P-glycoproteins of Haemonchus contortus: development of real-time PCR assays for gene expression studies

Expression of transporter genes in anthelmintic resistant isolates of Haemonchus contortus

ATP-binding cassette (ABC) transporters, including P-glycoproteins (PGP), have been implicated in drug resistance in different organisms including Haemonchus contortus. This study confirmed the resistance status of H. contortus isolates selected for ivermectin (IVM) and oxfendazole (OXF) resistances using the fecal egg count reduction test and evaluated the gene expression of seven ABC transporters using RT-qPCR for two biological scenarios: the effect of selection for anthelmintic resistance and the effect of drug exposure on gene expression. Gene expression results showed that selection for IVM resistance led to the significant upregulation of Hco-pgp-9a (1.5-fold), Hco-pgp-11 (3-fold) and Hco-haf-9 (1.5-fold) (p < 0.05). Similarly, selection for OXF resistance led to the significant upregulation of Hco-pgp-9a (3-fold), Hco-pgp-11 (4-fold) and Hco-haf-9 (2-fold) when comparing with the unselected ISE isolate (p < 0.05). Exposure of selected isolates to anthelmintics lead to no significant upregulation of the studied transporter genes. We also observed instances where there was strong intragroup variation regarding samples originating from parasites obtained from different individual hosts pointing that the interactions of the animal host with the tested anthelmintics may also play a role in the expression of the studied nematode genes.

Comparison of P-glycoprotein gene expression of two Haemonchus contortus isolates from Yucatan, Mexico, with resistant or susceptible phenotype to ivermectin in relation to a susceptible reference strain

The variability in the expression of different P-glycoprotein (P-gp) genes in parasitic nematodes of ruminants such as Haemonchus contortus (Hco-pgp) may be caused by different factors including nematode biology, geographical region and anthelmintic pressure. This study analysed the relative expression level of 10 P-gp genes in two H. contortus (Hco-pgp) field isolates from Yucatan, Mexico: 1) PARAISO (IVM-resistant) and 2) FMVZ-UADY (IVM-susceptible). These isolates were compared with a susceptible reference isolate from Puebla, Mexico, namely "CENID-SAI". In all cases H. contortus adult males were used. The Hco-pgp genes (1, 2, 3, 4, 9, 10, 11, 12, 14 and 16) were analysed for each isolate using the RT-qPCR technique. The Hco-pgp expressions were pairwise compared using the 2-ΔΔCt method and a t-test. The PARAISO isolate showed upregulation compared to the CENID-SAI isolate for Hco-pgp 1, 3, 9, 10 and 16 (P < 0.05), and the PARAISO isolate showed upregulation vs. FMVZ-UADY isolate for Hco-pgp 2 and 9 (P < 0.05), displaying 6.58- and 5.93-fold differences (P < 0.05), respectively. In contrast, similar Hco-pgp gene expression levels were recorded for FMVZ-UADY and CENID-SAI isolates except for Hco-pgp1 (P <0.1), which presented a significant upregulation (6.08-fold). The relative expression of Hco-pgp allowed confirming the IVM-resistant status of the PARAISO isolate and the IVM-susceptible status of the FMVZ-UADY isolate when compared to the CENID-SAI reference isolate. Therefore, understanding the association between the Hco-pgp genes expression of H. contortus and its IVM resistance status could help identifying the genes that could be used as molecular markers in the diagnosis of IVM resistance. However, it is important to consider the geographic origin of the nematode isolate and the deworming history at the farm of origin.

Analysis of P-gp genes relative expression associated to ivermectin resistance in Haemonchus contortus larval stages from in vitro cultures (L3 and xL3) and from gerbils (Meriones unguiculatus) (L4) as models of study

The aim of the study was to compare the relative gene expression of Haemonchus contortus P-glycoprotein genes (Hco-pgp) between fourth (L4), infective (L3), and transitory infective (xL3) larval stages as laboratory models to study ivermectin (IVM) resistance. The H. contortus resistant to IVM (IVMr) and susceptible to IVM (IVMs) strains were used to develop xL3in vitro culture and to infect Meriones unguiculatus (gerbils) to collect L4 stages. Morphometric differences were evaluated from 25 individuals of H. contortus from each strain. Relative gene expression from xL3 and L4 was determined between comparison of IVMr stages and from IVMr vs IVMs stages. Seven Hco-pgp genes (1, 2, 3, 4, 9, 10, and 16) were analysed by RT-qPCR using L3 stage as control group, per strain, and GAPDH and β-tubulin as constitutive genes. Morphological changes were confirmed between xL3 and L4 developing oral shape, oesophagus, and intestinal tube. In addition, the body length and width showed statistical differences (p < 0.05). The Hco-pgp1, 2, 3, and 4 genes (p < 0.05) were upregulated from 7.1- to 463.82-fold changes between IVMr stages, and Hco-pgp9 (13.12-fold) and Hco-pgp10 (13.56-fold) genes showed differences between L4 and xL3, respectively. The comparative study between IVMr vs IVMs strains associated to xL3 and L4 displayed significant upregulation for most of the Hco-pgp genes among 4.89-188.71 fold-change. In conclusion, these results suggest the use of H. contortus xL3 and L4 as suitable laboratory models to study IVMr associated with Hco-pgp genes to contribute to the understanding of anthelmintic resistance.

