Role of cyclooxygenase in ventricular effects of adrenomedullin: is adrenomedullin a double-edged sword in sepsis?

MECHANISMS OF CARDIAC DYSFUNCTION IN SEPSIS

ABSTRACT

Studies in animal models of sepsis have elucidated an intricate network of signaling pathways that lead to the dysregulation of myocardial Ca 2+ handling and subsequently to a decrease in cardiac contractile force, in a sex- and model-dependent manner. After challenge with a lethal dose of LPS, male animals show a decrease in cellular Ca 2+ transients (ΔCa i ), with intact myofilament function, whereas female animals show myofilament dysfunction, with intact ΔCa i . Male mice challenged with a low, nonlethal dose of LPS also develop myofilament desensitization, with intact ΔCa i . In the cecal ligation and puncture (CLP) model, the causative mechanisms seem similar to those in the LPS model in male mice and are unknown in female subjects. ΔCa i decrease in male mice is primarily due to redox-dependent inhibition of sarco/endoplasmic reticulum Ca 2+ ATP-ase (SERCA). Reactive oxygen species (ROS) are overproduced by dysregulated mitochondria and the enzymes NADPH/NADH oxidase, cyclooxygenase, and xanthine oxidase. In addition to inhibiting SERCA, ROS amplify cardiomyocyte cytokine production and mitochondrial dysfunction, making the process self-propagating. In contrast, female animals may exhibit a natural redox resilience. Myofilament dysfunction is due to hyperphosphorylation of troponin I, troponin T cleavage by caspase-3, and overproduction of cGMP by NO-activated soluble guanylate cyclase. Depleted, dysfunctional, or uncoupled mitochondria likely synthesize less ATP in both sexes, but the role of energy deficit is not clear. NO produced by NO synthase (NOS)-3 and mitochondrial NOSs, protein kinases and phosphatases, the processes of autophagy and sarco/endoplasmic reticulum stress, and β-adrenergic insensitivity may also play currently uncertain roles.

Effects of Adrenomedullin on Atrial Electrophysiology and Pulmonary Vein Arrhythmogenesis

Adrenomedullin, a peptide with vasodilatory, natriuretic, and diuretic effects, may be a novel agent for treating heart failure. Heart failure is associated with an increased risk of atrial fibrillation (AF), but the effects of adrenomedullin on atrial arrhythmogenesis remain unclear. This study investigated whether adrenomedullin modulates the electrophysiology of the atria (AF substrate) or pulmonary vein (PV; AF trigger) arrhythmogenesis. Conventional microelectrode or whole-cell patch clamps were used to study the effects of adrenomedullin (10, 30, and 100 pg/mL) on the electrical activity, mechanical response, and ionic currents of isolated rabbit PV and sinoatrial node tissue preparations and single PV cardiomyocytes. At 30 and 100 pg/mL, adrenomedullin significantly reduced the spontaneous beating rate of the PVs from 2.0 ± 0.4 to 1.3 ± 0.5 and 1.1 ± 0.5 Hz (reductions of 32.9% ± 7.1% and 44.9 ± 8.4%), respectively, and reduced PV diastolic tension by 12.8% ± 4.1% and 14.5% ± 4.1%, respectively. By contrast, adrenomedullin did not affect sinoatrial node beating. In the presence of L-NAME (a nitric oxide synthesis inhibitor, 100 μM), adrenomedullin (30 pg/mL) did not affect the spontaneous beating rate or diastolic tension of the PVs. In the single-cell experiments, adrenomedullin (30 pg/mL) significantly reduced the L-type calcium current (I_Ca-L) and reverse-mode current of the sodium-calcium exchanger (NCX). Adrenomedullin reduces spontaneous PV activity and PV diastolic tension by reducing I_Ca-L and NCX current and thus may be useful for treating atrial tachyarrhythmia.

Adrecizumab: an investigational agent for the biomarker-guided treatment of sepsis

Introduction: Sepsis is a major health problem with a high incidence and mortality. ADM, a free-circulating peptide mainly expressed and secreted by vascular endothelial cells, shows vasodilatory properties and causes hypotension when present in higher concentrations during sepsis. Areas covered: Adrecizumab (ADZ) (HAM 8101) is a humanized targeted therapy directed against the N-terminus of adrenomedullin (ADM). ADZ inhibits excessive circulating sepsis-induced ADM and stimulates protective effects on the endothelial barrier, and decreases interstitial vasodilatory effects. ADZ demonstrated a promising safety profile in healthy subjects in phase I studies. According to these results, a phase II proof of concept study enrolling 300 septic patients is currently in course (NCT03085758). Expert opinion: ADZ is the first humanized antibody directed against ADM. The main interest of ADZ is its potential use as a 'biomarker-guided therapy' in septic patients with high circulating ADM. ADZ is increasingly seen as a potential adjunct therapy to restore endothelial function in septic shock. A positive pivotal phase III trial is indeed needed to convince the intensive care community to prescribe ADZ in septic shock patients. Further, it would be of interest to see whether ADZ might also benefit other critical diseases such as cardiogenic shock where endothelial dysfunction has also been described.

