Stimulation of prostaglandin synthesis by human endothelial cells exposed to hypoxia

Unraveling the Impact of Extracellular Vesicle-Depleted Serum on Endothelial Cell Characteristics over Time

Extracellular vesicles (EVs) are produced by all kinds of cells, including endothelial cells. It has been observed that EVs present in fetal bovine serum (FBS), broadly used in cell culture, can be a confounding factor and lead to misinterpretation of results. To investigate this phenomenon, human brain microvascular endothelial cells (HBMECs) were cultured for 2 or 24 h in the presence of EV-depleted FBS (EVdS). Cell death, gene and protein expression, and the presence of EVs isolated from these cells were evaluated. The uptake of EVs, intercellular adhesion molecule 1 (ICAM-1) expression, and monocyte adhesion to endothelial cells exposed to EVs were also evaluated. Our results revealed higher apoptosis rates in cells cultured with EVdS for 2 and 24 h. There was an increase in interleukin 8 (IL8) expression after 2 h and a decrease in interleukin 6 (IL6) and IL8 expression after 24 h of culture. Among the proteins identified in EVs isolated from cells cultured for 2 h (EV2h), several were related to ribosomes and carbon metabolism. EVs from cells cultured for 24 h (EV24h) presented a protein profile associated with cell adhesion and platelet activation. Additionally, HBMECs exhibited increased uptake of EV2h. Treatment of endothelial cells with EV2h resulted in greater ICAM-1 expression and greater adherence to monocytes than did treatment with EV24h. According to our data, HBMEC cultivated with EVdS produce EVs with different physical characteristics and protein levels that vary over time.

Pathophysiology, mechanisms, and managements of tissue hypoxia

Oxygen is needed to generate aerobic adenosine triphosphate and energy that is required to support vital cellular functions. Oxygen delivery (DO₂) to the tissues is determined by convective and diffusive processes. The ability of the body to adjust oxygen extraction (ERO₂) in response to changes in DO₂ is crucial to maintain constant tissue oxygen consumption (VO₂). The capability to increase ERO₂ is the result of the regulation of the circulation and the effects of the simultaneous activation of both central and local factors. The endothelium plays a crucial role in matching tissue oxygen supply to demand in situations of acute drop in tissue oxygenation. Tissue oxygenation is adequate when tissue oxygen demand is met. When DO₂ is severely compromised, a critical DO₂ value is reached below which VO₂ falls and becomes dependent on DO₂, resulting in tissue hypoxia. The different mechanisms of tissue hypoxia are circulatory, anaemic, and hypoxic, characterised by a diminished DO₂ but preserved capacity of increasing ERO₂. Cytopathic hypoxia is another mechanism of tissue hypoxia that is due to impairment in mitochondrial respiration that can be observed in septic conditions with normal overall DO₂. Sepsis induces microcirculatory alterations with decreased functional capillary density, increased number of stopped-flow capillaries, and marked heterogeneity between the areas with large intercapillary distance, resulting in impairment of the tissue to extract oxygen and to satisfy the increased tissue oxygen demand, leading to the development of tissue hypoxia. Different therapeutic approaches exist to increase DO₂ and improve microcirculation, such as fluid therapy, transfusion, vasopressors, inotropes, and vasodilators. However, the effects of these agents on microcirculation are quite variable.

Venous leg symptoms, ecchymosis, and coldness in patients with peripheral varicose vein: A multicenter assessment and validation study (VEIN-VIOLET study)

OBJECTIVES

We aimed to evaluate peripheral varicose vein symptoms including ecchymosis and coldness by using the Venous Insufficiency Epidemiological and Economic Study-Quality of Life/Symptoms (VEINES-QoL/Sym) questionnaire.

METHODS

A total of 1120 patients were enrolled to the analysis after the exclusion of 199 patients who did not match the inclusion criteria. Patients were asked to answer the VEINES-Sym questionnaire and questions about ecchymosis and coldness. Scores of ecchymosis and coldness were calculated similar to VEINES-Sym questionnaire. Classifications of peripheral varicose vein were made according to the clinical part of clinical, etiological, anatomical, and pathophysiological classification system and patients with grade 2 or higher were considered as positive for peripheral varicose vein.

RESULTS

Frequency of symptoms present in the VEINES-Sym instrument, ecchymosis and coldness were significantly higher in patients with peripheral varicose vein. Mean score of each symptom was significantly lower in peripheral varicose vein patients including scores of ecchymosis and coldness. Logistic regression analysis revealed that presence of hemorrhoids and all symptoms in VEINES-Sym questionnaire except restless leg were significantly and independently associated with peripheral varicose vein. Besides, ecchymosis (odds ratio: 2.04, 95% confidence interval: 1.34-3.08, p = 0.008) but not coldness was significantly and independently associated with peripheral varicose vein. There was also significant correlation of VEINES-Sym score with ecchymosis (r = 0.43, p < 0.001) and coldness (r = 0.47, p < 0.001).

CONCLUSIONS

Venous leg symptoms present in VEINES-Sym questionnaire except restless legs, presence of hemorrhoids and ecchymosis are significantly and independently associated with peripheral varicose vein. Not only ecchymosis but also coldness has shown an independent association with total VEINES-Sym score.

Therapeutic potential of flavonoids in the treatment of chronic venous insufficiency

Chronic venous insufficiency (CVI) is a common disorder associated with a variety of symptoms in later disease stages; despite the high prevalence of this pathology, suitable pharmaceutical therapies have not been explored to date. In this context, it was recently reported that a chronic increase in venous wall stress or biomechanical stretch is sufficient to cause development of varicose veins. Recent evidence demonstrate that flavonoids are natural substances that convey the circulatory system functionality, playing a key role in blood flow. Particularly, troxerutin, diosmin and horse chestnut extract, appear protective for the management of vascular diseases. The aim of the present study was to evaluate the effect of a flavonoid compound, containing troxerutin, diosmin and horse chestnut extract on in vitro model on HUVECs cells, due to its production of vasculoregulatory and vasculotropic molecules, on an ex-vivo model on mesenteric vessel contraction, to regularize mesenteric microcirculation and on in vivo model of CVI-induced by saphene vein ligation. Furthermore, the flavonoid compound capacity of extensibility and compatibility with peripheral veins was investigated through a tissue block culture study. The degree of absorption, the contractile venous activity, the histological analysis, the immunoistochemical and immunofluorescence evaluation for VEGF and CD34 were performed, together with inflammatory mediators dosage. For the first time, this research revealed the therapeutic potential of a compound, enriched with flavonoids, to be a supportive treatment, suitable to reduce varicose vein pathophysiology and to regularize venous tone.

Macrophages and the maintenance of homeostasis

There have been many chapters written about macrophage polarization. These chapters generally focus on the role of macrophages in orchestrating immune responses by highlighting the T-cell-derived cytokines that shape these polarizing responses. This bias toward immunity is understandable, given the importance of macrophages to host defense. However, macrophages are ubiquitous and are involved in many different cellular processes, and describing them as immune cells is undoubtedly an oversimplification. It disregards their important roles in development, tissue remodeling, wound healing, angiogenesis, and metabolism, to name just a few processes. In this chapter, we propose that macrophages function as transducers in the body. According to Wikipedia, “A transducer is a device that converts energy from one form to another.” The word transducer is a term used to describe both the “sensor,” which can interpret a wide range of energy forms, and the “actuator,” which can switch voltages or currents to affect the environment. Macrophages are able to sense a seemingly endless variety of inputs from their environment and transduce these inputs into a variety of different response outcomes. Thus, rather than functioning as immune cells, they should be considered more broadly as cellular transducers that interpret microenvironmental changes and actuate vital tissue responses. In this chapter, we will describe some of the sensory stimuli that macrophages perceive and the responses they make to these stimuli to achieve their prime directive, which is the maintenance of homeostasis.

