RAGE mediates amyloid-beta peptide transport across the blood-brain barrier and accumulation in brain

Amyloid-beta peptide (Abeta) interacts with the vasculature to influence Abeta levels in the brain and cerebral blood flow, providing a means of amplifying the Abeta-induced cellular stress underlying neuronal dysfunction and dementia. Systemic Abeta infusion and studies in genetically manipulated mice show that Abeta interaction with receptor for advanced glycation end products (RAGE)-bearing cells in the vessel wall results in transport of Abeta across the blood-brain barrier (BBB) and expression of proinflammatory cytokines and endothelin-1 (ET-1), the latter mediating Abeta-induced vasoconstriction. Inhibition of RAGE-ligand interaction suppresses accumulation of Abeta in brain parenchyma in a mouse transgenic model. These findings suggest that vascular RAGE is a target for inhibiting pathogenic consequences of Abeta-vascular interactions, including development of cerebral amyloidosis.

Angiotensin inhibition enhances drug delivery and potentiates chemotherapy by decompressing tumour blood vessels

Cancer and stromal cells actively exert physical forces (solid stress) to compress tumour blood vessels, thus reducing vascular perfusion. Tumour interstitial matrix also contributes to solid stress, with hyaluronan implicated as the primary matrix molecule responsible for vessel compression because of its swelling behaviour. Here we show, unexpectedly, that hyaluronan compresses vessels only in collagen-rich tumours, suggesting that collagen and hyaluronan together are critical targets for decompressing tumour vessels. We demonstrate that the angiotensin inhibitor losartan reduces stromal collagen and hyaluronan production, associated with decreased expression of profibrotic signals TGF-β1, CCN2 and ET-1, downstream of angiotensin-II-receptor-1 inhibition. Consequently, losartan reduces solid stress in tumours resulting in increased vascular perfusion. Through this physical mechanism, losartan improves drug and oxygen delivery to tumours, thereby potentiating chemotherapy and reducing hypoxia in breast and pancreatic cancer models. Thus, angiotensin inhibitors -inexpensive drugs with decades of safe use - could be rapidly repurposed as cancer therapeutics.

Resistin promotes endothelial cell activation: further evidence of adipokine-endothelial interaction

BACKGROUND

Adipocyte-derived hormones may represent a mechanism linking insulin resistance to cardiovascular disease. In the present study, we evaluated the direct effects of resistin, a novel adipocyte-derived hormone, on endothelial activation.

METHODS AND RESULTS

Endothelial cells (ECs) were incubated with human recombinant resistin (10 to 100 ng/ML, 24 hours), and endothelin-1 (ET-1) release, ET-1 mRNA expression, and nitric oxide (NO) production were assessed. Transient transfection assays were used to evaluate the effects of resistin on transcription of human ET-1 gene promoter. Furthermore, the effects of resistin on AP-1-mutated ET-1 promoter were evaluated. The effects of resistin on expression of vascular cell adhesion molecule (VCAM-1) and monocyte chemoattractant chemokine (MCP-1) were studied in addition to CD40 receptor, CD40 ligand-induced MCP-1 expression, and tumor necrosis factor receptor-associated factor-3 (TRAF3), an inhibitor of CD40 signaling. Incubation of ECs with resistin resulted in an increase in ET-1 release and ET-1 mRNA expression, with no change in NO production. Whereas treatment with resistin resulted in an increase in ET-1 promoter activity, the AP-1-mutated promoter was inactive after resistin stimulation. Additionally, resistin-treated cells showed increased expression of VCAM-1 and MCP-1, with concomitant reductions in TRAF-3 expression. Resistin did not alter CD40 receptor expression; however, increased CD40 ligand induced MCP-1 production.

CONCLUSIONS

The novel adipokine resistin exerts direct effects to promote EC activation by promoting ET-1 release, in part by inducing ET-1 promoter activity via the AP-1 site. Furthermore, resistin upregulates adhesion molecules and chemokines and downregulates TRAF-3, an inhibitor of CD40 ligand signaling. In this fashion, resistin may be mechanistically linked to cardiovascular disease in the metabolic syndrome.

Microvascular and macrovascular reactivity is reduced in subjects at risk for type 2 diabetes

