Interleukin-2 protects against endothelial dysfunction induced by high glucose levels in rats

Interleukin-35 inhibits lipopolysaccharide-induced endothelial cell activation by downregulating inflammation and apoptosis

Inflammation is an essential factor contributing to sepsis-induced endothelial cell (EC) activation. Interleukin-35 (IL-35) is an anti-inflammatory/immunosuppressive cytokine that exerts protective effects on many inflammatory diseases. In this study, we investigated the effects of IL-35 on lipopolysaccharide (LPS)-induced EC activation and the potential underlying mechanism. Human umbilical vein endothelial cells (HUVECs) were incubated with LPS (1 μg/ml) for 24 h and then cocultured with different concentrations (0, 1, 10, or 100 ng/ml) of recombinant human IL-35 (rhIL-35) for 12 h. Flow cytometry analysis revealed that IL-35 inhibited LPS-induced HUVEC apoptosis in a dose-dependent manner. RT-qPCR and Western blot analyses showed significantly higher mRNA and protein levels of the adhesion molecules intercellular adhesion molecule-1 (ICAM-1) and vascular cell adhesion molecule-1 (VCAM-1) and the inflammatory factors IL-6 and IL-8 in the LPS group than in the control group. These changes were alleviated by IL-35 treatment, suggesting that IL-35 protects ECs by downregulating inflammation. Furthermore, IL-35 induced signal transducer and activator of transcription 1 (STAT1) and STAT4 activation and promoted their interaction. Blocking STAT1 or STAT4 expression by fludarabine (STAT1 inhibitor) treatment or siRNA-STAT4-interfering fragment transfection inhibited the protective effect of IL-35 on ECs. Moreover, we observed a similar protective effect of IL-35 treatment on ECs in a mouse sepsis model induced by intraperitoneal LPS injection. This study indicated that IL-35 exerts anti-inflammatory and antiapoptotic effects on LPS-induced EC activation by activating the STAT1 and STAT4 signaling pathways.

The Effect of an Atherogenic Diet and Acute Hyperglycaemia on Endothelial Function in Rabbits Is Artery Specific

Hyperglycaemia has a toxic effect on blood vessels and promotes coronary artery disease. It is unclear whether the dysfunction caused by hyperglycaemia is blood vessel specific and whether the dysfunction is exacerbated following an atherogenic diet. Abdominal aorta, iliac, and mesenteric arteries were dissected from New Zealand White rabbits following either a 4-week normal or atherogenic diet (n = 6–12 per group). The arteries were incubated ex vivo in control or high glucose solution (20 mM or 40 mM) for 2 h. Isometric tension myography was used to determine endothelial-dependent vasodilation. The atherogenic diet reduced relaxation as measured by area under the curve (AUC) by 25% (p < 0.05), 17% (p = 0.06) and 40% (p = 0.07) in the aorta, iliac, and mesenteric arteries, respectively. In the aorta from the atherogenic diet fed rabbits, the 20 mM glucose altered EC₅₀ (p < 0.05). Incubation of the iliac artery from atherogenic diet fed rabbits in 40 mM glucose altered EC₅₀ (p < 0.05). No dysfunction occurred in the mesentery with high glucose incubation following either the normal or atherogenic diet. High glucose induced endothelial dysfunction appears to be blood vessel specific and the aorta may be the optimal artery to study potential therapeutic treatments of hyperglycaemia induced endothelial dysfunction.

Trimebutine maleate relaxes the isolated rat thoracic aorta: The role of nitric oxide and L-type calcium channels

Trimebutine maleate (TMB), a widely prescribed drug for functional gastrointestinal disorders, has been reported to regulate smooth muscle contractility by modulating multiple ion channel activities in the gastrointestinal tract. However, its action on isolated aorta has not yet been reported. The aim of the present study was to evaluate in vitro vasorelaxant properties and the underlying pharmacological mechanisms of TMB in isolated rat thoracic aortic rings. Vascular activity experiments were performed on thoracic aorta isolated from Sprague-Dawley rats in vitro, including endothelium-intact and endothelium-denuded aortic rings. TMB (10^-10 -10^-5  mol/L) induced relaxation in endothelium-intact aortic rings precontracted by phenylephrine with a potency similar to that of carbachol. TMB-induced relaxation was not altered by glibenclamide and atropine in endothelium-intact aortic rings. However, L-NAME and endothelium denudation significantly reduced but not completely reversed the vasorelaxant effect of TMB. Also, TMB-induced relaxation wasn't affected by diclofenac in endothelium-intact aortic rings. TMB at 10^-5  mol/L significantly reduced the CaCl₂ -induced contractions in endothelium-intact aortic rings stimulated with KCl, but not stimulated with phenylephrine under Ca²⁺ free conditions. Moreover, TMB at 10^-5  mol/L effectively attenuated Bay-K8644-induced contractions in aortic rings. These results suggest that TMB-induced relaxation was mediated by both endothelium-dependent and endothelium-independent manner in isolated rat thoracic aorta. The mechanism of TMB-induced relaxation at low concentrations is partially related to NO- and endothelium-dependent but unrelated to prostanoids formation. However, inhibition of Ca²⁺ influx through voltage-operated calcium channels and L-type Ca²⁺ channel blocking effect appears to be involved in the mechanism of vasorelaxant effect of TMB at high concentrations.

