Carbazole

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:

other: Acceptable, well-documented publication which meets basic scientific principles

Data source

Reference

Reference 1

Reference Type:

publication

Title:

The Metabolism of Carbazole in Rats and Rabbits

Author:

Johns SR and Wright SE

Year:

1964

Bibliographic source:

J Med Chem 7 (2), 158-161

Reference 2

Reference Type:

publication

Title:

Metabolism of Carbazole

Author:

Johns SR and Wright SE

Year:

1962

Bibliographic source:

Experientia 18, 416-417

Materials and methods

Objective of study:

excretion

metabolism

Test guideline

Qualifier:

no guideline followed

Principles of method if other than guideline:

Isolation and identification of metabolites of carbazole in the urine of rats and rabbit after i.p. injection or oral administration using non labeled and C14-radiolabeled carbazole

GLP compliance:

no

Test material

Test material information

Constituent 1

Reference substance name:

Carbazole

EC Number:

201-696-0

EC Name:

Carbazole

Cas Number:

86-74-8

Molecular formula:

C12H9N

IUPAC Name:

9H-carbazole

Details on test material:

- Name of test material (as cited in study report): carbazole
C14-radiolabeled carbazole was synthezised in a three step synthesis starting from C14-aniline.
- Analytical purity: no data
- Specific activity (if radiolabelling): 6.0 x 10E5 d.p.m./mg
- Locations of the label (if radiolabelling): C-atom in one benzene-nucleus
- no further information on test substance

Radiolabelling:

yes

Test animals

Species:

other: rats and rabbit

Strain:

not specified

Sex:

not specified

Administration / exposure

Route of administration:

other: rats: intraperitoneal injection; rabbit: oral, gavage

Vehicle:

other: rats: propylene glycol; rabbit: acacia suspension

Duration and frequency of treatment / exposure:

single dose exposure

Doses / concentrations

Remarks:

Doses / Concentrations:
rats: 4 mg/kg; rabbit: 1 g; rats (radiolabeled test compound): 4.13 x 10E5 d.p.m./rat

No. of animals per sex per dose / concentration:

rats: no data; rabbit: 1; rats (radiolabeled test compound): total of 6 animals in 3 groups (2 animals per group)

Control animals:

no

Details on dosing and sampling:

METABOLITE CHARACTERISATION STUDIES
- Tissues and body fluids sampled: urine
- Time and frequency of sampling: rats: for 3 days; rabbit: daily for 3 days, rats (radiolabeled test compound): daily for 3 days for each of the 3 groups
- From how many animals: rats: no data; rabbit: 1 animal; rats (radiolabeled test compound): 6 animals
- Method type(s) for identification: co-chromatography with authentic samples on paper and thin-layer chromatography, liquid scintillation counting

TREATMENT FOR CLEAVAGE OF CONJUGATES (if applicable): 0.5 N hydrochloric acid, ß-glucuronidase

Results and discussion

Toxicokinetic / pharmacokinetic studies

Details on excretion:

65% of the radioactivity, administered as C14-carbazole to rats (4.13 x 10E5 d.p.m./rat), was excreted in urine within 3 days (day 1: 61%; day 2: 3.5%; day 3: 0.5%; mean for six rats).

Metabolite characterisation studies

Metabolites identified:

yes

Details on metabolites:

In the urine of rabbit and rats, the glucuronide of 3-hydroxycarbazole was identified as major metabolite of carbazole.

Any other information on results incl. tables

Rabbit

After oral application of 1 g of carbazole, a two-fold increase in glucuronide content was observed in urine during the first day returning to normal after 3 days. Isolation of glucuronides from urine resulted in a gum which was methylated and acetylated to form the tri-O-acetylglucuronide methyl ester. From the reaction mixture, three products were isolated by chromatography over neutral alumina: 3-methoxycarbazole as byproduct of the processing of urine, a tri-O-acetyl methyl ester of a hydroxycarbazole glucuronide as major metabolite, and a small amount of a third product, also a tri-O-acetyl methyl ester of a glucuronide with a symmetrically disubstituted carbazole structure conjugated as indicated by IR spectra.

 

After hydrolysis of the hydroxycarbazole glucuronide using ß-glucuronidase, the resulting phenolic product was identified as 3-hydroxycarbazole by comparative paper and thin-layer chromatography with an authentic reference sample.

 

Rat

In the urine of rats treated i.p. with a single carbazole dose of 4 mg/kg, a major metabolite was isolated and purified by paper chromatography using several solvent systems. After hydrolysis of the purified product with 0.5 N hydrochloric acid, the phenolic product showed the same chromatographic characteristics as the hydrolysis product from rabbit urine. Identification was accomplished by chromatographic comparison with an authentic sample and the identity proven to be 3-hydroxycarbazole.

 

After i.p. injection of radiolabeled carbazole into rats, the three-day urine contained 65% of radioactivity (mean of 6 rats). Acid hydrolysis resulted in an ether-extractable fraction which could be further separated by paper chromatography. Distribution of radioactivity in different fractions of urine was as follows.

 

Initial dose				100 % (2.48 x 10E6 d.p.m.)
	Urine                             acid hydrolysis			65 % (1.61 x 10E6 d.p.m.)
		ether extract                            paper chromatography		55 % (1.36 x 10E6 d.p.m.)
			moving band radioactivity (isolated 3-hydro­xycarbazole)	33 % (0.82 x 10E6 d.p.m.)
			starting line radioactivity (at least 2 more metabolites)	20 % (0.50 x 10E6 d.p.m.)
		aqueous phase		10 % (0.25 x 10E6 d.p.m.)

 

Elution of the moving band radioactivity with methanol yielded 3-hydroxycarbazole (33%) as demonstrated by co-chromatography with an authentic sample. Re-chromatography of the starting-line radioactivity with a more polar solvent revealed at least two more phenolic products with unknown structure (possibly di- and polyhydroxylated carbazoles).

Applicant's summary and conclusion

Conclusions:

Interpretation of results (migrated information): low bioaccumulation potential based on study results
In experiments using rats and rabbit, the glucuronide of 3-hydroxycarbazole was demonstrated to be the major metabolite.
After administration of C14-labeled carbazole to rats, 65% of the radioactivity administered was found in the 3 d urine. After acid hydrolysis of the urine, 55% of the total radioactive dose distributed into an ether extract of the urine. After further purification, 33% of the dose were isolated from the ether extract as 3-hydroxycarbazole. Another 10% of total radioactivity in the ether extract could be attributed to at least two more phenolic carbazole derivatives more polar than 3-hydroxcarbazole (possibly di- and polyhydroxylated carbazoles).