Adrenomedullin and Adrenomedullin-Targeted Therapy As Treatment Strategies Relevant for Sepsis

Sepsis remains a major medical challenge, for which, apart from improvements in supportive care, treatment has not relevantly changed over the last few decades. Vasodilation and vascular leakage play a pivotal role in the development of septic shock, with vascular leakage being caused by disrupted endothelial integrity. Adrenomedullin (ADM), a free circulating peptide involved in regulation of endothelial barrier function and vascular tone, is implicated in the pathophysiology of sepsis. ADM levels are increased during sepsis, and correlate with extent of vasodilation, as well as with disease severity and mortality. In vitro and preclinical in vivo data show that administration of ADM exerts anti-inflammatory, antimicrobial, and protective effects on endothelial barrier function during sepsis, but other work suggests that it may also decrease blood pressure, which could be detrimental for patients with septic shock. Work has been carried out to negate ADMs putative negative effects, while preserving or even potentiating its beneficial actions. Preclinical studies have demonstrated that the use of antibodies that bind to the N-terminus of ADM results in an overall increase of circulating ADM levels and improves sepsis outcome. Similar beneficial effects were obtained using coadministration of ADM and ADM-binding protein-1. It is hypothesized that the mechanism behind the beneficial effects of ADM binding involves prolongation of its half-life and a shift of ADM from the interstitium to the circulation. This in turn results in increased ADM activity in the blood compartment, where it exerts beneficial endothelial barrier-stabilizing effects, whereas its detrimental vasodilatory effects in the interstitium are reduced. Up till now, in vivo data on ADM-targeted treatments in humans are lacking; however, the first study in septic patients with an N-terminus antibody (Adrecizumab) is currently being conducted.

Dysregulation of intracellular calcium transporters in animal models of sepsis-induced cardiomyopathy

Sepsis-induced cardiomyopathy (SIC) develops as the result of myocardial calcium (Ca) dysregulation. Here we reviewed all published studies that quantified the dysfunction of intracellular Ca transporters and the myofilaments in animal models of SIC. Cardiomyocytes isolated from septic animals showed, invariably, a decreased twitch amplitude, which is frequently caused by a decrease in the amplitude of cellular Ca transients (ΔCai) and sarcoplasmic reticulum (SR) Ca load (CaSR). Underlying these deficits, the L-type Ca channel is downregulated, through mechanisms that may involve adrenomedullin-mediated redox signaling. The SR Ca pump is also inhibited, through oxidative modifications (sulfonylation) of one reactive thiol group (on Cys) and/or modulation of phospholamban. Diastolic Ca leak of ryanodine receptors is frequently increased. In contrast, Na/Ca exchange inhibition may play a partially compensatory role by increasing CaSR and ΔCai. The action potential is usually shortened. Myofilaments show a bidirectional regulation, with decreased Ca sensitivity in milder forms of disease (due to troponin I hyperphosphorylation) and an increase (redox mediated) in more severe forms. Most deficits occurred similarly in two different disease models, induced by either intraperitoneal administration of bacterial lipopolysaccharide or cecal ligation and puncture. In conclusion, substantial cumulative evidence implicates various Ca transporters and the myofilaments in SIC pathology. What is less clear, however, are the identity and interplay of the signaling pathways that are responsible for Ca transporters dysfunction. With few exceptions, all studies we found used solely male animals. Identifying sex differences in Ca dysregulation in SIC becomes, therefore, another priority.

Lipopolysaccharide and cytokines inhibit rat cardiomyocyte contractility in vitro

BACKGROUND

Sepsis-induced cardiomyopathy (SIC) is thought to be the result of detrimental effects of inflammatory mediators on the cardiac muscle. Here we studied the effects of prolonged (24 ± 4 h) exposure of adult rat ventricular myocytes (ARVM) to bacterial lipopolysaccharide (LPS) and inflammatory cytokines tumor necrosis factor (TNF) and interleukins-1 (IL-1) and IL-6.

MATERIALS AND METHODS

We measured sarcomere shortening (SS) and cellular calcium (Ca(2+)) transients (ΔCai, with fura-2 AM) in isolated cardiomyocytes externally paced at 5 Hz at 37°C.

