2,4,6,8,10-pentamethylcyclopentasiloxane

Endpoint summary

Key value for chemical safety assessment

Genetic toxicity in vitro

Description of key information

Gene mutation (Bacterial reverse mutation assay / Ames test): Negative with and without activation in all strains tested (OECD TG 471) (Harlan Cytotest Cell Research, 2010a)
Cytogenicity in mammalian cells: Negative with and without activation in cultured human lymphocytes (OECD 473) (Harlan Cytotest Cell Research, 2010b)
Mutagenicity in mammalian cells: Negative with and without activation in L5178Y mouse lymphoma cells (OECD TG 476) (Harlan Cytotest Cell Research, 2010c)

Link to relevant study records

Reference

Reference 1

Endpoint:

in vitro gene mutation study in bacteria

Type of information:

experimental study

Adequacy of study:

key study

Study period:

2010 -05-26 to 2010-06-18

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

OECD Guideline 471 (Bacterial Reverse Mutation Assay)

Deviations:

no

Qualifier:

according to guideline

Guideline:

EU Method B.13/14 (Mutagenicity - Reverse Mutation Test Using Bacteria)

Deviations:

no

GLP compliance:

yes (incl. QA statement)

Type of assay:

bacterial reverse mutation assay

Target gene:

Histidine for Salmonella.
Tryptophan for E. coli

Species / strain / cell type:

E. coli WP2 uvr A

Additional strain / cell type characteristics:

not applicable

Species / strain / cell type:

S. typhimurium TA 1535, TA 1537, TA 98 and TA 100

Additional strain / cell type characteristics:

not applicable

Metabolic activation:

with and without

Metabolic activation system:

Phenobarbital/beta-Naphthoflavone induced rat liver S9

Test concentrations with justification for top dose:

3, 10; 33; 100; 333; 1000; 2500; and 5000 µg/plate / pre-experiment/experiment I
33; 100; 333; 1000; 2500; and 5000 µg/plate / experiment II

Vehicle / solvent:

- Vehicle(s)/solvent(s) used: Ethanol
- Justification for choice of solvent/vehicle: Better than other

Untreated negative controls:

yes

Remarks:

TA 1535, TA 100

Negative solvent / vehicle controls:

yes

True negative controls:

no

Positive controls:

yes

Positive control substance:

other: Sodium azide, NaN3

Remarks:

Without metabolic activation

Untreated negative controls:

yes

Remarks:

TA 1537, TA 98

Negative solvent / vehicle controls:

yes

True negative controls:

no

Positive controls:

yes

Positive control substance:

other: 4-nitro-o-phenylene-diamine, 4-NOPD

Remarks:

Without metabolic activation

Untreated negative controls:

yes

Remarks:

WP2 uvrA

Negative solvent / vehicle controls:

yes

True negative controls:

no

Positive controls:

yes

Positive control substance:

methylmethanesulfonate

Remarks:

Without metabolic activation

Untreated negative controls:

yes

Remarks:

TA 1535, TA 1537, TA 98, TA 100, WP2 uvrA

Negative solvent / vehicle controls:

yes

True negative controls:

no

Positive controls:

yes

Positive control substance:

other: 2-aminoanthracene, 2-AA

Remarks:

With metabolic activation

Details on test system and experimental conditions:

METHOD OF APPLICATION: in medium; in agar (plate incorporation); preincubation
DURATION
- Preincubation period: 1 hour
- Exposure duration: 72 hours
NUMBER OF REPLICATIONS: 3 plates

DETERMINATION OF CYTOTOXICITY
A reduction in the number of spontaneous revertants (below the induction factor of 0.5) or a clearing of the bacterial background lawn.

Evaluation criteria:

A test item is considered as a mutagen if a biologically relevant increase in the number of revertants exceeding the threshold of twice (strains TA 98, TA 100, and WP2 uvrA) or thrice (strains TA 1535 and TA 1537) the colony count of the corresponding solvent control is observed.
A dose dependent increase is considered biologically relevant if the threshold is exceeded at more than one concentration.
An increase exceeding the threshold at only one concentration is judged as biologically relevant if reproduced in an independent second experiment.
A dose dependent increase in the number of revertant colonies below the threshold is regarded as an indication of a mutagenic potential if reproduced in an independent second experiment. However, whenever the colony counts remain within the historical range of negative and solvent controls such an increase is not considered biologically relevant.

