Interactions between thromboxane A₂, thromboxane/prostaglandin (TP) receptors, and endothelium-derived hyperpolarization

Eicosanoid signaling in neuroinflammation associated with Alzheimer's disease

Alzheimer's disease (AD) is a prevalent neurodegenerative condition affecting a substantial portion of the global population. It is marked by a complex interplay of factors, including the accumulation of amyloid plaques and tau tangles within the brain, leading to neuroinflammation and neuronal damage. Recent studies have underscored the role of free lipids and their derivatives in the initiation and progression of AD. Eicosanoids, metabolites of polyunsaturated fatty acids like arachidonic acid (AA), emerge as key players in this scenario. Remarkably, eicosanoids can either promote or inhibit the development of AD, and this multifaceted role is determined by how eicosanoid signaling influences the immune responses within the brain. However, the precise molecular mechanisms dictating the dual role of eicosanoids in AD remain elusive. In this comprehensive review, we explore the intricate involvement of eicosanoids in neuronal function and dysfunction. Furthermore, we assess the therapeutic potential of targeting eicosanoid signaling pathways as a viable strategy for mitigating or halting the progression of AD.

Sex-specific differences in the mechanisms for enhanced thromboxane A2-mediated vasoconstriction in adult offspring exposed to prenatal hypoxia

BACKGROUND

Prenatal hypoxia, a common pregnancy complication, leads to impaired cardiovascular outcomes in the adult offspring. It results in impaired vasodilation in coronary and mesenteric arteries of the adult offspring, due to reduced nitric oxide (NO). Thromboxane A2 (TxA2) is a potent vasoconstrictor increased in cardiovascular diseases, but its role in the impact of prenatal hypoxia is unknown. To prevent the risk of cardiovascular disease by prenatal hypoxia, we have tested a maternal treatment using a nanoparticle-encapsulated mitochondrial antioxidant (nMitoQ). We hypothesized that prenatal hypoxia enhances vascular TxA2 responses in the adult offspring, due to decreased NO modulation, and that this might be prevented by maternal nMitoQ treatment.

METHODS

Pregnant Sprague-Dawley rats received a single intravenous injection (100 µL) of vehicle (saline) or nMitoQ (125 µmol/L) on gestational day (GD)15 and were exposed to normoxia (21% O2) or hypoxia (11% O2) from GD15 to GD21 (term = 22 days). Coronary and mesenteric arteries were isolated from the 4-month-old female and male offspring, and vasoconstriction responses to U46619 (TxA2 analog) were evaluated using wire myography. In mesenteric arteries, L-NAME (pan-NO synthase (NOS) inhibitor) was used to assess NO modulation. Mesenteric artery endothelial (e)NOS, and TxA2 receptor expression, superoxide, and 3-nitrotyrosine levels were assessed by immunofluorescence.

RESULTS

Prenatal hypoxia resulted in increased U46619 responsiveness in coronary and mesenteric arteries of the female offspring, and to a lesser extent in the male offspring, which was prevented by nMitoQ. In females, there was a reduced impact of L-NAME in mesenteric arteries of the prenatal hypoxia saline-treated females, and reduced 3-nitrotyrosine levels. In males, L-NAME increased U46619 responses in mesenteric artery to a similar extent, but TxA2 receptor expression was increased by prenatal hypoxia. There were no changes in eNOS or superoxide levels.

CONCLUSIONS

Prenatal hypoxia increased TxA2 vasoconstrictor capacity in the adult offspring in a sex-specific manner, via reduced NO modulation in females and increased TP expression in males. Maternal placental antioxidant treatment prevented the impact of prenatal hypoxia. These findings increase our understanding of how complicated pregnancies can lead to a sex difference in the programming of cardiovascular disease in the adult offspring.

Capillary leak and endothelial permeability in critically ill patients: a current overview

Capillary leak syndrome (CLS) represents a phenotype of increased fluid extravasation, resulting in intravascular hypovolemia, extravascular edema formation and ultimately hypoperfusion. While endothelial permeability is an evolutionary preserved physiological process needed to sustain life, excessive fluid leak-often caused by systemic inflammation-can have detrimental effects on patients' outcomes. This article delves into the current understanding of CLS pathophysiology, diagnosis and potential treatments. Systemic inflammation leading to a compromise of endothelial cell interactions through various signaling cues (e.g., the angiopoietin-Tie2 pathway), and shedding of the glycocalyx collectively contribute to the manifestation of CLS. Capillary permeability subsequently leads to the seepage of protein-rich fluid into the interstitial space. Recent insights into the importance of the sub-glycocalyx space and preserving lymphatic flow are highlighted for an in-depth understanding. While no established diagnostic criteria exist and CLS is frequently diagnosed by clinical characteristics only, we highlight more objective serological and (non)-invasive measurements that hint towards a CLS phenotype. While currently available treatment options are limited, we further review understanding of fluid resuscitation and experimental approaches to target endothelial permeability. Despite the improved understanding of CLS pathophysiology, efforts are needed to develop uniform diagnostic criteria, associate clinical consequences to these criteria, and delineate treatment options.

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.

Cerebral Malaria and Neuronal Implications of Plasmodium Falciparum Infection: From Mechanisms to Advanced Models

Reorganization of host red blood cells by the malaria parasite Plasmodium falciparum enables their sequestration via attachment to the microvasculature. This artificially increases the dwelling time of the infected red blood cells within inner organs such as the brain, which can lead to cerebral malaria. Cerebral malaria is the deadliest complication patients infected with P. falciparum can experience and still remains a major public health concern despite effective antimalarial therapies. Here, the current understanding of the effect of P. falciparum cytoadherence and their secreted proteins on structural features of the human blood-brain barrier and their involvement in the pathogenesis of cerebral malaria are highlighted. Advanced 2D and 3D in vitro models are further assessed to study this devastating interaction between parasite and host. A better understanding of the molecular mechanisms leading to neuronal and cognitive deficits in cerebral malaria will be pivotal in devising new strategies to treat and prevent blood-brain barrier dysfunction and subsequent neurological damage in patients with cerebral malaria.

UV-B filter octylmethoxycinnamate-induced vascular endothelial disruption on rat aorta: In silico and in vitro approach

Throughout human life, an extensive and varied range of emerging environmental contaminants, called endocrine disruptors (EDCs), cause adverse health effects, including in the cardiovascular (CV) system. Cardiovascular diseases (CVD) are worryingly one of the leading causes of all mortality and mobility worldwide. The UV-B filter octylmethoxycinnamate (also designated octinoxate, or ethylhexyl methoxycinnamate (CAS number: 5466-77-3)) is an EDC widely present in all personal care products. However, to date, there are no studies evaluating the OMC-induced effects on vasculature using animal models to improve human cardiovascular health. This work analysed the effects of OMC on rat aorta vasculature and explored the modes of action implicated in these effects. Our results indicated that OMC relaxes the rat aorta by endothelium-dependent mechanisms through the signaling pathways of cyclic nucleotides and by endothelium-independent mechanisms involving inhibition of L-Type voltage-operated Ca²⁺ channels (L-Type VOCC). Overall, OMC toxicity on rat aorta may produce hypotension via vasodilation due to excessive NO release and blockade of L-Type VOCC. Moreover, the OMC-induced endothelial dysfunction may also occur by promoting the endothelial release of endothelin-1. Therefore, our findings demonstrate that exposure to OMC alters the reactivity of the rat aorta and highlight that long-term OMC exposure may increase the risk of human CV diseases.

The Role of Endothelial Cells in the Onset, Development and Modulation of Vein Graft Disease

Endothelial cells comprise the intimal layer of the vasculature, playing a crucial role in facilitating and regulating aspects such nutrient transport, vascular homeostasis, and inflammatory response. Given the importance of these cells in maintaining a healthy haemodynamic environment, dysfunction of the endothelium is central to a host of vascular diseases and is a key predictor of cardiovascular risk. Of note, endothelial dysfunction is believed to be a key driver for vein graft disease-a pathology in which vein grafts utilised in coronary artery bypass graft surgery develop intimal hyperplasia and accelerated atherosclerosis, resulting in poor long-term patency rates. Activation and denudation of the endothelium following surgical trauma and implantation of the graft encourage a host of immune, inflammatory, and cellular differentiation responses that risk driving the graft to failure. This review aims to provide an overview of the current working knowledge regarding the role of endothelial cells in the onset, development, and modulation of vein graft disease, as well as addressing current surgical and medical management approaches which aim to beneficially modulate endothelial function and improve patient outcomes.

