The role of arginine and arginine-metabolizing enzymes during Giardia - host cell interactions in vitro

The arginine and nitric oxide metabolic pathway regulate the gut colonization and expansion of Ruminococcous gnavus

Ruminococcus gnavus is a mucolytic commensal bacterium whose increased gut colonization has been associated with chronic inflammatory and metabolic diseases in humans. Whether R. gnavus metabolites can modulate host intestinal physiology remains largely understudied. We performed untargeted metabolomic and bulk RNA-seq analyses using R. gnavus monocolonization in germ-free mice. Based on transcriptome-metabolome correlations, we tested the impact of specific arginine metabolites on intestinal epithelial production of nitric oxide (NO) and examined the effect of NO on the growth of various strains of R. gnavus in vitro and in nitric oxide synthase 2 (Nos2)-deficient mice. R. gnavus produces specific arginine, tryptophan, and tyrosine metabolites, some of which are regulated by the environmental richness of sialic acid and mucin. R. gnavus colonization promotes expression of amino acid transporters and enzymes involved in metabolic flux of arginine and associated metabolites into NO. R. gnavus induced elevated levels of NOS2, while Nos2 ablation resulted in R. gnavus expansion in vivo. The growth of various R. gnavus strains can be inhibited by NO. Specific R. gnavus metabolites modulate intestinal epithelial cell NOS2 abundance and reduce epithelial barrier function at higher concentrations. Intestinal colonization and interaction with R. gnavus are partially regulated by an arginine-NO metabolic pathway, whereby a balanced control by the gut epithelium may restrain R. gnavus growth in healthy individuals. Disruption in this arginine metabolic regulation will contribute to the expansion and blooming of R. gnavus.

Giardia intestinalis extracellular vesicles induce changes in gene expression in human intestinal epithelial cells in vitro

Giardiasis is a common waterborne zoonotic disease caused by Giardia intestinalis. Upon infection, Giardia releases excretory and secretory products (ESPs) including secreted proteins (SPs) and extracellular vesicles (EVs). Although the interplay between ESPs and intestinal epithelial cells (IECs) has been previously described, the functions of EVs in these interactions and their differences from those of SPs require further exploration. In the present study, EVs and EV-depleted SPs were isolated from Giardia ESPs. Proteomic analyses of isolated SPs and EVs showed 146 and 91 proteins, respectively. Certain unique and enriched proteins have been identified in SPs and EVs. Transcriptome analysis of Caco-2 cells exposed to EVs showed 96 differentially expressed genes (DEGs), with 56 upregulated and 40 downregulated genes. Gene Ontology (GO), Kyoto Encyclopedia of Genes and Genomes (KEGG), and Gene Set Enrichment Analysis (GSEA) indicated that Caco-2 genes related to metabolic processes, the HIF-1 signaling pathway, and the cAMP signaling pathway were affected. This study provides new insights into host-parasite interactions, highlighting the potential significance of EVs on IECs during infections.

The ArgR-Regulated ADI Pathway Facilitates the Survival of Vibrio fluvialis under Acidic Conditions

Vibrio fluvialis is an emerging foodborne pathogenic bacterium that can cause severe cholera-like diarrhea and various extraintestinal infections, posing challenges to public health and food safety worldwide. The arginine deiminase (ADI) pathway plays an important role in bacterial environmental adaptation and pathogenicity. However, the biological functions and regulatory mechanisms of the pathway in V. fluvialis remain unclear. In this study, we demonstrate that L-arginine upregulates the expression of the ADI gene cluster and promotes the growth of V. fluvialis. The ADI gene cluster, which we proved to be comprised of two operons, arcD and arcACB, significantly enhances the survival of V. fluvialis in acidic environments both in vitro (in culture medium and in macrophage) and in vivo (in mice). The mRNA level and reporter gene fusion analyses revealed that ArgR, a transcriptional factor, is necessary for the activation of both arcD and arcACB transcriptions. Bioinformatic analysis predicted the existence of multiple potential ArgR binding sites at the arcD and arcACB promoter regions that were further confirmed by electrophoretic mobility shift assay, DNase I footprinting, or point mutation analyses. Together, our study provides insights into the important role of the ArgR-ADI pathway in the survival of V. fluvialis under acidic conditions and the detailed molecular mechanism. These findings will deepen our understanding of how environmental changes and gene expression interact to facilitate bacterial adaptations and virulence.

A core UPS molecular complement implicates unique endocytic compartments at the parasite-host interface in Giardia lamblia

Unconventional protein secretion (UPS) plays important roles in cell physiology. In contrast to canonical secretory routes, UPS does not generally require secretory signal sequences and often bypasses secretory compartments such as the ER and the Golgi apparatus. Giardia lamblia is a protist parasite with reduced subcellular complexity which releases several proteins, some of them virulence factors, without canonical secretory signals. This implicates UPS at the parasite-host interface. No dedicated machinery nor mechanism(s) for UPS in Giardia are currently known, although speculations on the involvement of endocytic organelles called PV/PECs, have been put forth. To begin to address the question of whether PV/PECs are implicated in virulence-associated UPS and to define the composition of molecular machinery involved in protein release, we employed affinity purification and mass spectrometry, coupled to microscopy-based subcellular localization and signal correlation quantification to investigate the interactomes of 11 reported unconventionally secreted proteins, all predicted to be cytosolic. A subset of these are associated with PV/PECs. Extended and validated interactomes point to a core PV/PECs-associated UPS machinery, which includes uncharacterized and Giardia-specific coiled-coil proteins and NEK kinases. Finally, a subset of the alpha-giardin protein family was enriched in all PV/PECs-associated protein interactomes, highlighting a previously unappreciated role for these proteins at PV/PECs and in UPS. Taken together, our results provide the first characterization of a virulence-associated UPS protein complex in Giardia lamblia at PV/PECs, suggesting a novel link between these primarily endocytic and feeding organelles and UPS at the parasite-host interface.

Amino acid metabolism in immune cells: essential regulators of the effector functions, and promising opportunities to enhance cancer immunotherapy

Amino acids are basic nutrients for immune cells during organ development, tissue homeostasis, and the immune response. Regarding metabolic reprogramming in the tumor microenvironment, dysregulation of amino acid consumption in immune cells is an important underlying mechanism leading to impaired anti-tumor immunity. Emerging studies have revealed that altered amino acid metabolism is tightly linked to tumor outgrowth, metastasis, and therapeutic resistance through governing the fate of various immune cells. During these processes, the concentration of free amino acids, their membrane bound transporters, key metabolic enzymes, and sensors such as mTOR and GCN2 play critical roles in controlling immune cell differentiation and function. As such, anti-cancer immune responses could be enhanced by supplement of specific essential amino acids, or targeting the metabolic enzymes or their sensors, thereby developing novel adjuvant immune therapeutic modalities. To further dissect metabolic regulation of anti-tumor immunity, this review summarizes the regulatory mechanisms governing reprogramming of amino acid metabolism and their effects on the phenotypes and functions of tumor-infiltrating immune cells to propose novel approaches that could be exploited to rewire amino acid metabolism and enhance cancer immunotherapy.

ROS-AMPK/mTOR-dependent enterocyte autophagy is involved in the regulation of Giardia infection-related tight junction protein and nitric oxide levels

Giardia duodenalis, a cosmopolitan noninvasive protozoan parasite of zoonotic concern and public health importance, infects the upper portions of the small intestine and causes one of the most common gastrointestinal diseases globally termed giardiasis, especially in situations lacking safe drinking water and adequate sanitation services. The pathogenesis of giardiasis is complex and involves multiple factors from the interaction of Giardia and intestinal epithelial cells (IECs). Autophagy is an evolutionarily conserved catabolic pathway that involves multiple pathological conditions including infection. Thus far, it remains uncertain if autophagy occurs in Giardia-infected IECs and if autophagic process is associated with the pathogenic factors of giardiasis, such as tight junction (TJ) barrier defects and nitric oxide (NO) release of IECs. Here Giardia-in vitro exposed IECs showed upregulation of a series of autophagy-related molecules, such as LC3, Beclin1, Atg7, Atg16L1, and ULK1, and downregulation of p62 protein. IEC autophagy induced by Giardia was further assessed by using autophagy flux inhibitor, chloroquine (CQ), with the ratio of LC3-II/LC3-I significantly increased and downregulated p62 significantly reversed. Inhibition of autophagy by 3-methyladenine (3-MA) rather than CQ could markedly reverse Giardia-induced downregulation of TJ proteins (claudin-1, claudin-4, occludin, and ZO-1; also known as epithelial cell markers) and NO release, implying the involvement of early-stage autophagy in TJ/NO regulation. We subsequently confirmed the role of ROS-mediated AMPK/mTOR signaling in modulating Giardia-induced autophagy, TJ protein expression, and NO release. In turn, impairment of early-stage autophagy by 3-MA and late-stage autophagy by CQ both exhibited an exacerbated effect on ROS accumulation in IECs. Collectively, we present the first attempt to link the occurrence of IEC autophagy with Giardia infection in vitro, and provides novel insights into the contribution of ROS-AMPK/mTOR-dependent autophagy to Giardia infection-related downregulation of TJ protein and NO levels.

