Tetramethyl orthosilicate

Genetic toxicity: in vitro

Administrative data

Endpoint:

in vitro cytogenicity / chromosome aberration study in mammalian cells

Remarks:

Type of genotoxicity: chromosome aberration

Type of information:

migrated information: read-across from supporting substance (structural analogue or surrogate)

Adequacy of study:

key study

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: see 'Remark'

Remarks:

The study was conducted according to the appropriate OECD test guideline, and in compliance with GLP. The original study was considered reliability 1. Read-across to the registered substance is considered scientifically justified and is reliability 2.

Data source

Reference

Reference Type:

study report

Title:

Unnamed

Year:

2002

Report date:

2002

Materials and methods

Test guideline

Qualifier:

according to guideline

Guideline:

OECD Guideline 473 (In Vitro Mammalian Chromosome Aberration Test)

GLP compliance:

yes

Type of assay:

in vitro mammalian chromosome aberration test

Test material

Test material information

Constituent 1

Reference substance name:

Tetraethyl orthosilicate

EC Number:

201-083-8

EC Name:

Tetraethyl orthosilicate

Cas Number:

78-10-4

IUPAC Name:

tetraethyl orthosilicate

Method

Species / strain

Species / strain / cell type:

Chinese hamster Ovary (CHO)

Metabolic activation:

with and without

Metabolic activation system:

Aroclor induced rat liver S9

Test concentrations with justification for top dose:

125 to 1500 µg/ml (without activation, 4 and 20h exposure), and 500 to 2080 µg/ml (with activation 4 hour exposure)

Vehicle / solvent:

- Vehicle(s)/solvent(s) used: DMSO
- Justification for choice of solvent: based on information provided by the Sponsor and compatibility with the target cells.

Controls

Controls 1

Untreated negative controls:

no

Negative solvent / vehicle controls:

yes

True negative controls:

no

Positive controls:

yes

Positive control substance:

mitomycin C

Remarks:

(without activation)

Controls 2

Untreated negative controls:

no

Negative solvent / vehicle controls:

yes

True negative controls:

no

Positive controls:

yes

Positive control substance:

cyclophosphamide

Remarks:

(with activation)

Details on test system and experimental conditions:

METHOD OF APPLICATION: in medium

DURATION

- Exposure duration: 4h / 20h (-S9), 4h (+S9)

- Expression time (cells in growth medium): 20h

- Fixation time (start of exposure up to fixation or harvest of cells): 20h

NUMBER OF REPLICATIONS: duplicate flasks

NUMBER OF CELLS EVALUATED: 200 metaphase spreads (100 per duplicate flask), per concentration.

DETERMINATION OF CYTOTOXICITY

- Method: percentage total growth

Evaluation criteria:

Cells examined for numerical and structural aberrations, and statistical significance calculated. For the result to be positive, the increase in aberrations must be statistically significant and dose related.

Toxicity is defined as a 50 % or greater reduction in cell growth.

Statistics:

The number and type of aberrations found, the percentage of structurally and numerically damaged cells (% aberrant cells) in the total population examined and mean aberrations per cell were calculated for each group. Fisher's exact test was used to compare pairwise the percent aberrant cells of each treatment group with that of the solvent control.

Statistical analysis of the percent aberrant cells was performed using the Fisher's exact test. Fisher's test was used to compare pairwise the percent aberrant cells of each treatment group with that of the solvent control. In the event of a positive Fisher's test at any test article dose level, the Cochran-Armitage test was used to measure dose-responsiveness.

Results and discussion

Test results

Species / strain:

Chinese hamster Ovary (CHO)

Metabolic activation:

with and without

Genotoxicity:

negative

Cytotoxicity / choice of top concentrations:

cytotoxicity

Remarks:

with metabolic activation: 1250 µg/ml; without metabolic activation: 1250 µg/ml

Vehicle controls validity:

valid

Untreated negative controls validity:

not applicable

Positive controls validity:

valid

Additional information on results:

TEST-SPECIFIC CONFOUNDING FACTORS
- Effects of pH: at highest test concentration was 7.4
- Effects of osmolality: checked

RANGE-FINDING/SCREENING STUDIES: Substantial toxicity (i.e., at least 50% cell growth inhibition, relative to the solvent control) was observed at dose level 2080 µg/ml in the non-activated 4 and 20 hour exposure groups and in the S9 activated 4 hour exposure group.