Cyclosporin A up-regulated thromboxane A2 receptor through activation of MAPK and NF-κB pathways in rat mesenteric artery

Cyclosporin A (CsA) is an immunosuppressant used in transplantation patients and inflammatory diseases. CsA-induced local vasoconstriction can lead to serious side effects including nephrotoxicity and hypertension. However, the underlying mechanisms are not fully understood. Mesenteric artery rings of rats were cultured with CsA and specific inhibitors for mitogen-activating protein kinases (MAPK) and nuclear factor-κB (NF-κB) signaling pathways. A sensitive myograph recorded thromboxane (TP) receptor-mediated vasoconstriction. Protein levels of key signaling molecules were assessed by Western blotting. The results show that CsA up-regulated the TP receptor expression with the enhanced vasoconstriction in a dose- and time-dependent manner. Furthermore, the blockage of MAPKs or NF-κB activation markedly attenuated CsA-enhanced vasoconstriction and the TP receptor protein expression. Rats subcutaneously injected with CsA for three weeks showed increased blood pressure in vivo and increased contractile responses to a TP agonist ex vivo. CsA also enhanced TP receptor, as well as p-ERK1/2, p-p38, p- IκBα, p-NF-κB P65 protein levels and decreased IκBα protein expression, demonstrating that CsA induced TP receptor enhanced-vasoconstriction via activation of MAPK and NF-κB pathways. In conclusion, CsA up-regulated the expression of TP receptors via activation of MAPK and NF-κB pathways. The results may provide novel options for prevention of CsA-associated hypertension.

Effect of drug interventions on cerebral hemodynamics in ischemic stroke patients

The ischemic penumbra is sensitive to alterations in cerebral perfusion. A myriad of drugs are used in acute ischemic stroke (AIS) management, yet their impact on cerebral hemodynamics is poorly understood. As part of the Cerebral Autoregulation Network led INFOMATAS project (Identifying New Targets for Management and Therapy in Acute Stroke), this paper reviews some of the most common drugs a patient with AIS will come across and their potential influence on cerebral hemodynamics with a particular focus being on cerebral autoregulation (CA). We first discuss how compounds that promote clot lysis and prevent clot formation could potentially impact cerebral hemodynamics, before focusing on how the different classes of antihypertensive drugs can influence cerebral hemodynamics. We discuss the different properties of each drug and their potential impact on cerebral perfusion and CA. With emerging interest in CA status of AIS patients, either during or soon after treatment when timely reperfusion and salvageable tissue is at its most critical, the properties of these pharmacological agents may be relevant for modelling cerebral perfusion accuracy and for setting individualised treatment strategies.

Thromboxane A2 synthase inhibition ameliorates endothelial dysfunction, memory deficits, oxidative stress and neuroinflammation in rat model of streptozotocin diabetes induced dementia

RATIONALE

Vascular dementia (VaD) is the second leading cause of dementia worldwide. It is very important to find the possible pharmacological agents which may be useful in management and therapy of VaD.

OBJECTIVES

The present study investigates the effect of ozagrel, a selective thromboxane A2 (TXA2) synthase inhibitor, in a rat model of VaD.

METHODS

Single intraperitoneal injection of streptozotocin [STZ, (50 mg/kg)] was administered to Wistar rats to induced diabetes-associated vascular endothelial dysfunction and memory impairment. Morris water maze (MWM) test was employed to assess learning and memory. Endothelial dysfunction was assessed in the isolated aorta by observing endothelial-dependent vasorelaxation and levels of serum nitrite. Various biochemical and histopathological estimations were also performed.

RESULTS

STZ treatment produced endothelial dysfunction, impairment of learning and memory, reduction in body weight and serum nitrite/nitrate, and increase in serum glucose, brain oxidative stress (increased brain thiobarbituric acid reactive species and decreased reduced glutathione levels), brain acetylcholinesterase activity and brain myeloperoxidase activity. Further a significant rise in brain tumor necrosis factor-α & interleukin-6 levels and brain neutrophil infiltration were also observed. Treatment of ozagrel (10 & 20 mg/kg, p. o.)/donepezil (0. 5 mg/kg, i.p., serving as standard) ameliorated STZ induced endothelial dysfunction; memory deficits; biochemical and histopathological changes.

CONCLUSIONS

It may be concluded that ozagrel markedly improved endothelial dysfunction; learning and memory; biochemical and histopathological alteration associated with STZ induced dementia and that TXA2 can be considered as an important therapeutic target for the management of VaD.

Increased cerebral endothelium-dependent vasodilation in rats in the postcardiac arrest period

Cardiovascular lability is common after cardiac arrest. We investigated whether altered endothelial function is present in cerebral and mesenteric arteries 2 and 4 h after resuscitation. Male Sprague-Dawley rats were anesthetized, intubated, ventilated, and intravascularly catheterized whereupon rats were randomized into four groups. Following 7 min of asphyxial cardiac arrest and subsequent resuscitation, cardiac arrest and sham rats were observed for either 2 or 4 h. Neuron-specific enolase levels were measured in blood samples. Middle cerebral artery segments and small mesenteric arteries were isolated and examined in microvascular myographs. qPCR and immunofluorescence analysis were performed on cerebral arteries. In cerebral arteries, bradykinin-induced vasodilation was inhibited in the presence of either calcium-activated K⁺ channel blockers (UCL1684 and senicapoc) or the nitric oxide (NO) synthase inhibitor, N^ω-nitro-L-arginine methyl ester hydrochloride (l-NAME), whereas the combination abolished bradykinin-induced vasodilation across groups. Neuron-specific enolase levels were significantly increased in cardiac arrest rats. Cerebral vasodilation was comparable between the 2-h groups, but markedly enhanced in response to bradykinin, NS309 (an opener of small and intermediate calcium-activated K⁺ channels), and sodium nitroprusside 4 h after cardiac arrest. Endothelial NO synthase and guanylyl cyclase subunit α-1 mRNA expression was unaltered after 2 h, but significantly decreased 4 h after resuscitation. In mesenteric arteries, the endothelium-dependent vasodilation was comparable between corresponding groups at both 2 and 4 h. Our findings show enhanced cerebral endothelium-dependent vasodilation 4 h after cardiac arrest mediated by potentiated endothelial-derived hyperpolarization and NO pathways. Altered cerebral endothelium-dependent vasodilation may contribute to disturbed cerebral perfusion after cardiac arrest.NEW & NOTEWORTHY This is the first study, to our knowledge, to demonstrate enhanced endothelium-dependent vasodilation in middle cerebral arteries in a cardiac arrest rat model. The increased endothelium-dependent vasodilation was a result of potentiated endothelium-derived hyperpolarization and endothelial nitric oxide pathways. Immunofluorescence microscopy confirmed the presence of relevant receptors and eNOS in cerebral arteries, whereas qPCR showed altered expression of genes related to guanylyl cyclase and eNOS. Altered endothelium-dependent vasoregulation may contribute to disturbed cerebral blood flow in the postcardiac arrest period.

8-iso-prostaglandin E2 induces nasal obstruction via thromboxane receptor in murine model of allergic rhinitis

Thromboxane receptor (TP) mediates nasal obstruction, a typical symptom of allergic rhinitis. Since it has been reported that several types of eicosanoids, such as non-enzymatic oxidation product of arachidonic acid isoprostane, act as a TP ligand, there is a possibility that some other eicosanoids contribute to the TP-mediated nasal obstruction. The aim of this study is to investigate the mechanisms of TP-mediated nasal obstruction. Intranasal challenges of ovalbumin (OVA) induced nasal obstruction in mice. Pharmacological blockade of TP receptor but not thromboxane A₂ synthase inhibited OVA-induced nasal obstruction. Simultaneous analysis of eicosanoids in nasal lavage fluid and the responses in trans-endothelial resistance suggested that 8-iso-prostaglandin E₂ (PGE₂ ) can be a candidate for TP ligand. Intranasal challenge of 8-iso-PGE₂ induced vascular hyperpermeability and nasal obstruction in TP receptor-dependent manner. Wholemount immunostaining of nasal septum mucosa revealed that 8-iso-PGE₂ increased plasma leakage accompanied by distention of venous sinusoids. This study shows that 8-iso-PGE₂ is a contributor in TP-mediated nasal obstruction in mice.