Specific TLR-mediated HSP70 activation plays a potential role in host defense against the intestinal parasite Giardia duodenalis

Giardia duodenalis, an important flagellated noninvasive protozoan parasite, infects the upper small intestine and causes a disease termed giardiasis globally. Few members of the heat shock protein (HSP) family have been shown to function as potential defenders against microbial pathogens, while such information is lacking for Giardia. Here we initially screened and indicated that in vitro Giardia challenge induced a marked early upregulation of HSP70 in intestinal epithelial cells (IECs). As noted previously, apoptotic resistance, nitric oxide (NO)-dependent cytostatic effect and parasite clearance, and epithelial barrier integrity represent effective anti-Giardia host defense mechanisms. We then explored the function of HSP70 in modulating apoptosis, NO release, and tight junction (TJ) protein levels in Giardia-IEC interactions. HSP70 inhibition by quercetin promoted Giardia-induced IEC apoptosis, viability decrease, NO release reduction, and ZO-1 and occludin downregulation, while the agonist celastrol could reverse these Giardia-evoked effects. The results demonstrated that HSP70 played a previously unrecognized and important role in regulating anti-Giardia host defense via attenuating apoptosis, promoting cell survival, and maintaining NO and TJ levels. Owing to the significance of apoptotic resistance among those defense-related factors mentioned earlier, we then elucidated the anti-apoptotic mechanism of HSP70. It was evident that HSP70 could negatively regulate apoptosis in an intrinsic way via direct inhibition of Apaf-1 or ROS-Bax/Bcl-2-Apaf-1 axis, and in an extrinsic way via cIAP2-mediated inhibition of RIP1 activity. Most importantly, it was confirmed that HSP70 exerted its host defense function by downregulating apoptosis via Toll-like receptor 4 (TLR4) activation, upregulating NO release via TLR4/TLR2 activation, and upregulating TJ protein expression via TLR2 activation. HSP70 represented a checkpoint regulator providing the crucial link between specific TLR activation and anti-Giardia host defense responses. Strikingly, independent of the checkpoint role of HSP70, TLR4 activation was proven to downregulate TJ protein expression, and TLR2 activation to accelerate apoptosis. Altogether, this study identified HSP70 as a potentially vital defender against Giardia, and revealed its correlation with specific TLR activation. The clinical importance of HSP70 has been extensively demonstrated, while its role as an effective therapeutic target in human giardiasis remains elusive and thus needs to be further clarified.

Streptococcal arginine deiminase regulates endothelial inflammation, mTOR pathway and autophagy

Endothelial cells (EC) are active participants in the inflammation process. During the infection, the change in endothelium properties provides the leukocyte infiltrate formation and restrains pathogen dissemination due to coagulation control. Pathogenic microbes are able to change the endothelium properties and functions in order to invade the bloodstream and disseminate in the host organism. Arginine deiminase (ADI), a bacterial arginine-hydrolyzing enzyme, which causes the amino acid deficiency, important for endothelium biology. Previous research implicates altered metabolism of arginine in the development of endothelial dysfunction and inflammation. It was shown that arginine deficiency, as well as overabundance affects the balance of mechanical target of rapamycin (mTOR)/S6 kinase (S6K) pathway, arginase and endothelial nitric oxide synthase (eNOS) resulted in reactive oxygen species (ROS) production and EC activation. ADI creating a deficiency of arginine can interfere cellular arginine-dependent processes. Thus, this study was aimed at investigation of the influence of streptococcal ADI on the metabolism and inflammations of human umbilical vein endothelial cells (HUVEC). The action of ADI was studied by comparing the effect Streptococcus pyogenes M49-16 paternal strain expressing ADI and its isogenic mutant M49-16delArcA with the inactivated gene ArcA. Based on comparison of the parental and mutant strain effects, it can be concluded, that ADI suppressed mTOR signaling pathway and enhanced autophagy. The processes failed to return to the basic level with arginine supplement. Our study also demonstrates that ADI suppressed endothelial proliferation, disrupted actin cytoskeleton structure, increased phospho-NF-κB p65, CD62P, CD106, CD54, CD142 inflammatory molecules expression, IL-6 production and lymphocytes-endothelial adhesion. In spite of the ADI-mediated decrease in arginine concentration in the cell-conditioned medium, the enzyme enhanced the production of nitric oxide in endothelial cells. Arginine supplementation rescued proliferation, actin cytoskeleton structure, brought NO production to baseline and prevented EC activation. Additional evidence for the important role of arginine bioavailability in the EC biology was obtained. The results allow us to consider bacterial ADI as a pathogenicity factor that can potentially affect the functions of endothelium.

Nitric oxide in parasitic infections: a friend or foe?

The complex interaction between the host and the parasite remains a puzzling question. Control of parasitic infections requires an efficient immune response that must be balanced against destructive pathological consequences. Nitric oxide is a nitrogenous free radical which has many molecular targets and serves diverse functions. Apart from being a signaling messenger, nitric oxide is critical for controlling numerous infections. There is still controversy surrounding the exact role of nitric oxide in the immune response against different parasitic species. It proved protective against intracellular protozoa, as well as extracellular helminths. At the same time, it plays a pivotal role in stimulating detrimental pathological changes in the infected hosts. Several reports have discussed the anti-parasitic and immunoregulatory functions of nitric oxide, which could directly influence the control of the infection. Nevertheless, there is scarce literature addressing the harmful cytotoxic impacts of this mediator. Thus, this review provides insights into the most updated concepts and controversies regarding the dual nature and opposing sides of nitric oxide during the course of different parasitic infections.

Identification of target genes regulated by encystation-induced transcription factor Myb2 using knockout mutagenesis in Giardia lamblia

BACKGROUND

Encystation is one of the two processes comprising the life cycle of Giardia lamblia, a protozoan pathogen with tetraploid genome. Giardia lamblia Myb2 (GlMyb2) is a distinct encystation-induced transcription factor whose binding sites are found in the promoter regions of many encystation-induced genes, including its own.

METHODS

Two sequential CRISPR/Cas9 experiments were performed to remove four glmyb2 alleles. The expression level of G. lamblia cyst wall protein 1 (GlCWP1), a well-known target gene of GlMyb2, was measured via western blotting and immunofluorescence assays. Chromatin immunoprecipitation experiments using anti-GlMyb2 antibodies were performed on the encysting G. lamblia cells. Quantitative real-time PCR was performed to confirm an expression of candidate GlMyb2-regulated genes by comparing the transcript level for each target candidate in wild-type and knockout mutant Giardia. The promoter region of glcwp1 was analyzed via deletion and point mutagenesis of the putative GlMyb2 binding sites in luciferase reporters.

RESULTS

Characterization of the null glmyb2 mutant indicated loss of functions related to encystation, i.e. cyst formation, and expression of GlCWP1. The addition of the wild-type glmyb2 gene to the null mutant restored the defects in encystation. Chromatin immunoprecipitation experiments revealed dozens of target genes. Nineteen genes were confirmed as GlMyb2 regulons, which include the glmyb2 gene, six for cyst wall proteins, five for signal transduction, two for transporter, two for metabolic enzymes, and three with unknown functions. Detailed analysis on the promoter region of glcwp1 defined three GlMyb2 binding sites important in its encystation-induced expression.

CONCLUSIONS

Our data confirm that GlMyb2 acts as a transcription activator especially during encystation by comparing the glmyb2 knockout mutant with the wild type. Further investigation using glmyb2 null mutant will provide knowledge regarding transcriptional apparatus required for the encystation process of G. lamblia.

Gut Non-Bacterial Microbiota: Emerging Link to Irritable Bowel Syndrome

As a common functional gastrointestinal disorder, irritable bowel syndrome (IBS) significantly affects personal health and imposes a substantial economic burden on society, but the current understanding of its occurrence and treatment is still inadequate. Emerging evidence suggests that IBS is associated with gut microbial dysbiosis, but most studies focus on the bacteria and neglect other communities of the microbiota, including fungi, viruses, archaea, and other parasitic microorganisms. This review summarizes the latest findings that link the nonbacterial microbiota with IBS. IBS patients show less fungal and viral diversity but some alterations in mycobiome, virome, and archaeome, such as an increased abundance of Candida albicans. Moreover, fungi and methanogens can aid in diagnosis. Fungi are related to distinct IBS symptoms and induce immune responses, intestinal barrier disruption, and visceral hypersensitivity via specific receptors, cells, and metabolites. Novel therapeutic methods for IBS include fungicides, inhibitors targeting fungal pathogenic pathways, probiotic fungi, prebiotics, and fecal microbiota transplantation. Additionally, viruses, methanogens, and parasitic microorganisms are also involved in the pathophysiology and treatment. Therefore, the gut nonbacterial microbiota is involved in the pathogenesis of IBS, which provides a novel perspective on the noninvasive diagnosis and precise treatment of this disease.