Abnormalities in vascular reactivity in the micro- and macrocirculation are well established in type 2 diabetes. However, little is known about changes in vascular reactivity in those at risk for developing type 2 diabetes. To address this situation, the vascular reactivity in both the micro- and macrocirculation was studied in four age and sex comparable groups: 30 healthy normoglycemic subjects with no history of type 2 diabetes in a first-degree relative (controls), 39 healthy normoglycemic subjects with a history of type 2 diabetes in one or both parents (relatives), 32 subjects with impaired glucose tolerance (IGT), and 42 patients with type 2 diabetes without vascular complications (diabetes). Laser Doppler perfusion imaging was used to measure vasodilation in the forearm skin in response to iontophoresis of 1% acetylcholine chloride (Ach) (endothelium-dependent) and 1% sodium nitroprusside (SNP) (endothelium-independent), whereas high-resolution ultrasound images were used to measure brachial artery diameter changes during reactive hyperemia. Plasma concentrations of endothelin-1 (ET-1), von Willebrand factor (vWF), soluble intercellular adhesion molecule (sICAM), and soluble vascular cell adhesion molecule (sVCAM) were also measured as indicators of endothelial cell activation. The vasodilatory responses to Ach, expressed as percent increase of blood flow over baseline, were reduced in relatives (98 +/- 48, mean +/- SD), IGT (94 +/- 52), and diabetes (74 +/- 45) compared with controls (126 +/- 67) (P < 0.001 controls versus relatives, IGT, and diabetes). The responses to SNP were similarly reduced: controls (123 +/- 46), relatives (85 +/- 46), IGT (83 +/- 48), and diabetes (65 +/- 31) (P < 0.001 controls versus relatives, IGT, and diabetes) as were the responses in the brachial artery diameter during reactive hyperemia: controls (13.7 +/- 6.1), relatives (10.5 +/- 6.7), IGT (9.8 +/- 4.5), and diabetes (8.4 +/- 5.0) (P < 0.01 controls versus relatives, IGT, and diabetes). Women had greater responses than men in both the micro- and macrovascular circulatory tests, but a similar progressive reduction was observed in both sexes with increasing degrees of glucose intolerance. A significant inverse correlation was found between microvascular reactivity and systolic blood pressure, fasting plasma glucose, HDL cholesterol, fasting plasma insulin, and homeostasis model assessment (HOMA) values, an index of insulin resistance. BMI and diastolic blood pressure had a significant inverse correlation only with endothelium-dependent vasodilation. In the macrocirculation, systolic blood pressure, HbA1c, HDL cholesterol, and HOMA had significant correlation with brachial artery diameter changes. Compared with control subjects, ET-1 was significantly higher in all groups, vWF was higher only in the diabetic group, sICAM levels were higher in the IGT and diabetic groups, while sVCAM concentrations were higher in the relatives and those with diabetes (P < 0.05). On stepwise multivariate analysis, age, sex, fasting plasma glucose, and BMI were the most important contributing factors to the variation of vascular reactivity. Addition of all clinical and biochemical measures explained only 32-37% of the variation in vascular reactivity. These results suggest that abnormalities in vascular reactivity and biochemical markers of endothelial cell activation are present early in individuals at risk of developing type 2 diabetes, even at a stage when normal glucose tolerance exists, and that factors in addition to insulin resistance may be operative.

The importance of endothelin-1 for vascular dysfunction in cardiovascular disease

Endothelin (ET)-1 is a potent vasoconstrictor peptide originally isolated from endothelial cells. Its production is stimulated in a variety of different cell types under the influence of risk factors for cardiovascular disease and during the development of cardiovascular disease. Based on these observations and the biological effects induced by ET-1, including profound vasoconstriction, pro-inflammatory actions, mitogenic and proliferative effects, stimulation of free radical formation and platelet activation, ET-1 has been implicated as an important factor in the development of vascular dysfunction and cardiovascular disease. In the following the pathogenic role of ET-1, the mechanisms underlying the involvement of ET-1 for the development of vascular dysfunction and the potentially beneficial therapeutic effects of selective ET(A) and dual ET(A)/ET(B) receptor antagonists will be discussed. In particular the changes of pathophysiological importance mediated by ET-1 in clinical studies are reviewed. These changes may be of significance for the development of various cardiovascular diseases beyond pulmonary arterial hypertension which is the currently approved indication for ET receptor antagonists.

Peroxisome proliferator-activated receptor activators inhibit thrombin-induced endothelin-1 production in human vascular endothelial cells by inhibiting the activator protein-1 signaling pathway

Endothelin-1 (ET-1), a 21-amino acid vasoactive peptide mainly produced by vascular endothelial cells, is involved in the regulation of vascular tone and smooth muscle cell proliferation. Peroxisome proliferator-activated receptors (PPARs), key players in lipid and glucose metabolism, have been implicated in metabolic disorders that are predisposing to atherosclerosis. Because of the potential role of ET-1 in vascular disorders such as hypertension and atherosclerosis, we investigated the regulation of ET-1 expression by PPAR activators. Western blot and reverse transcription-polymerase chain reaction analyses demonstrated that both PPARalpha and PPARgamma are expressed in human coronary artery endothelial cells as well as in endothelial cell lines such as HMEC-1 and ECV304. In bovine aortic endothelial cells and HMEC-1 cells, both PPARalpha and PPARgamma ligands inhibited thrombin-induced ET-1 secretion, whereas basal ET-1 secretion was only slightly suppressed. Reverse transcription-polymerase chain reaction experiments showed that this inhibition of ET-1 production occurs at the gene expression level. Using transient transfection assays, we demonstrated that PPARs downregulate thrombin-activated transcription of the human ET-1 promoter. Transactivation studies with c-Jun and c-Fos expression plasmids indicated that PPARs negatively interfere with the activator protein-1 signaling pathway, which mediates thrombin activation of ET-1 gene transcription. Furthermore, electrophoretic mobility shift assays demonstrated that PPAR activators reduce the thrombin-stimulated binding activity of bovine aortic endothelial cell nuclear extracts as well as c-Jun binding to an activator protein-1 consensus site. Taken together, these data indicate that (1) both PPARalpha and PPARgamma are expressed in human vascular endothelial cells and (2) PPAR activators inhibit thrombin-induced ET-1 biosynthesis, indicating a novel role for PPARs in vascular endothelial function.

