEC(105 wk) could be established due to histological changes of the nasal region in females at 500 ppm (1.5 mg/L). The LOAEC is considered 500 ppm (1.5 mg/L). The NOAEC for systemic effects was 2000 ppm (6 mg/L).