Giardia duodenalis enolase is secreted as monomer during trophozoite-epithelial cell interactions, activates plasminogen and induces necroptotic damage

Enolase, a multifunctional protein expressed by multiple pathogens activates plasminogen to promote proteolysis on components of the extracellular matrix, an important event in early host-pathogen interactions. A secreted form of enolase that is released upon the interaction of trophozoites with epithelial cells has been detected in the secretome of G. duodenalis. However, the role of enolase in the host-pathogen interactions remains largely unknown. In this work, the effects of G. duodenalis enolase (Gd-eno) on the epithelial cell model (IEC-6) were analyzed. Firstly, the coding sequence of Giardia enolase was cloned and the recombinant protein used to raise antibodies that were then used to define the localization and role of enolase in epithelial cell-trophozoite interactions. Gd-eno was detected in small cytoplasmic vesicles as well as at the surface and is enriched in the region of the ventral disk of Giardia trophozoites. Moreover, the blocking of the soluble monomeric form of the enzyme, which is secreted upon interaction with IEC-6 cells by the anti-rGd-eno antibodies, significantly inhibited trophozoite attachment to intestinal IEC-6 cell monolayers. Further, rGd-eno was able to bind human plasminogen (HsPlg) and enhanced plasmin activity in vitro when the trophozoites were incubated with the intrinsic plasminogen activators of epithelial cells. In IEC-6 cells, rGd-eno treatment induced a profuse cell damage characterized by copious vacuolization, intercellular separation and detachment from the substrate; this effect was inhibited by either anti-Gd-eno Abs or the plasmin inhibitor ϵ- aminocaproic acid. Lastly, we established that in epithelial cells rGd-eno treatment induced a necroptotic-like process mediated by tumor necrosis factor α (TNF-α) and the apoptosis inducing factor (AIF), but independent of caspase-3. All together, these results suggest that Giardia enolase is a secreted moonlighting protein that stimulates a necroptotic-like process in IEC-6 epithelial cells via plasminogen activation along to TNFα and AIF activities and must be considered as a virulence factor.

Giardial lipid rafts share virulence factors with secreted vesicles and participate in parasitic infection in mice

Giardia lamblia, a protozoan parasite, is a major cause of waterborne infection, worldwide. While the trophozoite form of this parasite induces pathological symptoms in the gut, the cyst form transmits the infection. Since Giardia is a noninvasive parasite, the actual mechanism by which it causes disease remains elusive. We have previously reported that Giardia assembles cholesterol and GM1 glycosphingolipid-enriched lipid rafts (LRs) that participate in encystation and cyst production. To further delineate the role of LRs in pathogenesis, we isolated LRs from Giardia and subjected them to proteomic analysis. Various cellular proteins including potential virulence factors-e.g., giardins, variant surface proteins, arginine deaminases, elongation factors, ornithine carbomyltransferases, and high cysteine-rich membrane proteins-were found to be present in LRs. Since Giardia secretes virulence factors encapsulated in extracellular vesicles (EVs) that induce proinflammatory responses in hosts, EVs released by the parasite were isolated and subjected to nanoparticle tracking and proteomic analysis. Two types of EV-i.e., small vesicles (SVs; <100 nm, exosome-like particles) and large vesicles (LVs; 100-400 nm, microvesicle-like particles)-were identified and found to contain a diverse group of proteins including above potential virulence factors. Although pretreatment of the parasite with two giardial lipid raft (gLR) disruptors, nystatin (27 μM) and oseltamivir (20 μM), altered the expression profiles of virulence factors in LVs and SVs, the effects were more robust in the case of SVs. To examine the potential role of rafts and vesicles in pathogenicity, Giardia-infected mice were treated with oseltamivir (1.5 and 3.0 mg/kg), and the shedding of cysts were monitored. We observed that this drug significantly reduced the parasite load in mice. Taken together, our results suggest that virulence factors partitioning in gLRs, released into the extracellular milieu via SVs and LVs, participate in spread of giardiasis and could be targeted for future drug development.

Dual RNA Sequencing Reveals Key Events When Different Giardia Life Cycle Stages Interact With Human Intestinal Epithelial Cells In Vitro

Giardia intestinalis is a protozoan parasite causing diarrheal disease, giardiasis, after extracellular infection of humans and other mammals’ intestinal epithelial cells (IECs) of the upper small intestine. The parasite has two main life cycle stages: replicative trophozoites and transmissive cysts. Differentiating parasites (encysting cells) and trophozoites have recently been shown to be present in the same regions of the upper small intestine, whereas most mature cysts are found further down in the intestinal system. To learn more about host-parasite interactions during Giardia infections, we used an in vitro model of the parasite’s interaction with host IECs (differentiated Caco-2 cells) and Giardia WB trophozoites, early encysting cells (7 h), and cysts. Dual RNA sequencing (Dual RNAseq) was used to identify differentially expressed genes (DEGs) in both Giardia and the IECs, which might relate to establishing infection and disease induction. In the human cells, the largest gene expression changes were found in immune and MAPK signaling, transcriptional regulation, apoptosis, cholesterol metabolism and oxidative stress. The different life cycle stages of Giardia induced a core of similar DEGs but at different levels and there are many life cycle stage-specific DEGs. The metabolic protein PCK1, the transcription factors HES7, HEY1 and JUN, the peptide hormone CCK and the mucins MUC2 and MUC5A are up-regulated in the IECs by trophozoites but not cysts. Cysts specifically induce the chemokines CCL4L2, CCL5 and CXCL5, the signaling protein TRKA and the anti-bacterial protein WFDC12. The parasite, in turn, up-regulated a large number of hypothetical genes, high cysteine membrane proteins (HCMPs) and oxidative stress response genes. Early encysting cells have unique DEGs compared to trophozoites (e.g. several uniquely up-regulated HCMPs) and interaction of these cells with IECs affected the encystation process. Our data show that different life cycle stages of Giardia induce different gene expression responses in the host cells and that the IECs in turn differentially affect the gene expression in trophozoites and early encysting cells. This life cycle stage-specific host-parasite cross-talk is an important aspect to consider during further studies of Giardia’s molecular pathogenesis.

The arginine deaminase system plays distinct roles in Borrelia burgdorferi and Borrelia hermsii

Borrelia species are amino acid auxotrophs that utilize di- and tri- peptides obtained through their oligopeptide transport system to supply amino acids for replicative growth during their enzootic cycles. However, Borrelia species from both the Lyme disease (LD) and relapsing fever (RF) groups harbor an amino acid transport and catabolism system, the Arginine Deiminase System (ADI), that could potentially augment intracellular L-arginine required for growth. RF spirochetes contain a “complete”, four gene ADI (arcA, B, D, and C) while LD spirochetes harbor arcA, B, and sometimes D but lack arcC (encoding carbamate kinase). In this study, we evaluated the role of the ADI system in bacterial survival and virulence and discovered important differences in RF and LD ADIs. Both in vitro and in a murine model of infection, B. hermsii cells significantly reduced extracellular L-arginine levels and that reduction was dependent on arginine deiminase expression. Conversely, B. burgdorferi did not reduce the concentration of L-arginine during in vitro growth experiments nor during infection of the mammalian host, suggesting a fundamental difference in the ability to directly utilize L-arginine compared to B. hermsii. Further experiments using a panel of mutants generated in both B. burgdorferi and B. hermsii, identified important differences in growth characteristics and ADI transcription and protein expression. We also found that the ADI system plays a key role in blood and spleen colonization in RF spirochetes. In this study we have identified divergent metabolic strategies in two closely related human pathogens, that ultimately impacts the host-pathogen interface during infection.

Reports of tick-borne diseases have been steadily increasing in the US and the number of Lyme disease cases caused by B. burgdorferi have tripled since the late 1990’s. Although less common, cases of tick-borne relapsing fever, caused by B. hermsii and B. turicatae in the US, have increased as well. While transmitted by different ticks and maintained in unique enzootic cycles, the closely related spirochetes B. burgdorferi and B. hermsii share numerous genetic features including a truncated and streamlined capacity for metabolic activity. In this study we combine genetic and biochemical assays to define the role of the ADI in the infective cycles of B. burgdorferi and B. hermsii. When we compared B. burgdorferi and B. hermsii, we identified important differences in their respective ADI’s including operon arrangement, sensitivity to L-arginine and L-ornithine levels, as well as gene and protein expression. In addition, we show that arginine deiminase is required to reduce host L-arginine levels during murine infection with B. hermsii. This study provides new insights into the metabolic activities of two medically relevant spirochetes and highlights the dynamic nature of host-pathogen interactions.