GATA transcription factors in the developing and adult heart

During the past decade, emerging evidence has accumulated of different nuclear transcription factors in regulation of cardiac development and growth as well as in cardiac hypertrophy and heart failure. GATA-4, -5 and -6 are zinc finger transcription factors that are expressed in the developing heart and GATA-4 and -6 continue expression in the adult cardiac myocytes. GATA-4 and -6 regulate expression of several cardiac-specific genes, and during murine embryonic development, GATA-4 is essential for proper cardiac morphogenesis. In support of this, mutations of gene for GATA-4 or for its cofactors have been associated with human congenital heart disease. Pressure overload of the heart in vivo as well as hypertrophic stimulation of cardiac myocytes in vitro provide adequate stimulus for activation of GATA-4. Activity of GATA-4 transcription factor is subject to regulation at the level of gene expression and through post-translational modifications of GATA-4 protein. A number of genes induced during cardiac hypertrophy possess functional GATA sites in their promoter region and cardiac-specific overexpression of GATA-4 or -6 leads to cardiac hypertrophy. In addition, a pattern of interactions between GATA-4 and its numerous cofactors have been identified, showing an increasing complexity in regulatory mechanisms. The present review discusses current evidence of the role and regulation of GATA transcription factors in the heart, with an emphasis in the GATA-4 and development of cardiac hypertrophy.

Glycogen synthase kinase-3beta is a negative regulator of cardiomyocyte hypertrophy

Hypertrophy is a basic cellular response to a variety of stressors and growth factors, and has been best characterized in myocytes. Pathologic hypertrophy of cardiac myocytes leads to heart failure, a major cause of death and disability in the developed world. Several cytosolic signaling pathways have been identified that transduce prohypertrophic signals, but to date, little work has focused on signaling pathways that might negatively regulate hypertrophy. Herein, we report that glycogen synthase kinase-3beta (GSK-3beta), a protein kinase previously implicated in processes as diverse as development and tumorigenesis, is inactivated by hypertrophic stimuli via a phosphoinositide 3-kinase-dependent protein kinase that phosphorylates GSK-3beta on ser 9. Using adenovirus-mediated gene transfer of GSK-3beta containing a ser 9 to alanine mutation, which prevents inactivation by hypertrophic stimuli, we demonstrate that inactivation of GSK-3beta is required for cardiomyocytes to undergo hypertrophy. Furthermore, our data suggest that GSK-3beta regulates the hypertrophic response, at least in part, by modulating the nuclear/cytoplasmic partitioning of a member of the nuclear factor of activated T cells family of transcription factors. The identification of GSK-3beta as a transducer of antihypertrophic signals suggests that novel therapeutic strategies to treat hypertrophic diseases of the heart could be designed that target components of the GSK-3 pathway.

Angiotensin II stimulates cardiac myocyte hypertrophy via paracrine release of TGF-beta 1 and endothelin-1 from fibroblasts

OBJECTIVE

We sought to determine whether angiotensin II (Ang II) promotes hypertrophy of cardiac directly or via paracrine mechanisms mediated by cardiac fibroblasts.

METHODS

We studied neonatal rat cardiac myocytes and fibroblasts in culture as a model system. Paracrine effects of Ang II were identified using conditioned medium and co-culture experiments.

RESULTS

Ang II type 1 (AT1) receptors responsible for myocyte growth localized to fibroblasts in radioligand binding, emulsion autoradiography, Western analysis, and immunofluorescence staining experiments. The bulk of AT1 receptor binding in myocyte cultures (1343 +/- 472 sites/cell) was to Ang II receptors on contaminating fibroblasts (9747 +/- 2126 sites/cell). Ang II induced significant paracrine trophic effects on myocytes in conditioned medium (40% increase in protein synthesis over control) and co-culture (4-fold increase over control) experiments. TGF-beta 1 and endothelin-1 were paracrine mediators of hypertrophy in neutralization experiments.

CONCLUSIONS

Ang II stimulates cardiac myocyte hypertrophy via paracrine release of TGF-beta 1 and endothelin-1 from cardiac fibroblasts in a neonatal rat cell culture model.

