Mechanistic links between periodontitis and diabetes

Introduction: A complex two-way link between periodontitis and diabetes is widely accepted. Although the mechanisms underlying this link have not been fully elucidated, disruption of host immunity (neutrophil function, cytokine release), tissue biochemistry, accumulation of advanced glycation end products (AGEs), matrix metalloproteases (MMPs) levels and the oral microbiota have been implicated. Aims and objectives: This project aims to investigate potential mechanisms through analysis of the impact of AGEs (a consequence of hyperglycaemia), on biofilm composition and telomerase immortalised gingival keratinocytes (TIGK). In addition, presented here is a preliminary feasibility study for comparison of oral biofilm composition and functionality, neutrophil function, and saliva and gingival crevicular fluid (GCF) cytokine and MMP profiles from healthy and periodontitis individuals. Methods: The study characterised receptor for AGE (RAGE) expression in TIGK cells and the consequent immune response initiated by AGE/RAGE interactions in these cells. Model oral biofilms (comprising five periodontal species) grown in the presence and absence of AGE were characterised using culture dependent methods. Complex biofilms, derived from combined saliva/tongue/plaque inocula, grown with AGE concentrations representative of hyperglycaemia or health were analysed using next generation sequencing. In a preliminary study, biofilms were also co-cultured with TIGK cells in media supplemented with high AGE concentrations to determine changes in inflammatory responses. Individuals with periodontitis and healthy controls were recruited through DenTCRU for the preliminary clinical study. Neutrophil migration, phagocytosis and respiratory burst in these individuals were analysed. Plaque, GCF and saliva were collected for analysis of cytokine and MMP expression and oral microbiome profiles. Results: The expression of RAGE by TIGK cells, at either the mRNA or protein level, did not change with varying concentrations of AGE. The addition of AGE to model five species biofilms encouraged the growth of A. naeslundii while reducing the proportion of P. gingivalis in the biofilms. Analysis of complex biofilms indicated enrichment of genera including Prevotella, Streptococcus and Veillonella and decreases in Fusobacterium, Campylobacter and Bacteroides amongst others. The preliminary clinical study indicated feasibility of analysing neutrophil function and cytokine and MMP profiles from saliva and GCF. While impairment of neutrophil functions, increase in MMP8 and MMP9, changes in biofilm compositions and increases in cytokines in saliva (IL-8, IL-1β and MCP-1), plasma (IL-8 and IL-1β) and GCF (IL-8,IL-1β and MCP-1) were observed in periodontitis, further analysis using a larger cohort of individual’s ± periodontitis is required for these to reach significance. Conclusion: Together the results suggest AGEs can alter the composition of biofilms, appearing to encourage the growth of health associated genera. Preliminary co-culture experiments demonstrate co-culture of TIGK cells with complex biofilms decreases IL-8 and IL-6 release.