Our view of the endothelium was transformed around 30 years ago, from one of an inert barrier to that of a key endocrine organ central to cardiovascular function. This dramatic change followed the ...discoveries that endothelial cells (ECs) elaborate the vasodilators prostacyclin and nitric oxide. The key to these discoveries was the use of the quintessentially pharmacological technique of bioassay. Bioassay also revealed endothelium‐derived hyperpolarizing factor (EDHF), particularly important in small arteries and influencing blood pressure and flow distribution. The basic idea of EDHF as a diffusible factor causing smooth muscle hyperpolarization (and thus vasodilatation) has evolved into one of a complex pathway activated by endothelial Ca2+ opening two Ca2+‐sensitive K+‐channels, KCa2.3 and KCa3.1. Combined application of apamin and charybdotoxin blocked EDHF responses, revealing the critical role of these channels as iberiotoxin was unable to substitute for charybdotoxin. We showed these channels are arranged in endothelial microdomains, particularly within projections towards the adjacent smooth muscle, and close to interendothelial gap junctions. Activation of KCa channels hyperpolarizes ECs, and K+ efflux through them can act as a diffusible ‘EDHF’ stimulating Na+/K+‐ATPase and inwardly rectifying K‐channels. In parallel, hyperpolarizing current can spread from the endothelium to the smooth muscle through myoendothelial gap junctions upon endothelial projections. The resulting radial hyperpolarization mobilized by EDHF is complemented by spread of hyperpolarization along arteries and arterioles, effecting distant dilatation dependent on the endothelium. So the complexity of the endothelium still continues to amaze and, as knowledge evolves, provides considerable potential for novel approaches to modulate blood pressure.
LINKED ARTICLES This article is part of a themed issue on Vascular Endothelium in Health and Disease. To view the other articles in this issue visit http://dx.doi.org/10.1111/bph.2011.164.issue‐3
Increasing evidence suggests that some cannabinoids mediate their effects independently of the known cannabinoid CB
1 and CB
2 receptors. Two recently published patents indicate that several ...cannabinoid receptor ligands also bind to the orphan G-protein-coupled receptor GPR55. This receptor is reported to be expressed in several tissues and might function in lipid or vascular biology. Thus, GPR55 might represent a new cannabinoid receptor.
Background and Purpose
Lysophosphatidylinositol (LPI), a lipid signalling molecule, activates GPR55 and elevates intracellular Ca2+. Here, we examine the actions of LPI in the rat resistance ...mesenteric artery and Ca2+ responses in endothelial cells isolated from the artery.
Experimental Approach
Vascular responses were studied using wire myographs. Single‐cell fluorescence imaging was performed using a MetaFluor system. Hypotensive effects of LPI were assessed using a Biopac system.
Key Results
In isolated arteries, LPI‐induced vasorelaxation was concentration‐ and endothelium‐dependent and inhibited by CID 16020046, a GPR55 antagonist. The CB1 receptor antagonist AM 251 had no effect, whereas rimonabant and O‐1918 significantly potentiated LPI responses. Vasorelaxation was reduced by charybdotoxin and iberiotoxin, alone or combined. LPI decreased systemic arterial pressure. GPR55 is expressed in rat mesenteric artery. LPI caused biphasic elevations of endothelial cell intracellular Ca2+. Pretreatment with thapsigargin or 2‐aminoethoxydiphenyl borate abolished both phases. The PLC inhibitor U73122 attenuated the initial phase and enhanced the second phase, whereas the Rho‐associated kinase inhibitor Y‐27632 abolished the late phase but not the early phase .
Conclusions and Implications
LPI is an endothelium‐dependent vasodilator in the rat small mesenteric artery and a hypotensive agent. The vascular response involves activation of Ca2+‐sensitive K+ channels and is not mediated by CB1 receptors, but unexpectedly enhanced by antagonists of the ‘endothelial anandamide’ receptor. In endothelial cells, LPI utilizes PLC‐IP3 and perhaps ROCK‐RhoA pathways to elevate intracellular Ca2+. Overall, these findings support an endothelial site of action for LPI and suggest a possible role for GPR55 in vasculature.
