The role of the cytoskeletal protein, tubulin, in the mode of action and mechanism of drug resistance to benzimidazoles

Innovative restriction site created PCR-RFLP for detection of benzimidazole resistance in Teladorsagia circumcincta

Benzimidazole compounds, especially albendazole, are the most commonly used anthelmintics for deworming of small ruminants in Iran. It is believed that the therapeutic effects of the benzimidazoles (BZs) come through their binding capacity to the beta-tubulin isotype 1. Substitution of phenylalanine to tyrosine at position 200 of this polypeptide confers resistance to BZs. Several investigators developed different biological- and molecular-based techniques to demonstrate the occurrence of resistance in helminthes against BZs. To address the determination of resistance at position 200 of beta-tubulin isotype 1, we developed an innovative restriction site created polymerase chain reaction-restriction fragment length polymorphism, in which nucleotide A at the position of 637 upstream flanked by the first two coding sequences of the phenylalanine (TT) triplet was substituted through the nucleotide G. The introduced modification in forward primer (UTvet MF-primer) leads to the creation of restriction site (AACGTT) for PSP1. Therefore, in the case of normal allele only, PSP1 can cut the corresponding PCR product. In the first step, the genomic DNA was isolated from each single Teladorsagia circumcincta collected either from the abomasa of untreated (n = 35) or of 5 mg/kg BW 2.5% albendazole suspension-treated (n = 40) sheep. It was amplified with the primer pair, creating PCR product of 403 bp in length. In the second step, the PCR product was extracted from agarose gel and amplified with the modified forward primer (UTvet MF-primer) and the same reverse primer as in step 1, creating a PCR product of 222 bp. The PCR product was then cut with PSP1 to obtain in the case of normal allele two DNA products (183 and 39 bp). Eight of the 35 worms collected from the untreated sheep were BZ(SS) homozygotes, and the rest (27) were BZ(RS) heterozygotes. In our preliminary experiment, we could not find a BZ(RR) homozygote form within the examined samples. Five out of 40 worms collected from the albendazole-treated sheep were BZ(RR) homozygotes, whereas the rest (35) were BZ(RS) heterozygotes. No BZ(SS) homozygote form was detected within this group.

Expression of recombinant β-tubulin alleles from Cylicocyclus nassatus (Cyathostominae)

Small strongyles (Cyathostominae) are common nematode parasites of horses that have developed resistance to the benzimidazole anthelmintics used to control their populations. Evidence suggests that the principal mechanism of resistance involves a phenylalanine-to-tyrosine mutation at codon 200 in the beta-tubulin proteins that are components of microtubules. Other works, however, suggest that a phenylalanine-to-tyrosine mutation at codon 167, or alternative mechanisms, may be involved. As part of an ongoing project examining the role that these two beta-tubulin mutations may play in benzimidazole resistance, we have cloned the wild-type allele and the two alleles with the phenylalanine-to-tyrosine mutations at codons 167 and 200 of the beta-tubulin isotype 1 gene from the small strongyle Cylicocyclus nassatus. In this work, we describe the construction of expression vectors containing these alleles and their expression in Escherichia coli.

Small strongyle infection: consequences of larvicidal treatment of horses with fenbendazole and moxidectin

The study was undertaken to evaluate adverse effects of larvicidal treatment in horses naturally infected with cyathostomins. Out of 24 ponies kept on pasture, four animals were housed in September and anthelmintically cured to serve as worm-free controls (group C-0). The others were housed in December. Eight animals each were treated 8 weeks later with 5 x 7.5mg/kg fenbendazole (FBZ) or 1 x 0.4 mg/kg moxidectin (MOX). Four animals remained untreated (group C-i). Two, 4, 6 and 14 days after the end of treatment two animals of each of the treated groups were necropsied together with group C-0 and C-i animals. Infected animals before treatment showed weight loss, eosinophilia, increased plasma protein and globulin contents. Treatment was followed by weight gain and temporal plasma protein and globulin increase. Proportions of CD4+ and CD8+ T lymphocytes in the peripheral blood did not differ between the groups before treatment but dropped significantly temporally after FBZ treatment. Group C-0 was worm-free at necropsy. Group C-i animals contained variable numbers of luminal and tissue cyathostomins. Histological sections showed larval stages in the lamina propria und submucosa surrounded by macrophages. Either treatment was effective against luminal parasites and reduced the number of larvae in the bowel wall beginning 4-6 days after FBZ and 6-14 days after MOX treatment. Histologically, as a first reaction after FBZ application T lymphocytes accumulated around morphologically intact L4 in the submucosa. Subsequently T lymphocytes associated with eosinophils infiltrated the submucosa. Parasites became enclosed by granulomas with eosinophils adhering to and invading the larvae which started to disintegrate on day 4. Later on, particularly on day 14 inflammation extended into the mucosa and was frequently associated with ulcerations. Third stage larvae in general and L4 in the lamina propria, however, seemed not to be affected until day 14 and even then, parasites did usually not generate extensive inflammation. After MOX treatment severe morphologically detectable alterations of tissue larvae could not be observed earlier than day 14. Different from FBZ treatment, larvae disintegrated and were obviously resorbed without causing severe inflammation in the gut wall. In conclusion treatment with either drug was efficacious against tissue larvae of cyathostomins but there may be different clinical consequences: in contrast to MOX effects, killing of larvae due to FBZ was associated with severe tissue damage, which clinically may correspond to reactions caused by synchronous mass emergence of fourth stage larvae, i.e., may mimic larval cyathostominosis.

Adult triclabendazole-resistant Fasciola hepatica: surface and subsurface tegumental responses to in vitro treatment with the sulphoxide metabolite of the experimental fasciolicide compound alpha

Mature Fasciola hepatica of the triclabendazole-resistant Sligo isolate were incubated in vitro with 10 microg/ml of the sulphoxide metabolite of compound alpha [5-chloro-2-methylthio-6-(1-naphthyloxy)-H-benzimidazole]; the metabolite will be referred to as alpha.SO. Changes resulting from drug treatment were examined by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and tubulin immunocytochemistry (ICC). SEM revealed that disruption to the tegumental surface mainly took the form of swelling and blebbing. Extensive spine loss occurred on the ventral surface of the oral cone, and sloughing of the tegument was observed along the lateral margins of the fluke. Examination of sections from the anterior mid-body region at the TEM level revealed that treatment with alpha.SO led to swelling of the basal infolds and mitochondria within the tegumental syncytium; also, accumulations of secretory bodies beneath the apical plasma membrane. The tegumental cell bodies contained swollen mitochondria and cisternae of granular endoplasmic reticulum, but few Golgi complexes were observed. An increase in T2 secretory bodies was observed, whilst in the T1 tegumental cells, the T1 secretory bodies had decreased in number. Immunocytochemical (ICC) studies showed that incubation with alpha.SO, ABZ.SO and TCBZ.SO did not cause significant changes to the distribution of tubulin within the tegumental syncytium of the Sligo isolate. In contrast, alpha.SO, ABZ.SO and TCBZ.SO caused severe disruption to tubulin organization within the syncytial layer of the TCBZ-susceptible Cullompton isolate. The EM results confirm that compound alpha is a fasciolicide capable of disrupting the tegument of mature TCBZ-resistant F. hepatica; however, this was not accompanied by any change in tubulin immunoreactivity.