RESULTS

SS decreased after incubation with LPS (100 μg/mL), IL-1 (100 ng/mL), and IL-6 (30 ng/mL), but not with lesser doses of these mediators, or TNF (10-100 ng/mL). A combination of LPS (100 μg/mL), TNF, IL-1, and IL-6 (each 100 ng/mL; i.e., "Cytomix-100") induced a maximal decrease in SS and ΔCai. Sarcoplasmic reticulum (SR) Ca(2+) load (CaSR, measured with caffeine) was unchanged by Cytomix-100; however, SR fractional release (ΔCai/CaSR) was decreased. Underlying these effects, Ca(2+) influx into the cell (via L-type Ca(2+) channels, LTCC) and Ca(2+) extrusion via Na(+)/Ca(2+) exchange were decreased by Cytomix-100. SR Ca(2+) pump (SERCA) (SR Ca(2+) ATPase) was not affected.

CONCLUSIONS

Prolonged exposure of ARVM to a mixture of LPS and inflammatory cytokines inhibits cell contractility. The effect is mediated by the inhibition of Ca(2+) influx via LTCC, and partially opposed by the inhibition of Na(+)/Ca(2+) exchange. Because both mechanisms are commonly seen in animal models of SIC, we conclude that prolonged challenge with Cytomix-100 of ARVM may represent an accurate in vitro model for SIC.

Epitope specificity of anti-Adrenomedullin antibodies determines efficacy of mortality reduction in a cecal ligation and puncture mouse model

Introduction

Adrenomedullin (ADM), a circulating vasodilatory peptide, plays an important role in the development of sepsis-associated hemodynamic and microcirculatory disorders. While administration of exogenous ADM had beneficial effects in several septic animal models, elevated ADM concentrations are associated with a bad outcome. This prompted us to test the effect of various anti-ADM antibodies in a cecal ligation and puncture (CLP) mouse model.

Methods

To gain new potential compounds for the treatment or prevention of septic shock we followed an alternative strategy to influence the ADM system: High-affinity anti-ADM antibodies with different epitope specificities were developed and their antagonist activity in vitro and their ability to reduce mortality in a CLP mouse model were assessed.

Results

An anti-ADM antibody directed against the N-terminus substantially increased the survival of mice in a CLP model (HR = 0.077 (CI = 0.0189 to 0.315), p = 0.0004), whereas other antibodies with similar affinities but different epitope specificities were much less potent. The efficacious antibody, in contrast to an anti-C-terminal antibody, only partially inhibited ADM agonist activity in vitro. Healthy mice were not negatively affected by the N-terminal antibody.

Conclusions

An anti-N-terminal ADM antibody, as opposed to antibodies with other epitope specificities, strongly reduces mortality in CLP mice.

Electronic supplementary material

The online version of this article (doi:10.1186/2197-425X-1-3) contains supplementary material, which is available to authorized users.

Adrenomedullin binding improves catecholamine responsiveness and kidney function in resuscitated murine septic shock

Purpose

Adrenomedullin (ADM) has been referred to as a double-edged sword during septic shock: On one hand, ADM supplementation improved organ perfusion and function, attenuated systemic inflammation, and ultimately reduced tissue apoptosis and mortality. On the other hand, ADM overproduction can cause circulatory collapse and organ failure due to impaired vasoconstrictor response and reduced myocardial contractility. Since most of these data originate from un-resuscitated shock models, we tested the hypothesis whether the newly developed anti-ADM antibody HAM1101 may improve catecholamine responsiveness and thus attenuate organ dysfunction during resuscitated murine, cecal ligation and puncture (CLP)-induced septic shock.

Methods

Immediately after CLP, mice randomly received vehicle (phosphate-buffered saline, n = 11) or HAM1101 (n = 9; 2 μg·g⁻¹). Fifteen hours after CLP, animals were anesthetized, mechanically ventilated, instrumented, and resuscitated with hydroxyethylstarch and continuous i.v. norepinephrine to achieve normotensive hemodynamics (mean arterial pressure > 50 to 60 mmHg).

Results

HAM1101 pretreatment reduced the norepinephrine infusion rates required to achieve hemodynamic targets, increased urine flow, improved creatinine clearance, and lowered neutrophil gelatinase-associated lipocalin blood levels, which coincided with reduced expression of the inducible nitric oxide synthase and formation of peroxynitrite (nitrotyrosine immunostaining) in the kidney and aorta, ultimately resulting in attenuated systemic inflammation and tissue apoptosis.

Conclusions

During resuscitated murine septic shock, early ADM binding with HAM1101 improved catecholamine responsiveness, blunted the shock-related impairment of energy metabolism, reduced nitrosative stress, and attenuated systemic inflammatory response, which was ultimately associated with reduced kidney dysfunction and organ injury.

Electronic supplementary material

The online version of this article (doi:10.1186/2197-425X-1-2) contains supplementary material, which is available to authorized users.

Relationship between vascular reactivity and expression of HMGB1 in a rat model of septic aorta

Intruoduction

High mobility group box 1 (HMGB1), a ubiquitous nuclear protein, induces several inflammatory diseases and functions as a fatal factor when released extracellularly. The effect of HMGB1 on vascular reactivity during sepsis remains to be clarified.