Prostaglandin contribution to postexercise hyperemia is dependent on tissue oxygenation during rhythmic and isometric contractions

The role of prostaglandins (PGs) in exercise hyperemia is controversial. We tested their contributions in moderate intensity forearm exercise, whether their release is oxygen (O₂)‐dependent or affected by aging. A total of 12 young (21 ± 1 years) and 11 older (66 ± 2 years) recreationally active men performed rhythmic and isometric handgrip contractions at 60% maximum voluntary contraction for 3 min during air breathing after placebo, after cyclooxygenase (COX) inhibition with aspirin, while breathing 40% O₂ and during their combination (aspirin + 40% O₂). Forearm blood flow (FBF) was recorded with venous occlusion plethysmography (forearm vascular conductance (FVC): FBF/mean arterial pressure). Venous efflux of PGI₂ and PGE₂ were assessed by immunoassay. Postcontraction increases in FVC were similar for rhythmic and isometric contractions in young and older men, and accompanied by similar increases in efflux of PGI₂ and PGE₂. Aspirin attenuated the efflux of PGI₂ by 75%–85%, PGE₂ by 50%–70%, (p < .05 within group; p > .05 young versus. older), and postcontraction increases in FVC by 22%–27% and 17%–21% in young and older men, respectively (p < .05 within group and young versus. older). In both age groups, 40% O₂ and aspirin + 40% O₂ caused similar inhibition of the increases in FVC and efflux of PGs as aspirin alone (p < .05 within group). These results indicate that PGs make substantial contributions to the postcontraction hyperemia of rhythmic and isometric contractions at moderate intensities in recreationally active young and older men. Given PGI₂ is mainly released by endothelium and PGE₂ by muscle fibers, we propose PG generation is dependent on the contraction‐induced falls in O₂ at these sites.

Reactive hyperemia: a review of methods, mechanisms, and considerations

Reactive hyperemia is a well-established technique for noninvasive assessment of peripheral microvascular function and a predictor of all-cause and cardiovascular morbidity and mortality. In its simplest form, reactive hyperemia represents the magnitude of limb reperfusion following a brief period of ischemia induced by arterial occlusion. Over the past two decades, investigators have employed a variety of methods, including brachial artery velocity by Doppler ultrasound, tissue reperfusion by near-infrared spectroscopy, limb distension by venous occlusion plethysmography, and peripheral artery tonometry, to measure reactive hyperemia. Regardless of the technique used to measure reactive hyperemia, blunted reactive hyperemia is believed to reflect impaired microvascular function. With the advent of several technological advancements, together with an increased interest in the microcirculation, reactive hyperemia is becoming more common as a research tool and is widely used across multiple disciplines. With this in mind, we sought to review the various methodologies commonly used to assess reactive hyperemia and current mechanistic pathways believed to contribute to reactive hyperemia and reflect on several methodological considerations.

Symptoms in Dilating Venous Disease

Lower extremity venous diseases or insufficiency include clinically deteriorating conditions with morphological and functional alterations of the venous system, including venous hypertension, vascular wall structural abnormality, and venous valvar incompetency in association with an inflammatory process. In fact, the same pathophysiological processes are the main underlying mechanisms of other venous insufficiencies in different vascular territories such as Peripheral Varicose Vein (PVV), varicocele, Pelvic Varicosities or Congestion Syndrome (PCS) and Hemorrhoidal Disease (HD). Regarding the anatomical continuity of lower extremity venous system, urogenital system (pampiniform plexus in male and broad ligament and ovarian veins in female) and anorectal venous system, it is reasonable to expect common symptoms such as pain, burning sensation, pruritis, swelling, which arise directly from the involved tissue itself. High coexistence rate of PVV, varicocele/PCS and HD between each other underlines not only the same vascular wall abnormality as an underlying etiology but also the existence of common symptoms originating from the involved tissue in dilating venous disease. Accordingly, it might be reasonable to query the common symptoms of venous dilating disease in other venous vascular regions in patients with complaints of any particular venous territory.

Escin: a review of its anti-edematous, anti-inflammatory, and venotonic properties

This review discusses historical and recent pharmacological and clinical data on the anti-edematous, anti-inflammatory, and venotonic properties of escin (Reparil^®). Escin, the active component of Aesculus hippocastanum, or horse chestnut, is available as orally absorbable dragées and as a transdermal gel. The anti-inflammatory and anti-edematous effects of escin have been studied over many years in pre-clinical models. More recent data confirm the anti-inflammatory properties of escin in reducing vascular permeability in inflamed tissues, thereby inhibiting edema formation. The venotonic effects of escin have been demonstrated primarily by in vitro studies of isolated human saphenous veins. The ability of escin to prevent hypoxia-induced disruption to the normal expression and distribution of platelet endothelial cell-adhesion molecule-1 may help explain its protective effect on blood vessel permeability. Escin oral dragées and transdermal gel have both demonstrated efficacy in blunt trauma injuries and in chronic venous insufficiency. Both oral escin and the transdermal gel are well tolerated.

Therapeutic potential of natural compounds in inflammation and chronic venous insufficiency

The term varicose vein refers to the twisted and swollen vein visible under the skin surface which occurs most commonly in the leg. Epidemiological studies report a varying percentage of incidences from 2 to 56% in men and <1-60% in women. Venous insufficiency is most often caused by the damage to the valves and walls of the veins. The mechanism of varicose vein formation is complex. It is, however, based on hypotensive blood vessels, hypoxia, and other mechanisms associated with inflammation. This work describes mechanisms related to the formation and development of the varicose vein. It discusses risk factors, pathogenesis of chronic venous disease, markers of the epithelial and leukocyte activation, state of hypoxia and inflammation, reactive oxygen species (ROS) generation, and oxidative stress. Additionally, this paper describes substances of plant origin used in the treatment of venous insufficiency. It also considers the structure of the molecules, their properties, and their mechanisms of action, the structure-activity relationship and chemical properties of flavonoids and other substances. The flavonoids include quercetin derivatives, micronized purified flavonoid fraction (Daflon), natural pine bark extract (Pycnogenol), and others such as triterpene saponine, extracts from Ruscus aculeatus and Centella asiatica, Ginkgo biloba extract, coumarin dereivatives that are used in chronic venous insufficiency. Flavonoids are natural substances found in plants, including fruits, vegetables, flowers, and others. They are important to the circulatory system and critical to blood vessels and the blood flow. Additionally, they have antioxidant, antiinflammatory properties.

Cellular Stress Responses and Gut Microbiota in Inflammatory Bowel Disease

Progresses in the past two decades have greatly expanded our understanding of inflammatory bowel disease (IBD), an incurable disease with multifaceted and challenging clinical manifestations. The pathogenesis of IBD involves multiple processes on the cellular level, which include the stress response signaling such as endoplasmic reticulum (ER) stress, oxidative stress, and hypoxia. Under physiological conditions, the stress responses play key roles in cell survival, mucosal barrier integrity, and immunomodulation. However, they can also cause energy depletion, trigger cell death and tissue injury, promote inflammatory response, and drive the progression of clinical disease. In recent years, gut microflora has emerged as an essential pathogenic factor and therapeutic target for IBD. Altered compositional and metabolic profiles of gut microbiota, termed dysbiosis, are associated with IBD. Recent studies, although limited, have shed light on how ER stress, oxidative stress, and hypoxic stress interact with gut microorganisms, a potential source of stress in the microenvironment of gastrointestinal tract. Our knowledge of cellular stress responses in intestinal homeostasis as well as their cross-talks with gut microbiome will further our understanding of the pathogenesis of inflammatory bowel disease and probably open avenues for new therapies.

