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Toxicological information

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:
April to June 2004
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
other: see 'Remark'
Remarks:
GLP - guideline study, tested with the source substance Methylparaben. According to the ECHA guidance document “Practical guide 6: How to report read-across and categories (March 2010)”, the reliability was changed from RL1 to RL2 to reflect the fact that this study was conducted on a read-across substance.

Data source

Reference
Reference Type:
study report
Title:
Unnamed
Year:
2004
Report Date:
2004

Materials and methods

Test guideline
Qualifier:
according to
Guideline:
OECD Guideline 428 (Skin Absorption: In Vitro Method)
Deviations:
no
GLP compliance:
yes

Test material

Reference
Name:
Unnamed
Type:
Constituent
Type:
Constituent
Details on test material:
Lot No.: M3146
Physical Characteristics: White powder
Stability: The test substance appeared to be stable under the conditions of the study; no evidence of instability was observed.
Molecular weight: 152
Formula: C8H8O3
Purity: 99.9%
Octanol-water partition coefficient: 1.87

The radiolabeled test substance was supplied by Amersham Biosciences U.K, Ltd. and assigned Haskell Laboratory No. 22705-84 upon receipt.
Phenyl-14C(U)methylparaben
Code: CFQ13765
Batch: 1
Specific activity: 97µCi/mg
Purity: 99.5%

Test animals

Species:
other: human and rat
Strain:
Wistar
Sex:
male
Details on test animals and environmental conditions:
A. Rat Skin
Male Wistar rats, approx. 6-8 weeks of age, were supplied by Charles river Laboratories, Inc., Raleigh, North Carolina. Following a required quarantine period, rats were removed from stock and uniquely identified by tail markings. Rats were sacrificed by carbon dioxide asphyxiation, the fur from the dorsal region carefully shaved using clippers, and the skin excised. Skin specimens were identified using Haskell animal number.

B. Human Skin
Samples of human abdominal skin from local surgeons were obtained fresh. The source and identity of the akin sample (sex, anatomical locale and approx. age of donor) was documented in the study recoreds. Skin specimens were identified using unique code.

At the time of harvest both rat and human skin specimens were placed in Hepes-buffered Hanks´balanced salt solution and were maintained on wet ice until prepared for use. All skin specimens were used less than 4 hours following removal from donor.

Administration / exposure

Type of coverage:
other: in vitro study
Vehicle:
other: Oil-in-water
Duration of exposure:
24 hours
Doses:
0.8% Methylparaben solution
approx. 65 µg/cm2
No. of animals per group:
Replicates:
A. Rat: n = 10
B. Human: n= 13
Control animals:
no
Details on study design:
In vitro study, please refer to "Details on in vitro test system" below
Details on in vitro test system (if applicable):
The penetration kinetics and first-pass metabolism of Methylparaben in viable rat and human skin has been determined. The active ingredient was formulated as oil-in-water emulsion at a target concentration of 0.8% and 0.4%. Samples of fresh rat and human skin were dermatomed to approx. 450 µm and mounted stratum corneum uppermost, onto a flow-through diffusion cell system with an exposure area of 0.64 cm2. The underside of each skin specimen was perfused with sterile-filtered Hepes-buffered Hanks´balanced salt solution containing gentimicin (0.05 mg/mL) and bovine serum albumin (3.75%). Each formulated emulsion was applied as a finite dose at a rate of 10 mL/cm2 to rat ( n=10 replicates) and human skin (n=13 replicates). Penetration was followed using [14C]-labeled active ingredient, which was uniformly blended into emulsions. The amount of active applied per area skin was approx. 65 µg/cm2 and 36 µg/cm2 . The applied formulation remained in contact with the skins for 24 hours without occlusion. During 24 hour exposure period, serial receptor fluid samples were collected hourly for the first 6 hours and then every other hour until termination. At the end of the exposure period, the skin surface was washed with a dilute soap solution to remove excess formulation and then tape-stripped to remove the stratum-corneum. Distribution of the applied radiolabeled material was determined by liquid scintillation counting. First-pass metabolism was determined by quantitative analysis of serial receptor fluid samples and the principle metabolite 4-Hydroxybenzoic acid using HPLC-mass spectrometry. Receptor fluid samples representing each formulation, from both rat and human experiments, were also analysed by radiochromatography and LC-MS.

