Zinc-sensing receptor activation induces endothelium-dependent hyperpolarization-mediated vasorelaxation of arterioles

BACKGROUND

The micronutrient zinc (Zn2+) is critical for cell function as intracellular signaling and endogenous ligand for Zn2+ sensing receptor (ZnR). Although cytosolic Zn2+ (cyt) signaling in the vascular system was studied previously, role of the ZnR has not been explored in vascular physiology.

METHODS

ZnR-mediated relaxation response of human submucosal arterioles and the mesenteric arterioles from wide-type (WT), ZnR-/- and TRPV4-/- mice were determined by a Mulvany-style wire myograph. The perfused vessel density (PVD) of mouse mesenteric arterioles was also measured in in vivo study. The expression of ZnR in arterioles and vascular endothelial cells (VEC) were examined by immunofluorescence staining, and its function was characterized in VEC by Ca2+ imaging and patch clamp study.

RESULTS

ZnR expression was detected on human submucosal arterioles, murine mesenteric arterioles and VEC but not in ZnR-/- mice. ZnR activation predominately induced endothelium-dependent hyperpolarization (EDH)-mediated vasorelaxation of arterioles in vitro and in vivo via Ca2+ signaling, which is totally different from endothelium-dependent vasorelaxation via Zn2+ (cyt) signaling reported previously. Furthermore, ZnR-induced vasorelaxation via EDH was significantly impaired in ZnR-/- and TRPV4-/- mice. Mechanistically, ZnR induced endothelium-dependent vasorelaxation predominately via PLC/IP3/IP3R and TRPV4/SOCE. The role of ZnR in regulating Ca2+ signaling and ion channels on VEC was verified by Ca2+ imaging and patch clamp techniques.

CONCLUSION

ZnR activation induces endothelium-dependent vasorelaxation of resistance vessels predominately via TRPV4/Ca2+/EDH pathway. We therefore not only provide new insights into physiological role of ZnR in vascular system but also may pave a potential pathway for developing Zn2+-based treatments for vascular disease.

Induction of KLF2 by Exercise Activates eNOS to Improve Vasodilatation in Diabetic Mice

Diabetic endothelial dysfunction associated with diminished endothelial nitric oxide (NO) synthase (eNOS) activity accelerates the development of atherosclerosis and cardiomyopathy. However, the approaches to restore eNOS activity and endothelial function in diabetes remain limited. The current study shows that enhanced expression of Krüppel-like factor 2 (KLF2), a shear stress-inducible transcription factor, effectively improves endothelial function through increasing NO bioavailability. KLF2 expression is suppressed in diabetic mouse aortic endothelium. Running exercise and simvastatin treatment induce endothelial KLF2 expression in db/db mice. Adenovirus-mediated endothelium-specific KLF2 overexpression enhances both endothelium-dependent relaxation and flow-mediated dilatation, while it attenuates oxidative stress in diabetic mouse arteries. KLF2 overexpression increases the phosphorylation of eNOS at serine 1177 and eNOS dimerization. RNA-sequencing analysis reveals that KLF2 transcriptionally upregulates genes that are enriched in the cyclic guanosine monophosphate-protein kinase G-signaling pathway, cAMP-signaling pathway, and insulin-signaling pathway, all of which are the upstream regulators of eNOS activity. Activation of the phosphoinositide 3-kinase-Akt pathway and Hsp90 contributes to KLF2-induced increase of eNOS activity. The present results suggest that approaches inducing KLF2 activation, such as physical exercise, are effective to restore eNOS activity against diabetic endothelial dysfunction.

ARTICLE HIGHLIGHTS

Exercise and statins restore the endothelial expression of Krüppel-like factor 2 (KLF2), which is diminished in diabetic db/db mice. Endothelium-specific overexpression of KLF2 improves endothelium-dependent relaxation and flow-mediated dilation through increasing nitric oxide bioavailability. KLF2 promotes endothelial nitric oxide synthase (eNOS) coupling and phosphorylation in addition to its known role in eNOS transcription. KLF2 upregulates the expression of several panels of genes that regulate eNOS activity.

Activation of Coronary Arteriolar PKCβ2 Impairs Endothelial NO-Mediated Vasodilation: Role of JNK/Rho Kinase Signaling and Xanthine Oxidase Activation

Protein kinase C (PKC) activation can evoke vasoconstriction and contribute to coronary disease. However, it is unclear whether PKC activation, without activating the contractile machinery, can lead to coronary arteriolar dysfunction. The vasoconstriction induced by the PKC activator phorbol 12,13-dibutyrate (PDBu) was examined in isolated porcine coronary arterioles. The PDBu-evoked vasoconstriction was sensitive to a broad-spectrum PKC inhibitor but not affected by inhibiting PKCβ2 or Rho kinase. After exposure of the vessels to a sub-vasomotor concentration of PDBu (1 nmol/L, 60 min), the endothelium-dependent nitric oxide (NO)-mediated dilations in response to serotonin and adenosine were compromised but the dilation induced by the NO donor sodium nitroprusside was unaltered. PDBu elevated superoxide production, which was blocked by the superoxide scavenger Tempol. The impaired NO-mediated vasodilations were reversed by Tempol or inhibition of PKCβ2, xanthine oxidase, c-Jun N-terminal kinase (JNK) and Rho kinase but were not affected by a hydrogen peroxide scavenger or inhibitors of NAD(P)H oxidase and p38 kinase. The PKCβ2 protein was detected in the arteriolar wall and co-localized with endothelial NO synthase. In conclusion, activation of PKCβ2 appears to compromise NO-mediated vasodilation via Rho kinase-mediated JNK signaling and superoxide production from xanthine oxidase, independent of the activation of the smooth muscle contractile machinery.

Vasodilation and blood pressure-lowering effect mediated by 5,6-EEQ lactone in 5/6 nephrectomy hypertensive rats

Microvascular dysfunction is a key contributor to vascular hypertension, one of the most common chronic diseases in the world. Microvascular dysfunction leads to the loss of nitric oxide-mediated endothelial dilation and the subsequent compensatory function of endothelium-derived hyperpolarizing (EDH) factors in the regulation of vascular tone. Previously, we showed that lactone metabolite derived from arachidonic acid induces endothelial-dependent vasodilation in isolated human microvessels. Based on structural similarities, we hypothesize that additional lactone metabolites formed from eicosapentaenoic fatty acid (EPA) may bear EDH properties.

AIM

To elucidate the vasodilatory and blood pressure (BP)-reducing characteristics of the 5,6-EEQ (5,6-epoxyeicosatetraenoic acids) lactone (EPA-L) in hypertensive 5/6 nephrectomy (5/6Nx) rats.

METHODS

5/6Nx hypertensive rats intravenously administrated with EPA-L for five days. BP, blood and urine chemistry, and kidney function were detected and analyzed. Vascular dilation was detected using a pressure myograph with or without Ca²⁺ - activated K⁺ (K_Ca) endothelial channel inhibitors. KCNN3 and KCNN4 gene expression (mRNA) detected in mesenteric arteries from 5/6Nx and NT rats.

RESULTS

EPA-L administration to 5/6Nx rats significantly (p < 0.05) reduced BP and heart rate without affecting kidney function. 5/6Nx rat mesenteric arterioles exhibited a lower dilation response to acetylcholine (10^-7 mol/l) than normotensive (NT) vessels, while EPA-L administration restored the vessel relaxation response. The EPA-L-driven relaxation of mesenteric arteries was significantly reduced by pretreatment with TRAM-34 and apamin. However, K_Ca channel expression did not significantly differ between 5/6Nx and NT mesenteric arteries.

CONCLUSION

EPA-L reduces BP by improving microvessel dilation involving calcium-dependent potassium endothelial channels.

Red Blood Cell-Mediated S-Nitrosohemoglobin-Dependent Vasodilation: Lessons Learned from a β-Globin Cys93 Knock-In Mouse

Significance: Red blood cell (RBC)-mediated vasodilation plays an important role in oxygen delivery. This occurs through hemoglobin actions, at least in significant part, to convert heme-bound nitric oxide (NO) (in tense [T]/deoxygenated-state hemoglobin) into vasodilator S-nitrosothiol (SNO) (in relaxed [R]/oxygenated-state hemoglobin), convey SNO through the bloodstream, and release it into tissues to increase blood flow. The coupling of hemoglobin R/T state allostery, both to NO conversion into SNO and to SNO release (along with oxygen), under hypoxia supports the model of a three-gas respiratory cycle (O2/NO/CO2). Recent Advances: Oxygenation of tissues is dependent on a single, strictly conserved Cys residue in hemoglobin (βCys93). Hemoglobin couples SNO formation/release at βCys93 to O2 binding/release at hemes ("thermodynamic linkage"). Mice bearing βCys93Ala hemoglobin that is unable to generate SNO-βCys93 establish that SNO-hemoglobin is important for R/T allostery-regulated vasodilation by RBCs that couple blood flow to tissue oxygenation. Critical Issues: The model for RBC-mediated vasodilation originally proposed by Stamler et al. in 1996 has been largely validated: SNO-βCys93 forms in vivo, dilates blood vessels, and is hypoxia-regulated, and RBCs actuate vasodilation proportionate to hypoxia. Numerous compensations in βCys93Ala animals to alleviate tissue hypoxia (discussed herein) are predicted to preserve vasodilatory responses of RBCs but impair linkage to R/T transition in hemoglobin. This is borne out by loss of responsivity of mutant RBCs to oxygen, impaired blood flow responses to hypoxia, and tissue ischemia in βCys93-mutant animals. Future Directions: SNO-hemoglobin mediates hypoxic vasodilation in the respiratory cycle. This fundamental physiology promises new insights in vascular diseases and blood disorders.