Detection of benzimidazole resistance in Haemonchus contortus using RFLP-PCR technique

Benzimidazole (BZ) resistance in Haemonchus contortus is linked primarily with the mutation in the beta-tubulin isotype 1 gene that substitute phenylalanine (Phe) to tyrosine (Tyr) at 200 codon of the gene. In the present study, a new restriction fragment length polymorphism-polymerase chain reaction (RFLP-PCR) technique has been developed for detection of BZ resistance in the beta-tubulin isotype 1 gene of H. contortus. The technique utilizes two primers viz. AvikaF and AvikaR to amplify the region containing mutation in the beta-tubulin gene followed by restriction digestion. After digestion, the 'rr' individuals (homozygous resistant) revealed 257 and 48 bp bands, the 'rS' individuals (heterozygous) showed 305, 257 and 48 bp bands, while 'SS' individuals (homozygous susceptible) revealed uncut 305 bp band. A total of 162 adult male H. contortus collected from Avikanagar, Jaipur and Bikaner regions (54 from each region) were genotyped for analyzing BZ resistance in the beta-tubulin gene. Out of which, 130 adults were 'rr' types, 20 'rS' types and 12 'SS' types. The results showed that genotypic frequencies of different genotypes (rr, rS and SS) were highly significant difference among the three regions (P<0.001). The 'rr' individuals were higher (98%) in Jaipur followed by Avikanagar (93%) and Bikaner (50%) regions. Overall, the prevalence of BZ resistant allele (r) was higher (86%) as compared to BZ susceptible allele (S) (14%). The technique was also found suitable for genotyping of larvae of H. contortus and yielded reproducible results. The study indicated that RFLP-PCR is an easy, reproducible and less expensive than allele specific PCR. This technique will be helpful in establishing the prevalence rate of BZ resistance in H. contortus and can also be utilized for existing worm control programme.

Molecular diagnosis of anthelmintic resistance

Conventional and real time polymerase chain reaction-based tests have been developed for the diagnosis of anthelmintic resistance (AR) in populations of several small and large ruminant as well as horse gastro-intestinal nematode species. To date, molecular markers that correlate well with AR are available only for the detection of benzimidazole resistance. Recently, however, a single nucleotide polymorphism was found in vitro to be of functional relevance for reduced drug efficacy to macrocylic lactones. The focus of the present review, therefore, is the molecular mechanism of action of these two drug classes and potential applications of this knowledge to the diagnosis of AR. It is argued that a prerequisite for future molecular diagnosis will be tests providing reliable and exact quantification of resistance related alleles in DNA extracted from representative pools of parasites.

Altered drug influx/efflux and enhanced metabolic activity in triclabendazole-resistant liver flukes

Triclabendazole (TCBZ) is a halogenated benzimidazole compound that possesses high activity against immature and adult stages of the liver fluke, Fasciola hepatica. The intensive use of TCBZ in endemic areas of fascioliasis has resulted in the development of liver flukes resistant to this compound. TCBZ sulphoxide (TCBZSO) and TCBZ sulphone (TCBZSO2) are the main molecules recovered in the bloodstream of TCBZ-treated animals. In order to gain some insight into the possible mechanisms of resistance to TCBZ, the goals of the work described here were: to compare the ex vivo transtegumental diffusion of TCBZ parent drug and its sulpho-metabolites (TCBZSO and TCBZSO2) into TCBZ-susceptible and -resistant liver flukes; and to assess the comparative pattern of TCBZ biotransformation by TCBZ-susceptible and -resistant F. hepatica. For the tegumental diffusion studies, TCBZ-susceptible (Cullompton) and -resistant (Sligo) adult flukes collected from untreated infected sheep were incubated (15-180 min) in KRT buffer containing either TCBZ, TCBZSO or TCBZSO2 (5 nmol.ml-1). For the metabolism studies, microsomal fractions obtained from TCBZ-susceptible and -resistant flukes were incubated for 60 min with TCBZ (40 microM), and the amount of the formed metabolic product (TCBZSO) was measured. Drug/metabolite concentrations were quantified by HPLC. All the assayed TCBZ-related molecules penetrated through the tegument of both TCBZ-susceptible and -resistant flukes. However, significantly lower (approximately 50%) concentrations of TCBZ and TCBZSO were recovered within the TCBZ-resistant flukes compared to the TCBZ-susceptible ones over the 180 min incubation period. The rate of TCBZ sulphoxidative metabolism into TCBZSO was significantly higher (39%) in TCBZ-resistant flukes. The flavin-monooxigenase (FMO) enzyme system appears to be the main metabolic pathway involved in the formation of TCBZSO in both TCBZ-susceptible and -resistant flukes. The altered drug influx/efflux and enhanced metabolic capacity identified in TCBZ-resistant liver flukes may account for the development of resistance to TCBZ.

Triclabendazole: new skills to unravel an old(ish) enigma

Triclabendazole was introduced in the early 1980s for the treatment of Fasciola hepatica infections in livestock. Due to its high activity against immature flukes, it has become established as the principal anti-fluke drug on the market. More recently, triclabendazole has been used to treat human cases of fascioliasis and is now the drug of choice for this infection, too. Resistance to triclabendazole was first reported in 1995 in a field population in Australia and, since that time, resistant populations have been identified in several countries in Europe. Parallel to the spread of resistance has been a sharp increase in the prevalence of fascioliasis, which has been attributed largely to climate changes. Consequently, farmers are faced with an alarming scenario, as none of the other fasciolicides on the market possess such high activity against the damaging immature stages of fluke. The main aim of this review is to assess current understanding of the mechanism of action of triclabendazole against the fluke and the mechanism by which the fluke has become resistant to it. The use of triclabendazole against animal and human infections is summarized and suggestions are given on ways to deal with resistance. Gaps in the knowledge of various aspects of its use are highlighted and this may serve to open up future research areas.

Evaluation of the efficacy of albendazole sulphoxide and praziquantel in combination on Taenia crassiceps cysts: in vitro studies

OBJECTIVES

Praziquantel and albendazole are currently used for chemotherapeutic treatment of neurocysticercosis. Albendazole has been found to be more effective than praziquantel; however, it is well known that not all patients will show a complete resolution of cysts. Searching for more effective treatments, this study was designed to evaluate the effect of the combination of praziquantel and albendazole sulphoxide in a Taenia crassiceps in vitro model as well as the kind of interaction between both drugs.

METHODS

In order to determine the concentration that produced 50% effect (EC50), T. crassiceps cysts were incubated in culture medium containing praziquantel (0.005-0.04 microg/mL), albendazole sulphoxide (0.021-0.16 microg/mL) or the combination of praziquantel and albendazole sulphoxide in a fixed-dose ratio (1:1). The experimental concentration (EC50Exp) of the combination was determined from the concentration-response curve constructed from the combined drug treatment. Isobolographic analyses were used to define the nature of the interaction between praziquantel and albendazole sulphoxide. Morphological and ultrastuctural alterations after different treatments over the parasite tissue were observed by light and transmission electron microscopy.

RESULTS

The changes in ultrastructure were more marked with the praziquantel and albendazole sulphoxide combination. Also the cysticidal effect of the combination was observed earlier than that of each drug alone. When isobolographic analysis was employed, we found that the experimental EC50 value (0.042 microg/mL) was not significantly different from the theoretical EC50 value (0.035 microg/mL), which indicates an additive interaction between praziquantel and albendazole sulphoxide.

CONCLUSIONS

Our study suggests that the combination of praziquantel and albendazole sulphoxide could potentially improve the current neurocysticercosis treatment.

In vitro effects of flubendazole on Echinococcus granulosus protoscoleces

The aim of the present work was to determine the in vitro protoscolicidal effect of flubendazole (FLBZ) against Echinococcus granulosus. Protoscoleces of E. granulosus were incubated with FLBZ at concentrations of 10, 5 and 1 microg/ml. The first signs of FLBZ-induced damage were observed 3 days post-incubation. A clear protoscolicidal effect, reducing the vitality of protoscoleces to 35.6+/-0.7%, was observed after 18 days of incubation. After 25 days of FLBZ incubation (5 microg/ml), the percentage of vital protoscoleces was 13.9+/-5.9%. Protoscolex mortality was 100% (10 and 1 microg/ml) and 0.7+/-0.7% (5 microg/ml) after FLBZ incubation for 30 days. Results of vitality tests were consistent with the tissue damage observed at the ultrastructural level. The primary site of damage was the tegument of the parasite. The morphological changes included contraction of the soma region, formation of blebs on the tegument, rostellar disorganization, loss of hooks and destruction of microtriches. The data reported in this article demonstrate a clear in vitro effect of FLBZ against E. granulosus protoscoleces.

