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CELLULAR AND MOLECULAR

Enzyme-Mediated Protein Haptenation of Dapsone and Sulfamethoxazole in Human Keratinocytes: II. Expression and Role of Flavin-Containing Monooxygenases and Peroxidases

Division of Pharmaceutics (P.M.V., S.R., C.K.S.), College of Pharmacy, and Inflammation Program, Department of Internal Medicine, Carver College of Medicine (W.M.N.), University of Iowa and Veterans Administration Hospital, Iowa City, Iowa; Department of Pediatrics and Pharmacology and Toxicology (S.B.K., R.N.H.), Medical College of Wisconsin and Children's Research Institute, Children's Hospital and Health Systems, Milwaukee, Wisconsin; and Department of Environmental and Molecular Toxicology and the Linus Pauling Institute (S.K.K., D.E.W.), Oregon State University, Corvallis, Oregon

Arylamine compounds, such as sulfamethoxazole (SMX) and dapsone (DDS), are metabolized in epidermal keratinocytes to arylhydroxylamine metabolites that auto-oxidize to arylnitroso derivatives, which in turn bind to cellular proteins and can act as antigens/immunogens. Previous studies have demonstrated that neither cytochromes P450 nor cyclooxygenases mediate this bioactivation in normal human epidermal keratinocytes (NHEKs). In this investigation, we demonstrated that methimazole (MMZ), a prototypical substrate of the flavin-containing monooxygenases (FMOs), attenuated the protein haptenation observed in NHEKs exposed to SMX or DDS. In addition, recombinant FMO1 and FMO3 were able to bioactivate both SMX and DDS, resulting in covalent adduct formation. Western blot analysis confirmed the presence of FMO3 in NHEKs, whereas FMO1 was not detectable. In addition to MMZ, 4-aminobenzoic acid hydrazide (ABH) also attenuated SMX- and DDS-dependent protein haptenation in NHEKs. ABH did not alter the bioactivation of these drugs by recombinant FMO3, suggesting its inhibitory effect in NHEKs was due to its known ability to inhibit peroxidases. Studies confirmed the presence of peroxidase activity in NHEKs; however, immunoblot analysis and reverse transcription-polymerase chain reaction indicated that myeloperoxidase, lactoperoxidase, and thyroid peroxidase were absent. Thus, our results suggest an important role for FMO3 and yet-to-be identified peroxidases in the bioactivation of sulfonamides in NHEKs.

Address correspondence to: Dr. Craig K. Svensson, Dean, College of Pharmacy, Nursing and Health Sciences, Purdue University, West Lafayette, IN 47907. E-mail: svensson{at}purdue.edu

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				S. Roychowdhury, P. M. Vyas, and C. K. Svensson Formation and Uptake of Arylhydroxylamine-Haptenated Proteins in Human Dendritic Cells Drug Metab. Dispos., April 1, 2007; 35(4): 676 - 681. [Abstract] [Full Text] [PDF]