Endothelial cell activation by endotoxin involves superoxide/NO-mediated nitration of prostacyclin synthase and thromboxane receptor stimulation

Peroxynitrite: a multifaceted oxidizing and nitrating metabolite

Peroxynitrite, a short-lived and reactive oxidant, emerges from the diffusion-controlled reaction between the superoxide radical and nitric oxide. Evidence shows that peroxynitrite is a critical mediator in physiological and pathological processes such as the immune response, inflammation, cancer, neurodegeneration, vascular dysfunction, and aging. The biochemistry of peroxynitrite is multifaceted, involving one- or two-electron oxidations and nitration reactions. This minireview highlights recent findings of peroxynitrite acting as a metabolic mediator in processes ranging from oxidative killing to redox signaling. Selected examples of nitrated proteins (i.e., 3-nitrotyrosine) are surveyed to underscore the role of this post-translational modification on cell homeostasis. While accumulated evidence shows that large amounts of peroxynitrite participates of broad oxidation and nitration events in invading pathogens and host tissues, a closer look supports that low to moderate levels selectively trigger signal transduction cascades. Peroxynitrite probes and redox-based pharmacology are instrumental to further understand the biological actions of this reactive metabolite.

E-cigarette effects on vascular function in animals and humans

Smoking tobacco cigarettes is a significant (cardiovascular) health risk factor. Although the number of tobacco cigarette users declined over the last decades, shisha smoking and e-cigarette vaping partially compensated for this health benefit. E-cigarettes may create highly addicted dual users (vaping and smoking). E-cigarettes seem not to represent a healthier alternative to tobacco smoking, although they may be less harmful. E-cigarette vaping causes oxidative stress, inflammation, endothelial dysfunction, and associated cardiovascular sequelae. This is primarily due to a significant overlap of toxic compounds in the vapor compared to tobacco smoke and, accordingly, a substantial overlap of pathomechanistic features between vaping and smoking. Whereas the main toxins in vapor are reactive aldehydes such as formaldehyde and acrolein, the toxic mixture in smoke is more complex, comprising particulate matter, reactive gases, transition metals, volatile organic compounds, and N-nitrosamines. However, it seems that both lifestyle drugs impair endothelial function to a quite similar extent, which may be due to the role of oxidative stress as the central pathomechanism to mediate endothelial dysfunction and vascular damage. Finally, the main selling argument for e-cigarette use that they help to quit smoking and get rid of nicotine addiction may be false because it seems that e-cigarettes instead trigger the opposite-younger entrance age and more frequent use. With our review, we summarize the adverse health impact of tobacco cigarettes and e-cigarettes, emphasizing the detrimental effects on endothelial function and cardiovascular health.

Paracrine Role of the Endothelium in Metabolic Homeostasis in Health and Nutrient Excess

The vascular endothelium traditionally viewed as a simple physical barrier between the circulation and tissue is now well-established as a key organ mediating whole organism homeostasis by release of a portfolio of anti-inflammatory and pro-inflammatory vasoactive molecules. Healthy endothelium releases anti-inflammatory signaling molecules such as nitric oxide and prostacyclin; in contrast, diseased endothelium secretes pro-inflammatory signals such as reactive oxygen species, endothelin-1 and tumor necrosis factor-alpha (TNFα). Endothelial dysfunction, which has now been identified as a hallmark of different components of the cardiometabolic syndrome including obesity, type 2 diabetes and hypertension, initiates and drives the progression of tissue damage in these disorders. Recently it has become apparent that, in addition to vasoactive molecules, the vascular endothelium has the potential to secrete a diverse range of small molecules and proteins mediating metabolic processes in adipose tissue (AT), liver, skeletal muscle and the pancreas. AT plays a pivotal role in orchestrating whole-body energy homeostasis and AT dysfunction, characterized by local and systemic inflammation, is central to the metabolic complications of obesity. Thus, understanding and targeting the crosstalk between the endothelium and AT may generate novel therapeutic opportunities for the cardiometabolic syndrome. Here, we provide an overview of the role of the endothelial secretome in controlling the function of AT. The endothelial-derived metabolic regulatory factors are grouped and discussed based on their physical properties and their downstream signaling effects. In addition, we focus on the therapeutic potential of these regulatory factors in treating cardiometabolic syndrome, and discuss areas of future study of potential translatable and clinical significance. The vascular endothelium is emerging as an important paracrine/endocrine organ that secretes regulatory factors in response to nutritional and environmental cues. Endothelial dysfunction may result in imbalanced secretion of these regulatory factors and contribute to the progression of AT and whole body metabolic dysfunction. As the vascular endothelium is the first responder to local nutritional changes and adipocyte-derived signals, future work elucidating the changes in the endothelial secretome is crucial to improve our understanding of the pathophysiology of cardiometabolic disease, and in aiding our development of new therapeutic strategies to treat and prevent cardiometabolic syndrome.

Revisiting pharmacology of oxidative stress and endothelial dysfunction in cardiovascular disease: Evidence for redox-based therapies

According to the latest Global Burden of Disease Study data, non-communicable diseases in general and cardiovascular disease (CVD) in particular are the leading cause of premature death and reduced quality of life. Demographic shifts, unhealthy lifestyles and a higher burden of adverse environmental factors provide an explanation for these findings. The expected growing prevalence of CVD requires enhanced research efforts for identification and characterisation of novel therapeutic targets and strategies. Cardiovascular risk factors including classical (e.g. hypertension, diabetes, hypercholesterolaemia) and non-classical (e.g. environmental stress) factors induce the development of endothelial dysfunction, which is closely associated with oxidant stress and vascular inflammation and results in CVD, particularly in older adults. Most classically successful therapies for CVD display vasoprotective, antioxidant and anti-inflammatory effects, but were originally designed with other therapeutic aims. So far, only a few 'redox drugs' are in clinical use and many antioxidant strategies have not met expectations. With the present review, we summarise the actual knowledge on CVD pathomechanisms, with special emphasis on endothelial dysfunction, adverse redox signalling and oxidative stress, highlighting the preclinical and clinical evidence. In addition, we provide a brief overview of established CVD therapies and their relation to endothelial dysfunction and oxidative stress. Finally, we discuss novel strategies for redox-based CVD therapies trying to explain why, despite a clear link between endothelial dysfunction and adverse redox signalling and oxidative stress, redox- and oxidative stress-based therapies have not yet provided a breakthrough in the treatment of endothelial dysfunction and CVD.

Regulation of Vascular Function and Inflammation via Cross Talk of Reactive Oxygen and Nitrogen Species from Mitochondria or NADPH Oxidase-Implications for Diabetes Progression

Oxidative stress plays a key role for the development of cardiovascular, metabolic, and neurodegenerative disease. This concept has been proven by using the approach of genetic deletion of reactive oxygen and nitrogen species (RONS) producing, pro-oxidant enzymes as well as by the overexpression of RONS detoxifying, antioxidant enzymes leading to an amelioration of the severity of diseases. Vice versa, the development and progression of cardiovascular diseases is aggravated by overexpression of RONS producing enzymes as well as deletion of RONS detoxifying enzymes. We have previously identified cross talk mechanisms between different sources of RONS, which can amplify the oxidative stress-mediated damage. Here, the pathways and potential mechanisms leading to this cross talk are analyzed in detail and highlighted by selected examples from the current literature and own data including hypoxia, angiotensin II (AT-II)-induced hypertension, nitrate tolerance, aging, and others. The general concept of redox-based activation of RONS sources via “kindling radicals” and enzyme-specific “redox switches” as well as the interaction with redox-sensitive inflammatory pathways are discussed. Here, we present evidence for the existence of such cross talk mechanisms in the setting of diabetes and critically assess their contribution to the severity of diabetic complications.

