Carvedilol ameliorates endothelial dysfunction in streptozotocin-induced diabetic rats

The beta-blocker, carvedilol has an additional endothelium-dependent vasodilating properties in patients with hypertension or heart failure. Whether carvedilol can improve endothelium-dependent relaxation in a diabetic animal model and its mechanism of action are unknown. The aim of this study was to investigate the effect of carvedilol on the endothelial-response of aortas from diabetic rats and the underlying mechanism. Acetylcholine-induced endothelium-dependent relaxation, sodium nitroprusside (SNP)-induced endothelium-independent relaxation, and expression of nitric oxide synthase 3 (NOS3) mRNA were measured in aortas isolated from both non-diabetic and streptozotocin-induced diabetic rats. The level of NO in serum was also measured 5 weeks after carvedilol administration (1 or 10 mg/kg/day). Endothelium-dependent relaxation declined along with the decrease of serum NO level in aortas from diabetic rats. Treatment with carvedilol for 5 weeks prevented the inhibition of endothelium-dependent relaxation and the decrease of serum NO levels caused by diabetes. The expression of NOS3 mRNA, protein expression and NOS3 phosphorylation at Ser1177 in diabetic rat aorta was very low in untreated diabetic aortas compared with the healthy group. Administration of carvedilol not only significantly increased the expression of NOS3 mRNA but also protein expression and NOS3 phosphorylation at Ser1177 in the healthy and diabetic groups. In conclusion, chronic carvedilol administration significantly ameliorated the endothelial dysfunction in diabetic rat aortas, in which increased NO level, up-regulated NOS3 mRNA and phosphorylation at Ser1177 may be involved.     

Akt/eNOS pathway activation in endothelium-dependent relaxation is preserved in aortas from female, but not from male, type 2 diabetic mice

Cardiovascular problems are major causes of morbidity and mortality, the main problems being coronary artery disease and atherosclerosis, in type 2 diabetes mellitus. However, female gender is a protective factor in the development of, for example, atherosclerosis and hypertension. Our aim was to investigate possible gender differences in the activation of Akt/eNOS signaling in aortas from a mouse type 2 diabetic model. Nonfasting plasma glucose was significantly above control in the diabetic mice (both males and females). Plasma insulin was not different between the age-matched controls and the diabetic mice (of either gender). In diabetic males (vs male controls and/or diabetic females): (a) systemic blood pressure was elevated, (b) the clonidine- and insulin-induced Akt-dependent aortic relaxations were impaired, but the ACh-induced Akt-independent and SNP-induced endothelium-independent aortic relaxations were not, (c) Akt and eNOS expression levels were lower, (d) both Akt phosphorylation at Ser(473) and eNOS phosphorylation at Ser(1177) in the aorta were lower under clonidine- or insulin-stimulation, but not under ACh-stimulation. These results suggest that in mice: (i) endothelial functions mediated via the Akt/eNOS pathway are abrogated in type 2 diabetes only in males and (ii) in females (vs males), eNOS expression is elevated and the endothelium resists dysfunction.     

替米沙坦对高血压大鼠血管ACE2表达及氧化应激水平的影响

目的探讨替米沙坦干预对自发性高血压大鼠(SHR)血管组织血管紧张素转换酶2(ACE2)基因表达、一氧化氮(NO)及氧化应激水平的影响。方法选取10周龄SHR及其同源对照WKY大鼠,分别给予替米沙坦(5、10 mg.kg-1.d-1)或安慰剂,为期10周。采用Western blot检测治疗后大鼠主动脉组织中ACE2蛋白及内皮型NO合酶(eNOS)磷酸化水平。分别采用硝酸还原酶比色法与硫代巴比妥酸比色法测定大鼠主动脉组织中NO和丙二醛(MDA)含量。结果与WKY对照组相比,SHR大鼠主动脉组织中ACE2蛋白和Ser1177-eNOS磷酸化水平明显降低(ACE2:0.39±0.05vs 1.00±0.06;p-eNOS:0.43±0.06 vs 1.00±0.04;P值均<0.01),伴NO水平下调及MDA含量增加(NO mmol.g-1protein:11.5±2.1 vs 27.8±4.9;MDA nmol.g-1 protein:393.9±17.9 vs 186.3±14.5;P值均<0.01),而经替米沙坦治疗后SHR低、高剂量治疗组大鼠主动脉组织中ACE2蛋白和Ser1177-eNOS磷酸化水平增加(ACE2:0.62±0.06,0.65±0.07 vs 0.39±0.05;p-eNOS:0.68±0.07,0.71±0.06 vs0.43±0.06;P值均<0.05),伴NO水平升高(19.2±3.3,23.9±3.2 vs 11.5±2.1 mmol.g-1protein;P值均<0.05)与MDA含量下调(271.9±16.1,249.2±19.6 vs 393.9±17.9nmol.g-1protein;P值均<0.05)。结论长期替米沙坦治疗通过提升高血压大鼠血管ACE2表达及eNOS磷酸化水平,可促使血管NO生成及氧化应激水平改善,提示替米沙坦对高血压具有一定的血管保护功效。     

