Mechanisms linking periodontitis and diabetes

Background + Aims

• Tumour necrosis factor-alpha (TNF-α) is an inflammatory signalling protein involved in periodontal tissue destruction and insulin resistance (where cells respond less effectively to insulin).
• Blocking this shared pathway may help clarify how inflammation connects type 2 diabetes and periodontitis.
• This study aimed to:
  • Investigate whether TNF-α inhibition alters periodontal destruction, glucose metabolism and early kidney complications in obese diabetic rats with experimental periodontitis.

Materials + Methods

• The study initially included 80 male rats: 45 obese diabetic Zucker rats and 35 lean controls.
• Animals were allocated to 5 groups:
  • Lean controls
  • Lean rats with periodontitis
  • Obese controls
  • Obese rats with periodontitis
  • Obese rats with periodontitis receiving etanercept – a drug that binds and blocks TNF-α.
• Etanercept was injected under the skin x3/week, beginning 1 week before periodontitis was induced.
• Ligatures placed around the upper second molars induced periodontitis for approximately 4-weeks, within a 5-week experiment.
• Metabolic assessments included glucose tolerance, fasting insulin and HOMA-IR (an estimate of insulin resistance calculated from fasting glucose and insulin).
• Periodontal destruction was measured using direct bone measurements and radiographs. Kidney assessments included organ weight, urinary albumin, creatinine clearance and gene expression. Circulating inflammatory cytokines were also measured.

Results

• Etanercept-treated obese rats had significantly lower fasting insulin and HOMA-IR than untreated obese groups, although values remained higher than in lean controls.
• Treatment did not clearly improve post-meal glucose levels, and glucose tolerance remained poorer in obese groups than in lean animals.
• Untreated obese rats with periodontitis had significantly less radiographic bone support than lean rats with periodontitis.
• Etanercept-treated obese rats had radiographic bone support that was not significantly different from lean rats with periodontitis. The authors interpreted this as attenuation of diabetes-associated breakdown, although the same pattern was not demonstrated by direct bone-loss measurements.
• Treatment attenuated kidney enlargement, but did not significantly reduce urinary albumin excretion. Creatinine clearance and measured kidney gene expression did not differ significantly between groups.
• Periodontitis did not significantly worsen glucose tolerance, insulin-resistance markers or measured kidney complications during the experiment. Circulating TNF-α, IL-1β and IL-6 also showed no significant group differences.

Limitations