Beta-adrenergic stimulation contributes to maintenance of endothelial barrier functions under baseline conditions

cAMP: A master regulator of cadherin-mediated binding in endothelium, epithelium and myocardium

Regulation of cadherin-mediated cell adhesion is crucial not only for maintaining tissue integrity and barrier function in the endothelium and epithelium but also for electromechanical coupling within the myocardium. Therefore, loss of cadherin-mediated adhesion causes various disorders, including vascular inflammation and desmosome-related diseases such as the autoimmune blistering skin dermatosis pemphigus and arrhythmogenic cardiomyopathy. Mechanisms regulating cadherin-mediated binding contribute to the pathogenesis of diseases and may also be used as therapeutic targets. Over the last 30 years, cyclic adenosine 3',5'-monophosphate (cAMP) has emerged as one of the master regulators of cell adhesion in endothelium and, more recently, also in epithelial cells as well as in cardiomyocytes. A broad spectrum of experimental models from vascular physiology and cell biology applied by different generations of researchers provided evidence that not only cadherins of endothelial adherens junctions (AJ) but also desmosomal contacts in keratinocytes and the cardiomyocyte intercalated discs are central targets in this scenario. The molecular mechanisms involve protein kinase A- and exchange protein directly activated by cAMP-mediated regulation of Rho family GTPases and S665 phosphorylation of the AJ and desmosome adaptor protein plakoglobin. In line with this, phosphodiesterase 4 inhibitors such as apremilast have been proposed as a therapeutic strategy to stabilize cadherin-mediated adhesion in pemphigus and may also be effective to treat other disorders where cadherin-mediated binding is compromised.

Acute Respiratory Distress Syndrome; A Review of Recent Updates and a Glance into the Future

Acute respiratory distress syndrome (ARDS) is a rapidly progressive form of respiratory failure that accounts for 10% of admissions to the ICU and is associated with approximately 40% mortality in severe cases. Despite significant mortality and healthcare burden, the mainstay of management remains supportive care. The recent pandemic of SARS-CoV-2 has re-ignited a worldwide interest in exploring the pathophysiology of ARDS, looking for innovative ideas to treat this disease. Recently, many trials have been published utilizing different pharmacotherapy targets; however, the long-term benefits of these agents remain unknown. Metabolomics profiling and stem cell transplantation offer strong enthusiasm and may completely change the outlook of ARDS management in the near future.

Pathophysiological, Cellular, and Molecular Events of the Vascular System in Anaphylaxis

Anaphylaxis is a systemic hypersensitivity reaction that can be life threatening. Mechanistically, it results from the immune activation and release of a variety of mediators that give rise to the signs and symptoms of this pathological event. For years, most of the research in anaphylaxis has focused on the contribution of the immune component. However, approaches that shed light on the participation of other cellular and molecular agents are necessary. Among them, the vascular niche receives the various signals (e.g., histamine) that elicit the range of anaphylactic events. Cardiovascular manifestations such as increased vascular permeability, vasodilation, hypotension, vasoconstriction, and cardiac alterations are crucial in the pathophysiology of anaphylaxis and are highly involved to the development of the most severe cases. Specifically, the endothelium, vascular smooth muscle cells, and their molecular signaling outcomes play an essential role downstream of the immune reaction. Therefore, in this review, we synthesized the vascular changes observed during anaphylaxis as well as its cellular and molecular components. As the risk of anaphylaxis exists both in clinical procedures and in routine life, increasing our knowledge of the vascular physiology and their molecular mechanism will enable us to improve the clinical management and how to treat or prevent anaphylaxis.

Key Message

Anaphylaxis, the most severe allergic reaction, involves a variety of immune and non-immune molecular signals that give rise to its pathophysiological manifestations. Importantly, the vascular system is engaged in processes relevant to anaphylactic events such as increased vascular permeability, vasodilation, hypotension, vasoconstriction, and decreased cardiac output. The novelty of this review focuses on the fact that new studies will greatly improve the understanding of anaphylaxis when viewed from a vascular molecular angle and specifically from the endothelium. This knowledge will improve therapeutic options to treat or prevent anaphylaxis.

Catecholaminergic Vasopressors Reduce Toll-Like Receptor Agonist-Induced Microvascular Endothelial Cell Permeability But Not Cytokine Production

Supplemental Digital Content is available in the text.

OBJECTIVES:

Catecholaminergic vasopressors are the cornerstone of circulatory shock management. Nevertheless, catecholamines have problematic side effects, arousing a growing interest in noncatecholaminergic agents such as vasopressin or angiotensin-II. However, their respective effects on sepsis-associated microvascular endothelial dysfunction such as permeability or inflammation remain elusive. We investigated the role of catecholamines and other vasopressors on Toll-like receptor agonists-induced microvascular endothelial permeability and inflammation.

SETTING:

University research laboratory/cell research.

SUBJECTS:

Human pulmonary microvascular endothelial cells from multiple donors.

INTERVENTION:

Confluent monolayers of human pulmonary microvascular endothelial cells were treated with Toll-like receptor agonists (lipopolysaccharide, Poly[I:C], or tripalmitoyl-S-glyceryl cysteine) in the presence or absence of epinephrine, norepinephrine, vasopressin, and angiotensin-II. Permeability was inferred from transendothelial resistance, measured using electrical cell impedance sensing, where decreased transendothelial resistance is consistent with increased permeability. Cell-cell junction molecule expression was assessed via immunofluorescence microscopy and flow cytometry. We quantified cytokines in supernatants of Toll-like receptor agonist-treated human pulmonary microvascular endothelial cells.

MEASUREMENTS AND MAIN RESULTS:

Epinephrine and norepinephrine both ameliorate lipopolysaccharide, polyinosinic:polycytidylic acid, or tripalmitoyl-S-glyceryl cysteine–induced reductions in transendothelial resistance, a surrogate for endothelial permeability. In contrast, the noncatecholaminergic agents, vasopressin, and angiotensin-II did not affect Toll-like receptor agonists-induced reductions in transendothelial resistance. β1- and β2-adrenergic receptor antagonists reduced the effects of the catecholamines on transendothelial resistance, whereas α-adrenergic receptor antagonists did not. We observed that epinephrine and norepinephrine induced actin cytoskeletal rearrangement and normalized the membrane expression of proteins involved with adherens-junctions (vascular endothelial-cadherin) and tight-junctions (zona occludens-1). Despite having a substantial effect on endothelial permeability, epinephrine and norepinephrine did not affect human pulmonary microvascular endothelial cell survival or production of interleukin-8, interleukin-6, or monocyte chemoattractant protein-1 (CCL-2) induced by Toll-like receptor agonists, suggesting that these functions are regulated separately from permeability.