Endothelial dysfunction in small arteries is a ubiquitous, early feature of cardiovascular disease, including hypertension. Dysfunction reflects reduced bioavailability of endothelium-derived nitric ...oxide (NO) and depressed endothelium-dependent hyperpolarization that enhances vasoreactivity. We measured smooth muscle membrane potential and tension, smooth muscle calcium, and used real-time quantitative polymerase chain reaction in small arteries and isolated tubes of endothelium to investigate how dysfunction enhances vasoreactivity. Rat nonmyogenic mesenteric resistance arteries developed vasomotion to micromolar phenylephrine (α1-adrenoceptor agonist); symmetrical vasoconstrictor oscillations mediated by L-type voltage-gated Ca channels (VGCCs). Inhibiting NO synthesis abolished vasomotion so nanomolar phenylephrine now stimulated rapid, transient depolarizing spikes in the smooth muscle associated with chaotic vasomotion/vasospasm. Endothelium-dependent hyperpolarization block also enabled phenylephrine-vasospasm but without spikes or chaotic vasomotion. Depolarizing spikes were Ca-based and abolished by either T-type or L-type VGCCs blockers with depressed vasoconstriction. Removing NO also enabled transient spikes/vasoconstriction to Bay K-8644 (L-type VGCC activator). However, these were abolished by the L-type VGCC blocker nifedipine but not T-type VGCC block. Phenylephrine also initiated T-type VGCC-transient spikes and enhanced vasoconstriction after NO loss in nonmyogenic arteries from spontaneously hypertensive rats. In contrast to mesenteric arteries, myogenic coronary arteries displayed transient spikes and further vasoconstriction spontaneously on loss of NO. T-type VGCC block abolished these spikes and additional vasoconstriction but not myogenic tone. Therefore, in myogenic and nonmyogenic small arteries, reduced NO bioavailability engages T-type VGCCs, triggering transient depolarizing spikes in normally quiescent vascular smooth muscle to cause vasospasm. T-type block may offer a means to suppress vasospasm without inhibiting myogenic tone mediated by L-type VGCCs.
Endocannabinoids and the Heart Hiley, C Robin
Journal of cardiovascular pharmacology,
2009-April, 2009-Apr, 2009-04-00, 20090401, Letnik:
53, Številka:
4
Journal Article
Recenzirano
Odprti dostop
Endocannabinoids, such as anandamide and 2-arachidonoylglycerol, are synthesized from membrane phospholipids in the heart and other cardiovascular tissues. They activate cannabinoid CB1 and CB2 ...receptors, transient receptor potential V1 (TRPV1), peroxisome proliferator-activated receptors, and perhaps a novel vascular G-protein-coupled receptor. Inactivation is by cellular uptake and fatty acid amide hydrolase. Endocannabinoids relax coronary and other arteries and decrease cardiac work but seem not to be involved in tonic regulation of cardiovascular function. They act as a stress response system, which is activated, for example, in myocardial infarction and circulatory shock. Endocannabinoids are largely protective; they decrease tissue damage and arrhythmia in myocardial infarction and may reduce progression of atherosclerosis (CB2 receptor stimulation inhibits lesion progression), and fatty acid amide hydrolase knockout mice (which have enhanced endocannabinoid levels) show decreased cardiac dysfunction with age compared with wild types. However, endocannabinoids may mediate doxorubicin-induced cardiac dysfunction. Their signaling pathways are not fully elucidated but they can lead to changed expression of a variety of genes, including those involved in inflammatory responses. There is potential for therapeutic targeting of endocannabinoids and their receptors, but their apparent involvement in both protective and deleterious actions on the heart means that careful risk assessment is needed before any treatment can be introduced.
Lysophosphatidylinositol (LPI), a lipid signalling molecule, activates GPR55 and elevates intracellular Ca(2+). Here, we examine the actions of LPI in the rat resistance mesenteric artery and Ca(2+) ...responses in endothelial cells isolated from the artery.
