Mechanisms linking periodontitis and diabetes

Background + Aims

• The human microbiome plays a vital role in health, with links between gut microbiota and metabolic disorders like type 2 diabetes mellitus (T2DM).
• The oral microbiota, particularly the subgingival microbiome, is thought to be influenced by diabetes.
• Chronic periodontitis (CP) is more common in patients with diabetes, and their subgingival microbiota is thought to differ from patients without diabetes, harbouring higher levels of pathogens such as Porphyromonas gingivalis and Tannerella forsythia.
• It has been hypothesised that poor glycaemic control can alter microbial composition in periodontal pockets, with elevated HbA1c levels creating a glucose-rich gingival environment that may further challenge the subgingival microbiota.
• This study explores the subgingival microbiome of CP patients with varying glycaemic status.

Materials + Methods

• The study included 21 T2DM patients (HbA1c > 6.5%) diagnosed for ≥3 years and prescribed oral hypoglycaemic medication.
• Participants were recruited from endocrinology clinics and underwent oral examinations at the University of São Paulo, Brazil.
• Inclusion criteria were:
  • Age ≥40 years old
  • ≥15 natural teeth
  • Severe periodontitis – ≥30% of sites with probing depth (PD) ≥4 mm and ≥20 sites with PD >6 mm.
• Exclusion criteria included:
  • HIV
  • Hepatitis
  • Cancer history
  • Smoking
  • Alcohol use
  • Pregnancy
  • Morbid obesity (BMI ≥40 kg/m²).
• HbA1c levels were measured 15 days before plaque sample collection, classifying patients into 2 groups:
  • Adequate glycaemic control (DMA) (HbA1c <7.8%, DMA group, n=11)
  • Inadequate control (DMI) (HbA1c ≥8%, DMI group, n=10)
• Subgingival biofilm samples were collected from moderate (PD 4–6 mm) and deep pockets (PD ≥7 mm) using mini-five Gracey curettes.
  • Samples were pooled by pocket depth, transferred to TE buffer, frozen at −80°C, and subjected to DNA extraction using the Master Pure DNA Extraction Kit.
• Statistical analyses were performed to compare microbial diversity and community composition between groups.

Results

• The study analysed subgingival microbiota in 21 T2DM patients with adequate (DMA) and inadequate (DMI) glycaemic control. Despite similar clinical periodontal parameters, the two groups differed significantly in HbA1c levels (p < 0.001).
• Microbial analyses revealed that:
  • DMA patients exhibited higher biodiversity compared to DMI (ANOSIM p = 0.022, Adonis p = 0.042).
  • The Firmicutes/Bacteroidetes ratio was comparable between groups, and periodontopathogens such as gingivalis and T. forsythia were prevalent in both groups, showing no significant differences.
  • At the phylum level (the broadest taxonomic classification within bacterial taxonomy), the study found that subgingival samples from DMI patients had a significantly lower abundance of Tenericutes compared to DMA patients.
  • DMA patients demonstrated higher levels of Alphaproteobacteria (a Proteobacteria), and Eubacteriaceae, Lachnospiraceae, and Peptostreptococcaceae (Firmicutes families).
  • DMI presented with lower proportions of certainTreponema species and exhibited higher levels of certain Prevotellaceaespecies within Bacteroidetes but lower levels of other phylotypes.
  • No significant differences were found for Fusobacteria, Synergistetes, or Actinobacteria between groups, though slight differences inCoriobacteriaceae and Atopobium levels were observed.

Limitations