PTPRG is an ischemia risk locus essential for HCO3--dependent regulation of endothelial function and tissue perfusion

Acid-base conditions modify artery tone and tissue perfusion but the involved vascular-sensing mechanisms and disease consequences remain unclear. We experimentally investigated transgenic mice and performed genetic studies in a UK-based human cohort. We show that endothelial cells express the putative HCO3--sensor receptor-type tyrosine-protein phosphatase RPTPγ, which enhances endothelial intracellular Ca2+-responses in resistance arteries and facilitates endothelium-dependent vasorelaxation only when CO2/HCO3- is present. Consistent with waning RPTPγ-dependent vasorelaxation at low [HCO3-], RPTPγ limits increases in cerebral perfusion during neuronal activity and augments decreases in cerebral perfusion during hyperventilation. RPTPγ does not influence resting blood pressure but amplifies hyperventilation-induced blood pressure elevations. Loss-of-function variants in PTPRG, encoding RPTPγ, are associated with increased risk of cerebral infarction, heart attack, and reduced cardiac ejection fraction. We conclude that PTPRG is an ischemia susceptibility locus; and RPTPγ-dependent sensing of HCO3- adjusts endothelium-mediated vasorelaxation, microvascular perfusion, and blood pressure during acid-base disturbances and altered tissue metabolism.

The protective role of calcitonin gene-related peptide (CGRP) in high-glucose-induced oxidative injury in rat aorta endothelial cells

Endothelial dysfunction is considered to be an initial indicator in diabetes-induced macrovascular complications. Evidence has shown that CGRP is an important neuropeptide active in vascular system, especially in vasorelaxation. This study aimed to investigate the role of CGRP in high-glucose-induced endothelial dysfunction in rat aorta endothelial cells (RAECs). Quantitative-real time PCR and western blots were used to determine the efficiency of overexpression and interference of CGRP. After incubation with normal glucose (5.5 mM) or high glucose (33 mM), the cell viability and cell apoptosis were tested. Afterwards, the Nitric Oxide (NO) production, the mRNA expression of inducible nitric oxide synthase (iNOS), endothelial nitric oxide synthase (eNOS) and angiotensin II (Ang II) and the level of reactive oxygen species (ROS) were determined. The involvement of ERK1/2-NOX4 was determined through western blots and the translocation of p47phox was also observed via cell immunofluorescence. CGRP alleviated the high-glucose-induced cell apoptosis while CGRP did not have an obvious impact on cell viability. Meanwhile, CGRP increased the NO production as well as the eNOS mRNA expression and reversely decreased the stimulated expression of iNOS and Ang II by high glucose. In addition, CGRP attenuated the high-glucose-stimulated intracellular ROS production by ERK1/2-NOX4 and the translocation of p47phox. These results indicated the protective role of CGRP in high-glucose-induced oxidative injury in RAECs possibly through inhibiting ERK1/2-NOX4. Our findings might help to further understand the potential role and possible mechanism of CGRP in endothelial dysfunction caused by high glucose.

The pregnane X receptor and its microbiota-derived ligand indole 3-propionic acid regulate endothelium-dependent vasodilation

We proposed that circulating metabolites generated by the intestinal microbiota can affect vascular function. One such metabolite, indole 3-propionic acid (IPA), can activate the pregnane X receptor(PXR), a xenobiotic-activated nuclear receptor present in many tissues, including the vascular endothelium. We hypothesized that IPA could regulate vascular function by modulating PXR activity. To test this, Pxr^+/+ mice were administered broad-spectrum antibiotics for 2 wk with IPA supplementation. Vascular function was evaluated by bioassay using aorta and pulmonary artery ring tissue from antibiotic-treated Pxr^+/+ and Pxr^-/-mice, supplemented with IPA, and using aorta tissue maintained in organ culture for 24 h in the presence of IPA. Endothelium-dependent, nitric oxide(NO)-mediated muscarinic and proteinase-activated receptor 2(PAR2)-stimulated vasodilation was assessed. Endothelial nitric oxide synthase (eNOS) abundance was evaluated in intact tissue or in aorta-derived endothelial cell cultures from Pxr^+/+ and Pxr^-/- mice, and vascular Pxr levels were assessed in tissues obtained from Pxr^+/+ mice treated with antibiotics and supplemented with IPA. Antibiotic-treated Pxr^+/+ mice exhibited enhanced agonist-induced endothelium-dependent vasodilation, which was phenocopied by tissues from either Pxr^-/- or germ-free mice. IPA exposure reduced the vasodilatory responses in isolated and cultured vessels. No effects of IPA were observed for tissues obtained from Pxr^-/- mice. Serum nitrate levels were increased in antibiotic-treated Pxr^+/+and Pxr^-/- mice. eNOS abundance was increased in aorta tissues and cultured endothelium from Pxr^-/- mice. PXR stimulation reduced eNOS expression in cultured endothelial cells from Pxr^+/+ but not Pxr^-/- mice. The microbial metabolite IPA, via the PXR, plays a key role in regulating endothelial function. Furthermore, antibiotic treatment changes PXR-mediated vascular endothelial responsiveness by upregulating eNOS.

TRAIL protects against endothelial dysfunction in vivo and inhibits angiotensin-II-induced oxidative stress in vascular endothelial cells in vitro

The vascular endothelium is critical for maintenance of cardiovascular homeostasis. Endothelial dysfunction is a key event of atherosclerosis, with oxidative stress mediated by reactive oxygen species (ROS) playing a major role. Tumour necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL) is increasingly recognised to play a protective role in atherosclerosis, however the molecular mechanisms by which it exerts its beneficial effects are unclear. Here we examined if TRAIL could attenuate vascular oxidative stress and improve endothelial cell (EC) function. In coronary artery disease patients, plasma TRAIL levels were significantly reduced compared to healthy individuals, and negatively correlated with the levels of circulating 8-iso Prostaglandin F_2α, a marker of in vivo oxidative stress. In vivo, high-fat fed, atherosclerotic Trail^-/-Apoe^-/- mice exhibited a significant impairment in endothelial-dependent vasorelaxation, which correlated with increased vascular ROS and 4-hydroxynonenal compared to Apoe^-/- mice. Endothelial permeability measured by Evan's blue dye extravasation was increased in several organs of Trail^-/- mice compared to wild-type mice, which correlated with a decrease in VE-cadherin expression. In vitro in ECs, angiotensin II (AngII)-induced ROS generation involving the mitochondria, NADPH oxidase-4 (NOX-4) and eNOS, was inhibited by pre-treatment with TRAIL. Furthermore, AngII-augmented VCAM-1 expression and monocyte adhesion to ECs was inhibited by TRAIL. Finally, AngII reduced VE-cadherin expression and redistributed this protein, all of which was brought back to baseline by TRAIL pre-treatment. These findings demonstrate for the first time that TRAIL protects against several forms of endothelial dysfunction involving its ability to control EC ROS generation. Understanding the role TRAIL plays in normal physiology and disease, may lead to potential new therapies to improve endothelial function and atherosclerosis.

The Role of Midkine in Arteriogenesis, Involving Mechanosensing, Endothelial Cell Proliferation, and Vasodilation

Mechanical forces in blood circulation such as shear stress play a predominant role in many physiological and pathophysiological processes related to vascular responses or vessel remodeling. Arteriogenesis, defined as the growth of pre-existing arterioles into functional collateral arteries compensating for stenosed or occluded arteries, is such a process. Midkine, a pleiotropic protein and growth factor, has originally been identified to orchestrate embryonic development. In the adult organism its expression is restricted to distinct tissues (including tumors), whereby midkine is strongly expressed in inflamed tissue and has been shown to promote inflammation. Recent investigations conferred midkine an important function in vascular remodeling and growth. In this review, we introduce the midkine gene and protein along with its cognate receptors, and highlight its role in inflammation and the vascular system with special emphasis on arteriogenesis, particularly focusing on shear stress-mediated vascular cell proliferation and vasodilatation.

Endothelial Insulin Receptor Restoration Rescues Vascular Function in Male Insulin Receptor Haploinsufficient Mice

Reduced systemic insulin signaling promotes endothelial dysfunction and diminished endogenous vascular repair. We investigated whether restoration of endothelial insulin receptor expression could rescue this phenotype. Insulin receptor knockout (IRKO) mice were crossed with mice expressing a human insulin receptor endothelial cell-specific overexpression (hIRECO) to produce IRKO-hIRECO progeny. No metabolic differences were noted between IRKO and IRKO-hIRECO mice in glucose and insulin tolerance tests. In contrast with control IRKO littermates, IRKO-hIRECO mice exhibited normal blood pressure and aortic vasodilatation in response to acetylcholine, comparable to parameters noted in wild type littermates. These phenotypic changes were associated with increased basal- and insulin-stimulated nitric oxide production. IRKO-hIRECO mice also demonstrated normalized endothelial repair after denuding arterial injury, which was associated with rescued endothelial cell migration in vitro but not with changes in circulating progenitor populations or culture-derived myeloid angiogenic cells. These data show that restoration of endothelial insulin receptor expression alone is sufficient to prevent the vascular dysfunction caused by systemically reduced insulin signaling.

