Fermentable Dietary Fiber Promotes Helminth Infection and Exacerbates Host Inflammatory Responses

Optimizing Akkermansia muciniphila Isolation and Cultivation: Insights into Gut Microbiota Composition and Potential Growth Promoters in a Chinese Cohort

The study aims to analyze the composition of the gut microbiota in Chinese individuals using metagenomic sequencing technology, with a particular focus on the abundance of Akkermansia muciniphila (Akk). To improve the efficiency of Akk isolation and identification accuracy, modifications were made to the enrichment culture medium and 16S rRNA universal primers. Additionally, potential growth-promoting factors that stimulate Akk growth were explored through in vitro screening. The research results revealed that the abundance of Akk in Chinese fecal samples ranged from 0.004% to 0.4%. During optimization, a type of animal protein peptide significantly enhanced the enrichment efficiency of Akk, resulting in the isolation of three Akk strains from 14 fecal samples. Furthermore, 17 different growth-promoting factors were compared, and four factors, including galactose, sialic acid, lactose, and chitosan, were identified as significantly promoting Akk growth. Through orthogonal experiments, the optimal ratio of these four growth-promoting factors was determined to be 1:1:2:1. After adding 1.25% of this growth-promoting factor combination to the standard culture medium, Akk was cultivated at 37° for 36 h, achieving an OD600nm value of 1.169, thus realizing efficient proliferation and optimized cultivation of Akk. This study provides important clues for a deeper understanding of the gut microbiota composition in Chinese individuals, while also offering effective methods for the isolation and cultivation of Akk, laying the groundwork for its functional and application research in the human body.

Diet composition drives tissue-specific intensity of murine enteric infections

Diet composition plays a large role in regulating gut health and enteric infection. In particular, synthetic "Western-style" diets may predispose to disease, while whole-grain diets containing high levels of crude fiber are thought to promote gut health. Here, we show that, in contrast to this paradigm, mice fed with unrefined chow are significantly more susceptible to infection with Trichuris muris, a caecum-dwelling nematode, than mice fed with refined, semi-synthetic diets (SSDs). Moreover, mice fed with SSD supplemented with inulin, a fermentable fiber, developed chronic T. muris burdens, whereas mice fed with SSD efficiently cleared the infection. Diet composition significantly impacted infection-induced changes in the host gut microbiome. Mice infected with the bacterium Citrobacter rodentium were also more susceptible to pathogen colonization when fed with either chow or inulin-enriched SSD. However, transcriptomic analysis of tissues from mice fed with either SSD or inulin-enriched SSD revealed that, in contrast to T. muris, increased C. rodentium infection appeared to be independent of the host immune response. Accordingly, exogenous treatment with interleukin (IL)-25 reduced T. muris burdens in inulin-fed mice, whereas IL-22 treatment was unable to restore resistance to C. rodentium colonization. Diet-mediated effects on pathogen burden were more pronounced for large intestine-dwelling pathogens, as effects on small the intestinal helminth (Heligmosomoides polygyrus) were less evident, and protozoan (Giardia muris) infection burdens were equivalent in mice fed with chow, inulin-enriched SSD, or SSD, despite higher cyst excretion in chow-fed mice. Collectively, our results point to a tissue- and pathogen-restricted effect of dietary fiber levels on enteric infection intensity.IMPORTANCEEnteric infections induce dysbiosis and inflammation and are a major public health burden. As the gut environment is strongly shaped by diet, the role of different dietary components in promoting resistance to infection is of interest. While diets rich in fiber or whole grain are normally associated with improved gut health, we show here that these components predispose the host to higher levels of pathogen infection. Thus, our results have significance for interpreting how different dietary interventions may impact on gastrointestinal infections. Moreover, our results may shed light on our understanding of how gut flora and mucosal immune function is influenced by the food that we eat.

