Fikret Er

Ischemic Preconditioning for Prevention of Contrast Medium–Induced Nephropathy Randomized Pilot RenPro Trial (Renal Protection Trial)

Background— Contrast medium–induced acute kidney injury is associated with substantial morbidity and mortality. The underlying mechanism has been attributed in part to ischemic kidney injury. The aim of this randomized, double-blind, sham-controlled trial was to assess the impact of remote ischemic preconditioning on contrast medium–induced acute kidney injury. Methods and Results— Patients with impaired renal function (serum creatinine >1.4 mg/dL or estimated glomerular filtration rate <60 mL · min−1 · 1.73 m−2) undergoing elective coronary angiography were randomized in a 1:1 ratio to standard care with (n=50) or without ischemic preconditioning (n=50; intermittent arm ischemia through 4 cycles of 5-minute inflation and 5-minute deflation of a blood pressure cuff). Overall, both study groups were at high risk of developing contrast medium–induced acute kidney injury according to the Mehran risk score. The primary end point was the incidence of contrast medium–induced kidney injury, defined as an increase in serum creatinine ≥25% or ≥0.5 mg/dL above baseline at 48 hours after contrast medium exposure. Contrast medium–induced acute kidney injury occurred in 26 patients (26%), 20 (40%) in the control group and 6 (12%) in the remote ischemic preconditioning group (odds ratio, 0.21; 95% confidence interval, 0.07–0.57; P =0.002). No major adverse events were related to remote ischemic preconditioning. Conclusions— Remote ischemic preconditioning before contrast medium use prevents contrast medium–induced acute kidney injury in high-risk patients. Our findings merit a larger trial to establish the effect of remote ischemic preconditioning on clinical outcomes. Clinical Trial Registration— URL: [http://www.germanctr.de][1]. Unique identifier: U1111-1118-8098. # Clinical Perspective {#article-title-44} [1]: http://www.germanctr.de.Background— Contrast medium–induced acute kidney injury is associated with substantial morbidity and mortality. The underlying mechanism has been attributed in part to ischemic kidney injury. The aim of this randomized, double-blind, sham-controlled trial was to assess the impact of remote ischemic preconditioning on contrast medium–induced acute kidney injury. Methods and Results— Patients with impaired renal function (serum creatinine >1.4 mg/dL or estimated glomerular filtration rate <60 mL · min−1 · 1.73 m−2) undergoing elective coronary angiography were randomized in a 1:1 ratio to standard care with (n=50) or without ischemic preconditioning (n=50; intermittent arm ischemia through 4 cycles of 5-minute inflation and 5-minute deflation of a blood pressure cuff). Overall, both study groups were at high risk of developing contrast medium–induced acute kidney injury according to the Mehran risk score. The primary end point was the incidence of contrast medium–induced kidney injury, defined as an increase in serum creatinine ≥25% or ≥0.5 mg/dL above baseline at 48 hours after contrast medium exposure. Contrast medium–induced acute kidney injury occurred in 26 patients (26%), 20 (40%) in the control group and 6 (12%) in the remote ischemic preconditioning group (odds ratio, 0.21; 95% confidence interval, 0.07–0.57; P=0.002). No major adverse events were related to remote ischemic preconditioning. Conclusions— Remote ischemic preconditioning before contrast medium use prevents contrast medium–induced acute kidney injury in high-risk patients. Our findings merit a larger trial to establish the effect of remote ischemic preconditioning on clinical outcomes. Clinical Trial Registration— URL: http://www.germanctr.de. Unique identifier: U1111-1118-8098.