The activation of G protein-coupled estrogen receptor induces relaxation via cAMP as well as potentiates contraction via EGFR transactivation in porcine coronary arteries

Estrogen exerts protective effects against cardiovascular diseases in premenopausal women, but is associated with an increased risk of both coronary heart disease and stroke in older postmenopausal women. Studies have shown that activation of the G-protein-coupled estrogen receptor 1 (GPER) can cause either relaxation or contraction of arteries. It is highly likely that these dual actions of GPER may contribute to the seemingly paradoxical effects of estrogen in regulating coronary artery function. The objective of this study was to test the hypothesis that activation of GPER enhances agonist-stimulated porcine coronary artery contraction via epidermal growth factor receptor (EGFR) transactivation and its downstream extracellular signal-regulated kinases (ERK1/2) pathway. Isometric tension studies and western blot were performed to determine the effect of GPER activation on coronary artery contraction. Our findings demonstrated that G-1 caused concentration-dependent relaxation of ET-1-induced contraction, while pretreatment of arterial rings with G-1 significantly enhanced ET-1-induced contraction. GPER antagonist, G-36, significantly inhibited both the G-1-induced relaxation effect and G-1-enhanced ET-1 contraction. Gallein, a Gβγ inhibitor, significantly increased G-1-induced relaxation, yet inhibited G-1-enhanced ET-1-mediated contraction. Similarly, inhibition of EGFR with AG1478 or inhibition of Src with phosphatase 2 further increased G-1-induced relaxation responses in coronary arteries, but decreased G-1-enhanced ET-1-induced contraction. Western blot experiments in porcine coronary artery smooth muscle cells (PCASMC) showed that G-1 increased tyrosine phosphorylation of EGFR, which was inhibited by AG-1478. Furthermore, enzyme-linked immunosorbent assays showed that the level of heparin-binding EGF (HB-EGF) released by ET-1 treatment increased two-fold; whereas pre-incubation with G-1 further increased ET-1-induced HB-EGF release to four-fold over control conditions. Lastly, the role of ERK1/2 was determined by applying the MEK inhibitor, PD98059, in isometric tension studies and detecting phospho-ERK1/2 in immunoblotting. PD98059 potentiated G-1-induced relaxation response, but blocked G-1-enhanced ET-1-induced contraction. By western blot, G-1 treatment decreased phospho-ERK1/2, however, in the presence of the adenylyl cyclase inhibitor, SQ22536, G-1 significantly increased ERK1/2 phosphorylation in PCASMC. These data demonstrate that activation of GPER induces relaxation via cAMP as well as contraction via a mechanism involving transactivation of EGFR and the phosphorylation of ERK1/2 in porcine coronary arteries.

Melatonin mediates vasodilation through both direct and indirect activation of BKCa channels

Melatonin, synthesized primarily by the pineal gland, is a neuroendocrine hormone with high membrane permeability. The vascular effects of melatonin, including vasoconstriction and vasodilation, have been demonstrated in numerous studies. However, the mechanisms underlying these effects are not fully understood. Large-conductance Ca²⁺-activated K⁺ (BK_Ca) channels are expressed broadly on smooth muscle cells and play an important role in vascular tone regulation. This study explored the mechanisms of myocyte BK_Ca channels and endothelial factors underlying the action of melatonin on the mesenteric arteries (MAs). Vascular contractility and patch-clamp studies were performed on myocytes of MAs from Wistar rats. Melatonin induced significant vasodilation on MAs. In the presence of N^ω-nitro-l-arginine methyl ester (l-NAME), a potent endothelial oxide synthase (eNOS) inhibitor, melatonin elicited concentration-dependent relaxation, with lowered pIC₅₀ The effect of melatonin was significantly attenuated in the presence of BK_Ca channel blocker iberiotoxin or MT1/MT2 receptor antagonist luzindole in both (+) l-NAME and (-) l-NAME groups. In the (+) l-NAME group, iberiotoxin caused a parallel rightward shift of the melatonin concentration-relaxation curve, with pIC₅₀ lower than that of luzindole. Both inside-out and cell-attached patch-clamp recordings showed that melatonin significantly increased the open probability, mean open time and voltage sensitivity of BK_Ca channels. In a cell-attached patch-clamp configuration, the melatonin-induced enhancement of BK_Ca channel activity was significantly suppressed by luzindole. These findings indicate that in addition to the activation of eNOS, melatonin-induced vasorelaxation of MAs is partially attributable to its direct (passing through the cell membrane) and indirect (via MT1/MT2 receptors) activation of the BK_Ca channels on mesenteric arterial myocytes.

Berberine reduced blood pressure and improved vasodilation in diabetic rats

Hyperglycemia and hypertension are considered to be the two leading risk factors for vascular disease in diabetic patients. However, few pharmacologic agents could provide a combinational therapy for controlling hyperglycemia and hypertension at the same time in diabetes. The objectives of this study are to investigate whether berberine treatment could directly reduce blood pressure and identify the molecular mechanism underlying the vascular protection of berberine in diabetic rats. Berberine was intragastrically administered with different dosages of 50, 100 and 200 mg/kg/day to diabetic rats for 8 weeks since the injection of streptozotocin. The endothelium-dependent/-independent relaxation in middle cerebral arteries was investigated. The activity of large-conductance Ca²⁺-activated K⁺ channel (BK_Ca) was investigated by recording whole-cell currents, analyzing single-channel activities and assessing the expressions of α- and β1-subunit at protein or mRNA levels. Results of the study suggest that chronic administration of 100 mg/kg/day berberine not only lowered blood glucose but also reduced blood pressure and improved vasodilation in diabetic rats. Furthermore, berberine markedly increased the function and expression of BK_Ca β1-subunit in cerebral vascular smooth muscle cells (VSMCs) isolated from diabetic rats or when exposed to hyperglycemia condition. The present study provided initial evidences that berberine reduced blood pressure and improved vasodilation in diabetic rats by activation of BK_Ca channel in VSMCs, which suggested that berberine might provide a combinational therapy for controlling hyperglycemia and blood pressure in diabetes. Furthermore, our work indicated that activation of BK_Ca channel might be the underlying mechanism responsible for the vascular protection of berberine in diabetes.

Compensatory Vasodilator Mechanisms in the Ophthalmic Artery of Endothelial Nitric Oxide Synthase Gene Knockout Mice

Nitric oxide (NO) generated by endothelial nitric oxide synthase (eNOS) plays an important role in the maintenance of ocular vascular homeostasis. Therefore, perturbations in vascular NO synthesis have been implicated in the pathogenesis of several ocular diseases. We recently reported that eNOS contributes significantly to vasodilation of the mouse ophthalmic artery. Interestingly, dilatory responses were also retained in eNOS gene-deficient mice (eNOS-/-), indicating inherent endothelial adaptive mechanism(s) that act as back-up systems in chronic absence of eNOS to preserve vasorelaxation. Thus, this study endeavoured to identify the compensatory mechanism(s) in the ophthalmic artery of eNOS-/- mice employing isolated arterial segments and pharmacological inhibitors in vitro. Endothelium removal virtually abolished acetylcholine (ACh)-induced vasodilation, suggesting an obligatory involvement of the endothelium in cholinergic control of vascular tone. However, non-NOS and non-cyclooxygenase components compensate for eNOS deficiency via endothelium-derived hyperpolarizing factors (EDHFs). Notably, arachidonic acid-derived metabolites of the 12-lipoxygenase pathway were key mediators in activating the inwardly rectifying potassium channels to compensate for chronic lack of eNOS. Conclusively, endothelium-dependent cholinergic responses of the ophthalmic artery in the eNOS-/- mice are largely preserved and, this vascular bed has the ability to compensate for the loss of normal vasodilator responses solely via EDHFs.

Absence of Endothelial ERα Results in Arterial Remodeling and Decreased Stiffness in Western Diet-Fed Male Mice

The role of estrogen receptor-α (ERα) signaling in the vasculature of females has been described under different experimental conditions and our group recently reported that lack of endothelial cell (EC) ERα in female mice fed a Western diet (WD) results in amelioration of vascular stiffness. Conversely, the role of ERα in the male vasculature in this setting has not been explored. In conditions of overnutrition and insulin resistance, augmented arterial stiffness, endothelial dysfunction, and arterial remodeling contribute to the development of cardiovascular disease. Here, we used a rodent model of decreased ERα expression in ECs [endothelial cell estrogen receptor-α knockout (EC-ERαKO)] to test the hypothesis that, similar to our findings in females, loss of ERα signaling in the endothelium of insulin-resistant males would result in decreased arterial stiffness. EC-ERαKO male mice and same-sex littermates were fed a WD (high in fructose and fat) for 20 weeks and then assessed for vascular function and stiffness. EC-ERαKO mice were heavier than littermates but exhibited decreased vascular stiffness without differences in endothelial-dependent vasodilatory responses. Mesenteric arteries from EC-ERαKO mice had significantly increased diameters, wall cross-sectional areas, and mean wall thicknesses, indicative of outward hypertrophic remodeling. This remodeling paralleled an increased vessel wall content of collagen and elastin, inhibition of matrix metalloproteinase activation and a decrease of the incremental modulus of elasticity. In addition, internal elastic lamina fenestrae were more abundant in the EC-ERαKO mice. In conclusion, loss of endothelial ERα reduces vascular stiffness in male mice fed a WD with an associated outward hypertrophic remodeling of resistance arteries.

Angiotensin-(1-7)-dependent vasorelaxation of the renal artery exhibits unique angiotensin and bradykinin receptor selectivity

Angiotensin-(1-7) [Ang-(1-7)] exhibits blood pressure lowering actions, inhibits cell growth, and reduces tissue inflammation and fibrosis which may functionally antagonize an activated Ang II-AT₁ receptor axis. Since the vascular actions of Ang-(1-7) and the associated receptor/signaling pathways vary in different vascular beds, the current study established the vasorelaxant properties of the heptapeptide in the renal artery of male Wistar male rats. Ang-(1-7) produced an endothelium-dependent vasodilator relaxation of isolated renal artery segments pre-contracted by a sub-maximal concentration of phenylephrine (PE) (3×10^-7M). Ang-(1-7) induced vasodilation of the rat renal artery with an ED₅₀ of 3±1nM and a maximal response of 42±5% (N=10). The two antagonists (10^-5M each) for the AT₇/Mas receptor (MasR) [D-Pro⁷]-Ang-(1-7) and [D-Ala⁷]-Ang-(1-7) significantly reduced the maximal response to 12±1% and 18±3%, respectively. Surprisingly, the AT₂R receptor antagonist PD123319, the AT₁R antagonist losartan and B₂R antagonist HOE140 (10^-6M each) also significantly reduced Ang-(1-7)-induced relaxation to 12±2%, 22±3% and 14±7%, respectively. Removal of the endothelium or addition of the soluble guanylate cyclase (sGC) inhibitor ODQ (10^-5M) essentially abolished the vasorelaxant response to Ang-(1-7) (10±4% and 10±2%, P <0.05). Finally, the NOS inhibitor LNAME (10^-4M) reduced the response to 13±2% (p<0.05), but the cyclooxygenase inhibitor indomethacin failed to block the Ang-(1-7) response. We conclude that Ang-(1-7) exhibits potent vasorelaxant actions in the isolated renal artery that are dependent on an intact endothelium and the apparent stimulation of a NO-sGC pathway. Moreover, Ang-(1-7)-dependent vasorelaxation was sensitive to antagonists against the AT₇/Mas, AT₁, AT₂ and B₂ receptor subtypes.