Endothelial KLF2 links local arterial shear stress levels to the expression of vascular tone-regulating genes

Lung Krüppel-like factor (LKLF/KLF2) is an endothelial transcription factor that is crucially involved in murine vasculogenesis and is specifically regulated by flow in vitro. We now show a relation to local flow variations in the adult human vasculature: decreased LKLF expression was noted at the aorta bifurcations to the iliac and carotid arteries, coinciding with neointima formation. The direct involvement of shear stress in the in vivo expression of LKLF was determined independently by in situ hybridization and laser microbeam microdissection/reverse transcriptase-polymerase chain reaction in a murine carotid artery collar model, in which a 4- to 30-fold induction of LKLF occurred at the high-shear sites. Dissection of the biomechanics of LKLF regulation in vitro demonstrated that steady flow and pulsatile flow induced basal LKLF expression 15- and 36-fold at shear stresses greater than approximately 5 dyne/cm2, whereas cyclic stretch had no effect. Prolonged LKLF induction in the absence of flow changed the expression of angiotensin-converting enzyme, endothelin-1, adrenomedullin, and endothelial nitric oxide synthase to levels similar to those observed under prolonged flow. LKLF repression by siRNA suppressed the flow response of endothelin-1, adrenomedullin, and endothelial nitric oxide synthase (P < 0.05). Thus, we demonstrate that endothelial LKLF is regulated by flow in vivo and is a transcriptional regulator of several endothelial genes that control vascular tone in response to flow.

Endothelin-1 transgenic mice develop glomerulosclerosis, interstitial fibrosis, and renal cysts but not hypertension

The human endothelin-1 (ET-1) gene under the control of its natural promoter was transferred into the germline of mice. The transgene was expressed predominantly in the brain, lung, and kidney. Transgene expression was associated with a pathological phenotype manifested by signs such as age-dependent development of renal cysts, interstitial fibrosis of the kidneys, and glomerulosclerosis leading to a progressive decrease in glomerular filtration rate. This pathology developed in spite of only slightly elevated plasma and tissue ET-1 concentrations. Blood pressure was not affected even after the development of an impaired glomerular filtration rate. Therefore, these transgenic lines provide a new blood pressure-independent animal model of ET-1-induced renal pathology leading to renal fibrosis and fatal kidney disease.

Endothelin-1 promotes myofibroblast induction through the ETA receptor via a rac/phosphoinositide 3-kinase/Akt-dependent pathway and is essential for the enhanced contractile phenotype of fibrotic fibroblasts

The endothelins are a family of endothelium-derived peptides that possess a variety of functions, including vasoconstriction. Endothelin-1 (ET-1) is up-regulated during tissue repair and promotes myofibroblast contraction and migration, hence contributing to matrix remodeling during tissue repair. Here, we show that addition of ET-1 to normal lung fibroblasts induces expression of proteins that contribute to a contractile phenotype, including alpha-smooth muscle actin (alpha-SMA), ezrin, moesin, and paxillin. We confirm that ET-1 enhances the ability of lung fibroblasts to contract extracellular matrix, a function essential for tissue repair, through induction of de novo protein synthesis. Blockade of the Akt/phosphoinositide 3-kinase (PI3-kinase) pathway with LY294002 and wortmannin prevents the ability of ET-1 to induce alpha-SMA, ezrin, paxillin, and moesin and to promote matrix contraction. Dominant negative rac and Akt blocked the ability of ET-1 to promote formation of alpha-SMA stress fibers. Using specific ET-1 receptor inhibitors, we show that ET-1 induces collagen matrix contraction through the ETA, but not the ETB, receptor. Relative to normal pulmonary fibroblasts, fibroblasts cultured from scars of patients with the fibrotic disease systemic sclerosis (scleroderma) show enhanced ET-1 expression and binding. Systemic sclerosis lung fibroblasts show increased ability to contract a collagen matrix and elevated expression of the procontractile proteins alpha-SMA, ezrin, paxillin, and moesin, which are greatly reduced by antagonizing endogenous ET-1 signaling. Thus, blocking ET-1 or the PI3-kinase/Akt cascades might be beneficial in reducing scar formation in pulmonary fibrosis.

The role of endothelial insulin signaling in the regulation of vascular tone and insulin resistance

Insulin receptors (IRs) on vascular endothelial cells have been suggested to participate in insulin-regulated glucose homeostasis. To directly address the role of insulin action in endothelial function, we have generated a vascular endothelial cell IR knockout (VENIRKO) mouse using the Cre-loxP system. Cultured endothelium of VENIRKO mice exhibited complete rearrangement of the IR gene and a more than 95% decrease in IR mRNA. VENIRKO mice were born at the expected Mendelian ratio, grew normally, were fertile, and exhibited normal patterns of vasculature in the retina and other tissues. Glucose homeostasis under basal condition was comparable in VENIRKO mice. Both eNOS and endothelin-1 mRNA levels, however, were reduced by approximately 30-60% in endothelial cells, aorta, and heart, while vascular EGF expression was maintained at normal levels. Arterial pressure tended to be lower in VENIRKO mice on both low- and high-salt diets, and on a low-salt diet VENIRKO mice showed insulin resistance. Thus, inactivation of the IR on endothelial cell has no major consequences on vascular development or glucose homeostasis under basal conditions, but alters expression of vasoactive mediators and may play a role in maintaining vascular tone and regulation of insulin sensitivity to dietary salt intake.