The Significance of Pain in Chronic Venous Disease and its Medical Treatment

Chronic venous disease (CVeD) is a highly prevalent condition in the general population, and it has a significant impact on quality of life. While it is usually manifested by obvious signs, such as varicose veins and venous ulcers, other symptoms of the disease are less specific. Among the other symptoms, which include heaviness, swelling, muscle cramps and restless legs, pain is the symptom that most frequently compels CVeD patients to seek medical aid. However, there is a substantial discrepancy between pain severity and clinically detectable signs of CVeD, questioned by several opposing studies. Further evaluation is needed to clarify this subject, and to analyse whether pain development predicts objective CVeD progression. General management of CVeD starts with advising lifestyle changes, such as lowering body mass index and treating comorbidities. However, the mainstay of treatment is compression therapy, with the additional use of pharmacological substances. Venoactive drugs proved to be the drugs of choice for symptom alleviation and slowing the progression of CVeD, with micronized purified flavonoid fraction being the most effective one. Interventional therapy is reserved for advanced stages of the disease.

Reduced membrane cholesterol after chronic hypoxia limits Orai1-mediated pulmonary endothelial Ca2+ entry

Endothelial dysfunction in chronic hypoxia (CH)-induced pulmonary hypertension is characterized by reduced store-operated Ca²⁺ entry (SOCE) and diminished Ca²⁺-dependent production of endothelium-derived vasodilators. We recently reported that SOCE in pulmonary arterial endothelial cells (PAECs) is tightly regulated by membrane cholesterol and that decreased membrane cholesterol is responsible for impaired SOCE after CH. However, the ion channels involved in cholesterol-sensitive SOCE are unknown. We hypothesized that cholesterol facilitates SOCE in PAECs through the interaction of Orai1 and stromal interaction molecule 1 (STIM1). The role of cholesterol in Orai1-mediated SOCE was initially assessed using CH exposure in rats (4 wk, 380 mmHg) as a physiological stimulus to decrease PAEC cholesterol. The effects of Orai1 inhibition with AnCoA4 on SOCE were examined in isolated PAEC sheets from control and CH rats after cholesterol supplementation, substitution of endogenous cholesterol with epicholesterol (Epichol), or vehicle treatment. Whereas cholesterol restored endothelial SOCE in CH rats, both Epichol and AnCoA4 attenuated SOCE only in normoxic controls. The Orai1 inhibitor had no further effect in cells pretreated with Epichol. Using cultured pulmonary endothelial cells to allow better mechanistic analysis of the molecular components of cholesterol-regulated SOCE, we found that Epichol, AnCoA4, and Orai1 siRNA each inhibited SOCE compared with their respective controls. Epichol had no additional effect after knockdown of Orai1. Furthermore, Epichol substitution significantly reduced STIM1-Orai1 interactions as assessed by a proximity ligation assay. We conclude that membrane cholesterol is required for the STIM1-Orai1 interaction necessary to elicit endothelial SOCE. Furthermore, reduced PAEC membrane cholesterol after CH limits Orai1-mediated SOCE. NEW & NOTEWORTHY This research demonstrates a novel contribution of cholesterol to regulate the interaction of Orai1 and stromal interaction molecule 1 required for pulmonary endothelial store-operated Ca²⁺ entry. The results provide a mechanistic basis for impaired pulmonary endothelial Ca²⁺ influx after chronic hypoxia that may contribute to pulmonary hypertension.

Intestinal hypoxia and hypoxia-induced signalling as therapeutic targets for IBD

Tissue hypoxia occurs when local oxygen demand exceeds oxygen supply. In chronic inflammatory conditions such as IBD, the increased oxygen demand by resident and gut-infiltrating immune cells coupled with vascular dysfunction brings about a marked reduction in mucosal oxygen concentrations. To counter the hypoxic challenge and ensure their survival, mucosal cells induce adaptive responses, including the activation of hypoxia-inducible factors (HIFs) and modulation of nuclear factor-κB (NF-κB). Both pathways are tightly regulated by oxygen-sensitive prolyl hydroxylases (PHDs), which therefore represent promising therapeutic targets for IBD. In this Review, we discuss the involvement of mucosal hypoxia and hypoxia-induced signalling in the pathogenesis of IBD and elaborate in detail on the role of HIFs, NF-κB and PHDs in different cell types during intestinal inflammation. We also provide an update on the development of PHD inhibitors and discuss their therapeutic potential in IBD.

Regulation of Coronary Blood Flow

The heart is uniquely responsible for providing its own blood supply through the coronary circulation. Regulation of coronary blood flow is quite complex and, after over 100 years of dedicated research, is understood to be dictated through multiple mechanisms that include extravascular compressive forces (tissue pressure), coronary perfusion pressure, myogenic, local metabolic, endothelial as well as neural and hormonal influences. While each of these determinants can have profound influence over myocardial perfusion, largely through effects on end-effector ion channels, these mechanisms collectively modulate coronary vascular resistance and act to ensure that the myocardial requirements for oxygen and substrates are adequately provided by the coronary circulation. The purpose of this series of Comprehensive Physiology is to highlight current knowledge regarding the physiologic regulation of coronary blood flow, with emphasis on functional anatomy and the interplay between the physical and biological determinants of myocardial oxygen delivery. © 2017 American Physiological Society. Compr Physiol 7:321-382, 2017.

Eicosanoids: Emerging contributors in stem cell-mediated wound healing

Eicosanoids are bioactive lipid products primarily derived from the oxidation of arachidonic acid (AA). The individual contributions of eicosanoids and stem cells to wound healing have been of great interest. This review focuses on how stem cells work in concert with eicosanoids to create a beneficial environment in the wound bed and in the promotion of wound healing. Stem cells contribute to wound healing through modulating inflammation, differentiating into skin cells or endothelial cells, and exerting paracrine effects by releasing various potent growth factors. Eicosanoids have been shown to stimulate proliferation, migration, homing, and differentiation of stem cells, all of which contribute to the process of wound healing. Increasing evidence has shown that eicosanoids improve wound healing through increasing stem cell densities, stimulating differentiation, and enhancing the angiogenic properties of stem cells. Chronic wounds have become a major problem in health care. Therefore, research regarding the effects of stem cells and eicosanoids in the promotion wound healing is of great importance.

Eating and arterial endothelial function: a meta-analysis of the acute effects of meal consumption on flow-mediated dilation

Given that endothelial dysfunction precedes atherosclerotic cardiovascular disease, exploring the parameters that modify postprandial flow-mediated dilation (FMD) is important for public health. The objectives of the study are to estimate the population effect of meal ingestion on FMD and to determine how the effect varied based on patient characteristics and modifiable methodological features. Articles published before June 2015 were located using MEDLINE, PubMed and Web of Science. One hundred fifty-four effects were derived from 78 articles involving 2,548 subjects were selected. Included articles required measurement of FMD in adults before and after meal ingestion. Effects were analysed using an unstandardized mean gain random effects model, and significant moderators were analysed using meta-regression. Meal consumption significantly reduced FMD by a heterogeneous mean effect size delta (Δ) of -2.03 (95% CI: [-2.28, -1.77]), an ~2% reduction in FMD. FMD reductions were larger among normal weight individuals, males, those with a cardio-metabolic disorder, those with elevated baseline FMD, and individuals with impaired glucose tolerance at baseline. Macronutrient meal ingestion significantly reduced FMD, an effect that was moderated by body mass index, sex and two-way interactions between disease status and both baseline FMD and baseline blood glucose levels.

