An appraisal of natural products active against parasitic nematodes of animals

Anogeissus leiocarpus (DC.) Guill. & Perr. (Combretaceae): A review of the traditional uses, phytochemistry and pharmacology of African birch

Anogeissus leiocarpus (DC.) Guill. & Perr. belongs to the family Combretaceae and is used both by African traditional medical practitioners and livestock rearers to treat diseases such as African trypanosomiasis, animal diarrhoea, asthma, cancer, cough, diabetes, dysentery, erectile dysfunction, fever, giardiasis, helminthiases, meningitis, menstrual disorders, monkeypox, oral infections, poliomyelitis, sickle cell anaemia, snake bites, toothache, urinary schistosomiasis, and yellow fever. Some of these activities have been associated with the presence of polyphenols in the plant which include ellagic acid derivatives, flavonoids, stilbenes, tannins, and triterpenes. Several bioactive molecules have been identified from A. leiocarpus. These include the main active constituents, ellagitannins, ellagic acid derivates, flavonoids and triterpenes. Pharmacological studies have confirmed its antibacterial, antifungal, antihyperglycemic, antihypertensive, antimalarial, antioxidative, antiparasitic, antitumour and anti-ulcer effects. The stem bark has been investigated mainly for biological activities and phytochemistry, and it is the most mentioned plant part highlighted by the traditional users in ethnomedicinal surveys. In vitro and in vivo models, which revealed a wide range of pharmacological actions against parasites causing helminthiasis, leishmaniasis, malaria and trypanosomiasis, have been used to study compounds from A. leiocarpus. Because of its uses in African traditional medicine and veterinary practices, A. leiocarpus has received considerable attention from researchers. The current review provides a comprehensive overview and critical appraisal of scientific reports on A. leiocarpus, covering its traditional uses, pharmacological activities and phytochemistry.

Anthelmintic Effect of Cannabidiol against Echinococcus granulosus sensu stricto

Cystic echinococcosis is a global parasitic zoonosis caused by infection with the larval stage of Echinococcus granulosus sensu lato. Cystic echinococcosis affects more than 1 million people worldwide, causing important economic costs in terms of management and livestock associated losses. Albendazole is the main drug used in treating human cystic echinococcosis. In spite of this, its low aqueous solubility, poor absorption, and consequently erratic bioavailability are the cause of its chemotherapeutic failures. Based on the described problem, new treatment alternatives urgently need to be developed. The aim of the present research was to study the in vitro and in vivo efficacy of cannabidiol (CBD), the second most abundant component of the Cannabis sativa plant, was demonstrated against E. granulosus sensu stricto. CBD (50 µg/mL) caused a decrease in protoscoleces viability of 80 % after 24 h of treatment which was consistent with the observed tegumental alterations. Detachment of the germinal layer was observed in 50 ± 10% of cysts treated with 50 µg/mL of CBD during 24 h. In the clinical efficacy study, all treatments reduced the weight of cysts recovered from mice compared with the control group. However, this reduction was only significant with ABZ suspension and the CBD + ABZ combination. As we could observe by the SEM study, the co-administration of CBD with ABZ suspension caused greater ultrastructural alteration of the germinal layer in comparison with that provoked with the monotherapy. Further in vivo research will be conducted by changing the dose and frequency of CBD and CBD + ABZ treatments and new available CBD delivery systems will also be assayed to improve bioavailability in vivo.

Nontoxic effects of thymol, carvacrol, cinnamaldehyde, and garlic oil on dung beetles: A potential alternative to ecotoxic anthelmintics

The sustainability of the traditional extensive livestock sector will only be possible if healthy dung-decomposing insect communities are preserved. However, many current pharmaceutical anthelmintics are harmful to dung beetles, their presence can have a negative impact on biological systems. Phytochemical anthelmintics are an alternative to ecotoxic synthetic pharmaceutical anthelmintics, although ecotoxicological tests of their possible indirect effects on dung beetles are required to demonstrate their viability. In this study, the potential ecotoxicity of thymol, carvacrol, cinnamaldehyde and garlic oil (diallyl disulfide and diallyl trisulfide) were tested for the first time. Inhibition of antennal response was measured as a relevant parameter by obtaining relevant toxicity thresholds derived from concentration‒response curves, such as the IC50. All phytochemical compounds tested were demonstrated to be suitable alternative candidates to the highly ecotoxic compound ivermectin, considering their non-toxicity to nontarget organisms. Residues of the phytochemical antiparasitics found in cattle droppings were extremely low, even undetectable in the case of diallyl disulfide and diallyl trisulfide. Furthermore, our results showed that none of the phytochemical compounds have ecotoxic effects, even at extremely high concentrations, including those almost 1000 times higher than what is most likely to be found in dung susceptible to ingestion by dung beetles in the field. We can conclude that the four selected phytochemical compounds meet the requirements to be considered reliable alternatives to ecotoxic veterinary medicinal products, such as ivermectin.

Effect of Selected Entomopathogenic Fungal Species on Embryonic Development of Ascaris suum (Nematoda)

The aim of the study was to evaluate the potential of using five selected species of entomopathogenic fungi (Beauveria bassiana, B. brongniartii, Conidiobolus coronatus, Isaria fumosorosea, and Metarhizium robertsii) in the bioregulation of the dispersive stages of the parasitic nematode-Ascaris suum. Experimental cultures of each of the selected entomopathogenic fungi, as well as a control culture without fungi, were incubated with A. suum eggs at 26 °C for 28 days. Development of the A. suum eggs was observed using a light microscope on the 7th, 14th, 21st, and 28th days of incubation. The API-ZYM® test was used to determine, semiquantitatively, the activity of 19 hydrolytic enzymes from the entomopathogenic fungi. The cytotoxicity of the fungi was determined using tetrazole salt MTT. It was found that none of the five tested strains of entomopathogenic fungi showed an ovicidal effect, and none of them colonized the A. suum egg shells. However, ovistatic activity was observed mainly until the 14th day of incubation by I. fumosorosea, M. robertsii, and B. bassiana. In the MTT test, M. robertsii showed moderate cytotoxicity, while the other species showed low cytotoxicity. Among the strains tested, I. fumosorosea showed the highest spectrum of hydrolase production (13 out of 19 enzymes gave a positive reaction from 3 to 5; 20-40 nM or more). The absence of morphological changes in the A. suum egg shells suggests that the antagonistic effect of the studied entomopathogenic fungi may be due to their cytotoxicity, associated with the production of secondary metabolites-toxins (M. robertsii) and enzymatic activity (I. fumosorosea).

Model nematodes as a practical innovation to promote high throughput screening of natural products for anthelmintics discovery in South Asia: Current challenges, proposed practical and conceptual solutions

With the increasing prevalence of anthelmintic resistance in animals recorded globally, and the threat of resistance in human helminths, the need for novel anthelmintic drugs is greater than ever. Most research aimed at discovering novel anthelmintic leads relies on high throughput screening (HTS) of large libraries of synthetic small molecules in industrial and academic settings in developed countries, even though it is the tropical countries that are most plagued by helminth infections. Tropical countries, however, have the advantage of possessing a rich flora that may yield natural products (NP) with promising anthelmintic activity. Focusing on South Asia, which produces one of the world's highest research outputs in NP and NP-based anthelmintic discovery, we find that limited basic research and funding, a lack of awareness of the utility of model organisms, poor industry-academia partnerships and lack of technological innovations greatly limit anthelmintics research in the region. Here we propose that utilizing model organisms including the free-living nematode Caenorhabditis elegans, that can potentially allow rapid target identification of novel anthelmintics, and Oscheius tipulae, a closely related, free-living nematode which is found abundantly in soil in hotter temperatures, could be a much-needed innovation that can enable cost-effective and efficient HTS of NPs for discovering compounds with anthelmintic/antiparasitic potential in South Asia and other tropical regions that historically have devoted limited funding for such research. Additionally, increased collaborations at the national, regional and international level between parasitologists and pharmacologists/ethnobotanists, setting up government-industry-academia partnerships to fund academic research, creating a centralized, regional collection of plant extracts or purified NPs as a dereplication strategy and HTS library, and holding regional C. elegans/O. tipulae-based anthelmintics workshops and conferences to share knowledge and resources regarding model organisms may collectively promote and foster a NP-based anthelmintics landscape in South Asia and beyond.

