Objective:
Vascular disease associated with endothelial dysfunction is a major cause of morbidity in patients with type-1 diabetes. Endothelin (ET)-1 plays a role in diabetes-induced vascular complications, since ET-1 type A receptor blockade reduces diabetes-induced vascular injury. However, whether ET-1 contributes to diabetes-induced endothelial dysfunction remains unproven. We hypothesized that vascular ET-1 overexpression will exaggerate diabetes-induced endothelial dysfunction.
Methods:
Diabetes was induced by streptozotocin treatment (STZ, 55 mg/kg/day, ip) for 5 days in 6-week-old male wild-type (WT) mice and in mice overexpressing ET-1 restricted to the endothelium (eET-1). Mice were studied 14 weeks later. Blood was collected to determine glucose. Mesenteric artery reactivity and remodeling were evaluated using pressurized myography and aortic fibronectin expression by immnunofluorescence.
Results:
STZ-induced diabetes was confirmed by a 3-fold increase in glycemia in WT and eET-1 (
P
<0.001). Diabetes impaired endothelium-dependent relaxation (EDR) reponses to acetylcholine in WT (60.9±6.4% vs 83.9±3.4%,
P
<0.05) and eET-1 (48.6±5.1% vs 81.5±5.2%,
P
<0.001). EDR impairment was exaggerated in eET-1 compared to WT (
P
<0.05). Meclofenamic acid, an inhibitor of cyclooxygenase, increased EDR in eET-1 compared to WT (78.4±9.4% vs 66.7±3.2%,
P
<0.01), which was not observed in diabetic mice. L-NAME, an inhibitor of nitric oxide (NO) synthase, completely blocked EDR in WT, eET-1 and diabetic WT, but not in diabetic eET-1 (4.1±1.6%, 6.4±5.7%, 2.2±4.6% and 26.6±4.6%,
P
<0.05). Apamin plus Tram34, inhibitors of endothelium-dependent hyperpolarization inhibited EDR in the four groups. Endothelium-independent relaxation to sodium nitroprusside, a NO donor, was similar in the four groups. Diabetes reduced media/lumen in WT (2.7±0.3 vs 3.6±0.3,
P
<0.05) and eET-1 (2.9±0.2 vs 3.8±0.3,
P
<0.05). Diabetes decreased aortic fibronectin expression in WT (94.0±11.0 vs. 151.9±21.8 RFU/μm
2
,
P
<0.05) and eET-1 (66.3±8.7 vs. 146.6±20.7 RFU/μm
2
,
P
<0.05).
Conclusion:
ET-1 contributes to alterations in several pathways mediating endothelium-dependent relaxation in type-1 diabetes, leading to exaggerated endothelial dysfunction.
Comment on “Alpha-Lipoic Acid and Antioxidant Diet Help to Improve Endothelial Dysfunction in Adolescents with Type 1 Diabetes: A Pilot Trial”