Ameliorative effect of berberine on endothelial dysfunction in diabetic rats induced by high-fat diet and streptozotocin

Berberine can improve insulin resistance, lower blood glucose, and regulate lipid metabolism disorders which cause endothelial dysfunction, leading to vascular complications of type 2 diabetes mellitus. The aim of the present study was to investigate the effects of berberine on endothelial dysfunction of aortas in type 2 diabetes mellitus rats and its mechanism. Wistar rats were randomly divided into four groups: diabetic rats, control rats, diabetic rats treated with berberine (100 mg/kg), and control rats treated with berberine. The serum fasting blood glucose, insulin, total cholesterol, triglyceride and nitric oxide (NO) levels were tested. Acetylcholine-induced endothelium-dependent relaxation and sodium nitroprusside induced endothelium-independent relaxation were measured in aortas for estimating endothelial function. The expression of endothelial nitric oxide synthase (eNOS) mRNA was measured by RT-PCR, and the protein expressions of eNOS and NADPH oxidase (NOX4) were analyzed by western blot. The results showed that berberine significantly decreased fasting blood glucose, and triglyceride levels in diabetic rats. Berberine also improved endothelium-dependent vasorelaxation impaired in aorta. The expressions of eNOS mRNA and protein were significantly increased, while NOX4 protein expression was decreased in aortas from diabetic rats with berberine treatment. Moreover, serum NO levels were elevated after berberine treatment. In conclusion, berberine restores diabetic endothelial dysfunction through enhanced NO bioavailability by up-regulating eNOS expression and down-regulating expression of NADPH oxidase.     

2型糖尿病大鼠主动脉内皮细胞氧化损伤及缬沙坦的保护作用

目的探讨2型糖尿病大鼠氧化应激与主动脉内皮细胞损伤的关系,观察缬沙坦对两者的影响。方法SD大鼠,用长期高能量饮食加小剂量注射链脲佐菌素(STZ)的方法复制模型。注射STZ12wk末,将大鼠分为3组:正常组、糖尿病组、缬沙坦治疗组(24mg·kg-1·d-1,灌胃给药8wk)。在注射STZ12和20wk末,检测大鼠的内皮依赖性血管舒张反应及主动脉内皮形态,血清超氧化物歧化酶(SOD)和谷胱甘肽过氧化物酶(GSH-Px)活性,丙二醛(MDA)和一氧化氮(NO)含量,以及主动脉一氧化氮合酶(NOS)基因表达情况。结果①12wk末,糖尿病大鼠主动脉对低浓度乙酰胆碱(ACh)舒张反应减弱,局部内皮隆起,血清SOD、GSH-Px活性增强,MDA和NO含量增加,主动脉iNOS mRNA表达明显上调,eNOS mRNA表达无明显改变。②20wk末,糖尿病大鼠主动脉对各浓度ACh的反应性均减弱,主动脉内皮变性、坏死,血清SOD、GSH-Px活性减弱,MDA含量进一步增加,NO含量下降,主动脉iNOS mRNA表达仍升高,eNOS mRNA表达降低,缬沙坦治疗后能减轻主动脉病变,改善血清SOD、GSH-Px、MDA、NO及主动脉NOS mRNA表达的异常。结论糖尿病大鼠的氧化应激和NO系统的紊乱参与了主动脉病变过程,增强机体抗氧化能力及调节NO生成可能是缬沙坦发挥主动脉保护作用的机制之一。     