Methods

A rat model of abdominal sepsis was produced by cecal ligation and puncture (CLP) under sevoflurane anesthesia (n = 28). Anti-HMGB1 antibody at a dose of 4 or 0.4 mg/kg, or normal saline was injected twice intravenously, i.e., immediately after the CLP surgery and 4 h thereafter. Rats in the sham group underwent laparotomy, and the cecum was manipulated but not ligated or punctured. The descending thoracic aorta was excised 12 h after the CLP surgery and cut into rings of approximately 3 mm in length. Changes in the expression of HMGB1 and vascular reactivity were examined in the rings shortly after harvest and 4 h thereafter.

Results

HMGB1 was identified immunohistochemically and by Western blotting in the nuclei of vascular endothelial and smooth muscle cells in all groups shortly after excision of the aorta, but its expression was augmented only in the CLP groups 4 h thereafter. Degenerated smooth muscle cells were also observed after CLP. Anti-HMGB1 antibody dose-dependently inhibited the augmentation of HMGB1 expression and the morphological changes induced by CLP. The expression of HMGB1 partly correlated with suppression of vascular reactivity.

Conclusion

The present results strongly suggest that HMGB1 plays an important role in vascular malfunction from an early phase of sepsis.

Contribution of vasoactive eicosanoids and nitric oxide production to the effect of selective cyclooxygenase-2 inhibitor, NS-398, on endotoxin-induced hypotension in rats

Our previous studies with the use of non-selective cyclooxygenase (COX) inhibitor, indomethacin, demonstrated that prostanoids produced during endotoxaemia increase inducible nitric oxide synthase (iNOS) protein expression and nitric oxide synthesis, and decrease cyctochrome P450 (CYP) 4A1 protein expression and CYP 4A activity. The results suggest that dual inhibition of iNOS and COX by indomethacin restores blood pressure presumably due to increased production of 20-hydroxyeicosatetraenoic acid (20-HETE) derived from CYP 4A in endotoxaemic rats. The present study examined whether increased levels of vasoconstrictor eicosanoids, 20-HETE, prostaglandin F(2α) (PGF(2α) )and thromboxane A(2) (TxA(2) ), would contribute to the effect of selective COX-2 inhibition to prevent endotoxin (ET)-induced fall in blood pressure associated with an increase in the production of vasodilator prostanoids, prostaglandin I(2) (PGI(2) ) and prostaglandin E(2) (PGE(2) ) and nitric oxide synthesis. Mean arterial blood pressure fell by 31 mmHg and heart rate (HR) rose by 90 beats/min. in male Wistar rats treated with ET (10 mg/kg, i.p.). The fall in mean arterial pressure and increase in HR were associated with increased levels of 6-keto-prostaglandin F(1α) (6-keto-PGF(1α) ), PGE(2) , TxB(2) , and nitrite in the serum, kidney, heart, thoracic aorta and/or superior mesenteric artery. Systemic and renal 20-HETE and PGF(2α) levels were also decreased in endotoxaemic rats. These effects of ET were prevented by a selective COX-2 inhibitor, N-(2-cyclohexyloxy-4-nitrophenyl)methansulphonamide (10 mg/kg, i.p.), given 1 hr after injection of ET. These data suggest that an increase in 20-HETE and PGF(2α) levels associated with decreased production of PGI(2) , PGE(2) , and TxA(2) , and nitric oxide synthesis contributes to the effect of selective COX-2 inhibitor to prevent the hypotension during rat endotoxaemia.

Activation of the PGI(2)/IP system contributes to the development of circulatory failure in a rat model of endotoxic shock

Prostacyclin levels are increased in septic patients and several animal models of septic shock, and selective inhibition of cyclooxygenase-2 improved cardiovascular dysfunction in rats treated with lipopolysaccharide (LPS). Here, we examine the specific role of prostacyclin and of the receptor for prostacyclin (IP) in the development of LPS-induced circulatory failure. Intravenous injection of LPS (10 mg/kg) into male Sprague-Dawley rats caused a strong increase in plasma prostacyclin levels, which was paralleled by a decrease in blood pressure and an increase in heart rate. Moreover, LPS injection increased the mRNA expression of the IP receptor in the heart, aorta, lung, liver, adrenal glands, and kidneys. Cotreatment with the IP antagonist CAY-10441 (1, 10, 30, and 100 mg/kg) dose-dependently moderated the LPS-induced changes in mean arterial blood pressure, heart rate, cardiac output, and systemic vascular resistance. The development of cardiovascular failure was ameliorated by CAY-10441 in spite of the typical LPS-induced increases in plasma levels of cytokines and NO. In vitro, cytokines dose- and time-dependently induced IP expression in rat vascular smooth muscle cells. Incubation of cells with the stable IP agonist iloprost in the presence of the phosphodiesterase inhibitor 3-isobutyl-1-mehylxanthine resulted in higher cAMP levels in cytokine-treated cells compared with untreated cells. Taken together, our data demonstrate a prominent role of the prostacyclin/IP system in the development of LPS-induced cardiovascular failure.

