Enantiomeric behaviour of albendazole and fenbendazole sulfoxides in domestic animals: Pharmacological implications

Metabolic mechanism and pharmacological study of albendazole in secondary hepatic alveolar echinococcosis (HAE) model rats

Albendazole (ABZ) is the primary treatment for alveolar echinococcosis (AE); however, its limited solubility impacts oral bioavailability, affecting therapeutic outcomes. In this study, various ABZ-solubilizing formulations, including albendazole crystal dispersion system (ABZ-CSD), albendazole hydrochloride-hydroxypropyl methylcellulose phthalate composite (TABZ-HCl-H), and albendazole hydroxyethyl sulfonate-hydroxypropyl methylcellulose phthalate composite (TABZ-HES-H), were developed and evaluated. Physicochemical properties as well as liver enzyme activity were analyzed and their pharmacodynamics in an anti-secondary hepatic alveolar echinococcosis (HAE) rat model were investigated. The formulations demonstrated improved solubility, exhibiting enhanced inhibitory effects on microcysts in HAE model rats compared to albendazole tablets. However, altered hepatic drug-metabolizing enzymes in HAE model rats led to increased ABZ levels and reduced ABZ-SO production, potentially elevating drug toxicity. These findings emphasize the importance of dose adjustments in patient administration, considering the impact of alveolar echinococcosis on rat hepatic drug metabolism.

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.+.

Repurposing of Benzimidazole Anthelmintic Drugs as Cancer Therapeutics

Simple Summary

Although non-prescription anthelmintics are often used for cancer treatment, there is a lack of information regarding their anti-cancer effects in clinical settings. The aims of our review are to describe the possibilities and limitations of the anti-cancer effects of benzimidazole anthelmintics and to suggest ways to overcome these limitations. The results of the current review illustrate the potential development of anthelmintics as a useful strategy for cancer treatment based on much preclinical evidence. Furthermore, they suggest that more rigorous studies on whole anti-cancer pathways and development strategies, including formulations, could result in significantly enhanced anti-cancer effects of benzimidazoles as a repurposed cancer therapy in clinical settings.

Abstract

Benzimidazoles have shown significant promise for repurposing as a cancer therapy. The aims of this review are to investigate the possibilities and limitations of the anti-cancer effects of benzimidazole anthelmintics and to suggest ways to overcome these limitations. This review included studies on the anti-cancer effects of 11 benzimidazoles. Largely divided into three parts, i.e., preclinical anti-cancer effects, clinical anti-cancer effects, and pharmacokinetic properties, we examine the characteristics of each benzimidazole and attempt to elucidate its key properties. Although many studies have demonstrated the anti-cancer effects of benzimidazoles, there is limited evidence regarding their effects in clinical settings. This might be because the clinical trials conducted using benzimidazoles failed to restrict their participants with specific criteria including cancer entities, cancer stages, and genetic characteristics of the participants. In addition, these drugs have limitations including low bioavailability, which results in insufficient plasma concentration levels. Additional studies on whole anti-cancer pathways and development strategies, including formulations, could result significant enhancements of the anti-cancer effects of benzimidazoles in clinical situations.

Pharmacokinetics and therapeutic efficacies of fenbendazole in comparison with levamisole in helminth-infected Caspian turtles (Mauremys caspica)

The pharmacokinetics and bioavailability of fenbendazole and levamisole were determined in Caspian turtles after a single intravenous (i.v.) and subcutaneous (s.c.) administration. Thirty turtles diagnosed as naturally infected with Serpinema microcephalus and Falcaustra armenica nematodes received fenbendazole (50 mg/kg) or levamisole (10 mg/kg) by i.v. and s.c. administrations. Blood samples were collected at time 0, 0.125, 0.25, 0.5, 1, 2, 4, 8, 12, 24, and 48 h after drug administration. Plasma drug concentrations were determined by a validated high-performance liquid chromatography method. Data were analyzed by noncompartmental methods. The mean elimination half-life of levamisole was 5.16 h and 12.03 h for i.v. and s.c. routes, respectively, and for fenbendazole, the mean elimination half-life was 25.38 h (i.v.) and 29.77 h (s.c.). The total clearance and volume of distribution at steady-state for levamisole and fenbendazole following i.v. administration were 0.22, 0.44 ml/g/h, and 1.06 and 7.35 ml/g, respectively. For the s.c. route, the peak plasma concentration of levamisole and fenbendazole was 10.53 and 5.24 μg/mL, respectively. The s.c. bioavailability of levamisole and fenbendazole was complete. Considering high anthelmintic efficacy and bioavailability after s.c. administration of levamisole and fenbendazole, and the absence of adverse effects, this route of administration is an easy and efficacious way of treating nematodes in Caspian turtles.

