Hexyl salicylate

Dermal absorption

Administrative data

Endpoint:

dermal absorption in vitro / ex vivo

Type of information:

experimental study

Adequacy of study:

key study

Study period:

24th May - 11th November 2016

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Data source

Reference

Reference Type:

study report

Title:

Unnamed

Year:

2016

Report date:

2016

Materials and methods

Test guideline

Test guideline 1

Qualifier:

according to guideline

Guideline:

OECD Guideline 428 (Skin Absorption: In Vitro Method)

Version / remarks:

2004

Deviations:

no

Test guideline 2

Qualifier:

according to guideline

Guideline:

EU Method B.45 (Skin Absorption: In Vitro Method)

Version / remarks:

2008

Deviations:

no

GLP compliance:

yes

Test material

Test material information

Constituent 1

Reference substance name:

Hexyl salicylate

EC Number:

228-408-6

EC Name:

Hexyl salicylate

Cas Number:

6259-76-3

Molecular formula:

C13H18O3

IUPAC Name:

hexyl salicylate

Details on test material:

Material Hexyl Salicylate
Batch number 0000078475

Specific details on test material used for the study:

Non-radiolabelled test material: hexyl salicylate Batch 50064843 (99.882% purity), expiry April 2018
Radiolabelled test material: hexyl salicylate Batch 745-106-0613-A-20160405-JKR (99.8% radiochemical purity; specific activity 61.3 mCi/mmol (10.11 MBq/mg)), expiry April 2021

Radiolabelling:

yes

Administration / exposure

Details on in vitro test system (if applicable):

SKIN PREPARATION
- Source of skin: human
- Ethical approval if human skin: yes
- Type of skin: breast / abdomen
- Preparative technique: dermatome
- Thickness of skin (in mm): 0.2-0.4
- Membrane integrity check: yes, using tritiated water
- Storage conditions: frozen
- Justification of species, anatomical site and preparative technique: standard methods and techniques

PRINCIPLES OF ASSAY
- Diffusion cell: 9 mm automated flow-through cells
- Receptor fluid: physiological saline with 6% PEG 20 (absorption assay)
- Flow-through system: yes
- Test temperature: 32 +/-1 degrees C
- Humidity: ambient
- Occlusion: no

Results and discussion

Absorption in different matrices:

The mean absorption of hexyl salicylate (100%) into the receptor fluid over the 24-hour study duration was 15.78 µg/cm2, representing 0.15% of the applied dose. The mean maximal flux was
0.84 µg/cm-2.h and the lag time was 4.9 hours.

The mean absorption of hexyl salicylate (20% solution in dipropylene glycol) into the receptor fluid was 13.58 µg/cm2, representing 0.64% of the applied dose. The mean maximal flux was 0.83 µg/cm2.h and the lag time was 7.2 hours.

The mean absorption of hexyl salicylate (0.1% solution in dipropylene glycol) into the receptor fluid was 0.103 µg/cm2, representing 1.00% of the applied dose. The mean maximal flux through human skin was 0.007 µg/cm2.h and the lag time was 7.8 hours.

The mean total absorption (defined as the radioactivity present in the receptor fluid, the receptor compartment wash and the skin membranes (excluding tape strips)) was 0.53 ± 0.14% (100%), 3.04 ± 1.43% (20% solution) and 2.34 ± 0.69% (0.01% solution). The mean potentially absorbed dose (defined as the radioactivity present in the receptor fluid, the receptor compartment wash, the skin membranes and the stratum corneum (except for the first 2 tape strips)) was 0.65 ± 0.19% (100%), 5.20 ± 2.41% (20% solution) and 2.58 ± 0.77% (0.01% solution).

Total recovery:

The mean recovery of hexyl salicylate in human skin was 98.5 +/- 1.9%, 97.6 +/- 0.9% and 93.5 +/- 2.0% for the 100%, 20% and 0.1% solutions, respectively.

Percutaneous absorption

Percutaneous absorption 1

Key result

Time point:

24 h

Dose:

100%

Parameter:

percentage

Absorption:

0.8 %

Remarks on result:

other: Potentially absorbed dose, taking into account the potential for metabolism to salicylic acid.

Percutaneous absorption 2

Key result

Time point:

24 h

Dose:

20%

Parameter:

percentage

Absorption:

7.8 %

Remarks on result:

other: Potentially absorbed dose, taking into account the potential for metabolism to salicylic acid.