Implications of Endothelial Cell-Mediated Dysfunctions in Vasomotor Tone Regulation

Cardiovascular diseases (CVD) constitute the major cause of death worldwide and show a higher prevalence in the adult population. The human umbilical cord consistsof two arteries and one vein, both composed of three tunics. The tunica intima, lined with endothelial cells, regulates vascular tone through the production/release of vasoregulatory substances. These substances can be vasoactive factors released by endothelial cells (ECs) that cause vasodilation (NO, PGI2, EDHF, and Bradykinin) or vasoconstriction (ET1, TXA2, and Ang II) depending on the cell type (ECs or SMC) that reacts to the stimulus. Vascular studies using ECs are important for the analysis of cardiovascular diseases since endothelial dysfunction is an important CVD risk factor. In this paper, we will address the morphological characteristics of the human umbilical cord and its component vessels. the constitution of the vascular endothelium, and the evolution of human umbilical cord-derived endothelial cells when isolated. Moreover, the role played by the endothelium in the vasomotor tone regulation, and how it may be associated with the existence of CVD, were discussed.

Docosahexaenoic acid inhibits U46619- and prostaglandin F2α-induced pig coronary and basilar artery contractions by inhibiting prostanoid TP receptors

Docosahexaenoic acid (DHA, an n-3 polyunsaturated fatty acid) inhibits U46619 (a TP receptor agonist)- and prostaglandin F_2α-induced contractions in rat aorta and mesenteric arteries. However, whether these effects could be replicated in vasospasm-prone vessels, such as coronary and cerebral arteries, remains unknown. Here, we evaluated the changes in pig coronary and basilar artery tensions and intracellular Ca²⁺ concentrations in human prostanoid TP or FP receptor-expressing cells. We aimed to clarify whether DHA inhibits U46619- and prostaglandin F_2α-induced contractions in spasm-prone blood vessels and determine if the TP receptor is the primary target for DHA. In both pig coronary and basilar arteries, DHA suppressed U46619- and prostaglandin F_2α-induced sustained contractions in a concentration-dependent manner, but did not affect contractions induced by 80 mM KCl. SQ 29,548 (a TP receptor antagonist) suppressed U46619- and prostaglandin F_2α-induced contractions by approximately 100% and 60%, respectively. DHA suppressed both U46619- and prostaglandin F_2α-induced increases in intracellular Ca²⁺ concentrations in human TP receptor-expressing cells. However, DHA did not affect prostaglandin F_2α-induced increases in intracellular Ca²⁺ concentrations in human FP receptor-expressing cells. These findings suggest that DHA potently inhibits TP receptor-mediated contractions in pig coronary and basilar arteries, and the primary mechanism underlying its inhibitory effects on arterial contractions involves inhibiting TP receptors.

Vitamin D Deficiency Reduces Vascular Reactivity of Coronary Arterioles in Male Rats

BACKGROUND

Vitamin D deficiency (VDD) may be considered an independent cardiovascular (CV) risk factor, and it is well known that CV risk is higher in males. Our goal was to investigate the pharmacological reactivity and receptor expression of intramural coronary artery segments of male rats in cases of different vitamin D supply.

METHODS

Four-week-old male Wistar rats were divided into a control group (n = 11) with optimal vitamin D supply (300 IU/kgbw/day) and a VDD group (n = 11, <0.5 IU/kgbw/day). After 8 weeks of treatment, intramural coronary artery segments were microprepared, their pharmacological reactivity was examined by in vitro microangiometry, and their receptor expression was investigated by immunohistochemistry.

RESULTS

Thromboxane A₂ (TXA₂)-agonist induced reduced vasoconstriction, testosterone (T) and 17-β-estradiol (E2) relaxations were significantly decreased, a significant decrease in thromboxane receptor (TP) expression was shown, and the reduction in estrogen receptor-α (ERα) expression was on the border of significance in the VDD group.

CONCLUSIONS

VD-deficient male coronary arteries showed deteriorated pharmacological reactivity to TXA₂ and sexual steroids (E2, T). Insufficient vasoconstrictor capacity was accompanied by decreased TP receptor expression, and vasodilator impairments were mainly functional. The decrease in vasoconstrictor and vasodilator responses results in narrowed adaptational range of coronaries, causing inadequate coronary perfusion that might contribute to the increased CV risk in VDD.

Ozagrel a thromboxane A2 synthase inhibitor extenuates endothelial dysfunction, oxidative stress and neuroinflammation in rat model of bilateral common carotid artery occlusion induced vascular dementia

The present study investigates the potential of ozagrel, a thromboxane A2 (TXA2) synthase inhibitor, in bilateral common carotid artery occlusion (BCCAo) induced vascular dementia (VaD). Wistar rats were subjected to BCCAo procedure under anesthesia to induce VaD. Morris water maze (MWM) test was employed on 7th day post-surgery to determine learning and memory. Endothelial dysfunction was assessed in isolated aorta by observing endothelial dependent vasorelaxation and levels of serum nitrite. A battery of biochemical and histopathological estimations was performed. Expression analysis of inflammatory cytokines TNF-α and IL-6 was carried out by RT-PCR. BCCAo produced significant impairment in endothelium dependent vasorelaxation and decrease in serum nitrite levels indicating endothelial dysfunction along with poor performance on MWM represents impairment of learning and memory. There was a significant rise in brain oxidative stress level (indicated by increase in brain thiobarbituric acid reactive species and decrease in reduced glutathione levels); increase in brain acetylcholinesterase activity; brain myeloperoxidase activity; brain TNF-α & IL-6 levels, brain TNF-α & IL-6 mRNA expression and brain neutrophil infiltration (as marker of inflammation) were also observed. Treatment of ozagrel (10 & 20 mg/kg, p. o.)/donepezil (0. 5 mg/kg, i.p., serving as standard) ameliorated BCCAo induced endothelial dysfunction; memory deficits; biochemical and histopathological changes in a significant manner. It may be concluded that ozagrel markedly improved endothelial dysfunction; learning and memory; biochemical and histopathological alteration associated with BCCAo induced VaD and that TXA2 can be considered as an important therapeutic target for the treatment of VaD.

Downregulation of Soluble Guanylate Cyclase and Protein Kinase G With Upregulated ROCK2 in the Pulmonary Artery Leads to Thromboxane A2 Sensitization in Monocrotaline-Induced Pulmonary Hypertensive Rats

Thromboxane A2 (TXA₂) promotes various physiological responses including pulmonary artery (PA) contraction, and pathophysiological implications have been suggested in cardiovascular diseases including pulmonary hypertension. Here, we investigated the role of TXA₂ receptor (TP)-mediated signaling in the pathophysiology of pulmonary arterial hypertension (PAH). The sensitivity of PA to the contractile agonist could be set by relaxing signals such as the nitric oxide (NO), soluble guanylate cyclase (sGC), and cGMP-dependent kinase (PKG) pathways. Changes in the TP agonist (U46619)-induced PA contraction and its modulation by NO/cGMP signaling were analyzed in a monocrotaline-induced PAH rat model (PAH-MCT). In the myograph study, PA from PAH-MCT showed higher responsiveness to U46619, that is decreased EC₅₀. Immunoblot analysis revealed a lower expression of eNOS, sGC, and PKG, while there was a higher expression of RhoA-dependent kinase 2 (ROCK2) in the PA from PAH-MCT than in the control. In PAH-MCT, the higher sensitivity to U46619 was reversed by 8-Br-cGMP, a membrane-permeable cGMP analog, but not by the NO donor, sodium nitroprusside (SNP 30 μM). In contrast, in the control PA, inhibition of sGC by its inhibitor (1H- [1,2,4] oxadiazolo [4,3-a] quinoxalin-1-one (ODQ), 10 μM) lowered the threshold of U46619-induced contraction. In the presence of ODQ, SNP treatment had no effect whereas the addition of 8-Br-cGMP lowered the sensitivity to U46619. The inhibition of ROCK by Y-27632 attenuated the sensitivity to U46619 in both control and PAH-MCT. The study suggests that the attenuation of NO/cGMP signaling and the upregulation of ROCK2 increase the sensitivity to TXA₂ in the PAH animal, which might have pathophysiological implications in patients with PAH.

Ameliorative effect of ozagrel, a thromboxane A2 synthase inhibitor, in hyperhomocysteinemia-induced experimental vascular cognitive impairment and dementia

The present study investigates the effect of ozagrel, a selective thromboxane A2 (TXA2) inhibitor, in rat model of hyperhomocysteinemia (HHcy)-induced vascular cognitive impairment and dementia (VCID). Wistar rats were administered L-methionine (1.7 g/kg/day; p.o. × 8 weeks) to induce VCID. Morris water maze (MWM) test was employed to assess learning and memory. Endothelial dysfunction was assessed in the isolated aorta by observing endothelial-dependent vasorelaxation and levels of serum nitrite. Various biochemical and histopathological estimations were also performed. L-methionine produced significant impairment in endothelium-dependent vasorelaxation and decreases serum nitrite levels indicating endothelial dysfunction. Further, these animals performed poorly on MWM, depicting impairment of learning and memory. Further, a significant rise in brain oxidative stress level (indicated by increase in brain thiobarbituric acid-reactive species and decrease in reduced glutathione levels), brain acetylcholinesterase activity, brain myeloperoxidase activity, brain TNF-α and IL-6 levels, and brain leukocyte (neutrophil) infiltration was also observed. Treatment of ozagrel (10 and 20 mg/kg, p. o.)/donepezil (0.5 mg/kg, i.p., serving as standard) ameliorated L-methionine-induced endothelial dysfunction, memory deficits, and biochemical and histopathological changes. It may be concluded that ozagrel markedly improved endothelial dysfunction, learning and memory, and biochemical and histopathological alteration associated with L-methionine-induced VCID and that TXA2 can be considered as an important therapeutic target for the management of VCID.

