2,6-dimethyloct-7-en-2-yl formate

Genetic toxicity: in vitro

Administrative data

Endpoint:

in vitro gene mutation study in bacteria

Type of information:

experimental study

Adequacy of study:

key study

Study period:

12 January 2018 - 16 April 2018

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Data source

Reference

Reference Type:

study report

Title:

Unnamed

Year:

2018

Report date:

2018

Materials and methods

Test guideline

Qualifier:

according to guideline

Guideline:

OECD Guideline 471 (Bacterial Reverse Mutation Assay)

Deviations:

no

GLP compliance:

yes (incl. QA statement)

Type of assay:

bacterial reverse mutation assay

Test material

Test material information

Constituent 1

Reference substance name:

2,6-dimethyloct-7-en-2-yl formate

EC Number:

246-788-1

EC Name:

2,6-dimethyloct-7-en-2-yl formate

Cas Number:

25279-09-8

Molecular formula:

C11H20O2

IUPAC Name:

2,6-dimethyloct-7-en-2-ol

Test material form:

liquid

Method

Species / strain

Species / strain / cell type:

S. typhimurium TA 1535, TA 1537, TA 98, TA 100 and TA 102

Additional strain / cell type characteristics:

other: rfa mutation (histidine dependence), uvrB mutation (biotin dependence)

Metabolic activation:

with and without

Test concentrations with justification for top dose:

Test 1: 0.0015, 0.005, 0.015, 0.05, 0.15, 0.5, 1.5 and 5 µL/plate (all strains)
Test 2: 0.03, 0.06, 0.13, 0.25, 0.5 and 1 µL/plate (TA1537, TA1535, TA98 and TA100) and 0.16, 0.31, 0.63, 1.25, 2.5, and 5 µL/plate (TA102)

Vehicle / solvent:

- Vehicle(s)/solvent(s) used: DMSO
- Justification for choice of solvent/vehicle: A preliminary solubility and precipitation test was used. The substance was insoluble in distilled water.

Controls

Negative solvent / vehicle controls:

yes

Positive controls:

yes

Positive control substance:

9-aminoacridine

2-nitrofluorene

sodium azide

mitomycin C

other: 2-Aminoanthracene

Details on test system and experimental conditions:

METHOD OF APPLICATION: in agar (plate incorporation)
Tubes containing 2 mL of molten top agar with 0.5 mM histidine/biotin were maintained at 45 ± 2 °C. A volume of 500 µL of 0.2 M phosphate buffer was added in the absence of metabolic activation system and 500 µL of 5% v/v S9 mix (Test 1) or 10% v/v S9 (Test 2) was added in the presence of metabolic activation system. Volume of 100 µL of the relevant stock solution of test item, DMSO and relevant positive control were used for treatment, as a negative control and as a positive control, respectively. Finally, 100 µL of bacterial culture (1 - 2 x 10E9 bacteria/mL) was added to the tubes and mixed. Two sets were maintained for each concentration of dihydromyrcenyl formate, positive control and negative control. The petriplates were incubated at 37 ± 1 °C for 48 hours and then examined to assess the state of background bacterial lawn inhibition and reduction in number of colonies.

DURATION
- Expression time (cells in growth medium): 48 h

NUMBER OF REPLICATIONS: 2 (Test 1) and 3 (Test 2)

DETERMINATION OF CYTOTOXICITY
- Method: Cytotoxicity was detectable as decrease in the number of revertant colonies per plate and/or by a thinning of the bacterial background lawn.

OTHER EXAMINATIONS:
Cell viability test: Fresh cultures for the test were prepared by inoculating frozen permanent cultures to a flask containing 10 mL of sterile nutrient broth N° 2 (Oxoid). The flasks were then incubated at 37 ± 1 °C in an orbital shaking incubator (120 rpm) for 15 h up to early stationary or late exponential phase. After the incubation period, the culture flasks were removed from the orbital shaking incubator. Aseptically, the cultures were diluted with oxoid nutrient broth (ONB) and the optical density was measured at 660 nm using a Spectrophotometer (Model visiscan 167, manufactured by Systronics). Oxoid nutrient broth was used as the control blank. Cell viability of the tester strains was determined prior to treatment. The optical density of the cultures was found to be in the acceptable range and so they were used for the study.

