Kirsten Leineweber

β1‐ and β2‐Adrenoceptor polymorphisms and cardiovascular diseases

β1‐ and β2‐Adrenoceptors (AR) play a pivotal role in the regulation of cardiovascular function. Both β‐AR subtypes are polymorphic: two single nucleotide polymorphisms (SNPs) have been described for the β1‐ (Ser49Gly, Arg389Gly) and four for the β2‐AR (Arg‐19Cys, Arg16Gly, Gln27Glu, Thr164Ile), and they are possibly of functional relevance. In recombinant cell systems, Gly49‐β1‐AR are more susceptible to agonist‐promoted down‐regulation than Ser49‐β1‐AR, whereas Arg389‐β1‐AR are three to four times more responsive to agonist‐evoked stimulation than Gly389‐β1‐AR. With respect to β2‐AR, the Cys‐19 variant is associated with greater β2‐AR expression than the Arg‐19 variant; Gly16‐β2‐AR are more susceptible, whereas Glu27‐β2‐AR are almost resistant to agonist‐promoted down‐regulation; Thr164‐β2‐AR are three to four times more responsive to agonist‐evoked stimulation than Ile164‐β2‐AR. Several studies addressed potential phenotypic consequences of these SNPs in vivo by influencing and/or contributing to the pathophysiology of cardiovascular/pulmonary diseases such as hypertension, congestive heart failure, arrhythmias or asthma. At present, it appears that these β‐AR SNPs are very likely not disease‐causing genes but possibly predictive for the responsiveness to agonists and antagonists. Patients carrying one or two alleles of the Gly389‐β1‐AR are poor or non‐responders to agonists and antagonists, whereas patients homozygous for the Arg389‐β1‐AR are good responders. Subjects carrying the Ile164‐β2‐AR exhibit blunted responses to β2‐AR stimulation. Asthma patients carrying the Arg16‐Gln27‐Thr164‐β2‐AR haplotype who receive regularly short‐ or long‐acting β2‐AR agonists are rather susceptible to agonist‐induced desensitization and in consequence exhibit reduced bronchodilating and ‐protective effects and/or increased asthma exacerbations. The clinical relevance of these findings is still under debate.

Human β2-adrenergic receptor gene haplotypes and venodilation in vivo

β2‐Adrenergic receptors (β2‐ARs) are polymorphic. In vitro studies have shown that agonist‐promoted down‐regulation is enhanced for Arg16Gly and blunted for Gln27Glu β2‐AR variants; Thr164Ile β2‐ARs exhibit reduced responsiveness to agonist stimulation. Our objective was to determine whether β2‐AR polymorphisms affect β2‐AR‐mediated venodilation in healthy subjects in vivo.

Cyclic Adenosine Monophosphate in Acute Myocardial Infarction With Heart Failure Slayer or Savior

Cyclic adenosine monophosphate (cAMP) is a tightly regulated second messenger that is critically involved in many intracellular processes. In cardiomyocytes, the activation of a number of membrane receptors, notably β-receptors and muscarinic receptors, acts through stimulatory or inhibitory G-proteins (Gαs/Gαi) on adenylyl cyclase (AC), which synthesizes cAMP from ATP. cAMP is degraded by phosphodiesterases (PDE). Thereafter, cAMP activates protein kinase A (PKA), which, in turn, through phosphorylation of L-type calcium channels, ryanodine receptors, phospholamban, and troponin I, improves excitation-contraction coupling and increases heart rate, as well as contraction amplitude and relaxation. PKA also phosphorylates nuclear cAMP-response element binding proteins to activate transcription.1 There are at least 9 isoforms of AC; the mammalian myocardium expresses mainly AC V and VI. AC V is the predominant isoform in adult cardiac tissue, whereas AC VI expression decreases with age. Both isoforms are phosphorylated by PKA and thereby inhibited, thus providing a feedback regulation and potential desensitization pathway.2,3 Transgenic mice with cardiac-directed overexpression of AC VI have normal cAMP and cardiac function at rest but increased responses in both cAMP and function to β-adrenergic stimulation,4 as confirmed in the present study by Takahasi et al.5 Article p 388 The prevailing notion is that increased myocardial cAMP in settings of acute myocardial ischemia is detrimental. In fact, β-adrenergic agonists that increase cAMP formation disrupt perfusion-contraction matching and promote infarction in controlled animal models of myocardial ischemia, both by increasing myocardial energetic requirements and by an unfavorable flow redistribution away from the ischemic subendocardium.6 Apart from increasing infarct size, cAMP promotes ventricular tachyarrhythmias in ischemia/reperfusion.7 Although increased cAMP acutely increases left ventricular function in heart failure, most trials with either β-adrenergic agonists or PDE inhibitors have revealed increased mortality, possibly secondary to tachyarrhythmias.1 The present article by Takahashi et …