Gut microbiota-mediated polyphenol metabolism is restrained by parasitic whipworm infection and associated with altered immune function in mice

Polyphenols are phytochemicals commonly found in plant-based diets which have demonstrated immunomodulatory and anti-inflammatory properties. However, the interplay between polyphenols and pathogens at mucosal barrier surfaces has not yet been elucidated in detail. Here, we show that proanthocyanidin (PAC) polyphenols interact with gut parasites to influence immune function and gut microbial-derived metabolites in mice. PAC intake inhibited mastocytosis during infection with the small intestinal roundworm Heligmosomoides polygyrus, and altered the host tissue transcriptome at the site of infection with the large intestinal whipworm Trichuris muris, with a notable enhancement of type-1 inflammatory and interferon-driven gene pathways. In the absence of infection, PAC intake promoted the expansion of Turicibacter within the gut microbiota, increased fecal short chain fatty acids, and enriched phenolic metabolites such as phenyl-γ-valerolactones in the cecum. However, these putatively beneficial effects were reduced in PAC-fed mice infected with T. muris, suggesting concomitant parasite infection can attenuate gut microbial-mediated PAC catabolism. Collectively, our results suggest an inter-relationship between a phytonutrient and infection, whereby PAC may augment parasite-induced inflammation (most prominently with the cecum dwelling T. muris), and infection may abrogate the beneficial effects of health-promoting phytochemicals.

Another decade of Trichuris muris research: An update and application of key discoveries

The mouse whipworm, Trichuris muris, has been used for over 60 years as a tractable model for human trichuriasis, caused by the related whipworm species, T. trichiura. The history of T. muris research, from the discovery of the parasite in 1761 to understanding the lifecycle and outcome of infection with different doses (high versus low dose infection), as well as the immune mechanisms associated with parasite expulsion and chronic infection have been detailed in an earlier review published in 2013. Here, we review recent advances in our understanding of whipworm biology, host-parasite interactions and basic immunology brought about using the T. muris mouse model, focussing on developments from the last decade. In addition to the traditional high/low dose infection models that have formed the mainstay of T. muris research to date, novel models involving trickle (repeated low dose) infection in laboratory mice or infection in wild or semi-wild mice have led to important insights into how immunity develops in situ in a multivariate environment, while the use of novel techniques such as the development of caecal organoids (enabling the study of larval development ex vivo) promise to deliver important insights into host-parasite interactions. In addition, the genome and transcriptome analyses of T. muris and T. trichiura have proven to be invaluable tools, particularly in the context of vaccine development and identification of secreted products including proteins, extracellular vesicles and micro-RNAs, shedding further light on how these parasites communicate with their host and modulate the immune response to promote their own survival.

Dietary non-starch polysaccharides impair immunity to enteric nematode infection

BACKGROUND

The influence of diet on immune function and resistance to enteric infection and disease is becoming ever more established. Highly processed, refined diets can lead to inflammation and gut microbiome dysbiosis, whilst health-promoting dietary components such as phytonutrients and fermentable fibres are thought to promote a healthy microbiome and balanced mucosal immunity. Chicory (Cichorium intybus) is a leafy green vegetable rich in fibres and bioactive compounds that may promote gut health.

RESULTS

Unexpectedly, we here show that incorporation of chicory into semisynthetic AIN93G diets renders mice susceptible to infection with enteric helminths. Mice fed a high level of chicory leaves (10% dry matter) had a more diverse gut microbiota, but a diminished type-2 immune response to infection with the intestinal roundworm Heligmosomoides polygyrus. Furthermore, the chicory-supplemented diet significantly increased burdens of the caecum-dwelling whipworm Trichuris muris, concomitant with a highly skewed type-1 immune environment in caecal tissue. The chicory-supplemented diet was rich in non-starch polysaccharides, particularly uronic acids (the monomeric constituents of pectin). In accordance, mice fed pectin-supplemented AIN93G diets had higher T. muris burdens and reduced IgE production and expression of genes involved in type-2 immunity. Importantly, treatment of pectin-fed mice with exogenous IL-25 restored type-2 responses and was sufficient to allow T. muris expulsion.

CONCLUSIONS

Collectively, our data suggest that increasing levels of fermentable, non-starch polysaccharides in refined diets compromises immunity to helminth infection in mice. This diet-infection interaction may inform new strategies for manipulating the gut environment to promote resistance to enteric parasites.