CONCLUSIONS:

Our findings demonstrate that treatment with epinephrine or norepinephrine strongly reduces endothelial permeability induced by agonists of multiple Toll-like receptors (Toll-like receptor-2, Toll-like receptor-3, Toll-like receptor-4) in vitro. Our studies suggest that both β1- and β2-adrenergic receptors mediate the stabilizing effects of epinephrine and norepinephrine on the endothelial barrier.

cAMP Compartmentalization in Cerebrovascular Endothelial Cells: New Therapeutic Opportunities in Alzheimer's Disease

The vascular hypothesis used to explain the pathophysiology of Alzheimer’s disease (AD) suggests that a dysfunction of the cerebral microvasculature could be the beginning of alterations that ultimately leads to neuronal damage, and an abnormal increase of the blood–brain barrier (BBB) permeability plays a prominent role in this process. It is generally accepted that, in physiological conditions, cyclic AMP (cAMP) plays a key role in maintaining BBB permeability by regulating the formation of tight junctions between endothelial cells of the brain microvasculature. It is also known that intracellular cAMP signaling is highly compartmentalized into small nanodomains and localized cAMP changes are sufficient at modifying the permeability of the endothelial barrier. This spatial and temporal distribution is maintained by the enzymes involved in cAMP synthesis and degradation, by the location of its effectors, and by the existence of anchor proteins, as well as by buffers or different cytoplasm viscosities and intracellular structures limiting its diffusion. This review compiles current knowledge on the influence of cAMP compartmentalization on the endothelial barrier and, more specifically, on the BBB, laying the foundation for a new therapeutic approach in the treatment of AD.

Adjuvant Inhaled Corticosteroids in Community-Acquired Pneumonia: A Review Article

Community-acquired pneumonia is still a major cause of morbidity and mortality worldwide. Since the inflammatory response induced by the immune system is often a major contributor to the lung injury, it becomes reasonable to assess the potential benefit of anti-inflammatory agents in treating community-acquired pneumonia. The role of corticosteroids as adjunct anti-inflammatory agents in treating community-acquired pneumonia is still controversial. Several studies have assessed the benefit of their use in patients with community-acquired pneumonia. In most of those studies, the route of corticosteroids administration was systemic. The aim of this article is to provide a concise review of the role of corticosteroids in treating community-acquired pneumonia when administered via inhalational route, with the potential benefit of avoiding systemic side effects of corticosteroids while exerting the same anti-inflammatory effects on the lungs. Conclusion: the use of inhaled corticosteroids may be of benefit in certain patient subsets with community-acquired pneumonia. Further randomized controlled trials are needed for better determination of such patient subsets.

Molecular Dambusters: What Is Behind Hyperpermeability in Bradykinin-Mediated Angioedema?

In the last few decades, a substantial body of evidence underlined the pivotal role of bradykinin in certain types of angioedema. The formation and breakdown of bradykinin has been studied thoroughly; however, numerous questions remained open regarding the triggering, course, and termination of angioedema attacks. Recently, it became clear that vascular endothelial cells have an integrative role in the regulation of vessel permeability. Apart from bradykinin, a great number of factors of different origin, structure, and mechanism of action are capable of modifying the integrity of vascular endothelium, and thus, may participate in the regulation of angioedema formation. Our aim in this review is to describe the most important permeability factors and the molecular mechanisms how they act on endothelial cells. Based on endothelial cell function, we also attempt to explain some of the challenging findings regarding bradykinin-mediated angioedema, where the function of bradykinin itself cannot account for the pathophysiology. By deciphering the complex scenario of vascular permeability regulation and edema formation, we may gain better scientific tools to be able to predict and treat not only bradykinin-mediated but other types of angioedema as well.

Superior Effects of Nebulized Epinephrine to Nebulized Albuterol and Phenylephrine in Burn and Smoke Inhalation-Induced Acute Lung Injury

The severity of burn and smoke inhalation-induced acute lung injury (BSI-ALI) is associated with alveolar and interstitial edema, bronchospasm, and airway mucosal hyperemia. Previously, we have reported beneficial effects of epinephrine nebulization on BSI-ALI. However, the underlying mechanisms of salutary effects of nebulized epinephrine remain unclear. The present study compared the effects of epinephrine, phenylephrine, and albuterol on a model of BSI-ALI. We tested the hypothesis that both α1- and β2-agonist effects are required for ameliorating more efficiently the BSI-ALI. Forty percent of total body surface area, 3rd-degree cutaneous burn, and 48-breaths of cotton smoke inhalation were induced to 46 female Merino sheep. Postinjury, sheep were mechanically ventilated and cardiopulmonary hemodynamics were monitored for 48 h. Sheep were allocated into groups: control, n = 17; epinephrine, n = 11; phenylephrine, n = 6; and albuterol, n = 12. The drug nebulization began 1 h postinjury and was repeated every 4 h thereafter. In the results, epinephrine group significantly improved oxygenation compared to other groups, and significantly reduced pulmonary vascular permeability index, lung wet-to-dry weight ratio, and lung tissue growth factor-β1 level compared with albuterol and control groups. Epinephrine and phenylephrine groups significantly reduced trachea wet-to-dry weight ratio and lung vascular endothelial growth factor-A level compared with control group. Histopathologically, epinephrine group significantly reduced lung severity scores and preserved vascular endothelial-cadherin level in pulmonary arteries. In conclusion, the results of our studies suggest that nebulized epinephrine more effectively ameliorated the severity of BSI-ALI than albuterol or phenylephrine, possibly by its combined α1- and β2-agonist properties.

cAMP signaling primes lung endothelial cells to activate caspase-1 during Pseudomonas aeruginosa infection

Activation of the inflammasome-caspase-1 axis in lung endothelial cells is emerging as a novel arm of the innate immune response to pneumonia and sepsis caused by Pseudomonas aeruginosa. Increased levels of circulating autacoids are hallmarks of pneumonia and sepsis and induce physiological responses via cAMP signaling in targeted cells. However, it is unknown whether cAMP affects other functions, such as P. aeruginosa-induced caspase-1 activation. Herein, we describe the effects of cAMP signaling on caspase-1 activation using a single cell flow cytometry-based assay. P. aeruginosa infection of cultured lung endothelial cells caused caspase-1 activation in a distinct population of cells. Unexpectedly, pharmacological cAMP elevation increased the total number of lung endothelial cells with activated caspase-1. Interestingly, addition of cAMP agonists augmented P. aeruginosa infection of lung endothelial cells as a partial explanation underlying cAMP priming of caspase-1 activation. The cAMP effect(s) appeared to function as a priming signal because addition of cAMP agonists was required either before or early during the onset of infection. However, absolute cAMP levels measured by ELISA were not predictive of cAMP-priming effects. Importantly, inhibition of de novo cAMP synthesis decreased the number of lung endothelial cells with activated caspase-1 during infection. Collectively, our data suggest that lung endothelial cells rely on cAMP signaling to prime caspase-1 activation during P. aeruginosa infection.