Helicobacter pylori Pathogenicity Islands and Giardia lamblia Cysteine Proteases in Role of Coinfection and Pathogenesis

Helicobacter pylori is a well-known human-specific stomach pathogen that infects more than half of the world’s population. The infection with this bacterium can cause a variety of gastrointestinal problems, including chronic gastritis, peptic ulcers, and even cancer. H. pylori is a highly infectious bacterium. H. pylori causes an increase in gastric mucosa pH or gastric mucosa intestinal metaplasia. These modifications in the stomach environment are necessary for G. lamblia colonization to occur. Giardia lamblia is a flagellate protozoan parasite that can cause giardiasis in humans and other mammals. It dwells in the duodenum and upper jejunum. Globally, over 280 million cases of human giardiasis are predicted to occur each year. Simultaneous human colonization by G. lamblia and H. pylori is a typical occurrence since the viruses’ predisposing factors are similar in both groups. Giardiasis is a parasitic infection that affects both children and adults worldwide. Infection with Giardia is more common in underdeveloped countries. Globally, more than 200 million cases of giardiasis are detected each year. In contrast, the presence of G. lamblia in the host body triggers an immunological response comparable to that of H. pylori, with lymphocytes strongly polarized towards Th1. As a result, their combined presence exacerbates host tissue damage. The major goal of this seminar is to describe the pathophysiology, immunology, and clinical aspects of G. lamblia and H. pylori coinfection using a comprehensive search of PubMed, Lancet, and Google Scholar sources. Upper gastrointestinal problems such as upper abdominal pain, abdominal bloating, nausea, vomiting, epigastric pain/burning, and belching are all caused by both organisms. Differentiation by physical examination is impossible in people infected with both bacteria. For this coinfection distinction, a laboratory diagnosis is required. G. lamblia and H. pylori, when present together, have a synergistic effect on the host and can cause serious damage. As a result, researchers should delve deeper into the mechanics underlying this potential microbial interaction.

Immune cell arrival kinetics to peritoneum and role during murine-experimental trichomoniasis

Trichomonas vaginalis causes trichomoniasis, an inflammatory process related to an increased rate of HIV transmission. In order to study T. vaginalis infection response in a microorganism-free environment, an infection model was established providing a host–parasite interaction system useful to study the interplay between immune cells and the parasite. Infected mice peritoneal cells were immunophenotyped at different times after infection using flow cytometry. Neutrophils and macrophages showed the most relevant increase from third to 12th day post-infection. A high number of B lymphocytes were present on 15th day post-infection, and an increase in memory T cells was observed on sixth day post-infection. The levels of NO increased at day 10 post-infection; no significant influence was observed on T. vaginalis clearance. Increased viability of T. vaginalis was observed when the NETs inhibitors, metformin and Cl− amidine, were administrated, highlighting the importance of this mechanism to control parasite infection (43 and 86%, respectively). This report presents a comprehensive cell count of the immune cells participating against trichomoniasis in an in vivo interaction system. These data highlight the relevance of innate mechanisms such as specific population changes of innate immune cells and their impact on the T. vaginalis viability.

Giardia duodenalis Virulence - "To Be, or Not To Be"

Purpose of review

Here, we review recent progress made on the genetic characterization of Giardia duodenalis assemblages and their relationship with virulence. We also discuss the implications of virulence factors in the pathogenesis of giardiasis, and advances in the development of vaccines and drugs based on knowledge of virulence markers.

Recent findings

The use of transcriptomic and proteomic technologies as well as whole genome sequencing (WGS) from single cysts has allowed the assembly of the draft genome sequences for assemblages C and D of G. duodenalis. These findings, along with the published genomes for assemblages A, B, and E, have allowed comparative genomic investigations. In addition, the use of these methodologies for the characterization of the secretomes of trophozoite-epithelial cell interactions for assemblages A/B has led to the identification of virulence markers including energy metabolism enzymes, proteinases, high-cysteine membrane proteins (HCMPs), and variant surface proteins (VSPs). Recently, some drugs and vaccines, targeting virulence factors have been developed, offering possible alternatives to current treatment and prevention options against giardiasis.

Summary

Among the nine recognized species of Giardia, G. duodenalis stands out because of its broad spectrum of hosts and its socio-economic importance. This species comprises eight genetic assemblages (A to H), of which A and B are zoonotic, and the other assemblages have narrow host specificities. Assemblages A and B may be considered as the most virulent ones, but the existence of asymptomatic carriers and considerable genetic variability within and among these assemblages hampers the definition of common virulence factors. The attachment of Giardia trophozoites to epithelial cells and structural cytoskeleton components of the adhesive disk, such as giardins or tubulins, is proposed to play key roles, but toxins have not yet been precisely defined. However, recent transcriptomic and proteomic analyses of the secretomes of trophozoites representing assemblages A and B and interacting with particular epithelial cell lines have defined a series of virulence factors, including glycolytic (e.g., enolase) and arginolytic (e.g., arginine deiminase) enzymes, cysteine proteases (e.g., giardipain-1) and VSPs (e.g., VSP9B10A). Other factors, such as HCMPs and tenascins, have been consistently found to be excreted/secreted, but their role(s) in the pathogenesis of giardiasis has not yet been elucidated. Interestingly, recent investigations of single cysts representing assemblages C and D using advanced sequencing and informatic methods have suggested that the transcription/expression profiles of virulence factors vary both within and between assemblages, thus assemblage-specific molecules might allow adaptation to the microenvironment within the host. Importantly, some drugs active against cysteine-rich proteins of Giardia, including giardipain-1, VSPs and arginine deiminase, have been shown to be targeted by cysteine-modifying compounds as disulfiram, L-canavanin and allicin. On the other hand, VSPs are presently considered as key vaccine candidates because they induce protection against Giardia in rodents and dogs. Overall, this review reveals that much more work is needed to identify, characterize, and understand the roles of virulence factors in Giardia and to assess their validity as drug and vaccine targets. Clear, advanced omics and informatic tools should assist in this future endeavor, with a focus on targeting virulence factors that are common and/or unique to distinct assemblages to develop new and effective interventions against Giardia.

Giardia duodenalis: Biology and Pathogenesis

Giardia duodenalis captured the attention of Leeuwenhoek in 1681 while he was examining his own diarrheal stool, but, ironically, it did not really gain attention as a human pathogen until the 1960s, when outbreaks were reported. Key technological advances, including in vitro cultivation, genomic and proteomic databases, and advances in microscopic and molecular approaches, have led to an understanding that this is a eukaryotic organism with a reduced genome rather than a truly premitochondriate eukaryote. This has included the discovery of mitosomes (vestiges of mitochondria), a transport system with many of the features of the Golgi apparatus, and even evidence for a sexual or parasexual cycle. Cell biology approaches have led to a better understanding of how Giardia survives with two nuclei and how it goes through its life cycle as a noninvasive organism in the hostile environment of the lumen of the host intestine. Studies of its immunology and pathogenesis have moved past the general understanding of the importance of the antibody response in controlling infection to determining the key role of the Th17 response. This work has led to understanding of the requirement for a balanced host immune response that avoids the extremes of an excessive response with collateral damage or one that is unable to clear the organism. This understanding is especially important in view of the remarkable ranges of early manifestations, which range from asymptomatic to persistent diarrhea and weight loss, and longer-term sequelae that include growth stunting in children who had no obvious symptoms and a high frequency of postinfectious irritable bowel syndrome (IBS).

Pomegranate Peel Extract Is a Potential Alternative Therapeutic for Giardiasis

Giardiasis is a major diarrheal disease affecting approximately 2.5 million children annually in developing countries. Several studies have reported the resistance of Giardia lamblia (G. lamblia) to multiple drugs. Therefore, identifying an effective drug for giardiasis is a necessity. This study examined the antiparasitic effect of Punica granatum (pomegranate) and evaluated its therapeutic efficacy in rats infected with G. lamblia. In vitro study showed high efficacy of pomegranate peel ethanolic extract in killing G. lamblia cysts as demonstrated by eosin vital staining. We showed that treating infected rats with pomegranate extract resulted in a marked reduction in the mean number of G. lamblia cysts and trophozoites in feces and intestine respectively. Interestingly, the number of G. lamblia trophozoites and cysts were significantly lower in the pomegranate extract-treated group compared to the metronidazole-positive control group. Moreover, pomegranate extract treatment significantly induced nitric oxide (NO) and reduced serum IL-6 and TNF-α, compared to infected untreated rats. Histological and scanning electron microscopy (SEM) examination of the jejunum and duodenum of pomegranate extract-treated animals confirmed the antiparasitic effect of the extract, and demonstrated the restoration of villi structure with reduction of villi atrophy, decreased infiltration of lymphocytes, and protection of intestinal cells from apoptotic cell death. In conclusion, our data show that the pomegranate peel extract is effective in controlling G. lamblia infections, which suggests that it could be a viable treatment option for giardiasis.

