The effects of fenbendazole, flubendazole and mebendazole on activities of hepatic cytochromes P450 in pig

Unravelling drug-drug interactions in pigs: Induction of hepatic cytochrome P450 1A (CYP1A) metabolism after the in-feed medication with the anthelmintic fenbendazole

The anthelmintic fenbendazole (FBZ) undergoes hepatic S‑oxygenation by monooxygenases belonging to the cytochrome P450 (CYP) and flavin-monooxygenase (FMO) families. The in-feed medication with FBZ induced CYP1A-dependent metabolism in pig liver. This fact may alter the metabolism of the anthelmintic itself, and of CYP1A substrates like aflatoxin B1 (AFB1). This work evaluated the effect of the in-feed administration of FBZ on CYP1A-dependent metabolism, on its own pattern of hepatic S‑oxygenation, and on the metabolism of AFB1. Landrace piglets remained untreated (n = 5) or received a pre-mix of FBZ (n = 6) in feed for 9 days. Pigs were slaughtered for preparation of liver microsomes used for: CYP content determination; monitoring the CYP1A-dependent enzyme activities, 7-ethoxyresorufin O-deethylase (EROD) and 7-methoxyresorufin O-demethylase (MROD); measurement of FBZ (50 μM) S‑oxygenation, and AFB1 (16 nM) disappearance from the incubation medium. In microsomes of FBZ-treated animals, EROD and MROD increased 19-fold (p = 0.002) and 14-fold (p = 0.003), respectively. An enhanced (3-fold, p = 0.004) participation of the CYP pathway in FBZ S‑oxygenation was observed in the liver of piglets treated with the anthelmintic (210 ± 69 pmol/min.nmol CYP) compared to untreated animals (68 ± 34 pmol/min.nmol CYP). AFB1 metabolism was 93% higher (p = 0.009) in the liver of FBZ-treated compared to untreated pigs. Positive and significant (p < 0.05) correlations were observed between CYP1A-dependent enzyme activities and FBZ or AFB1 metabolism. The sustained administration of FBZ caused an auto-induction of the CYP1A-dependent S‑oxygenation of this anthelmintic. The CYP1A induction triggered by the anthelmintic could amplify the production of AFB1 metabolites in pig liver, including the hepatotoxic AFB1-derived epoxide.+.

Tacrine First-Phase Biotransformation and Associated Hepatotoxicity: A Possible Way to Avoid Quinone Methide Formation

Tacrine was withdrawn from clinical use as a drug against Alzheimer's disease in 2013, mainly due to drug-induced liver injury. The culprit of tacrine-associated hepatotoxicity is believed to be the 7-OH-tacrine metabolite, a possible precursor of quinone methide (Qmeth), which binds to intracellular -SH proteins. In our study, several different animal and human models (liver microsomes, primary hepatocytes, and liver slices) were used to investigate the biotransformation and hepatotoxicity of tacrine and its 7-substituted analogues (7-methoxy-, 7-phenoxy-, and 7-OH-tacrine). Our goal was to find the most appropriate in vitro model for studying tacrine hepatotoxicity and, through rational structure modifications, to develop derivatives of tacrine that are less prone to Qmeth formation. Our results show that none of animal models tested accurately mimic human tacrine biotransformation; however, the murine model seems to be more suitable than the rat model. Tacrine metabolism was overall most accurately mimicked in three-dimensional (3D) spheroid cultures of primary human hepatocytes (PHHs). In this system, tacrine and 7-methoxytacrine were hydroxylated to 7-OH-tacrine, whereas 7-phenoxytacrine formed, as expected, only trace amounts. Surprisingly, however, our study showed that 7-OH-tacrine was the least hepatotoxic (7-OH-tacrine < tacrine < 7-methoxytacrine < 7-phenoxytacrine) even after doses had been adjusted to achieve the same intracellular concentrations. The formation of Qmeth-cysteine and Qmeth-glutathione adducts after human liver microsome incubation was confirmed by all of the studied tacrine derivatives, but these findings were not confirmed after incubation with 3D PHH spheroids. Therefore, the presented data call into question the suggested previously hypothesized mechanism of toxicity, and the results open new avenues for chemical modifications to improve the safety of novel tacrine derivatives.

Mebendazole and temozolomide in patients with newly diagnosed high-grade gliomas: results of a phase 1 clinical trial

Background

Mebendazole is an anthelmintic drug introduced for human use in 1971 that extends survival in preclinical models of glioblastoma and other brain cancers.