六味地黄汤对糖尿病大鼠心肌病变的影响

目的 通过研究六味地黄汤对糖尿病大鼠心肌细胞病理变化的影响,为其治疗糖尿病心脏并发症的药理作用提供实验依据.方法 随机将大鼠分为正常组、糖尿病组、六味地黄汤低、中、高剂量组(100、200和400mg.·kg-1·d-1)和罗格列酮组(100 mg·kg-1·d-1).除正常组外,其余各组采用腹腔注射链脲佐菌素法诱发糖尿病大鼠模型,造模成功后饲养4周,然后连续灌胃给药4周.于末次给药12 h后取材,观察大鼠心肌细胞的形态学变化及细胞凋亡指数.结果 与罗格列酮干预组相比,高剂量六味地黄汤能显著抑制糖尿病大鼠心肌细胞的形态学病变及细胞凋亡(P＜0.01),中剂量组亦具有一定抑制作用.结论 六味地黄汤对糖尿病心肌细胞的病理变化具有一定的抑制作用,可治疗该并发症.     

芝麻素对2型糖尿病大鼠主动脉内皮功能的保护作用

目的探讨芝麻素改善2型糖尿病大鼠主动脉内皮功能损伤的作用及可能机制。方法采用长期高脂饮食加小剂量链脲佐菌素(streptozotocin,STZ)建立2型糖尿病大鼠模型。灌服不同剂量芝麻素(120、60 mg.kg-1.d-1)8周后处死动物。离体血管灌流法测大鼠主动脉内皮依赖性舒张反应及NO生物活性,测血清丙二醛(malondialdehyde,MDA)含量和总抗氧化能力(total antioxidative capacity,T-AOC),Western blot测主动脉内皮型一氧化氮合酶(endothelial nitricoxide synthase,eNOS)、硝基酪氨酸(nitrotyrosine,NT)和还原型辅酶Ⅱ(NADPH)氧化酶亚基P47phox蛋白表达。结果与模型组相比,芝麻素(120 mg.kg-1.d-1)组内皮依赖性血管舒张功能增强,NO活性升高;血清MDA含量降低,T-AOC水平升高;主动脉eNOS蛋白表达增高,NT和P47phox蛋白表达降低。结论芝麻素可改善糖尿病大鼠血管内皮功能,其机制与上调血管eNOS表达和减轻NO氧化失活有关。     

Mechanisms of beta 3-adrenoceptor-induced eNOS activation in right atrial and left ventricular human myocardium

beta-Adrenoceptors are important modulators of cardiac function. The present study investigated beta(3)-adrenergic eNOS activation in human myocardium. We measured nitric oxide (NO) liberation (diaminofluorescence) and signal transduction (immunohistochemistry, phosphorylation of eNOS(Ser1177), eNOS(Thr495), eNOS(Ser114), Akt/protein kinase B (Akt/PKB), and eNOS translocation) in human right atrial (RA, aortocoronary-bypass OP) and left ventricular nonfailing (LV, rejected donor hearts) myocardium after application of BRL 37344 (BRL), a preferential beta(3)-adrenoceptor agonist. In both RA and LV, BRL (10 microl) induced a liberation of NO. An eNOS activation via translocation was only observed in RA after application of BRL (10 microM). Yet, the NO liberation in both LV and RA was accompanied by phosphorylation of eNOS(Ser1177) and Akt/PKB. BRL-induced eNOS phosphorylation was abolished by LY292004, a blocker of PI-3 kinase. eNOS-Ser(114) phosphorylation was unchanged in RA, but decreased in LV after beta(3)-adrenergic stimulation. BRL did not alter phosphorylation of eNOS(Thr495). In conclusion, receptor-dependent eNOS activation is differentially regulated in the human heart. In the left ventricle, eNOS activation via phosphorylation seems to be of major importance, whereas in human atrial myocardium eNOS translocation is the predominant mechanism induced by beta(3)-adrenergic activation.     