Chronic Hypoxia Inhibits Contraction of Fetal Arteries by Increased Endothelium-Derived Nitric Oxide and Prostaglandin Synthesis

OBJECTIVE

Chronic hypoxia causes redistribution of fetal cardiac output by mechanisms poorly understood. We tested the hypothesis that chronic hypoxia alters vascular reactivity of arteries from near-term fetal guinea pigs.

METHODS

Pregnant guinea pigs (50 days, term = 65 days) were exposed to either normoxia (room air) or hypoxia (12% O2) for 14 days. Carotid artery ring segments from anesthetized fetuses were mounted onto myographs for measurement of force. Contractile responses to cumulative addition of prostaglandin F2alpha (PGF2alpha, 10(-9) M to 10(-5) M), U46619, a thromboxane mimetic (10(-12) M to 12(-6) M), and KCl (10 to 120 mM) were measured in the presence and absence of INDO (INDO, 10(-5) M) alone and INDO plus nitro-L-arginine (LNA, 10(-4) M), or INDO plus N6-iminoethyl-L-lysine (LNIL, 5 x 10(-5) M, a selective iNOS inhibitor), and measured in endothelium-intact and denuded arteries. Nitric oxide synthase (NOS) activity was measured in isolated arteries by 14C-L-arginine to 14C-L-citrulline conversion.

RESULTS

Hypoxia decreased contractile responses to both PGF2alpha and U46619 under control conditions. Maximal contraction to both agonists was increased in hypoxemic arteries after INDO alone and INDO + LNA compared to normoxic controls. Endothelium-denudation abolished the differences between the groups. KCl contraction was unaffected by hypoxia. LNIL potentiated maximal PGF(2alpha) contraction but was similar between groups. Hypoxia increased (P < .05) total and Ca(2+)-dependent NOS activities by 1.7- and 2.1-fold, respectively, but had no effect on Ca(2+)-independent activity.

CONCLUSION

Chronic hypoxia alters vascular reactivity of fetal carotid arteries by increasing the contribution of both vasodilator prostaglandins and nitric oxide and suggests that changes in local vascular mechanisms may be altered by chronic hypoxia.

Phospholipid scramblase 1 is required for β2-glycoprotein I binding in hypoxia and reoxygenation-induced endothelial inflammation

Multiple pathologic conditions, including hemorrhage, tumor angiogenesis, and ischemia-reperfusion events, will result in hypoxia and subsequent reperfusion. Previous studies have analyzed the lipid changes within whole tissues and indicated that ischemia-reperfusion altered tissue and cellular phospholipids. Using an in vitro cell culture model of hypoxia and reoxygenation, we examined the endothelial lipid changes. We hypothesized that phospholipid scramblase 1, a protein that regulates bilayer asymmetry, is involved in altering the phospholipids of endothelial cells during hypoxia, a component of ischemia, leading to β2-glycoprotein I and IgM binding and subsequent lipid-mediated, inflammatory responses. We have completed the first comprehensive study of steady-state phospholipid scramblase 1 mRNA levels, protein expression, and activity under conditions of hypoxia and reoxygenation. Phospholipid scramblase 1 regulates phosphatidylserine exposure in response to oxygen stress, leading to β2-glycoprotein I and IgM binding and lipid-mediated, inflammatory responses.

Membrane lipid interactions in intestinal ischemia/reperfusion-induced Injury

Ischemia, lack of blood flow, and reperfusion, return of blood flow, are a common phenomenon affecting millions of Americans each year. Roughly 30,000 Americans per year experience intestinal ischemia-reperfusion (IR), which is associated with a high mortality rate. Previous studies of the intestine established a role for neutrophils, eicosanoids, the complement system and naturally occurring antibodies in IR-induced pathology. Furthermore, data indicate involvement of a lipid or lipid-like moiety in mediating IR-induced damage. It has been proposed that antibodies recognize exposure of neo-antigens, triggering action of the complement cascade. While it is evident that the pathophysiology of IR-induced injury is complex and multi-factorial, we focus this review on the involvement of eicosanoids, phospholipids and neo-antigens in the early pathogenesis. Lipid changes occurring in response to IR, neo-antigens exposed and the role of a phospholipid transporter, phospholipid scramblase 1 will be discussed.

Application of a nitric oxide sensor in biomedicine

In the present study, we describe the biochemical properties and effects of nitric oxide (NO) in intact and dysfunctional arterial and venous endothelium. Application of the NO electrochemical sensor in vivo and in vitro in erythrocytes of healthy subjects and patients with vascular disease are reviewed. The electrochemical NO sensor device applied to human umbilical venous endothelial cells (HUVECs) and the description of others NO types of sensors are also mentioned.

Phytochemicals in ocular health: Therapeutic potential and delivery challenges

Diabetic retinopathy (DR) and age-related macular degeneration (AMD) are the leading causes of blindness in adults. The impact of these conditions on the quality of life is increasing in significance with a rise in life expectancy. The role of hyperglycemia, oxidative stress and inflammatory responses in the development and/or progression of DR and AMD, and several other sight threatening ocular diseases, is well established. In proliferative retinopathy, signals sent by the retina for nourishment, triggers the growth of fragile and abnormal blood vessels. Changes in ocular pressure may lead to rupture of these blood vessels causing severe vision problems. Recent in vitro and preclinical studies demonstrate that certain phytochemicals possessing potent antioxidant and anti-inflammatory activity and ocular blood flow enhancing properties may be very useful in the treatment of, or as a prophylactic measure for, DR and AMD. Apart from these properties they have also been investigated for their anti-bacterial, hormonal, enzyme stimulation, and anti-angiogenic activities. The attractive aspect of these potential therapeutic candidates is that they can act on multiple pathways identified in the etiology of DR, AMD, cataract and other ocular diseases. However, results from clinical trials have been somewhat ambiguous, raising questions about the concentrations of these bioflavonoids achieved in the neural retina following oral administration. Unfortunately, as of date, an efficient noninvasive means to deliver therapeutic agents/candidates to the back-of-the eye is still not available. This review examines some of these promising natural agents and discusses the challenges encountered in delivering them to the posterior segment ocular tissues through the oral route.

Contribution of non-endothelium-dependent substances to exercise hyperaemia: are they O(2) dependent?