Methods

A single-center dose-escalation and safety study of mebendazole in 24 patients with newly diagnosed high-grade gliomas in combination with temozolomide was conducted. Patients received mebendazole in combination with adjuvant temozolomide after completing concurrent radiation plus temozolomide. Dose-escalation levels were 25, 50, 100, and 200 mg/kg/day of oral mebendazole. A total of 15 patients were enrolled at the highest dose studied of 200 mg/kg/day. Trough plasma levels of mebendazole were measured at 4, 8, and 16 weeks.

Results

Twenty-four patients (18 glioblastoma and 6 anaplastic glioma) were enrolled with a median age of 49.8 years. Four patients (at 200 mg/kg) developed elevated grade 3 alanine aminotransferase (ALT) and/or aspartate transaminase (AST) after 1 month, which reversed with lower dosing or discontinuation. Plasma levels of mebendazole were variable but generally increased with dose. Kaplan–Meier analysis showed a 21-month median overall survival with 41.7% of patients alive at 2 years and 25% at 3 and 4 years. Median progression-free survival (PFS) from the date of diagnosis for 17 patients taking more than 1 month of mebendazole was 13.1 months (95% confidence interval [CI]: 8.8–14.6 months) but for 7 patients who received less than 1 month of mebendazole PFS was 9.2 months (95% CI: 5.8–13.0 months).

Conclusion

Mebendazole at doses up to 200 mg/kg demonstrated long-term safety and acceptable toxicity. Further studies are needed to determine mebendazole’s efficacy in patients with malignant glioma.

Porcine cytochrome P450 3A: current status on expression and regulation

The cytochrome P450s (CYPs) constitute a family of enzymes maintaining vital functions in the body and are mostly recognized for their significant role in detoxification. Of the CYP subfamilies, CYP3A, is one of the most active in the clearance of drugs and other xenobiotics. During the last decades, much focus has been on exploring different models for human CYP3A regulation, expression and activity. In that respect, the growing knowledge of the porcine CYP3As is of great interest. Although many aspects of porcine CYP3A regulation and activity are still unknown, the current literature provides a basic understanding of the porcine CYP3As that can be used e.g., when translating results from studies done in the porcine model into human settings. In this review, the current knowledge about porcine CYP3A expression, regulation, activity and metabolic significance are highlighted. Future research needs are also identified.

The Influence of Chestnut Wood and Flubendazole on Morphology of Small Intestine and Lymphocytes of Peripheral Blood, Spleen and Jejunum in Broiler Chickens

The study examined subpopulations of lymphocytes in peripheral blood, spleen, and jejunum including morphology of that segment in broiler chicken farm after treatment with flubendazole (Flimabend) and natural extract from chestnut wood (Farmatan). A total of 24 forty-day-old Kalimero-Super Master hybrid chickens were divided into 4 groups (n=6): the Fli group received Flimabend per os, 100 mg/g suspension in 1.43 mg of active substance/kg body weight during 7 day of experiment, Far group received Farmatan per os at 0.2 % concentration for 6 hours per day during 5 day (experimental days – from 3 to 7); the Far+Fli group received a combination of doses administered in the same way as for the first two groups; and control –C group with no active substance administration. The results demonstrated mild increase of leukocytes, lymphocytes, monocytes, leucocyte common antigen CD45, IgM+ and IgA+ cells in peripheral blood after administration of Flimabend. Similarly, subpopulations of followed lymphocytes (CD3+, CD4+, CD8+, IgM+) were increased in the jejunum after application of that drug. On the other hand, administration of Farmatan revealed opposite effect on determined immunocompetent cells what proves anti-inflammatory effect. Morphology of villi was also negatively influenced by administration of Flimabend. Administration of Farmatan suggests also its preventive administration in chickens. This tanin-containing drug as plant natural product may be used due to its antibacterial activity and as promising alternative to conventional drug with possible antihelminthic effect.