Praziquantel and albendazole damaging action on in vitro developing Mesocestoides corti (Platyhelminthes: Cestoda)

Parasitic flatworms present several steps of body architecture rearrangement during their fast transition from one developmental stage to another, which are, at least in part, responsible for their evasion from host immune response. Besides, different developmental stages present different degrees of susceptibility to drug action, and the identification of more susceptible stages is of importance for the definition of therapeutical approaches. Mesocestoides corti (syn. Mesocestoides vogae) is considered a good model to study cestode biology because it can be easily manipulated both in vivo and in vitro and due to its relatively close relationship to cestodes of medical relevance, such as those from genera Echinococcus or Taenia. We have analyzed the damaging action of two broad spectrum anthelmintic drugs (praziquantel and albendazole) throughout the in vitro strobilization process of M. corti in order to identify developmental stages or body structures more susceptible to these drugs. Tetrathyridia (larval stage) and segmented-induced worms were cultivated and treated with praziquantel and albendazole. Whole mounted samples, taken from different developmental stages, were fixed and stained with fluorophore-labeled WGA lectin and phalloidin for the analysis of tegument and muscles, respectively. Confocal laser scanning microscopy was used to identify anatomical changes and lesions caused by each anthelmintic drug in a 3D view. We demonstrated that both praziquantel and albendazole cause extensive tissue damage, especially on tegument, and that adult forms were the most susceptible to drug exposure.

Immunolocalization of cytoskeletal components in the tegument of the 3-week-old juvenile and adult Fasciola gigantica

Components of three cytoskeletal elements, namely, microtubule, intermediate and actin filaments have been localised in the tegument of the 3-week-old juvenile and adult Fasciola gigantica by means of immunofluorescence and immunoperoxidase techniques, using mouse monoclonal anti-alpha-tubulin, anti-cytokeratin antibodies and biotinylated-phalloidin, respectively. The immunostaining with the above probes were also performed in adult Schistosoma mansoni for comparison. The presence of tubulin, indicative of microtubules, was demonstrated in the tegumental cell bodies, their cytoplasmic processes, and the basal layer of the tegumental syncytium of F. gigantica. While in S. mansoni, tubulin appeared as vertical lines stretching across the whole thickness of the syncytium. Cytokeratin, representing one type of intermediate filaments, was detected in the tegumental cell bodies, their cytoplasmic processes, tegumental syncytium and spines of F. gigantica. In contrast, cytokeratin was evident only in the syncytium of S. mansoni, but not in the spines. Phalloidin, which could bind to actin, a subunit of microfilament, was detected in the tegumental cell bodies, their processes, and the microtrabecular network which form the scaffold of the tegumental syncytium of F. gigantica. In S. mansoni, actin was localized in similar tissues except the syncytium was not stained while spines exhibited intense staining. In F. gigantica, the presence of microtubules and actin filaments in the tegumental cells, their processes and in the syncytium could mediate the movement of secretory granules from the cell bodies towards the basal as well as the apical layer of the tegument. Cytokeratin filaments may serve to reinforce the integrity of the tegumental syncytium as well as the spines.

Eurytrema pancreaticum: the in vitro effect of praziquantel and triclabendazole on the adult fluke

The efficacy and tolerance of the 80 microg/ml praziquantel (PZQ) and 40 microg/ml triclabendazole (TCZ) against adult stage Eurytrema pancreaticum in vitro were investigated at 3, 12, and 15 h incubation. Motility of the flukes and histopathological changes were studied. Sudden paralysis and death were observed after exposed to PZQ as early as 3h incubation. In contrast, the TCZ treated flukes showed active mobility at all intervals. By light microscopic examination, severe damages in various organs such as tegument, muscle, and testes were observed early at 12h incubation of these drugs. PZQ caused more severe damage to flukes than TCZ. There were vigorous contraction of musculature, progressive shrinkage of circular and longitudinal muscles, vacuolization and disintegration of the tegument disrupting the worms' outer surface including detachment of spines in the PZQ treatment. The cells in testes were slightly increased in size and followed by degeneration leaving several hollow spaces. The uterus and vitelline glands remained unaffected. The direct observation of the fluke motility and light microscopic study highly suggested that PZQ was more effective than TCZ treatment for the eurytremiasis infection.

Changes to oxfendazole chiral kinetics and anthelmintic efficacy induced by piperonyl butoxide in horses

REASONS FOR PERFORMING THE STUDY

The study of novel pharmacological strategies to control parasitism in horses is required since many parasite species have developed resistance to anthelmintic drugs.

OBJECTIVES

To evaluate the effects of piperonyl butoxide (PB) (a metabolic inhibitor) on the plasma availability and enantiomeric behaviour of oxfendazole (OFZ) given orally to horses, and to compare the clinical efficacy of OFZ given either alone or co-administered with PB in naturally parasitised horses.

METHODS

Fifteen naturally parasitised crossbred male ponies were allocated into 3 groups (n = 5) and treated orally as follows: Group I (control) received distilled water as placebo; Group II was dosed with OFZ (10 mg/kg bwt); and Group III was treated with OFZ (10 mg/kg bwt) co-administered with PB (63 mg/kg bwt). Jugular blood samples were obtained over 120 h post treatment. Three weeks after treatments, all experimental horses were subjected to euthanasia.

RESULTS

The observed maximum plasma concentration (Cmax) and area under the concentration vs. time curve (AUC) values for OFZ increased 3- and 5-fold, respectively, in the presence of PB. The plasma concentration profiles of fenbendazole (FBZ), a metabolite generated from OFZ, were significantly lower after the treatment with OFZ alone (AUC = 0.8 microg x h/ml) compared to those obtained after the OFZ + PB treatment (AUC = 2.7 microg x h/ml). The enhanced pharmacokinetic profiles correlated with increased anthelmintic efficacy. The combination OFZ + PB showed 100% efficacy against mature nematode parasites. The efficacy against cyathostome L3 larvae increased from 94% (Group II) to 98.7% (Group III). Consistently, the number of L4 larvae recovered from OFZ + PB treated horses (Group III) (n = 146) was significantly lower (P<0.05) than that recovered from Group II (n = 1397).

CONCLUSIONS

The use of PB as a metabolic inhibitor may be useful to enhance OFZ activity against mature and migrating larvae of different parasite species in horses.

POTENTIAL RELEVANCE

Metabolic inhibitors may be used to enhance the activity of benzimidazole anthelmintics and extend the effective lifespan of benzimidazole drugs in the face of increasing resistance.

Giardia lamblia: Evaluation of the in vitro effects of nocodazole and colchicine on trophozoites

Giardia lamblia is the most commonly detected parasite in the intestinal tract of humans and other mammals causing giardiasis. Giardia presents several cytoskeletal structures with microtubules as major components such as the ventral adhesive disk, eight flagella axonemes, the median body and funis. Many drugs have already been tested as antigiardial agents, such as albendazole and mebendazole, which act by specifically inhibiting tubulin polymerization and hence microtubule assembly. In the present work, we used the microtubule inhibitors nocodazole and colchicine in order to investigate their direct and indirect effects on Giardia ultrastructure and attachment to the glass surface, respectively. Axenically grown G. lamblia trophozoites were treated with nocodazole or colchicine for different time intervals and analyzed by light and electron microscopy. It was observed that trophozoites became completely misshapen, detached from the glass surface and failed to complete cell division. The main alterations observed included disc fragmentation, presence of large vacuoles, and appearance of electrondense deposits made of tubulin. The cytokinesis was blocked, but not the karyokinesis, and membrane blebs were observed. These findings show that Giardia behavior and cytoskeleton are clearly affected by the commonly used microtubule targetting agents colchicine and nozodazole.

