Registration Dossier

Administrative data

Endpoint:
dermal absorption in vitro / ex vivo
Type of information:
read-across from supporting substance (structural analogue or surrogate)
Adequacy of study:
key study
Study period:
Not reported
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
other: see 'Remark'
Remarks:
A valid study is available for the analogue substance benzyl acetate. It is a GLP compliant study conducted in compliance with agreed protocols, with no or minor deviations from standard testing guidelines. The read-across is considered to be suitable based on the structural and “mechanistic action” similarities between the target substance (1-phenylethyl acetate) and source substance (benzyl acetate) and their similar physico-chemical properties.

Data source

Reference
Reference Type:
publication
Title:
Percutaneous absorption of benzyl actetate through rat skin in vitro. 3. A comparision with human skin
Author:
Garnett, A., Hotchkiss, S.A.M. and Caldwell, J.
Year:
1994
Bibliographic source:
Fd Chem. Toxic. Vol 32, No. 11, pp. 1061-1065

Materials and methods

Test guideline
Qualifier:
equivalent or similar to guideline
Guideline:
OECD Guideline 428 (Skin Absorption: In Vitro Method)
Deviations:
no
Principles of method if other than guideline:
The absorption of benzyl acetate was compared in an in vitro model using both human and rat skin in flow-through diffusion cells following topical application of neat radiolabelled benzyl acetate. Absorption of the test substance was measured over a 72 hour period.
GLP compliance:
not specified

Test material

Constituent 1
Chemical structure
Reference substance name:
Benzyl acetate
EC Number:
205-399-7
EC Name:
Benzyl acetate
Cas Number:
140-11-4
Molecular formula:
C9H10O2
IUPAC Name:
benzyl acetate
Details on test material:
- Name of test material: [methylene-14C]Benzyl acetate and unlabelled benzyl acetate- Radiochemical purity: > 96 %- Specific activity: 53 mCi/mmol- Smiles notation : c1(COC(C)=O)ccccc1- Structural formula attached as image file : see Fig.1- Molecular formula: C9H10O2- Molecular weight : 150.2 g/mol
Radiolabelling:
yes
Remarks:
[methylene-14C]Benzyl acetate

Test animals

Details on test animals or test system and environmental conditions:
Not applicable

Administration / exposure

Duration of exposure:
Up to 72 hours
Doses:
10 µL (33.1 mg/cm²) aliquots of neat benzyl acetate was applied to the exposed epidermal surface of rat or human skin.
No. of animals per group:
Not applicable
Details on in vitro test system (if applicable):
SKIN PREPARATION- Source of skin: Rat skin was obtained from male Fischer 344 rats. Human skin was obtained from surgical resection patients.- Type of skin: Dorsal skin from rats, breast or abdominal from humans- Preparative technique: Rat skin (shaved) was dissected from male Fischer 344 rats from the dorsal region on each day of the experiment. The skin was dissected of excess fat and tissue. Human skin was washed in normal saline to remove surface blood and then treated in the same way as the rat tissues. Full-thickness skin was cut into circles with a diameter of 1.7 cm. The samples were placed in diffusion cells in a flow-through diffusion cell apparatus and equilibrated for 30 minutes. - Storage conditions: Rat skin samples were used as soon as they were prepared.PRINCIPLES OF ASSAY- Receptor fluid: The underside of the tissue was in contact with continuously flowing receptor fluid of HEPES-buffered Hanks' balanced salt solution supplemented with 0.5 % v/v gentamicin. The flow rate of the receptor fluid was 1.5 mL/h.- Test temperature: The skin surface temperature was maintained at 21 ± 1 °C- Occlusion: The test substance was applied to the exposed epidermal surface of the skin then occluded with a teflon cap.

Results and discussion

Percutaneous absorptionopen allclose all
Dose:
10 µL (33.1 mg/cm²)
Parameter:
percentage
Absorption:
17.8 %
Remarks on result:
other: 72 h
Remarks:
In human skin
Dose:
10 µL (33.1 mg/cm²)
Parameter:
percentage
Absorption:
55.8 %
Remarks on result:
other: 72 h
Remarks:
In rat skin

Any other information on results incl. tables

Table 1: Recovery of radioactivity

Source of recovery

Recovery at 72 hours (% applied dose)

Rat

Human

Receptor fluid

55.8 ± 5.0

17.8 ± 3.3*

Skin

20.6 ± 0.3

10.2 ± 0.1*

Swab

1.1 ± 0.4

6.6 ± 3.7*

Diffusion Cell

4.3 ± 0.1

7.8 ± 1.5

Cap

15.2 ± 3.6

59.9 ± 0.5*

Total

96.8 ± 1.9

103.5 ± 1.8

Values are means ± SD (n-12)

