Registration Dossier

Administrative data

Endpoint:
dermal absorption in vitro / ex vivo
Type of information:
experimental study
Adequacy of study:
key study
Study period:
4 May 2005 to 28 July 2005
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
other: Studies were conducted according to generally valid and/or internationally accepted testing guidelines.

Data source

Reference
Reference Type:
study report
Title:
Unnamed
Year:
2005
Report Date:
2005

Materials and methods

Test guideline
Qualifier:
according to
Guideline:
other: 40 CFR Parts 9 and 799; as published in the Federal Register/Vol. 69/No. 80/Monday, April 26, 2004/Rules and Regulations
GLP compliance:
yes (incl. certificate)

Test material

Reference
Name:
Unnamed
Type:
Constituent
Details on test material:
Non-radiolabeled Tetrahydrofuran:- Name of test material: Tetrahydrofuran- Source: BASF Corporation, Mount Olive, NJ (USA)- Molecular formula: C4H8O- Molecular weight: 72.1066- Physical state: Colorless liquid with ether-like odor- Analytical purity: 99.99% (BASF, Certificate of Analysis)- Impurities: 80 ppm water; 0.5 ppm peroxide; 305 ppm BHT (as stabilizer)- Purity test date: 24 June 2004- Lot/batch No.: G41764BBA- Stability under test conditions: Stable- Date received: 14 February 2005- Storage condition of test material: In the dark and containers purged of air using nitrogen- Other: density: 0.886; boiling point, 66 deg CRadiolabeled 14C-Tetrahydrofuran:- Source: American Radiolabeled Chemicals, Inc., St. Louis, MO (USA)- Product designation: ARC 1819 Tetrahydrofuran [14C]- Lot No.: 050418- Radiochemical purity: 99%- Specific activity: 5 mCi/mmol- Locations of the label: uniformly on all carbon atoms- Storage conditions: recommended -20 deg C- Preparation: from [14C]-1,4-butanediol by dehydration and the product purified by distillation.
Radiolabelling:
yes

Test animals

Species:
human
Strain:
other: not applicable
Sex:
male/female
Details on test animals and environmental conditions:
Human Cadaver Skin SamplesCryopreserved human cadaver trunk skin (New York Firefighter’s Skin Bank, NY, NY) without obvious signs of skin disease, obtained within 24 hours of death, was used in this study.

Administration / exposure

Type of coverage:
other: For 60-minute and 14-hour, cells occluded with rubber stopper and wrapped with nitrile membrane
Vehicle:
other: either water for 10 or 30% solutions or neat tetrahydrofuran
Duration of exposure:
10 minute, 60 minute or 14 hours
Doses:
10% and 30% in water and neat tetrahydrofurantarget dose of 800 μL using a calibrated positive displacement pipette
No. of animals per group:
All formulations were tested in triplicate on sections of skin from 3 donors.
Control animals:
no
Details on in vitro test system (if applicable):
Preparation of Skin Samples:Skin samples was collected by dermatome and were of approximately 0.25 - 0.90 mm thickness. These were processed for cryopreservation, sealed in a water-impermeable plastic bag, and stored at < -70 ºC until the day of each experiment. Prior to use, these skin samples were thawed by placing bags in ~37 ºC water, then rinsing in water to remove any adherent blood or other material from the surface. Skin thickness was determined using a micrometer and recorded.Diffusion Cell:Skin from each donor was cut into multiple smaller sections and fitted on 0.8 cm2 static Franz Diffusion Cells (Crown Glass Co., Somerville, NJ). The dermal chambers were filled to capacity with a receptor solution of phosphate-buffered isotonic saline (PBS), pH 7.4 ± 0.1 and the epidermal chamber was left open to ambient laboratory environment. The cells were then placed in a diffusion apparatus in which the dermal receptor solution was stirred magnetically at ~600 RPM and its temperature maintained to achieve a skin surface temperature of 32.0 ± 1.0 ºC.Initial Skin Integrity Determination:The permeability of skin samples to tritiated water was determined before application of the test products. Following a brief (0.5-1 hour) equilibrium period, 3H2O (PerkinElmer, Boston, MA, sp. Act. ~ 0.5 μCi/mL) was layered across the top of the skin so that the entire exposed surface was covered (approximately 100-150 μL). After 5 minutes the 3H2O aqueous layer was removed. At 30 minutes after dosing the receptor solution was collected and analyzed for radioactive content by liquid scintillation counting. Skin specimens in which absorption of 3H2O was less than 1.75 μL-equ. were considered acceptable. In addition, the same integrity test method was used for post-study assessment of the skin following exposure to the test articles.Test Article Administration:Following the initial integrity test, each Cell reservoir was replenished with fresh PBS. Subsequently, the test article was applied to triplicate sections of the same donor skin at a target dose of 800 μL using a calibrated positive displacement pipette. Following dose application (60 min, and 14 hr duration Cells only), the Cell chimney was occluded with a silicone stopper over-wrapped with a nitrile membrane held in placed with an O-ring to prevent THF evaporation from the surface of the skin.

