Identification and activity of inhibitors of the essential nematode-specific metalloprotease DPY-31.

Infection by parasitic nematodes is widespread in the developing world causing extensive morbidity and mortality. Furthermore, infection of animals is a global problem, with a substantial impact on food production. Here we identify small molecule inhibitors of a nematode-specific metalloprotease, DPY-31, using both known metalloprotease inhibitors and virtual screening. This strategy successfully identified several µM inhibitors of DPY-31 from both the human filarial nematode Brugia malayi, and the parasitic gastrointestinal nematode of sheep Teladorsagia circumcincta. Further studies using both free living and parasitic nematodes show that these inhibitors elicit the severe body morphology defect 'Dumpy' (Dpy; shorter and fatter), a predominantly non-viable phenotype consistent with mutants lacking the DPY-31 gene. Taken together, these results represent a start point in developing DPY-31 inhibition as a totally novel mechanism for treating infection by parasitic nematodes in humans and animals.

Host genetic influences on the anthelmintic efficacy of papaya-derived cysteine proteinases in mice.

Eight strains of mice, of contrasting genotypes, infected with Heligmosomoides bakeri were studied to determine whether the anthelmintic efficacy of papaya latex varied between inbred mouse strains and therefore whether there is an underlying genetic influence on the effectiveness of removing the intestinal nematode. Infected mice were treated with 330 nmol of crude papaya latex or with 240 nmol of papaya latex supernatant (PLS). Wide variation of response between different mouse strains was detected. Treatment was most effective in C3H (90·5-99·3% reduction in worm counts) and least effective in CD1 and BALB/c strains (36·0 and 40·5%, respectively). Cimetidine treatment did not improve anthelmintic efficacy of PLS in a poor drug responder mouse strain. Trypsin activity, pH and PLS activity did not differ significantly along the length of the gastro-intestinal (GI) tract between poor (BALB/c) and high (C3H) drug responder mouse strains. Our data indicate that there is a genetic component explaining between-mouse variation in the efficacy of a standard dose of PLS in removing worms, and therefore warrant some caution in developing this therapy for wider scale use in the livestock industry, and even in human medicine.

A highly conserved, inhibitable astacin metalloprotease from Teladorsagia circumcincta is required for cuticle formation and nematode development.

Parasitic nematodes cause chronic, debilitating infections in both livestock and humans worldwide, and many have developed multiple resistance to the currently available anthelmintics. The protective collagenous cuticle of these parasites is required for nematode survival and its synthesis has been studied extensively in the free-living nematode, Caenorhabditis elegans. The collagen synthesis pathway is a complex, multi-step process involving numerous key enzymes, including the astacin metalloproteases. Nematode astacinsare crucial for C. elegans development, having specific roles in hatching, moulting and cuticle synthesis. NAS-35 (also called DPY-31) is a homologue of a vertebrate procollagen C-proteinase and performs a central role in cuticle formation of C. elegans as its mutation causes temperature-sensitive lethality and cuticle defects. The characterisation of DPY-31 from the ovine gastrointestinal nematode Teladorsagia circumcincta and its ability to rescue the C. elegans mutant is described. Compounds with a hydroxamate functional group have previously been shown to be potent inhibitors of procollagen C-proteinases and were therefore examined for inhibitory activity against the T. circumcincta enzyme. Phenotypic screening against T. circumcincta, Haemonchus contortus and C. elegans larval stages identified compounds that caused body morphology phenotypes consistent with the inhibition of proteases involved in cuticle collagen synthesis. These compounds correspondingly inhibited the activity of recombinant T. circumcincta DPY-31, supporting the hypothesis that this enzyme may represent a potentially novel anthelmintic drug target.

Enzymology of the nematode cuticle: A potential drug target?

All nematodes possess an external structure known as the cuticle, which is crucial for their development and survival. This structure is composed primarily of collagen, which is secreted from the underlying hypodermal cells. Extensive studies using the free-living nematode Caenorhabditis elegans demonstrate that formation of the cuticle requires the activity of an extensive range of enzymes. Enzymes are required both pre-secretion, for synthesis of component proteins such as collagen, and post-secretion, for removal of the previous developmental stage cuticle, in a process known as moulting or exsheathment. The excretion/secretion products of numerous parasitic nematodes contain metallo-, serine and cysteine proteases, and these proteases are conserved across the nematode phylum and many are involved in the moulting/exsheathment process. This review highlights the enzymes required for cuticle formation, with a focus on the post-secretion moulting events. Where orthologues of the C. elegans enzymes have been identified in parasitic nematodes these may represent novel candidate targets for future drug/vaccine development.

The astacin metalloprotease moulting enzyme NAS-36 is required for normal cuticle ecdysis in free-living and parasitic nematodes.