Statistics:

According to the OECD guideline 471, a statistical analysis of the data is not mandatory.

Key result

Species / strain:

other: TA 1535, TA 1537, TA 98, TA 100, WP2 uvrA

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:

TEST-SPECIFIC CONFOUNDING FACTORS

- Precipitation:

Precipitation of the test item in the overlay agar was observed in the test tubes at 2,500 µg/plate and 5,000 µg/plate in experiment I. Precipitation of the test item in the overlay agar on the incubated agar plates was observed in experiment I at 2,500 µg/plate and at 5,000 µg/plate without S9 mix and from 1000 µg/plate up to 5000 µg/plate with S9 mix and in experiment II at 5000 µg/plate with S9 mix. The undissolved particles had no influence on the data recording.

- Other confounding effects:
COMPARISON WITH HISTORICAL CONTROL DATA: performed
ADDITIONAL INFORMATION ON CYTOTOXICITY:
No reduced background growth was observed in all strains in both experiments with and without metabolic activation.
No toxic effects, evident as a reduction in the number of revertants (below the indication factor of 0.5) were observed in all strains with and without S9 mix in both experiments.

    Summary of Results Experiment I

Study Name: 1323707	Study Code: Harlan CCR 1323707
Experiment: 1323707 VV Plate	Date Plated: 26/05/2010
Assay Conditions:	Date Counted: 01/06/2010

Metabolic Activation	Test Group	Dose Level (per plate)		Revertant Colony Counts (Mean ±SD)
				TA 1535	TA 1537	TA 98	TA 100	WP2 uvrA
Without Activation	Ethanol			15 ± 3	13 ± 3	27 ± 4	133 ± 3	46 ± 14
	Untreated			15 ± 4	7 ± 2	31 ± 2	127 ± 12	49 ± 6
	2,4,6,8,10 -Pentamethyl	3 µg		15 ± 2	11 ± 3	31 ± 4	131 ± 9	43 ± 7
	cyclopentasiloxane	10 µg		15 ± 6	11 ± 2	25 ± 4	124 ± 4	43 ± 8
		33 µg		16 ± 4	12 ± 3	28 ± 8	116 ± 2	47 ± 8
		100 µg		17 ± 1	10 ± 3	29 ± 7	126± 8	44 ± 9
		333 µg		13 ± 4	10 ± 3	29 ± 6	119 ± 20	43 ± 1
		1000 µg		15 ± 1	10 ± 4	27 ± 5	127 ± 21	50 ± 8
		2500 µg		15 ± 7^P	13 ± 4^P	26 ± 6^P	127 ± 1^P	55 ± 4^P
		5000 µg		16 ± 4^P	8 ± 2^P	28 ± 7^P	132 ± 12^P	53 ± 3^P
	NaN3	10 µg		1607 ± 44			1981 ± 75
	4-NOPD	10 µg				339 ± 48
	4-NOPD	50 µg			68 ± 6
	MMS	3.0 µL						894 ± 49
With Activation	Ethanol			19 ± 4^B M	15 ± 5	49 ± 11	153 ± 12	67 ± 11
	Untreated			20 ± 3^B M	23 ± 6	45 ± 9	149 ± 6	60 ± 5
	2,4,6,8,10 -Pentamethyl	3 µg		21 ± 2^B M	15 ± 5	46 ± 5	136 ± 5	59 ± 10
	cyclopentasiloxane	10 µg		20 ± 4^B M	13 ± 3	49 ± 7	143 ± 10	57 ± 5
		33 µg		19 ± 4^B M	14 ± 2	48 ± 8	152 ± 8	55 ± 2
		100 µg		20 ± 3^B M	14 ± 2	48 ± 14	146 ± 19	55 ± 7
		333 µg		18 ± 5^B M	14 ± 1	53 ± 2	143 ± 16	53 ± 4
		1000 µg		16 ± 2^B M P	15 ± 1^P	45 ± 9^P	140 ± 13^P	63 ± 8^P
		2500 µg		15 ± 4^B M P	11 ± 1^P M	40 ± 3^P M	144 ± 18^P	72 ± 2^P
		5000 µg		13 ± 3^B M P	11 ± 1^P M	37 ± 3^P M	158 ± 30^P	52 ± 6^P M
	2-AA	2.5 µg		360 ± 16	559 ± 67	1863 ± 139	2919 ± 130
	2-AA	10.0 µg						262 ± 11

