2-methylpropan-2-ol

Basic toxicokinetics

Administrative data

Endpoint:

basic toxicokinetics

Type of information:

experimental study

Adequacy of study:

key study

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: No information on GLP status. Study used a single dose level.

Data source

Reference

Reference Type:

publication

Title:

Biotransformation of [12C]-and [2-13C]-Labeled Methyl tert-Butyl Ether, Ethyl tert-Butyl Ether, and tert-Butyl Alcohol in Rats: Identification of Metabolites in Urine by [13C] Nuclear Magnetic Resonance and Gas Chromatography/Mass Spectrometry

Author:

Bernauer U, Amberg A, Scheutzow D and Dekant W

Year:

1998

Bibliographic source:

Chem Res Toxicol 1998, 11, 651-658

Materials and methods

Objective of study:

metabolism

Test guideline

Qualifier:

equivalent or similar to guideline

Guideline:

OECD Guideline 417 (Toxicokinetics)

Deviations:

yes

Remarks:

The guideline states that for single dose administration, at least two dose levels should be used. This study used a single dose.

GLP compliance:

not specified

Test material

Test material information

Constituent 1

Reference substance name:

2-methylpropan-2-ol

EC Number:

200-889-7

EC Name:

2-methylpropan-2-ol

Cas Number:

75-65-0

Molecular formula:

C4H10O

IUPAC Name:

2-methylpropan-2-ol

Constituent 2

Reference substance name:

tertiary butyl alcohol

IUPAC Name:

tertiary butyl alcohol

Details on test material:

Preparation of radiolabeled tertiary butyl alcohol: An ethereal solution of CH3J was slowly added to Mg turnings covered by diethyl ether and iodine was added to initiate the Grignard reaction. The mixture was stirred at flux, an ethereal solution of [2-13C]-acetone was added, and the mixture was kept at flux for 2 h. After cooling, hydrolysis was performed by adding ice-cold, saturated NH4Cl solution. The aqueous layer was extracted 5 times with diethyl ether; ethereal layers were combined and dried over Na2CO3. The solvent was evaporated and the residue was distilled to yield [2-13C]-tertiary butyl alcohol (42% yield, 97% GC/FID purity). The structure of the reaction product was confirmed by GC/MS and [1H] and [13C] NMR.

Rats were treated with either natural carbon isotope ratio ([12C])- or [13C]-tertiary butyl alcohol. No information was provided on the source of the [12C]-labeled material.

Radiolabelling:

yes

Test animals

Species:

rat

Strain:

Fischer 344

Sex:

male

Details on test animals or test system and environmental conditions:

TEST ANIMALS:
-Source: Harlan Winkelmann (Borchen, FRG)
-Animals: 3 males/ experiment
-Weight at receipt: 220-260 g
-Housing: group housed in steel cages (4 rats/ cage) during quarantine; animals kept in individual metabolism cages for 3 days before and 72 hr after dosing
-Diet: Altromin provided ad libitum
-Water: tap water provided ad libitum

ENVIRONMENTAL CONDITIONS:
-Temperature (°C): 21
-Humidity: kept constant
-Photoperiod (hrs dark/ hrs light): 12 hours light/ dark

Administration / exposure

Route of administration:

oral: gavage

Vehicle:

corn oil

Details on exposure:

Tertiary butyl alcohol in corn oil was administered by gavage at a single dose level of 250 mg/kg bw. Three male rats received the test material at natural carbon isotope ratio while three males received [13C]-enriched test material.

Duration and frequency of treatment / exposure:

single exposure

Doses / concentrations

Remarks:

Doses / Concentrations:
[12C]- or [13C]-tertiary butyl alcohol by gavage (250 mg/kg bw in corn oil)

No. of animals per sex per dose / concentration:

3 males/ experiment

Control animals:

other: Control urine was collected prior to dosing

Positive control reference chemical:

No

Details on study design:

Control urine in rats was collected during the 3-day acclimation period prior to dosing.