[Adrenergic mechanisms of regulation of pulmonary microvessels tonicity and endothelial permeability]

The review contains the data on adrenergic mechanisms of regulation of pulmonary microvessels tonicity and endothelial permeability. On smooth muscle cells of pulmonary vessels there are postsynaptic α1A-, α1B-, α1D- and α2A-, α2B-, α2C-adrenoreceptors whose activation by norepinephrine induces vasoconstriction. Excitation of β1- and β2-subtypes of adrenoreceptors leads to vasodilatation, Activation of α1-2- and β1-3-adrenoreceptors of the endothelium contributes to enhancement of nitric oxide synthesis. The resulting reaction of pulmonary microvessels in response to administration of catecholamines appears be determined by interaction of adrenergic mechanisms of regulation of tonicity of smooth muscle cells and synthesis of nitric oxide by the endothelium. Constrictor and dilator reactions of pulmonary venous vessels in response to activation of α- and β-adrenoreceptors, respectively, are more pronounced than in pulmonary arteries and make a significant contribution to the shifts of pulmonary vascular resistance. Excitation of α2- and β2-adrenoreceptors of endothelial cells of microvessels of the lungs contributes to a decrease in their permeability. In order to find out the role of adrenergic mechanisms in shifts of the capillary filtration coefficient in simulating various pathology of pulmonary circulation, it is necessary to carry out integral studies that would make it possible to evaluate alterations in macro- and microhaemodynamics of the lungs.

In vitro analysis of drugs that improve hyperglycemia-induced blood-brain barrier dysfunction

BACKGROUND

Blood-brain barrier (BBB) disruptions are a key feature of hyperglycemia (HG)-induced cerebral damage. Patients with diabetes mellitus often have other cerebrovascular disease risk factors including hypertension, dyslipidemia, arrhythmia, and atherosclerosis obliterans. However, whether the drugs for these comorbidities are effective for improving HG-induced BBB damage is unclear.

METHODS

We investigated the effect of pitavastatin, candesartan, cilostazol, propranolol, and eicosapentaenoic acid on HG-induced BBB damage. In vitro BBB models consisting of primary cultures of rat brain capillary endothelial cells were subjected to HG (55 mM d-glucose).

RESULTS

We observed a significant decrease in transendothelial electrical resistance (TEER) with HG, showing that HG compromised the integrity of the in vitro BBB model. No significant decrease in cell viability was seen with HG, but HG increased the production of reactive oxygen species. Pitavastatin and candesartan inhibited decreases in TEER induced by HG.

CONCLUSIONS

In summary, pitavastatin and candesartan improved HG-induced BBB damage and this in vitro model of HG-induced BBB dysfunction contributes to the search for BBB protective drugs.

Catecholamines facilitate VEGF-dependent angiogenesis via β2-adrenoceptor-induced Epac1 and PKA activation

Chronic stress has been associated with the progression of cancer and antagonists for β-adrenoceptors (βAR) are regarded as therapeutic option. As they are also used to treat hemangiomas as well as retinopathy of prematurity, a role of endothelial β₂AR in angiogenesis can be envisioned. We therefore investigated the role of β₂AR-induced cAMP formation by analyzing the role of the cAMP effector molecules exchange factor directly activated by cAMP 1 (Epac1) and protein kinase A (PKA) in endothelial cells (EC). Epac1-deficient mice showed a reduced amount of pre-retinal neovascularizations in the model of oxygen-induced retinopathy, which is predominantly driven by vascular endothelial growth factor (VEGF). siRNA-mediated knockdown of Epac1 in human umbilical vein EC (HUVEC) decreased angiogenic sprouting by lowering the expression of the endothelial VEGF-receptor-2 (VEGFR-2). Conversely, Epac1 activation by β₂AR stimulation or the Epac-selective activator cAMP analog 8-p-CPT-2’-O-Me-cAMP (8-pCPT) increased VEGFR-2 levels and VEGF-dependent sprouting. Similar to Epac1 knockdown, depletion of the monomeric GTPase Rac1 decreased VEGFR-2 expression. As Epac1 stimulation induces Rac1 activation, Epac1 might regulate VEGFR-2 expression through Rac1. In addition, we found that PKA was also involved in the regulation of angiogenesis in EC since the adenylyl cyclase (AC) activator forskolin (Fsk), but not 8-pCPT, increased sprouting in Epac1-depleted HUVEC and this increase was sensitive to a selective synthetic peptide PKA inhibitor. In accordance, β₂AR- and AC-activation, but not Epac1 stimulation increased VEGF secretion in HUVEC.

Our data indicate that high levels of catecholamines, which occur during chronic stress, prime the endothelium for angiogenesis through a β₂AR-mediated increase in endothelial VEGFR-2 expression and VEGF secretion.

Mind the gap: mechanisms regulating the endothelial barrier

The endothelial barrier consists of intercellular contacts localized in the cleft between endothelial cells, which is covered by the glycocalyx in a sievelike manner. Both types of barrier-forming junctions, i.e. the adherens junction (AJ) serving mechanical anchorage and mechanotransduction and the tight junction (TJ) sealing the intercellular space to limit paracellular permeability, are tethered to the actin cytoskeleton. Under resting conditions, the endothelium thereby builds a selective layer controlling the exchange of fluid and solutes with the surrounding tissue. However, in the situation of an inflammatory response such as in anaphylaxis or sepsis intercellular contacts disintegrate in post-capillary venules leading to intercellular gap formation. The resulting oedema can cause shock and multi-organ failure. Therefore, maintenance as well as coordinated opening and closure of interendothelial junctions is tightly regulated. The two principle underlying mechanisms comprise spatiotemporal activity control of the small GTPases Rac1 and RhoA and the balance of the phosphorylation state of AJ proteins. In the resting state, junctional Rac1 and RhoA activity is enhanced by junctional components, actin-binding proteins, cAMP signalling and extracellular cues such as sphingosine-1-phosphate (S1P) and angiopoietin-1 (Ang-1). In addition, phosphorylation of AJ components is prevented by junction-associated phosphatases including vascular endothelial protein tyrosine phosphatase (VE-PTP). In contrast, inflammatory mediators inhibiting cAMP/Rac1 signalling cause strong activation of RhoA and induce AJ phosphorylation finally leading to endocytosis and cleavage of VE-cadherin. This results in dissolution of TJs the outcome of which is endothelial barrier breakdown.

β₂-Adrenoceptor Blockade Deteriorates Systemic Anaphylaxis by Enhancing Hyperpermeability in Anesthetized Mice

Purpose

Patients treated with propranolol, a nonselective β-adrenoceptor antagonist, develop severe anaphylaxis, but the mechanism remains unknown. We determined effects of β₁- and β₂-adrenoceptor antagonists on the anaphylaxis-induced increase in vascular permeability in mice.

Methods

In anesthetized ovalbumin-sensitized C57BL mice, mean arterial blood pressure (MBP) was measured, and Evans blue dye extravasation and hematocrit (Hct) were assessed at 20 minutes after antigen injection. The following pretreatment groups (n=7/group) were studied: (1) sensitized control (non-pretreatment), (2) propranolol, (3) the selective β₂-adrenoceptor antagonist ICI 118,551, (4) the selective β₁-adrenoceptor antagonist atenolol, (5) adrenalectomy, (6) the selective β₂-adrenoceptor agonist terbutaline, and (7) non-sensitized groups.

Results

The antigen injection decreased MBP, and increased Hct and vascular permeability in the kidney, lung, mesentery, and intestine, but not in the liver or spleen. Pretreatment with ICI 118,551, propranolol and adrenalectomy, but not atenolol, reduced the survival rate and augmented the increases in Hct and vascular permeability in the kidney, intestine, and lung as compared with the sensitized control group. Pretreatment with terbutaline abolished the antigen-induced alterations. Plasma epinephrine levels were increased significantly in the sensitize control mice.