Nematodes represent one of the most abundant and species-rich groups of animals on the planet, with parasitic species causing chronic, debilitating infections in both livestock and humans worldwide. The prevalence and success of the nematodes is a direct consequence of the exceptionally protective properties of their cuticle. The synthesis of this cuticle is a complex multi-step process, which is repeated 4 times from hatchling to adult and has been investigated in detail in the free-living nematode, Caenorhabditis elegans. This process is known as moulting and involves numerous enzymes in the synthesis and degradation of the collagenous matrix. The nas-36 and nas-37 genes in C. elegans encode functionally conserved enzymes of the astacin metalloprotease family which, when mutated, result in a phenotype associated with the late-stage moulting defects, namely the inability to remove the preceding cuticle. Extensive genome searches in the gastrointestinal nematode of sheep, Haemonchus contortus, and in the filarial nematode of humans, Brugia malayi, identified NAS-36 but not NAS-37 homologues. Significantly, the nas-36 gene from B. malayi could successfully complement the moult defects associated with C. elegans nas-36, nas-37 and nas-36/nas-37 double mutants, suggesting a conserved function for NAS-36 between these diverse nematode species. This conservation between species was further indicated when the recombinant enzymes demonstrated a similar range of inhibitable metalloprotease activities.

Collagen processing and cuticle formation is catalysed by the astacin metalloprotease DPY-31 in free-living and parasitic nematodes.

The exoskeleton or cuticle performs many key roles in the development and survival of all nematodes. This structure is predominantly collagenous in nature and requires numerous enzymes to properly fold, modify, process and cross-link these essential structural proteins. The cuticle structure and its collagen components are conserved throughout the nematode phylum but differ from the collagenous matrices found in vertebrates. This structure, its formation and the enzymology of nematode cuticle collagen biogenesis have been elucidated in the free-living nematode Caenorhabditis elegans. The dpy-31 gene in C. elegans encodes a procollagen C-terminal processing enzyme of the astacin metalloprotease or bone morphogenetic protein class that, when mutated, results in a temperature-sensitive lethal phenotype associated with cuticle defects. In this study, orthologues of this essential gene have been identified in the phylogenetically diverse parasitic nematodes Haemonchus contortus and Brugia malayi. The DPY-31 protein is expressed in the gut and secretory system of C. elegans, a location also confirmed when a B. malayi transcriptional dpy-31 promoter-reporter gene fusion was expressed in C. elegans. Functional conservation between the nematode enzymes was supported by the fact that heterologous expression of the H. contortus dpy-31 orthologue in a C. elegans dpy-31 mutant resulted in the full rescue of the mutant body form. This interspecies conservation was further established when the recombinant nematode enzymes were found to have a similar range of inhibitable protease activities. In addition, the recombinant DPY-31 enzymes from both H. contortus and B. malayi were shown to efficiently process the C. elegans cuticle collagen SQT-3 at the correct C-terminal procollagen processing site.

The kunitz domain protein BLI-5 plays a functionally conserved role in cuticle formation in a diverse range of nematodes.

The cuticle of parasitic nematodes performs many critical functions and is essential for proper development and for protection from the host immune response. The biosynthesis, assembly, modification and turnover of this exoskeleton have been most extensively studied in the free-living nematode, Caenorhabditis elegans, where it represents a complex multi-step process involving a whole suite of enzymes. The biosynthesis of the cuticle has an additional level of complexity, as many of the enzymes also require additional proteins to aid their activation and selective inhibition. Blister-5 (BLI-5) represents a protein with a kunitz-type serine protease interacting domain and is involved in cuticle collagen biosynthesis in C. elegans, through its interaction with subtilisin-like processing enzymes (such as BLI-4). Mutation of the bli-5 gene causes blistering of the collagenous adult cuticle. Homologues of BLI-5 have been identified in several parasitic species that span different nematode clades. In this study, we molecularly and biochemically characterize BLI-5 homologues from the clade V nematodes C. elegans and Haemonchus contortus and from the clade III filarial nematode Brugia malayi. The nematode BLI-5 orthologues possess a shared domain structure and perform similar in vitro and in vivo functions, performing important proteolytic enzyme functions. The results demonstrate that the bli-5 genes from these diverse parasitic nematodes are able to complement a C. elegansbli-5 mutant and thereby support the use of the C. elegans model system to examine gene function in the experimentally less-amenable parasitic species.

Combined extracellular matrix cross-linking activity of the peroxidase MLT-7 and the dual oxidase BLI-3 is critical for post-embryonic viability in Caenorhabditis elegans.

