Melatonin: A look at protozoal and helminths.

Melatonin is a pleiotropic neurohormone found in different animal, plant, and microorganism species. It is a product resulting from tryptophan metabolism in the pineal gland and is widely known for its ability to synchronize the circadian rhythm to antitumor functions in different types of cancers. The molecular mechanisms responsible for its immunomodulatory, antioxidant and cytoprotective effects involve binding to high-affinity G protein-coupled receptors and interactions with intracellular targets that modulate signal transduction pathways. In vitro and in vivo studies have reported the therapeutic potential of melatonin in different infectious and parasitic diseases. In this review, the protective and pathophysiological roles of melatonin in fighting protozoan and helminth infections and the possible mechanisms involved against these stressors will be discussed.

Exogenous Transforming Growth Factor-ß1 and Its Helminth-Derived Mimic Attenuate the Heart's Inflammatory Response to Ischemic Injury and Reduce Mature Scar Size.

Coronary reperfusion after acute ST-elevation myocardial infarction (STEMI) is standard therapy to salvage ischemic heart muscle. However, subsequent inflammatory responses within the infarct lead to further loss of viable myocardium. Transforming growth factor (TGF)-ß1 is a potent anti-inflammatory cytokine released in response to tissue injury. The aim of this study was to investigate the protective effects of TGF-ß1 after MI. In patients with STEMI, there was a significant correlation (P = 0.003) between higher circulating TGF-ß1 levels at 24 hours after MI and a reduction in infarct size after 3 months, suggesting a protective role of early increase in circulating TGF-ß1. A mouse model of cardiac ischemia reperfusion was used to demonstrate multiple benefits of exogenous TGF-ß1 delivered in the acute phase. It led to a significantly smaller infarct size (30% reduction, P = 0.025), reduced inflammatory infiltrate (28% reduction, P = 0.015), lower intracardiac expression of inflammatory cytokines IL-1ß and chemokine (C-C motif) ligand 2 (>50% reduction, P = 0.038 and 0.0004, respectively) at 24 hours, and reduced scar size at 4 weeks (21% reduction, P = 0.015) after reperfusion. Furthermore, a low-fibrogenic mimic of TGF-ß1, secreted by the helminth parasite Heligmosomoides polygyrus, had an almost identical protective effect on injured mouse hearts. Finally, genetic studies indicated that this benefit was mediated by TGF-ß signaling in the vascular endothelium.

Cooperation of ILC2s and TH2 cells in the expulsion of intestinal helminth parasites.

Type 2 immune responses form a critical defence against enteric worm infections. In recent years, mouse models have revealed shared and unique functions for group 2 innate lymphoid cells and T helper 2 cells in type 2 immune response to intestinal helminths. Both cell types use similar innate effector functions at the site of infection, whereas each population has distinct roles during different stages of infection. In this Perspective, we review the underlying mechanisms used by group 2 innate lymphoid cells and T helper 2 cells to cooperate with each other and suggest an overarching model of the interplay between these cell types over the course of a helminth infection.

The parasitic worm product ES-62 protects the osteoimmunology axis in a mouse model of obesity-accelerated ageing.