Effect of Ivermectin on the Expression of P-Glycoprotein in Third-Stage Larvae of Haemonchus contortus Isolated from China

Haemonchus contortus poses a severe hazard to the healthy development of the sheep industry and threatens the welfare of sheep. Ivermectin is the primary anthelmintic used for the prevention and treatment of H. contortus parasitism. However, the widespread and uncontrolled application of ivermectin has resulted in the development and spread of resistant strains of H. contortus. P-glycoprotein (P-gp) plays important roles in the pharmacology and toxicology of ivermectin, and changes in P-gp expression levels can be used to analyze the resistance of H. contortus to ivermectin. This study aimed to analyze the effects of ivermectin on P-gp expression in H. contortus L3 larvae isolated from China and to evaluate whether changes in P-gp expression levels can be used to analyze resistant H. contortus strains. In the absence of drug treatment, the ivermectin-resistant strains isolated in China showed increased expression of P-gp11 (p < 0.01) compared with sensitive strains from elsewhere, whereas the expressions of P-gp2 and P-gp9.1 were downregulated (p < 0.01). When the same strain was compared before and after drug treatment, obvious differences in expression were observed between the different strains. Ivermectin-induced P-gp expression was found to be very complex among the L3 larvae of different strains. In addition, it was confirmed that using P-gp to determine ivermectin resistance in H. contortus strains from different geographic environments can yield different results.

Importance of ABC Transporters in the Survival of Parasitic Nematodes and the Prospect for the Development of Novel Control Strategies

ABC transporters, a family of ATP-dependent transmembrane proteins, are responsible for the active transport of a wide range of molecules across cell membranes, including drugs, toxins, and nutrients. Nematodes possess a great diversity of ABC transporters; however, only P-glycoproteins have been well-characterized compared to other classes. The ABC transport proteins have been implicated in developing resistance to various classes of anthelmintic drugs in parasitic nematodes; their role in plant and human parasitic nematodes still needs further investigation. Therefore, ABC transport proteins offer a potential opportunity to develop nematode control strategies. Multidrug resistance inhibitors are becoming more attractive for controlling nematodes due to their potential to increase drug efficacy in two ways: (i) by limiting drug efflux from nematodes, thereby increasing the amount of drug that reaches its target site, and (ii) by reducing drug excretion by host animals, thereby enhancing drug bioavailability. This article reviews the role of ABC transporters in the survival of parasitic nematodes, including the genes involved, their regulation and physiological roles, as well as recent developments in their characterization. It also discusses the association of ABC transporters with anthelmintic resistance and the possibility of targeting them with next-generation inhibitors or nutraceuticals (e.g., polyphenols) to control parasitic infections.

Assembly and Analysis of Haemonchus contortus Transcriptome as a Tool for the Knowledge of Ivermectin Resistance Mechanisms

Haemonchus contortus (Hc) is an important parasitic nematode of small ruminants. In this study we assembled the transcriptome of Hc as a model to contribute to the knowledge about the profile of the differential gene expression between two Mexican Hc strains under different anthelmintic resistance statuses, one susceptible and the other resistant to ivermectin (IVMs and IVMr, respectively), in order to improve and/or to have new strategies of control and diagnosis. The transcript sequence reads were assembled and annotated. Overall, ~127 Mbp were assembled and distributed into 77,422 transcript sequences, and 4394 transcripts of the de novo transcriptome were matched base on at least one of the following criteria: (1) Phylum Nemathelminthes and Platyhelminthes, important for animal health care, and (2) ≥55% of sequence identity with other organisms. The gene ontology (GO) enrichment analysis (GOEA) was performed to study the level of gene regulation to IVMr and IVMs strains using Log Fold Change (LFC) filtering values ≥ 1 and ≥ 2. The upregulated-displayed genes obtained via GOEA were: 1993 (for LFC ≥ 1) and 1241 (for LFC ≥ 2) in IVMr and 1929 (for LFC ≥ 1) and 835 (for LFC ≥ 2) in IVMs. The enriched GO terms upregulated per category identified the intracellular structure, intracellular membrane-bounded organelle and integral component of the cell membrane as some principal cellular components. Meanwhile, efflux transmembrane transporter activity, ABC-type xenobiotic transporter activity and ATPase-coupled transmembrane transporter activity were associated with molecular function. Responses to nematicide activity, pharyngeal pumping and positive regulation of synaptic assembly were classified as biological processes that might be involved in events related to the anthelmintic resistance (AR) and nematode biology. The filtering analysis of both LFC values showed similar genes related to AR. This study deepens our knowledge about the mechanisms behind the processes of H. contortus in order to help in tool production and to facilitate the reduction of AR and promote the development of other control strategies, such as anthelmintic drug targets and vaccines.