The molecular nature of benzimidazole resistance in helminths

The economic importance of benzimidazole (BZ) resistance has resulted in the isolation of resistant populations of helminths and their study (see pp 127-129 this issue). Recent research indicates that BZs act by binding to free beta-tubulin in the cell and inhibiting the formation of microtubules. The effects of BZs on other processes in the cell, such as transport and anaerobic metabolism, probably result from the inhibition of one or more of the functions of tubulin (see pp 112-115, this issue). In this article, Marleen Roos examines the evidence for changes in the beta-tubulin structure and the rate of its synthesis in BZ-resistant parasitic nematodes.

A possible model of benzimidazole binding to beta-tubulin disclosed by invoking an inter-domain movement

Although it is well established that benzimidazole (BZMs) compounds exert their therapeutic effects through binding to helminth beta-tubulin and thus disrupting microtubule-based processes in the parasites, the precise location of the benzimidazole-binding site on the beta-tubulin molecule has yet to be determined. In the present study, we have used previous experimental data as cues to help identify this site. Firstly, benzimidazole resistance has been correlated with a phenylalanine-to-tyrosine substitution at position 200 of Haemonchus contortus beta-tubulin isotype-I. Secondly, site-directed mutagenesis studies, using fungi, have shown that other residues in this region of the protein can influence the interaction of benzimidazoles with beta-tubulin. However, the atomic structure of the alphabeta-tubulin dimer shows that residue 200 and the other implicated residues are buried within the protein. This poses the question: how might benzimidazoles interact with these apparently inaccessible residues? In the present study, we present a mechanism by which those residues generally believed to interact with benzimidazoles may become accessible to the drugs. Furthermore, by docking albendazole-sulphoxide into a modelled H. contortus beta-tubulin molecule we offer a structural explanation for how the mutation conferring benzimidazole resistance in nematodes may act, as well as a possible explanation for the species-specificity of benzimidazole anthelmintics.

Flowcytometric assessment of the effect of drugs on Giardia lamblia trophozoites in vitro

The effect of albendazole, vincristine and metronidazole on the adherence, morphology, cell cycle and viability of Giardia lamblia trophozoites was evaluated. Albendazole rendered the trophozoites unable to attach which is a prerequisite for establishment of Giardia infection. The adherence assay showed that albendazole caused the detachment of trophozoites at a significantly lower concentration (0.1 microg/ml) as compared to metronidazole and vincristine (40 and 60 microg/ml, respectively) in the time period of 9 h. However, at the higher concentration (10 microg/ml) albendazole caused the similar effect within the time period of 3 h. The microscopic studies revealed that albendazole brought about gross morphological changes in G. lamblia, i.e., rounding of trophozoites and disruption of ventral adhesive disc along with vacuolation in cytoplasm. Metronidazole caused the ballooning of cytoplasm and induced the most lethal effect on trophozoites (8.17% viability) as compared to vincristine and albendazole (72.13 and 65.49% viability) as shown by flowcytometric analysis. Further, the flowcytometric findings indicated that the three drugs led to the arrest of growth of trophozoites at different stages of cell cycle. Albendazole and vincristine interfered with the formation of spindle/basal body microtubules thereby arresting the cell cycle in G2 + M phase whereas metronidazole arrested the growth in S-phase by inhibiting the DNA segregation and cell division. Hence, flowcytometry has been usefully employed to study the effect of drugs on viability and DNA of G. lamblia trophozoites in the present study.

Characterisation of benzimidazole binding with recombinant tubulin from Giardia duodenalis, Encephalitozoon intestinalis, and Cryptosporidium parvum

The binding kinetics of several benzimidazole compounds were determined with recombinant tubulin from benzimidazole-sensitive and -insensitive organisms. This study utilised the naturally occurring high efficacy of the benzimidazoles for the parasitic protozoa Giardia duodenalis and Encephalitozoon intestinalis, and low efficacy with Cryptosporidium parvum. Direct kinetic analysis of the benzimidazole-beta-tubulin interaction was performed using a fluorescence-based quenching method to determine the apparent association (k(on)) and dissociation (k(off)) rate constants from which the affinity constant (K(a)) was calculated. The binding kinetics were determined with recombinant alpha- and beta-tubulin from the parasitic protozoa with several benzimidazole R(2)-carbamate analogues. The affinity constant for the binding of several benzimidazoles with beta-tubulin from benzimidazole-sensitive protozoa was found to be significantly greater than binding to beta-tubulin from benzimidazole-insensitive protozoa. Additionally, the high affinity of several benzimidazole derivatives (albendazole, fenbendazole, mebendazole) for monomeric beta-tubulin and heterodimeric alphabeta-tubulin from benzimidazole-sensitive protozoa was also clearly demonstrated. The affinity constants determined with beta-tubulin from G. duodenalis and E. intestinalis also supported the observed in vitro efficacy of these compounds. The binding characteristics of the benzimidazoles with the highest in vitro efficacy (albendazole, fenbendazole, mebendazole) was reflected in their high association and slow dissociation rates with the beta-tubulin monomer or dimer from benzimidazole-sensitive protozoa compared with insensitive ones. Benzimidazole-bound alphabeta-tubulin heterodimers also had a significantly lower rate of microtubule assembly compared with benzimidazole-free alphabeta-heterodimers. The incorporation of benzimidazole-bound alphabeta-heterodimers into assembling microtubules was shown to arrest polymerisation in vitro although the addition of benzimidazole compounds to assembled microtubules did not result in depolymerisation. These findings indicate that a benzimidazole-beta-tubulin cap may be formed at the growing end of the microtubule and this cap prevents elongation of the microtubule.

Antitumor activity of albendazole against the human colorectal cancer cell line HT-29: in vitro and in a xenograft model of peritoneal carcinomatosis

The peritoneal surface remains an important failure site for patients with colorectal cancer. We have recently shown that albendazole (ABZ), a safe and effective anthelmintic drug, has profound antitumor activity in hepatocellular cancer. Furthermore, albendazole also possesses unique physiochemical and pharmacokinetic properties probably making it a potential drug for use in the regional treatment of peritoneal carcinomatosis (PC). The current study was therefore designed to investigate this concept under both in vitro and in vivo conditions using human colorectal cancer cells HT-29. In cell culture, studies were conducted to investigate the effect of ABZ and its major metabolites, albendazole sulfoxide (ABZ-SO) and albendazole sulfone (ABZ-SO2) on the growth of human colorectal cell line HT-29. We also investigated the effects of ABZ on the cell cycle and the possible induction of apoptosis in these cells. Male nude mice inoculated intraperitoneally (i.p.) with HT-29 cells were treated with various schedules of ABZ given i.p. or orally for 6 weeks. Response was evaluated as the number of peritoneal tumor nodules present in animals at the end of the treatment period. In vitro, ABZ treatment of cells for 5 days led to profound inhibition of growth. (3)H-Thymidine assay and trypan blue viable cell counts confirmed the dose- and time-dependency of the ABZ effect, while recovery experiments revealed the reversible nature of this inhibition. ABZ-SO and ABZ-SO2 were also evaluated in cell culture studies and compared with the parent drug. In HT-29 cells, the IC(50) values were calculated to be 0.12 microM for ABZ and 2.35 microM for ABZ-SO. The other metabolite, ABZ-SO2, was completely inactive. Studies on the mechanism of ABZ action, revealed arrest of HT-29 cells at the G(2)/M phase of the cell cycle, while TUNEL, DNA laddering and caspase-3 activity all confirmed ABZ induced apoptosis. In nude mice with peritoneal HT-29 xenografts, ABZ profoundly inhibited peritoneal tumor growth. While alternate i.p. dosing (ABZ, 150 mg/kg) led to the highest degree of tumor growth suppression (P<0.001), schedules such as once-weekly dosing and even a single dose for the entire course of treatment (6 weeks) were also effective in reducing peritoneal tumor growth. However, no such activity was observed when ABZ was administered orally. This study shows for the first time the potent effect of regionally administered ABZ in suppressing the growth of peritoneal tumors of human colorectal origin. The effect is thought to be brought about by arresting tumor cells at the G(2)/M phase of the cycle and apoptosis. These findings provide evidence for potential value of ABZ in the treatment of regional PC arising from colorectal cell lines.

