Dioctyl ether

Endpoint summary

Link to relevant study record(s)

Reference

Endpoint:

dermal absorption in vitro / ex vivo

Type of information:

experimental study

Adequacy of study:

key study

Study period:

2009

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

OECD Guideline 428 (Skin Absorption: In Vitro Method)

Deviations:

no

GLP compliance:

yes

Radiolabelling:

no

Species:

other: in vitro

Type of coverage:

open

Vehicle:

unchanged (no vehicle)

Duration of exposure:

24 hours

Doses:

30 µL

Details on study design:

The aim of the present study was to investigate the in vitro penetration of dioctyl ether (DOE) from the product Cetiol OE at human skin of 3 different donors in vitro according to SCCP requirements and to OECD Guideline 428. The test item was only checked for penetration characteristics into the skin, not for permeation properties across the skin into an aqueous acceptor medium. Because of its low water solubility it is not possible to detect the emollient in the usually used acceptor buffer KRB, pH 7.4.
The product provided by the customer was used undiluted. The first step of the study was to establish an analytical method for quantification of DOE. The described analytical method was developed to quantify the compound in the used extraction medium. The method was validated under GLP conditions for this purpose. At the same time the stability of DOE was tested over 24 hours at 25 °C in the extraction medium employed in the penetration studies (methanol). At the beginning of the study, the DOE content in the test item was determined by LC-MS in triplicate. Additionally the content of DOE in Cetiol OE after skin contact was determined. The penetration of DOE from the test item was investigated at human skin from 3 donors in two fold (n=2) for each donor (totalizing n=6) conformable to the SOP M 019 at Across Barriers. The skin specimen was internally encoded according to the corresponding SOP A 005 at Across Barriers. Full thickness skin was used. The skin thickness was measured immediately before
performing the studies. At the end of the penetration experiment the remaining DOE content at the skin surface was determined. For that goal the test item was collected with cotton swabs and transferred to a falcon tube with the extraction medium; this is the so-called wash procedure. After removing residual emollient, the concentration of DOE in the skin - in the Stratum corneum and deeper skin layers - was quantified. The upper corneous layer of the skin was stripped off and the residual skin was cryo-sectioned. The content of DOE in the filter placed under the skin was measured. After the in vitro study a mass recovery was carried out to determine the mass balance and local distribution of DOE in the different skin compartments. For that goal a quotient of total mass of DOE at the end of the study on the skin surface, in Stratum corneum, Epidermis/Dermis and the
used filter versus the applied amount of DOE in the test item at the start of the study was calculated. Parallel to the in vitro studies with DOE at human skin, the permeability of Caffeine was carried out (MEA: multiple endpoint analysis) at a concentration of 10 mg/L in Krebs-Ringer-buffer (KRB) at pH 7.4 (n=2 for 2 skin donors, n=3 for 1 skin donor). Caffeine is a recommended marker molecule of the OECD Guideline for the quality control of human skin. The results of the Caffeine permeation were compared with the permeability coefficients of previous studies on historical human skin membranes of different origin at Across Barriers.

Details on in vitro test system (if applicable):

SKIN PREPARATION
- Source of skin: human skin
- Type of skin: abdomen

PRINCIPLES OF ASSAY
- Diffusion cell: Franz cell
- Test temperature: 25%
- Occlusion: no
- Reference substance(s): caffeine

Signs and symptoms of toxicity:

not examined

Dermal irritation:

not examined

Absorption in different matrices:

The mass recovery calculations present amounts and percentages of compound which penetrated and remained in the donor compartment. The mean amount of DOE removed from the skin surface (skin wash) ranged from 103.90 % to 120.51 % of the dose applied. The mean recovery in the two first tape strips was 0.20 % ±0.09 % during all performed experiments. In the further 18 tape strips a mean recovery of 0.52 % ±0.27 % was documented. The mean absorbed dose of DOE, sum of the amounts found in the viable epidermis, dermis and filter, was 0.30 % ±0.15 %. That means, most of the test item remains at the skin surface, a small amount migrates into the Stratum corneum and an even smaller amount enters the deeper skin layers.

Total recovery:

The results from the extraction method have shown that methanol was suitable for performing the penetration experiments presenting recovery values which has ranged between 95.01 % to 118.42 % for the higher concentration of DOE, which complies to the acceptance limit 100 ±20 %. For the lower concentration the mean recovery values were between 90.05 % - 125.34 %.

