Periodontitis, Microbiomes and their Role in Alzheimer's Disease

Functional role of the biofilm regulator CsgD in Salmonella enterica sv. Typhi

Introduction

Typhoid fever is an infectious disease primarily caused by Salmonella enterica sv. Typhi (S. Typhi), a bacterium that causes as many as 20 million infections and 600,000 deaths annually. Asymptomatic chronic carriers of S. Typhi play a major role in the transmission of typhoid fever, as they intermittently shed the bacteria and can unknowingly infect humans in close proximity. An estimated 90% of chronic carriers have gallstones; biofilm formation on gallstones is a primary factor in the establishment and maintenance of gallbladder carriage. CsgD is a central biofilm regulator in Salmonella, but the S. Typhi csgD gene has a mutation that introduces an early stop codon, resulting in a protein truncated by 8 amino acids at the C-terminus. In this study, we investigate the role of role of CsgD in S. Typhi.

Methods

We introduced a fully functional copy of the csgD gene from S. Typhimurium into S. Typhi under both a native and a constitutive promoter and tested for red, dry, and rough (Rdar) colony morphology, curli fimbriae, cellulose, and biofilm formation.

Results and discussion

We demonstrate that although CsgD-regulated curli and cellulose production were partially restored, the introduction of the S. Typhimurium csgD did not induce the Rdar colony morphology. Interestingly, we show that CsgD does not have a significant role in S. Typhi biofilm formation, as biofilm-forming capacities depend more on the isolate than the CsgD regulator. This data suggests the presence of an alternative biofilm regulatory process in this human-restricted pathogen.

Effects of Toothpaste Containing 2% Zinc Citrate on Gingival Health and Three Related Bacteria-A Randomized Double-Blind Study

OBJECTIVES

Gingivitis is the initial stage of periodontitis, one of the most common oral diseases and the primary cause of tooth loss. This study aims to evaluate the effect of toothpaste containing 2% zinc citrate on gingival health and the abundance of three bacteria related to gingivitis and periodontitis.

METHODS AND MATERIALS

Eleven volunteers with the same oral health status were randomly assigned to the treatment (n = 5) and control (n = 6) groups. The control group used fluoride toothpaste, while the treatment group used fluoride toothpaste supplemented with 2% zinc citrate for 3 months. The plaque index, gingival index, and bleeding index were measured at baseline (0 day), 3 weeks, and 3 months. Dental plaque from four areas of the mouth (FDI criteria) was collected at the same timepoints. A total of 132 dental plaque samples were analyzed using quantitative PCR (qPCR) to monitor the abundance of Actinobacillus actinomycetemcomitans, Porphyromonas gingivalis, and Tannerella forsythia.

RESULTS

Toothpaste containing 2% zinc citrate significantly lowered the gingival index and reduced gum bleeding but did not affect the plaque index. It also reduced the total abundance of the three bacteria related to gingivitis and periodontitis in dental plaque over a long-term period.

CONCLUSIONS

Toothpaste with 2% zinc citrate persistently improves gingival health and reduces the presence of gingivitis-associated bacteria in dental plaque.

TRIAL REGISTRATION

Chinese Clinical Trial Registry (Clinical trial registration no.: ChiCTR1900020592) (09/01/2019).

The association between oral diseases and neurodegenerative disorders

BACKGROUND

The association between cognitive neurodegenerative disease and oral diseases has been under great interest recently. Several studies have suggested a connection between periodontitis and Alzheimer's disease (AD) or other neurodegenerative disorders.

OBJECTIVE

This study aimed to review the potential mechanisms between oral diseases and neurodegenerative diseases.

METHODS

The study was executed as a literature review of English-language publications from 2018-2022. The databases used for the search were PubMed, Cochrane, Scopus, and Web of Science. The search phrases used were "neurodegenerative diseases" AND "oral health" and "neurodegenerative diseases" AND "oral diseases."

RESULTS

The linkage between the two disease groups was observed in several distinct publications and several potential mechanisms were found. The link between periodontitis and AD proved to be the most significant. The effect was accentuated in elderly people where individuals possessed also other risk factors for neurodegenerative diseases and had generally worse oral health conditions.

CONCLUSIONS

Oral diseases may be risks for neurodegenerative changes along many different pathways. Good oral health should be acknowledged as a potential preventative or risk-reducing act against neurodegenerative diseases.

Bibliometric Study of Periodontitis and Alzheimer's Disease: Trends, Collaboration, and Emerging Patterns

AIM

To perform a bibliometric study of periodontal disease and Alzheimer's disease (AD) focusing on trends, collaborative efforts, and emerging patterns.

MATERIALS AND METHODS

From January 2018 to May 2024, an observational study was carried out utilizing metadata extracted from the Scopus database. A search methodology, specifically designed for this database, was developed using MeSH terms combined with Boolean operators such as "AND" and "OR". The Bibliometrix tool was employed to facilitate the study, using indicators including the number of citations and publications, the authorship of the publication, the country of origin, the year of publication, the type of publication, the H-index, WorldMap, Sankey diagram, keyword analysis, topic evolution, and scientific findings.

RESULTS

A total of 50.7 and 27.3% of the publications were in Q1 and Q2 quartile journals. The University of Central Lancashire has the most publications (17), but the University of California at San Francisco has the highest impact (1545 citations per publication). The journal Periodontology 2000 had a total of 643 citations per publication. Sim Kaur Singhrao (16) and Ingar Olsen (10) were the authors with the most publications, whereas Eric C Reynolds had the highest impact with 1,300 citations.

CONCLUSIONS

This bibliometric study found a gradual growth in publications, with the highest number of studies during 2021 and 2022, followed by a decrease in subsequent years, with Q1 and Q2 journals predominating. In terms of scientific productivity, the United States is the leading country in this area of research. The journal Periodontology 2000 had the highest number of citations, demonstrating the particular interest of periodontology in studying the association between periodontal disease and systemic diseases.

CLINICAL SIGNIFICANCE

The present study is significant because the relationship between periodontitis and Alzheimer is currently considered a novel multidisciplinary research opportunity, given that it includes both medical and dental specialties. This research also provides a valuable contribution to academics, universities, and research centers because it will allow us to understand trends and new research horizons and identify the most productive authors. How to cite this article: Matta-Pacheco J, Tsukamoto-Jaramillo A, Tinedo-López PL, et al. Bibliometric Study of Periodontitis and Alzheimer's Disease: Trends, Collaboration, and Emerging Patterns. J Contemp Dent Pract 2024;25(9):863-868.

Trajectory of brain-derived amyloid beta in Alzheimer's disease: where is it coming from and where is it going?

Alzheimer's disease (AD) is a progressive neurological disorder that primarily impacts cognitive function. Currently there are no disease-modifying treatments to stop or slow its progression. Recent studies have found that several peripheral and systemic abnormalities are associated with AD, and our understanding of how these alterations contribute to AD is becoming more apparent. In this review, we focuse on amyloid‑beta (Aβ), a major hallmark of AD, summarizing recent findings on the source of brain-derived Aβ and discussing where and how the brain-derived Aβ is cleared in vivo. Based on these findings, we propose future strategies for AD prevention and treatment, from a novel perspective on Aβ metabolism.

Prunin Laurate Derived from Natural Substances Shows Antibacterial Activity against the Periodontal Pathogen Porphyromonas gingivalis

Periodontal disease is an inflammatory disease caused by infection with periodontopathogenic bacteria. Oral care is essential to prevent and control periodontal disease, which affects oral and systemic health. However, many oral hygiene products currently on the market were developed as disinfectants, and their intense irritation makes their use difficult for young children and older people. This study investigated the antibacterial effects of prunin laurate (Pru-C12) and its analogs on periodontopathogenic bacteria, Porphyromonas gingivalis (P. gingivalis). Pru-C12 and its analogs inhibited in vitro bacterial growth at more than 10 μM and biofilm formation at 50 µM. Among its analogs, only Pru-C12 showed no cytotoxicity at 100 µM. Three of the most potent inhibitors also inhibited the formation of biofilms. Furthermore, Pru-C12 inhibited alveolar bone resorption in a mouse experimental periodontitis model by P. gingivalis infection. These findings may be helpful in the development of oral hygiene products for the prevention and control of periodontal disease and related disorders.