Natural products as anthelmintics: safeguarding animal health

Covering literature to December 2022This review provides a comprehensive account of all natural products (500 compounds, including 17 semi-synthetic derivatives) described in the primary literature up to December 2022, reported to be capable of inhibiting the egg hatching, motility, larval development and/or the survival of helminths (i.e., nematodes, flukes and tapeworms). These parasitic worms infect and compromise the health and welfare, productivity and lives of commercial livestock (i.e., sheep, cattle, horses, pigs, poultry and fish), companion animals (i.e., dogs and cats) and other high value, endangered and/or exotic animals. Attention is given to chemical structures, as well as source organisms and anthelmintic properties, including the nature of bioassay target species, in vivo animal hosts, and measures of potency.

Nematocidal Activity of Ethanol and Aqueous Extracts of Persea americana Seeds against Heligmosomoides polygyrus using the Worm Microtracker Method

Background

Infections with gastrointestinal helminths constitute a serious obstacle to the good health of the local population in most African Countries. The aim of this study was to evaluate the anthelminthic activity of Persea americana ethanol and aqueous extracts against Heligmosomoides polygyrus using the worm microtracker.

Method

Aqueous and ethanolic extracts of P. americana were prepared. Different concentrations of the extracts were tested against the egg and larvae stages of H. polygyrus using an automated high-throughput method. Briefly, embryonated eggs and larvae of this parasite were obtained after the incubation of fresh eggs at 25°C for 24, 48, and 96 hours for embryonated eggs, L1 and L2 larvae, respectively. One hundred microliters of the plant extracts at various concentrations were put in contact in a 96-well microplate with a suspension of 100 embryonated eggs in a total volume of 200 μL and incubated in a worm microtracker where the motility of the worms was recorded every 30 minutes for the ovicidal activity. The final tested extract concentration was 5, 2.5, 1.25, 0.625, and 0.3125 mg/mL, whereas ringer solution (0.95%) and 1.5% Dimethyl sulfoxide (DMSO) were used as negative controls and levamisole as positive control. The same method was used for larvicidal activities. The anthelmintic activity was determined using the average movement of the worms in the tested product compared with the negative control (1.5% DMSO and ringer solution).

Results

The egg hatching rates of H. polygyrus had IC50 of 0.49 mg/mL (95% confidence interval: 71.70-92.03) and 0.22 mg/mL (95% confidence interval: 74.28-86.18) for the ethanol and aqueous extract, respectively. These IC50 indicate that the aqueous extract is more active for the inhibition of hatching at a 95% confidence interval. The aqueous and ethanol extracts presented mean inhibitory hatching rates of 78.33 ± 1.67% and 75.67 ± 1.15% at 5 mg/mL, respectively, with no significant differences. The highest percentage of inhibition of L1 larva was observed at 5 mg/mL with 89 ± 2.3%and 85 ± 2.7% for the ethanol and aqueous extracts, respectively. The lowest percentage of inhibition was observed at 0.3125 mg/mL, with 54.67 ± 3.38% and 49 ± 2.64% for the ethanol and aqueous extract, respectively. No significant differences were observed between the two extracts at 5 mg/mL with an inhibitory percentage of 90.67 ± 3.05% (ethanol) and 89.33 ± 2.08% (aqueous).

Conclusion

Extracts of P. americana seeds possess nematocidal activity, however, further in silico and in vivo investigations are necessary to confirm their anthelminthic activity.

Exploring the Chain Release Mechanism from an Atypical Apicomplexan Polyketide Synthase

Polyketide synthases (PKSs) are megaenzymes that form chemically diverse polyketides and are found within the genomes of nearly all classes of life. We recently discovered the type I PKS from the apicomplexan parasite Toxoplasma gondii, TgPKS2, which contains a unique putative chain release mechanism that includes ketosynthase (KS) and thioester reductase (TR) domains. Our bioinformatic analysis of the thioester reductase of TgPKS2, TgTR, suggests differences compared to other systems and hints at a possibly conserved release mechanism within the apicomplexan subclass Coccidia. To evaluate this release module, we first isolated TgTR and observed that it is capable of 4 electron (4e-) reduction of octanoyl-CoA to the primary alcohol, octanol, utilizing NADH. TgTR was also capable of generating octanol in the presence of octanal and NADH, but no reactions were observed when NADPH was supplied as a cofactor. To biochemically characterize the protein, we measured the catalytic efficiency of TgTR using a fluorescence assay and determined the TgTR binding affinity for cofactor and substrates using isothermal titration calorimetry (ITC). We additionally show that TgTR is capable of reducing an acyl carrier protein (ACP)-tethered substrate by liquid chromatography mass spectrometry and determine that TgTR binds to holo-TgACP4, its predicted cognate ACP, with a KD of 5.75 ± 0.77 μM. Finally, our transcriptional analysis shows that TgPKS2 is upregulated ∼4-fold in the parasite's cyst-forming bradyzoite stage compared to tachyzoites. Our study identifies features that distinguish TgPKS2 from well-characterized systems in bacteria and fungi and suggests it aids the T. gondii cyst stage.

Molecular interaction analysis of the lignans from Piper cubeba in complex with Haemonchus contortus phosphomethyltransferase

In vitro larvicidal assays carried out previously by our research group with cubebin, dihydrocubebin and hinokinin, lignans extracted from the fruits of Piper cubeba, against Haemonchus contortus larvae showed strong action larvicidal these compounds. Hinokinin was the most active (EC50 = 0.34 µg/mL) with strong action on the cuticle of the larvae as observed by scanning electron microscopy of the L3 stage. Therefore, to understand the mechanism of action of these compounds in silico studies were carried out using the enzyme phosphomethyltransferase of Haemonchus contortus that contain PMT-1 and PMT-2 di-domains responsible for phosphocholine synthesis, which is one of the main lipids in nematodes. This pathway is not found in mammals, so this enzyme is an important biological target for the development of new anthelmintics. Results of molecular docking, molecular dynamic and a density functional theory calculations studies with the three lignans show few interactions with PMT-1. However, hinokinin has important interactions with PMT-2, that can deactivate the enzyme and interrupt the phosphocholine synthesis, which is an essential compound for the development and maintenance of the nematode cuticle and its survive. Therefore, the previous results of the in vitro assay allied with in silico results, now realized; suggest that hinokinin may be a possible selective target for the development of new anthelmintics against Haemonchus contortus since the PMT-2 domain is present in this nematode.