Biodegradation of anthelmintics in soils: does prior exposure of soils to anthelmintics accelerate their dissipation?

Anthelmintics (AHs) control animal infections with gastrointestinal nematodes. They reach soil through animal faeces deposited on soils or through manuring. Although soil constitutes a major AH sink, we know little about the mechanisms controlling their soil dissipation. We employed studies with fumigated and non-fumigated soils collected from 12 sheep farms with a variable record of albendazole (ABZ), ivermectin (IVM) and eprinomectin (EPM) use. From each farm, we collected soils from inside small ruminant barn facilities (series A, high exposure) and the associated grazing pastures (series B, low exposure). We asked the following questions: (a) What is the role of soil microorganisms in AH dissipation? (b) Does repeated exposure of soils to AHs lead to their accelerated biodegradation? (c) Which soil physicochemical properties control AH dissipation? Soil fumigation significantly retarded ABZ (DT₅₀ 1.9 and 4.33 days), IVM (34.5 and 108.7 days) and EPM dissipation (30 and 121 days) suggesting a key role of soil microorganisms in AH dissipation. No significant acceleration in AH dissipation was evident in soils from units with a record of the administration of AHs or in soil series A vs series B, suggesting that the level of prior exposure was not adequate to induce their enhanced biodegradation. Significant positive and negative correlations of soil total organic carbon (TOC) and ABZ and IVM dissipation, respectively, were observed. Soil adsorption of AHs increased in the order IVM > ABZ > EPM. TOC controlled soil adsorption of IVM and EPM, but not of ABZ, in support of the contrasting effect of TOC on IVM and ABZ dissipation.

Identification of indicator PPCPs in landfill leachates and livestock wastewaters using multi-residue analysis of 70 PPCPs: Analytical method development and application in Yangtze River Delta, China

The source apportionment of pharmaceuticals and personal care products (PPCPs) in the water environment based on indicators (i-PPCPs) requires a comprehensive characterization of various emission sources using reliable analytical methods for a wide spectrum of PPCPs. In this study, a robust and sensitive method based on solid phase extraction (SPE) and ultra-high performance liquid chromatography coupled with tandem mass spectrometry (UHPLC-MS/MS) for analyzing 70 PPCPs belonging to 17 therapeutic classes in landfill leachates and livestock wastewaters was developed. The SPE cartridges, sample pH, elution solvents and chelating agent additions were optimized, and acceptable recoveries (60- 130% for 67 target compounds), low method quantification limits (landfill leachate: 3- 1309 ng/L; livestock wastewater: 3- 686 ng/L) and high precisions (repeatability: 0- 20% for over 99% injections; reproducibility: 0- 20% for over 90% injections) were obtained. Using the optimized analytical method to characterize PPCPs in the typical landfill leachate and livestock wastewater in Yangtze River Delta, China, we found anthelmintics, which were first reported in landfill leachates globally, exhibited the highest concentration (albendazole, maximum concentration of 61.6 μg/L), and therefore proposed albendazole as one of the promising i-PPCP candidates in landfill leachates. In livestock wastewaters, antibiotics lincomycin was the most abundant PPCP (maximum concentration: 735 μg/L) and identified as an i-PPCP candidate for livestock-originated contamination. In addition, 15 non-antibiotic PPCPs were first investigated in the livestock wastewater in China and some non-steroidal anti-inflammatory drugs, acetaminophen, diclofenac and naproxen, were detected at similar concentration level (1.16- 91.1 μg/L) to antibiotics, highlighting the necessity to include representative non-antibiotic PPCPs in the studies of emerging contaminants in livestock wastewaters. The developed method provides a tool to comprehensively investigate PPCPs in high-strength wastewater, and the preliminary findings in the characterization of typical landfill leachates and livestock wastewaters are helpful to select i-PPCPs for the source apportionment of PPCPs in Yangtze River Delta, China.