Manipulating the diseased oral microbiome: the power of probiotics and prebiotics

Dental caries and periodontal disease are amongst the most prevalent global disorders. Their aetiology is rooted in microbial activity within the oral cavity, through the generation of detrimental metabolites and the instigation of potentially adverse host immune responses. Due to the increasing threat of antimicrobial resistance, alternative approaches to readdress the balance are necessary. Advances in sequencing technologies have established relationships between disease and oral dysbiosis, and commercial enterprises seek to identify probiotic and prebiotic formulations to tackle preventable oral disorders through colonisation with, or promotion of, beneficial microbes. It is the metabolic characteristics and immunomodulatory capabilities of resident species which underlie health status. Research emphasis on the metabolic environment of the oral cavity has elucidated relationships between commensal and pathogenic organisms, for example, the sequential metabolism of fermentable carbohydrates deemed central to acid production in cariogenicity. Therefore, a focus on the preservation of an ecological homeostasis in the oral environment may be the most appropriate approach to health conservation. In this review we discuss an ecological approach to the maintenance of a healthy oral environment and debate the potential use of probiotic and prebiotic supplementation, specifically targeted at sustaining oral niches to preserve the delicately balanced microbiome.

The Effect of Bacterial Composition Shifts in the Oral Microbiota on Alzheimer's Disease

Alzheimer's disease (AD), a neurological disorder, despite significant advances in medical science, has not yet been definitively cured, and the exact causes of the disease remain unclear. Due to the importance of AD in the clinic, large expenses are spent annually to deal with this neurological disorder, and neurologists warn of an increase in this disease in elderly in the near future. It has been believed that microbiota dysbiosis leads to Alzheimer's as a multi-step disease. In this regard, the presence of footprints of perturbations in the oral microbiome and the predominance of pathogenic bacteria and their effect on the nervous system, especially AD, is a very interesting topic that has been considered by researchers in the last decade. Some studies have looked at the mechanisms by which oral microbiota cause AD. However, many aspects of this interaction are still unclear as to how oral microbiota composition can contribute to this disease. Understanding this interaction requires extensive collaboration by interdisciplinary researchers to explore all aspects of the issue. In order to reveal the link between the composition of the oral microbiota and this disease, researchers from various domains have sought to explain the mechanisms of shift in oral microbiota in AD in this review.

Advances in the Study of the Pathology and Treatment of Alzheimer's Disease and Its Association with Periodontitis

Alzheimer's disease (AD) has become one of the leading causes of health problems in the elderly, and studying its causes and treatments remains a serious challenge for researchers worldwide. The two main pathological features of Alzheimer's disease are the extracellular deposition of β-amyloid (Aβ) to form senile plaques and the intracellular aggregation of hyperphosphorylated Tau protein to form neurofibrillary tangles (NFTs). Researchers have proposed several hypotheses to elucidate the pathogenesis of AD, but due to the complexity of the pathophysiologic factors involved in the development of AD, no effective drugs have been found to stop the progression of the disease. Currently, the mainstay drugs used to treat AD can only alleviate the patient's symptoms and do not have a therapeutic effect. As researchers explore interactions among diseases, much evidence suggests that there is a close link between periodontitis and AD, and that periodontal pathogenic bacteria can exacerbate Aβ deposition and Tau protein hyperphosphorylation through neuroinflammatory mechanisms, thereby advancing the pathogenesis of AD. This article reviews recent advances in the pathogenesis of AD, available therapeutic agents, the relevance of periodontitis to AD, and mechanisms of action.

Establishment of a consensus protocol to explore the brain pathobiome in patients with mild cognitive impairment and Alzheimer's disease: Research outline and call for collaboration

Microbial infections of the brain can lead to dementia, and for many decades microbial infections have been implicated in Alzheimer's disease (AD) pathology. However, a causal role for infection in AD remains contentious, and the lack of standardized detection methodologies has led to inconsistent detection/identification of microbes in AD brains. There is a need for a consensus methodology; the Alzheimer's Pathobiome Initiative aims to perform comparative molecular analyses of microbes in post mortem brains versus cerebrospinal fluid, blood, olfactory neuroepithelium, oral/nasopharyngeal tissue, bronchoalveolar, urinary, and gut/stool samples. Diverse extraction methodologies, polymerase chain reaction and sequencing techniques, and bioinformatic tools will be evaluated, in addition to direct microbial culture and metabolomic techniques. The goal is to provide a roadmap for detecting infectious agents in patients with mild cognitive impairment or AD. Positive findings would then prompt tailoring of antimicrobial treatments that might attenuate or remit mounting clinical deficits in a subset of patients.

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.

Profiling the oral microbiomes in patients with Alzheimer's disease

OBJECTIVES

To analyse the characteristics of the oral microbiomes and expected to find biomarkers about Alzheimer's disease (AD).

SUBJECTS AND METHODS

AD patients (n = 26) and cognitive intact people (n = 26) were examined for cognition, depression, oral health and collected saliva and gingival crevicular fluid (GCF) in the morning. Full-length 16S rRNA gene was amplified and sequencing was performed using the PacBio platform.

RESULTS

The predominant bacterium of salivary microbiome and periodontal microbiome from AD patients was Streptococcus oralis and Porphyromonas gingivalis, respectively. With respect to β diversity analysis, there was a significance difference in periodontal microbiome between AD patients and cognitively intact subjects. The relative abundance of Veillonella parvula significantly increased in oral microbiomes from AD patients. Interestingly, the dominant species were different between early-onset AD and late-onset AD patients. Moreover, the predominant species were changed as the clinical severity of AD. Furthermore, the correlation analysis revealed that V. parvula was associated with AD in both saliva and GCF and that P. gingivalis was associated with AD only in GCF.

CONCLUSIONS

In this study, the microbiome community of oral microbes was altered in AD patients and periodontal microbiome was sensitive to cognition changes. Moreover, V. parvula and P. gingivalis were associated with AD.

Subgingival microbiome at different levels of cognition

Oral health and declining cognition may have a bi-directional association. We characterized the subgingival microbiota composition of subjects from normal cognition to severe cognitive decline in two cohorts. Memory and Periodontitis (MINOPAR) include 202 home-living participants (50-80 years) in Sweden. Finnish Oral Health Studies in Older Adults (FINORAL) include 174 participants (≥65 years) living in long-term care in Finland. We performed oral examination and assessed the cognitive level with Mini Mental State Examination (MMSE). We sequenced the 16S-rRNA gene (V3-V4 regions) to analyse the subgingival bacterial compositions. The microbial diversities only tended to differ between the MMSE categories, and the strongest determinants were increased probing pocket depth (PPD) and presence of caries. However, abundances of 101 taxa were associated with the MMSE score. After adjusting for age, sex, medications, PPD, and caries, only eight taxa retained the significance in the meta-analyses of the two cohorts. Especially Lachnospiraceae [XIV] at the family, genus, and species level increased with decreasing MMSE. Cognitive decline is associated with obvious changes in the composition of the oral microbiota. Impaired cognition is accompanied with poor oral health status and the appearance of major taxa of the gut microbiota in the oral cavity. Good oral health-care practices require special deliberations among older adults.

Studying ancient human oral microbiomes could yield insights into the evolutionary history of noncommunicable diseases

Noncommunicable diseases (NCDs) have played a critical role in shaping human evolution and societies. Despite the exceptional impact of NCDs economically and socially, little is known about the prevalence or impact of these diseases in the past as most do not leave distinguishing features on the human skeleton and are not directly associated with unique pathogens. The inability to identify NCDs in antiquity precludes researchers from investigating how changes in diet, lifestyle, and environments modulate NCD risks in specific populations and from linking evolutionary processes to modern health patterns and disparities. In this review, we highlight how recent advances in ancient DNA (aDNA) sequencing and analytical methodologies may now make it possible to reconstruct NCD-related oral microbiome traits in past populations, thereby providing the first proxies for ancient NCD risk. First, we review the direct and indirect associations between modern oral microbiomes and NCDs, specifically cardiovascular disease, diabetes mellitus, rheumatoid arthritis, and Alzheimer's disease. We then discuss how oral microbiome features associated with NCDs in modern populations may be used to identify previously unstudied sources of morbidity and mortality differences in ancient groups. Finally, we conclude with an outline of the challenges and limitations of employing this approach, as well as how they might be circumvented. While significant experimental work is needed to verify that ancient oral microbiome markers are indeed associated with quantifiable health and survivorship outcomes, this new approach is a promising path forward for evolutionary health research.

