Differential Responses of Pattern Recognition Receptors to Outer Membrane Vesicles of Three Periodontal Pathogens

Bacteriophages and bacterial extracellular vesicles, threat or opportunity?

Emergence of antimicrobial-resistant bacteria (AMR) is one of the health major problems worldwide. The scientists are looking for a novel method to treat infectious diseases. Phage therapy is considered a suitable approach for treating infectious diseases. However, there are different challenges in this way. Some biological aspects can probably influence on therapeutic results and further investigations are necessary to reach a successful phage therapy. Bacteriophage activity can influence by bacterial defense system. Bacterial extracellular vesicles (BEVs) are one of the bacterial defense mechanisms which can modify the results of bacteriophage activity. BEVs have the significant roles in the gene transferring, invasion, escape, and spreading of bacteriophages. In this review, the defense mechanisms of bacteria against bacteriophages, especially BEVs secretion, the hidden linkage of BEVs and bacteriophages, and its possible consequences on the bacteriophage activity as well phage therapy will be discussed.

The Role of Bacterial Extracellular Membrane Nanovesicles in Atherosclerosis: Unraveling a Potential Trigger

PURPOSE OF REVIEW

In this review, we explore the intriguing and evolving connections between bacterial extracellular membrane nanovesicles (BEMNs) and atherosclerosis development, highlighting the evidence on molecular mechanisms by which BEMNs can promote the athero-inflammatory process that is central to the progression of atherosclerosis.

RECENT FINDINGS

Atherosclerosis is a chronic inflammatory disease primarily driven by metabolic and lifestyle factors; however, some studies have suggested that bacterial infections may contribute to the development of both atherogenesis and inflammation in atherosclerotic lesions. In particular, the participation of BEMNs in atherosclerosis pathogenesis has attracted special attention. We provide some general insights into how the immune system responds to potential threats such as BEMNs during the development of atherosclerosis. A comprehensive understanding of contribution of BEMNs to atherosclerosis pathogenesis may lead to the development of targeted interventions for the prevention and treatment of the disease.

Outer Membrane Vesicles Derived from Adherent-Invasive Escherichia coli Induce Inflammatory Response and Alter the Gene Expression of Junction-Associated Proteins in Human Intestinal Epithelial Cells

Adherent-invasive Escherichia coli (AIEC) pathobionts, which are characterized by their ability to adhere to and invade intestinal epithelial cells, are associated with the etiopathogenesis of inflammatory bowel diseases (IBDs). Outer membrane vesicles (OMVs) released by AIEC strains can facilitate the interaction of these bacteria with host cells through delivering bacterial effectors. The aim of this study was to determine the ability of OMVs derived from AIEC strain LF82 to induce the host immune response, leading to production of proinflammatory cytokines and also altering the gene expression of junction-associated proteins in the human epithelial colorectal adenocarcinoma Caco-2 cell line. OMVs were extracted from AIEC strain LF82, and the cell viability of Caco-2 cells treated with these vesicles was assessed by MTT assay. The morphology and size distribution of vesicles were analyzed using transmission electron microscopy and dynamic light scattering, respectively. Gene expression of occludin, ZO-1, claudin-2, E-cadherin, TLR-2, and TLR-4 in response to OMVs was assessed in Caco-2 cells by RT-qPCR. Moreover, the secretion of IL-8 and TNF-α into the supernatant of Caco-2 cells upon treatment with OMVs was measured using ELISA. Our results demonstrated that OMVs upregulated the gene expression level of TLRs and also altered the gene expression level of junction-associated proteins. OMVs derived from AIEC may play a major role in the promotion of intestinal inflammation and epithelial barrier dysfunction. However, further investigations are needed to elucidate the putative role of OMVs in the pathogenesis of AIEC and IBD.

Global trends in research on aging associated with periodontitis from 2002 to 2023: a bibliometric analysis

Background

Aging has been implicated in many chronic inflammatory diseases, including periodontitis. Periodontitis is an inflammatory disease caused by long-term irritation of the periodontal tissues by the plaque biofilm on the surface of the teeth. However, only a few bibliometric analyses have systematically studied this field to date. This work sought to visualize research hot spots and trends in aging associated with periodontitis from 2002 to 2023 through bibliometric approaches.

Methods

Graphpad prism v8.0.2 was used to analyse and plot annual papers, national publication trends and national publication heat maps. In addition, CtieSpace (6.1.6R (64-bit) Advanced Edition) and VOSviewer (version 1.6.18) were used to analyse these data and visualize the scientific knowledge graph.

Results

The number of documents related to aging associated with periodontitis has steadily increased over 21 years. With six of the top ten institutions in terms of publications coming from the US, the US is a major driver of research in this area. journal of periodontology is the most published journal in the field. Tonetti MS is the most prolific authors and co-cited authors in the field. Journal of Periodontology and Journal of Clinical Periodontology are the most popular journals in the field with the largest literature. Periodontitis, Alzheimer's disease, and peri-implantitis are current hot topics and trends in the field. Inflammation, biomarkers, oxidative stress cytokines are current research hotspots in this field.

Conclusion

Our research found that global publications regarding research on aging associated with periodontitis increased dramatically and were expected to continue increasing. Inflammation and aging, and the relationship between periodontitis and systemic diseases, are topics worthy of attention.

Hemophore-like proteins of the HmuY family in the oral and gut microbiome: unraveling the mystery of their evolution

SUMMARY

Heme (iron protoporphyrin IX, FePPIX) is the main source of iron and PPIX for host-associated pathogenic bacteria, including members of the Bacteroidota (formerly Bacteroidetes) phylum. Porphyromonas gingivalis, a keystone oral pathogen, uses a unique heme uptake (Hmu) system, comprising a hemophore-like protein, designated as the first member of the novel HmuY family. Compared to classical, secreted hemophores utilized by Gram-negative bacteria or near-iron transporter domain-based hemophores utilized by Gram-positive bacteria, the HmuY family comprises structurally similar proteins that have undergone diversification during evolution. The best characterized are P. gingivalis HmuY and its homologs from Tannerella forsythia (Tfo), Prevotella intermedia (PinO and PinA), Bacteroides vulgatus (Bvu), and Bacteroides fragilis (BfrA, BfrB, and BfrC). In contrast to the two histidine residues coordinating heme iron in P. gingivalis HmuY, Tfo, PinO, PinA, Bvu, and BfrA preferentially use two methionine residues. Interestingly, BfrB, despite conserved methionine residue, binds the PPIX ring without iron coordination. BfrC binds neither heme nor PPIX in keeping with the lack of conserved histidine or methionine residues used by other members of the HmuY family. HmuY competes for heme binding and heme sequestration from host hemoproteins with other members of the HmuY family to increase P. gingivalis competitiveness. The participation of HmuY in the host immune response confirms its relevance in relation to the survival of P. gingivalis and its ability to induce dysbiosis not only in the oral microbiome but also in the gut microbiome or other host niches, leading to local injuries and involvement in comorbidities.

Bacterial membrane vesicles: orchestrators of interkingdom interactions in microbial communities for environmental adaptation and pathogenic dynamics

Bacterial membrane vesicles (MVs) have attracted increasing attention due to their significant roles in bacterial physiology and pathogenic processes. In this review, we provide an overview of the importance and current research status of MVs in regulating bacterial physiology and pathogenic processes, as well as their crucial roles in environmental adaptation and pathogenic infections. We describe the formation mechanism, composition, structure, and functions of MVs, and discuss the various roles of MVs in bacterial environmental adaptation and pathogenic infections. Additionally, we analyze the limitations and challenges of MV-related research and prospect the potential applications of MVs in environmental adaptation, pathogenic mechanisms, and novel therapeutic strategies. This review emphasizes the significance of understanding and studying MVs for the development of new insights into bacterial environmental adaptation and pathogenic processes. Overall, this review contributes to our understanding of the intricate interplay between bacteria and their environment and provides valuable insights for the development of novel therapeutic strategies targeting bacterial pathogenicity.

Porphyromonas gingivalis and the pathogenesis of Alzheimer's disease

The cause of Alzheimer's disease (AD), and the pathophysiological mechanisms involved, remain major unanswered questions in medical science. Oral bacteria, especially those species associated with chronic periodontitis and particularly Porphyromonas gingivalis, are being linked causally to AD pathophysiology in a subpopulation of susceptible individuals. P. gingivalis produces large amounts of proteolytic enzymes, haem and iron capture proteins, adhesins and internalins that are secreted and attached to the cell surface and concentrated onto outer membrane vesicles (OMVs). These enzymes and adhesive proteins have been shown to cause host tissue damage and stimulate inflammatory responses. The ecological and pathophysiological roles of P. gingivalis OMVs, their ability to disperse widely throughout the host and deliver functional proteins lead to the proposal that they may be the link between a P. gingivalis focal infection in the subgingivae during periodontitis and neurodegeneration in AD. P. gingivalis OMVs can cross the blood brain barrier and may accelerate AD-specific neuropathology by increasing neuroinflammation, plaque/tangle formation and dysregulation of iron homeostasis, thereby inducing ferroptosis leading to neuronal death and neurodegeneration.