Humic acid induces the endothelial nitric oxide synthase phosphorylation at Ser1177 and Thr495 Via Hsp90α and Hsp90β upregulation in human umbilical vein endothelial cells

Humic acid (HA) has been implicated as a contributory factor for blackfoot disease, which is an endemic peripheral vascular disease. We investigated the effect of HA on the regulation of endothelial nitric oxide (NO) synthase (eNOS) in human umbilical vein endothelial cells (HUVECs) to evaluate the involvement of eNOS and related factors in peripheral vascular impairment with HA exposure. Treatment of HUVECs with HA induced upregulation of eNOS. This result coincides with those of previous studies. Furthermore this is the first study to report that HA induces upregulation of heat shock protein (Hsp)90α, Hsp90β, eNOS phosphorylation at Ser1177, and eNOS phosphorylation at Thr495, as compared to that in the control. In contrast, treatment with BAPTA, an intracellular Ca²⁺ chelator, inhibited upregulation of these proteins induced by HA. This study demonstrates that HA treatment leads to increases in both Hsp90α and Hsp90β proteins and indicates that Hsp90α leads to eNOS phosphorylation at Ser1177 and that Hsp90β leads to eNOS phosphorylation at Thr495, respectively. Upregulation of eNOS, Hsp90α, and Hsp90β in HUVECs is regulated by intracellular Ca²⁺ accumulation induced by HA. These results suggest that upregulation of eNOS phosphorylation at Ser1177 and eNOS phosphorylation at Thr495 produce NO and superoxide anions, respectively, resulting in generation of peroxynitrite, which causes impairment of vascular endothelial cells. © 2013 Wiley Periodicals, Inc. Environ Toxicol 30: 223–231, 2015.     

The dual targeting of EGFR and ErbB2 with the inhibitor Lapatinib corrects high glucose-induced apoptosis and vascular dysfunction by opposing multiple diabetes-induced signaling changes

The epidermal growth factor receptors, EGFR and EGFR2 (ErbB2), appear important mediators of diabetes-induced vascular dysfunction. We investigated whether targeted dual inhibition of EGFR and ErbB2 with Lapatinib would be effective in treating diabetes-induced vascular dysfunction in a rat model of type 1 diabetes. In streptozotocin-induced diabetes, chronic 4-week oral or acute, ex vivo, administration of Lapatinib prevented the development of vascular dysfunction as indicated by the attenuation of the hyper-reactivity of the diabetic mesenteric vascular bed (MVB) to norephinephrine without correcting hyperglycemia. Chronic in vivo or acute ex vivo Lapatinib treatment also significantly attenuated diabetes-induced increases in phosphorylation of EGFR, ErbB2, ERK1/2, AKT, ROCK2 and IkB-alpha as well as normalized the reduced levels of phosphorylated FOXO3A, and eNOS (Ser1177) in the diabetic MVB. Similar results were observed in vascular smooth muscle cells (VSMCs) cultured in high glucose (25?mM) treated with Lapatinib or small interfering RNA (siRNA) targeting the ErbB2 receptor. Lapatinib also prevented high glucose-induced apoptosis in VSMC. Thus, Lapatinib corrects hyperglycemia-induced apoptosis and vascular dysfunction with concomitant reversal of diabetes or high glucose-induced signaling changes in EGFR/ErbB2 and downstream signaling pathways implying that targeted dual inhibition of EGFR/ErbB2 might be an effective vasculoprotective treatment strategy in diabetic patients.     

Angiostatin Inhibition of Vascular Endothelial Growth Factor– Stimulated Nitric Oxide Production in Endothelial Cells

Angiostatin (AS), a proteolytic fragment of plasminogen, is a potent antiangiogenic factor. It was reported that AS attenuates the vasodilatory response to vascular endothelial growth factor (VEGF) in isolated interventricular arterioles. Here, we investigated the effect of AS on nitric oxide (NO) production in human umbilical vein endothelial cells (HUVECs). AS inhibited VEGF-stimulated NO production in a dose-dependent manner, whereas AS alone did not affect basal NO production. Disruption of kringle structures by reduction of disulfide bonds resulted in the loss of the inhibitory effect of AS on VEGF-stimulated NO production. To elucidate how AS might impair VEGF activation of endothelial NO synthase (eNOS), we further examined whether AS would affect Ca²⁺-dependent and -independent pathways of eNOS activation. AS had no effect on the transient increase in cytosolic Ca²⁺ levels elicited by VEGF. In contrast, AS prevented VEGF-potentiated eNOS phosphorylation at Ser1177. These results clearly indicate that AS inhibits VEGF-stimulated NO production in HUVECs without affecting basal NO production. The kringle structures of AS are required for this effect, and impairment of Ser1177 phosphorylation of eNOS might be involved in the inhibition of VEGF-stimulated NO production by AS.     