Despite significant increases in human lifespan over the last century, adoption of high calorie diets (HCD) has driven global increases in type-2 diabetes, obesity and cardiovascular disease, disorders precluding corresponding improvements in healthspan. Reflecting that such conditions are associated with chronic systemic inflammation, evidence is emerging that infection with parasitic helminths might protect against obesity-accelerated ageing, by virtue of their evolution of survival-promoting anti-inflammatory molecules. Indeed, ES-62, an anti-inflammatory secreted product of the filarial nematode Acanthocheilonema viteae, improves the healthspan of both male and female C57BL/6J mice undergoing obesity-accelerated ageing and also extends median lifespan in male animals, by positively impacting on inflammatory, adipose metabolic and gut microbiome parameters of ageing. We therefore explored whether ES-62 affects the osteoimmunology axis that integrates environmental signals, such as diet and the gut microbiome to homeostatically regulate haematopoiesis and training of immune responses, which become dysregulated during (obesity-accelerated) ageing. Of note, we find sexual dimorphisms in the decline in bone health, and associated dysregulation of haematopoiesis and consequent peripheral immune responses, during obesity-accelerated ageing, highlighting the importance of developing sex-specific anti-ageing strategies. Related to this, ES-62 protects trabecular bone structure, maintaining bone marrow (BM) niches that counter the ageing-associated decline in haematopoietic stem cell (HSC) functionality highlighted by a bias towards myeloid lineages, in male but not female, HCD-fed mice. This is evidenced by the ability of ES-62 to suppress the adipocyte and megakaryocyte bias and correspondingly promote increases in B lymphocytes in the BM. Furthermore, the consequent prevention of ageing-associated myeloid/lymphoid skewing is associated with reduced accumulation of inflammatory CD11c+ macrophages and IL-1ß in adipose tissue, disrupting the perpetuation of inflammation-driven dysregulation of haematopoiesis during obesity-accelerated ageing in male HCD-fed mice. Finally, we report the ability of small drug-like molecule analogues of ES-62 to mimic some of its key actions, particularly in strongly protecting trabecular bone structure, highlighting the translational potential of these studies.

The Potential Role of the Serotonin Transporter as a Drug Target against Parasitic Infections: A Scoping Review of the Literature.

BACKGROUND: Several in vitro and in vivo biological activities of serotonin, 5- hydroxytryptamine (5-HT), as a bioactive molecule, and its transporter (5-HT-Tr) were evaluated in parasitic infections. OBJECTIVE: Herein, the roles of 5-HT and 5-HTR in helminths and protozoan infections with medical and veterinary importance are reviewed. METHODS: We searched information in 4 main databases and reviewed published literature about the serotonin transporter's role as a promising therapeutic target against pathogenic parasitic infections between 2000 and 2021. RESULTS: Based on recent investigations, 5-HT and 5-HT-Tr play various roles in parasite infections, including biological function, metabolic activity, organism motility, parasite survival, and immune response modulation. Moreover, some of the 5-HT-TR in Schistosoma mansoni showed an excess of favorite substrates for biogenic amine 5-HT compared to their mammalian hosts. Furthermore, the main neuronal protein related to the G protein-coupled receptor (GPCR) was identified in S. mansoni and Echinococcus granulosus, playing main roles in these parasites. In addition, 5-HT increased in toxoplasmosis, giardiasis, and Chagas disease. On the other hand, in Plasmodium spp., different forms of targeted 5-HTR stimulate Ca2+ release, intracellular inositol triphosphate (ITP), cAMP, and protein kinase A (PKA) activity. CONCLUSION: This review summarized the several functional roles of the 5-HT and the importance of the 5-HT-TR as a drug target with minimal harm to the host to fight against helminths and protozoan infections. Hopefully, this review will shed light on research regarding serotonin transporter-based therapies as a potential drug target soon.

MicroRNAs in Helminth Parasites: A Systematic Review.

BACKGROUND: MicroRNAs (miRNAs) are about 22-nucleotide, small, noncoding RNAs that control gene expression post-transcriptionally. Helminth parasites usually express a unique repertoire of genes, including miRNAs, across different developmental stages with subtle regulatory mechanisms. OBJECTIVE: There is a necessity to investigate the involvement of miRNAs in the development of parasites, host-parasite interaction, immune evasion and their abilities to govern infection in hosts. MiRNAs present in helminth parasites have been summarized in the current systematic review (SR). METHODS: Electronic databases, including PubMed, Scopus, ProQuest, Embase, and Google Scholar search engine, were searched to identify helminth miRNA studies published from February 1993 till December 2019. Only the published articles in English were included in the study. RESULTS: A total of 1769 articles were preliminarily recorded. Following the strict inclusion and exclusion criteria, 105 studies were included in this SR. Most of these studies focused on the identification of miRNAs in helminth parasites and/or probing of differentially expressed host miRNA profiles in specific relevant tissues, while 12 studies aimed to detect parasite-derived miRNAs in host circulating system and 15 studies characterized extracellular vesicles (EV)-derived miRNAs secreted by parasites. CONCLUSION: In the current SR, information regarding all miRNAs expressed in helminth parasites has been comprehensively provided and the utility of helminth parasitesderived miRNAs in diagnosis and control of parasitic infections has been discussed. Furthermore, functional studies on helminth-derived miRNAs have also been presented.