Enrichment of infection-associated bacteria in the low biomass brain bacteriota of Alzheimer's disease patients

Alzheimer's disease (AD) is a neurodegenerative disease accompanied by neuroimmune inflammation in the frontal cortex and hippocampus. Recently, the presence of bacteria in AD-affected brains has been documented, prompting speculation about their potential role in AD-associated neuroinflammation. However, the characterization of bacteriota in human brains affected by AD remains inconclusive. This study aimed to investigate potential associations between specific bacteria and AD pathology by examining brain tissues from AD-associated neurodegenerative regions (frontal cortex and hippocampus) and the non-AD-associated hypothalamus. Employing 16S rRNA gene sequencing, 30 postmortem brain tissue samples from four individuals with normal brain histology (N) and four AD patients were analyzed, along with three blank controls. A remarkably low biomass characterized the brain bacteriota, with their overall structures delineated primarily by brain regions rather than the presence of AD. While most analyzed parameters exhibited no significant distinction in the brain bacteriota between the N and AD groups, the unique detection of Cloacibacterium normanense in the AD-associated neurodegenerative regions stood out. Additionally, infection-associated bacteria, as opposed to periodontal pathogens, were notably enriched in AD brains. This study's findings provide valuable insights into potential link between bacterial infection and neuroinflammation in AD.

Proteome and immune responses of extracellular vesicles derived from macrophages infected with the periodontal pathogen Tannerella forsythia

Periodontitis is a chronic inflammatory disease caused by periodontal pathogens in subgingival plaque and is associated with systemic inflammatory diseases. Extracellular vesicles (EVs) released from host cells and pathogens carry a variety of biological molecules and are of interest for their role in disease progression and as diagnostic markers. In the present study, we analysed the proteome and inflammatory response of EVs derived from macrophages infected with Tannerella forsythia, a periodontal pathogen. The EVs isolated from the cell conditioned medium of T. forsythia-infected macrophages were divided into two distinct vesicles, macrophage-derived EVs and T. forsythia-derived OMVs, by size exclusion chromatography combined with density gradient ultracentrifugation. Proteome analysis showed that in T. forsythia infection, macrophage-derived EVs were enriched with pro-inflammatory cytokines and inflammatory mediators associated with periodontitis progression. T. forsythia-derived OMVs harboured several known virulence factors, including BspA, sialidase, GroEL and various bacterial lipoproteins. T. forsythia-derived OMVs induced pro-inflammatory responses via TLR2 activation. In addition, we demonstrated that T. forsythia actively released OMVs when T. forsythia encountered macrophage-derived soluble molecules. Taken together, our results provide insight into the characterisation of EVs derived from cells infected with a periodontal pathogen.

Extracellular vesicles of the probiotic bacteria E. coli O83 activate innate immunity and prevent allergy in mice

BACKGROUND

E. coli O83 (Colinfant Newborn) is a Gram-negative (G-) probiotic bacterium used in the clinic. When administered orally, it reduces allergic sensitisation but not allergic asthma. Intranasal administration offers a non-invasive and convenient delivery method. This route bypasses the gastrointestinal tract and provides direct access to the airways, which are the target of asthma prevention. G- bacteria such as E. coli O83 release outer membrane vesicles (OMVs) to communicate with the environment. Here we investigate whether intranasally administered E. coli O83 OMVs (EcO83-OMVs) can reduce allergic airway inflammation in mice.

METHODS

EcO83-OMVs were isolated by ultracentrifugation and characterised their number, morphology (shape and size), composition (proteins and lipopolysaccharide; LPS), recognition by innate receptors (using transfected HEK293 cells) and immunomodulatory potential (in naïve splenocytes and bone marrow-derived dendritic cells; BMDCs). Their allergy-preventive effect was investigated in a mouse model of ovalbumin-induced allergic airway inflammation.

RESULTS

EcO83-OMVs are spherical nanoparticles with a size of about 110 nm. They contain LPS and protein cargo. We identified a total of 1120 proteins, 136 of which were enriched in OMVs compared to parent bacteria. Proteins from the flagellum dominated. OMVs activated the pattern recognition receptors TLR2/4/5 as well as NOD1 and NOD2. EcO83-OMVs induced the production of pro- and anti-inflammatory cytokines in splenocytes and BMDCs. Intranasal administration of EcO83-OMVs inhibited airway hyperresponsiveness, and decreased airway eosinophilia, Th2 cytokine production and mucus secretion.

CONCLUSIONS

We demonstrate for the first time that intranasally administered OMVs from probiotic G- bacteria have an anti-allergic effect. Our study highlights the advantages of OMVs as a safe platform for the prophylactic treatment of allergy. Video Abstract.

Periodontitis promotes bacterial extracellular vesicle-induced neuroinflammation in the brain and trigeminal ganglion

Gram-negative bacteria derived extracellular vesicles (EVs), also known as outer membrane vesicles, have attracted significant attention due to their pathogenic roles in various inflammatory diseases. We recently demonstrated that EVs secreted by the periodontopathogen Aggregatibacter actinomycetemcomitans (Aa) can cross the blood-brain barrier (BBB) and that their extracellular RNA cargo can promote the secretion of proinflammatory cytokines, such as IL-6 and TNF-α, in the brain. To gain more insight into the relationship between periodontal disease (PD) and neuroinflammatory diseases, we investigated the effect of Aa EVs in a mouse model of ligature-induced PD. When EVs were administered through intragingival injection or EV-soaked gel, proinflammatory cytokines were strongly induced in the brains of PD mice. The use of TLR (Toll-like receptor)-reporter cell lines and MyD88 knockout mice confirmed that the increased release of cytokines was triggered by Aa EVs via TLR4 and TLR8 signaling pathways and their downstream MyD88 pathway. Furthermore, the injection of EVs through the epidermis and gingiva resulted in the direct retrograde transfer of Aa EVs from axon terminals to the cell bodies of trigeminal ganglion (TG) neurons and the subsequent activation of TG neurons. We also found that the Aa EVs changed the action potential of TG neurons. These findings suggest that EVs derived from periodontopathogens such as Aa might be involved in pathogenic pathways for neuroinflammatory diseases, neuropathic pain, and other systemic inflammatory symptoms as a comorbidity of periodontitis.

Roles of bacterial extracellular vesicles in systemic diseases

Accumulating evidence suggests that in various systems, not all bidirectional microbiota-host interactions involve direct cell contact. Bacterial extracellular vesicles (BEVs) may be key participants in this interkingdom crosstalk. BEVs mediate microbiota functions by delivering effector molecules that modulate host signaling pathways, thereby facilitating host-microbe interactions. BEV production during infections by both pathogens and probiotics has been observed in various host tissues. Therefore, these vesicles released by microbiota may have the ability to drive or inhibit disease pathogenesis in different systems within the host. Here, we review the current knowledge of BEVs and particularly emphasize their interactions with the host and the pathogenesis of systemic diseases.

Bacterial outer membrane vesicles in cancer: Biogenesis, pathogenesis, and clinical application

Outer membrane vesicles (OMVs) are spherical, nano-sized particles of bilayer lipid structure secreted by Gram-negative bacteria. They contain a series of cargos from bacteria and are important messengers for communication between bacteria and their environment. OMVs play multiple roles in bacterial survival and adaptation and can affect host physiological functions and disease development by acting on host cell membranes and altering host cell signaling pathways. This paper summarizes the mechanisms of OMV genesis and the multiple roles of OMVs in the tumor microenvironment. Also, this paper discusses the prospects of OMVs for a wide range of applications in drug delivery, tumor diagnosis, and therapy.