Impairment of both nitric oxide-mediated and EDHF-type relaxation in small mesenteric arteries from rats with streptozotocin-induced diabetes

BACKGROUND AND PURPOSE

To investigate whether diabetes affects either or both nitric oxide (NO)-mediated and endothelium-derived hyperpolarizing factor (EDHF)-type relaxation in endothelium-dependent relaxation of mesenteric arteries from streptozotocin-induced diabetic rats.

EXPERIMENTAL APPROACH

Wire myography was employed to examine endothelial function of mesenteric arteries. Superoxide levels were measured by L-012 and lucigenin-enhanced chemiluminescence. Western blotting was used to quantify protein expression levels.

KEY RESULTS

Superoxide levels were significantly increased in diabetic mesenteric arteries compared with normal arteries. Diabetes significantly reduced the sensitivity to the endothelium-dependent relaxant, acetylcholine (ACh) in mesenteric arteries. When the contribution of NO to relaxation was abolished by N-nitro-L-arginine (L-NNA) + a soluble guanylate cyclase inhibitor (ODQ), the sensitivity to ACh was significantly decreased in the diabetic arteries compared with normal arteries, indicating an impaired EDHF-type relaxation despite increased expression of intermediate- and small-conductance calcium-activated potassium channels. Conversely, when the contribution of EDHF was inhibited with TRAM-34 + apamin + iberiotoxin, maximum relaxations to ACh were significantly decreased in diabetic compared with normal arteries, suggesting that the contribution of NO was also impaired by diabetes. Basal levels of NO release, indicated by contraction to L-NNA, were also significantly decreased in diabetic arteries. Western blot analysis demonstrated that diabetic arteries had an increased expression of Nox2, decreased pSer⁴⁷³Akt and a reduced proportion of endothelial NO synthase (eNOS) expressed as a dimer, indicating uncoupling.

CONCLUSION AND IMPLICATIONS

The contribution of both NO and EDHF-type relaxations was impaired in diabetes and was caused by increased oxidative stress, decreased pSer⁴⁷³Akt and/or eNOS uncoupling.     

Endothelium-dependent and -independent relaxation and VASP serines 157/239 phosphorylation by cyclic nucleotide-elevating vasodilators in rat aorta

Endothelium-dependent vasodilation is thought to be mediated primarily by the NO/cGMP signaling pathway whereas cAMP-elevating vasodilators are considered to act independent of the endothelial cell layer. However, recent functional data suggest that cAMP-elevating vasodilators such as beta-receptor agonists, adenosine or forskolin may also be endothelium-dependent. Here we used functional and biochemical assays to analyze endothelium-dependent, cGMP- and cAMP-mediated signaling in rat aorta. Acetylcholine and sodium nitroprusside (SNP) induced a concentration-dependent relaxation of phenylephrine-precontracted aorta. This response was reflected by the phosphorylation of the vasodilator-stimulated phosphoprotein (VASP), a validated substrate of cGMP- and cAMP-dependent protein kinases (cGK, cAK), on Ser(157) and Ser(239). As expected, the effects of acetylcholine were endothelium-dependent. However, relaxation induced by the beta-receptor agonist isoproterenol was also almost completely impaired after endothelial denudation. At the biochemical level, acetylcholine- and isoproterenol-evoked cGK and cAK activation, respectively, as measured by VASP Ser(239) and Ser(157) phosphorylation, was strongly diminished. Furthermore, the effects of isoproterenol were repressed by eNOS inhibition when endothelium was present. We also observed that the relaxing and biochemical effects of forskolin were at least partially endothelium-dependent. We conclude that cAMP-elevating vasodilators, i.e. isoproterenol and to a lesser extent also forskolin, induce vasodilation and concomitant cyclic nucleotide protein kinase activation in the vessel wall in an endothelium-dependent way.     