Conclusions

Blockade of β₂-adrenoceptor can deteriorate systemic anaphylaxis by augmenting hyperpermeability-induced increase in plasma extravasation by inhibiting beneficial effects of epinephrine released from the adrenal glands in anesthetized mice.

Endothelial Regulator of Calcineurin 1 Promotes Barrier Integrity and Modulates Histamine-Induced Barrier Dysfunction in Anaphylaxis

Anaphylaxis, the most serious and life-threatening allergic reaction, produces the release of inflammatory mediators by mast cells and basophils. Regulator of calcineurin 1 (Rcan1) is a negative regulator of mast-cell degranulation. The action of mediators leads to vasodilation and an increase in vascular permeability, causing great loss of intravascular volume in a short time. Nevertheless, the molecular basis remains unexplored on the vascular level. We investigated Rcan1 expression induced by histamine, platelet-activating factor (PAF), and epinephrine in primary human vein (HV)-/artery (HA)-derived endothelial cells (ECs) and human dermal microvascular ECs (HMVEC-D). Vascular permeability was analyzed in vitro in human ECs with forced Rcan1 expression using Transwell migration assays and in vivo using Rcan1 knockout mice. Histamine, but neither PAF nor epinephrine, induced Rcan1-4 mRNA and protein expression in primary HV-ECs, HA-ECs, and HMVEC-D through histamine receptor 1 (H1R). These effects were prevented by pharmacological inhibition of calcineurin with cyclosporine A. Moreover, intravenous histamine administration increased Rcan1 expression in lung tissues of mice undergoing experimental anaphylaxis. Functional in vitro assays showed that overexpression of Rcan1 promotes barrier integrity, suggesting a role played by this molecule in vascular permeability. Consistent with these findings, in vivo models of subcutaneous and intravenous histamine-mediated fluid extravasation showed increased response in skin, aorta, and lungs of Rcan1-deficient mice compared with wild-type animals. These findings reveal that endothelial Rcan1 is synthesized in response to histamine through a calcineurin-sensitive pathway and may reduce barrier breakdown, thus contributing to the strengthening of the endothelium and resistance to anaphylaxis. These new insights underscore its potential role as a regulator of sensitivity to anaphylaxis in humans.

Mechanisms of endothelial cell dysfunction in cystic fibrosis

Although cystic fibrosis (CF) patients exhibit signs of endothelial perturbation, the functions of the cystic fibrosis conductance regulator (CFTR) in vascular endothelial cells (EC) are poorly defined. We sought to uncover biological activities of endothelial CFTR, relevant for vascular homeostasis and inflammation. We examined cells from human umbilical cords (HUVEC) and pulmonary artery isolated from non-cystic fibrosis (PAEC) and CF human lungs (CF-PAEC), under static conditions or physiological shear. CFTR activity, clearly detected in HUVEC and PAEC, was markedly reduced in CF-PAEC. CFTR blockade increased endothelial permeability to macromolecules and reduced trans‑endothelial electrical resistance (TEER). Consistent with this, CF-PAEC displayed lower TEER compared to PAEC. Under shear, CFTR blockade reduced VE-cadherin and p120 catenin membrane expression and triggered the formation of paxillin- and vinculin-enriched membrane blebs that evolved in shrinking of the cell body and disruption of cell-cell contacts. These changes were accompanied by enhanced release of microvesicles, which displayed reduced capability to stimulate proliferation in recipient EC. CFTR blockade also suppressed insulin-induced NO generation by EC, likely by inhibiting eNOS and AKT phosphorylation, whereas it enhanced IL-8 release. Remarkably, phosphodiesterase inhibitors in combination with a β₂ adrenergic receptor agonist corrected functional and morphological changes triggered by CFTR dysfunction in EC. Our results uncover regulatory functions of CFTR in EC, suggesting a physiological role of CFTR in the maintenance EC homeostasis and its involvement in pathogenetic aspects of CF. Moreover, our findings open avenues for novel pharmacology to control endothelial dysfunction and its consequences in CF.

The neuropeptide galanin promotes an anti-thrombotic phenotype on endocardial endothelial cells from heart failure patients

Thromboembolic complications are a significant cause of mortality and re-hospitalization in heart failure (HF) patients. One source of thrombi is the ventricular endocardial surface that becomes increasingly pro-thrombotic as HF progresses. Anticoagulation comes with bleeding risks so identifying therapeutic agents for improving cardiac endothelial health are of critical clinical importance. Endocardial endothelial cells are closely apposed to cardiac sympathetic nerves. In HF, cardiac sympathetic nerves are dysregulated and promote disease progression. Whether endocardial endothelial health and function is impacted by sympathetic dysregulation in HF is unknown. Also unexplored is the impact of neuropeptides, such as galanin and neuropeptide Y (NPY), co-released from sympathetic nerve terminals, on endothelial health. In this study we examined the effect of sympathetic nerve-released neurotransmitters and neuropeptides on the procoagulant phenotype of cultured human endocardial endothelial cells from HF patients. As a functional readout of procoagulant state we examined thrombin-mediated von Willebrand factor (vWF) extrusion and multimer expression. We demonstrate that vWF extrusion and multimer expression is promoted by thrombin, that isoproterenol (a beta-adrenergic receptor agonist) augments this effect, whereas co-treatment with the beta-blockers propranolol and carvedilol blocks this effect. We also show that vWF extrusion and multimer expression is attenuated by treatment with the neuropeptide galanin, but not with NPY. Our results are consistent with a protective role of beta-blockers and galanin on endocardial endothelial health in heart failure. Improving endothelial health through galanin therapy is a future clinical application of this study.

Intraspinal Pressure Monitoring and Extensive Duroplasty in the Acute Phase of Traumatic Spinal Cord Injury: A Systematic Review

OBJECTIVE

The prognosis in cervical spinal cord injury is poor, and surgical and neurointensive care management need further improvement. Monitoring of the intraspinal pressure (ISP) at an early stage after traumatic spinal cord injury (tSCI) is useful clinically.

MATERIALS AND METHODS

Obtaining continuous spinal cord perfusion pressure (SCPP) measurements based on the difference between mean arterial pressure and ISP allows offering best medical and surgical treatment during this critical phase of tSCI. A search was carried out with PubMed, Embase, and Google Scholar up to January 10, 2017. Articles resulting from these searches and relevant references cited in those articles were reviewed.

RESULTS

The optimal SCPP was found to be between 90 and 100 mm Hg and mean arterial pressure of 110-130. Laminectomy alone was found to be ineffective in the reduction of ISP because it does not lower the pressure exerted by dura on the swollen spinal cord. Therefore, bony decompression with durotomy or duroplasty seems to be the procedure of choice to reduce the ISP less than 20 mm Hg.

CONCLUSIONS

A randomized controlled trial is required to determine whether laminectomy with durotomy and monitoring of ISP with SCPP optimization improve neurological recovery after tSCI.