This review considers the contributions to exercise hyperaemia of substances released into the interstitial fluid, with emphasis on whether they are endothelium dependent or O(2) dependent. The early phase of exercise hyperaemia is attributable to K(+) released from contracting muscle fibres and acting extraluminally on arterioles. Hyperpolarization of vascular smooth muscle and endothelial cells induced by K(+) may also facilitate the maintained phase, for example by facilitating conduction of dilator signals upstream. ATP is released into the interstitium from muscle fibres, at least in part through cystic fibrosis transmembrane conductance regulator-associated channels, following the fall in intracellular H(+). ATP is metabolized by ectonucleotidases to adenosine, which dilates arterioles via A(2A) receptors, in a nitric oxide-independent manner. Evidence is presented that the rise in arterial achieved by breathing 40% O(2) attenuates efflux of H(+) and lactate, thereby decreasing the contribution that adenosine makes to exercise hyperaemia; efflux of inorganic phosphate and its contribution may likewise be attenuated. Prostaglandins (PGs), PGE(2) and PGI(2), also accumulate in the interstitium during exercise, and breathing 40% O(2) abolished the contribution of PGs to exercise hyperaemia. This suggests that PGE(2) released from muscle fibres and PGI(2) released from capillaries and venular endothelium by a fall in their local act extraluminally to dilate arterioles. Although modest hyperoxia attenuates exercise hyperaemia by improving O(2) supply, limiting the release of O(2)-dependent adenosine and PGs, higher O(2) concentrations may have adverse effects. Evidence is presented that breathing 100% O(2) limits exercise hyperaemia by generating O(2)(-), which inactivates nitric oxide and decreases PG synthesis.

Mechanisms of metabolic coronary flow regulation

Coronary blood flow is tightly adjusted to the oxygen requirements of the myocardium. The underlying control mechanisms keep coronary venous pO(2) at a rather constant level around 20mm Hg under a variety of physiological conditions. Because coronary flow may increase more than 5-fold during exercise without any signs of under- or overperfusion, coronary flow must be controlled, at least in part, in a feed forward manner. Likely metabolic factors contributing to feed forward control are carbon dioxide and reactive oxygen species. Adaptation of coronary flow to exercise under physiological conditions involves in addition to metabolic control feed forward neuronal and endothelium-dependent control. Under pathological conditions, e.g. vessel stenosis or anemia, or specific environmental conditions, e.g. high altitude exposure, cardiac oxygenation may become critical, especially if oxygen demand is increased during physical exercise. Under such conditions the fall of coronary pO(2) may directly result in opening of oxygen sensitive potassium or closure of calcium channels. Furthermore the fall of pO(2) results in the production of vasoactive metabolites, e.g. adenosine, nitric oxide or prostaglandins, and in proton accumulation. All of these adaptations support a reduction of coronary vessel resistance. This article is part of a Special Issue entitled "Coronoray Blood Flow".

Metabolic shifts in immunity and inflammation

Sites of ongoing inflammation and triggered immune responses are characterized by significant changes in metabolic activity. Recent studies have indicated that such shifts in tissue metabolism result from a combination of profound recruitment of inflammatory cells (neutrophils and monocytes) and high proliferation rates among lymphocyte populations. The resultant shifts in energy supply and demand can result in metabolic acidosis and diminished delivery and/or availability of oxygen, leading to hypoxia extensive enough to trigger transcriptional and translation changes in tissue phenotype. Such phenotypic shifts can imprint fundamental changes to tissue metabolism. In this study, we review recent work addressing metabolic changes and metabolic control of inflammation and immunity.

Hypoxia-mediated expression of 5-lipoxygenase-activating protein involves HIF-1alpha and NF-kappaB and microRNAs 135a and 199a-5p

Hypoxia occurs in a number of pathological states, such as pulmonary, hematological, and cardiovascular disorders. In this study, we examined the molecular mechanism by which hypoxia contributes to increased leukotriene formation. Our studies showed hypoxia augmented the expression of 5-lipoxygenase activating protein (FLAP), a key enzyme in leukotriene formation, in both human pulmonary microvascular endothelial cells and a transformed human brain endothelial cell line. Hypoxia-induced FLAP mRNA expression involved activation of NADPH-oxidase, PI-3 kinase, mitogen-activated protein kinase, NF-kappaB, and hypoxia-inducible factor (HIF)-1alpha. Hypoxia-induced FLAP promoter activity was attenuated on mutation of hypoxia-response elements (HREs) and NF-kappaB binding motif in the FLAP promoter. Hypoxia also augmented binding of HIF-1alpha to HREs in FLAP promoter as demonstrated by EMSA with nuclear extracts. Furthermore, chromain immunoprecipitation analysis showed HIF-1alpha bound to HREs in native chromatin obtained from hypoxia-treated cells. Next, we examined the role of HIF-1alpha regulated microRNAs on FLAP expression. Our studies showed decreased expression of miR-135a and miR-199a-5p in response to hypoxia. However, overexpression of anti-miR-135a and anti-miR-199a-5p oligonucleotides led to a several fold increased FLAP mRNA and protein expression. These studies demonstrate for the first time that hypoxia-mediated FLAP expression is regulated by HREs and NF-kappaB site in its promoter, and negatively regulated by miR-135a and miR-199a-5p, which target the 3'-UTR of FLAP mRNA. An understanding of these regulatory pathways provides new avenues to ameliorate leukotriene formation and hence reactive airway disease, and inflammation in individuals who have sickle cell disease.

Endothelial dysfunction: from molecular mechanisms to measurement, clinical implications, and therapeutic opportunities

Endothelial dysfunction has been implicated as a key factor in the development of a wide range of cardiovascular diseases, but its definition and mechanisms vary greatly between different disease processes. This review combines evidence from cell-culture experiments, in vitro and in vivo animal models, and clinical studies to identify the variety of mechanisms involved in endothelial dysfunction in its broadest sense. Several prominent disease states, including hypertension, heart failure, and atherosclerosis, are used to illustrate the different manifestations of endothelial dysfunction and to establish its clinical implications in the context of the range of mechanisms involved in its development. The size of the literature relating to this subject precludes a comprehensive survey; this review aims to cover the key elements of endothelial dysfunction in cardiovascular disease and to highlight the importance of the process across many different conditions.

Signaling mechanisms of endogenous angiogenesis inhibitors derived from type IV collagen

Vascular basement membrane (VBM) derived molecules are regulators of certain biological activities such as cell growth, differentiation and angiogenesis. Angiogenesis is regulated by a systematic controlled balance between VBM derived antiangiogenic factors and proangiogenic growth factors. In the normal physiological state, equilibrium is maintained between the antiangiogenic and proangiogenic factors. The antiangiogenic factors (molecules), which are generated by the proteolytic cleavage of the VBM, include; α1 chain non-collagenous (NC1) domain of type XVIII collagen (endostatin) and the NC1 domains from the alpha chains of Type IV collagen considered as endogenous angiogenesis inhibitors. These collagen derived NC1 domains have a pivotal role in the regulation of tumor angiogenesis, thus making them attractive alternate candidates for cancer therapies. In this review we illustrate a comprehensive overview of the knowledge gained from the signaling mechanisms of Type IV collagen derived endogenous inhibitors in angiogenesis.

[Pathophysiology of pain in venous disease]

Pain is the leading complaint of patients with venous disease. It has a significant effect on the patient's quality-of-life. For the clinician and the researcher however it is difficult to apprehend how pain is related to the venous disease, both because of the multiple factors involved and because of the lack of any strong relationship between pain symptoms and the severity of the venous disease. Currently, several hypotheses concerning the pathogenesis of pain in venous disease have focused on the causal impact of local inflammation. Over the last five years, a large body of evidence has been accumulation showing an inflammatory reaction around varicose veins, but the precise mechanism of how inflammatory mediators interact with venous nociceptors, which might explain part of the variability in pain observed in venous disease, remains elusive, both clinically and experimentally.