Environmental influences on Streptococcus sanguinis membrane vesicle biogenesis

Membrane vesicles are produced by Gram-negative and Gram-positive bacteria. While membrane vesicles are potent elicitors of eukaryotic cells and involved in cell-cell communication, information is scarce about their general biology in the context of community members and the environment. Streptococcus sanguinis, a Gram-positive oral commensal, is prevalent in the oral cavity and well-characterized for its ability to antagonize oral pathobionts. We have found that production and dissemination of membrane vesicles by S. sanguinis is dependent on environmental and community factors. Co-culture with interacting commensal Corynebacterium durum, as well as with the periodontal pathobiont Filifactor alocis had no effect on S. sanguinis vesicle number and size, whereas the periodontal pathobiont Porphyromonas gingivalis abolished S. sanguinis vesicle production. Using both correlation and differential expression analyses to examine the transcriptomic changes underlying vesicle production, we found that differential expression of genes encoding proteins related to the cytoplasmic membrane and peptidoglycan correlate with the abundance of membrane vesicles. Proteomic characterizations of the vesicle cargo identified a variety of proteins, including those predicted to influence host interactions or host immune responses. Cell culture studies of gingival epithelial cells demonstrated that both crude and highly purified membrane vesicles could induce the expression of IL-8, TNF-α, IL-1β, and Gro-α within 6 hours of inoculation at levels comparable to whole cells. Our findings suggest that production of membrane vesicles by S. sanguinis is heavily influenced by community and environmental factors and plays an important role in communication with host cells.

Characterization of the Inflammatory Response Evoked by Bacterial Membrane Vesicles in Intestinal Cells Reveals an RIPK2-Dependent Activation by Enterotoxigenic Escherichia coli Vesicles

Although the immunomodulatory potency of bacterial membrane vesicles (MVs) is widely acknowledged, their interactions with host cells and the underlying signaling pathways have not been well studied. Herein, we provide a comparative analysis of the proinflammatory cytokine profile secreted by human intestinal epithelial cells exposed to MVs derived from 32 gut bacteria. In general, outer membrane vesicles (OMVs) from Gram-negative bacteria induced a stronger proinflammatory response than MVs from Gram-positive bacteria. However, the quality and quantity of cytokine induction varied between MVs from different species, highlighting their unique immunomodulatory properties. OMVs from enterotoxigenic Escherichia coli (ETEC) were among those showing the strongest proinflammatory potency. In depth analyses revealed that the immunomodulatory activity of ETEC OMVs relies on a so far unprecedented two-step mechanism, including their internalization into host cells followed by intracellular recognition. First, OMVs are efficiently taken up by intestinal epithelial cells, which mainly depends on caveolin-mediated endocytosis as well as the presence of the outer membrane porins OmpA and OmpF on the MVs. Second, lipopolysaccharide (LPS) delivered by OMVs is intracellularly recognized by novel caspase- and RIPK2-dependent pathways. This recognition likely occurs via detection of the lipid A moiety as ETEC OMVs with underacylated LPS exhibited reduced proinflammatory potency but similar uptake dynamics compared to OMVs derived from wild-type (WT) ETEC. Intracellular recognition of ETEC OMVs in intestinal epithelial cells is pivotal for the proinflammatory response as inhibition of OMV uptake also abolished cytokine induction. The study signifies the importance of OMV internalization by host cells to exercise their immunomodulatory activities. IMPORTANCE The release of membrane vesicles from the bacterial cell surface is highly conserved among most bacterial species, including outer membrane vesicles (OMVs) from Gram-negative bacteria as well as vesicles liberated from the cytoplasmic membrane of Gram-positive bacteria. It is becoming increasingly evident that these multifactorial spheres, carrying membranous, periplasmic, and even cytosolic content, contribute to intra- and interspecies communication. In particular, gut microbiota and the host engage in a myriad of immunogenic and metabolic interactions. This study highlights the individual immunomodulatory activities of bacterial membrane vesicles from different enteric species and provides new mechanistic insights into the recognition of ETEC OMVs by human intestinal epithelial cells.

Outer-Membrane Vesicles of Fusobacterium necrophorum: A Proteomic, Lipidomic, and Functional Characterization

Outer-membrane vesicles (OMVs) are extruded nanostructures shed by Gram-negative bacteria, containing periplasmic contents, and often including virulence factors with immunogenic properties. To assess their potential for use in vaccine development, we purified OMVs from the Fusobacterium necrophorum subspecies necrophorum, an opportunistic necrotic infection-causing pathogen, and characterized these structures using proteomics, lipid-profiling analyses, and cytotoxicity assays. A proteomic analysis of density-gradient-purified F. necrophorum OMVs identified 342 proteins, a large proportion of which were outer-membrane proteins (OMPs), followed by cytoplasmic proteins, based on a subcellular-localization-prediction analysis. The OMPs and toxins were among the proteins with the highest intensity identified, including the 43-kDa-OMP-, OmpA-, and OmpH-family proteins, the cell-surface protein, the FadA adhesin protein, the leukotoxin-LktA-family filamentous adhesin, the N-terminal domain of hemagglutinin, and the OMP transport protein and assembly factor. A Western blot analysis confirmed the presence of several OMPs and toxins in the F. necrophorum OMVs. The lipid-profiling analysis revealed phospholipids, sphingolipids, and acetylcarnitine as the main lipid contents of OMVs. The lactate-dehydrogenase-cytotoxicity assays showed that the OMVs had a high degree of cytotoxicity against a bovine B-lymphocyte cell line (BL-3 cells). Thus, our data suggest the need for further studies to evaluate the ability of OMVs to induce immune responses and assess their vaccine potential in vivo.

Association between periodontitis and the prevalence and prognosis of prediabetes: a population-based study

BACKGROUND

Diagnosis and intervention of prediabetes is an emerging method for preventing diabetic progression and complications. Periodontitis has been reported to strongly correlate with the dysregulation of glucose metabolism. Nonetheless, the relationship between periodontal status and the prevalence of prediabetes as well as its prognosis remains elusive. This study aimed to investigate the association of periodontitis with the prevalence of prediabetes and furtherly explore the all-cause mortality of different periodontal status among patients with prediabetes.

METHODS

The dateset from the National Health and Nutrition Examination Survey (NHANES) was utilized for our study. Participants were divided into two groups (with or without periodontitis) and further assigned into subgroups by different grades of periodontitis to analyze the association between periodontitis and prevalence of prediabetes. Then we analyzed the association between all-cause mortality and periodontitis among patients with prediabetes. Weighted multivariate logistic/Cox regression models were adopted in our study.

RESULTS

A total of 15390 participants were included and divided into a periodontitis group (n = 5033) and a nonperiodontitis group (n = 10357). The results showed that participants with periodontitis had a higher risk of prediabetes. After adjusting for covariables, more severe periodontitis was positively related to prediabetes (moderate vs. no periodontitis: OR = 1.46, 95% CI: 1.29-1.65; severe vs. no periodontitis: OR = 1.62, 95% CI 1.31-2.01). Furtherly, we explored the association between all-cause mortality and periodontal status among patients diagnosed with prediabetes (n = 4518) and found that severe (HR = 1.806, 95% CI 1.19-2.74) and moderate periodontitis (HR = 2.42, 95% CI 1.95-3.01) were associated with elevated all-cause mortality among patients with prediabetes.

CONCLUSIONS

In general, the results suggest that periodontitis is positively associated with the prevalence and mortality of prediabetes. These results suggest that good management of periodontal status could be a potential strategy to reduce the occurrence and development of prediabetes.

The role and mechanisms of gram-negative bacterial outer membrane vesicles in inflammatory diseases

Outer membrane vesicles (OMVs) are spherical, bilayered, and nanosized membrane vesicles that are secreted from gram-negative bacteria. OMVs play a pivotal role in delivering lipopolysaccharide, proteins and other virulence factors to target cells. Multiple studies have found that OMVs participate in various inflammatory diseases, including periodontal disease, gastrointestinal inflammation, pulmonary inflammation and sepsis, by triggering pattern recognition receptors, activating inflammasomes and inducing mitochondrial dysfunction. OMVs also affect inflammation in distant organs or tissues via long-distance cargo transport in various diseases, including atherosclerosis and Alzheimer's disease. In this review, we primarily summarize the role of OMVs in inflammatory diseases, describe the mechanism through which OMVs participate in inflammatory signal cascades, and discuss the effects of OMVs on pathogenic processes in distant organs or tissues with the aim of providing novel insights into the role and mechanism of OMVs in inflammatory diseases and the prevention and treatment of OMV-mediated inflammatory diseases.