PPARδ Is Required for Exercise to Attenuate Endoplasmic Reticulum Stress and Endothelial Dysfunction in Diabetic Mice

Physical activity has profound benefits on health, especially on cardiometabolic wellness. Experiments in rodents with trained exercise have shown that exercise improves vascular function and reduces vascular inflammation by modulating the balance between nitric oxide (NO) and oxidative stress. However, the upstream regulator of exercise-induced vascular benefits is unclear. We aimed to investigate the involvement of peroxisome proliferator-activated receptor δ (PPARδ) in exercise-induced vascular functional improvement. We show that PPARδ is a crucial mediator for exercise to exert a beneficial effect on the vascular endothelium in diabetic mice. In db/db mice and high-fat diet-induced obese mice, 4 weeks of treadmill exercise restored endothelium-dependent vasodilation of aortas and flow-mediated vasodilation in mesenteric resistance arteries, whereas genetic ablation of Ppard abolished such improvements. Exercise induces AMPK activation and subsequent PPARδ activation, which help to reduce endoplasmic reticulum (ER) and oxidative stress, thus increasing NO bioavailability in endothelial cells and vascular tissues. Chemical chaperones 4-phenylbutyric acid and tauroursodeoxycholic acid decrease ER stress and protect against endothelial dysfunction in diabetic mice. The results demonstrate that PPARδ-mediated inhibition of ER stress contributes to the vascular benefits of exercise and provides potentially effective targets for treating diabetic vasculopathy.

A Common CD36 Variant Influences Endothelial Function and Response to Treatment with Phosphodiesterase 5 Inhibition

CONTEXT

The scavenger receptor CD36 influences the endothelial nitric oxide-cGMP pathway in vitro. Genetic variants that alter CD36 level are common in African Americans (AAs), a population at high risk of endothelial dysfunction.

OBJECTIVE

To examine if the minor allele (G) of coding CD36 variant rs3211938 (G/T) which reduces CD36 level by approximately 50% influences endothelial function, insulin sensitivity (IS), and the response to treatment with the nitric oxide-cGMP potentiator sildenafil.

DESIGN

IS (frequently sampled iv glucose tolerance) and endothelial function (flow mediated dilation [FMD]) were determined in age- and body mass index-matched obese AA women with or without the G allele of rs3211938 (protocol 1). Effect of chronic sildenafil treatment on IS and FMD was tested in AA women with metabolic syndrome and with/without the CD36 variant, using a randomized, placebo-controlled trial (protocol 2).

SETTING

Two-center study.

PARTICIPANTS

Obese AA women.

INTERVENTION

A total of 20-mg sildenafil citrate or placebo thrice daily for 4 weeks.

MAIN OUTCOME

IS, FMD.

RESULTS

G allele carriers have lower FMD (P = .03) and cGMP levels (P = .01) than noncarriers. Sildenafil did not improve IS, mean difference 0.12 (95% confidence interval [CI], -0.33 to 0.58; P = .550). However, there was a significant interaction between FMD response to sildenafil and rs3211938 (P = .018). FMD tended to improve in G carriers, 2.9 (95% CI, -0.9 to 6.8; P = .126), whereas it deteriorated in noncarriers, -2.6 (95% CI, -5.1 to -0.1; P = .04).

CONCLUSIONS

The data document influence of a common genetic variant on susceptibility to endothelial dysfunction and its response to sildenafil treatment.

Functional inhibition of urea transporter UT-B enhances endothelial-dependent vasodilatation and lowers blood pressure via L-arginine-endothelial nitric oxide synthase-nitric oxide pathway

Mammalian urea transporters (UTs), UT-A and UT-B, are best known for their role in urine concentration. UT-B is especially distributed in multiple extrarenal tissues with abundant expression in vascular endothelium, but little is known about its role in vascular function. The present study investigated the physiological significance of UT-B in regulating vasorelaxations and blood pressure. UT-B deletion in mice or treatment with UT-B inhibitor PU-14 in Wistar-Kyoto rats (WKYs) and spontaneous hypertensive rats (SHRs) reduced blood pressure. Acetylcholine-induced vasorelaxation was significantly augmented in aortas from UT-B null mice. PU-14 concentration-dependently produced endothelium-dependent relaxations in thoracic aortas and mesenteric arteries from both mice and rats and the relaxations were abolished by N(ω)-nitro-L-arginine methyl ester. Both expression and phosphorylation of endothelial nitric oxide synthase (eNOS) were up-regulated and expression of arginase I was down-regulated when UT-B was inhibited both in vivo and in vitro. PU-14 induced endothelium-dependent relaxations to a similar degree in aortas from 12 weeks old SHRs or WKYs. In summary, here we report for the first time that inhibition of UT-B plays an important role in regulating vasorelaxations and blood pressure via up-regulation of L-arginine-eNOS-NO pathway, and it may become another potential therapeutic target for the treatment of hypertension.

Influence of Electroacupuncture Stimulation on Nitric Monoxide Production in Vascular Endothelial Cells in Rats

BACKGROUND/AIM

In Chinese medicine, blood stasis termed as 'Oketsu' means 'preceding state' or 'symptomatic of sickness'. Traditional Chinese medicine may improve blood flow by vasodilation or blood clotting inhibition. Although acupuncture influences the blood circulatory system, its underlying mechanisms remain unclear. Herein we evaluated changes in NO, as reflected by changes in NO2 (-), platelet aggregation, oxidative stress and endocrine responses after acupuncture stimulation in rats.

MATERIALS AND METHODS

Acupuncture stimulation was administered to rats randomly divided into five groups: control, N(G)-nitro-L-arginine methyl ester hydrochloride (L-NAME) injection, restraint stress (RS), restraint plus acupuncture stimulation (RA), and restraint plus acupuncture with L-NAME (RLA).

RESULTS

Compared to those in the RS group, levels of NO2 (-), endothelial nitric oxide synthase (NOS) protein and its mRNA significantly increased and those of hydroperoxide and soluble P-selectin significantly decreased in the RA group.

CONCLUSION

Acupuncture stimulation regulates vascular endothelium NOS function and affects vascular resistance and blood characteristics through NO. Additionally, NO produced may modulate excessive reactive oxygen development and blood platelet activation.

Toll-like receptor 4-induced endoplasmic reticulum stress contributes to impairment of vasodilator action of insulin

Impairment of vasodilator action of insulin is associated with endothelial dysfunction and insulin resistance. Activation of Toll-like receptor 4 (TLR4) induces proinflammatory response and endoplasmic reticulum (ER) stress. Saturated fatty acids (SFA) activate TLR4, which induces ER stress and endothelial dysfunction. Therefore, we determined whether TLR4-mediated ER stress is an obligatory step mediating SFA-induced endothelial dysfunction. Palmitate stimulated proinflammatory responses and ER stress, and this was suppressed by knockdown of TLR4 in primary human aortic endothelial cells (HAEC). Next, we examined the role of TLR4 in vasodilatory responses in intact vessels isolated from wild-type (WT, C57BL/6) and TLR4-KO mice after feeding high-fat (HFD) or normal chow diet (NCD) for 12 wk. Arterioles isolated from HFD WT mice exhibited impaired insulin-stimulated vasodilation compared with arterioles isolated from NCD WT mice. Deficiency of TLR4 was protective from HFD-induced impairment of insulin-stimulated vasodilation. There were no differences in acetylcholine (Ach)- or sodium nitroprusside (SNP)-stimulated vasodilation between the two groups. Furthermore, we examined whether ER stress is involved in SFA-induced impairment of vasodilator actions of insulin. Infusion of palmitate showed the impairment of vasodilatory response to insulin, which was ameliorated by coinfusion with tauroursodeoxycholic acid (TUDCA), an ER stress suppressor. Taken together, the results suggest that TLR4-induced ER stress may be an obligatory step mediating the SFA-mediated endothelial dysfunction.

Angiotensin type 1 receptor A1166C gene polymorphism is associated with endothelial dysfunction and in-stent restenosis after percutaneous coronary intervention

BACKGROUND AND PURPOSE

Percutaneous coronary intervention (PCI) has been commonly used in the treatment of ischemic cardiovascular diseases, but the postprocedural in-stent restenosis (ISR) associated with altered endothelial functions has limited the clinical application of it; preventive medication with aspirin and statins has underlying adverse effects despite lowered risk of ISR. The purpose of this study was to investigate the role of angiotensin type 1 receptor (AT1R) A1166C gene polymorphisms in the development of endothelial dysfunction and ISR after PCI.

METHODS

A total of 483 ST-segment elevation myocardial infarction (STEMI) patients undergoing PCI were prospectively genotyped using polymerase chain reaction (PCR) and restriction fragment length polymorphism assay. The demographic, clinical, laboratory and angiographic parameters were recorded peri-procedurally and the patients were followed within 3 years. The flow-mediated dilation (FMD) was used to reflect the short-term changes in endothelial functions among different genotypes. The significance of AT1R gene polymorphisms in the development of ISR was analyzed using univariable and multivariable models.

RESULTS

Amongst 483 patients, the distribution of the AT1R genotypes (AA, AC and CC) was associated with the levels of blood biomarkers of oxidative stress and deteriorated FMD after PCI (P<0.05). In univariable and multivariable logistic regression analysis, it was shown that AT1R CC genotype is strongly associated with the development of restenosis within 3 years after PCI (OR=3.736; P<0.001; calibrated OR=4.104; P<0.001).

CONCLUSION

The CC AT1R genotype was associated with deteriorated endothelial functions in the target vessels of PCI and intermediate to long-term ISR. Our findings contribute to the foundation of genome-based prevention for high risk groups of cardiovascular diseases and pretreatment for the patients undergoing PCI.