Randomized Clinical Trial of a Combination of an Inhaled Corticosteroid and Beta Agonist in Patients at Risk of Developing the Acute Respiratory Distress Syndrome

OBJECTIVES

Effective pharmacologic treatments directly targeting lung injury in patients with the acute respiratory distress syndrome are lacking. Early treatment with inhaled corticosteroids and beta agonists may reduce progression to acute respiratory distress syndrome by reducing lung inflammation and enhancing alveolar fluid clearance.

DESIGN

Double-blind, randomized clinical trial (ClinicalTrials.gov: NCT01783821). The primary outcome was longitudinal change in oxygen saturation divided by the FIO2 (S/F) through day 5. We also analyzed categorical change in S/F by greater than 20%. Other outcomes included need for mechanical ventilation and development of acute respiratory distress syndrome.

SETTING

Five academic centers in the United States.

PATIENTS

Adult patients admitted through the emergency department at risk for acute respiratory distress syndrome.

INTERVENTIONS

Aerosolized budesonide/formoterol versus placebo bid for up to 5 days.

MEASUREMENTS AND MAIN RESULTS

Sixty-one patients were enrolled from September 3, 2013, to June 9, 2015. Median time from presentation to first study drug was less than 9 hours. More patients in the control group had shock at enrollment (14 vs 3 patients). The longitudinal increase in S/F was greater in the treatment group (p = 0.02) and independent of shock (p = 0.04). Categorical change in S/F improved (p = 0.01) but not after adjustment for shock (p = 0.15). More patients in the placebo group developed acute respiratory distress syndrome (7 vs 0) and required mechanical ventilation (53% vs 21%).

CONCLUSIONS

Early treatment with inhaled budesonide/formoterol in patients at risk for acute respiratory distress syndrome is feasible and improved oxygenation as assessed by S/F. These results support further study to test the efficacy of inhaled corticosteroids and beta agonists for prevention of acute respiratory distress syndrome.

Increased microvascular permeability in mice lacking Epac1 (Rapgef3)

Aim

Maintenance of the blood and extracellular volume requires tight control of endothelial macromolecule permeability, which is regulated by cAMP signalling. This study probes the role of the cAMP mediators rap guanine nucleotide exchange factor 3 and 4 (Epac1 and Epac2) for in vivo control of microvascular macromolecule permeability under basal conditions.

Methods

Epac1^−/− and Epac2^−/− C57BL/6J mice were produced and compared with wild‐type mice for transvascular flux of radio‐labelled albumin in skin, adipose tissue, intestine, heart and skeletal muscle. The transvascular leakage was also studied by dynamic contrast‐enhanced magnetic resonance imaging (DCE‐MRI) using the MRI contrast agent Gadomer‐17 as probe.

Results

Epac1^−/− mice had constitutively increased transvascular macromolecule transport, indicating Epac1‐dependent restriction of baseline permeability. In addition, Epac1^−/− mice showed little or no enhancement of vascular permeability in response to atrial natriuretic peptide (ANP), whether probed with labelled albumin or Gadomer‐17. Epac2^−/− and wild‐type mice had similar basal and ANP‐stimulated clearances. Ultrastructure analysis revealed that Epac1^−/− microvascular interendothelial junctions had constitutively less junctional complex.

Conclusion

Epac1 exerts a tonic inhibition of in vivo basal microvascular permeability. The loss of this tonic action increases baseline permeability, presumably by reducing the interendothelial permeability resistance. Part of the action of ANP to increase permeability in wild‐type microvessels may involve inhibition of the basal Epac1‐dependent activity.

Epinephrine inhibits vascular hyperpermeability during platelet-activating factor- or ovalbumin-induced anaphylaxis

Platelet-activating factor (PAF) has been shown to play a critical role in mediating vascular hyperpermeability during anaphylaxis.

Long-term cilostazol administration ameliorates memory decline in senescence-accelerated mouse prone 8 (SAMP8) through a dual effect on cAMP and blood-brain barrier

Phosphodiesterases (PDEs), which hydrolyze and inactivate 3', 5'-cyclic adenosine monophosphate (cAMP) and 3', 5'-cyclic guanosine monophosphate (cGMP), play an important role in synaptic plasticity that underlies memory. Recently, several PDE inhibitors were assessed for their possible therapeutic efficacy in treating cognitive disorders. Here, we examined how cilostazol, a selective PDE3 inhibitor, affects brain functions in senescence-accelerated mouse prone 8 (SAMP8), an animal model of age-related cognitive impairment. Long-term administration of cilostazol restored the impaired context-dependent conditioned fear memory of SAMP8 to match that in normal aging control substrain SAMR1. Cilostazol also increased the number of cells containing phosphorylated cAMP-responsive element binding protein (CREB), a downstream component of the cAMP pathway. Finally, cilostazol improves blood-brain barrier (BBB) integrity, demonstrated by reduced extravasation of 2-deoxy-2-¹⁸F-fluoro-d-glucose and Evans Blue dye in the brains of SAMP8. This improvement in BBB integrity was associated with an increased amount of zona occludens protein 1 (ZO-1) and occludin proteins, components of tight junctions integral to the BBB. The results suggest that long-term administration of cilostazol exerts its beneficial effects on age-related cognitive impairment through a dual mechanism: by enhancing the cAMP system in the brain and by maintaining or improving BBB integrity.

Activation peptide of coagulation factor IX regulates endothelial permeability

Endothelial hyperpermeability is involved in several critical illnesses, and its regulatory mechanisms have been intensively investigated. It was recently reported that the activation peptide of coagulation factor IX enhances cell matrix and intercellular adhesion. The aim of this study was to investigate the role of activation peptide of coagulation factor IX in intercellular adhesion of endothelial cells and evaluate its effects on endothelial permeability. In the presence of activation peptide, cells spread with lamellipodium-like broad protrusions multidirectionally, increasing the area of adhesion to matrix by 16% within 30 minutes. In intercellular adhesion, treatment with activation peptide induced overlapping of adjacent cell edges and remodeling of intercellular adhesion sites, with colocalization of the adherens junction proteins VE-cadherin and β-catenin and a marker protein of the lateral border recycling compartment, PECAM. Activation peptide decreased gaps between cells by 66% in cultured endothelial cells and suppressed increased endothelial cell monolayer permeability induced by interleukin-1β in a dose-dependent manner. Treatment with activation peptide decreased eNOS protein expression and altered its subcellular distribution, decreasing intracellular cGMP. An analogue of cGMP suppressed the effects of activation peptide on cell spreading. In addition, the effect of activation peptide on hyperpermeability was investigated in mice injected with lipopolysaccharide. Intravenous injection of lipopolysaccharide increased lung weight by 28%, and treatment with activation peptide significantly suppressed the increase in lung weight to 5%. Our results indicate that activation peptide of factor IX regulates endothelial intercellular adhesion and thus could be used in the treatment of vascular hyperpermeability.