α-酮酸在早期2型糖尿病肾病治疗中的作用

目的观察α-酮酸在早期2型糖尿病肾病治疗中的作用。方法将60例微量白蛋白尿期2型糖尿病肾病患者随机分为:(1)治疗组(n=30),予以低蛋白饮食(蛋白质0.6 g.kg-1.d-1,包括α-酮酸2.4 g,3/d);(2)对照组(n=30),予以常规蛋白饮食(蛋白质1.0 g.kg-1.d-1,不服用α-酮酸)。分别于治疗前、治疗24周后测定:(1)肾脏相关指标:血清尿素(BUN)、肌酐(Cr)、肾小球滤过率(GFR)、尿白蛋白(Alb)、尿转铁蛋白(TRF);(2)营养相关指标:血红蛋白(Hb)、血清白蛋白、体重指数(BMI);(3)代谢相关指标:空腹血糖(FPG)、餐后2h血糖(PPG)、糖化血红蛋白(HbAlc)、空腹血清胰岛素(FINS)、血清甘油三酯(TG)、血清胆固醇(TC)。计算胰岛素敏感指数(ISI)及胰岛素抵抗指数(HOMA-IR)。结果24周后治疗组尿Alb定量、尿TRF较对照组明显下降(P<0.01),血FINS及胰岛素抵抗指数也明显降低(P<0.05)、ISI提高(P<0.05),两组间血清Alb、Hb、FPG、PPG、HbA1c及血脂等无明显差异。结论α-酮酸联合低蛋白饮食(LPD)...     

Protective effect of ligustrazine against myocardial ischaemia reperfusion in rats: the role of endothelial nitric oxide synthase

1. The aim of the present study was to determine whether ligustrazine (2,3,5,6-tetramethylpyrazine; TMP) exerts a cardioprotective effect during myocardial ischaemia reperfusion (IR), and to investigate the underlying mechanisms and the role of endothelial nitric oxide synthase (eNOS) in cardioprotection. 2. Sprague-Dawley rats were divided into a sham group and five IR groups: IR control, TMP pretreated, TMP + wortmannin (a phosphatidylinositol 3-kinase (PI3K) inhibitor), N(G) -nitro-L-arginine methyl ester (L-NAME; a NOS inhibitor) and TMP + L-NAME. IR was produced by 35 min of regional ischaemia followed by 120 min of reperfusion. Myocardial infarct size, oxidative stress, myocardial apoptosis, nitric oxide (NO) production, and expression of phosphorylated protein kinase B (Akt) and eNOS were measured. 3. TMP markedly decreased infarct size and attenuated myocardial apoptosis, as evidenced by a decrease in the apoptotic index and reduced caspase-3 activity. TMP treatment caused a marked increase in NO production. Cotreatment with wortmannin or L-NAME completely blocked the TMP-induced NO increase. TMP induced phosphorylation of Akt at Ser 473 (1.61 ± 0.18 vs 0.79 ± 0.10 in the IR control group) and phosphorylation of eNOS at Ser1177 (1.87 ± 0.33 vs 0.94 ± 0.22 in the IR control group). Wortmannin abrogated the phosphorylation of Akt and eNOS induced by TMP. 4. These data suggest that ligustrazine has anti-apoptotic and cardioprotective effects against myocardial IR injury and that it acts through the PI3K/Akt pathway. In addition, the phosphorylation of eNOS with subsequent NO production was found to be an important downstream effector that contributes significantly to the cardioprotective effect of TMP.     

Acetylcholine-induced relaxation in blood vessels from endothelial nitric oxide synthase knockout mice

1. Isometric tension was recorded in isolated rings of aorta, carotid, coronary and mesenteric arteries taken from endothelial nitric oxide synthase knockout mice (eNOS(-/-) mice) and the corresponding wild-type strain (eNOS(+/+) mice). The membrane potential of smooth muscle cells was measured in coronary arteries with intracellular microelectrodes. 2. In the isolated aorta, carotid and coronary arteries from the eNOS(+/+) mice, acetylcholine induced an endothelium-dependent relaxation which was inhibited by N(omega)-L-nitro-arginine. In contrast, in the mesenteric arteries, the inhibition of the cholinergic relaxation required the combination of N(omega)-L-nitro-arginine and indomethacin. 3. The isolated aorta, carotid and coronary arteries from the eNOS(-/-) mice did not relax in response to acetylcholine. However, acetylcholine produced an indomethacin-sensitive relaxation in the mesenteric artery from eNOS(-/-) mice. 4. The resting membrane potential of smooth muscle cells from isolated coronary arteries was significantly less negative in the eNOS(-/-) mice (-64.8 +/- 1.8 mV, n = 20 and -58.4 +/- 1.9 mV, n = 17, for eNOS(+/+) and eNOS(-/-) mice, respectively). In both strains, acetylcholine, bradykinin and substance P did not induce endothelium-dependent hyperpolarizations whereas cromakalim consistently produced hyperpolarizations (- 7.9 +/- 1.1 mV, n = 8 and -13.8 +/- 2.6 mV, n = 4, for eNOS(+/+) and eNOS(-/-) mice, respectively). 5. These findings demonstrate that in the blood vessels studied: (1) in the eNOS(+/+) mice, the endothelium-dependent relaxations to acetylcholine involve either NO or the combination of NO plus a product of cyclo-oxygenase but not EDHF; (2) in the eNOS(-/-) mice, NO-dependent responses and EDHF-like responses were not observed. In the mesenteric arteries acetylcholine releases a cyclo-oxygenase derivative.     