Interactions between the genes of vasodilatation pathways influence blood pressure and nitric oxide level in hypertension

BACKGROUND

This study investigates the contribution of genetic interactions between the β-2 adrenergic receptor (ADRB2) and nitric oxide synthase (NOS3) genes to the complex etiology of hypertension.

METHODS

Using single nucleotide polymorphism (SNP) markers, we studied potential interactions between ADRB2 and NOS3 variants and their correlation with clinical, biochemical, and expression levels in 546 individuals with hypertension and 884 age-, sex-, and ethnicity-matched unrelated control subjects. Generalized multifactor dimensionality reduction (GMDR) analysis identified the models for genotype interaction.

RESULTS

The best models to represent association of genotypes with augmented hypertension susceptibility were the 4- and 5-locus interacting GMDR models of ADRB2 and NOS3 compared with within-gene 6-locus ADRB2 and 2-locus NOS3 (odds ratio (OR) = 4.8, P = 0.04; OR = 5.6, P = 0.02, respectively). Stratification of 4- and 5-locus GMDR models on the basis of risk alleles (in increasing order) increased the ORs from 1.26 to 14.17 and from 0.81 to 14.18, respectively, and correlated linearly with increased systolic blood pressure, diastolic blood pressure, and mean arterial pressure and decreased nitric oxide level (P ≤ 0.0004). We performed various analyses, such as single-locus, genetic interactions, sliding-window, and comparative analysis. Each analysis consistently revealed the 46A allele of ADRB2 46G/A SNP and 4a allele of NOS3 4b/4a SNP to be associated with risk of hypertension. These risk-conferring markers were associated with decreased ADRB2 and NOS3 expression and decreased nitric oxide level in the patients (P ≤ 0.04).

CONCLUSIONS

Evidence of interaction between the genetic loci of ADRB2 and NOS3 points to varied clinical, biochemical, and expression levels and a role in hypertension susceptibility.

FGF23 directly impairs endothelium-dependent vasorelaxation by increasing superoxide levels and reducing nitric oxide bioavailability

Fibroblast growth factor 23 (FGF23) is secreted primarily by osteocytes and regulates phosphate and vitamin D metabolism. Elevated levels of FGF23 are clinically associated with endothelial dysfunction and arterial stiffness in chronic kidney disease (CKD) patients; however, the direct effects of FGF23 on endothelial function are unknown. We hypothesized that FGF23 directly impairs endothelial vasorelaxation by hindering nitric oxide (NO) bioavailability. We detected expression of all four subtypes of FGF receptors (Fgfr1-4) in male mouse aortas. Exogenous FGF23 (90-9,000 pg/ml) did not induce contraction of aortic rings and did not relax rings precontracted with PGF2α. However, preincubation with FGF23 (9,000 pg/ml) caused a ∼36% inhibition of endothelium-dependent relaxation elicited by acetylcholine (ACh) in precontracted aortic rings, which was prevented by the FGFR antagonist PD166866 (50 nM). Furthermore, in FGF23-pretreated (9,000 pg/ml) aortic rings, we found reductions in NO levels. We also investigated an animal model of CKD (Col4a3(-/-) mice) that displays highly elevated serum FGF23 levels and found they had impaired endothelium-dependent vascular relaxation and reduced nitrate production compared with age-matched wild types. To elucidate a mechanism for the FGF23-induced impairment, we measured superoxide levels in endothelial cells and aortic rings and found that they were increased following FGF23 treatment. Crucially, treatment with the superoxide scavenger tiron reduced superoxide levels and also restored aortic relaxation to ACh. Therefore, our data suggest that FGF23 increases superoxide, inhibits NO bioavailability, and causes endothelial dysfunction in mouse aorta. Together, these data provide evidence that high levels of FGF23 contribute to cardiovascular dysfunction.

Endothelial constitutive nitric oxide synthase, angiotensin converting enzyme, angiotensin II type 1 receptor gene polymorphisms and endothelial functions in healthy individuals

INTRODUCTION

Endothelial dysfunction is recognized as an early and initiating event in the pathogenesis of coronary artery disease. Gene polymorphisms of endothelial constitutive nitric oxide synthase (ecNOS), angiotensin converting enzyme (ACE) and angiotensin II type 1 receptor (AT1R) have been found to be associated with atherosclerosis.  We aimed to investigate the possible effects of ecNOS, ACE and AT1R gene polymorphisms on endothelial functions in healthy population.

MATERIALS AND METHODS

In 255 healthy subjects (male/female: 119/136 mean age 35.1±2.3 years)  ecNOS, ACE and AT1R gene polymorphisms were assessed by polymerase chain reaction (PCR). Endothelium dependent (EDD, flow-mediated) and endothelium independent vasodilation (EID) were measured by high resolution brachial artery ultrasound and 0.5 mg sublingual nitroglycerine respectively.

RESULTS

ecNOS and ACE genes had no significant effect on EDD and EID. However, subjects with AT1RAC+CC genotypes had lower EDD compared to subjects with AT1RAA genotype in females (19.4 ± 6.6% vs 21.5 ± 7.8%, p = 0.041). EDD and EID were significantly negatively associated with  age, body mass index, serum creatinine, glucose, uric acid and hemoglobin levels. When the data on age, uric acid, BMI, glucose, creatinine, and hemoglobin were split into 3 as low-1/3, mid-1/3 and  high 1/3, there was significant graded decrease in EDD and EID with these parameters. In multiple regression analysis, age and presence of AT1RAC+CC genotype  retained as significant independent factors predicting endothelial functions.

CONCLUSIONS

Gene polymorphisms of endothelial constitutive nitric oxide synthase and  angiotensin converting enzyme had no effect on endothelial functions. However, the presence of angiotensin II type 1 receptor polymorhism (AT1RAC+CC genotype) seemed to adversely affect the endothelial functions as reflected by impaired endothelium dependent and independent vasodilatation in healthy individuals.

Phosphodiesterase 5 attenuates the vasodilatory response in renovascular hypertension

NO/cGMP signaling plays an important role in vascular relaxation and regulation of blood pressure. The key enzyme in the cascade, the NO-stimulated cGMP-forming guanylyl cyclase exists in two enzymatically indistinguishable isoforms (NO-GC1, NO-GC2) with NO-GC1 being the major NO-GC in the vasculature. Here, we studied the NO/cGMP pathway in renal resistance arteries of NO-GC1 KO mice and its role in renovascular hypertension induced by the 2-kidney-1-clip-operation (2K1C). In the NO-GC1 KOs, relaxation of renal vasculature as determined in isolated perfused kidneys was reduced in accordance with the marked reduction of cGMP-forming activity (80%). Noteworthy, increased eNOS-catalyzed NO formation was detected in kidneys of NO-GC1 KOs. Upon the 2K1C operation, NO-GC1 KO mice developed hypertension but the increase in blood pressures was not any higher than in WT. Conversely, operated WT mice showed a reduction of cGMP-dependent relaxation of renal vessels, which was not found in the NO-GC1 KOs. The reduced relaxation in operated WT mice was restored by sildenafil indicating that enhanced PDE5-catalyzed cGMP degradation most likely accounts for the attenuated vascular responsiveness. PDE5 activation depends on allosteric binding of cGMP. Because cGMP levels are lower, the 2K1C-induced vascular changes do not occur in the NO-GC1 KOs. In support of a higher PDE5 activity, sildenafil reduced blood pressure more efficiently in operated WT than NO-GC1 KO mice. All together our data suggest that within renovascular hypertension, cGMP-based PDE5 activation terminates NO/cGMP signaling thereby providing a new molecular basis for further pharmacological interventions.

[Enhanced expression of EPHX2 gene in the kidney of the hypertensive ISIAH rats]

Epoxyeicosatrienoic acids (EETs) have antihypertensive properties and play a part in the maintenance of renal microvascular function. EETs mediate vasodilation of rat preglomerular microvessels and activate ion channels. Ephx2 is coding for the soluble epoxide hydrolase (sEH) which catalyze the degradation of EETs. Renal cortex and renal medulla were tested for Ephx2 mRNA level in hypertensive ISIAH and normotensive WAG rats at rest and emotional stress conditions. The microarray analysis and real-time PCR were used to assess the transcriptional activity of Ephx2. Enhanced transcriptional activity of Ephx2 in both renal structures of ISIAH rats was found at rest and stress conditions. The emotional stress caused elevation of Ephx2 mRNA level in renal medulla of ISIAH rats and opposite response--a decrease in Ephx2 expression in the renal medulla and cortex of WAG rats.The results suggest Ephx2 participation in the control of the vascular tone changes in kidney promoting the hypertensive state in the ISIAH rats.

Effect of metabolic abnormalities on endothelial dysfunction in normotensive offspring of subject with hypertension

AIM

Essential hypertension (EH) is often accompanied by hyperinsulinemia/insulin resistance (IR) and deranged adiponectin secretion. IR may in turn be associated with endothelial dysfunction and increased levels of asymmetric dimethylarginine (ADMA). Therefore, we aimed to determine metabolic abnormalities in normotensive offspring of subjects with essential hypertension (familial trait-FT) and to examine their relations to endothelium-dependent vasodilation of the brachial artery (BA).

METHODS

We included 77 subjects, 38 were normotensive individuals with FT aged 28-39 (mean 33) years and 39 age-matched Controls without FT. Insulin, adiponectin and ADMA plasma levels were determined by radioimmunoassay. Using high-resolution ultrasound, BA diameters at rest and during reactive hyperemia (flow-mediated dilation-FMD) were measured.

RESULTS

Subjects with FT had higher insulin and lower adiponectin levels than controls (13.65±6.70 vs. 7.09±2.20 mE/L; P<0.001 and 13.60±5.98 vs. 17.27±7.17 mg/L respectively; P<0.05). Insulin and adiponectin levels were negatively interrelated (r=-0.33, P=0.003). ADMA levels were comparable in both groups. The study group had worse FMD than Controls (6.11±3.28 vs. 10.20±2.07%; P<0.001). IR was independently associated with FMD (partial R2=0.23, P<0.001).

