Abstract
Skin is the major target of allergic reactions to paraphenylenediamine (PPD). Such small molecules require activation to become immunogenic. The balance between activation and/or detoxification processes is critical for immunogenic potentials of compounds. Therefore, we investigated N-acetylation (NAT) capacities of human skin for PPD to gain a better understanding of its mechanisms of action. PPD is acetylated to monoacetyl-PPD (MAPPD), which in turn is acetylated to N,N′-diacetyl-PPD (DAPPD). This was found using cytosolic fractions from human skin (n = 9) and cultured normal human epidermal keratinocytes (n = 7). The cutaneous activities for MAPPD formation ranged from 0.41 to 3.68 nmol/mg/min (9-fold variation) and DAPPD formation from 0.65 to 3.25 nmol/mg protein/min (5-fold), respectively. Similar results were obtained with keratinocytes. NAT activities toward both substrates, PPD and MAPPD, were correlated in keratinocytes (r = 0.930), suggesting that the reactions were catalyzed by the same enzyme. Formation of MAPPD and DAPPD was competitively inhibited in the presence ofp-aminobenzoic acid (300 μM), a typical NAT1 substrate, but not by sulfamethazine. These kinetic characteristics suggest that the acetylation of PPD in human skin and keratinocytes is predominantly attributable to the polymorphic NAT1, although both mRNAs (NAT1 and NAT2) are synthesized in human skin and keratinocytes. The metabolism of PPD by NAT1 in human skin and keratinocytes as well as the virtual absence of NAT2 activity may have important toxicological implications. In the case of PPD, our results emphasize thatN-acetylation status may be a susceptibility factor for the development of an allergy to PPD.
Footnotes
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Send reprint requests to: Brunhilde Blömeke, Ph.D., Department of Dermatology, University Hospital RWTH Aachen, Pauwelsstrasse 30, D-52074 Aachen, Germany. E-mail:b.bloemeke{at}rwth-aachen.de
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↵1 This study was supported by the Tokai University Research Fellowship Program (Y.K.), START 52/96-S RWTH Aachen, and the European Union PL963713 (B.B.).
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↵2 Present address: Department of Dermatology, Tokai University School of Medicine, Isehara, Kanagawa, Japan.
- Abbreviations:
- PPD
- paraphenylenediamine
- BB
- N,N′-bis(4-aminophenyl)-2,5-diamino-1,4-quinone-diimine
- DAPPD
- N,N′-diacetyl-paraphenylenediamine
- AcCoA
- acetyl CoA
- MAPPD
- monoacetyl-paraphenylenediamine
- NAT1
- N-acetyltransferase 1
- NAT2
- N-acetyltransferase 2
- PABA
- p-aminobenzoic acid
- RT
- reverse transcription
- PCR
- polymerase chain reaction
- SMZ
- sulfamethazine
- Received May 24, 1999.
- Accepted August 31, 1999.
- The American Society for Pharmacology and Experimental Therapeutics
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