Genotype confirmation test: The genotype of the tester strain was confirmed for all the strains regularly (once a month). The tester strains of Salmonella typhimurium were tested for histidine dependence, biotin dependence, histidine and biotin dependence, rfa mutation, uvrB mutation through sensitivity to ultraviolet light and the R-factor resistance for ampicillin and tetracycline.

Sterility Check for the Operating System: Top agar, S9 mix, Solvent, Test item, ONB solution, 0.2 M Sodium Phosphate Buffer, MGA Plate.

Rationale for test conditions:

Hence DMSO was selected as the vehicle for treatment. Precipitation was not observed at the tested concentration of 5 µL/plate. Hence 5 µL/plate was selected as the highest concentration to be tested for initial toxicity-mutation test both in the absence and presence (5% v/v S9 mix) of metabolic activation.

Evaluation criteria:

The conditions necessary for determining a positive result were: there should be a dose related increase in the mean revertants per plate of at least one tester strain over a minimum of two increasing doses of the test item either in the absence or presence of the metabolic activation system.
Biological relevance of the results was considered first:
Strains TA1535, TA1537:
Data sets were judged positive, when the increase in mean revertants at the peak of the dose response was equal to or greater than 3.0 times the mean negative control value.
Strain TA98, TA100 and TA102:
Data sets were judged positive, when the increase in mean revertants at the peak of the dose response was equal to or greater than 2.0 times the mean negative control value.
A response that did not meet all three of the above criteria (magnitude, concentration-responsiveness, reproducibility) was not evaluated as positive.
Negative results obtained in the initial toxicity-mutation test were confirmed by a second trial, using the same method as specified above, with an alteration in concentration spacing.

Statistics:

Statistical analysis was used as an aid in the evaluation of dose response.

Results and discussion

Test results

Key result

Species / strain:

S. typhimurium, other: TA1537, TA1535, TA98, TA100 and TA102

Metabolic activation:

with and without

Genotoxicity:

negative

Cytotoxicity / choice of top concentrations:

cytotoxicity

Untreated negative controls validity:

valid

Positive controls validity:

valid

Additional information on results:

No increase in the number of revertant colonies was observed both in the absence and presence of metabolic activation at any of the tested concentration in all the tester strains.

TEST-SPECIFIC CONFOUNDING FACTORS
- Precipitation: No observed.
- Definition of acceptable cells for analysis:
- Other confounding effects: Cell viability and genotype confirmatory tests were performed (see above). The cells were determind to be suitable for the test.

HISTORICAL CONTROL DATA (with ranges, means and standard deviation and confidence interval (e.g. 95%)
- Positive historical control data: Revertants per plate (mean ± SD)
Without S9 mix
TA1537: 274.27 ± 94.89
TA 1535: 376.70 ± 113.61
TA98: 542.14 ± 148.27
TA100: 880.92 ± 175.36
TA102: 1058.59 ± 152.48

With S9 mix
TA1537: 300.52 ± 98.11
TA 1535: 419.02 ± 122.05
TA98: 671.47 ± 171.10
TA100: 968.94 ± 158.04
TA102: 1088.70 ± 154.86

Positive controls in the absence of metabolic activation:
TA1537 = 9-Aminoacridine Hydrochloride Monohydrate (75 µg/plate), TA1535 = Sodium Azide (0.5 µg/plate), TA98 = 2-Nitrofluorene (7.5 µg/plate), TA100 = Sodium Azide (5 µg/plate), TA102 = Mitomycin-C (0.5 µg/plate).
Positive controls in the presence of metabolic activation
2Aa = 2-Aminoanthracene (10 µg/plate for TA1537, TA1535, TA102 and 5 µg/plate for TA98 and TA100)

- Negative (DMSO) historical control data: Revertants per plate (mean ± SD)
Without S9 mix
TA1537: 8.40 ± 2.73
TA 1535: 18.37 ± 4.44
TA98: 22.79 ± 4.92
TA100: 131.37 ± 10.65
TA102: 228.89 ± 12.48

With S9 mix
TA1537: 8.96 ± 3.02
TA 1535: 20.03 ± 4.97
TA98: 24.24 ± 5.43
TA100: 134.50 ± 10.53
TA102: 232.55 ± 13.12

ADDITIONAL INFORMATION ON CYTOTOXICITY:
- Measurement of cytotoxicity used: Cytotoxicity was characterised by inhibition of the bacterial background lawn and/or reduction in the number of revertant colonies. Cytotoxycity was observed:
Test 1: +/- S9, TA1537, TA1535, TA98 and TA100 (1.5 and 5 µL/plate)
Test 2: +/- S9,TA1537, TA1535, TA98 and TA100 (1 µL/plate)
- Other observations when applicable: No.