Endothelin-1 increases vascular superoxide via endothelin(A)-NADPH oxidase pathway in low-renin hypertension

BACKGROUND

Angiotensin II-induced hypertension is associated with NAD(P)H oxidase-dependent superoxide production in the vessel wall. Vascular superoxide level is also increased in deoxycorticosterone acetate (DOCA)-salt hypertension, which is associated with a markedly depressed plasma renin activity because of sodium retention. However, the mechanisms underlying superoxide production in low-renin hypertension are undefined.

METHODS AND RESULTS

This study investigated (1) whether and how endothelin-1 (ET-1), which is increased in DOCA-salt hypertensive rats, contributes to arterial superoxide generation and (2) the effect of gene transfer of manganese superoxide dismutase and endothelial nitric oxide synthase. Both superoxide and ET-1 levels were significantly elevated in carotid arteries of DOCA-salt rats compared with that of the sham-operated controls. ET-1 concentration-dependently stimulated superoxide production in vitro in carotid arteries of normotensive rats. The increase in arterial superoxide in both ET-1-treated normotensive and DOCA-salt rats was reversed by a selective ET(A) receptor antagonist, ABT-627, the flavoprotein inhibitor diphenyleneiodonium, and the NADPH oxidase inhibitor apocynin but not by the nitric oxide synthase inhibitor N(omega)-L-arginine methyl ester or the xanthine oxidase inhibitor allopurinol. Furthermore, in vivo blockade of ET(A) receptors significantly reduced arterial superoxide levels, with a concomitant decrease of systolic blood pressure in DOCA-salt rats. Ex vivo gene transfer of manganese superoxide dismutase or endothelial nitric oxide synthase also suppressed superoxide levels in carotid arteries of DOCA-salt rats.

CONCLUSIONS

These findings suggest that ET-1 augments vascular superoxide production at least in part via an ET(A)/NADPH oxidase pathway in low-renin mineralocorticoid hypertension.

Heterozygous deficiency of hypoxia-inducible factor-2alpha protects mice against pulmonary hypertension and right ventricular dysfunction during prolonged hypoxia

Chronic hypoxia induces pulmonary vascular remodeling, leading to pulmonary hypertension, right ventricular hypertrophy, and heart failure. Heterozygous deficiency of hypoxia-inducible factor-1alpha (HIF-1alpha), which mediates the cellular response to hypoxia by increasing expression of genes involved in erythropoiesis and angiogenesis, has been previously shown to delay hypoxia-induced pulmonary hypertension. HIF-2alpha is a homologue of HIF-1alpha and is abundantly expressed in the lung, but its role in pulmonary hypertension remains unknown. Therefore, we analyzed the pulmonary response of WT and viable heterozygous HIF-2alpha-deficient (Hif2alpha(+/-)) mice after exposure to 10% O(2) for 4 weeks. In contrast to WT mice, Hif2alpha(+/-) mice were fully protected against pulmonary hypertension and right ventricular hypertrophy, unveiling a critical role of HIF-2alpha in hypoxia-induced pulmonary vascular remodeling. Pulmonary expression levels of endothelin-1 and plasma catecholamine levels were increased threefold and 12-fold respectively in WT but not in Hif2alpha(+/-) mice after hypoxia, suggesting that HIF-2alpha-mediated upregulation of these vasoconstrictors contributes to the development of hypoxic pulmonary vascular remodeling.

Endothelial mitochondrial oxidative stress determines podocyte depletion in segmental glomerulosclerosis

Focal segmental glomerular sclerosis (FSGS) is a primary kidney disease that is commonly associated with proteinuria and progressive loss of glomerular function, leading to development of chronic kidney disease (CKD). FSGS is characterized by podocyte injury and depletion and collapse of glomerular capillary segments. Progression of FSGS is associated with TGF-β activation in podocytes; however, it is not clear how TGF-β signaling promotes disease. Here, we determined that podocyte-specific activation of TGF-β signaling in transgenic mice and BALB/c mice with Adriamycin-induced glomerulosclerosis is associated with endothelin-1 (EDN1) release by podocytes, which mediates mitochondrial oxidative stress and dysfunction in adjacent endothelial cells via paracrine EDN1 receptor type A (EDNRA) activation. Endothelial dysfunction promoted podocyte apoptosis, and inhibition of EDNRA or scavenging of mitochondrial-targeted ROS prevented podocyte loss, albuminuria, glomerulosclerosis, and renal failure. We confirmed reciprocal crosstalk between podocytes and endothelial cells in a coculture system. Biopsies from patients with FSGS exhibited increased mitochondrial DNA damage, consistent with EDNRA-mediated glomerular endothelial mitochondrial oxidative stress. Our studies indicate that segmental glomerulosclerosis develops as a result of podocyte-endothelial crosstalk mediated by EDN1/EDNRA-dependent mitochondrial dysfunction and suggest that targeting the reciprocal interaction between podocytes and endothelia may provide opportunities for therapeutic intervention in FSGS.