Redox Regulation via Glutaredoxin-1 and Protein S-Glutathionylation

Significance: Over the past several years, oxidative post-translational modifications of protein cysteines have been recognized for their critical roles in physiology and pathophysiology. Cells have harnessed thiol modifications involving both oxidative and reductive steps for signaling and protein processing. One of these stages requires oxidation of cysteine to sulfenic acid, followed by two reduction reactions. First, glutathione (reduced glutathione [GSH]) forms a S-glutathionylated protein, and second, enzymatic or chemical reduction removes the modification. Under physiological conditions, these steps confer redox signaling and protect cysteines from irreversible oxidation. However, oxidative stress can overwhelm protein S-glutathionylation and irreversibly modify cysteine residues, disrupting redox signaling. Critical Issues: Glutaredoxins mainly catalyze the removal of protein-bound GSH and help maintain protein thiols in a highly reduced state without exerting direct antioxidant properties. Conversely, glutathione S-transferase (GST), peroxiredoxins, and occasionally glutaredoxins can also catalyze protein S-glutathionylation, thus promoting a dynamic redox environment. Recent Advances: The latest studies of glutaredoxin-1 (Glrx) transgenic or knockout mice demonstrate important distinct roles of Glrx in a variety of pathologies. Endogenous Glrx is essential to maintain normal hepatic lipid homeostasis and prevent fatty liver disease. Further, in vivo deletion of Glrx protects lungs from inflammation and bacterial pneumonia-induced damage, attenuates angiotensin II-induced cardiovascular hypertrophy, and improves ischemic limb vascularization. Meanwhile, exogenous Glrx administration can reverse pathological lung fibrosis. Future Directions: Although S-glutathionylation modifies many proteins, these studies suggest that S-glutathionylation and Glrx regulate specific pathways in vivo, and they implicate Glrx as a potential novel therapeutic target to treat diverse disease conditions. Antioxid. Redox Signal. 32, 677-700.

Crosstalk of mitochondria with NADPH oxidase via reactive oxygen and nitrogen species signalling and its role for vascular function

Cardiovascular diseases are associated with and/or caused by oxidative stress. This concept has been proven by using the approach of genetic deletion of reactive species producing (pro-oxidant) enzymes as well as by the overexpression of reactive species detoxifying (antioxidant) enzymes leading to a marked reduction of reactive oxygen and nitrogen species (RONS) and in parallel to an amelioration of the severity of diseases. Likewise, the development and progression of cardiovascular diseases is aggravated by overexpression of RONS producing enzymes as well as deletion of antioxidant RONS detoxifying enzymes. Thus, the consequences of the interaction (redox crosstalk) of superoxide/hydrogen peroxide produced by mitochondria with other ROS producing enzymes such as NADPH oxidases (Nox) are of outstanding importance and will be discussed including the consequences for endothelial nitric oxide synthase (eNOS) uncoupling as well as the redox regulation of the vascular function/tone in general (soluble guanylyl cyclase, endothelin-1, prostanoid synthesis). Pathways and potential mechanisms leading to this crosstalk will be analysed in detail and highlighted by selected examples from the current literature including hypoxia, angiotensin II-induced hypertension, nitrate tolerance, aging and others. The general concept of redox-based activation of RONS sources via "kindling radicals" and enzyme-specific "redox switches" will be discussed providing evidence that mitochondria represent key players and amplifiers of the burden of oxidative stress.

LINKED ARTICLES

This article is part of a themed section on Redox Biology and Oxidative Stress in Health and Disease. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v174.12/issuetoc.

Alleviating Promotion of Inflammation and Cancer Induced by Nonsteroidal Anti-Inflammatory Drugs

Clinical Relevance

Nonsteroidal Anti-Inflammatory Drugs (NSAIDs) including aspirin are of intensive use nowadays. These drugs exert their activity via the metabolism of arachidonic acid (AA) by cyclooxygenase inhibition. Though beneficial for health in some instances, both unspecific and specific cyclooxygenase inhibitor activity interfere with AA metabolism producing also proinflammatory lipids that may promote cancer.

Materials and Methods

This review is based on available literature on clinical uses, biochemical investigations, molecular medicine, pharmacology, toxicity, and epidemiology-clinical studies on NSAIDs and other drugs that may be used accordingly, which was collected from electronic (SciFinder, Medline, Science Direct, and ACS among others) and library searches of books and journals.

Results

Relevant literature supports the notion that NDSAID use may also promote proinflammatory biochemical events that are also related to precancerous predisposition. Several agents are proposed that may be employed in immediate future to supplement and optimize treatment with NSAIDs. In this way serious side effects arising from promotion of inflammation and cancer, especially in chronic NSAID users and high risk groups of patients, could be avoided.

Endothelial dysfunction and vascular disease - a 30th anniversary update

The endothelium can evoke relaxations of the underlying vascular smooth muscle, by releasing vasodilator substances. The best-characterized endothelium-derived relaxing factor (EDRF) is nitric oxide (NO) which activates soluble guanylyl cyclase in the vascular smooth muscle cells, with the production of cyclic guanosine monophosphate (cGMP) initiating relaxation. The endothelial cells also evoke hyperpolarization of the cell membrane of vascular smooth muscle (endothelium-dependent hyperpolarizations, EDH-mediated responses). As regards the latter, hydrogen peroxide (H₂ O₂ ) now appears to play a dominant role. Endothelium-dependent relaxations involve both pertussis toxin-sensitive G_i (e.g. responses to α₂ -adrenergic agonists, serotonin, and thrombin) and pertussis toxin-insensitive G_q (e.g. adenosine diphosphate and bradykinin) coupling proteins. New stimulators (e.g. insulin, adiponectin) of the release of EDRFs have emerged. In recent years, evidence has also accumulated, confirming that the release of NO by the endothelial cell can chronically be upregulated (e.g. by oestrogens, exercise and dietary factors) and downregulated (e.g. oxidative stress, smoking, pollution and oxidized low-density lipoproteins) and that it is reduced with ageing and in the course of vascular disease (e.g. diabetes and hypertension). Arteries covered with regenerated endothelium (e.g. following angioplasty) selectively lose the pertussis toxin-sensitive pathway for NO release which favours vasospasm, thrombosis, penetration of macrophages, cellular growth and the inflammatory reaction leading to atherosclerosis. In addition to the release of NO (and EDH, in particular those due to H₂ O₂ ), endothelial cells also can evoke contraction of the underlying vascular smooth muscle cells by releasing endothelium-derived contracting factors. Recent evidence confirms that most endothelium-dependent acute increases in contractile force are due to the formation of vasoconstrictor prostanoids (endoperoxides and prostacyclin) which activate TP receptors of the vascular smooth muscle cells and that prostacyclin plays a key role in such responses. Endothelium-dependent contractions are exacerbated when the production of nitric oxide is impaired (e.g. by oxidative stress, ageing, spontaneous hypertension and diabetes). They contribute to the blunting of endothelium-dependent vasodilatations in aged subjects and essential hypertensive and diabetic patients. In addition, recent data confirm that the release of endothelin-1 can contribute to endothelial dysfunction and that the peptide appears to be an important contributor to vascular dysfunction. Finally, it has become clear that nitric oxide itself, under certain conditions (e.g. hypoxia), can cause biased activation of soluble guanylyl cyclase leading to the production of cyclic inosine monophosphate (cIMP) rather than cGMP and hence causes contraction rather than relaxation of the underlying vascular smooth muscle.

