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Link to relevant study record(s)

Reference
Endpoint:
dermal absorption in vitro / ex vivo
Type of information:
experimental study
Adequacy of study:
supporting study
Study period:
08 April 2010 to 05 May 2010
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
Reason / purpose:
reference to same study
Qualifier:
according to
Guideline:
OECD Guideline 428 (Skin Absorption: In Vitro Method)
Version / remarks:
(2004) and the accompanying OECD Guidance Document No. 28 Guidance Document for the Conduct of Skin Absorption Studies (2004)
GLP compliance:
yes
Specific details on test material used for the study:
- Source and lot/batch No.of test material: American Radiolabelled Chemicals Inc, batch no. 090109
- Radiochemical purity: 93.6%
- Specific activity: 5 mCi/mmol
- Locations of the label: carbonyl carbon
Radiolabelling:
yes
Species:
other: full-thickness human skin
Details on test animals and environmental conditions:
Six samples of full-thickness human skin (4 abdomen and 2 breast) were obtained from female patients aged 19 to 63 years old attending St. John’s Hospital, NHS Lothian, Livingston, UK. On arrival at Charles River, these samples were cleaned of subcutaneous fat and connective tissue using a scalpel blade. The skin samples were washed in cold running water and dried using tissue paper.

The skin samples were then cut into smaller pieces (where appropriate), wrapped in aluminium foil, put into self sealing plastic bags and stored at -20°C until they were used in the study.
Type of coverage:
other:
Remarks:
occluded and unoccluded skin were assessed
Vehicle:
other: leave-on hair styling cream
Duration of exposure:
24 hours
Doses:
The leave-on hair styling cream containing 2% (w/v) radiolabelled test substance was applied (concentration by radioactivity was 2.11% w/v), at an application rate of about 20 mg/cm² (469 µg equiv. OFPMA/cm²).
Details on in vitro test system (if applicable):
SKIN PREPARATION
- Source of skin: female patients aged 19 to 63 years old attending St. John’s Hospital, NHS Lothian, Livingston, UK
- Type of skin: breast or abdomen
- Preparative technique: Split-thickness membranes were prepared by pinning the full-thickness skin, stratum corneum uppermost, onto a raised cork board and cutting at a setting equivalent to 200-400 μm depth using a Zimmer® electric dermatome.
- Thickness of skin (in mm): full-thickness 1430 to 2130 µm; split-thickness 400 µm
- Membrane integrity check: A tritiated water barrier integrity test was performed and any human skin sample exhibiting absorption greater than 0.6% of the applied dose was excluded from subsequent absorption measurements.
- Storage conditions: The split-thickness membranes were stored at about -20°C.

PRINCIPLES OF ASSAY
- Diffusion cell: automated flow-through diffusion cell apparatus
- Receptor fluid: Phosphate buffered saline containing polyoxyethylene 20-oleyl ether (PEG, about 6%, w/v), sodium azide (about 0.01%), streptomycin (about 0.1 mg/mL) and penicillin G (about 100 units/mL)
- Solubility of test substance in receptor fluid: solubility of OFPMA in phosphate buffered saline is 900 mg/L
- Flow-through system: flow rate 1.451 to 1.571 mL/h
- Test temperature: 31.9 to 32.8 °C
- Occlusion: For twelve of the cells (Test Group 1), the donor chambers were occluded with an occlusive trap containing carbon filters. For the other twelve cells (Test Group 2), the donor chamber was left open to the atmosphere and the system was used inside a fume hood.
Total recovery:
The mean mass balance of the occluded test group was 96.01% (standard deviation of 6.25%) of the applied radioactivity.

