Wisuda Suvitayavat

Type 1 diabetes and hypercholesterolaemia reveal the contribution of endothelium-derived hyperpolarizing factor to endothelium-dependent relaxation of the rat aorta

1 The present study evaluated the effect of diabetes, hypercholesterolaemia and their combination on the contribution of nitric oxide (NO) and endothelium‐derived hyperpolarizing factor (EDHF) to relaxation of rat isolated aortic rings and the potential contribution of oxidant stress to the disturbance of endothelial function. 2 Thoracic aortic rings from control, diabetic, hypercholesterolaemic and diabetic plus hypercholesterolaemic rats were suspended in organ baths for tension recording. Generation of superoxide by the aorta was measured using lucigenin‐enhanced chemiluminescence. 3 The maximal response to acetylcholine (ACh) was significantly reduced in diabetic or hypercholesterolaemic rats compared with control rats. In rats with diabetes plus hypercholesterolaemia, both the sensitivity and maximal response to ACh was impaired. In control rats, the response to ACh was abolished by the NO synthase inhibitor NG‐nitro‐l‐arginine (l‐NNA) or inhibition of soluble guanylate cyclase with 1H‐[1,2,4]oxadiazolo[4,3‐a]quinoxalin‐1‐one (ODQ). In contrast, in rats with diabetes, hypercholesterolaemia or both, relaxation to ACh was resistant to inhibition by l‐NNA or ODQ, but abolished by additional inhibition of KCa channels with charybdotoxin plus apamin. 4 The generation of superoxide was not significantly enhanced in aortic rings from either diabetic or hypercholesterolaemic rats, but was significantly increased in aortic rings from rats with diabetes plus hypercholesterolaemia. 5 These results suggest that when diabetes and hypercholesterolaemia impair endothelium‐dependent relaxation, due to a diminished contribution from NO, a compensatory contribution of EDHF to endothelium‐dependent relaxation of the aorta is revealed. The attenuation of NO‐mediated relaxation, at least in the presence of both diabetes and hypercholesterolaemia, is associated with enhanced superoxide generation.

Anti-angiogenic actions of the mangosteen polyphenolic xanthone derivative α-mangostin☆

Retinal neovascularization is a major cause of vision loss in diseases characterized by retinal ischemia and is characterized by the pathological growth of abnormal vessels. Vascular endothelial growth factor (VEGF) is known to play an important role in this process. Oxidative stress has been strongly implicated in up-regulation of VEGF associated with neovascularization in various tissues. Hence, compounds with anti-oxidant actions can prevent neovascularization. α-Mangostin, a component of mangosteen (Garcinia mangostana Linn), has been shown to have an anti-oxidant property in pathological conditions involving angiogenesis such as cancer. However, the effect of α-mangostin on ROS formation and angiogenic function in microvascular endothelial cells has not been studied. Hence, this study demonstrated the anti-angiogenic effects of α-mangostin in relation to ROS formation in bovine retinal endothelial cells (REC). α-Mangostin significantly and dose-dependently reduced formation of ROS in hypoxia-treated REC. α-Mangostin also significantly and dose-dependently suppressed VEGF-induced increases in permeability, proliferation, migration and tube formation in REC and blocked angiogenic sprouting in the ex vivo aortic ring assay. In addition, α-mangostin inhibited VEGF-induced phosphorylation of VEGFR2 and ERK1/2-MAPK. According to our results, α-mangostin reduces oxidative stress and limits VEGF-induced angiogenesis through a process involving abrogation of VEGFR2 and ERK1/2-MAPK activation.

Obesity Alters the Peripheral Circadian Clock in the Aorta and Microcirculation

Perturbation of daily rhythm increases cardiovascular risk. The aim of this study was to determine whether obesity alters circadian gene expression and microvascular function in lean mice and obese (db/db) mice.

Nitric oxide signalling is involved in diarylheptanoid‐induced increases in femoral arterial blood flow in ovariectomized rats

The mechanisms by which the hexane extract of Curcuma comosa increases femoral blood flow (FBF) in ovariectomized rats are not known. Thus, the aim of the present study was to investigate the acute effects and modes of action of the diarylheptanoid (3R)‐1,7‐diphenyl‐(4E,6E)‐4,6‐heptadien‐3‐ol (D3), a phyto‐oestrogen isolated from C. comosa, on FBF in ovariectomized rats. On Day 7 after ovariectomy, rats were injected once intra‐arterially with D3 (100, 200, 400 and 800 μg/kg), 17β‐oestradiol (E2; 1, 2, 4 and 8 μg/kg) or vehicle. In some experiments, rats were injected with NG‐nitro‐l‐arginine methyl ester (l‐NAME; 10 mg/kg) 120 min after 800 μg/kg D3 or 4 μg/kg E2. In other experiments, rats were injected with 10 mg/kg l‐NAME, 900 μg/kg 1H‐[1,2,4]oxadiazolo[4,3‐a]quinoxalin‐1‐one (ODQ) or 900 μg/kg ICI 182 780 30 min prior to the injection of 800 μg/kg D3 or 4 μg/kg E2. Mean arterial blood pressure (mABP) and FBF were recorded using a pressure transducer and a laser Doppler flow meter, respectively. Both D3 and E2 dose‐dependently increased FBF without changing mABP or heart rate. The EC50 at 120 min for D3 and E2 was 195.8 and 1.8 μg/kg, respectively. In addition, D3 and E2 dose‐dependently decreased femoral vascular resistance (FVR). The EC50 of D3 was about 100‐fold greater than that of E2. The effects of D3 and E2 on FBF and FVR were diminished by intravenous injection of 10 mg/kg l‐NAME. Furthermore, 30 min pretreatment with l‐NAME (10 mg/kg), ODQ (900 μg/kg) or ICI 182 780 (900 μg/kg) blocked the effects of D3 and E2 on FBF and FVR. The results of the present study suggest that the phyto‐oestrogen D3 increases FBF in ovariectomized rats via oestrogen receptor and nitric oxide–guanylyl cyclase signalling, which, in turn, relaxes femoral vascular resistance.