CONCLUSION

Increased insulin and decreased adiponectin levels along with endothelial dysfunction are present in normotensive subjects with FT. IR and hypoadiponectinemia are interrelated, but only hyperinsulinemia has an independent adverse influence on endothelial function. Results of our study did not confirm the role of ADMA in pathogenesis of evolving hypertension.

Redox factor-1 activates endothelial SIRTUIN1 through reduction of conserved cysteine sulfhydryls in its deacetylase domain

Apurinic/Apyrmidinic Endonuclease 1/Redox Factor-1 (APE1/Ref-1) is a reductant which is important for vascular homeostasis. SIRTUIN1 (SIRT1) is a lysine deacetylase that also promotes endothelium-dependent vasorelaxation. We asked if APE1/Ref-1 governs the redox state and activity of SIRT1, and whether SIRT1 mediates the effect of APE1/Ref-1 on endothelium-dependent vascular function. APE1/Ref-1 maintains sulfhydryl (thiol) groups of cysteine residues in SIRT1 in the reduced form and promotes endothelial SIRT1 activity. APE1/Ref-1 stimulates SIRT1 activity by targeting highly conserved vicinal thiols 371 and 374 which form a zinc tetra-thiolate motif in the deacetylase domain of SIRT1. Cysteine residues in the N-terminal redox domain of APE1/Ref-1 are essential for reducing SIRT1 and stimulating its activity. APE1/Ref-1 protects endothelial SIRT1 from hydrogen peroxide-induced oxidation of sulfhydryls and from inactivation. APE1/Ref-1 also promotes lysine deacetylation of the SIRT1 target endothelial nitric oxide synthase (eNOS). SIRT1 mutated at cysteines 371 and 374, which renders it non-reducible by APE1/Ref-1, prevents lysine deacetylation of eNOS by APE1/Ref-1. SIRT1 free thiol (reduced sulfhydryl) content and deacetylase activity are diminished in all examined tissues of APE1/Ref-1^+/− mice, including the vasculature. Overexpression of SIRT1 in aortas of APE1/Ref-1^+/− mice restores endothelium-dependent vasorelaxation and bioavailable nitric oxide (NO) to levels similar to those observed in wild-type mice. Thus, APE1/Ref-1, by maintaining functionally important cysteine sulfhydryls in SIRT1 in the reduced form, promotes endothelial SIRT1 activity. This reductive activation of endothelial SIRT1 by APE1/Ref-1 mediates the effect of APE1/Ref-1 on eNOS acetylation, promoting endothelium-derived NO and endothelium-dependent vasorelaxation.

cGMP-dependent protein kinase contributes to hydrogen sulfide-stimulated vasorelaxation

A growing body of evidence suggests that hydrogen sulfide (H₂S) is a signaling molecule in mammalian cells. In the cardiovascular system, H₂S enhances vasodilation and angiogenesis. H₂S-induced vasodilation is hypothesized to occur through ATP-sensitive potassium channels (K_ATP); however, we recently demonstrated that it also increases cGMP levels in tissues. Herein, we studied the involvement of cGMP-dependent protein kinase-I in H₂S-induced vasorelaxation. The effect of H₂S on vessel tone was studied in phenylephrine-contracted aortic rings with or without endothelium. cGMP levels were determined in cultured cells or isolated vessel by enzyme immunoassay. Pretreatment of aortic rings with sildenafil attenuated NaHS-induced relaxation, confirming previous findings that H₂S is a phosphodiesterase inhibitor. In addition, vascular tissue levels of cGMP in cystathionine gamma lyase knockouts were lower than those in wild-type control mice. Treatment of aortic rings with NaHS, a fast releasing H₂S donor, enhanced phosphorylation of vasodilator-stimulated phosphoprotein in a time-dependent manner, suggesting that cGMP-dependent protein kinase (PKG) is activated after exposure to H₂S. Incubation of aortic rings with a PKG-I inhibitor (DT-2) attenuated NaHS-stimulated relaxation. Interestingly, vasodilatory responses to a slowly releasing H₂S donor (GYY 4137) were unaffected by DT-2, suggesting that this donor dilates mouse aorta through PKG-independent pathways. Dilatory responses to NaHS and L-cysteine (a substrate for H₂S production) were reduced in vessels of PKG-I knockout mice (PKG-I−/−). Moreover, glibenclamide inhibited NaHS-induced vasorelaxation in vessels from wild-type animals, but not PKG-I−/−, suggesting that there is a cross-talk between K_ATP and PKG. Our results confirm the role of cGMP in the vascular responses to NaHS and demonstrate that genetic deletion of PKG-I attenuates NaHS and L-cysteine-stimulated vasodilation.

Defective Cx40 maintains Cx37 expression but intact Cx40 is crucial for conducted dilations irrespective of hypertension

The gap junction channel protein connexin40 (Cx40) is crucial in vascular and renal physiology, because Cx40-deficient mice exhibit impaired conduction of endothelium-dependent dilations and pronounced hypertension. The latter precludes mechanistic insights into the role of endothelial Cx40, because long-lasting hypertension itself may affect conduction and Cx expression. We aimed to identify endothelial Cx40 functions, their dependency on the conductive capability, and to separate these from hypertension-related alterations. We assessed conduction and Cx expression in mice with cell type-specific deletion of Cx40 and in mice expressing a defective Cx40 (Cx40A96S) identified in humans, which forms nonconducting gap junction channels. Confined arteriolar stimulation with acetylcholine or bradykinin elicited local dilations that conducted upstream without attenuation of the amplitude for distances up to 1.2-mm in controls with a floxed Cx40 gene (Cx40(fl/fl)). Conducted responses in hypertensive animals devoid of Cx40 in renin-producing cells were unaltered but remote dilations were reduced in normotensive animals deficient for Cx40 in endothelial cells (Cx40(fl/fl):Tie2-Cre). Surprisingly, Cx37 expression was undetectable by immunostaining in arteriolar endothelium only in Cx40(fl/fl):Tie2-Cre; however, transcriptional activity of Cx37 in the cremaster was comparable with Cx40(fl/fl) controls. Cx40A96S mice were hypertensive with preserved expression of Cx40 and Cx37. Nevertheless, conducted responses were blunted. We conclude that endothelial Cx40 is necessary to support conducted dilations initiated by endothelial agonists and to locate Cx37 into the plasma membrane. These functions are unaltered by long-lasting hypertension. In the presence of a nonconducting Cx40, Cx37 is present but cannot support the conduction highlighting the importance of endothelial Cx40.

Essential role of microRNA-155 in regulating endothelium-dependent vasorelaxation by targeting endothelial nitric oxide synthase

Nitric oxide generated by endothelial nitric oxide synthase (eNOS) plays an important role in maintaining cardiovascular homeostasis. Under various pathological conditions, abnormal expression of eNOS contributes to endothelial dysfunction and the development of cardiovascular diseases. A variety of pathological stimuli has been reported to decrease eNOS expression mainly through decreasing eNOS mRNA stability by regulating the binding of several cytosolic proteins to the cis-acting sequences within eNOS mRNA 3' untranslated regions. However, the detailed mechanisms remain elusive. Because microRNAs inhibit gene expression through binding to the 3' untranslated regions of their target mRNAs, microRNAs may be the important posttranscriptional modulators of eNOS expression. Here, we provided evidence that eNOS is a direct target of miR-155. Overexpression of miR-155 decreased, whereas inhibition of miR-155 increased, eNOS expression and NO production in human umbilical vein endothelial cells and acetylcholine-induced endothelium-dependent vasorelaxation in human internal mammary arteries. Inflammatory cytokines including tumor necrosis factor-α increased miR-155 expression. Inhibition of miR-155 reversed tumor necrosis factor-α-induced downregulation of eNOS expression and impairment of endothelium-dependent vasorelaxation. Moreover, we observed that simvastatin attenuated tumor necrosis factor-α-induced upregulation of miR-155 and ameliorated the effects of tumor necrosis factor-α on eNOS expression and endothelium-dependent vasodilation. Simvastatin decreased miR-155 expression through interfering mevalonate-geranylgeranyl-pyrophosphate-RhoA signaling pathway. These findings indicated that miR-155 is an essential regulator of eNOS expression and endothelium-dependent vasorelaxation. Inhibition of miR-155 may be a new therapeutic approach to improve endothelial dysfunction during the development of cardiovascular diseases.

Association of a functional polymorphism (C59038T) in GTP cyclohydrolase 1 gene and Type 2 diabetic macrovascular disease in the Chinese population

Nitric oxide (NO) unavailability plays an important role in the progression of macrovascular diseases in Type 2 diabetes (T2DM). C59038T polymorphism in GTP cyclohydrolase 1 (GCH1) gene is a functional mutation involved in NO metabolism and cardiovascular risk in a multiethnic population. To clarify the relationship between C59038T polymorphism and macrovascular disease in T2DM, an association study was performed among 611 unrelated T2DM patients. C59038T polymorphism was detected by polymerase chain reaction (PCR) restriction fragment length polymorphism. The PCR products after digestion displayed three genotypes, including CC, CT, and TT. The prevalence of cardiovascular disease, cerebrovascular disease, and peripheral vascular disease was significantly higher in T2DM patients with TT genotype than those with CC or CT genotype (P<.001). Compared with CC or CC+CT genotype, T2DM patients with TT genotype had a significantly increased risk of macrovascular disease (P<.001, P=.001), with odds ratio for 4.717 [95% confidence interval: 3.056-7.370] and 4.082 (2.716-5.868), respectively. Subjects with TT genotype showed lower levels of plasma NOx (nitrite and nitrate), flow-mediated artery dilatation and activities of superoxide dismutase but higher levels of plasma malonaldehyde and intima-media thickness of carotid artery than those with CC or CT genotype (P<.05). This study demonstrated that in Chinese T2DM population, C59038T polymorphism was associated with an increased risk of macrovascular disease, which was likely due to its effects on NO metabolism, oxidative stress, and subsequently vascular dysfunction.

