The apelin receptor inhibits the angiotensin II type 1 receptor via allosteric trans-inhibition

Background and Purpose

The apelin receptor (APJ) is often co-expressed with the angiotensin II type-1 receptor (AT1) and acts as an endogenous counter-regulator. Apelin antagonizes Ang II signalling, but the precise molecular mechanism has not been elucidated. Understanding this interaction may lead to new therapies for the treatment of cardiovascular disease.

Experimental Approach

The physical interaction of APJ and AT1 receptors was detected by co-immunoprecipitation and bioluminescence resonance energy transfer (BRET). Functional and pharmacological interactions were measured by G-protein-dependent signalling and recruitment of β-arrestin. Allosterism and cooperativity between APJ and AT1 were measured by radioligand binding assays.

Key Results

Apelin, but not Ang II, induced APJ : AT1 heterodimerization forced AT1 into a low-affinity state, reducing Ang II binding. Likewise, apelin mediated a concentration-dependent depression in the maximal production of inositol phosphate (IP₁) and β-arrestin recruitment to AT1 in response to Ang II. The signal depression approached a limit, the magnitude of which was governed by the cooperativity indicative of a negative allosteric interaction. Fitting the data to an operational model of allosterism revealed that apelin-mediated heterodimerization significantly reduces Ang II signalling efficacy. These effects were not observed in the absence of apelin.

Conclusions and Implications

Apelin-dependent heterodimerization between APJ and AT1 causes negative allosteric regulation of AT1 function. As AT1 is significant in the pathogenesis of cardiovascular disease, these findings suggest that impaired apelin and APJ function may be a common underlying aetiology.

Linked Article

This article is commented on by Goupil et al., pp. 1101–1103 of this issue. To view this commentary visit http://dx.doi.org/10.1111/bph.12040     

Putative role for apelin in pressure/volume homeostasis and cardiovascular disease

Apelin is a peptide recently isolated from bovine stomach extracts which appears to act as an endogenous ligand for the previously orphaned G-protein-coupled APJ receptor. The apelin gene encodes for a pre-propeptide consisting of 77 amino acids with mature apelin likely to be derived from the C-terminal region as either a 36, 17 or 13 amino acid peptide. Apelin mRNA expression and peptide immunoreactivity has been described in a variety of tissues including gastrointestinal tract, adipose tissue, brain, kidney, liver, lung and at various sites within the cardiovascular system. Apelin is strongly expressed in the heart with expression also present in the large conduit vessels, coronary vessels and endothelial cells. Message expression for the APJ receptor is similarly distributed throughout the brain and periphery, again including cardiovascular tissue. Consistent with this pattern of distribution, apelin and APJ have been shown to exhibit some role in the regulation of fluid homeostasis. In addition, a growing number of studies have reported cardiovascular actions of apelin. Not only has apelin been observed to alter arterial pressure, but the peptide also exhibits endothelium-dependent vasodilator actions in vivo and positive inotropic actions in the isolated heart. Furthermore, differences in apelin and APJ expression have been described in patients with congestive heart failure and circulating levels of apelin are also reported to change in heart failure. Taken together, these studies suggest a role for apelin in pressure/volume homeostasis and in the pathophysiology of cardiovascular disease. As such, manipulation of this peptide system may offer benefit to the syndrome of heart failure with potential clinical applications in humans.     

Daily administration of the TP receptor antagonist terutroban improved endothelial function in high-cardiovascular-risk patients with atherosclerosis

AIMS

The specific TP receptor antagonist terutroban improves endothelial function after a single dose in patients with coronary artery disease. Our aim was to evaluate the effects and dose dependency of repeated-dose terutroban on endothelial function and platelet aggregation in high-cardiovascular-risk patients with carotid atherosclerosis.

METHODS

We randomly allocated 48 patients taking 300 mg aspirin per day to placebo or to one of three terutroban dosages (2.5, 5 or 10 mg) for 15 days in a double-blind study. Flow-mediated vasodilatation was evaluated before and 2 h after the first oral dose on day 0 and 2 h after the last oral dose on day 14.

RESULTS

On day 0 and day 14, all three terutroban dosages improved flow-mediated vasodilatation and abolished platelet aggregation induced by the TP receptor agonist U46619, without changing the aggregation response to ADP or collagen.

