Registration Dossier

Administrative data

Endpoint:
dermal absorption in vitro / ex vivo
Type of information:
experimental study
Adequacy of study:
supporting study
Study period:
Not applicable
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
other: The study follows the standard guidelines for a dermal penetration study, and was conducted according to GLP. However, the recovery of AMP at the end of the study was impacted by the poor containment of the more volatile base form of AMP.
Cross-referenceopen allclose all
Reason / purpose:
reference to same study
Reason / purpose:
reference to other study

Data source

Reference
Reference Type:
study report
Title:
Unnamed
Year:
2007
Report Date:
2007

Materials and methods

Test guideline
Qualifier:
equivalent or similar to
Guideline:
OECD Guideline 428 (Skin Absorption: In Vitro Method)
Principles of method if other than guideline:
Not applicable
GLP compliance:
yes (incl. certificate)

Test material

Reference
Name:
Unnamed
Type:
Constituent
Details on test material:
The test article was identified in this study as follows:
[14C]-AMP (molecular weight = 91.1 g/mol; specific activity = 25 mCi/mmol)


[14C]-AMP was provided by The Dow Chemical Company prepared in three formulations, identified in this study as follows:

1. AMP ULTRA PC 2000™ (Batch No. TA074801Z1) – Contains 94.85 mg AMP/g and 0.27 mg 14C-AMP/g, for a total calculated value of 95.12 mg AMP/g (Paste)

2. 40% aqueous solution (w/v, pH 9.5) prepared from AMP ULTRA PC2000™ – Contains 0.26 mg 14C-AMP/g (Liquid)

3. Control Lotion B with pure AMP (Lot BP200500759.06) – Contains 40 mg AMP/g and 0.26 mg 14C-AMP/g, for a total calculated value of 40.26 mg AMP/g (equivalent to the level of AMP in cosmetic lotions)


Ultra PC 2000™, 40% aqueous, and Neat Control Lotion B formulations were evaluated for radiochemical concentration, which was determined to be, respectively, 79.3, 86.2, or 87.6% in a first shipment of formulations, and 80.3, 88.9, or 92.4% in a second shipment of formulations.
Radiolabelling:
yes
Remarks:
[14C]-aminomethylpropanol

Test animals

Species:
other: rat and human skin
Strain:
Sprague-Dawley
Sex:
not specified
Details on test animals and environmental conditions:
Not applicable

Administration / exposure

Duration of exposure:
24 hours
No. of animals per group:
Not applicable
Details on study design:
The objectives of this study were to evaluate the rate and amount of [14C]-AMP absorption across fresh human and Sprague-Dawley rat skin after in vitro exposure, and to evaluate the disposition of [14C]-aminomethylpropanol ([14C]-AMP) in the various layers (stratum corneum, epidermis, and dermis) of fresh human and Sprague-Dawley rat skin after in vitro exposure.
Details on in vitro test system (if applicable):
See below.

Results and discussion

Absorption in different matrices:
Not applicable
Percutaneous absorptionopen allclose all
Dose:
20 μL/cm2
Parameter:
percentage
Absorption:
ca. 43 %
Remarks on result:
other: 24 hours
Remarks:
Rat skin, AMP Ultra PC 2000
Dose:
20 μL/cm2
Parameter:
percentage
Absorption:
ca. 50.9 %
Remarks on result:
other: 24 hours
Remarks:
Rat skin, 40% Aqueous AMP solution
Dose:
20 μL/cm2
Parameter:
percentage
Absorption:
ca. 30 %
Remarks on result:
other: 24 hours
Remarks:
Rat skin, Neat Control Lotion B, 4% AMP
Dose:
20 μL/cm2
Parameter:
percentage
Absorption:
ca. 16.7 %
Remarks on result:
other: 24 hours
Remarks:
Human skin, AMP Ultra PC 2000
Dose:
20 μL/cm2
Parameter:
percentage
Absorption:
ca. 14.1 %
Remarks on result:
other: 24 hours
Remarks:
Human skin, 40% Aqueous AMP solution
Dose:
20 μL/cm2
Parameter:
percentage
Absorption:
ca. 6.6 %
Remarks on result:
other: 24 hours
Remarks:
Human skin, Neat Control Lotion B, 4% AMP

Any other information on results incl. tables

Tables and Figures - see attached document

Rat

The barrier function tests showed that for full thickness Sprague-Dawley rat skin, less than 1% of the tritiated water applied on the epidermal surface was absorbed through the skin disks in 20 minutes (Table 1). These results indicate that all the skin disks used in the experiments possessed acceptable barrier function.

Flux rates associated with the percutaneous absorption of [14C]-AMP in Sprague-Dawley rat skin with the Ultra PC 2000™, 40% aqueous, and Neat Control Lotion B formulations are presented in Tables 2 to 4, respectively. The flux rates are graphed for the Ultra PC 2000™, 40% aqueous, and Neat Control Lotion B formulations in Figures 1 to 3, respectively, and a comparison of the absorption of the three formulations is presented in Figure 4.