High glucose/High Lipids impair vascular adiponectin function via inhibition of caveolin-1/AdipoR1 signalsome formation

Reduced levels of adiponectin (APN) contribute to cardiovascular injury in the diabetic population. Recent studies demonstrate elevated circulating APN levels are associated with endothelial dysfunction during pre-diabetes, suggesting the development of APN resistance. However, mechanisms leading to, and the role of, vascular APN resistance in endothelial dysfunction remain unidentified. The current study determined whether diabetes cause endothelial APN resistance, and by what mechanisms. Under high glucose/high lipids (HG/HL), APN-stimulated nitric oxide production by HUVEC was decreased, phosphorylation of eNOS, AMPK, and Akt was attenuated (P<0.01), and APN's anti-TNFα effect was blunted (P<0.01). APN receptor expression remained normal, whereas Cav1 expression was reduced in HG/HL cells (P<0.01). The AdipoR1/Cav1 signaling complex was dissociated in HG/HL cells. Knock-down of Cav1 inhibited APN's anti-oxidative and anti-inflammatory actions. Conversely, preventing HG/HL-induced Cav1 downregulation by Cav1 overexpression preserved APN signaling in HG/HL cells. Knock-in of a wild type Cav1 in Cav1 knock-down cells restored caveolae structure and rescued APN signaling. In contrast, knock-in of a mutated Cav1 scaffolding domain restored caveolae structure, but failed to rescue APN signaling in Cav1 knock-down cells. Finally, AdipoR1/Cav1 interaction was significantly reduced in diabetic vascular tissue, and the vasorelaxative response to APN was impaired in diabetic animals. The current study demonstrates for the first time the interaction between AdipoR1 and Cav1 is critical for adiponectin-mediated vascular signaling. The AdipoR1/Cav1 interaction is adversely affected by HG/HL, due largely to reduced Cav1 expression, supporting a potential mechanism for the development of APN resistance, contributing to diabetic endothelial dysfunction.

A review on thromboangiitis obliterans pathophysiology: thrombosis and angiitis, which is to blame?

A century has passed since thromboangiitis obliterans (TAO), or Buerger's disease, was first described, but the etiology remains unclear. It is still uncertain as to whether thrombosis or vascular inflammation is the first event. TAO is an episodic inflammatory and thrombotic-occlusive vascular disease of unknown origin. The involvement of the distal vessels and nerves within the neuro-vascular bundles occurs almost always in legs and occasionally in arms. The cumulative data demonstrate that at the cellular and molecular levels, at least four main components of inflammatory reactions, including endothelial cells, platelets, leukocytes and sensory neurons, might be involved in TAO pathogenesis. The interactions among these cells in an altered microenvironment of small- and medium-sized vessels may also orchestrate the onset of TAO events. In this review, the factors that may promote thrombosis and angiitis are reconsidered at three levels: (1) host characteristics such as male gender and genetic background; (2) probable triggers including cigarette smoking and infectious agents; and (3) environmental factors such as chronic anxiety and mental stress as a consequence of low socioeconomic status. At each level, the interactions among vascular endothelium, platelets, leukocytes and sensory neurons are discussed.

Redox signaling pathways involved in neuronal ischemic preconditioning

There is extensive evidence that the restoration of blood flow following cerebral ischemia contributes greatly to the pathophysiology of ischemia mediated brain injury. The initiating stimulus of reperfusion injury is believed to be the excessive production of reactive oxygen (ROS) and nitrogen (RNS) species by the mitochondria. ROS and RNS generation leads to mitochondrial protein, lipid and DNA oxidation which impedes normal mitochondrial physiology and initiates cellular death pathways. However not all ROS and RNS production is detrimental. It has been demonstrated that low levels of ROS production are protective and may serve as a trigger for activation of ischemic preconditioning. Ischemic preconditioning is a neuroprotective mechanism which is activated upon a brief sublethal ischemic exposure and is sufficient to provide protection against a subsequent lethal ischemic insult. Numerous proteins and signaling pathways have been implicated in the ischemic preconditioning neuroprotective response. In this review we examine the origin and mechanisms of ROS and RNS production following ischemic/reperfusion and the role of free radicals in modulating proteins associated with ischemic preconditioning neuroprotection.

Protein tyrosine nitration and thiol oxidation by peroxynitrite-strategies to prevent these oxidative modifications

The reaction product of nitric oxide and superoxide, peroxynitrite, is a potent biological oxidant. The most important oxidative protein modifications described for peroxynitrite are cysteine-thiol oxidation and tyrosine nitration. We have previously demonstrated that intrinsic heme-thiolate (P450)-dependent enzymatic catalysis increases the nitration of tyrosine 430 in prostacyclin synthase and results in loss of activity which contributes to endothelial dysfunction. We here report the sensitive peroxynitrite-dependent nitration of an over-expressed and partially purified human prostacyclin synthase (3.3 μM) with an EC₅₀ value of 5 μM. Microsomal thiols in these preparations effectively compete for peroxynitrite and block the nitration of other proteins up to 50 μM peroxynitrite. Purified, recombinant PGIS showed a half-maximal nitration by 10 μM 3-morpholino sydnonimine (Sin-1) which increased in the presence of bicarbonate, and was only marginally induced by freely diffusing NO₂-radicals generated by a peroxidase/nitrite/hydrogen peroxide system. Based on these observations, we would like to emphasize that prostacyclin synthase is among the most efficiently and sensitively nitrated proteins investigated by us so far. In the second part of the study, we identified two classes of peroxynitrite scavengers, blocking either peroxynitrite anion-mediated thiol oxidations or phenol/tyrosine nitrations by free radical mechanisms. Dithiopurines and dithiopyrimidines were highly effective in inhibiting both reaction types which could make this class of compounds interesting therapeutic tools. In the present work, we highlighted the impact of experimental conditions on the outcome of peroxynitrite-mediated nitrations. The limitations identified in this work need to be considered in the assessment of experimental data involving peroxynitrite.

Functional enhancement of AT1R potency in the presence of the TPαR is revealed by a comprehensive 7TM receptor co-expression screen

Background

Functional cross-talk between seven transmembrane (7TM) receptors can dramatically alter their pharmacological properties, both in vitro and in vivo. This represents an opportunity for the development of novel therapeutics that potentially target more specific biological effects while causing fewer adverse events. Although several studies convincingly have established the existence of 7TM receptor cross-talk, little is known about the frequencey and biological significance of this phenomenon.

Methodology/Principal Findings

To evaluate the extent of synergism in 7TM receptor signaling, we took a comprehensive approach and co-expressed 123 different 7TM receptors together with the angiotensin II type 1 receptor (AT1R) and analyzed how each receptor affected the angiotensin II (AngII) response. To monitor the effect we used integrative receptor activation/signaling assay called Receptor Selection and Amplification Technology (R-SAT). In this screen the thromboxane A2α receptor (TPαR) was the only receptor which significantly enhanced the AngII-mediated response. The TPαR-mediated enhancement of AngII signaling was significantly reduced when a signaling deficient receptor mutant (TPαR R130V) was co-expressed instead of the wild-type TPαR, and was completely blocked both by TPαR antagonists and COX inhibitors inhibiting formation of thromboxane A₂ (TXA₂).

Conclusions/Significance

We found a functional enhancement of AT1R only when co-expressed with TPαR, but not with 122 other 7TM receptors. In addition, the TPαR must be functionally active, indicating the AT1R enhancement is mediated by a paracrine mechanism. Since we only found one receptor enhancing AT1R potency, our results suggest that functional augmentation through 7TM receptor cross-talk is a rare event that may require specific conditions to occur.

Vascular aging: chronic oxidative stress and impairment of redox signaling-consequences for vascular homeostasis and disease

Characteristic morphological and molecular alterations such as vessel wall thickening and reduction of nitric oxide occur in the aging vasculature leading to the gradual loss of vascular homeostasis. Consequently, the risk of developing acute and chronic cardiovascular diseases increases with age. Current research of the underlying molecular mechanisms of endothelial function demonstrates a duality of reactive oxygen and nitrogen species in contributing to vascular homeostasis or leading to detrimental effects when formed in excess. Furthermore, changes in function and redox status of vascular smooth muscle cells contribute to age-related vascular remodeling. The age-dependent increase in free radical formation causes deterioration of the nitric oxide signaling cascade, alters and activates prostaglandin metabolism, and promotes novel oxidative posttranslational protein modifications that interfere with vascular and cell signaling pathways. As a result, vascular dysfunction manifests. Compensatory mechanisms are initially activated to cope with age-induced oxidative stress, but become futile, which results in irreversible oxidative modifications of biological macromolecules. These findings support the 'free radical theory of aging' but also show that reactive oxygen and nitrogen species are essential signaling molecules, regulating vascular homeostasis.

