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Toxicological information

Basic toxicokinetics

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Administrative data

Endpoint:
basic toxicokinetics in vitro / ex vivo
Type of information:
experimental study
Adequacy of study:
key study
Study period:
No data
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
other: Very well designed and described study. Fully relevant to identify the mechanism of metabolism of quinoline in rat and in human. However, it's only an in vitro study

Data source

Reference
Reference Type:
publication
Title:
Cytochrome P450 species involved in the metabolism of quinoline
Author:
Reigh G, McMahon H, Ishizaki M, Ohara T, Shimane K, Esumi Y, Green C, Ninomiya S
Year:
1996
Bibliographic source:
Carcinogenesis 17(9): 1989-1996

Materials and methods

Objective of study:
metabolism
Test guideline
Qualifier:
no guideline available
Principles of method if other than guideline:
Analysis of the metabolites obtained by incubation of quinoline with rat and human microsomes using cDNA-expressed cytochrome P450s, correlations with specific cytochrome P450-linked monooxygenase activities in human liver microsomes and inhibition by specific inhibitors and antibodies.
GLP compliance:
not specified

Test material

Reference
Name:
Unnamed
Type:
Constituent
Details on test material:
Supplier: Nacalai Tesque (Japan)
No further data
Radiolabelling:
no

Test animals

Species:
other: rat and human
Details on test animals and environmental conditions:
liver microsomes from male Sprague Dawley rats treated with 3-methylcholanthrene
microsomes from human liver
microsomes from the human B lymphoblastoid cell line AHH-1 expressing individual human and rat CYP enzymes and human epoxyde hydrolase

Administration / exposure

Route of administration:
other: incubation in medium
Vehicle:
unchanged (no vehicle)
Details on exposure:
In each case the incubation mixture (0.5 ml) contained the following, unless otherwise stated: 1 mg/ml microsomal protein, 1 mg/ml NADP+, 1 mg/ml glucose 6-phosphate, 0.4 U/ml glucose 6-phosphate dehydrogenase and 0.05 mM quinoline. NADP+, glucose 6-phosphate and quinoline were prepared in potassium phosphate buffer (0.1 M, pH 7.4), but in the case of the cDNA-expressed CYP2A6 Tris-HCI buffer (0.1 M, pH 7.4) was used as the activity of CYP2A6 is inhibited by phosphate. Incubation was at 37°C for 1-2 h, depending on the experiment and reactions were terminated by the addition of 1/10th of the reaction volume of 10% trichloroacetic acid and centrifuged at 14 000 g to remove precipitated protein. Supernatants were passed through a 0.4 µm filter prior to injection onto the HPLC column.
Duration and frequency of treatment / exposure:
1-2 h once
Doses / concentrations
Remarks:
Doses / Concentrations:
0.05 mM
No. of animals per sex per dose:
not relevant
Positive control:
none
Details on study design:
All these different experiments were carried out:
- Identification of metabolites : using a UV-vis photodiode array detector attached to the HPLC column, metabolite peaks were identified by comparison of their UV spectra with UV spectra of the standard compounds or to published spectra.

- Comparison of quinoline metabolite profiles in human and rat liver microsomes

- Incubation of quinoline with Gentest microsomes (human): prepared from a B lymphoblastoid cell line individually expressing human CYP1A1, 1A2, 2A6or, 2B6, 2C9 or, 2D6, 2E1 or and 3A4 or (or; NADPH cytochrome P450 reductase) and with control microsomes from a cell line containing vector only and a cell line expressing only the reductase: to identify the CYP enzymes involved in the formation of the different metabolites.

- Correlation of quinoline metabolite formation with specific CYP-linked activities in human liver microsomes

- Inhibition of quinoline metabolism in human liver microsomes by specific antibodies and inhibitors

- kinetic analysis of quinoline metabolism in human liver microsomes to establish whether metabolite formation was mono- or biphasic
Details on dosing and sampling:
No data about quantification and detection limits of the HPLC method
Statistics:
The correlation analysis was performed using linear regression analysis and calculation of correlation coefficients.

Results and discussion

Preliminary studies:
no data

Toxicokinetic / pharmacokinetic studies

Details on absorption:
not studied
Details on distribution in tissues:
not studied
Details on excretion:
not studied

Metabolite characterisation studies

Metabolites identified:
yes
Details on metabolites:
3-hydroxyquinoline
quinoline -1-oxide
quinoline-5,6-diol
quinoline-5,6-epoxide

Any other information on results incl. tables

CYP2A6 is the principal cytochrome P450 involved in the formation of quinoline-1-oxide in human liver microsomes (correlation coefficient r=0.95), but is formed in only minute quantities in rat liver microsomes. CYP2E1 is the principal cytochrome P450 involved in the formation of 3-hydroxyquinoline (r=0.93) in human liver microsomes and is involved in the formation in rat liver microsomes. A high correlation coefficient (r=0.91) between CYP2A6 activity and quinoline-5,6-diol formation in human liver microsomes was observed, but this most likely reflects the involvement of CYP2A6 in the formation of quinoline-5,6­epoxide, from which the quinoline-5,6-diol is formed, as conversion of quinoline-5,6-epoxide to quinoline-5,6-diol on incubation of the epoxide with CYP2A6 could not be demonstrated.

A cDNA-expressed human microsomal epoxide hydrolase, however, efficiently converted the epoxide to the diol and the microsomal epoxide inhibitor cyclohexene oxide inhibited quinoline-5,6-diol formation in rat liver microsomes.

A preliminary kinetic analysis of quinoline metabolism in human liver microsomes was carried out and Eadie-Hofstee plots indicate that the formation of quinoline-5,6-diol is monophasic, while that of quinoline-1-oxide and 3-hydroxyquinoline is biphasic.

Applicant's summary and conclusion

Conclusions:
Interpretation of results (migrated information): other:
The CYP enzymes that are involved in the metabolism of quinoline in rat and human have been identified. Differences between rat and human metabolism profiles have also been observed: Q-1-oxide is barely detectable when quinoline is incubated with rat microsomes while it is clearly observed with human microsomes. On the opposite, the epoxide metabolite is detected in higher quantities with the rat microsomes.
Executive summary:

An in vitro metabolism study was performed with quinoline using incubation of rat or human liver microsomes and microsomes expressing specific individual CYP enzymes of rat or human.

The CYP enzymes that are involved in the metabolism of quinoline in rat and human have been identified. Differences between rat and human metabolism profiles have also been observed: Q-1-oxide is barely detectable when quinoline is incubated with rat microsomes while it is clearly observed with human microsomes. On the opposite, the epoxide metabolite is detected in higher quantities with the rat microsomes.