The Putative Role of Pathogenic Oral Microorganisms in Chronic Kidney Disease

Hickey, Niall Anthony (2019) The Putative Role of Pathogenic Oral Microorganisms in Chronic Kidney Disease. Doctoral thesis (PhD), Manchester Metropolitan University.

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Abstract

Chronic kidney disease and chronic periodontitis are common diseases that are found disproportionately comorbid with each other and have been reported to have a detrimental effect on the progression of each respective disease. They have an overlap in risk factors and both are underpinned by systemic inflammation along with a wide selection of immunological and non-specific effects that can affect the body over the lifespan of the conditions. The oral microorganisms involved in chronic periodontitis have demonstrated the ability to translocate and elicit distal effects in a variety of systemic diseases but currently there has been little research into the associations with chronic kidney disease. Previous studies have investigated the directionality of the relationship between these two diseases; however, there is a lack of evidence on how these diseases may be interacting at the local sites such as the oral cavity and systemic level, especially looking at periodontitis associated microbial products that could damage the kidneys. The aim of this study was to investigate the microbial products produced by periodontitis associated microorganisms using a novel metabolomics approach and identify if any of these products are capable of eliciting in vitro a cytotoxic (cell viability testing), migratory (wound healing assay) and fibrotic response (qPCR) in renal cells. A selection of microorganisms associated with periodontitis were cultivated in a novel media representative of the diseased environment, and the microbial products secreted in bacterial supernatants over their lifecycle were collected. These supernatants were prepared for testing by centrifugation and filtering at 0.2 µM in order to remove microbial cells; the prepared samples were stored at -80oC. A novel metabolomics approach utilising liquid chromatography mass spectroscopy was developed and trialled as a fast screening method for identifying potentially toxic metabolites but it was not suitable for this study. Testing of the collected microbial supernatants against human kidney cells identified that only Porphyromonas gingivalis supernatants were capable of inducing a cytotoxic and mild anti-migratory effect. Tests to identify the causative agent behind XV these effects suggest this effect could be protein derived, as the addition of a protease inhibitor attenuated the cytotoxic effects of the supernatants, suggesting the role of microbe specific proteases known as Gingipains. Investigations in the fibrotic potential of the collected supernatants showed that only Porphyromonas gingivalis supernatants were capable of significantly inducing the production of a three pro-fibrotic markers: Collagen, type I, alpha 1, transforming growth factor β and tissue inhibitor of metalloproteinases 1. In conclusion, this study showed that one periodontitis associated microorganism, Porphyromonas gingivalis is capable of eliciting cytotoxic and mild anti-migratory effects in renal cells, along with inducing the production of three pro-fibrotic markers. This study sheds light on how this key microorganism may pay a role in the mediation of chronic kidney disease.