Nitric oxide-mediated protein modification in cardiovascular physiology and pathology

Nitric oxide (NO) is a key regulator of cardiovascular functions including the control of vascular tone, anti-inflammatory properties of the endothelium, cardiac contractility, and thrombocyte activation and aggregation. Numerous experimental data support the view that NO not only acts via cyclic guanosine monophosphate (cGMP)-dependent mechanisms but also modulates protein function by nitrosation, nitrosylation, glutathiolation, and nitration, respectively. To understand how NO regulates all of these diverse biological processes on the molecular level a comprehensive assessment of NO-mediated cGMP-dependent and independent targets is required. Novel proteomic approaches allow the simultaneous identification of large quantities of proteins modified in an NO-dependent manner and thereby will considerably deepen our understanding of the role NO plays in cardiovascular physiology and pathophysiology.

Activation of AMP-activated protein kinase alleviates high-glucose-induced dysfunction of brain microvascular endothelial cell tight-junction dynamics

The blood-brain barrier, formed by specialized brain endothelial cells that are interconnected by tight junctions, strictly regulates paracellular permeability to maintain an optimal extracellular environment for brain homeostasis. Diabetes is known to compromise the blood-brain barrier, although the underlying mechanism remains unknown. The aim of this study was to elucidate the molecular mechanisms underlying disruption of the blood-brain barrier in diabetes and to determine whether activation of AMP-activated protein kinase prevents diabetes-induced blood-brain barrier dysfunction. Exposure of human brain microvascular endothelial cells to high glucose (25 mmol/L D-glucose), but not to high osmotic conditions (20 mmol/L L-glucose plus 5 mmol/L D-glucose), for 2h to 1 week significantly increased the permeability of the blood-brain barrier in parallel with lowered expression levels of zonula occludens-1, occludin, and claudin-5, three proteins that are essential to maintaining endothelial cell tight junctions. In addition, high glucose significantly increased the generation of superoxide anions. Adenoviral overexpression of superoxide dismutase or catalase significantly attenuated the high-glucose-induced reduction of endothelial cell tight-junction proteins. Furthermore, administration of apocynin reversed the effects of high glucose on endothelial cell tight-junction proteins. Finally, activation of AMP-activated protein kinase with 5-amino-4-imidazole carboxamide riboside or adenoviral overexpression of constitutively active AMP-activated protein kinase mutants abolished both the induction of NAD(P)H oxidase-derived superoxide anions and the tight-junction protein degradation induced by high glucose. We conclude that high glucose increases blood-brain barrier dysfunction in diabetes through induction of superoxide anions and that the activation of AMP-activated protein kinase protects the integrity of the blood-brain barrier by suppressing the induction of NAD(P)H oxidase-derived superoxide anions.

Endothelial calcium-activated potassium channels as therapeutic targets to enhance availability of nitric oxide

The vascular endothelium plays a critical role in vascular health by controlling arterial diameter, regulating local cell growth, and protecting blood vessels from the deleterious consequences of platelet aggregation and activation of inflammatory responses. Circulating chemical mediators and physical forces act directly on the endothelium to release diffusible relaxing factors, such as nitric oxide (NO), and to elicit hyperpolarization of the endothelial cell membrane potential, which can spread to the surrounding smooth muscle cells via gap junctions. Endothelial hyperpolarization, mediated by activation of calcium-activated potassium (K(Ca)) channels, has generally been regarded as a distinct pathway for smooth muscle relaxation. However, recent evidence supports a role for endothelial K(Ca) channels in production of endothelium-derived NO, and indicates that pharmacological activation of these channels can enhance NO-mediated responses. In this review we summarize the current data on the functional role of endothelial K(Ca) channels in regulating NO-mediated changes in arterial diameter and NO production, and explore the tempting possibility that these channels may represent a novel avenue for therapeutic intervention in conditions associated with reduced NO availability such as hypertension, hypercholesterolemia, smoking, and diabetes mellitus.

Exposure to lipopolysaccharide and/or unconjugated bilirubin impair the integrity and function of brain microvascular endothelial cells

Background

Sepsis and jaundice are common conditions in newborns that can lead to brain damage. Though lipopolysaccharide (LPS) is known to alter the integrity of the blood-brain barrier (BBB), little is known on the effects of unconjugated bilirubin (UCB) and even less on the joint effects of UCB and LPS on brain microvascular endothelial cells (BMEC).

Methodology/Principal Findings

Monolayers of primary rat BMEC were treated with 1 µg/ml LPS and/or 50 µM UCB, in the presence of 100 µM human serum albumin, for 4 or 24 h. Co-cultures of BMEC with astroglial cells, a more complex BBB model, were used in selected experiments. LPS led to apoptosis and UCB induced both apoptotic and necrotic-like cell death. LPS and UCB led to inhibition of P-glycoprotein and activation of matrix metalloproteinases-2 and -9 in mono-cultures. Transmission electron microscopy evidenced apoptotic bodies, as well as damaged mitochondria and rough endoplasmic reticulum in BMEC by either insult. Shorter cell contacts and increased caveolae-like invaginations were noticeable in LPS-treated cells and loss of intercellular junctions was observed upon treatment with UCB. Both compounds triggered impairment of endothelial permeability and transendothelial electrical resistance both in mono- and co-cultures. The functional changes were confirmed by alterations in immunostaining for junctional proteins β-catenin, ZO-1 and claudin-5. Enlargement of intercellular spaces, and redistribution of junctional proteins were found in BMEC after exposure to LPS and UCB.

Conclusions

LPS and/or UCB exert direct toxic effects on BMEC, with distinct temporal profiles and mechanisms of action. Therefore, the impairment of brain endothelial integrity upon exposure to these neurotoxins may favor their access to the brain, thus increasing the risk of injury and requiring adequate clinical management of sepsis and jaundice in the neonatal period.

High temperature triggers the metabolism of S-nitrosothiols in sunflower mediating a process of nitrosative stress which provokes the inhibition of ferredoxin-NADP reductase by tyrosine nitration

High temperature (HT) is considered a major abiotic stress that negatively affects both vegetative and reproductive growth. Whereas the metabolism of reactive oxygen species (ROS) is well established under HT, less is known about the metabolism of reactive nitrogen species (RNS). In sunflower (Helianthus annuus L.) seedlings exposed to HT, NO content as well as S-nitrosoglutathione reductase (GSNOR) activity and expression were down-regulated with the simultaneous accumulation of total S-nitrosothiols (SNOs) including S-nitrosoglutathione (GSNO). However, the content of tyrosine nitration (NO(2) -Tyr) studied by high-performance liquid chromatography with tandem mass spectrometry (LC-MS/MS) and by confocal laser scanning microscope was induced. Nitroproteome analysis under HT showed that this stress induced the protein expression of 13 tyrosine-nitrated proteins. Among the induced proteins, ferredoxin-NADP reductase (FNR) was selected to evaluate the effect of nitration on its activity after heat stress and in vitro conditions using 3-morpholinosydnonimine (SIN-1) (peroxynitrite donor) as the nitrating agent, the FNR activity being inhibited. Taken together, these results suggest that HT augments SNOs, which appear to mediate protein tyrosine nitration, inhibiting FNR, which is involved in the photosynthesis process.