Genotype‐dependent time course of lymphocyte β2‐adrenergic receptor down‐regulation

Volunteers homozygous for Glu27 β2‐adrenergic receptor (β2AR) polymorphism have delayed onset of agonist‐induced desensitization of cardiac β2AR responses.

Characterization of the GNAQ promoter and association of increased Gq expression with cardiac hypertrophy in humans

AIMS Transgenic mice with cardiac overexpression of Gq develop cardiac hypertrophy, apoptosis, and heart failure. Similar mechanisms may contribute to human left ventricular hypertrophy (LVH). However, mechanisms regulating transcription of the human GNAQ gene encoding the Gq protein are unknown and single-nucleotide polymorphisms have not been reported. METHODS AND RESULTS We delineated essential elements for transcription in the human GNAQ promoter using reporter assays and showed promoter induction by serum and angiotensin II. Sequencing of the whole promoter revealed a common (minor allele frequency 0.48) dinucleotide polymorphism at position -694/-695, resulting in an exchange of two adjacent nucleotides (TT > GC). The GC allele had increased transcription factor binding and was associated with enhanced transcriptional activation by serum or angiotensin II, resulting in enhanced Gq expression and intracellular signalling. Genotyping a population-based survey (n = 1204) revealed a higher prevalence of LVH in individuals with the GC/GC genotype [odds ratio (OR) 4.07; 95% CI 1.63-10.16; P = 0.003], this effect being more pronounced in women (OR 5.52; P = 0.005). CONCLUSION A novel polymorphism in the Gq promoter region is associated with enhanced promoter activity, Gq expression, intracellular signal transduction, and increased prevalence of LVH, particularly in women.

Unchanged G-protein-coupled receptor kinase activity in the aging human heart

OBJECTIVES We sought to find out whether G-protein-coupled receptor kinase (GRK) activity is also increased in the aging human heart. BACKGROUND In the aging and failing human heart, cardiac beta-adrenoceptors (beta-AR) are desensitized. In heart failure (HF), an increase in cardiac GRK activity considerably contributes to this beta-AR desensitization. METHODS We assessed GRK activity (by in vitro rhodopsin phosphorylation) in the right atria (RA) from 16 children (mean age 9 +/- 2 years) and 17 elderly patients (mean age 67 +/- 2 years) without apparent HF and in the RA from four patients with end-stage HF.Cytosolic and membranous GRK activities in the RA from children were not significantly different from those in elderly patients; in contrast, cytosolic and membranous GRK activities in the RA from patients with end-stage HF were significantly increased. CONCLUSIONS In contrast to the failing human heart, in the aging human heart, GRK activity is not increased. Thus, GRK activity appears to not play an important role in beta-AR desensitization in the aging human heart.

