L-tryptophan

Genetic toxicity: in vivo

Administrative data

Endpoint:

in vivo mammalian cell study: DNA damage and/or repair

Remarks:

Type of genotoxicity: DNA damage and/or repair

Type of information:

experimental study

Adequacy of study:

key study

Study period:

1994

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: Acceptable, well documented publication/study report which meets basic scientific principles

Data source

Reference

Reference Type:

publication

Title:

An in vivo-in vitro replicative DNA synthesis (RDS) test using rat hepatocytes as an early prediction assay for nongenotoxic hepatocarcinogens - screening of 22 known positives and 25 noncarcinogens

Author:

Uno Y, Takasawa H, Miyagawa M, Inoue Y, Murata T & Yoshikawa K

Year:

1994

Bibliographic source:

Mutat Res 320, 189-205

Materials and methods

Test guideline

Qualifier:

no guideline followed

Principles of method if other than guideline:

Rats were administered test chemicals by single oral gavage or s.c. injection. Simple acute toxicity testing was first conducted, and the maximum tolerated dose (MTD) of each sample was set at about half the LD50 with a limit of 2000 mg/kg. Time-course experiments were then performed, and replicate DNA synthesis (RDS) observed at 24, 39 and 48 h after MTD and 1/2 MTD treatments with each compound.

GLP compliance:

no

Type of assay:

other: in vivo replicative DNA synthesis

Test material

Test material information

Constituent 1

Reference substance name:

L-tryptophan

EC Number:

200-795-6

EC Name:

L-tryptophan

Cas Number:

73-22-3

Molecular formula:

C11H12N2O2

IUPAC Name:

L-tryptophan

Details on test material:

not further specified

Test animals

Species:

rat

Strain:

Fischer 344

Sex:

male

Details on test animals or test system and environmental conditions:

Male F344 rats (9 weeks old) were obtained from Charles River Laboratories and housed four per cage in a room maintained at 20-24°C with a 12-h light/dark cycle. All animals received rodent chow and tap water ad libitum.

Administration / exposure

Route of administration:

other: oral gavage or s.c. injection

Vehicle:

corn oil

Duration of treatment / exposure:

single dosing

Frequency of treatment:

single dosing

Post exposure period:

24, 39 and 48 h

Doses / concentrations

Remarks:

Doses / Concentrations:
0, 1000 or 2000 mg/kg bw
Basis:

No. of animals per sex per dose:

4

Control animals:

yes, concurrent no treatment

Examinations

Tissues and cell types examined:

rat hepatocytes

Details of tissue and slide preparation:

Hepatocyte isolation and measurement of RDS incidence
Livers were perfused in situ with EGTA and collagenase type IV solution. Perfused livers were minced and filtered, and hepatocytes were suspended in Hanks’ balanced salt solution. Hepatocyte viability was determined using the conventional trypan blue exclusion test. About 2*10E+4 viable cells were seeded into each well of a Lab-Tek chamber and incubated for 4 h at 37°C, under 5% CO2 in Williams’ medium E containing 370 kBq/ml [3H]thymidine. RDS incidences were calculated as the percentage of [3H]thymidine-incorporating cells relative to 2000 hepatocytes counted per animal under the autoradiograph.

Evaluation criteria:

When the maximum RDS incidence was >= 2%, it was considered to indicate a positive response. An incidence less than 1% was judged to be negative. An incidence between 1 and 2% was considered equivocal, and a dose-response experiment was subsequently performed. In this second experiment - when the incidence was >= 1% at any of the doses - a final judgement of positive was made, whereas a response of < 1% was rated as negative.

Statistics:

The statistical significance of differences in hepatocyte viability was checked with Student’s t-test or the Welch test (alpha = 0.05)

Results and discussion

Test results

Sex:

male

Genotoxicity:

negative

Toxicity:

not specified

Any other information on results incl. tables

The RDS incidences (%) for the applied doses of 1000 or 2000 mg/kg bw (24, 39 or 48 hrs) were given with 0.6/0.5/0.4 and 0.3/0.9/0.9, respectively. In controls the RDS incidence was 0.5%.

Applicant's summary and conclusion

Conclusions:

Interpretation of results (migrated information): negative
For an evaluation of the applicability of an in vivo replicative DNA synthesis (RDS) test using rat hepatocytes, male F344 rats were dosed once (oral or s.c.) with 1000 or 2000 mg L-tryptophan/kg bw. The observation time of RDS was 24 – 48 hr. Under the conditions of this assay, L-tryptophan did not induce replicative DNA synthesis in rat hepatocytes and there was also no adverse effect concerning cell viability at the tested concentrations.