Inositol 1, 4, 5-trisphosphate receptor interacts with the SNARE domain of syntaxin 1B

Inositol 1, 4, 5-trisphosphate receptors (IP(3)Rs) are intracellular ligand-gated Ca(2+) channels that mediate Ca(2+) release from the endoplasmic reticulum (ER) into the cytosol and function in diverse cellular processes including fertilization, muscle contraction, apoptosis, secretion, and synaptic plasticity. The Ca(2+) release activity of IP(3)Rs is tightly regulated by many factors including IP(3)R-binding proteins. We show that IP(3)Rs interact with syntaxin 1 (Syx1), a membrane trafficking protein that regulates various plasma-membrane ion channels including N-, P/Q, and L-type voltage-gated Ca(2+) channels, voltage-gated potassium channels, and an epithelial sodium channel. We found that a SNARE-domain of Syx1B, one of the two Syx1 isoforms, directly interacted with the type1 IP(3)R (IP(3)R1) internal coupling domain, a known modulator for channel opening. These results indicate that Syx1B is an IP(3)R-interacting protein and that its interaction may play a crucial role in regulating the channel activity of IP(3)Rs in Syx1B-expressing cells.

The thromboxane/endoperoxide receptor (TP): the common villain

The stimulation of thromboxane/endoperoxide receptors (TP) elicits diverse physiological/pathophysiological reactions, including platelet aggregation and contraction of vascular smooth muscle. Furthermore, the activation of endothelial TP promotes the expression of adhesion molecules and favors adhesion and infiltration of monocytes/macrophages. In various cardiovascular diseases, endothelial dysfunction is predominantly the result of the release of endothelium-derived contracting factors that counteract the vasodilator effect of nitric oxide produced by the endothelial nitric oxide synthase. Endothelium-dependent contractions involve the activation of cyclooxygenases, the production of reactive oxygen species along with that of endothelium-derived contracting factors, which diffuse toward the vascular smooth muscle cells and activate their TP. TP antagonists curtail the endothelial dysfunction in diseases such as hypertension and diabetes, are potent antithrombotic agents, and reduce vascular inflammation. Therefore, TP antagonists, because of this triple activity, may have a unique potential for the treatment of cardiovascular disorders.

Endothelial dysfunction: a strategic target in the treatment of hypertension?

Endothelial dysfunction is a common feature of hypertension, and it results from the imbalanced release of endothelium-derived relaxing factors (EDRFs; in particular, nitric oxide) and endothelium-derived contracting factors (EDCFs; angiotensin II, endothelins, uridine adenosine tetraphosphate, and cyclooxygenase-derived EDCFs). Thus, drugs that increase EDRFs (using direct nitric oxide releasing compounds, tetrahydrobiopterin, or L-arginine supplementation) or decrease EDCF release or actions (using cyclooxygenase inhibitor or thromboxane A2/prostanoid receptor antagonists) would prevent the dysfunction. Many conventional antihypertensive drugs, including angiotensin-converting enzyme inhibitors, calcium channel blockers, and third-generation beta-blockers, possess the ability to reverse endothelial dysfunction. Their use is attractive, as they can address arterial blood pressure and vascular tone simultaneously. The severity of endothelial dysfunction correlates with the development of coronary artery disease and predicts future cardiovascular events. Thus, endothelial dysfunction needs to be considered as a strategic target in the treatment of hypertension.

TP receptors and oxidative stress hand in hand from endothelial dysfunction to atherosclerosis

Thromboxane A(2) and the activation of TP receptors that it causes play an important role in platelet aggregation and therefore in thrombosis. However, TP receptors are also involved in the pathologies of the vascular wall including impaired endothelium-dependent vasodilation, increased oxidant generation, and increased expression of adhesion molecules. The beneficial effects of TP antagonists on the vascular wall attenuate these features of vascular disease. They are not shared by aspirin. In fact, TP antagonists are active in patients treated with aspirin, indicating that their potential beneficial effects are mediated by mechanisms different from the antithrombotic actions of aspirin. Our studies have demonstrated the vascular benefits of TP antagonists in experimental animals, particularly in models of diabetes mellitus, in which elevated levels of eicosanoids play a role not only in vascular pathologies but also in those of the kidney and other tissues. They suggest that TP blockade protects against fundamental and widespread tissular dysfunction associated with metabolic disease including hyperlipidemia and hyperglycemia. TP receptor antagonists represent a promising avenue for the prevention of vascular disease in part because of these pleiotropic actions that extend beyond their antithrombotic properties.

Cardiovascular consequences when nitric oxide and lipid signaling converge

The identification of nitric oxide ((*)NO) as an endogenously produced free radical mediator of endothelial-dependent relaxation and host defense has fundamentally changed concepts of cell signal transduction. Ligand-receptor oriented paradigms of cell signaling were originally centered on the concept of a high affinity and specific interaction between a ligand and its receptor, resulting in the activation of secondary signaling events such as gene expression or modulation of catalytic protein function. While (*)NO ligation of the heme iron of soluble guanylate cyclase is consistent with this perspective, the readily diffusible and broadly reactive (*)NO is increasingly appreciated to react with a vast array of target molecules that mediate paracrine vasodilator actions, inhibition of thrombosis and neointimal proliferation, and both pro- and antiinflammatory signaling reactions that are not affected by inhibitors of soluble guanylate cyclase. There is an expanding array of functionally significant "off target" collateral reactions mediated by (*)NO that are guanylate cyclase-independent and rather are dictated by anatomic distribution and the formation of secondary (*)NO-derived species. These reactions are a critical element of redox-regulated signaling and are addressed herein in the context of the oxidation of unsaturated fatty acids to vascular and inflammatory signaling mediators. Because of their abundance and the intrinsic reactivity of unsaturated lipid intermediates and eicosanoid metabolism enzymes with (*)NO and other oxides of nitrogen, lipid signaling mechanisms are a significant target for regulation by (*)NO in the vascular compartment. This convergence of (*)NO and lipid signaling pathways thus adds another level of regulation to physiological responses such as vasodilation, thrombosis, and inflammation. Herein, interactions between (*)NO and lipid signaling events are placed in the context of cardiovascular regulation.

Endothelial dysfunction and vascular disease

The endothelium can evoke relaxations (dilatations) of the underlying vascular smooth muscle, by releasing vasodilator substances. The best characterized endothelium-derived relaxing factor (EDRF) is nitric oxide (NO). The endothelial cells also evoke hyperpolarization of the cell membrane of vascular smooth muscle (endothelium-dependent hyperpolarizations, EDHF-mediated responses). Endothelium-dependent relaxations involve both pertussis toxin-sensitive G(i) (e.g. responses to serotonin and thrombin) and pertussis toxin-insensitive G(q) (e.g. adenosine diphosphate and bradykinin) coupling proteins. The release of NO by the endothelial cell can be up-regulated (e.g. by oestrogens, exercise and dietary factors) and down-regulated (e.g. oxidative stress, smoking and oxidized low-density lipoproteins). It is reduced in the course of vascular disease (e.g. diabetes and hypertension). Arteries covered with regenerated endothelium (e.g. following angioplasty) selectively loose the pertussis toxin-sensitive pathway for NO release which favours vasospasm, thrombosis, penetration of macrophages, cellular growth and the inflammatory reaction leading to atherosclerosis. In addition to the release of NO (and causing endothelium-dependent hyperpolarizations), endothelial cells also can evoke contraction (constriction) of the underlying vascular smooth muscle cells by releasing endothelium-derived contracting factor (EDCF). Most endothelium-dependent acute increases in contractile force are due to the formation of vasoconstrictor prostanoids (endoperoxides and prostacyclin) which activate TP receptors of the vascular smooth muscle cells. EDCF-mediated responses are exacerbated when the production of NO is impaired (e.g. by oxidative stress, ageing, spontaneous hypertension and diabetes). They contribute to the blunting of endothelium-dependent vasodilatations in aged subjects and essential hypertensive patients.

Increased arachidonic acid-induced thromboxane generation impairs skeletal muscle arteriolar dilation with genetic dyslipidemia

OBJECTIVE

The aim of this study was to determine if arachidonic acid (AA)-induced skeletal muscle arteriolar dilation is altered with hypercholesterolemia in ApoE and low-density lipoprotein receptor (LDLR) gene deletion mice fed a normal diet. This study also determined contributors to altered AA-induced dilation between dyslipidemic mice and controls, C57/Bl/6J (C57).

