Major involvement of rabbit liver cytochrome P4501A in thiabendazole 5-hydroxylation

Abstract

1. Thiabendazole is a widely used food preservative and anthelmintic drug for breeding animal species. In order to characterize precisely the cytochrome P450 isozyme(s) involved in its major route of metabolism, a rapid and sensitive spectrofluorimetric method was developed for the simultaneous determination of thiabendazole and its main hepatic metabolite 5-hydroxythiabendazole. 2. The kinetics of thiabendazole 5-hydroxylation were determined in microsomal preparations from control rabbits or animals previously treated with either beta-naphthoflavone, isosafrole, phenobarbital, rifampicin or clofibrate. These treatments led to specific induction of CYP1A1, 1A2, 2B4, 3A6 and 4A1 respectively. 3. By considering this panel of characterised microsomal preparations, only those obtained from BNF-treated rabbits exhibited an increase in thiabendazole 5-hydroxylase activity Ethoxyresorufin O-deethylation in these microsomes was solely inhibited by thiabendazole. These argue for a specific involvement of the CYP1A subfamily. 4. In the CYP1A subfamily, CYP1A2 appears to be responsible for basal 5-hydroxylation and further unidentified metabolism of thiabendazole in control livers. However, the major involvement of CYP1A1 is supported by the following characteristics of 5-hydroxylation of thiabendazole: (1) the correlation with CYP1A1 expression and (2) the inhibition by ellipticine and not by furafylline, inhibitors of CYP1A1 and CYP1A2 respectively. 5. All these data demonstrated that the rabbit cytochrome P4501A is predominantly involved in thiabendazole 5-hydroxylation which has been suspected to be critical in terms of safety of the parent drug.

The effects of mebendazole on P4501A activity in rat hepatocytes and HepG2 cells. Comparison with tiabendazole and omeprazole

“…In our experiments, a slight increase in the P4501A protein level (Western blotting) was observed in rat hepatocytes treated with tiabendazole and there was also a considerable protein increase in HepG2 cells. As tiabendazole metabolites were reported to bind covalently to tissue proteins (Yoneyama et al 1985;Rey-Grobellet et al 1996a;Coulet et al 2000), including microsomal proteins (Yoneyama & Ichikawa 1986), the hypothesis that tiabendazole inhibits EROD and MROD activity through the binding of tiabendazole metabolites to P4501A enzymes may be proposed. Thus, induction of P4501A by tiabendazole could be masked by the inhibition of the corresponding enzymes.…”

“…The induction of P4501A by mebendazole may also increase the risk of mutagenesis and cocarcinogenesis, as P4501A is the major enzyme involved in the biological activation of various environmental pollutants (Parke et al 1990). Cotreatment with tiabendazole and mebendazole may result in increasing toxicity of tiabendazole as tiabendazole metabolites (products of P4501A2) were reported to be responsible for the nephrotoxicity and teratogenity of tiabendazole (Mizutani et al 1992;Rey-Grobellet et al 1996a;Coulet et al 2000). Simultaneous or successive therapy with the benzimidazole anthelmintic mebendazole and the antiulcer drug omeprazole, or with tiabendazole, may lead to significant increase of P4501A induction.…”

Thalidomide-induced Suppression of Embryo Fibroblast Proliferation Requires CYP1A1-Mediated Activation

“…Furthermore, the addition of CYP1A inhibitors (furafylline and ␣-naphthoflavone) and anti-rat CYP1A1 antibody reversed the suppression, suggesting the involvement of CYP1A forms in the production of reactive thalidomide metabolites. CYP1A1 and CYP1A2 were constitutively expressed in rabbit liver (Rey-Grobellet et al, 1996). In rabbit liver microsomes, CYP1A1 and CYP1A2 proteins were detected by anti-rat CYP1A1 antibody, which inhibited the suppressive effect of thalidomide (Fig.…”

Genotoxic and aneugenic properties of an imidazole derivative

“…It is also used in the preservation of food for breeding animal species, as well as in postharvest treatment to preserve citrus fruits during transport and storage (Reygrobellet et al, 1996;Sasaki et al, 1997). The introduction of TBZ represented a breakthrough in the therapy of cutaneous Larva migrans and Strongyloide stercoralis infection (Davies et al, 1993).…”