COMPARISON WITH HISTORICAL CONTROL DATA: The percentage of cells with structural aberrations in the test article-treated groups was statistically increased above that of the solvent control at dose level 1250 µg/ml (p

Remarks on result:

other: strain/cell type: Chinese hamster ovary cells

Remarks:

Migrated from field 'Test system'.

Any other information on results incl. tables

For the chromosome aberration assay, CHO cells were seeded at approximately 5 x l0 5 cells/25 cm2 flask and were incubated at 37+/- 1C  in a humidified atmosphere of 5+/-1% CO2 in air for 16-24 hours.

Treatment time: 4hrs
Recovery time: 16 hrs
Harvest time: 20 hrs
S9: none
Toxicity at highest dose scored: 52% at 1250 µg/ml
Mitotic index reduction: 4%
Lowest Effective Dose (LED) for structural aberrations: none
LED for numerical aberrations: none

Treatment time: 20 hrs
Recovery time: 0 hrs
Harvest time: 20 hrs
S9: none
Toxicity at highest dose scored: 56% at 1250 µg/ml
Mitotic index reduction: none
Lowest Effective Dose (LED) for structural aberrations: none
LED for numerical aberrationTreatment time: 4hrs

Treatment time: 4 hrs
Recovery time: 16 hrs
Harvest time: 20 hrs
S9: yes
Toxicity at highest dose scored: 54% at 1250 µg/ml
Mitotic index reduction: 10%
Lowest Effective Dose (LED) for structural aberrations: none
LED for numerical as: none

Summary of results of chromosome aberration test (200 cells scored)

Concentration µg/ml	S9 activation	Treatment time (hours)	Mean mitotic index	Aberrations per cell (Mean +/- SD)	Cells with aberrations
					Numerical (%)	Structural (%)
Solvent control	without	4	15.7	0.015 +/- 0.122	3.0	1.5
250		4	16.0	0.005 +/- 0.071	2.5	0.5
750		4	15.2	0.005 +/- 0.071	3.0	0.5
1250		4	15.0	0.010 +/- 0.100	2.5	1.0
Positive control		4	15.5	0130 +/- 0.484	4.0	10.0
Solvent control	with	4	16.6	0	2.0	0
500		4	15.1	0.005 +/- 0.071	2.5	0.5
750		4	15.7	0	1.5	0
1250		4	14.9	0.030 +/- 0.198	3.5	2.5
Positive control		4	13.5	0.200 +/- 0.576	3.0	14.0
Solvent control	without	20	15.6	0.010 +/-0.100	2.0	1.0
250		20	14.8	0	3.5	0
750		20	15.6	0.010 +/- 0.141	2.0	0.5
1500		20	15.9	0.005 +/- 0.071	2.5	0.5
Positive control		20	15.3	0.210 +/- 0.598	3.5	15.0

The percentage of structurally damaged cells in the mitomycin (positive  control in non-activated system) treatment (15%) was statistically  significant.

The percentage of structurally damaged cells in the cyclophosphamide  (positive control in activated system) treatment (14%) was statistically  significant.

Applicant's summary and conclusion

Conclusions:

Interpretation of results (migrated information):
negative with and without metabolic activation

Tetraethyl orthosilicate, CAS No. 78-10-4, has been tested in CHO cells a reliable study according to OECD 473 and in compliance with GLP. A slight increase in the number of structural chromosome aberrations above the concurrent vehicle controls was observed; this was considered not of biological significance as the percentage of aberrant cells in the treated group, 2.5%, was within the historical control range of 0.0% to 6.5% . No increase in numerical chromosome aberrations was observed. It is concluded that the test substance is negative for the induction of chromosome aberrations under the conditions of the test.