The Antitumor Potentials of Benzimidazole Anthelmintics as Repurposing Drugs

The development of refractory tumor cells limits therapeutic efficacy in cancer by activating mechanisms that promote cellular proliferation, migration, invasion, metastasis, and survival. Benzimidazole anthelmintics have broad-spectrum action to remove parasites both in human and veterinary medicine. In addition to being antiparasitic agents, benzimidazole anthelmintics are known to exert anticancer activities, such as the disruption of microtubule polymerization, the induction of apoptosis, cell cycle (G2/M) arrest, anti-angiogenesis, and blockage of glucose transport. These antitumorigenic effects even extend to cancer cells resistant to approved therapies and when in combination with conventional therapeutics, enhance anticancer efficacy and hold promise as adjuvants. Above all, these anthelmintics may offer a broad, safe spectrum to treat cancer, as demonstrated by their long history of use as antiparasitic agents. The present review summarizes central literature regarding the anticancer effects of benzimidazole anthelmintics, including albendazole, parbendazole, fenbendazole, mebendazole, oxibendazole, oxfendazole, ricobendazole, and flubendazole in cancer cell lines, animal tumor models, and clinical trials. This review provides valuable information on how to improve the quality of life in patients with cancers by increasing the treatment options and decreasing side effects from conventional therapy.

Development of a simple high-throughput assay for directed evolution of enantioselective sulfoxide reductases

We report on the development of high-throughput fluorogenic assay that can streamline directed evolution of enantioselective sulfoxide reductases. As a model, methionine sulfoxide reductase A (MsrA) has been evolved to expand its limited substrate scope. The resulting mutant MsrA can resolve a range of new challenging racemic sulfoxides with high efficiency including the pharmaceutically relevant albendazole sulfoxide. The simplicity and the level of throughput make this method also suitable for the screening of metagenomic libraries in future for the discovery of new enzymes with similar reactivities.

Drug resistance in Giardia: Mechanisms and alternative treatments for Giardiasis

The use of chemotherapeutic drugs is the main resource against clinical giardiasis due to the lack of approved vaccines. Resistance of G. duodenalis to the most used drugs to treat giardiasis, metronidazole and albendazole, is a clinical issue of growing concern and yet unknown impact, respectively. In the search of new drugs, the completion of the Giardia genome project and the use of biochemical, molecular and bioinformatics tools allowed the identification of ligands/inhibitors for about one tenth of ≈150 potential drug targets in this parasite. Further, the synthesis of second generation nitroimidazoles and benzimidazoles along with high-throughput technologies have allowed not only to define overall mechanisms of resistance to metronidazole but to screen libraries of repurposed drugs and new pharmacophores, thereby increasing the known arsenal of anti-giardial compounds to some hundreds, with most demonstrating activity against metronidazole or albendazole-resistant Giardia. In particular, cysteine-modifying agents which include omeprazole, disulfiram, allicin and auranofin outstand due to their pleiotropic activity based on the extensive repertoire of thiol-containing proteins and the microaerophilic metabolism of this parasite. Other promising agents derived from higher organisms including phytochemicals, lactoferrin and propolis as well as probiotic bacteria/fungi have also demonstrated significant potential for therapeutic and prophylactic purposes in giardiasis. In this context the present chapter offers a comprehensive review of the current knowledge, including commonly prescribed drugs, causes of therapeutic failures, drug resistance mechanisms, strategies for the discovery of new agents and alternative drug therapies.

Occurrence and distribution of pharmaceutical and personal care products, artificial sweeteners, and pesticides in groundwater from an agricultural area in Korea