Studying ancient human oral microbiomes could yield insights into the evolutionary history of noncommunicable diseases

Noncommunicable diseases (NCDs) have played a critical role in shaping human evolution and societies. Despite the exceptional impact of NCDs economically and socially, little is known about the prevalence or impact of these diseases in the past as most do not leave distinguishing features on the human skeleton and are not directly associated with unique pathogens. The inability to identify NCDs in antiquity precludes researchers from investigating how changes in diet, lifestyle, and environments modulate NCD risks in specific populations and from linking evolutionary processes to modern health patterns and disparities. In this review, we highlight how recent advances in ancient DNA (aDNA) sequencing and analytical methodologies may now make it possible to reconstruct NCD-related oral microbiome traits in past populations, thereby providing the first proxies for ancient NCD risk. First, we review the direct and indirect associations between modern oral microbiomes and NCDs, specifically cardiovascular disease, diabetes mellitus, rheumatoid arthritis, and Alzheimer's disease. We then discuss how oral microbiome features associated with NCDs in modern populations may be used to identify previously unstudied sources of morbidity and mortality differences in ancient groups. Finally, we conclude with an outline of the challenges and limitations of employing this approach, as well as how they might be circumvented. While significant experimental work is needed to verify that ancient oral microbiome markers are indeed associated with quantifiable health and survivorship outcomes, this new approach is a promising path forward for evolutionary health research.

Ishige okamurae Attenuates Neuroinflammation and Cognitive Deficits in Mice Intracerebroventricularly Injected with LPS via Regulating TLR-4/MyD88-Dependent Pathways

Neuroinflammation is one of the critical causes of neuronal loss and cognitive impairment. We aimed to evaluate the anti-neuroinflammatory properties of Ishige okamuae using mice intracerebroventricularly injected with lipopolysaccharides (LPS) and LPS-treated C6 glioma cells. We found that the short- and long-term memory deficits of LPS-injected mice were improved by oral administration of Ishige okamurae extracts (IOE). LPS-induced neuronal loss, increase in amyloid-β plaque, and expression of COX-2 and iNOS were restored by IOE. In addition, LPS-induced activation of Toll-like receptor-4 (TLR-4) and its downstream molecules, such as MyD88, NFκB, and mitogen-activated protein kinases (MAPKs), were significantly attenuated in the brains of mice fed with IOE. We found that pretreatment of IOE to C6 glioma cells ameliorated LPS-induced expression of TLR-4 and its inflammatory cascades, such as MyD88 expression, reactive oxygen species production, MAPKs phosphorylation, and NFκB phosphorylation with consequent downregulation of COX-2, iNOS, proinflammatory cytokines, and nitric oxide expression. Furthermore, IOE (0.2 µg/mL) was found to have equivalent efficacy with 10 μM of MyD88 inhibitor in preventing LPS-induced inflammatory responses in C6 glioma cells. Taken together, these results strongly suggest that IOE could be developed as a promising anti-neuroinflammatory agent which is able to control the TLR-4/MyD88-dependent signaling pathways.

Is Periodontitis Associated with Age-Related Cognitive Impairment? The Systematic Review, Confounders Assessment and Meta-Analysis of Clinical Studies

It has been suggested that molecular pathological mechanisms responsible for periodontitis can be linked with biochemical alterations in neurodegenerative disorders. Hypothetically, chronic systemic inflammation as a response to periodontitis plays a role in the etiology of cognitive impairment. This study aimed to determine whether periodontitis (PDS) is a risk factor for age-related cognitive impairment (ACI) based on evidence of clinical studies. A comprehensive, structured systematic review of existing data adhering to the Preferred Reporting Items for Systematic Review and Meta Analyses (PRISMA) guidelines was carried out. Five electronic databases, PubMed, Embase, Scopus, Web of Science, and Cochrane, were searched for key terms published in peer-reviewed journals until January 2021. The Newcastle-Ottawa scale was used to assess the quality of studies and risk of bias. The primary and residual confounders were explored and evaluated. A meta-analysis synthesizing quantitative data was carried out using a random-effects model. Seventeen clinical studies were identified, including 14 cohort, one cross-sectional, and two case-control studies. Study samples ranged from 85 to 262,349 subjects, with follow-up between 2 and 32 years, and age above 45 years, except for two studies. The findings of studies suggesting the PDS-ACI relationship revealed substantial differences in design and methods. A noticeable variation related to the treatment of confounders was observed. Quality assessment unveiled a moderate quality of evidence and risk of bias. The subgroups meta-analysis and pooled sensitivity analysis of results from seven eligible studies demonstrated overall that the presence of PDS is associated with an increased risk of incidence of cognitive impairment (OR = 1.36, 95% CI 1.03-1.79), particularly dementia (OR = 1.39, 95% CI 1.02-1.88) and Alzheimer's disease (OR = 1.03 95% CI 0.98-1.07)). However, a considerable heterogeneity of synthesized data (I2 = 96%) and potential publication bias might affect obtained results. While there is a moderate statistical association between periodontitis and dementia, as well as Alzheimer's disease, the risk of bias in the evidence prevents conclusions being drawn about the role of periodontitis as a risk factor for age-related cognitive impairment.

Application of antimicrobial photodynamic therapy to treat subgingival multidrug-resistant bacterial infections in ICU patients

BACKGROUND

Drug-resistant bacterial infections have received much attention in recent years. Antimicrobial photodynamic therapy (aPDT) is an effective antimicrobial strategy. This study aimed to evaluate the therapeutic effect of methylene blue (MB)-mediated aPDT against subgingival multidrug-resistant (MDR) bacterial infections in intensive care unit (ICU) patients.

METHODS

Eighty-three patients who were hospitalized in the ICU of the Second Affiliated Hospital of Nanchang University from July 2019 to June 2021 were selected. The intraoral partitioned control test was conducted. Teeth that met the criteria were selected from different quadrants of the same patient, randomly divided into three groups, namely, A, B, and C, and treated with aPDT, chlorhexidine gargle, or normal saline. The counts of MDR bacteria in the gingival crevicular fluid were assessed in the different groups at different time points before and after treatment.

RESULTS

The MDR bacterial count decreased immediately after aPDT and was significantly different from that in the chlorhexidine gargle rinse group and the normal saline rinse group (P<0.05). There was no significant difference among the three groups at 6, 12, and 24 hours after treatment (P>0.05).

CONCLUSION

aPDT can be used to treat subgingival MDR bacterial infections, but the long-term effects of treatment need to be further studied.

Structural Mimicry in Microbial and Antimicrobial Amyloids

The remarkable variety of microbial species of human pathogens and microbiomes generates significant quantities of secreted amyloids, which are structured protein fibrils that serve diverse functions related to virulence and interactions with the host. Human amyloids are associated largely with fatal neurodegenerative and systemic aggregation diseases, and current research has put forward the hypothesis that the interspecies amyloid interactome has physiological and pathological significance. Moreover, functional and molecular-level connections between antimicrobial activity and amyloid structures suggest a neuroimmune role for amyloids that are otherwise known to be pathological. Compared to the extensive structural information that has been accumulated for human amyloids, high-resolution structures of microbial and antimicrobial amyloids are only emerging. These recent structures reveal both similarities and surprising departures from the typical amyloid motif, in accordance with their diverse activities, and advance the discovery of novel antivirulence and antimicrobial agents. In addition, the structural information has led researchers to postulate that amyloidogenic sequences are natural targets for structural mimicry, for instance in host-microbe interactions. Microbial amyloid research could ultimately be used to fight aggressive infections and possibly processes leading to autoimmune and neurodegenerative diseases.