Secondary Metabolites, Biological Activities, and Industrial and Biotechnological Importance of Aspergillus sydowii

Marine-derived fungi are renowned as a source of astonishingly significant and synthetically appealing metabolites that are proven as new lead chemicals for chemical, pharmaceutical, and agricultural fields. Aspergillus sydowii is a saprotrophic, ubiquitous, and halophilic fungus that is commonly found in different marine ecosystems. This fungus can cause aspergillosis in sea fan corals leading to sea fan mortality with subsequent changes in coral community structure. Interestingly, A. sydowi is a prolific source of distinct and structurally varied metabolites such as alkaloids, xanthones, terpenes, anthraquinones, sterols, diphenyl ethers, pyrones, cyclopentenones, and polyketides with a range of bioactivities. A. sydowii has capacity to produce various enzymes with marked industrial and biotechnological potential, including α-amylases, lipases, xylanases, cellulases, keratinases, and tannases. Also, this fungus has the capacity for bioremediation as well as the biocatalysis of various chemical reactions. The current work aimed at focusing on the bright side of this fungus. In this review, published studies on isolated metabolites from A. sydowii, including their structures, biological functions, and biosynthesis, as well as the biotechnological and industrial significance of this fungus, were highlighted. More than 245 compounds were described in the current review with 134 references published within the period from 1975 to June 2023.

Comprehensive chemical profiling of Bassia indica Wight. aerial parts extract using UPLC-ESI-MS/MS, and its antiparasitic activity in Trichinella spiralis infected mice: in silico supported in vivo study

BACKGROUND

Trichinellosis is a public health threat infected both animals and humans as a result of eating undercooked meat. It caused by Trichinella spiralis that has widespread drug resistance and even developed many sophisticated strategies for their survival, this increases the demand in searching for new anthelmintic drugs from natural source.

METHODS

Our objectives were to test the in vitro and in vivo anthelmintic activity of Bassia indica BuOH frac., and to characterize its chemical composition using UPLC-ESI-MS/MS. Besides an in silico molecular docking study with the prediction of the PreADMET properties.

RESULTS

In vitro investigation of B. indica BuOH frac., showed severe destruction of the adult worm and larvae, marked cuticle swelling, areas with vesicles, blebs and loss of annulations. This was assured via in vivo study, which revealed a significant reduction (P < 0.05) in the mean adult worm count with efficacy of 47.8% along with a significant decrease (P < 0.001) in the mean larval count per gram muscle with efficacy 80.7%. Histopathological examinations of the small intestine and muscular sections showed marked improvement. In addition, immunohistochemical findings demonstrated that B. indica BuOH frac. depressed the proinflammatory cytokines expressions of TNF-α, which was obviously upregulated by T. spiralis. Precise chemical investigation of the BuOH frac. using UPLC-ESI-MS/MS resulted in the identification of 13 oleanolic type triterpenoid saponins; oleanolic acid 3-O-6´-O-methyl-β-D-glucurono-pyranoside (1), chikusetsusaponin-IVa (2) and its methyl ester (3), chikusetsusaponin IV (4) and its methyl ester (5), momordin-Ic (6) and its methyl ester (7), betavulgaroside-I (8), -II (9) -IV (10), -X (11), licorice-saponin-C₂ (12) and -J₂ (13). In addition, 6 more phenolics were identified as syringaresinol (14), 3,4-di-O-caffeoylquinic acid (15), 3-O-caffeoyl-4-O-dihydrocaffeoylquinic acid (16), 3,4-di-O-caffeoylquinic acid butyl ester (17), 3,5-di-O-galloyl-4-O-digalloylquinic acid (18) and quercetin 3-O-(6´´-feruloyl)-sophoroside (19). The auspicious anthelmintic activity was further ascertained using in silico molecular docking approach that targeted certain protein receptors (β-tubulin monomer, tumor necrosis factor alpha (TNF-α), cysteine protease (Ts-CF1), calreticulin protein (Ts-CRT)), all the docked compounds (1-19) fit into the binding site of the active pocket with binding affinities noteworthy than albendazole. In addition, ADMET properties, drug score and drug likeness were predicted for all compounds.

Antihelminthic Activity of Lophira Lanceolata on Heligmosomoides polygyrus Using an Automated High-Throughput Method

Background

There are about 13 parasitic infections that are responsible for significant morbidity and mortality but have not received the attention they deserve; thus, they are now known as "neglected tropical diseases" (NTDs). This study was aimed at evaluating the antihelminthic activities of Lophira lanceolata using an automated high-throughput method.

Methods

The antihelminthic activity effect of the extracts against H. polygyrus was determined using an automated high-throughput method. For the egg-hatching test, 100 μL of embryonated egg suspension (60 eggs) was added to 100 μL of various concentrations of extracts, levamisole, and 1.5% DMSO in a 96-well round-bottom microtitre plate. After mixing, the 96-well microplate was placed in WMicroTracker and incubated for 24 h at 25°C; the movements were recorded every 30 minutes. The same procedure was used for the larval motility assays, where 100 μL of L1 or L2 larvae (50 larvae) were put in contact with 100 μL of various concentrations of extracts.

Results

The ovicidal activity (hatching) had an IC₅₀ of 1.4 mg/mL for the ethanol extract. The aqueous and ethanol extracts of L. lanceolata showed larvicidal activity on the L1 larvae with IC₅₀ of 1.85 mg/mL and 2.4 mg/mL, respectively, as well as on the L2 larvae with IC₅₀ values of 1.08 mg/mL and 1.02 mg/mL for the aqueous and ethanol extracts, respectively. These results showed that the aqueous extract exhibited a stronger inhibitory power on the hatching rate of parasites than ethanol extracts, while the contrary effect was observed for the larval motility assays.

Conclusion

This study provides scientific data on the use of L. lanceolata by the local population for the treatment of helminthiases. However, in vivo and toxicity tests are necessary to assess its activity and safety.

Salt-Tolerant Plants as Sources of Antiparasitic Agents for Human Use: A Comprehensive Review

Parasitic diseases, especially those caused by protozoans and helminths, such as malaria, trypanosomiasis, leishmaniasis, Chagas disease, schistosomiasis, onchocerciasis, and lymphatic filariasis, are the cause of millions of morbidities and deaths every year, mainly in tropical regions. Nature has always provided valuable antiparasitic agents, and efforts targeting the identification of antiparasitic drugs from plants have mainly focused on glycophytes. However, salt-tolerant plants (halophytes) have lately attracted the interest of the scientific community due to their medicinal assets, which include antiparasitic properties. This review paper gathers the most relevant information on antiparasitic properties of halophyte plants, targeting human uses. It includes an introduction section containing a summary of some of the most pertinent characteristics of halophytes, followed by information regarding the ethnomedicinal uses of several species towards human parasitic diseases. Then, information is provided related to the antiprotozoal and anthelmintic properties of halophytes, determined by in vitro and in vivo methods, and with the bioactive metabolites that may be related to such properties. Finally, a conclusion section is presented, addressing perspectives for the sustainable exploitation of selected species.

An Inventory of Anthelmintic Plants across the Globe

A wide range of novelties and significant developments in the field of veterinary science to treat helminth parasites by using natural plant products have been assessed in recent years. To the best of our knowledge, to date, there has not been such a comprehensive review of 19 years of articles on the anthelmintic potential of plants against various types of helminths in different parts of the world. Therefore, the present study reviews the available information on a large number of medicinal plants and their pharmacological effects, which may facilitate the development of an effective management strategy against helminth parasites. An electronic search in four major databases (PubMed, Scopus, Web of Science, and Google Scholar) was performed for articles published between January 2003 and April 2022. Information about plant species, local name, family, distribution, plant tissue used, and target parasite species was tabulated. All relevant studies meeting the inclusion criteria were assessed, and 118 research articles were included. In total, 259 plant species were reviewed as a potential source of anthelmintic drugs. These plants can be used as a source of natural drugs to treat helminth infections in animals, and their use would potentially reduce economic losses and improve livestock production.