Absorption of [14C]-AMP in the Ultra PC 2000™ formulation gradually increased throughout the incubation, and appeared to approach a plateau, with a maximum mean flux rate of 291 μg/cm2/hr at 24 hours. Absorption of [14C]-AMP in the 40% aqueous formulation increased progressively, but had not reached a plateau by 24 hours. The mean flux rate at 24 hours was 411 μg/cm2/hr. Absorption of [14C]-AMP in the Neat Control Lotion B formulation gradually increased throughout the incubation, and appeared to approach a plateau, with a maximum mean flux rate of 197 μg/cm2/hr at 24 hours. As summarized in Figure 4, the absorption of [14C]-AMP was comparable in the three formulations, although unlike the Ultra PC 2000™ and Neat Control Lotion B formulations, the 40% aqueous formulation does not appear to have reached a steady-state by 24 hours.

The cutaneous disposition of [14C]-AMP in Sprague-Dawley rat skin, expressed as μg/cm2, in the Ultra PC 2000™, 40% aqueous, and Neat Control Lotion B formulations is presented in Tables 5 to 7, respectively. The cutaneous disposition of [14C]-AMP, expressed as percent of applied dose, in the Ultra PC 2000™, 40% aqueous, and Neat Control Lotion B formulations is presented in Tables 8 to 10, respectively.

In general, the total recovered dose for all three formulations was relatively low. After 24 hours, the mean total absorbed dose of [14C]-AMP with the Ultra PC 2000™ formulation was 43.0%, and the mean total recovered dose was 59.6%. The dose was primarily recovered from the skin wipes (16.7%), the epidermis (14.3%), and the receptor fluid (21.2%). With the 40% aqueous formulation, the mean total absorbed dose of [14C]-AMP was 50.9%, and the mean total recovered dose was 60.6%. The dose was primarily recovered from the skin wipes (9.68%), the epidermis (18.9%), and the receptor fluid (19.7%). With the Neat Control Lotion B formulation, the mean total absorbed dose of [14C]-AMP was 30.0%, and the mean total recovered dose was 56.8%. The dose was primarily recovered from the skin wipes (26.8%) and the receptor fluid (17.3%), with smaller recoveries in the epidermis (5.33%) and the dermis (3.44%). No evidence of marked accumulation of [14C]-AMP in skin tissue was evident.

Human

Due to the low recovery of applied dose of the AMP Ultra PC 2000™ formulation with human skin, the Sponsor requested that this portion of the study be repeated with an additional donor. This additional donor is designated Donor 2. The barrier function tests showed that for human skin from Donors 1 and 2 used in this study, less than 0.3% of the tritiated water applied on the epidermal surface was absorbed through the skin disks in 20 minutes (Tables 11 and 12). These results indicate that all of the skin disks used in the study possessed acceptable barrier function.

Flux rates associated with the percutaneous absorption of [14C]-AMP in human skin with the Ultra PC 2000™, 40% aqueous, and Neat Control Lotion B formulations are presented in Tables 13, 14, and 15, respectively. The flux rates are graphed for the Ultra PC 2000™, 40% aqueous, and Neat Control Lotion B formulations in Figures 5 to 7 (donors 1 and 2), , 8, and 9, respectively, and a comparison of the absorption of the three formulations is presented in Figure 10.

Absorption of [14C]-AMP in the Ultra PC 2000™ formulation increased progressively throughout the incubation, and appeared to approach a plateau in donor 1 while it appeared continue upward in donor 2, with a maximum mean flux rate of 128 μg/cm2/hr at 24 hours. Absorption of [14C]-AMP in the 40% aqueous formulation also increased progressively, and appeared to approach a plateau, with a maximum mean flux rate of 111 μg/cm2/hr at 24 hours. The pattern of absorption of [14C]-AMP in the Neat Control Lotion B formulation was variable between the replicate skin disks (Figure 7). Two of the replicates (skin disks 13 and 14) showed much higher flux rates at 2 hours than the other 4 replicates. Reduced barrier function (Table 11) does not appear to adequately explain these observations, as no correlation between barrier function values and high flux rates is evident. Using all 6 replicate skin disks (skin disks 13–18), the mean maximal flux rate of 107 μg/cm2/hr occurred at 2 hours, followed by a gradual reduction in flux rates through 24 hours. As summarized in Figure 8, the absorption of [14C]-AMP is similar in the Ultra PC 2000™ and 40% aqueous formulations, gradually increasing or approaching a steady-state by 24 hours, while the Neat Control Lotion B formulation shows a rapid absorption phase followed by a gradual decline in flux rates through 24 hours. The cutaneous disposition of [14C]-AMP in human skin, expressed as μg/cm2, in the Ultra PC 2000™, 40% aqueous, and Neat Control Lotion B formulations is presented in Tables 16, 17, and 18, respectively.

The cutaneous disposition of [14C]-AMP, expressed as percent of applied dose, in the Ultra PC 2000™, 40% aqueous, and Neat Control Lotion B formulations is presented in Tables 19, 20, and 21, respectively.

