Specific impairment of endothelium-derived hyperpolarizing factor-type relaxation in mesenteric arteries from streptozotocin-induced diabetic mice

Repeated glucose spikes and insulin resistance synergistically deteriorate endothelial function and bardoxolone methyl ameliorates endothelial dysfunction

Background

Both insulin resistance and postprandial glucose spikes are known for their potential to induce vascular endothelial dysfunction in individuals with metabolic syndrome. However, these factors are inextricable, and therefore, their relative contributions to inducing endothelial dysfunction remain elusive. In this study, we aimed to disentangle the effects of these factors and clarify whether bardoxolone methyl (CDDO-Me), a novel nuclear factor erythroid 2-related factor 2 (Nrf2) activator, protects against glucose spike-induced endothelial dysfunction.

Methods

We induced glucose spikes twice daily for a duration of 1 week to rats fed a standard/control diet (CD) and Western-type diet (WTD). Endothelium-dependent relaxation (EDR) was evaluated using isolated thoracic aortas. Gene expression and dihydroethidium (DHE)-fluorescence studies were carried out; the effect of CDDO-Me on aortic endothelial dysfunction in vivo was also evaluated.

Results

Neither WTD-induced insulin resistance nor pure glucose spikes significantly deteriorated EDR. However, under high-glucose (20 mM) conditions, the EDR of thoracic aortas of WTD-fed rats subjected to glucose spikes was significantly impaired. In this group of rats, we observed significantly enhanced DHE fluorescence as a marker of reactive oxygen species, upregulation of an oxidative stress-related gene (NOX2), and downregulation of an antioxidant gene (SOD2) in the thoracic aortas. As expected, treatment of the thoracic aorta of this group of rats with antioxidant agents significantly improved EDR. We also noted that pretreatment of aortas from the same group with CDDO-Me attenuated endothelial dysfunction, accompanied by a correction of the redox imbalance, as observed in gene expression and DHE fluorescence studies.

Conclusions

For the first time, we showed that insulin resistance and glucose spikes exert a synergistic effect on aortic endothelial dysfunction. Furthermore, our study reveals that CDDO-Me ameliorates endothelial dysfunction caused by glucose spikes in a rat model of metabolic syndrome.

Endothelium-Dependent Hyperpolarization (EDH) in Diabetes: Mechanistic Insights and Therapeutic Implications

Diabetes mellitus is one of the major risk factors for cardiovascular disease and is an important health issue worldwide. Long-term diabetes causes endothelial dysfunction, which in turn leads to diabetic vascular complications. Endothelium-derived nitric oxide is a major vasodilator in large-size vessels, and the hyperpolarization of vascular smooth muscle cells mediated by the endothelium plays a central role in agonist-mediated and flow-mediated vasodilation in resistance-size vessels. Although the mechanisms underlying diabetic vascular complications are multifactorial and complex, impairment of endothelium-dependent hyperpolarization (EDH) of vascular smooth muscle cells would contribute at least partly to the initiation and progression of microvascular complications of diabetes. In this review, we present the current knowledge about the pathophysiology and underlying mechanisms of impaired EDH in diabetes in animals and humans. We also discuss potential therapeutic approaches aimed at the prevention and restoration of EDH in diabetes.

Serelaxin treatment reverses vascular dysfunction and left ventricular hypertrophy in a mouse model of Type 1 diabetes

Serelaxin prevents endothelial dysfunction in the mouse aorta ex vivo and inhibits apoptosis in cardiomyocytes under acute hyperglycaemia. Less is known about the effects of serelaxin in an in vivo mouse model of diabetes. Therefore, we tested the hypothesis in streptozotocin (STZ)-treated mice that serelaxin is able to reverse diabetes-induced vascular dysfunction and cardiac remodelling. Mice were divided into citrate buffer + placebo, STZ + placebo and STZ + serelaxin (0.5 mg/kg/d, 2 weeks) groups. After 12 weeks of diabetes, sensitivity to the endothelium-dependent agonist acetylcholine (ACh) was reduced in the mesenteric artery. This was accompanied by an enhanced vasoconstrictor prostanoid contribution and a decrease in endothelium-derived hyperpolarisation (EDH)-mediated relaxation. Serelaxin restored endothelial function by increasing nitric oxide (NO)-mediated relaxation but not EDH. It also normalised the contribution of vasoconstrictor prostanoids to endothelial dysfunction and suppressed diabetes-induced hyper-responsiveness of the mesenteric artery to angiotensin II. Similarly, diabetes reduced ACh-evoked NO-mediated relaxation in the aorta which was reversed by serelaxin. In the left ventricle, diabetes promoted apoptosis, hypertrophy and fibrosis; serelaxin treatment reversed this ventricular apoptosis and hypertrophy, but had no effect on fibrosis. In summary, serelaxin reversed diabetes-induced endothelial dysfunction by enhancing NO-mediated relaxation in the mouse vasculature and attenuating left ventricular hypertrophy and apoptosis.