Vascular responses were studied using wire myographs. Single-cell fluorescence imaging was performed using a MetaFluor system. Hypotensive effects of LPI were assessed using a Biopac system.
In isolated arteries, LPI-induced vasorelaxation was concentration- and endothelium-dependent and inhibited by CID 16020046, a GPR55 antagonist. The CB1 receptor antagonist AM 251 had no effect, whereas rimonabant and O-1918 significantly potentiated LPI responses. Vasorelaxation was reduced by charybdotoxin and iberiotoxin, alone or combined. LPI decreased systemic arterial pressure. GPR55 is expressed in rat mesenteric artery. LPI caused biphasic elevations of endothelial cell intracellular Ca(2+). Pretreatment with thapsigargin or 2-aminoethoxydiphenyl borate abolished both phases. The PLC inhibitor U73122 attenuated the initial phase and enhanced the second phase, whereas the Rho-associated kinase inhibitor Y-27632 abolished the late phase but not the early phase.
LPI is an endothelium-dependent vasodilator in the rat small mesenteric artery and a hypotensive agent. The vascular response involves activation of Ca(2+)-sensitive K(+) channels and is not mediated by CB1 receptors, but unexpectedly enhanced by antagonists of the 'endothelial anandamide' receptor. In endothelial cells, LPI utilizes PLC-IP3 and perhaps ROCK-RhoA pathways to elevate intracellular Ca(2+). Overall, these findings support an endothelial site of action for LPI and suggest a possible role for GPR55 in vasculature.
Intratumoural heterogeneity (ITH) is well recognised in prostate cancer (PC), but its role in high-risk disease is uncertain. A prospective, single-arm, translational study using targeted multiregion ...prostate biopsies was carried out to study genomic and T-cell ITH in clinically high-risk PC aiming to identify drivers and potential therapeutic strategies.
Forty-nine men with elevated prostate-specific antigen and multiparametric-magnetic resonance imaging detected PC underwent image-guided multiregion transperineal biopsy. Seventy-nine tumour regions from 25 patients with PC underwent sequencing, analysis of mutations, copy number and neoepitopes combined with tumour infiltrating T-cell subset quantification.
We demonstrated extensive somatic nucleotide variation and somatic copy number alteration heterogeneity in high-risk PC. Overall, the mutational burden was low (0.93/Megabase), but two patients had hypermutation, with loss of mismatch repair (MMR) proteins, MSH2 and MSH6. Somatic copy number alteration burden was higher in patients with metastatic hormone-naive PC (mHNPC) than in those with high-risk localised PC (hrlPC), independent of Gleason grade. Mutations were rarely ubiquitous and mutational frequencies were similar for mHNPC and hrlPC patients. Enrichment of focal 3q26.2 and 3q21.3, regions containing putative metastasis drivers, was seen in mHNPC patients. We found evidence of parallel evolution with three separate clones containing activating mutations of β-catenin in a single patient. We demonstrated extensive intratumoural and intertumoural T-cell heterogeneity and high inflammatory infiltrate in the MMR-deficient (MMRD) patients and the patient with parallel evolution of β-catenin. Analysis of all patients with activating Wnt/β-catenin mutations demonstrated a low CD8+/FOXP3+ ratio, a potential surrogate marker of immune evasion.
The PROGENY (PROstate cancer GENomic heterogeneitY) study provides a diagnostic platform suitable for studying tumour ITH. Genetic aberrations in clinically high-risk PC are associated with altered patterns of immune infiltrate in tumours. Activating mutations of Wnt/β-catenin signalling pathway or MMRD could be considered as potential biomarkers for immunomodulation therapies.