Percutaneous absorption 3

Key result

Time point:

24 h

Dose:

0.1%

Parameter:

percentage

Absorption:

2.7

Remarks on result:

other: Potentially absorbed dose, taking into account the potential for metabolism to salicylic acid.

Conversion factor human vs. animal skin:

Not applicable

Any other information on results incl. tables

Summary of the dermal absorption phase

Group	A	B		C
Concentration of hexyl salicylate	100%	20%		0.1%
Number of replicates	8	8		8
Maximal flux (µg.cm-2.h-1)	0.84 ± 0.12	0.83 ± 0.21		0.007 ± 0.001
	Recovery (% of dose, mean±SD)
Amount in receptor fluid	0.15 ± 0.02		0.64 ± 0.15		1.00 ± 0.16
Amount in receptor compartment wash	0.009 ± 0.001		0.072 ± 0.017		0.037 ± 0.018
Amount in (stripped) skin	0.38 ± 0.14		2.33 ± 1.32		1.30 ± 0.62
Amount in tape strips 1+2	0.12 ± 0.09		2.62 ± 1.76		0.12 ± 0.08
Amount in tape strips 3-last	0.12 ± 0.08		2.16 ± 1.11		0.24 ± 0.15
Amount in skin wash	97.6 ± 1.8		87.9 ± 4.3		90.0 ± 3.1
Total recovery	98.5 ± 1.9		97.6 ± 0.9		93.5 ± 2.0
Absorbed dose 1	0.53 ± 0.14		3.04 ± 1.43		2.34 ± 0.69
Potentially absorbed dose 2	0.65 ± 0.19		5.20 ± 2.41		2.58 ± 0.77

1: the absorbed dose is defined as the amount in the receptor fluid, the receptor compartment wash and skin membrane, excluding tape strips

2: the potentially absorbed dose is defined as the amount in the receptor fluid, the receptor compartment wash, the skin and stratum corneum (except for the first two tape strips)

Applicant's summary and conclusion

Conclusions:

Dermal absorption values of 0.8%, 7.8% and 2.7% are calculated for hexyl salicylate concentrations of 100%, 20% and 0.1% respectively, taking into account the potential for metabolism to salicylic acid in viable skin.

Executive summary:

The dermal absorption of 14C-radiolabelled hexyl salicylate was investigated in vitro in human skin membranes using flow-through diffusion cells and physiological saline containing 6% PEG 20 as the receptor medium. Hexyl salicylate (undiluted or as 10% or 0.1% dilutions in dipropylene glycol) was applied to split-thickness abdominal or breast skin membranes (n=8) obtained from four female donors. Exposure was terminated by washing at 8 hours with a 3% soap solution and the skin membranes were tape-stripped at termination of the study 24 hours after exposure. At each concentration of hexyl salicylate, the majority of the applied radioactivity was removed by washing at 8 hours (97.6%, 87.9% and 93.5% at concentrations of 100%, 20% and 0.1%, respectively). Only relatively small amounts of radioactivity (0.15%, 0.64% and 1.00%, respectively) were detected in the receptor fluid.

 

In a separate metabolism phase, 14C-radiolabelled hexyl salicylate (0.1% in dipropylene glycol) was applied to breast or abdomen skin membranes (n=3) from two female donors using static diffusion cells and tissue culture medium as receptor fluid. The skin membranes were used shortly following receipt and without freezing, in order to maintain metabolic capacity. Analysis of the receptor fluid showed an absence of hexyl salicylate, but identified salicylic acid as the major component, indicating extensive metabolism of hexyl salicylate by dermal esterases. Hexyl salicylate and salicylic acid were identified in the skin extracts.  Calculation of a dermal absorption value for hexyl salicylate must take into account the potential for metabolism to salicylic acid in the skin. The dermal absorption values indicated in the dermal absorption phase of this study may underestimate the total level of absorption, as little or no metabolism would have occurred in the non-viable skin membranes used in this phase. For the purposes of the risk assessment, a conservative assumption is that all of the hexyl salicylate present in the skin (i.e. all of the radioactivity not removed by washing at the end of the exposure period) is potentially metabolised and absorbed a salicylic acid. Dermal absorption values of 0.8%, 7.8% and 2.7% are therefore calculated for hexyl salicylate concentrations of 100%, 20% and 0.1% respectively.