Hyaluronidase 1 Deficiency Preserves Endothelial Function and Glycocalyx Integrity in Early Streptozotocin-Induced Diabetes

Hyaluronic acid (HA) is a major component of the glycocalyx involved in the vascular wall and endothelial glomerular permeability barrier. Endocytosed hyaluronidase HYAL1 is known to degrade HA into small fragments in different cell types, including endothelial cells. In diabetes, the size and permeability of the glycocalyx are altered. In addition, patients with type 1 diabetes present increased plasma levels of both HA and HYAL1. To investigate the potential implication of HYAL1 in the development of diabetes-induced endothelium dysfunction, we measured endothelial markers, endothelium-dependent vasodilation, arteriolar glycocalyx size, and glomerular barrier properties in wild-type and HYAL1 knockout (KO) mice with or without streptozotocin (STZ)-induced diabetes. We observed that 4 weeks after STZ injections, the lack of HYAL1 1) prevents diabetes-induced increases in soluble P-selectin concentrations and limits the impact of the disease on endothelium-dependent hyperpolarization (EDH)-mediated vasorelaxation; 2) increases glycocalyx thickness and maintains glycocalyx structure and HA content during diabetes; and 3) prevents diabetes-induced glomerular barrier dysfunction assessed using the urinary albumin-to-creatinine ratio and urinary ratio of 70- to 40-kDa dextran. Our findings suggest that HYAL1 contributes to endothelial and glycocalyx dysfunction induced by diabetes. HYAL1 inhibitors could be explored as a new therapeutic approach to prevent vascular complications in diabetes.

The Dipeptidyl Peptidase-4 Inhibitor Linagliptin Preserves Endothelial Function in Mesenteric Arteries from Type 1 Diabetic Rats without Decreasing Plasma Glucose

The aim of the study was to investigate the effect of the DPP-4 inhibitor linagliptin on the mechanism(s) of endothelium-dependent relaxation in mesenteric arteries from STZ-induced diabetic rats. Both normal and diabetic animals received linagliptin (2 mg/kg) daily by oral gavage for a period of 4 weeks. To measure superoxide generation in mesenteric arteries, lucigenin-enhanced chemiluminescence was used. ACh-induced relaxation of mesenteric arteries was assessed using organ bath techniques and Western blotting was used to investigate protein expression. Pharmacological tools (1μM TRAM-34, 1μM apamin, 100 nM Ibtx, 100 μM L-NNA, 10 μM ODQ) were used to distinguish between NO and EDH-mediated relaxation. Linagliptin did not affect plasma glucose, but did decrease vascular superoxide levels. Diabetes reduced responses to ACh but did not affect endothelium-independent responses to SNP. Linagliptin improved endothelial function indicated by a significant increase in responses to ACh. Diabetes impaired the contribution of both nitric oxide (NO) and endothelium-dependent hyperpolarization (EDH) to endothelium-dependent relaxation and linagliptin treatment significantly enhanced the contribution of both relaxing factors. Western blotting demonstrated that diabetes also increased expression of Nox2 and decreased expression and dimerization of endothelial NO synthase, effects that were reversed by linagliptin. These findings demonstrate treatment of type 1 diabetic rats with linagliptin significantly reduced vascular superoxide levels and preserved both NO and EDH-mediated relaxation indicating that linagliptin can improve endothelial function in diabetes independently of any glucose lowering activity.