Results and discussion

Signs and symptoms of toxicity:
not examined
Dermal irritation:
not examined
Total recovery:
10-Minute dose duration study (mean ± SD):- Total recovery: 83.83 ± 1.66% (10% tetrahydrofuran); 88.55 ± 1.61% (30% tetrahydrofuran); 103.76 ± 2.11 (100% tetrahydrofuran)60-Minute dose duration study:- Total recovery: 75.73 ± 0.60% (10% tetrahydrofuran); 82.40 ± 0.53% (30% tetrahydrofuran); 104.31 ± 1.09 (100% tetrahydrofuran)14-Hour dose duration study (10% tetrahydrofuran only):- Total recovery: 58.47 ± 1.91%
Percutaneous absorptionopen allclose all
Dose:
10% tetrahydrofuran
Parameter:
percentage
Absorption:
0.1 %
Remarks on result:
other: 10-Minute
Remarks:
0.07 +/- 0.02
Dose:
30% tetrahydrofuran
Parameter:
percentage
Absorption:
0.4 %
Remarks on result:
other: 10-Minute
Remarks:
0.38 +/- 0.11
Dose:
100% tetrahydrofuran
Parameter:
percentage
Absorption:
0 %
Remarks on result:
other: 10-Minute
Remarks:
0.03 +/- 0.01
Dose:
10% tetrahydrofuran
Parameter:
percentage
Absorption:
2 %
Remarks on result:
other: 60-Minute
Remarks:
2.00 +/- 0.51
Dose:
30% tetrahydrofuran
Parameter:
percentage
Absorption:
7.5 %
Remarks on result:
other: 60-Minute
Remarks:
7.54 +/- 1.31
Dose:
100% tetrahydrofuran
Parameter:
percentage
Absorption:
0.6 %
Remarks on result:
other: 60-Minute
Remarks:
0.65 +/- 0.28
Dose:
10% tetrahydrofuran
Parameter:
percentage
Absorption:
22.1 %
Remarks on result:
other: 14-Hour
Remarks:
22.07 +/- 1.96

Any other information on results incl. tables

Changes in barrier function based on tritiated water integrity test:

Positive and significant changes in the percent of tritiated water permeation through skin samples between a first and second post-dose integrity test were only observed with 100% tetrahydrofuran solutions. In the case of 10-minute exposures to 100% tetrahydrofuran, 112.6±56.8% and 72.3±55.9% changes were reported in the first and second integrity tests, respectively. These were statistically significantly different from control skin sections (p < 0.05). In the case of 60-minute exposures to 100% tetrahydrofuran, 565.5±213.5% and 460.4±213.7% changes were reported in the first and second integrity tests, respectively. These were statistically significantly different from control skin sections (p < 0.05).

Mean flux values (absorption rates):

The mean (±SD) flux rate for tetrahydrofuran from the 14-hour studies was 1.360±0.237 mg/cm2/hr (based on steady-state measurements for hours 1 to 6. The mean (±SD) flux rate for tetrahydrofuran from the 14-hour studies was 1.006±0.143 mg/cm2/hr (based on steady-state measurements for hours 4 to 14.

Determination of Kpvalues

Dermal permeability (Kp) values were calculated by dividing the steady-state absorption rates by the concentration of tetrahydrofuran. The Kpvalue based on measurements during hours 1 to 6 of the 14-hour studies was 0.015±0.003 cm/hr. The Kpvalue based on measurements during hours 4 to 14 of the 14-hour studies was 0.011±0.002 cm/hr.

Applicant's summary and conclusion

Conclusions:
The data indicate that the 10%- and 30%-tetrahydrofuran in water solutions did not significantly alter the barrier function of the skin, as assessed by the percutaneous absorption of 3H20. However, neat (100%) tetrahydrofuran exposure to the skin did alter the skin’s barrier function, suggesting damage did occur to the stratum corneum of the skin. Therefore, the results from the 10%- and 30%-tetrahydrofuran solutions may better represent human skin permeability to tetrahydrofuran in un-damaged skin from short term exposures. Two permeability coefficients (Kp) were calculated to be 0.015 ± 0.003 cm/hr, for the absorption period of t = 1-6 hrs, and 0.011 ± 0.002 cm/hr, for the absorption period of t = 4-14 hrs based on the mean rate of penetration derived from the time spans indicated as observed during the 14 hour dose duration study. The first of these may represent the upper limit of initial or early steady-state like penetration whereas the second may represent a more conservative representation of tetrahydrofuran absorption over longer periods of time.Based on the results obtained in these studies, tetrahydrofuran may be considered a substance representative of a very fast penetrant of human skin.
Executive summary:

The current study was designed to characterize the percutaneous absorption of toxicokinetics of tetrahydrofuran and to determine its permeability constant (Kp), and to assess its short-term and infinite dose absorption rates through human cadaver skin using static diffusion cells (Franz type). The study was conducted in accordance with an Environmental Protection Agency’s test rule (40 CFR Parts 9 and 799; as published in the Federal Register, Vol. 69, No. 80, Monday, April 26, 2004). Penetration of tetrahydrofuran, either neat or as an aqueous solution, through human skin was determined at 10- and 60-minute time points for 10, 30 or 100% tetrahydrofuran or at 14 hours for 10% tetrahydrofuran. The percentage absorption rates for tetrahydrofuran in the 10-minute studies were as follows: 0.05±0.02 (10% tetrahydrofuran), 0.81±0.23 (30% tetrahydrofuran) and 0.24±0.09 (100% tetrahydrofuran). The percentage absorption rates for tetrahydrofuran in the 60-minute studies were as follows: 1.42±0.36 (10% tetrahydrofuran), 16.03±2.78 (30% tetrahydrofuran) and 4.61±2.01 (100% tetrahydrofuran). The percentage absorption rate for 10% tetrahydrofuran in the 14-hour study was 15.64±1.39. From the 14-hour study, Kpvalues of 0.015±0.003 cm/hr (steady-state for hours 1 to 6) and 0.011±0.002 (steady-state for hours 4 to 14) were obtained.  Tetrahydrofuran may be considered to be a very fast penetrant of human skin.