Antiparasitic Tannin-Rich Plants from the South of Europe for Grazing Livestock: A Review

Internal parasites are one of the main causes of health threats in livestock production, especially in extensive livestock farming. Despite the environmental toxic effects (loss of dung beetles, biodiversity, and other issues) and resistance phenomenon derived from their prolonged use, anti-parasitic chemical pharmaceuticals are frequently used, even in organic farming. Such a situation within the context of climate change requires urgent exploration of alternative compounds to solve these problems and apparent conflicts between organic farming objectives regarding the environment, public health, and animal health. This review is focused on some plants (Artemisia spp., Cichorium intybus L., Ericaceae family, Hedysarum coronarium L., Lotus spp., Onobrychis viciifolia Scop.) that are well known for their antiparasitic effect, are voluntarily grazed and ingested, and can be spontaneously found or cultivated in southern Europe and other regions with a Mediterranean climate. The differences found between effectiveness, parasite species affected, in vitro/in vivo experiments, and active compounds are explored. A total of 87 papers where antiparasitic activity of those plants have been studied are included in this review; 75% studied the effect on ruminant parasites, where gastrointestinal nematodes were the parasite group most studied (70%), and these included natural (31%) and experimental (37%) infections.

Anthelmintic Agents from African Medicinal Plants: Review and Prospects

Soil-transmitted helminthiasis affects more than 1.5 billion people globally and largely remains a sanitary problem in Africa. These infections place a huge economic burden on poor countries and affect livestock production, causing substantial economic losses and poor animal health. The emergence of anthelmintic resistance, especially in livestock, and the potential for its widespread in humans create a need for the development of alternative therapies. Medicinal plants play a significant role in the management of parasitic diseases in humans and livestock, especially in Africa. This report reviews anthelmintic studies that have been conducted on medicinal plants growing in Africa and published within the past two decades. A search was made in various electronic databases, and only full articles in English were included in the review. Reports show that aqueous and hydroalcoholic extracts and polar fractions obtained from these crude extracts form the predominant (80%) form of the extracts studied. Medicinal plants, extracts, and compounds with different chemical groups have been studied for their anthelmintic potential. Polyphenols and terpenoids are the most reported groups. More than 64% of the studies employed in vitro assays against parasitic and nonparasitic nematode models. Egg hatch inhibition, larval migration inhibition, and paralysis are the common parameters assessed in vitro. About 72% of in vivo models involved small ruminants, 15% rodents, and 5% chicken. Egg and worm burden are the main factors assessed in vivo. There were no reports on interventions in humans cited within the period under consideration. Also, few reports have investigated the potential of combining plant extracts with common anthelmintic drugs. This review reveals the huge potential of African medicinal plants as sources of anthelmintic agents and the dire need for in-depth clinical studies of extracts, fractions, and compounds from African plants as anthelmintic agents in livestock, companion animals, and humans.

PharmacoGenetic targeting of a C. elegans essential neuron provides an in vivo screening for novel modulators of nematode ion channel function

Chemical or drug treatments are successfully used to treat parasitic nematode infections that impact human, animal and plant health. Many of these exert their effects through modifying neural function underpinning behaviours essential for parasite viability. Selectivity against the parasite may be achieved through distinct pharmacological properties of the parasite nervous system, as exemplified by the success of the ivermectin which target a glutamate-gated chloride channel found only in invertebrates. Despite the success of the ivermectins, emerging resistance and concerns around eco-toxicity are driving the search for new nematocidal chemicals or drugs. Here, we describe the potential of a 5-HT-gated chloride channel MOD-1, which is involved in vital parasite behaviours with constrained distribution in the invertebrate phyla. This ion channel has potential pharmacophores that could be targeted by new nematocidal chemicals and drugs. We have developed a microtiter based bioassay for MOD-1 pharmacology based on its ectopic expression in the Caenorhabditis elegans essential neuron M4. We have termed this technology 'PhaGeM4' for 'Pharmacogenetic targeting of M4 neuron'. Exposure of transgenic worms harbouring ectopically expressed MOD-1 to 5-HT results in developmental arrest. By additional expression of a fluorescence marker in body wall muscle to monitor growth we demonstrate that this assay is suitable for the identification of receptor agonists and antagonists. Indeed, the developmental progression is a robustly quantifiable bioassay that resolves MOD-1 activation by quipazine, 5-carboxyamidotryptamine and fluoxetine and highlight methiothepin as a potent antagonist. This assay has the intrinsic ability to highlight compounds with optimal bioavailability and furthermore to filter out off-target effects. It can be extended to the investigation of other classes of membrane receptors and modulators of neuronal excitation. This approach based on heterologous modulation of the essential M4 neuron function offers a route to discover new effective and selective anthelmintics potentially less confounded by disruptive environmental impact.

Oscillatoria sp. as a Potent Anti-phytopathogenic Agent and Plant Immune Stimulator Against Root-Knot Nematode of Soybean cv. Giza 111

BACKGROUND

Plant-parasitic nematodes are one of the major constraints to soybean production around the world. Plant-parasitic nematodes cause an estimated $78 billion in annual crop losses worldwide, with a 10-15% crop yield loss on average. Consequently, finding and applying sustainable methods to control diseases associated with soybean is currently in serious need.

METHODS

In this study, we isolated, purified, characterized, and identified a novel cyanobacterial strain Oscillatoria sp. (blue-green alga). Based on its microscopic examination and 16S rRNA gene sequence, the aqueous and methanolic extracts of Oscillatoria were used to test their nematicidal activity against Meloidogyne incognita hatchability of eggs after 72 h of exposure time and juvenile mortality percentage in vitro after 24, 48, and 72 h of exposure time and reduction percentage of galls, eggmass, female number/root, and juveniles/250 soil. Also, the efficacy of the extract on improving the plant growth parameter and chlorophyll content under greenhouse conditions on soybean plant cv. Giza 111 was tested. Finally, the expression of PR-1, PR-2, PR-5, and PR15 (encoding enzymes) genes contributing to plant defense in the case of M. incognita invasion was studied and treated with Oscillatoria extract.

RESULTS

The aqueous and methanolic extracts of Oscillatoria sp. had nematicidal activity against M. incognita. The percentage of mortality and egg hatching of M. incognita were significantly increased with the increase of time exposure to Oscillatoria extract 96.7, 97, and 98 larvae mortality % with S concentration after 24, 48, and 72 h of exposure time. The aqueous extract significantly increased the percentage of Root-Knot nematodes (RKN) of egg hatching, compared with Oxamyl and methanol extract at 96.7 and 97% after 72 h and 1 week, respectively. With the same concentration in the laboratory experiment. Furthermore, water extracts significantly reduced the number of galls in soybean root, egg masses, and female/root by 84.1, 87.5, and 92.2%, respectively, as well as the percentage of J2s/250 g soil by 93.7%. Root, shoot lengths, dry weight, number of pods/plant, and chlorophyll content of soybean treated with Oscillatoria water extract were significantly higher than the control increasing by 70.3, 94.1, 95.5, and 2.02%, respectively. The plant defense system's gene expression was tracked using four important pathogenesis-related genes, PR-1, PR-2, PR-5, and PR15, which encode enzymes involved in plant defense.