Eukaryote-Conserved Methylarginine Is Absent in Diplomonads and Functionally Compensated in Giardia

Methylation is a common posttranslational modification of arginine and lysine in eukaryotic proteins. Methylproteomes are best characterized for higher eukaryotes, where they are functionally expanded and evolved complex regulation. However, this is not the case for protist species evolved from the earliest eukaryotic lineages. Here, we integrated bioinformatic, proteomic, and drug-screening data sets to comprehensively explore the methylproteome of Giardia duodenalis-a deeply branching parasitic protist. We demonstrate that Giardia and related diplomonads lack arginine-methyltransferases and have remodeled conserved RGG/RG motifs targeted by these enzymes. We also provide experimental evidence for methylarginine absence in proteomes of Giardia but readily detect methyllysine. We bioinformatically infer 11 lysine-methyltransferases in Giardia, including highly diverged Su(var)3-9, Enhancer-of-zeste and Trithorax proteins with reduced domain architectures, and novel annotations demonstrating conserved methyllysine regulation of eukaryotic elongation factor 1 alpha. Using mass spectrometry, we identify more than 200 methyllysine sites in Giardia, including in species-specific gene families involved in cytoskeletal regulation, enriched in coiled-coil features. Finally, we use known methylation inhibitors to show that methylation plays key roles in replication and cyst formation in this parasite. This study highlights reduced methylation enzymes, sites, and functions early in eukaryote evolution, including absent methylarginine networks in the Diplomonadida. These results challenge the view that arginine methylation is eukaryote conserved and demonstrate that functional compensation of methylarginine was possible preceding expansion and diversification of these key networks in higher eukaryotes.

A Complementary Herbal Product for Controlling Giardiasis

Giardiasis is an intestinal protozoal disease caused by Giardia lamblia. The disease became a global health issue due to development of resistance to commonly used drugs. Since many plant-derived products have been used to treat many parasitic infestations, we aimed to assess the therapeutic utility of Artemisia annua (A. annua) for giardiasis. We showed that NO production was significantly reduced whereas serum levels of IL-6, IFN-γ, and TNF-α were elevated in infected hamsters compared to uninfected ones. Additionally, infection resulted in increased numbers of intraepithelial lymphocytes and reduced villi heights, goblet cell numbers, and muscularis externa thickness. We also showed that inducible NO synthase (iNOS) and caspase-3 were elevated in the intestine of infected animals. However, treatment with A. annua significantly reduced the intestinal trophozoite counts and IEL numbers, serum IL-6, IFN-γ, and TNF-α, while increasing NO and restoring villi heights, GC numbers, and ME thickness. Moreover, A. annua treatment resulted in lower levels of caspase-3, which indicates a protective effect from apoptotic cell death. Interestingly, A. annua therapeutic effects are comparable to metronidazole. In conclusion, our results show that A. annua extract is effective in alleviating infection-induced intestinal inflammation and pathological effects, which implies its potential therapeutic utility in controlling giardiasis.

Giardia spp. and the Gut Microbiota: Dangerous Liaisons

Alteration of the intestinal microbiome by enteropathogens is commonly associated with gastrointestinal diseases and disorders and has far-reaching consequences for overall health. Significant advances have been made in understanding the role of microbial dysbiosis during intestinal infections, including infection with the protozoan parasite Giardia duodenalis, one of the most prevalent gut protozoa. Altered species composition and diversity, functional changes in the commensal microbiota, and changes to intestinal bacterial biofilm structure have all been demonstrated during the course of Giardia infection and have been implicated in Giardia pathogenesis. Conversely, the gut microbiota has been found to regulate parasite colonization and establishment and plays a critical role in immune modulation during mono and polymicrobial infections. These disruptions to the commensal microbiome may contribute to a number of acute, chronic, and post-infectious clinical manifestations of giardiasis and may account for variations in disease presentation within and between infected populations. This review discusses recent advances in characterizing Giardia-induced bacterial dysbiosis in the gut and the roles of dysbiosis in Giardia pathogenesis.

Enzymology of the pathway for ATP production by arginine breakdown

In cells, the breakdown of arginine to ornithine and ammonium ion plus carbon dioxide is coupled to the generation of metabolic energy in the form of ATP. The arginine breakdown pathway is minimally composed of arginine deiminase, ornithine transcarbamoylase, carbamate kinase, and an arginine/ornithine antiporter; ammonia and carbon dioxide most likely diffuse passively across the membrane. The genes for the enzymes and transporter have been cloned and expressed, and the proteins have been purified from Lactococcus lactis IL1403 and incorporated into lipid vesicles for sustained production of ATP. Here, we study the kinetic parameters and biochemical properties of the individual enzymes and the antiporter, and we determine how the physicochemical conditions, effector composition, and effector concentration affect the enzymes. We report the KM and VMAX values for catalysis and the native oligomeric state of all proteins, and we measured the effect of pathway intermediates, pH, temperature, freeze-thaw cycles, and salts on the activity of the cytosolic enzymes. We also present data on the protein-to-lipid ratio and lipid composition dependence of the antiporter.

Metabolic Reconstruction Elucidates the Lifestyle of the Last Diplomonadida Common Ancestor

Diplomonads are a group of microbial eukaryotes found in oxygen-poor environments. There are both parasitic (e.g., Giardia intestinalis) and free-living (e.g., Trepomonas) members in the group.

The identification of ancestral traits is essential to understanding the evolution of any group. In the case of parasitic groups, this helps us understand the adaptation to this lifestyle and a particular host. Most diplomonads are parasites, but there are free-living members of the group nested among the host-associated diplomonads. Furthermore, most of the close relatives within Fornicata are free-living organisms. This leaves the lifestyle of the ancestor unclear. Here, we present metabolic maps of four different diplomonad species. We identified 853 metabolic reactions and 147 pathways present in at least one of the analyzed diplomonads. Our study suggests that diplomonads represent a metabolically diverse group in which differences correlate with different environments (e.g., the detoxification of arsenic). Using a parsimonious analysis, we also provide a description of the putative metabolism of the last Diplomonadida common ancestor. Our results show that the acquisition and loss of reactions have shaped metabolism since this common ancestor. There is a net loss of reaction in all branches leading to parasitic diplomonads, suggesting an ongoing reduction in the metabolic capacity. Important traits present in host-associated diplomonads (e.g., virulence factors and the synthesis of UDP-N-acetyl-d-galactosamine) are shared with free-living relatives. The last Diplomonadida common ancestor most likely already had acquired important enzymes for the salvage of nucleotides and had a reduced capacity to synthesize nucleotides, lipids, and amino acids de novo, suggesting that it was an obligate host-associated organism.

IMPORTANCE Diplomonads are a group of microbial eukaryotes found in oxygen-poor environments. There are both parasitic (e.g., Giardia intestinalis) and free-living (e.g., Trepomonas) members in the group. Diplomonads are well known for their anaerobic metabolism, which has been studied for many years. Here, we reconstructed whole metabolic networks of four extant diplomonad species as well as their ancestors, using a bioinformatics approach. We show that the metabolism within the group is under constant change throughout evolutionary time, in response to the environments that the different lineages explore. Both gene losses and gains are responsible for the adaptation processes. Interestingly, it appears that the last Diplomonadida common ancestor had a metabolism that is more similar to extant parasitic than free-living diplomonads. This suggests that the host-associated lifestyle of parasitic diplomonads, such as the human parasite G. intestinalis, is an old evolutionary adaptation.

Comparative Transcriptomics of Shiga Toxin-Producing and Commensal Escherichia coli and Cytokine Responses in Colonic Epithelial Cell Culture Infections

Ingestion of Shiga toxin-producing Escherichia coli (STEC) can result in a range of illness severity from asymptomatic to hemorrhagic colitis and death; thus risk assessment of STEC strains for human pathogenicity is important in the area of food safety. Illness severity depends in part on the combination of virulence genes carried in the genome, which can vary between strains even of identical serotype. To better understand how core genes are regulated differently among strains and to identify possible novel STEC virulence gene candidates that could be added to the risk assessment repertoire, we used comparative transcriptomics to investigate global gene expression differences between two STEC strains associated with severe illness and a commensal E. coli strain during in vitro intestinal epithelial cell (IEC) infections. Additionally, we compared a wide array of concomitant cytokine levels produced by the IECs. The cytokine expression levels were examined for a pattern representing STEC pathogenicity; however, while one STEC strain appeared to elicit a proinflammatory response, infection by the other strain produced a pattern comparable to the commensal E. coli. This result may be explained by the significant differences in gene content and expression observed between the STEC strains. RNA-Seq analysis revealed considerable disparity in expression of genes in the arginine and tryptophan biosynthesis/import pathways between the STEC strains and the commensal E. coli strain, highlighting the important role some amino acids play in STEC colonization and survival. Contrasting differential expression patterns were observed for genes involved in respiration among the three strains suggesting that metabolic diversity is a strategy utilized to compete with resident microflora for successful colonization. Similar temporal expression results for known and putative virulence genes were observed in the STEC strains, revealing strategies used for survival prior to and after initial adherence to IECs. Additionally, three genes encoding hypothetical proteins located in mobile genetic elements were, after interrogation of a large set of E. coli genomes, determined to likely represent novel STEC virulence factors.