Insights into the functional expansion of the astacin peptidase family in parasitic helminths.

Helminths secrete a plethora of proteins involved in parasitism-related processes such as tissue penetration, migration, feeding and immunoregulation. Astacins, a family of zinc metalloproteases belonging to the peptidase family M12, are one of the most abundantly represented protein families in the secretomes of helminths. Despite their involvement in virulence, very few studies have addressed the role of this loosely defined protein group in parasitic helminths. Herein, we have analysed the predicted proteomes from 154 helminth species and confirmed the expansion of the astacin family in several nematode taxa. The astacin domain associated with up to 110 other domains into 145 unique domain architectures, where CUB and ShK constitute the principal and nearly independent bi-domain frameworks. The presence of co-existing domains suggests promiscuous adaptable functions to several roles. These activities could be related either to substrate specificity or to higher-order functions, such as anti-angiogenesis and immunomodulation, where the astacin domain would play an accessory role. Furthermore, some phylogenetically restricted mutations in the astacin domain affected residues located at the active cleft and binding sub-pockets, suggesting adaptation to different substrate specificities. Altogether, these findings suggest the astacin domain is a highly adaptable module that fulfils multiple proteolytic needs of the parasitic lifestyle. This study contributes to the understanding of helminth-secreted astacins and, ultimately, provides the foundation to guide future investigations about the role of this diverse family of proteins in host-parasite interactions.

Helminth-induced CD9+ B-cell subset alleviates obesity-associated inflammation via IL-10 production.

It has been shown that helminth infection can protect against obesity and improve insulin sensitivity to a certain extent, based on epidemiological investigations and animal experiments. Meanwhile, helminths induce a network of regulatory immune cells, including regulatory B cells (Bregs). However, the molecule characteristics and function of these Bregs in improving whole-body metabolic homeostasis remains largely unclear. We established a mouse model with chronic Schistosoma japonicum infection, and compared the differences in B10 cells (CD19+CD5+CD1dhi) and B10- cells (CD19+CD5-CD1d-) from splenic B cells of infected mice using RNA-seq. A unique Breg population was identified. Furthermore, these Bregs were evaluated for their ability to produce inhibitory cytokines in vitro and suppress obesity when adoptively transferred into mice on a high-fat diet. We found that schistosome infection could expand Breg cell populations in mice. CD9 was demonstrated to be a key surface marker for most murine IL-10+ B cells in spleen. CD19+CD9+ B cells produced more IL-10 than conventional B10 cells. Adoptive transfer of CD9+ B cells had the capacity to alleviate obesity-associated inflammation via promoting Tregs, Th2 cells and decreasing Th1, Th17 cells in high-fat diet mice. In conclusion, schistosome infection can induce regulatory CD9+ B cell production, which plays a critical role in the regulation of metabolic disorders through IL-10 production.

IL-33: A central cytokine in helminth infections.

IL-33 is an alarmin cytokine which has been implicated in allergy, fibrosis, inflammation, tumorigenesis, metabolism, and homeostasis. However, amongst its strongest roles are in helminth infections, where IL-33 usually (but not always) is central to induction of an effective anti-parasitic immune response. In this review, we will summarise the literature around this fascinating cytokine, its activity on immune and non-immune cells, the unique (and sometimes counterintuitive) responses it induces, and how it can coordinate the immune response during infections by parasitic helminths. Finally, we will summarise some of the ways that parasites have developed to modulate the IL-33 pathway for their own benefit.

Basophils in antihelminth immunity.