This study investigated the occurrence and distribution of 33 pharmaceutical and personal care products (PPCPs), five artificial sweeteners (ASs), and six pesticides in groundwater in rural agricultural and rural non-agricultural area in South Korea. A total of 31 target compounds (15 antibiotics, four anthelmintics, seven other PPCPs, four ASs, and one pesticide) were detected in agricultural groundwater at concentrations from not detected (ND) to 49.3 ng/L for PPCPs, ND to 1340 ng/L for ASs, and ND to 116 ng/L for pesticides. Four target compounds (two PPCPs and two ASs) were detected in rural non-agricultural groundwater in the range of 0.085-5.74 ng/L for PPCPs and 5.64-1330 ng/L for ASs. Among the target compounds, ASs, especially acesulfame (detection frequency 69% in rural agricultural areas and 100% in the rural non-agricultural area) were predominantly detected in both agricultural (mean: 32.9 ng/L) and non-agricultural (mean: 536 ng/L) groundwater, but different occurrence patterns were observed according to the sources of contamination. Known markers of sewage leakage were detected in both agricultural and non-agricultural groundwater samples (e.g., acesulfame (69% and 100%), caffeine (88% and 100%), and crotamiton (62% and 100%)), while compounds related to agricultural activities were only observed in agricultural groundwater (e.g., sulfathiazole (38%), sulfamethoxazole (31%), oxfendazole (69%), and carbofuran (42%)).

Progress in the pharmacological treatment of human cystic and alveolar echinococcosis: Compounds and therapeutic targets

Human cystic and alveolar echinococcosis are helmintic zoonotic diseases caused by infections with the larval stages of the cestode parasites Echinococcus granulosus and E. multilocularis, respectively. Both diseases are progressive and chronic, and often fatal if left unattended for E. multilocularis. As a treatment approach, chemotherapy against these orphan and neglected diseases has been available for more than 40 years. However, drug options were limited to the benzimidazoles albendazole and mebendazole, the only chemical compounds currently licensed for treatment in humans. To compensate this therapeutic shortfall, new treatment alternatives are urgently needed, including the identification, development, and assessment of novel compound classes and drug targets. Here is presented a thorough overview of the range of compounds that have been tested against E. granulosus and E. multilocularis in recent years, including in vitro and in vivo data on their mode of action, dosage, administration regimen, therapeutic outcomes, and associated clinical symptoms. Drugs covered included albendazole, mebendazole, and other members of the benzimidazole family and their derivatives, including improved formulations and combined therapies with other biocidal agents. Chemically synthetized molecules previously known to be effective against other infectious and non-infectious conditions such as anti-virals, antibiotics, anti-parasites, anti-mycotics, and anti-neoplastics are addressed. In view of their increasing relevance, natural occurring compounds derived from plant and fungal extracts are also discussed. Special attention has been paid to the recent application of genomic science on drug discovery and clinical medicine, particularly through the identification of small inhibitor molecules tackling key metabolic enzymes or signalling pathways.

Human cystic and alveolar echinococcosis (CE and AE), caused by the larval stages of the helminths Echinococcus granulosus and E. multilocularis, respectively, are progressive and chronic diseases affecting more than 1 million people worldwide. Both are considered orphan and neglected diseases by the World Health Organization. As a treatment approach, chemotherapy is limited to the use of benzimidazoles, drugs that stop parasite growth but do not kill the parasite. To compensate this therapeutic shortfall, new treatment alternatives are urgently needed. Here, we present the state-of-the-art regarding the alternative compounds and new formulations of benzimidazoles assayed against these diseases until now. Some of these new and modified compounds, either alone or in combination, could represent a step forward in the treatment of CE and AE. Unfortunately, few compounds have reached clinical trials stage in humans and, when assayed, the design of these studies has not allowed evidence-based conclusions. Thus, there is still an urgent need for defining new compounds or improved formulations of those already assayed, and also for a careful design of clinical protocols that could lead to the draw of a broad international consensus on the use of a defined drug, or a combination of drugs, for the effective treatment of CE and AE.

Comparison of Albendazole Cytotoxicity in Terms of Metabolite Formation in Four Model Systems

Introduction

Albendazole is used to treat endoparasitic diseases in animals and humans. After oral administration, it is quickly oxidised into its pharmacologically active metabolite albendazole sulfoxide and then to sulfone. However, it is not clear which compound is responsible for toxic effects towards mammalian cells.

Material and Methods

The model systems comprised cultures of isolated rat hepatocytes, two hepatoma cell lines (FaO, HepG2), and non-hepatic Balb/c 3T3 line. Cells were exposed for 24, 48, and 72 h to eight concentrations of albendazole ranging from 0.05 to 100 µg/mL. At all three time points cytotoxic effects were assessed by MTT assay and metabolites in the culture media were determined by LC-MS/MS analysis.