Impairment of IKCa channels contributes to uteroplacental endothelial dysfunction in rat diabetic pregnancy

Diabetes in rat pregnancy is associated with impaired vasodilation of the maternal uteroplacental vasculature. In the present study, we explored the role of endothelial cell (EC) Ca(2+)-activated K(+) channels of small conductance (SKCa channels) and intermediate conductance (IKCa channels) in diabetes-induced uterine vascular dysfunction. Diabetes was induced by injection of streptozotocin to second-day pregnant rats and confirmed by the development of maternal hyperglycemia. Control rats were injected with citrate buffer. Changes in smooth muscle cell intracellular Ca(2+) concentration, membrane potential, and vasodilation induced by SKCa/IKCa channel activators were studied in uteroplacental arteries of control and diabetic rats. The impact of diabetes on SKCa- and IKCa-mediated currents was explored in freshly dissociated ECs. NS309 evoked a potent vasodilation that was effectively inhibited by TRAM-34 but not by apamin. NS309-induced smooth muscle cell intracellular Ca(2+) concentration, membrane potential, and dilator responses were significantly diminished by diabetes; N-cyclohexyl-N-2-(3,5-dimethyl-pyrazol-1-yl)-6-methyl-4-pyrimidinamine (CyPPA)-evoked responses were not affected. Ca(2+)-activated ion currents in ECs were insensitive to paxilline, markedly inhibited by charybdotoxin (ChTX), and diminished by apamin. NS309-induced EC currents were generated mostly due to activation of ChTX-sensitive channels. Maternal diabetes resulted in a significant reduction in ChTX-sensitive currents with no effect on apamin-sensitive or CyPPA-induced currents. We concluded that IKCa channels play a prevalent role over SKCa channels in the generation of endothelial K(+) currents and vasodilation of uteroplacental arteries. Impaired function of IKCa channels importantly contributes to diabetes-induced uterine endothelial dysfunction. Therapeutic restoration of IKCa channel function may be a novel strategy for improvement of maternal uteroplacental blood flow in pregnancies complicated by diabetes.

Type 2 diabetes: increased expression and contribution of IKCa channels to vasodilation in small mesenteric arteries of ZDF rats

Impaired endothelial function, which is dysregulated in diabetes, also precedes hypertension. We hypothesized that in Type 2 diabetes, the impaired endothelium-dependent relaxation is due to a loss of endothelium-derived hyperpolarization (EDH) that is regulated by impaired ion channel function. Zucker diabetic fatty (ZDF), Zucker heterozygote, and homozygote lean control rats were used as the experimental models in our study. Third-order mesenteric arteries were dissected and mounted on a pressure myograph; mRNA was quantified by RT-PCR and channel proteins by Western blotting. Under nitric oxide (NO) synthase and cyclooxygenase inhibition, endothelial stimulation with ACh fully relaxes control but not diabetic arteries. In contrast, when small-conductance calcium-activated potassium (KCa) channels and intermediate- and large-conductance KCa (I/BKCa) are inhibited with apamin and charybdotoxin, NO is able to compensate for ACh-induced relaxation in control but not in diabetic vessels. After replacement of charybdotoxin with 1-[(2-chlorophenyl)diphenylmethyl]-1H-pyrazole (TRAM-34; IKCa inhibitor), ACh-induced relaxation in diabetic animals is attenuated. Specific inhibition with TRAM-34 or charybdotoxin attenuates ACh relaxation in diabetes. Stimulation with 1-ethyl-2-benzimidazolinone (IKCa activator) shows a reduced relaxation in diabetes. Activation of BKCa with 1,3-dihydro-1-[2-hydroxy-5-(trifluoromethyl)phenyl]-5-(trifluoromethyl)-2H-benzimidazol-2-one NS619 leads to similar relaxations of control and diabetic arteries. RT-PCR and Western blot analysis demonstrate elevated mRNA and protein expression levels of IKCa in diabetes. Our results suggest that the compensatory effect of NO and EDH-associated, endothelium-dependent relaxation is reduced in ZDF rats. Specific blockade of IKCa with TRAM-34 reduces NO and EDH-type relaxation in diabetic rats, indicating an elevated contribution of IKCa in diabetic small mesenteric artery relaxation. This finding correlates with increased IKCa mRNA and protein expression in this vessel.

3',4'-Dihydroxyflavonol reduces superoxide and improves nitric oxide function in diabetic rat mesenteric arteries

Background

3',4'-Dihydroxyflavonol (DiOHF) is an effective antioxidant that acutely preserves nitric oxide (NO) activity in the presence of elevated reactive oxygen species (ROS). We hypothesized that DiOHF treatment (7 days, 1 mg/kg per day s.c.) would improve relaxation in mesenteric arteries from diabetic rats where endothelial dysfunction is associated with elevated oxidant stress.

