High Fructose Consumption Exacerbates Vascular Dysfunction In Type 2 Diabetes Mellitus: A Potential Role of Innate Immunity via Amplified Toll‐Like Receptor 4 Signaling

Abstract

Type 2 diabetes mellitus (T2DM) ranks as the 7th leading cause of death within the U.S. and is one of the major risk factors for the development of cardiovascular disease. Excessive consumption of beverages containing high fructose (HF) within the last decade has been correlated with an increase in the incidence of T2DM. Previous studies showed that HF leads to a vascular dysfunction, but the underlying mechanisms involved are poorly understood. Toll like receptor 4 (TLR4), a key component of the innate immune system, which activates pro‐inflammatory pathways, is associated with complications in T2DM. Previous findings from our lab demonstrated that vascular TLR4 is involved in the pathogenesis of diabetic vascular dysfunction. Thus, we hypothesize that a diet consisting of HF exacerbates vascular complications in T2DM via activation of TLR4 signaling. Twelve‐week‐old female Goto‐Kakizaki (GK) rats, a non‐obese strain that develops T2DM in adult age, were used in this study. GK rats were placed on one of two diets: 15% fructose solution in drinking water (HF group) or normal drinking tap water (control group) for 14 weeks. Surprisingly, the HF group did not display an increase in blood glucose (136± 9 vs. 126± 8 mg/dL control, n=5) or body weight (230± 12 vs. 216± 20g control, n=5); however, they did possess greater levels of triglycerides (122.33± 8 vs. 62.93± 5 mg/dl control, p<0.01, n=5). Importantly, free fatty acids that are derived from triglycerides are known to be activators of TLR4 signaling. Using tail‐cuff plethysmography, we found that the HF group exhibited a greater increase in systolic blood pressure (156± 4 vs. 122± 9mmHg control, p<0.05, n=5). To further assess the effects of HF on the vascular function, aortas from both groups were isolated and mounted using wire myograph to measure vascular relaxation and contraction to concentration‐dependent acetylcholine (ACh) and phenylephrine (PE), respectively. HF consumption significantly impaired endothelial relaxation to ACh (35% reduction vs. control, p<0.01, n=5) and intensified contraction to PE to a greater level than aortas from the control group (45% increase, p<0.05, n=5). To further determine whether HF activates TLR4 signaling within the cardiovascular system, western blots were performed. We found that TLR4 expression was greatly increased in hearts (2.0 fold increase vs. control, p<0.001, n=5) and aortas (2.3 fold increase vs. control, p<0.05, n=5) from the HF group. Similarly, MyD88, a specific adaptor protein of TLR4 signaling, was also increased in the hearts (1.7 fold increase vs. control, p<0.05, n=5) and aortas (1.5 fold increase vs. control, p<0.05, n=5) from the HF group, suggesting that HF alters cardiac and vascular TLR4 signaling. Of note, marked increase of NF‐κB expression, an inflammatory marker and specific downstream target of TLR4 signaling, was also observed in aortas from the HF group (2.6 fold increase vs. control, p<0.05, n=5). Taken together, our results indicate that a HF diet in diabetic rats further impairs vascular function, increases blood pressure, and may correlate with an over activation of TLR4 signaling pathways in cardiac and vascular tissue.Support or Funding InformationNIH