CONCLUSIONS

Oscillatoria extract is a potential nematicide against root-knot nematode invasion in soybean.

Albatrellus confluens (Alb. & Schwein.) Kotl. & Pouz.: Natural Fungal Compounds and Synthetic Derivatives with In Vitro Anthelmintic Activities and Antiproliferative Effects against Two Human Cancer Cell Lines

Neglected tropical diseases affect the world's poorest populations with soil-transmitted helminthiasis and schistosomiasis being among the most prevalent ones. Mass drug administration is currently the most important control measure, but the use of the few available drugs is giving rise to increased resistance of the parasites to the drugs. Different approaches are needed to come up with new therapeutic agents against these helminths. Fungi are a source of secondary metabolites, but most fungi remain largely uninvestigated as anthelmintics. In this report, the anthelmintic activity of Albatrellus confluens against Caenorhabditis elegans was investigated using bio-assay guided isolation. Grifolin (1) and neogrifolin (2) were identified as responsible for the anthelmintic activity. Derivatives 4-6 were synthesized to investigate the effect of varying the prenyl chain length on anthelmintic activity. The isolated compounds 1 and 2 and synthetic derivatives 4-6, as well as their educts 7-10, were tested against Schistosoma mansoni (adult and newly transformed schistosomula), Strongyloides ratti, Heligmosomoides polygyrus, Necator americanus, and Ancylostoma ceylanicum. Prenyl-2-orcinol (4) and geranylgeranyl-2-orcinol (6) showed promising activity against newly transformed schistosomula. The compounds 1, 2, 4, 5, and 6 were also screened for antiproliferative or cytotoxic activity against two human cancer lines, viz. prostate adenocarcinoma cells (PC-3) and colorectal adenocarcinoma cells (HT-29). Compound 6 was determined to be the most effective against both cell lines with IC₅₀ values of 16.1 µM in PC-3 prostate cells and 33.7 µM in HT-29 colorectal cells.

Low-Molecular-Weight Secondary Metabolites from Fungi: Cerrena unicolor as a New Proposal of an Effective Preparation against Rhabditis Nematodes

Plants and fungi are known as a valuable source of natural medicines used in the treatment of various diseases. Many of them are used to treat human and animal gastrointestinal diseases caused by parasites. The aim of this study was to investigate for the first time the antinematode properties of extracellular low-molecular subfractions (ex-LMS) obtained from the liquid growth medium of idiophasic Cerrena unicolor cultures. The fungal fractions were isolated according to a procedure previously described by Jaszek et al. The in vitro tests were performed using nematodes of the Rhabditis genus. As demonstrated by the results, the total fraction with a molecular weight < 10 kDa (CU-A) and the 0.02−1.5 kDa fraction (CU-B) had nematicidal activity. It was found that the analyzed substances induced movement disturbances caused by the paralysis of the back part of the nematode’s body. The degree of body paralysis was proportional to the increase in the concentration of the tested fractions. Summarizing the obtained results in the context of the available literature data, it seems that C. unicolor may be a good new candidate for research on nematode infections.

A validated high-throughput method for assaying rat lungworm (Angiostrongylus cantonensis) motility when challenged with potentially anthelmintic natural products from Hawaiian fungi

Parasitic nematodes devastate human and animal health. The limited number of anthelmintics available is concerning, especially because of increasing drug resistance. Anthelmintics are commonly derived from natural products, e.g. fungi and plants. This investigation aimed to develop a high-throughput whole organism screening method based on a motility assay using the wMicroTracker system. Anthelmintic activity of extracts from Hawaiian fungi was screened against third-stage larvae of the parasitic nematode Angiostrongylus cantonensis , categorized according to the degree of motility reduction. Of the 108 crude samples and fractionated products, 48 showed some level of activity, with 13 reducing motility to 0–25% of the maximum exhibited, including two pure compounds, emethacin B and epicoccin E, neither previously known to exhibit anthelmintic properties. The process of bioassay-guided fractionation is illustrated in detail based on analysis of one of the crude extracts, which led to isolation of lamellicolic anhydride, a compound with moderate activity. This study validates the wMicroTracker system as an economical and high-throughput option for testing large suites of natural products against A. cantonensis , adds to the short list of diverse parasites for which it has been validated and highlights the value of A. cantonensis and Hawaiian fungi for discovery of new anthelmintics.

Volatile Organic Compounds from Bacillus aryabhattai MCCC 1K02966 with Multiple Modes against Meloidogyne incognita

Plant-parasitic nematodes cause severe losses to crop production and economies all over the world. Bacillus aryabhattai MCCC 1K02966, a deep-sea bacterium, was obtained from the Southwest Indian Ocean and showed nematicidal and fumigant activities against Meloidogyne incognita in vitro. The nematicidal volatile organic compounds (VOCs) from the fermentation broth of B. aryabhattai MCCC 1K02966 were investigated further using solid-phase microextraction gas chromatography-mass spectrometry. Four VOCs, namely, pentane, 1-butanol, methyl thioacetate, and dimethyl disulfide, were identified in the fermentation broth. Among these VOCs, methyl thioacetate exhibited multiple nematicidal activities, including contact nematicidal, fumigant, and repellent activities against M. incognita. Methyl thioacetate showed a significant contact nematicidal activity with 87.90% mortality at 0.01 mg/mL by 72 h, fumigant activity in mortality 91.10% at 1 mg/mL by 48 h, and repellent activity at 0.01-10 mg/mL. In addition, methyl thioacetate exhibited 80-100% egg-hatching inhibition on the 7th day over the range of 0.5 mg/mL to 5 mg/mL. These results showed that methyl thioacetate from MCCC 1K02966 control M. incognita with multiple nematicidal modes and can be used as a potential biological control agent.

Correlation Effects in Trimeric Acylphloroglucinols

Trimeric acylphloroglucinols (T-ACPLs) are a subclass of the large class of acylphloroglucinols—derivatives of 1,3,5-trihydroxybenzene containing an R–C=O group. T-ACPL molecules contain three acylphloroglucinol moieties linked by methylene bridges. Many of them are present in natural sources and exhibit biological activities, often better than the corresponding activities of monomeric acylphloroglucinols. All the stable conformers of T-ACPLs contain seven intramolecular hydrogen bonds, which constitute the dominant stabilising factors. A total of 38 different T-ACPLs, including both naturally occurring and model molecules, have been calculated at the HF and DFT/B3LYP levels. The DFT/B3LYP calculations were carried out both without and with Grimme’s dispersion correction, to highlight the dispersion (and, therefore, also electron correlation) effects for these molecules. The roles of dispersion are evaluated considering the effects of Grimme’s correction on the estimation of the conformers’ energies, the description of the characteristics of the individual hydrogen bonds, the conformers’ geometries and other molecular properties. Overall, the results offer a comprehensive overview of the conformational preferences of T-ACPL molecules, their intramolecular hydrogen bond patterns, and the correlation effects on their properties.