The mean mass balance of the unoccluded test group was 6.21% (SD = 0.51%) of the applied radioactivity. This very low mass balance was considered to be as a result of the test item volatility.
Key result
Time point:
24 h
Dose:
469 µg equiv. OFPMA/cm²
Parameter:
rate
Absorption:
1.53 %
Remarks on result:
other: Dermal Delivery (sum of absorbed dose, epidermis and dermis)
Remarks:
(7.18 μg equiv./cm²; occluded sample)
Time point:
24 h
Dose:
469 µg equiv. OFPMA/cm²
Parameter:
rate
Absorption:
1.18 %
Remarks on result:
other: Absorbed dose (sum of the receptor fluid and receptor rinse)
Remarks:
(5.52 μg equiv./cm²; occluded sample)
Time point:
24 h
Dose:
469 µg equiv. OFPMA/cm²
Parameter:
rate
Absorption:
0.49 %
Remarks on result:
other: Dermal Delivery (sum of absorbed dose, epidermis and dermis)
Remarks:
(2.32 μg equiv./cm²; unoccluded sample)
Time point:
24 h
Dose:
469 µg equiv. OFPMA/cm²
Parameter:
rate
Absorption:
0.18 %
Remarks on result:
other: Absorbed dose (sum of the receptor fluid and receptor rinse)
Remarks:
(0.87 μg equiv./cm²; unoccluded sample)

For the occluded sample, the total dislodgeable dose was 93.25% of the applied radioactivity. The mean total unabsorbed dose was 94.48% of the applied radioactivity. The absorbed dose (1.18%) was the sum of the receptor fluid (1.17%) and the receptor rinse (<0.01%). Dermal delivery (1.53%) was the sum of the absorbed dose, the epidermis (0.19%) and the dermis (0.17%). Steady state absorption was not observed over the 24 hour assessment period and, therefore, a lag time could not be calculated.

 

For the unoccluded sample, the total dislodgeable dose was 5.02% of the applied radioactivity. The mean total unabsorbed dose was 5.71% of the applied radioactivity. The absorbed dose (0.18%) was the sum of the receptor fluid (0.18%) and the receptor rinse (<0.01%). Dermal delivery (0.49%) was the sum of the absorbed dose, the epidermis (0.12%) and the dermis (0.19%). Steady state absorption was not observed over the 24 h assessment period and, therefore, a lag time could not be calculated.

Conclusions:
Following topical application of [14C]-OFPMA in the test preparation (2%, w/v) to occluded skin, the absorbed dose and dermal delivery of [14C]-OFPMA were 1.18% (5.52 μg equiv./cm2) and 1.53% (7.18 μg equiv./cm2), respectively. The total dislodgeable dose was 93.25%. The mass balance was complete (96.01%). Steady state absorption was not observed over the 24 hour assessment period and, therefore, a lag time could not be calculated.
Executive summary:

The in vitro dermal absorption of OFPMA was determined according to OECD Guideline 428 and the accompanying OECD Guidance Document No. 28. Split-thickness human skin membranes were mounted into flow-through diffusion cells. Receptor fluid was pumped underneath the skin at a flow rate of about 1.5 mL/h. The skin surface temperature was maintained at about 32°C throughout the experiment. A tritiated water barrier integrity test was performed and any human skin sample exhibiting absorption greater than 0.6% of the applied dose was excluded from subsequent absorption measurements.

 

The test preparation containing [14C]-OFPMA (2%, w/v) was applied, at an application rate of about 20 mg/cm² (469 μg equiv.OFPMA/cm²), to 24 human split-thickness skin membranes mounted into flow-through diffusion cells in vitro. Immediately after dosing, the donor chamber of 12 cells was covered with an occlusive trap containing carbon filters in an attempt to collect any volatile OFPMA. The remaining 12 cells remained unoccluded and so were open to the atmosphere, simulating the intended consumer use.