Methodology/Principal Findings

In mesenteric arteries from diabetic rats there was an increase in ROS, measured by L-012 and 2',7'-dichlorodihydrofluorescein diacetate fluorescence. NADPH oxidase-derived superoxide levels, assayed by lucigenin chemiluminescence, were also significantly increased in diabetic mesenteric arteries (diabetes, 4892±946 counts/mg versus normal 2486±344 counts/mg, n = 7–10, p<0.01) associated with an increase in Nox2 expression but DiOHF (2094±300 counts/mg, n = 10, p<0.001) reversed that effect. Acetylcholine (ACh)-induced relaxation of mesenteric arteries was assessed using wire myography (pEC₅₀ = 7.94±0.13 n = 12). Diabetes significantly reduced the sensitivity to ACh and treatment with DiOHF prevented endothelial dysfunction (pEC₅₀, diabetic 6.86±0.12 versus diabetic+DiOHF, 7.49±0.13, n = 11, p<0.01). The contribution of NO versus endothelium-derived hyperpolarizing factor (EDHF) to ACh-induced relaxation was assessed by evaluating responses in the presence of TRAM-34+apamin+iberiotoxin or N-nitro-L-arginine+ODQ respectively. Diabetes impaired the contribution of both NO (maximum relaxation, R_max diabetic 24±7 versus normal, 68±10, n = 9–10, p<0.01) and EDHF (pEC₅₀, diabetic 6.63±0.15 versus normal, 7.14±0.12, n = 10–11, p<0.01) to endothelium-dependent relaxation. DiOHF treatment did not significantly affect the EDHF contribution but enhanced NO-mediated relaxation (R_max 69±6, n = 11, p<0.01). Western blotting demonstrated that diabetes also decreased expression and increased uncoupling of endothelial NO synthase (eNOS). Treatment of the diabetic rats with DiOHF significantly reduced vascular ROS and restored NO-mediated endothelium-dependent relaxation. Treatment of the diabetic rats with DiOHF also increased eNOS expression, both in total and as a dimer.

Conclusions/Significance

DiOHF improves NO activity in diabetes by reducing Nox2-dependent superoxide production and preventing eNOS uncoupling to improve endothelial function.

Endothelium-derived hyperpolarizing factor and diabetes

In addition to its role as a barrier between blood and tissues, the vascular endothelium is responsible for the synthesis and released of a number of vasodilators including prostaglandins, nitric oxide and endothelium-derived hyperpolarizing factor (EDHF). As one of these vasodilators, the specific nature of EDHF has not been fully elucidated, although a number of roles have been proposed. Importantly, many conditions, such as hypertension, hyperlipidemia, heart failure, ischemia-reperfusion and diabetes mellitus comprise vascular endothelial dysfunction with EDHF dysregulation. This article reviews reports on the role of EDHF in diabetes-related endothelial dysfunction.

Gender differences in the effects of streptozotocin-induced diabetes on parasympathetic vasodilatation in the rat submandibular gland

OBJECTIVES

Submandibular vasodilatory responses are impaired in male streptozotocin-diabetic rats. However, the effects of diabetes on submandibular vascular reactivity in female rats have not been examined. The purpose of this study was to determine whether there are gender differences in the effects of diabetes on parasympathetic vasodilatation in the rat submandibular gland.

METHODS

Diabetes was induced using streptozotocin, and vascular responses (calculated as the % increase in submandibular vascular conductance) to parasympathetic stimulation (1-10 Hz) were measured using laser-Doppler flowmetry. To estimate the relative contributions of nitric oxide (NO), prostacyclin (PGI2) and endothelium-derived hyperpolarizing factor (EDHF), vascular conductance was measured before and after inhibition of cyclooxygenase (COX) and NO synthase (NOS).

RESULTS

Frequency-dependent increases in blood flow were observed in both male and female rats, but the contribution of EDHF was greater in females than in males. Further, PGI2 appeared to play a role only in males. Vasodilatory responses were diminished in all diabetic animals, and when compared with their respective controls the degree of impairment was similar in males and females. However, in diabetic males inhibition of COX and NOS had little or no effect, whereas inhibition of NO, but not COX, resulted in a further significant decrease in vascular responses in diabetic females.

CONCLUSIONS

Parasympathetic vasodilatation in the rat submandibular gland is diminished equally in diabetic males and females. However, in males diabetes predominantly impairs PGI2- and NO-dependent vasodilatation, whereas in females the contribution of EDHF-mediated pathways are affected and NO-dependent vasodilatation is preferentially maintained.