Hypoxia regulates PGE(2) release and EP1 receptor expression in osteoblastic cells

Changes in regional O(2) tension that occur during fracture and skeletal unloading may stimulate local bone cell activity and ultimately regulate bone maintenance and repair. The mechanisms by which bone cells sense and respond to changes in O(2) tension are unclear. In this study we investigated the effects of low O(2) on activation of the hypoxia response element (HRE), prostaglandin E(2) (PGE(2)) production, PGE(2) receptor (EP) expression and proliferation in MC3T3-E1 osteoblastic cells. Cells were cultured for up to 72 h in 2% O(2) (considered hypoxic), 5% O(2) (in the range of normal O(2) tension in vivo) or 21% O(2) (commonly used for cell culture). Cells cultured in 2% O(2) showed activation of the HRE, increased PGE(2) release, increased EP1 expression, and reduced cell proliferation compared to cells grown at 21% O(2). Similarly, cells cultured in 5% O(2) showed increased expression of EP1 and a trend toward a decrease in proliferation, but no activation of the HRE or increase in PGE(2) levels. Expression of EP2, EP3 and EP4 were not affected by O(2) tension. The differences in EP receptor profile observed in cells grown at 5% compared to 21% O(2) suggest that bone cell phenotype may be altered under routine cell culture conditions. Furthermore, our data suggest that hypoxia-dependent PGE(2) production and EP1 expression in bone cells may play a role in bone remodeling and repair in regions of compromised or damaged bone, where O(2) tension is low.

The prognostic value of muscle StO2 in septic patients

OBJECTIVE

To quantify sepsis-induced alterations in changes in muscle tissue oxygenation (StO(2)) after an ischemic challenge using near-infrared spectroscopy (NIRS), and to test the hypothesis that these alterations are related to outcome.

DESIGN

Prospective study.

SETTING

Thirty-one-bed, university hospital Department of Intensive Care.

PATIENTS

Seventy-two patients with severe sepsis or septic shock, 18 hemodynamically stable, acutely ill patients without infection, and 18 healthy volunteers.

INTERVENTIONS

Three-minute occlusion of the brachial artery using a cuff inflated 50[Symbol: see text]mmHg above systolic arterial pressure.

MEASUREMENTS AND MAIN RESULTS

Thenar eminence StO(2) was measured continuously by NIRS before (StO(2)baseline), during, and after the 3-min occlusion. Changes in StO(2) were assessed by the slope of increase in StO(2) during the first 14 s following the ischemic period and by the difference between the maximum StO(2) and StO(2)baseline (Delta). The slope was lower in septic patients than in controls and volunteers [2.3 (1.3-3.6), 4.8 (3.5-6.0), and 4.7 (3.2-6.3) %/s, p < 0.001]. Delta was also significantly lower in septic patients than in the other groups. Slopes were lower in septic patients with than without shock [2.0 (1.2-2.9) vs 3.2 (1.8-4.5) %/s, p < 0.05]. In 52 septic patients, in whom the slope was obtained every 24 h for 48 h, slopes were higher in survivors than in non-survivors and tended to increase in survivors but not in non-survivors.

CONCLUSIONS

Altered recovery in StO(2) after an ischemic challenge is frequent in septic patients and more pronounced in the presence of shock. The presence and persistence of these alterations in the first 24[Symbol: see text]h of sepsis are associated with worse outcome.

Intermittent hypoxia changes HIF-1alpha phosphorylation pattern in endothelial cells: unravelling of a new PKA-dependent regulation of HIF-1alpha

Vascularized tumors are exposed to intermittent hypoxia, that is, hypoxia followed by periods of reoxygenation. Abnormal structure and dysfunction of tumor blood vessels are responsible for these conditions. These repeated short periods of hypoxia concern tumor cells as well as endothelial cells. However, the effects of intermittent hypoxia are poorly understood. The aim of this study was to investigate the effects of intermittent hypoxia on endothelial cells and particularly on HIF-1alpha, a central actor in adaptive response to hypoxia. For that, endothelial cells were exposed to four repeated cycles of 1-h hypoxia followed by 30 min of reoxygenation. We showed that repeated cycles of hypoxia/reoxygenation induced a modification in HIF-l alpha phosphorylation pattern: a progressive increase in HIF-1alpha phosphorylated form was observed during the hypoxic periods. Activation of p42/p44, Akt and PKA was observed in parallel. PKA was shown to be involved in the phosphorylation of HIF-lalpha under intermittent hypoxia, while p42/p44 and Akt were not. As HIF-1 activity is often associated with enhanced cell survival, a better knowledge of the effects of intermittent hypoxia on endothelial cells and the highlight of particular mechanisms induced by intermittent hypoxia are essential to understand the behavior of endothelial cells during neo-angiogenesis.

Endothelium protectant and contractile effects of the antivaricose principle escin in rat aorta

The triterpene saponin escin is the active component of the extract of seeds of Aesculus hippocastanum used in the treatment of chronic venous insufficiency. Escin is also used experimentally to increase membrane permeability in isolated cells. Since endothelial dysfunction is postulated to be involved in venous insufficiency, the possible endothelium-protectant effect of escin was explored in rat aortic rings, a model widely used to study such effects with cardiovascular agents. Escin enhanced endothelium-dependent relaxation induced by acetylcholine when such relaxation had been reduced by exposure to the superoxide ion generator pyrogallol. This effect was attributed to enhanced nitric oxide production by endothelial nitric oxide synthase, a calcium-dependent enzyme, activated by the increased endothelial cell permeability to calcium induced by escin. Another effect of escin thought to contribute to its therapeutic activity is its ability to produce venous contraction. The compound was found to induce concentration-related contraction also in rat aortic rings. This response was partially inhibited by removal of the endothelium or by preincubation with indomethacin, and was completely abolished by incubation in a calcium-free perfusion fluid. Contraction was considered to be due mainly to the aforementioned effect on calcium permeability, with some mediation by release of endothelial vasoconstrictor prostanoids. It was concluded that, in rat aorta, escin possesses an endothelium-protectant action and a direct contractile effect. The former could contribute to its beneficial effect in the treatment of venous insufficiency, while the latter could constitute a limiting side effect.

Identification and Reduction of Cryoinjury in Endothelial Cells: A First Step toward Establishing a Cell Bank for Vascular Tissue Engineering

We analyzed a cryopreservation protocol which improves long-term storage of endothelial cells (EC) for tissue engineering purposes. Human umbilical vein EC were frozen in a high-potassium solution containing 10% dimethyl sulfoxide using 3 different cooling rates. After a storage time in liquid nitrogen of 1, 4, or 12 months, samples were thawed and compared to fresh cells in terms of growth rates, anti-inflammatory, and anticoagulant functions. Independent of cooling rate and storage time, the retrieval after cryopreservation ranged between 60% and 80%. However, viability of the cells cryopreserved at 10 degrees C/min decreased significantly from 78 +/- 5% to 64 +/-3% with storage. Storage time of 4 months resulted in a decreased cell multiplication factor over 4 and 12 days in culture. The lag phases returned to normal in the next passage. Thawed cells showed increased metabolic activity, reduced expression of thrombomodulin, and unchanged basal expression of adhesion molecules. However, the tumor necrosis factor-induced expression of adhesion molecules was significantly increased after long-term storage. This effect was partially compensated after expansion of the cells, whereas the prostacyclin release increased. Expansion of cryopreserved/thawed EC resulted in highly proliferative cells with antithrombotic properties and a capacity for inflammatory reactions, which makes them suitable for vascular tissue engineering.