Key to Positive Controls		Key to Plate Postfix Codes
NaN3 2-AA 4-NOPD MMS	sodium azide 2-aminoanthracene 4-nitro-o-phenylene-diamine methyl methane sulfonate	P B M	Precipitate Extensive bacterial growth Manual count

 Summary of Results Experiment II

Study Name: 1323707	Study Code: Harlan CCR 1323707
Experiment: 1323707 HV2 Pre	Date Plated: 15/06/2010
Assay Conditions:	Date Counted: 18/06/2010

Metabolic Activation	Test Group	Dose Level (per plate)		Revertant Colony Counts (Mean ±SD)
				TA 1535	TA 1537	TA 98	TA 100	WP2 uvrA
Without Activation	Ethanol			13 ± 1	10 ± 4	38 ± 3	157 ± 22	63 ± 12
	Untreated			16 ± 1	8 ± 1	26 ± 4	169 ± 7	49 ± 6
	2,4,6,8,10 -Pentamethyl	33 µg		11 ± 3	7 ± 2	33 ± 4	146 ± 11	50 ± 6
	cyclopentasiloxane	100 µg		11 ± 4	9 ± 2	34 ± 7	147 ± 20	58 ± 4
		333 µg		15 ± 1	12 ± 2	30 ± 9	153 ± 7	52 ± 12
		1000 µg		17 ± 3	9 ± 2	30 ± 4	158 ± 19	66 ± 3
		2500 µg		16 ± 3	14 ± 0	33 ± 2	165 ± 27	63 ± 12
		5000 µg		14 ± 2	13 ± 2	37 ± 11	171 ± 12	62 ± 7
	NaN3	10 µg		1833 ± 83			1860 ± 166
	4-NOPD	10 µg				516 ± 37
	4-NOPD	50 µg			63 ± 6
	MMS	3.0 µL						412 ± 42
With Activation	Ethanol			22 ± 6	13 ± 3	37 ± 8	179 ± 4	76 ± 8
	Untreated			19 ± 7	18 ± 5	35 ± 6	173 ± 16	72 ± 11
	2,4,6,8,10 -Pentamethyl	33 µg		18 ± 4	12 ± 6	46 ± 4	169 ± 7	64 ± 11
	cyclopentasiloxane	100 µg		20 ± 3	13 ± 3	51 ± 7	167 ± 11	67 ± 7
		333 µg		25 ± 5	7 ± 1	44 ± 17	162 ± 8	70 ± 14
		1000 µg		15 ± 4	12 ± 3	48 ± 6	162 ± 17	74 ± 17
		2500 µg		19 ± 4	9 ± 1	45 ± 9	164 ± 20	68 ± 10
		5000 µg		15 ± 5^P	8 ± 1^P M	41 ± 2^P	168 ± 12^P	77 ± 12^P
	2-AA	2.5 µg		468 ± 26	544 ± 49	2941 ± 199	3505 ± 286
	2-AA	10.0 µg						428 ± 19

Key to Positive Controls		Key to Plate Postfix Codes
NaN3 2-AA 4-NOPD MMS	sodium azide 2-aminoanthracene 4-nitro-o-phenylene-diamine methyl methane sulfonate	P M	Precipitate Manual count

Conclusions:

2,4,6,8,10-Pentamethylcyclotetrasiloxane has been tested according to OECD 471 and in compliance with GLP. No increase in the number of revertants per plate was observed in either the initial plate incorporation assay or the independent repeat preincubation assay. Vehicle and positive controls gave expected results. It is concluded that the test substance was negative for mutagenicity to bacteria under the conditions of the test.

