3,7-dimethylnona-1,6-dien-3-ol

Dermal absorption

Administrative data

Endpoint:

dermal absorption in vitro / ex vivo

Type of information:

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

Adequacy of study:

key study

Study period:

No data

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: see 'Remark'

Remarks:

Study was not performed according to GLP. An equivalent or similar guideline to OECD 428 is used. Study is reported extensively. Ethyllinalool and linalool are structural homologues which differ only by a methyl-group. Their physical-chemical properties are comparable and available experimental data on same toxicological endpoints, showed identical toxicological properties. Therefore, it is assumed that all toxicological properties are as well comparable and thus read-across is justified.

Cross-reference

Reason / purpose for cross-reference:

reference to same study

Data source

Reference

Reference Type:

study report

Title:

Unnamed

Year:

2007

Report date:

2007

Materials and methods

Test guideline

Qualifier:

equivalent or similar to guideline

Guideline:

OECD Guideline 428 (Skin Absorption: In Vitro Method)

Principles of method if other than guideline:

Not relevant

GLP compliance:

no

Test material

Test material information

Constituent 1

Reference substance name:

Linalool

EC Number:

201-134-4

EC Name:

Linalool

Cas Number:

78-70-6

Molecular formula:

C10H18O

IUPAC Name:

3,7-dimethylocta-1,6-dien-3-ol

Details on test material:

Linalool Pure FCC
- Name of test material (as cited in study report): Linalool
- Substance type: Terpenoid alcohol
- Physical state: Liquid (colourless to very pale yellow)

[1,2-14C]Linalool
See "Confidential details on test material"

Radiolabelling:

yes

Remarks:

[1,2-14C]Linalool

Test animals

Species:

human

Strain:

other: Not relevant

Sex:

female

Details on test animals or test system and environmental conditions:

Not relevant

Administration / exposure

Type of coverage:

other: Open and occlusive (greased coverslip to diffusion cell donor chamber)

Vehicle:

other: 70:30 ethanol/water (v/v)

Duration of exposure:

24 hours

Doses:

- Actual doses: 40.2 mg/ml (4.02%)
- Dose volume: 5 ul/cm2 = 201 ug/cm2

No. of animals per group:

12 replicates/condition (open/occlusive) of 7 different donors

Control animals:

yes

Remarks:

one control cell (open, only vehicle), and benzoic acid as reference control

Details on study design:

DOSE PREPARATION
- Method for preparation of dose suspensions: 199.7 mg linalool in 5 ml ethanol/water (70/30 v/v). 0.53 mg labelled linalool added to 2 ml of this solution.

VEHICLE
- Amount(s) applied (volume or weight with unit): 5 ul/cm2 * 1.2 cm2 = 6 ul
- Concentration (if solution): 4.02%
- Purity ethanol: 99.7-100%

REMOVAL OF TEST SUBSTANCE
After 24 hours with dry cotton bud

SAMPLE PREPARATION
- Storage procedure: In tightly sealed vials
- Preparation details: Extraction from media with different solvents (acetonitrile, optisolve for tape strips, methanol)

ANALYSIS
- Method type for identification: Liquid scintillation counting

Details on in vitro test system (if applicable):

SKIN PREPARATION
- Source of skin: 7 different donors
- Type of skin: Breast and abdominal
- Preparative technique: According to accepted method
- Membrane integrity check: Yes, by assessing permeation of tritiated water
- Storage conditions: -20 degrees Celsius

PRINCIPLES OF ASSAY
- Diffusion cell: Franz-type
- Receptor fluid: PBS
- Solubility of test substance in receptor fluid: 1 mg/ml
- Static system: Yes, containing diffusion cell donor and receptor chamber
- Test temperature: 37.0 +/- 0.5 degrees Celsius (skin surface: 32 +/- 1 degrees Celsius)
- Occlusion: Open and closed
- Reference substance(s): Benzoic acid (3.99 mg/ml in 50/50 (v/v) ethanol/water)

Results and discussion

Signs and symptoms of toxicity:

not examined

Remarks:

in vitro study

Dermal irritation:

not examined

Remarks:

in vitro study

Absorption in different matrices:

See field "results including tables and figures"

Total recovery:

- Total recovery (mean +/- SD):
Unoccluded: 8.01 +/- 2.1%
Occluded: 36.3 +/- 10.1%
Control: no radiolabel contamination was detected in any of the compartments
Overall evaporative loss: ~97%
Permeation benzoic acid: 89.6 +/- 3.0%, indicating a valid test system
- Recovery of applied dose acceptable: No, recovery should be 100 +/- 10%
- Results adjusted for incomplete recovery of the applied dose: No, but evaporative loss is determined

Percutaneous absorption

Percutaneous absorption 1

Dose:

40.2 mg/ml

Parameter:

percentage

Absorption:

ca. 0.7 %

Remarks on result:

other: 0.5 h

Remarks:

Open conditions (excl. epidermis)

Percutaneous absorption 2

Dose:

40.2 mg/ml

Parameter:

percentage

Absorption:

ca. 1.3 %

Remarks on result:

other: 1 h

Remarks:

Open conditions (excl. epidermis)

Percutaneous absorption 3

Dose:

40.2 mg/ml

Parameter:

percentage

Absorption:

ca. 2.7 %

Remarks on result:

other: 6 h

Remarks:

Open conditions (excl. epidermis)

Percutaneous absorption 4

Dose:

40.2 mg/ml

Parameter:

percentage

Absorption:

ca. 2.9 %

Remarks on result:

other: 12 h

Remarks:

Open conditions (excl. epidermis)