Different mechanisms involved in liraglutide and glucagon-like peptide-1 vasodilatation in rat mesenteric small arteries

BACKGROUND AND PURPOSE

Glucagon-like peptide-1 (GLP-1) is an incretin hormone that regulates insulin biosynthesis and secretion in a glucose-dependent manner and has been reported to induce vasodilatation. Here, we examined the possible vasorelaxant effect of GLP-1 and its underlying mechanisms.

EXPERIMENTAL APPROACH

Rat mesenteric arteries (diameter ≈ 200-400 μm) and human s.c. arteries were mounted in microvascular myographs for isometric tension recordings. The effect of GLP-1 on vascular responses was examined under normoglycaemic conditions and at high glucose concentrations.

KEY RESULTS

In rat mesenteric arteries and human s.c. arteries without branches, physiological concentrations (1-100 nM) of GLP-1(7-36) and liraglutide failed to cause relaxation or affect contractions evoked by electrical field stimulation. In contrast to GLP-1(7-36), liraglutide induced relaxations antagonized by the GLP-1 receptor antagonist, exendin-(9-39), in branched mesenteric arteries. In contrast to liraglutide, GLP-1 leftward shifted the concentration relaxation curves for bradykinin in s.c. arteries from patients with peripheral arterial disease, an effect resistant to exendin-(9-39). Under normoglycaemic conditions, neither GLP-1 nor liraglutide affected ACh relaxation in rat mesenteric arteries. In arteries exposed to 40 mM glucose, GLP-1, in contrast to liraglutide, potentiated ACh-induced relaxation by a mechanism that was not antagonized by exendin-(9-39). GLP-1 decreased superoxide levels measured with dihydroethidium in rat mesenteric arteries exposed to 40 mM glucose.

CONCLUSIONS AND IMPLICATIONS

GLP-1 receptors are involved in the liraglutide-induced relaxation of branched arteries, under normoglycaemic conditions, while GLP-1 inhibition of vascular superoxide levels contributes to GLP-1 receptor-independent potentiation of endothelium-dependent vasodilatation in hyperglycaemia.

Paeonol Suppresses Neuroinflammatory Responses in LPS-Activated Microglia Cells

In this work, we assessed the anti-inflammatory effects of paeonol (PAE) in LPS-activated N9 microglia cells, as well as its underlying molecular mechanisms. PAE had no adverse effect on the viability of murine microglia N9 cell line within a broad range (0.12∼75 μM). When N9 cell line was activated by LPS, PAE (0.6, 3, 15 μM) significantly suppressed the release of proinflammatory products, such as nitric oxide (NO), interleukin-1β (IL-1β), and prostaglandin E2 (PGE2), demonstrated by the ELISA assay. Moreover, the levels of cyclooxygenase-2 (COX-2) and inducible nitric oxide synthase (iNOS) were significantly reduced in PAE-treated N9 microglia cells. We also examined some proteins involved in immune signaling pathways and found that PAE treatment significantly decreased the expression of TLR4, MyD88, IRAK4, TNFR-associated factor 6 (TRAF6), p-IkB-α, and NF-kB p65, as well as the mitogen-activated protein kinase (MAPK) pathway molecules p-P38, p-JNK, and p-ERK, indicating that PAE might act on these signaling pathways to inhibit inflammatory responses. Overall, we found that PAE had anti-inflammatory effect on LPS-activated N9 microglia cells, possibly via inhibiting the TLR4 signaling pathway, and it could be a potential drug therapy for inflammation-associated neurodegenerative diseases.

The Effects of Copper on Brain Microvascular Endothelial Cells and Claudin Via Apoptosis and Oxidative Stress

Many neurodegenerative diseases are related to copper although the effects on brain microvascular endothelial cells (BMECs) are poorly understood. In the present study, a primary BMEC culture model was established to evaluate the effects of copper on brain microvascular endothelial cells and whether claudin-1, claudin-3, claudin-5, and claudin-12 isoforms contribute to apoptosis and intrinsic antioxidant activity. Our results showed that copper ions had dual effects on BMECs by regulating intracellular reactive oxygen species (ROS) levels. Copper levels between 30 and 120 μM could enhance viability and promote proliferation. On the other hand, copper cytotoxicity was a result of apoptosis indicating a redox-independent manner of cell death. Expression levels of claudins were also regulated by copper in a concentration-dependent manner. We identified four claudin isoforms (1, 3, 5, and 12) and showed that their expression levels were regulated as a group by copper. Antioxidant activity of BMECs was also copper regulated, and superoxide dismutase and catalase were the main contributors to BMEC antioxidant functions. Together, our results indicated that copper had dual effects on BMEC growth and intrinsic antioxidant activities played a crucial role in BMEC survival and tight junction.

