Oliver Zolk

Expression of Endothelin-1, Endothelin-Converting Enzyme, and Endothelin Receptors in Chronic Heart Failure

BACKGROUNDnElevated plasma levels of endothelin (ET)-1 have been reported in association with heart diseases, including heart failure. Furthermore, it has been suggested that ET-1 acts as a local autocrine/paracrine factor with biological activities such as vasoconstriction, mitogenesis, and inotropic effects on the heart. This study investigated alterations of ET-1, ET receptor, and endothelin-converting enzyme (ECE) expression in left ventricular myocardium from patients with end-stage heart failure.nnnMETHODS AND RESULTSnmRNA concentrations of ETA and ETB receptors, prepro-ET-1 (ppET-1), and ECE in left ventricles from nonfailing donors hearts (NF) and from patients with end-stage chronic heart failure (NYHA functional class IV) due to dilated cardiomyopathy (DCM) were compared by use of a competitive reverse transcription-polymerase chain reaction technique. There was no significant difference in mRNA expression for ppET-1, ECE-1, and ETA receptors, whereas a significant reduction of ETB-receptor mRNA was observed in DCM hearts. 125I-labeled ET-1 radioligand binding studies demonstrated a significant downregulation of ETB receptors, whereas ETA-receptor density was increased in membranes from DCM hearts. Phosphoramidon-sensitive ECE activity and immunodetectable amounts of ECE protein in left ventricular membrane preparations did not differ between NF and DCM hearts. Finally, immunoreactive ET-1 concentrations were increased in DCM hearts.nnnCONCLUSIONSnThe present study demonstrates changes in the ET-receptor expression pattern in favor of the ETA receptor in human end-stage heart failure. Furthermore, activation of the cardiac ET system with increased tissue ET-1 concentrations in the failing myocardium is observed. This is more likely due to decreased clearance than to increased synthesis, because ppET-1 gene expression and ECE activity are unchanged.

Endothelin Receptors in the Failing and Nonfailing Human Heart

BACKGROUNDnIn patients with chronic heart failure (CHF), plasma endothelin-1 (ET-1) levels are increased. We studied whether the cardiac ET-receptor system is altered in CHF patients.nnnMETHODS AND RESULTSnWe assessed ET-evoked inositol phosphate (IP) formation in slices from right atria and left ventricles from 6 potential heart transplant donors (NFH) and 15 patients with end-stage CHF; in membranes from the same tissues, we studied ET-induced inhibition of isoprenaline- and forskolin-stimulated adenylyl cyclase and ET-receptor density. ET (10[-9] to 10[-6] mol/L, ET-1 >>> ET-3) increased IP formation in right atria and left ventricles through ET(A)-receptor stimulation in a concentration-dependent manner; no difference in potency or efficacy between NFH and CHF hearts was observed. ET-1 (10[-10] to 10[-6] mol/L), via ET(A)-receptor stimulation, inhibited isoprenaline- and forskolin-stimulated adenylyl cyclase in right atria but not in left ventricles, whereas carbachol inhibited adenylyl cyclase in both tissues; again, the potency and efficacy of ET- or carbachol-induced adenylyl cyclase inhibition was not different between NFH and CHF hearts. [125I]ET-1 binding revealed the coexistence of ET(A) and ET(B) receptors in both tissues; however, the density of ET(A) receptors was not significantly different between NFH and CHF hearts. Finally, the immunodetectable amount of left ventricular Gq/11 protein did not differ between NFH and CHF hearts.nnnCONCLUSIONSnIn the human heart, ET(A) and ET(B) receptors coexist; however, only ET(A) receptors are of functional importance. In right atria, ET(A) receptors couple to IP formation and inhibition of adenylyl cyclase; in left ventricles, they couple only to IP formation. In end-stage CHF, the functional responsiveness of the cardiac ET(A)-receptor system is not altered.

Evidence for protein phosphatase inhibitor-1 playing an amplifier role in β-adrenergic signaling in cardiac myocytes