Metabolic coronary flow regulation--current concepts

The concept of metabolic coronary flow control provides a rationale for the close relationship of coronary flow and myocardial metabolic rate of oxygen. The concept is based on the presence of an oxygen (metabolic) sensor coupled functionally to effector mechanisms, which control vascular tone. Four modes of metabolic control models have been proposed. 1) An oxygen sensor located in the wall of coronary vessels coupling to smooth muscle tension. Endothelial prostaglandin production may support this concept. 2) An oxygen sensing mechanism located in the myocardium and changing metabolism in response to changes of local pO(2). Adenosine is a metabolite produced at an accelerated rate when the supply-to-demand relationship for oxygen falls. 3) Sensing of oxygen turnover may be achieved by carbon dioxide production and, potentially, by mitochondrial production of reactive oxygen species. 4) The red blood cell might serve as an oxygen sensor in response to changes of haemoglobin oxygenation. A potential link to vessel relaxation may be red cell ATP release. A large body of experimental evidence supports the notion that K(ATP) channels play a significant role causing smooth muscle hyper-polarization. However, additional yet unknown effector mechanisms must exist, because block of K(ATP) channels does not lead to deterioration of coronary flow control under conditions of exercise. Thus, although several lines of evidence show that metabolic flow regulation is effective during hypoxic conditions,mechanisms mediating normoxic metabolic flow control still await further clarification.

Role of NO and prostaglandins in acute hypoxic vasoconstriction in sheep pulmonary veins

The aim of this study was to investigate the effect of hypoxia on and the role of nitric oxide (NO) and cyclooxgenase inhibition in hypoxia-induced vasoconstriction in sheep isolated pulmonary veins. We used the potent pulmonary vasoconstrictor U46619, a thromboxane analog, as a precontractile agent. Our results showed that hypoxia caused a vasoconstriction both under resting tone and in U46619 (10(-6) mol/l) precontracted pulmonary veins. In the presence of the nonselective NO synthase inhibitior Nomega-nitro-L-arginine methyl ester (L-NAME; 3 x 10(-5) mol/l), the hypoxic pulmonary vasoconstriction (HPV) was significantly increased in veins under resting force. However, there was a decrease in HPV in pulmonary veins precontracted with U46619 in the presence of L-NAME. Moreover, L-NAME markedly augmented the U46619-induced pulmonary contractions under normoxic conditions. Cyclooxygenase inhibition with indomethacin (10(-5) mol/l) significantly reduced the HPV both under resting tone and in precontracted veins. Indomethacin also significantly decreased the U46619-induced pulmonary contractions prior to the induction of hypoxia. Our findings suggest that NO and prostaglandins can act as a modulators of the hypoxic vasoconstriction in isolated pulmonary veins.

Contribution of prostaglandins to the dilation that follows isometric forearm contraction in human subjects: effects of aspirin and hyperoxia

In 11 healthy volunteers, we evaluated, in a double-blind crossover study, whether the vasodilation that follows isometric contraction is mediated by prostaglandins (PGs) and/or is O2 dependent. Subjects performed isometric handgrip for 2 min at 60% maximal voluntary contraction (MVC), after pretreatment with placebo or aspirin (600 mg orally), when breathing air or 40% O2. Forearm blood flow was measured in the dominant forearm by venous occlusion plethysmography. Arterial blood pressure was also recorded, allowing calculation of forearm vascular conductance (FVC; forearm blood flow/arterial blood pressure). During air breathing, aspirin significantly reduced the increase in FVC that followed contraction at 60% MVC: from a baseline of 0.09 +/- 0.011 [mean +/- SE, conductance units (CU)], the peak value was reduced from 0.24 +/- 0.03 to 0.14 +/- 0.01 CU. Breathing 40% O2 similarly reduced the increase in FVC relative to that evoked when breathing air; the peak value was 0.24 +/- 0.03 vs. 0.15 +/- 0.02 CU. However, after aspirin, breathing 40% O2 had no further effect on the contraction-evoked increase in FVC (the peak value was 0.15 +/- 0.02 vs. 0.16 +/- 0.02 CU). Thus the present study indicates that prostaglandins make a substantial contribution to the peak of the vasodilation that follows isometric contraction of forearm muscles at 60% MVC. Given that hyperoxia similarly reduced the vasodilation and attenuated the effect of aspirin, we propose that the stimulus for prostaglandin synthesis and release is hypoxia of the endothelium.

Pressure-induced smooth muscle cell depolarization in pulmonary arteries from control and chronically hypoxic rats does not cause myogenic vasoconstriction

Chronic obstructive pulmonary diseases, as well as prolonged residence at high altitude, can result in generalized airway hypoxia, eliciting an increase in pulmonary vascular resistance. We hypothesized that a portion of the elevated pulmonary vascular resistance following chronic hypoxia (CH) is due to the development of myogenic tone. Isolated, pressurized small pulmonary arteries from control (barometric pressure congruent with 630 Torr) and CH (4 wk, barometric pressure = 380 Torr) rats were loaded with fura 2-AM and perfused with warm (37 degrees C), aerated (21% O(2)-6% CO(2)-balance N(2)) physiological saline solution. Vascular smooth muscle (VSM) intracellular Ca(2+) concentration ([Ca(2+)](i)) and diameter responses to increasing intraluminal pressure were determined. Diameter and VSM cell [Ca(2+)](i) responses to KCl were also determined. In a separate set of experiments, VSM cell membrane potential responses to increasing luminal pressure were determined in arteries from control and CH rats. VSM cell membrane potential in arteries from CH animals was depolarized relative to control at each pressure step. VSM cells from both groups exhibited a further depolarization in response to step increases in intraluminal pressure. However, arteries from both control and CH rats distended passively to increasing intraluminal pressure, and VSM cell [Ca(2+)](i) was not affected. KCl elicited a dose-dependent vasoconstriction that was nearly identical between control and CH groups. Whereas KCl administration resulted in a dose-dependent increase in VSM cell [Ca(2+)](i) in arteries taken from control animals, this stimulus elicited only a slight increase in VSM cell [Ca(2+)](i) in arteries from CH animals. We conclude that the pulmonary circulation of the rat does not demonstrate pressure-induced vasoconstriction.

Hypoxic pulmonary vasoconstriction in cardiothoracic surgery: basic mechanisms to potential therapies

Hypoxic pulmonary vasoconstriction is postulated to be an adaptive mechanism to match lung perfusion with ventilation; however, the consequences of the maladaptive effects of pulmonary vasoconstriction represent formidable therapeutic challenges. Understanding the basic mechanisms of hypoxic pulmonary vasoconstriction will enhance the assimilation of translational research into clinical practice. The purposes of this review are to (1) define basic mechanisms of pulmonary vasoconstriction and vasorelaxation; (2) delineate the biphasic contractile response to hypoxia; (3) critically examine data that support the mediator hypothesis versus the ion channel hypothesis; and (4) explore potential mechanistic-based therapies for hypoxic pulmonary vasoconstriction.