The effect of adrenomedullin on the L-type calcium current in myocytes from septic shock rats: signaling pathway

Adrenomedullin (ADM) is upregulated in cardiac tissue under various pathophysiological conditions, particularly in septic shock. The intracellular mechanisms involved in the effect of ADM on adult rat ventricular myocytes are still to be elucidated. Ventricular myocytes were isolated from adult rats 4 h after an intraperitoneal injection of lipopolysaccharide (LPS, 10 mg/kg). Membrane potential and L-type calcium current ( ICa,L) were determined using whole cell patch-clamp methods. APD in LPS group was significantly shorter than control values (time to 50% repolarization: LPS, 169 ± 2 ms; control, 257 ± 2 ms, P < 0.05; time to 90% repolarization: LPS, 220 ± 2 ms; control, 305 ± 2 ms, P < 0.05). ICa,Ldensity was significantly reduced in myocytes from the LPS group (−3.2 ± 0.8 pA/pF) compared with that of control myocytes (−6.7 ± 0.3 pA/pF, P < 0.05). The ADM antagonist ADM-(22-52) reversed the shortened APD and abolished the reduction of ICa,Lin shock myocytes. In myocytes from control rats, incubating with ADM for 1 h induced a marked decrease in peak ICa,Ldensity. This effect was reversed by ADM-(22-52). The Giprotein inhibitor, pertussis toxin (PTX), the protein kinase A (PKA) inhibitor, KT-5720, and the specific cyclooxygenase 2 (COX-2) inhibitor, nimesulide, reversed the LPS-induced reduction in peak ICa,L. The results suggest a COX-2-involved PKA-dependent switch from Gscoupled to PTX-sensitive Gicoupling by ADM in adult rat ventricular myocytes. The present study delineates the intracellular pathways involved in ADM-mediated effects on ICa,Lin adult rat ventricular myocytes and also suggests a role of ADM in sepsis.

Mice heterozygous for adrenomedullin exhibit a more extreme inflammatory response to endotoxin-induced septic shock

Adrenomedullin (AM) is a highly conserved peptide that can act as a potent vasodilator, anti-microbial factor and anti-inflammatory factor. Several studies have implicated diverse roles for AM in regulating the inflammatory and hemodynamic responses to septic shock. Moreover, during sepsis the receptors that mediate AM signaling [calcitonin receptor-like receptor (calcrl) and receptor activity modifying proteins (RAMP) 2 and 3] undergo dynamic and robust changes in their expression. Although numerous studies have used animal models to study the role of administered or increased AM in septic animals, genetic studies to determine the consequences of reduced AM during septic shock have not yet been performed. Here, we used a murine model of lipopolysaccharide (LPS)-induced septic shock to assess the inflammatory response in mice heterozygous for the AM gene. Following LPS challenge, AM(+/-) mice had higher expression of TNF-alpha and IL-1beta than LPS-treated wild-type (WT) controls. Consequently, serum TNF-alpha was also significantly elevated in LPS-treated AM(+/-) mice compared to WT LPS-treated mice. We also observed higher serum levels of liver enzymes, suggesting more advanced end-organ damage in mice with genetically reduced AM. Finally, we found that RAMP2 and calcrl expression levels were markedly reduced in LPS-treated mice, whereas RAMP3 expression was significantly elevated. Importantly, these changes in receptor gene expression were conserved in AM(+/-) mice, demonstrating that AM peptide itself does not impact directly on the expression of the genes encoding its receptors. We, therefore, conclude that during septic shock the dynamic modulation of AM and its receptors primarily functions to dampen the inflammatory response.

Atrial myocardium is the predominant inotropic target of adrenomedullin in the human heart

Adrenomedullin (ADM) is an endogenous peptide with favorable hemodynamic effects in vivo. In this study, we characterized the direct functional effects of ADM in isolated preparations from human atria and ventricles. In electrically stimulated human nonfailing right atrial trabeculae, ADM (0.0001–1 μmol/l) increased force of contraction in a concentration-dependent manner, with a maximal increase by 35 ± 8% (at 1 μmol/l; P < 0.05). The positive inotropic effect was accompanied by a disproportionate increase in calcium transients assessed by aequorin light emission [by 76 ± 20%; force/light ratio (ΔF/ΔL) 0.58 ± 0.15]. In contrast, elevation of extracellular calcium (from 2.5 to 3.2 mmol/l) proportionally increased force and aequorin light emission (ΔF/ΔL 1.0 ± 0.1; P < 0.05 vs. ADM). Consistent with a cAMP-dependent mechanism, ADM (1 μmol/l) increased atrial cAMP levels by 90 ± 12%, and its inotropic effects could be blocked by the protein kinase A (PKA) inhibitor H-89. ADM also exerted positive inotropic effects in failing atrial myocardium and in nonfailing and failing ventricular myocardium. The inotropic response was significantly weaker in ventricular vs. atrial myocardium and in failing vs. nonfailing myocardium. In conclusion, ADM exerts Ca2+-dependent positive inotropic effects in human atrial and less-pronounced effects in ventricular myocardium. The inotropic effects are related to increased cAMP levels and stimulation of PKA. In heart failure, the responsiveness to ADM is reduced in atria and ventricles.

