Biochemical characterization of ecto-nucleotide pyrophosphatase/phosphodiesterase (E-NPP, E.C. 3.1.4.1) from rat heart left ventricle

In the present study we investigate the biochemical properties of the members of NPP family in synaptosomes prepared from rat heart left ventricles. Using p-nitrophenyl-5′-thymidine monophosphate (p-Nph-5′-TMP) as substrate for E-NPPs in rat cardiac synaptosomes, we observed an alkaline pH dependence, divalent cation dependence and the K _M value corresponded to 91.42 ± 13.97 μM and the maximal velocity (V _max ) value calculated was 63.79 ± 3.59 nmol p-nitrophenol released/min/mg of protein (mean ± SD, n = 4). Levamisole (1 mM), was ineffective as inhibitor of p-Nph-5′-TMP hydrolysis in pH 8.9 (optimum pH for the enzyme characterized). Suramin (0.25 mM) strongly reduced the hydrolysis of p-Nph-5′-TMP by about 46%. Sodium azide (10 and 20 mM) and gadolinium chloride (0.3 and 0.5 mM), E-NTPases inhibitors, had no effects on p-Nph-5′-TMP hydrolysis. RT-PCR analysis of left ventricle demonstrated the expression of NPP2 and NPP3 enzymes, but excluded the presence of NPP1 member. By quantitative real-time PCR we identified the NPP3 as the enzyme with the highest expression in rat left ventricle. The demonstration of the presence of the E-NPP family in cardiac system, suggest that these enzymes could contribute with the fine-tuning control of the nucleotide levels at the nerve terminal endings of left ventricles that are involved in several cardiac pathologies.     

Role of cardiovascular nitric oxide system in C-type natriuretic peptide effects

The aims were to evaluate the role of cardiovascular nitric oxide (NO)-system in C-type natriuretic peptide (CNP) actions and to investigate receptor types and signaling pathways involved in this interaction. Wistar rats were infused with saline or CNP. Mean arterial pressure (MAP) and nitrites and nitrates (NOx) excretion were determined. NO synthase (NOS) activity and NOS expression (Western blot) were analyzed in atria, ventricle and aorta. CNP decreased MAP and increased NOx excretion. CNP estimulated NOS activity, inducing no changes on cardiac and vascular endothelial NOS expression. NOS activity induced by CNP was abolished by suramin and calmidazoliumand but it is not modified by anantin. CNP would interact with NPR-C receptor coupled via G proteins leading to the activation Ca(2+)-calmodulin dependent endothelial NOS, increasing NO production which would induce the reduction in cardiac myocyte contractility and ANP synthesis and secretion in right atria and the relaxation of vascular smooth muscle.     

Stacking geometry for non‐canonical G:U wobble base pair containing dinucleotide sequences in RNA: dispersion‐corrected DFT‐D study

Emergence of thousands of crystal structures of noncoding RNA molecules indicates its structural and functional diversity. RNA function is based upon a large variety of structural elements which are specifically assembled in the folded molecules. Along with the canonical Watson‐Crick base pairs, different orientations of the bases to form hydrogen‐bonded non‐canonical base pairs have also been observed in the available RNA structures. Frequencies of occurrences of different non‐canonical base pairs in RNA indicate their important role to maintain overall structure and functions of RNA. There are several reports on geometry and energetic stabilities of these non‐canonical base pairs. However, their stacking geometry and stacking stability with the neighboring base pairs are not well studied. Among the different non‐canonical base pairs, the G:U wobble base pair (G:U W:WC) is most frequently observed in the RNA double helices. Using quantum chemical method and available experimental data set we have studied the stacking geometry of G:U W:WC base pair containing dinucleotide sequences in roll‐slide parameters hyperspace for different values of twist. This study indicates that the G:U W:WC base pair can stack well with the canonical base pairs giving rise to large interaction energy. The overall preferred stacking geometry in terms of roll, twist and slide for the eleven possible dinucleotide sequences is seen to be quite dependent on their sequences. © 2015 Wiley Periodicals, Inc. Biopolymers 103: 328–338, 2015.     