Apigenin and naringenin ameliorate PKCβII-associated endothelial dysfunction via regulating ROS/caspase-3 and NO pathway in endothelial cells exposed to high glucose

Endothelial dysfunction is a key event in the progression of atherosclerosis with diabetes. Increasing cell apoptosis may lead to endothelial dysfunction. Apigenin and naringenin are two kinds of widely used flavones. In the present study, we investigated whether and how apigenin and naringenin reduced endothelial dysfunction induced by high glucose in endothelial cells. We showed that apigenin and naringenin protected against endothelial dysfunction via inhibiting phosphorylation of protein kinase C βII (PKCβII) expression and downstream reactive oxygen species (ROS) production in endothelial cells exposed to high glucose. Furthermore, we demonstrated that apigenin and naringenin reduced high glucose-increased apoptosis, Bax expression, caspase-3 activity and phosphorylation of NF-κB in endothelial cells. Moreover, apigenin and naringenin effectively restored high glucose-reduced Bcl-2 expression and Akt phosphorylation. Importantly, apigenin and naringenin significantly increased NO production in endothelial cells subjected to high glucose challenge. Consistently, high glucose stimulation impaired acetylcholine (ACh)-mediated vasodilation in the rat aorta, apigenin and naringenin treatment restored the impaired endothelium-dependent vasodilation via dramatically increasing eNOS activity and nitric oxide (NO) level. Taken together, our results manifest that apigenin and naringenin can ameliorate endothelial dysfunction via regulating ROS/caspase-3 and NO pathway.

Stimulation of nitric oxide production contributes to the antiplatelet and antithrombotic effect of new peptide pENW (pGlu-Asn-Trp)

INTRODUCTION

New peptide pGlu-Asn-Trp (pENW), initially extracted from snake venom, significantly attenuates the formation of arterial and venous thrombi in vivo, and has modest in-vitro antiplatelet activity. This study was designed to investigate the underlying mechanisms.

METHODS

The rat carotid thrombosis model induced by FeCl3 was established to evaluate the antithrombotic activity of pENW. The effects of pENW on the production of nitric oxide (NO), as well as the expression and activity of endothelial nitric oxide synthase (eNOS), were determined. The vasorelaxant effect of pENW was evaluated using isolated rat aortic rings in the absence or presence of N(G)-nitro-L-arginine methyl ester (L-NAME, eNOS inhibitor). Furthermore, the in-vitro antiplatelet activity of pENW was investigated with the addition of sodium nitroprusside (SNP, NO donor) and/or L-NAME to further prove the role of NO and eNOS in the inhibitory effect of pENW on platelet aggregation.

RESULTS

In vivo, pENW inhibited thrombus formation induced by endothelial injury in a dose-dependent manner, with a significantly prolonged time to the occurrence of arterial occlusion. It was shown that pENW offered protection for blood vessels from oxidative injury. pENW significantly increased NO production in rats treated with pENW at 4 or 2mg/kg body weight. Furthermore, the production of NO from the cultured vascular endothelial cells was increased with the treatment of 10(-4)M and 10(-5)M pENW; pENW also enhanced eNOS expression and activity both in vivo and in vitro, and elicited a concentration-dependent vasorelaxation which was significantly inhibited by L-NAME. Notably, pENW inhibited ADP-induced platelet aggregation, and the inhibition was more significant in the presence of NO. The inhibition of platelet aggregation by pENW was significantly abolished by L-NAME.

CONCLUSIONS

The in-vivo antiplatelet and antithrombotic effects of pENW are at least partly mediated by the increased production of endogenous NO via up-regulation and stimulation of eNOS. The findings suggest that pENW could potentially be developed as a novel therapeutic agent in the treatment of platelet-driven disorders.

The DPP-4 inhibitor linagliptin and the GLP-1 receptor agonist exendin-4 improve endothelium-dependent relaxation of rat mesenteric arteries in the presence of high glucose

The aim of the study was to investigate the effects of the DPP-4 inhibitors and GLP-1R agonist, exendin-4 on the mechanism(s) of endothelium-dependent relaxation in rat mesenteric arteries exposed to high glucose concentration (40 mM). Organ bath techniques were employed to investigate vascular endothelial function in rat mesenteric arteries in the presence of normal (11 mM) or high (40 mM) glucose concentrations. Pharmacological tools (1μM TRAM-34, 1μM apamin, 100 nM Ibtx, 100 μM l-NNA, 10 μM ODQ) were used to distinguish between NO and EDHF-mediated relaxation. Superoxide anion levels were assessed by L-012 and lucigenin enhanced-chemiluminescence techniques. Incubation of mesenteric rings with high glucose for 2 h caused a significant increase in superoxide anion generation and a significant impairment of endothelium-dependent relaxation. Exendin-4 and DPP-4 inhibitor linagliptin, but not sitagliptin or vildagliptin, significantly reduced vascular superoxide and improved endothelium-dependent relaxation in the presence of high glucose. The beneficial actions of exendin-4, but not linagliptin, were attenuated by the GLP-1R antagonist exendin fragment (9-39). Further experiments demonstrated that the presence of high glucose impaired the contribution of both nitric oxide and endothelium-dependent hyperpolarisation to relaxation and that linagliptin improved both mechanisms involved in endothelium-dependent relaxation. These findings demonstrate that high glucose impaired endothelium-dependent relaxation can be improved by exendin-4 and linagliptin, likely due to their antioxidant activity and independently of any glucose lowering effect.