It has been appreciated that basophilia is a common feature of helminth infections for approximately 50 years. The ability of basophils to secrete IL-4 and other type 2 cytokines has supported the prevailing notion that basophils contribute to antihelminth immunity by promoting optimal type 2 T helper (Th2) cell responses. While this appears to be the case in several helminth infections, emerging studies are also revealing that the effector functions of basophils are extremely diverse and parasite-specific. Further, new reports now suggest that basophils can restrict type 2 inflammation in a manner that preserves the integrity of helminth-affected tissue. Finally, exciting data has also demonstrated that basophils can regulate inflammation by participating in neuro-immune interactions. This article will review the current state of basophil biology and describe how recent studies are transforming our understanding of the role basophils play in the context of helminth infections.

Identification of enzymes that have helminth-specific active sites and are required for Rhodoquinone-dependent metabolism as targets for new anthelmintics.

Soil transmitted helminths (STHs) are major human pathogens that infect over a billion people. Resistance to current anthelmintics is rising and new drugs are needed. Here we combine multiple approaches to find druggable targets in the anaerobic metabolic pathways STHs need to survive in their mammalian host. These require rhodoquinone (RQ), an electron carrier used by STHs and not their hosts. We identified 25 genes predicted to act in RQ-dependent metabolism including sensing hypoxia and RQ synthesis and found 9 are required. Since all 9 have mammalian orthologues, we used comparative genomics and structural modeling to identify those with active sites that differ between host and parasite. Together, we found 4 genes that are required for RQ-dependent metabolism and have different active sites. Finding these high confidence targets can open up in silico screens to identify species selective inhibitors of these enzymes as new anthelmintics.

Parasite worm antigens instruct macrophages to release immunoregulatory extracellular vesicles.

Emerging evidence suggests that immune cells not only communicate with each other through cytokines, chemokines, and cell surface receptors, but also by releasing small membranous structures known as extracellular vesicles (EVs). EVs carry a variety of different molecules that can be taken up by recipient cells. Parasitic worms are well known for their immunomodulatory properties, but whether they can affect immune responses by altering EV-driven communication between host immune cells remains unclear. Here we provide evidence that stimulation of bone marrow-derived macrophages (BMDMs) with soluble products of Trichuris suis (TSPs), leads to the release of EVs with anti-inflammatory properties. Specifically, we found that EVs from TSP-pulsed BMDMs, but not those from unstimulated BMDMs can suppress TNFα and IL-6 release in LPS-stimulated BMDMs and BMDCs. However, no polarization toward M1 or M2 was observed in macrophages exposed to EVs. Moreover, EVs enhanced reactive oxygen species (ROS) production in the exposed BMDMs, which was associated with a deregulated redox homeostasis as revealed by pathway analysis of transcriptomic data. Proteomic analysis identified cytochrome p450 (CYP450) as a potential source of ROS in EVs from TSP-pulsed BMDMs. Finally, pharmacological inhibition of CYP450 activity could suppress ROS production in those BMDMs. In summary, we find that TSPs can modulate immune responses not only via direct interactions but also indirectly by eliciting the release of EVs from BMDMs that exert anti-inflammatory effects on recipient cells.

Proteomic approaches to drive advances in helminth extracellular vesicle research.

Helminths can interact with their hosts in many different ways, including through the secretion of soluble molecules (such as lipids, glycans and proteins) and extracellular vesicles (EVs). The field of helminth secreted EVs has significantly advanced in recent years, mainly due to the molecular characterisation of EV proteomes and research highlighting the potential of EVs and their constituent molecules in the diagnosis and control of parasitic infections. Despite these advancements, the lack of appropriate isolation and purification methods is impeding the discovery of suitable biomarkers for the differentiation of helminth EV populations. In the present review we offer our viewpoint on the different proteomic techniques and approaches that have been developed, as well as solutions to common pitfalls and challenges that could be applied to advance the study of helminth EVs.

Mining Helminths for Novel Therapeutics.

Helminths are an emerging source of therapeutics for dysregulated inflammatory diseases. Excretory/secretory (ES) molecules, released during infection, are responsible for many of these immunomodulatory effects and are likely to have evolved as a means for parasite survival in the host. While the mechanisms of action of these molecules have not been fully defined, evidence demonstrates that they target various pathways in the immune response, ranging from initiation to effector cell modulation. These molecules are applied in controlling specific effector mechanisms of type 1 and type 2 immune responses. Recently, studies have further focused on their therapeutic potential in specific disease models. Here we review recent findings on ES molecule modulation of immune functions, specifically highlighting their clinical implications for future use in inflammatory disease therapeutics.