Delayed AICD therapy and cardiac arrest resulting from undersensing of ventricular fibrillation in a subject with hypertrophic cardiomyopathy–A case report

Defibrillation testing is no longer routinely performed after automatic implantable cardioverter-defibrillator (AICD) implantation. However, certain subjects undergoing AICD implantation may be at higher risk of undersensing of ventricular arrhythmias resulting in potentially fatal outcomes. We present the case of a 30-year-old woman with hypertrophic cardiomyopathy (HCM; ‘asymmetric septal hypertophy’ morphologic variant) and prophylactic AICD who experienced an out of hospital cardiac arrest. AICD interrogation revealed undersensing as a result of intermittent high amplitude electrograms during an episode of ventricular fibrillation (VF). The subject underwent replacement and repositioning of the AICD lead along with pulse generator replacement (that utilized a different VF sensing algorithm) with appropriate sensing of VF and successful defibrillation testing. The presence of intermittent high amplitude electrograms during episodes of VF in AICDs using the AGC function should be recognized as a situation that may necessitate interventions to prevent undersensing and consequent delay in therapy.     

Decrease in Plasma Cyclophilin A Concentration at 1 Month after Myocardial Infarction Predicts Better Left Ventricular Performance and Synchronicity at 6 Months: A Pilot Study in Patients with ST Elevation Myocardial Infarction

Background: Cyclophilin A (CyPA) concentration increases in acute coronary syndrome. In an animal model of acute myocardial infarction, administration of angiotensin-converting-enzyme inhibitor was associated with lower left ventricular (LV) CyPA concentration and improved LV performance. This study investigated the relationships between changes in plasma CyPA concentrations and LV remodeling in patients with ST-elevation myocardial infarction (STEMI).Methods and Results: We enrolled 55 patients who underwent percutaneous coronary intervention for acute STEMI. Plasma CyPA, matrix metalloproteinase (MMP), interleukin-6 and high-sensitivity C-reactive protein concentrations were measured at baseline and at one-month follow-up. Echocardiography was performed at baseline and at one-, three-, and six-month follow-up. Patients with a decrease in baseline CyPA concentration at one-month follow-up (n = 28) had a significant increase in LV ejection fraction (LVEF) (from 60.2 ± 11.5% to 64.6 ± 9.9%, p < 0. 001) and preserved LV synchrony at six months. Patients without a decrease in CyPA concentration at one month (n = 27) did not show improvement in LVEF and had a significantly increased systolic dyssynchrony index (SDI) (from 1.170 ± 0.510% to 1.637 ± 1.299%, p = 0.042) at six months. Multiple linear regression analysis showed a significant association between one-month CyPA concentration and six-month LVEF. The one-month MMP-2 concentration was positively correlated with one-month CyPA concentration and LV SDI.Conclusions: Decreased CyPA concentration at one-month follow-up after STEMI was associated with better LVEF and SDI at six months. Changes in CyPA, therefore, may be a prognosticator of patient outcome.     

Entrainment during Ablation of Ischemic Ventricular Tachycardia. What is explanation for Post Pacing Interval shorter than the tachycardia cycle length?

Entrainment mapping of ischemic ventricular tachycardia at a site in the left ventricle where radiofrequency ablation was successful in terminating the tachycardia revealed a post-pacing interval shorter than the tachycardia cycle length. The reason for the same is explained in the current report.     

Co-variation in frequency and severity of cardiovascular and skeletal defects in Sprague-Dawley rats after maternal administration of dimethadione, the N-demethylated metabolite of trimethadione