Polyamine and Its Metabolite H2O2 Play a Key Role in the Conversion of Embryogenic Callus into Somatic Embryos in Upland Cotton (Gossypium hirsutum L.)

The objective of this study was to increase understanding about the mechanism by which polyamines (PAs) promote the conversion of embryogenic calli (EC) into somatic embryos in cotton (Gossypium hirsutum L.). We measured the levels of endogenous PAs and H2O2, quantified the expression levels of genes involved in the PAs pathway at various stages of cotton somatic embryogenesis (SE), and investigated the effects of exogenous PAs and H2O2 on differentiation and development of EC. Putrescine (Put), spermidine (Spd), and spermine (Spm) significantly increased from the EC stage to the early phase of embryo differentiation. The levels of Put then decreased until the somatic embryo stage whereas Spd and Spm remained nearly the same. The expression profiles of GhADC genes were consistent with changes in Put during cotton SE. The H2O2 concentrations began to increase significantly at the EC stage, during which time both GhPAO1 and GhPAO4 expressions were highest and PAO activity was significantly increased. Exogenous Put, Spd, Spm, and H2O2 not only enhanced embryogenic callus growth and embryo formation, but also alleviated the effects of D-arginine and 1, 8-diamino-octane, which are inhibitors of PA synthesis and PAO activity. Overall, the results suggest that both PAs and their metabolic product H2O2 are essential for the conversion of EC into somatic embryos in cotton.

Endothelium-dependent and -independent vasorelaxant actions and mechanisms induced by total flavonoids of Elsholtzia splendens in rat aortas

Elsholtzia splendens (ES) is, rich in flavonoids, used to repair copper contaminated soil in China, which has been reported to benefit cardiovascular systems as folk medicine. However, few direct evidences have been found to clarify the vasorelaxation effect of total flavonoids of ES (TFES). The vasoactive effect of TFES and its underlying mechanisms in rat thoracic aortas were investigated using the organ bath system. TFES (5-200mg/L) caused a concentration-dependent vasorelaxation in endothelium-intact rings, which was not abolished but significantly reduced by the removal of endothelium. The nitric oxide synthase (NOS) inhibitor N(ω)-nitro-l-arginine methyl ester (100μM) and the guanylate cyclase inhibitor 1H-[1,2,4]oxadiazolo[4,2-α]quinoxalin-1-one (30μM) significantly blocked the endothelium-dependent vasorelaxation of TFES. Meanwhile, NOS activity in endothelium-intact aortas was concentration-dependently elevated by TFES. However, indomethacin (10μM) did not affect TFES-induced vasorelaxation. Endothelium-independent vasorelaxation of TFES was significantly attenuated by KATP channel blocker glibenclamide. The accumulative Ca(2+)-induced contraction in endothelium-denuded aortic rings primed with KCl or phenylephrine was markedly weakened by TFES. These results revealed that the NOS/NO/cGMP pathway is likely involved in the endothelium-dependent vasorelaxation induced by TFES, while activating KATP channel, inhibiting intracellular Ca(2+) release, blocking Ca(2+) channels and decreasing Ca(2+) influx into vascular smooth muscle cells might contribute to the endothelium-independent vasorelaxation conferred by TFES.

Effects of cisplatin on the contractile function of thoracic aorta of Sprague-Dawley rats

DNA-damaging agents have been reported to be associated with cardiovascular complications, however, the underlying mechanisms remain to be clarified. In the present study, the possible vascular effects of cisplatin was assessed by measuring its effects on the contractile function of thoracic aortic rings dissected from Sprague-Dawley (SD) rats. Contraction of the aortic ring was induced by 60 mM KCl or 10^-6 M phenylephrine (PE) in an ex vivo perfusion system. Cisplatin (200 μM) counteracted KCl- and PE-induced contraction by 57.6 and 91.8%, respectively, in endothelium-intact aortic rings. Similar results were obtained in endothelium-denuded aortas. Electromicroscopy analysis revealed severe damage to blood vessel walls in vivo by cisplatin. In addition, cisplatin significantly inhibited adenosine triphosphate (ATP)-induced intracellular Ca²⁺ concentration ([Ca²⁺]_i) increases in human umbilical vein endothelial cells (HUVECs). These results suggested that the DNA-damaging agent cisplatin can affect the contractile function of thoracic aortas. In addition, in accordance with its DNA-damaging properties, the cardiovascular toxicity of cisplatin may be the result of its direct cytotoxicity.