Coronary atherosclerosis and cardiovascular risk in masters male marathon runners : Rationale and design of the marathon study

Background:Regular physical exercise is recommended to reduce cardiovascular mortality. And yet, atherosclerosis is the main cause of exercise-associated death in persons beyond age 35. The need for risk stratification in marathon runners is under discussion. The predictive value of modern imaging- and non-imaging-based markers of risk that can be used for risk stratification in masters endurance athletes still deserves exploration.Methods:Male runners > 50 years who have completed at least five marathon races during the preceding 3 years and do not suffer from coronary artery disease, angina nor diabetes mellitus are studied to assess the predictive value of established and modern imaging- based and biochemical cardiovascular risk factors. Laboratory parameters including clinical chemistry, hematology and hormone measurements are determined. Lifestyle-related risk factors, psychosocial and socioeconomic variables are explored using standardized questionnaires. Coronary, carotid, femoral and aortic atherosclerosis is measured using electronbeam computed tomography and ultrasound. In addition, a resting ECG, a bicycle stress test and heart rate variability are performed. Myocardial morphology and function are assessed using echocardiography and magnetic resonance imaging. Participants are invited to compete in a marathon race to quantify the association of coronary atherosclerosis with marathon-related changes of cardiac troponin levels and the extent of marathon-induced inflammation. At the cellular level, the effect on the amount of circulating progenitor cells (EPCs) is determined by FACS analysis. Changes in laboratory parameters and hormone levels are also studied. Annual long-term follow-up including hospital records and death certificates is performed. Data are compared with those from a general unselected cohort from the Heinz Nixdorf Recall Study.Conclusion:This study should contribute to cardiovascular risk assessment in the growing number of masters marathon runners with a focus on assessing the predictive value of modern imaging techniques and biochemical markers for comprehensive risk stratification.ZusammenfassungHintergrund:Regelmäßige körperliche Aktivität eignet sich zur Prävention der Arteriosklerose und kardiovaskulärer Ereignisse. Und dennoch ist die Arteriosklerose die Hauptursache sportassoziierter Todesfälle jenseits des 35. Lebensjahrs. Der prädiktive Nutzen moderner bildgebender Verfahren und biochemischer Marker, die für eine Risikostratifizierung in Frage kommen, wurde bei älteren Ausdauersportlern bislang nicht hinreichend untersucht.Methodik:Es werden Männer > 50 Jahre untersucht, die in den vergangenen 3 Jahren mindestens fünf Marathonläufe absolviert haben und keine bekannte Herzkrankheit oder Angina pectoris und keinen Diabetes mellitus aufweisen. Etablierte Risikofaktoren sowie moderne bildgebende und biochemische Risikomarker werden gemessen. Lebensstilassoziierte, psychosoziale und sozioökonomische Risikofaktoren werden mit standardisierten Fragebögen erhoben. Die Arteriosklerose der Koronararterien, der Karotiden, der Femoralarterien und der Aorta wird mittels Elektronenstrahltomographie und Ultraschall quantifiziert. Zusätzlich werden ein Ruhe-EKG, eine Fahrradergometrie und eine Messung der Herzfrequenzvariabilität durchgeführt. Morphologie und Funktion des linken Ventrikels werden echokardiographisch und magnetresonanztomographisch erfasst. Die Teilnehmer wurden gebeten, an einem Marathonwettkampf teilzunehmen, um die Assoziation von Koronarsklerose und dem marathoninduzierten Anstieg von kardialem Troponin in Abhängigkeit von der erwarteten Entzündungsreaktion zu untersuchen. Auf zellulärer Ebene wird der Effekt auf die Anzahl zirkulierender endothelialer Vorläuferzellen (EPCs) mittels FACS-Analyse bestimmt. Die Ereignisrate im Verlauf wird jährlich erfragt. Es werden auch Krankenhausdokumente und Sterbeunterlagen ausgewertet. Die Daten können im Vergleich zur Allgemeinbevölkerung aus der Heinz-Nixdorf-Recall-Studie analysiert werden.Schlussfolgerung:Diese Studie kann einen Beitrag zur kardiovaskulären Risikostratifikation in der wachsenden Gruppe älterer Marathonläufer leisten. Der prädiktive Wert der bildgebenden und biochemischen Marker für kardiovaskuläre Ereignisse wird untersucht.