Results and discussion

Signs and symptoms of toxicity:
not specified
Remarks:
in vitro study
Dermal irritation:
not specified
Remarks:
in vitro study
Absorption in different matrices:
Following application of a 0.8% Methylparaben emulsion to viable rat and human skin, a greater amount of total radioactivity penetrated human skin (79.36%) compared to rat skin (54.94%). A major portion of the total radioactivity that had penetrated rat skin was metabolised to 4-Hydroxybenzoic acid (53.9%), with a smaller portion (23.8%) accounted for as unmetabolised Methylparaben. By comparison, a lesser portion of the total radioactivity that had penetrated viable human skin had been metabolised to 4-Hydroxybenzoic acid (35.1%), with the majority (60.3%) accounted for as unmetabolised Methylparaben.
Total recovery:
Material balance
A. Rat skin
Absorbable dose
- Receptor fluid: 54.94 +/- 5.92 %
- Receptor wash: 0.43 +/- 0.20 %
- Skin: 12.23 +/- 5.57 %
=> Total absorbable : 67.61 +/- 6.06 %
Unabsorbed dose
- Skin wash: 17.81 +/- 2.82 %
- Donor chamber: 0.03 +/- 0.01 %
- Tape strips: 5.65 +/- 1.12 %
=> Total unabsorbed: 23.49 +/- 2.40 %
=> Total recovered: 91.09 +/- 5.66 %

B. Human skin
Absorbable dose
- Receptor fluid: 79.36 +/- 15.62 %
- Receptor wash: 0.46 +/- 0.11 %
- Skin: 4.88 +/- 2.01 %
=> Total absorbable : 84.69 +/- 15.46 %
Unabsorbed dose
- Skin wash: 14.65 +/- 8.76 %
- Donor chamber: 0.42 +/- 0.94 %
- Tape strips: 6.13 +/- 12.01 %
=> Total unabsorbed: 21.21 +/- 20.48 %
=> Total recovered: 105.91 +/- 15.10 %
Percutaneous absorptionopen allclose all
Dose:
65 µg/cm2
Parameter:
percentage
Absorption:
ca. 67.6 %
Remarks on result:
other: 24 hours
Remarks:
Rat skin
Dose:
65 µg/cm2
Parameter:
percentage
Absorption:
ca. 84.7 %
Remarks on result:
other: 24 hours
Remarks:
Human skin
Conversion factor human vs. animal skin:
no data

Any other information on results incl. tables

none

Applicant's summary and conclusion

Conclusions:
These data show, based on dermatomed viable rat and human skin model and analysis of receptor fluid samples, that the dermal bioavailability of Methylparaben from oil-in-water emulsion was greater for human skin than rat skin.
A. Rat skin
- amount penetrated skin: 54.94% 24 hours after application
- 53.9% of the penetrated amount metabolised to 4-Hydroxybenzoic acid

B. Human skin
- amount penetrated skin: 79.36% 24 hours after application
- 35.1% of the penetrated amount metabolised to 4-Hydroxybenzoic acid
Executive summary:

The penetration kinetics and first-pass metabolism of Methylparaben in viable rat and human skin has been determined. The active ingredient was formulated as oil-in-water emulsion at a target concentration of 0.8% and 0.4%. Samples of fresh rat and human skin were dermatomed to approx. 450 µm and mounted stratum corneum uppermost, onto a flow-through diffusion cell system with an exposure area of 0.64 cm2. The underside of each skin specimen was perfused with sterile-filtered Hepes-buffered Hanks´balanced salt solution containing gentimicin (0.05 mg/mL) and bovine serum albumin (3.75%). Each formulated emulsion was applied as a finite dose at a rate of 10 mL/cm2 to rat ( n=10 replicates) and human skin (n=13 replicates). Penetration was followed using [14C]-labeled active ingredient, which was uniformly blended into emulsions. The amount of active applied per area skin was approx. 65 µg/cm2 and 36 µg/cm2 . The applied formulation remained in contact with the skins for 24 hours without occlusion. During 24 hour exposure period, serial receptor fluid samples were collected hourly for the first 6 hours and then every other hour until termination. At the end of the exposure period, the skin surface was washed with a dilute soap solution to remove excess formulation and then tape-stripped to remove the stratum-corneum. Distribution of the applied radiolabeled material was determined by liquid scintillation counting. First-pass metabolism was determined by quantitative analysis of serial receptor fluid samples and the principle metabolite 4-Hydroxybenzoic acid using HPLC-mass spectrometry. Receptor fluid samples representing each formulation, from both rat and human experiments, were also analysed by radiochromatography and LC-MS.

Following application of a 0.8% Methylparaben emulsion to viable rat and human skin, a greater amount of total radioactivity penetrated human skin (79.36%) compared to rat skin (54.94%). A major portion of the total radioactivity that had penetrated rat skin was metabolised to 4-Hydroxybenzoic acid (53.9%), with a smaller portion (23.8%) accounted for as unmetabolised Methylparaben. By comparison, a lesser portion of the total radioactivity that had penetrated viable human skin had been metabolised to 4-Hydroxybenzoic acid (35.1%), with the majority (60.3%) accounted for as unmetabolised Methylparaben.