CONCLUSION

Terutroban, by chronically improving endothelium-dependent vasodilatation and inhibiting platelet aggregation, may prove useful for preventing cardiovascular events in high-risk patients.     

Update on apelin peptides as putative targets for cardiovascular drug discovery

Introduction: The physiological importance of GPCR/ligand pathways is highlighted by the fact that numerous pathologies are attributed to their signaling dysfunction. Over 50% of the pharmaceutical drugs currently used to treat human disease are based on compounds that interact with GPCRs. Apelin/APJ constitutes a novel endogenous peptide/GPCR system proposed to be involved in a wide range of physiological functions. Early evidence suggests that apelin/APJ may hold promise as a target for development of novel therapeutic agents which may counteract a number of pathologies including cardiovascular disease. Despite advances in treatment of cardiovascular disease, incidence, prevalence, morbidity and economic costs remain high necessitating the development of new treatment paradigms.

Areas covered: This review summarizes apelin/APJ structure, distribution and regulation; presents evidence for a role of apelin in pressure/volume homeostasis and in the pathophysiology of cardiovascular disease; summarizes data on beneficial effects of apelin in preclinical, animal models of cardiovascular disease and measurement of plasma levels of apelin across the full spectrum of cardiovascular disease in humans; and notes the first studies describing bioactivity of apelin peptides in human healthy volunteers and patients with heart failure.

Expert opinion: More clarity is needed on the precise physiological/pathophysiological role of the apelin/APJ system in human health and disease. Nonetheless, preclinical studies and initial studies in humans show that APJ antagonism may represent a novel therapeutic target for patients with cardiovascular disease. Development of appropriately validated assays for apelin will clarify circulating levels of the peptide in health and disease. Development of suitable agonists/antagonists will pave the way for much needed future studies essential for advancing this promising field of drug discovery.     

Update on apelin peptides as putative targets for cardiovascular drug discovery

Introduction: The physiological importance of GPCR/ligand pathways is highlighted by the fact that numerous pathologies are attributed to their signaling dysfunction. Over 50% of the pharmaceutical drugs currently used to treat human disease are based on compounds that interact with GPCRs. Apelin/APJ constitutes a novel endogenous peptide/GPCR system proposed to be involved in a wide range of physiological functions. Early evidence suggests that apelin/APJ may hold promise as a target for development of novel therapeutic agents which may counteract a number of pathologies including cardiovascular disease. Despite advances in treatment of cardiovascular disease, incidence, prevalence, morbidity and economic costs remain high necessitating the development of new treatment paradigms. Areas covered: This review summarizes apelin/APJ structure, distribution and regulation; presents evidence for a role of apelin in pressure/volume homeostasis and in the pathophysiology of cardiovascular disease; summarizes data on beneficial effects of apelin in preclinical, animal models of cardiovascular disease and measurement of plasma levels of apelin across the full spectrum of cardiovascular disease in humans; and notes the first studies describing bioactivity of apelin peptides in human healthy volunteers and patients with heart failure. Expert opinion: More clarity is needed on the precise physiological/pathophysiological role of the apelin/APJ system in human health and disease. Nonetheless, preclinical studies and initial studies in humans show that APJ antagonism may represent a novel therapeutic target for patients with cardiovascular disease. Development of appropriately validated assays for apelin will clarify circulating levels of the peptide in health and disease. Development of suitable agonists/antagonists will pave the way for much needed future studies essential for advancing this promising field of drug discovery.     

Ivabradine: the evidence of its therapeutic impact in angina

Introduction:

Stable angina pectoris (SAP) is a widely prevalent disease affecting 30 000 to 40 000 per million people in Europe and the US. SAP is associated with reductions in quality of life and ability to work, and increased use of healthcare resources. Ivabradine is a drug with a unique therapeutic target, the I_f current of the sinus node, developed for the treatment of cardiovascular diseases including SAP. It has an exclusive heart rate reducing effect, without any negative effect on left ventricular function or coronary vasodilatation.

Aims:

The aim of this paper is to review the evidence concerning the use of ivabradine in the treatment of SAP.