Time point:

24 h

Dose:

30 µL

Parameter:

percentage

Absorption:

> 0 - < 1 %

Table 1: Mean amount [µg/cm²] of DOE in the samples from the three in vitro experiments

Cumulative amount [µg/cm²] of DOE in the samples
Sample	Skin 336-01-0808		Skin 337-01-0908		Skin 340-01-0908		All skins used
	Mean	SD	Mean	SD	Mean	SD	Mean	SD
Dose applied	7721.03	157.56	7601.82	0.00	7946.60	267.21	7756.48	251.03
Formulation	9300.54	1.76	8293.74	273.46	8255.67	257.58	8616.65	580.83
2 Tape strips	13.58	6.02	20.61	4.02	11.54	3.36	15.24	6.60
18 Tape strips	45.07	30.21	41.47	8.51	33.68	7.46	40.07	21.06
Cryocuts	13.12	1.40	13.93	0.16	36.38	6.50	17.81	7.87
Filter	3.74	0.62	3.04	0.69	9.64	3.83	5.47	4.09

Table 2: Mean recovery rate and dose absorbed [%] of DOE in the samples from the three in vitro experiments

Recovery and dose absorbed [%] of DOE in the samples
Sample	Skin 336-01-0808		Skin 337-01-0908		Skin 340-01-0908		All skins used
	Mean	SD	Mean	SD	Mean	SD	Mean	SD
Formulation	120.51	2.48	109.10	3.60	103.90	0.25	111.17	8.09
2 Tape strips	0.17	0.07	0.27	0.05	0.15	0.05	0.20	0.09
18 Tape strips	0.58	0.38	0.55	0.11	0.43	0.11	0.52	0.27
Cryocuts	0.17	0.01	0.18	0.00	0.34	0.09	0.23	0.10
Filter	0.05	0.01	0.04	0.01	0.12	0.05	0.07	0.05
Dose absorbed	0.22	0.02	0.22	0.01	0.46	0.15	0.30	0.15
Total recovery	121.48	2.01	110.14	3.77	104.93	0.55	112.18	8.04

Conclusions:

Most of the test item remains at the skin surface, a small amount migrates into the Stratum corneum and an even smaller amount enters the deeper skin layers.

Executive summary:

The LC-MS method was successfully developed and validated with regard to method selectivity, linearity, accuracy and precision in the extraction medium employed for the penetration experiments (methanol). Furthermore, the test compound has demonstrated good stability over the period of 24 hours at RT in methanol. The content of DOE was determined in triplicate in the test solution and mean value was 108.0 %, which complies to the acceptance criteria of 100±10 %. The results from the extraction method have shown that methanol was suitable for performing the penetration experiments presenting recovery values which has ranged between 95.01 % to 118.42 % for the higher concentration of DOE, which complies to the acceptance limit 100±20 %. For the lower concentration the mean recovery values were between 90.05 % - 125.34 %.

The mass recovery calculations present amounts and percentages of compound which penetrated and remained in the donor compartment. The mean amount of DOE removed from the skin surface (skin wash) ranged from 103.90 % to 120.51 % of the dose applied. The mean recovery in the two first tape strips was 0.20 %±0.09 % during all performed experiments. In the further 18 tape strips a mean recovery of 0.52 %±0.27 % was documented. The mean absorbed dose of DOE, sum of the amounts found in the viable epidermis, dermis and filter, was 0.30 %±0.15 %. That means, most of the test item remains at the skin surface, a small amount migrates into the Stratum corneum and an even smaller amount enters the deeper skin layers.

Key value for chemical safety assessment

Bioaccumulation potential:

no bioaccumulation potential

Additional information

No study is available in which the toxicokinetic properties (distribution, metabolism, elimination) of diocytlether were investigated.

Information about the dermal absorption behaviour was tested.

 

The expected toxicokinetic behaviour is derived from the physicochemical properties, the results from the available toxicological studies and the available literature following the information given in guidance document 7c.

 

Diocytlether having a molecular weight of ~240 g/mol is a liquid with a water solubility of <1 mg/L (20°C) . It has a low volatility of <40P (20°C) has a lipophilic character (log Pow >6.5). The structure shows no hydrolysable groups or ionic elements. The surface tension is 56.6 mN/m.

 

 

Oral and GI absorption:

Substance is not soluble in water and in GI fluids. It will not easily pass through aqueous pores or epithelial barriers. The substance may be taken up by micellular solubilisation. The limited systemic toxicity furthermore does not indicate an absorption through the GI tract.

 

 

Inhalative absorption:

Substance is not easily soluble in mucus and does not easily pass through aqueous pores or epithelial barriers. An absorption via the lung is therefore not assumed.

 

 

Dermal absorption:

Due to the physico chemical information, the substance can be assumed to be absorbed via the skin. A low transfer between the stratum corneum and the epidermis is assumed. Experimental data show that the penetration through the skin is below 1%. As a consequence the systemic availablity should be low after dermal exposure.

 

 

Distribution:

The molecular weight points to a wide distribution. On the other side due to the low solubility a bad distribution can be assumed. A distribution into fat cells is possible.

 

 

Accumulative potential:

Based on the PC information the main site of accumulation is assumed to be the adipose tissue as well as skin. The substance will be sloughed off with the skin. No accumulation in bone or in lung is predicted.

 

Metabolism:No detailed information can be derived concerning the metabolism.

 

Reactivity:Available studies on genotoxicity were negative, i. e. there is no indication of a reactivity of dioctylether or its metabolites under the test conditions.

 

Excretion:

Due to the physico chemical information an excretion of the substance via the urine is quesionable. An exalation is not assumed due to the low vapor pressure.