Comparison of biotransformation and efficacy of aminoacetonitrile anthelmintics in vitro

The present in vitro study was designed to test and compare anthelmintic activity, hepatotoxicity, and biotransformation of four selected aminoacetonitrile derivatives (AADs): monepantel (MOP, anthelmintic approved for the treatment), AAD-970, AAD-1154, and AAD-1336. Micro-agar larval development test, MTT test of cytotoxicity, and biotransformation study coupled with Ultra high performance liquid chromatography-tandem mass spectrometry (UHPLC-MS/MS) technique were used for this purpose. Larvae of two Haemonchus contortus strains (drug susceptible and multi-drug resistant) and primary cultures of rat and ovine hepatocytes served as model systems. All AADs (including MOP) exhibited significant larvicidal effect in H. contortus susceptible as well as multi-resistant strains, much higher than those of reference anthelmintics thiabendazole and flubendazole. AAD-1154 provides the best results for most tested parameters among all AADs in this study. The cytotoxicity test showed that all AADs can be considered as nontoxic for hepatocytes. In the biotransformation study, Phase I and Phase II metabolites of AADs were identified and schemes of possible metabolic pathways in ovine hepatocytes were proposed. Biotransformation of MOP was much more extensive than biotransformation of other AADs. Based on obtained results, AAD-1154 and AAD-1336 can be considered as promising candidates for further in vivo testing.

Gene and protein expression and cellular localisation of cytochrome P450 enzymes of the 1A, 2A, 2C, 2D and 2E subfamilies in equine intestine and liver

BACKGROUND

Among the cytochrome P450 enzymes (CYP), families 1-3 constitute almost half of total CYPs in mammals and play a central role in metabolism of a wide range of pharmaceuticals. This study investigated gene and protein expression and cellular localisation of CYP1A, CYP2A, CYP2C, CYP2D and CYP2E in equine intestine and liver. Real-time polymerase chain reaction (RT-PCR) was used to analyse gene expression, western blot to examine protein expression and immunohistochemical analyses to investigate cellular localisation.

RESULTS

CYP1A and CYP2C were the CYPs with the highest gene expression in the intestine and also showed considerable gene expression in the liver. CYP2E and CYP2A showed the highest gene expression in the liver. CYP2E showed moderate intestinal gene expression, whereas that of CYP2A was very low or undetectable. For CYP2D, rather low gene expression levels were found in both intestine and the liver. In the intestine, CYP gene expression levels, except for CYP2E, exhibited patterns resembling those of the proteins, indicating that intestinal protein expression of these CYPs is regulated at the transcriptional level. For CYP2E, the results showed that the intestinal gene expression did not correlate to any visible protein expression, indicating that intestinal protein expression of this CYP is regulated at the post-transcriptional level. Immunostaining of intestine tissue samples showed preferential CYP staining in enterocytes at the tips of intestinal villi in the small intestine. In the liver, all CYPs showed preferential localisation in the centrilobular hepatocytes.

CONCLUSIONS

Overall, different gene expression profiles were displayed by the CYPs examined in equine intestine and liver. The CYPs present in the intestine may act in concert with those in the liver to affect the oral bioavailability and therapeutic efficiency of substrate drugs. In addition, they may play a role in first-pass metabolism of feed constituents and of herbal supplements used in equine practice.

The toxicity and adverse effects of selected drugs in animals – overview

Therapeutic products quite often are causes of poisoning in both small and large animals. Drug poisonings in animals occur commonly due to off-label use of medicines, wrong dosage, negligence, accidental ingestion and deliberate poisonings. Toxicity of veterinary drugs may become evident also in therapeutic doses when adverse effects may occur. The aim of this review is to inform veterinary specialists about both veterinary and human drugs, specifically antiparasitics, non-steroidal anti-inflammatory drugs and other medicinal substances, which are most often reported to cause acute poisonings or adverse reactions in animals and to contribute to their broader knowledge and more accurate use of medicines, improving instructions to the animal owners and, hopefully, decrease the incidence of drug poisonings in animals.

Investigation of the metabolism of monepantel in ovine hepatocytes by UHPLC/MS/MS

Monepantel (MOP) belongs to a new class of anthelmintic drugs known as aminoacetonitrile derivatives. It was approved for use in veterinary practice in Czech Republic in 2011. So far, biotransformation and transport of MOP in target animals have been studied insufficiently, although the study of metabolic pathways of anthelmintics is very important for the efficacy of safety of therapy and evaluation of the risk of drug-drug interactions. The aim of this study was to identify MOP metabolites and to suggest the metabolic pathways of MOP in sheep. For this purpose, primary culture of ovine hepatocytes was used as a model in vitro system. After incubation, medium samples and homogenates of hepatocytes were extracted separately using solid-phase extraction. Analysis was performed using a hybrid quadrupole-time-of-flight analyzer with respect to high mass accuracy measurements in full scan and tandem mass spectra for the confirmation of an elemental composition. The obtained results revealed S-oxidation to sulfoxide and sulfone and arene hydroxylation as MOP phase I biotransformations. From phase II metabolites, MOP glucuronides, sulfates, and acetylcysteine conjugates were found. Based on the obtained results, a scheme of the metabolic pathway of MOP in sheep has been proposed.