The protein phosphatase inhibitor‐1 (PPI‐1) inhibits phosphatase type‐1 (PP1) only when phosphorylated by protein kinase A and could play a pivotal role in the phosphorylation/dephosphorylation balance. Rat cardiac PPI‐1 was cloned by reverse transcriptase‐polymerase chain reaction, expressed in Eschericia coli, evaluated in phosphatase assays, and used to generate an antiserum. An adenovirus was constructed encoding PPI‐1 and green fluorescent protein (GFP) under separate cytomegalovirus promotors (AdPPI‐1/GFP). A GFP‐only virus (AdGFP) served as control. Engineered heart tissue (EHT) from neonatal rat cardiomyocytes and adult rat cardiac myocytes (ARCMs) were used as model systems. PPI‐1 expression was determined in human ventricular samples by Northern blots. Compared with AdGFP, AdPPI‐1/GFP‐infected neonatal rat cardiomyocytes displayed a 73% reduction in PP1 activity. EHTs infected with AdPPI‐1/GFP exhibited a fivefold increase in isoprenaline sensitivity. AdPPI‐1/GFP‐infected ARCMs displayed enhanced cell shortening as well as enhanced phospholamban phosphorylation when stimulated with 1 nM isoprenaline. PPI‐1 mRNA levels were reduced by 57±12% in failing hearts with dilated and ischemic cardiomyopathy (n=8 each) compared with nonfailing hearts (n=8). In summary, increased PPI‐1 expression enhances myocyte sensitivity to isoprenaline, indicating that PPI‐1 acts as an amplifier in β‐adrenergic signaling. Decreased PPI‐1 in failing human hearts could participate in desensitization of the cAMP pathway.

Decreased Expression of the Cardiac LIM Domain Protein MLP in Chronic Human Heart Failure

BACKGROUNDnThe cardiac LIM domain protein MLP, a member of the cysteine-rich protein family, is an essential regulator of cardiac muscle development. Mice with a disruption of the MLP gene resemble the morphological and clinical picture of dilated cardiomyopathy and heart failure in humans. We investigated whether altered MLP expression is significant for the pathogenesis of human heart failure.nnnMETHODS AND RESULTSnImmunohistochemistry and in situ hybridization confirmed the expression of MLP protein and mRNA in human cardiomyocytes. Western blot analysis revealed that the MLP peptide was present in the contractile protein fraction but not in the cytosolic or membrane fraction and that the binding of MLP to myofibrils required functional zinc finger domains. MLP immunoreactivity was decreased approximately 50% (P<0.05) in the left ventricular myocardium of patients with chronic heart failure due to dilated or ischemic cardiomyopathy compared with non-failing donor hearts. MLP mRNA expression, as assessed by Northern blot experiments, was not significantly different between failing and non-failing control hearts, which suggests that decreased MLP synthesis or increased MLP protein turnover, rather than a decreased number of RNA transcripts, may play a role.nnnCONCLUSIONSnBecause MLP may promote myofibril assembly, the down-regulation of this adapter protein might play an essential role in myofibril derangement or impaired myofibril rearrangement in the failing human myocardium.

Salt Induces Vascular AT1 Receptor Overexpression In Vitro and In Vivo

The molecular events governing salt-sensitive hypertension are currently unknown. Because the renin-angiotensin system plays a central role in blood pressure regulation, as well as electrolyte balance, it may be closely involved in the phenomenon of salt sensitivity. Therefore, we examined the effect of a high salt diet (8%) on aortic angiotensin type 1 (AT1) receptor expression in Sprague-Dawley rats by means of radioligand binding assays and quantitative polymerase chain reaction. High salt intake caused an increase of AT1 receptor mRNA and AT1 receptor density to approximately 160% compared with control levels. Northern analysis revealed that incubation of vascular smooth muscle cells (VSMCs) with an increased concentration of sodium chloride (by 10 mmol/L) caused a time-dependent elevation of AT1 receptor mRNA levels, with a maximum of 241+/-28% after 24 hours. There was a similar increase in AT1 receptor density in VSMCs in response to sodium chloride, as assessed by radioligand binding assays. The salt-induced AT1 receptor upregulation led to an enhanced functional response of VSMCs on stimulation with angiotensin II, since the angiotensin II-elicited intracellular calcium response was significantly increased in cells preincubated for 24 hours with the high salt concentration. Thus, sodium chloride may directly induce AT1 receptor upregulation in vitro as well as in vivo; this suggests a potential mechanism participating in salt-induced hypertension because the AT1 receptor activation is tightly coupled to blood pressure regulation.

Paraoxonase-1 Q192R polymorphism and antiplatelet effects of clopidogrel in patients undergoing elective coronary stent placement.