An Investigation into the Effects of Outer Membrane Vesicles and Lipopolysaccharide of Porphyromonas gingivalis on Blood-Brain Barrier Integrity, Permeability, and Disruption of Scaffolding Proteins in a Human in vitro Model

BACKGROUND

The effects of the key pathogens and virulence factors associated with gum disease such as Porphyromonas gingivalis (P. gingivalis) on the central nervous system is of great interest with respect to development of neuropathologies and hence therapeutics and preventative strategies. Chronic infections and associated inflammation are known to weaken the first line of defense for the brain, the blood-brain barrier (BBB).

OBJECTIVE

The focus of this study is to utilize an established human in vitro BBB model to evaluate the effects of P. gingivalis virulence factors lipopolysaccharide (LPS) and outer membrane vesicles (OMVs) on a primary-derived human model representing the neurovascular unit of the BBB.

METHODS

Changes to the integrity of the BBB after application of P. gingivalis LPS and OMVs were investigated and correlated with transport of LPS. Additionally, the effect of P. gingivalis LPS and OMVs on human brain microvascular endothelial cells in monolayer was evaluated using immunofluorescence microscopy.

RESULTS

The integrity of the BBB model was weakened by application of P. gingivalis LPS and OMVs, as measured by a decrease in electrical resistance and a recovery deficit was seen in comparison to the controls. Application of P. gingivalis OMVs to a monoculture of human brain microvascular endothelial cells showed disruption of the tight junction zona occludens protein (ZO-1) compared to controls.

CONCLUSION

These findings show that the integrity of tight junctions of the human BBB could be weakened by association with P. gingivalis virulence factors LPS and OMVs containing proteolytic enzymes (gingipains).

Analysis of the Effects of Food Additives on Porphyromonas gingivalis

This study aims to investigate six food additives (octanoic acid, decanoic acid, acesulfame K, aspartame, saccharin, and sucralose) used in foods for the elderly or people with dysphagia because of the effect of these food additives on Porphyromonas gingivalis (P. gingivalis), which is a keystone pathogen of periodontal diseases. The growth of P. gingivalis was inhibited by 5 mM octanoic acid, 1.25 mM decanoic acid, 1.25% acesulfame K, 0.0625% aspartame, 0.03125% saccharin, and 0.625% sucralose. In addition, these food additives showed bactericidal activity for planktonic P. gingivalis (5 mM octanoic acid, 5 mM decanoic acid, 0.25% aspartame, 0.25% saccharin, and 5% sucralose). Moreover, biofilm formation was inhibited by 10 mM octanoic acid, 10 mM decanoic acid, 10% acesulfame K, 0.35% aspartame, 0.5% saccharin, and 7.5% sucralose. Moreover, the same concentration of these food additives without aspartame killed P. gingivalis in the biofilm. Aspartame and sucralose did not show cytotoxicity to human cell lines at concentrations that affected P. gingivalis. These findings may be useful in clarifying the effects of food additives on periodontopathogenic bacteria.

An Association of Pathogens and Biofilms with Alzheimer's Disease

As one of the leading causes of dementia, Alzheimer's disease (AD) is a condition in which individuals experience progressive cognitive decline. Although it is known that beta-amyloid (Aβ) deposits and neurofibrillary tangles (NFT) of tau fibrils are hallmark characteristics of AD, the exact causes of these pathologies are still mostly unknown. Evidence that infectious diseases may cause AD pathology has been accumulating for decades. The association between microbial pathogens and AD is widely studied, and there are noticeable correlations between some bacterial species and AD pathologies, especially spirochetes and some of the oral microbes. Borrelia burgdorferi has been seen to correlate with Aβ plaques and NFTs in infected cells. Because of the evidence of spirochetes in AD patients, Treponema pallidum and other oral treponemes are speculated to be a potential cause of AD. T. pallidum has been seen to form aggregates in the brain when the disease disseminates to the brain that closely resemble the Aβ plaques of AD patients. This review examines the evidence as to whether pathogens could be the cause of AD and its pathology. It offers novel speculations that treponemes may be able to induce or correlate with Alzheimer's disease.

Gram-negative bacteria and their lipopolysaccharides in Alzheimer's disease: pathologic roles and therapeutic implications

Alzheimer's disease (AD) is the most serious age-related neurodegenerative disease and causes destructive and irreversible cognitive decline. Failures in the development of therapeutics targeting amyloid-β (Aβ) and tau, principal proteins inducing pathology in AD, suggest a paradigm shift towards the development of new therapeutic targets. The gram-negative bacteria and lipopolysaccharides (LPS) are attractive new targets for AD treatment. Surprisingly, an altered distribution of gram-negative bacteria and their LPS has been reported in AD patients. Moreover, gram-negative bacteria and their LPS have been shown to affect a variety of AD-related pathologies, such as Aβ homeostasis, tau pathology, neuroinflammation, and neurodegeneration. Moreover, therapeutic approaches targeting gram-negative bacteria or gram-negative bacterial molecules have significantly alleviated AD-related pathology and cognitive dysfunction. Despite multiple evidence showing that the gram-negative bacteria and their LPS play a crucial role in AD pathogenesis, the pathogenic mechanisms of gram-negative bacteria and their LPS have not been clarified. Here, we summarize the roles and pathomechanisms of gram-negative bacteria and LPS in AD. Furthermore, we discuss the possibility of using gram-negative bacteria and gram-negative bacterial molecules as novel therapeutic targets and new pathological characteristics for AD.

Analysis the Link between Periodontal Diseases and Alzheimer's Disease: A Systematic Review

The hypothesis of an infectious connection from the oro-pharyngeal sphere to the brain underlines the interest in analyzing the link between periodontal disease and Alzheimer’s disease. The aim of this systematic review was to examine the link between Alzheimer’s disease and periodontal disease in patients aged 65 and over. Databases (PubMed (MEDLINE), the Cochrane Library, and Embase) were analyzed for relevant references up to 21 June 2021. The authors independently selected the studies and extracted the data. The quality of included studies was checked using the National Institutes of Health’s quality assessment tools. Five studies were included. The selected studies described in their results an increase in F. nucleatum in Alzheimer’s disease patients (adjusted p = 0.02), and its incidence was linked to C. rectus and P. gingivalis (adjusted HR = 1.22 (1.04–1.43), p = 0.012) as well as A. naeslundii (crude HR = 2.0 (1.1–3.8)). The presence of periodontitis at baseline was associated with a six-fold increase in the rate of cognitive decline over a 6-month follow-up period (ADAS-Cog mean change = 2.9 ± 6.6). The current review suggests an association between periodontal disease and Alzheimer’s disease. The treatment of periodontal disease could be a way to explore Alzheimer’s disease prevention.

Lipocalin 2 as a link between ageing, risk factor conditions and age-related brain diseases

Chronic (neuro)inflammation plays an important role in many age-related central nervous system (CNS) diseases, including Alzheimer's disease, Parkinson's disease and vascular dementia. Inflammation also characterizes many conditions that form a risk factor for these CNS disorders, such as physical inactivity, obesity and cardiovascular disease. Lipocalin 2 (Lcn2) is an inflammatory protein shown to be involved in different age-related CNS diseases, as well as risk factor conditions thereof. Lcn2 expression is increased in the periphery and the brain in different age-related CNS diseases and also their risk factor conditions. Experimental studies indicate that Lcn2 contributes to various neuropathophysiological processes of age-related CNS diseases, including exacerbated neuroinflammation, cell death and iron dysregulation, which may negatively impact cognitive function. We hypothesize that increased Lcn2 levels as a result of age-related risk factor conditions may sensitize the brain and increase the risk to develop age-related CNS diseases. In this review we first provide a comprehensive overview of the known functions of Lcn2, and its effects in the CNS. Subsequently, this review explores Lcn2 as a potential (neuro)inflammatory link between different risk factor conditions and the development of age-related CNS disorders. Altogether, evidence convincingly indicates Lcn2 as a key constituent in ageing and age-related brain diseases.