Endothelium as a Therapeutic Target in Diabetes Mellitus: From Basic Mechanisms to Clinical Practice

Endothelium plays an essential role in human homeostasis by regulating arterial blood pressure, distributing nutrients and hormones as well as providing a smooth surface that modulates coagulation, fibrinolysis and inflammation. Endothelial dysfunction is present in Diabetes Mellitus (DM) and contributes to the development and progression of macrovascular disease, while it is also associated with most of the microvascular complications such as diabetic retinopathy, nephropathy and neuropathy. Hyperglycemia, insulin resistance, hyperinsulinemia and dyslipidemia are the main factors involved in the pathogenesis of endothelial dysfunction. Regarding antidiabetic medication, metformin, gliclazide, pioglitazone, exenatide and dapagliflozin exert a beneficial effect on Endothelial Function (EF); glimepiride and glibenclamide, dipeptidyl peptidase-4 inhibitors and liraglutide have a neutral effect, while studies examining the effect of insulin analogues, empagliflozin and canagliflozin on EF are limited. In terms of lipid-lowering medication, statins improve EF in subjects with DM, while data from short-term trials suggest that fenofibrate improves EF; ezetimibe also improves EF but further studies are required in people with DM. The effect of acetylsalicylic acid on EF is dose-dependent and lower doses improve EF while higher ones do not. Clopidogrel improves EF, but more studies in subjects with DM are required. Furthermore, angiotensin- converting-enzyme inhibitors /angiotensin II receptor blockers improve EF. Phosphodiesterase type 5 inhibitors improve EF locally in the corpus cavernosum. Finally, cilostazol exerts favorable effect on EF, nevertheless, more data in people with DM are required.

Cyp2j5-Gene Deletion Affects on Acetylcholine and Adenosine-Induced Relaxation in Mice: Role of Angiotensin-II and CYP-Epoxygenase Inhibitor

Previously, we showed vascular endothelial overexpression of human-CYP2J2 enhances coronary reactive hyperemia in Tie2-CYP2J2 Tr mice, and eNOS^−/− mice had overexpression of CYP2J-epoxygenase with adenosine A_2A receptor-induced enhance relaxation, but we did not see the response in CYP2J-epoxygenase knockout mice. Therefore, we hypothesized that Cyp2j5-gene deletion affects acetylcholine- and 5'-N-ethylcarboxamidoadenosine (NECA) (adenosine)-induced relaxation and their response is partially inhibited by angiotensin-II (Ang-II) in mice. Acetylcholine (Ach)-induced response was tested with N-(methylsulfonyl)-2-(2-propynyloxy)-benzenehexanamide (MS-PPOH, CYP-epoxygenase inhibitor; 10⁻⁵M) and Ang-II (10⁻⁶M). In Cyp2j5^−/− mice, ACh-induced relaxation was different from C57Bl/6 mice, at 10⁻⁵ M (76.1 ± 3.3 vs. 58.3 ± 5.2, P < 0.05). However, ACh-induced relaxation was not blocked by MS-PPOH in Cyp2j5^−/−: 58.5 ± 5.0%, P > 0.05, but blocked in C57Bl/6: 52.3 ± 7.5%, P < 0.05, and Ang-II reduces ACh-induced relaxation in both Cyp2j5^−/− and C57Bl/6 mice (38.8 ± 3.9% and 45.9 ± 7.8, P <0.05). In addition, NECA-induced response was tested with Ang-II. In Cyp2j5^−/− mice, NECA-induced response was not different from C57Bl/6 mice at 10⁻⁵M (23.1 ± 2.1 vs. 21.1 ± 3.8, P > 0.05). However, NECA-induced response was reduced by Ang-II in both Cyp2j5^−/− and C57Bl/6 mice (−10.8 ± 2.3% and 3.2 ± 2.7, P < 0.05). Data suggest that ACh-induced relaxation in Cyp2j5^−/− mice depends on nitric oxide (NO) but not CYP-epoxygenases, and the NECA-induced different response in male vs. female Cyp2j5^−/− mice when Ang-II treated.

Molecular mechanisms underlying the actions of arachidonic acid-derived prostaglandins on peripheral nociception

Arachidonic acid-derived prostaglandins not only contribute to the development of inflammation as intercellular pro-inflammatory mediators, but also promote the excitability of the peripheral somatosensory system, contributing to pain exacerbation. Peripheral tissues undergo many forms of diseases that are frequently accompanied by inflammation. The somatosensory nerves innervating the inflamed areas experience heightened excitability and generate and transmit pain signals. Extensive studies have been carried out to elucidate how prostaglandins play their roles for such signaling at the cellular and molecular levels. Here, we briefly summarize the roles of arachidonic acid-derived prostaglandins, focusing on four prostaglandins and one thromboxane, particularly in terms of their actions on afferent nociceptors. We discuss the biosynthesis of the prostaglandins, their specific action sites, the pathological alteration of the expression levels of related proteins, the neuronal outcomes of receptor stimulation, their correlation with behavioral nociception, and the pharmacological efficacy of their regulators. This overview will help to a better understanding of the pathological roles that prostaglandins play in the somatosensory system and to a finding of critical molecular contributors to normalizing pain.

CYP2J2-produced epoxyeicosatrienoic acids attenuate ischemia/reperfusion-induced acute kidney injury by activating the SIRT1-FoxO3a pathway

Cytochrome P450 (CYP) epoxygenases can metabolize arachidonic acids to epoxyeicosatrienoic acids (EETs), which play a protective role in the renal system, but their involvement in ischemia/reperfusion (I/R)-induced acute kidney injury remains unknown. Here, using a rat model, we demonstrated that forced CYP2J2 expression attenuated I/R-induced renal dysfunction and protected histological integrity. We showed that CYP2J2 significantly decreased I/R-induced upregulation of blood urea nitrogen and serum creatinine and enhanced autophagy during I/R treatment. In addition, we determined the protective effect of CYP2J2 against I/R-caused apoptosis. We demonstrated that CYP2J2 overexpression attenuated the downregulation of SIRT1 and FoxO3a by I/R-induced injury. Moreover, exogenous 11,12-EET addition obviously promoted I/R-induced autophagic flux and suppressed I/R-induced apoptosis through SIRT1-FoxO3a signaling activation. Our data indicate that CYP2J2-produced EETs improve I/R-caused kidney injury by activating the SIRT1-FoxO3a signaling pathway, which protects from renal I/R injury.

Sildenafil reduces aortic endothelial dysfunction and structural damage in spontaneously hypertensive rats: Role of NO, NADPH and COX-1 pathways

Arterial hypertension is a condition associated with endothelial dysfunction, accompanied by an imbalance in the production of reactive oxygen species (ROS) and NO. The aim of this study was to investigate and elucidate the possible mechanisms of sildenafil, a selective phosphodiesterase-5 inhibitor, actions on endothelial function in aortas from spontaneously hypertensive rats (SHR). SHR treated with sildenafil (40 mg/kg/day, p.o., 3 weeks) were compared to untreated SHR and Wistar-Kyoto (WKY) rats. Systolic blood pressure (SBP) was measured by tail-cuff plethysmography and vascular reactivity was determined in isolated rat aortic rings. Circulating endothelial progenitor cells and systemic ROS were measured by flow cytometry. Plasmatic total antioxidant capacity, NO production and aorta lipid peroxidation were determined by spectrophotometry. Scanning electron microscopy was used for structural analysis of the endothelial surface. Sildenafil reduced high SBP and partially restored the vasodilator response to acetylcholine and sodium nitroprusside in SHR aortic rings. Using selective inhibitors, our experiments revealed an augmented participation of NO, with a simultaneous decrease of oxidative stress and of cyclooxygenase-1 (COX-1)-derived prostanoids contribution in the endothelium-dependent vasodilation in sildenafil-treated SHR compared to non-treated SHR. Also, the relaxant responses to sildenafil and 8-Br-cGMP were normalized in sildenafil-treated SHR and sildenafil restored the pro-oxidant/antioxidant balance and the endothelial architecture. In conclusion, sildenafil reverses endothelial dysfunction in SHR by improving vascular relaxation to acetylcholine with increased NO bioavailability, reducing the oxidative stress and COX-1 prostanoids, and improving cGMP/PKG signaling. Also, sildenafil reduces structural endothelial damage. Thus, sildenafil is a promising novel pharmacologic strategy to treat endothelial dysfunction in hypertensive states reinforcing its potential role as adjuvant in the pharmacotherapy of cardiovascular diseases.