Any other information on results incl. tables

Test 1: Without metabolic activation (-S9)

Concentration of test item (µL/plate)	His^+Revertant Colonies/Plate [Absence of Metabolic Activation]
	TA1537		TA1535		TA98		TA100		TA102
	Mean	SD	Mean	SD	Mean	SD	Mean	SD	Mean	SD
NC (DMSO)	3.50	3.54	20.00	7.07	24.00	8.49	134.50	12.02	235.00	28.28
0.0015	8.50	2.12	18.00	5.66	23.50	12.02	136.00	2.83	241.00	21.21
0.005	6.00	0.00	15.00	7.07	24.50	9.19	140.00	7.07	236.50	12.02
0.015	6.00	2.83	21.00	7.07	25.50	6.36	132.00	2.83	231.50	27.58
0.05	6.00	1.41	20.50	0.71	25.00	11.31	139.00	2.83	235.50	16.26
0.15	6.50	0.71	18.50	6.36	23.50	12.02	129.00	19.80	244.00	14.14
0.5	4.00	2.83	19.50	9.19	24.00	7.07	138.00	4.24	237.00	4.24
1.5	0.00	0.00	0.00	0.00	0.00	0.00	0.00	0.00	239.50	20.51
5	0.00	0.00	0.00	0.00	0.00	0.00	0.00	0.00	239.50	7.78
PC	497.00	164.05	472.50	40.31	790.00	0.00	883.50	12.02	1074.50	37.48
2Aa	-	-	-	-	-	-	140.00	15.56	-	-

Test 1: With metabolic activation (+S9)

Concentration of test item (µL/plate)	His^+Revertant Colonies/Plate [Presence of Metabolic Activation (5% v/v S9 mix)]
	TA1537		TA1535		TA98		TA100		TA102
	Mean	SD	Mean	SD	Mean	SD	Mean	SD	Mean	SD
NC (DMSO)	7.50	6.36	21.50	10.61	25.50	7.78	145.50	17.68	245.00	24.04
0.0015	7.00	0.00	17.50	10.61	27.00	8.49	152.00	9.90	236.50	12.02
0.005	6.00	2.83	21.00	8.49	22.00	14.14	144.00	12.73	243.00	12.73
0.015	7.50	2.12	21.00	11.31	25.50	4.95	138.00	18.38	239.50	16.26
0.05	7.50	4.95	22.50	7.78	26.00	4.24	144.00	5.66	240.00	8.49
0.15	6.00	4.24	21.00	9.90	23.50	9.19	138.00	9.90	239.50	16.26
0.5	6.00	1.41	21.50	4.95	22.50	3.54	143.50	10.61	245.00	24.04
1.5	0.00	0.00	0.00	0.00	0.00	0.00	0.00	0.00	235.00	21.21
5	0.00	0.00	0.00	0.00	0.00	0.00	0.00	0.00	243.50	23.33
PC-2Aa	512.00	66.47	661.00	45.25	852.50	51.62	940.50	27.58	1080.50	86.97

Test 2: Without metabolic activation (-S9)