The metabolic fate of ivermectin in host (Ovis aries) and parasite (Haemonchus contortus)

Ivermectin (IVE), one of the most important anthelmintics, is often used in the treatment of haemonchosis in ruminants. The objective of our work was (1) to find and identify phase I and II metabolites of IVE formed by the Barber's pole worm (Haemonchus contortus), and (2) to compare IVE metabolites in helminths with IVE biotransformation in sheep (Ovis aries) as host species. Ultrahigh-performance liquid chromatography/tandem mass spectrometry (UHPLC/MS/MS) was used for this purpose. During in vitro incubations, microsomes (from adult worms or from ovine liver) and a primary culture of ovine hepatocytes were incubated with IVE. In the ex vivo study, living H. contortus adults were incubated in the presence of 1 μM IVE for 24 h. The results showed that the H. contortus enzymatic system is not able to metabolize IVE. On the other hand, 7 different phase I as well as 9 phase II IVE metabolites were detected in ovine samples using UHPLC/MS/MS analyses. Most of these metabolites have not been described before. Haemonchus contortus is not able to deactivate IVE through biotransformation; therefore, biotransformation does not contribute to the development of IVE-resistance in the Barber's pole worm.

Transfer of flubendazole and tylosin from feed at cross-contamination levels to various poultry matrices

Residues of veterinary drugs and feed additives used extensively in animal husbandry are sometimes found in edible matrices. In this study, broilers received experimental feed, containing either flubendazole or tylosin, at cross-contamination levels of 2.5%, 5%, and 10% of the therapeutic dose to determine the transfer ratio of these molecules from feed to poultry matrices. Breast and thigh muscle and liver samples were collected during treatment and depletion periods and then analyzed using liquid chromatography-tandem mass spectrometry. The parent molecule flubendazole and its 2 major metabolites were quantified. After 3 to 5 d, a plateau phase was reached, and a few days after withdrawal of the experimental feed, a depletion of residues was noted. Significant difference between both muscle types was noted for flubendazole. Strong metabolization of flubendazole in the liver was seen. For tylosin, no residue concentrations above the limit of quantification could be detected in muscle. None of the residue concentrations for either molecule exceeded the corresponding maximum residue limits.

Activities of biotransformation enzymes and flubendazole metabolism in lambs (Ovis aries): effect of gender and flubendazole therapy

The effect of flubendazole (FLU) therapy on in vitro FLU biotransformation and the activities of selected biotransformation enzymes were investigated in male and female lambs. Four experimental groups were used: control (untreated) ewes and rams and FLU-treated ewes and rams (orally, 15 mg/kg per day, for three consecutive days). Subcellular fractions were prepared from liver and intestinal mucosa 24 h after the final dosage was administered. Activities of cytochromes P450 (CYP), flavine monooxygenases (FMO), carbonyl reducing enzymes, UDP-glucuronosyl transferase (UGT) and glutathione S-transferase were tested. Significant gender differences were observed for FMO-mediated activity (2-fold higher in ram lambs) and UGT activity (up to 30% higher in ewe lambs), but no gender differences were observed in FLU metabolism. FLU-treatment of lambs moderately changed the activities of some CYPs, FMO, and UGT in liver microsomes. In vitro FLU reduction was not altered in the liver, but was slightly higher in the small intestine of FLU pre-treated lambs. This correlated with the higher carbonyl reductase activities measured in the gut mucosa of these animals.