Phospholipase Cgamma1 signalling regulates lipopolysaccharide-induced cyclooxygenase-2 expression in cardiomyocytes

Lipopolysaccharide (LPS) induces cyclooxygenase-2 (COX-2) expression in cardiomyocytes, which plays a role in myocardial depression during endotoxemia. The purpose of this study was to investigate the role of phosphatidylinositol (PI)-phospholipase Cgamma1 (PLCgamma1) in cardiac COX-2 expression in vitro and in vivo. In cultured mouse neonatal cardiomyocytes, LPS increased PLCgamma1 phosphorylation and COX-2 expression. Knockdown of PLCgamma1 with specific siRNA or inhibition of PI-PLC with U73122 attenuated COX-2 mRNA and protein expression induced by LPS (1 microg/ml). PLCgamma1 activation by LPS also increased ERK1/2 MAPK phosphorylation, and inhibition of ERK1/2 MAPK blocked the effect of PLCgamma1 on COX-2 expression. Furthermore, activation of PLCgamma1 is a consequence of the Src family activation since inhibition of Src abrogated whereas over-expression of Src enhanced PLCgamma1 phosphorylation and COX-2 expression in LPS-stimulated cardiomyocytes. To investigate the role of PLCgamma1 in endotoxemia, wild-type and PLCgamma1(+/-) adult mice were pre-treated with U73122, or its inactive analog, U73343 (9 mg/kg, i.p.), or vehicle for 15 min followed by LPS (4 mg/kg, i.p.) for 4 h. U73122 or heterozygous deletion of PLCgamma1 decreased cardiac COX-2 expression. The phosphorylation of ERK1/2 MAPK induced by LPS was also attenuated in U73122- or PLCgamma1(+/-) compared to U73343-treated or wild-type littermate hearts, respectively. In conclusion, our study suggests that PLCgamma1 signalling represents a novel pathway regulating cardiac COX-2 expression during LPS stimulation. The Src family is responsible for PLCgamma1 activation, which signals the ERK1/2 MAPK pathway, resulting in COX-2 production in LPS-stimulated cardiomyocytes.

Participation of adrenomedullin and its relation with vascular endothelial growth factor in androgen regulation of prostatic blood flow in vivo

OBJECTIVES

We had previously reported that androgen-regulated prostatic blood flow and vascular endothelial growth factor (VEGF) were involved in the signal transduction pathway. Adrenomedullin (ADM) is a multifunctional regulatory peptide with mitogenic and angiogenic capabilities that are regulated by androgen. ADM is abundantly expressed in the prostate. We focused on ADM and evaluated its participation and relation with VEGF in androgen prostatic blood flow regulation using a castrated rat model.

METHODS

We examined the effect of locally injected dihydrotestosterone (DHT) and ADM, and the co-administration of DHT with an ADM receptor antagonist (ADM 22-52) on prostatic blood flow. Furthermore, prostatic blood flow was evaluated after ADM and VEGF administration with each other's antagonist, VEGF neutralizing antibody and ADM 22-52, respectively. Changes in the mRNA expression levels of ADM in the prostate after castration and successive androgen stimulation were also evaluated.

RESULTS

The administration of ADM promptly increased prostatic blood flow in a dose-dependent manner within 30 minutes. The DHT-induced increase in prostatic blood flow was completely abolished by co-administration with anti-ADM. Anti-ADM inhibited the VEGF-induced prostatic blood flow elevation, but a VEGF neutralizing antibody did not affect the ADM-mediated blood flow elevation. Furthermore, upregulation of the ADM gene induced by DHT was inhibited by co-administration with a VEGF-neutralizing antibody.

CONCLUSIONS

These results have clearly demonstrated the direct regulation of prostatic blood flow by ADM and its involvement in androgenic prostatic blood flow regulation. Furthermore, ADM was estimated to be a downstream mediator of VEGF action in the signal transduction pathway.

Paradoxical rebound platelet activation after painkillers cessation: missing risk for vascular events?

BACKGROUND

Several reliable reports strongly indicate that the use of nonsteroidal anti-inflammatory drugs (NSAIDs) and cyclooxygenase-2 (COX-2) inhibitors is associated with an increased risk of cardiovascular events. Considering the key role of platelets in coronary atherosclerosis and the fact that antiplatelet therapy with aspirin (and more recently, clopidogrel) has been associated with reduced vascular mortality, we sought to determine the effect of therapy and withdrawal of NSAIDs and COX-2 inhibitors on platelet activity.