Expression of Piwi Genes during the Regeneration of Lineus sanguineus (Nemertea, Pilidiophora, Heteronemertea).

The transposon silencer piwi genes play important roles in germline determination and maintenance, gametogenesis, and stem-cell self-renewal, and the expression of certain piwi genes is indispensable for regeneration. Knowledge about piwi genes is needed for phylum Nemertea, which contains members (e.g., Lineus sanguineus) with formidable regeneration capacity. By searching the L. sanguineus genome, we identified six Argonaute genes including three ago (Ls-Ago2, Ls-Ago2a, and Ls-Ago2b) and three piwi (Ls-piwi1, Ls-piwi2, and Ls-piwi3) genes. In situ hybridization revealed that, in intact females, Ls-piwi2 and Ls-piwi3 were not expressed, while Ls-piwi1 was expressed in ovaries. During regeneration, Ls-piwi1 and Ls-pcna (proliferating cell nuclear antigen) had strong and similar expressions. The expression of Ls-piwi1 became indetectable while Ls-pcna continued to be expressed when the differentiation of new organs was finished. During anterior regeneration, expression signals of Ls-piwi2 and Ls-piwi3 were weak and only detected in the blastema stage. During posterior regeneration, no expression was observed for Ls-piwi2. To date, no direct evidence has been found for the existence of congenital stem cells in adult L. sanguineus. The "pluripotent cells" in regenerating tissues are likely to be dedifferentiated from other type(s) of cells.

An atypical and functionally diverse family of Kunitz-type cysteine/serine proteinase inhibitors secreted by the helminth parasite Fasciola hepatica.

Fasciola hepatica is a global parasite of humans and their livestock. Regulation of parasite-secreted cathepsin L-like cysteine proteases associated with virulence is important to fine-tune parasite-host interaction. We uncovered a family of seven Kunitz-type (FhKT) inhibitors dispersed into five phylogenetic groups. The most highly expressed FhKT genes (group FhKT1) are secreted by the newly excysted juveniles (NEJs), the stage responsible for host infection. The FhKT1 inhibitors do not inhibit serine proteases but are potent inhibitors of parasite cathepsins L and host lysosomal cathepsin L, S and K cysteine proteases (inhibition constants < 10 nM). Their unusual inhibitory properties are due to (a) Leu15 in the reactive site loop P1 position that sits at the water-exposed interface of the S1 and S1' subsites of the cathepsin protease, and (b) Arg19 which forms cation-π interactions with Trp291 of the S1' subsite and electrostatic interactions with Asp125 of the S2' subsite. FhKT1.3 is exceptional, however, as it also inhibits the serine protease trypsin due to replacement of the P1 Leu15 in the reactive loop with Arg15. The atypical Kunitz-type inhibitor family likely regulate parasite cathepsin L proteases and/or impairs host immune cell activation by blocking lysosomal cathepsin proteases involved in antigen processing and presentation.

Helminth-derived peptide GK-1 induces Myd88-dependent pro-inflammatory signaling events in bone marrow-derived antigen-presenting cells.

GK-1 is an immunomodulatory, 18-aa-long peptide that has been proved to promote the activation of mouse peritoneal macrophages and LPS-pulsed mouse bone marrow-derived dendritic cells (BM-DCs). This study is aimed to explore the mechanisms underlying the activation of these antigen-presenting cells (APCs) by GK-1. In our study, GK-1 up-regulated in vitro the expression of CD86 and CD40, and it increased the secretion of NO in bone marrow-derived macrophages (BMDMs). In BM-DCs, GK-1 upregulated the expression of MHC class II and CD86. Additionally, GK-1 was found to be involved in the phosphorylation of MAPK p38, JNK and ERK 1/2 and in Myd88-dependent activation of NF-κB in both antigen-presenting cell types. In vivo, GK-1 increased the secretion of IL-15, CCL2, and IL-6 through a Myd88-dependent mechanism. This study demonstrated that GK-1 promotes the activation and effector activity of APCs through a mechanism dependent on Myd88, probably involving a Toll-like receptor as a target.