From Normal Flora to Brain Abscesses: A Review of Streptococcus intermedius

Streptococcus intermedius is a β-hemolytic Gram-positive member of the Streptococcus anginosus group (SAG). Despite being a part of the normal microbiota, it is one of the most common pathogens associated with brain and liver abscesses and thoracic empyema, increasing as a result the morbidity and mortality rates in affected patients. Though there are numerous published case reports on S. intermedius infections, it is still understudied compared to other SAG members. Our knowledge of the genomic factors contributing to its dissemination to the brain and abscess development is also limited to few characterized genes. In this review, we summarize our current knowledge on S. intermedius identification methods, virulence factors, and insight provided by the whole-genome and correlate patients’ metadata, symptoms, and disease outcome with S. intermedius infections in 101 recent case reports obtained from PubMed. This combined information highlights the gaps in our understanding of S. intermedius pathogenesis, suggesting future research directions to unveil the factors contributing to abscess development.

Giardia lamblia Decreases NF-κB p65RelA Protein Levels and Modulates LPS-Induced Pro-Inflammatory Response in Macrophages

The protozoan Giardia lamblia is the most common cause of parasitic gastrointestinal infection worldwide. The parasite developed sophisticated, yet not completely disclosed, mechanisms to escape immune system and growth in the intestine. To further understand the interaction of G. lamblia with host immune cells, we investigated the ability of parasites to modulate the canonical activation of mouse macrophages (Raw 264.7 cell line) and human monocyte-derived macrophages triggered by the TLR4 agonist, lipopolysaccharide (LPS). We observed that G. lamblia impairs LPS-evoked pro-inflammatory status in these macrophage-like cells through inhibition of cyclooxygenase-2 and inducible nitric oxide synthase expression and subsequent NO production. This effect was in part due to the activity of three G. lamblia proteases, a 135 kDa metalloprotease and two cysteine proteases with 75 and 63 kDa, that cleave the p65^RelA subunit of the nuclear factor-kappa B (NF-κB). Moreover, Tnf and Ccl4 transcription was increased in the presence of the parasite. Overall, our data indicates that G. lamblia modulates macrophages inflammatory response through impairment of the NF-κB, thus silencing a crucial signaling pathway of the host innate immune response.

Drug resistance in Giardia: Mechanisms and alternative treatments for Giardiasis

The use of chemotherapeutic drugs is the main resource against clinical giardiasis due to the lack of approved vaccines. Resistance of G. duodenalis to the most used drugs to treat giardiasis, metronidazole and albendazole, is a clinical issue of growing concern and yet unknown impact, respectively. In the search of new drugs, the completion of the Giardia genome project and the use of biochemical, molecular and bioinformatics tools allowed the identification of ligands/inhibitors for about one tenth of ≈150 potential drug targets in this parasite. Further, the synthesis of second generation nitroimidazoles and benzimidazoles along with high-throughput technologies have allowed not only to define overall mechanisms of resistance to metronidazole but to screen libraries of repurposed drugs and new pharmacophores, thereby increasing the known arsenal of anti-giardial compounds to some hundreds, with most demonstrating activity against metronidazole or albendazole-resistant Giardia. In particular, cysteine-modifying agents which include omeprazole, disulfiram, allicin and auranofin outstand due to their pleiotropic activity based on the extensive repertoire of thiol-containing proteins and the microaerophilic metabolism of this parasite. Other promising agents derived from higher organisms including phytochemicals, lactoferrin and propolis as well as probiotic bacteria/fungi have also demonstrated significant potential for therapeutic and prophylactic purposes in giardiasis. In this context the present chapter offers a comprehensive review of the current knowledge, including commonly prescribed drugs, causes of therapeutic failures, drug resistance mechanisms, strategies for the discovery of new agents and alternative drug therapies.

Pathogenesis and post-infectious complications in giardiasis

Giardia is an important cause of diarrhoea, and results in post-infectious and extra-intestinal complications. This chapter presents a state-of-the art of our understanding of how this parasite may cause such abnormalities, which appear to develop at least in part in Assemblage-dependent manner. Findings from prospective longitudinal cohort studies indicate that Giardia is one of the four most prevalent enteropathogens in early life, and represents a risk factor for stunting at 2 years of age. This may occur independently of diarrheal disease, in strong support of the pathophysiological significance of the intestinal abnormalities induced by this parasite. These include epithelial malabsorption and maldigestion, increased transit, mucus depletion, and disruptions of the commensal microbiota. Giardia increases epithelial permeability and facilitates the invasion of gut bacteria. Loss of intestinal barrier function is at the core of the acute and post-infectious complications associated with this infection. Recent findings demonstrate that the majority of the pathophysiological responses triggered by this parasite can be recapitulated by the effects of its membrane-bound and secreted cysteine proteases.

Transcriptomic and proteomic analyses of Giardia intestinalis: Intestinal epithelial cell interactions

Giardia intestinalis is a unicellular protozoan parasite that infects the small intestines of humans and animals. Giardiasis, the disease caused by the parasite, occurs globally across socioeconomic boundaries but is mainly endemic in developing countries and particularly within young children, where pronounced effects manifests in a failure to thrive condition. The molecular pathogenesis of Giardia has been studied using in vitro models of human and rat intestinal epithelial cells (IECs) and parasites from the two major human genotypes or assemblages (A and B). High-quality, genome sequencing of representative isolates from assemblages A (WB) and B (GS) has enabled exploration of these host-parasite models using 'omics' technologies, allowing deep and quantitative analyses of global gene expression changes in IECs and parasites during their interactions, cross-talk and competition. These include a major up-regulation of immune-related genes in the IECs early after the start of interactions, as well as competition between host cells and parasites for nutrients like sugars, amino acids and lipids, which is also reflected in their secretome interactions. Unique parasite proteins dominate these interactions, with many major up-regulated genes being either hypothetical proteins or members of Giardia-specific gene families like the high-cysteine-rich membrane proteins (HCMPs), variable surface proteins (VSPs), alpha-giardins and cysteine proteases. Furthermore, these proteins also dominate in the secretomes, suggesting that they are important virulence factors in Giardia and crucial molecular effectors at the host-parasite interface.

Immune response markers in sera of children infected with Giardia duodenalis AI and AII subassemblages

In this study, we evaluated serum markers of immune responses in children infected with G. duodenalis and compared them with the characterized parasite isolates. The reactivity indexes (RI) of IgG (1.503 ± 0.819) and IgA (2.308 ± 1.935) antibodies were significantly higher (P < 0.001) in infected children than in non-infected children. There were also statistically significantly higher serum levels (P < 0.05) of IFN-γ (393.10 ± 983.90 pg/mL) as well as serum (30.03 ± 10.92 μmol/L) and saliva nitric oxid derivatives (NO_x) (192.4 ± 151.2 μmol/L) in children infected with G. duodenalis compared to the group of non-parasitized children (127.4 ± 274.30 pg/mL; 25.82 ± 7.74 μmol/L and 122.5 ± 105.90 μmol/L, respectively). Regarding the characterized genetic variants of G. duodenalis and the immune response profiles, no differences were observed in terms of antibody reactivity or levels of serum cytokine and NO_x among children infected with AI or AII subassemblages. The elevated levels of IFN-γ and NO_x indicate that G. duodenalis intestinal infection in humans induces a cellular immune response detectable at the systemic level. Moreover, no significant differences in the antibody reactivity profile or the cytokine and NO_x production in the sera of children infected with AI or AII G. duodenalis variants were observed, suggesting that subtypes of the parasite do not influence the immune response profile.

Giardia duodenalis: Role of secreted molecules as virulent factors in the cytotoxic effect on epithelial cells

During the course of giardiasis in humans and experimental models, G. duodenalis trophozoites express and secrete several proteins (ESPs) affecting structural, cellular and soluble components of the host intestinal milieu. These include the toxin-like molecules CRP136 and ESP58 that induce intestinal hyper-peristalsis. After the completion of the Giardia genome database and using up-to date transcriptomic and proteomic approaches, secreted 'virulence factors' have also been identified and experimentally characterized. This repertoire includes arginine deiminase (ADI) that competes for arginine, an important energy source for trophozoites, some high-cysteine membrane proteins (HCMPs) and VSP88, a versatile variant surface protein (VSP) that functions as an extracellular protease. Another giardial protein, enolase, moonlights as a metabolic enzyme that interacts with the fibrinolytic system and damages host epithelial cells. Other putative Giardia virulence factors are cysteine proteases that degrade multiple host components including mucin, villin, tight junction proteins, immunoglobulins, defensins and cytokines. One of these proteases, named giardipain-1, decreases transepithelial electrical resistance and induces apoptosis in epithelial cells. A putative role for tenascins, present in the Giardia's secretome, is interfering with the host epidermal growth factor. Based on the roles that these molecules play, drugs may be designed to interfere with their functions. This review presents a comprehensive description of secreted Giardia virulence factors. It further describes their cytotoxic mechanisms and roles in the pathophysiology of giardiasis, and then assesses their potential as targets for drug development.