Diet-microbiota crosstalk and immunity to helminth infection

Helminths are large multicellular parasites responsible for widespread chronic disease in humans and animals. Intestinal helminths live in close proximity with the host gut microbiota and mucosal immune network, resulting in reciprocal interactions that closely influence the course of infections. Diet composition may strongly regulate gut microbiota composition and intestinal immune function and therefore may play a key role in modulating anti-helminth immune responses. Characterizing the multitude of interactions that exist between different dietary components (e.g., dietary fibres), immune cells, and the microbiota, may shed new light on regulation of helminth-specific immunity. This review focuses on the current knowledge of how metabolism of dietary components shapes immune response during helminth infection, and how this information may be potentially harnessed to design new therapeutics to manage parasitic infections and associated diseases.

Gastrointestinal worms and bacteria: From association to intervention

A plethora of studies, both experimental and epidemiological, have indicated the occurrence of associations between infections by gastrointestinal (GI) helminths and the composition and function of the host gut microbiota. Given the worldwide risk and spread of anthelmintic resistance, particularly for GI parasites of livestock, a better understanding of the mechanisms underpinning the relationships between GI helminths and the gut microbiome, and between the latter and host health, may assist the development of novel microbiome-targeting and other bacteria-based strategies for parasite control. In this article, we review current and prospective methods to manipulate the host gut microbiome, and/or to exploit the immune stimulatory and modulatory properties of gut bacteria (and their products) to counteract the negative impact of GI worm infections; we also discuss the potential applications of these intervention strategies in programmes aimed to aid the fight against helminth diseases of humans and livestock.

Inulin: properties and health benefits

Inulin, a soluble dietary fiber, is widely found in more than 36 000 plant species as a reserve polysaccharide. The primary sources of inulin, include Jerusalem artichoke, chicory, onion, garlic, barley, and dahlia, among which Jerusalem artichoke tubers and chicory roots are often used as raw materials for inulin production in the food industry. It is universally acknowledged that inulin as a prebiotic has an outstanding effect on the regulation of intestinal microbiota via stimulating the growth of beneficial bacteria. In addition, inulin also exhibits excellent health benefits in regulating lipid metabolism, weight loss, lowering blood sugar, inhibiting the expression of inflammatory factors, reducing the risk of colon cancer, enhancing mineral absorption, improving constipation, and relieving depression. In this review paper, we attempt to present an exhaustive overview of the function and health benefits of inulin.

Trickle infection with Heligmosomoides polygyrus results in decreased worm burdens but increased intestinal inflammation and scarring

Introduction

Intestinal roundworms cause chronic debilitating disease in animals, including humans. Traditional experimental models of these types of infection use a large single-dose infection. However, in natural settings, hosts are exposed to parasites on a regular basis and when mice are exposed to frequent, smaller doses of Heligmosomoides polygyrus, the parasites are cleared more quickly. Whether this more effective host response has any negative consequences for the host is not known.

Results

Using a trickle model of infection, we found that worm clearance was associated with known resistance-related host responses: increased granuloma and tuft cell numbers, increased levels of granuloma IgG and decreased intestinal transit time, as well as higher serum IgE levels. However, we found that the improved worm clearance was also associated with an inflammatory phenotype in and around the granuloma, increased smooth muscle hypertrophy/hyperplasia, and elevated levels of Adamts gene expression.

Discussion

To our knowledge, we are the first to identify the involvement of this protein family of matrix metalloproteinases (MMPs) in host responses to helminth infections. Our results highlight the delicate balance between parasite clearance and host tissue damage, which both contribute to host pathology. When continually exposed to parasitic worms, improved clearance comes at a cost.