* P<0.05

- Comparison of absorption in rat and human skin: Absorption through rat skin was significantly higher than human skin at all time points. Penetration through rat skin was extensive reaching 34.3 ± 3.9 % (11.3 ± 1.3 mg/cm²) by 24 hours and increasing to 55.8 ± 5.0 % (18.5 ± 1.7 mg/cm²) of the applied dose at 72 hours. In human skin, 5.5 ± 0.1 % (1.8 ± 0.0 g/cm²) by 24 hours and 17.8 ± 3.3 % (5.9 ± 1.1 mg/cm²) by 72 hours.

 

- Comparison of the rate of absorption: The rate of absorption through rat skin between 0 and 36 hours was significantly greater than human skin. No species difference, in the rate of absorption, was noted between 48 and 72 hours. The rate of benzyl acetate absorption increased very rapidly during the first 8 hours of exposure. The rate reached a maximum of 0.6 ± 0.1 mg/cm²/hr at 8 hours, this was maintained for approximately two hours and declined from then to 0.3 ± 0.0 and 0.1 ± 0.0 mg/cm²/hr at 24 and 72 hours respectively. The rate of absorption through human skin increased relatively slowly over the first 18 hours reaching a maximum of 0.1 ± 0.0 mg/cm²/hr maintaining this rate for up to 24 hours before slowly declining to 0.01 ± 0.0 mg/cm²/hr at 72 hours.

 

- Recovery: The recovery of the test substance from the skin at the end of the experiment showed a significant interspecies difference. The amount of radioactivity recovered from both species was relatively low, but was significantly greater in the human skin (6.6 ± 3.7 %) from rat skin (1.1 ± 0.4 %). The recovery from the Teflon caps was high with human skin (59.9 ± 0.5 %) and significantly greater in rat skin (15.2 ± 3.6 %). Some radioactivity was found on the diffusion cells, however the total recovery of radioactivity under the conditions of the test was greater than 96 % in human and rat skin.

 

- Intra- and inter-experimental variation: In three separate experiments with rat skin, the absorption at 24 hours was 33.5 ± 4.1, 36.4 ± 4.4 and 33.1 ± 3.3 %. The mean coefficient of variation within each experiment was 10.0-12.2 % at 24 hours. When the absorption was studied individually using human skin from different individuals, the absorption was 5.7 ± 0.0, 5.1 ± 0.0 and 5.8 ± 0.3 % at 24 hours. The mean coefficient of variation was 0.1 %.

When all data were compared, absorption through rat skin was 34.3 ± 3.9 % at 24 hours with an inter-experimental coefficient variation of 11.4 %. The mean absorption in human skin was 5.5 ± 0.1 % with an inter-experimental variation coefficient of 1.8 %.

ANALOGUE APPROACH JUSTIFICATION:

- See attached “Justification for read-across” document for full details.

- In summary, important considerations for the use of read-across for acute toxicity are: i) 1-phenylethyl acetate (the target chemical) has similar physico-chemical properties as benzyl acetate (the source substance), ii) there are structural similarities between the two chemicals, iii) the OECD QSAR Toolbox assigns an identical toxicity profiles to both chemicals, and iv) both chemicals have been tested for acute oral toxicity, which demonstrated that neither substance requires classification for acute toxicity and that the benzyl acetate will represent a worst-case scenario, and are adequate for classification and labelling and risk assessment purposes.

The information reported in this summary is included to demonstrate comparability between the source (benzyl acetate) and target (1-phenyl-ethyl acetate) substance.

Applicant's summary and conclusion

Conclusions:
Under the conditions of the test, low level absorption of the test substance, benzyl acetate through human skin was demonstrated indicating that some low level systemic exposure may occur in humans. The study did demonstrate that human skin in less permeable than rat skin.
Executive summary:

The absorption of benzyl acetate was compared in an in vitro model using both human and rat skin in flow-through diffusion cells following topical application 10 µL (33.1 mg/cm²) of neat radiolabelled benzyl acetate. The study was comparable to the OECD guideline 428, with as additional examination performed examining the inter-species difference of the absorption of the test substance. Absorption of the test substance was measured over a 72 hour period. Under the conditions of the test, low level absorption of the test substance, benzyl acetate through human skin was demonstrated (17.8 ± 3.3 %) indicating that some low level systemic exposure may occur in humans. The study did demonstrate that human skin in less permeable than rat skin, with the absorption through rat skin reaching 55.8 ± 5.0 %.