METHODS

Gracilis muscle arterioles were isolated, with mechanical responses assessed following a challenge with AA under control conditions and after elements of AA metabolism pathways were inhibited. Conduit arteries from each strain were used to assess AA-induced production of PGI(2) and TxA(2).

RESULTS

Arterioles from ApoE and LDLR exhibited a blunted dilation to AA versus C57. While responses were cyclo-oxygenase-dependent in all strains, inhibition of thromboxane synthase or blockade of PGH(2)/TxA(2) receptors improved dilation in ApoE and LDLR only. AA-induced generation of PGI(2) was comparable across strains, although TxA(2) generation was increased in ApoE and LDLR. Arteriolar reactivity to PGI(2) and TxA(2) was comparable across strains. Treatment with TEMPOL improved dilation and reduced TxA(2) production with AA in ApoE and LDLR.

CONCLUSIONS

These results suggest that AA-induced arteriolar dilation is constrained in ApoE and LDLR via an increased production of TxA(2). While partially due to elevated oxidant stress, additional mechanisms contribute that are independent of acute alterations in oxidant tone.

Influence of dietary phytosterols and phytostanols on diastolic blood pressure and the expression of blood pressure regulatory genes in SHRSP and WKY inbred rats

The aim of the present study was to determine the impact of increased consumption of phytosterols or phytostanols on blood pressure and renal blood pressure regulatory gene expression in stroke-prone spontaneously hypertensive (SHRSP) and normotensive Wistar–Kyoto (WKY) inbred rats. SHRSP and WKY inbred rats (10/group) were fed a control diet or a diet supplemented with phytosterols or phytostanols (2·0 g/kg diet). After 5 weeks, SHRSP rats demonstrated higher systolic and diastolic blood pressures than WKY inbred rats. SHRSP rats that consumed the phytosterol or phytostanol supplemental diets displayed a 2- or 3-fold respective increase in the diastolic blood pressure than those that consumed the control diet. Angiotensinogen (Agt), angiotensin I-converting enzyme 1 (Ace1), nitric oxide synthase (Nos) 1,Nos3, cyclooxygenase 2 (Cox2) and THUMP domain containing 1 were expressed at higher levels in SHRSP compared with WKY inbred rats.Reninand angiotensin II receptor type 1a were expressed at lower levels in SHRSP than WKY inbred rats. Phytostanol supplementation up-regulated the expression ofAce1andNos3in SHRSP rats. Phytosterol supplementation increased the mRNA levels ofNos1and spondin 1 (Spon1) in SHRSP and WKY inbred rats.Cox2mRNA levels were elevated in both phytosterol- and phytostanol-supplemented SHRSP and WKY inbred rats. Therefore, the increased blood pressure in SHRSP rats may be partly due to altered renal expression of blood pressure regulatory genes. Specifically, up-regulation ofAce1,Nos1,Nos3,Cox2andSpon1were associated with the increased diastolic blood pressure observed in phytosterol- or phytostanol-supplemented SHRSP rats.

Suppression of the JNK pathway by induction of a metabolic stress response prevents vascular injury and dysfunction

BACKGROUND

Oxidative injury and dysfunction of the vascular endothelium are early and causal features of many vascular diseases. Single antioxidant strategies to prevent vascular injury have met with mixed results.

METHODS AND RESULTS

Here, we report that induction of a metabolic stress response with adenosine monophosphate kinase (AMPK) prevents oxidative endothelial cell injury. This response is characterized by stabilization of the mitochondrion and increased mitochondrial biogenesis, resulting in attenuation of oxidative c-Jun N-terminal kinase (JNK) activation. We report that peroxisome proliferator coactivator 1alpha is a key downstream target of AMPK that is both necessary and sufficient for the metabolic stress response and JNK attenuation. Moreover, induction of the metabolic stress response in vivo attenuates reactive oxygen species-mediated JNK activation and endothelial dysfunction in response to angiotensin II in wild-type mice but not in animals lacking either the endothelial isoform of AMPK or peroxisome proliferator coactivator 1alpha.

CONCLUSIONS

These data highlight AMPK and peroxisome proliferator coactivator 1alpha as potential therapeutic targets for the amelioration of endothelial dysfunction and, as a consequence, vascular disease.

Protein nitration in placenta - functional significance

Crucial roles of the placenta are disrupted in early and mid-trimester pregnancy loss, preeclampsia, eclampsia and intrauterine growth restriction. The pathophysiology of these disorders includes a relative hypoxia of the placenta, ischemia/reperfusion injury, an inflammatory response and oxidative stress. Reactive oxygen species including nitric oxide (NO), carbon monoxide and superoxide have been shown to participate in trophoblast invasion, regulation of placental vascular reactivity and other events. Superoxide, which regulates expression of redox sensitive genes, has been implicated in up-regulation of transcription factors, antioxidant production, angiogenesis, proliferation and matrix remodeling. When superoxide and nitric oxide are present in abundance, their interaction yields peroxynitrite a potent pro-oxidant, but also alters levels of nitric oxide, which in turn affect physiological functions. The peroxynitrite anion is extremely unstable thus evidence of its formation in vivo has been indirect via the occurrence of nitrated moieties including nitrated lipids and nitrotyrosine residues in proteins. Formation of 3-nitrotyrosine (protein nitration) is a "molecular fingerprint" of peroxynitrite formation. Protein nitration has been widely reported in a number of pathological states associated with inflammation but is reported to occur in normal physiology and is thought of as a prevalent, functionally relevant post-translational modification of proteins. Nitration of proteins can give either no effect, a gain or a loss of function. Nitration of a range of placental proteins is found in normal pregnancy but increased in pathologic pregnancies. Evidence is presented for nitration of placental signal transduction enzymes and transporters. The targets and extent of nitration of enzymes, receptors, transporters and structural proteins may markedly influence placental cellular function in both physiologic and pathologic settings.

Endothelium-dependent contractions: when a good guy turns bad!

Endothelial cells can induce contractions of the underlying vascular smooth muscle by generating vasoconstrictor prostanoids (endothelium-dependent contracting factor; EDCF). The endothelial COX-1 isoform of cyclooxygenase appears to play the dominant role in the phenomenon. Its activation requires an increase in intracellular Ca(2+) concentration. The production of EDCF is inhibited acutely and chronically by nitric oxide (NO), and possibly by endothelium-dependent hyperpolarizing factor (EDHF). The main prostanoids involved in endothelium-dependent contractions appear to be endoperoxides (PGH(2)) and prostacyclin, which activate thromboxane-prostanoid (TP) receptors of the vascular smooth muscle cells. Oxygen-derived free radicals can facilitate the production and/or the action of EDCF. Endothelium-dependent contractions are exacerbated by ageing, obesity, hypertension and diabetes, and thus are likely to contribute to the endothelial dysfunction observed in older people and in essential hypertensive patients.