Background— Recently published data indicate that the paraoxonase-1 (PON1) Q192R genotype—and not as previously shown activity of cytochrome P450 (CYP) 2C19—is the major determinant of metabolic bioactivation of clopidogrel and thereby variability of antiplatelet effect of clopidogrel. We sought to investigate whether the PON1 Q192R gene polymorphism affects platelet reactivity in patients undergoing elective coronary stent placement. Methods and Results— The study included 760 consecutive patients undergoing elective coronary stent placement after loading with clopidogrel 600 mg. Platelet function was assessed by adenosine diphosphate-induced (ADP 5 and 20 &mgr;mol/L) platelet aggregation and by flow-cytometric analysis of platelet surface protein expression before clopidogrel, at the time of coronary stent placement, and before discharge after coronary stent placement. PON1 Q192R genotype [NM_000446.5:c.575A>G single nucleotide polymorphism (rs662)] was analyzed by TaqMan polymerase chain reaction. Residual platelet aggregation (ADP 5 &mgr;mol/L) at predischarge was 8.0% (3.0% to 17.0%) [median (interquartile range)] in PON1 QQ192 patients (n=384), 8.0% (3.0% to 15.0%) in PON1 QR192 (n=304), and 11.0% (3.0% to 18.0%) in PON1 RR192 (n=72; P=0.603). By multivariable linear regression, residual platelet aggregation was not associated with PON1 QQ192/QR192 (partial &eegr;2<0.001, P=0.728) but with CYP2C19*2 loss-of-function allele (partial &eegr;2=0.045, P<0.001) as well as any CYP2C19*17 gain-of-function allele (partial &eegr;2=0.012, P=0.004). All other platelet assays also showed no significant association between PON1 Q192R genotype and antiplatelet effect of clopidogrel. The 1-year incidence of death and myocardial infarction did not differ between PON1 Q192R genotypes. Conclusions— On-treatment platelet reactivity in patients undergoing coronary stent placement after loading with clopidogrel 600 mg was not associated with PON1 Q192R genotype. Clinical Trial Registration— URL: http://www.clinicaltrials.gov. Unique identifier: NCT00457236.

Augmented Expression of Cardiotrophin-1 in Failing Human Hearts Is Accompanied by Diminished Glycoprotein 130 Receptor Protein Abundance

Background—Cardiotrophin-1 (CT-1), a member of the interleukin-6 superfamily, is a potent inducer of cardiomyocyte hypertrophy that prolongs myocyte survival. Although cardiac CT-1 gene expression is known to be upregulated in some animal models of congestive heart failure, the activation state of the CT-1 system in patients with congestive heart failure is unknown. Methods and Results—This study was designed to determine left ventricular expression of CT-1 and its glycoprotein 130 (gp130)/leukemia inhibitory factor receptor complex in human end-stage heart failure due to ischemic and dilated cardiomyopathy. In addition, we investigated the activation state of signal transducer and activator of transcription 3 (STAT3), the downstream effector of gp130 signaling. In the failing left ventricular myocardium, expression levels of CT-1 mRNA and protein were significantly increased by 142% and 68%, respectively, compared with non-failing donor hearts. Immunohistochemistry confirmed the increased expression of CT-1 in cardiac myocytes. Although gp130 gene expression was increased by 91% (P <0.001), gp130 protein abundance was significantly diminished by 34% in the failing myocardium. In contrast, leukemia inhibitory factor receptor and suppressor of cytokine signaling-3 protein concentrations were not changed. In addition, the ratio of activated tyrosine phosphorylated STAT3 to total STAT3 was not significantly altered in failing hearts compared with non-failing controls. Conclusions—Our data suggest that gp130 receptor downregulation balances enhanced CT-1 expression in human heart failure and thereby inhibits excessive activation of the gp130 signaling pathway.

Atorvastatin desensitizes β-adrenergic signaling in cardiac myocytes via reduced isoprenylation of G-protein γ-subunits

Statins exert pleiotropic, cholesterol‐independent effects by reducing isoprenylation of monomeric GTPases. Here we examined whether statins also reduce isoprenylation of γ‐subunits of heterotrimeric G‐proteins and thereby affect β‐adrenergic signaling and regulation of force in cardiac myocytes. Neonatal rat cardiac myocytes (NRCM) were treated with atorvastatin (0.1–10 μmol/l; 12–48 h) and examined for adenylyl cyclase regulating G‐protein α‐ (Gα), β‐ (Gβ), and γ‐ (Gγ) subunits and cAMP accumulation. Engineered heart tissue (EHT) from NRCM was used to evaluate contractile consequences. In atorvastatin‐treated NRCM, a second band of Gγ3 with a lower apparent molecular weight appeared in cytosol and particulate fractions that was absent in vehicle‐treated NRCM, but also seen after GGTI‐298, a geranylgeranyl transferase inhibitor. In parallel, Gβ accumulated in the cytosol and total cellular content of Gαs was reduced. In atorvastatin‐treated NRCM, the cAMP‐increasing effect of isoprenaline was reduced. Likewise, the positive inotropic effect of isoprenaline was desensitized and reduced after treatment with atorvastatin. The effects of atorvastatin were abolished by mevalonate and/or geranylgeranyl pyrophosphate, but not by farnesyl pyrophosphate or squalene. Taken together, the results of this study show that atorvastatin desensitizes NRCM to β‐adrenergic stimulation by a mechanism that involves reduced isoprenylation of Gγ and subsequent reductions in the cellular content of Gαs.