NCT02022371
The actions of the anandamide-like mono-unsaturated fatty acid oleoylethanolamide (OEA) were first linked to satiety and control of food intake and recently reported to relax resistance vessels. This ...study characterizes its vasorelaxant mechanisms. Vasorelaxation to OEA were assessed in third order branches of rat superior mesenteric artery using a wire myograph. The roles of the endothelium, KCa channels, perivascular sensory nerves, NO, cannabinoid receptors, and the phospholipase C (PLC)/inositol trisphosphate (InsP3) and RhoA/ROCK signalling pathways, were assessed. OEA caused concentration- and endothelium-dependent vasorelaxation (pEC50=6.7±0.1, Rmax=93.1±2.5%). L-NAME greatly reduced the response (residual relaxation of only 24.6±12.8%). Capsaicin and pertussis toxin significantly reduced the vasorelaxation. Precontraction with KCl abolished the response. TRAM-34 had no effect, but both iberiotoxin and apamin+charybdotoxin markedly shifted the OEA concentration–response curve to the right (∼5-fold). O-1918 but not rimonabant attenuated the vasorelaxation. Both the CB1 receptor antagonist, AM251 and the CB2 receptor antagonist, AM630, given alone or in combination, reduced the response to OEA. Inhibition of PLC by U73122, ROCK by Y-27632 and antagonism of inositol trisphosphate (InsP3) receptors by 2-APB abolished OEA vasorelaxation. OEA vasorelaxation involves an endothelial site of action but not the known cannabinoid receptors. It involves Ca2+ released from InsP3-sensitive endothelial stores by mechanisms involving RhoA kinase and phospholipase C. It is likely that the released Ca2+ causes NO generation and opening of mainly large-conductance KCa channels. This study demonstrates a possible novel endothelial target that might be important in the control of regional blood flow induced by this lipid molecule.
Nitric oxide (NO{bullet}) competitively inhibits oxygen consumption by mitochondria at cytochrome c oxidase and S-nitrosates thiol proteins. We developed mitochondria-targeted S-nitrosothiols ...(MitoSNOs) that selectively modulate and protect mitochondrial function. The exemplar MitoSNO1, produced by covalently linking an S-nitrosothiol to the lipophilic triphenylphosphonium cation, was rapidly and extensively accumulated within mitochondria, driven by the membrane potential, where it generated NO{bullet} and S-nitrosated thiol proteins. MitoSNO1-induced NO{bullet} production reversibly inhibited respiration at cytochrome c oxidase and increased extracellular oxygen concentration under hypoxic conditions. MitoSNO1 also caused vasorelaxation due to its NO{bullet} generation. Infusion of MitoSNO1 during reperfusion was protective against heart ischemia-reperfusion injury, consistent with a functional modification of mitochondrial proteins, such as complex I, following S-nitrosation. These results support the idea that selectively targeting NO{bullet} donors to mitochondria is an effective strategy to reversibly modulate respiration and to protect mitochondria against ischemia-reperfusion injury.
Patients treated with curative-intent lung radiotherapy are in the group at highest risk of severe complications and death from COVID-19. There is therefore an urgent need to reduce the risks ...associated with multiple hospital visits and their anti-cancer treatment. One recommendation is to consider alternative dose-fractionation schedules or radiotherapy techniques. This would also increase radiotherapy service capacity for operable patients with stage I-III lung cancer, who might be unable to have surgery during the pandemic.
Here we identify reduced-fractionation for curative-intent radiotherapy regimes in lung cancer, from a literature search carried out between 20/03/2020 and 30/03/2020 as well as published and unpublished audits of hypofractionated regimes from UK centres. Evidence, practical considerations and limitations are discussed for early-stage NSCLC, stage III NSCLC, early-stage and locally advanced SCLC. We recommend discussion of this guidance document with other specialist lung MDT members to disseminate the potential changes to radiotherapy practices that could be made to reduce pressure on other departments such as thoracic surgery. It is also a crucial part of the consent process to ensure that the risks and benefits of undergoing cancer treatment during the COVID-19 pandemic and the uncertainties surrounding toxicity from reduced fractionation have been adequately discussed with patients. Furthermore, centres should document all deviations from standard protocols, and we urge all colleagues, where possible, to join national/international data collection initiatives (such as COVID-RT Lung) aimed at recording the impact of the COVID-19 pandemic on lung cancer treatment and outcomes.
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