The possible role of bacteria, viruses, and parasites in initiation and exacerbation of irritable bowel syndrome

Irritable bowel syndrome (IBS) is a prolonged and disabling functional gastrointestinal disorder with the incidence rate of 18% in the world. IBS could seriously affect lifetime of patients and cause high economic burden on the community. The pathophysiology of the IBS is hardly understood, whereas several possible mechanisms, such as visceral hypersensitivity, irregular gut motility, abnormal brain-gut relations, and the role of infectious agents, are implicated in initiation and development of this syndrome. Different studies demonstrated an alteration in B-lymphocytes, mast cells (MC), T-lymphocytes, and cytokine concentrations in intestinal mucosa or systemic circulation that are likely to contribute to the formation of the IBS. Therefore, IBS could be developed in those with genetic predisposition. Infections' role in initiation and exacerbation of IBS has been investigated by quite several clinical studies; moreover, the possible role of some pathogens in development and exacerbation of this disease has been described. It appears that the main obligatory pathogens correspond with the IBS disease, Clostridium difficile, Escherichia coli, Mycobacterium avium subspecies paratuberculosis, Campylobacter concisus, Campylobacter jejuni, Chlamydia trachomatis, Helicobacter pylori, Pseudomonas aeruginosa, Salmonella spp, Shigella spp, and viruses, particularly noroviruses. A number of pathogenic parasites (Blastocystis, Dientamoeba fragilis, and Giardia lamblia) may also be involved in the progression and exacerbation of the disease. Based on the current knowledge, the current study concludes that the most common bacterial, viral, and parasitic pathogens may be involved in the development and progression of IBS.

Dietary l-arginine Supplementation Alleviates the Intestinal Injury and Modulates the Gut Microbiota in Broiler Chickens Challenged by Clostridium perfringens

Our previous reports suggested that Dietary l-arginine supplementation attenuated gut injury of broiler chickens infected with Clostridium perfringens by enhancing intestinal immune responses, absorption and barrier function, but its effect on the gut microbiome of broiler chickens remains unclear. This experiment aimed at evaluating the effects of Dietary l-arginine supplementation on the gut bacterial community composition and function of broiler chickens challenged with C. perfringens. In total, 105 1-day-old male Arbor Acres broiler chickens were assigned to three groups: Control (CTL), C. perfringens-challenged (CP), and C. perfringens-challenged and fed diet supplemented with 0.3% l-arginine (ARGCP) groups. The challenge led to macroscopic and histomorphological gut lesions, decreased villus height and increased the number of Observed species, Shannon, Chao1 and ACE indices of ileal microbiota, whereas l-arginine addition reversed these changes. Moreover, the three treatments harbored distinct microbial communities (ANOSIM, P < 0.05). At the genus level, 24 taxa (e.g., Nitrosomonas spp., Coxiella spp., Ruegeria spp., and Thauera spp.) were significantly more abundant in CP group than in CTL group (P < 0.05), whereas the levels of 23 genera of them were significantly decreased by l-arginine supplementation (P < 0.05). The abundances of only 3 genera were different between CTL and ARGCP groups (P < 0.05). At the species level, the challenge promoted the relative abundance of Nitrospira sp. enrichment culture clone M1-9, Bradyrhizobium elkanii, Nitrospira bacterium SG8-3, and Pseudomonas veronii, which was reversed by l-arginine supplementation (P < 0.05). Furthermore, the challenge decreased the levels of Lactobacillus gasseri (P < 0.05). Predictive functional profiling of microbial communities by PICRUSt showed that compared with CP group, ARGCP group had enriched pathways relating to membrane transport, replication and repair, translation and nucleotide metabolism and suppressed functions corresponding to amino acid and lipid metabolisms (P < 0.05). The relative abundances of KEGG pathways in l-arginine-fed broilers were almost equal to those of the controls. In conclusion, l-arginine alleviated the gut injury and normalized the ileal microbiota of C. perfringens-challenged chickens to resemble that of unchallenged controls in terms of microbial composition and functionality.

Responses of the Differentiated Intestinal Epithelial Cell Line Caco-2 to Infection With the Giardia intestinalis GS Isolate

Giardia intestinalis is a parasitic protist that causes diarrhea in humans, affecting mainly children of the developing world, elderly and immunocompromised individuals. Humans are infected by two major Giardia assemblages (i.e. genetic subtypes), A and B, with the latter being the most common. So far, there is little information on molecular or cellular changes during infections with assemblage B. Here, we used RNA sequencing to study transcriptional changes in Caco-2 intestinal epithelial cells (IECs) co-incubated with assemblage B (GS isolate) trophozoites for 1.5, 3, and 4.5 h. We aimed to identify early molecular events associated with the establishment of infection and followed cellular protein changes up to 10 h. IEC transcriptomes showed a dominance of immediate early response genes which was sustained across all time points. Transcription of inflammatory cytokines (e.g., cxcl1-3, ccl2, 1l1a, and il1b) peaked at 1.5 and 3 h of infection. Compared to co-incubation with assemblage A Giardia, we identified the induction of novel cytokines (cxcl8, cxcl10, csf1, cx3cl1, il12a, il11) and showed that inflammatory signaling is mediated by Erk1/2 phosphorylation (mitogen activated protein kinase, MAPK), nuclear factor kappa B (NFκB) and adaptor protein-1 (AP-1). We also showed that GS trophozoites attenuate P38 (MAPK) phosphorylation in IECs. Low amounts of IL-8, CXCL1 and CCL20 proteins were measured in the interaction medium, which was attributed to cytokine degradation by trophozoite secreted proteases. Based on the transcriptome, the decay of cytokines mRNA mediated by zinc finger protein 36 might be another mechanism controlling cytokine levels at later time points. IEC transcriptomes suggested homeostatic responses to counter oxidative stress, glucose starvation, and disturbances in amino acid and lipid metabolism. A large group of differentially transcribed genes were associated with cell cycle arrest and induction of apoptosis, which was validated at protein level. IEC transcriptomes also suggested changes in tight junction's integrity, microvilli structure and the extracellular mucin layer. This is the first study to illuminate transcriptional and protein regulatory events underlying IECs responses and pathogenesis during Giardia assemblage B infection. It highlights differences compared to assemblage A infections which might account for the differences observed in human infections with the two assemblages.

1H HR-MAS NMR spectroscopy to study the metabolome of the protozoan parasite Giardia lamblia

Knowledge of the metabolic profile and exchange processes in the protozoan parasite Giardia lamblia is of importance for a better understanding of the biochemical processes and for the development of drugs to control diseases caused by G. lamblia. In the current paper, ¹H High Resolution Magic Angle Spinning (HR-MAS) NMR spectroscopy was directly applied to G. lamblia trophozoite suspensions to analyze the detectable small metabolites with a minimum of intervention. Thirty-one components were identified with main contributions from amino acids such as alanine and ornithine. The reproducibility, variability, and stability of the metabolites were investigated. Citrulline was found to be formed as an intermediate and citrulline levels depended on the stage of cell growth. Glucose-1-phosphate was found to be formed in relatively high amounts after cell harvesting if enzymes were not inactivated. In addition, the metabolic footprint of Giardia trophozoites, i.e. changes in the culture medium induced by G. lamblia, was investigated by liquid state NMR spectroscopy of culture media before and after inoculation. A quantitative comparison of the NMR spectra revealed component changes in the culture media during growth. The results suggested that not glucose but rather arginine serves as main energy supply. Biochemical functions of intracellular components and their metabolic exchange with the culture medium are discussed. The results provide an important basis for the design of HR-MAS NMR based metabolomic studies of G. lamblia in particular and any protozoan parasite samples in general.

Characterization of the Giardia intestinalis secretome during interaction with human intestinal epithelial cells: The impact on host cells

BACKGROUND

Giardia intestinalis is a non-invasive protozoan parasite that causes giardiasis in humans, the most common form of parasite-induced diarrhea. Disease mechanisms are not completely defined and very few virulence factors are known.

METHODOLOGY

To identify putative virulence factors and elucidate mechanistic pathways leading to disease, we have used proteomics to identify the major excretory-secretory products (ESPs) when Giardia trophozoites of WB and GS isolates (assemblages A and B, respectively) interact with intestinal epithelial cells (IECs) in vitro.