The Two Faces of Bacterial Membrane Vesicles: Pathophysiological Roles and Therapeutic Opportunities

Bacterial membrane vesicles (MVs) are nanosized lipid particles secreted by lysis or blebbing mechanisms from Gram-negative and -positive bacteria. It is becoming increasingly evident that MVs can promote antimicrobial resistance but also provide versatile opportunities for therapeutic exploitation. As non-living facsimiles of parent bacteria, MVs can carry multiple bioactive molecules such as proteins, lipids, nucleic acids, and metabolites, which enable them to participate in intra- and interspecific communication. Although energetically costly, the release of MVs seems beneficial for bacterial fitness, especially for pathogens. In this review, we briefly discuss the current understanding of diverse MV biogenesis routes affecting MV cargo. We comprehensively highlight the physiological functions of MVs derived from human pathogens covering in vivo adaptation, colonization fitness, and effector delivery. Emphasis is given to recent findings suggesting a vicious cycle of MV biogenesis, pathophysiological function, and antibiotic therapy. We also summarize potential therapeutical applications, such as immunotherapy, vaccination, targeted delivery, and antimicrobial potency, including their experimental validation. This comparative overview identifies common and unique strategies for MV modification used along diverse applications. Thus, the review summarizes timely aspects of MV biology in a so far unprecedented combination ranging from beneficial function for bacterial pathogen survival to future medical applications.

Interactions between extracellular vesicles and microbiome in human diseases: New therapeutic opportunities

In recent decades, accumulating research on the interactions between microbiome homeostasis and host health has broadened new frontiers in delineating the molecular mechanisms of disease pathogenesis and developing novel therapeutic strategies. By transporting proteins, nucleic acids, lipids, and metabolites in their versatile bioactive molecules, extracellular vesicles (EVs), natural bioactive cell-secreted nanoparticles, may be key mediators of microbiota-host communications. In addition to their positive and negative roles in diverse physiological and pathological processes, there is considerable evidence to implicate EVs secreted by bacteria (bacterial EVs [BEVs]) in the onset and progression of various diseases, including gastrointestinal, respiratory, dermatological, neurological, and musculoskeletal diseases, as well as in cancer. Moreover, an increasing number of studies have explored BEV-based platforms to design novel biomedical diagnostic and therapeutic strategies. Hence, in this review, we highlight the recent advances in BEV biogenesis, composition, biofunctions, and their potential involvement in disease pathologies. Furthermore, we introduce the current and emerging clinical applications of BEVs in diagnostic analytics, vaccine design, and novel therapeutic development.

Composition and functions of bacterial membrane vesicles

Extracellular vesicles are produced by species across all domains of life, suggesting that vesiculation represents a fundamental principle of living matter. In Gram-negative bacteria, membrane vesicles (MVs) can originate either from blebs of the outer membrane or from endolysin-triggered explosive cell lysis, which is often induced by genotoxic stress. Although less is known about the mechanisms of vesiculation in Gram-positive and Gram-neutral bacteria, recent research has shown that both lysis and blebbing mechanisms also exist in these organisms. Evidence has accumulated over the past years that different biogenesis routes lead to distinct types of MV with varied structure and composition. In this Review, we discuss the different types of MV and their potential cargo packaging mechanisms. We summarize current knowledge regarding how MV composition determines their various functions including support of bacterial growth via the disposal of waste material, nutrient scavenging, export of bioactive molecules, DNA transfer, neutralization of phages, antibiotics and bactericidal functions, delivery of virulence factors and toxins to host cells and inflammatory and immunomodulatory effects. We also discuss the advantages of MV-mediated secretion compared with classic bacterial secretion systems and we introduce the concept of quantal secretion.

The role of extracellular vesicles in periodontitis: pathogenesis, diagnosis, and therapy

Periodontitis is a prevalent disease and one of the leading causes of tooth loss. Biofilms are initiating factor of periodontitis, which can destroy periodontal tissue by producing virulence factors. The overactivated host immune response is the primary cause of periodontitis. The clinical examination of periodontal tissues and the patient's medical history are the mainstays of periodontitis diagnosis. However, there is a lack of molecular biomarkers that can be used to identify and predict periodontitis activity precisely. Non-surgical and surgical treatments are currently available for periodontitis, although both have drawbacks. In clinical practice, achieving the ideal therapeutic effect remains a challenge. Studies have revealed that bacteria produce extracellular vesicles (EVs) to export virulence proteins to host cells. Meanwhile, periodontal tissue cells and immune cells produce EVs that have pro- or anti-inflammatory effects. Accordingly, EVs play a critical role in the pathogenesis of periodontitis. Recent studies have also presented that the content and composition of EVs in saliva and gingival crevicular fluid (GCF) can serve as possible periodontitis diagnostic indicators. In addition, studies have indicated that stem cell EVs may encourage periodontal regeneration. In this article, we mainly review the role of EVs in the pathogenesis of periodontitis and discuss their diagnostic and therapeutic potential.

Activation of bone marrow-derived dendritic cells and CD4+ T cell differentiation by outer membrane vesicles of periodontal pathogens

Outer membrane vesicles (OMVs) released from gram-negative bacteria harbor diverse molecules to communicate with host cells. In this study, we evaluated the OMVs of periodontal pathogens for their effects on the activation of dendritic cells and CD4⁺ T cell differentiation. OMVs of Porphyromonas gingivalis ATCC 33277, Treponema denticola ATCC 33521, and Tannerella forsythia ATCC 43037 (‘red complex’ pathogens) were isolated by density gradient ultracentrifugation. Mouse bone marrow-derived dendritic cells (BMDCs) were treated with OMVs, and OMV-primed BMDCs were cocultured with naïve CD4⁺ T cells to analyze the polarization of effector helper T cells. The OMVs upregulated maturation markers, including MHC class II, CD80, CD86, and CD40, on BMDCs. OMVs of P. gingivalis and T. forsythia induced the expression of the proinflammatory cytokines IL-1β, IL-6, IL-23, and IL-12p70 in BMDCs. In T. denticola OMV-primed BMDCs, proinflammatory cytokines were poorly detected, which may be attributed to posttranslational degradation due to the highly proteolytic nature of OMVs. In cocultures of naïve CD4⁺ T cells with OMV-primed BMDCs, OMVs of P. gingivalis and T. denticola induced the differentiation of Th17 cells, whereas T. forsythia OMVs induced Th1 cell differentiation. These results demonstrate that OMVs derived from the ‘red complex’ periodontal pathogens induce maturation of BMDCs and differentiation of naïve CD4⁺ T cells to Th1 or Th17 cells.

Roles of extracellular vesicles in periodontal homeostasis and their therapeutic potential

Periodontal tissue is a highly dynamic and frequently stimulated area where homeostasis is easily destroyed, leading to proinflammatory periodontal diseases. Bacteria-bacteria and cell-bacteria interactions play pivotal roles in periodontal homeostasis and disease progression. Several reviews have comprehensively summarized the roles of bacteria and stem cells in periodontal homeostasis. However, they did not describe the roles of extracellular vesicles (EVs) from bacteria and cells. As communication mediators evolutionarily conserved from bacteria to eukaryotic cells, EVs secreted by bacteria or cells can mediate interactions between bacteria and their hosts, thereby offering great promise for the maintenance of periodontal homeostasis. This review offers an overview of EV biogenesis, the effects of EVs on periodontal homeostasis, and recent advances in EV-based periodontal regenerative strategies. Specifically, we document the pathogenic roles of bacteria-derived EVs (BEVs) in periodontal dyshomeostasis, focusing on plaque biofilm formation, immune evasion, inflammatory pathway activation and tissue destruction. Moreover, we summarize recent advancements in cell-derived EVs (CEVs) in periodontal homeostasis, emphasizing the multifunctional biological effects of CEVs on periodontal tissue regeneration. Finally, we discuss future challenges and practical perspectives for the clinical translation of EV-based therapies for periodontitis.

Outer Membrane Vesicles: Biogenesis, Functions, and Issues

This review focuses on nonlytic outer membrane vesicles (OMVs), a subtype of bacterial extracellular vesicles (BEVs) produced by Gram-negative organisms focusing on the mechanisms of their biogenesis, cargo, and function. Throughout, we highlight issues concerning the characterization of OMVs and distinguishing them from other types of BEVs. We also highlight the shortcomings of commonly used methodologies for the study of BEVs that impact the interpretation of their functionality and suggest solutions to standardize protocols for OMV studies.

