Exposure to Porphyromonas gingivalis and Modifiable Risk Factors Modulate Risk for Early Diabetic Retinopathy

Interaction between Infection of Porphyromonas gingivalis, A Keystone Microbe of Oral Microbiome, and Serum Levels of Lutein/Zeaxanthin Is Associated with Risk for Age-related Macular Degeneration

Porphyromonas gingivalis (P. gingivalis) functions as a catalyst bacterium in the development of periodontitis, and the serum antibody level against P. gingivalis is considered a surrogate marker for the activity level of periodontopathic microbiome. The chronic systemic inflammation induced by P. gingivalis elevates the risk of various systemic and neurodegenerative disorders, including atherosclerosis, diabetes, and Alzheimer's disease. Although the connection between human microbiome and age-related macular degeneration (AMD) remains relatively unexplored, it is noteworthy that AMD shares risk factors and etiological mechanisms with diseases related to P. gingivalis. To investigate the potential association between periodontopathic microbiome and AMD occurrence, we conducted a candidate microbe approach case-control study. Our hypothesis was tested by examining the correlation between serum P. gingivalis immunoglobulin G (IgG) levels and AMD. Comparing the lowest IgG category (≤ 57 enzyme-linked immunosorbent assay units (EU)) with higher categories revealed escalating risks: the second higher category (58-65 EU) conferred almost a 30% increased risk (odds ratio (OR) = 1.28, 95% confidence interval (CI): 1.17 to 1.4), the third higher category (66-119 EU) conferred nearly a 60% increase (OR = 1.58, 95% CI: 1.46 to 1.72), and the highest category (> 119 EU) conveyed over a two-fold risk (OR = 2.04, 95% CI: 1.62 to 2.58) of early AMD. Aligning with the notion that the microbiome composition is significantly shaped by the host's diet, our analysis indicates that sustaining elevated serum levels of lutein/zeaxanthin (≥ 0.35 μmol/L or ≥ 20 μg/dL) might potentially mitigate the P. gingivalis-related AMD risk by as much as 35% (P for interaction < 0.0001). Although the precise mechanism requires additional exploration, these findings suggest a connection between nutrition and oral microbiome, emphasizing their collective role in maintaining eye health.

SIGNIFICANCE STATEMENT

While our oral microbiome may impact eye health, nutritional factors could play a modulatory role in mitigating the associated risk.

Macrophage-Hosted Porphyromonas gingivalis Is a Risk Factor for Cataract Development

Purpose

We studied the regulatory association of Porphyromonas gingivalis (PG) and cataracts.

Methods

PCR and FISH assays were used for detecting PG 16s ribosomal RNA genome, Immunofluorescence was for expression of RpgA in anterior capsular epithelium and fibrosis markers in anterior subcapsular cataract (ASC) model. Flow cytometry was for reactive oxygen species and apoptosis. RNA deep sequencing is for differential gene expression analysis.

Results

PG's 16s ribosomal RNA gene is positively in 43.3% (101/233 cases) of aqueous humor (AH) samples of patients with cataracts, which differs from 4.7% (6/127) of PG-positive AH in patients with glaucoma. Diabetic and high myopia cataracts increase PG-positive AH compared with age-related cataracts. No PG is observed in AH of congenital cataracts. PG is positive in 82% to 94% of the cataractous anterior capsule tissues from high myopia and age-related, congenital, and diabetic cataracts. The PG-positive cells in the cataractous anterior capsular epithelium are CD68+/CD14+ macrophages, but not anterior epithelial cells. In rat ASC models, PG injected via the tail vein or PG-carried bone marrow monocytes can migrate into the equatorial lens epithelium in form of PG-positive macrophages, which promote ASC progression with upregulation of collagen, fibronectin and α smooth muscle actin (α-SMA) expression, and increase 8-OHdG levels and α-SMA expression in the surrounding lens epithelial cells. Kyoto Encyclopedia of Genes and Genomes and Gene Ontology analysis of the RNA sequencing dataset of ASC tissues shows that signaling pathways related to epithelial-mesenchymal transition, oxidative stress, and cell death are up-regulated in PG + ASC compared with that in ASC alone. Co-culture of supernatants of Raw264.7/PG+ cells with rat primary lens epithelial cells increases the 8-OHdG levels, mitochondrial fission, apoptosis, and expression of α-SMA.

