Mechanisms linking periodontitis and diabetes

Background + Aims

• Periodontitis, a chronic inflammatory condition, is a leading cause of tooth loss in adults and is exacerbated by diabetes-related hyperglycemia.
• Diabetes promotes periodontal inflammation and disrupts alveolar bone homeostasis, contributing to tissue damage. Alveolar bone homeostasis involves the endocrine system, signaling interactions between bone and immune cells, and mechanically loaded forces. It relies on bone-resorbing osteoclasts, bone-producing osteoblasts, their precursors and immunoregulatory mediators.
• Elevated levels of inflammatory markers, such as TNF and C-reactive protein (CRP), are observed in individuals with both periodontitis and diabetes.
• While CRP is traditionally viewed as an inflammation marker, recent research suggests it plays an active role in chronic inflammatory diseases, glucose metabolism, and potentially bone homeostasis. However, its exact mechanisms in periodontitis and diabetes remain unclear.
• This study investigates the role of CRP in regulating alveolar bone homeostasis in periodontitis and diabetes using rat models that mimic human CRP expression patterns. Findings aim to inform strategies to mitigate bone loss by targeting CRP in periodontitis and diabetes.

Materials + Methods

• The study utilised both in vivo and in vitro approaches to explore the role of CRP in alveolar bone homeostasis under periodontitis and diabetes conditions.
• In vivo study:
  • Male Sprague–Dawley (SD) rats and CRP knockout on SD background (KO) rats, both aged one month, were used.
  • The rats were randomly assigned to four groups:
    • Control (no periodontitis or diabetes)
    • Periodontitis – induced by inserting a ligature between the left maxillary molars
    • Diabetes – induced through a high-fat diet and streptozotocin injection
    • Combined diabetes and periodontitis (DP)
  • CRP expression in serum and periodontal tissue was analysed using enzyme-linked immunoassay and immunohistochemistry.
  • CRP levels were significantly higher in the DP group compared to controls.
• In vitro study:
  • Human periodontal ligament cells (hPDLCs) were extracted from premolars of healthy patients aged 10–18 years requiring extractions for orthodontic purposes.
  • Periodontal tissue was harvested from the mid-third of roots.
  • Cells were cultured under standard conditions
  • hPDLCs from 3–5 were passages were used for experiments.
• Data were analysed using unpaired Student’s t-test for two-group comparisons and one-way ANOVA with Tukey post hoc tests for multiple comparisons. Statistical significance was set at p < 0.05.

Results

• In vivo:
  • In DP rats, CRP levels were highest, accompanied by significant bone loss, reduced bone density, and altered trabecular structure compared to controls. Immunohistochemistry revealed elevated CRP-positive cells in periodontal tissues, confirming its role in disease exacerbation.
  • CRP deficiency in knockout (KO) rats mitigated alveolar bone resorption in both periodontitis and DP models, reducing bone loss and improving bone structure parameters. CRP deficiency also decreased markers of bone resorption, such as RANKL and TNF, while increasing bone formation markers like osteocalcin (OCN).
• In vitro:
  • CRP knockdown alleviated the inhibitory effects of high glucose and lipopolysaccharide (LPS) on osteogenic differentiation in hPDLCs, improving markers like ALP and RUNX2. CRP knockdown also reduced osteoclastogenic activity by suppressing the RANKL/OPG ratio,
  • CRP overexpression promoted the inhibitory effects of high glucose and LPD on reducing osteogenic protein expression. CRP overexpression further exaggerated the RANKL/OPG ratio.
  • The PI3K/AKT signalling pathway was identified as a key mediator.
    • High glucose and LPS suppressed PI3K/AKT activation
    • CRP knockdown activated the PI3K/AKT pathway promoting osteogenesis and reducing osteoclastogenesis (formation of osteoclasts – bone resorbing cells).

Limitations