Details on dosing and sampling:

Following dosing, all animals were kept in individual glass metabolism cages for 72 hours. Urine samples for analysis were collected in 24-h intervals for 48 hr. No information was provided on the collection of feces or volatile organics. No mass-balance of radioactivity was performed. Metabolites in urine were quantified and identified by [13C] NMR (for experiment conducted with [13C]-labeled compound) and GC/MS.

Statistics:

no information

Results and discussion

Metabolite characterisation studies

Metabolites identified:

yes

Details on metabolites:

Following oral administration of 250 mg/kg bw [12C]- or [13C]-tertiary butyl alcohol to male rats, [13C]-acetone, tertiary butyl alcohol, and its glucuronide were identified as minor metabolites; 2-methyl-1,2-propanediol, 2-hydroxyisobutyrate, and the presumed tertiary butyl alcohol sulfate were the major metabolites present. [13C]-Tertiary butyl alcohol as the origin of the excreted [13C]-acetone was confirmed by the mass spectra confirming the presence of [13C].

Any other information on results incl. tables

The purpose of this study was to investigate the biotransformation of tertiary butyl alcohol in male Fischer 344 rats following oral administration and compare the metabolic urinary profile of rats with that of a human male also administered [13C]-tertiary butyl alcohol by the oral route. Details of the study in a single human male are located in Section 7.10.5 of this submission. Based on a comparison of NMR spectra, the metabolic profile in both species was qualitatively similar. Conjugation of tertiary butyl alcohol with glucuronic acid resulted in urinary excretion of the glucuronide conjugate in both species. There was also indirect evidence for formation of a sulfate conjugate of tertiary butyl alcohol. Intensities of the [13C] signal in the NMR spectra of rat urine suggest this is a major pathway of tertiary butyl alcohol biotransformation in the rat. The authors suggested that low recovery of the presumed tertiary butyl alcohol sulfate in human urine was based on a low affinity of human sulfotransferase-(s) for tertiary butyl alcohol. The presence of 2-methyl-1,2-propanediol and 2-hydroxyisobutyrate in urine of both species suggest further oxidative metabolism of tertiary butyl alcohol. The likely pathway for the formation of these metabolites involves oxidation of tertiary butyl alcohol by cytochromes P450 to give 2-methyl-1,2-propanediol which is further oxidized to 2-hydroxyisobutyrate. [13C]-Acetone was also reported as a minor metabolite in male rats.

Applicant's summary and conclusion

Conclusions:

Interpretation of results (migrated information): bioaccumulation potential cannot be judged based on study results
The study showed that, in vivo, tertiary butyl alcohol is metabolized in rats to 2-methyl-1,2-propandiol, 2-hydroxyisobutyrate, unconjugated tertiary butyl alcohol, tertiary butyl alcohol glucuronide, tertiary butyl alcohol sulfate, and acetone. Since the study was designed to investigate only the urinary metabolic excretion profile and relative levels (major vs. minor) of urinary metabolites following oral administration of tertiary butyl alcohol and did not include mass-balance data, no conclusion can be made on the potential for bioaccumulation.

Executive summary:

In a metabolism study designed to investigate the biotransformation of tertiary butyl alcohol following oral administration and compare the urinary metabolic profile of rats and a human administered a single dose of tertiary butyl alcohol by the oral route, rats were administered a single dose of either [12C]- or [13C]-tertiary butyl alcohol in corn oil by oral gavage. There was a qualitatively similar metabolic profile in both rats and the single human. The major metabolites identified in the urine of both species were 2-methyl-1,2-propanediol and 2-hydroxyisobutyrate. Unconjugated tertiary butyl alcohol and tertiary butyl alcohol glucuronide were present as minor metabolites. Differences were also observed. In the rat, the presumed tertiary butyl alcohol sulfate was present as a major metabolite while in the single human, only traces of the sulfate were present. [13C]-Acetone was also reported as a minor metabolite in rats while no acetone was reported in human urine.