Lack of endothelium-derived hyperpolarizing factor (EDHF) up-regulation in endothelial dysfunction in aorta in diabetic rats

It is not known whether the impairment of nitric oxide (NO)-dependent vasodilation of the aorta of diabetic rats is associated with any changes in the endothelial production of vasoactive prostanoids and endothelium-derived hyperpolarizing factor (EDHF). Therefore, we analyzed the contribution of NO, vasoactive prostanoids and EDHF to the decreased endothelium-dependent vasorelaxation in Sprague-Dawley rats at 4 and 8 weeks after diabetes mellitus induced by streptozotocin (STZ). The acetylcholine-induced (Ach) endothelium-dependent relaxation was significantly decreased in the thoracic aorta 8 weeks after the STZ-injection (Ach 10(-6) M: 73.1 +/- 7.4% and 56.7 +/- 7.9% for control and diabetic rats, respectively). The sodium nitroprusside-induced (NaNP) endothelium-independent vasodilation was also impaired in the diabetic rats (8 weeks after STZ) (NaNP 10(-8) M: 74.2 +/- 11.4% and 35.9 +/- 9.4% for control and diabetic rats, respectively). In contrast, the basal NO production, as assessed by the N omega-nitro-L-arginine methyl ester (L-NAME)-induced vasoconstriction was not modified in diabetes. Moreover, the amount of 6-keto-PGF(1 alpha) (stable metabolite of prostacyclin / prostaglandin I2 / PGI2 ), 12-L-hydroxy-5,8,10-heptadecatrienoic acid (12-HHT) and thromboxane B2 (TxB2 ) (stable metabolite of thromboxane A2 - TxA2) were significantly increased in the 8 weeks diabetic rat aorta. The EDHF-pathway did not change in the aortic endothelium during the development of STZ-induced diabetes. Our results indicate that STZ-induced diabetes mellitus did not modify the basal NO production, but induced the impairment of acetylcholine- and sodium nitroprusside-induced vasodilation in the thoracic aorta. In parallel with the impairment of NO-dependent vasodilation, the basal PGI2, 12-HHT and TxA2 synthesis were increased. The EDHF-pathway did not contribute to the endothelium-dependent relaxation either in control or diabetic aorta. The above alterations in the endothelial function may play an important role in the development of endothelial dysfunction and vascular complications of diabetes.     

Gomisin J from Schisandra chinensis induces vascular relaxation via activation of endothelial nitric oxide synthase

Gomisin J (GJ) is a lignan contained in Schisandra chinensis (SC) which is a well-known medicinal herb for improvement of cardiovascular symptoms in Korean. Thus, the present study examined the vascular effects of GJ, and also determined the mechanisms involved. Exposure of rat thoracic aorta to GJ (1-30μg/ml) resulted in a concentration-dependent vasorelaxation, which was more prominent in the endothelium (ED)-intact aorta. ED-dependent relaxation induced by GJ was markedly attenuated by pretreatment with L-NAME, a nitric oxide synthase (NOS) inhibitor. In the intact endothelial cells of rat thoracic aorta, GJ also enhanced nitric oxide (NO) production. In studies using human coronary artery endothelial cells, GJ enhanced phosphorylation of endothelial NOS (eNOS) at Ser(1177) with increased cytosolic translocation of eNOS, and subsequently increased NO production. These effects of GJ were attenuated not only by calcium chelators including EGTA and BAPTA-AM, but also by LY294002, a PI3K/Akt inhibitor, indicating calcium- and PI3K/Akt-dependent activation of eNOS by GJ. Moreover, the levels of intracellular calcium were increased immediately after GJ administration, but Akt phosphorylation was started to increase at 20min of GJ treatment. Based on these results with the facts that ED-dependent relaxation occurred rapidly after GJ treatment, it was suggested that the ED-dependent vasorelaxant effects of GJ were mediated mainly by calcium-dependent activation of eNOS with subsequent production of endothelial NO.     

