Cited by 169Pharmacogenetics and Drug MetabolismDrug-Induced Hepatotoxicity and ProtectionDrug-Induced Adverse Reactions

N4-hydroxylation of sulfamethoxazole by cytochrome P450 of the cytochrome P4502C subfamily and reduction of sulfamethoxazole hydroxylamine in human and rat hepatic microsomes

Cribb, A E, Spielberg, S P, Griffin, G P·1995·Drug Metabolism and Disposition

Abstract

The N4-hydroxylation of sulfamethoxazole (SMX) to its hydroxylamine (SMX-HA) metabolite is the first step in the formation of reactive metabolites responsible for mediating hypersensitivity reactions associated with this compound. In rat hepatic microsomes, the NADPH-dependent oxidation of SMX to SMX-HA was increased 3-fold by pretreatment of rats with phenobarbital. Other cytochrome P450 (CYP) inducers were ineffective. The constitutive and induced SMX N-hydroxylation activities were inhibited by tolbutamide, and induction of SMX-HA activity paralleled the induction of progesterone 21-hydroxylase activity, a marker for CYP2C6. SMX N-hydroxylation in phenobarbital-treated rat hepatic microsomes was inhibited 70% by anti-CYP2C6 antisera. Thus, the N4-hydroxylation of SMX by rat hepatic microsomes was mediated by members of the CYP2C subfamily, probably CYP2C6. In a panel of human microsomes, SMX-HA formation correlated with tolbutamide hydroxylase activity (r = 0.75; p = 0.01); CYP2C9 content (r = 0.79; p < 0.01) and was inhibited 70% by 500 microM tolbutamide and 90% by 100 microM sulfaphenazole. Recombinant CYP2C9 catalyzed the N-hydroxylation of SMX. SMX-HA formation in human hepatic microsomes was therefore mediated predominantly by CYP2C9. CYP-mediated reduction of SMX-HA to SMX was markedly induced in dexamethasone and phenobarbital-treated rat hepatic microsomes, and was attributed to CYP3A and CYP2B forms. In uninduced rat and human hepatic microsomes, SMX-HA reduction was mediated predominantly by an NADH-dependent microsomal hydroxylamine reductase under aerobic conditions. Under anaerobic conditions, troleandomycin at > or = 1 microM inhibited the reduction of SMX-HA in human hepatic microsomes by 45%, whereas sulfaphenazole had no effect.(ABSTRACT TRUNCATED AT 250 WORDS)

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Crossref · 10.1016/s0090-9556(25)06552-3

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Authors
Cribb, A. E., Spielberg, S. P., & Griffin, G. P.
Affiliations
Merck & Co., Inc., Rahway, NJ, USA (United States) (US)
Venue
Drug Metabolism and Disposition
Publisher
Elsevier BV
Published
1995-03
Volume
23
Issue
3
Pages
406-414
ISSN
0090-9556 (ISSN-L)
OpenAlex
W1743904312
Cited by
169
References
0
Citations by year
2026: 4 · 2025: 4 · 2024: 1 · 2022: 2 · 2021: 2 · 2020: 3 · 2019: 6 · 2018: 4 · 2017: 4 · 2016: 3 · 2015: 5 · 2014: 7 · 2013: 2 · 2012: 6
FWCI
6.89
Type
journal article
Language
en
Open access
closed
Locations
  • Drug Metabolism and Disposition (publishedVersion)
  • PubMed (publishedVersion)
  • PubMed
Topics
  • Life Sciences › Pharmacology, Toxicology and Pharmaceutics › Pharmacology › Pharmacogenetics and Drug Metabolism
  • Life Sciences › Pharmacology, Toxicology and Pharmaceutics › Pharmacology › Drug-Induced Hepatotoxicity and Protection
  • Health Sciences › Medicine › Pharmacology › Drug-Induced Adverse Reactions
Keywords
sulfamethoxazole, CYP2C6, CYP2C9, CYP3A, CYP2B, liver microsomes, drug metabolism, phenobarbital induction, tolbutamide, sulfaphenazole, hydroxylamine reductase, troleandomycin, sulfonamide hypersensitivity
MeSH terms
Animals, Cytochrome P-450 Enzyme System, Humans, Hydroxylation, Male, Microsomes, Liver, Oxidation-Reduction, Sulfamethoxazole, Rats, Sprague-Dawley, Rats

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