Poor Oral Health and Its Neurological Consequences: Mechanisms of Porphyromonas gingivalis Involvement in Cognitive Dysfunction

Porphyromonas Gingivalis May Seek the Alzheimer's Disease Brain to Acquire Iron from Its Surplus

Iron accumulates in the brain of subjects with Alzheimer’s disease (AD). Here it promotes the aggregation of amyloid-β plaques in which it is abundant. Iron induces amyloid-β neurotoxicity by damaging free radicals and causing oxidative stress in brain areas with neurodegeneration. It can also bind to tau in AD and enhance the toxicity of tau through co-localization with neurofibrillary tangles and induce accumulation of these tangles. Porphyromonas gingivalis is a key oral pathogen in the widespread biofilm-induced disease “chronic” periodontitis, and recently, has been suggested to have an important role in the pathogenesis of AD. P. gingivalis has an obligate requirement for iron. The current paper suggests that P. gingivalis seeks the AD brain, where it has been identified, to satisfy this need. If this is correct, iron chelators binding iron could have beneficial effects in the treatment of AD. Indeed, studies from both animal AD models and humans with AD have indicated that iron chelators, e.g., lactoferrin, can have such effects. Lactoferrin can also inhibit P. gingivalis growth and proteinases and its ability to form biofilm.

Low levels of salivary lactoferrin may affect oral dysbiosis and contribute to Alzheimer's disease: A hypothesis

Recently it has been reported that reduced levels of salivary lactoferrin (LF) can be a plausible biomarker for amyloid beta (Aβ) accumulation in Alzheimer's disease (AD) brains. This could mean that reduced levels of salivary LF act as a trigger for oral dysbiosis and that low LF levels could change the oral microbiota. A chemical change in the composition of saliva has not yet been considered as a cause for microbial dysbiosis but does present an opportunity to view oral dysbiosis as a plausible contributory factor in the development of AD pathophysiology. Oral dysbiosis has largely been reported as a result of inadequate oral hygiene and dry mouth in elderly subjects. Here we discuss if the deficiency of LF in saliva and gingival fluid of AD patients can facilitate proliferation of oral pathogens, and as a result their spread elsewhere in the body. Additionally, we ask if LF in the AD brain could be overexposed as a result of chronic infection. Together these outcomes will indicate if reduced levels of salivary LF can act as a trigger of oral dysbiosis.

Is Porphyromonas gingivalis involved in Parkinson's disease?

Porphyromonas gingivalis, a major subgingival plaque bacterium in periodontitis, has recently attracted much attention as a possible microbial driver in Alzheimer's disease. In the present paper, another common neuroinflammatory disease, Parkinson's disease (PD), is discussed. A recent study found major virulence factors of P. gingivalis such as gingipain R1 (RgpA) and lipopolysaccharide in the blood circulation of a PD population. The current review reveals how features such as systemic inflammation, hypercoagulation, presence of amyloid fibrin(ogen) in plasma, and marked ultrastructural changes in platelets, probably induced by P. gingivalis, may affect the development of PD. Several other clinical studies have also demonstrated an association between periodontitis and PD. Even if the risk of periodontal diseases causing neurological disorders needs to be better substantiated, that should not keep us from trying to prevent them by performing careful daily dental hygiene.

Oral microbiota and autism spectrum disorder (ASD)

Autism spectrum disorder (ASD) is associated with several oropharyngeal abnormalities, including dysbiosis in the oral microbiota. Since the oral cavity is the start of the gastrointestinal tract, this strengthens and extends the notion of a microbial gut-brain axis in ASD and even raises the question whether a microbial oral-brain axis exists. It is clear that oral bacteria can find their way to the brain through a number of pathways following routine dental procedures. A connection between the oral microbiota and a number of other brain disorders has been reported. As the evidence so far for an association between the oral microbiota and ASDs rests on a few reports only, further studies in this field are necessary. The current review discusses a possible relationship between oral bacteria and the biologic and symptomologic aspects of ASD, focusing on the clinical implications for diagnostic and therapeutic development.

Cachexia and Cognitive Function in the Community-Dwelling Older Adults: Mediation Effects of Oral Health

BACKGROUND

Cognitive impairment and poor oral health are common problems in older adults and are associated with malnutrition. However, it is unclear how they are related to cachexia in community-dwelling older adults. The aim of this study was to examine the relationships among cachexia, cognitive function, and oral health in community-dwelling older adults.

METHODS

This study is a secondary analysis of a data-set. Data were collected in the community setting on older adults who applied for government-funded long-term care services in Hong Kong in 2017. Subjects were community-dwelling and aged ≥60 years. The outcome variable was cachexia. The predictors were cognitive function and oral health. The covariates included demographics and comorbidities associated with cachexia or malnutrition. Path analysis was employed to examine the associations among cachexia, cognitive function, and oral health using the software SAS/STAT and Mplus.

RESULTS

This analysis included 12,940 subjects. The prevalence of cachexia was 1.3%. Cognitive function was also found to have a direct effect on the oral health indicators of chewing problems (OR=1.073, p<0.001), brushing teeth problems (OR=1.349, p<0.001), and swallowing problems (coeff.=0.177, p<0.001). Oral health indicators with a direct effect on cachexia included dry mouth (OR=1.250, p<0.001), brushing teeth problems (OR = 1.185, p<0.01), and swallowing problems (OR=1.231, p<0.001). Cognitive function had no significant direct effect, but had a significant indirect effect on cachexia (OR=1.100, p<0.001) which is mediated by brushing teeth problems (OR=1.052, p<0.001) and swallowing problems (OR=1.038, p<0.001).

CONCLUSION

Cognitive impairment causes cachexia indirectly through poor oral health. This study recommends adding cognitive function when screening community-dwelling older adults for cachexia. Health policymakers should stress regular oral health screening and interventions, and encourage increased utilization of oral health services by community-dwelling older adults with cognitive problems.

Porphyromonas gingivalis and its CRISPR-Cas system

The clustered regularly interspaced short palindromic repeats (CRISPRs) and their associated proteins (Cas) are immune systems in prokaryotes present in most Bacteria and Archaea. They provide adaptive immunity against foreign elements such as bacteriophages/viruses, plasmids and transposons. During immunization a small sequence of foreign DNA, a so-called spacer is integrated into the CRISPR locus in the host cell. Spacers are then transcribed into small RNA guides that direct cleavage of foreign DNA by Cas nucleases. Immunization through spacer acquisition is transferred vertically to the progeny. It is possible that this genetic immune system of bacteria participates in modulating the microbiome of ‘chronic’ periodontitis, in which Porphyromonas gingivalis has been identified as a keystone pathogen causing microbial dysbiosis. An in-depth review of our current knowledge on the CRISPR-Cas systems in P. gingivalis is given in this paper with the attempt to understand how this anaerobic bacterium may protect itself in the periodontal pocket where bacteriophages are abundant and even out-number bacteria.