Executive summary:

This study was performed to investigate the potential of 2,4,6,8,10- pentamethylcyclopentasiloxane to induce gene mutations in the plate incorporation test (Experiment I) and the pre-incubation test (Experiment II) using the Salmonella typhimurium strains TA 1535, TA 1537, TA 98, and TA 100, and the Escherichia coli strain WP2 uvrA.

The assay was performed in two independent experiments both with and without liver microsomal activation. Each concentration, including the controls, was tested in triplicate. The test item was tested at the following concentrations:

Pre-Experiment/Experiment I: 3; 10; 33; 100; 333; 1,000; 2,500; and 5,000 Ng/plate

Experiment II: 33; 100; 333; 1,000; 2,500; and 5,000 Ng/plate

No reduced background growth was observed in all strains in both experiments with and without metabolic activation.

No toxic effects, evident as a reduction in the number of revertants (below the indication factor of 0.5) were observed in all strains with and without S9 mix in both experiments.

No substantial increase in revertant colony numbers of any of the five tester strains was observed following treatment with 2,4,6,8,10-pentamethylcyclopentasiloxane at any dose level, neither in the presence nor absence of metabolic activation (S9 mix).

There was also no tendency of higher mutation rates with increasing concentrations in the range below the generally acknowledged border of biological relevance. Appropriate reference mutagens were used as positive controls and showed a distinct increase of induced revertant colonies.

In conclusion, it can be stated that during the described mutagenicity test and under the experimental conditions reported, the test item did not induce gene mutations by base pair changes or frameshifts in the genome of the strains used.

Therefore, 2,4,6,8,10-pentamethylcyclopentasiloxane is considered to be non-mutagenic in this Salmonella typhimurium and Escherichia coli reverse mutation assay.

Reference 2

Endpoint:

in vitro cytogenicity / chromosome aberration study in mammalian cells

Type of information:

experimental study

Adequacy of study:

key study

Study period:

2010-06-07 to 2010-07-23

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

OECD Guideline 473 (In Vitro Mammalian Chromosome Aberration Test)

Deviations:

no

Qualifier:

according to guideline

Guideline:

EU Method B.10 (Mutagenicity - In Vitro Mammalian Chromosome Aberration Test)

Deviations:

no

GLP compliance:

yes (incl. QA statement)

Type of assay:

in vitro mammalian chromosome aberration test

Species / strain / cell type:

lymphocytes: peripheral human

Details on mammalian cell type (if applicable):

- Type and identity of media: Dulbeccos' modified Eagle's medium/Ham's F12 medium
- Properly maintained: yes

Metabolic activation:

with and without

Metabolic activation system:

phenobarbital/beta-naphthoflavone induced rat liver S9

Test concentrations with justification for top dose:

With metabolic activation:
Experiment I: 19.5, 34.1, 59.7, 104.4, 182.8, 319.9, 559.8, 979.6, 1714.3, 3000.0 µg/ml
Experiment II: 19.5, 34.1, 59.7, 104.4, 182.8, 319.9 µg/ml

Without metabolic activation:
Experiment I: 19.5, 34.1, 59.7, 104.4, 182.8, 319.9, 559.8, 979.6, 1714.3, 3000.0 µg/ml
Experiment II: 59.7, 104.4, 182.8, 319.9, 559.8, 979.6, 1714.3, 3000.0 µg/ml

Vehicle / solvent:

- Vehicle(s)/solvent(s) used: Ethanol
- Justification for choice of solvent/vehicle: solubility and relatively low cytotoxicity in accordance to the OECD Guideline 473

Untreated negative controls:

no

Negative solvent / vehicle controls:

yes

True negative controls:

no

Positive controls:

yes

Positive control substance:

ethylmethanesulphonate

Remarks:

without metabolic activation

Untreated negative controls:

no

Negative solvent / vehicle controls:

yes

True negative controls:

no

Positive controls:

yes

Positive control substance:

cyclophosphamide

Remarks:

with metabolic activation

Details on test system and experimental conditions:

Two independent experiments were performed. In Experiment I the exposure period was 4 hours with and without metabolic activation. In Experiment II the exposure period was 4 hours with S9 mix and 22 hours without S9 mix. The chromosomes were prepared 22 hours after start of treatment with the test item. Evaluation of two cultures per dose group.
METHOD OF APPLICATION: in culture medium

DURATION
- Exposure duration: 4 hours (+/- S9 mix) and 22 hours (- S9 mix)
- Fixation time (start of exposure up to fixation or harvest of cells): 22 hours


SPINDLE INHIBITOR (cytogenetic assays): Colcemid
STAIN (for cytogenetic assays): Giemsa


NUMBER OF REPLICATIONS: about 1.5


NUMBER OF CELLS EVALUATED: 100 per culture


DETERMINATION OF CYTOTOXICITY
- Method: mitotic index

Evaluation criteria:

Evaluation of the cultures was performed (according to standard protocol of the "Arbeitsgruppe der Industrie, Cytogenetik") using NIKON microscopes with 100x oil immersion objectives. Breaks, fragments, deletions, exchanges, and chromosome disintegrations were recorded as structural chromosome aberrations. Gaps were recorded as well but not included in the calculation of the aberration rates. At least 100 well spread metaphases per culture were scored for cytogenetic damage on coded slides.
Only metaphases with characteristic chromosome numbers of 46 ± 1 were included in the analysis. To describe a cytotoxic effect the mitotic index (% cells in mitosis) was determined.

Statistics:

Statistical significance was confirmed by means of the Fisher´s exact test (p < 0.05).

Key result

Species / strain:

lymphocytes: periferal human

Metabolic activation:

with and without

Genotoxicity:

negative

Cytotoxicity / choice of top concentrations:

no cytotoxicity nor precipitates, but tested up to recommended limit concentrations

Vehicle controls validity:

valid

Untreated negative controls validity:

not examined

Positive controls validity:

valid

Additional information on results:

The test item 2,4,6,8,10-pentamethylcyclopentasiloxane, dissolved in ethanol, was assessed for its potential to induce chromosomal aberrations in human lymphocytes in vitro in the absence and presence of metabolic activation by S9 mix.
Two independent experiments were performed. In Experiment I the exposure period was 4 hours with and without S9 mix. In Experiment II the exposure period was 4 hours with S9 mix and 22 hours without S9 mix. The chromosomes were prepared 22 hours (Exp. I & II) after the start of treatment with the test item.
In each experimental group two parallel cultures were analysed. At least 100 metaphases per culture were scored for structural chromosomal aberrations. 1000 cells were counted per culture for determination of the mitotic index.
The highest treatment concentration in this study, 3000.0 µg/ml (approx. 10 mM) was chosen with respect to the OECD Guideline for in vitro mammalian cytogenetic tests considering the molecular weight of the test item.
In Experiment I and II in the presence of S9 mix, visible precipitation of the test item in the culture medium was observed at 59.7 µg/ml and above at the end of treatment. In Experiment II precipitation occurred at 319.9 µg/mL and above in the absence of S9 mix at the end of treatment. In Experiment I osmolarity was markedly decreased at the two highest evaluated concentrations (3000.0 µg/ml: 343 mOsm; 1714.3 µg/ml: 367 mOsm; solvent control: 436 mOsm). The validity of the study is not affected since no relevant findings in the number of cells carrying chromosomal aberrations were observed. No relevant influence on pH value was observed (solvent control: pH 7.3 versus pH 7.3 at 3000.0 µg/ml). No relevant influence in the osmolarity or pH value was observed in Experiment II (solvent control: 387 mOsm, pH 7.5 versus 351 mOsm and pH 7.5 at 3000.0 µg/ml). Phase separation was observed in Experiment I at 559.8 µL/ml and above in the absence and presence of S9 mix and in Experiment II at 319.9 µL/ml in the absence of S9 mix at the end of treatment.
In this study, at both preparation intervals, in the absence as well as in the presence of S9 mix, no biologically relevant cytotoxicity indicated by clearly reduced mitotic indices could be observed.
In both experiments, in the absence and presence of S9 mix, no biologically relevant increase in the number of cells carrying structural chromosome aberrations was observed. The aberration rates of the cells after treatment with the test item (0.0 – 2.3 % aberrant cells, excluding gaps) were slightly above the range of the solvent control values (0.0 - 1.5 % aberrant cells, excluding gaps) and within the range of the laboratory historical solvent control data.
No evidence of an increase in polyploid metaphases was noticed after treatment with the test item as compared to the control cultures.
In both experiments, either EMS (825.0 µg/ml) or CPA (7.5 or 15.0 µg/ml) were used as positive controls and showed distinct increases in cells with structural chromosome aberrations.