Cardiac β-adrenoceptor changes in monocrotaline-treated rats: Differences between membrane preparations from whole ventricles and isolated ventricular cardiomyocytes

In monocrotaline (MCT)-treated rats the &bgr;-adrenoceptor-G-protein-adenylyl cyclase system—determined in crude membrane preparations from whole ventricular tissue—was desensitized not only in right (RV) but also in left ventricles (LV). This study aimed to assess the specific contribution of cardiomyocytes to these &bgr;-adrenoceptor changes. Six-week-old male Wistar rats were treated with 60 mg/kg body weight MCT intraperitoneally; within 4–6 weeks, rats developed marked RV hypertrophy. Cardiomyocytes were isolated from RVs and LVs. In RV cardiomyocytes of MCT-treated rats, &bgr;-adrenoceptor density was significantly reduced whereas it was unaltered in LV cardiomyocytes. Reduction of RV cardiomyocyte &bgr;-adrenoceptors was due to a selective &bgr;1-adrenoceptor reduction. Isoprenaline (100 &mgr;M)–induced cAMP increase was significantly reduced in RV but not in LV cardiomyocytes of MCT-treated rats. G protein–coupled receptor kinase activity was increased in RV but not in LV cardiomyocytes. &agr;1-Adrenoceptor density and noradrenaline-induced increase in inositol phosphate formation were significantly reduced only in RV but not in LV cardiomyocytes from MCT-treated rats. It is concluded that in cardiomyocytes of MCT-treated rats, cardiac &bgr;-adrenoceptors and &agr;1-adrenoceptors are chamber-specifically desensitized only in the RV. Thus, changes in cardiac &bgr;-adrenoceptors determined in membrane preparations from whole tissue homogenates do not correctly reflect changes occurring in cardiomyocytes.

Coronary Atherosclerosis and Cardiovascular Risk in Masters Male Marathon Runners