Garlic-Derived Metabolites Exert Antioxidant Activity, Modulate Gut Microbiota Composition and Limit Citrobacter rodentium Infection in Mice

The garlic-derived compounds propyl propane thiosulfinate (PTS) and propyl propane thiosulfonate (PTSO) are metabolites with putative health benefits against intestinal inflammation that may be related to their antioxidant activity. However, the underlying mechanisms remain unclear, and whether PTS-PTSO can promote gut health by altering the microbiota and exert protection against enteric pathogens needs further investigation. Here, we explored the antioxidant activity of PTS-PTSO in murine macrophages in vitro, and in an in vivo model of bacterial infection with the bacterial pathogen Citrobacter rodentium. PTS-PTSO attenuated reactive oxygen species in lipopolysaccharide-stimulated macrophages in a nuclear factor erythroid factor 2-related factor 2 (Nrf2)-dependent manner, decreased nitric oxide levels both in macrophages in vitro and in the sera of mice fed PTS-PTSO, and had putatively beneficial effects on the commensal gut microbiota. Importantly, PTS-PTSO decreased faecal C. rodentium counts, concomitant with upregulation of Nrf2-related genes in colon tissue. Thus, PTS-PTSO mediates Nrf2-mediated antioxidant activity and modulates gut microbiota, which may protect the host against C. rodentium colonization. Our results provide further insight into how PTS-PTSO and related bioactive dietary compounds may reduce enteric infections.

Garlic-derived organosulfur compounds regulate metabolic and immune pathways in macrophages and attenuate intestinal inflammation in mice

Scope: Garlic is a source of bioactive phytonutrients that may have anti‐inflammatory or immunomodulatory properties. The mechanism(s) underlying the bioactivity of these compounds and their ability to regulate responses to enteric infections remains unclear.

Methods and Results: This study investigates if a garlic‐derived preparation (PTSO‐PTS) containing two organosulfur metabolites, propyl‐propane thiosulfonate (PTSO), and propyl‐propane thiosulfinate (PTS), regulate inflammatory responses in murine macrophages and intestinal epithelial cells (IEC) in vitro, as well as in a model of enteric parasite‐induced inflammation. PTSO‐PTS decreases lipopolysaccharide‐induced secretion of TNFα, IL‐6, and IL‐27 in macrophages. RNA‐sequencing demonstrates that PTSO‐PTS strongly suppresses pathways related to immune and inflammatory signaling. PTSO‐PTS induces the expression of a number of genes involved in antioxidant responses in IEC during exposure to antigens from the parasite Trichuris muris. In vivo, PTSO‐PTS does not affect T. muris establishment or intestinal T‐cell responses but significantly alters cecal transcriptomic responses. Notably, a reduction in T. muris‐induced expression of Tnf, Saa2, and Nos2 is observed.

Conclusion: Garlic‐derived organosulfur compounds exert anti‐inflammatory effects in macrophages and IEC, and regulate gene expression during intestinal infection. These compounds and related organic molecules may thus hold potential as functional food components to improve gut health in humans and animals.

The phytonutrient cinnamaldehyde limits intestinal inflammation and enteric parasite infection

Phytonutrients such as cinnamaldehyde (CA) have been studied for their effects on metabolic diseases, but their influence on mucosal inflammation and immunity to enteric infection are not well documented. Here, we show that consumption of CA in mice significantly down-regulates transcriptional pathways connected to inflammation in the small intestine, and alters T-cell populations in mesenteric lymph nodes. During infection with the enteric helminth Heligomosomoides polygyrus, CA treatment attenuated infection-induced changes in biological pathways connected to cell cycle and mitotic activity, and tended to reduce worm burdens. Mechanistically, CA did not appear to exert activity through a prebiotic effect, as CA treatment did not significantly change the composition of the gut microbiota. Instead, in vitro experiments showed that CA directly induced xenobiotic metabolizing pathways in intestinal epithelial cells and suppressed endotoxin-induced inflammatory responses in macrophages. Collectively, our results show that CA down-regulates inflammatory pathways in the intestinal mucosa and can limit the pathological response to enteric infection. These properties appear to be largely independent of the gut microbiota, and instead connected to the ability of CA to induce antioxidant pathways in intestinal cells. Our results encourage further investigation into the use of CA and related phytonutrients as functional food components to promote intestinal health in humans and animals.