Summary of results of the chromosomal aberration study with
2,4,6,8,10-pentamethylcyclopentasiloxane

Exp.		Preparation			Test item	Mitotic indices	Aberrant cells
		interval			concentration	in %	in %
					in µg/ml	of control	incl. gaps*	excl. gaps*	carrying exchanges
	Exposure period 4 hrs without S9 mix
I		22 hrs			Solvent control^1	100.0	0.5	0.5	0.0
					Positive control^2	73.0	18.0	16.5^S	2.5
					979.6	116.6	1.5	1.5	0.0
					1714.3	109.5	1.5	1.0	0.0
					3000.0	109.8	3.0	1.5	0.0
			Exposure period 22 hrs without S9 mix
II		22 hrs			Solvent control^1	100.0	1.5	1.5	0.0
					Positive control^2	52.8	28.0	27.5^S	9.0
					104.4	125.2	0.5	0.5	0.0
					182.8	111.0	2.0	1.5	0.0
					319.9^P	102.5	3.5	1.5	0.0
				Exposure period 4 hrs with S9 mix
I		22 hrs			Solvent control^1	100.0	1.5	1.5	0.0
					Positive control^3	48.4	17.0	16.0^S	2.0
					19.5	82.1	0.0	0.0	0.0
					34.1	78.8	1.5	1.5	0.0
					59.7^#P	90.5	2.3	2.3	0.0
II		22 hrs			Solvent control1	100.0	0.0	0.0	0.0
					Positive control^4	54.4	12.5	11.0^S	2.5
					19.5	103.5	1.0	1.0	0.0
					34.1	97.9	0.5	0.5	0.0
					59.7^P	94.0	2.0	1.5	0.0

*  Including cells carrying exchanges

^#   Evaluation of 200 metaphases per culture

^P  Precipitation occurred at the end of treatment

^S  Aberration frequency statistically significant higher than corresponding control values

¹   Ethanol  0.5 % (v/v)

²     EMS  825.0 µg/ml

³   CPA      7.5 µg/ml

⁴   CPA    15.0 µg/ml

Conclusions:

2,4,6,8,10-Pentamethylcyclopentasiloxane has been tested according to OECD 473 and in compliance with GLP. No increase in the number of structural chromosomal aberrations in human lymphocytes was observed when tested with and without activation in either the initial or the independent repeat experiment. Vehicle and positive controls gave expected results. It is concluded that the test substance is negative for the induction of chromosome aberrations under the conditions of this test.

Executive summary:

The test item 2,4,6,8,10-pentamethylcyclopentasiloxane, dissolved in ethanol, was assessed for its potential to induce structural chromosomal aberrations in human lymphocytes in vitro in two independent experiments. The following study design was performed:

	Without S9 mix		With S9 mix
	Exp. I	Exp. II	Exp. I & II
Exposure period	4 hrs	22 hrs	4 hrs
Recovery	18 hrs	-	18 hrs
Preparation interval	22 hrs	22 hrs	22 hrs

In each experimental group two parallel cultures were analysed. Per culture at least 100 metaphases were scored for structural chromosomal aberrations.

The highest applied concentration in this study (3000.0 µg/mL of the test item, approx. 10 mM) was chosen with regard to the molecular weight of the test item and with respect to the current OECD Guideline 473.

Dose selection of the cytogenetic experiment was performed considering the toxicity data and the occurrence of test item precipitation in accordance with OECD Guideline 473.

In the absence and presence of S9 mix, no cytotoxicity was observed up to the highest applied concentration.