Reactive oxygen-derived free radicals are key to the endothelial dysfunction of diabetes

Vascular complications are an important pathological issue in diabetes that lead to the further functional deterioration of several organs. The balance between endothelium-dependent relaxing factors and endothelium-dependent contracting factors (EDCFs) is crucial in controlling local vascular tone and function under normal conditions. Diabetic endothelial dysfunction is characterized by reduced endothelium-dependent relaxations and/or enhanced endothelium-dependent contractions. Elevated levels of oxygen-derived free radicals are the initial source of endothelial dysfunction in diabetes. Oxygen-derived free radicals not only reduce nitric oxide bioavailability, but also facilitate the production and/or action of EDCFs. Thus, the endothelial balance tips towards vasoconstrictor responses over the course of diabetes.

Normothermic and hypothermic models for studying the deleterious effects of hypoxia-reoxygenation on EDHF-mediated relaxation in isolated porcine coronary arteries

INTRODUCTION

The vasomotor response of the coronary artery is altered by hypoxia-reoxygenation (H-R) induced damage. The aim of our study was to compare and evaluate normothermic and hypothermic models which are suitable for future drug studies of vasoprotective action against H-R injury.

METHODS

Porcine coronary arterial rings were isolated and placed in Krebs-Henseleit (K-H) solution. Rings were exposed to normoxic conditions (control group) and two different H-R conditions: the first induced by a 95% N(2)-5% CO(2) gas mixture (40- and 60-min hypoxia) in a normothermic protocol, and the second induced by hypothermic (4 degrees C) hypoxia-reoxygenation in an air-tight beaker filled with K-H solution (24- and 48-hours hypoxia). Reoxygenation was applied by introducing K-H solution aerated with a 95% O(2)-5% CO(2) mixture under normothermic (37 degrees C) conditions. To test the EDHF-mediated relaxation by substance P, rings were first incubated in L-NNA, nitric oxide synthase inhibitor, and indomethacin, cyclooxygenase inhibitor, and then pre-contracted with thromboxane analogue U-46619. Analysis of the maximum relaxation of the arterial rings was performed by one-way ANOVA, followed by Bonferroni's post-test.

RESULTS

Distal segments of the coronary artery responded faster to contraction induced by U-46619 and were relaxed by substance P to a greater extent than proximal segments. Maximal relaxations of arterial rings induced by a 10 nM solution of substance P were significantly reduced (p<0.001) from the values for normoxic rings (81.0+/-1.0%, n=30) after 40-min H-R (50.5+/-5.3%, n=30), 60-min H-R (32.1+/-3.5%, n=30), 24-hours hypothermic H-R (56.0+/-2.3%, n=30) and after 48-hours hypothermic H-R (38.5+/-5.1%, n=30).

CONCLUSIONS

The model employing 40-min normothermic H-R is as effective as 24-hours hypothermic H-R, and 60-min normothermic H-R as 48-hours hypothermic H-R for studying the deleterious effects of H-R on EDHF-mediated relaxation.

Uterine artery function in a mouse model of pregnancy complicated by diabetes

It has been demonstrated previously that endothelium-dependent vasodilatation is impaired in myometrial arteries from women with gestational diabetes, which may play a role in mediating complications observed in diabetic pregnancies. It is not known which aspects of endothelium-dependent vasodilatation are impaired, thus a mouse model of pregnancy complicated by streptozotocin-induced diabetes was established to investigate underlying mechanisms. Uterine arteries from term-pregnant, diabetic and control C57Bl6/J mice were assessed using acetylcholine (ACh; 10(-10)-10(-5)M) in the presence or absence of a nitric oxide (NO) synthase inhibitor (L-NNA; 10(-5)M), a cyclooxygenase (COX) inhibitor (indomethacin; 10(-5)M) or the two in combination. Sensitivity to ACh was comparable between diabetic and control mice. However, the contribution of endothelium-dependent vasodilators was significantly altered. L-NNA significantly inhibited the relaxation of arteries from diabetic compared to control mice (65+/-11% vs 18+/-6%; p<.05). L-NNA and indomethacin significantly inhibited the relaxation of arteries from diabetic mice compared to control (87+/-5% vs 33+/-14%; p<0.05). These data indicate that endothelium-dependent relaxation of the uterine artery of control, pregnant mice was largely mediated by the non-NO/non-COX component. Surprisingly, arteries from diabetic mice were primarily dependent on NO, which may affect compensatory capacity as the disease progresses.

