Indole

Basic toxicokinetics

Administrative data

Endpoint:

basic toxicokinetics in vivo

Type of information:

experimental study

Adequacy of study:

key study

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

data from handbook or collection of data

Justification for type of information:

data is from peer reviewed journals

Data source

Reference

Reference Type:

publication

Title:

Metabolism of the test chemical in rat

Author:

King et.al

Year:

1966

Bibliographic source:

Biochem. J. (1966)

Materials and methods

Objective of study:

excretion

metabolism

Test guideline

Qualifier:

according to guideline

Guideline:

other: As mentioned below

Principles of method if other than guideline:

To study the metabolic fate of the test chemical in rats

GLP compliance:

not specified

Test material

Radiolabelling:

yes

Test animals

Species:

rat

Strain:

Wistar

Sex:

female

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Source: Animal Supplies (London) Ltd.]
- Age at study initiation:
- Weight at study initiation: weight about 200g.
- Housing:
- Diet (e.g. ad libitum): maintained on 25g./day of Diet 41B (Joseph Rank Ltd.)
- Water (e.g. ad libitum): free access to water
- Acclimation period:

ENVIRONMENTAL CONDITIONS
- Temperature (°C):
- Humidity (%):
- Air changes (per hr):
- Photoperiod (hrs dark / hrs light):

IN-LIFE DATES: From: To:

Administration / exposure

Route of administration:

oral: gavage

Vehicle:

arachis oil

Details on exposure:

PREPARATION OF DOSING SOLUTIONS: [14C]Indole and unlabelled indole were administered orally as solutions in arachis oil (5%, w/v).

DIET PREPARATION
- Rate of preparation of diet (frequency):
- Mixing appropriate amounts with (Type of food):
- Storage temperature of food:

Duration and frequency of treatment / exposure:

3 days

Doses / concentrations

Remarks:

64- 80 mg/kg

No. of animals per sex per dose / concentration:

number not specified

Control animals:

yes, concurrent vehicle

Details on study design:

- Dose selection rationale: no data available
- Rationale for animal assignment (if not random):

Details on dosing and sampling:

TOXICOKINETIC / PHARMACOKINETIC STUDY (Absorption, distribution, excretion) : Rats given [14C]indole were placed in a plastic metabolism chamber through which a current of air was drawn. The outgoing air was passed through two wash-bottles in series containing acetone at - 30° to trap volatile organic compounds and then through two wash-bottles containing 4N-NaOH to remove respiratory CO2.
- Tissues and body fluids sampled (delete / add / specify): urine, faeces, blood, plasma, serum or other tissues, cage washes, bile : urine and faeces
- Time and frequency of sampling: Urine and faeces were collected daily. After 3 days the animals were killed and e radioactivity of the tissues was determined.
- Other:
METABOLITE CHARACTERISATION STUDIES
- Tissues and body fluids sampled (delete / add / specify): urine, faeces, tissues, cage washes, bile : urine and faeces, bile
- Time and frequency of sampling: Urine and faeces were collected daily. After 3 days the animals were killed and e radioactivity of the tissues was determined.
- From how many animals: (samples pooled or not) : All the test animals
- Method type(s) for identification (e.g. GC-FID, GC-MS, HPLC-DAD, HPLC-MS-MS, HPLC-UV, Liquid scintillation counting, NMR, TLC) :The urine was examined for metabolites qualitatively by chromatography
and radioautography, and quantitatively by reverse isotope dilution.
- Limits of detection and quantification:
- Other: Polythene cannulae were fitted into the common bile duct of rats and the animals were then allowed to recover from the operation for 24hr. They were then dosed orally with [14C]- indole and bile was collected for 48hr. into a tube kept at - 10° to minimize any possible action of biliary enzymes on conjugates. The total radioactivity of the bile was estimated and that of any metabolite present by reverse isotope dilution.

Results and discussion

Main ADME results

Type:

excretion

Results:

81% appears in the urine, 11% in the faeces and 2.4% as carbon dioxide in the expired air

Toxicokinetic / pharmacokinetic studies

Details on excretion:

>80% of the radiolabel in the urine within 48 h.