Veterinary anthelmintics: old and new

Between 1960 and 1980, extraordinary success was achieved in anthelmintic development for animals. In these 20 years, drugs with diverse structure, novel activity and enviable safety were produced for a global livestock industry leading to the productivity gains needed to support a human population that grew by 1.5 billion during the same period. The following 20 years have been spent refining existing molecules with niche activity (parasite and host specificity), improving delivery systems and worrying about the inexorable spread of drug resistance. The challenge for the next 20 years will be to use the technologies available to design and produce new drugs and biological controls. Then, to use the lessons of the past to ensure that the new drugs enjoy a longer useful lifespan and contribute to an animal health industry (livestock and companion) which enriches the lives of a global population. Old and new veterinary anthelmintics comprise a very large field, which could not be comprehensively reviewed in a short article. The present mini-review focuses on major chemical discoveries, formulation developments, administration strategies and new products.

Measurement of triclabendazole and its metabolites in liver flukes: method development and full validation

The trematode parasite Fasciola hepatica is still the cause of considerable loss in livestock production all over the world. The knowledge of the pharmacological properties of the available flukicidal drugs is critical to control this parasite. Triclabendazole is an halogenated benzimidazole anthelmintic with potent flukicidal activity. A simple reversed-phase high-performance liquid chromatographic analytical method has been developed, validated and applied for the quantitative determination of the flukicidal drug triclabendazole and its sulpho- and hydroxy-metabolites in the liver fluke, F. hepatica. Triclabendazole, triclabendazole sulphoxide, triclabendazole sulphone, hydroxy-triclabendazole, hydroxy-triclabendazole sulphoxide and hydroxy-triclabendazole sulphone were measured simultaneously in this trematode parasite. Linearity, resolution, precision, accuracy, recovery, limits of detection and quantification of the method were determined. Drug extraction from the parasite's tissue homogenate was effectively performed using liquid extraction (acetonitrile), avoiding clean up by solid phase extraction, prior to analysis by reversed-phase high-performance liquid chromatography. The resolution of all the halogenated benzimidazole thiol molecules assayed was obtained on a C(18) reversed-phase (5 microm, 250 mm x 4.6 mm) column using acetonitrile and ammonium acetate as the mobile phase and ultraviolet detection at 300 nm. Regression analyses were linear over the concentration range examined (from 0.272 to 16.331 nmol/100 mg trematode protein) and the correlation coefficients of the calibration curves ranged between 0.996 and 1.000. The calculated limits of detection of the proposed method for the parent drug and its metabolites ranged between 0.007 and 0.079 nmol/100 mg trematode protein. The extraction efficiency for the different analytes from the parasite material was greater than 71%. The results obtained indicated that the developed chromatographic method was selective, accurate and easy to reproduce. The developed procedure was successfully applied to quantify triclabendazole/metabolites in F. hepatica incubated under ex vivo conditions, demonstrating to be efficient for the determination of the most extensively used flukicidal drug available for veterinary medicine, and its metabolites. The analytical method described here is an useful tool for the measurement of this flukicidal compound in different studies addresses to evaluate drug influx/eflux and metabolism in its main target parasite.

Synthesis and antiparasitic activity of albendazole and mebendazole analogues

Albendazole (Abz) and Mebendazole (Mbz) analogues have been synthesized and in vitro tested against the protozoa Giardia lamblia, Trichomonas vaginalis and the helminths Trichinella spiralis and Caenorhabditis elegans. Results indicate that compounds 4a, 4b (Abz analogues), 12b and 20 (Mbz analogues) are as active as antiprotozoal agents as Metronidazole against G. lamblia. Compound 9 was 58 times more active than Abz against T. vaginalis. Compounds 8 and 4a also shown high activity against this protozoan. Compounds 4b and 5a were as active as Abz. None of the Mbz analogues showed activity against T. vaginalis. The anthelmintic activity presented by these compounds was poor.

Comparative assessment of the access of albendazole, fenbendazole and triclabendazole to Fasciola hepatica: effect of bile in the incubation medium

The work reported here describes the comparative ability of albendazole (ABZ), fenbendazole (FBZ) and triclabendazole (TCBZ) to penetrate through the tegument of mature Fasciola hepatica, and the influence of the physicochemical composition of the incubation medium on the drug diffusion process. The data obtained from the trans-tegumental diffusion kinetic studies were complemented with the determination of lipid-to-water partition coefficients (octanol-water) for the benzimidazole (BZD) anthelmintic drugs assayed. Sixteen-week-old F. hepatica were obtained from untreated artificially infected sheep. The flukes were incubated (37 degrees C) over 60 and 90 min in incubation media (pH 7.4) prepared with different proportions of ovine bile and Krebs' Ringer Tris (KRT) buffer (100, 75, 50, 25 and 0% of bile) containing either ABZ, FBZ or TCBZ at a final concentration of 5 nmol/ml. After the incubation time expired, the liver fluke material was chemically processed and analysed by high performance liquid chromatography (HPLC) to measure drug concentrations within the parasite. Additionally, the octanol-water partition coefficients (PC) for each molecule were calculated (as an indicator of drug lipophilicity) using reversed phase HPLC. The 3 BZD molecules were recovered from F. hepatica at both incubation times in all incubation media assayed. The trans-tegumental diffusion of the most lipophilic molecules ABZ and FBZ (higher PC values) tended to be greater than that observed for TCBZ. Interestingly, the uptake of ABZ by the liver flukes was significantly greater than that measured for TCBZ, the most widely used flukicidal BZD compound. This differential uptake pattern may be a relevant issue to be considered to deal with TCBZ-resistant flukes. Drug concentrations measured within the parasite were lower in the incubations containing the highest bile proportions. The highest total availabilities of the 3 compounds were obtained in liver flukes incubated in the absence of bile. Altogether, these findings demonstrated that the entry of the drug into a target parasite may not only depend on a concentration gradient, the lipophilicity of the molecule and absorption surface, but also on the physicochemical composition of the parasite's surrounding environment.

Efficacy of antigiardial drugs

The flagellated protozoa Giardia duodenalis is the most commonly detected parasite in the intestinal tract of humans. Infections with the parasite result in diarrhoeal disease in humans and animals, with infants at risk from failure-to-thrive syndrome. The incidence of giardiasis worldwide may be as high as 1000 million cases. Current recommended treatments include the nitroheterocyclic drugs tinidazole, metronidazole and furazolidone, the substituted acridine, quinacrine, and the benzimidazole, albendazole. Paromomycin is also used in some situations, and nitazoxanide is proving to be useful. However, treatment failures have been reported with all of the common antigiardial agents, and drug resistance to all available drugs has been demonstrated in the laboratory. In addition, clinical resistance has been reported, including cases where patients failed both metronidazole and albendazole treatments. The identification of new antigiardial drugs is an important consideration for the future, but maintaining the usefulness of the existing drugs is the most cost-effective measure to ensure the continued availability of antigiardial drugs.

Ex Vivo Anthelmintic Activity of Albendazole-Sulphoxide Enantiomers

The antiparasitic activity of racemic albendazole-sulphoxide (Ricobendazole = racRBZ) and its (+) and (-) enantiomers was tested in an ex vivo murine model for Trichinella spiralis infection. Larvae were isolated from the muscle of infected mice and exposed to concentrations between 0.01 and 1 microg/ml of the racemic mixture or to each of its enantiomers. The activity of each compound was then assayed by measuring the ability of the treated larvae to infect naive mice (larval viability). At a concentration of 0.5 microg/ml, all 3 compounds were highly effective in reducing the viability of the larvae, achieving reductions of 91.26% (racRBZ), 96.7% (+), and 89.2% (-), when compared with untreated controls. At lower concentrations (0.1 microg/ml), only treatment with (+)RBZ rendered a significant reduction in larval viability in comparison with controls (84.3%; P < 0.01), whereas at 0.01 microg/ml, none of the compounds altered larval viability (P > 0.05).