Regulation of β-adrenergic receptor trafficking and lung microvascular endothelial cell permeability by Rab5 GTPase

Rab5 GTPase modulates the trafficking of the cell surface receptors, including G protein-coupled β-adrenergic receptors (β-ARs). Here, we have determined the role of Rab5 in regulating the internalization of β-ARs in lung microvascular endothelial cells (LMECs) and in maintaining the integrity and permeability of endothelial cell barrier. Our data demonstrate that lipopolysaccharide (LPS) treatment disrupts LMEC barrier function and reduces the cell surface expression of β-ARs. Furthermore, the activation of β-ARs, particularly β2-AR, is able to protect the LMEC permeability from LPS injury. Moreover, siRNA-mediated knockdown of Rab5 inhibits both the basal and agonist-provoked internalization of β-ARs, therefore, enhancing the cell surface expression of the receptors and receptor-mediated ERK1/2 activation. Importantly, knockdown of Rab5 not only inhibits the LPS-induced effects on β-ARs but also protects the LMEC monolayer permeability. All together, these data provide strong evidence indicating a crucial role of Rab5-mediated internalization of β-ARs in functional regulation of LMECs.

Adducin is involved in endothelial barrier stabilization

Adducins tightly regulate actin dynamics which is critical for endothelial barrier function. Adducins were reported to regulate epithelial junctional remodeling by controlling the assembly of actin filaments at areas of cell-cell contact. Here, we investigated the role of α-adducin for endothelial barrier regulation by using microvascular human dermal and myocardial murine endothelial cells. Parallel transendothelial electrical resistance (TER) measurements and immunofluorescence analysis revealed that siRNA-mediated adducin depletion impaired endothelial barrier formation and led to severe fragmentation of VE-cadherin immunostaining at cell-cell borders. To further test whether the peripheral localization of α-adducin is functionally linked with the integrity of endothelial adherens junctions, junctional remodeling was induced by a Ca(2+)-switch assay. Ca(2+)-depletion disturbed both linear vascular endothelial (VE)-cadherin and adducin location along cell junctions, whereas their localization was restored following Ca(2+)-repletion. Similar results were obtained for α-adducin phosphorylated at a site typical for PKA (pSer481). To verify that endothelial barrier properties and junction reorganization can be effectively modulated by altering Ca(2+)-concentration, TER measurements were performed. Thus, Ca(2+)-depletion drastically reduced TER, whereas Ca(2+)-repletion led to recovery of endothelial barrier properties resulting in increased TER. Interestingly, the Ca(2+)-dependent increase in TER was also significantly reduced after efficient α-adducin downregulation. Finally, we report that inflammatory mediator-induced endothelial barrier breakdown is associated with loss of α-adducin from the cell membrane. Taken together, our results indicate that α-adducin is involved in remodeling of endothelial adhesion junctions and thereby contributes to endothelial barrier regulation.

cAMP controls the restoration of endothelial barrier function after thrombin-induced hyperpermeability via Rac1 activation

Inflammatory mediators like thrombin disrupt endothelial adherens junctions (AJs) and barrier integrity leading to oedema formation followed by resealing of AJs and a slow recovery of the barrier function. The molecular mechanisms of this process have not yet been fully delineated. The aim of the present study was to analyse the molecular mechanism of endothelial barrier recovery and thrombin was used as model inflammatory mediator. Thrombin caused a strong increase in endothelial permeability within 10 min accompanied by loss of Rac1 but not cdc42 activity, drop in cellular cAMP contents, and a strong activation of the endothelial contractile machinery mainly via RhoA/Rock signalling. Activation of RhoA/Rock signalling precedes and is dependent upon a rise in the cytosolic Ca²⁺ concentration. Inhibition of cytosolic Ca²⁺ rise but not MLCK or Rock enhances the recovery of endothelial barrier function. The cellular cAMP contents increased gradually during the barrier recovery phase (30–60 min after thrombin challenge) accompanied by an increase in Rac1 activity. Inhibition of Rac1 activity using a specific pharmacological inhibitor (NSC23766) abrogated the endothelial barrier recovery process, suggesting a Rac1‐dependent phenomenon. Likewise, inhibition of either adenylyl cyclase or the cAMP‐effectors PKA and Epac (with PKI and ESI‐09, respectively) caused an abrogation of Rac1 activation, resealing of endothelial AJs and recovery of endothelial barrier function. The data demonstrate that endothelial barrier recovery after thrombin challenge is regulated by Rac1 GTPase activation. This Rac1 activation is due to increased levels of cellular cAMP and activation of downstream signalling during the barrier recovery phase.

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In the present study, we analysed the changes in the dynamic activities of members of the Rho family of GTPases and the role of endogenous cAMP signalling in the restoration of thrombin‐induced EC hyperpermeability. To imitate the in vivo conditions, the thrombin was present during whole experiments. The study demonstrates that challenging the human umbilical vein endothelial cell (HUVEC) monolayers with thrombin results in a prompt activation (within first 10 min) of RhoA/Rock signalling and inhibition of Rac1 activity accompanied by a reduction in cellular cAMP contents. During the recovery phase of EC barrier function (30–60 min), an activation of Rac1 but not cdc42 occurs which is accompanied by an increase in intracellular levels of cAMP. Inhibition of adenylyl cyclase (AC) or downstream cAMP signalling abrogates Rac1 activation during the recovery phase and impedes the restoration of EC barrier function.

cAMP with other signaling cues converges on Rac1 to stabilize the endothelial barrier- a signaling pathway compromised in inflammation

cAMP is one of the most potent signaling molecules to stabilize the endothelial barrier, both under resting conditions as well as under challenge of barrier-destabilizing mediators. The two main signaling axes downstream of cAMP are activation of protein kinase A (PKA) as well as engagement of exchange protein directly activated by cAMP (Epac) and its effector GTPase Rap1. Interestingly, both pathways activate GTP exchange factors for Rac1, such as Tiam1 and Vav2 and stabilize the endothelial barrier via Rac1-mediated enforcement of adherens junctions and strengthening of the cortical actin cytoskeleton. On the level of Rac1, cAMP signaling converges with other barrier-enhancing signaling cues induced by sphingosine-1-phosphate (S1P) and angiopoietin-1 (Ang1) rendering Rac1 as an important signaling hub. Moreover, activation of Rap1 and inhibition of RhoA also contribute to barrier stabilization, emphasizing that regulation of small GTPases is a central mechanism in this context. The relevance of cAMP/Rac1-mediated barrier protection under pathophysiologic conditions can be concluded from data showing that inflammatory mediators causing multi-organ failure in systemic inflammation or sepsis interfere with this signaling axis on the level of cAMP or Rac1. This is in line with the well-known efficacy of cAMP to abrogate the barrier breakdown in response to most barrier-compromising stimuli. New is the notion that the tight endothelial barrier under resting conditions is maintained by (1) continuous cAMP formation induced by hormones such as epinephrine or (2) by activation of Rac1 downstream of S1P that is secreted by erythrocytes and activated platelets.