Evidence review:

Ivabradine is an effective antianginal and antiischemic drug, not inferior to the beta blocker atenolol and the calcium channel antagonist (CCA) amlodipine. It decreases the frequency of angina attacks and increases the time to anginal symptoms during exercise. Because of its exclusive chronotropic effect, ivabradine is not associated with the typical adverse reactions associated with beta blockers or other antianginal drugs.

Clinical value:

Clinical evidence shows that ivabradine is a very good antiischemic and antianginal agent, being as effective as beta blockade and CCA therapy in controlling myocardial ischemia and symptoms of stable angina. Ongoing studies will determine the potential of ivabradine to improve morbidity and mortality in coronary artery disease and heart failure.     

CGRP function-blocking antibodies inhibit neurogenic vasodilatation without affecting heart rate or arterial blood pressure in the rat

Background and purpose:

Calcitonin gene-related peptide (CGRP) receptor antagonists effectively abort migraine headache and inhibit neurogenic vasodilatation in humans as well as rat models. Monoclonal antibodies typically have long half-lives, and we investigated whether or not function-blocking CGRP antibodies would inhibit neurogenic vasodilatation with a long duration of action and therefore be a possible approach to preventive therapy of migraine. During chronic treatment with anti-CGRP antibodies, we measured cardiovascular function, which might be a safety concern of CGRP inhibition.

Experimental approach:

We used two rat blood flow models that measure electrically stimulated vasodilatation in the skin or in the middle meningeal artery (MMA). These vasomotor responses are largely dependent on the neurogenic release of CGRP from sensory afferents. To assess cardiovascular function during chronic systemic anti-CGRP antibody treatment, we measured heart rate and blood pressure in conscious rats.

Key results:

Treatment with anti-CGRP antibodies inhibited skin vasodilatation or the increase in MMA diameter to a similar magnitude as treatment with CGRP receptor antagonists. Although CGRP antibody treatment had a slower onset of action than the CGRP receptor antagonists, the inhibition was still evident 1 week after dosing. Chronic treatment with anti-CGRP antibodies had no detectable effects on heart rate or blood pressure.

Conclusions and implications:

We showed for the first time that anti-CGRP antibodies exert a long lasting inhibition of neurogenic vasodilatation in two different rat models of arterial blood flow. We have provided strong preclinical evidence that anti-CGRP antibody may be a suitable drug candidate for the preventive treatment of migraine.     

Quercetin and its major metabolites selectively modulate cyclic GMP-dependent relaxations and associated tolerance in pig isolated coronary artery

Background and purpose:

Quercetin is a major flavonoid that contributes to the reduced risk of cardiovascular disease associated with dietary ingestion of fruits and vegetables. We have pharmacologically characterized the effect of quercetin, and its sulphate and glucuronide metabolites, on vasoconstrictor and vasodilator responses in the porcine isolated coronary artery.

Experimental approach:

Segments of the porcine coronary artery were prepared for either isometric tension recording or determination of cyclic GMP content. The effect of quercetin and metabolites on submaximal responses to U46619 was examined in the presence and absence of substance P, bradykinin, forskolin, sodium nitroprusside (SNP) and glyceryl trinitrate (GTN).

Key results:

Quercetin and quercetin 3′-sulphate inhibited endothelin and U46619-induced contractions with greater potency (three- to fivefold) against the former, while quercetin 3-glucoronide was inactive. Quercetin enhanced both the cyclic GMP content of the artery (threefold) and cyclic GMP-dependent relaxations to GTN and SNP (two to threefold), but forskolin-induced relaxations were unaffected. Although the effect of quercetin was qualitatively similar to that noted for UK-114,542, a selective inhibitor of phosphodiesterase 5, it was still evident against SNP-induced relaxations in the presence of 10 nM UK-114,542. Quercetin and quercetin 3′-sulphate significantly reduced the development of GTN-associated ‘tolerance’.

Conclusions and implications:

Quercetin and quercetin 3′-sulphate inhibited receptor-mediated contractions of the porcine isolated coronary artery by an endothelium-independent action. Quercetin selectively enhanced cyclic-GMP-dependent relaxations by a mechanism not involving phosphodiesterase 5 inhibition. In addition, quercetin and quercetin 3′-sulphate opposed GTN-induced tolerance in vitro, which may be beneficial for patients treated for angina pectoris.     