METHODS

Platelet characteristics from 34 aspirin-naive volunteers who were receiving NSAIDs and COX-2 inhibitors were compared with 138 drug-free controls. Platelets were assessed twice at baseline (at least 1 month of NSAIDs and COX-2 inhibitors) and after a 14-day washout. We used adenosine diphosphate-induced conventional aggregometry, the point-of-care Ultegra analyzer (Ultegra Accumetrics, San Diego, Calif), and whole blood flow cytometry.

RESULTS

Platelet activity during therapy with NSAIDs and COX-2 inhibitors was similar and unremarkable between groups. However, there was a highly significant increase of platelet activity as assessed by conventional aggregometry (P=.0003), Ultegra analyzer readings (P=.03), and expression of GPIIb/IIIa (P=.02), P-selectin (P=.03), and platelet endothelial cell adhesion molecule-1 (P=.001) after withdrawal from NSAIDs and COX-2 inhibitors.

CONCLUSIONS

These data suggest that drug cessation, rather than continuous therapy with NSAIDs and COX-2 inhibitors, may be associated with rebound platelet activation, which may predispose one to a higher risk of vascular events. This hypothesis requires intensive testing in crossover randomized studies and may justify more aggressive antiplatelet regimens in patients after discontinuation of therapy with NSAIDs and COX-2 inhibitors.

Gs and Gi coupling of adrenomedullin in adult rat ventricular myocytes

Adrenomedullin (ADM) acts as an autocrine or a paracrine factor in the regulation of cardiac function. The intracellular mechanisms involved in the direct effect of ADM on adult rat ventricular myocytes (ARVMs) are still to be elucidated. In ARVMs from normal rats, ADM produced an initial (<30 min) increase in cell shortening and Ca2+ transients and a marked decrease in both on prolonged incubation (>1 h). Both effects were sensitive to ADM antagonist ADM-(22–52). Treatment with SQ-22536, an inhibitor of adenylate cyclase, blocked the positive inotropic effect of ADM and potentiated its negative inotropic effect. The negative inotropic effect was sensitive to inhibition by pertussis toxin (PTX), an inhibitor of Gi proteins and KT-5720, an inhibitor of PKA. The observations suggest a switch from Gs-coupled to PTX-sensitive, PKA-dependent Gi coupling by ADM in ARVMs. The ADM-mediated Gi-signaling system involves cAMP-dependent pathways because SQ-22536 further increased the negative inotropic actions of ADM. Also, because ADM is overproduced by ARVMs in our rat model of septic shock, ARVMs from LPS-treated rats were subjected to treatment with ADM-(22–52) and PTX. The decrease in cell shortening and Ca2+ transients in LPS-treated ARVMs could be reversed back with ADM-(22–52) and PTX. This indicates that ADM plays a role in mediating the negative inotropic effect in LPS-treated ARVM through the activation of Gi signaling. This study delineates the intracellular pathways involved in ADM-mediated direct inotropic effects on ARVMs and also suggests a role of ADM in sepsis.

Adrenomedullin: molecular mechanisms and its role in cardiac disease

Adrenomedullin (AM) is a potent, long-lasting vasoactive peptide originally isolated from human pheochromocytoma. Since its discovery, serum and tissue AM expression have been shown to be increased in experimental models and in patients with cardiac hypertrophy, myocardial infarction and end-stage heart failure with several beneficial effects. Considerable evidence exists for a wide range of autocrine, paracrine and endocrine mechanisms for AM which include vasodilatory, anti-apoptotic, angiogenic, anti-fibrotic, natriuretic, diuretic and positive inotropic. Thus, through regulation of body fluid or direct cardiac mechanisms, AM has additive and beneficial effects in the context of heart disease. Notable molecular mechanisms of AM include cyclic adenosine monophosphate, guanosine-3',5'-monophosphate, PI3K/Akt and MAPK-ERK-mediated cascades. Given the endogenous and multifunctional nature of AM, we consider this molecule to have great potential in the treatment of cardiovascular diseases. In agreement, early experimental and preliminary clinical studies suggest that AM is a new and promising therapy for cardiovascular diseases.