In both independent experiments, neither a statistically significant nor a biologically relevant increase in the number of cells carrying structural chromosomal aberrations was observed after treatment with the test item.

No evidence of an increase in polyploid metaphases was noticed after treatment with the test item as compared to the control cultures.

Appropriate mutagens were used as positive controls. They induced statistically significant increases (p < 0.05) in cells with structural chromosome aberrations.

Reference 3

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

Qualifier:

according to guideline

Guideline:

OECD Guideline 476 (In Vitro Mammalian Cell Gene Mutation Test)

GLP compliance:

yes (incl. QA statement)

Type of assay:

mammalian cell gene mutation assay

Target gene:

autosomal thymidine kinase (TK) locus

Species / strain / cell type:

mouse lymphoma L5178Y cells

Metabolic activation:

with and without

Metabolic activation system:

Phenobarbital/beta-naphthoflavone induced rat live S9

Test concentrations with justification for top dose:

Experiment 1 (-S9): 46.9-3000 µg/ml; Experiment 1 (+S9) and Experiment 2 (+/-S9): 187.5-3000 µg/ml

Vehicle / solvent:

- Vehicle(s)/solvent(s) used: Ethanol
- Justification for choice of solvent/vehicle: solubility properties and relative non-toxicity to the cell cultures

Untreated negative controls:

no

Negative solvent / vehicle controls:

yes

True negative controls:

no

Positive controls:

yes

Positive control substance:

methylmethanesulfonate

Remarks:

without metabolic activation; 13.0 - 19.5 µg/ml = 0.12 - 0.18 mM

Untreated negative controls:

no

Negative solvent / vehicle controls:

yes

True negative controls:

no

Positive controls:

yes

Positive control substance:

cyclophosphamide

Remarks:

with metabolic activation; 3.0 – 6.0 µg/ml = 10.7 – 21.4 µM

Details on test system and experimental conditions:

Experimental Performance
In the mutation experiment 1x10^7 (3x10^6 during 24 h exposure) cells/flask (80 cm2 flasks) suspended in 10 mL RPMI me­dium with 3 % horse serum (15 % during 24 h exposure) will be exposed to various concentrations of the test item either in the presence or absence of metabolic activation. Positive and solvent controls are performed in parallel. After 4 h (24 h in the second experiment without metabolic activation) the test item is removed by centrifugation (425 g, 10 min) and the cells are washed twice with "saline G". Subsequently the cells are resuspended in 30 mL complete culture medium and incubated for an expression and growth period of totally 48 h.
The cell density is determined each day and adjusted to 3x 10^5 cells/ml, if necessary. The relative suspension growth (RSG) of the treated cell cultures is calculated by the day 1 fold-increase in cell number multiplied by the day 2 fold-increase in cell number according to the method of Clive and Spector (11).
After the expression period the cultures are seeded into microtiter plates. Cells from each experimental group will be seeded into 2 microtiter plates so that each well contains approximately 4x10^3 cells in selective medium (see below) with TFT (Serva, 69042 Heidelberg, Germany). The viability (cloning efficiency) will be determined by seeding about 2 cells per well into microtiter plates (same medium without TFT). The plates are incubated at 37°+- 1.5 °C in 4.5 % CO2/95.5 % humidified air for 10 - 15 days. Then the plates will be evaluated.
Complete Culture Medium
RPMI 1640 medium (GIBCO, invitrogen) supplemented with 15 % horse serum (HS, GIBCO, invitrogen) (3 % HS during 4 hour treatment), 1% of 100 U/100 µg/mL Penicil­lin/Streptomycin, 220 µg/mL Sodium-Pyruvate, and 0.5 – 0.75 % Amphotericin used as antifungal (11).
Selective Medium
RPMI 1640 (complete culture medium) by addition of 5 µg/mL TFT.
Saline G Solution
The "saline G" solution is composed as follows (per litre):
NaCl 8000 mg
KCl 400 mg
Glucose 1100 mg
Na2HPO4.7H2O 290 mg
KH2PO4 150 mg
pH: 7.2

Evaluation criteria:

A test item is classified as mutagenic if the induced mutation frequency reproducibly exceeds a threshold of 126 colonies per 10^6 cells above the corresponding solvent control.
A relevant increase of the mutation frequency should be dose-dependent.
A mutagenic response is considered to be reproducible if it occurs in both parallel cultures.
However, in the evaluation of the test results the historical variability of the mutation rates in the solvent controls of this study are taken into consideration.
Results of test groups are generally rejected if the relative total growth is less than 10 % of the vehicle control unless the exception criteria specified by the IWGT recommendations are fulfilled.
Whenever a test item is considered mutagenic according to the above mentioned criteria, the ratio of small versus large colonies is used to differentiate point mutations from clastogenic effects. If the increase of the mutation frequency is accompanied by a reproducible and dose dependent shift in the ratio of small versus large colonies clastogenic effects are indicated.
A test item is classified as non-mutagenic if the induced mutation frequency does not reproducibly exceed a threshold of 126 colonies per 106 cells above the corresponding solvent control.
A test item not meeting the conditions for a classification as mutagenic or non-mutagenic will be considered equivocal in this assay and may be considered for further investigation.

Statistics:

A linear regression (least squares) will be performed to assess a possible dose dependent increase of mutant frequencies using SYSTAT 11 (SYSTAT Software, Inc., 501, Canal Boulevard, Suite C, Richmond, CA 94804, USA) statistics software. The number of mutant colonies obtained for the groups treated with the test item will be compared to the solvent control groups. A trend is judged as significant whenever the p-value (probability value) is below 0.05. However, both, biological relevance and statistical significance will be considered together.

Key result

Species / strain:

mouse lymphoma L5178Y cells

Metabolic activation:

with and without

Genotoxicity:

negative

Cytotoxicity / choice of top concentrations:

no cytotoxicity nor precipitates, but tested up to recommended limit concentrations

Vehicle controls validity:

valid

Untreated negative controls validity:

not applicable

Positive controls validity:

valid

Conclusions:

2,4,6,8,10-Pentamethylcyclopentasiloxane has been tested according to OECD 476 and in compliance with GLP. No increase in the number of mutant colonies was observed when tested with and without activation in either the initial or the independent repeat experiment. Vehicle and positive controls gave expected results. It is concluded that the test substance is negative for the induction of mutations in L5178Y cells under the conditions of the test.

Endpoint conclusion

Endpoint conclusion:

no adverse effect observed (negative)

Genetic toxicity in vivo

Endpoint conclusion

Endpoint conclusion:

no study available

Additional information

Information is available on in vitro gene mutation in bacteria as well as on in vitro cytogenicity and mutagenicity in mammalian cells.

2,4,6,8,10-Pentamethylcyclotetrasiloxane has been tested according to OECD 471 and in compliance with GLP. No increase in the number of revertants per plate was observed in either the initial plate incorporation assay or the independent repeat preincubation assay. Vehicle and positive controls gave expected results. It is concluded that the test substance was negative for mutagenicity to bacteria under the conditions of the test (Harlan Cytotest Cell Research, 2010a).

2,4,6,8,10-Pentamethylcyclopentasiloxane has been tested according to OECD 473 and in compliance with GLP. No increase in the number of structural chromosomal aberrations in human lymphocytes was observed when tested with and without activation in either the initial or the independent repeat experiment. Vehicle and positive controls gave expected results. It is concluded that the test substance is negative for the induction of chromosome aberrations under the conditions of this test (Harlan Cytotest Cell Research, 2010b).

2,4,6,8,10-Pentamethylcyclopentasiloxane has been tested according to OECD 476 and in compliance with GLP. No increase in the number of mutant colonies was  observed when tested with and without activation in either the initial or the independent repeat experiment. Vehicle and positive controls gave expected results. It is concluded that the test substance is negative for the induction of mutations in L5178Y cells under the conditions of the test (Harlan Cytotest Cell Research, 2010c).

Justification for classification or non-classification

Based on the available information, 2,4,6,8,10-pentamethylcyclotetrasiloxane does not require classification for genetic toxicity according to Regulation (EC) No 1272/2008.