Genetically engineered SCN5A mutant pig hearts exhibit conduction defects and arrhythmias

SCN5A encodes the α subunit of the major cardiac sodium channel Na_V1.5. Mutations in SCN5A are associated with conduction disease and ventricular fibrillation (VF); however, the mechanisms that link loss of sodium channel function to arrhythmic instability remain unresolved. Here, we generated a large-animal model of a human cardiac sodium channelopathy in pigs, which have cardiac structure and function similar to humans, to better define the arrhythmic substrate. We introduced a nonsense mutation originally identified in a child with Brugada syndrome into the orthologous position (E558X) in the pig SCN5A gene. SCN5A^E558X/+ pigs exhibited conduction abnormalities in the absence of cardiac structural defects. Sudden cardiac death was not observed in young pigs; however, Langendorff-perfused SCN5A^E558X/+ hearts had an increased propensity for pacing-induced or spontaneous VF initiated by short-coupled ventricular premature beats. Optical mapping during VF showed that activity often began as an organized focal source or broad wavefront on the right ventricular (RV) free wall. Together, the results from this study demonstrate that the SCN5A^E558X/+ pig model accurately phenocopies many aspects of human cardiac sodium channelopathy, including conduction slowing and increased susceptibility to ventricular arrhythmias.     

The Cyclic Peptide Ecumicin Targeting ClpC1 Is Active against Mycobacterium tuberculosis In Vivo

Drug-resistant tuberculosis (TB) has lent urgency to finding new drug leads with novel modes of action. A high-throughput screening campaign of >65,000 actinomycete extracts for inhibition of Mycobacterium tuberculosis viability identified ecumicin, a macrocyclic tridecapeptide that exerts potent, selective bactericidal activity against M. tuberculosis in vitro, including nonreplicating cells. Ecumicin retains activity against isolated multiple-drug-resistant (MDR) and extensively drug-resistant (XDR) strains of M. tuberculosis. The subcutaneous administration to mice of ecumicin in a micellar formulation at 20 mg/kg body weight resulted in plasma and lung exposures exceeding the MIC. Complete inhibition of M. tuberculosis growth in the lungs of mice was achieved following 12 doses at 20 or 32 mg/kg. Genome mining of lab-generated, spontaneous ecumicin-resistant M. tuberculosis strains identified the ClpC1 ATPase complex as the putative target, and this was confirmed by a drug affinity response test. ClpC1 functions in protein breakdown with the ClpP1P2 protease complex. Ecumicin markedly enhanced the ATPase activity of wild-type (WT) ClpC1 but prevented activation of proteolysis by ClpC1. Less stimulation was observed with ClpC1 from ecumicin-resistant mutants. Thus, ClpC1 is a valid drug target against M. tuberculosis, and ecumicin may serve as a lead compound for anti-TB drug development.     

Expectations and limitations due to brachial plexus injury: a qualitative study

Purpose

This study described physical and psychosocial limitations associated with adult brachial plexus injuries (BPI) and patients’ expectations of BPI surgery.

Methods

During in-person interviews, preoperative patients were asked about expectations of surgery and preoperative and postoperative patients were asked about limitations due to BPI. Postoperative patients also rated improvement in condition after surgery. Data were analyzed with qualitative and quantitative techniques.

Results

Ten preoperative and 13 postoperative patients were interviewed; mean age was 37 years, 19 were men, all were employed/students, and most injuries were due to trauma. Preoperative patients cited several main expectations, including pain-related issues, and improvement in arm movement, self-care, family interactions, and global life function. Work-related expectations were tailored to employment type. Preoperative and postoperative patients reported that pain, altered sensation, difficulty managing self-care, becoming physically and financially dependent, and disability in work/school were major issues. All patients reported making major compensations, particularly using the uninjured arm. Most reported multiple mental health effects, were distressed with long recovery times, were self-conscious about appearance, and avoided public situations. Additional stresses were finding and paying for BPI surgery. Some reported BPI impacted overall physical health, life priorities, and decision-making processes. Four postoperative patients reported hardly any improvement, four reported some/a good deal, and five reported a great deal of improvement.

Conclusions

BPI is a life-altering event affecting physical function, mental well-being, financial situation, relationships, self-image, and plans for the future. This study contributes to clinical practice by highlighting topics to address to provide comprehensive BPI patient-centered care.     

Intracellular calcium cycling, early afterdepolarizations, and reentry in simulated long QT syndrome.

OBJECTIVES: The purpose of this study was to investigate interactions between early afterdepolarizations (EADs) and reentry in long QT (LQT) syndromes. BACKGROUND: EADs, a characteristic feature of congenital and acquired LQT syndromes, are classically bradycardia dependent. Mechanisms by which they promote tachyarrhythmias such as torsades de pointes and ventricular fibrillation are not fully understood. Recent evidence suggests that EADs also may occur at rapid heart rates as a sequela of spontaneous sarcoplasmic reticulum (SR) Ca(2+) release related to intracellular Ca(2+) overload. Here, we performed computer simulations to explore the arrhythmogenic consequences of this phenomenon. METHODS: We used a modified version of the Luo-Rudy dynamic model in one-dimensional and two-dimensional cardiac tissue with the time-dependent K(+) currents I(Kr) or I(Ks) reduced by 50% to simulate acquired and congenital LQT syndromes. RESULTS: (1) Spontaneous SR Ca(2+) release prolonged action potential duration but did not induce overt EADs unless K(+) current density was reduced to simulate acquired and congenital LQT syndromes. (2) In simulated LQT syndromes, EADs were capable of both terminating and reinitiating one-dimensional reentry. (3) A similar phenomenon in simulated 2D tissue led to reinitiation of spiral wave reentry that otherwise would have self-terminated. (4) Reentry reinitiation occurred only when the L-type Ca(2+) current and SR Ca(i) cycling were potentiated to simulate moderate sympathetic stimulation, consistent with the known arrhythmogenic effects of sympathetic activation (and protection by beta-blockers) in LQT syndromes. CONCLUSIONS: These computer simulations suggest that EADs related to spontaneous SR Ca(2+) release can enhance arrhythmogenesis in LQT syndromes by reinitiating reentry.