Comparative analysis on transcriptomics of ivermectin resistant and susceptible strains of Haemonchus contortus

Background

Ivermectin (IVM) is one of the most important and widely used anthelmintics in veterinary medicine. However, its efficacy is increasingly compromised by widespread resistance, and the exact mechanism of IVM resistance remains unclear for most parasitic nematodes, including Haemonchus contortus, a blood-sucking parasitic nematode of small ruminants.

Methods

In this study, an H. contortus IVM-resistant strain from Zhaosu, Xinjiang, China, was isolated and assessed by the control test, faecal egg count reduction test (FECRT) and the larval development assay (LDA). Subsequently, comparative analyses on the transcriptomics of IVM-susceptible and IVM-resistant adult worms of this parasite were carried out using RNA sequencing (RNA-seq) and bioinformatics.

Results

In total, 543 (416 known, 127 novel) and 359 (309 known, 50 novel) differentially expressed genes (DEGs) were identified in male and female adult worms of the resistant strain compared with those of the susceptible strain, respectively. In addition to several previously known candidate genes which were supposed to be associated with IVM resistance and whose functions were involved in receptor activity, transport, and detoxification, we found some new potential target genes, including those related to lipid metabolism, structural constituent of cuticle, and important pathways such as antigen processing and presentation, lysosome, autophagy, apoptosis, and NOD1-like receptor signalling pathways. Finally, the results of quantitative real-time polymerase chain reaction confirmed that the transcriptional profiles of selected DEGs (male: 8 genes, female: 10 genes) were consistent with those obtained by the RNA-seq.

Conclusions

Our results indicate that IVM has multiple effects, including both neuromuscular and non-neuromuscular targets, and provide valuable information for further studies on the IVM resistance mechanism in H. contortus.

Graphical Abstract

Supplementary Information

The online version contains supplementary material available at 10.1186/s13071-022-05274-y.

Constitutive and differential expression of transport protein genes in Parascaris univalens larvae and adult tissues after in vitro exposure to anthelmintic drugs

The equine roundworm Parascaris univalens has developed resistance to the three anthelmintic substances most commonly used in horses. The mechanisms responsible for resistance are believed to be multi-genic, and transport proteins such as the P-glycoprotein (Pgp) family have been suggested to be involved in resistance in several parasites including P. univlaens. To facilitate further research into the mechanisms behind drug metabolism and resistance development in P. univalens we aimed to develop an in vitro model based on larvae. We developed a fast and easy protocol for hatching P. univalens larvae for in vitro studies, resulting in a hatching rate of 92 %. The expression of transport protein genes pgp-2, pgp-9, pgp-11.1, pgp-16.1 and major facilitator superfamily (MFS) genes PgR006_g137 and PgR015_g078 were studied in hatched larvae exposed to the anthelmintic drugs ivermecin (IVM) 10^-9 M, pyrantel citrate (PYR) 10^-6 M and thiabendazole (TBZ) 10^-5 M for 24 h. In comparison, the expression of these transport protein genes was studied in the anterior end and intestinal tissues of adult worms in vitro exposed to IVM, TBZ and PYR, at the same concentrations as larvae, for 3 h, 10 h and 24 h. Larval exposure to sub-lethal doses of IVM for 24 h did not affect the expression levels of any of the investigated genes, however larvae exposed to PYR and TBZ for 24 h showed significantly increased expression of pgp-9. In vitro drug exposure of adult worms did not result in any significant increases in expression of transport protein genes. Comparisons of constitutive expression between larvae and adult worm tissues showed that pgp-9, pgp-11.1, pgp-16.1 and MFS gene PgR015_g078 were expressed at lower levels in larvae than in adult tissues, while pgp-2 and MFS gene PgR006_g137 had similar expression levels in larvae and adult worms. All investigated transport protein genes were expressed at higher rates in the intestine than in the anterior end of adult worms, except pgp-11.1 where the expression was similar between the two tissues. This high constitutive expression in the intestine suggests that this is an important site for xenobiotic efflux in P. univalens. Despite the fact that the results of this study show differences in expression of transport protein genes between larvae and adult tissues, we believe that the larval assay system described here will be an important tool for further research into the molecular mechanisms behind anthelmintic resistance development and for other in vitro studies.