Gender differences in vascular reactivity to endothelin-1 (1-31) in mesenteric arteries from diabetic mice

Endothelin-1 (1-31) [ET-1 (1-31)], a novel member of the ET family, comprises 31 amino acids and is derived from the selective hydrolysis of big ET-1 by chymase. Although ET-1 (1-31) reportedly exerts biological effects by direct or indirect [via its conversion to ET-1 (1-21)] mechanisms, it is unclear whether in diabetes the vascular effects of ET-1 (1-31) display gender differences. We investigated this question by exposing mesenteric artery rings to ET-1 (1-31), using arteries from mice in the early or chronic phase of diabetes. In the early stage of diabetes, the ET-1 (1-31)-induced contraction was similar between age- and sex-matched control and streptozotocin (STZ)-induced diabetic mice. In the chronic stage of diabetes, the ET-1 (1-31)-induced contraction was enhanced in diabetic female mice, but not in diabetic male mice (vs. both age-matched control and early-stage diabetic mice). This enhancement was largely prevented by Y27632 (Rho kinase inhibitor), PD98059 [inhibitor of extracellular signal related kinases 1 and 2 (ERK1/2)], or SP600125 [C-jun terminal kinase (JNK) inhibitor]. These data indicate that the ET-1 (1-31)-induced vasoconstriction in the mesenteric artery may be specifically enhanced in established diabetic female mice, and that this enhancement may be due to alterations in the activities of Rho/Rho kinase or mitogen-activated protein kinase.

Downregulation of connexin40 is associated with coronary endothelial cell dysfunction in streptozotocin-induced diabetic mice

Vascular endothelial cells (ECs) play a major role in regulating vascular tone and in revascularization. There is increasing evidence showing endothelial dysfunction in diabetes, although little is known about the contribution of connexins (Cxs) to vascular complications in the diabetic heart. This study was designed to investigate the role of Cxs in coronary endothelial dysfunction in diabetic mice. Coronary ECs isolated from diabetic mice exhibit lowered protein levels of Cx37 and Cx40 (but not Cx43) and a loss of gap junction intercellular communication (GJIC). Vasodilatation induced by the assumed contribution of EC-dependent hyperpolarization was significantly reduced in the diabetic coronary artery (CA). Cx40-specific inhibitory peptide (40)GAP27 strongly attenuated endothelium-dependent relaxation in diabetic CA at the concentration that does not affect the relaxation in control CA, suggesting that the total amount of Cx40 is lower in diabetic CA than in control CA. In diabetic mice, coronary capillary density was significantly decreased in vivo. In vitro, GJIC inhibitor attenuated the ability of EC capillary network formation. High-glucose treatment caused a decrease in Cx40 protein expression in ECs and impaired endothelial capillary network formation, which was restored by Cx40 overexpression. Furthermore, we found that the hyperglycemia-induced decrease in Cx40 was associated with inhibited protein expression of Sp1, a transcriptional factor that regulates Cx40 expression. These data suggest that downregulation of Cx40 protein expression and resultant inhibition of GJIC contribute to coronary vascular dysfunction in diabetes.

Down-regulation of endogenous nitric oxide synthase inhibitors on endothelial SK3 expression

OBJECTIVES

To investigate role of endogenous nitric oxide synthase inhibitor asymmetric dimethylarginine (ADMA) in down-regulation of the expression of endothelial SK3 in atherosclerosis.

METHODS

Apolipoprotein E deficient (apo E(-/-)) mice aged 11 approximately 12 weeks were treated with ADMA (5 mg/kg per day, subcutaneous injection) for 4 weeks. Cultured human umbilical venous endothelial cells (HUVECs) were treated with different concentrations of lysophosphatidylcholine (LPC) or ADMA for 48 h. Plasma levels of ADMA were determined by high performance liquid chromatogram (HPLC); protein and mRNA levels of SK3 in the aortas of mice and cultured cells were detected by immunofluorescence, western blot and RT-PCR, respectively.

RESULTS

Concomitantly with the elevated plasma levels of ADMA, the expressions of both SK3 protein and mRNA in aortas of apo E(-/-) mice were significantly reduced in comparison to those of the wild-type mice. Moreover, 4-week treatment of ADMA made levels of SK3 expression even lower. In cultured HUVECs, either LPC or ADMA notably decreased the expressions of both SK3 protein and mRNA in a concentration dependent manner.

CONCLUSIONS

Endogenous ADMA may be an important factor for down-regulation of the expression of endothelial SK3 in atherosclerotic animals.

A high-sodium diet in streptozotocin-induced diabetic rats impairs endothelium-derived hyperpolarizing factor-mediated vasodilation

We examined endothelium-derived hyperpolarizing factor (EDHF)-mediated relaxation of mesenteric arteries in high-sodium loaded streptozotocin (STZ)-induced diabetic rats. The study shows that acetylcholine (ACh)-induced, EDHF-mediated relaxation is relatively maintained in STZ-induced diabetic rats, but after a high-sodium diet was given, the function was significantly impaired in STZ-induced diabetic rats.