Evaluating efficacy of a novel dentifrice in reducing probing depths in Stage I and II periodontitis maintenance patients: A randomized, double-blind, positive controlled clinical trial

BACKGROUND

Compliance to periodontal maintenance therapy (PMT) is essential for long-term periodontal health. Between PMT visits, patients must maintain good oral hygiene. A dentifrice with demonstrable clinical benefits for use between PMT visits would be highly desirable. The aim of this clinical study was to investigate the effect of a novel dental gel on probing depths (PD) and inflammation when used as a home care dentifrice in Stage I and II periodontitis patients.

METHODS

This double-blind clinical study randomized 65 subjects with Stage I and II periodontitis to the novel dental gel containing 2.6% EDTA, and a commercially available anti-gingivitis dentifrice with 0.454% stannous fluoride. Primary endpoint was PD at 6 months for those sites with baseline PD ≥ 4 mm and secondary endpoints included whole mouth mean scores of modified gingival index (MGI), modified sulcus bleeding index (mSBI) and plaque index (PI). No SRP was performed at baseline.

RESULTS

Subjects using the novel dentifrice showed significant PD reductions of 1.18 mm (from 4.27 mm at baseline to 3.09 mm at 6 months) compared to 0.93 mm (from 4.23 mm at baseline to 3.30 mm at 6 months) shown for those using the positive control dentifrice. Difference between treatments at 6 months was 0.21 mm with P-value = 0.0126. Significant improvements in MGI (P = 0.0000), mSBI (P = 0.0000), and PI (P = 0.0102) were also observed in 6 months.

CONCLUSION

The novel dentifrice showed significant reductions in PD and gingival inflammation over 6 months solely as a home care dentifrice without baseline SRP in Stage I and II periodontitis maintenance patients.

Porphyromonas gingivalis outside the oral cavity

Porphyromonas gingivalis, a Gram-negative anaerobic bacillus present in periodontal disease, is considered one of the major pathogens in periodontitis. A literature search for English original studies, case series and review articles published up to December 2019 was performed using the MEDLINE, PubMed and GoogleScholar databases, with the search terms "Porphyromonas gingivalis" AND the potentially associated condition or systemic disease Abstracts and full text articles were used to make a review of published research literature on P. gingivalis outside the oral cavity. The main points of interest of this narrative review were: (i) a potential direct action of the bacterium and not the systemic effects of the inflammatory acute-phase response induced by the periodontitis, (ii) the presence of the bacterium (viable or not) in the organ, or (iii) the presence of its virulence factors. Virulence factors (gingipains, capsule, fimbriae, hemagglutinins, lipopolysaccharide, hemolysin, iron uptake transporters, toxic outer membrane blebs/vesicles, and DNA) associated with P. gingivalis can deregulate certain functions in humans, particularly host immune systems, and cause various local and systemic pathologies. The most recent studies linking P. gingivalis to systemic diseases were discussed, remembering particularly the molecular mechanisms involved in different infections, including cerebral, cardiovascular, pulmonary, bone, digestive and peri-natal infections. Recent involvement of P. gingivalis in neurological diseases has been demonstrated. P. gingivalis modulates cellular homeostasis and increases markers of inflammation. It is also a factor in the oxidative stress involved in beta-amyloid production.

The Effect of Periodontitis on Dementia and Cognitive Impairment: A Meta-Analysis

The association between periodontal disease and dementia/cognitive impairment continues to receive increasing attention. However, whether periodontal disease is a risk factor for dementia/cognitive impairment is still uncertain. This meta-analysis was conducted to comprehensively analyze the effect of periodontitis on dementia and cognitive impairment, and to assess the periodontal status of dementia patients at the same time. A literature search was undertaken on 19 October 2020 using PubMed, Web of Science, and Embase with different search terms. Two evaluators screened studies according to inclusion and exclusion criteria, and a third evaluator was involved if there were disagreements; this process was the same as that used for data extraction. Included studies were assessed with the Newcastle-Ottawa Scale (NOS), and results were analyzed using software Review Manager 5.2. Twenty observational studies were included. In the comparison between periodontitis and cognitive impairment, the odds ratio (OR) was 1.77 (95% confidence interval (CI), 1.31–2.38), which indicated that there was a strong relationship between periodontitis and cognitive impairment. There was no statistical significance in the effect of periodontitis on dementia (OR = 1.59; 95%CI, 0.92–2.76). The subgroup analysis revealed that moderate or severe periodontitis was significantly associated with dementia (OR = 2.13; 95%CI, 1.25–3.64). The mean difference (MD) of the community periodontal index (CPI) and clinical attachment level (CAL) was 0.25 (95%CI, 0.09–0.40) and 1.22 (95%CI, 0.61–1.83), respectively. In this meta-analysis, there was an association between periodontitis and cognitive impairment, and moderate or severe periodontitis was a risk factor for dementia. Additionally, the deterioration of periodontal status was observed among dementia patients.

Oral Microbiota and Salivary Levels of Oral Pathogens in Gastro-Intestinal Diseases: Current Knowledge and Exploratory Study

Various bi-directional associations exist between oral health and gastro-intestinal diseases. The oral microbiome plays a role in the gastro-intestinal carcinogenesis and fusobacteria are the most investigated bacteria involved. This paper aims to review the current knowledge and report the preliminary data on salivary levels of Fusobacterium nucleatum, Porphyromonas gingivalis and Candida albicans in subjects with different gastro-intestinal conditions or pathologies, in order to determine any differences. The null hypothesis was "subjects with different gastro-intestinal diseases do not show significant differences in the composition of the oral microbiota". Twenty-one subjects undergoing esophagastroduodenoscopy or colonscopy were recruited. For each subject, a salivary sample was collected before the endoscopy procedure, immediately stored at -20 °C and subsequently used for genomic bacterial DNA extraction by real-time PCR. Low levels of F. nucleatum and P. gingivalis were peculiar in the oral microbiota in subjects affected by Helicobater pylori-negative chronic gastritis without cancerization and future studies will elucidate this association. The level of C. albicans did not statistically differ among groups. This preliminary study could be used in the future, following further investigation, as a non-invasive method for the search of gastrointestinal diseases and associated markers.

On the Possible Relevance of Bottom-up Pathways in the Pathogenesis of Alzheimer's Disease

Dementia is an increasing health problem in older aged populations worldwide. Age-related changes in the brain can be observed decades before the first symptoms of cognitive decline appear. Cognitive impairment has chronic inflammatory components, which can be enhanced by systemic immune activation. There exist mutual interferences between inflammation and cognitive deficits. Signs of an activated immune system i.e. increases in the serum concentrations of soluble biomarkers such as neopterin or accelerated tryptophan breakdown along the kynurenine axis develop in a significant proportion of patients with dementia and correlate with the course of the disease, and they also have a predictive value. Changes in biomarker concentrations are reported to be associated with systemic infections by pathogens such as cytomegalovirus (CMV) and bacterial content in saliva. More recently, the possible influence of microbiome composition on Alzheimer's disease (AD) pathogenesis has been observed. These observations suggest that brain pathology is not the sole factor determining the pathogenesis of AD. Interestingly, patients with AD display drastic changes in markers of immune activation in the circulation and in the cerebrospinal fluid. Other data have suggested the involvement of factors extrinsic to the brain in the pathogenesis of AD. However, currently, neither the roles of these factors nor their importance has been clearly defined.