Force Sensing by Piezo Channels in Cardiovascular Health and Disease

Mechanical forces are fundamental in cardiovascular biology, and deciphering the mechanisms by which they act remains a testing frontier in cardiovascular research. Here, we raise awareness of 2 recently discovered proteins, Piezo1 and Piezo2, which assemble as transmembrane triskelions to combine exquisite force sensing with regulated calcium influx. There is emerging evidence for their importance in endothelial shear stress sensing and secretion, NO generation, vascular tone, angiogenesis, atherosclerosis, vascular permeability and remodeling, blood pressure regulation, insulin sensitivity, exercise performance, and baroreceptor reflex, and there are early suggestions of relevance to cardiac fibroblasts and myocytes. Human genetic analysis points to significance in lymphatic disease, anemia, varicose veins, and potentially heart failure, hypertension, aneurysms, and stroke. These channels appear to be versatile force sensors, used creatively to inform various force-sensing situations. We discuss emergent concepts and controversies and suggest that the potential for new important understanding is substantial.

Pharmacological inhibition of the F1 -ATPase/P2Y1 pathway suppresses the effect of apolipoprotein A1 on endothelial nitric oxide synthesis and vasorelaxation

AIM

The contribution of apolipoprotein A1 (APOA1), the major apolipoprotein of high-density lipoprotein (HDL), to endothelium-dependent vasodilatation is unclear, and there is little information regarding endothelial receptors involved in this effect. Ecto-F₁ -ATPase is a receptor for APOA1, and its activity in endothelial cells is coupled to adenosine diphosphate (ADP)-sensitive P2Y receptors (P2Y ADP receptors). Ecto-F₁ -ATPase is involved in APOA1-mediated cell proliferation and HDL transcytosis. Here, we investigated the effect of lipid-free APOA1 and the involvement of ecto-F₁ -ATPase and P2Y ADP receptors on nitric oxide (NO) synthesis and the regulation of vascular tone.

METHOD

Nitric oxide synthesis was assessed in human endothelial cells from umbilical veins (HUVECs) and isolated mouse aortas. Changes in vascular tone were evaluated by isometric force measurements in isolated human umbilical and placental veins and by assessing femoral artery blood flow in conscious mice.

RESULTS

Physiological concentrations of lipid-free APOA1 enhanced endothelial NO synthesis, which was abolished by inhibitors of endothelial nitric oxide synthase (eNOS) and of the ecto-F₁ -ATPase/P2Y₁ axis. Accordingly, APOA1 inhibited vasoconstriction induced by thromboxane A2 receptor agonist and increased femoral artery blood flow in mice. These effects were blunted by inhibitors of eNOS, ecto-F₁ -ATPase and P2Y₁ receptor.

CONCLUSIONS

Using a pharmacological approach, we thus found that APOA1 promotes endothelial NO production and thereby controls vascular tone in a process that requires activation of the ecto-F₁ -ATPase/P2Y₁ pathway by APOA1. Pharmacological targeting of this pathway with respect to vascular diseases should be explored.

Acute-on-chronic liver disease enhances phenylephrine-induced endothelial nitric oxide release in rat mesenteric resistance arteries through enhanced PKA, PI3K/AKT and cGMP signalling pathways

Acute-on-chronic liver disease is a clinical syndrome characterized by decompensated liver fibrosis, portal hypertension and splanchnic hyperdynamic circulation. We aimed to determine whether the alpha-1 agonist phenylephrine (Phe) facilitates endothelial nitric oxide (NO) release by mesenteric resistance arteries (MRA) in rats subjected to an experimental microsurgical obstructive liver cholestasis model (LC). Sham-operated (SO) and LC rats were maintained for eight postoperative weeks. Phe-induced vasoconstriction (in the presence/absence of the NO synthase –NOS- inhibitor L-NAME) and vasodilator response to NO donor DEA-NO were analysed. Phe-induced NO release was determined in the presence/absence of either H89 (protein kinase –PK- A inhibitor) or LY 294002 (PI3K inhibitor). PKA and PKG activities, alpha-1 adrenoceptor, endothelial NOS (eNOS), PI3K, AKT and soluble guanylate cyclase (sGC) subunit expressions, as well as eNOS and AKT phosphorylation, were determined. The results show that LC blunted Phe-induced vasoconstriction, and enhanced DEA-NO-induced vasodilation. L-NAME increased the Phe-induced contraction largely in LC animals. The Phe-induced NO release was greater in MRA from LC animals. Both H89 and LY 294002 reduced NO release in LC. Alpha-1 adrenoceptor, eNOS, PI3K and AKT expressions were unchanged, but sGC subunit expression, eNOS and AKT phosphorylation and the activities of PKA and PKG were higher in MRA from LC animals. In summary, these mechanisms may help maintaining splanchnic vasodilation and hypotension observed in decompensated LC.

Diverse associations between oxidative stress and thromboxane A2 in hypertensive glomerular injury

We examined the potential contributions of oxidative stress and thromboxane A2 (TXA2) to the development of regional heterogeneity in hypertensive glomerular injury using stroke-prone spontaneously hypertensive rats (SHRSP), an animal model of human essential hypertension. We also examined the effect of antioxidant treatment on the regional expression of thromboxane synthase (TXAS) mRNA using a microdissection method. Increases in the glomerular expression of TXAS mRNA were observed in the SHRSP at 15 weeks of age compared with those in the age-matched normotensive control Wistar-Kyoto (WKY) rats: 2.4-fold and 3.1-fold in the superficial and juxtamedullary glomeruli, respectively (P < 0.05). The heme oxygenase-1 mRNA expression was markedly increased (greater than eightfold, P < 0.05) in both the superficial and juxtamedullary glomeruli in the SHRSP compared with the expression in the WKY rats. In contrast to our expectations, the treatment of SHRSP with tempol (a superoxide dismutase mimetic) significantly (P < 0.05) increased the TXAS mRNA expression in the superficial glomeruli and did not improve the histological injury or albuminuria, which were both aggravated. Moreover, ozagrel (a TXAS inhibitor) had a suppressive effect on the TXAS mRNA expression and significantly (P < 0.05) improved the histological injury. These results indicated that although TXA2 and oxidative stress are linked to each other, TXA2 rather than oxidative stress may be a better therapeutic target to improve hypertensive glomerular injury.

Significance of urinary 11-dehydro-thromboxane B2 in age-related diseases: Focus on atherothrombosis

Platelet activation plays a key role in atherogenesis and atherothrombosis. Biochemical evidence of increased platelet activation in vivo can be reliably obtained through non-invasive measurement of thromboxane metabolite (TXM) excretion. Persistent biosynthesis of TXA₂ has been associated with several ageing-related diseases, including acute and chronic cardio-cerebrovascular diseases and cardiovascular risk factors, such as cigarette smoking, type 1 and type 2 diabetes mellitus, obesity, hypercholesterolemia, hyperhomocysteinemia, hypertension, chronic kidney disease, chronic inflammatory diseases. Given the systemic nature of TX excretion, involving predominantly platelet but also extraplatelet sources, urinary TXM may reflect either platelet cyclooxygenase-1 (COX-1)-dependent TX generation or COX-2-dependent biosynthesis by inflammatory cells and/or platelets, or a combination of the two, especially in clinical settings characterized by low-grade inflammation or enhanced platelet turnover. Although urinary 11-dehydro-TXB₂ levels are largely suppressed with low-dose aspirin, incomplete TXM suppression by aspirin predicts the future risk of vascular events and death in high-risk patients and may identify individuals who might benefit from treatments that more effectively block in vivo TX production or activity. Several disease-modifying agents, including lifestyle intervention, antidiabetic drugs and antiplatelet agents besides aspirin have been shown to reduce TX biosynthesis. Taken together, these aspects may contribute to the development of promising mechanism-based therapeutic strategies to reduce the progression of atherothrombosis. We intended to critically review current knowledge on both the pathophysiological significance of urinary TXM excretion in clinical settings related to ageing and atherothrombosis, as well as its prognostic value as a biomarker of vascular events.