Tissue-specific up-regulation of arginase I and II induced by p38 MAPK mediates endothelial dysfunction in type 1 diabetes mellitus

Background and Purpose

Emerging evidence suggests a selective up-regulation of arginase I in diabetes causing coronary artery disease; however, the mechanisms behind this up-regulation are still unknown. Activated p38 MAPK has been reported to increase arginase II in various cardiovascular diseases. We therefore tested the role of p38 MAPK in the regulation of arginase I and II expression and its effect on endothelial dysfunction in diabetes mellitus.

Experimental Approach

Endothelial function was determined in septal coronary (SCA), left anterior descending coronary (LAD) and mesenteric (MA) arteries from healthy and streptozotocin-induced diabetic Wistar rats by wire myographs. Arginase activity and protein levels of arginase I, II, phospho-p38 MAPK and phospho-endothelial NOS (eNOS) (Ser¹¹⁷⁷) were determined in these arteries from diabetic and healthy rats treated with a p38 MAPK inhibitor in vivo.

Key Results

Diabetic SCA and MA displayed impaired endothelium-dependent relaxation, which was prevented by arginase and p38 MAPK inhibition while LAD relaxation was not affected. Arginase I, phospho-p38 MAPK and eNOS protein expression was increased in diabetic coronary arteries. In diabetic MA, however, increased expression of arginase II and phospho-p38 MAPK, increased arginase activity and decreased expression of eNOS were observed. All these effects were reversed by p38 MAPK inhibition.

Conclusions and Implications

Diabetes-induced activation of p38 MAPK causes endothelial dysfunction via selective up-regulation of arginase I expression in coronary arteries and arginase II expression in MA. Therefore, regional differences appear to exist in the arginase isoforms contributing to endothelial dysfunction in type 1 diabetes mellitus.     

Structural apelin analogues: mitochondrial ROS inhibition and cardiometabolic protection in myocardial ischaemia reperfusion injury

Background and Purpose

Mitochondria-derived oxidative stress is believed to be crucially involved in cardiac ischaemia reperfusion (I/R) injury, although currently no therapies exist that specifically target mitochondrial reactive oxygen species (ROS) production. The present study was designed to evaluate the potential effects of the structural analogues of apelin-12, an adipocyte-derived peptide, on mitochondrial ROS generation, cardiomyocyte apoptosis, and metabolic and functional recovery to myocardial I/R injury.

Experimental Approach

In cultured H9C2 cardiomyoblasts and adult cardiomyocytes, oxidative stress was induced by hypoxia reoxygenation. Isolated rat hearts were subjected to 35 min of global ischaemia and 30 min of reperfusion. Apelin-12, apelin-13 and structural apelin-12 analogues, AI and AII, were infused during 5 min prior to ischaemia.

Key Results

In cardiac cells, mitochondrial ROS production was inhibited by the structural analogues of apelin, AI and AII, in comparison with the natural peptides, apelin-12 and apelin-13. Treatment of cardiomyocytes with AI and AII decreased cell apoptosis concentration-dependently. In a rat model of I/R injury, pre-ischaemic infusion of AI and AII markedly reduced ROS formation in the myocardial effluent and attenuated cell membrane damage. Prevention of oxidative damage by AI and AII was associated with the improvement of functional and metabolic recovery after I/R in the heart.

Conclusions and Implications

These data provide the evidence for the potential of the structural apelin analogues in selective reduction of mitochondrial ROS generation and myocardial apoptosis and form the basis for a promising therapeutic strategy in the treatment of oxidative stress-related heart disease.     

Plasma ghrelin levels are closely associated with severity and morphology of angiographically-detected coronary atherosclerosis in Chineses patients with diabetes mellitus

Aim:

Low plasma ghrelin level was found to be associated with diabetes, and ghrelin was shown to inhibit pro-atherogenic changes in experimental models of atherosclerosis. The aim of this study was to investigate the relationship between plasma ghrelin levels and coronary atherosclerotic lesions in Chinese patients with diabetes.