Crucial importance of the endothelial K+ channel SK3 and connexin40 in arteriolar dilations during skeletal muscle contraction

Skeletal muscle activity requires substantial increases in blood flow, and the underlying vasodilation involves endothelial activity, but the contribution of the endothelium-dependent hyperpolarizing factor (EDHF) is only poorly defined. In EDHF signaling, endothelial hyperpolarization mediated by the Ca(2+)-activated K(+) channels SK3 and IK1 is a key step and also initiates gap junction-dependent conducted dilations. We assessed the role of SK3, IK1, and connexin40 (Cx40) in muscular contraction-induced dilations in the microcirculation in vivo. Hitherto, arterioles were observed in the electrically stimulated cremaster skeletal muscle of anesthetized mice lacking SK3, IK1, or Cx40 using intravital microscopy. Genetic deficiency of SK3, but not of IK1, strongly attenuated dilations to muscular contraction. Similarly, pharmacologic blockade of SK3 by the specific blocker UCL1684 impaired such dilations in wild-type and IK1-deficient mice. In contrast, IK1 was required for acetylcholine-induced dilations. Genetic deficiency of Cx40 also attenuated dilations induced by muscular contraction but not by acetylcholine. These data support the concept that endothelial hyperpolarization through activation of SK3 contributes to exercise hyperemia and the hyperpolarization ascends the vascular tree through gap junctions formed by Cx40 to orchestrate dilation. The differential impact of SK3- and IK1-deficiency on dilations to distinct stimuli suggests stimulus-dependent activation of these endothelial channels.

MicroRNAs are necessary for vascular smooth muscle growth, differentiation, and function

OBJECTIVE

Regulation of vascular smooth muscle (VSM) proliferation and contractile differentiation is an important factor in vascular development and subsequent cardiovascular diseases. Recently, microRNAs (miRNAs) have been shown to regulate fundamental cellular processes in a number of cell types, but the integrated role of miRNAs in VSM in blood vessels is unknown. Here, we investigated the role of miRNAs in VSM by deleting the rate-limiting enzyme in miRNA synthesis, Dicer.

METHODS AND RESULTS

Deletion of Dicer in VSM results in late embryonic lethality at embryonic day 16 to 17, associated with extensive internal hemorrhage. The loss of VSM Dicer results in dilated, thin-walled blood vessels caused by a reduction in cellular proliferation. In addition, blood vessels from VSM-deleted Dicer mice exhibited impaired contractility because of a loss of contractile protein markers. We found this effect to be associated with a loss of actin stress fibers and partly rescued by overexpression of microRNA (miR)-145 or myocardin.

CONCLUSIONS

Dicer-dependent miRNAs are important for VSM development and function by regulating proliferation and contractile differentiation.

Endothelial function and endothelial nitric oxide synthase intron 4a/b polymorphism in primary hyperparathyroidism

BACKGROUND AND AIM

Patients with symptomatic primary hyperparathyroidism (pHT) have increased cardiovascular morbidity and mortality. Endothelial nitric oxide synthase (eNOS) intron 4a/b polymorphism is associated with coronary artery disease and hypertension in various populations. Our aim is to evaluate endothelial function in patients with pHT during pre-operative hypercalcemic and post-operative normocalcemic periods and to determine whether intron 4a/b polymorphism of eNOS gene influences endothelial function.

SUBJECTS AND METHODS

Forty patients with pHT (age 48.48+/-11.64 yr) were examined pre-operatively and reexamined 5.8+/-1.9 months after parathyroidectomy. Forty-three healthy subjects (age 47.13+/-8.14 yr) were served as control group. Endothelial function was determined by flow-mediated dilation of brachial artery (FMD). eNOS4a/b polymorphism was detected by polymerase chain reaction.

RESULTS

FMD was significantly lower in patients pre-operatively compared with controls (8.48+/-1.78% vs 19.49+/-2.34%, p<0.001). FMD improved significantly after parathyroidectomy (16.19+/-2.16%, p<0.001 compared with pre-operative measurements), but was still significantly lower than controls (p<0.001). The distribution of eNOS4a/b genotype frequencies was not significantly different between patients and controls. Logistic regression analysis showed that increased serum calcium (>2.47 mmol/l) and PTH concentrations (>7.75 pmol/l) were significant independent predictors of lower FMD (<16.7%). ENOS4a/b polymorphism did not enter in this model.

CONCLUSION

Impaired endothelial function in patients with pHT improves after successful parathyroid surgery. No compelling data are evident to suggest that eNOS4a/b polymorphism modifies the endothelial function in patients with pHT.

Transcriptional control of human adipose tissue blood flow

Adipose tissue is highly vascularized and expresses several genes involved in vasodilatory and vasoconstrictive regulation. We took a transcriptional approach to study the relationships between adipose tissue blood flow (ATBF) and genes involved in vasoactive processes. As ATBF is impaired in obesity, we tested whether body weight interfered with the transcriptional regulation of ATBF. The mRNA content (real-time PCR) of 26 genes was quantified in subcutaneous adipose tissue biopsies from 28 healthy men with a wide range of BMI. ATBF was measured by 133Xe washout. None of the transcripts was related to fasting ATBF (ATBFF). However, the expression levels of two transcripts involved in vasodilation (natriuretic peptide receptor A/guanylate cyclase A (NPRA) and endothelial nitric oxide synthase (eNOS)) were positively associated with postprandial ATBF (r = 0.53 and r = 0.55, P < 0.01, respectively). Although BMI was negatively related to the mRNA content of NPRA and eNOS (r = -0.78 and r = -0.63, P < 0.01, respectively), the strong associations found between postprandial ATBF and the two transcripts were not affected by obesity. Several genes were subject to coordinated regulation of expression. This study demonstrates for the first time that ATBF responsiveness to nutrient intake is related to the transcription of two genes expressed in adipose tissue and directly involved in vasodilatory actions (eNOS and NPRA), suggesting that part of the regulation of ATBF is at a transcriptional level. Interestingly, these associations were not secondary to changes in BMI. We also found that certain genes involved in the regulation of ATBF are subject to coordinate regulation of expression suggesting physiological autoregulation.

Functional estrogen receptor alpha promoter polymorphism is associated with improved endothelial-dependent vasolidation

Estrogen receptor alpha (ERalpha) mediates beneficial actions on endothelial nitric oxide synthase (eNOS) and cholesterol metabolism. Genetic variations in the promoter of the ERalpha may therefore influence vascular function. We have identified a single nucleotide polymorphism (T>C) in the transcriptional element "ERNE" upstream of ERalpha which abolished the negative effect of this element in luciferase reporter assays and was associated with reduction in LDL cholesterol in a small association study. We have now examined for the association of this putative functional polymorphism with endothelial function. Endothelial-dependent relaxation (EDR) was measured in organ bath preparations of human saphenous vein obtained from 101 individuals (81 males and 20 females) undergoing coronary artery bypass surgery. The presence of the variant C allele was associated with enhanced EDR independently of hypercholesterolaemia, smoking and diabetes, as well as sex (ANOVA for ACh induced relaxation: p=0.033). In males, the presence of the C allele was associated with a 225% augmentation of endothelial-dependent relaxation compared to wild-type (55.5+/-10%; n=3 vs. 24.7+/-1%; n=78; p<0.001). In summary, a polymorphism in the ERalpha negative transcriptional element which results in increased transcription in vitro is associated with substantial augmentation of endothelial-dependent vasorelaxation.

Propagated endothelial Ca2+ waves and arteriolar dilation in vivo: measurements in Cx40BAC GCaMP2 transgenic mice

To study endothelial cell (EC)- specific Ca(2+) signaling in vivo we engineered transgenic mice in which the Ca(2+) sensor GCaMP2 is placed under control of endogenous connexin40 (Cx40) transcription regulatory elements within a bacterial artificial chromosome (BAC), resulting in high sensor expression in arterial ECs, atrial myocytes, and cardiac Purkinje fibers. High signal/noise Ca(2+) signals were obtained in Cx40(BAC)-GCaMP2 mice within the ventricular Purkinje cell network in vitro and in ECs of cremaster muscle arterioles in vivo. Microiontophoresis of acetylcholine (ACh) onto arterioles triggered a transient increase in EC Ca(2+) fluorescence that propagated along the arteriole with an initial velocity of approximately 116 microm/s (n=28) and decayed over distances up to 974 microm. The local rise in EC Ca(2+) was followed (delay, 830+/-60 ms; n=8) by vasodilation that conducted rapidly (mm/s), bidirectionally, and into branches for distances exceeding 1 mm. At intermediate distances (300 to 600 microm), rapidly-conducted vasodilation occurred without changing EC Ca(2+), and additional dilation occurred after arrival of a Ca(2+) wave. In contrast, focal delivery of sodium nitroprusside evoked similar local dilations without Ca(2+) signaling or conduction. We conclude that in vivo responses to ACh in arterioles consists of 2 phases: (1) a rapidly-conducted vasodilation initiated by a local rise in EC Ca(2+) but independent of EC Ca(2+) signaling at remote sites; and (2) a slower complementary dilation associated with a Ca(2+) wave that propagates along the endothelium.

Associations between connexin37 gene polymorphism and markers of subclinical atherosclerosis: the Cardiovascular Risk in Young Finns study

OBJECTIVE

Connexin37 (cx37) C1019T polymorphism has been shown to associate with coronary artery disease in different populations. We investigated whether this polymorphism associates with carotid artery intima-media thickness (IMT), carotid artery compliance (CAC) and brachial artery flow mediated dilatation (FMD) - i.e., early ultrasound markers of subclinical atherosclerosis - in a clinically healthy population of young Finnish adults.

METHODS AND RESULTS

1440 individuals from the Cardiovascular Risk in Young Finns study were genotyped and studied using cardiovascular risk factor and ultrasound data obtained in 2001. In linear regression models, no significant association between the cx37 polymorphism and carotid IMT, CAC or brachial artery FMD (ANOVA, p=0.159, 0.151 and 0.547), respectively, was found in the whole population or in women and men separately.