Endothelial dysfunction and arterial pressure regulation during early diabetes in mice: roles for nitric oxide and endothelium-derived hyperpolarizing factor

We determined whether nitric oxide (NO) counters the development of hypertension at the onset of diabetes in mice, whether this is dependent on endothelial NO synthase (eNOS), and whether non-NO endothelium-dependent vasodilator mechanisms are altered in diabetes in mice. Male mice were instrumented for chronic measurement of mean arterial pressure (MAP). In wild-type mice, MAP was greater after 5 wk of N(omega)-nitro-L-arginine methyl ester (L-NAME; 100 mg x kg(-1) x day(-1) in drinking water; 97 +/- 3 mmHg) than after vehicle treatment (88 +/- 3 mmHg). MAP was also elevated in eNOS null mice (113 +/- 4 mmHg). Seven days after streptozotocin treatment (200 mg/kg iv) MAP was further increased in L-NAME-treated mice (108 +/- 5 mmHg) but not in vehicle-treated mice (88 +/- 3 mmHg) nor eNOS null mice (104 +/- 3 mmHg). In wild-type mice, maximal vasorelaxation of mesenteric arteries to acetylcholine was not altered by chronic L-NAME or induction of diabetes but was reduced by 42 +/- 6% in L-NAME-treated diabetic mice. Furthermore, the relative roles of NO and endothelium-derived hyperpolarizing factor (EDHF) in acetylcholine-induced vasorelaxation were altered; the EDHF component was enhanced by L-NAME and blunted by diabetes. These data suggest that NO protects against the development of hypertension during early-stage diabetes in mice, even in the absence of eNOS. Furthermore, in mesenteric arteries, diabetes is associated with reduced EDHF function, with an apparent compensatory increase in NO function. Thus, prior inhibition of NOS results in endothelial dysfunction in early diabetes, since the diabetes-induced reduction in EDHF function cannot be compensated by increases in NO production.

Apocynin normalizes hyperreactivity to phenylephrine in mesenteric arteries from cholesterol-fed mice by improving endothelium-derived hyperpolarizing factor response

We studied the relationship among endothelial function, oxidative stress, and phenylephrine (PE; alpha(1)-adrenoceptor agonist)-induced contraction in mesenteric arteries from high-cholesterol (HC)-diet-fed mice. In HC mice (vs age-matched normal-diet-fed mice): (1) PE-induced contraction in endothelium-intact rings was enhanced (endothelial denudation increased contraction in "normal-diet" rings, but did not enhance it further in "HC" rings); (2) the enhanced PE-induced contraction was further enhanced in the presence of N(G)-nitro-L-arginine (L-NNA; nitric oxide synthase inhibitor) or L-NNA plus indomethacin (cyclooxygenase inhibitor) [to preserve endothelium-derived hyperpolarizing factor (EDHF)], but unchanged in the presence of charybdotoxin plus apamin (to block EDHF); (3) ACh-induced EDHF-type relaxation was reduced; and (4) oxidative stress [indicated by the plasma 8-isoprostane level (reliable systemic marker) and aortic superoxide production] was greater. In HC mice, PE-induced contraction was normalized by apocynin [NAD(P)H oxidase inhibitor] or tempol (superoxide dismutase mimetic), but enhanced by NADH [NAD(P)H oxidase substrate]. Oral dietary supplementation with apocynin (30 mg/kg/day for 4 weeks) corrected the above abnormalities. Hence: (1) PE-induced contraction is modulated by the endothelium, and the enhanced contractility in HC mice results from defective EDHF signaling and elevated oxidative stress, and (2) apocynin normalizes PE-induced contraction in HC mice by improving EDHF signaling.

Mechanisms underlying lysophosphatidylcholine-induced potentiation of vascular contractions in the Otsuka Long-Evans Tokushima Fatty (OLETF) rat aorta

BACKGROUND AND PURPOSE

The effect of lysophosphatidylcholine (LPC) on aortic contractions in Otsuka Long-Evans Tokushima Fatty (OLETF) rats, a type 2 diabetic model, was studied.

