Abstract
Diabetes mellitus is associated with endothelial dysfunction; it causes progressive vascular damage resulting from an impaired endothelium-dependent vasorelaxation. In the diabetes state, presence of hyperglycemia and insulin resistance predisposes to endothelial dysfunction. Clinacanthus nutans, widely used as a traditional medicine for diabetes is reported to have hypoglycemic, hypolipidemic, antioxidant, and anti-inflammatory properties. However, the possibility of C. nutans affecting the vascular endothelial function in diabetes remains unclear. This study was aimed at evaluating the effects of C. nutans methanolic leaves extract (CNME) on endothelial function in a type 2 diabetes (T2DM) rat model. Sixty male Sprague-Dawley rats were divided into five groups (n = 12 per group): nondiabetic control, nondiabetic treated with four weeks of CNME (500 mg/kg/daily), untreated diabetic rats, diabetic treated with metformin (300 mg/kg/daily), and diabetic treated with CNME (500 mg/kg/daily). T2DM was induced by a single intraperitoneal injection of low-dose streptozotocin (STZ) to rats fed with high-fat diet (HFD). Endothelial-dependent and endothelial-independent relaxations and contractions of the thoracic aorta were determined using the organ bath. Aortic endothelial nitric oxide synthase (eNOS) expression was determined using Western blotting. Endothelial-dependent relaxation was reduced in diabetic rats. Both diabetic groups treated with CNME or metformin significantly improved the impairment in endothelium-dependent vasorelaxation; this was associated with increased expression of aortic eNOS protein. CNME- and metformin-treated groups also reduced aortic endothelium-dependent and aortic endothelium-independent contractions in diabetics. Both of these diabetic-treated groups also reduced blood glucose levels and increased body weight compared to the untreated diabetic group. In conclusion, C. nutans improves endothelial-dependent vasodilatation and reduces endothelial-dependent contraction, thus ameliorating endothelial dysfunction in diabetic rats. This may occur due to its effect on increasing eNOS protein expression.
Highlights
Cardiovascular disease is the leading cause of death worldwide
Post hoc analysis showed no significant difference in body weight among study groups at week 0
At week 15, the body weights of C and C +C. nutans methanolic leaves extract (CNME) groups were significantly increased, whereas it was reduced in the DM group compared to week 0
Summary
Cardiovascular disease is the leading cause of death worldwide. Diabetes mellitus is an important independent risk factor for the development of atherosclerosis and cardiovascular diseases. Endothelial cells line the inner blood vessels; it regulates vascular tone and maintains the vascular homeostasis. Dysfunction of the endothelium, termed endothelial dysfunction (ED), refers to diminished availability of the primary endothelium-derived relaxing factor (EDRF) nitric oxide (NO) and increased production of vasoconstrictors [1]. ED plays a central role in the pathogenesis of atherosclerosis in diabetes and other cardiovascular diseases. It occurs early, before morphological changes are visible in the vessel wall. NO is formed in the endothelial cells via enzymatic action of endothelial NO synthase (eNOS) with several cofactors such as tetrahydrobiopterin and nicotinamide adenine dinucleotide phosphate (NADPH)
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