Clinical studies have shown that metabolic syndrome (MetS) is associated with increased risk of developing periodontitis. However, the underlying mechanisms remain largely unknown. Since it is known that lipopolysaccharide (LPS)-activated toll-like receptor 4 signaling pathways play a crucial role in periodontitis, we hypothesized that MetS enhances LPS-induced periodontal inflammation and alveolar bone loss. In this study, we induced MetS in C57BL/6 mice by feeding them high-fat diet (HFD), and we induced periodontitis by periodontal injection of Aggregatibacter actinomycetemcomitans LPS. We found that mice fed a HFD had significantly increased body weight, plasma lipids, insulin, and insulin resistance when compared with mice fed regular chow, indicating that the mice developed MetS. We also found that a HFD markedly increased LPSinduced alveolar bone loss, osteoclastogenesis, and inflammatory infiltration. Analysis of gene expression in periodontal tissue revealed that HFD and LPS injection cooperatively stimulated expression of cytokines that are known to be involved in periodontal tissue inflammation and osteoclastogenesis-such as interleukin 6, monocyte-chemotactic protein 1, receptor activator of nuclear factor kappa-B ligand, and macrophage colony-stimulating factor. To further understand the potential mechanisms involved in MetS-boosted tissue inflammation, our in vitro studies showed that palmitic acid-the most abundant saturated fatty acid (SFA) and the major SFA in the HFD used in our animal study-potently enhanced LPS-induced proinflammatory gene expression in macrophages. In sum, this study demonstrated that MetS was associated with increased periodontal inflammation and alveolar bone loss in an LPS-induced periodontitis animal model. This study also suggests that SFA palmitic acid may play an important role in MetS-associated periodontitis by enhancing LPS-induced expression of inflammatory cytokines in macrophages.

Studies in recent years have shown a positive relationship between metabolic syndrome (MS) and periodontal disease (PD). Given that patients with MS take statins to reduce cholesterol, and statins also have anti-inflammatory effects, it is important to determine if statin intake hinders the progression of MS-associated PD. In this study, PD was induced in Zucker fat rats (ZFRs), an animal model for MS, and in control lean rats by periodontal injection of Aggregatibacter actinomycetemcomitans lipopolysaccharide (LPS), while simvastatin was given to some of the rats via gavage. After 4 wk of treatment, alveolar bone loss was determined by micro-computed tomography. To explore the underlying mechanisms, we determined the effect of simvastatin on tissue inflammation and the expression of molecules involved in osteoclastogenesis. Results showed that while bone loss was increased by LPS in both ZFRs and the control lean rats, it was significantly more in the former than the latter. Simvastatin effectively alleviated bone loss in both ZFRs and the control rats. Results also showed that LPS stimulated leukocyte tissue infiltration and expression of molecules for osteoclastogenesis, but simvastatin significantly modulated the stimulation. This study demonstrated that simvastatin inhibited LPS-induced alveolar bone loss and periodontal tissue inflammation in rats with MS.

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