Endothelium-dependent control of cerebrovascular functions through age: exercise for healthy cerebrovascular aging

Cognitive performances are tightly associated with the maximal aerobic exercise capacity, both of which decline with age. The benefits on mental health of regular exercise, which slows the age-dependent decline in maximal aerobic exercise capacity, have been established for centuries. In addition, the maintenance of an optimal cerebrovascular endothelial function through regular exercise, part of a healthy lifestyle, emerges as one of the key and primary elements of successful brain aging. Physical exercise requires the activation of specific brain areas that trigger a local increase in cerebral blood flow to match neuronal metabolic needs. In this review, we propose three ways by which exercise could maintain the cerebrovascular endothelial function, a premise to a healthy cerebrovascular function and an optimal regulation of cerebral blood flow. First, exercise increases blood flow locally and increases shear stress temporarily, a known stimulus for endothelial cell maintenance of Akt-dependent expression of endothelial nitric oxide synthase, nitric oxide generation, and the expression of antioxidant defenses. Second, the rise in circulating catecholamines during exercise not only facilitates adequate blood and nutrient delivery by stimulating heart function and mobilizing energy supplies but also enhances endothelial repair mechanisms and angiogenesis. Third, in the long term, regular exercise sustains a low resting heart rate that reduces the mechanical stress imposed to the endothelium of cerebral arteries by the cardiac cycle. Any chronic variation from a healthy environment will perturb metabolism and thus hasten endothelial damage, favoring hypoperfusion and neuronal stress.

Tonic regulation of vascular permeability

Our major theme is that the layered structure of the endothelial barrier requires continuous activation of signalling pathways regulated by sphingosine-1-phosphate (S1P) and intracellular cAMP. These pathways modulate the adherens junction, continuity of tight junction strands, and the balance of synthesis and degradation of glycocalyx components. We evaluate recent evidence that baseline permeability is maintained by constant activity of mechanisms involving the small GTPases Rap1 and Rac1. In the basal state, the barrier is compromised when activities of the small GTPases are reduced by low S1P supply or delivery. With inflammatory stimulus, increased permeability can be understood in part as the action of signalling to reduce Rap1 and Rac1 activation. With the hypothesis that microvessel permeability and selectivity under both normal and inflammatory conditions are regulated by mechanisms that are continuously active, it follows that when S1P or intracellular cAMP are elevated at the time of inflammatory stimulus, they can buffer changes induced by inflammatory agents and maintain normal barrier stability. When endothelium is exposed to inflammatory conditions and subsequently exposed to elevated S1P or intracellular cAMP, the same processes restore the functional barrier by first re-establishing the adherens junction, then modulating tight junctions and glycocalyx. In more extreme inflammatory conditions, loss of the inhibitory actions of Rac1-dependent mechanisms may promote expression of more inflammatory endothelial phenotypes by contributing to the up-regulation of RhoA-dependent contractile mechanisms and the sustained loss of surface glycocalyx allowing access of inflammatory cells to the endothelium.

Exchange protein directly activated by cAMP (epac): a multidomain cAMP mediator in the regulation of diverse biological functions

Since the discovery nearly 60 years ago, cAMP is envisioned as one of the most universal and versatile second messengers. The tremendous feature of cAMP to tightly control highly diverse physiologic processes, including calcium homeostasis, metabolism, secretion, muscle contraction, cell fate, and gene transcription, is reflected by the award of five Nobel prizes. The discovery of Epac (exchange protein directly activated by cAMP) has ignited a new surge of cAMP-related research and has depicted novel cAMP properties independent of protein kinase A and cyclic nucleotide-gated channels. The multidomain architecture of Epac determines its activity state and allows cell-type specific protein-protein and protein-lipid interactions that control fine-tuning of pivotal biologic responses through the "old" second messenger cAMP. Compartmentalization of cAMP in space and time, maintained by A-kinase anchoring proteins, phosphodiesterases, and β-arrestins, contributes to the Epac signalosome of small GTPases, phospholipases, mitogen- and lipid-activated kinases, and transcription factors. These novel cAMP sensors seem to implement certain unexpected signaling properties of cAMP and thereby to permit delicate adaptations of biologic responses. Agonists and antagonists selective for Epac are developed and will support further studies on the biologic net outcome of the activation of Epac. This will increase our current knowledge on the pathophysiology of devastating diseases, such as diabetes, cognitive impairment, renal and heart failure, (pulmonary) hypertension, asthma, and chronic obstructive pulmonary disease. Further insights into the cAMP dynamics executed by the Epac signalosome will help to optimize the pharmacological treatment of these diseases.

Multiple facets of cAMP signalling and physiological impact: cAMP compartmentalization in the lung

Therapies involving elevation of the endogenous suppressor cyclic AMP (cAMP) are currently used in the treatment of several chronic inflammatory disorders, including chronic obstructive pulmonary disease (COPD). Characteristics of COPD are airway obstruction, airway inflammation and airway remodelling, processes encompassed by increased airway smooth muscle mass, epithelial changes, goblet cell and submucosal gland hyperplasia. In addition to inflammatory cells, airway smooth muscle cells and (myo)fibroblasts, epithelial cells underpin a variety of key responses in the airways such as inflammatory cytokine release, airway remodelling, mucus hypersecretion and airway barrier function. Cigarette smoke, being next to environmental pollution the main cause of COPD, is believed to cause epithelial hyperpermeability by disrupting the barrier function. Here we will focus on the most recent progress on compartmentalized signalling by cAMP. In addition to G protein-coupled receptors, adenylyl cyclases, cAMP-specific phospho-diesterases (PDEs) maintain compartmentalized cAMP signalling. Intriguingly, spatially discrete cAMP-sensing signalling complexes seem also to involve distinct members of the A-kinase anchoring (AKAP) superfamily and IQ motif containing GTPase activating protein (IQGAPs). In this review, we will highlight the interaction between cAMP and the epithelial barrier to retain proper lung function and to alleviate COPD symptoms and focus on the possible molecular mechanisms involved in this process. Future studies should include the development of cAMP-sensing multiprotein complex specific disruptors and/or stabilizers to orchestrate cellular functions. Compartmentalized cAMP signalling regulates important cellular processes in the lung and may serve as a therapeutic target.

Expression of orphan G-protein coupled receptor GPR174 in CHO cells induced morphological changes and proliferation delay via increasing intracellular cAMP

We established cell lines that stably express orphan GPCR GPR174 using CHO cells, and studied physiological and pharmacological features of the receptor. GPR174-expressing cells showed cell-cell adhesion with localization of actin filaments to cell membrane, and revealed significant delay of cell proliferation. Since the morphological changes of GPR174-cells were very similar to mock CHO cells treated with cholera toxin, we measured the concentration of intracellular cAMP. The results showed the concentration was significantly elevated in GPR174-cells. By measuring intracellular cAMP concentration in GPR174-cells, we screened lipids and nucleotides to identify ligands for GPR174. We found that lysophosphatidylserine (LysoPS) stimulated increase in intracellular cAMP in a dose-dependent manner. Moreover, phosphorylation of Erk was elevated by LysoPS in GPR174 cells. These LysoPS responses were inhibited by NF449, an inhibitor of Gα(s) protein. These results suggested that GPR174 was a putative LysoPS receptor conjugating with Gα(s), and its expression induced morphological changes in CHO cells by constitutively activating adenylyl cycles accompanied with cell conjunctions and delay of proliferation.