Methods:

Plasma ghrelin levels were measured using an ELISA kit. The severity of coronary artery disease (CAD) was determined via angiography. Composition of atherosclerotic plaques was detected via coronary CT angiography.

Results:

A total of 178 patients with diabetes were recruited. Among the patients, 70 were diagnosed with acute coronary syndrome (ACS), 82 with stable angina pectoris (SAP) and 26 without coronary angiographic finding (controls). A negative correlation was found between ghrelin levels and the severity of the CAD, as determined via the Gensini score (r=-0.2434; P=0.0217). In diabetic patients with CAD and a complex lesion, the plasma ghrelin levels were significantly lower than in those with a simple lesion (ACS group: 3.81±0.49 ng/mL vs 4.72±0.50 ng/mL, P<0.0001; SAP group: 4.21±0.52 ng/mL vs 4.76±0.59 ng/mL, P=0.0397). Angiographically-detected complex lesion was an independent factor associated with ghrelin levels (adjusted beta coefficient=-0.67, 95% CI -0.97 to -0.37, P<0.0001).

Conclusion:

Low plasma ghrelin level is closely related to angiographically-detected severity and the complex lesion morphology in Chinese diabetic patients with CAD.     

PAK1‐cofilin phosphorylation mediates human lung adenocarcinoma cells migration induced by apelin‐13

Adipocytokines apelin peptide, the ligand of APJ (putative receptor related to the angiotensin receptor AT₁), plays key roles in the pathogenesis and deterioration of cancer. In lung cancer, apelin elevating microvessel densities has been reported. Our previous research has characterized that apelin‐13 promoted lung adenocarcinoma cell proliferation. However, the effect of apelin on metastasis in lung adenocarcinoma and the underlying mechanisms remain unclear. This study shows that apelin‐13 induced human adenocarcinoma cell migration via the APJ receptor. Apelin‐13 phosphorylated PAK1 and cofilin increase the migration of lung adenocarcinoma cells. Moreover, the results verify that over‐exprssion of apelin and APJ contributed to reducing the effect of doxorubicin and razoxane on inhibiting lung adenocarcinoma cells metastasis. Hypoxia activated APJ expression and apelin release in lung adenocarcinoma cells. The results demonstrate a PAK1‐cofilin phosphorylation mechanism to mediate lung adenocarcinoma cells migration promoted by apelin‐13. This discovery further suggests that APJ and its downstream signalling is a potential target for anti‐metastatic therapies in lung adenocarcinoma patients.     

Cannabinoid-1 receptor activation induces reactive oxygen species-dependent and -independent mitogen-activated protein kinase activation and cell death in human coronary artery endothelial cells

Background and purpose:

Impaired endothelial activity and/or cell death play a critical role in the development of vascular dysfunction associated with congestive heart failure, diabetic complications, hypertension, coronary artery disease and atherosclerosis. Increasing evidence suggests that cannabinoid 1 (CB₁) receptor inhibition is beneficial in atherosclerosis and cardiovascular inflammation both in experimental models, as well as in humans. Here, we investigated the effects of CB₁ receptor activation with the endocannabinoid anandamide (AEA) or synthetic agonist HU210 on cell death and interrelated signal transduction pathways in human primary coronary artery endothelial cells (HCAECs).

Experimental approach:

Cell death, CB₁ receptor expression, reactive oxygen species (ROS) generation and activation of signal transduction pathways in HCAECs were determined by flow cytometry and molecular biology tools.

Key results:

In HCAECs expressing CB₁ receptors (demonstrated by Western immunoblot and flow cytometry) AEA (5–15 µM) or HU210 (30–1000 nM) triggered concentration- and time-dependent activation of p38 and c-Jun NH₂-terminal protein kinase (JNK)–mitogen-activated protein kinases (MAPKs), cell death and ROS generation. The AEA- or HU210-induced cell death and MAPK activation were attenuated by CB₁ antagonists [SR141716 (rimonabant) and AM281], inhibitors of p38 and JNK–MAPKs or the antioxidant N-acetylcysteine. N-acetylcysteine alone prevented AEA- or HU210-induced ROS generation, but only partially attenuated MAPK activation and cell death. In contrast, in combination with CB₁ antagonists, N-acetylcysteine completely prevented these effects.