Relaxation of rat aorta by farrerol correlates with potency to reduce intracellular calcium of VSMCs

Farrerol, isolated from Rhododendron dauricum L., has been proven to be an important multifunctional physiologically active component, but its vasoactive mechanism is not clear. The present study was performed to observe the vasoactive effects of farrerol on rat aorta and to investigate the possible underlying mechanisms. Isolated aortic rings of rat were mounted in an organ bath system and the myogenic effects stimulated by farrerol were studied. Intracellular Ca²⁺ ([Ca²⁺]_in) was measured by molecular probe fluo-4-AM and the activities of L-type voltage-gated Ca²⁺ channels (LVGC) were studied with whole-cell patch clamp in cultured vascular smooth muscle cells (VSMCs). The results showed that farrerol significantly induced dose-dependent relaxation on aortic rings, while this vasorelaxation was not affected by N^G-nitro-l-arginine methylester ester or endothelium denudation. In endothelium-denuded aortas, farrerol also reduced Ca²⁺-induced contraction on the basis of the stable contraction induced by KCl or phenylephrine (PE) in Ca²⁺-free solution. Moreover, after incubation with verapamil, farrerol can induce relaxation in endothelium-denuded aortas precontracted by PE, and this effect can be enhanced by ruthenium red, but not by heparin. With laser scanning confocal microscopy method, the farrerol-induced decline of [Ca²⁺]_in in cultured VSMCs was observed. Furthermore, we found that farrerol could suppress Ca²⁺ influx via LVGC by patch clamp technology. These findings suggested that farrerol can regulate the vascular tension and could be developed as a practicable vasorelaxation drug.

Effect of 7-difluoromethyl-5, 4'-dimethoxygenistein on aorta atherosclerosis in hyperlipidemia ApoE(-/-) mice induced by a cholesterol-rich diet

Purpose

7-Difluoromethyl–5, 4′-dimethoxygenistein (DFMG), prepared by the difluoromethylation and alkylation of Genistein, is an active new chemical entity. Its anti-atherosclerosis effect was found in a series of studies in vitro. In this article, we explored and evaluated the anti-atherosclerosis effect via its protection of endothelial function in ApoE^−/− mice that were fed a high-fat diet.

Methods

Five C57BL/6J mice were selected as a control group and were fed a 1% high-fat diet (control group, n = 5). Five ApoE^−/− mice that were fed a high-fat diet for 16 weeks were selected as the atherosclerosis model group (model group, n = 5). In the phase I study, 25 ApoE^−/− mice were provided a prophylactic treatment with different drugs at the beginning of the 16 week high-fat diet: 5 mg/gk genistein (genistein 1 group, n = 5), 5 mg/kg lovastatin (lovastatin1 group, n = 5), 2.5 mg/kg DFMG (DFMG L1 group, n = 5), 5 mg/kg DFMG (DFMG M1 group, n = 5), and 10 mg/kg DFMG (DFMG H1 group, n = 5). In the phase II study, 25 atherosclerosis model, ApoE^−/− mice were treated with different drugs and fed a high-fat diet for 16 weeks: 5 mg/gk genistein (genistein 2 group, n = 5), 5 mg/kg lovastatin (lovastatin 2 group, n = 5), 2.5 mg/kg DFMG (DFMG L2 group, n = 5), 5 mg/kg DFMG (DFMG M2 group, n = 5), and 10 mg/kg DFMG (DFMG H2 group, n = 5). The plasma levels of lipids, von Willebrand factor (vWF), and nitrite were compared between phases I and II. Endothelium-dependent relaxation (EDR), aortic lesion development, and quantification in thoracic aortas were measured during these two phase studies.

Results

Compared to the model group, the lipid and vWF plasma levels were significantly lower, the plasma nitrite levels were significantly higher, the fatty streaks of aortic lesions were significantly lower, and the endothelium dependent relaxation was significantly higher after both phase studies (P < 0.05). The DFMG supplementation led to significant plasma nitrite increment in all groups after both phase studies (P < 0.05). There were significantly decreased fatty streaks of aortic lesions in DFMG-prevented and DFMG-treated mice (P < 0.05). There was a significant increase in EDR in all prophylactic treatment groups and treatment groups (P < 0.05). We further demonstrated that the preventative effect was more obvious than the therapeutic effect.

Conclusion

Our results suggest that DFMG could work in prophylactic and therapeutic treatments for atherosclerosis development.

Betulinic acid ameliorates endothelium-dependent relaxation in L-NAME-induced hypertensive rats by reducing oxidative stress

Zizyphi Spinosi semen (ZSS) is one of the most widely used traditional Chinese herbs with protective effects on the cardiovascular system. It is not clear whether betulinic acid (BA), the key active constituent of ZSS, has beneficial cardiovascular effects on N(ω)-nitro-L-arginine methyl ester hydrochloride (L-NAME)-induced hypertensive rats. The objective of this study was to investigate the effect of BA on endothelium-dependent vasorelaxation in isolated aortic rings from L-NAME-induced hypertensive rats and its underlying mechanisms. Male Sprague-Dawley rats were injected with L-NAME (15 mg/kg/d, i.p.) for 4 weeks to induce hypertension. After treatment with L-NAME for 2 weeks, rats with mean blood pressure >120 mm Hg measured by tail-cuff method were considered hypertensive and then injected with BA (0.8, 4, 20 mg/kg/d, i.p.) for the last 2 weeks. The effect of BA on the tension of rat thoracic aortic rings was measured in an organ bath system. The levels of nitric oxide (NO), reactive oxygen species (ROS), and the activity of superoxide dismutase (SOD) and nitric oxide synthase (NOS) in aortas were assayed. We found that BA (0.1-100 μM) evoked a concentration-dependent vasorelaxation in endothelium-intact normal rat aortic rings, which was significantly attenuated by pretreatment with L-NAME (100 μM) or methylene blue (MB, 10 μM), but not by indomethacin (10 μM). Pretreatment with EC(50) (1.67 μM) concentration of BA enhanced the acetylcholine (ACh)-induced vasorelaxation, which was also markedly reversed by both L-NAME and MB. The blood pressure in hypertensive rats increased to 135.22±5.38 mm Hg (P<0.01 vs. control group), which was markedly attenuated by high dose of BA. The ACh-induced vasorelaxation in hypertensive rat aortic rings was impaired, which was markedly improved by chronic treatment with BA (20 mg/kg/d) for 2 weeks. The increase of ROS level and the decrease of NO level, SOD and eNOS activities in hypertensive rat aortas were all markedly inhibited by BA. These results indicate that BA decreased blood pressure and improved ACh-induced endothelium-dependent vasorelaxation in L-NAME-induced hypertension rats, which may be mediated by reducing oxidative stress and retaining the bioavailability of NO in the cardiovascular system.