Concentration of test item (µL/plate)		His^+Revertant Colonies/Plate [Absence of Metabolic Activation]
		TA1537		TA1535		TA98		TA100		TA102
		Mean	SD	Mean	SD	Mean	SD	Mean	SD	Mean	SD
NC (DMSO)		9.67	1.53	17.67	4.04	25.00	4.58	127.33	7.51	231.67	14.01
0.03*	0.16#	8.33	2.08	16.00	3.61	27.33	6.11	129.67	7.51	228.33	15.53
0.06*	0.31#	11.33	1.53	19.67	4.04	23.00	3.61	127.67	4.51	234.33	9.61
0.13*	0.63#	8.67	2.08	18.33	2.52	22.33	3.51	129.33	8.50	233.67	12.66
0.25*	1.25#	9.67	2.08	21.33	1.53	24.67	4.51	125.33	6.51	233.00	12.12
0.5*	2.5#	11.00	2.00	18.33	4.16	22.00	3.61	130.33	6.51	235.00	12.29
1*	5#	6.00	1.00	5.33	1.15	9.00	1.00	38.33	2.52	238.33	13.50
PC		255.67	23.71	338.67	16.26	774.67	7.51	924.67	9.61	1094.33	27.06
2Aa		-	-	-	-	-	-	135.33	6.43	-	-

Note: * Mark doses for tester strains TA1537, TA1535, TA98 and TA100. # Mark doses for tester strains TA102.

Test 2: With metabolic activation (+S9)

Concentration of test item (µL/plate)		His^+Revertant Colonies/Plate [Presence of Metabolic Activation (10% v/v S9 mix)]
		TA1537		TA1535		TA98		TA100		TA102
		Mean	SD	Mean	SD	Mean	SD	Mean	SD	Mean	SD
NC (DMSO)		11.33	2.52	19.00	4.58	28.67	5.03	133.33	11.59	236.33	6.66
0.03*	0.16#	10.00	2.00	20.00	4.58	27.00	7.94	134.67	9.07	245.33	11.15
0.06*	0.31#	12.00	1.00	17.67	3.21	27.33	3.06	130.67	11.06	238.00	7.21
0.13*	0.63#	10.00	1.00	21.00	3.61	24.67	3.21	134.67	12.06	237.00	8.89
0.25*	1.25#	11.33	3.06	19.00	3.61	30.00	3.61	134.67	7.57	236.67	7.02
0.5*	2.5#	10.00	1.00	20.67	2.08	22.67	2.52	134.67	10.26	235.33	7.09
1*	5#	4.00	1.00	6.00	1.00	10.00	2.00	47.67	5.69	239.33	7.64
PC-2Aa		256.33	18.45	342.00	11.14	748.33	10.50	1023.33	65.91	1062.00	34.39

Note: * Mark doses for tester strains TA1537, TA1535, TA98 and TA100. # Mark doses for tester strains TA102.

Applicant's summary and conclusion

Conclusions:

The test item was determined to be non-mutagenic to all of the five strains of Salmonella typhimurium viz., TA1537, TA1535, TA98, TA100 and TA102 when tested with and without metabolic activation up to 5 µL/plate.

Executive summary:

A bacterial reverse mutation assay was performed according to OECD Guideline 471 (GLP study) using five histidine deficient mutant tester strains of Salmonella typhimurium (i.e., TA1537, TA1535, TA98, TA100, and TA102). Two independent experiments, in the absence and presence of metabolic activation, were performed. In the initial test, bacterial cultures were exposed to the test item at 8 concentrations (two plates/concentration) between 0.0015 to 5 µL/plate. No increase in the number of revertant colonies (no mutagenic effect) were observed both in the absence and presence of the metabolic activation system (5% v/v S9 mix) in all the tester strains. To confirm the negative results obtained in the initial toxicity mutation test, confirmatory mutation test was conducted with an increased S9 concentration i.e., 10% v/v S9 mix and modified concentration spacing. In the confirmatory test, bacterial cultures were exposed to the test tiem at 6 concentrations (three plates/concentration) between 0.03 to 1 µL/plate for tester strains TA1537, TA1535, TA98, TA100 and  0.16 to 5 µL/plate for tester strain TA102 in both absence and presence (10 % v/v S9 mix) of metabolic activation system. After 48 hours of incubation at 37 ± 1°C, the revertant colonies were scored. Test item did not induce any significant increase in the number of revertants, in both trials, with and without S9 mix, in any of the five tester strains. All the values for the negative control were within historical control ranges of the laboratory and positive controls showed an increase in the number of revertant colonies, demonstrating the efficiency of the test system. All criteria for a valid study were met. From the results of this study, under the specified experimental conditions, test item was concluded to be non-mutagenic in the Bacterial Reverse Mutation Test using Salmonella typhimurium.