 

Percutaneous absorption was assessed by collecting receptor fluid in hourly fractions from 0 to 8 hours post application and then in 2-hourly fractions from 8 to 24 hours post application. At 24 hours post application, carbon traps were removed from the occluded cells and exposure was terminated by washing the skin surface of all 24 samples. The skin was then dried with tissue paper swabs. The underside of the skin was rinsed with receptor fluid. The skin was then removed from the flow-through diffusion cells, dried and the stratum corneum was removed with 20 successive tape strips. The remaining skin was divided into exposed and unexposed skin (i.e. the area of skin under the cell flange). The exposed epidermis was separated from the dermis. All skin samples were solubilised with Soluene-350® tissue solubiliser. All samples were analysed by liquid scintillation counting.

 

The absorbed dose and dermal delivery of [14C]-OFPMA under occluded conditions were 1.18% (5.52 μg equiv./cm²) and 1.53% (7.18 μg equiv./cm²), respectively. The total dislodgeable dose was 93.25%. The mass balance was complete (96.01%). For unoccluded skin, representing the intended consumer use, the absorbed dose and dermal delivery of [14C]-OFPMA were 0.18% (0.87 μg equiv./cm²) and 0.49% (2.32 μg equiv./cm²), respectively. The total dislodgeable dose was 5.02%. The mass balance was only 6.21% and losses were considered to be due to [14C]-OFPMA volatility. Volatility was confirmed by comparison with the results obtained under occlusive conditions. Steady state absorption was not observed over the 24 hour assessment period for either the occluded or unoccluded systems and, therefore, a lag time could not be calculated.

Description of key information

Based on consideration of physicochemical properties and the quickly occurring and transient symptoms of clinical toxicity following oral dosing, the substance would be expected to be absorbed by the mammalian system. Conservative absorption rates are set at 100% for oral, 1.53% for dermal and 100% for inhalation.

Clinical observations and the physicochemical properties of the substance suggest that there will be wide distribution of the substance to such organs as the liver, kidney and spleen. The substance is expected to be metabolised to carbon dioxide and ultimately octafluoropentanoic acid. Excretion will occur via exhalation of the carbon dioxide and the acid will be excreted in the urine. Unabsorbed parent compound would also be eliminated with faeces following oral dosing. Based on the available data, the substance is not expected to bioaccumulate.

Key value for chemical safety assessment

Bioaccumulation potential:
no bioaccumulation potential
Absorption rate - oral (%):
100
Absorption rate - dermal (%):
1.53
Absorption rate - inhalation (%):
100

Additional information

To date, little to no relevant analytical toxicokinetic testing data has been generated for OFPMA. However, information on the in vitro percutaneous absorption of OFPMA through human skin and information on the physicochemical properties can be used as a basis for the assessment of toxicokinetics.

Absorption

Diffusion of a substance across biological membranes into a test species is governed by the physicochemical properties of the substance, particularly its molecular size, log P, and water solubility (ECHA, 2017). The substance is a relatively small compound with a molecular size of 300 g/mol, a moderate log P of 3.03 and a moderate to low water solubility of 30 mg/L, which suggests there is the possibility that OFPMA is capable of diffusing across biological membranes.

Oral

At 25 °C, the substance has a hydrolysis half-life of 2.7 days at pH 4 and 4.1 days at pH 7, which provides an indication that the parent compound will be the relevant compound of potential concern present in the gastrointestinal tract. As the substance is neither a surfactant nor an irritant, there is no indication of the possibility for enhanced oral absorption due to damage to cell membranes.

A review of the physicochemical properties of the substance indicates the possibility of passive absorption following oral exposure. Specifically, a molecular size of 300 g/mol and a measured moderate log P of 3.03 are favourable for passive oral absorption. However, the moderate to low water solubility of 30 mg/L may limit the amount of passive oral absorption. The substance has low acute oral toxicity, and there was no indication of coloured urine and/or internal organs. However, both the acute and repeated dose oral studies reported symptoms of clinical toxicity which occurred quickly after dosing and were transient in nature. These quickly occurring and very transient symptoms suggest passive oral exposure did occur. Based on a consideration of the physicochemical properties and the available oral toxicity studies, a conservative default value for oral absorption of the substance is set as 100%.