The protein and microRNA cargo of extracellular vesicles from parasitic helminths - current status and research priorities.

Helminth parasites have a remarkable ability to persist within their mammalian hosts, which is largely due to their secretion of molecules with immunomodulatory properties. Although the soluble components of helminth secretions have been extensively studied, the discovery that helminths release extracellular vesicles (EVs) has added further complexity to the host-parasite interaction. Whilst several studies have begun to characterise the molecules carried by helminth EVs, work aimed at investigating their biological functions has been hindered by a lack of helminth-specific EV markers. To begin to address this, we summarised helminth EV literature to date. With a focus on the protein and microRNA (miRNA) cargo, we aimed to detect similarities and differences across those major groups of helminths for which data are available; namely nematodes, trematodes and cestodes. Pfam analysis revealed that although there is no universal EV marker for all helminth species, the EF-hand protein family was present in all EV datasets from cestodes and trematodes, and could serve as a platyhelminth EV biomarker. In contrast, M13 metallopeptidases and actin may have potential as markers for nematode EVs. As with proteins, many miRNA families appeared to be species-, stage-, or dataset-specific. Two miRNA families were common to nematode EVs (mir-10 and let-7); the miRNA cargo of EVs secreted by clade I species appeared somewhat different from species from other clades. Five miRNA families (mir-71, mir-10, mir-190, let-7 and mir-2) were shared by all trematode species examined. Our analysis has identified novel markers that may be used in studies aimed at characterising helminth EVs and interrogating their function at the host-parasite interface. In addition, we discuss the heterogeneity of methods used for helminth EV isolation and emphasise the need for a standardised approach in reporting on helminth EV data.

Bioaccumulation of Polychlorinated Biphenyls (PCBs) in Fish Host-Parasite Bentho-Pelagic Food Chain in Epe Lagoon, Lagos, Nigeria.

This paper investigates the concentrations of PCBs in the water and sediment media and its bio-concentration in the fish host-parasite bentho-pelagic food chain in Epe lagoon. Samples of water, sediment, plankton, mollusks, fish and intestinal helminth parasites were collected from three stations (Oriba, Imode and Ikosi) in Epe Lagoon. Concentration of total PCBs in the surface water and sediment across the stations ranges from 3.20 to 6.00 ppb and 405.50-860.70 ppb respectively. Imode had the highest concentrations. The plankton bio-concentrates most PCBs in Ikosi (286.70 ppb) followed by Imode concentration (165.40 ppb), then Oribo (92.60 ppb) with total bio-concentration of 544.60 ppb. Surface water temperature negatively and strongly correlates with PCBs in the plankton. The planktons bio-concentrates total PCBs 44 times than that in the surface water. Chrysichthys nigrodigitatus bio-concentrates total PCBs 48 times than that in the surface water. Bioaccumulation of PCBs in human food chain could pose health risk.

Unique glycan and lipid composition of helminth-derived extracellular vesicles may reveal novel roles in host-parasite interactions.

Although the study of helminth-derived extracellular vesicles (EVs) is in its infancy, proteomic studies of EVs from representatives of nematodes, cestodes and trematodes have identified homologs of mammalian EV proteins including components of the endosomal sorting complexes required for transport and heat-shock proteins, suggesting conservation of pathways of EV biogenesis and cargo loading between helminths and their hosts. However, parasitic helminth biology is unique and this is likely reflected in helminth EV composition and biological activity. This opinion article highlights two exceptional studies that identified EVs released by Heligmosomoides polygyrus and Fasciola hepatica which display differential lipid and glycan composition, respectively, when compared with EVs derived from mammalian cells. Furthermore, we discuss the potential implications of helminth EV lipid and glycan composition upon helminth infection and host pathology. Future studies, focusing on the unique composition and functional properties of helminth EVs, may prove crucial to the understanding of host-parasite communication.