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Dermal absorption

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Administrative data

Endpoint:
dermal absorption in vitro / ex vivo
Type of information:
migrated information: read-across from supporting substance (structural analogue or surrogate)
Adequacy of study:
key study
Study period:
1999
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
other: Acceptable well-documented study report which meets basic scientific principles.

Data source

Reference
Reference Type:
publication
Title:
Dermal absorption and distribution of topically dosed jet fuels Jet-A, JP-8, and JP-8(100)
Author:
Riviere J.E., Brooks J.D., Monteiro Riviere N.A., Budsaba K., Smith C.E.
Year:
1999
Bibliographic source:
Toxicology and Applied Pharmacology 160: 60-75

Materials and methods

Test guideline
Qualifier:
no guideline available
Principles of method if other than guideline:
In vitro isolated perfused porcine skin flap (IPPSF) Studies.
GLP compliance:
not specified

Test material

Reference
Name:
Unnamed
Type:
Constituent
Details on test material:
All jet fuels. Jet-A, JP-5, and JP8(100) were kindly supplied by Major T. Miller from Wright Patterson Air Force Base. To produce an aged JP-8 (puddle), JP-8 was allowed to evaporate in an open glass petri dish within a fume hood for 24 h (n = 2). The decline in mass was recorded using an analytical balance over the course of the 24-h period. The shape of the two evaporation curves was similar with no discernible 'plateau' evident. As expected, there was a first-order decay to approximately 30% of the initial mass. This remnant solution was then spiked with the radio tracer markers and used for all exposures.
Radiolabelling:
yes
Remarks:
14C-naphthalene, 3H-dodecane, 14C- hexadecane

Test animals

Species:
pig
Strain:
not specified
Sex:
not specified
Details on test animals and environmental conditions:
in vitro experiment

Administration / exposure

Type of coverage:
open
Vehicle:
unchanged (no vehicle)
Duration of exposure:
5 hours; 4 trials
Doses:
25 uL of Jet fuel with radio labeled tracers
Control animals:
no
Details on study design:
In vitro isolated perfused porcine skin flap (IPPSF) Studies.
In these studies, jet fuel mixtures were applied non-occluded to mimic field exposure conditions, and experiments were conducted for a total of 5 h in IPPSFs with 4 replicates per treatment condition. A 1 x 5 cm dosing area was drawn on the surface of the skin flap with a surgery marker. A dose, containing 25 uLof the specified jet fuel containing approximately 2 uCi of 14C-naphthalene plus 10 uCi of 3H-dodecane and 14C- hexadecane was applied directly to the surface of the skin flap. The specific activities of the marker compounds were sufficient that the added radiolabeled compounds had little effect on the final concentration of naphthalene (1.21% instead of 1.1%) and dodecane (4.701% instead of 4.7%). Single label studies were initially conducted and compared to the dual-label results to test whether using this dual-label experimental design had any effect on marker absorption. No effect was detected.
Perfusate samples (3 ml) were collected every 5 mm for the first 40 mm. then every 10 mm until 1.5 h. and then every 15 mm until termination at 5 h. At termination, several samples were taken for mass balance of the marker compounds. The surface of the dose area was swabbed twice with a 1% soap solution and gauze, and then 12 stratum corneum tape strips were collected using cellophane tape (3M Corporation, Minneapolis. MN). The entire dose area was removed. A 1x 1 cm core of the dose area was removed and frozen for subsequent depth of penetration studies. This consisted of laying the core sample epidermal side down in an aluminum foil boat and embedding in Tissue-Tek OCT compound (Miles. Inc., Elkhart, IN), snap freezing in liquid nitrogen, followed by sectioning (40 zm) on a Reichart-Jung Model 1800 Cryocut (Warner Lambert, Buffalo, NY). The remaining dosed area as well as the surrounding skin was separated from the fat and held for analysis. All samples (including swabs, tape strips, core sections, skin, fat, mass balance samples, etc.) were dissolved separately in Soluene. A representative volume of each sample was oxidized completely via a Packard Model 307 Tissue Oxidizer. The 3H and 14C samples were counted separately on a Packard Model 1900TR TriCarb Scintillation Counter.

Data analysis. Data was entered into a custom IPPSF database and the resulting analysis reported. Since all experiments were conducted using the identical marker doses across all fuels, and the absolute concentrations of these marker compounds were similar, these results are expressed as percentage applied dose to give a representative assessment of the absorption and cutaneous penetration of a complex mixture such as jet fuel. This is appropriate since the absolute concentrations of jet fuel hydrocarbons are not fixed across all fuels due to differences that arise from the natural sources of the petroleum and different refining processes. Area under the curve (AUC) in the perfusate was calculated using the trapezoidal method. Peak flux was the maximum flux (% dose/mm) observed at any one time point.