Green Veterinary Pharmacology Applied to Parasite Control: Evaluation of Punica granatum, Artemisia campestris, Salix caprea Aqueous Macerates against Gastrointestinal Nematodes of Sheep

Resistance to anthelmintic drugs in gastrointestinal nematodes (GIN) of sheep is of high concern for livestock production worldwide. In Calabria (southern Italy), many plants have been used in ethnoveterinary medicine for parasite control in small ruminants. Here, we present an in vivo evaluation of anthelmintic efficacy of three plant extracts. The first was based on bark and leaves of Salix caprea, the second and the third were based on the whole plant Artemisia campestris and whole fruit (seeds and peel) of Punica granatum, respectively. Anthelmintic efficacy was evaluated according to the fecal egg count reduction test (FECRT) performed with the FLOTAC technique. The results showed a significant anthelmintic effect of Punica granatum macerate (50%), a low effectiveness of the Artemisia campestris macerate (20%), and a complete ineffectiveness of Salix caprea macerate (0.1%). With these outcomes, we report a P. granatum-based remedy reducing 50% GIN egg output. This result was obtained without using any synthetic drug, paving the way for the employment of green veterinary pharmacology (GVP) as a complementary and sustainable method to reduce the use of chemicals and to counteract anthelmintic resistance.

Maca against Echinococcosis?-A Reverse Approach from Patient to In Vitro Testing

Drug-based treatment of alveolar echinococcosis (AE) with benzimidazoles is in most cases non-curative, thus has to be taken lifelong. Here, we report on a 56-year-old male AE patient who received standard benzimidazole treatment and biliary plastic stents, and additionally self-medicated himself with the Peruvian plant extract Maca (Lepidium meyenii). After 42 months, viable parasite tissue had disappeared. Based on this striking observation, the anti-echinococcal activity of Maca was investigated in vitro and in mice experimentally infected with Echinococcus multilocularis metacestodes. Albendazole (ABZ)-treated mice and mice treated with an ABZ+Maca combination exhibited a significantly reduced parasite burden compared to untreated or Maca-treated mice. As shown by a newly established UHPLC-MS/MS-based measurement of ABZ-metabolites, the presence of Maca during the treatment did not alter ABZ plasma levels. In vitro assays corroborated these findings, as exposure to Maca had no notable effect on E. multilocularis metacestodes, and in cultures of germinal layer cells, possibly unspecific, cytotoxic effects of Maca were observed. However, in the combined treatments, Maca inhibited the activity of ABZ in vitro. While Maca had no direct anti-parasitic activity, it induced in vitro proliferation of murine spleen cells, suggesting that immunomodulatory properties could have contributed to the curative effect seen in the patient.

Natural Products Are a Promising Source for Anthelmintic Drug Discovery

Parasitic nematodes infect almost all forms of life. In the human context, parasites are one of the major causative factors for physical and intellectual growth retardation in the developing world. In the agricultural setting, parasites have a great economic impact through a reduction in livestock performance or control cost. The main method of controlling these devastating conditions is the use of anthelmintic drugs. Unfortunately, there are only a few anthelmintic drug classes available in the market and significant resistance has developed in most of the parasitic species of livestock. Therefore, development of new anthelmintics with different modes of action is critical for sustainable parasitic control in the future. The drug development pipeline is broadly limited to two types of molecules, namely synthetic compounds and natural plant products. Compared to synthetic compounds, natural products are highly diverse, and many have historically proven valuable in folk medicine to treat various gastrointestinal ailments. This review focus on the use of traditional knowledge-based plant extracts in the development of new therapeutic leads, the approaches used as screening techniques, and common bottlenecks and opportunities in plant-based anthelmintic drug discovery.

High Throughput Screening of the NatureBank 'Marine Collection' in a Haemonchus Bioassay Identifies Anthelmintic Activity in Extracts from a Range of Sponges from Australian Waters

Widespread resistance in parasitic nematodes to most classes of anthelmintic drugs demands the discovery and development of novel compounds with distinct mechanisms of action to complement strategic or integrated parasite control programs. Products from nature-which assume a diverse 'chemical space'-have significant potential as a source of anthelmintic compounds. In the present study, we screened a collection of extracts (n = 7616) derived from marine invertebrates sampled from Australian waters in a high throughput bioassay for in vitro anti-parasitic activity against the barber's pole worm (Haemonchus contortus)-an economically important parasitic nematode of livestock animals. In this high throughput screen (HTS), we identified 58 active extracts that reduced larval motility by ≥70% (at 90 h), equating to an overall 'hit rate' of ~0.8%. Of these 58 extracts, 16 also inhibited larval development by ≥80% (at 168 h) and/or induced 'non-wild-type' (abnormal) larval phenotypes with reference to 'wild-type' (normal) larvae not exposed to extract (negative controls). Most active extracts (54 of 58) originated from sponges, three from chordates (tunicates) and one from a coral; these extracts represented 37 distinct species/taxa of 23 families. An analysis of samples by 1H NMR fingerprinting was utilised to dereplicate hits and to prioritise a set of 29 sponge samples for future chemical investigation. Overall, these results indicate that a range of sponge species from Australian waters represents a rich source of natural compounds with nematocidal or nematostatic properties. Our plan now is to focus on in-depth chemical investigations of the sample set prioritised herein.

Multipurpose peptides: The venoms of Amazonian stinging ants contain anthelmintic ponericins with diverse predatory and defensive activities

In the face of increasing drug resistance, the development of new anthelmintics is critical for controlling nematodes that parasitise livestock. Although hymenopteran venom toxins have attracted attention for applications in agriculture and medicine, few studies have explored their potential as anthelmintics. Here we assessed hymenopteran venoms as a possible source of new anthelmintic compounds by screening a panel of ten hymenopteran venoms against Haemonchus contortus, a major pathogenic nematode of ruminants. Using bioassay-guided fractionation coupled with liquid chromatography-tandem mass spectrometry, we identified four novel anthelmintic peptides (ponericins) from the venom of the neotropical ant Neoponera commutata and the previously described ponericin M-PONTX-Na1b from Neoponera apicalis venom. These peptides inhibit H. contortus development with IC₅₀ values of 2.8-5.6 μM. Circular dichroism spectropolarimetry indicated that the ponericins are unstructured in aqueous solution but adopt α-helical conformations in lipid mimetic environments. We show that the ponericins induce non-specific membrane perturbation, which confers broad-spectrum antimicrobial, insecticidal, cytotoxic, hemolytic, and algogenic activities, with activity across all assays typically correlated. We also show for the first time that ponericins induce spontaneous pain behaviour when injected in mice. We propose that the broad-spectrum activity of the ponericins enables them to play both a predatory and defensive role in neoponeran ants, consistent with their high abundance in venom. This study reveals a broader functionality for ponericins than previously assumed, and highlights both the opportunities and challenges in pursuing ant venom peptides as potential therapeutics.

The interplay between Trichuris and the microbiota

Parasitic worms are amongst the most common pathogens to infect humans and have a long-established history of inflicting disease in their hosts. There is a large body of evidence that states intestine-dwelling helminths ensure their survival by influencing the host immune response against them. In recent years, it has become apparent that the large and diverse microbial communities that exist in the gastrointestinal (GI) tract of the host and within the parasite itself have a pivotal role in worm survival and persistence. Using a variety of mouse models (including laboratory, germ-free and rewilded mice), there have been new insights into how bacteria and worms interact with each other; this includes the discovery that Trichuris is unable to hatch and/or infect their host in the absence of bacteria, and that these worms contain a Trichuris-specific gut microbiota. These interactions are determined in part by the capacity of the host, gut microbiota and worms to communicate via metabolites such as butyrate, which are microbially derived and have known immunoregulatory properties. By exploring the contribution of gut bacteria to worm infections and the intricate relationship that exists between them, an exciting and emerging field in whipworm parasitology is established.