EXPERIMENTAL APPROACH

Using OLETF rats and control (Long Evans Tokushima Otsuka (LETO)) rats, the effects of LPC on the contractions induced by high-K(+) (10-40 mM), UK14,304 (10 approximately 100 nM; a selective alpha(2)-adrenoceptor agonist) and sodium orthovanadate (SOV; 10 microM approximately 3 mM) in endothelium-denuded aortae were compared. Aortic ERK activity and the mRNA expression for GPR4 (a putative LPC receptor) were also measured.

KEY RESULTS

OLETF rats exhibited (vs. age-matched LETO rats): (1) greater potentiation of high-K(+)-induced contraction by 10 microM LPC - a potentiation attenuated by 10 microM genistein, protein tyrosine kinase (PTK) inhibitor, (2) greater potentiation of UK14,304 (10 approximately 100 nM)-induced contractions by LPC (1 microM approximately 10 microM) - a potentiation attenuated by 10 microM genistein, 50 microM tyrphostin A23 (PTK inhibitor) or 10 microM PD98059 (MEK 1/2 inhibitor), (3) greater basal and LPC (1 microM)-induced ERK activities, (4) greater basal and 100 nM UK14,304-stimulated ERK2 activities in both the absence and presence of 10 microM LPC, (5) greater SOV (10 microM approximately 3 mM)-induced contractions, (6) greater potentiation of SOV-induced contractions by 10 microM LPC - a potentiation suppressed by 10 microM PD98059 or 10 microM genistein, (7) upregulation of GPR4 mRNA.

CONCLUSIONS AND IMPLICATIONS

These results suggest that the LPC-induced potentiation of contractions in the OLETF rat aorta may be attributable to increased PTKs or ERK activity and/or to receptor upregulation.

Effects of anthocyanidin derivative (HK-008) on relaxation in rat perfused mesenterial bed

Anthocyanins, which are responsible for a variety of bright colors (including red, blue, and purple) in fruits, vegetables, and flowers, are consumed as dietary polyphenols. Anthocyanin-containing fruits are thought to decrease coronary heart disease and are used in anti-diabetic preparations. Diabetes is associated with a variety of cardiovascular complications that may be mediated by endothelial dysfunction, and so this study was designed mainly to characterize the influence of a synthesized anthocyanidin derivative (HK-008) over acetylcholine (ACh)-induced relaxation in mesenteric arterial beds isolated from rats. In a glucose-tolerance test in intact rats, HK-008 (30 mg/kg) reduced the glucose level as effectively as the same dose of glibenclamide. The aortic relaxation induced by pinacidil (an ATP-sensitive potassium channel opener) was greatly inhibited by glibenclamide (10 microM), and also significantly inhibited by HK-008 (10 microM). Interestingly, the ACh-induced relaxation in the perfused, preconstricted mesenteric arterial bed was significantly enhanced by HK-008 (10 microM), and this enhancement was significantly attenuated by indomethacin (10 microM). The ACh-induced mesenteric relaxation was impaired by an increase in oxidative stress, viz. superoxide-generating treatment [xanthine oxidase (XO; 0.1 U/ml) plus hypoxanthine (HX; 10 microM)]. However, this impairment was strongly suppressed by HK-008 (10 microM). These results suggest that HK-008 increases endothelium-induced relaxation by suppressing oxidative stress or modulating prostanoids signaling. This compound may therefore be useful against certain cardiovascular disorders.

Altered arachidonic acid-mediated responses in the perfused kidney of the streptozotocin-induced diabetic rat

Using perfused kidneys isolated from age-matched controls and streptozotocin (STZ)-induced diabetic rats, we investigated the effects of arachidonic acid (AA) on perfusion pressure in the presence of methoxamine. AA elicited a transient contraction followed by a sustained relaxation in each group. The amplitude of contraction was smaller in the diabetic group than in the control group, whereas the amplitude of the sustained relaxation was greater in the former than in the latter group. In the diabetic group, the AA-induced sustained relaxation was completely inhibited by indomethacin [cyclooxygenase (COX) inhibitor], SKF525A [cytochrome P450 (CYP450) inhibitor], or clotrimazole (epoxygenase inhibitor), but not by furegrelate [thromboxane A(2) (TXA(2))-synthase inhibitor], SQ29548 (TXA(2)-receptor antagonist), or baicalein [lipoxygenase (LOX) inhibitor]. In the diabetic kidney, more-or-less additive inhibitions of the AA-induced relaxation were seen when indomethacin was given with either SKF525A or clotrimazole. These results suggest that in the STZ-induced diabetic perfused kidney, vasorelaxant metabolites derived from AA (probably COX and/or CYP450 metabolites) are increased, and may serve to regulate vascular tone.