Endothelin 1 in cancer: biological implications and therapeutic opportunities

Activation of autocrine and paracrine signalling by endothelin 1 (ET1) binding to its receptors elicits pleiotropic effects on tumour cells and on the host microenvironment. This activation modulates cell proliferation, apoptosis, migration, epithelial-to-mesenchymal transition, chemoresistance and neovascularization, thus providing a strong rationale for targeting ET1 receptors in cancer. In this Review, we discuss the advances in our understanding of the diverse biological roles of ET1 in cancer and describe the latest preclinical and clinical progress that has been made using small-molecule antagonists of ET1 receptors that inhibit ET1-driven signalling.

Elevated blood urea nitrogen level as a predictor of mortality in patients admitted for decompensated heart failure

BACKGROUND

Hospitalization for decompensated heart failure is associated with high mortality after discharge. In heart failure, renal function involves both cardiovascular and hemodynamic properties. We studied the relation between renal dysfunction and mortality in patients admitted for decompensated heart failure.

METHODS

The prognostic importance of four measures of renal function-blood urea nitrogen, serum creatinine, blood urea nitrogen/creatinine ratio, and estimated creatinine clearance-was evaluated in 541 patients (mean [+/- SD] age, 63 +/- 14 years; 377 men [70%]) with a previous diagnosis of heart failure (96% with New York Heart Association class III or IV symptoms) who were admitted for clinical decompensation.

RESULTS

During a mean follow-up of 343 +/- 185 days, 177 patients (33%) died. In multivariable Cox regression models, the risk of all-cause mortality increased with each quartile of blood urea nitrogen, with an adjusted relative risk of 2.3 in patients in the upper compared with the lower quartiles (95% confidence interval [CI]: 1.3 to 4.1; P = 0.005). Creatinine and estimated creatinine clearance were not significant predictors of mortality after adjustment for other covariates. Blood urea nitrogen/creatinine ratio yielded similar prognostic information as blood urea nitrogen (adjusted relative risk = 2.3; 95% CI: 1.4 to 3.8; P = 0.0007 for patients in the upper compared with the lower quartiles).

CONCLUSION

Blood urea nitrogen is a simple clinical variable that provides useful prognostic information in patients admitted for decompensated heart failure. In this setting, elevated blood urea nitrogen levels probably reflect the cumulative effects of hemodynamic and neurohormonal alterations that result in renal hypoperfusion.

Molecular and cellular basis of pulmonary vascular remodeling in pulmonary hypertension

Clinical pulmonary hypertension is characterized by a sustained elevation in pulmonary arterial pressure. Pulmonary vascular remodeling involves structural changes in the normal architecture of the walls of pulmonary arteries. The process of vascular remodeling can occur as a primary response to injury, or stimulus such as hypoxia, within the resistance vessels of the lung. Alternatively, the changes seen in more proximal vessels may arise secondary to a sustained increase in intravascular pressure. To withstand the chronic increase in intraluminal pressure, the vessel wall becomes thickened and stronger. This "armouring" of the vessel wall with extra-smooth muscle and extracellular matrix leads to a decrease in lumen diameter and reduced capacity for vasodilatation. This maladaptive response results in increased pulmonary vascular resistance and consequently, sustained pulmonary hypertension. The process of pulmonary vascular remodeling involves all layers of the vessel wall and is complicated by the finding that cellular heterogeneity exists within the traditional compartments of the vascular wall: intima, media, and adventitia. In addition, the developmental stage of the organism greatly modifies the response of the pulmonary circulation to injury. This review focuses on the latest advances in our knowledge of these processes as they relate to specific forms of pulmonary hypertension and particularly in the light of recent genetic studies that have identified specific pathways involved in the pathogenesis of severe pulmonary hypertension.

