Investigating the function and possible biological role of an acetylcholine-gated chloride channel subunit (ACC-1) from the parasitic nematode Haemonchus contortus

Increased activity of CF3-derivatized levamisole at the ACC-2 receptor from the parasitic nematode Haemonchus contortus

The acetylcholine-gated chloride channel (ACC) family in parasitic nematodes represents a promising target for anthelmintic drug development. Levamisole, a widely known and utilized cholinergic agonist, has been used for decades to address many types of parasitic infections by targeting nematode nicotinic acetylcholine receptors (nAChRs) in nematodes. In this study, we report the synthesis and pharmacological evaluation of eight levamisole derivatives, five of which are novel, on the H. contortus ACC-2 receptor. This includes a CF3-derivatized compound we have identified as compound 6 whose structure contains levamisole as a backbone with the addition of a 2-trifluoromethyl benzyl group. Electrophysiological assays revealed that compound 6 exhibited a five-fold increase in sensitivity (EC50 20 μM) compared to levamisole (EC50 100 μM), our parent compound, with an EC50 comparable to that of acetylcholine (20 μM). Investigation of the in silico docking of compound 6 with H. contortus ACC-2 suggest that it interacts uniquely within the H. contortus ACC-2 binding pocket, which may contribute to its increased receptor sensitivity. These findings highlight the potential of structural modifications containing an electron-withdrawing group at the 2-position which can significantly enhance activity at the H. contortus ACC-2 receptor. This opens many avenues for the development of more effective treatments against parasitic nematodes, in an environment with increasing resistance.

The Haemonchus contortus LGC-39 subunit is a novel subtype of an acetylcholine-gated chloride channel

The nematode genome exhibits a vast array of Cys-loop receptors that are activated by a diverse set of neurotransmitters and anthelmintic drugs such as ivermectin and levamisole. While many Cys-loop receptors have been functionally and pharmacologically characterized, there remains a large subset of orphan receptors where the agonist remains unknown. We have identified an orphan Cys-loop receptor, LGC-39, from the parasitic nematode Haemonchus contortus that is a novel type of cholinergic-sensitive ligand-gated chloride channel. This receptor groups outside of the acetylcholine-gated chloride channel family, in the previously named GGR-1 (GABA/Glycine Receptor-1) group of Cys-loop receptors. We found that LGC-39 forms a functional homomeric receptor when expressed in Xenopus laevis oocytes and is activated by several cholinergic ligands including acetylcholine, methacholine and surprisingly, atropine with an EC₅₀ for atropine on the low μM range. A homology model was generated which revealed some key features of the LGC-39 ligand-binding pocket that may explain some of the elements important for atropine recognition of the LGC-39 receptor. Overall these results suggest that the GGR-1 family (now called LGC-57) of Cys-loop receptors includes novel acetylcholine-gated chloride channel subtypes and may represent important future drug targets.

Advances in our understanding of nematode ion channels as potential anthelmintic targets

Ion channels are specialized multimeric proteins that underlie cell excitability. These channels integrate with a variety of neuromuscular and biological functions. In nematodes, the physiological behaviors including locomotion, navigation, feeding and reproduction, are regulated by these protein entities. Majority of the antinematodal chemotherapeutics target the ion channels to disrupt essential biological functions. Here, we have summarized current advances in our understanding of nematode ion channel pharmacology. We review cys-loop ligand gated ion channels (LGICs), including nicotinic acetylcholine receptors (nAChRs), acetylcholine-chloride gated ion channels (ACCs), glutamate-gated chloride channels (GluCls), and GABA (γ-aminobutyric acid) receptors, and other ionotropic receptors (transient receptor potential (TRP) channels and potassium ion channels). We have provided an update on the pharmacological properties of these channels from various nematodes. This article catalogs the differences in ion channel composition and resulting pharmacology in the phylum Nematoda. This diversity in ion channel subunit repertoire and pharmacology emphasizes the importance of pursuing species-specific drug target research. In this review, we have provided an overview of recent advances in techniques and functional assays available for screening ion channel properties and their application.

High energy levels in the diet reduce the parasitic effect of Haemonchus contortus in Pelibuey sheep

Nutritional aspects modulate the parasitological and immune response in infected sheep. The aim of the present study was to evaluate the parasitological and humoral immune response of Pelibuey sheep experimentally infected with Haemonchus contortus that were fed diets with two different energy (n = 12) and protein (n = 12) levels. Twenty-four Pelibuey lambs infected with H. contortus were evaluated over 12 weeks. An additional six animals were considered as a control group. Fecal egg count (FEC) was determined, in addition to packed cell volume (PCV), total plasma protein (TPP), and immunoglobulin levels (IgA, IgG, and IgM) by indirect enzyme-linked immunosorbent assay (iELISA). Data were analyzed by repeated measures over time. The lambs that received a high-energy (HighE) diet had the lowest FEC (P < 0.01) regardless of whether they received a high (HighP) or low (LowP) level of protein. The effect of energy level was also observed over time: FEC values decreased and PCV and TPP values increased. Higher immunoglobulin levels were obtained for females (P < 0.05) than males yet, overall, the energy and protein levels of the diets did not affect the response of the immunoglobulins. Over time, however, an increase in IgG and IgM was observed, whereas the IgA level remained basal.

Toward integrative 'omics of the barber's pole worm and related parasitic nematodes

Advances in nucleic acid sequencing, mass spectrometry and computational biology have facilitated the identification, annotation and analysis of genes, transcripts, proteins and metabolites in model nematodes (Caenorhabditis elegans and Pristionchus pacificus) and socioeconomically important parasitic nematodes (Clades I, III, IV and V). Significant progress has been made in genomics and transcriptomics as well as in the proteomics and lipidomics of Haemonchus contortus (the barber's pole worm) - one of the most pathogenic representatives of the order Strongylida. Here, we review salient aspects of genomics, transcriptomics, proteomics, lipidomics, glycomics and functional genomics, and discuss the rise of integrative 'omics of this economically important parasite. Although our knowledge of the molecular biology, genetics and biochemistry of H. contortus and related species has progressed significantly, much remains to be explored, particularly in areas such as drug resistance, unique/unknown genes, host-parasite interactions, parasitism and the pathogenesis of disease, by integrating the use of multiple 'omics methods. This approach should lead to a better understanding of H. contortus and its relatives at a 'systems biology' level, and should assist in developing new interventions against these parasites.

Anthelmintics - From Discovery to Resistance III (Indian Rocks Beach, FL, 2018)

The third scientific meeting in the series “Anthelmintics: From Discovery to Resistance” was held in Indian Rocks Beach, Florida, at the end of January 2018. The meeting focused on a variety of topics related to the title, including the identification of novel targets and new leads, the mechanism of action of existing drugs and the genetic basis of resistance against them. Throughout there was an emphasis on the exploitation of new technologies and methods to further these aims. The presentations, oral and poster, covered basic, veterinary and medical science with strong participation by both academic and commercial researchers. This special issue contains selected papers from the meeting.