Results

The effective concentrations EC_50-72h showed that Balb/c 3T3 cells were the most sensitive to albendazole (0.2 ±0.1 µg/mL) followed by FaO (1.0 ±0.4 µg/mL), and HepG2 (6.4 ±0.1 µg/mL). In the case of isolated hepatocytes this value could not be attained up to the highest concentration used. Chemical analysis revealed that the concentrations of albendazole in hepatocytes and HepG2 and FaO culture media gradually decreased with incubation time, while the concentrations of its metabolites increased. The metabolism in isolated hepatocytes was dozens of times greater than in HepG2 and FaO cells. Two metabolites (albendazole sulfoxide, albendazole sulfone) were detected in isolated hepatocytes and HepG2 culture medium, one (albendazole sulfoxide) in FaO culture medium and none in Balb/c 3T3.

Conclusion

The obtained data indicate that metabolism of albendazole leads to its detoxification. The lower cytotoxic potential of metabolites was confirmed in the independent experiments in this study.

The sodium salt of the enantiomers of ricobendazole: Preparation, solubility and chiroptical properties

Albendazole (ABZ) is a sulfanyl-benzimidazole anthelmintic drug used worldwide in the treatment and prevention of parasitic diseases in animals and humans. Following oral administration, ABZ is rapidly oxidized into the pharmacologically active chiral sulfoxide metabolite known as ricobendazole (RBZ). As its achiral precursor, RBZ shows very low intestinal absorption due to its poor solubility in water (0.06mgmL^-1). To the best of our knowledge, there is no known example in human medicine of a water-soluble salt form of racemic or enantiomerically pure RBZ. In the present study, we describe in detail the preparation of the sodium (Na) salt of the enantiomers of RBZ through a two-step process: i) the multi-milligram resolution of RBZ by HPLC on the amylose-based Chiralpak IG chiral stationary phase under polar organic mode; ii) the salification of the isolated enantiomers of RBZ by reaction with sodium hydroxide solution. The spectroscopic and chiroptical properties of the RBZ-Na enantiomers were determined. Due to their unique solubility in 0.01M phosphate buffer at physiological pH (14.49mgmL^-1) and the high sample throughput obtained on semipreparative separation of the non-salified form, it is potentially possible to develop new anthelmintic enantiopure formulations with improved pharmacokinetic properties and lower toxicity.

Structure-based approaches for the design of benzimidazole-2-carbamate derivatives as tubulin polymerization inhibitors

Microtubules are highly dynamic assemblies of α/β-tubulin heterodimers whose polymerization inhibition is among one of the most successful approaches for anticancer drug development. Overexpression of the class I (βI) and class III (βIII) β-tubulin isotypes in breast and lung cancers and the highly expressed class VI (βVI) β-tubulin isotype in normal blood cells have increased the interest for designing specific tubulin-binding anticancer therapies. To this end, we employed our previously proposed model of the β-tubulin-nocodazole complex, supported by the recently determined X-ray structure, to identify the fundamental structural differences between β-tubulin isotypes. Moreover, we employed docking and molecular dynamics (MD) simulations to determine the binding mode of a series of benzimidazole-2-carbamete (BzC) derivatives in the βI-, βIII-, and βVI-tubulin isotypes. Our results demonstrate that Ala198 in the βVI isotype reduces the affinity of BzCs, explaining the low bone marrow toxicity for nocodazole. Additionally, no significant differences in the binding modes between βI- and βIII-BzC complexes were observed; however, Ser239 in the βIII isotype might be associated with the low affinity of BzCs to this isotype. Finally, our study provides insight into the β-tubulin-BzC interaction features essential for the development of more selective and less toxic anticancer therapeutics.