Flavonoids as vasorelaxant agents: synthesis, biological evaluation and quantitative structure activities relationship (QSAR) studies

A series of 2-(2-diethylamino)-ethoxychalcone and 6-prenyl(or its isomers)-flavanones 10a,b and 11a–g were synthesized and evaluated for their vasorelaxant activities against rat aorta rings pretreated with 1 μM phenylephrine (PE). Several compounds showed potent vasorelaxant activities. Compound 10a (EC₅₀ = 7.6 μM, E_max = 93.1%), the most potent one, would be a promising structural template for development of novel and more efficient vasodilators. Further, 2D-QSAR analysis of compounds 10a,b and 11c-e as well as thirty previously synthesized flavonoids 1-3 and 12-38 using Enhanced Replacement Method-Multiple Linear Regression (ERM-MLR) was further performed based on an optimal set of molecular descriptors (H5m, SIC2, DISPe, Mor03u and L3m), leading to a reliable model with good predictive ability (R_train² = 0.839, Q_loo² = 0.733 and R_test² = 0.804). The results provide good insights into the structure- activity relationships of the target compounds.

Terminal arteriolar network structure/function and plasma cytokine levels in db/db and ob/ob mouse skeletal muscle

OBJECTIVE

To investigate the terminal arteriolar network structure and function in relation to circulating plasma cytokine levels in db/db, ob/ob, and their genetic background control, C57/bl6, mice.

METHODS

Arteriolar network size and erythrocyte distribution were observed in the resting cremaster muscle (n = 45, pentobarbital 50 mg/kg i.p.). Structural remodeling and inflammatory state were related to 21 plasma cytokine levels.

RESULTS

db/db networks were shorter, had fewer branches, and smaller diameters than C57/bl6 controls. ob/ob networks were longer, with similar branch numbers, however with non-uniform diameters. Shunting of erythrocytes to the specific terminal arteriolar branches of the network (functional rarefaction) was prominent in db/db and ob/ob, with further evidence of shunting between networks seen as no flow to 50% of ob/ob arteriolar networks.

CONCLUSIONS

Altered levels of plasma cytokines are consistent with structural remodeling seen in db/db, and a pro-inflammatory state for both db/db and ob/ob. Differences in network structure alone predict overall reduced uniform oxygen delivery in db/db or ob/ob. Shunting probably increases heterogeneous oxygen delivery and is strain-dependent.

Short-term type 1 diabetes alters the mechanism of endothelium-dependent relaxation in the rat carotid artery

The aim of the present study was to examine the effect of an early stage of streptozotocin-induced diabetes on the mechanism(s) of endothelium-dependent relaxation. Diabetes was induced by a single injection of streptozotocin (48 mg/kg iv), and the ACh-induced relaxation of rat carotid arteries was examined 6 wk later. A diabetes-induced increase in superoxide levels, determined by L-012-induced chemiluminescence, from carotid arteries was associated with endothelial nitric oxide (NO) synthase (eNOS) uncoupling and increased catalytic subunit of NADPH oxidase expression. The sensitivity and maximum response to ACh were similar in normal and diabetic rats despite a decrease in NO release detected by 4-amino-5-methylamino-2′,7′-difluorofluorescein. In normal rats, N-nitro-l-arginine (100 μM) plus 1 H-[1,2,4]oxadiazolo-[4,3-a]quinoxalin-1-one (10 μM), to inhibit NOS and soluble guanylate cyclase (sGC), respectively, abolished ACh-induced relaxation, whereas in diabetic rats, the maximum relaxation to ACh was attenuated (maximum relaxation: 25 ± 5%), but not abolished, by that treatment. The remaining ACh-induced relaxation was abolished by NO scavengers, cupric chloride (to degrade nitrosothiols), or blockers of endothelial K+ channels. Western blot analysis of the carotid arteries indicated that diabetes significantly increased the expression of eNOS but decreased the proportion of eNOS expressed as the dimer. These findings demonstrate that in early diabetes, ACh-induced relaxation is maintained but is resistant to NOS inhibition. In early diabetes, nitrosothiol-mediated opening of K+ channels may act in conjunction with NO stimulation of sGC to maintain endothelium-dependent relaxation despite the increase in vascular superoxide levels.