Stimulation of Human Periodontal Ligament Fibroblasts Using Purified Dentilisin Extracted from Treponema denticola

Periodontal disease is a chronic multifactorial disease triggered by a complex of bacterial species. These interact with host tissues to cause the release of a broad array of pro-inflammatory cytokines, chemokines, and tissue remodelers, such as matrix metalloproteinases (MMPs), which lead to the destruction of periodontal tissues. Patients with severe forms of periodontitis are left with a persistent pro-inflammatory transcriptional profile throughout the periodontium, even after clinical intervention, leading to the destruction of teeth-supporting tissues. The oral spirochete, Treponema denticola , is consistently found at significantly elevated levels at sites with advanced periodontal disease. Of all T. denticola virulence factors that have been described, its chymotrypsin-like protease complex, also called dentilisin, has demonstrated a multitude of cytopathic effects consistent with periodontal disease pathogenesis, including alterations in cellular adhesion activity, degradation of various endogenous extracellular matrix-substrates, degradation of host chemokines and cytokines, and ectopic activation of host MMPs. Thus, the following model of T. denticola -human periodontal ligament cell interactions may provide new knowledge about the mechanisms that drive the chronicity of periodontal disease at the protein, transcriptional, and epigenetic levels, which could afford new putative therapeutic targets. This protocol was validated in: PLOS Pathog (2021), DOI: 10.1371/journal.ppat.1009311.

Coating and Corruption of Human Neutrophils by Bacterial Outer Membrane Vesicles

Porphyromonas gingivalis is a keystone oral pathogen that successfully manipulates the human innate immune defenses, resulting in a chronic proinflammatory state of periodontal tissues and beyond. Here, we demonstrate that secreted outer membrane vesicles (OMVs) are deployed by P. gingivalis to selectively coat and activate human neutrophils, thereby provoking degranulation without neutrophil killing. Secreted granule components with antibacterial activity, especially LL-37 and myeloperoxidase (MPO), are subsequently degraded by potent OMV-bound proteases known as gingipains, thereby ensuring bacterial survival. In contrast to neutrophils, the P. gingivalis OMVs are efficiently internalized by macrophages and epithelial cells. Importantly, we show that neutrophil coating is a conserved feature displayed by OMVs of at least one other oral pathogen, namely, Aggregatibacter actinomycetemcomitans. We conclude that P. gingivalis deploys its OMVs for a neutrophil-deceptive strategy to create a favorable inflammatory niche and escape killing. IMPORTANCE Severe periodontitis is a dysbiotic inflammatory disease that affects about 15% of the adult population, making it one of the most prevalent diseases worldwide. Importantly, periodontitis has been associated with the development of nonoral diseases, such as rheumatoid arthritis, pancreatic cancer, and Alzheimer's disease. Periodontal pathogens implicated in periodontitis can survive in the oral cavity only by avoiding the insults of neutrophils while at the same time promoting an inflamed environment where they successfully thrive. Our present findings show that outer membrane vesicles secreted by the keystone pathogen Porphyromonas gingivalis provide an effective delivery tool of virulence factors that protect the bacterium from being killed while simultaneously activating human neutrophils.

Bacteroides fragilis outer membrane vesicles preferentially activate innate immune receptors compared to their parent bacteria

The release of bacterial membrane vesicles (BMVs) has become recognized as a key mechanism used by both pathogenic and commensal bacteria to activate innate immune responses in the host and mediate immunity. Outer membrane vesicles (OMVs) produced by Gram-negative bacteria can harbor various immunogenic cargo that includes proteins, nucleic acids and peptidoglycan, and the composition of OMVs strongly influences their ability to activate host innate immune receptors. Although various Gram-negative pathogens can produce OMVs that are enriched in immunogenic cargo compared to their parent bacteria, the ability of OMVs produced by commensal organisms to be enriched with immunostimulatory contents is only recently becoming known. In this study, we investigated the cargo associated with OMVs produced by the intestinal commensal Bacteroides fragilis and determined their ability to activate host innate immune receptors. Analysis of B. fragilis OMVs revealed that they packaged various biological cargo including proteins, DNA, RNA, lipopolysaccharides (LPS) and peptidoglycan, and that this cargo could be enriched in OMVs compared to their parent bacteria. We visualized the entry of B. fragilis OMVs into intestinal epithelial cells, in addition to the ability of B. fragilis OMVs to transport bacterial RNA and peptidoglycan cargo into Caco-2 epithelial cells. Using HEK-Blue reporter cell lines, we identified that B. fragilis OMVs could activate host Toll-like receptors (TLR)-2, TLR4, TLR7 and nucleotide-binding oligomerization domain-containing protein 1 (NOD1), whereas B. fragilis bacteria could only induce the activation of TLR2. Overall, our data demonstrates that B. fragilis OMVs activate a broader range of host innate immune receptors compared to their parent bacteria due to their enrichment of biological cargo and their ability to transport this cargo directly into host epithelial cells. These findings indicate that the secretion of OMVs by B. fragilis may facilitate immune crosstalk with host epithelial cells at the gastrointestinal surface and suggests that OMVs produced by commensal bacteria may preferentially activate host innate immune receptors at the mucosal gastrointestinal tract.

Bacterial outer membrane vesicles as a candidate tumor vaccine platform

Cancer represents a serious concern for human life and health. Due to drug resistance and the easy metastasis of tumors, there is urgent need to develop new cancer treatment methods beyond the traditional radiotherapy, chemotherapy, and surgery. Bacterial outer membrane vesicles (OMVs) are a type of double-membrane vesicle secreted by Gram-negative bacteria in the process of growth and life, and play extremely important roles in the survival and invasion of those bacteria. In particular, OMVs contain a large number of immunogenic components associated with their parent bacterium, which can be used as vaccines, adjuvants, and vectors to treat diseases, especially in presenting tumor antigens or targeted therapy with small-molecule drugs. Some OMV-based vaccines are already on the market and have demonstrated good therapeutic effect on the corresponding diseases. OMV-based vaccines for cancer are also being studied, and some are already in clinical trials. This paper reviews bacterial outer membrane vesicles, their interaction with host cells, and their applications in tumor vaccines.

Bacterial subversion of NLR-mediated immune responses

Members of the mammalian Nod-like receptor (NLR) protein family are important intracellular sensors for bacteria. Bacteria have evolved under the pressure of detection by host immune sensing systems, leading to adaptive subversion strategies to dampen immune responses for their benefits. These include modification of microbe-associated molecular patterns (MAMPs), interception of innate immune pathways by secreted effector proteins and sophisticated instruction of anti-inflammatory adaptive immune responses. Here, we summarise our current understanding of subversion strategies used by bacterial pathogens to manipulate NLR-mediated responses, focusing on the well-studied members NOD1/2, and the inflammasome forming NLRs NLRC4, and NLRP3. We discuss how bacterial pathogens and their products activate these NLRs to promote inflammation and disease and the range of mechanisms used by bacterial pathogens to evade detection by NLRs and to block or dampen NLR activation to ultimately interfere with the generation of host immunity. Moreover, we discuss how bacteria utilise NLRs to facilitate immunotolerance and persistence in the host and outline how various mechanisms used to attenuate innate immune responses towards bacterial pathogens can also aid the host by reducing immunopathologies. Finally, we describe the therapeutic potential of harnessing immune subversion strategies used by bacteria to treat chronic inflammatory conditions.

Engineered bacterial membrane vesicles are promising carriers for vaccine design and tumor immunotherapy

Bacterial membrane vesicles (BMVs) have emerged as novel and promising platforms for the development of vaccines and immunotherapeutic strategies against infectious and noninfectious diseases. The rich microbe-associated molecular patterns (MAMPs) and nanoscale membrane vesicle structure of BMVs make them highly immunogenic. In addition, BMVs can be endowed with more functions via genetic and chemical modifications. This article reviews the immunological characteristics and effects of BMVs, techniques for BMV production and modification, and the applications of BMVs as vaccines or vaccine carriers. In summary, given their versatile characteristics and immunomodulatory properties, BMVs can be used for clinical vaccine or immunotherapy applications.

Methods of Bacterial Membrane Vesicle Production, Purification, Quantification, and Examination of Their Immunogenic Functions

Bacterial membrane vesicles (BMVs) released by Gram-negative and Gram-positive bacteria are a bona fide secretion system that enable the dissemination of bacterial effector molecules, and can trigger a range of responses in the host. The study of BMV production, composition, and functions can give insights into their roles in mediating bacterial survival, pathogenesis, and disease. Furthermore, BMVs can be harnessed to develop cutting-edge nano-therapeutics including targeted chemotherapy delivery, antimicrobials, and novel vaccines. Here we describe routine methods that can be used for small- or large-scale production, isolation, and purification of outer membrane vesicles produced by Gram-negative bacteria, and membrane vesicles produced by Gram-positive bacteria, which we collectively refer to as BMVs. We discuss methods that can be used to visualize BMVs by electron microscopy, and to quantify their DNA, RNA, and protein cargo. We outline a method for the fluorescent labeling of BMVs that can be applied to examine their ability to interact with and enter host cells using a range of in vitro and in vivo biological assays. Finally, we provide a cell culture-based method that can be used to examine a range of immunogenic properties of BMVs, including their cytotoxicity, ability to activate pathogen-recognition receptors (PRRs), induce autophagy and cytokine responses, and modulate cellular pathways.