As with rat skin incubations, the total recovered dose for all three formulations was relatively low, particularly with the Ultra PC 2000™ formulation. After 24 hours, the mean total absorbed dose of [14C]-AMP with the Ultra PC 2000™ formulation was 16.7%, and the mean total recovered dose was 25.1%. The dose was primarily recovered from the skin wipes (8.32%) and the receptor fluid (8.30%), with lesser amounts recovered in the dermal and epidermal skin layers. With the 40% aqueous formulation, the mean total absorbed dose of [14C]-AMP was 14.1%, and the mean total recovered dose was 59.2%. The dose was primarily recovered from the skin wipes (45.1%) and the receptor fluid (6.48%). With the Neat Control Lotion B formulation, the mean total absorbed dose of [14C]-AMP was 6.65%, and the mean total recovered dose was 52.1%. The dose was primarily recovered from the skin wipes (45.5%), the dermis layer (2.26%), and the receptor fluid (2.71%). No evidence of excessive accumulation of [14C]-AMP in skin tissue was evident.

The reduced recoveries of dose with the three formulations may be explained by the results of control incubations in which the recovery of applied dose from PTFE disks was determined after a 24-hour incubation in diffusion cells. This control was intended to evaluate the evaporative loss of test article from the diffusion cell apparatus when no absorption could take place. Tables 22 and 23 present the results for the three formulations. The percent recovery of the applied dose was 26.0, 68.2, and 64.7 for the Ultra PC 2000™, 40% aqueous, and neat control lotion B, indicating that significant loss of the test article due to evaporation had occurred, and accounting for the low recovery of applied dose in the main study.

Applicant's summary and conclusion

Conclusions:
The absorption and cutaneous disposition of [14C]-AMP in an Ultra PC 2000™ formulation, a 40% aqueous formulation, and a Neat Control Lotion B formulation were determined in rat and human skin. Rat skin showed gradually increasing flux rates for the three formulations, approaching a steady state through the 24-hour incubation. Maximal flux rates ranged from 197 to 411 μg/cm2/hr for the three formulations. The total absorbed dose as a percent of the applied dose ranged from 30.0 to 50.9 %. Human skin showed gradually increasing flux rates or rates approaching a steady state through the 24-hour incubation for the Ultra PC™ 2000 and 40% aqueous formulations. The Neat Control Lotion B formulation showed a rapid increase in flux rates through 2 hours, followed by a gradual decline through 24 hours. Maximal flux rates ranged from 107 to 128 μg/cm2/hr for the three formulations. The total absorbed dose as a percent of the applied dose was less than in rats, and ranged from 6.65 to 16.7 %. Recovery of the applied dose was low, however, evaporative loss of the test article from the test system could account for the low recovery of dose in both species. Rat skin had consistently higher flux rates than human skin, and the total absorbed dose was markedly higher in rat skin. This may explain
the higher recovery of the applied dose with the Ultra PC 2000™ formulation in rat skin relative to human skin (43.0% vs. 25.1%). That is, less evaporation of the dose could occur from rat skin because the dose was absorbed more rapidly and completely than human skin, so less test article was available for evaporation from rat skin. In both species, absorbed [14C]-AMP was primarily recovered from the receptor fluid. No evidence of marked accumulation of [14C]-AMP in skin tissue was evident.
Executive summary:

The objectives of this study were to evaluate the rate and amount of [14C]-aminomethylpropanol ([14C]-AMP) absorption across fresh human and Sprague-Dawley rat skin after in vitro exposure and to evaluate the disposition of [14C]-AMP in the various layers (stratum corneum, epidermis, and dermis) of fresh human and Sprague-Dawley rat skin after in vitro exposure.

Human and rat skin samples were incubated for 24 hours with the epidermal surface exposed to [14C]-AMP prepared in three formulations. The amount of [14C]-AMP absorbed across the skin and the disposition of [14C]-AMP in the various skin layers following this 24-hour incubation period were determined by liquid scintillation counting.

The absorption and cutaneous disposition of [14C]-AMP in an Ultra PC 2000™ formulation, a 40% aqueous formulation, and a Neat Control Lotion B formulation were determined in rat and human skin. Rat skin showed gradually increasing flux rates for the three formulations, approaching a steady state through the 24-hour incubation. Maximal flux rates ranged from 197 to 411 μg/cm2/hr for the three formulations. The total absorbed dose as a percent of the applied dose ranged from 30.0 to 50.9 %. Human skin showed gradually increasing flux rates or rates approaching a steady state through the 24-hour incubation for the Ultra PC 2000 and 40% aqueous formulations. The Neat Control Lotion B formulation showed a rapid increase in flux rates through 2 hours, followed by a gradual decline through 24 hours. Maximal flux rates ranged from 107 to 128 μg/cm2/hr for the three formulations. The total absorbed dose as a percent of the applied dose was less than in rats, and ranged from 6.65 to 16.7 %. Recovery of the applied dose was low, however, evaporative loss of the test article from the test system accounted for the low recovery of dose in both species. In both species, absorbed [14C]-AMP was primarily recovered from the receptor fluid. No evidence of marked accumulation of [14C]-AMP in skin tissue was evident.