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Molecular structure and hepatotoxicity: compared data about two closely related thiophene compounds
1Laboratoire de Chimie et Biochimie Pharmacologiques et Toxicologiques, Université Paris V, URA 400 CNRS, France.
Journal of Hepatology
|January 1, 1997
Summary
Tienilic acid (TA) and its isomer TAI exhibit distinct toxicities. TA’s metabolite specifically binds CYP2C9, causing immunoallergic effects, while TAI’s metabolite non-specifically binds proteins, leading to direct hepatotoxicity.
Area of Science:
- Pharmacology
- Toxicology
- Drug Metabolism
Background:
- Tienilic acid (TA) is a diuretic drug with known toxic effects.
- Its isomer, TAI, presents different toxicological profiles.
- Understanding the metabolic pathways and protein binding is crucial for explaining these differences.
Purpose of the Study:
- To investigate the differential toxic effects of tienilic acid (TA) and its isomer TAI.
- To elucidate the specific metabolic pathways and protein binding interactions of TA and TAI metabolites.
- To propose mechanisms underlying the distinct toxicities of these closely related compounds.
Main Methods:
- Incubation of TA and TAI with human liver microsomes.
- Analysis of metabolite formation and covalent binding patterns.
- Cytochrome P450 (CYP) enzyme phenotyping, focusing on CYP2C9.
Main Results:
- TA is primarily oxidized by CYP2C9 to a metabolite that specifically binds to CYP2C9.
- TAI is also oxidized by CYP2C9, but its reactive metabolite(s) bind non-specifically to multiple microsomal proteins.
- These distinct binding patterns correlate with observed toxicological differences.
Conclusions:
- The specific covalent binding of TA's sulfoxide metabolite to CYP2C9 is proposed to mediate immunoallergic toxic effects.
- The intense, non-specific covalent binding of TAI's reactive metabolite(s) to liver proteins likely causes direct hepatotoxicity.
- Metabolism and protein adduct formation by CYP2C9 play critical roles in the differential toxicity of TA and TAI.