Conclusions and implications:

CB₁ receptor activation in endothelial cells may amplify the ROS–MAPK activation–cell death pathway in pathological conditions when the endocannabinoid synthetic or metabolic pathways are dysregulated by excessive inflammation and/or oxidative/nitrosative stress, thereby contributing to the development of endothelial dysfunction and pathophysiology of multiple cardiovascular diseases.This article is part of a themed issue on Cannabinoids. To view the editorial for this themed issue visit http://dx.doi.org/10.1111/j.1476-5381.2010.00831.x     

Serelaxin-mediated signal transduction in human vascular cells: bell-shaped concentration–response curves reflect differential coupling to G proteins

Background and Purpose

In a recently conducted phase III clinical trial, RELAX-AHF, serelaxin infusion over 48 h improved short- and long-term clinical outcomes in patients with acute heart failure. In this study we used human primary cells from the umbilical vasculature to better understand the signalling mechanisms activated by serelaxin.

Experimental Approach

We examined the acute effects of serelaxin on signal transduction mechanisms in primary human umbilical vascular cells and its chronic actions on markers of cardiovascular function and disease.

Key Results

The RXFP1 receptor, the cognate serelaxin receptor, was expressed at the cell surface in HUVECs and human umbilical vein smooth muscle cells (HUVSMCs), human umbilical artery smooth muscle cells (HUASMCs) and human cardiac fibroblasts (HCFs), but not human umbilical artery endothelial cells. In HUVECs and HUVSMCs, serelaxin increased cAMP, cGMP accumulation and pERK1/2, and the concentration–response curves (CRCs) were bell-shaped. Similar bell-shaped CRCs for cGMP and pERK1/2 were observed in HCFs, whereas in HUASMCs, serelaxin increased cAMP, cGMP and pERK1/2 with sigmoidal CRCs. Gα_i/o and lipid raft disruption, but not Gα_s inhibition, altered the serelaxin CRC for cAMP and cGMP accumulation in HUVSMC but not HUASMC. Longer term serelaxin exposure increased the expression of neuronal NOS, VEGF, ET_β receptors and MMPs (gelatinases) in RXFP1 receptor-expressing cells.

Conclusions and Implications

Serelaxin caused acute and chronic changes in human umbilical vascular cells that were cell background dependent. Bell-shaped CRCs that were observed only in venous cells and fibroblasts involved Gα_i/o located within membrane lipid rafts.     

Role of the signal peptide in the synthesis and processing of the glucagon-like peptide-1 receptor

Background and purpose:

The glucagon-like peptide-1 receptor (GLP-1R) belongs to Family B of the G protein-coupled receptor superfamily and is a target for treatment of type 2 diabetes. Family B G protein-coupled receptors contain a putative N-terminal signal peptide, but its role in receptor synthesis and trafficking are unclear. Further, the signal peptide is not cleaved in at least one family member.

Experimental approach:

We examined receptor glycosylation and the role of the signal peptide in GLP-1R synthesis and trafficking using constructs containing epitope tags at the N- and/or C-terminus and in which the signal peptide sequence was either present or absent.

Key results:

The signal peptide was absolutely required for GLP-1R synthesis but could be substituted to some extent by increasing positive charge in the N-terminal region of the receptor flanking the signal peptide. The signal peptide is cleaved during synthesis and processing of the receptor. An enhanced GFP-epitope tag at the N-terminus of the receptor permitted synthesis of the receptor but blocked signal peptide cleavage and prevented trafficking to the plasma membrane. Cleavage site mutation allowed synthesis of a full-length receptor, blocked signal peptide cleavage and caused retention within the endoplasmic reticulum.

Conclusions and implications:

Signal peptide cleavage was not essential for receptor synthesis but was obligatory for processing and trafficking of receptors to the plasma membrane. Further, the GLP-1R is subject to N-linked glycosylation and only the mature, fully glycosylated form of the receptor is present in the plasma membrane. Inhibition of glycosylation prevents processing and cell surface expression of the GLP-1R.     