Luteolin reduces high glucose-mediated impairment of endothelium-dependent relaxation in rat aorta by reducing oxidative stress

While luteolin, a flavone rich in many plants, has some cardiovascular activity, it is not clear whether luteolin has beneficial effects on the vascular endothelial impairment in hyperglycemia/high glucose. Here, we reveal the protective effect of luteolin on endothelium-dependent relaxation in isolated rat aortic rings exposed to high glucose. The thoracic aorta of male Sprague-Dawley rats was rapidly dissected out and the effect of luteolin on the tension of aortic rings pretreated with high glucose (44mM) for 4h was measured in an organ bath system. The levels of nitric oxide (NO), hydroxy radical (OH(-)) and reactive oxygen species (ROS), and the activity of superoxide dismutase (SOD) and nitric oxide synthase (NOS) were measured in aortas. The vasorelaxation after treatment with luteolin for 8 weeks in aortic rings from diabetic rats was also determined. We found that exposure to high glucose decreased acetylcholine-induced endothelium-dependent relaxation. However, high mannitol had no effect on vasorelaxation. Luteolin evoked a concentration-dependent relaxation in aortic rings previously contracted by phenylephrine, and the pD(2) value was 5.24+/-0.04. The EC(50) of luteolin markedly attenuated the inhibition of relaxation induced by high glucose, which was significantly weakened by pretreatment with l-NAME (0.1mM), but not by indomethacin (0.01mM). Luteolin significantly inhibited the increase of ROS level and OH(-) formation, and the decrease of NO level, NOS and SOD activity caused by high glucose. The improving effect of luteolin on endothelium-dependent vasorelaxation in diabetic rat aortic rings was reversed by pretreatment with l-NAME or methylene blue. The results indicate that the decrease of endothelium-dependent relaxation in rat aortic rings exposed to high glucose is markedly attenuated by luteolin, which may be mediated by reducing oxidative stress and enhancing activity in the NOS-NO pathway.

Synthesis and biological activity of some 1,3-dihydro-2H-3-benzazepin-2-ones with a piperazine moiety as bradycardic agents

A series of 1,3-dihydro-2H-3-benzazepin-2-ones with a piperazine moiety were designed and synthesized by treating the common intermediate of 1,3-dihydro-7,8-dimethoxy-3-[3-(1-piperazinyl)propyl]-2H-3-benzazepin-2-ones with a variety of N-aryl-2-chloroacetamides and acyl chlorides. Their structures have been characterized by (1)H-NMR, MS, and elemental analysis. The title compounds were evaluated for their bradycardic activity in vitro. Most of the synthesized compounds exhibited some vasorelaxant activity and heart-rate-reducing activity with bradycardic potency.

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.

Apigenin protects endothelium-dependent relaxation of rat aorta against oxidative stress

Apigenin is shown to have cardiovascular effects, but the effects of apigenin on aortas injured by exogenous oxidants are unknown. The objective of this study was to investigate the effect of apigenin on endothelium-dependent vasorelaxation in isolated rat aortic rings exposed to superoxide anion produced by pyrogallol, and its mechanism. The male Sprague-Dawley rat thoracic aorta was rapidly dissected out and the effect of apigenin on tension of aortic rings pretreated with 500 microM pyrogallol, inducing oxidative stress injury, was measured. The activity of nitric oxide synthase (NOS), the level of nitric oxide (NO) and the inhibition of superoxide anion in aortic tissues were measured. We found that pretreatment with pyrogallol concentration-dependently decreased acetylcholine-induced endothelium-dependent vasorelaxation. Apigenin (0.5-72.0 microM) evoked a concentration-dependent relaxation in aortas (pD(2): 5.304+/-0.049), which was weakened by L-NAME (the maximal relaxation fell from 87.6+/-6.7% to 37.1+/-8.8%, P<0.01), but not by aminoguanidine and indomethacin. Apigenin markedly attenuated the inhibition of vasorelaxation induced by pyrogallol (the maximal relaxation elevated from 55.8%+/-6.6% to 69.5%+/-6.4%, and the pD(2) increased from 6.559+/-0.119 to 7.057+/-0.145, P<0.01) and increased the inhibition of superoxide anion (from 94.6% to 74.5%), the NO level (from 77.1% to 94.4%), and the constitutive NOS activity (from 35.1% to 62.5%). These results indicate that pyrogallol decreased endothelium-dependent vasorelaxation in rat aortas via oxidative stress, which was markedly attenuated by apigenin. This may be mediated by weakening the oxidative stress and the NO reduction.

Synthesis, biological evaluation of prenylflavonoids as vasorelaxant and neuroprotective agents

A series of prenylflavonoids with multiple hydroxyl groups were synthesized and evaluated for their vasorelaxant activities against rat aorta rings pre-contracted by phenylephrine (PE), as well as their neuroprotective effects against OGD induced PC12 cell injury. The results indicated that the prenyl group at A-ring of prenylflavonoids, as well as hydroxyl groups at B-ring was important for their activities. (+/-)Leachianone G 1b, bearing 8-prenyl and 2',4'-dihydoxyl groups, exhibited the most potent vasorelaxant and neuroprotective effects.

