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Toxicological information

Genetic toxicity: in vitro

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Administrative data

Endpoint:
in vitro gene mutation study in mammalian cells
Type of information:
experimental study
Adequacy of study:
key study
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
Justification for type of information:
Data is from study report

Data source

Reference
Reference Type:
study report
Title:
Unnamed
Year:
2015
Report Date:
2015

Materials and methods

Test guideline
Qualifier:
according to
Guideline:
OECD Guideline 476 (In Vitro Mammalian Cell Gene Mutation Test)
Principles of method if other than guideline:
The purpose of this study was to assess toxic and genotoxic effects of test chemical on Chinese Hamster Ovary (CHO) cells by using several different in vitro-based assays, including genotoxicity tests based on the OECD Guideline No. 476 “In Vitro Mammalian Cell Gene Mutation Test”.
GLP compliance:
yes
Type of assay:
in vitro mammalian cell gene mutation test using the Hprt and xprt genes

Test material

Reference
Name:
Unnamed
Type:
Constituent
Test material form:
liquid
Details on test material:
Chemical Name: 5-Decanolide
Molecular Formula: C10H18O2
Molecular Weight: 170.25 g/mol
Consistency: Colorless to light yellow oily liquid
Activity (Clinical Indication):Industrial Chemical
Storage Condition: At room temperature (RT)in ventilated cabinets.
Safety Precautions: Safety precautions included use of protective clothing, gloves, masks and eye protection (glasses).

Method

Target gene:
Cells deficient in hypoxanthine-guanine phosphoribosyl transferase (HPRT) due to the mutation HPRT+/- to HPRT-/- are resistant to cytotoxic effects of 6-thioguanine (TG). HPRT proficient cells are sensitive to TG (which causes inhibition of cellular metabolism and halts further cell division since HPRT enzyme activity is important for DNA synthesis), so mutant cells can proliferate in the presence of TG, while normal cells, containing hypoxanthine-guanine phosphoribosyl transferase cannot. This in vitro test is an assay for the detection of forward gene mutations at the in hypoxanthine-guanine phosphoribosyl transferase (HPRT) locus on the X chromosomes of hypodiploid, modal No. 20, CHO cells. Gene and chromosome mutations are considered as an initial step in the carcinogenic process.The hypodiploid CHO cells are exposed to the test item with and without exogenous metabolic activation. Following an expression time the descendants of the treated cell population are monitored for the loss of functional HPRT enzyme.HPRT catalyses the transformation of the purine analogue 6-thioguanine (TG) and thus rendering the analogue cytotoxic to normal cells. Hence, cells with mutations in the HPRT gene cannot phosphoribosylate the analogue and survive treatment with TG.Therefore, mutated cells are able to proliferate in the presence of TG whereas the non-mutated cells die. However, the mutant phenotype requires a certain period of time before it is completely expressed. The phenotypic expression is achieved by allowing exponential growth of the cells for 7 days.
Species / strain
Species / strain / cell type:
Chinese hamster Ovary (CHO)
Details on mammalian cell type (if applicable):
Cell line used: Chinese Hamster Ovary (CHO) cells
- Type and identity of media: Ham’s F12K (Kaighn’s) Medium including 2 mM Glutamine supplemented with 10% Foetal Bovine Serum (FBS; qualified, EU-approved, South America origin), penicillin (50 U/ml) and streptomycin (50 µg/ml).
- Properly maintained: Yes
- Periodically checked for Mycoplasma contamination: No detection for mycoplasma was performed
- Periodically checked for karyotype stability: No detection for karyotype stability was performed
Additional strain / cell type characteristics:
other: Hypodiploid, modal No. 20
Cytokinesis block (if used):
Not specified
Metabolic activation:
with and without
Metabolic activation system:
S9 liver microsomal fraction obtained from Arcolor 1254-induced male Sprague-Dawley rats (Supplier: Molecular Toxicology Inc. via Trinova Biochem GmbH, Giessen, Germany)
Test concentrations with justification for top dose:
0, 0.5, 1.0, 2.5 or 5.0 mM
Vehicle / solvent:
- Vehicle(s)/solvent(s) used: Ethanol
- Justification for choice of solvent/vehicle:Phenethyl phenylacetate was easily dissolved in ethanol.
Controls
Untreated negative controls:
yes
Negative solvent / vehicle controls:
yes
Remarks:
Ethanol
True negative controls:
no
Positive controls:
yes
Positive control substance:
7,12-dimethylbenzanthracene
other: N-ethyl-N-nitrosourea (ENU)
Details on test system and experimental conditions:
METHOD OF APPLICATION: In medium with pre-incubation
DURATION- Preincubation period:One week involving 3 days of incubation with Hypoxanthine-aminopterin-thymidine (HAT) in medium as a mutant cleansing stage, followed by overnight incubation with hypoxanthine-thymidine (HT) in medium prior to a 3-4 days incubation in regular cell medium. After seeding and prior to treatment, the mutant-free cells were incubated for an additional of 24 hours.
- Exposure duration:3 hours
- Expression time (cells in growth medium): 7 days
- Selection time (if incubation with a selection agent): 14 days
- Fixation time (start of exposure up to fixation or harvest of cells): 7 days (harvest of cells)
SELECTION AGENT (mutation assays): 6-thioguanine (TG)
SPINDLE INHIBITOR (cytogenetic assays): Not applicable
STAIN (for cytogenetic assays): Crystal violet
NUMBER OF REPLICATIONS: A minimum of 2 replicates per dose concentration including negative and positive control.
NUMBER OF CELLS EVALUATED: 5 x 10 E5 cells were plated 7 days after treatment and whatever cells left, after 14 days of incubation with the selection medium, were evaluated.
DETERMINATION OF CYTOTOXICITY- Method: mitotic index; cloning efficiency; relative total growth; other: After being exposed to the test chemical for 3 hours, in the absence or presence of S9, cells were trypsinized and 0.5 x 10 E5 cells per well was seeded in duplicates from two parallel duplicate cultures into 6-well plates in fresh medium. The relative total growth and cytotoxicity was evaluated 24 and 48 hours after seeding.
- OTHER:
Rationale for test conditions:
No data
Evaluation criteria:
The plates were scored for total number of colonies by manual counting. As a result, the mutation frequency could be calculated
Statistics:
Mean were observed.