Reduction in Regulatory T Cells in Early Pregnancy Causes Uterine Artery Dysfunction in Mice

Preeclampsia, fetal growth restriction, and miscarriage remain important causes of maternal and perinatal morbidity and mortality. These complications are associated with reduced numbers of a specialized T lymphocyte subset called regulatory T cells (Treg cells) in the maternal circulation, decidua, and placenta. Treg cells suppress inflammation and prevent maternal immunity toward the fetus, which expresses foreign paternal alloantigens. Treg cells are demonstrated to contribute to vascular homeostasis, but whether Treg cells influence the vascular adaptations essential for a healthy pregnancy is unknown. Thus, using a mouse model of Treg-cell depletion, we investigated the hypothesis that depletion of Treg cells would cause increased inflammation and aberrant uterine artery function. Here, we show that Treg-cell depletion resulted in increased embryo resorption and increased production of proinflammatory cytokines. Mean arterial pressure exhibited greater modulation by NO in Treg cell-deficient mice because the L-N^G-nitroarginine methyl ester-induced increase in mean arterial pressure was 46% greater compared with Treg cell-replete mice. Uterine artery function, which is essential for the supply of nutrients to the placenta and fetus, demonstrated dysregulated hemodynamics after Treg-cell depletion. This was evidenced by increased uterine artery resistance and pulsatility indices and enhanced conversion of bET-1 (big endothelin-1) to the active and potent vasoconstrictor, ET-1 (endothelin-1). These data demonstrate an essential role for Treg cells in modulating uterine artery function during pregnancy and implicate Treg-cell control of maternal vascular function as a key mechanism underlying normal fetal and placental development.

2-Ethylpyrazine Induces Vasodilatation by Releasing Nitric Oxide in the Endothelium

Oxygen transportation and regulation of some physiological processes are facilitated by blood flow. Furthermore, blood flow is regulated by various factors such as nitric oxide (NO) and the autonomic nerve system. In modern life, many people suffer from chilliness (hiesho) because of mental stress and an excessive use air-conditioning systems, which induces vasoconstriction in the peripheral skin. In this study, we focused on pyrazine derivatives, particularly compounds that are used as food flavoring materials, and investigated their effects on vascular function and blood flow. We examined the vasodilatory effect of pyrazine derivatives in the rat thoracic aorta and found 2-ethylpyrazine (2-EP) to be the most active pyrazine compound. Additionally, we found that 2-EP induces vasodilatation through the activities of endothelium-derived relaxing factors. 2-EP activates NO synthesis through the effect of endothelial NO synthase in the endothelium. As a result, cyclic GMP levels rise in smooth muscle cells and vasodilatation is induced. We also confirmed that 2-EP increases peripheral blood flow in rats. From these results, we concluded that 2-EP induces vasodilatation by inducing the release of NO and increasing peripheral blood flow.

Reduced coronary reactive hyperemia in mice was reversed by the soluble epoxide hydrolase inhibitor (t-AUCB): Role of adenosine A2A receptor and plasma oxylipins

Coronary reactive hyperemia (CRH) protects the heart against ischemia. Adenosine A_2AAR-deficient (A_2AAR^-/-) mice have increased expression of soluble epoxide hydrolase (sEH); the enzyme responsible for breaking down the cardioprotective epoxyeicosatrienoic acids (EETs) to dihydroxyeicosatrienoic acids (DHETs). sEH-inhibition enhances CRH, increases EETs, and modulates oxylipin profiles. We investigated the changes of oxylipins and their impact on CRH in A_2AAR^-/- and wild type (WT) mice. We hypothesized that the attenuated CRH in A_2AAR^-/- mice is mediated by changes in oxylipin profiles, and that it can be reversed by either sEH- or ω-hydroxylases-inhibition. Compared to WT mice, A_2AAR^-/- mice had attenuated CRH and changed oxylipin profiles, which were consistent between plasma and heart perfusate samples, including decreased EET/DHET ratios, and increased hydroxyeicosatetraenoic acids (HETEs). Plasma oxylipns in A_2AAR^-/- mice indicated an increased proinflammatory state including increased ω-terminal HETEs, decreased epoxyoctadecaenoic/dihydroxyoctadecaenoic acids (EpOMEs/DiHOMEs) ratios, increased 9-hydroxyoctadecadienoic acid, and increased prostanoids. Inhibition of either sEH or ω-hydroxylases reversed the reduced CRH in A_2AAR^-/- mice. In WT and sEH^-/- mice, blocking A_2AAR decreased CRH. These data demonstrate that A_2AAR-deletion was associated with changes in oxylipin profiles, which may contribute to the attenuated CRH. Also, inhibition of sEH and ω-hydroxylases reversed the reduction in CRH.

Deriving vascular smooth muscle cells from mesenchymal stromal cells: Evolving differentiation strategies and current understanding of their mechanisms

Vascular smooth muscle cells (VSMCs) play essential roles in regulating blood vessel form and function. Regeneration of functional vascular smooth muscle tissue to repair vascular diseases is an area of intense research in tissue engineering and regenerative medicine. For functional vascular smooth muscle tissue regeneration to become a practical therapy over the next decade, the field will need to have access to VSMC sources that are effective, robust and safe. While pluripotent stem cells hold good future promise to this end, more immediate translation is expected to come from approaches that generate functional VSMCs from adult sources of multipotent adipose-derived and bone marrow-derived mesenchymal stromal cells (ASCs and BMSCs). The research to this end is extensive and is dominated by studies relating to classical biochemical signalling molecules used to induce differentiation of ASCs and BMSCs. However, prolonged use of the biochemical induction factors is costly and can cause potential endotoxin contamination in the culture. Over recent years several non-traditional differentiation approaches have been devised to mimic defined aspects of the native micro-environment in which VSMCs reside to contribute to the differentiation of VSMC-like cells from ASCs and BMSCs. In this review, the promises and limitations of several non-traditional culture approaches (e.g., co-culture, biomechanical, and biomaterial stimuli) targeting VSMC differentiation are discussed. The extensive crosstalk between the underlying signalling cascades are delineated and put into a translational context. It is expected that this review will not only provide significant insight into VSMC differentiation strategies for vascular smooth muscle tissue engineering applications, but will also highlight the fundamental importance of engineering the cellular microenvironment on multiple scales (with consideration of different combinatorial pathways) in order to direct cell differentiation fate and obtain cells of a desired and stable phenotype. These strategies may ultimately be applied to different sources of stem cells in the future for a range of biomaterial and tissue engineering disciplines.

Involvement of connexin 43 phosphorylation and gap junctional communication between smooth muscle cells in vasopressin-induced ROCK-dependent vasoconstriction after hemorrhagic shock

We examined the roles played by gap junctions (GJs) and the GJ channel protein connexin 43 (Cx43) in arginine vasopressin (AVP)-induced vasoconstriction after hemorrhagic shock and their relationship to Rho kinase (ROCK) and protein kinase C (PKC). The results showed that AVP induced an endothelium-independent contraction in rat superior mesenteric arteries (SMAs). Blocking the GJs significantly decreased the contractile response of SMAs and vascular smooth muscle cells (VSMCs) to AVP after shock and hypoxia. The selective Cx43-mimetic peptide inhibited the vascular contractile effect of AVP after shock and hypoxia. AVP restored hypoxia-induced decrease of Cx43 phosphorylation at Ser²⁶² and gap junctional communication in VSMCs. Activation of RhoA with U-46619 increased the contractile effect of AVP. This effect was antagonized by the ROCK inhibitor Y27632 and the Cx43-mimetic peptide. In contrast, neither an agonist nor an inhibitor of PKC had significant effects on AVP-induced contraction after hemorrhagic shock. In addition, silencing of Cx43 with siRNA blocked the AVP-induced increase of ROCK activity in hypoxic VSMCs. In conclusion, AVP-mediated vascular contractile effects are endothelium and myoendothelial gap junction independent. Gap junctions between VSMCs, gap junctional communication, and Cx43 phosphorylation at Ser²⁶² play important roles in the vascular effects of AVP. RhoA/ROCK, but not PKC, is involved in this process.