Toxicokinetic parameters

Test no.:

#1

Toxicokinetic parameters:

other: 81% appears in the urine, 11% in the faeces and 2.4% as carbon dioxide in the expired air

Metabolite characterisation studies

Metabolites identified:

yes

Details on metabolites:

The chromatograms and radioautographs of the urine from rats dosed with indole revealed the presence of several metabolites, but most of the radioactivity was accounted for by six metabolites, namely indoxyl sulphate, indoxyl glucuronide, N-formylanthranilic acid, 5-hydroxyoxindole sulphate, 5-hydroxyoxindole glucuronide and an unidentified metabolite.Bile samples were collected at 48 hshowed that 0.56, 0.80, and 0.82% of the radiolabel was present as 5-hydroxyindole, 3-hydroxyindole sulfate, and total 3-hydroxyindole metabolites, respectively

Any other information on results incl. tables

When fed to rats, the 14C of [14C]indole (dose 70-80mg/kg) was fairly rapidly excreted, and in 2 days an average of 81% appears in the urine, 11% in the faeces and 2.4% as carbon dioxide in the expired air. Radioactivity was excreted in the urine as indoxyl sulphate (50% of the dose), indoxyl glucuronide (11%), oxindole (1.4%), isatin (5.8%), 5-hydroxyoxindole conjugates (3-1%), N-formylanthranilic acid (0.5%) and unchanged indole (0.07%). The faeces contain indoxyl sulphate (0.4% of the dose) and indole (0.2%), but the major metabolites have not been identified. When fed to rats with biliary cannulae an average of5.6% of a dose of [14C]indole (20-60 mg/kg) was excreted in the bile in 2 days. Radioactivity was present as indoxyl sulphate (0.8% dose) and 5-hydroxyoxindole conjugates (0-6%).Rats further metabolize indoxyl into N-formylanthranilic acid and anthranilic acid, and oxindole into 5-hydroxyoxindole.

Applicant's summary and conclusion

Conclusions:

When fed to rats, the 14C of [14C]indole (dose 70-80mg/kg) was fairly rapidly excreted, and in 2 days an average of 81% appears in the urine, 11% in the faeces and 2.4% as carbon dioxide in the expired air. Radioactivity was excreted in the urine as indoxyl sulphate (50% of the dose), indoxyl glucuronide (11%), oxindole (1.4%), isatin (5.8%), 5-hydroxyoxindole conjugates (3-1%), N-formylanthranilic acid (0.5%) and unchanged indole (0.07%). The faeces contain indoxyl sulphate (0.4% of the dose) and indole (0.2%), but the major metabolites have not been identified. When fed to rats with biliary cannulae an average of5.6% of a dose of [14C]indole (20-60 mg/kg) was excreted in the bile in 2 days. Radioactivity was present as indoxyl sulphate (0.8% dose) and 5-hydroxyoxindole conjugates (0-6%).Rats further metabolize indoxyl into N-formylanthranilic acid and anthranilic acid, and oxindole into 5-hydroxyoxindole.

Executive summary:

A study was conducted to determine the metabolic fate of the test chemical in rats. Female Wistar rats were used for the study. [14C]Indole and unlabelled indole were administered orally as solutions in arachis oil (5%, w/v). Rats given [14C]indole were placed in a plastic metabolism chamber through which a current of air was drawn. The outgoing air was passed through two wash-bottles in series containing acetone at - 30° to trap volatile organic compounds and then through two wash-bottles containing 4N-NaOH to remove respiratory CO2. Urine and faeces were collected daily. After 3 days the animals were killed and e radioactivity of the tissues was determined. The urine was examined for metabolites qualitatively by chromatography and radioautography, and quantitatively by reverse isotope dilution. Polythene cannulae were fitted into the common bile duct of rats and the animals were then allowed to recover from the operation for 24hr. They were then dosed orally with [14C]- indole and bile was collected for 48hr. into a tube kept at - 10° to minimize any possible action of biliary enzymes on conjugates. The total radioactivity of the bile was estimated and that of any metabolite present by reverse isotope dilution.Radioactive materials were counted as samples of infinite thickness with highsensitivity low-background counting equipment (Panax Equipment Ltd.) incorporating the MX 157 anti-coincidence Geiger Counter assembly (Mullard Ltd.). Urine and bile were counted as such, tissues and faeces as homogenates in water, and the¹⁴CO₂in the expired air as Ba^l4CO₃. Samples were counted for periods of time sufficient to record at least 10³counts net and to obtain a standard error of the mean less than 2%. When fed to rats, the 14C of [14C]indole (dose 70-80mg/kg) was fairly rapidly excreted, and in 2 days an average of 81% appears in the urine, 11% in the faeces and 2.4% as carbon dioxide in the expired air. Radioactivity was excreted in the urine as indoxyl sulphate (50% of the dose), indoxyl glucuronide (11%), oxindole (1.4%), isatin (5.8%), 5-hydroxyoxindole conjugates (3-1%), N-formylanthranilic acid (0.5%) and unchanged indole (0.07%). The faeces contain indoxyl sulphate (0.4% of the dose) and indole (0.2%), but the major metabolites have not been identified. When fed to rats with biliary cannulae an average of5.6% of a dose of [14C]indole (20-60 mg/kg) was excreted in the bile in 2 days. Radioactivity was present as indoxyl sulphate (0.8% dose) and 5-hydroxyoxindole conjugates (0-6%).Rats further metabolize indoxyl into N-formylanthranilic acid and anthranilic acid, and oxindole into 5-hydroxyoxindole.