Effects of extracellular vesicles derived from oral bacteria on osteoclast differentiation and activation

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.

Extracellular vesicles from periodontal pathogens regulate hepatic steatosis via Toll-like receptor 2 and plasminogen activator inhibitor-1

Plasminogen activator inhibitor-1 (PAI-1) is associated with nonalcoholic fatty liver disease (NAFLD) by lipid accumulation in the liver. In this study, we showed that extracellular vesicles (EVs) from the periodontal pathogens Filifactor alocis and Porphyromonas gingivalis induced steatosis by inducing PAI-1 in the liver and serum of mice fed a low-fat diet. PAI-1 induction was not observed in TLR2-/- mice. When tested using HEK-Blue hTLR2 cells, human TLR2 reporter cells, the TLR2-activating ability of serum from NAFLD patients (n = 100) was significantly higher than that of serum from healthy subjects (n = 100). Correlation analysis confirmed that PAI-1 levels were positively correlated with the TLR2-activating ability of serum from NAFLD patients and healthy subjects. Amphiphilic molecules in EVs were involved in PAI-1 induction. Our data demonstrate that the TLR2/PAI-1 axis is important for hepatic steatosis by EVs of periodontal pathogens.

Salivary Extracellular Vesicles: Biomarkers and Beyond in Human Diseases

Extracellular vesicles, as bioactive molecules, have been extensively studied. There are abundant studies in the literature on their biogenesis, secretion, structure, and content, and their roles in pathophysiological processes. Extracellular vesicles have been reviewed as biomarkers for use in diagnostic tools. Saliva contains many extracellular vesicles, and compared with other body fluids, it is easier to obtain in a non-invasive way, making its acquisition more easily accepted by patients. In recent years, there have been numerous new studies investigating the role of salivary extracellular vesicles as biomarkers. These studies have significant implications for future clinical diagnosis. Therefore, in this paper, we summarize and review the potential applications of salivary extracellular vesicles as biomarkers, and we also describe their other functions (e.g., hemostasis, innate immune defense) in both oral and non-oral diseases.

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.

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.

From Mouth to Muscle: Exploring the Potential Relationship between the Oral Microbiome and Cancer-Related Cachexia

Cancer cachexia is a multifactorial wasting syndrome associated with skeletal muscle and adipose tissue loss, as well as decreased appetite. It affects approximately half of all cancer patients and leads to a decrease in treatment efficacy, quality of life, and survival. The human microbiota has been implicated in the onset and propagation of cancer cachexia. Dysbiosis, or the imbalance of the microbial communities, may lead to chronic systemic inflammation and contribute to the clinical phenotype of cachexia. Though the relationship between the gut microbiome, inflammation, and cachexia has been previously studied, the oral microbiome remains largely unexplored. As the initial point of digestion, the oral microbiome plays an important role in regulating systemic health. Oral dysbiosis leads to the upregulation of pro-inflammatory cytokines and an imbalance in natural flora, which in turn may contribute to muscle wasting associated with cachexia. Reinstating this equilibrium with the use of prebiotics and probiotics has the potential to improve the quality of life for patients suffering from cancer-related cachexia.