BACKGROUND: The anticonvulsant trimethadione is a potent inducer of ventricular septation defects, both clinically and in rodents. Teratogenicity requires its N‐demethylation to dimethadione, the proximate teratogen. It was previously demonstrated trimethadione only induced membranous ventricular septation defects in rat (Fleeman et al., 2004 ), and our present goal is to determine whether direct administration of dimethadione increases the incidence and severity of septation defects. METHODS: Pregnant Sprague‐Dawley rats were divided into five groups and administered either distilled water (control) or four different regimens of dimethadione. The core treatment was 300 mg/kg dimethadione b.i.d. on gestation day 9, 10 with additional groups given one additional dose of dimethadione 12 hr earlier, 12 hr later or two additional doses 12 hr earlier and later. Caesarian sections occurred on gestation day 21 and fetuses were examined for standard developmental toxicity endpoints. RESULTS: The broadest dosing regimen yielded the highest incidence and the most severe heart and axioskeletal findings with a decrease in mean fetal body weight. The overall incidence of ventricular septation defects was 74%, of which 68% were membranous and 9% muscular. Outflow tract anomalies (17%) were also observed, as were malformations of the axioskeleton (97%), but not of the long bones, and of particular interest was the high incidence of sternoschesis. CONCLUSIONS: Unlike trimethadione, dimethadione induces more serious muscular septation defects that are believed to be more clinically relevant. This, when taken together with the high incidence of total septation anomalies suggests dimethadione is useful for the study of chemically induced ventricular septation defects. Birth Defects Res (Part B) 92:206–215, 2011. © 2011 Wiley‐Liss, Inc.     

Preservation of TSPO by chronic intermittent hypobaric hypoxia confers antiarrhythmic activity

Abnormal activation of mitochondrial translocator protein (TSPO) contributes to arrhythmogenesis during cardiac metabolic compromise; however, its role in the antiarrhythmic activities of chronic hypoxia adaptation remains unclear. Our results demonstrated that 80% of normoxic rats developed ischaemic VF, whereas this condition was seldom observed in rats with 14 days of chronic intermittent hypobaric hypoxia (CIHH). TSPO stimulation or inhibition affected the arrhythmias incidence in normoxic rats, but did not change the CIHH‐mediated antiarrhythmic effects. Abrupt and excessive elevation of TSPO activity was positively linked to ischaemic VF, and CIHH preserved TSPO activity during ischaemia. The preservation of TSPO activity by CIHH also contributed to the maintenance of intracellular Ca homeostasis. These results suggest that the blunt sensitivity of TSPO to ischaemic stress may be responsible for the antiarrhythmic effects by CIHH.     

Taxol,a microtubule stabilizer,prevents ischemic ventricular arrhythmias in rats

Microtubule integrity is important in cardio‐protection, and microtubule disruption has been implicated in the response to ischemia in cardiac myocytes. However, the effects of Taxol, a common microtubule stabilizer, are still unknown in ischemic ventricular arrhythmias. The arrhythmia model was established in isolated rat hearts by regional ischemia, and myocardial infarction model by ischemia/reperfusion. Microtubule structure was immunohistochemically measured. The potential mechanisms were studied by measuring reactive oxygen species (ROS), activities of oxidative enzymes, intracellular calcium concentration ([Ca²⁺]_i) and Ca²⁺ transients by using fluorometric determination, spectrophotometric assays and Fura‐2‐AM and Fluo‐3‐AM, respectively. The expression and activity of sarcoplasmic reticulum Ca²⁺‐ATPase (SERCA2a) was also examined using real‐time polymerase chain reaction, Western blot and pyruvate/Nicotinamide adenine dinucleotide‐coupled reaction. Our data showed that Taxol (0.1, 0.3 and 1 μM) effectively reduced the number of ventricular premature beats and the incidence and duration of ventricular tachycardia. The infarct size was also significantly reduced by Taxol (1 μM). At the same time, Taxol preserved the microtubule structure, increased the activity of mitochondrial electron transport chain complexes I and III, reduced ROS levels, decreased the rise in [Ca²⁺]_i and preserved the amplitude and decay times of Ca²⁺ transients during ischemia. In addition, SERCA2a activity was preserved by Taxol during ischemia. In summary, Taxol prevents ischemic ventricular arrhythmias likely through ameliorating abnormal calcium homeostasis and decreasing the level of ROS. This study presents evidence that Taxol may be a potential novel therapy for ischemic ventricular arrhythmias.