DERMAL PENETRATION AND METABOLISM OF p-AMINOPHENOL AND p-PHENYLENEDIAMINE: APPLICATION OF THE EPIDERM HUMAN RECONSTRUCTED EPIDERMIS MODEL.

This study by scientists at Procter & Gamble Co. demonstrated that MatTek’s EpiDerm in vitro human skin tissue equivalent showed excellent correlation to in vivo results for skin penetration and metabolism of two hair dye ingredients, further strengthening the evidence for the use of the EpiDerm reconstructed human skin micronucleus assay as a replacement for in vivo dermal genotoxicity testing. To address the provision of the 7th Amendment to the EU Cosmetics Directive banning the use of in vivo genotoxicity assays for testing cosmetic ingredients in 2009, the 3D EpiDerm™ reconstructed human skin micronucleus assay has been developed. To further characterise the EpiDerm tissue for potential use in genotoxicity testing, we have evaluated the dermal penetration and metabolism of two hair dye ingredients, p-aminophenol (PAP) and p-phenylenediamine (PPD) in this reconstructed epidermis model. When EpiDerm tissue was topically exposed to PAP or PPD for 30 min (typical for a hair dye exposure), the majority (80–>90%) of PAP or PPD was excluded from skin tissue and removed by rinsing. After a 23.5 h recovery period, the PAP fraction that did penetrate was completely N-acetylated to acetaminophen (APAP). Similarly, 30 min topical application of PPD resulted in the formation of the N-mono- and N,N’-diacetylated metabolites of PPD. These results are consistent with published data on the dermal metabolism of these compounds from other in vitro systems as well as from in vivo studies. When tissue was exposed topically (PAP) or via the culture media (PPD) for 24 h, there was good batch-to-batch and donor-to-donor reproducibility in the penetration and metabolism of PAP and PPD. Overall, the results demonstrate that these two aromatic amines are biotransformed in 3D EpiDerm tissue via N-acetylation. Characterising the metabolic capability of EpiDerm tissue is important for the evaluation of this model for use in genotoxicity testing.

7th Amendment to the EU Cosmetics Directive, Aromatic amines, Batch-to-batch reproducibility, Dermal metabolism, Dermal penetration, Donor-to-donor reproducibility, EPI-200-MNA, Epiderm , Genotoxicity test, Hair dyes, Metabolism, Micronucleus assay, N-acetylation, N-acetyltransferase, Reproducibility, Two hair dye ingredients, Xenobiotic metabolism

p-aminophenol, p-phenylenediamine