Increased vascular thromboxane generation impairs dilation of skeletal muscle arterioles of obese Zucker rats with reduced oxygen tension

This study determined if altered vascular prostacyclin (PGI(2)) and/or thromboxane A(2) (TxA(2)) production with reduced Po(2) contributes to impaired hypoxic dilation of skeletal muscle resistance arterioles of obese Zucker rats (OZRs) versus lean Zucker rats (LZRs). Mechanical responses were assessed in isolated gracilis muscle arterioles following reductions in Po(2) under control conditions and following pharmacological interventions inhibiting arachidonic acid metabolism and nitric oxide synthase and alleviating elevated vascular oxidant stress. The production of arachidonic acid metabolites was assessed using pooled arteries from OZRs and LZRs in response to reduced Po(2). Hypoxic dilation, endothelium-dependent in both strains, was attenuated in OZRs versus LZRs. Nitric oxide synthase inhibition had no significant impact on hypoxic dilation in either strain. Cyclooxygenase inhibition dramatically reduced hypoxic dilation in LZRs and abolished responses in OZRs. Treatment of arterioles from OZRs with polyethylene glycol-superoxide dismutase improved hypoxic dilation, and this improvement was entirely cyclooxygenase dependent. Vascular PGI(2) production with reduced Po(2) was similar between strains, although TxA(2) production was increased in OZRs, a difference that was attenuated by treatment of vessels from OZRs with polyethylene glycol-superoxide dismutase. Both blockade of PGH(2)/TxA(2) receptors and inhibition of thromboxane synthase increased hypoxic dilation in OZR arterioles. These results suggest that a contributing mechanism underlying impaired hypoxic dilation of skeletal muscle arterioles of OZRs may be an increased vascular production of TxA(2), which competes against the vasodilator influences of PGI(2). These results also suggest that the elevated vascular oxidant stress inherent in metabolic syndrome may contribute to the increased vascular TxA(2) production and may blunt vascular sensitivity to PGI(2).

Effects of dietary decosahexaenoic acid (DHA) on eNOS in human coronary artery endothelial cells

Endothelial dysfunction occurs in heart disease and may reduce functional capacity via attenuations in peripheral blood flow. Dietary decosahexaenoic acid (DHA) may improve this dysfunction, but the mechanism is unknown. This study determined if DHA enhances expression and activity of eNOS in cultured human coronary artery endothelial cells (HCAEC). HCAEC from 4 donors were treated with 5 nM, 50 nM, or 1 microM DHA for 7 days to model chronic DHA exposure. A trend for increased expression of endothelial nitric oxide synthase (eNOS) and phospho-eNOS was observed with 5 and 50 nM DHA. DHA also enhanced expression of 2 proteins instrumental in activation of eNOS: phospho-Akt (5 and 50 nM) and HSP90 (50 nM and 1 microM). Vascular endothelial growth factor-induced activation of Akt increased NOx in treated (50 nM DHA) versus untreated HCAEC (9.2 +/- 1.0 vs 3.3 +/- 1.1 micromol/microg protein/microL). Findings suggest that DHA enhances eNOS and Akt activity, augments HSP90 expression, and increases NO bioavailability in response to Akt kinase activation.

Regulation of the epithelial sodium channel by membrane trafficking

The epithelial Na(+) channel (ENaC) is a major regulator of salt and water reabsorption in a number of epithelial tissues. Abnormalities in ENaC function have been directly linked to several human disease states including Liddle's syndrome, psuedohypoaldosteronism, and cystic fibrosis and may be implicated in states as diverse as salt-sensitive hypertension, nephrosis, and pulmonary edema. ENaC activity in epithelial cells is highly regulated both by open probability and number of channels. Open probability is regulated by a number of factors, including proteolytic processing, while ENaC number is regulated by cellular trafficking. This review discusses current understanding of apical membrane delivery, cell surface stability, endocytosis, retrieval, and recycling of ENaC and the molecular partners that have so far been shown to participate in these processes. We review known sites and mechanisms of hormonal regulation of trafficking by aldosterone, vasopressin, and insulin. While many details of the regulation of ENaC trafficking remain to be elucidated, knowledge of these mechanisms may provide further insights into ENaC activity in normal and disease states.

Acetaminophen inhibits prostanoid synthesis by scavenging the PGHS-activator peroxynitrite

The primary pharmacological target of acetaminophen is prostaglandin endoperoxide H2 synthase (PGHS). The enzymatic catalytic mechanism is radical-based, initiated, and maintained by the persistent presence of peroxides, particularly peroxynitrite, which is termed "peroxide tone". Whereas the prevailing concept assumes a direct reduction of the active, oxidized enzyme by acetaminophen, here we show that acetaminophen is a potent scavenger of peroxynitrite (peroxynitrite-mediated phenol nitration, IC50 approximately 72 microM; Sin-1-mediated DHR123 oxidation, IC50 approximately 11 microM) and thus inhibits PGHS by eliminating the peroxide tone. Nanomolar concentrations of peroxynitrite increased the activity of isolated PGHS and prostacyclin formation by aortic endothelial cells. This elevated activity was efficiently inhibited by pharmacologically relevant concentrations of acetaminophen (IC50 approximately 10 microM for 6-keto-PGF1alpha) and other free radical scavengers. However, when the peroxide tone was provided by H2O2 or tert-butyl-OOH, acetaminophen had only negligible inhibitory effects. Our concept could help to explain the efficacy of acetaminophen to inhibit PGHS in cell types with moderate oxidant formation. However, high levels of peroxynitrite or other peroxides such as lipid peroxides formed at inflammatory sites might overwhelm the ability of acetaminophen to decrease PGHS activation. The concept presented herein provides a molecular basis to explain the excellent analgesic and antipyretic properties of acetaminophen together with its minimal anti-inflammatory effects.

Proteasome-dependent degradation of guanosine 5'-triphosphate cyclohydrolase I causes tetrahydrobiopterin deficiency in diabetes mellitus

BACKGROUND

Tetrahydrobiopterin (BH4) deficiency is reported to uncouple the enzymatic activity of endothelial nitric oxide synthase in diabetes mellitus. The mechanism by which diabetes actually leads to BH4 deficiency remains elusive. Here, we demonstrate that diabetes reduced BH4 by increasing 26S proteasome-dependent degradation of guanosine 5'-triphosphate cyclohydrolase I (GTPCH), a rate-limiting enzyme in the synthesis of BH4, in parallel with increased formation of both superoxide and peroxynitrite (ONOO-).

METHODS AND RESULTS

Exposure of human umbilical vein endothelial cells to high glucose concentrations (30 mmol/L D-glucose) but not to high osmotic conditions (25 mmol/L L-glucose plus 5 mmol/L D-glucose) significantly lowered the levels of both GTPCH protein and BH4. In addition, high glucose increased both the 26S proteasome activity and the ubiquitination of GTPCH. Inhibition of the 26S proteasome with either MG132 or PR-11 prevented the high glucose-triggered reduction of GTPCH and BH4. Exposure of human umbilical vein endothelial cells to exogenous ONOO- increased proteasome activity and 3-nitrotyrosine in 26S proteasome. Furthermore, adenoviral overexpression of superoxide dismutase and inhibition of endothelial nitric oxide synthase with N(G)-nitro-L-arginine methyl ester significantly attenuated the high glucose-induced activation of 26S proteasome and the reduction of GTPCH. Finally, administration of MG132 or a superoxide dismutase mimetic, tempol, reversed the diabetes mellitus-induced reduction of GTPCH and BH4 and endothelial dysfunction in streptozotocin-induced diabetes mellitus.

CONCLUSIONS

We conclude that diabetes mellitus triggers BH4 deficiency by increasing proteasome-dependent degradation of GTPCH.

Nitrotyrosine and protein carbonyls are equally distributed in HT22 cells after nitrosative stress

The generation of reactive oxygen and nitrogen species is an inevitable result of cellular metabolism and environmental influence. Such oxidation processes are always combined with the formation of various protein oxidation products. Environmental oxidants might either be activated inside the cell or act by themselves. Therefore, differences in the localization of oxidant formation might change the major compartment of oxidant action. Therefore, we employed NO donors (SNOC, DETA/NO, and Spe/NO) alone or in combination with the redox-cycling bipyridinium compound paraquat, the superoxide- and NO-releasing compound SIN-1, the relatively more lipophilic oxidants tert-butyl and cumene hydroperoxide, and peroxynitrite itself to test the ability of these compounds to generate oxidized and nitrated proteins in various cellular compartments. Combined treatment with oxidants and nitrating compounds led to the formation of protein carbonyls and nitrotyrosine with a severalfold higher concentration in the cytosol, compared to the nucleus. In fluorescence microscopy studies, the resulting protein modifications show a similar distribution of oxidized proteins and nitrotyrosine with highest concentrations in the perinuclear area. Studying the time- and concentration-dependent formation and degradation of protein carbonyls and nitrated proteins large similarities could be measured. Therefore, it can be concluded that formation, localization, and kinetics of protein carbonyl and nitrotyrosine formation parallel each other depending on the stress-inducing agent.