Action of Carvacrol on Parascaris sp. and Antagonistic Effect on Nicotinic Acetylcholine Receptors

Parascaris sp. is the only ascarid parasitic nematode in equids and one of the most threatening infectious organisms in horses. Only a limited number of compounds are available for treatment of horse helminthiasis, and Parascaris sp. worms have developed resistance to the three major anthelmintic families. In order to overcome the appearance of resistance, there is an urgent need for new therapeutic strategies. The active ingredients of herbal essential oils are potentially effective antiparasitic drugs. Carvacrol is one of the principal chemicals of essential oil from Origanum, Thymus, Coridothymus, Thymbra, Satureja and Lippia herbs. However, the antiparasitic mode of action of carvacrol is poorly understood. Here, the objective of the work was to characterize the activity of carvacrol on Parascaris sp. nicotinic acetylcholine receptor (nAChR) function both in vivo with the use of worm neuromuscular flap preparations and in vitro with two-electrode voltage-clamp electrophysiology on nAChRs expressed in Xenopus oocytes. We developed a neuromuscular contraction assay for Parascaris body flaps and obtained acetylcholine concentration-dependent contraction responses. Strikingly, we observed that 300 µM carvacrol fully and irreversibly abolished Parascaris sp. muscle contractions elicited by acetylcholine. Similarly, carvacrol antagonized acetylcholine-induced currents from both the nicotine-sensitive AChR and the morantel-sensitive AChR subtypes. Thus, we show for the first time that body muscle flap preparation is a tractable approach to investigating the pharmacology of Parascaris sp. neuromuscular system. Our results suggest an intriguing mode of action for carvacrol, being a potent antagonist of muscle nAChRs of Parascaris sp. worms, which may account for its antiparasitic potency.

Effects of Propolis on Infectious Diseases of Medical Relevance

Infectious diseases are a significant problem affecting the public health and economic stability of societies all over the world. Treatment is available for most of these diseases; however, many pathogens have developed resistance to drugs, necessitating the development of new therapies with chemical agents, which can have serious side effects and high toxicity. In addition, the severity and aggressiveness of emerging and re-emerging diseases, such as pandemics caused by viral agents, have led to the priority of investigating new therapies to complement the treatment of different infectious diseases. Alternative and complementary medicine is widely used throughout the world due to its low cost and easy access and has been shown to provide a wide repertoire of options for the treatment of various conditions. In this work, we address the relevance of the effects of propolis on the causal pathogens of the main infectious diseases with medical relevance; the existing compiled information shows that propolis has effects on Gram-positive and Gram-negative bacteria, fungi, protozoan parasites and helminths, and viruses; however, challenges remain, such as the assessment of their effects in clinical studies for adequate and safe use.

Isolation and Characterization of Strain Exiguobacterium sp. KRL4, a Producer of Bioactive Secondary Metabolites from a Tibetan Glacier

Extremophilic microorganisms represent a unique source of novel natural products. Among them, cold adapted bacteria and particularly alpine microorganisms are still underexplored. Here, we describe the isolation and characterization of a novel Gram-positive, aerobic rod-shaped alpine bacterium (KRL4), isolated from sediments from the Karuola glacier in Tibet, China. Complete phenotypic analysis was performed revealing the great adaptability of the strain to a wide range of temperatures (5-40 °C), pHs (5.5-8.5), and salinities (0-15% w/v NaCl). Genome sequencing identified KRL4 as a member of the placeholder genus Exiguobacterium_A and annotation revealed that only half of the protein-encoding genes (1522 of 3079) could be assigned a putative function. An analysis of the secondary metabolite clusters revealed the presence of two uncharacterized phytoene synthase containing pathways and a novel siderophore pathway. Biological assays confirmed that the strain produces molecules with antioxidant and siderophore activities. Furthermore, intracellular extracts showed nematocidal activity towards C. elegans, suggesting that strain KRL4 is a source of anthelmintic compounds.

Essential oils from Ocimum basilicum cultivars: analysis of their composition and determination of the effect of the major compounds on Haemonchus contortus eggs

The continuous use of synthetic anthelmintics against gastrointestinal nematodes (GINs) has resulted in the increased resistance, which is why alternative methods are being sought, such as the use of natural products. Plant essential oils (EOs) have been considered as potential products for the control of GINs. However, the chemical composition and, consequently, the biological activity of EOs vary in different plant cultivars. The aim of this study was to evaluate the anthelmintic activity of EOs from cultivars of Ocimum basilicum L. and that of their major constituents against Haemonchus contortus. The EOs from 16 cultivars as well the pure compound linalool, methyl chavicol, citral and eugenol were used in the assessment of the inhibition of H. contortus egg hatch. In addition, the composition of three cultivars was simulated using a combination of the two major compounds from each. The EOs from different cultivars showed mean Inhibition Concentration (IC50) varying from 0.56 to 2.22 mg/mL. The cultivar with the highest egg-hatch inhibition, Napoletano, is constituted mainly of linalool and methyl chavicol. Among the individual compounds tested, citral was the most effective (IC50 0.30 mg/mL). The best combination of compounds was obtained with 11% eugenol plus 64% linalool (IC50 0.44 mg/mL), simulating the Italian Large Leaf (Richters) cultivar. We conclude that different cultivars of O. basilicum show different anthelmintic potential, with cultivars containing linalool and methyl chavicol being the most promising; and that citral or methyl chavicol isolated should also be considered for the development of new anthelmintic formulations.

Anthelmintic Activity of Antioxidants: In Vitro Effects on the Liver Fluke Opisthorchis felineus

Currently, molecular parasitologists are searching for new agents against trematodiases. Redox metabolism is important for parasites as far as long-lived adult parasites inside a mammalian host are exposed to redox challenges. Antioxidants have been poorly studied as anthelmintic agents, in particular against the foodborne trematodes. Study of in vitro anthelmintic activity of nonenzymatic natural and synthetic antioxidants of various chemical structures was performed using standard motility and mortality assays against juvenile and adult Opisthorchis felineus worms. Promising agents have been found among both natural and synthetic compounds. The mitochondria-targeted antioxidant SkQ1 [10-(6′-plastoquinonyl)decyltriphenylphosphonium] in motility assays was as effective (half-maximal inhibitory concentration [IC₅₀] 0.6–1.4 μM) as praziquantel (IC₅₀ 0.47–1.4 μM), and SkQ1 was significantly more effective than praziquantel in mortality assays. Moreover, extensive tegument damage of the adult fluke was revealed after SkQ1 treatment. Flavonoids manifested potency too, with IC₅₀ values in a micromolar range (5.1–17.4 μM). Other natural and synthetic compounds tested against helminths were significantly less effective than praziquantel. Results of our study indicate that SkQ1 and flavonoids have high anthelmintic activities against the liver flukes. We propose that structure–activity relationship research might be worthwhile based on the structures of the most effective substances.