Characterizations and bioactivities of abendazole sulfoxide-loaded thermo-sensitive hydrogel

Albendazole (ABZ), a widely used anthelmintic, attributes its primary metabolite-albendazole sulfoxide (ABZSO)-as an effective agent against helminthes. For a purpose of long-lasting releasing ABZSO in a special lesion, the present study successfully manufactured ABZSO-loaded thermo-sensitive hydrogel, which was proved by FTIR and ¹H NMR, in the interim; in vitro and in vivo behaviors of the thermo-sensitive hydrogel containing ABZSO were studied too. The in vivo pharmacokinetics parameters indicated ABZSO-loaded hydrogel as a better choice for sustained release compared with simple ABZSO. Additionally, the effect of the prepared hydrogels against helminth was investigated by the lethality of Caenorhabditis elegans, the results indicated that the lethality of ABZSO-loaded hydrogel (1, 2, and 4 mg/ml, respectively) on C. elegans was higher than that of PLGA-PEG-PLGA group (P < 0.05). It suggested that the hydrogels loaded with albendazole sulfoxide could be considered highly effective against the nematode C. elegans.

Comparative pharmacokinetics and bioavailability of albendazole sulfoxide in sheep and goats, and dose-dependent plasma disposition in goats

Background

The aims of this study were to compare the pharmacokinetics of albendazole sulfoxide (ABZ-SO, ricobendazole) in goats and sheep at a dose of 5 mg/kg bodyweight (BW), after intravenous (IV) and subcutaneous (SC) administrations, and to investigate the effects of increased doses (10 and 15 mg/kg BW) on the plasma disposition of ABZ-SO in goats following SC administration. A total of 16 goats (Capra aegagrus hircus, eight males and eight females) and 8 sheep (Ovis aries, four males and four females) 12–16 months old and weighing 20–32 kg, were used. The study was designed according to two-phase crossover study protocol. In Phase-1, eight sheep were assigned as Group I and 16 goats were allocated into two groups (Group II and Group III). ABZ-SO was applied to Group I (sheep) and Group II (goats) animals subcutaneously, and to Group III (goats) animals intravenously, all at a dose rate of 5 mg/kg BW. In Phase-2, the sheep in the Group I received ABZ-SO intravenously in a dose of 5 mg/kg BW; the goats in Group II and Group III received ABZ-SO subcutaneously at a dose of 10 mg/kg and 15 mg/kg BW, respectively. Blood samples were collected from the jugular vein at different times between 1 and 120 h after drug administrations. The plasma concentrations of ABZ-SO and its metabolites were analysed by high performance liquid chromatography.

Results

In goats, the area under the curve, terminal half-life and plasma persistence of ABZ-SO were significantly smaller and shorter, respectively, compared with those observed in sheep following both IV and SC administrations at a dose of 5 mg/kg BW. On the other side, dose-dependent plasma dispositions of ABZ-SO were observed following SC administration at increased doses (10 and 15 mg/kg) in goats.

Conclusions

Consequently, ABZ-SO might be used at higher doses to provide higher plasma concentration and thus to achieve greater efficacy against the target parasites.

Probing the stereochemistry of successive sulfoxidation of the insecticide fenamiphos in soils

Successive sulfoxidation is widely recognized as a general characteristic of the metabolism of chiral or prochiral thioethers, producing sulfoxides, and sulfones. However, information related to the stereochemistry of this process in soils is rare. In this study, the biotic transformation of the insecticide fenamiphos (a model thioether) was followed over two months in three soils, through separate incubations with fenamiphos parent, the sulfoxide intermediate (FSO), the sulfone intermediate (FSO2), and their respective stereoisomers. The results showed that the successive sulfoxidation involved oxidation of fenamiphos to FSO and subsequently to FSO2 as well as diastereomerization/enantiomerization of FSO, all of which were primarily biotic and stereoselective. The concomitant hydrolysis of fenamiphos, FSO, and FSO2 to phenols that occurred at lower rates was biotically favorable, but not stereoselective. The stereochemistry of this successive sulfoxidation transferred principally through two parallel systems, R(+)-fenamiphos → SRPR(+)-/SSPR(-)-FSO → R(+)-FSO2 and S(-)-fenamiphos → SRPS(+)-/SSPS(-)-FSO → S(-)-FSO2, between which unidirectional intersystem crossing occurred at FSO via isomeric conversions and created a system of S(-)-fenamiphos → SRPR(+)-/SSPR(-)-FSO → R(+)-FSO2. This pattern accounts for the enrichment of the intermediates SSPR(-)-/SSPS(-)-FSO and R(+)-FSO2 that are toxicologically close to the highly toxic S(-)-fenamiphos, associated with soil application of fenamiphos. Selective formation/depletion of these intermediate stereoisomers leads to dramatic variations in the ecotoxicological effects of the thioether insecticide.