Plasma Level of Mitochondrial Coupling Factor 6 Increases in Patients With Coronary Heart Disease

BACKGROUND

The aim of the present study was to investigate alterations in the plasma level of coupling factor 6 (CF6), a novel endogenous inhibitor of prostacyclin, in patients with coronary heart disease.

METHODS AND RESULTS

In total, 35 patients with coronary heart disease and 20 age-matched healthy subjects were examined. Plasma levels of CF6 and 6-keto-prostaglandin (PG)F(1a) (a stable metabolite of prostacyclin) were measured using radioimmunoassay. The plasma level of CF6 was significantly increased in patients (254.1+/-29.8 pg/ml vs 219.4 +/-36.7 pg/ml in controls, p<0.0001), whereas that of 6-keto-PGF(1a) was significantly decreased (23.4 +/-2.3 pg/ml vs 26.1+/-4.5 pg/ml in controls, p=0.001). Moreover, after percutaneous transluminal coronary angioplasty (PTCA) and stent therapy, the level of CF6 was further increased by 30% to 330.4+/-26.0 pg/ml, and that of 6-keto-PGF (1a) was decreased by 42% to 13.5+/-2.0 pg/ml, compared with baseline (all p<0.01). Univariate analysis showed a significant result that the plasma level of CF6 was inversely correlated with that of 6-keto-PGF(1a) in the patients. The plasma ratio of CF6 to 6-keto-PGF(1a) was 8.4 in the control group and that in patients with coronary heart disease was increased to 24.4 after the therapy from 10.9 before therapy.

CONCLUSIONS

The results suggest that an increased CF6 level may be responsible in part for the decreased prostacyclin level observed in patients with coronary heart disease, in particular after PTCA and stent therapy. As a potential risk factor for coronary heart disease, CF6 might have important clinical significance.

Nitric oxide and peroxynitrite in health and disease

The discovery that mammalian cells have the ability to synthesize the free radical nitric oxide (NO) has stimulated an extraordinary impetus for scientific research in all the fields of biology and medicine. Since its early description as an endothelial-derived relaxing factor, NO has emerged as a fundamental signaling device regulating virtually every critical cellular function, as well as a potent mediator of cellular damage in a wide range of conditions. Recent evidence indicates that most of the cytotoxicity attributed to NO is rather due to peroxynitrite, produced from the diffusion-controlled reaction between NO and another free radical, the superoxide anion. Peroxynitrite interacts with lipids, DNA, and proteins via direct oxidative reactions or via indirect, radical-mediated mechanisms. These reactions trigger cellular responses ranging from subtle modulations of cell signaling to overwhelming oxidative injury, committing cells to necrosis or apoptosis. In vivo, peroxynitrite generation represents a crucial pathogenic mechanism in conditions such as stroke, myocardial infarction, chronic heart failure, diabetes, circulatory shock, chronic inflammatory diseases, cancer, and neurodegenerative disorders. Hence, novel pharmacological strategies aimed at removing peroxynitrite might represent powerful therapeutic tools in the future. Evidence supporting these novel roles of NO and peroxynitrite is presented in detail in this review.

Uncoupling of Endothelial Nitric Oxidase Synthase by Hypochlorous Acid

OBJECTIVE

The aim of the present study is to determine whether hypochlorous acid (HOCl), the major oxidant of leukocyte-derived myeloperoxidase (MPO), oxidizes the zinc-thiolate center of endothelial nitric oxide synthase (eNOS) and uncouples the enzyme.

METHODS AND RESULTS

Exposure of purified recombinant eNOS to HOCl (> or = 100 micromol/L) released zinc and disrupted the enzyme-active eNOS dimers. In parallel with increased detections of both O2*- and ONOO-, clinically relevant concentrations of HOCl disrupted eNOS dimers in cultured human umbilical vein endothelial cells (HUVEC) at concentration 10- to 100-fold lower than those required for recombinant eNOS. In HUVEC, HOCl increased the translocation of both p67(phox) and p47(phox) of NAD(P)H oxidase and the phosphorylation of atypical protein kinase C-zeta. Further, genetic or pharmacological inhibition of either NAD(P)H oxidase-derived O2*- or PKC-zeta or NOS abolished the effects of HOCl on eNOS dimers. Consistently, HOCl increased both O2*- and ONOO- and eNOS dimer oxidation in isolated mouse aortas from C57BL/6 but less in those of gp91(phox) knock-out mice. Finally, in human carotid atherosclerotic arteries, eNOS predominantly existed as monomers in parallel with increased staining of both MPO and 3-nitrotyrosine.

CONCLUSIONS

We conclude that HOCl uncouples eNOS by ONOO- generated from PKC-zeta-dependent NAD(P)H oxidase.

Microsphere embolism-induced endothelial nitric oxide synthase expression mediates disruption of the blood-brain barrier in rat brain

Microsphere embolism (ME)-induced up-regulation of endothelial nitric oxide synthase (eNOS) in endothelial cells of brain microvessels was observed 2-48 h after ischemia. eNOS induction preceded disruption of the blood-brain barrier (BBB) observed 6-72 h after ischemia. In vascular endothelial cells, ME-induced eNOS expression was closely associated with protein tyrosine nitration, which is a marker of generation of peroxynitrite. Leakage of rabbit IgG from microvessels was also evident around protein tyrosine nitration-immunoreactive microvessels. To determine whether eNOS expression and protein tyrosine nitration in vascular endothelial cells mediates BBB disruption in the ME brain, we tested the effect of a novel calmodulin-dependent NOS inhibitor, 3-[2-[4-(3-chloro-2-methylphenyl)-1-piperazinyl]ethyl]-5,6-dimethoxy-1-(4-imidazolylmethyl)-1H-indazole dihydrochloride 3.5 hydrate (DY-9760e), which inhibits eNOS activity and, in turn, protein tyrosine nitration. Concomitant with inhibition of protein tyrosine nitration in vascular endothelial cells, DY-9760e significantly inhibited BBB disruption as assessed by Evans blue (EB) excretion. DY-9760e also inhibited cleavage of poly (ADP-ribose) polymerase as a marker of the apoptotic pathway in vascular endothelial cells. Taken together with previous evidence in which DY-9760e inhibited brain edema, ME-induced eNOS expression in vascular endothelial cells likely mediates BBB disruption and, in turn, brain edema.

Superoxide, peroxynitrite and oxidative/nitrative stress in inflammation

A considerable body of evidence suggests that formation of potent reactive oxygen species and resulting oxidative/nitrative stress play a major role in acute and chronic inflammation and pain. Much of the knowledge in this field has been gathered by the use of pharmacological and genetic approaches. In this mini review, we will evaluate recent advances made towards understanding the roles of reactive oxygen species in inflammation, focusing in particular on superoxide and peroxynitrite. Given the limited space to cover this broad topic, here we will refer the reader to comprehensive review articles whenever possible.

The regulation and pharmacology of endothelial nitric oxide synthase

Nitric oxide (NO) is a small, diffusible, lipophilic free radical gas that mediates significant and diverse signaling functions in nearly every organ system in the body. The endothelial isoform of nitric oxide synthase (eNOS) is a key source of NO found in the cardiovascular system. This review summarizes the pharmacology of NO and the cellular regulation of endothelial NOS (eNOS). The molecular intricacies of the chemistry of NO and the enzymology of NOSs are discussed, followed by a review of the biological activities of NO. This information is then used to develop a more global picture of the pharmacological control of NO synthesis by NOSs in both physiologic conditions and pathophysiologic states.