Mechanisms linking periodontitis and diabetes

Background + Aims

• Diabetes risk and insulin resistance are associated with chronic systemic inflammation, often exacerbated by microbial factors. Inflammation interferes with insulin signalling, increasing diabetes susceptibility.
• Periodontitis, a chronic infection of the tooth-supporting structures, is linked to systemic inflammation and glucose intolerance. Emerging research suggests that early microbial changes in the subgingival environment may play a pivotal role in insulin resistance.
• The study aimed to investigate the relationship between subgingival bacterial composition, systemic inflammation, and insulin resistance in individuals living without diabetes.
• The hypothesis posited that dysbiosis (bacterial imbalances) in the subgingival microbiome would correlate with elevated inflammation and insulin resistance markers and that systemic inflammation would mediate this relationship.
• By identifying specific microbial signatures linked to inflammation and glucose regulation, the study hoped to improve early detection of diabetes risks and inform future intervention strategies.

Materials + Methods

• The ORIGINS study enrolled 152 adults aged 20–55 years, without a history of chronic inflammatory or cardiovascular conditions. Participants underwent periodontal examinations, microbial assessments, and blood tests.
• Subgingival plaque samples were collected and analysed for bacterial DNA using the Human Oral Microbe Identification Microarray. Key inflammatory markers were measured:
  • C-reactive protein
  • Interleukin-6
  • Tumour necrosis factor-alpha
  • Adiponectin
• Fasting glucose and insulin levels were used to calculate the Homeostasis Model Assessment of Insulin Resistance (HOMA-IR).
• Relationships between bacterial composition, inflammatory scores, and HOMA-IR were assessed using multivariable regressions. Mediation analysis evaluated whether inflammation explained the link between microbiota and insulin resistance.
• Relative abundances of bacterial phyla (e.g., Actinobacteria, Firmicutes, Proteobacteria) were examined, with a focus on their associations with inflammation and insulin resistance.

Results

• Actinobacteria and Proteobacteria were inversely associated with inflammation, while Firmicutes and TM7 were positively associated.
• Proteobacteria levels were linked to reduced HOMA-IR, and Firmicutes showed positive correlations with insulin resistance.
• Individual bacterial species, such as Parvimonas micra and Cardiobacterium hominis, displayed strong correlations with inflammatory markers and HOMA-IR.
• Firmicutes were most frequently associated with pro-inflammatory effects, while Actinobacteria promoted an anti-inflammatory profile.
• Systemic inflammation accounted for 27–98% of the associations between microbiota and insulin resistance.

Limitations