Functional Characterization of the Human Organic Cation Transporter 2 Variant p.270Ala>Ser

The organic cation transporter 2 (OCT2, SLC22A2) plays an important role for renal drug elimination. Recent clinical studies indicate an impact of the frequent nonsynonymous c.808G>T (p.270Ala>Ser) polymorphism on renal clearance of metformin and the extent of the metformin-cimetidine interaction. The role of this polymorphism for renal disposition of endogenous compounds and drugs other than metformin has not been investigated. In addition, it is unclear whether the observed genotype dependence of an OCT2-mediated drug-drug interaction might occur also with other OCT inhibitors. To address these issues, we generated human embryonic kidney cells stably expressing wild-type OCT2 or the p.270Ala>Ser variant. No differences in protein expression levels and membrane incorporation pattern were observed between the two cell lines. The p.270Ala>Ser variant significantly impaired uptake kinetics of 1-methyl-4-phenylpyridinium, dopamine, norepinephrine, and propranolol. Vmax values were significantly reduced for uptake of all four compounds mediated by the p.270Ala>Ser variant compared with wild-type OCT2. In addition, a significant difference in the affinity to wild-type and mutant OCT2 was observed for dopamine (Km dopamine: 932 ± 77 versus 1285 ± 132 μM). Moreover, out of a set of 27 compounds p.270Ala>Ser OCT2 was significantly less sensitive to inhibition by cimetidine, flurazepam, metformin, mexiletine, propranolol, and verapamil than wild-type OCT2 (e.g., for propranolol: IC50 wild type versus p.270Ala>Ser 189 versus 895 μM, P < 0.001). Our results indicate that the common OCT2 c.808G>T single nucleotide polymorphism significantly alters uptake of endogenous compounds and drugs. Moreover, for selected compounds the extent of OCT2-mediated drug interactions could depend on OCT2 c.808G>T genotype.

Angiotensin receptor antagonism and angiotensin converting enzyme inhibition improve diastolic dysfunction and Ca2+-ATPase expression in the sarcoplasmic reticulum in hypertensive cardiomyopathy

Background Hypertensive cardiomyopathy is a major risk factor for the development of chronic heart failure. Objective To investigate whether treatment with an angiotensin converting enzyme inhibitor (ACEI) or with an angiotensin type 1 receptor antagonist (AT1-RA) is sufficient to prevent the development of hypertensive cardiomyopathy and cardiac contractile dysfunction. Special emphasis was placed on the effects of both treatments on sarcoplasmic reticulum Ca2+-ATPase (SERCA 2a) gene expression as a major cause of impaired diastolic cardiac relaxation. Methods and results Eight-week-old rats harboring the mouse renin 2d gene [TG(mREN2)27] were treated for 8 weeks with 100 mg/kg captopril (Cap) in their food and 100 mg/kg of the AT1-RA Bay 10-6734 (Bay) in their food. Untreated TG(mREN2)27 and Sprague–Dawley rats (SDR) were used as controls. Both treatment regimens normalized the left ventricular weight, which was increased significantly (P < 0.001) in TG(mREN2)27. Both treatments normalized the left ventricular endsystolic and end-diastolic pressures, which were significantly (P < 0.001) higher in TG(mREN2)27 than they were in SDR, and they improved the velocity of the decrease in pressure [P < 0.05, Bay and Cap versus TG(mREN2)27]. Decreased left ventricular SERCA 2a mRNA and protein levels and increased atrial natriuretic peptide messenger RNA levels were normalized by Bay and Cap treatments (P < 0.05, Bay and Cap versus TG(mREN2)27, by Northern and Western blotting). According to radioimmunoassay and an enzyme assay, respectively, Bay, but not Cap, increased plasma angiotensin I concentrations and the renin activity above normal levels (P < 0.05), whereas myocardial angiotensin II concentrations (determined by radioimmunoassay), which were significantly (P < 0.05) increased in TG(mREN2)27, were normalized equally by Bay and Cap. Conclusions In renin-induced hypertensive cardiomyopathy, left ventricular diastolic dysfunction occurs at the stage of compensated myocardial hypertrophy. The decreased left ventricular relaxation velocity might be due to reduced SERCA 2a gene expression. In this model of hypertensive cardiomyopathy, AT1-RA and ACEI treatments are similarly effective at reducing the arterial pressure, preventing myocardial hypertrophy and diastolic contractile dysfunction. Normalization of SERCA 2a gene expression, either by AT1-RA or by ACEI treatment, might contribute to the improvement in diastolic function.