Benzimidazole-resistant beta-tubulin alleles in a population of parasitic nematodes (Cooperia oncophora) of cattle

Three anthelmintic classes with distinct mechanisms of action are commercially available. Selection of nematode populations resistant to all these drugs has occurred, particularly in trichostrongyloid parasites of sheep. Anthelmintic resistance in cattle parasites has only recently been recognized and appears to be less pronounced, even though very similar species infect both hosts. To understand the bases for differences in the rate of resistance development in sheep versus cattle parasites, it is important to first demonstrate that the same kinds of resistance alleles exist in both. The benzimidazoles (BZ), which have been used for more than 40 years, were chosen as an example. BZ-sensitive (BZ(S)) and BZ-resistant (BZ(R)) nematodes that parasitize sheep have been distinguished at the molecular level by a single nucleotide change in the codon for amino acid 200 of a beta-tubulin gene, a switch from TTC (phenylalanine) to TAC (tyrosine). PCR primers were designed to completely conserved regions of trichostrongyloid beta-tubulin genes and were used to amplify DNA fragments from Haemonchus contortus (cDNA from a BZ(S) and a BZ(R) library) as positive controls. The technique was then extended to the cattle parasites, Cooperia oncophora and Ostertagia ostertagi (from genomic DNA). Sequence analysis proved the presence of amplified BZ(S) alleles in all three species and BZ(R) alleles in the BZ(R) population of H. contortus. Based on these data, nested PCR primers using the diagnostic T or A as the most 3' nucleotide were designed for each species. Conditions for selective PCR were determined. To demonstrate feasibility, genomic DNA was recovered from individual H. contortus L(3) larvae from both BZ(S) and BZ(R) populations. Genomic DNA was also isolated from >70 individual adult male C. oncophora collected from a cattle farm in New Zealand with reported BZ resistance. Allele-specific PCR discriminated among heterozygotes and homozygotes in both species. This method could find utility in studying the molecular epidemiology of BZ resistance in cattle parasites and for defining the variables that limit the development and spread of anthelmintic resistance in this host.

Characterisation of a beta-tubulin gene from the monogenean parasite, Gyrodactylus salaris Malmberg, 1957

The cDNA and two partial genomic sequences of beta-tubulin genes have been isolated from the monogenean parasite Gyrodactylus salaris. The cDNA sequence is not represented by either of the genomic sequences, implying that at least three isotypes of the gene exist in G. salaris. The sequences show regions of high homology with other helminth beta-tubulin genes. This represents the first isolation of a beta-tubulin gene from a monogenean and contributes to the overall characterisation of these genes within the helminths. This is an important area, as anthelmintic resistance is increasing against benzimidazole drugs that target the beta-tubulin gene. Benzimidazole drugs have been tested successfully against Gyrodactylus parasites, but their use is not widespread. Should it increase, analysis of the beta-tubulin gene may provide a tool for monitoring resistance development and improving management practises. Use of the beta-tubulin gene in the identification of Gyrodactylus species may prove complex due to the presence of different isotypes.

TaqMan minor groove binder real-time PCR analysis of β-tubulin codon 200 polymorphism in small strongyles (Cyathostomin) indicates that the TAC allele is only moderately selected in benzimidazole-resistant populations

TaqMan minor groove binder probes were evaluated as to their suitability for the real-time allelic discrimination of the β-tubulin codon 200 TTC/TAC single nucleotide polymorphism in cyathostomin species. Amplification of titrated cloned full-length β-tubulin cDNA revealed that the TaqMan minor groove binder PCR is capable of specifically detecting as few as 10 copies. Testing of DNA from single adult and larval stages of several different species of cyathostomin allowed reproducible genotyping of individual worms. Using the real-time PCR approach, the throughput of samples was considerably increased compared with conventional post-PCR readout procedure. Only 7·8% homozygous TAC L3 were found among 102 L3 which were genotyped from phenotypically BZ-resistant small strongyle populations. The percentages of the homozygous TTC and heterozygous TTC/TAC were 41·3% and 50·9%, respectively. This resulted in a total TAC-allele percentage of only 33·3%. These findings correspond to data obtained by genotyping of an experimentally selected BZ-resistant cyathostomin population. It is concluded that the β-tubulin codon 200 polymorphism is not the sole mechanism involved in the process of BZ resistance in cyathostomins.

A light and electron microscopic study on the synergistic effect of pyrantel and the febantel metabolite febendazole on adult Toxocara canis in vitro

In the present study, we investigated the in vitro effects on the motility and morphology of tissues and organs of Toxocara canis of the two drug components of Drontal Plus and Welpan, pyrantel and fenbendazole (the active metabolite of the prodrug febantel), both alone and in combination. Although there was no significant difference observable between the effects of the single drugs and the drug combination on worm motility, the synergistic effect of pyrantel and fenbendazole was manifested by morphological alterations seen by light and electron microscopy. Thus, an earlier onset of damage to worm tissues and organs could be observed compared to the application of the individual drugs. In addition, a higher degree of damage and an increased number of vital organs were involved. There was dramatic, significantly greater and irreversible damage to the hypodermis, longitudinal muscle, intestine, nerve cords and genital organs induced by the pyrantel/fenbendazole combination. We hypothesise that these synergistic effects will also take place when dogs are treated either with Drontal Plus or Welpan in which lower dosages will be sufficient to destroy the worms.

Analysis of codon usage in beta-tubulin sequences of helminths

Codon usage bias has been shown to be correlated with gene expression levels in many organisms, including the nematode Caenorhabditis elegans. Here, the codon usage (cu) characteristics for a set of currently available beta-tubulin coding sequences of helminths were assessed by calculating several indices, including the effective codon number (Nc), the intrinsic codon deviation index (ICDI), the P2 value and the mutational response index (MRI). The P2 value gives a measure of translational pressure, which has been shown to be correlated to high gene expression levels in some organisms, but it has not yet been analysed in that respect in helminths. For all but two of the C. elegans beta-tubulin coding sequences investigated, the P2 value was the only index that indicated the presence of codon usage bias. Therefore, we propose that in general the helminth beta-tubulin sequences investigated here are not expressed at high levels. Furthermore, we calculated the correlation coefficients for the cu patterns of the helminth beta-tubulin sequences compared with those of highly expressed genes in organisms such as Escherichia coli and C. elegans. It was found that beta-tubulin cu patterns for all sequences of members of the Strongylida were significantly correlated to those for highly expressed C. elegans genes. This approach provides a new measure for comparing the adaptation of cu of a particular coding sequence with that of highly expressed genes in possible expression systems.Finally, using the cu patterns of the sequences studied, a phylogenetic tree was constructed. The topology of this tree was very much in concordance with that of a phylogeny based on small subunit ribosomal DNA sequence alignments.

Albendazole for the treatment of echinococcosis

Twenty years after the first cases of echinococcal disease were treated with albendazole, it has become an important component in the overall management of both cystic and alveolar echinococcosis. This paper reviews some of the key steps and issues facing those who work in clinical research and who deal on a day-to-day basis with echinococcal disease. In many situations, chemotherapy alone is sufficient, but it is also used as an adjunct to surgery and to minimally invasive approaches to cyst management. While treatment may not be as effective as hoped, attempts to provide new regimens are progressing to increase cure rates further. There is now a greater understanding of the limitations of all approaches, and treatment guidelines as developed by the World Health Organization are now widely followed. As diagnostic tools are ever more widely available, the question as to who should be treated in endemic communities has to be answered.