Laboratory assays reveal diverse phenotypes among microfilariae of Dirofilaria immitis isolates with known macrocyclic lactone susceptibility status

Prevention of canine heartworm disease caused by Dirofilaria immitis relies on chemoprophylaxis with macrocyclic lactone anthelmintics. Alarmingly, there are increased reports of D. immitis isolates with resistance to macrocyclic lactones and the ability to break through prophylaxis. Yet, there is not a well-established laboratory assay that can utilize biochemical phenotypes of microfilariae to predict drug resistance status. In this study we evaluated laboratory assays measuring cell permeability, metabolism, and P-glycoprotein-mediated efflux. Our assays revealed that trypan blue, propidium iodide staining, and resazurin metabolism could detect differences among D. immitis isolates but none of these approaches could accurately predict drug susceptibility status for all resistant isolates tested. P-glycoprotein assays suggested that the repertoire of P-gp expression is likely to vary among isolates, and investigation of pharmacological differences among different P-gp genes is warranted. Further research is needed to investigate and optimize laboratory assays for D. immitis microfilariae, and caution should be applied when adapting cell death assays to drug screening studies for nematode parasites.

Comparative study of transcription profiles of the P-glycoprotein transporters of two Haemonchus contortus isolates: Susceptible and resistant to ivermectin

The objective of this study was to analyze the mRNA transcription levels of ten functional genes of P-glycoproteins (P-gp) in free life stages, eggs and infective larvae (L₃) and in endoparasitic stages, fourth larval stage (L₄) and adult males of two native isolates of Haemonchus contortus: resistant and susceptible to IVM. The IVM resistant isolate was obtained from sheep naturally infected with H. contortus, and the susceptible isolate (with no pressure to IVM) conserved since 1990. The lethal effect of IVM was evaluated under in vitro conditions, which showed significant differences between susceptible and resistant H. contortus L₃ isolates (P < 0.01). The IVM susceptible isolate revealed a lethal effect of 79.22% at 11.42 mM, whereas that resistant isolate showed no lethal effect at any of the four assessed concentrations (1.43, 2.85, 5.71 and 11.42 mM) of IVM. The expression levels of ten Hco-pgp genes (1, 2, 3, 4, 9, 10, 11, 12, 14, and 16) were evaluated in the resistant isolate of H. contortus and compared to the susceptible isolate (as control), using two constitutive genes (GAPDH and β-tubulin). Up-regulation at two statistical significant values (P ≤ 0.05, 0.1) was the criterion to associate IVM resistance with the free life and endoparasitic stages of H. contortus. The expression levels in H. contortus adult nematodes showed 5.64 to 127.56-fold increase for Hco-pgp genes 1, 9, 12, 14, and 16, followed by an increase for Hco-pgp-2 (49.75-fold) and Hco-pgp-10 (106.40-fold) in L₄, and for Hco-pgp-16 (2.90-fold) in eggs (P ≤ 0.05). In addition, high expression levels with P < 0.1 were detected in H. contortus L₃, L₄, and adults for Hco-pgp genes 1, 4, 11, 12, and 16, with changes ranging from 2.17 to 29.72-fold. In conclusion, the highest expression was observed in the adult stage of H. contortus, and the most frequent gene with a significant P-value was Hco-pgp-16, revealing it plays an important role in IVM resistance.

Detection approaches for multidrug resistance genes of leukemia

Leukemia is a clonal malignant hematopoietic stem cell disease. It is the sixth most lethal cancer and accounts for 4% of all cancers. The main form of treatment for leukemia is chemotherapy. While some cancer types with a higher incidence than leukemia, such as lung and gastric cancer, have shown a sharp decline in mortality rates in recent years, leukemia has not followed this trend. Drug resistance is often regarded as the main clinical obstacle to effective chemotherapy in patients diagnosed with leukemia. Many resistance mechanisms have now been identified, and multidrug resistance (MDR) is considered the most important and prevalent mechanism involved in the failure of chemotherapy in leukemia. In order to reverse MDR and improve leukemia prognosis, effective detection methods are needed to identify drug resistance genes at initial diagnosis. This article provides a comprehensive overview of published approaches for the detection of MDR in leukemia. Identification of relevant MDR genes and methods for early detection of these genes will be needed in order to treat leukemia more effectively.

Proteomic Analysis of the Excretory and Secretory Proteins of Haemonchus contortus (HcESP) Binding to Goat PBMCs In Vivo Revealed Stage-Specific Binding Profiles

Haemonchus contortus is a parasitic gastrointestinal nematode, and its excretory and secretory products (HcESPs) interact extensively with the host cells. In this study, we report the interaction of proteins from HcESPs at different developmental stages to goat peripheral blood mononuclear cells (PBMCs) in vivo using liquid chromatography-tandem mass spectrometry. A total of 407 HcESPs that interacted with goat PBMCs at different time points were identified from a H. contortus protein database using SEQUEST searches. The L4 and L5 stages of H. contortus represented a higher proportion of the identified proteins compared with the early and late adult stages. Both stage-specific interacting proteins and proteins that were common to multiple stages were identified. Forty-seven interacting proteins were shared among all stages. The gene ontology (GO) distributions of the identified goat PBMC-interacting proteins were nearly identical among all developmental stages, with high representation of binding and catalytic activity. Cellular, metabolic and single-organism processes were also annotated as major biological processes, but interestingly, more proteins were annotated as localization processes at the L5 stage than at the L4 and adult stages. Based on the clustering of homologous proteins, we improved the functional annotations of un-annotated proteins identified at different developmental stages. Some unnamed H. contortus ATP-binding cassette proteins, including ADP-ribosylation factor and P-glycoprotein-9, were identified by STRING protein clustering analysis.