The nematode cuticle is a protective collagenous extracellular matrix that is modified, cross-linked, and processed by a number of key enzymes. This Ecdysozoan-specific structure is synthesized repeatedly and allows growth and development in a linked degradative and biosynthetic process known as molting. A targeted RNA interference screen using a cuticle collagen marker has been employed to identify components of the cuticle biosynthetic pathway. We have characterized an essential peroxidase, MoLT-7 (MLT-7), that is responsible for proper cuticle molting and re-synthesis. MLT-7 is an active, inhibitable peroxidase that is expressed in the cuticle-synthesizing hypodermis coincident with each larval molt. mlt-7 mutants show a range of body morphology defects, most notably molt, dumpy, and early larval stage arrest phenotypes that can all be complemented with a wild type copy of mlt-7. The cuticles of these mutants lacks di-tyrosine cross-links, becomes permeable to dye and accessible to tyrosine iodination, and have aberrant collagen protein expression patterns. Overexpression of MLT-7 causes mutant phenotypes further supporting its proposed enzymatic role. In combination with BLI-3, an H2O2-generating NADPH dual oxidase, MLT-7 is essential for post-embryonic development. Disruption of mlt-7, and particularly bli-3, via RNA interference also causes dramatic changes to the in vivo cross-linking patterns of the cuticle collagens DPY-13 and COL-12. This points toward a functionally cooperative relationship for these two hypodermally expressed proteins that is essential for collagen cross-linking and proper extracellular matrix formation.

Developing novel anthelmintics from plant cysteine proteinases.

Intestinal helminth infections of livestock and humans are predominantly controlled by treatment with three classes of synthetic drugs, but some livestock nematodes have now developed resistance to all three classes and there are signs that human hookworms are becoming less responsive to the two classes (benzimidazoles and the nicotinic acetylcholine agonists) that are licensed for treatment of humans. New anthelmintics are urgently needed, and whilst development of new synthetic drugs is ongoing, it is slow and there are no signs yet that novel compounds operating through different modes of action, will be available on the market in the current decade. The development of naturally-occurring compounds as medicines for human use and for treatment of animals is fraught with problems. In this paper we review the current status of cysteine proteinases from fruits and protective plant latices as novel anthelmintics, we consider some of the problems inherent in taking laboratory findings and those derived from folk-medicine to the market and we suggest that there is a wealth of new compounds still to be discovered that could be harvested to benefit humans and livestock.

In vitro anthelmintic effects of cysteine proteinases from plants against intestinal helminths of rodents.

Infections with gastrointestinal (GI) nematodes are amongst the most prevalent worldwide, especially in tropical climates. Control of these infections is primarily through treatment with anthelmintic drugs, but the rapid development of resistance to all the currently available classes of anthelmintic means that alternative treatments are urgently required. Cysteine proteinases from plants such as papaya, pineapple and fig are known to be substantially effective against three rodent GI nematodes, Heligmosomoides polygyrus, Trichuris muris and Protospirura muricola, both in vitro and in vivo. Here, based on in vitro motility assays and scanning electron microscopy, we extend these earlier reports, demonstrating the potency of this anthelmintic effect of plant cysteine proteinases against two GI helminths from different taxonomic groups - the canine hookworm, Ancylostoma ceylanicum, and the rodent cestode, Rodentolepis microstoma. In the case of hookworms, a mechanism of action targeting the surface layers of the cuticle indistinguishable from that reported earlier appears to be involved, and in the case of cestodes, the surface of the tegumental layers was also the principal location of damage. Hence, plant cysteine proteinases have a broad spectrum of activity against intestinal helminths (both nematodes and cestodes), a quality that reinforces their suitability for development as a much-needed novel treatment against GI helminths of humans and livestock.

Human gastrointestinal nematode infections: are new control methods required?

Gastrointestinal (GI) nematode infections affect 50% of the human population worldwide, and cause great morbidity as well as hundreds of thousands of deaths. Despite modern medical practices, the proportion of the population infected with GI nematodes is not falling. This is due to a number of factors, the most important being the lack of good healthcare, sanitation and health education in many developing countries. A relatively new problem is the development of resistance to the small number of drugs available to treat GI nematode infections. Here we review the most important parasitic GI nematodes and the methods available to control them. In addition, we discuss the current status of new anthelmintic treatments, particularly the plant cysteine proteinases from various sources of latex-bearing plants and fruits.

Signalling mechanisms underlying subversion of the immune response by the filarial nematode secreted product ES-62.

Secretion of immunomodulatory molecules is a key strategy employed by pathogens to enable their survival in host organisms. For example, arthropod-transmitted filarial nematodes, which achieve longevity within the infected host by suppressing and modulating the host immune response, produce excretory-secretory (ES) products that have been demonstrated to possess immunomodulatory properties. In this review we discuss the immunomodulatory effects of the phosphorylcholine-containing filarial nematode-secreted glycoprotein ES-62 and describe the intracellular signal transduction pathways it targets to achieve these effects.