Benzimidazole treatment of cystic echinococcosis

Hydatidosis (cystic echinococcosis, CE) constitutes a serious public health problem worldwide. Total surgical removal of a hydatid cyst is still considered the gold standard treatment for CE. Percutaneous treatment (PAIR), using either hypertonic saline or alcohol as a larvacidal agent, appears to be an additional effective form of treatment. Benzimidazoles (albendazole, ABZ; mebendazole, MBZ), given either alone or combined with praziquantel (PZ) are currently used for the treatment of non-surgical cases and as a supplementary treatment prior and post-surgery. Combined chemotherapy was found to be more effective than either of the agents given alone. ABZ is easily absorbed and more effective than MBZ. ABZ (12-15 mg/kg/day) and MBZ (30-70 mg/kg/day) given for 14-20 days prior to surgery and continued for an additional 3-24 months in a cyclic monthly form were found effective against the disease. Either increased or decreased circulating antigen levels, which consequently cause changes in the humoral (IgG, IgG1, IgG4, IgE) immune responses, have a prognostic value in successfully treated CE cases. However, although the cellular immune response to echinococcal antigens decreased in improved or cured CE patients, it was not considered of practical use in determining treatment efficacy. In certain cases successful treatment was also followed by elevated eosinophilia and erythrocyte sedimentation rates. In the present article, the mechanism of drug activities as well as the development of resistance against the drugs available are further discussed.

Transtegumental diffusion of benzimidazole anthelmintics into Moniezia benedeni: correlation with their octanol-water partition coefficients

The experiments described here report on the correlation between the ex vivo diffusion of different benzimidazole (BZD) anthelmintics into the cestode parasite Moniezia benedeni, and their octanol-water partition coefficients (P.C.). The characterisation of the drug diffusion process into target parasites is relevant to understand the mechanism of drug penetration and the pharmacological activity of anthelmintic drugs. Specimens of the tapeworm M. benedeni, used as a helminth parasite model, were obtained from untreated cattle killed at the local abattoir. The collected parasites were incubated (5-210 min) with either fenbendazole (FBZ), albendazole (ABZ), ricobendazole (RBZ), oxfendazole (OFZ), mebendazole (MBZ), oxibendazole (OBZ), or thiabendazole (TBZ), in a Kreb's Ringer Tris buffer medium at a final concentration of 5 nmol/ml. After the incubation time elapsed, samples of parasite material were chemically extracted and prepared for high performance liquid chromatography (HPLC) analysis to measure drug/metabolite concentrations. Additionally, the octanol-water P.C. for each molecule was estimated as an indicator of drug lipophilicity, using reversed phase HPLC analysis. All the incubated drugs were recovered from the tapeworms as early as 5 min post incubation. There was a high correlation (r=0.87) between drug lipophilicity, expressed as octanol-water P.C. (Log P), and drug availability within the parasite. The most lipophilic BZD compounds (FBZ, ABZ, and MBZ), with P.C. values higher than 3.7, were measured at significative higher concentrations within the tapeworm compared to those drugs with the lowest P.C. values. Considering the results from the current and previous studies, it is clear that passive diffusion is a major mechanism of BZD penetration into cestode parasites, where lipid solubility is a determinant factor influencing the diffusion of these anthelmintic molecules through the parasite tegument.

Voltammetric determination of fenbendazole in veterinarian formulations

A versatile voltammetric method for quantitative determination of fenbendazole (FBZ) in commercial tablets has been proposed, where direct dissolution of tablets is carried out in 0.1 mol l(-1) tetrabutylamoniun tetrafluorborate containing dimethylformamide solutions. Linear sweep (LSV), square wave (SWV) and differential pulse (DPV) voltammetry techniques were applied to study FBZ at a glassy carbon electrode, exhibiting a well defined irreversible oxidation peak at 1.15 V vs. SCE. This methodology allows a precise quantitative determination of FBZ presenting detection limits of 5.2 x 10(-5) (LSV), 5.0 x 10(-6) (DPV) and 5.0 x 10(-5) mol l(-1) (SWV).

Immunization with a tubulin-rich preparation from Trypanosoma brucei confers broad protection against African trypanosomosis

Tubulin from Trypanosoma brucei was purified to near homogeneity using a protocol which involved treatment with urea with subsequent renaturation and was then used to immunize mice. Renatured tubulin further purified by SDS-PAGE (denatured), synthetic tubulin peptides (STP), and rat brain tubulin (RbTub) were also used. Immunized mice were challenged with T. brucei, Trypanosoma congolense or Trypanosoma rhodesiense. Renatured T. brucei tubulin (nTbTub) induced protection in all mice tested, of which 60-80% (n = 81) was complete and the remainder partial. Denatured T. brucei tubulin (dTbTub), STP, or RbTub induced lower antibody levels than nTbTub and did not offer protection. However, in culture, the antibodies against dTbTub or STP killed trypanosomes although at lower dilutions than nTbTub, but those against RbTub did not. In Western blots anti-trypanosome antibodies recognized the tubulin of all the trypanosome species investigated but not vertebrate tubulin, whereas the anti-RbTUB antibodies recognized both trypanosome and vertebrate tubulin. Of the five mice given passive immunity by the transfer of anti-nTbTub serum, four were completely protected and one partially protected. These data suggest that tubulin is the relevant immunogen in the preparation used and could therefore be a promising target for the development of a parasite-specific, broad spectrum vaccine.

Synthesis and antiparasitic activity of 1H-benzimidazole derivatives

Compounds 1-18 have been synthesized and tested in vitro against the protozoa Giardia lamblia, Entamoeba histolytica and the helminth Trichinella spiralis. Inhibition of rat brain tubulin polymerization was also measured and compared for each compound. Results indicate that most of the compounds tested were more active as antiprotozoal agents than Metronidazole and Albendazole. None of the compounds was as active as Albendazole against T. spiralis. Although only compounds 3, 9 and 15 (2-methoxycarbonylamino derivatives) inhibited tubulin polymerization, these were not the most potent antiparasitic compounds.

Distinct characteristics of two intestinal protein compartments discriminated by using fenbendazole and a benzimidazole resistant isolate of Haemonchus contortus

The intestine of Haemonchus contortus is hypersensitive to the effects of the anthelmintic fenbendazole (FBZ). The effects are postulated to stem from disruption of microtubules and interference with apical secretory vesicle transport, followed by release of digestive enzymes into the intestinal cell cytoplasm. Here, FBZ caused marker proteins for both apical (pepsinogen-like protease, PEP-1) and basal (cystatin-like protein) protein compartments to became homogeneously distributed in the cytoplasm of H. contortus intestinal cells. The observations with PEP-1 support the hypothesis that release of hydrolytic enzymes into the intestinal cell cytoplasm contributes to the mechanism of benzimidazole efficacy. A benzimidazole resistant isolate of H. contortus expressed type 1 and 2 intestinal beta-tubulin transcripts that would encode predominantly tyr200 and phe200 variants, respectively. This isolate was resistant to the known intestinal cell alterations induced by FBZ treatment in the susceptible isolate, including inhibition of apical vesicle transport. These results implicate type 1 beta-tubulin in mediating apical vesicle transport in intestinal cells and suggest that the tyr200 variant is a determinant of FBZ resistance in intestinal cells. In contrast, the basal protein compartment demonstrated sensitivity to FBZ treatment in these otherwise "resistant" worms. Hence, distinct FBZ-sensitive components appear to be involved in distributing intestinal proteins into the described apical and basal compartments of normal worms.