Endothelium-independent relaxation and contraction of rat aorta induced by ethyl acetate extract from leaves of Morus alba (L.)

AIM OF THE STUDY

Based on screening for vasoactive traditional Chinese medicinal herbs, the present study was performed to investigate the vasoactive effects of an ethyl acetate extract from leaves of Morus alba (L.) (ELM) on rat thoracic aorta and the mechanisms underlying these effects.

MATERIALS AND METHODS

Isolated rat thoracic rings were mounted in an organ bath system and the effects of ELM on their responses were evaluated.

RESULTS

ELM (0.125-32.000g/l) induced a concentration-dependent relaxation (P<0.01 vs. control) both in endothelium-intact and -denuded aortas precontracted by high K(+) (6 x 10(-2)M) or 10(-6)M phenylephrine (PE). In endothelium-denuded aortas, ELM at the EC(50) concentration reduced Ca(2+)-induced contraction (P<0.01 vs. control) after PE or KCl had generated a stable contraction in Ca(2+)-free solution. And after incubation with verapamil, ELM induced contraction in endothelium-denuded aortas precontracted by PE (P<0.01 vs. control); this was abolished by ruthenium red (P<0.01 vs. ELM-treated endothelium-denuded group; P>0.05 vs. control), but not by heparin (P>0.01 vs. ELM-treated endothelium-denuded group; P<0.01 vs. control).

CONCLUSIONS

The results showed that ELM had dual vasoactive effects, and the relaxation was greater than the contraction. The relaxation was mediated by inhibition of voltage- and receptor-dependent Ca(2+) channels in vascular smooth muscle cells, while the contraction occurred via activation of ryanodine receptors in the sarcoplasmic reticulum.

Alcohol induces relaxation of rat thoracic aorta and mesenteric arterial bed

AIMS

The aim of this study was to investigate the effect of alcohol on rat artery and its underlying mechanism.

METHODS

The tension of isolated Sprague-Dawley rat thoracic aortic rings and the pressure of rat mesenteric arterial beds perfused with different concentrations of alcohol (0.1-7.0 per thousand) were measured.

RESULTS

At resting tensions, alcohol caused a concentration-dependent relaxation on endothelium-denuded aortic rings precontracted with KCl (6 x 10(-2) mol/L) or phenylephrine (PE, 10(-6) mol/L), and this effect was most evident on rings at a resting tension of 3 g. Alcohol induced much less vasodilation on endothelium-intact rings. Alcohol inhibited the CaCl(2)-induced contraction of endothelium-denuded aortic rings precontracted with KCl or PE. Incubation of rings with dantrolene (5 x 10(-5) mol/L), a ryanodine receptor blocker, or 2-aminoethyl diphenylborinate (7.5 x 10(-5) mol/L), an IP(3) receptor blocker, attenuated the vasodilating effect of alcohol on rings precontracted with PE. Alcohol also concentration-dependently relaxed rat mesenteric arterial beds precontracted with KCl (6 x 10(-2) mol/L) or PE (10(-5) mol/L), which was more potent on endothelium-denuded than on endothelium-intact beds.

CONCLUSIONS

Alcohol has a vasodilating effect on rat artery depending on the resting tension. Both extracellular and intracellular Ca(2+) mobilization of vascular smooth muscle cells are involved in the vascular effect of alcohol.

Endothelial dysfunction in diabetes mellitus

Diabetes mellitus is associated with an increased risk of cardiovascular disease, even in the presence of intensive glycemic control. Substantial clinical and experimental evidence suggest that both diabetes and insulin resistance cause a combination of endothelial dysfunctions, which may diminish the anti-atherogenic role of the vascular endothelium. Both insulin resistance and endothelial dysfunction appear to precede the development of overt hyperglycemia in patients with type 2 diabetes. Therefore, in patients with diabetes or insulin resistance, endothelial dysfunction may be a critical early target for preventing atherosclerosis and cardiovascular disease. Microalbuminuria is now considered to be an atherosclerotic risk factor and predicts future cardiovascular disease risk in diabetic patients, in elderly patients, as well as in the general population. It has been implicated as an independent risk factor for cardiovascular disease and premature cardiovascular mortality for patients with type 1 and type 2 diabetes mellitus, as well as for patients with essential hypertension. A complete biochemical understanding of the mechanisms by which hyperglycemia causes vascular functional and structural changes associated with the diabetic milieu still eludes us. In recent years, the numerous biochemical and metabolic pathways postulated to have a causal role in the pathogenesis of diabetic vascular disease have been distilled into several unifying hypotheses. The role of chronic hyperglycemia in the development of diabetic microvascular complications and in neuropathy has been clearly established. However, the biochemical or cellular links between elevated blood glucose levels, and the vascular lesions remain incompletely understood. A number of trials have demonstrated that statins therapy as well as angiotensin converting enzyme inhibitors is associated with improvements in endothelial function in diabetes. Although antioxidants provide short-term improvement of endothelial function in humans, all studies of the effectiveness of preventive antioxidant therapy have been disappointing. Control of hyperglycemia thus remains the best way to improve endothelial function and to prevent atherosclerosis and other cardiovascular complications of diabetes. In the present review we provide the up to date details on this subject.

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.