A Comprehensive Review of the Current and Future Role of the Microbiome in Pancreatic Ductal Adenocarcinoma

Simple Summary

This review summarizes the current literature related to the microbiome and pancreatic ductal adenocarcinoma (PDAC). The aim of this review is to explore the current role of the microbiome in the disease process, screening/diagnostics and to postulate the future role with regards to therapeutic strategies including chemotherapy, immunotherapy and surgery. We further explore the future of microbiome modulation (faecal microbiome transplants, bacterial consortiums, anti-microbials and probiotics), their applications and how we can improve the future of microbiome modulation in a bid to improve PDAC outcomes.

Abstract

Pancreatic ductal adenocarcinoma (PDAC) is expected to become the second most common cause of cancer death in the USA by 2030, yet progress continues to lag behind that of other cancers, with only 9% of patients surviving beyond 5 years. Long-term survivorship of PDAC and improving survival has, until recently, escaped our understanding. One recent frontier in the cancer field is the microbiome. The microbiome collectively refers to the extensive community of bacteria and fungi that colonise us. It is estimated that there is one to ten prokaryotic cells for each human somatic cell, yet, the significance of this community in health and disease has, until recently, been overlooked. This review examines the role of the microbiome in PDAC and how it may alter survival outcomes. We evaluate the possibility of employing microbiomic signatures as biomarkers of PDAC. Ultimately this review analyses whether the microbiome may be amenable to targeting and consequently altering the natural history of PDAC.

Outer Membrane Vesicles (OMVs) of Pseudomonas aeruginosa Provide Passive Resistance but Not Sensitization to LPS-Specific Phages

Outer membrane vesicles (OMVs) released from gram-negative bacteria are key elements in bacterial physiology, pathogenesis, and defence. In this study, we investigated the role of Pseudomonas aeruginosa OMVs in the anti-phage defence as well as in the potential sensitization to LPS-specific phages. Using transmission electron microscopy, virion infectivity, and neutralization assays, we have shown that both phages efficiently absorb on free vesicles and are unable to infect P. aeruginosa host. Nevertheless, the accompanying decrease in PFU titre (neutralization) was only observed for myovirus KT28 but not podovirus LUZ7. Next, we verified whether OMVs derived from wild-type PAO1 strain can sensitize the LPS-deficient mutant (Δwbpl PAO1) resistant to tested phages. The flow cytometry experiments proved a quite effective and comparable association of OMVs to Δwbpl PAO1 and wild-type PAO1; however, the growth kinetic curves and one-step growth assay revealed no sensitization event of the OMV-associated phage-resistant P. aeruginosa deletant to LPS-specific phages. Our findings for the first time identify naturally formed OMVs as important players in passive resistance (protection) of P. aeruginosa population to phages, but we disproved the hypothesis of transferring phage receptors to make resistant strains susceptible to LPS-dependent phages.

Considerations for the Analysis of Bacterial Membrane Vesicles: Methods of Vesicle Production and Quantification Can Influence Biological and Experimental Outcomes

Bacterial membrane vesicles (BMVs) are produced by all bacteria and facilitate a range of functions in host-microbe interactions and pathogenesis. Quantification of BMVs is a critical first step in the analysis of their biological and immunological functions. Historically, BMVs have been quantified by protein assay, which remains the preferred method of BMV quantification. However, recent studies have shown that BMV protein content can vary significantly between bacterial strains, growth conditions, and stages of bacterial growth, suggesting that protein concentration may not correlate directly with BMV quantity. Here, we show that the method used to quantify BMVs can alter experimental outcomes. We compared the enumeration of BMVs using different protein assays and nanoparticle tracking analysis (NTA). We show that different protein assays vary significantly in their quantification of BMVs and that their sensitivity varies when quantifying BMVs produced by different species. Moreover, stimulation of epithelial cells with an equivalent amount of BMV protein quantified using different protein assays resulted in significant differences in interleukin 8 (IL-8) responses. Quantification of Helicobacter pylori, Pseudomonas aeruginosa, and Staphylococcus aureus BMVs by NTA and normalization of BMV cargo to particle number revealed that BMV protein, DNA, and RNA contents were variable between strains and species and throughout bacterial growth. Differences in BMV-mediated activation of Toll-like receptors, NF-κB, and IL-8 responses were observed when stimulations were performed with equivalent BMV particle number but not equivalent protein amount. These findings reveal that the method of BMV quantification can significantly affect experimental outcomes, thereby potentially altering the observed biological functions of BMVs.

IMPORTANCE Recent years have seen a surge in interest in the roles of BMVs in host-microbe interactions and interbacterial communication. As a result of such rapid growth in the field, there is a lack of uniformity in BMV enumeration. Here, we reveal that the method used to enumerate BMVs can significantly alter experimental outcomes. Specifically, standardization of BMVs by protein amount reduced the ability to distinguish strain differences in the immunological functions of BMVs. In contrast, species-, strain-, and growth stage-dependent differences in BMV cargo content were evident when BMVs were enumerated by particle number, and this was reflected in differences in their ability to induce immune responses. These findings indicate that parameters critical to BMV function, including bacterial species, strain, growth conditions, and sample purity, should form the basis of standard reporting in BMV studies. This will ultimately bring uniformity to the field to advance our understanding of BMV functions.

Periodontitis and diabetes mellitus co-morbidity: A molecular dialogue

BACKGROUND

Type 2 diabetes mellitus (T2DM) and periodontitis are two biologically linked diseases that often coexist in complex interaction. While periodontitis may lead to insulin receptor desensitization, diabetes may increase the expression of inflammatory cytokines, such as Tumor Necrosis Factor-α (TNF-α) and Interleukin 6 (IL-6), in the gingival crevicular fluid and activate osteoclasts via Receptor activator of nuclear factor kappa-Β ligand (RANK-L) production, leading to bone resorption. However, the association between the two diseases processes, where one may exacerbate the progression of the other, is unclear. In addition, both diseases have similar mechanistic themes, such as chronic inflammation and oxidative stress. This review aimed to investigate the pathophysiological and molecular mechanisms underlying T2DM and periodontitis.

HIGHLIGHT

Uncontrolled diabetes is often associated with severe periodontitis, measured by clinical attachment loss. Alteration in the oral microbiome composition, which may activate the host inflammatory response and lead to irreversible oxidative stress, is a common finding in both diseases. An understanding of the molecular crosstalk between the two disease processes is crucial for developing therapeutic targets that inhibit bone resorption and halt the progression of periodontitis in patients with diabetes.

CONCLUSION

The Oral microbiome composition in T2DM and periodontitis shifts toward dysbiosis, favoring bacterial pathogens, such as Fusobacteria and Porphyromonas species. Both conditions are marked by pro-inflammatory immune activity via the activation of Interleukin 17 (IL-17), Interleukin 1 (IL-1), TNF-α, and Nuclear Factor Kappa Beta (NF-κB). Common molecular crosstalk signaling appears to involve advanced glycation end products (AGEs) and oxidative stress. Thus, future drug targets are multifactorial, ranging from modulatory of host inflammatory response to preventing the accumulation of AGEs and oxidative free radicals.

Extracellular vesicles derived from the periodontal pathogen Filifactor alocis induce systemic bone loss through Toll-like receptor 2

Periodontitis is an inflammatory disease induced by local infection in tooth-supporting tissue. Periodontitis is associated with systemic bone diseases, but little is known about the mechanism of the causal effect of periodontitis on systemic bone resorption. Bacteria-derived extracellular vesicles (EVs) act as natural carriers of virulence factors that are responsible for systemic inflammation. In this study, we investigated the role of EVs derived from Filifactor alocis, a Gram-positive, anaerobic periodontal pathogen, in systemic bone loss and osteoclast differentiation. F. alocis EVs accumulated in the long bones of mice after intraperitoneal administration. These EVs induced proinflammatory cytokines, osteoclastogenesis, and bone resorption via Toll-like receptor 2 (TLR2). The phase separation of F. alocis EVs showed that amphiphilic molecules were responsible for the induced bone resorption and osteoclastogenesis. The osteoclastogenic effects of F. alocis EVs were reduced by lipoprotein lipase. Proteomic analysis of the amphiphilic molecules identified seven lipoproteins. Our results indicate that lipoprotein-like molecules in F. alocis EVs may contribute to systemic bone loss via TLR2.