Dermal

The rate and extent of absorption of the substance following topical application of a leave-on hair styling cream with human skin was assessed (Charles River, 2010). Following topical application of radiolabelled substance as 2% w/v in a leave-on hair styling cream to occluded skin, the absorbed dose was determined to be 1.18% and the dermal delivery was determined to be 1.53%. Within the same study and following the same procedure, the absorbed dose for unoccluded skin was determined to be 0.18% and the dermal delivery was determined to be 0.49%. Based on this in vitro assessment, a conservative dermal absorption of the substance is set as 1.53%.

Inhalation

The volatility of the substance has been confirmed by comparison of the mass balance following occluded and unoccluded in vitro skin assessments of dermal absorption (Charles River, 2010) which indicate the substance is available for inhalation. At 25 °C, the substance has a hydrolysis half-life of 4.1 days at pH 7, which provides an indication that the parent compound will be the relevant compound of potential concern present in the lungs. The moderate log P value of 3.03 and moderate to low water solubility of 30 mg/L favours absorption directly across the respiratory tract epithelium by passive diffusion. The substance has low acute oral toxicity, and there was no indication of coloured urine and/or internal organs. However, both the acute and repeated dose oral studies reported symptoms of clinical toxicity which occurred quickly after dosing and were transient in nature. No signs of systemic toxicity were reported following inhalation exposure. The quickly occurring transient clinical symptoms reported following oral exposure indicate the potential for diffusion across biological membranes if inhaled. Based on a consideration of the physicochemical properties and the available oral and inhalation toxicity studies, a conservative default value for inhalation absorption of the substance is set as 100%.

Distribution

Both the acute and repeated dose oral studies reported symptoms of clinical toxicity which occurred quickly after dosing and were transient in nature. None of the dermal or inhalation toxicity studies reported any significant systemic toxicity. The transient symptoms of clinical toxicity which occurred quickly after oral dosing and the small molecular weight suggests a wide distribution of the substance in the animal system. The moderate to low lipophilicity of the substance suggests a preferential distribution to the fatty tissues. However, as discussed in detail in the PBT assessment, the substance is not considered to bioaccumulate as the log P is 3.03. The moderate log P combined with the moderate to low water solubility would allow for distribution of any absorbed substance to such organs as the liver, kidney and spleen.

Metabolism

The substance is anticipated to be metabolized to octafluoropentanol and methacrylic acid. The methacrylic acid is subsequently converted to carbon dioxide via the tricarboxylic acid cycle in both experimental animals and humans (WHO, 1998). The octafluoropentanol is expected to be converted to octafluoropentanal via alcohol dehydrogenase and octafluoropentanoic acid via aldehyde dehydrogenase.

Excretion

Following metabolism, the carbon dioxide will be excreted via the lungs during exhalation. The water soluble octafluoropentanoic acid will be excreted directly via the urine. Unabsorbed parent compound would also be eliminated with faeces following oral dosing. Based on the available data, and as discussed in detail in the PBT assessment, the substance is not expected to bioaccumulate.

REFERENCES

Charles River (2010). The In Vitro Percutaneous Absorption of Radiolabelled 2,2,3,3,4,4,5,5-Octafluoropentyl Methacrylate (OFPMA) in a Leave-on Cream Through Human Skin. Unpublished report. Charles River, Tranent Edinburgh, EH33 2NE UK. Test Facility Study No. 788748, Report No. 31376

 

ECHA (2017). Guidance on information requirements and chemical safety assessment. Chapter R.7c: Endpoint specific guidance. Volume 3.0, July 2017. Available at: https://echa.europa.eu/documents/10162/13632/information_requirements_r7c_en.pdf/e2e23a98-adb2-4573-b450-cc0dfa7988e5

 

WHO (1998). Concise International chemical assessment document 4. Methyl methacrylate. Geneva, Switzerland: World Health Organization (WHO). Available at: http://www.who.int/ipcs/publications/cicad/en/cicad04.pdf