Advances in the discovery and development of anthelmintics by harnessing natural product scaffolds

Widespread resistance to currently-used anthelmintics represents a major obstacle to controlling parasitic nematodes of livestock animals. Given the reliance on anthelmintics in many control regimens, there is a need for the continued discovery and development of new nematocides. Enabling such a focus are: (i) the major chemical diversity of natural products; (ii) the availability of curated, drug-like extract-, fraction- and/or compound-libraries from natural sources; (iii) the utility and practicality of well-established whole-worm bioassays for Haemonchus contortus-an important parasitic nematodes of livestock-to screen natural product libraries; and (iv) the availability of advanced chromatographic (HPLC), spectroscopic (NMR) and spectrometric (MS) techniques for bioassay-guided fractionation and structural elucidation. This context provides a sound basis for the identification and characterisation of anthelmintic candidates from natural sources. This chapter provides a background on the importance and impact of helminth infections/diseases, parasite control and aspects of drug discovery, and reviews recent work focused on (i) screening well-defined compound libraries to establish the methods needed for large-scale screening of natural extract libraries; (ii) discovering plant and marine extracts with nematocidal or nematostatic activity, and purifying bioactive compounds and assessing their potential for further development; and (iii) synthesising analogues of selected purified natural compounds for the identification of possible 'lead' candidates. The chapter describes some lessons learned from this work and proposes future areas of focus for drug discovery. Collectively, the findings from this recent work show potential for selected natural product scaffolds as candidates for future development. Developing such candidates via future chemical optimisation, efficacy and safety evaluations, broad spectrum activity assessments, and target identification represents an exciting prospect and, if successful, could pave the way to subsequent pre-clinical and clinical evaluations.

Combating Parasitic Nematode Infections, Newly Discovered Antinematode Compounds from Marine Epiphytic Bacteria

Parasitic nematode infections cause debilitating diseases and impede economic productivity. Antinematode chemotherapies are fundamental to modern medicine and are also important for industries including agriculture, aquaculture and animal health. However, the lack of suitable treatments for some diseases and the rise of nematode resistance to many available therapies necessitates the discovery and development of new drugs. Here, marine epiphytic bacteria represent a promising repository of newly discovered antinematode compounds. Epiphytic bacteria are ubiquitous on marine surfaces where they are under constant pressure of grazing by bacterivorous predators (e.g., protozoans and nematodes). Studies have shown that these bacteria have developed defense strategies to prevent grazers by producing toxic bioactive compounds. Although several active metabolites against nematodes have been identified from marine bacteria, drug discovery from marine microorganisms remains underexplored. In this review, we aim to provide further insight into the need and potential for marine epiphytic bacteria to become a new source of antinematode drugs. We discuss current and emerging strategies, including culture-independent high throughput screening and the utilization of Caenorhabditis elegans as a model target organism, which will be required to advance antinematode drug discovery and development from marine microbial sources.

Where are all the anthelmintics? Challenges and opportunities on the path to new anthelmintics

Control of helminth parasites is a key challenge for human and veterinary medicine. In the absence of effective vaccines and adequate sanitation, prophylaxis and treatment commonly rely upon anthelmintics. There are concerns about the development of drug resistance, side-effects, lack of efficacy and cost-effectiveness that drive the need for new classes of anthelmintics. Despite this need, only three new drug classes have reached the animal market since 2000 and no new classes of anthelmintic have been approved for human use. So where are all the anthelmintics? What are the barriers to anthelmintic discovery, and what emerging opportunities can be used to address this? This was a discussion group focus at the 2019 8th Consortium for Anthelmintic Resistance and Susceptibility (CARS) in Wisconsin, USA. Here we report the findings of the group in the broader context of the human and veterinary anthelmintic discovery pipeline, highlighting challenges unique to antiparasitic drug discovery. We comment on why the development of novel anthelmintics has been so rare. Further, we discuss potential opportunities for drug development moving into the 21st Century.

Comparative Evaluation of the In Vitro Anthelminthic Effects of the Leaves, Stem, and Seeds of Carica papaya (Linn) Using the Pheretima posthuma Model

This study was conducted to comparatively assess the anthelminthic activity of leaves, stem bark, and seeds of Carica papaya, in order to identify which of the plant parts possess the highest anthelminthic activity. Three concentrations of ethanolic and hydroethanolic extracts of the plant parts (1 mg/ml, 2.5 mg/ml, and 5 mg/ml) were prepared and tested against Pheretima posthuma using albendazole as the positive control and 0.9% normal saline solution as the negative control. Preliminary phytochemical investigation showed the presence of alkaloids, saponins, and reducing sugars of glycosides present in all the crude extracts of Carica papaya. Tannins were observed only in extracts of the leaves, while fixed oils were only present in the extracts of the seeds. The results of the anthelminthic activity testing indicated that all crude extracts prepared were more effective than albendazole in reducing paralysis time (p < 0.0001) and death time (p < 0.0001). It was further shown that the extracts from the seeds (SE and SHE) were more effective than the extracts from the stem bark and leaves both in reducing paralysis and death times. Fractionation of SE provided a fraction, SE_B, which was more effective than SE both in reducing paralysis and death times (p < 0.0001) and was established to contain fixed oils. The outcome of the current study has provided a scientific justification for the preference of the seeds of Carica papaya for the treatment of helminth infections and has shown that the fixed oils present in the seeds could be responsible for such activity.

Harnessing the gut microbiome in the fight against anthelminthic drug resistance

Intestinal helminth parasites present major challenges to the welfare of humans and threaten the global food supply. While the discovery of anthelminthic drugs empowered our ability to offset these harms to society, the alarming rise of anthelminthic drug resistance mitigates contemporary efforts to treat and control intestinal helminthic infections. Fortunately, emerging research points to potential opportunities to combat anthelminthic drug resistance by harnessing the gut microbiome as a resource for discovering novel therapeutics and informing responsible drug administration. In this review, we highlight research that demonstrates this potential and provide rationale to support increased investment in efforts to uncover and translationally utilize knowledge about how the gut microbiome mediates intestinal helminthic infection and its outcomes.

Anthelmintics in the future: current trends in the discovery and development of new drugs against gastrointestinal nematodes

The control of gastrointestinal nematodes (GINs), the most abundant and serious parasites of livestock, has become difficult because of the limited number of available drugs and fast development of drug resistance. Thus, considerable efforts have been devoted to developing new anthelmintics that are efficient against nematodes, especially resistant species. Here, we summarize the most recent results using various approaches: target-based or high-throughput screening (HTS) of compound libraries; the synthesis of new derivatives or new combinations of current anthelmintics; the repurposing of drugs currently approved for other indications; and lastly, the identification of active plant products. We also evaluate the advantages and disadvantages of each of these approaches.

Prosopis Plant Chemical Composition and Pharmacological Attributes: Targeting Clinical Studies from Preclinical Evidence

Members of the Prosopis genus are native to America, Africa and Asia, and have long been used in traditional medicine. The Prosopis species most commonly used for medicinal purposes are P. africana, P. alba, P. cineraria, P. farcta, P. glandulosa, P. juliflora, P. nigra, P. ruscifolia and P. spicigera, which are highly effective in asthma, birth/postpartum pains, callouses, conjunctivitis, diabetes, diarrhea, expectorant, fever, flu, lactation, liver infection, malaria, otitis, pains, pediculosis, rheumatism, scabies, skin inflammations, spasm, stomach ache, bladder and pancreas stone removal. Flour, syrup, and beverages from Prosopis pods have also been potentially used for foods and food supplement formulation in many regions of the world. In addition, various in vitro and in vivo studies have revealed interesting antiplasmodial, antipyretic, anti-inflammatory, antimicrobial, anticancer, antidiabetic and wound healing effects. The phytochemical composition of Prosopis plants, namely their content of C-glycosyl flavones (such as schaftoside, isoschaftoside, vicenin II, vitexin and isovitexin) has been increasingly correlated with the observed biological effects. Thus, given the literature reports, Prosopis plants have positive impact on the human diet and general health. In this sense, the present review provides an in-depth overview of the literature data regarding Prosopis plants' chemical composition, pharmacological and food applications, covering from pre-clinical data to upcoming clinical studies.