Evidence from two independent backcross experiments supports genetic linkage of microsatellite Hcms8a20, but not other candidate loci, to a major ivermectin resistance locus in Haemonchus contortus

Haemonchus contortus is the leading parasitic nematode species used to study anthelmintic drug resistance. A variety of candidate loci have been implicated as being associated with ivermectin resistance in this parasite but definitive evidence of their importance is still lacking. We have previously performed two independent serial backcross experiments to introgress ivermectin resistance loci from two H. contortus ivermectin-resistant strains - MHco4(WRS) and MHco10(CAVR) - into the genetic background of the ivermectin-susceptible genome reference strain MHco3(ISE). We have interrogated a number of candidate ivermectin resistance loci in the resulting backcross populations and assessed the evidence for their genetic linkage to an ivermectin resistance locus. These include the microsatellite marker Hcms8a20 and six candidate genes Hco-glc-5, Hco-avr-14, Hco-lgc-37 (previously designated Hco-hg-1), Hco-pgp-9 (previously designated Hco-pgp-1), Hco-pgp-2 and Hco-dyf-7. We have sampled the haplotype diversity of amplicon markers within, or adjacent to, each of these loci in the parental strains and fourth generation backcross populations to assess the evidence for haplotype introgression from the resistant parental strain into the genomic background of the susceptible parental strain in each backcross. The microsatellite Hcms8a20 locus showed strong evidence of such introgression in both independent backcrosses, suggesting it is linked to an important ivermectin resistance mutation in both the MHco4(WRS) and MHco10(CAVR) strains. In contrast, Hco-glc-5, Hco-avr-14, Hco-pgp-9 and Hco-dyf-7 showed no evidence of introgression in either backcross. Hco-lgc-37 and Hco-pgp-2 showed only weak evidence of introgression in the MHco3/4 backcross but not in the MHco3/10 backcross. Overall, these results suggest that microsatellite marker Hcms8a20, but not the other candidate genes tested, is linked to a major ivermectin resistance locus in the MHco4(WRS) and MHco10(CAVR) strains. This work also emphasises the need for genome-wide approaches to identify mutations responsible for the ivermectin resistance in this parasite.

ABC-B transporter genes in Dirofilaria immitis

Dirofilaria immitis is a filarial nematode causing infection and heartworm disease in dogs and other canids, cats, and occasionally in humans. Prevention with macrocyclic lactones (ML) is recommended during the mosquito transmission season. Recently, ML resistance has been reported. ABC-B transporter genes are thought to be involved in the mechanism of ML resistance in other nematodes. This study aimed to identify all the ABC-B transporter genes in D. immitis using as a reference the nDi.2.2 D. immitis whole genome, which is not completely annotated. Using bioinformatic tools and PCR amplification on pooled D. immitis genomic DNA and on pooled cDNA, nine ABC transporter genes including one pseudogene were characterized. Bioinformatic and phylogenetic analyses allowed identification of three P-glycoproteins (Pgps) (Dim-pgp-3 Dim-pgp-10, Dim-pgp-11), of two ABC-B half transporter genes (one ortholog of Cel-haf-4 and Cel-haf-9; and one ortholog of Cel-haf-1 and Cel-haf-3), of one ABC half transporter gene (ortholog of Cel-haf-5) that contained an ABC-C motif, and of one additional half transporter that would require functional study for characterization. The number of ABC-B transporter genes identified was lower than in Caenorhabditis elegans and Haemonchuscontortus. Further studies are needed to understand their possible role in ML resistance in D. immitis. These ABC transporters constitute a base for ML resistance investigation in D. immitis and advance our understanding of the molecular biology of this parasite.

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Identification of ABC-B full and half transporter genes in Dirofilaria immitis.

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Phylogenetic analysis of the D. immitis ABC-B transporter genes.

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Lower number of ABC-B transporter genes in D. immitis compared with Clade V nematodes.