FINDINGS

The main parts of the IEC and parasite secretomes are constitutively released proteins, the majority of which are associated with metabolism but several proteins are released in response to their interaction (87 and 41 WB and GS proteins, respectively, 76 and 45 human proteins in response to the respective isolates). In parasitized IECs, the secretome profile indicated effects on the cell actin cytoskeleton and the induction of immune responses whereas that of Giardia showed anti-oxidation, proteolysis (protease-associated) and induction of encystation responses. The Giardia secretome also contained immunodominant and glycosylated proteins as well as new candidate virulence factors and assemblage-specific differences were identified. A minor part of Giardia ESPs had signal peptides (29% for both isolates) and extracellular vesicles were detected in the ESPs fractions, suggesting alternative secretory pathways. Microscopic analyses showed ESPs binding to IECs and partial internalization. Parasite ESPs reduced ERK1/2 and P38 phosphorylation and NF-κB nuclear translocation. Giardia ESPs altered gene expression in IECs, with a transcriptional profile indicating recruitment of immune cells via chemokines, disturbances in glucose homeostasis, cholesterol and lipid metabolism, cell cycle and induction of apoptosis.

CONCLUSIONS

This is the first study identifying Giardia ESPs and evaluating their effects on IECs. It highlights the importance of host and parasite ESPs during interactions and reveals the intricate cellular responses that can explain disease mechanisms and attenuated inflammatory responses during giardiasis.

Host specificity in the Giardia duodenalis species complex

Giardia duodenalis is a unicellular flagellated parasite that infects the gastrointestinal tract of a wide range of mammalian species, including humans. Investigations of protein and DNA polymorphisms revealed that G. duodenalis should be considered as a species complex, whose members, despite being morphologically indistinguishable, can be classified into eight groups, or Assemblages, separated by large genetic distances. Assemblages display various degree of host specificity, with Assemblages A and B occurring in humans and many other hosts, Assemblage C and D in canids, Assemblage E in hoofed animals, Assemblage F in cats, Assemblage G in rodents, and Assemblage H in pinnipeds. The factors determining host specificity are only partially understood, and clearly involve both the host and the parasite. Here, we review the results of in vitro and in vivo experiments, and clinical observations to highlight relevant biological and genetic differences between Assemblages, with a focus on human infection.

Dietary l-arginine inhibits intestinal Clostridium perfringens colonisation and attenuates intestinal mucosal injury in broiler chickens

We investigated the effects of dietary l-arginine level and feeding duration on the intestinal damage of broilers induced by Clostridium perfringens (CP) in vivo, and the antimicrobial effect of its metabolite nitric oxide (NO) in vitro. The in vivo experiment was designed as a factorial arrangement of three dietary treatments×two challenge statuses. Broilers were fed a basal diet (CON) or a high-arginine diet (ARG) containing 1·87 % l-arginine, or CON for the first 8 d and ARG from days 9 to 28 (CON/ARG). Birds were co-infected with or without Eimeria and CP (EM/CP). EM/CP challenge led to intestinal injury, as evidenced by lower plasma d-xylose concentration (P<0·01), higher paracellular permeability in the ileum (P<0·05) and higher numbers of Escherichia coli (P<0·05) and CP (P<0·001) in caecal digesta; however, this situation could be alleviated by l-arginine supplementation (P<0·05). The intestinal claudin-1 and occludin mRNA expression levels were decreased (P<0·05) following EM/CP challenge; this was reversed by l-arginine supplementation (P<0·05). Moreover, EM/CP challenge up-regulated (P<0·05) claudin-2, interferon-γ (IFN-γ), toll-like receptor 2 and nucleotide-binding oligomerisation domain 1 (NOD1) mRNA expression, and l-arginine supplementation elevated (P<0·05) IFN-γ, IL-10 and NOD1 mRNA expression. In vitro study showed that NO had bacteriostatic activity against CP (P<0·001). In conclusion, l-arginine supplementation could inhibit CP overgrowth and alleviate intestinal mucosal injury by modulating innate immune responses, enhancing barrier function and producing NO.

Expression and secretion of the Giardia duodenalis variant surface protein 9B10A by transfected trophozoites causes damage to epithelial cell monolayers mediated by protease activity

Giardia duodenalis is the protozoan parasite responsible for most cases of parasitic diarrhea worldwide. The pathogenic mechanisms of giardiasis have not yet been fully characterized. In this context parasite's excretory/secretory products have been related to the damage induced by the parasite on enterocytes. Among these is the Variable Surface Proteins (VSPs) family involved in antigenic variation and in the induction of protective response. In proteomic analyses carried out to identify the proteases with high molecular weight secreted by Giardia trophozoites during the initial phase of interaction with IEC-6 cell monolayers we identified the VSP9B10A protein. In silico bioinformatics analyses predicted a central region in residues 324-684 displaying the catalytic triad and the substrate binding pocket of cysteine proteases. The analysis of the effect of the VSP9B10A protein on epithelial cell monolayers using trophozoites that were transfected with a plasmid carrying the vsp9b10a gene sequence under the control of a constitutive promoter showed that transfected trophozoites expressing the VSP9B10A protein caused cytotoxic damages on IEC-6 and MDCK cell monolayers. This was characterized by loss of cell-cell contacts and cell detachment from the substrate while no damage was observed with trophozoites that did not express the VSP9B10A protein. The same cytotoxic effect was detected when IEC-6 cell monolayers were incubated only with supernatants from co-cultures of IEC-6 cell monolayers with VSP9B10A transfected trophozoites and this effect was not observed when transfected trophozoites were incubated with a monospecific polyclonal antibody anti-VSP9B10A previous to interaction with IEC-6 monolayers. These results demonstrate that the VSP9B10A protein secreted upon interaction with epithelial cells caused damage in these cells. Thus this protein might be considered as a conditional virulence factor candidate. To our knowledge this is the first report on the proteolytic activity from a Giardia VSP opening new research lines on these proteins.

Proteomic and functional analyses reveal pleiotropic action of the anti-tumoral compound NBDHEX in Giardia duodenalis

Giardiasis, a parasitic diarrheal disease caused by Giardia duodenalis, affects one billion people worldwide. Treatment relies only on a restricted armamentarium of drugs. The disease burden and the increase in treatment failure highlight the need for novel, safe and well characterized drug options. The antitumoral compound NBDHEX is effective in vitro against Giardia trophozoites and inhibits glycerol-3-phosphate dehydrogenase. Aim of this work was to search for additional NBDHEX protein targets. The intrinsic NBDHEX fluorescence was exploited in a proteomic analysis to select and detect modified proteins in drug treated Giardia. In silico structural analysis, intracellular localization and functional assays were further performed to evaluate drug effects on the identified targets. A small subset of Giardia proteins was covalently bound to the drug at specific cysteine residues. These proteins include metabolic enzymes, e.g. thioredoxin reductase (gTrxR), as well as elongation factor 1B-γ (gEF1Bγ), and structural proteins, e.g. α-tubulin. We showed that NBDHEX in vitro binds to recombinant gEF1Bγ and gTrxR, but only the last one could nitroreduce NBDHEX leading to drug modification of gTrxR catalytic cysteines, with concomitant disulphide reductase activity inhibition and NADPH oxidase activity upsurge. Our results indicate that NBDHEX reacts with multiple targets whose roles and/or functions are specifically hampered. In addition, NBDHEX is in turn converted to reactive intermediates extending its toxicity. The described NBDHEX pleiotropic action accounts for its antigiardial activity and encourages the use of this drug as a promising alternative for the future treatment of giardiasis.

Arginine deiminase pathway enzymes: evolutionary history in metamonads and other eukaryotes

BACKGROUND

Multiple prokaryotic lineages use the arginine deiminase (ADI) pathway for anaerobic energy production by arginine degradation. The distribution of this pathway among eukaryotes has been thought to be very limited, with only two specialized groups living in low oxygen environments (Parabasalia and Diplomonadida) known to possess the complete set of all three enzymes. We have performed an extensive survey of available sequence data in order to map the distribution of these enzymes among eukaryotes and to reconstruct their phylogenies.

RESULTS

We have found genes for the complete pathway in almost all examined representatives of Metamonada, the anaerobic protist group that includes parabasalids and diplomonads. Phylogenetic analyses indicate the presence of the complete pathway in the last common ancestor of metamonads and heterologous transformation experiments suggest its cytosolic localization in the metamonad ancestor. Outside Metamonada, the complete pathway occurs rarely, nevertheless, it was found in representatives of most major eukaryotic clades.

CONCLUSIONS

Phylogenetic relationships of complete pathways are consistent with the presence of the Archaea-derived ADI pathway in the last common ancestor of all eukaryotes, although other evolutionary scenarios remain possible. The presence of the incomplete set of enzymes is relatively common among eukaryotes and it may be related to the fact that these enzymes are involved in other cellular processes, such as the ornithine-urea cycle. Single protein phylogenies suggest that the evolutionary history of all three enzymes has been shaped by frequent gene losses and horizontal transfers, which may sometimes be connected with their diverse roles in cellular metabolism.