Investigation of diversity and isotypes of the beta-tubulin cDNA in several small strongyle (Cyathostominae) species

The diversity of the beta-tubulin cDNAs of the cyathostominae and the occurrence of further isotypes were examined in adult worms isolated from an anthelmintic-naïve horse. cDNAs encoding beta-tubulin from Cyathostomum catinatum, Cylicocyclus nassatus, Cylicocyclus insigne, Cylicocyclus radiatus, Cylicocyclus elongatus, Cyathostomum coronatum, and Cyathostomum pateratum were characterized using specific primers developed from the cDNA sequence of Cc. nassatus. The cDNA sequences span 1,429 bp and show identities ranging from 95.6 to 100%. The deduced protein sequences span 448 amino acids and were 98-100% identical. The amino acid sequences of the 7 species varied within and between species at 10 positions. A 3' Rapid Amplification of cDNA ends using a degenerate forward primer was carried out with cDNA from Cy. pateratum, Cy. coronatum, Cy. catinatum, and Cc. nassatus to investigate the occurrence of further beta-tubulin isotypes. The expected polymerase chain reaction (PCR) product of 400 bp, including 306 bp of coding sequence, was amplified, as was an additional fragment of 600 nucleotides in the case of Cy. pateratum, Cy. coronatum, and Cy. catinatum. Sequencing of the PCR products revealed no evidence for the existence of a second beta-tubulin isotype in cyathostomes. The variation in size was caused by a length polymorphism within the 3' untranslated region, and 2 functional mRNAs seem to be transcribed from the same gene.

Classical ligands bind tubulin of trypanosomes and inhibit their growth in vitro

Tubulin ligands known to be toxic to certain organisms or cells were tested for their ability to inhibit proliferation of trypanosomes in culture. Tubulin was purified from Trypanosoma brucei brucei or rat brain by poly-L-lysine affinity chromatography and used in binding studies in order to compare the binding of [3H]mebendazole to trypanosome and mammalian tubulin. All the compounds tested in culture inhibited trypanosome proliferation in a concentration-dependent manner. The concentration required to inhibit trypanosome proliferation by 50 or 90% (IC50 or IC90) in 24 hr was determined for each compound. There were no significant differences (P > 0.05) among the benzimidazoles (BZs), but colchicine and vinblastine caused significantly greater inhibitions than the BZs (P < 0.02 and P < 0.005, respectively). Increasing the incubation time to 72 hr caused a 2- to 4-fold lowering of the IC50 and IC90 values for all the drugs. In the binding assays, there was higher total binding of [3H]mebendazole to trypanosome than rat brain tubulin. The results suggest that the inhibition of trypanosome growth was caused by the specific interaction of these ligands with trypanosome tubulin. Trypanosome tubulin is, therefore, a reasonable target against which novel drugs can be developed to control trypanosomiasis.

Resistance to antiparasitic drugs: the role of molecular diagnosis

Chemotherapy is central to the control of many parasite infections of both medical and veterinary importance. However, control has been compromised by the emergence of drug resistance in several important parasite species. Such parasites cover a broad phylogenetic range and include protozoa, helminths and arthropods. In order to achieve effective parasite control in the future, the recognition and diagnosis of resistance will be crucial. This demand for early, accurate diagnosis of resistance to specific drugs in different parasite species can potentially be met by modern molecular techniques. This paper summarises the resistance status of a range of important parasites and reviews the available molecular techniques for resistance diagnosis. Opportunities for applying successes in some species to other species where resistance is less well understood are explored. The practical application of molecular techniques and the impact of the technology on improving parasite control are discussed.

Characteristics of a flubendazole resistant isolate of Oesophagostomum dentatum from Germany

Two controlled tests were performed to investigate the benzimidazole resistance of a nodular worm isolate "GIBZ" from a pig breeding farm in Germany. In Trial I, groups of five pigs, artificially infected with Oesophagostomum larvae isolated from that farm were treated with flubendazole at a single dose of 5 mg kg(-1) bodyweight (BW) or remained untreated. In Trial II, three groups of three pigs each infected with larvae after a further laboratory passage of this isolate were treated with flubendazole either at a single dose of 5 mg kg(-1) BW or at a divided dose of 1.5 mg kg(-1) BW daily for 5 consecutive days, or with fenbendazole at a single dose of 5 mg kg(-1) BW, the fourth infected group remained untreated. The respective doses of anthelmintics were mixed with a small amount of feed and administered to individual pigs in both trials. Fecal egg counts before and after treatment and post-mortem worm burdens 7 days after (last) treatment were examined to assess the anthelmintic efficacies. Only infections with Oesophagostomum dentatum were found in both trials. In Trial I, the mean worm count reduction by flubendazole was 30% as compared to the untreated controls. In Trial II, flubendazole administered at a single or divided dose reduced the mean worm burden by 0 and 85%, respectively, whereas fenbendazole was 100% effective. These results establish resistance to flubendazole in the isolate "GIBZ" of O. dentatum. The failure to reveal side resistance to fenbendazole may be explained by that the currently recommended dose rate of this compound is supra-optimal for porcine nodular worms.

Caenorhabditis elegans: how good a model for veterinary parasites?

The organism about which most is known on a molecular level is a nematode, the free-living organism Caenorhabditis elegans. This organism has served as a reasonable model for the discovery of anthelmintic drugs and for research on the mechanism of action of anthelmintics. Useful information on mechanisms of anthelmintic resistance has also been obtained from studies on C. elegans. Unfortunately, there has not been a large-scale extension of genetic techniques developed in C. elegans to research on parasitic species of veterinary (or human) parasites. Much can be learned about the essentials of nematode biology by studying C. elegans, but discovering the basic biology of nematode parasitism can only be gained through comparative studies on multiple parasitic species.

Characterisation of a beta-tubulin gene from the liver fluke, Fasciola hepatica

This study represents the first beta-tubulin sequence from a trematode parasite, namely, the liver fluke, Fasciola hepatica. PCR of genomic DNA showed that at least one beta-tubulin gene from F. hepatica contains no introns. A number of amino acids in the primary sequence of fluke tubulin are different from those described previously in various nematode species and the cestode, Echinococcus multilocularis. beta-Tubulin is an important target for benzimidazole anthelmintics, although (with the exception of triclabendazole) they show limited activity against F. hepatica. The amino acid differences in fluke beta-tubulin are discussed in relation to the selective toxicity of benzimidazoles against helminths and the mechanism of drug resistance.

Pilot study of albendazole in patients with advanced malignancy. Effect on serum tumor markers/high incidence of neutropenia

Our preclinical studies have shown that the widely used antiparasitic drug albendazole has potent antiproliferative activity against colorectal cancer (CRC) and hepatocellular carcinoma (HCC). This trial was designed to evaluate albendazole in a small number of patients (n = 7) with either HCC or CRC and hepatic metastases refractory to other forms of therapy. Albendazole was given at 10 mg/kg/day orally in two divided doses for a period of 28 days. To follow the effect of treatment, tumor markers, carcinoembryonic antigen (CEA) or alpha-feto protein (AFP), were measured routinely in these patients. A range of hematological and biochemical indices were also serially measured to monitor bone marrow, kidney or liver toxicity. Albendazole therapy resulted in a decrease in CEA in 2 patients. In the remaining 5 with measurable tumor markers, serum CEA or AFP was stabilized in 3 patients, while in the other 2, after an initial stabilization (5-10 days), the markers began to increase. In the 7 patients completing the trial, albendazole was well tolerated and there were no significant changes in any hematological, kidney or liver function tests, but 3 patients were withdrawn for severe neutropenia which was probably contributory to the death of 1 patient. These data support our previous experimental results demonstrating that albendazole has antitumor effects.

Caenorhabditis elegans and the study of gene function in parasites

The free-living nematode Caenorhabditis elegans is a tractable experimental model system for the study of both vertebrate and invertebrate biology. Its most significant advantages are its simplicity, both in anatomy and in genomic organization, and the elaborate methods that have been developed to attribute function to previously uncharacterized genes. Importantly, > 40% of parasitic nematode genes exhibit high levels of homology to genes within the C. elegans genome. Studying such genes using the C. elegans model should yield new insights into key molecules and their possible implications in parasite survival, leading to the discovery of new drug targets and vaccine candidates.