Skin metabolism of aminophenols: Human keratinocytes as a suitable in vitro model to qualitatively predict the dermal transformation of 4-amino-2-hydroxytoluene in vivo

Journal Article · Sun Feb 15 04:00:00 EST 2009 · Toxicology and Applied Pharmacology

DOI:https://doi.org/10.1016/j.taap.2008.11.014· OSTI ID:21182738

Hewitt, N J ^[1]; Kunze, G ^[2]; Wenker, M ^[3]; Hein, D W ^[4]; Beck, H ^[2]; Skare, J ^[5]

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1. Wingertstrasse 25, 64390 Erzhausen (Germany)
2. Procter and Gamble Co., Central Product Safety, Cosmital SA, Marly (Switzerland)
3. NOTOX B.V., Hambakenwetering 7, 5231 DD 's-Hertogenbosch (Netherlands)
4. Department of Pharmacology and Toxicology, University of Louisville School of Medicine, 40292 Kentucky (United States)
5. Procter and Gamble Co., Central Product Safety, Sharon Woods Technical Center, Cincinnati, OH 45241 (United States)

4-Amino-2-hydroxytolune (AHT) is an aromatic amine ingredient in oxidative hair colouring products. As skin contact occurs during hair dyeing, characterisation of dermal metabolism is important for the safety assessment of this chemical class. We have compared the metabolism of AHT in the human keratinocyte cell line HaCaT with that observed ex-vivo in human skin and in vivo (topical application versus oral (p.o.) and intravenous (i.v.) route). Three major metabolites of AHT were excreted, i.e. N-acetyl-AHT, AHT-sulfate and AHT-glucuronide. When 12.5 mg/kg AHT was applied topically, the relative amounts of each metabolite were altered such that N-acetyl-AHT product was the major metabolite (66% of the dose in comparison with 37% and 32% of the same applied dose after i.v. and p.o. administration, respectively). N-acetylated products were the only metabolites detected in HaCaT cells and ex-vivo whole human skin discs for AHT and p-aminophenol (PAP), an aromatic amine known to undergo N-acetylation in vivo. Since N-acetyltransferase 1 (NAT1) is the responsible enzyme, kinetics of AHT was further compared to the standard NAT1 substrate p-aminobenzoic acid (PABA) in the HaCaT model revealing similar values for K{sub m} and V{sub max}. In conclusion NAT1 dependent dermal N-acetylation of AHT represents a 'first-pass' metabolism effect in the skin prior to entering the systemic circulation. Since the HaCaT cell model represents a suitable in vitro assay for addressing the qualitative contribution of the skin to the metabolism of topically-applied aromatic amines it may contribute to a reduction in animal testing.

• OSTI ID: 21182738
• Journal Information: Toxicology and Applied Pharmacology, Journal Name: Toxicology and Applied Pharmacology Journal Issue: 1 Vol. 235; ISSN TXAPA9; ISSN 0041-008X
• Country of Publication: United States
• Language: English

Related Subjects

60 APPLIED LIFE SCIENCES
ACETYLATION
AMINES
ENZYMES
HAIR
IN VITRO
IN VIVO
METABOLISM
METABOLITES
OXIDATION
PABA
RISK ASSESSMENT
TRANSFORMATIONS