Evaluation of pharmaceuticals and personal care products with emphasis on anthelmintics in human sanitary waste, sewage, hospital wastewater, livestock wastewater and receiving water

We investigated 33 pharmaceuticals and personal care products (PPCPs) with emphasis on anthelmintics and their metabolites in human sanitary waste treatment plants (HTPs), sewage treatment plants (STPs), hospital wastewater treatment plants (HWTPs), livestock wastewater treatment plants (LWTPs), river water and seawater. PPCPs showed the characteristic specific occurrence patterns according to wastewater sources. The LWTPs and HTPs showed higher levels (maximum 3000 times in influents) of anthelmintics than other wastewater treatment plants, indicating that livestock wastewater and human sanitary waste are one of principal sources of anthelmintics. Among anthelmintics, fenbendazole and its metabolites are relatively high in the LWTPs, while human anthelmintics such as albendazole and flubendazole are most dominant in the HTPs, STPs and HWTPs. The occurrence pattern of fenbendazole's metabolites in water was different from pharmacokinetics studies, showing the possibility of transformation mechanism other than the metabolism in animal bodies by some processes unknown to us. The river water and seawater are generally affected by the point sources, but the distribution patterns in some receiving water are slightly different from the effluent, indicating the influence of non-point sources.

In vitro analysis of albendazole sulfoxide enantiomers shows that (+)-(R)-albendazole sulfoxide is the active enantiomer against Taenia solium

Albendazole is an anthelmintic drug widely used in the treatment of neurocysticercosis (NCC), an infection of the brain with Taenia solium cysts. However, drug levels of its active metabolite, albendazole sulfoxide (ABZSO), are erratic, likely resulting in decreased efficacy and suboptimal cure rates in NCC. Racemic albendazole sulfoxide is composed of ABZSO (+)-(R)- and (-)-(S) enantiomers that have been shown to differ in pharmacokinetics and activity against other helminths. The antiparasitic activities of racemic ABZSO and its (+)-(R)- and (-)-(S) enantiomers against T. solium cysts were evaluated in vitro. Parasites were collected from naturally infected pigs, cultured, and exposed to the racemic mixture or to each enantiomer (range, 10 to 500 ng/ml) or to praziquantel as a reference drug. The activity of each compound against cysts was assayed by measuring the ability to evaginate and inhibition of alkaline phosphatase (AP) and parasite antigen release. (+)-(R)-ABZSO was significantly more active than (-)-(S)-ABZSO in suppressing the release of AP and antigen into the supernatant in a dose- and time-dependent manner, indicating that most of the activity of ABZSO resides in the (+)-(R) enantiomer. Use of this enantiomer alone may lead to increased efficacy and/or less toxicity compared to albendazole.

Exacerbation of acetaminophen hepatotoxicity by the anthelmentic drug fenbendazole

Fenbendazole is a broad-spectrum anthelmintic drug widely used to prevent or treat nematode infections in laboratory rodent colonies. Potential interactions between fenbendazole and hepatotoxicants such as acetaminophen are unknown, and this was investigated in this study. Mice were fed a control diet or a diet containing fenbendazole (8-12 mg/kg/day) for 7 days prior to treatment with acetaminophen (300 mg/kg) or phosphate buffered saline. In mice fed a control diet, acetaminophen administration resulted in centrilobular hepatic necrosis and increases in serum transaminases, which were evident within 12 h. Acetaminophen-induced hepatotoxicity was markedly increased in mice fed the fenbendazole-containing diet, as measured histologically and by significant increases in serum transaminase levels. Moreover, in mice fed the fenbendazole-containing diet, but not the control diet, 63% mortality was observed within 24 h of acetaminophen administration. Fenbendazole by itself had no effect on liver histology or serum transaminases. To determine if exaggerated hepatotoxicity was due to alterations in acetaminophen metabolism, we analyzed sera for the presence of free acetaminophen and acetaminophen-glucuronide. We found that there were no differences in acetaminophen turnover. We also measured cytochrome P450 (cyp) 2e1, cyp3a, and cyp1a2 activity. Whereas fenbendazole had no effect on the activity of cyp2e1 or cyp3a, cyp1a2 was suppressed. A prolonged suppression of hepatic glutathione (GSH) was also observed in acetaminophen-treated mice fed the fenbendazole-containing diet when compared with the control diet. These data demonstrate that fenbendazole exacerbates the hepatotoxicity of acetaminophen, an effect that is related to persistent GSH depletion. These findings are novel and suggest a potential drug-drug interaction that should be considered in experimental protocols evaluating mechanisms of hepatotoxicity in rodent colonies treated with fenbendazole.