Dominant-Negative Suppression of HCN Channels Markedly Reduces the Native Pacemaker Current If and Undermines Spontaneous Beating of Neonatal Cardiomyocytes

Background—The pacemaker current If contributes to spontaneous diastolic depolarization of cardiac autonomic cells. In heterologous expression, HCN channels exhibit a hyperpolarization-activated inward current similar to If. However, the links between HCN genes and native If are largely inferential, and it remains unknown whether If is essential for cardiac pacing. Methods and Results—To clarify this situation, we generated a GYG402–404AYA pore mutation of HCN2, which rendered the channel nonfunctional and suppressed wild-type HCN2 in a dominant-negative manner in Chinese hamster ovary cells. In addition, HCN2-AYA suppressed IHCN4 in a dominant-negative manner when coexpressed with wild-type HCN4, indicating that the 2 isoforms HCN2 and HCN4 are able to coassemble to form heteromultimeric complexes. Given that HCN2 and HCN4 are the dominant HCN mRNA transcripts in neonatal rat ventricle, we expressed HCN2-AYA in neonatal cardiocytes using adenoviral gene transfer to test the effect of HCN suppression on native If. If density was indeed reduced markedly, from 7.8±1.6 pA/pF (n=13) in control cells to 0.3±0.2 pA/pF (n=11) in HCN2-AYA–infected cells when measured at −130 mV (P <0.001). To probe the effect of HCN on cardiac pacing, we infected spontaneously beating neonatal monolayers with adenoviral vectors expressing wild-type and mutant HCN channels. Infection with HCN2 and HCN4 accelerated the beating rate significantly, to 230.5±8.6 bpm (n=12) and 223.5±12.3 bpm (n=10), respectively, compared with control cultures (83.4±4.5 bpm, n=13, P <0.001). Conversely, HCN2-AYA completely undermined spontaneous pacing of neonatal cardiocytes. Conclusions—HCN channels are the major molecular component of native If and are critical for spontaneous beating of neonatal cardiomyocytes.

Endothelin induces differentiation of ANP-EGFP expressing embryonic stem cells towards a pacemaker phenotype

Currently, only limited insight into mechanisms promoting the differentiation and specification of the mammalian cardiac conduction system is available. Therefore, we established a murine embryonic stem (ES) cell line stably expressing the enhanced green fluorescent protein (EGFP) under the transcriptional control of the human atrial natriuretic peptide (ANP) promoter to further characterize the development of very early stages of the mammalian cardiac conduction tissue. The cardiac nature of ANP‐EGFP positive cells was confirmed by immunostaining. In ANP‐EGFP expressing ES cell‐derived cardiomyocytes, a distinct sublineage of pacemaker cells could be identified. Pacemaker cells displayed a spindle shape and exhibited a higher spontaneous beating rate, faster If current activation and larger If current densities compared with triangular atrial‐like cardiocytes. Exposure to endothelin‐1 significantly increased the percentage of pacemaker‐like cells without affecting their electrophysiological properties. These findings were corroborated by immunostaining with antibodies against connexin 40 and connexin 45, known markers for cardiac conduction tissue. Conversely, treatment of ANP‐EGFP expressing ES cells with neuregulin‐1 exhibited no effect on differentiation. These results indicate that ANP‐EGFP expression enables the identification of ES cell‐derived pacemaker cells by their fluorescence and morphology and that endothelin‐1 promotes the development of ANP‐EGFP positive cardiomyocytes to a pacemaker‐like phenotype.

Testosterone Induces Cytoprotection by Activating ATP-Sensitive K+ Channels in the Cardiac Mitochondrial Inner Membrane

Background—Whereas in the past, androgens were mainly believed to exert adverse effects on the cardiovascular system, recent experimental data postulate a benefit of testosterone for recovery of myocardial function after ischemia/reperfusion injury. Thus, we examined whether testosterone might improve myocardial tolerance to ischemia due to activation of mitochondrial (mitoKATP) and/or sarcoplasmatic (sarcKATP) KATP channels. Methods and Results—In a cellular model of ischemia, testosterone significantly decreased the rate of ischemia-induced death of cardiomyocytes that could be prevented by 5-hydroxydecainoic acid but was unaffected by the sarcKATP blocker HMR1098 and the testosterone receptor antagonist flutamide. To index mitoKATP, mitochondrial flavoprotein fluorescence was measured. Testosterone induced a highly significant increase in mitochondrial flavoprotein fluorescence in intact myocytes and isolated mitoplasts that could be abolished by 5-hydroxydecainoic acid. Testosterone-mediated flavoprotein oxidation of mitoplasts was K+ dependent and ATP sensitive. In mitoplast-attached single-channel recordings, testosterone directly activated an ATP-sensitive K+ channel of the inner mitochondrial membrane. Addition of the KATP channel opener diazoxide and pinacidil to the cytosolic solution activated the ATP-sensitive K+ current comparable to testosterone, whereas 5-hydroxydecainoic acid and glibenclamide inhibited the testosterone-induced current. Patch-clamp experiments of intact myocytes in whole-cell configuration did not demonstrate any effect of testosterone on sarcKATP channels. Conclusions—Our results provide direct evidence for the existence of cardiac mitoKATP and a link between testosterone-induced cytoprotection and activation of mitoKATP. Endogenous testosterone might play a more important role in recovery after myocardial infarction than is currently assumed.