Insulin resistance in spontaneously hypertensive rats is associated with endothelial dysfunction characterized by imbalance between NO and ET-1 production

Insulin stimulates production of NO in vascular endothelium via activation of phosphatidylinositol (PI) 3-kinase, Akt, and endothelial NO synthase. We hypothesized that insulin resistance may cause imbalance between endothelial vasodilators and vasoconstrictors (e.g., NO and ET-1), leading to hypertension. Twelve-week-old male spontaneously hypertensive rats (SHR) were hypertensive and insulin resistant compared with control Wistar-Kyoto (WKY) rats (systolic blood pressure 202 +/- 11 vs. 132 +/- 10 mmHg; fasting plasma insulin 5 +/- 1 vs. 0.9 +/- 0.1 ng/ml; P < 0.001). In WKY rats, insulin stimulated dose-dependent relaxation of mesenteric arteries precontracted with norepinephrine (NE) ex vivo. This depended on intact endothelium and was blocked by genistein, wortmannin, or N(omega)-nitro-l-arginine methyl ester (inhibitors of tyrosine kinase, PI3-kinase, and NO synthases, respectively). Vasodilation in response to insulin (but not ACh) was impaired by 20% in SHR (vs. WKY, P < 0.005). Preincubation of arteries with insulin significantly reduced the contractile effect of NE by 20% in WKY but not SHR rats. In SHR, the effect of insulin to reduce NE-mediated vasoconstriction became evident when insulin pretreatment was accompanied by ET-1 receptor blockade (BQ-123, BQ-788). Similar results were observed during treatment with the MEK inhibitor PD-98059. In addition, insulin-stimulated secretion of ET-1 from primary endothelial cells was significantly reduced by pretreatment of cells with PD-98059 (but not wortmannin). We conclude that insulin resistance in SHR is accompanied by endothelial dysfunction in mesenteric vessels with impaired PI3-kinase-dependent NO production and enhanced MAPK-dependent ET-1 secretion. These results may reflect pathophysiology in other vascular beds that directly contribute to elevated peripheral vascular resistance and hypertension.

Pulmonary clearance of circulating endothelin-1 in dogs in vivo: exclusive role of ETB receptors

The pulmonary circulation plays an important role in the removal of circulating endothelin-1 (ET-1). Plasma ET-1 levels are increased in pulmonary hypertensive states of various etiologies (e.g., idiopathic, heart failure, and congenital anomalies) in proportion to the severity of pulmonary hypertension. It is possible that reduced pulmonary clearance of this peptide contributes to the hyperendothelinemia of those pathologies. The ETA and ETB receptors are abundant in lung tissues: on the vascular endothelium, the ETB receptor is predominant and may contribute to ET-1 extraction through receptor-mediated endocytosis. We designed experiments to determine and quantify the importance of the ETA and ETB receptors in the pulmonary extraction of circulating ET-1 in anesthetized dogs. The single-pass cumulative tracer ET-1 extraction by the lung was measured with the indicator-dilution technique before and 5 min after intrapulmonary injection of the specific ETA antagonist BQ-123 (n = 5, 120-960 nmol) and the specific ETB antagonist BQ-788 (n = 6, 1,000 nmol). The inhibitors had no significant effect on pulmonary and systemic hemodynamics. Mean cumulative pulmonary ET-1 extraction was not modified by BQ-123 [control (C): 36 +/- 4%, antagonist (A): 34 +/- 6%] but was completely abolished by BQ-788 (C: 34 +/- 6%, A: 0 +/- 2%, P < 0.001). The pulmonary rate constant (K) for ET-1 removal was also unaffected by BQ-123 (C: 0.050 +/- 0.0085 s-1, A: 0.047 +/- 0.012 s-1) but significantly decreased and became close to zero after BQ-788 (C: 0.058 +/- 0.014 s-1, A: 0.009 +/- 0.007 s-1, P < 0.1). We conclude that the ETB receptor is completely and exclusively responsible for pulmonary ET-1 removal in vivo. Future studies are needed to show whether desensitization or downregulation of the ETB receptor may contribute to the increase in circulating ET-1 levels in conditions associated with pulmonary hypertension. This novel pulmonary endothelial cell function may play a protective role by modulating circulating ET-1 levels in the systemic circulation.

The contribution of interleukin (IL)-4 and IL-13 to the epithelial-mesenchymal trophic unit in asthma

Interleukin (IL)-4 and IL-13 are key proinflammatory cytokines in asthma. Studies in transgenic mice show that both cytokines cause inflammation, but only IL-13 causes subepithelial fibrosis, a characteristic feature of asthma. We compared the in vitro profibrogenic effects of IL-4 and IL-13 using bronchial fibroblasts from asthmatic subjects. In the presence of transforming growth factor (TGF)-beta the cells transformed into contractile myofibroblasts and expressed alpha-smooth muscle actin and procollagen I. IL-4 and IL-13 also stimulated proliferation, but were relatively ineffective in promoting myofibroblast transformation. TGF-beta was more potent than the cytokines in stimulating release of endothelin-1 and vascular endothelial growth factor, whereas IL-4 and IL-13 were more potent stimuli for eotaxin release. Although neither IL-4 nor IL-13 induced profibrotic responses, both cytokines caused a corticosteroid-insensitive stimulation of TGF-beta2 release from primary bronchial epithelial cells. These data indicate that epithelial activation by IL-13 or IL-4 plays a critical role in initiating remodeling through release of TGF-beta2. TGF-beta2 then activates the underlying myofibroblasts to secrete matrix proteins and smooth muscle and vascular mitogens to propagate remodeling changes into the submucosa. In contrast, direct activation of submucosal fibroblasts by IL-4 and IL-13 has a proinflammatory effect via eotaxin release and recruitment of eosinophils into the airways.