Contribution of the Microbiota and their Secretory Products to Inflammation and Colorectal Cancer Pathogenesis: The Role of Toll-like Receptors

Alterations in diversity and function of the gut microbiome are associated with concomitant changes in immune response, including chronic inflammation. Chronic inflammation is a major risk factor for colorectal cancer (CRC). An important component of the inflammatory response system are the toll-like receptors (TLRs). TLRs are capable of sensing microbial components, including nucleic acids, lipopolysaccharides, and peptidoglycans, as well as bacterial outer membrane vesicles (OMV). OMVs can be decorated with or carry as cargo these TLR activating factors. These microbial factors can either promote tolerance or activate signaling pathways leading to chronic inflammation. Herein we discuss the role of the microbiome and the OMVs that originate from intestinal bacteria in promoting chronic inflammation and the development of colitis-associated CRC. We also discuss the contribution of TLRs in mediating the microbiome-inflammation axis and subsequent cancer development. Understanding the role of the microbiome and its secretory factors in TLR response may lead to the development of better cancer therapeutics.

Membrane vesicles from periodontal pathogens and their potential roles in periodontal disease and systemic illnesses

Periodontium is an ordered ecological system where a dynamic equilibrium exists between oral microorganisms and the host defense system, and periodontal disease occurs whenever the balance is broken. Periodontal pathogens mainly include gram-negative anaerobic bacteria and emerging gram-positive microbes, which have a large variety of virulence factors and influence disease initiation and progression. Recently, different types of bacterial membrane vesicles (MVs), formed by bubbling of membrane materials from living cells or in conditions of endolysin-triggered cell death, have gained interests as a novel virulence factor for periodontopathogens. MVs load multiple sorted cargo molecules, such as proteins, lipids, and genetic materials, and actively participate in toxin transport, signal delivery, and periodontal disease pathogenesis. Since periodontitis is recognized as a risk factor for many systemic diseases, periodontal MVs could work as a bridge for periodontal diseases and systemic illnesses. Furthermore, MVs with unique nature and advantages are promising candidates as vaccines and drug delivery vehicles. In this review, we provided an overview of different types and compositions of periodontal MVs, described their involvements in the pathogenesis of periodontitis and several general diseases, and discussed potential applications of periodontal MVs in vaccination and drug delivery.

Staphylococcus aureus membrane vesicles contain immunostimulatory DNA, RNA and peptidoglycan that activate innate immune receptors and induce autophagy

Gram‐positive bacteria ubiquitously produce membrane vesicles (MVs), and although they contribute to biological functions, our knowledge regarding their composition and immunogenicity remains limited. Here we examine the morphology, contents and immunostimulatory functions of MVs produced by three Staphylococcus aureus strains; a methicillin resistant clinical isolate, a methicillin sensitive clinical isolate and a laboratory‐adapted strain. We observed differences in the number and morphology of MVs produced by each strain and showed that they contain microbe‐associated molecular patterns (MAMPs) including protein, nucleic acids and peptidoglycan. Analysis of MV‐derived RNA indicated the presence of small RNA (sRNA). Furthermore, we detected variability in the amount and composition of protein, nucleic acid and peptidoglycan cargo carried by MVs from each S. aureus strain. S. aureus MVs activated Toll‐like receptor (TLR) 2, 7, 8, 9 and nucleotide‐binding oligomerization domain containing protein 2 (NOD2) signalling and promoted cytokine and chemokine release by epithelial cells, thus identifying that MV‐associated MAMPs including DNA, RNA and peptidoglycan are detected by pattern recognition receptors (PRRs). Moreover, S. aureus MVs induced the formation of and colocalized with autophagosomes in epithelial cells, while inhibition of lysosomal acidification using bafilomycin A1 resulted in accumulation of autophagosomal puncta that colocalized with MVs, revealing the ability of the host to degrade MVs via autophagy. This study reveals the ability of DNA, RNA and peptidoglycan associated with MVs to activate PRRs in host epithelial cells, and their intracellular degradation via autophagy. These findings advance our understanding of the immunostimulatory roles of Gram‐positive bacterial MVs in mediating pathogenesis, and their intracellular fate within the host.

Sphingolipid-Containing Outer Membrane Vesicles Serve as a Delivery Vehicle To Limit Macrophage Immune Response to Porphyromonas gingivalis

Sphingolipids (SLs) are essential structural components of mammalian cell membranes. Our group recently determined that the oral anaerobe Porphyromonas gingivalis delivers its SLs to host cells and that the ability of P. gingivalis to synthesize SLs limits the elicited host inflammatory response during cellular infection.

Sphingolipids (SLs) are essential structural components of mammalian cell membranes. Our group recently determined that the oral anaerobe Porphyromonas gingivalis delivers its SLs to host cells and that the ability of P. gingivalis to synthesize SLs limits the elicited host inflammatory response during cellular infection. As P. gingivalis robustly produces outer membrane vesicles (OMVs), we hypothesized that OMVs serve as a delivery vehicle for SLs, that the SL status of the OMVs may impact cargo loading to OMVs, and that SL-containing OMVs limit elicited host inflammation similar to that observed by direct bacterial challenge. Transwell cell culture experiments determined that in comparison to the parent strain W83, the SL-null mutant elicited a hyperinflammatory immune response from THP-1 macrophage-like cells with elevated tumor necrosis factor alpha (TNF-α), interleukin 1β (IL-1β), and IL-6. Targeted assessment of Toll-like receptors (TLRs) identified elevated expression of TLR2, unchanged TLR4, and elevated expression of the adaptor molecules MyD88 and TRIF (Toll/IL-1 receptor domain-containing adaptor-inducing beta interferon) by SL-null P. gingivalis. No significant differences in gingipain activity were observed in our infection models, and both strains produced OMVs of similar sizes. Using comparative two-dimensional gel electrophoresis, we identified differences in the protein cargo of the OMVs between parent and SL-null strain. Importantly, use of purified OMVs recapitulated the cellular inflammatory response observed in the transwell system with whole bacteria. These findings provide new insights into the role of SLs in P. gingivalis OMV cargo assembly and expand our understanding of SL-OMVs as bacterial structures that modulate the host inflammatory response.

Immunomodulatory roles and novel applications of bacterial membrane vesicles

Bacteria release extracellular vesicles (EVs) known as bacterial membrane vesicles (BMVs) during their normal growth. Gram-negative bacteria produce BMVs termed outer membrane vesicles (OMVs) that are composed of a range of biological cargo and facilitate numerous bacterial functions, including promoting pathogenesis and mediating disease in the host. By contrast, less is understood about BMVs produced by Gram-positive bacteria, which are referred to as membrane vesicles (MVs), however their contribution to mediating bacterial pathogenesis has recently become evident. In this review, we summarise the mechanisms whereby BMVs released by Gram-negative and Gram-positive bacteria are produced, in addition to discussing their key functions in promoting bacterial survival, mediating pathogenesis and modulating host immune responses. Furthermore, we discuss the mechanisms whereby BMVs produced by both commensal and pathogenic organisms can enter host cells and interact with innate immune receptors, in addition to how they modulate host innate and adaptive immunity to promote immunotolerance or drive the onset and progression of disease. Finally, we highlight current and emerging applications of BMVs in vaccine design, biotechnology and cancer therapeutics.

Expression of Toll-like receptors 2 and 4 in the saliva of patients with systemic lupus erythematosus and chronic periodontitis

OBJECTIVE

The aim of this study was to investigate the expression of salivary Toll-like receptors (TRL) 2 and 4 in patients with systemic lupus erythematosus (SLE) and chronic periodontitis (CP).

METHODS

A case-control study was conducted with 77 participants (42 SLE and 35 non-SLE) stratified according to CP diagnosis criteria. Periodontal parameters consisted of clinical attachment level (CAL), probing depth (PD), the visible plaque index (VPI), and the gingival bleeding index (GBI). Salivary TRL 2 and 4 expressions were determined by quantitative real-time polymerase chain reaction (RT-PCR). Statistical analysis included Mann-Whitney U test, Kruskal-Wallis test, Spearman's correlation rank, and multiple linear regression.

RESULTS

Patients with isolated SLE or CP had higher TLR 2 and TLR 4 expression in their saliva samples (P < 0.05). The group with both SLE and CP had lower TLR 2 and 4 expressions (P < 0.05). TLR 2 and TLR 4 showed significant negative correlations with PD, CAL, and GBI in SLE patients, and a significant positive correlation with periodontal parameters in non-SLE patients. CP was independently associated with reduction of TLR2 and TLR4 expression, even after adjusting for clinical data and current drug use.