Single-channel properties support a potential contribution of hyperpolarization-activated cyclic nucleotide-gated channels and If to cardiac arrhythmias.

Background—The pacemaker current If is present in atrial and ventricular myocytes. However, it remains controversial whether If overexpression in diseased states might play a role for arrhythmogenesis, because first If activation in whole-cell recordings hardly overlapped the diastolic voltage of working myocardium. Methods and Results—To obtain further insight into IHCN and If properties, we provide for the first time detailed single-channel analysis of heterologously expressed hyperpolarization-activated cyclic nucleotide-gated (HCN) isoforms and native human If. HCN subtypes differed significantly in single-channel amplitude, conductance, and activation kinetics. Interestingly, threshold potentials of HCN isoforms were more positive than would have been expected from whole-cell measurements. Single-channel properties of cells cotransfected with HCN2 and HCN4 were distinct from cells expressing HCN2 or HCN4 alone, demonstrating that different HCN isoforms can influence current properties of a single HCN channel complex, thus providing direct functional evidence for HCN heteromerization. Pooled data of homomeric and heteromeric HCN channels and of native If extrapolated from maximum likelihood fits indicated a multistate gating scheme comprising 5 closed- and 4 open-channel states. Single-channel characteristics of If in human atrial myocytes closely resembled those of HCN4 or HCN2+HCN4, supporting the hypothesis that native If channels in atrial myocardium are heteromeric complexes composed of HCN4 and/or HCN2. Most interestingly, half-maximal activation of single-channel atrial If (−68.3±4.9 mV; k=−9.9±1.5; n=8) was well within the diastolic voltage range of human atrial myocardium. Conclusions—These observations support a potential contribution of HCN/If to the arrhythmogenesis of working myocardium under pathological conditions.

Remote Ischemic Preconditioning and Renoprotection: From Myth to a Novel Therapeutic Option?

There is currently no effective prophylactic regimen available to prevent contrast-induced AKI (CI-AKI), a frequent and life-threatening complication after cardiac catheterization. Therefore, novel treatment strategies are required to decrease CI-AKI incidence and to improve clinical outcomes in these patients. Remote ischemic preconditioning (rIPC), defined as transient brief episodes of ischemia at a remote site before a subsequent prolonged ischemia/reperfusion injury of the target organ, is an adaptational response that protects against ischemic and reperfusion insult. Indeed, several studies demonstrated the tissue-protective effects of rIPC in various target organs, including the kidneys. In this regard, rIPC may offer a novel noninvasive and virtually cost-free treatment strategy for decreasing CI-AKI incidence. This review evaluates the current experimental and clinical evidence for rIPC as a potential renoprotective strategy, and discusses the underlying mechanisms and key areas for future research.

Andersen mutations of KCNJ2 suppress the native inward rectifier current IK1 in a dominant-negative fashion

