2,6-xylidine

Basic toxicokinetics

Administrative data

Endpoint:

basic toxicokinetics in vivo

Type of information:

experimental study

Adequacy of study:

weight of evidence

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: Well documented publications, acceptable for assessment

Data source

Reference

Reference 1

Reference Type:

other: PhD Thesis

Title:

Unnamed

Year:

1986

Reference 2

Reference Type:

other: Abstract

Title:

Unnamed

Year:

1987

Reference 3

Reference Type:

publication

Title:

The in vivo oxidative metabolism of 2,4- and 2,6-Dimethylaniline in the dog and rat

Author:

Short CR, et al.

Year:

1989

Bibliographic source:

Toxicology 57, 45-58

Reference 4

Reference Type:

secondary source

Title:

The in vivo oxidative metabolism of 2,4- and 2,6 dimethylaniline in the dog and the rat

Author:

Short CR, et al.

Year:

1989

Bibliographic source:

Toxicology 57, 45-58 (1989), cited in: IARC Monograph 57, 328 (1993)

Materials and methods

Objective of study:

metabolism

Test guideline

Qualifier:

no guideline followed

Principles of method if other than guideline:

The purpose of the investigation was to determine whether species differences in the oxidative metabolism of 2,4-DMA and 2,6-DMA could be related to species specific hepatotoxicities in rat and dog.

GLP compliance:

no

Test material

Test material information

Constituent 1

Reference substance name:

2,6-xylidine

EC Number:

201-758-7

EC Name:

2,6-xylidine

Cas Number:

87-62-7

Molecular formula:

C8H11N

IUPAC Name:

2,6-dimethylaniline

Test material form:

liquid

Details on test material:

Name of test material: 2,6-dimethylaniline

Specific details on test material used for the study:

- Name of test material (as cited in study report): 2,6-dimethylaniline
- Analytical purity: >99 %
- Supplier Aldrich Chemical Co., Inc.

Radiolabelling:

no

Test animals

Species:

dog

Strain:

Beagle

Sex:

male

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Source: of Veterinary Medicine breeding program
- Age at study initiation: 2 years
- Fasting period before study: none
- Housing: individual
- Individual metabolism cages: yes
- Diet: Purina Field and Farm Dog Chow ad libitum
- Water: ad libitum
- Acclimation period: no data


ENVIRONMENTAL CONDITIONS
- standardized

Administration / exposure

Route of administration:

oral: capsule

Vehicle:

unchanged (no vehicle)

Details on exposure:

PREPARATION OF DOSING SOLUTIONS:
test substance was applied as gelatine capsules

Duration and frequency of treatment / exposure:

10 days

Doses / concentrations

Doses / concentrations 1

Dose / conc.:

25 mg/kg bw/day

Remarks:

2,4-DMA (group 1)

Doses / concentrations 2

Dose / conc.:

25 mg/kg bw/day

Remarks:

2,6-DMA (group 2)

No. of animals per sex per dose / concentration:

5 males per group

Control animals:

no

Positive control reference chemical:

not done

Details on study design:

The test substance was administered orally in gelatin capsules with no vehicle. Dogs were weighed every 5 days and doses were adjusted in order to maintain a constant weight/weight (mg/kg) dose.

Details on dosing and sampling:

METABOLITE CHARACTERISATION STUDIES
- Tissues and body fluids sampled: urine
- Time and frequency of sampling: days 1 and 10 of treatment, 24-h urine samples were collected
- From how many animals: 5 per group, samples were not pooled
- Method type(s) for identification GC-MS

Statistics:

Analysis of variance and Dunnett's test were used to compare the effects of PB, 3MC and SKF-525A on urinary excretory products of 2,4- and 2,6-DMA on Days 1 and 10 of treatment. A paired t-test was used to compare the effect of length of treatment (Day 1 vs. Day 10) on urinary excretory products within each rat and dog treatment group (10) . Differences were accepted at the (P < 0.05) level.

Results and discussion

Metabolite characterisation studies

Metabolites identified:

yes

Details on metabolites:

2,4-DMA was excreted in the urine of treated dogs largely as the parent compound, 6-hydroxy-2,4-DMA (6-HDMA), and 4-amino-3-methylbenzoic acid (4-AMBA). A trace level of N,2,4-trimethylamine was occasionally detected, but concentrations were too low for quantitation. 6-Hydroxylation was the major pathway in the dog, with a relatively much smaller amount of 4-AMBA, and no AAMBA, occurring as urinary metabolites. As with rats, 10 days of treatment with 2,4-DMA did not alter the urine content of 2,4-DMA or metabolites significantly. Dogs excreted approximately the same amount of 2,4-DMA/24-h period as rats, but total metabolite excretion was several-fold higher than for rats.

2,6-DMA was excreted in the urine of dogs as the parent compound, 4-HDMA and 2-amino-3-methylbenzoic acid (2-AMBA). A compound with an apparent molecular weight of 135 was also observed in the urine of dogs treated with 2,6-DMA. The mass spectrum of the unknown did not correlate with any standard on hand. Four possible structures of molecular weight 135 were proposed: 4-imino-3,5-dimethylquinone, its isomer 3-imino-2,4-dimethylquinone,
2,6-dimethyl-nitrosobenzene and 2-amino-3-methylbenzaldehyde, 2,6-Dimethylnitrosobenzene and 2-amino-3-methyl-benzaldehyde were eliminated on the basis of retention times and mass spectra . The formula 4-imino-2,6-dimethyl-quinone would appear to be the best choice for the unknown. 4-Hydroxy-2,6-DMA is a major metabolite of 2,6-DMA in the dog; hydroxylation occurring at the proposed location of the quinone's oxygen. Quinone formation could proceed in vivo or in vitro from the hydroxy compound. The possibility that the oxygen may be located meta to the nitrogen cannot be ruled out, but appears unlikely considering the metabolism of related compounds. N,2,6-Trimethylalanine, 2,6-dimethyl-nitrosobenzene and the glycine conjugate of 2-AMBA were also detected. These latter 4 compounds were observed in trace levels only and were not quantitated. The major excretory product of 2,6-DMA detected in dog urine after 1 or 10 days of treatment was 4-HDMA. Although the mean concentration of the metabolite recovered in urine decreased 3-fold with treatment, the difference between Day 1 and 10 means was not significant. The concentration of the 2-AMBA, however, did decrease significantly to about one-third that on Day 1.

Applicant's summary and conclusion

Conclusions:

Metabolism of 2,4-DMA in the dog was considerably different than in the rat, with 6-hydroxylation being the major pathway. Previous reports have demonstrated that the dog and other carnivores oxidized aniline preferentially in the ortho rather than in the para position. Rodents on the other hand, have shown a preference for hydroxylation in the para position, although o-hydroxylation does occur. This relationship appears to also hold true for bridged dianilines [i.e., 4,4'-methylene-bis-dianiline (MDA)]. Nevertheless, the dog did form a smaller amount of 4-AMBA.

Additionally, the major metabolite of 2,6-DMA in both the rat and dog was the p-hydroxy-product. The lack of N-acetylation of 4-AMBA, which appeared to be complete in the rat, is not an unexpected finding in the dog, a species known to be deficient in N-acetyltransferase activity. The lack of a significant effect of repeated 2,4-DMA or 2,6-DMA administration on the appearance of AAMBA or 4-HDMA indicates that neither xylidine induced its own metabolism .