The Role of Inflammation and Infection in Age-Related Neurodegenerative Diseases: Lessons From Bacterial Meningitis Applied to Alzheimer Disease and Age-Related Macular Degeneration

Age-related neurodegenerative diseases, such as Alzheimer disease (AD) and age-related macular degeneration (AMD), are multifactorial and have diverse genetic and environmental risk factors. Despite the complex nature of the diseases, there is long-standing, and growing, evidence linking microbial infection to the development of AD dementia, which we summarize in this article. Also, we highlight emerging research findings that support a role for parainfection in the pathophysiology of AMD, a disease of the neurosensory retina that has been shown to share risk factors and pathological features with AD. Acute neurological infections, such as Bacterial Meningitis (BM), trigger inflammatory events that permanently change how the brain functions, leading to lasting cognitive impairment. Neuroinflammation likewise is a known pathological event that occurs in the early stages of chronic age-related neurodegenerative diseases AD and AMD and might be triggered as a parainfectious event. To date, at least 16 microbial pathogens have been linked to the development of AD; on the other hand, investigation of a microbe-AMD relationship is in its infancy. This mini-review article provides a synthesis of existing evidence indicating a contribution of parainfection in the aetiology of AD and of emerging findings that support a similar process in AMD. Subsequently, it describes the major immunopathological mechanisms that are common to BM and AD/AMD. Together, this evidence leads to our proposal that both AD and AMD may have an infectious aetiology that operates through a dysregulated inflammatory response, leading to deleterious outcomes. Last, it draws fresh insights from the existing literature about potential therapeutic options for BM that might alleviate neurological disruption associated with infections, and which could, by extension, be explored in the context of AD and AMD.

Role of the gut microbiome in Alzheimer's disease

Alzheimer's disease (AD) is the most common form of dementia, affecting millions of individuals each year and this number is expected to significantly increase. The complicated microorganisms residing in human gut are closely associated with our health. Emerging evidence has suggested possible involvement of human gut microbiome in AD. Symbiotic gut microbiomes are known to maintain brain health by modulating host's barriers integrity, metabolic system, immune system, nervous system and endocrine system. However, in the event of gut dysbiosis and barriers disruption, gut pathobionts disrupt homeostasis of the metabolic system, immune system, nervous system, and endocrine system, resulting in deterioration of neurological functions and subsequently promoting development of AD. Multiple therapeutic approaches, such as fecal microbiome transplant, antibiotics, prebiotics, probiotics, symbiotic, and diet are discussed as potential treatment options for AD by manipulating the gut microbiome to reverse pathological alteration in the systems above.

The oralome and its dysbiosis: New insights into oral microbiome-host interactions

The oralome is the summary of the dynamic interactions orchestrated between the ecological community of oral microorganisms (comprised of up to approximately 1000 species of bacteria, fungi, viruses, archaea and protozoa - the oral microbiome) that live in the oral cavity and the host. These microorganisms form a complex ecosystem that thrive in the dynamic oral environment in a symbiotic relationship with the human host. However, the microbial composition is significantly affected by interspecies and host-microbial interactions, which in turn, can impact the health and disease status of the host. In this review, we discuss the composition of the oralome and inter-species and host-microbial interactions that take place in the oral cavity and examine how these interactions change from healthy (eubiotic) to disease (dysbiotic) states. We further discuss the dysbiotic signatures associated with periodontitis and caries and their sequalae, (e.g., tooth/bone loss and pulpitis), and the systemic diseases associated with these oral diseases, such as infective endocarditis, atherosclerosis, diabetes, Alzheimer's disease and head and neck/oral cancer. We then discuss current computational techniques to assess dysbiotic oral microbiome changes. Lastly, we discuss current and novel techniques for modulation of the dysbiotic oral microbiome that may help in disease prevention and treatment, including standard hygiene methods, prebiotics, probiotics, use of nano-sized drug delivery systems (nano-DDS), extracellular polymeric matrix (EPM) disruption, and host response modulators.

Targeting Impaired Antimicrobial Immunity in the Brain for the Treatment of Alzheimer's Disease

Alzheimer's disease (AD) is the most common form of dementia and aging is the most common risk factor for developing the disease. The etiology of AD is not known but AD may be considered as a clinical syndrome with multiple causal pathways contributing to it. The amyloid cascade hypothesis, claiming that excess production or reduced clearance of amyloid-beta (Aβ) and its aggregation into amyloid plaques, was accepted for a long time as the main cause of AD. However, many studies showed that Aβ is a frequent consequence of many challenges/pathologic processes occurring in the brain for decades. A key factor, sustained by experimental data, is that low-grade infection leading to production and deposition of Aβ, which has antimicrobial activity, precedes the development of clinically apparent AD. This infection is chronic, low grade, largely clinically silent for decades because of a nearly efficient antimicrobial immune response in the brain. A chronic inflammatory state is induced that results in neurodegeneration. Interventions that appear to prevent, retard or mitigate the development of AD also appear to modify the disease. In this review, we conceptualize further that the changes in the brain antimicrobial immune response during aging and especially in AD sufferers serve as a foundation that could lead to improved treatment strategies for preventing or decreasing the progression of AD in a disease-modifying treatment.

Eye on the Enigmatic Link: Dysbiotic Oral Pathogens in Ocular Diseases; The Flip Side

Mouth and associated structures were regarded as separate entities from the rest of the body. However, there is a paradigm shift in this conception and oral health is now considered as a fundamental part of overall well-being. In recent years, the subject of oral-foci of infection has attained a resurgence in terms of systemic morbidities while limited observations denote the implication of chronic oral inflammation in the pathogenesis of eye diseases. Hitherto, there is a paucity for mechanistic insights underlying the reported link between periodontal disease (PD) and ocular comorbidities. In light of prevailing scientific evidence, this review article will focus on the understudied theme, that is, the impact of oral dysbiosis in the induction and/or progression of inflammatory eye diseases like diabetic retinopathy, scleritis, uveitis, glaucoma, age-related macular degeneration (AMD). Furthermore, the plausible mechanisms by which periodontal microbiota may trigger immune dysfunction in the Oro-optic-network and promote the development of PD-associated AMD have been discussed.

Chronic Periodontitis and Alzheimer Disease: A Putative Link of Serum Proteins Identification by 2D-DIGE Proteomics

Increasing evidence indicates Chronic Periodontitis (CP) is a comorbidity of Alzheimer’s disease (AD), which is the most common form of age-related dementia, and for the latter, effective diagnostic and treatment strategies are lacking. Although inflammation is present in both diseases, the exact mechanisms and cross-links between CP and AD are poorly understood; and a direct association between the two has not been reported. This study aimed to identify a direct serum proteins link between AD and CP. Two-dimensional differential in-gel electrophoresis was employed to analyze serum samples from 12 CP patients and 12 age-matched controls. Furthermore, to determine the molecular link between CP and AD, neuroblastoma SK-N-SH APPwt cells were treated with 1 μg/ml of lipopolysaccharide from Porphyromonas gingivalis (P.g-LPS). Ten differentially expressed proteins were identified in CP patients. Among them, nine proteins were up-regulated, and one protein was down-regulated. Of the 10 differentially expressed proteins, five proteins were reportedly involved in the pathology of AD: Cofilin-2, Cathepsin B, Clusterin, Triosephosphate isomerase, and inter-alpha-trypsin inhibitor heavy chain H4 (ITI-H4). Western blotting indicated significantly higher expression of Cofilin-2, Cathepsin B, and Clusterin and lower expression of ITI-H4 in the CP group than in the Control group. The serum concentration of Cathepsin B has a good correlation with MMSE scores. Moreover, the protein level of Cathepsin B (but not that of ADAM10 and BACE1) increased significantly along with a prominent increase in Aβ_1–40 and Aβ_1–42 in the cell lysates of P.g-LPS-treated SK-N-SH APPwt cells. Cathepsin B inhibition resulted in a sharp decrease in Aβ_1–40 and Aβ_1–42 in the cell lysates. Furthermore, TNF-α was one of the most important inflammatory cytokines for the P.g-LPS-induced Cathepsin B upregulation in SK-N-SH APPwt cells. These results show that CP and AD share an association, while Cathepsin B could be a key link between the two diseases. The discovery of the identical serum proteins provides a potential mechanism underlying the increased risk of AD in CP patients, which could be critical for elucidating the pathophysiology of AD.