Role of NF-κB activation in LPS-induced endothelial barrier breakdown

Endothelial barrier breakdown contributes to organ failure in sepsis. The key mechanism by which the potent sepsis inductor lipopolysaccharide (LPS) disrupts the endothelial barrier is controversial. Here, we tested the hypothesis that NF-κB activation is critically involved in endothelial barrier breakdown. Application of LPS to monolayers of porcine pulmonary artery endothelial cells (PAEC) and human dermal microvascular endothelial cells (HDMEC) induced a rapid and sustained activation of NF-κB as revealed by translocation of its subunit p65 into the nuclei in nuclear extraction assays and by immunostaining. Measurements of transendothelial electrical resistance (TER) and intercellular gap formation demonstrated significant breakdown of endothelial barrier properties following LPS treatment for 3 h. Interestingly, monolayers recovered spontaneously beginning after 10 h. Increased cAMP prevented LPS-induced loss of endothelial barrier properties, but did not block NF-κB activation. Application of the cell-permeable NEMO-binding domain (NBD) synthetic peptide was effective to prevent NF-κB activation, but did neither block LPS-induced loss of TER nor intercellular gap formation. NBD peptide alone did not alter endothelial barrier properties, but enhanced the barrier-compromising effects when applied in combination with LPS. Similarly, siRNA-mediated knock-down of p65 in HDMECs did not prevent LPS-induced barrier breakdown. Known targets of NF-κB-derived protein expression of caveolin or vasodilator-stimulated phosphoprotein (VASP) remained unaltered by LPS treatment of endothelial cells. In summary, our data indicate that NF-κB activation by LPS is not critically involved in disruption of endothelial barrier properties. Rather, our data suggest that NF-κB activation acts as a part of a rescue mechanism.

Propranolol treatment of infantile hemangioma endothelial cells: A molecular analysis

Infantile hemangiomas (IHs) are non-malignant, largely cutaneous vascular tumors affecting approximately 5-10% of children to varying degrees. During the first year of life, these tumors are strongly proliferative, reaching an average size ranging from 2 to 20 cm. These lesions subsequently stabilize, undergo a spontaneous slow involution and are fully regressed by 5 to 10 years of age. Systemic treatment of infants with the non-selective β-adrenergic receptor blocker, propranolol, has demonstrated remarkable efficacy in reducing the size and appearance of IHs. However, the mechanism by which this occurs is largely unknown. In this study, we sought to understand the molecular mechanisms underlying the effectiveness of β blocker treatment in IHs. Our data reveal that propranolol treatment of IH endothelial cells, as well as a panel of normal primary endothelial cells, blocks endothelial cell proliferation, migration, and formation of the actin cytoskeleton coincident with alterations in vascular endothelial growth factor receptor-2 (VEGFR-2), p38 and cofilin signaling. Moreover, propranolol induces major alterations in the protein levels of key cyclins and cyclin-dependent kinase inhibitors, and modulates global gene expression patterns with a particular affect on genes involved in lipid/sterol metabolism, cell cycle regulation, angiogenesis and ubiquitination. Interestingly, the effects of propranolol were endothelial cell-type independent, affecting the properties of IH endothelial cells at similar levels to that observed in neonatal dermal microvascular and coronary artery endothelial cells. This data suggests that while propranolol markedly inhibits hemangioma and normal endothelial cell function, its lack of endothelial cell specificity hints that the efficacy of this drug in the treatment of IHs may be more complex than simply blockage of endothelial function as previously believed.

Does β2-adrenergic stimulation attenuate fluid extravasation during hypothermic cardiopulmonary bypass? An experimental study in pigs

OBJECTIVES

Hypothermic cardiopulmonary bypass (CPB) is associated with increased fluid filtration, edema formation and, occasionally, organ dysfunction. Cold-induced reduction in endothelial barrier function may play a role. β(2)-adrenergic activation elevates cellular cyclic adenosine monophosphate (cAMP) which maintains endothelial barrier properties. In this study, we tested whether β-adrenergic stimulation could influence the increase in fluid extravasation observed during hypothermic CPB.

MATERIALS AND METHODS

Fourteen pigs randomly received terbutaline infusion (T-group) (n=7) or a control infusion (C-group) (n=7). All animals were given 60 min of normothermic CPB, followed by 90 min of hypothermic CPB. Fluid input and losses, plasma volume, colloid osmotic pressures (plasma, interstitial fluid), hematocrit, serum proteins and total tissue water content were measured and the fluid extravasation rates (FER) calculated.

STATISTICS

by SPSS. Values presented as mean ± SD. Repeated measure analysis of variance was performed and a t-test used when appropriate.

RESULTS

The commencement of normothermic CPB resulted in a 20% hemodilution, with an abrupt increase in fluid requirements during the first 10 min. FER increased from 0.18 (0.06) pre-bypass to 0.78 (0.27) ml/kg/min (T-group) (p=0.002) and from 0.16 (0.05) to 0.93 (0.26) ml/kg/min (C-group) (p<0.001) with no between-group differences. Thereafter, FER stabilized at a level of 0.32 (0.13) and 0.27 (0.14) ml/kg/min in the T-group and C-group, respectively. After the start of cooling, FER increased in the T-group to 0.55 (0.12) ml/kg/min (P=0.046) and in the C-group to 0.54 (0.13) ml/kg/min (P=0.006), with no between-group differences (P=0.738).

CONCLUSION

In the present experimental study, we were unable to demonstrate any clinically relevant modulating effect of terbutaline on fluid extravasation during hypothermic cardiopulmonary bypass.

Vascular endothelial hyperpermeability induces the clinical symptoms of Clarkson disease (the systemic capillary leak syndrome)

The systemic capillary leak syndrome (SCLS) is a rare disorder characterized by transient episodes of hypotensive shock and anasarca thought to arise from reversible microvascular barrier dysfunction. Although the high prevalence of a monoclonal gammopathy of unknown significance in SCLS suggests a pathogenic contribution of endogenous immunoglobulins, the mechanisms of vascular hyperpermeability remain obscure. Herein, we report clinical and molecular findings on 23 patients, the largest SCLS case series to date. Application of episodic SCLS sera, but neither the purified immunoglobulin fraction nor sera obtained from patients during remission, to human microvascular endothelial cells caused vascular endothelial cadherin internalization, disruption of interendothelial junctions, actin stress fiber formation, and increased permeability in complementary functional assays without inducing endothelial apoptosis. Intravenous immunoglobulin, one promising therapy for SCLS, mitigated the permeability effects of episodic sera. Consistent with the presence of endogenous, nonimmunoglobulin, circulating permeability factor(s) constrained to SCLS episodes, we found that vascular endothelial growth factor (VEGF) and angiopoietin 2 (Ang2), were elevated in episodic SCLS sera but not in remission sera. Ab-based inhibition of Ang2 counteracted permeability induced by episodic SCLS sera. Comparable experiments with anti-VEGF Ab (bevacizumab) yielded less interpretable results, probably because of endothelial toxicity of VEGF withdrawal. Our results support a model of SCLS pathogenesis in which nonimmunoglobulin humoral factors such as VEGF and Ang2 contribute to transient endothelial contraction, suggesting a molecular mechanism for this highly lethal disorder.