Effects of in vitro exposure to ivermectin and levamisole on the expression patterns of ABC transporters in Haemonchus contortus larvae

This study investigated the interaction of ATP binding cassette (ABC) transport proteins with ivermectin (IVM) and levamisole (LEV) in larvae of susceptible and resistant isolates of Haemonchus contortus in vitro by measuring transcription patterns following exposure to these anthelmintics. Furthermore, we studied the consequences of drug exposure by measuring the sensitivity of L₃ to subsequent exposure to higher drug concentrations using larval migration assays. The most highly transcribed transporter genes in both susceptible and resistant L₃ were pgp-9.3, abcf-1, mrp-5, abcf-2, pgp-3, and pgp-10. The resistant isolate showed significantly higher transcription of pgp-1, pgp-9.1 and pgp-9.2 compared to the susceptible isolate. Five P-gp genes and the haf-6 gene showed significantly higher transcription (up to 12.6-fold) after 3 h exposure to IVM in the resistant isolate. Similarly, five P-gp genes, haf-6 and abcf-1 were transcribed at significantly higher levels (up to 10.3-fold) following 3 h exposure to LEV in this isolate. On the other hand, there were no significant changes in transcriptional patterns of all transporter genes in the susceptible isolate following 3 and 6 h exposure to IVM or LEV. In contrast to these isolate-specific transcription changes, both isolates showed an increase in R-123 efflux following exposure to the drugs, suggesting that the drugs stimulated activity of existing transporter proteins in both isolates. Exposure of resistant larvae to IVM or LEV resulted, in some instances, in an increase in the proportion of the population able to migrate at the highest IVM concentrations in subsequent migration assays. The significant increase in transcription of some ABC transporter genes following 3 h exposure to both IVM and LEV in the resistant isolate only, suggests that an ability to rapidly upregulate protective pathways in response to drugs may be a component of the resistance displayed by this isolate.

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We studied interaction of anthelmintics with ABC transporters in Haemonchus contortus.

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pgp-1, 2, -9.1, -10, and -11 and haf-6 up-regulated after 3 h exposure to ivermectin.

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Up-regulation occurred in a drug-resistant isolate but not in a -susceptible isolate.

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A proportion of the drug exposed larvae showed tolerance to subsequent drug treatment.

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Rapid up-regulation of transporters may be component of resistance in parasitic nematodes.

Haemonchus contortus: Applications in Drug Discovery

Haemonchus contortus is an important pathogen of small ruminants and is therefore a crucially important target for anthelmintic chemotherapy. Its large size and fecundity have been exploited for the development of in vitro screens for anthelmintic discovery that employ larval and adult stages in several formats. The ability of the parasite to develop to the young adult stage in Mongolian jirds (Meriones unguiculatus) provides a useful small animal model that can be used to screen compounds prior to their evaluation in infected sheep. This chapter summarizes the use of H. contortus for anthelmintic discovery, offers a perspective on current strategies in this area and suggests research challenges that could lead to improvements in the anthelmintic discovery process.

Haemonchus contortus P-glycoproteins interact with host eosinophil granules: a novel insight into the role of ABC transporters in host-parasite interaction

Eosinophils are one of the major mammalian effector cells encountered by helminths during infection. In the present study, we investigated the effects of eosinophil granule exposure on the sheep parasitic nematode Haemonchus contortus as a model. H. contortus eggs exposed to eosinophil granule products showed increased rhodamine 123 efflux and this effect was not due to loss of egg integrity. Rh123 is known to be a specific P-glycoprotein (Pgp) substrate and led to the hypothesis that in addition to their critical role in xenobiotic resistance, helminth ABC transporters such as Pgp may also be involved in the detoxification of host cytotoxic products. We showed by quantitative RT-PCR that, among nine different H. contortus Pgp genes, Hco-pgp-3, Hco-pgp-9.2, Hco-pgp-11 and, Hco-pgp-16 were specifically up-regulated in parasitic life stages suggesting a potential involvement of these Pgps in the detoxification of eosinophil granule products. Using exsheathed L3 larvae that mimic the first life stage in contact with the host, we demonstrated that eosinophil granules induced a dose dependent overexpression of Hco-pgp-3 and the closely related Hco-pgp-16. Taken together, our results provide the first evidence that a subset of helminth Pgps interact with, and could be involved in the detoxification of, host products. This opens the way for further studies aiming to explore the role of helminth Pgps in the host-parasite interaction, including evasion of the host immune response.

Genetic variants and increased expression of Parascaris equorum P-glycoprotein-11 in populations with decreased ivermectin susceptibility