The experimental compartments which were analyzed in these studies used the following definitions: (1) Surface is the residue removed by washing the surface of the IPPSF at termination of the experiment plus the residues remaining in the dosing template. (2) Stratum corneum is the residue extracted from the outermost stratum corneum via 12 tape strips at the termination of the experiment. (3) Dosed skin is the residue that remained in the dosed skin plus the depth of penetration core taken at termination. (4) Absorption is the cumulative amount of the marker compound collected in the effluent over the course of the 5-h experiment. (5) Fat is the residue remaining in the fat when it was separated from the dermis at the end of the experiment. (6) Penetration is the summation of the label in the effluent plus skin plus fat, but not stratum corneum nor surface. (7) Evaporative loss is that label which was lost to evaporation. Our previous studies in the IPPSF indicated that the penetration estimate is the best empirical correlate to predict eventual in vivo absorption in humans.

Statistical significance of absorption and penetration parameters were determined using ANOVA or by a priori-defined orthogonal contrasts where appropriate at the 0.05 level of significance. A least significance difference (LSD) procedure was used for multiple comparisons on overall tissue disposition.
Details on in vitro test system (if applicable):
A 1 x 5 cm dosing area was drawn on the surface of the skin flap with a surgery marker. A dose, containing 25 uL of the specified jet fuel containing approximately 2 uCi of 14C-naphthalene plus 10 uCi of 3H-dodecane and 14C- hexadecane was applied directly to the surface of the skin flap. Perfusate samples (3 ml) were collected every 5 mm for the first 40 mm. then every 10 mm until 1.5 h. and then every 15 mm until termination at 5 h. At termination, several samples were taken for mass balance of the marker compounds. The surface of the dose area was swabbed twice with a 1% soap solution and gauze, and then 12 stratum corneum tape strips were collected using cellophane tape (3M Corporation, Minneapolis. MN). The entire dose area was removed. A 1x 1 cm core of the dose area was removed and frozen for subsequent depth of penetration studies. This consisted of laying the core sample epidermal side down in an aluminum foil boat and embedding in Tissue-Tek OCT compound (Miles. Inc., Elkhart, IN), snap freezing in liquid nitrogen, followed by sectioning (40 zm) on a Reichart-Jung Model 1800 Cryocut (Warner Lambert, Buffalo, NY). The remaining dosed area as well as the surrounding skin was separated from the fat and held for analysis.

Results and discussion

Signs and symptoms of toxicity:
not examined
Dermal irritation:
not examined

Applicant's summary and conclusion

Conclusions:
Within JP-8, the rank order of absorption for all marker components was (mean +/- SEM; % dose) naphthalene (1.17 +/- 0.07)> dodecane (0.63 +/- 0.04) > hexadecane (0.18 +/- 0.08).  The area under the curve (AUC) was determined to be (mean +/- SEM; % dose-h/mL): naphthalene (0.0199 +/- 0.0020)> dodecane (0.0107 +/- 0.0009) > hexadecane (0.0017 +/- 0.0003). In contrast, deposition within dosed skin showed the reverse pattern.
Executive summary:

The purpose of these studies was to assess the percutaneous absorption and cutaneous disposition of topically applied (25 uL/5 cm2) neat Jet-A, JP-8, and JP-8(100) jet fuels by monitoring the absorptive flux of the marker components 14C naphthalene and 4H dodecane simultaneously applied non-occluded to isolated perfused porcine skin flaps (IPPSF) (a = 4). Absorption of 14C hexadecane was estimated from JP-8 fuel. Absorption and disposition of naphthalene and dodecane were also monitored using a nonvolatile JP-8 fraction reflecting exposure to residual fuel that might occur 24 h after a jet fuel spill. In all studies, perfusate, stratum corneum, and skin concentrations were measured over 5 h. Naphthalene absorption had a clear peak absorptive flux at less than 1 h, while dodecane and hexadecane had prolonged, albeit significantly lower, absorption flux profiles. Within JP-8, the rank order of absorption for all marker components was (mean +/- SEM; % dose) naphthalene (1.17 +/- 0.07)> dodecane (0.63 +/- 0.04) > hexadecane (0.18 +/- 0.08).  The area under the curve (AUC) was determined to be (mean +/- SEM; % dose-h/mL): naphthalene (0.0199 +/- 0.0020)> dodecane (0.0107 +/- 0.0009) > hexadecane (0.0017 +/- 0.0003). In contrast, deposition within dosed skin showed the reverse pattern.