Conclusions

Chronic infection with PG can access the lens epithelium via macrophages during stress conditions, which promotes cataract development by possibly elevating oxidative stress, apoptosis, and epithelial-mesenchymal transition in lens tissues. PG infection is a novel a risk factor for cataract development.

Clinical periodontal diagnosis

Periodontal diseases include pathological conditions elicited by the presence of bacterial biofilms leading to a host response. In the diagnostic process, clinical signs such as bleeding on probing, development of periodontal pockets and gingival recessions, furcation involvement and presence of radiographic bone loss should be assessed prior to periodontal therapy, following active therapy, and during long-term supportive care. In addition, patient-reported outcomes such as increased tooth mobility, migration, and tilting should also be considered. More important to the patient, however, is the fact that assessment of signs of periodontal diseases must be followed by an appropriate treatment plan. Furthermore, it should be realized that clinical and radiographic periodontal diagnosis is based on signs which may not reflect the presence of active disease but rather represent the sequelae of a previous bacterial challenge. Hence, the aim of the present review is to provide a summary of clinical and radiographic diagnostic criteria required to classify patients with periodontal health or disease.

Do Oral Pathogens Inhabit the Eye and Play a Role in Ocular Diseases?

Fascinatingly, the immune-privileged healthy eye has a small unique population of microbiota. The human microbiome project led to continuing interest in the ocular microbiome. Typically, ocular microflorae are commensals of low diversity that colonize the external and internal sites of the eye, without instigating any disorders. Ocular commensals modulate immunity and optimally regulate host defense against pathogenic invasion, both on the ocular surface and neuroretina. Yet, any alteration in this symbiotic relationship culminates in the perturbation of ocular homeostasis and shifts the equilibrium toward local or systemic inflammation and, in turn, impaired visual function. A compositional variation in the ocular microbiota is associated with surface disorders such as keratitis, blepharitis, and conjunctivitis. Nevertheless, innovative studies now implicate non-ocular microbial dysbiosis in glaucoma, age-related macular degeneration (AMD), uveitis, and diabetic retinopathy. Accordingly, prompt identification of the extra-ocular etiology and a methodical understanding of the mechanisms of invasion and host-microbial interaction is of paramount importance for preventative and therapeutic interventions for vision-threatening conditions. This review article aims to explore the current literature evidence to better comprehend the role of oral pathogens in the etiopathogenesis of ocular diseases, specifically AMD.

Oral microbiota in human systematic diseases

Oral bacteria directly affect the disease status of dental caries and periodontal diseases. The dynamic oral microbiota cooperates with the host to reflect the information and status of immunity and metabolism through two-way communication along the oral cavity and the systemic organs. The oral cavity is one of the most important interaction windows between the human body and the environment. The microenvironment at different sites in the oral cavity has different microbial compositions and is regulated by complex signaling, hosts, and external environmental factors. These processes may affect or reflect human health because certain health states seem to be related to the composition of oral bacteria, and the destruction of the microbial community is related to systemic diseases. In this review, we discussed emerging and exciting evidence of complex and important connections between the oral microbes and multiple human systemic diseases, and the possible contribution of the oral microorganisms to systemic diseases. This review aims to enhance the interest to oral microbes on the whole human body, and also improve clinician’s understanding of the role of oral microbes in systemic diseases. Microbial research in dentistry potentially enhances our knowledge of the pathogenic mechanisms of oral diseases, and at the same time, continuous advances in this frontier field may lead to a tangible impact on human health.