Downregulation of Thromboxane A2 Receptor Occurs Mainly via Nuclear Factor-KappaB Signaling Pathway in Rat Renal Artery

Thromboxane A₂ (TXA₂) acts on TXA₂ receptors (TP) to regulate renal artery blood flow and subsequently contributes to the pathogenesis of renal ischemia. The present study was designed to examine if nuclear factor-kappaB (NF-κB) signaling pathway is involved in the downregulation of TP receptors in rat renal artery. Rat renal artery segments were organ cultured for 6 or 24 h. Downregulation of TP receptors was monitored using myograph (contractile function), real-time PCR (receptor mRNA), and immunohistochemistry (receptor protein). Specific inhibitors (MG-132 and BMS345541) for NF-κB signaling pathway were used to dissect the underlying molecular mechanisms involved. Compared to fresh (noncultured) segments, organ culture of the renal artery segments for 24 h induced a significant rightward shift of U46619 (TP receptor agonist) contractile response curves (pEC₅₀: 6.89 ± 0.06 versus 6.48 ± 0.04, P < 0.001). This decreased contractile response to U46619 was paralleled with decreased TP receptor mRNA and protein expressions in the renal artery smooth muscle cells. Specific inhibitors (MG-132 and BMS345541) for NF-κB signaling pathway significantly abolished the decreased TP protein expression and receptor-mediated contractions. In conclusion, downregulation of TP receptors in the renal artery smooth muscle cells occurs mainly via the NF-κB signaling pathway.

Altered expression of eNOS, prostacyclin synthase, prostaglandin G/H synthase, and thromboxane synthase in porcine aortic endothelial cells after exposure to human serum-relevance to xenotransplantation

Under normal conditions, the activity of platelets is stringently and precisely balanced between activation and quiescent state. This guarantees rapid hemostasis and avoids uncontrolled thrombosis. However, excessive platelet activation and resulting thrombotic microangiopathy are frequently observed in pig-to-primate xenotransplantation models. Endothelium-derived inhibitory mechanisms play an important role in regulation of platelet activation. These mainly include nitric oxide (NO), prostacyclin PGI₂ , and adenosine, which are synthesized by endothelial NO synthases (eNOS), prostacyclin synthase, and CD39/CD73, respectively. We investigated whether endothelium-derived regulatory mechanisms are affected in porcine aortic endothelial cells (PAECs) after exposure to human serum. In the present study, exposure of PAECs or porcine iliac arteries to human serum suppressed gene expression of eNOS and prostacyclin synthase, while induced gene expression of prostaglandin G/H synthase and thromboxane synthase. Simultaneously, exposure to human serum reduced NO and PGI₂ production in PAEC culture supernatants. Thus, human serum altered the balance of endothelium-derived inhibitory mechanisms in PAECs, which may indicate a regulatory mechanism of excessive platelet activation in pig-to-primate xenotransplantation.

Peroxynitrite formed during a transient episode of brain ischaemia increases endothelium-derived hyperpolarization-type dilations in thromboxane/prostaglandin receptor-stimulated rat cerebral arteries

AIM

Increased thromboxane A₂ and peroxynitrite are hallmarks of cerebral ischaemia/reperfusion (I/R). Stimulation of thromboxane/prostaglandin receptors (TP) attenuates endothelium-derived hyperpolarization (EDH). We investigated whether EDH-type middle cerebral artery (MCA) relaxations following TP stimulation are altered after I/R and the influence of peroxynitrite.

METHODS

Vascular function was determined by wire myography after TP stimulation with the thromboxane A₂ mimetic 9,11-dideoxy-9α, 11α -methano-epoxy prostaglandin F2α (U46619) in MCA of Sprague Dawley rats subjected to MCA occlusion (90 min)/reperfusion (24 h) or sham operation, and in non-operated (control) rats. Some rats were treated with saline or the peroxynitrite decomposition catalyst 5,10,15,20-tetrakis(4-sulfonatophenyl)porphyrinato iron (III) (20 mg kg^-1 ). Protein expression was evaluated in MCA and in human microvascular endothelial cells submitted to hypoxia (overnight)/reoxygenation (24 h) (H/R) using immunofluorescence and immunoblotting.

RESULTS

In U46619-pre-constricted MCA, EDH-type relaxation by the proteinase-activated receptor 2 agonist serine-leucine-isoleucine-glycine-arginine-leucine-NH₂ (SLIGRL) was greater in I/R than sham rats due to an increased contribution of small-conductance calcium-activated potassium channels (SK_Ca ), which was confirmed by the enlarged relaxation to the SK_Ca activator N-cyclohexyl-N-2-(3,5-dimethyl-pyrazol-1-yl)-6-methyl-4-pyrimidinamine. I/R and H/R induced endothelial protein tyrosine nitration and filamentous-actin disruption. In control MCA, either cytochalasin D or peroxynitrite disrupted endothelial filamentous-actin and augmented EDH-type relaxation. Furthermore, peroxynitrite decomposition during I/R prevented the increase in EDH-type responses.

CONCLUSION

Following TP stimulation in MCA, EDH-type relaxation to SLIGRL is greater after I/R due to endothelial filamentous-actin disruption by peroxynitrite, which prevents TP-induced block of SK_Ca input to EDH. These results reveal a novel mechanism whereby peroxynitrite could promote post-ischaemic brain injury.

Vascular endothelial overexpression of human CYP2J2 (Tie2-CYP2J2 Tr) modulates cardiac oxylipin profiles and enhances coronary reactive hyperemia in mice

Arachidonic acid is metabolized to epoxyeicosatrienoic acids (EETs) by cytochrome (CYP) P450 epoxygenases, and to ω-terminal hydroxyeicosatetraenoic acids (HETEs) by ω-hydroxylases. EETs and HETEs often have opposite biologic effects; EETs are vasodilatory and protect against ischemia/reperfusion injury, while ω-terminal HETEs are vasoconstrictive and cause vascular dysfunction. Other oxylipins, such as epoxyoctadecaenoic acids (EpOMEs), hydroxyoctadecadienoic acids (HODEs), and prostanoids also have varied vascular effects. Post-ischemic vasodilation in the heart, known as coronary reactive hyperemia (CRH), protects against potential damage to the heart muscle caused by ischemia. The relationship among CRH response to ischemia, in mice with altered levels of CYP2J epoxygenases has not yet been investigated. Therefore, we evaluated the effect of endothelial overexpression of the human cytochrome P450 epoxygenase CYP2J2 in mice (Tie2-CYP2J2 Tr) on oxylipin profiles and CRH. Additionally, we evaluated the effect of pharmacologic inhibition of CYP-epoxygenases and inhibition of ω-hydroxylases on CRH. We hypothesized that CRH would be enhanced in isolated mouse hearts with vascular endothelial overexpression of human CYP2J2 through modulation of oxylipin profiles. Similarly, we expected that inhibition of CYP-epoxygenases would reduce CRH, whereas inhibition of ω-hydroxylases would enhance CRH. Compared to WT mice, Tie2-CYP2J2 Tr mice had enhanced CRH, including repayment volume, repayment duration, and repayment/debt ratio (P < 0.05). Similarly, inhibition of ω-hydroxylases increased repayment volume and repayment duration, in Tie2-CYP2J2 Tr compared to WT mice (P < 0.05). Endothelial overexpression of CYP2J2 significantly changed oxylipin profiles, including increased EETs (P < 0.05), increased EpOMEs (P < 0.05), and decreased 8-iso-PGF2α (P < 0.05). Inhibition of CYP epoxygenases with MS-PPOH attenuated CRH (P < 0.05). Ischemia caused a decrease in mid-chain HETEs (5-, 11-, 12-, 15-HETEs P < 0.05) and HODEs (P < 0.05). These data demonstrate that vascular endothelial overexpression of CYP2J2, through changing the oxylipin profiles, enhances CRH. Inhibition of CYP epoxygenases decreases CRH, whereas inhibition of ω-hydroxylases enhances CRH.

Vascular Endothelial Over-Expression of Human Soluble Epoxide Hydrolase (Tie2-sEH Tr) Attenuates Coronary Reactive Hyperemia in Mice: Role of Oxylipins and ω-Hydroxylases

Cytochromes P450 metabolize arachidonic acid (AA) into two vasoactive oxylipins with opposing biologic effects: epoxyeicosatrienoic acids (EETs) and omega-(ω)-terminal hydroxyeicosatetraenoic acids (HETEs). EETs have numerous beneficial physiological effects, including vasodilation and protection against ischemia/reperfusion injury, whereas ω-terminal HETEs induce vasoconstriction and vascular dysfunction. We evaluated the effect of these oxylipins on post-ischemic vasodilation known as coronary reactive hyperemia (CRH). CRH prevents the potential harm associated with transient ischemia. The beneficial effects of EETs are reduced after their hydrolysis to dihydroxyeicosatrienoic acids (DHETs) by soluble epoxide hydrolase (sEH). ω-terminal HETEs are formed by ω-hydroxylase family members. The relationship among endothelial over-expression of sEH (Tie2-sEH Tr), the changes in oxylipins it may produce, the pharmacologic inhibition of ω-hydroxylases, activation of PPARγ, and CRH response to a brief ischemia is not known. We hypothesized that CRH is attenuated in isolated mouse hearts with endothelial sEH over-expression through modulation of oxylipin profiles, whereas both inhibition of ω-hydroxylases and activation of PPARγ enhance CRH. Compared to WT mice, Tie2-sEH Tr mice had decreased CRH, including repayment volume, repayment duration, and repayment/debt ratio (P < 0.05), whereas inhibition of ω-hydroxylases increased these same CRH parameters in Tie2-sEH Tr mice. Inhibition of sEH with t-AUCB reversed the decreased CRH in Tie2-sEH Tr mice. Endothelial over-expression of sEH significantly changed oxylipin profiles, including decreases in DHETs, mid-chain HETEs, and prostaglandins (P < 0.05). Treatment with rosiglitazone, PPARγ-agonist, enhanced CRH (P < 0.05) in both Tie2-sEH Tr and wild type (WT) mice. These data demonstrate that endothelial over-expression of sEH (through changing the oxylipin profiles) attenuates CRH, whereas inhibition of ω-hydroxylases and activation of PPARγ enhance it.