Insulin stimulates both endothelin and nitric oxide activity in the human forearm

BACKGROUND

The mechanism of the hemodynamic effect of insulin in the skeletal muscle circulation has not been fully elucidated. The purpose of this study was to assess whether the hemodynamic response to insulin involves the concurrent release of endothelin (ET-1) and nitric oxide (NO), 2 substances with opposing vasoactive properties.

METHODS AND RESULTS

Bioactivity of ET-1 and NO was assessed without insulin and during insulin infusion in the forearm circulation of healthy subjects by use of blockers of ET-1 receptors and by NO synthesis inhibition. In the absence of hyperinsulinemia, ET-1 receptor blockade did not result in any significant change in forearm blood flow from baseline (P=0.29). Intra-arterial insulin administration did not significantly modify forearm blood flow (P=0. 88). However, in the presence of hyperinsulinemia, ET-1 receptor antagonism was associated with a significant vasodilator response (P<0.001). In the presence of ET-1 receptor blockade, the vasoconstrictor response to NO inhibition by N(G)-monomethyl-L-arginine was significantly higher after insulin infusion than in the absence of hyperinsulinemia (P=0.006).

CONCLUSIONS

These findings suggest that in the skeletal muscle circulation, insulin stimulates both ET-1 and NO activity. An imbalance between the release of these 2 substances may be involved in the pathophysiology of hypertension and atherosclerosis in insulin-resistant states associated with endothelial dysfunction.

Human pulmonary circulation is an important site for both clearance and production of endothelin-1

BACKGROUND

Animal studies suggest a major role of the pulmonary circulation in the clearance of circulating endothelin-1 (ET-1). The contribution of the human pulmonary circulation to plasma ET-1 clearance, however, has never been quantified. The absence of an AV gradient in plasma ET-1 has previously been interpreted as evidence that the lungs do not have a role in modulating circulating ET-1 levels. This study was designed to quantify and discern between pulmonary ET-1 clearance and production in humans.

METHODS AND RESULTS

We studied 13 subjects by combining the multiple indicator-dilution technique with the measurement of immunoreactive ET-1 (irET-1). All patients had normal left ventricular ejection fractions (61 +/- 7%, mean +/- SD) and baseline hemodynamics. Mean pulmonary ET-1 extraction was 47 +/- 7%. The ET-1 extracted does not return to circulation and can be characterized by a sequestration rate constant: Kseq = 0.048 +/- 0.019 s-1. There was no significant difference between irET-1 levels from the pulmonary artery and aorta (0.61 +/- 0.29 and 0.68 +/- 0.33 pg/mL, respectively; P = .22); the normal lung consequently produces an amount of ET-1 that is quantitatively similar to the amount that has been extracted.

CONCLUSIONS

The human lung is an important site for both clearance and production of ET-1. There is a normal physiological balance of ET-1 across the pulmonary circulation, which explains the absence of difference in AV ET-1 levels despite a 47 +/- 7% clearance. Reduced pulmonary clearance or increased production of this peptide may contribute to the increase in circulating levels found in various cardiovascular conditions.

sucker encodes a zebrafish Endothelin-1 required for ventral pharyngeal arch development

Mutation of sucker (suc) disrupts development of the lower jaw and other ventral cartilages in pharyngeal segments of the zebrafish head. Our sequencing, cosegregation and rescue results indicate that suc encodes an Endothelin-1 (Et-1). Like mouse and chick Et-1, suc/et-1 is expressed in a central core of arch paraxial mesoderm and in arch epithelia, both surface ectoderm and pharyngeal endoderm, but not in skeletogenic neural crest. Long before chondrogenesis, suc/et-1 mutant embryos have severe defects in ventral arch neural crest expression of dHAND, dlx2, msxE, gsc, dlx3 and EphA3 in the anterior arches. Dorsal expression patterns are unaffected. Later in development, suc/et-1 mutant embryos display defects in mesodermal and endodermal tissues of the pharynx. Ventral premyogenic condensations fail to express myoD, which correlates with a ventral muscle defect. Further, expression of shh in endoderm of the first pharyngeal pouch fails to extend as far laterally as in wild types. We use mosaic analyses to show that suc/et-1 functions nonautonomously in neural crest cells, and is thus required in the environment of postmigratory neural crest cells to specify ventral arch fates. Our mosaic analyses further show that suc/et-1 nonautonomously functions in mesendoderm for ventral arch muscle formation. Collectively our results support a model for dorsoventral patterning of the gnathostome pharyngeal arches in which Et-1 in the environment of the postmigratory cranial neural crest specifies the lower jaw and other ventral arch fates.