Targeting Infectious Agents as a Therapeutic Strategy in Alzheimer's Disease

Alzheimer's disease (AD) is the most prevalent dementia in the world. Its cause(s) are presently largely unknown. The most common explanation for AD, now, is the amyloid cascade hypothesis, which states that the cause of AD is senile plaque formation by the amyloid β peptide, and the formation of neurofibrillary tangles by hyperphosphorylated tau. A second, burgeoning theory by which to explain AD is based on the infection hypothesis. Much experimental and epidemiological data support the involvement of infections in the development of dementia. According to this mechanism, the infection either directly or via microbial virulence factors precedes the formation of amyloid β plaques. The amyloid β peptide, possessing antimicrobial properties, may be beneficial at an early stage of AD, but becomes detrimental with the progression of the disease, concomitantly with alterations to the innate immune system at both the peripheral and central levels. Infection results in neuroinflammation, leading to, and sustained by, systemic inflammation, causing eventual neurodegeneration, and the senescence of the immune cells. The sources of AD-involved microbes are various body microbiome communities from the gut, mouth, nose, and skin. The infection hypothesis of AD opens a vista to new therapeutic approaches, either by treating the infection itself or modulating the immune system, its senescence, or the body's metabolism, either separately, in parallel, or in a multi-step way.

Acyl homoserine lactone-mediated quorum sensing in the oral cavity: a paradigm revisited

Acyl homoserine lactones (AHLs), the quorum sensing (QS) signals produced by Gram-negative bacteria, are currently considered to play a minor role in the development of oral biofilm since their production by oral pathogens has not been ascertained thus far. However, we report the presence of AHLs in different oral samples and their production by the oral pathogen Porphyromonas gingivalis. The importance of AHLs is further supported by a very high prevalence of AHL-degradation capability, up to 60%, among bacteria isolated from dental plaque and saliva samples. Furthermore, the wide-spectrum AHL-lactonase Aii20J significantly inhibited oral biofilm formation in different in vitro biofilm models and caused important changes in bacterial composition. Besides, the inhibitory effect of Aii20J on a mixed biofilm of 6 oral pathogens was verified using confocal microscopy. Much more research is needed in order to be able to associate specific AHLs with oral pathologies and to individuate the key actors in AHL-mediated QS processes in dental plaque formation. However, these results indicate a higher relevance of the AHLs in the oral cavity than generally accepted thus far and suggest the potential use of inhibitory strategies against these signals for the prevention and treatment of oral diseases.

Time to test antibacterial therapy in Alzheimer's disease

Alzheimer's disease is associated with cerebral accumulation of amyloid-β peptide and hyperphosphorylated tau. In the past 28 years, huge efforts have been made in attempting to treat the disease by reducing brain accumulation of amyloid-β in patients with Alzheimer's disease, with no success. While anti-amyloid-β therapies continue to be tested in prodromal patients with Alzheimer's disease and in subjects at risk of developing Alzheimer's disease, there is an urgent need to provide therapeutic support to patients with established Alzheimer's disease for whom current symptomatic treatment (acetylcholinesterase inhibitors and N-methyl d-aspartate antagonist) provide limited help. The possibility of an infectious aetiology for Alzheimer's disease has been repeatedly postulated over the past three decades. Infiltration of the brain by pathogens may act as a trigger or co-factor for Alzheimer's disease, with Herpes simplex virus type 1, Chlamydia pneumoniae, and Porphyromonas gingivalis being most frequently implicated. These pathogens may directly cross a weakened blood-brain barrier, reach the CNS and cause neurological damage by eliciting neuroinflammation. Alternatively, pathogens may cross a weakened intestinal barrier, reach vascular circulation and then cross blood-brain barrier or cause low grade chronic inflammation and subsequent neuroinflammation from the periphery. The gut microbiota comprises a complex community of microorganisms. Increased permeability of the gut and blood-brain barrier induced by microbiota dysbiosis may impact Alzheimer's disease pathogenesis. Inflammatory microorganisms in gut microbiota are associated with peripheral inflammation and brain amyloid-β deposition in subjects with cognitive impairment. Oral microbiota may also influence Alzheimer's disease risk through circulatory or neural access to the brain. At least two possibilities can be envisaged to explain the association of suspected pathogens and Alzheimer's disease. One is that patients with Alzheimer's disease are particularly prone to microbial infections. The other is that microbial infection is a contributing cause of Alzheimer's disease. Therapeutic trials with antivirals and/or antibacterials could resolve this dilemma. Indeed, antiviral agents are being tested in patients with Alzheimer's disease in double-blind placebo-controlled studies. Although combined antibiotic therapy was found to be effective in animal models of Alzheimer's disease, antibacterial drugs are not being widely investigated in patients with Alzheimer's disease. This is because it is not clear which bacterial populations in the gut of patients with Alzheimer's disease are overexpressed and if safe, selective antibacterials are available for them. On the other hand, a bacterial protease inhibitor targeting P. gingivalis toxins is now being tested in patients with Alzheimer's disease. Clinical studies are needed to test if countering bacterial infection may be beneficial in patients with established Alzheimer's disease.

Microbial extracellular RNAs and their roles in human diseases

IMPACT STATEMENT

The number of commensal bacteria in the body surpasses the number of actual human cells. Thus, various interactions between microbes and human cells constitute an inevitable phenomenon. Recent evidence has led to bacterial extracellular RNAs (exRNAs) being proposed as good candidates for microbe-host inter-kingdom communication tools as they can modulate the expression of host genes. However, research findings on the relevance of interactions between extracellular RNA and human diseases are still in their infancy. Nevertheless, substantial data suggest that microbial exRNAs are implicated in various human diseases both at local and distant sites. By exploring various scenarios for the involvement of microbial exRNAs in human diseases, we may better understand the role of exRNAs as "communication signals" for diseases and thereby develop novel therapeutic strategies by using them and their carrier extracellular vesicles.

Invasion of Human Retinal Pigment Epithelial Cells by Porphyromonas gingivalis leading to Vacuolar/Cytosolic localization and Autophagy dysfunction In-Vitro

Recent epidemiological  studies link Periodontal disease(PD) to age-related macular degeneration (AMD). We documented earlier that Porphyromonas gingivalis(Pg), keystone oral-pathobiont, causative of PD, efficiently invades human gingival epithelial and blood-dendritic cells. Here, we investigated the ability of dysbiotic Pg-strains to invade human-retinal pigment epithelial cells(ARPE-19), their survival, intracellular localization, and the pathological effects, as dysfunction of RPEs leads to AMD. We show that live, but not heat-killed Pg-strains adhere to and invade ARPEs. This involves early adhesion to ARPE cell membrane, internalization and localization of Pg within single-membrane vacuoles or cytosol, with some nuclear localization apparent. No degradation of Pg or localization inside double-membrane autophagosomes was evident, with dividing Pg suggesting a metabolically active state during invasion. We found significant downregulation of autophagy-related genes particularly, autophagosome complex. Antibiotic protection-based recovery assay further confirmed distinct processes of adhesion, invasion and amplification of Pg within ARPE cells. This is the first study to demonstrate invasion of human-RPEs, begin to characterize intracellular localization and survival of Pg within these cells. Collectively, invasion of RPE by Pg and its prolonged survival by autophagy evasion within these cells suggest a strong rationale for studying the link between oral infection and AMD pathogenesis in individuals with periodontitis.

Knock-on effect of periodontitis to the pathogenesis of Alzheimer's disease?

Background

Alzheimer’s disease has chronic inflammatory components, which can be enhanced by systemic immune activation resulting in inflammation or vice versa. There is growing evidence that chronic periodontitis drives systemic inflammation and finally Alzheimer’s disease. Thus, a link might exist between oral pathogens and Alzheimer’s disease. This may be of special significance as there is an age-related incidence of chronic periodontitis.

Methods

In this study, 20 consecutive patients with probable Alzheimer’s disease were investigated. Diagnosis was established by cognitive tests, routine laboratory tests and cerebral magnetic resonance tomography. In 35% of these patients with cognitive impairment pathogenic periodontal bacteria were found.

Results

The presence of Porphyromonas gingivalis, the key pathogen and one of the species involved in chronic periodontitis, was found to be associated with lower mini mental state examination scores (p < 0.05) and with a tendency to lower scores in the clock drawing test (p = 0.056). Furthermore, association between lower serum concentrations of the immune biomarker neopterin and the presence of Treponema denticola (p < 0.01) as well as of kynurenine were found in Alzheimer patients positive vs. negative for Tannerella forsytia (p < 0.05).