Inducibility of AhR-regulated CYP genes by β-naphthoflavone in the liver, lung, kidney and heart of the pig

The presence and inducibility of CYP enzymes belonging to the family 1 (CYP 1A1, 1A2 and 1B1) and AhR have been studied in liver, lung, kidney and heart of control and beta-naphthoflavone (beta NF)-treated pigs. Segments of so far undescribed genes for porcine CYP 1A2, 1B1 and AhR were identified by RT-PCR and their sequences found to be highly homologous to those of the corresponding human genes. The mRNA level of CYP 1A1 was induced by beta NF, although to a different extent, in liver, lung, kidney and heart. This transcriptional activation of CYP 1A1 was accompanied in microsomes of all these organs by an induction of 7-ethoxyresorufin deethylase activity (a marker of this isoform) and an increase in a protein band immunoreactive with anti-rat CYP 1A1. An increase in CYP 1A2 transcription and in activity of microsomal 7-methoxyresorufin demethylase and acetanilide 4-hydroxylase (both markers of 1A2) was observed in the liver and, to a very small extent, in the lung but not in kidney and heart. As to CYP 1B1, its transcription was detected in liver, lung and heart only following the beta NF treatment; however this mRNA expression did result in any detectable microsomal 17beta-estradiol 4-hydroxylase activity (a marker of this isoform). The CYPs induced by beta NF were further investigated by using some other marker activities. It was found that porcine CYP 1A1 and 1A2, unlike the human counterparts, could only deethylate 7-ethoxycomarin to a very small extent, if at all, whereas 7-ethoxy 4-trifluoromethylcoumarin was a good substrate for pig CYP 1A1. Overall, our results demonstrated a differential expression and regulation of the AhR-mediated CYP genes in liver, lung, kidney and heart of the pig.naphthoflavone.

Activities of biotransformation enzymes in pheasant (Phasianus colchicus) and their modulation by in vivo administration of mebendazole and flubendazole

Basal activities of certain pheasant hepatic and intestinal biotransformation enzymes and modulation of their activities by anthelmintics flubendazole (FLBZ) and mebendazole (MBZ) were investigated in subcellular fractions that were prepared from liver and small intestine of control and FLBZ or MBZ treated birds. Several oxidation, reduction and conjugation enzyme activities were assessed. In the liver, treatment of pheasants by FLBZ or MBZ caused very slight or no changes in monooxygenase activities and conjugation enzymes. More significative changes were detected in small intestine. Metyrapone and daunorubicin reductase activities were increased by both substances in the liver. This is the first evidence that certain benzimidazoles modulate reductases of carbonyl group. With respect to the relatively slight extent of the changes caused by FLBZ or MBZ we can assume that repeated administration of therapeutic doses of both FLBZ and MBZ has probably no serious influence on pheasant biotransformation enzyme system.

The effects of flubendazole and mebendazole on cytochromes P4501A in pheasant hepatocytes

Many benzimidazoles are known inducers of cytochromes P4501A (CYP1A) in laboratory animals and cell lines. As flubendazole and mebendazole are benzimidazole anthelmintics often used in a pheasant, in the present study an effect of these drugs in primary cultures of pheasant (Phasianus colchicus) hepatocytes was investigated. After 48 h incubation of the hepatocytes with the benzimidazoles (0.2-5 microM), CYP1A activities -- ethoxyresorufin O-deethylation (EROD) and methoxyresorufin O-demethylation (MROD) activities were measured and the CYP1A protein levels were determined by Western blotting. None of the tested benzimidazoles influenced the CYP1A protein content. No pharmacologically significant enhancement of CYP1A after exposure of the hepatocytes to flubendazole and mebendazole was found. Inhibition of the EROD/MROD activities caused by both tested substances was observed only at the highest concentration (5 microM). From a point of view of CYP1A induction or inhibition, the treatment of pheasants by both anthelmintics tested seems to be safe. Our study demonstrates the inter-species differences in CYP1A inducibility and the importance of induction/inhibition studies on target animals.

Modulation of porcine biotransformation enzymes by anthelmintic therapy with fenbendazole and flubendazole

Fenbendazole (FEN) and flubendazole (FLU) are benzimidazole anthelmintics often used in pig management for the control of nematodoses. The in vivo study presented here was designed to test the influence of FLU and FEN on cytochrome P4501A and other cytochrome P450 (CYP) isoforms, UDP-glucuronosyl transferase and several carbonyl reducing enzymes. The results indicated that FEN (in a single therapeutic dose as well as in repeated therapeutic doses) caused significant induction of pig CYP1A, while FLU did not show an inductive effect towards this isoform. Some of the other hepatic and intestinal biotransformation enzymes that were assayed were moderately influenced by FEN or FLU. Strong CYP1A induction following FEN therapy in pigs may negatively affect the efficacy and pharmacokinetics of FEN itself or other simultaneously or consecutively administered drugs. From the perspective of biotransformation enzyme modulation, FLU would appear to be a more convenient anthelmintic therapy of pigs than FEN.