Effect of periodontitis on insulin resistance and the onset of type 2 diabetes mellitus in Zucker diabetic fatty rats

Background: Studies indicate that an association exists between periodontitis and type 2 diabetes mellitus (T2DM) and/or obesity, with chronic inflammation hypothesized as the common denominator. The purpose of this study was to determine the causal effect of periodontitis and the concomitant impact of diet on the onset of insulin resistance (IR) and T2DM using a rat model system that simulates human obesity and T2DM. Methods: Twenty-eight, 5-week-old female Zucker diabetic fatty (ZDF, fa/fa) rats were divided into four groups of seven animals: high-fat fed-periodontitis (HF/P), high-fat fed-no periodontitis (HF/C), low-fat fed-periodontitis (LF/P), and low-fat fed-no periodontitis (LF/C). Periodontitis was induced by ligature placement. Fasting plasma insulin and glucose levels were measured, and glucose tolerance tests were performed to assess glucose homeostasis, IR, and the onset of T2DM. The level of tumor necrosis factor-alpha (TNF-alpha), leptin, triglycerides, and free fatty acids were determined in week 13 at sacrifice. Results: HF/P rats developed more severe IR compared to HF/C rats (P<0.01) and LF/P or LF/C rats (P<0.001) as measured by fasting insulin levels and homeostasis model assessment analysis. The onset of severe IR occurred similar to 3 weeks earlier in HF/P rats compared to HF/C rats. HF/P rats developed impaired (110 to 125 mg/dl) and frank fasting hyperglycemia (>125 mg/dl) 2 weeks earlier than HF/C rats. There was no difference in the severity and onset of IR and T2DM between LF/P and LF/C rats. The level of TNF-alpha was significantly higher in HF/P rats compared to HF/C rats (P<0.01). Conclusion: Periodontitis accelerated the onset of severe IR and impaired glucose homeostasis in high-fat fed ZDF rats.