Macrocyclic lactones (MLs) represent the major drug class for control of parasitic infections in humans and animals. However, recently reports of treatment failures became more frequent. In addition to human and ruminant parasitic nematodes this also is the case for the horse-nematode Parascaris equorum. Nevertheless, to date the molecular basis of ML resistance is still not understood. Unspecific resistance mechanisms involving transporters such as P-glycoproteins (Pgps) are expected to contribute to ML resistance in nematodes. Here, complete sequences of two P. equorum Pgps were cloned and identified as orthologs of Caenorhabditis elegans Ppg-11 and an unnamed Caenorhabditis briggsae Pgp designated as Pgp-16 using phylogenetic analysis. Quantitative real-time PCR was used to compare expression between tissues. Significantly higher PeqPgp-11 expression was found in the gut for both genders, whereas for PeqPgp-16 the body wall was identified as predominant expression site. Furthermore, Pgps were analyzed regarding their participation in resistance development. Using SeqDoC analyses, Pgp-sequences of P. equorum populations with different ML susceptibility were compared. This approach revealed three single nucleotide polymorphisms (SNPs) causing missense mutations in the PeqPgp-11 sequence which correlated with decreased ML susceptibility. However, no resistance associated differences in mRNA expression levels were detected between embryonated eggs of these populations. In contrast, comparison of two pre-adult groups with different ivermectin (IVM) susceptibility revealed the presence of the three SNPs and in addition statistically significant PeqPgp-11 overexpression in the group of worms with reduced susceptibility. These results indicate that Pgp-11 might be involved in IVM resistance in P. equorum as it shows increased expression in an IVM exposed life-cycle stage of an IVM resistant population as well as occurrence of putatively resistance associated SNPs in populations with reduced IVM susceptibility. These SNPs are promising diagnostic candidates for detection of ML resistance with potential also for other parasitic nematode species.

Caenorhabditis elegans: modest increase of susceptibility to ivermectin in individual P-glycoprotein loss-of-function strains

P-glycoproteins (Pgps) are members of the ABC transporter superfamily and are involved in detoxification mechanisms of single- and multicellular organisms. Their importance for survival of organisms in the presence of harmful drug concentrations has been widely studied in cancer cells but Pgp-dependent drug resistance of parasites has also been demonstrated. Ivermectin (IVM), a widely used anthelmintic in human and veterinary medicine, is a known substrate at least of mammalian Pgps and resistance against IVM is proposed to be associated with Pgps. The consequences of loss of Pgp function for the development of the model nematode Caenorhabditis elegans were analysed in the presence of IVM. Either strains missing only a single Pgp were used or Pgp activity generally was inhibited using verapamil (VPL). Loss-of-function of individual Pgp resulted in a statistically significant increase in IVM susceptibility in terms of impaired development with decreases in EC₅₀ values between 1.5- and 4.3-fold. Absence of seven Pgps resulted in a higher impact on IVM susceptibility of C. elegans since it resulted in EC₅₀ values decreased by 2.4- to 4.3-fold. This increase in IVM susceptibility was even more pronounced than that observed when Pgp function was blocked in general by VPL (approximately 2.5-fold). This study demonstrates clearly that Pgps are of importance for IVM detoxification in the model organism C. elegans and that some Pgps obviously have a higher impact than others.

Comparative tissue pharmacokinetics and efficacy of moxidectin, abamectin and ivermectin in lambs infected with resistant nematodes: Impact of drug treatments on parasite P-glycoprotein expression

The high level of resistance to the macrocyclic lactones has encouraged the search for strategies to optimize their potential as antiparasitic agents. There is a need for pharmaco-parasitological studies addressing the kinetic-dynamic differences between various macrocyclic lactones under standardized in vivo conditions. The current work evaluated the relationship among systemic drug exposure, target tissue availabilities and the pattern of drug accumulation within resistant Haemonchus contortus for moxidectin, abamectin and ivermectin. Drug concentrations in plasma, target tissues and parasites were measured by high performance liquid chromatography. Additionally, the efficacy of the three molecules was evaluated in lambs infected with resistant nematodes by classical parasitological methods. Furthermore, the comparative determination of the level of expression of P-glycoprotein (P-gp2) in H. contortus recovered from lambs treated with each drug was performed by real time PCR. A longer persistence of moxidectin (P < 0.05) concentrations in plasma was observed. The concentrations of the three compounds in the mucosal tissue and digestive contents were significant higher than those measured in plasma. Drug concentrations were in a range between 452 ng/g (0.5 day post-treatment) and 32 ng/g (2 days post-treatment) in the gastrointestinal (GI) contents (abomasal and intestinal). Concentrations of the three compounds in H. contortus were in a similar range to those observed in the abomasal contents (positive correlation P = 0.0002). Lower moxidectin concentrations were recovered within adult H. contortus compared to abamectin and ivermectin at day 2 post-treatment. However, the efficacy against H. contortus was 20.1% (ivermectin), 39.7% (abamectin) and 89.6% (moxidectin). Only the ivermectin treatment induced an enhancement on the expression of P-gp2 in the recovered adult H. contortus, reaching higher values at 12 and 24 h post-administration compared to control (untreated) worms. This comparative pharmacological evaluation of three of the most used macrocyclic lactones compounds provides new insights into the action of these drugs.