Conclusions

Data indicate a possible association of specific periodontal pathogens with cognitive impairment, Treponema denticola and Tannerella forsytia may alter the host immune response in Alzheimer’s disease. Albeit still preliminary, findings of the study may point to a possible role of an altered salivary microbiome as a causal link between chronic periodontitis and cognitive impairment in Alzheimer’s disease.

The Role of Periodontitis and Periodontal Bacteria in the Onset and Progression of Alzheimer's Disease: A Systematic Review

The evidence of a connection between the peripheral inflammatory processes and neurodegenerative diseases of the central nervous system is becoming more apparent. This review of the related literature highlights the most recent clinical, epidemiological, and in vitro studies trying to investigate possible connections between periodontal bacteria and the onset and progression of Alzheimer's disease. This review was conducted by searching databases such as PubMed and Scopus using keywords or combinations such as Alzheimer's Disease AND periodontal or dementia AND periodontitis OR periodontal. After eliminating overlaps and screening the articles not related to these issues, we identified 1088 records and proceeded to the selection of articles for an evaluation of the associative assumptions. The hypothesis suggested by the authors and confirmed by the literature is that the bacterial load and the inflammatory process linked to periodontal disease can intensify inflammation at the level of the central nervous system, favoring the occurrence of the disease. The analysis of the literature highlights how periodontal disease can directly contribute to the peripheral inflammatory environment by the introduction of periodontal or indirect pathogenic bacteria and proinflammatory cytokines locally produced at the periodontal level following bacterial colonization of periodontal defects.

Examining the association between oral health status and dementia: A nationwide nested case-controlled study

Alzheimer’s disease as a consequence of chronic brain inflammation mediated by infectious microbes including the oral microbiome continues to attract support. Taiwan’s National Insurance database was used to evaluate associations between dental health and Alzheimer’s disease; 209,112 new cases of Alzheimer’s disease were matched 1:4 with 836,448 dementia-free controls to test the hypothesis that better dental health would be associated with less occurrence of dementia. Ten year dental records and conditional logistic regression models were used to estimate the odds ratios associated with Alzheimer’s disease. Subgroup analyses compared vascular Alzheimer’s disease and sporadic Alzheimer’s disease. As the population aged, Alzheimer’s disease diagnoses were more frequent with a 10 fold upward inflection after 60. Nearly 56% of sporadic Alzheimer’s disease patients were women but less than 50% had vascular Alzheimer’s disease. Comorbidities were 10–20% higher in the Alzheimer’s disease patients than in controls, but stroke, chronic infection, and pneumonia were 40–45% more common in the vascular Alzheimer’s disease patients. Heart disease, hypertension, diabetes, stroke, peripheral artery disease, pneumonia, and herpetic disease (HSV) were all associated with higher odds of Alzheimer’s disease. HSV was not a factor in the vascular Alzheimer’s disease. Routine dental procedures tended to lower odds ratios. Root canals and extractions that restore oral homeostasis were associated with lower odds of dementia. However, when extractions exceeded four, the odds of Alzheimer’s disease rose. The fact that Alzheimer’s disease was not associated with periodontal procedures per se but with more frequent periodontal emergencies suggested again a chronic issue. Dental health costs suggest that good dental care was associated with lower odds of Alzheimer’s disease except for radiographic costs which were consistently associated with higher odds, independent of oral health. Common comorbid conditions were associated with higher odds of Alzheimer’s disease and oral health care was associated with lower odds, providing support for the hypothesis that the oral microbiome is a factor in the development of Alzheimer’s disease.

Impact statement

This study clearly demonstrates the power and value of a nationally applied digital medical record. Longitudinal studies of gradually developing pathologies like dementia have often been limited by sample size and narrow and incomplete medical histories. The Taiwan National Insurance database provides an unparalleled opportunity for detailed analyses of associations between current medical conditions and a spectrum of prior medical and dental events. The temporal impact of the database will only become more important as the past historical record progressively expands going forward. The inclusion of dental records in assessing the relationship with subsequent dementia is very important because this information is often unavailable or dependent on subject recall. This study clearly establishes associations between a variety of suspected cardiovascular and metabolic factors and the odds of dementia. A critical outcome should include the design of targeted interventions and the subsequent assessment of their efficacy.

Interaction of Oral and Toothbrush Microbiota Affects Oral Cavity Health

Tooth brushing is necessary to maintain oral health. Little research has been carried out to explore microbial diversity in toothbrushes and to study the potential impact of these bacteria on human health. In the present study, 20 participants were enrolled, and the microbial diversity in their oral cavity and toothbrushes was investigated using high-throughput sequencing. Our results indicate that 1,136 and 976 operational taxonomic units (OTUs) were obtained from groups CB (samples from toothbrushes of participants using traditional Chinese medicinal toothpaste) and AB (samples from toothbrushes of those using antibacterial toothpaste), respectively. The pathogens Acinetobacter baumannii, Staphylococcus aureus, and Candida albicans were identified on toothbrushes. The presence of these pathogens increases the chance for the host to get infectious diseases, neurodegenerative diseases, cardiovascular diseases, and cancers. Moreover, our in vitro results indicate that traditional Chinese medicinal toothpaste and antibacterial toothpaste can not only inhibit the growth of pathogens but also markedly inhibit the growth of probiotics Lactobacillus salivarius and Streptococcus salivarius. Therefore, the inhibitory effect of toothpaste on probiotics, together with the existence of pathogens in toothbrushes, indicates a potential risk of tooth brushing for people in a sub-healthy state.

Oral microbiota and Alzheimer's disease: Do all roads lead to Rome?

Alzheimer's disease (AD) is a progressive neurodegenerative pathology affecting milions of people worldwide associated with deposition of senile plaques. While the genetic and environmental risk factors associated with the onset and consolidation of late onset AD are heterogeneous and sporadic, growing evidence also suggests a potential link between some infectious diseases caused by oral microbiota and AD. Oral microbiota dysbiosis is purported to contribute either directly to amyloid protein production, or indirectly to neuroinflammation, occurring as a consequence of bacterial invasion. Over the last decade, the development of Human Oral Microbiome database (HOMD) has deepened our understanding of oral microbes and their different roles during the human lifetime. Oral pathogens mostly cause caries, periodontal disease, and edentulism in aged population, and, in particular, alterations of the oral microbiota causing chronic periodontal disease have been associated with the risk of AD. Here we describe how different alterations of the oral microbiota may be linked to AD, highlighting the importance of a good oral hygiene for the prevention of oral microbiota dysbiosis.

Microbiological evaluation of LOCATOR® Legacy attachments: A cross-sectional clinical study

Objective

This retrospective cross‐sectional study aimed to evaluate quantitatively the oral microbiome in the tri‐lobe central cavity of Locator Legacy attachment and verify whether it harbors a different, potentially more pathogenic, bacterial spectrum than the adjacent edentulous ridge.

Materials and Methods

Edentulous patients rehabilitated with implant overdentures using Locator Legacy attachments were recruited for this study. The clinical examination comprised probing depths, mobility, peri‐implant, and periodontal health along with intraoral swabs for microbiological evaluation, polymerase chain reaction (PCR) testing, and candida culture. The swabs were collected from the trilobed cavity of the attachment and the adjacent edentulous ridge. PCR was performed to detect six specific bacteria, Porphyromonas gingivalis, Aggregatibacter actinomycetemcomitans, Tannerella forsythia, Treponema denticola, Prevotella intermedia, and Parvimonas micra. Statistical analyses were performed using McNemar's test and Wilcoxon's rank sum test with the significance set to p < .05.

Results

A total of 50 participants with a mean age of 71.5 ± 9.6 years participated in the study. No significant differences in the microbiome were found between samples from the ridge and the attachment. No significantly different numbers in the candida cultures were identified, and the presence of a removable prostheses did not demonstrate a significant association with the prevalence of candida.

Conclusions

Within the limits of this study and the investigated bacterial species, the trilobed cavity of the attachment does not seem to increase the bacterial load.