Percutaneous absorption 5

Dose:

40.2 mg/ml

Parameter:

percentage

Absorption:

ca. 3 %

Remarks on result:

other: 24 h

Remarks:

Open conditions (excl. epidermis)

Percutaneous absorption 6

Dose:

40.2 mg/ml

Parameter:

percentage

Absorption:

ca. 1.3 %

Remarks on result:

other: 0.5 h

Remarks:

Occluded conditions (excl. epidermis)

Percutaneous absorption 7

Dose:

40.2 mg/ml

Parameter:

percentage

Absorption:

ca. 3.4 %

Remarks on result:

other: 1 h

Remarks:

Occluded conditions (excl. epidermis)

Percutaneous absorption 8

Dose:

40.2 mg/ml

Parameter:

percentage

Absorption:

ca. 10.1 %

Remarks on result:

other: 6 h

Remarks:

Occluded conditions (excl. epidermis)

Percutaneous absorption 9

Dose:

40.2 mg/ml

Parameter:

percentage

Absorption:

ca. 11.7 %

Remarks on result:

other: 12 h

Remarks:

Occluded conditions (excl. epidermis)

Percutaneous absorption 10

Dose:

40.2 mg/ml

Parameter:

percentage

Absorption:

ca. 12.7 %

Remarks on result:

other: 24 h

Remarks:

Occluded conditions (excl. epidermis)

Conversion factor human vs. animal skin:

Not applicable

Any other information on results incl. tables

Distribution of linalool and percentage absorption in different compartments:

Mean (+/- SD) distribution of linalool in all compartments (ug/cm2) (after 24 hours)		24h wipe	Donor chamber	Strip 1*	Strips 2-3	Strips 4-6	Strips 7-10	Epidermis	Filter paper	Receptor phase
Unoccluded conditions	Mean	5.41	2.16	0.399	0.553	0.295	0.172	0.65	0.609	5.95
	SD	1.06	0.9	0.256	0.443	0.164	0.097	0.448	0.191	3.17
Occluded conditions	Mean	6.32	36.7	0.317	0.312	0.227	0.161	1.02	2.39	25.6
	SD	1.83	18.1	0.232	0.204	0.13	0.098	0.51	0.71	7.5

* Skin membranes were stripped 10 times and the strips were grouped

Absorption (%) of linalool in all compartments (after 24 hours)		24h wipe	Donor chamber	Strip 1*	Strips 2-3	Strips 4-6	Strips 7-10	Epidermis	Filter paper	Receptor phase
Unoccluded conditions	Mean	2.67	1.07	0.198	0.274	0.146	0.085	0.321	0.301	2.95
	SD	0.52	0.44	0.128	0.221	0.082	0.049	0.223	0.095	1.58
Occluded conditions	Mean	3.14	18.2	0.158	0.155	0.113	0.08	0.506	1.19	12.7
	SD	0.91	9.0	0.116	0.101	0.065	0.049	0.253	0.35	3.7

* Skin membranes were stripped 10 times and the strips were grouped

Read across:

Ethyllinalool and linalool are structural homologues which differ only by a methyl-group. Their physical-chemical properties are comparable and available experimental data on same toxicological endpoints, showed identical toxicological properties. Therefore, it is assumed that all toxicological properties are as well comparable and thus read-across is justified. Toxicokinetic data were identified for linalool which was shown to be rapidly and completely absorbed and excreted upon oral administration. Although toxicokinetic data on ethyllinalool were not identified, it can be reasonably assumed that ethyllinalool is absorbed, distributed, metabolized and excreted via the same mechanisms as linalool. This assumption is supported by (i) comparable vapor pressure, water solubility and log Pow and (ii) in silico metabolism prediction for ethyllinalool using computational software METEOR version 12. It is predicted that ethyllinalool may be glucuronidated at the hydroxyl-group and / or hydroxylated at the allylic positions and at the terminal methyl-group with subsequent glucuronidation.

Applicant's summary and conclusion

Conclusions:

Under the conditions of this test, linalool was found to penetrate through human skin. Occlusion of the test system resulted in a higher absorption rate after 24 hours (3.0% after open application versus 12.7% after occlusion). However, a large portion of the applied dose evaporated within 24 hours.

Executive summary:

This study was conducted to determine the skin penetrating potential of linalool. An in vitro diffusion cell test system was used (methods equivalent or similar to OECD guideline 428). Prepared human skin membranes were exposed open and occluded to 40.2 mg/ml (201 ug/cm2, 1.2 cm2 cell) radiolabelled linalool (in 70/30% ethanol/water) for 24 hours and the amount of test substance left on the skin (by wipe), in the donor chamber, stratum corneum (tape strips), epidermis, filter paper and receptor chamber were determined by liquid scintillation counting. One control skin membrane was used (unoccluded) where only the vehicle was added. Evaporation loss was also determined in an additional experiment. A reference substance (benzoic acid) was used to test the validity of the test sytem.

Linalool was found to penetrate through skin and after 24 hours 3.0% of the applied dose was recovered in receptor fluid in the open test system, versus 12.7% in the receptor fluid in the occluded test system. It was found that about 97% of the applied linalool dose evaporated within 24 hours, resulting in a very low total recovery in the open test system. Benzoic acid was found to penetrate rapidly through skin, total recovery was 89.6%. The test system is therefore shown to be valid.

Under the conditions of this test, linalool was found to penetrate through human skin. Occlusion of the test system resulted in a higher absorption rate after 24 hours (3.0% versus 12.7%). However, a large portion (97%) of the applied dose evaporated within 24 hours. Thus, systemic exposure to topically applied linalool is low.