The apelinergic system: a promising therapeutic target

Importance of the field: Apelin is a bioactive peptide known as the ligand of the G-protein-coupled receptor APJ. In recent years, there has been a growing body of evidence regarding the importance of apelin and APJ in the pathophysiology of cardiovascular, metabolic and gastrointestinal diseases, brain signalling, HIV infection and tumor angiogenesis. Therefore, the apelinergic system is involved in the pathogenesis of several diseases that represent a major burden to our society.

Areas covered in this review: The goal of this paper is to give an up-to-date review of existing information on apelin/APJ since the discovery of apelin in 1998, with particular focus on their involvement in the regulation of human body systems and potential therapeutic applications.

What the reader will gain: An overview of the most important physiological functions of the apelinergic system and the diseases that may benefit in the future from its modulation as a therapeutic target.

Take home message: Today, the established biological effects of apelin involve major cardiovascular actions, neoangiogenesis, immunologic modulation and insulinemia control as well as body fluid and glucose homeostasis. However, the physiological and pathophysiological role of endogenous apelin is still unsettled and a better and profound knowledge of this system in humans is necessary for the development of novel apelinergic-based therapeutic targets.     

Resistance to endotoxic shock in mice lacking natriuretic peptide receptor-A

Background and purpose:

Excessive production of nitric oxide (NO) by inducible NO synthase (iNOS) is thought to underlie the vascular dysfunction, systemic hypotension and organ failure that characterize endotoxic shock. Plasma levels of atrial natriuretic peptide (ANP), brain natriuretic peptide (BNP) and C-type natriuretic peptide (CNP) are raised in animal models and humans with endotoxic shock and correlate with the associated cardiovascular dysfunction. Since both NO and natriuretic peptides play important roles in cardiovascular homeostasis via activation of guanylate cyclase-linked receptors, we used mice lacking natriuretic peptide receptor (NPR)-A (NPR1) to establish if natriuretic peptides contribute to the cardiovascular dysfunction present in endotoxic shock.

Experimental approach:

Wild-type (WT) and NPR-A knockout (KO) mice were exposed to lipopolysaccharide (LPS) and vascular dysfunction (in vitro and in vivo), production of pro-inflammatory cytokines, and iNOS expression and activity were evaluated.

Key results:

LPS-treated WT animals exhibited a marked fall in mean arterial blood pressure (MABP) whereas NPR-A KO mice maintained MABP throughout. LPS administration caused a greater suppression of vascular responses to the thromboxane-mimetic U46619, ANP, acetylcholine and the NO-donor spermine-NONOate in WT versus NPR-A KO mice. This differential effect on vascular function was paralleled by reduced pro-inflammatory cytokine production, iNOS expression and activity (plasma [NO_x] and cyclic GMP).

Conclusions and implications:

These observations suggest that NPR-A activation by natriuretic peptides facilitates iNOS expression and contributes to the vascular dysfunction characteristic of endotoxic shock. Pharmacological interventions that target the natriuretic peptide system may represent a novel approach to treat this life-threatening condition.     

Adherence to statin or aspirin or both in patients with established cardiovascular disease: exploring healthy behaviour vs. drug effects and 10-year follow-up of outcome

Aims

To characterize adherence in patients with established cardiovascular disease taking statins and aspirin and to estimate the effects of adherence due to health behaviour, a lack of beneficial drug effect, or both on recurrence of cardiovascular disease or all-cause mortality over 10 years.

Methods

A population-based cohort study using a record-linkage database in Tayside, Scotland. Subjects with cardiovascular disease (n = 7657; 4185 aspirin-alone cohort, 671 statin-alone cohort and 2801 combination use cohort) were studied between 1993 and 2003. The effects of adherence on recurrence of cardiovascular disease or mortality were assessed using Poisson regression model.

Results

In subjects taking both aspirin and statins, those adherent to statins but not aspirin had a lower risk of recurrence [adjusted risk ratio (RR) 0.64; 95% confidence interval 0.49, 0.82], but those adherent to aspirin but not statins has no such effect (adjusted RR 0.91; 0.72, 1.15), suggesting that adherence behaviour alone was not responsible for the beneficial effect. Within the group adherent to aspirin, ≥80% adherence to statins was associated with reduced recurrence compared with those poorly adherent (adjusted RR 0.76; 0.62, 0.94), but no such effect of aspirin was seen in those adherent to statins. Similar results were found for all-cause mortality.