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.

Effects of Aspirin on Endothelial Function and Hypertension

PURPOSE OF REVIEW

Endothelial dysfunction is intimately related to the development of various cardiovascular diseases, including hypertension, and is often used as a target for pharmacological treatment. The scope of this review is to assess effects of aspirin on endothelial function and their clinical implication in arterial hypertension.

RECENT FINDINGS

Emerging data indicate the role of platelets in the development of vascular inflammation due to the release of proinflammatory mediators, for example, triggered largely by thromboxane. Vascular inflammation further promotes oxidative stress, diminished synthesis of vasodilators, proaggregatory and procoagulant state. These changes translate into vasoconstriction, impaired circulation and thrombotic complications. Aspirin inhibits thromboxane synthesis, abolishes platelets activation and acetylates enzymes switching them to the synthesis of anti-inflammatory substances. Aspirin pleiotropic effects have not been fully elucidated yet. In secondary prevention studies, the decrease in cardiovascular events with aspirin outweighs bleeding risks, but this is not the case in primary prevention settings. Ongoing trials will provide more evidence on whether to expand the use of aspirin or stay within current recommendations.

Endothelium-Derived Hyperpolarization and Coronary Vasodilation: Diverse and Integrated Roles of Epoxyeicosatrienoic Acids, Hydrogen Peroxide, and Gap Junctions

Myocardial perfusion and coronary vascular resistance are regulated by signaling metabolites released from the local myocardium that act either directly on the VSMC or indirectly via stimulation of the endothelium. A prominent mechanism of vasodilation is EDH of the arteriolar smooth muscle, with EETs and H(2)O(2) playing important roles in EDH in the coronary microcirculation. In some cases, EETs and H(2)O(2) are released as transferable hyperpolarizing factors (EDHFs) that act directly on the VSMCs. By contrast, EETs and H(2)O(2) can also promote endothelial KCa activity secondary to the amplification of extracellular Ca(2+) influx and Ca(2+) mobilization from intracellular stores, respectively. The resulting endothelial hyperpolarization may subsequently conduct to the media via myoendothelial gap junctions or potentially lead to the release of a chemically distinct factor(s). Furthermore, in human isolated coronary arterioles dilator signaling involving EETs and H(2)O(2) may be integrated, being either complimentary or inhibitory depending on the stimulus. With an emphasis on the human coronary microcirculation, this review addresses the diverse and integrated mechanisms by which EETs and H(2)O(2) regulate vessel tone and also examines the hypothesis that myoendothelial microdomain signaling facilitates EDH activity in the human heart.

Endothelin-1 shifts the mediator of bradykinin-induced relaxation from NO to H2 O2 in resistance arteries from patients with cardiovascular disease

BACKGROUND AND PURPOSE

We tested the hypothesis that in resistance arteries from cardiovascular disease (CVD) patients, effects of an endothelium-dependent vasodilator depend on the contractile stimulus.

EXPERIMENTAL APPROACH

Arteries dissected from parietal pericardium of cardiothoracic surgery patients were studied by myography and imaging techniques. Segments were sub-maximally contracted by K(+) , the TxA2 analogue U46619 or endothelin-1 (ET-1).

KEY RESULTS

Relaxing effects of Na-nitroprusside were comparable, but those of bradykinin (BK) were bigger in the presence of ET-1 compared with K(+) or U46619. BK-induced relaxation was (i) abolished by L-NAME in K(+) -contracted arteries, (ii) partly inhibited by L-NAME in the presence of U46619 and (iii) not altered by indomethacin, L-NAME plus inhibitors of small and intermediate conductance calcium-activated K(+) channels, but attenuated by catalase, in ET-1-contracted arteries. This catalase-sensitive relaxation was unaffected by inhibitors of NADPH oxidases or allopurinol. Exogenous H2 O2 caused a larger relaxation of ET-1-induced contractions than those evoked by K(+) or U46619 in the presence of inhibitors of other endothelium-derived relaxing factors. Catalase-sensitive staining of cellular ROS with CellROX Deep Red was significantly increased in the presence of both 1 μM BK and 2 nM ET-1 but not either peptide alone.

CONCLUSIONS AND IMPLICATIONS

In resistance arteries from patients with CVD, exogenous ET-1 shifts the mediator of relaxing responses to the endothelium-dependent vasodilator BK from NO to H2 O2 and neither NADPH oxidases, xanthine oxidase nor NOS appear to be involved in this effect. This might have consequences for endothelial dysfunction in conditions where intra-arterial levels of ET-1 are enhanced.

Vascular endothelial dysfunction and pharmacological treatment

The endothelium exerts multiple actions involving regulation of vascular permeability and tone, coagulation and fibrinolysis, inflammatory and immunological reactions and cell growth. Alterations of one or more such actions may cause vascular endothelial dysfunction. Different risk factors such as hypercholesterolemia, homocystinemia, hyperglycemia, hypertension, smoking, inflammation, and aging contribute to the development of endothelial dysfunction. Mechanisms underlying endothelial dysfunction are multiple, including impaired endothelium-derived vasodilators, enhanced endothelium-derived vasoconstrictors, over production of reactive oxygen species and reactive nitrogen species, activation of inflammatory and immune reactions, and imbalance of coagulation and fibrinolysis. Endothelial dysfunction occurs in many cardiovascular diseases, which involves different mechanisms, depending on specific risk factors affecting the disease. Among these mechanisms, a reduction in nitric oxide (NO) bioavailability plays a central role in the development of endothelial dysfunction because NO exerts diverse physiological actions, including vasodilation, anti-inflammation, antiplatelet, antiproliferation and antimigration. Experimental and clinical studies have demonstrated that a variety of currently used or investigational drugs, such as angiotensin-converting enzyme inhibitors, angiotensin AT1 receptors blockers, angiotensin-(1-7), antioxidants, beta-blockers, calcium channel blockers, endothelial NO synthase enhancers, phosphodiesterase 5 inhibitors, sphingosine-1-phosphate and statins, exert endothelial protective effects. Due to the difference in mechanisms of action, these drugs need to be used according to specific mechanisms underlying endothelial dysfunction of the disease.

Metabolic Serum Profiles for Patients Receiving Allogeneic Stem Cell Transplantation: The Pretransplant Profile Differs for Patients with and without Posttransplant Capillary Leak Syndrome

Allogeneic stem cell transplantation is commonly used in the treatment of younger patients with severe hematological diseases, and endothelial cells seem to be important for the development of several posttransplant complications. Capillary leak syndrome is a common early posttransplant complication where endothelial cell dysfunction probably contributes to the pathogenesis. In the present study we investigated whether the pretreatment serum metabolic profile reflects a risk of posttransplant capillary leak syndrome. We investigated the pretransplant serum levels of 766 metabolites for 80 consecutive allotransplant recipients. Patients with later capillary leak syndrome showed increased pretherapy levels of metabolites associated with endothelial dysfunction (homocitrulline, adenosine) altered renal regulation of fluid and/or electrolyte balance (betaine, methoxytyramine, and taurine) and altered vascular function (cytidine, adenosine, and methoxytyramine). Additional bioinformatical analyses showed that capillary leak syndrome was also associated with altered purine/pyrimidine metabolism (i.e., metabolites involved in vascular regulation and endothelial functions), aminoglycosylation (possibly important for endothelial cell functions), and eicosanoid metabolism (also involved in vascular regulation). Our observations are consistent with the hypothesis that the pretransplant metabolic status can be a marker for posttransplant abnormal fluid and/or electrolyte balance.