Hypoxic Regulation of Angiopoietin-2 Expression in Endothelial Cells

Exposure of endothelial cells to hypoxia-induced angiopoietin-2 (Ang2) expression. The increase in Ang2 mRNA levels occurred by transcriptional regulation and by post-transcriptional increase in mRNA stability. Induction of Ang2 mRNA resulted in an increase of intracellular and secreted Ang2 protein levels. Since the transcriptional regulation of several genes involved in angiogenesis during hypoxia is mediated by hypoxia-inducible factor-1 (HIF-1), it was conceivable that Ang2 expression might be regulated by the same oxygen-dependent mechanism. However, our data showed that pharmacological HIF inducers, CoCl(2) and DFO, did not affect Ang2 expression. Moreover, HIF-1-deficient hepatoma cell (Hepa1 c4) and its wild-type counterpart (Hepa1 c1c4) up-regulates Ang2 during hypoxia. These results indicated that hypoxia-driven Ang2 expression may be independent of the HIF pathway. Using neutralizing VEGF antibody or pharmacological inhibitors of VEGF receptors, we showed that hypoxia-induced VEGF participates but could not account completely for Ang2 expression during hypoxia. In addition, hypoxia elicited an increase of cyclooxygenase-2 (COX-2) expression and a parallel increase in prostanglandin E(2) (PGE(2)) and prostacyclin (PGI(2)) production. COX-2 inhibitors decreased the hypoxic induction of Ang2 and the hypoxic induction of PGE(2) and PGI(2) in a dose-dependent manner. Similarly, COX-2 but not COX-1 antisense treatment decreased hypoxic induction of Ang2 expression, and this effect was reversed by exogenous PGE(2). Finally, exogenous PGE(2) and PGI(2) were able to stimulate Ang2 under normoxic conditions. These findings suggest that COX-2-dependent prostanoids may play an important role in the regulation of hypoxia-induced Ang2 expression.

Diabetes mellitus impairs vasodilation to hypoxia in human coronary arterioles: reduced activity of ATP-sensitive potassium channels

ATP-sensitive K+ channels (K(ATP)) contribute to vasomotor regulation in some species. It is not fully understood the extent to which K(ATP) participate in regulating vasomotor tone under physiological and pathophysiological conditions in the human heart. Arterioles dissected from right atrial appendage were studied with video microscopy, membrane potential recordings, reverse transcription-polymerase chain reaction, and immunohistochemistry. Hypoxia produced endothelium-independent vasodilation and membrane hyperpolarization of vascular smooth muscle cells, both of which were attenuated by glibenclamide. Aprikalim, a selective K(ATP) opener, also induced a potent endothelium-independent and glibenclamide-sensitive vasodilation with membrane hyperpolarization. Reverse transcription-polymerase chain reaction detected mRNA expression for K(ATP) subunits, and immunohistochemistry confirmed the localization of the inwardly rectifying Kir6.1 protein in the vasculature. In patients with type 1 or type 2 diabetes mellitus (DM), vasodilation was reduced to both aprikalim (maximum dilation, DM(+) 90+/-2% versus DM(-) 96+/-1%, P<0.05) and hypoxia (maximum dilation, DM(+) 56+/-8% versus DM(-) 85+/-5%, P<0.01) but was not altered to sodium nitroprusside or bradykinin. Baseline myogenic tone and resting membrane potential were not affected by DM. We conclude that DM impairs human coronary arteriolar dilation to K(ATP) opening, leading to reduced dilation to hypoxia. This reduction in K(ATP) function could contribute to the greater cardiovascular mortality and morbidity in DM.

Endothelium and Venotropic Drugs in Chronic Venous Insufficiency: A Review

Objective:

To review the literature concerning chronic venous disease of the leg and the mechanisms of action of venotropic drugs.

Methods:

The authors identified relevant papers from their own collection and from medical literature databases.

Synthesis:

Endothelial cell activation caused by ex-posure to the hypoxic conditions that develop during blood stasis in chronic venous insufficiency patients is proposed to be one factor initiating a pro-inflammatory process in the leg veins. Recruited and activated neutrophils would then be responsible for alterations of the venous wall, typical of what is observed in varicose veins. Venotropic drugs used in the treatment of chronic venous insufficiency patients have long been known to decrease vascular permeability and increase venous tone. Recently, it has been shown that they are also able to prevent endothelial cell activation by hypoxia and a precise biochemical target common to all of them has been identified: the mitochondrial respiratory chain.

Conclusion:

The influence of venotropic drugs on the mitochondrial respiratory chain provides a rational explanation for the therapeutic benefit to patients of this class of drugs.

Hypoxic induction of cox-2 regulates proliferation of human pulmonary artery smooth muscle cells

Chronic hypoxia-induced pulmonary hypertension results partly from proliferation of smooth muscle cells in small peripheral pulmonary arteries. Therefore, we examined the effect of hypoxia on growth of pulmonary artery smooth muscle cells (PASMCs) from human distal pulmonary arteries. Initial studies identified that serum-induced proliferation of explant-derived PASMCs was inhibited under hypoxic conditions (3-4 kPa in medium). However, selection of hypoxia-stimulated cells was achieved by culturing cells at low density under conditions of prolonged hypoxia (1-2 wk). In hypoxia-inhibited and -stimulated cells, Western blotting revealed hypoxic induction of cyclooxygenase (COX)-2, which was dependent on the activation of p38(MAPK), but not COX-1, inducible nitric oxide synthase (iNOS), or hemoxygenase-1 (HO-1). Hypoxic induction of COX-2 was also observed in the media of pulmonary arteries in lung organ culture. Hypoxia induced a 4- to 5-fold increase (P < 0.001) in prostaglandin (PG)E(2), PGD(2), PGF(2alpha), and 6-keto-PGF(1alpha) release from PASMCs. Hypoxic inhibition of proliferation was attenuated by incubation with indomethacin (10 micro M), or the COX-2 antagonist, NS398 (10 micro M), but not by the COX-1 antagonist, valeryl salicylate (0.5 mM). In conclusion, we have isolated cells from human peripheral pulmonary arteries that are either inhibited or stimulated by culture under hypoxic conditions. In both cell types hypoxia modulates cell proliferation by induction of COX-2 and production of antiproliferative prostaglandins. Induction of COX-2 may contribute to the inhibition of hypoxia-induced pulmonary vascular remodeling.

Interactions of adenosine, prostaglandins and nitric oxide in hypoxia-induced vasodilatation: in vivo and in vitro studies

Adenosine, prostaglandins (PG) and nitric oxide (NO) have all been implicated in hypoxia-evoked vasodilatation. We investigated whether their actions are interdependent. In anaesthetised rats, the PG synthesis inhibitors diclofenac or indomethacin reduced muscle vasodilatation evoked by systemic hypoxia or adenosine, but not that evoked by iloprost, a stable analogue of prostacyclin (PGI(2)), or by an NO donor. After diclofenac, the A(1) receptor agonist CCPA evoked no vasodilatation: we previously showed that A(1), but not A(2A), receptors mediate the hypoxia-induced muscle vasodilatation. Further, in freshly excised rat aorta, adenosine evoked a release of NO, detected with an NO-sensitive electrode, that was abolished by NO synthesis inhibition, or endothelium removal, and reduced by ~50 % by the A(1) antagonist DPCPX, the remainder being attenuated by the A(2A) antagonist ZM241385. Diclofenac reduced adenosine-evoked NO release by ~50 % under control conditions, abolished that evoked in the presence of ZM241385, but did not affect that evoked in the presence of DPCPX. Adenosine-evoked NO release was also abolished by the adenyl cyclase inhibitor 2',5'-dideoxyadenosine, while dose-dependent NO release was evoked by iloprost. Finally, stimulation of A(1), but not A(2A), receptors caused a release of PGI(2) from rat aorta, assessed by radioimmunoassay of its stable metabolite, 6-keto PGF(1alpha), that was abolished by diclofenac. These results suggest that during systemic hypoxia, adenosine acts on endothelial A(1) receptors to increase PG synthesis, thereby generating cAMP, which increases the synthesis and release of NO and causes muscle vasodilatation. This pathway may be important in other situations involving these autocoids.