CONCLUSIONS

The connexin37 C1019T polymorphism is not related with markers of subclinical atherosclerosis in young adults.

Heritability of flow-mediated dilation: a twin study

BACKGROUND

Endothelial dysfunction assessed by brachial artery flow-mediated dilation (FMD) is a marker for early atherosclerotic vascular disease and future cardiovascular events.

OBJECTIVE

To estimate the heritability of brachial artery FMD using a twin design.

METHODS

We estimated the heritability of FMD using 94 middle-aged male twin pairs. FMD was measured by ultrasound, and traditional coronary heart disease risk factors were measured. Genetic modeling techniques were used to determine the relative contributions of genes and environment to the variation in FMD.

RESULTS

The mean age of the twin participants was 54.9 +/- 2.8 years. The mean FMD was 0.047 +/- 0.030. The intraclass correlation coefficient was higher in MZ twins [0.38, 95% confidence interval (CI) 0.32-0.43] than in DZ twins (0.19, 95% CI 0.11-0.26), suggesting a role of genetic influence in FMD variation. Structural equation modeling showed that both genetic and unique environmental factors contributed significantly to the variation in FMD. The crude FMD heritability was 0.37 (95% CI 0.15-0.54). After adjustment for traditional cardiovascular risk factors, including age, total cholesterol, blood pressure, and body mass index, the heritability of FMD was 39% (95% CI 0.18-0.56). The remaining variation in FMD could be explained by individual-specific environment.

CONCLUSION

This is the first study using twins to estimate the relative contributions of genetics and environment to the variation in FMD in a US population. Our results demonstrate a moderate genetic effect on brachial artery FMD, independent of traditional coronary risk factors. Our data also highlight the importance of unique environment on the variability in FMD.

ACE gene insertion/deletion polymorphism modulates capillary permeability in hypertension

A D/D (deletion/deletion) polymorphism within the ACE (angiotensin 1-converting enzyme) gene increases the risk of microalbuminuria, a predictor of atherosclerotic vascular disease, in essential hypertension. It is unknown, however, whether this genetic profile is accompanied by disturbed macromolecular permeability of systemic capillary endothelium, possibly in the context of generalized endothelial dysfunction. In the present study, the ACE gene polymorphism was determined by PCR in 79 never-treated uncomplicated hypertensive men and 16 normotensive men as controls. Evaluation variables were TERalb (transcapillary escape rate of albumin; the 1-h decline rate of intravenous (125)I-albumin, a measure of integrity of systemic capillary endothelium), albuminuria and forearm vasodilation to intra-arterial acetylcholine, an index of NO (nitric oxide)-mediated vasomotion, in addition to a series of sensitive parameters of albumin permeation (blood pressure, metabolic status and smoking habits). Analyses were done by comparing D/D homozygotes with grouped I/D (insertion/deletion) and I/I (insertion/insertion) subjects. TERalb was higher in D/D hypertensives, who had higher albuminuria, more frequent microalbuminuria and comparable forearm responsiveness to intra-arterial acetylcholine. Fasting glucose and insulin, insulin sensitivity, 24-h blood pressure, smoking habits and metabolic parameters did not differ between the two groups. TERalb and urine albumin values were positively associated in the hypertensive subjects. In conclusion, ACE D/D homozygosis, independently of several confounding factors, associates with higher TERalb in men with essential hypertension. This may reflect noxious genetic influences on systemic vascular permeability, a critical control mechanism for atherogenesis in the absence of grossly impaired NO-mediated arteriolar responsiveness. The parallel behaviour of TERalb and albuminuria suggests some shared genetically mediated determinant of renal and systemic microvascular abnormalities in hypertension.

Angiotensin-converting enzyme gene polymorphism and coronary reactivity in young men

The purpose of the study was to examine whether the insertion/deletion (I/D) polymorphism of the angiotensin-converting enzyme (ACE) gene affects the vasodilatory properties of coronary arteries in healthy men. The ACE genotypes of 128 men (mean age 35 +/- 4 years) were determined and related to myocardial blood flow. The blood flow was measured by positron emission tomography at rest and during vasodilation caused by adenosine or dipyridamole infusion. The coronary flows and resistances at rest and during stimulation with adenosine or dipyridamole did not differ between the ACE genotypes. Furthermore, this polymorphism had no effect on coronary flow reserve corrected by a rate-pressure product. In conclusion, the ACE I/D polymorphism does not seem to affect myocardial reactivity--an early indicator of atherosclerosis--in healthy subjects.

Vasorelaxant effects of icariin on isolated canine coronary artery

Owing to its cardiovascular therapeutical effects, icariin, a flavonoid isolated from Epimedii herba, is considered to be the major active constituent of Epimedii herba. The aim of this study is to investigate the effect of icariin on precontracted coronary artery isolated from canine. Coronary artery segments were isolated from normal anesthetized Beagle dogs and cut into 5-mm rings. The rings were mounted in an organ chamber and contracted by either 40 mM KCl or 10 microM PGF2alpha, and vasorelaxant tone to icariin was measured. Treatment of icariin could significantly produce a relaxation of precontracted coronary arterial rings with intact endothelium in a concentration-dependent manner. Comparatively, the vasorelaxation disappeared in denuded-endothelium rings. Furthermore, the vasorelaxant effect of icariin was blocked by Nomega-Nitro- L-arginine Methyl Ester (L-NAME), 1H-[1, 2, 4]-oxadiazolo [4, 3-a] quinoxalin-1-one (ODQ) but not by indomethacin and glibenclamide, respectively. Tetraethylammonium (TEA) could partly antagonize the vasorelaxant effect triggered by icariin. There was no significant gene expression difference of the endothelial nitric oxide synthase (eNOS) gene in coronary arterial rings among the different concentrations of icariin by RT-PCR, but the activity of eNOS was increased in a concentration-dependent manner after icariin exposure. These results suggest that icariin produces NO-dependent relaxation in the isolated canine coronary artery, and the possible mechanism is involved in the activation of eNOS protein and NO-cGMP pathway.

The 1976C>T polymorphism in the adenosine A2A receptor gene does not affect the vasodilator response to adenosine in humans in vivo

The 1976C>T polymorphism in the adenosine A2A receptor gene (ADORA2A) modulates the psychological response to administration of the adenosine receptor antagonist caffeine. We quantified the vascular response to adenosine and caffeine to determine the relevance of this variant allele in the physiological response to these agents. We selected 10 study participants with the TT genotype and 10 CC controls, matched for activities of other proteins involved in the metabolism of adenosine. The vasodilator response to the intrabrachial administration of adenosine (0.5, 1.5, 5.0, 15.0, and 50.0 microg/min/dl; venous occlusion plethysmography) was not different between the groups (P=0.4). In addition, the effect of subsequent administration of caffeine (90 microg/min/dl) was not different (P=0.7). We conclude that the 1976C>T polymorphism does not affect the vascular response to adenosine and caffeine in humans in vivo. Therefore, this polymorphism does not contribute to the variation in the effects of adenosine receptor stimulation.

Purinergic 2X1 receptors mediate endothelial dependent vasodilation to ATP

ATP is an important endogenous mediator in the cardiovascular system. It induces endothelium dependent vasodilation, but the precise receptor pathway activated in this response is currently under debate. We have used traditional bioassay techniques to show that ATP-induced vasodilation in mesenteric vessels is endothelium-dependent. Furthermore, ATP-induced vasodilation was inhibited by both suramin and 2',3'-O-(2,4,6-trinitrophenyl)-ATP (TNP-ATP), consistent with a P2X(1)-, P2X(2)-, or P2X(3)-mediated event and was not potentiated by ivermectin, indicating that these responses were not P2X(4) receptor-mediated. ATP did not induce vasodilation in vessels from P2X (-/-)(1) mice, confirming an absolute requirement for this receptor. Finally, in pure cell populations of mouse mesenteric artery endothelial cells, we show that P2X(1) mRNA is specifically expressed. However, in line with observations in the brain, the P2X(1) present in endothelial cells does not seem to be recognized by conventional antibodies. Together, these results show that ATP-induced vasodilation is mediated by P2X(1) receptor activation on mesenteric arterial endothelial cells. These observations establish a critical role for P2X(1) receptors in the ATP vasodilator pathway.

CYBA C242T gene polymorphism and flow-mediated vasodilation in a population of young adults: the Cardiovascular Risk in Young Finns Study

OBJECTIVE

Nicotinamide adenine dinucleotide phosphate (NADPH) oxidase is a major source of the superoxide anion that contributes to decreased nitric oxide bioavailability in the vasculature. The C242T polymorphism of the CYBA gene that encodes p22phox, a component of NADPH oxidase, has been found to modulate superoxide production. We examined the relationship of the C242T polymorphism with endothelial-dependent brachial artery flow-mediated vasodilatation (FMD) in a population-based sample of young healthy adults.

METHODS

FMD, defined as the increased percentage in brachial artery diameter after reactive hyperemia, was assessed by ultrasound and the C242T polymorphism using a 5' nuclease assay in 2058 subjects aged 24-39 years.

RESULTS

The mean values of brachial artery FMD were 8.0 +/- 4.4% in all study subjects (n = 2058), and 7.8 +/- 4.4, 8.2 +/- 4.5, and 8.7 +/- 4.5% in subjects with the CC (n = 1362), CT (n = 616), and TT (n = 80) genotypes of the C242T CYBA polymorphism, respectively (P = 0.02 for trend). The association remained significant (P = 0.019) in multivariate analyses adjusted for age, sex, obesity indices, smoking habits, blood pressure, serum glucose, lipids, and C-reactive protein. The relationship between FMD and the C242T polymorphism was stronger (P = 0.004) in overweight subjects (body mass index > or = 25 kg/m, n = 895) and ever-smokers (P = 0.008, n = 1082), whereas no relationship was found in normal-weight subjects and non-smokers (P = 0.824 and P = 0.438, respectively).

CONCLUSION

The C242T polymorphism of the CYBA gene seems to be related to endothelial function in a population-based sample of young healthy adults. Overweight and smoking status may modify this genetic effect.