Effect of adrenomedullin and proadrenomedullin N-terminal 20 peptide on sugar transport in the rat intestine

Previous studies have shown immunostaining of adrenomedullin (AM) and proadrenomedullin N-terminal 20 peptide (PAMP) throughout the gastrointestinal tract. Based on these data, we decided to investigate the effect of these peptides on intestinal sugar absorption using everted rings from Wistar rat intestine. PAMP increases alpha-methylglucoside (MG) uptake at concentrations ranging from 10(-12) to 10(-7) M. AM shows a dual effect inhibiting sugar absorption at low concentrations (10(-12) to 10(-11) M) and increasing MG uptake at higher concentrations (10(-8) to 10(-6) M). In all cases, the effect is phloridzin-sensitive, indicating that the peptides alter SGLT1 function without modifying the non-mediated component of absorption. The enhancing effect of 10(-8) M AM and PAMP seems to be mediated by elevation of cAMP and is accompanied by an increase on SGLT1 expression in the brush-border membrane of the enterocytes. The inhibitory effect of 10(-12) M AM could be mediated by either cAMP reduction or, more probably, by other second messenger able to inhibit sugar absorption. PKC is not involved in the action of either AM or PAMP. These results demonstrate that both peptides play a role in the regulation of the active transport of sugars in the intestine.

Adrenomedullin gene expression and levels in the cardiovascular system after treatment with lipopolysaccharide

To study the effect of septicaemia, the temporal changes in tissue adrenomedullin (AM) and preproAM mRNA levels were studied in the heart and blood vessels after lipopolysaccharide (LPS) injection. Radioimmunoassay and solution hybridization-RNase protection assays were used to follow the changes in AM and its mRNA levels respectively after intraperitoneal injection of 10 mg/kg LPS in rats. The preproAM mRNA levels increased at 1 h in the right atrium after LPS injection, while the AM contents decreased at 1 h in the left atrium. The preproAM mRNA levels increased at 3 and 6 h in the left ventricle, whereas it increased at 6 h in the right ventricles after LPS injection. There was an increase in preproAM mRNA levels at 1 and 3 h in the mesenteric artery, while AM levels were increased at 1, 3 and 6 h. However, there were no such changes in the thoracic aorta. There were also increases in tumour necrosis factor-alpha (TNF-alpha), interleukin (IL)-1beta and IL-6 in the heart, and in the mesenteric artery (TNF-alpha and IL-1beta) and in thoracic aorta (IL-1beta and IL-6). The present results suggest that the biosynthesis and secretion of AM may be increased in cardiovascular tissues of rats injected with LPS, and that AM may play multiple roles in inflammation.

Circulating cardiovascular markers and mediators in acute illness: an update

An update is given of the circulating markers and mediators of cardiovascular dysfunction in acute illness. Some of these circulating markers reflect mediator action on the peripheral vasculature, such as endothelium-derived endothelin and nitrite/nitritate, the stable end products of nitric oxide. Other markers mainly reflect actions on the heart, such as the natriuretic peptide family, released from the heart upon dilatation, serving as a marker of congestive heart failure and potentially having negative inotropic effects. Indeed, some factors may be both markers as well as mediators of cardiovascular dysfunction of the acutely ill and bear prognostic significance. Assessing circulating levels may help refine clinical judgment of the cardiovascular derangements encountered at the bedside, together with clinical signs and hemodynamic variables. For instance, assessing natriuretic peptides in patients with pulmonary edema of unclear origin may help to diagnose congestive heart failure and cardiogenic pulmonary edema, when the pulmonary capillary wedge pressure is not measured or inconclusive. Future aligning of hemodynamic abnormalities with patterns of circulating cardiovascular markers/mediators may help to stratify patients for inclusion in studies to assess the causes, response to therapy and prognosis of cardiovascular derangements in the acutely ill.

Endothelin-1-mediated coronary vasoconstriction deteriorates myocardial depression in hearts isolated from lipopolysaccharide-treated rats: Interaction with nitric oxide

1. The aim of the present study was to evaluate the contribution of disturbance of coronary perfusion to myocardial depression in hearts isolated from lipopolysaccharide (LPS)-treated rats and to investigate the involvement of endothelin (ET)-1 and nitric oxide (NO). 2. Rats were treated with LPS (10 mg/kg, i.p.) and, 4 h later, plasma ET-1 concentrations were measured by radioimmunoassay and hearts were excised for perfusion at a constant perfusion flow. The selective ETA receptor antagonist BQ-123, in the absence or presence of aminoguanidine, a specific inhibitor of inducible NO synthase, was given 15 min before LPS challenge. Coronary perfusion pressure (CPP) and measures of myocardial contractile function were recorded. 3. In hearts isolated from LPS-treated rats, there was a marked increase in CPP that was abolished by pretreatment with BQ-123. In parallel, an increase in plasma ET-1 concentrations was seen in these rats. Lipopolysaccharide also induced decreases in left ventricular developed pressure (LVDP), the product of LVDP and heart rate and maximal rate of rise/fall of left ventricular pressure (+/- dP/dtmax). Single treatment with BQ-123 or aminoguanidine attenuated LPS-induced myocardial depression. However, when these two drugs were given simultaneously, myocardial depression elicited by LPS was blocked significantly. 4. Endothelin-1-mediated coronary vasoconstriction, together with NO, contributes to myocardial depression in hearts isolated from LPS-treated rats.