Enantiomerical pharmacokinetic prevalence of (+) albendazole sulphoxide in Trichinella spiralis muscle larvae

In a previous work, it was demonstrated that (+) albendazole sulphoxide (SOABZ) has higher anthelmintic activity than (-) SOABZ (Bolás-Fernández et al. J Parasitol 90:407-409, 2004). In this work, the pharmacokinetics characteristics of SOABZ and its enantiomeric forms were studied in an ex vivo model system for Trichinella spiralis isolated muscle larvae. To this end, samples of either racemic or purified SOABZ enantiomers were added to the incubation medium. Quantification of either albendazole, racemic SOABZ or its enantiomers was performed by validated HPLC methods and the effect of different SOABZ concentrations in relation to time of contact with the larvae was also analysed. Obviously, higher concentration of SOABZ in the medium leads to higher concentrations of SOABZ inside the larvae which increased in an exponential mode, thus indicating a simple diffusion process. At least 18 h of contact with the drug was required to achieve anthelmintic effects. Besides, after this time, the concentration of (+) SOABZ inside the larvae was significantly higher than that of the (-) SOABZ. From these results, it can be concluded that the higher activity found in the previous work is clearly related to the pharmacokinetic prevalence of (+) enantiomer inside the larvae.

Association of two single-isomer anionic CD in NACE for the chiral and achiral separation of fenbendazole, its sulphoxide and sulphone metabolites: application to their determination after in vitro metabolism

A NACE method was developed for the separation of fenbendazole (FBZ), a prochiral drug giving rise to chiral (oxfendazole or OFZ) and nonchiral (FBZ sulphone or FBZSO(2)) metabolites. First, the effect of the nature and the concentration of CD as well as that of the acidic BGE on the enantiomeric separation of OFZ were studied. OFZ enantiomers were completely resolved using a BGE made up of 10 mM ammonium formate and 0.5 M TFA in methanol containing 10 mM heptakis(2,3-di-O-acetyl-6-O-sulfo)-beta-CD and 10 mM heptakis(2,3-di-O-methyl-6-O-sulfo)-beta-CD. Moreover, the NACE method was found to be particularly well suited to the simultaneous determination of FBZ, OFZ enantiomers, and FBZSO(2). Thiabendazole was selected as an internal standard. The CD-NACE potential was then evaluated for in vitro metabolism studies using FBZ as a model case. The OFZ enantiomers and FBZSO(2) could be detected after incubation of FBZ in the phenobarbital-induced male rat liver microsomes systems.

The control of hookworm infection in China

BACKGROUND

Hookworm is still one of the three main soil-transmitted helminths prevalent in China, and 39 million cases infected with hookworm were estimated in China in 2006.

RESULTS

The main approach to the control of hookworm infections in China consists of large-scale deworming, rebuilding sanitation systems in rural areas and health education. The availability of low-cost, safe and single-dose albendazole make large-scale deworming programs possible in China. Currently, sanitary latrines with three-cells are recommended by government for the control of soil-transmitted helminths, since 35% of helminth infections and 83% of worm eggs could be reduced after using this kind of sanitary latrine. In addition, economic prosperity contributes greatly to the reduction of hookworm prevalence, but the inequity of economic and social development among different regions of China provides a scenario that the worst threat of hookworm infection is located in the poorest areas of southern and central China. Therefore, it is necessary to put more investments into prophylaxis and treatment of hookworm in these poor regions.

CONCLUSION

Although the prevalence of hookworm infection has fallen significantly in the last 15 years in China, the current strategy for controlling hookworm infections still needs to be strengthened along with the three-pronged approach, e.g. distributing anthelmintic drugs in schools and undertaking large-scale of hookworm deworming, improving water supplies and sanitation, and proper health education.