Background:Regular physical exercise is recommended to reduce cardiovascular mortality. And yet, atherosclerosis is the main cause of exercise-associated death in persons beyond age 35. The need for risk stratification in marathon runners is under discussion. The predictive value of modern imaging- and non-imaging-based markers of risk that can be used for risk stratification in masters endurance athletes still deserves exploration.Methods:Male runners > 50 years who have completed at least five marathon races during the preceding 3 years and do not suffer from coronary artery disease, angina nor diabetes mellitus are studied to assess the predictive value of established and modern imaging- based and biochemical cardiovascular risk factors. Laboratory parameters including clinical chemistry, hematology and hormone measurements are determined. Lifestyle-related risk factors, psychosocial and socioeconomic variables are explored using standardized questionnaires. Coronary, carotid, femoral and aortic atherosclerosis is measured using electronbeam computed tomography and ultrasound. In addition, a resting ECG, a bicycle stress test and heart rate variability are performed. Myocardial morphology and function are assessed using echocardiography and magnetic resonance imaging. Participants are invited to compete in a marathon race to quantify the association of coronary atherosclerosis with marathon-related changes of cardiac troponin levels and the extent of marathon-induced inflammation. At the cellular level, the effect on the amount of circulating progenitor cells (EPCs) is determined by FACS analysis. Changes in laboratory parameters and hormone levels are also studied. Annual long-term follow-up including hospital records and death certificates is performed. Data are compared with those from a general unselected cohort from the Heinz Nixdorf Recall Study.Conclusion:This study should contribute to cardiovascular risk assessment in the growing number of masters marathon runners with a focus on assessing the predictive value of modern imaging techniques and biochemical markers for comprehensive risk stratification.ZusammenfassungHintergrund:Regelmäßige körperliche Aktivität eignet sich zur Prävention der Arteriosklerose und kardiovaskulärer Ereignisse. Und dennoch ist die Arteriosklerose die Hauptursache sportassoziierter Todesfälle jenseits des 35. Lebensjahrs. Der prädiktive Nutzen moderner bildgebender Verfahren und biochemischer Marker, die für eine Risikostratifizierung in Frage kommen, wurde bei älteren Ausdauersportlern bislang nicht hinreichend untersucht.Methodik:Es werden Männer > 50 Jahre untersucht, die in den vergangenen 3 Jahren mindestens fünf Marathonläufe absolviert haben und keine bekannte Herzkrankheit oder Angina pectoris und keinen Diabetes mellitus aufweisen. Etablierte Risikofaktoren sowie moderne bildgebende und biochemische Risikomarker werden gemessen. Lebensstilassoziierte, psychosoziale und sozioökonomische Risikofaktoren werden mit standardisierten Fragebögen erhoben. Die Arteriosklerose der Koronararterien, der Karotiden, der Femoralarterien und der Aorta wird mittels Elektronenstrahltomographie und Ultraschall quantifiziert. Zusätzlich werden ein Ruhe-EKG, eine Fahrradergometrie und eine Messung der Herzfrequenzvariabilität durchgeführt. Morphologie und Funktion des linken Ventrikels werden echokardiographisch und magnetresonanztomographisch erfasst. Die Teilnehmer wurden gebeten, an einem Marathonwettkampf teilzunehmen, um die Assoziation von Koronarsklerose und dem marathoninduzierten Anstieg von kardialem Troponin in Abhängigkeit von der erwarteten Entzündungsreaktion zu untersuchen. Auf zellulärer Ebene wird der Effekt auf die Anzahl zirkulierender endothelialer Vorläuferzellen (EPCs) mittels FACS-Analyse bestimmt. Die Ereignisrate im Verlauf wird jährlich erfragt. Es werden auch Krankenhausdokumente und Sterbeunterlagen ausgewertet. Die Daten können im Vergleich zur Allgemeinbevölkerung aus der Heinz-Nixdorf-Recall-Studie analysiert werden.Schlussfolgerung:Diese Studie kann einen Beitrag zur kardiovaskulären Risikostratifikation in der wachsenden Gruppe älterer Marathonläufer leisten. Der prädiktive Wert der bildgebenden und biochemischen Marker für kardiovaskuläre Ereignisse wird untersucht.

Is there a role of the Thr164Ile-β2-adrenoceptor polymorphism for the outcome of chronic heart failure?

ObjectiveThe Thr164Ile-β2-adrenoceptor (AR) polymorphism exhibits lower affinities for catecholamines and reduced basal and agonist-stimulated adenylyl cyclase activity in vitro. It has been suggested that patients with chronic heart failure (CHF) due to ischemic or dilated cardiomyopathy carrying the Thr164Ile-β2AR polymorphism exhibit much more rapid progression to death or heart transplantation (HTX) than CHF-patients carrying the homozygous Thr164-β2AR. This study aimed to further evaluate the role of the Thr164Ile-β2AR in CHF. For this we hypothesized that the Thr164Ile-β2AR variant should be more abundant in HTX-patients than in patients with stable CHF or healthy controls.Methods and ResultsWe genotyped 309 HTX-patients, 520 stable CHF-patients and 328 healthy controls for the three β2AR variants Arg16Gly, Gln27Glu and Thr164Ile. The prevalence of the Thr164Ile-β2AR variant was not considerably different in HTX-patients (2.3%) from that in CHF-patients (1.9%) or healthy controls (2.1%). Similarly, the frequency of the minor Ile164-allele was f(−)=0.0106 in HTX-patients, f(−)=0.0096 in CHF-patients and f(−)=0.0113 in healthy controls.ConclusionsThe prevalence of the hypofunctional Thr164Ile-β2AR variant and the frequency of the Ile164-allele were almost identical in CHF-patients, who had undergone HTX, with those in patients with stable CHF or in healthy controls. Thus, the role of the Thr164Ile-β2AR in CHF remains questionable.