Results and discussion

Test results
Species / strain:
Chinese hamster Ovary (CHO)
Metabolic activation:
with and without
Genotoxicity:
negative
Cytotoxicity / choice of top concentrations:
no cytotoxicity
Vehicle controls validity:
valid
Untreated negative controls validity:
valid
Positive controls validity:
valid
Additional information on results:
No data
Remarks on result:
other: No mutagenic effect were observed.

Any other information on results incl. tables

GENE MUTATION TEST

 

Table 1A.Effect of 5-Decanolide exposure on gene toxicity in CHO cells. After being exposed to the test chemical for 3 hrs, cells was washed with sterile PBS and then incubated for 7 days at 37°C, 5% CO2. After 7 days, cells were re-seeded in new 6-well plates in the absence or presence of 10mM TG as a selection agent and returned to the incubator for 14 days at 37°C, 5% CO2. On day 15, all 6-well plates were stained with crystal violet and the number of colonies were counted manually. The results are presented as the total number of colonies found in the number of independent wells analyzed (e.g. 0 colonies in 4 wells will give 0/4) (n = 2 samples from 2 independent cultures).

 

 

With S9

Without S9

 

with TG

without TG

with TG

without TG

Neg. control

0/4

773/4

0/4

856/4

Pos. control

0/4

788/4

36/4

769/4

0.5 mM

0/4

773/4

0/4

720/4

1.0 mM

0/4

603/4

0/4

747/4

2.5 mM

0/4

666/4

0/4

725/4

5.0 mM

0/4

611/4

0/4

403/4

 

 

 

Table 1B.Mutation frequency in CHO cells after 3 hrs of exposure to 5-Decanolide in the absence or presence of 4% S9 liver microsomal fraction. N/A, no colonies present in the samples selected with TG, i.e. no mutation frequency could be determined.

 

 

With S9

Without S9

Neg. control

N/A

N/A

Pos. control

N/A

4.18x10-4

0.5 mM

N/A

N/A

1.0 mM

N/A

N/A

2.5 mM

N/A

N/A

5.0 mM

N/A

N/A

Applicant's summary and conclusion

Conclusions:
Based on the results of the current study, it can be concluded that the given test chemical does not give rise to gene mutations when exposed at ≤ 5.0 mM for 3 hrs or more, and it does not give rise to cytotoxicity in CHO cells at concentrations of ≤ 5.0 mM.
Executive summary:

An in vitro mammalian cell gene mutation study was designed and conducted to determine the genotoxicity profile of the given test chemical as per OECD Guideline 476 (In Vitro Mammalian Cell Gene Mutation Test) when administered to Chinese Hamster Ovary (CHO) cells.

A preliminary dose-finding study was conducted prior to the main study. A range of different test chemical concentrations were tested in 96-well plates and analyzed by two commonly used assays, i.e. the colorimetric assay of 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) and the bicinchoninic acid (BCA) assay to assess cell viability and protein concentration, respectively.

From the basis of the results from the MTT and BCA assays, test concentrations of the test chemical was chosen to be included in the gene toxicity test.

In the genotoxicity test, the given test chemical was administered to CHO cells for 3 hrs at the dose levels of 0, 0.5, 1.0, 2.5 or 5.0 mM and in the absence or presence of exogenous metabolic activation. CHO cells representing the negative controls were exposed to the vehicle. Positive controls, such as N-ethyl-N-nitrosourea (ENU) experiments without metabolic activation and 7,12-dimethylbenz(a) anthracene in experiments with metabolic activation, were also included in each test.

The results showed indication of gene mutations occurring only in the positive control ENU while no other treatment gave rise to gene toxicity. No cytotoxic effects was observed in CHO cells when exposed towards test chemical for 3 hrs in the absence or presence of S9 liver microsomal fraction.

Based on the results of the current study, it can be concluded that the given test chemical does not give rise to gene mutations when exposed at ≤ 5.0 mM for 3 hrs or more, and it does not give rise to cytotoxicity in CHO cells at concentrations of ≤ 5.0 mM.