CONCLUSION

Reduced TRL 2 and 4 expression in saliva was associated with the presence of CP in SLE patients. Key Points • Patients affected by isolated CP or SLE had higher TLR2 and TLR4 expression. • TLR under-expression may be associated with a worse periodontal status in SLE. • Abnormalities in TLRs expression may increase the susceptibility to periodontitis.

Characterizing Different Probiotic-Derived Extracellular Vesicles as a Novel Adjuvant for Immunotherapy

Extracellular vesicles (EVs) secreted from probiotics, defined as live microorganisms with beneficial effects on the host, are expected to be new nanomaterials for EV-based therapy. To clarify the usability of probiotic-derived EVs in terms of EV-based therapy, we systematically evaluated their characteristics, including the yield, physicochemical properties, the cellular uptake mechanism, and biological functions, using three different types of probiotics: Bifidobacterium longum, Clostridium butyricum, and Lactobacillus plantarum WCFS1. C. butyricum secreted the largest amounts of EVs, whereas all the EVs showed comparable particle sizes and zeta potentials, ranging from 100 to 150 nm and -8 to -10 mV, respectively. The silkworm larvae plasma assay indicated that these EVs contain peptidoglycan that activates the host's immune response. Moreover, a cellular uptake study of probiotic-derived EVs in RAW264.7 cells (mouse macrophage-like cells) and DC2.4 cells (mouse dendritic cells) in the presence of inhibitors (cytochalasin B, chlorpromazine, and methyl-β-cyclodextrin) revealed that probiotic-derived EVs were mainly taken up by these immune cells via clathrin-mediated endocytosis and macropinocytosis. Furthermore, all the probiotic-derived EVs stimulated the innate immune system through the production of inflammatory cytokines (TNF-α and IL-6) from these immune cells, clarifying their utility as a novel adjuvant formulation. These findings on probiotic-derived EVs are valuable for understanding the biological significance of probiotic-derived EVs and the development of EV-based immunotherapy.

The Role of Porphyromonas gingivalis Outer Membrane Vesicles in Periodontal Disease and Related Systemic Diseases

Periodontal disease is a chronic infectious disease associated with a variety of bacteria, which can cause damage to the periodontal support structure and affect a variety of systemic system diseases such as cancer, cardiovascular disease, diabetes, rheumatoid arthritis, non-alcoholic fatty liver, and Alzheimer's disease. Porphyromonas gingivalis (P. gingivalis) is the most important pathogenic bacteria for periodontal disease. It can produce outer membrane vesicles (OMVs) and release them into the environment, playing an important role in its pathogenesis. This article focuses on P. gingivalis OMVs, reviews its production and regulation, virulence components, mode of action and related diseases, with a view to providing new ideas for the prevention and treatment of diseases related to P. gingivalis infections.

Detection of Bacterial Membrane Vesicles by NOD-Like Receptors

Bacterial membrane vesicles (BMVs) are nanoparticles produced by both Gram-negative and Gram-positive bacteria that can function to modulate immunity in the host. Both outer membrane vesicles (OMVs) and membrane vesicles (MVs), which are released by Gram-negative and Gram-positive bacteria, respectively, contain cargo derived from their parent bacterium, including immune stimulating molecules such as proteins, lipids and nucleic acids. Of these, peptidoglycan (PG) and lipopolysaccharide (LPS) are able to activate host innate immune pattern recognition receptors (PRRs), known as NOD-like receptors (NLRs), such as nucleotide-binding oligomerisation domain-containing protein (NOD) 1, NOD2 and NLRP3. NLR activation is a key driver of inflammation in the host, and BMVs derived from both pathogenic and commensal bacteria have been shown to package PG and LPS in order to modulate the host immune response using NLR-dependent mechanisms. Here, we discuss the packaging of immunostimulatory cargo within OMVs and MVs, their detection by NLRs and the cytokines produced by host cells in response to their detection. Additionally, commensal derived BMVs are thought to shape immunity and contribute to homeostasis in the gut, therefore we also highlight the interactions of commensal derived BMVs with NLRs and their roles in limiting inflammatory diseases.

Pathogenesis Mediated by Bacterial Membrane Vesicles

The release of extracellular vesicles (EVs) is a process conserved across the three domains of life. Amongst prokaryotes, EVs produced by Gram-negative bacteria, termed outer membrane vesicles (OMVs), were identified more than 50 years ago and a wealth of literature exists regarding their biogenesis, composition and functions. OMVs have been implicated in benefiting numerous metabolic functions of their parent bacterium. Additionally, OMVs produced by pathogenic bacteria have been reported to contribute to pathology within the disease setting. By contrast, the release of EVs from Gram-positive bacteria, known as membrane vesicles (MVs), has only been widely accepted within the last decade. As such, there is a significant disproportion in knowledge regarding MVs compared to OMVs. Here we provide an overview of the literature regarding bacterial membrane vesicles (BMVs) produced by pathogenic and commensal bacteria. We highlight the mechanisms of BMV biogenesis and their roles in assisting bacterial survival, in addition to discussing their functions in promoting disease pathologies and their potential use as novel therapeutic strategies.

Treponema denticola stimulates Oncostatin M cytokine release and de novo synthesis in neutrophils and macrophages

Oncostatin M (OSM) is a pleiotropic cytokine elevated in a number of inflammatory conditions including periodontal disease. OSM is produced by a variety of immune cells and has diverse functionality such as regulation of metabolic processes, cell differentiation, and the inflammatory response to bacterial pathogens. The oral cavity is under constant immune surveillance including complementary neutrophil and macrophage populations, due to a persistent symbiotic bacterial presence. Periodontal disease is characterized by a dysbiotic bacterial community, with an abundance of Treponema denticola. Despite strong associations with severe periodontal disease, the source and mechanism of the release of OSM have not been defined in the oral cavity. We show that OSM protein is elevated in the gingival epithelium and immune cell infiltrate during periodontal disease. Furthermore, salivary and oral neutrophil OSM is elevated in correlation with the presence of T. denticola. In an air pouch infection model, T. denticola stimulated higher levels of OSM than the oral pathogen Porphorymonas gingivalis, despite differential recruitment of innate immune cells suggesting T. denticola has distinct properties to elevate OSM levels. OSM release and transcription were increased in isolated human blood, oral neutrophils, or macrophages exposed to T. denticola in vitro as measured by ELISA, qPCR, and microscopy. Using transcription, translation, and actin polymerization inhibition, we found that T. denticola stimulates both OSM release through degranulation and de novo synthesis in neutrophils and also OSM release and synthesis in macrophages. Differential induction of OSM by T. denticola may promote clinical periodontal disease.

Staphylococcus aureus secretes immunomodulatory RNA and DNA via membrane vesicles

Bacterial-derived RNA and DNA can function as ligands for intracellular receptor activation and induce downstream signaling to modulate the host response to bacterial infection. The mechanisms underlying the secretion of immunomodulatory RNA and DNA by pathogens such as Staphylococcus aureus and their delivery to intracellular host cell receptors are not well understood. Recently, extracellular membrane vesicle (MV) production has been proposed as a general secretion mechanism that could facilitate the delivery of functional bacterial nucleic acids into host cells. S. aureus produce membrane-bound, spherical, nano-sized, MVs packaged with a select array of bioactive macromolecules and they have been shown to play important roles in bacterial virulence and in immune modulation through the transmission of biologic signals to host cells. Here we show that S. aureus secretes RNA and DNA molecules that are mostly protected from degradation by their association with MVs. Importantly, we demonstrate that MVs can be delivered into cultured macrophage cells and subsequently stimulate a potent IFN-β response in recipient cells via activation of endosomal Toll-like receptors. These findings advance our understanding of the mechanisms by which bacterial nucleic acids traffic extracellularly to trigger the modulation of host immune responses.

Emerging role of bacterial extracellular vesicles in cancer

Shedding of microbial extracellular vesicles constitutes a universal mechanism for inter-kingdom and intra-kingdom communication that is conserved among prokaryotic and eukaryotic microbes. In this review we delineate fundamental aspects of bacterial extracellular vesicles (BEVs) including their biogenesis, cargo composition, and interactions with host cells. We critically examine the evidence that BEVs from the host gut microbiome can enter the circulatory system to disseminate to distant organs and tissues. The potential involvement of BEVs in carcinogenesis is evaluated and future research ideas explored. We further discuss the potential of BEVs in microbiome-based liquid biopsies for cancer diagnostics and bioengineering strategies for cancer therapy.