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Thiabendazole is an inducer of cytochrome P4501A1 in cultured rabbit hepatocytes
L Aix1, X Rey-Grobellet, G Larrieu
1Laboratoire de Pharmacologie-Toxicologie, INRA, Toulouse, France.
Abstract:
The effect of TBZ (30-100 microM) was investigated on cytochromes P450 of cultured rabbit hepatocytes considered 72 h after plating. At the highest concentrations and without apparent cellular toxicity, the drug provokes a dose-dependent increase in total microsomal cytochrome P450 and a rise in EROD activity which was correlated to a specific increase in P4501A1 level. Northern blot analysis of RNA reveals an increased level of mRNA specific to P4501A1. The transcriptional activation of this isoenzyme is proposed because of the significant inhibition of the above-mentioned increases when actinomycin was added to the culture medium. Data obtained from competition experiments demonstrate that TBZ is not a ligand of Ah receptor. A down-regulation process could explain the slight decrease in both ANOH and P4502E1 level observed in hepatocytes treated with the highest dose of TBZ.
Insights
The drug TBZ (Tibenzate) increases cytochrome P450 levels in rabbit liver cells, specifically P4501A1, through transcriptional activation. Higher doses may down-regulate other P450 enzymes.
Area of Science:
- Pharmacology
- Hepatology
- Biochemistry
Background:
- Cytochromes P450 (CYPs) are crucial enzymes in drug metabolism.
- Understanding how xenobiotics affect CYP expression is vital for drug safety and efficacy.
- Rabbit hepatocytes are a common model for studying drug-induced CYP changes.
Purpose of the Study:
- To investigate the effects of TBZ on cytochrome P450 expression and activity in cultured rabbit hepatocytes.
- To determine the specific CYP isoforms affected by TBZ exposure.
- To elucidate the mechanism underlying TBZ-induced changes in CYP levels.
Main Methods:
- Primary rabbit hepatocytes were cultured and treated with varying concentrations of TBZ (30-100 microM).
- Microsomal protein content, EROD activity, and specific CYP isoform levels (P4501A1, P4502E1) were measured.
- Northern blot analysis was used to assess mRNA levels for P4501A1.
- Transcriptional inhibition was studied using actinomycin, and Ah receptor binding was assessed via competition assays.
Main Results:
- TBZ caused a dose-dependent increase in total microsomal cytochrome P450 and EROD activity.
- This increase was specifically linked to elevated P4501A1 levels and its corresponding mRNA.
- Actinomycin significantly inhibited TBZ-induced increases, suggesting transcriptional activation of P4501A1.
- TBZ did not bind to the Ah receptor.
- A slight decrease in ANOH and P4502E1 levels was observed at the highest TBZ concentration, potentially due to down-regulation.
Conclusions:
- TBZ induces P4501A1 expression in rabbit hepatocytes via transcriptional activation, independent of the Ah receptor.
- The drug's effect on P4502E1 may involve a down-regulatory mechanism.
- These findings highlight TBZ's potential to modulate drug-metabolizing enzyme activity.