Conclusions

Poor health behaviour is not a sufficient explanation of adverse outcome in poorly adherent patients. Adverse outcome is more likely to be driven by foregone drug benefits.

WHAT IS ALREADY KNOWN ABOUT THIS SUBJECT

• Aspirin and statins are widely-used drugs in patients with cardiovascular disease.
• There is less information on healthy behaviour vs. drug effects.

WHAT THIS STUDY ADDS

• Long-term adherence to aspirin and statin treatments in patients with established cardiovascular disease has been investigated.
• Poor health behaviour is not a sufficient explanation of adverse outcome in poorly adherent patients.

     

P2Y12 polymorphisms and antiplatelet effects of aspirin in patients with coronary artery disease

Aims

Recently, two genetic polymorphisms of the platelet ADP receptor P2Y₁₂ (haplotypes H2 and 34T) have been implicated in increased platelet aggregation and atherothrombotic risk. It was suggested that these polymorphisms contribute to a diminished response to antiplatelet drugs. Therefore, we investigated the effects of these polymorphisms on platelet aggregation in aspirin-treated patients with coronary artery disease (CAD).

Methods

Platelet aggregation was studied in platelet-rich plasma from 124 patients with CAD treated with 100 mg aspirin day⁻¹. P2Y₁₂ ADP receptor polymorphisms were determined by PCR-RFLP. The 52G > T polymorphism was used as tag-SNP for the H2 haplotype. Aggregation was induced by 1 mg l⁻¹ collagen. In a subgroup (n = 72), a concentration-response curve to collagen (0.5–10 mg l⁻¹), aggregation at 2 μmol l⁻¹ ADP and 1 mmol l⁻¹ arachidonic acid were determined.

Results

Whereas arachidonic acid-induced aggregation was inhibited in all patients, collagen and ADP-induced aggregation were highly variable. However, aggregation did not differ significantly between carriers and noncarriers of the 52T-allele (1 mg l⁻¹ collagen: 32.7% (21.9–38.6%) vs. 32.5% (21.2–41.6%); P = 0.77; ADP: 33.1% (29.9–40.9%) vs. 39.1% (31.5–49.7%); P = 0.34), respectively. EC₅₀ values were 1.26 mg l⁻¹ (0.79–2.02) and 1.54 mg l⁻¹ (0.98–2.4) collagen in noncarriers and carriers of the H2 haplotype, respectively (P = 0.56). Moreover, the 34°C > T polymorphism did not significantly affect any of the aggregatory responses.

Conclusions

Low-dose aspirin inhibits platelet aggregation to the same extent in patients carrying or not carrying the P2Y₁₂ H2 haplotype and/or the 34T allele. Our data do not support the hypothesis that these polymorphisms contribute to an attenuated antiplatelet effect of aspirin.

What is already known about this subject

• Genetic polymorphisms of the P2Y₁₂ ADP receptor on platelets have been shown to contribute to variability in platelet aggregation in healthy humans.
• P2Y₁₂ ADP receptor polymorphisms are more frequently present in patients with vascular disease than in healthy people.
• The majority of patients with vascular disease receive acetylsalicylic acid as an anti-aggregatory agent, which has also been shown to induce a variable response; however, the role of P2Y₁₂ ADP receptor polymorphisms in the platelet response to acetylsalicylic acid in patients with vascular disease has not yet been studied.

What this study adds

• The present data show that the platelet response to acetylsalicylic acid is independent of the presence or absence of P2Y₁₂ ADP receptor polymorphisms in patients with stable coronary artery disease who have had their first myocardial infarction.
• This is important, as studies in healthy humans had suggested that carriers of P2Y₁₂ ADP receptor polymorphisms may be at increased risk of experiencing cardiovascular events.
• However, the observed variability of the platelet response to the cyclooxygenase inhibitor acetylsalicylic acid (in our study) and to the P2Y₁₂ ADP receptor blocker clopidogrel (in a study by Angiolillo et al.[18]) in patients with coronary artery disease is clearly not determined by common P2Y₁₂ ADP receptor polymorphisms.