In vitro formation, disposition and toxicity of N-acetoxy-sulfamethoxazole, a potential mediator of sulfamethoxazole toxicity.

Abstract

Variation in the formation and disposition of the hydroxylamine of (SMX-HA) is thought to play an important role in the pathogenesis of sulfamethoxazole (SMX)-induced idiosyncratic adverse drug reactions. We hypothesized that, in analogy to carcinogenic arylamines, SMX-HA might be further converted to an electrophilic N-acetoxy metabolite which could play a role in mediating SMX toxicity. Accordingly, we chemically synthesized N-acetoxy-SMX, and examined the characteristics of its formation, metabolism, cytotoxicity and mutagenicity in human and bacterial test systems. The human arylamine N-acetyl-transferases, (NAT)1 and NAT2, were capable of converting SMX-HA to N-acetoxy-SMX. NAT1 and NAT2 possessed similar affinities for SMX-HA (apparent Km values of 650 and 520 microM, respectively), but the apparent maximal velocity of the NAT1-mediated acetylation was higher than that of NAT2. (1332 vs. 37 nmol/min/U of immunoreactive NAT protein). Human peripheral blood mononuclear cells 12,000 x g supernatant fractions converted N-acetoxy-SMX mainly back to SMX-HA, and also to a lesser extent to SMX, at clinically relevant concentrations. Similar pathways were observed in human hepatic cytosolic fractions. In a cytotoxicity assay, N-acetoxy-SMX was significantly more toxic to human peripheral blood mononuclear cells than SMX-HA (16.6 vs. 11.5% dead cells at a concentration of 300 microM). N-acetoxy-SMX was weakly mutagenic to the Salmonella typhimurium TA100 strain in the Ames test. These data suggest that the N-acetoxy metabolites of sulfonamides could potentially play a role in mediating sulfonamide idiosyncratic adverse drug reactions.

• Authors: H Nakamura, J Uetrecht, A E Cribb, M A Miller, N Zahid, J Hill, P D Josephy, D M Grant, S P Spielberg
• Journal: The Journal of pharmacology and experimental therapeutics (J Pharmacol Exp Ther) Vol. 274 Issue 3 Pg. 1099-104 (Sep 1995) ISSN: 0022-3565 [Print] United States
• PMID: 7562475 (Publication Type: Journal Article, Research Support, Non-U.S. Gov't)

Chemical References

• Hydroxamic Acids
• N-acetoxysulfamethoxazole
• Recombinant Proteins
• Acetyltransferases
• Sulfamethoxazole

Topics

• Acetyltransferases (metabolism)
• Biotransformation
• Cytosol (enzymology)
• Humans
• Hydroxamic Acids (metabolism)
• In Vitro Techniques
• Leukocytes, Mononuclear (metabolism)
• Liver (enzymology)
• Mutagenicity Tests
• Recombinant Proteins (metabolism)
• Salmonella typhimurium (genetics)
• Sulfamethoxazole (analogs & derivatives, metabolism, pharmacokinetics, toxicity)