Moxidectin and the avermectins: Consanguinity but not identity

The avermectins and milbemycins contain a common macrocyclic lactone (ML) ring, but are fermentation products of different organisms. The principal structural difference is that avermectins have sugar groups at C13 of the macrocyclic ring, whereas the milbemycins are protonated at C13. Moxidectin (MOX), belonging to the milbemycin family, has other differences, including a methoxime at C23. The avermectins and MOX have broad-spectrum activity against nematodes and arthropods. They have similar but not identical, spectral ranges of activity and some avermectins and MOX have diverse formulations for great user flexibility. The longer half-life of MOX and its safety profile, allow MOX to be used in long-acting formulations. Some important differences between MOX and avermectins in interaction with various invertebrate ligand-gated ion channels are known and could be the basis of different efficacy and safety profiles. Modelling of IVM interaction with glutamate-gated ion channels suggest different interactions will occur with MOX. Similarly, profound differences between MOX and the avermectins are seen in interactions with ABC transporters in mammals and nematodes. These differences are important for pharmacokinetics, toxicity in animals with defective transporter expression, and probable mechanisms of resistance. Resistance to the avermectins has become widespread in parasites of some hosts and MOX resistance also exists and is increasing. There is some degree of cross-resistance between the avermectins and MOX, but avermectin resistance and MOX resistance are not identical. In many cases when resistance to avermectins is noticed, MOX produces a higher efficacy and quite often is fully effective at recommended dose rates. These similarities and differences should be appreciated for optimal decisions about parasite control, delaying, managing or reversing resistances, and also for appropriate anthelmintic combination.

Proteomic profiling and protein identification by MALDI-TOF mass spectrometry in unsequenced parasitic nematodes

Lack of genomic sequence data and the relatively high cost of tandem mass spectrometry have hampered proteomic investigations into helminths, such as resolving the mechanism underpinning globally reported anthelmintic resistance. Whilst detailed mechanisms of resistance remain unknown for the majority of drug-parasite interactions, gene mutations and changes in gene and protein expression are proposed key aspects of resistance. Comparative proteomic analysis of drug-resistant and -susceptible nematodes may reveal protein profiles reflecting drug-related phenotypes. Using the gastro-intestinal nematode, Haemonchus contortus as case study, we report the application of freely available expressed sequence tag (EST) datasets to support proteomic studies in unsequenced nematodes. EST datasets were translated to theoretical protein sequences to generate a searchable database. In conjunction with matrix-assisted laser desorption ionisation time-of-flight mass spectrometry (MALDI-TOF-MS), Peptide Mass Fingerprint (PMF) searching of databases enabled a cost-effective protein identification strategy. The effectiveness of this approach was verified in comparison with MS/MS de novo sequencing with searching of the same EST protein database and subsequent searches of the NCBInr protein database using the Basic Local Alignment Search Tool (BLAST) to provide protein annotation. Of 100 proteins from 2-DE gel spots, 62 were identified by MALDI-TOF-MS and PMF searching of the EST database. Twenty randomly selected spots were analysed by electrospray MS/MS and MASCOT Ion Searches of the same database. The resulting sequences were subjected to BLAST searches of the NCBI protein database to provide annotation of the proteins and confirm concordance in protein identity from both approaches. Further confirmation of protein identifications from the MS/MS data were obtained by de novo sequencing of peptides, followed by FASTS algorithm searches of the EST putative protein database. This study demonstrates the cost-effective use of available EST databases and inexpensive, accessible MALDI-TOF MS in conjunction with PMF for reliable protein identification in unsequenced organisms.

P-glycoproteins and other multidrug resistance transporters in the pharmacology of anthelmintics: Prospects for reversing transport-dependent anthelmintic resistance

Parasitic helminths cause significant disease in animals and humans. In the absence of alternative treatments, anthelmintics remain the principal agents for their control. Resistance extends to the most important class of anthelmintics, the macrocyclic lactone endectocides (MLs), such as ivermectin, and presents serious problems for the livestock industries and threatens to severely limit current parasite control strategies in humans. Understanding drug resistance is important for optimizing and monitoring control, and reducing further selection for resistance. Multidrug resistance (MDR) ABC transporters have been implicated in ML resistance and contribute to resistance to a number of other anthelmintics. MDR transporters, such as P-glycoproteins, are essential for many cellular processes that require the transport of substrates across cell membranes. Being overexpressed in response to chemotherapy in tumour cells and to ML-based treatment in nematodes, they lead to therapy failure by decreasing drug concentration at the target. Several anthelmintics are inhibitors of these efflux pumps and appropriate combinations can result in higher treatment efficacy against parasites and reversal of resistance. However, this needs to be balanced against possible increased toxicity to the host, or the components of the combination selecting on the same genes involved in the resistance. Increased efficacy could result from modifying anthelmintic pharmacokinetics in the host or by blocking parasite transporters involved in resistance. Combination of anthelmintics can be beneficial for delaying selection for resistance. However, it should be based on knowledge of resistance mechanisms and not simply on mode of action classes, and is best started before resistance has been selected to any member of the combination. Increasing knowledge of the MDR transporters involved in anthelmintic resistance in helminths will play an important role in allowing for the identification of markers to monitor the spread of resistance and to evaluate new tools and management practices aimed at delaying its spread.