Oral dysbiosis initiates periodontal disease in experimental kidney disease.

Background and hypothesis: It is presently unclear why there is a high prevalence of periodontal disease in individuals living with chronic kidney disease (CKD). Whilst some have argued that periodontal disease causes CKD, we hypothesised that alterations in saliva and the oral microenvironment in organisms with kidney disease may initiate periodontal disease by causing dysbiosis of the oral microbiota.

Methods: Experimental kidney disease was created using adenine feeding and subtotal nephrectomy in rats, and by adenine feeding in mice. Loss of periodontal bone height was assessed using a dissecting microscope supported by micro-CT, light, confocal and electron microscopy, and immunohistochemistry. Salivary biochemistry was assessed using NMR spectroscopy. The oral microbiome was evaluated using culture-based and molecular methods, and the transmissibility of dysbiosis was assessed using co-caging and microbial transfer experiments into previously germ-free recipient mice.

Results: We demonstrate that experimental kidney disease causes a reproducible reduction of alveolar bone height, without gingival inflammation or overt hyperparathyroidism but with evidence of failure of bone formation at the periodontal crest. We show that kidney disease alters the biochemical composition of saliva and induces progressive dysbiosis of the oral microbiota, with microbial samples from animals with kidney disease displaying reduced overall bacterial growth, increased alpha diversity, reduced abundance of key components of the healthy oral microbiota such as Streptococcus and Rothia, and an increase in minor taxa including those from gram-negative phyla Proteobacteria and Bacteroidetes. Co-housing diseased rats with healthy ones ameliorates the periodontal disease phenotype, whilst transfer of oral microbiota from mice with kidney disease causes periodontal disease in germ-free animals with normal kidney function.

Conclusions: We advocate that periodontal disease should be regarded as a complication of kidney disease, initiated by oral dysbiosis through mechanisms independent of overt inflammation or hyperparathyroidism.