OBJECTIVE The Andersens syndrome is a hereditary disease, which is characterized by cardiac arrhythmias, periodic paralysis and dysmorphic features. Recently, mutations of the KCNJ2 gene, which encodes the inward rectifying potassium channel subunit Kir2.1, have been identified in affected individuals. However, the functional effects of these mutations have not yet been fully elucidated. METHODS AND RESULTS To clarify this situation we generated known Andersen disease mutants of KCNJ2 which did not yield any measurable K(+) currents in CHO cells indicating that the Andersen mutants failed to form functional homomultimeric complexes. EGFP-tagged KCNJ2 wild-type and mutant channels distributed in a similar homogeneous pattern in the cell membrane suggesting that protein trafficking was not altered by the Andersen mutations but rather implicating that the mutations rendered the KCNJ2 channel non-functional. In heterologous coexpression experiments the Andersen mutants exerted a dominant-negative effect on wild-type KCNJ2. However, the extent of suppression varied between the different KCNJ2 mutants. Given our results in CHO cells, we expressed the disease mutant KCNJ2-S136F in neonate rat cardiomyocytes using adenoviral gene transfer to test the effect of Andersen mutants on native I(K1). I(K1) density was indeed significantly reduced in KCNJ2-S136F-infected cells (n=9) compared to control cells (n=9) over a voltage range from -70 to -150 mV (P<0.05). CONCLUSION These results support that Kir2.x channels are a critical component of native I(K1) in neonate rat cardiomyocytes and that a dominant-negative suppression of I(K1) in native cells is the pathophysiological correlate of the Andersens syndrome.

Arginine vasopressin (AVP) and treatment with arginine vasopressin receptor antagonists (vaptans) in congestive heart failure, liver cirrhosis and syndrome of inappropriate antidiuretic hormone secretion (SIADH).

Arginine vasopressin (AVP) is the major physiological regulator of renal water excretion and blood volume. The AVP pathways of V1aR-mediated vasoconstriction and V2R-induced water retention represent a potentially attractive target of therapy for edematous diseases. Experimental and clinical evidence suggests beneficial effects of AVP receptor antagonists by increasing free water excretion and serum sodium levels. This review provides an update on the therapeutic implication of newly developed AVP receptor antagonists in respective disorders, such as chronic heart failure, liver cirrhosis and syndrome of inappropriate antidiuretic hormone secretion.

K+ channel regulator KCR1 suppresses heart rhythm by modulating the pacemaker current If.

Hyperpolarization-activated, cyclic nucleotide sensitive (HCN) channels underlie the pacemaker current If, which plays an essential role in spontaneous cardiac activity. HCN channel subunits (HCN1-4) are believed to be modulated by additional regulatory proteins, which still have to be identified. Using biochemistry, molecularbiology and electrophysiology methods we demonstrate a protein-protein interaction between HCN2 and the K+ channel regulator protein 1, named KCR1. In coimmunoprecipitation experiments we show that KCR1 and HCN2 proteins are able to associate. Heterologously expressed HCN2 whole-cell current density was significantly decreased by KCR1. KCR1 profoundly suppressed IHCN2 single-channel activity, indicating a functional interaction between KCR1 and the HCN2 channel subunit. Endogenous KCR1 expression could be detected in adult and neonatal rat ventriculocytes. Adenoviral-mediated overexpression of KCR1 in rat cardiomyocytes (i) reduced If whole-cell currents, (ii) suppressed most single-channel gating parameters, (iii) altered the activation kinetics, (iv) suppressed spontaneous action potential activity, and (v) the beating rate. More importantly, siRNA-based knock-down of endogenous KCR1 increased the native If current size and single-channel activity and accelerated spontaneous beating rate, supporting an inhibitory action of endogenous KCR1 on native If. Our observations demonstrate for the first time that KCR1 modulates IHCN2/If channel gating and indicate that KCR1 serves as a regulator of cardiac automaticity.

Local Thrombolysis for Successful Treatment of Acute Stroke in an Adolescent with Cardiac Myxoma

Intracardiac myxomas are the most common benign cardiac tumors in adults. They are a rare source of cardiogenic embolisms and sudden death, especially in young patients. This report describes the case of a male adolescent who presented with right-sided paresis and aphasia. Magnetic resonance imaging of the brain revealed an ischemic stroke without evidence of acute bleeding. Intra-arterial local thrombolysis was immediately started. An echocardiographic screening after successful thrombolysis with a remarkable recovery of symptoms detected a thrombotic-like mass in the left atrium. The mass was excised surgically, confirmed as a benign atrial myxoma, and the patient was discharged with restitution ad integrum. Thus, contrary to some critical reports, thrombolytic therapy for acute ischemic strokes due to atrial myxomas may be safe and highly effective.