Methylglyoxal scavengers attenuate endothelial dysfunction induced by methylglyoxal and high concentrations of glucose

BACKGROUND AND PURPOSE

Endothelial dysfunction is a feature of hypertension and diabetes. Methylglyoxal (MG) is a reactive dicarbonyl metabolite of glucose and its levels are elevated in spontaneously hypertensive rats and in diabetic patients. We investigated if MG induces endothelial dysfunction and whether MG scavengers can prevent endothelial dysfunction induced by MG and high glucose concentrations.

EXPERIMENTAL APPROACH

Endothelium-dependent relaxation was studied in aortic rings from Sprague-Dawley rats. We also used cultured rat aortic and human umbilical vein endothelial cells. The MG was measured by HPLC and Western blotting and assay kits were used.

KEY RESULTS

Incubation of aortic rings with MG (30 µM) or high glucose (25 mM) attenuated endothelium-dependent, acetylcholine-induced relaxation, which was restored by two different MG scavengers, aminoguanidine (100 µM) and N-acetyl cysteine (NAC) (600 µM). Treatment of cultured endothelial cells with MG or high glucose increased cellular MG levels, effects prevented by aminoguanidine and NAC. In cultured endothelial cells, MG and high glucose reduced basal and bradykinin-stimulated nitric oxide (NO) production, cGMP levels, and serine-1177 phosphorylation and activity of endothelial NO synthase (eNOS), without affecting threonine-495 and Akt phosphorylation or total eNOS protein. These effects of MG and high glucose were attenuated by aminoguanidine or NAC.

CONCLUSIONS AND IMPLICATIONS

Our results show for the first time that MG reduced serine-1177 phosphorylation, activity of eNOS and NO production. MG caused endothelial dysfunction similar to that induced by high glucose. Specific and safe MG scavengers have potential to prevent endothelial dysfunction induced by MG and high glucose concentrations.     

Oleanolic acid induces relaxation and calcium-independent release of endothelium-derived nitric oxide

Background and purpose:

The present study investigated the mechanisms by which oleanolic acid, a component of olive oil, increases release of nitric oxide (NO).

Experimental approach:

Measurements of isometric tension, NO concentration, or endothelial cell calcium were made in rat isolated mesenteric arteries. Immunoblotting for endothelial NOS (eNOS) and Akt kinase were performed in primary cultures of human umbilical vein endothelial cells (HUVECs).

Key results:

Oleanolic acid (3–30 μM) evoked endothelium-dependent relaxations in noradrenaline-contracted rat superior and small mesenteric arteries. In rat superior mesenteric arteries, oleanolic acid induced simultaneous increases in NO concentration and relaxation, and these responses were inhibited by an inhibitor of NOS, asymmetric dimethyl-L-arginine (300 μM) and by the NO scavenger, oxyhaemoglobin (10 μM). Oleanolic acid-evoked NO increases were not reduced in Ca²⁺-free solution and in the presence of an inhibitor of endoplasmic reticulum calcium-ATPase, thapsigargin (1 μM). Oleanolic acid evoked relaxation without changes in endothelial cell calcium, but decreased smooth muscle calcium in arterial segments. Oleanolic acid failed to increase calcium in HUVECs, but increased time-dependently phosphorylation of Akt kinase at Serine⁴⁷³ (Akt-Ser⁴⁷³) and eNOS at Serine¹¹⁷⁷ (eNOS-Ser¹¹⁷⁷), which was attenuated by inhibitors of phosphoinositide-3-kinase.

Conclusions and implications:

This study provides direct evidence that a component of olive oil, oleanolic acid, activated endothelium-dependent release of NO and decreased smooth muscle cell calcium followed by relaxation. The oleanolic acid-evoked endothelium-derived NO release was independent of endothelial cell calcium and involved phosphoinositide-3-kinase-dependent phosphorylation of Akt-Ser⁴⁷³ followed by phosphorylation of eNOS-Ser¹¹⁷⁷.