Control of lymphocyte functions by gut microbiota-derived short-chain fatty acids

A mounting body of evidence indicates that dietary fiber (DF) metabolites produced by commensal bacteria play essential roles in balancing the immune system. DF, considered nonessential nutrients in the past, is now considered to be necessary to maintain adequate levels of immunity and suppress inflammatory and allergic responses. Short-chain fatty acids (SCFAs), such as acetate, propionate, and butyrate, are the major DF metabolites and mostly produced by specialized commensal bacteria that are capable of breaking down DF into simpler saccharides and further metabolizing the saccharides into SCFAs. SCFAs act on many cell types to regulate a number of important biological processes, including host metabolism, intestinal functions, and immunity system. This review specifically highlights the regulatory functions of DF and SCFAs in the immune system with a focus on major innate and adaptive lymphocytes. Current information regarding how SCFAs regulate innate lymphoid cells, T helper cells, cytotoxic T cells, and B cells and how these functions impact immunity, inflammation, and allergic responses are discussed.

Embracing nature's complexity: Immunoparasitology in the wild

A wealth of research is dedicated to understanding how resistance against parasites is conferred and how parasite-driven pathology is regulated. This research is in part driven by the hope to better treatments for parasitic diseases of humans and livestock, and in part by immunologists who use parasitic infections as biomedical tools to evoke physiological immune responses. Much of the current mechanistic knowledge has been discovered in laboratory studies using model organisms, especially the laboratory mouse. However, wildlife are also hosts to a range of parasites. Through the study of host-parasite interactions in these non-laboratory systems we can gain a deeper understanding of parasite immunology in a more natural, complex environment. With a focus on helminth parasites, we here explore the insights gained into parasite-induced immune responses through (for immunologists) non-conventional experimental systems, and how current core findings from laboratory studies are reflected in these more natural conditions. The quality of the immune response is undoubtedly a central player in susceptibility versus resistance, as many laboratory studies have shown. Yet, in the wild, parasite infections tend to be chronic diseases. Whilst reading our review, we encourage the reader to consider the following questions which may (only) be answered by studying naturally occurring parasites in the wild: a) what type of immune responses are mounted against parasites in different hosts in the wild, and how do they vary within an individual over time, between individuals of the same species and between species? b) can we use wild or semi-wild study systems to understand the evolutionary drivers for tolerance versus resistance towards a parasite? c) what determines the ability of the host to cope with an infection and is there a link with the type of immune response mounted? d) can we modulate environmental factors to manipulate a wild animal's immune response to parasitic infections, with translation potential for humans, wildlife, and livestock? and e) in context of this special issue, what lessons for Type 2 immunity can we glean from studying animals in their natural environments? Further, we aim to integrate some of the knowledge gained in semi-wild and wild settings with knowledge gained from traditional laboratory-based research, and to raise awareness for the opportunities (and challenges) that come with integrating a multitude of naturally-occurring variables into immunoparasitological research.

The Prebiotic-Like Effects of Coprinus comatus Polysaccharides on Gut Microbiota in Normal Mice and Those with Acute Alcoholic Liver Injury: A Comparative Study

This study aims to investigate the prebiotic-like effects of Coprinus comatus polysaccharides (CCP) on gut microbiota. Mice were divided into four groups: normal group (NG), alcohol group (AG), polysaccharides group (PG), and alcohol + polysaccharides group (APG). The gut microbiota structure of feces was analyzed by determining the V3-V4 region sequence in 16S rDNA. The results showed CCP could increase the diversity of gut microbiota. Compared with NG, PG had a significantly higher relative abundance of Firmicutes and Lactobacillaceae and a lower abundance of Rikenellaceae. These changes in gut microbiota result in positive effects on gut due to a series of prebiotic-like effects of CCP. At the same time, CCP could improve some adverse changes in gut microbiota caused by acute alcohol intake, such as the increased proportion of Firmicutes, Bacteroidetes, Muribaculaceae, and Lachnospiraceae and the decreased proportion of Rikenellaceae. In conclusion, the CCP has certain prebiotic effects not only on normal mice but also on mice with acute alcoholic liver injury.