Rajesh Kabra

Nedd4-2 Induces Endocytosis and Degradation of Proteolytically Cleaved Epithelial Na+ Channels

As a pathway for Na+ reabsorption, the epithelial Na+ channel ENaC is critical for Na+ homeostasis and blood pressure control. Na+ transport is regulated by Nedd4-2, an E3 ubiquitin ligase that decreases ENaC expression at the cell surface. To investigate the underlying mechanisms, we proteolytically cleaved/activated ENaC at the cell surface and then quantitated the rate of disappearance of cleaved channels using electrophysiological and biochemical assays. We found that cleaved ENaC channels were rapidly removed from the cell surface. Deletion or mutation of the Nedd4-2 binding motifs in α, β, and γENaC dramatically reduced endocytosis, whereas a mutation that disrupts a YXXØ endocytosis motif had no effect. ENaC endocytosis was also decreased by silencing of Nedd4-2 and by expression of a dominant negative Nedd4-2 construct. Conversely, Nedd4-2 overexpression increased ENaC endocytosis in human embryonic kidney 293 cells but had no effect in Fischer rat thyroid epithelia. In addition to its effect on endocytosis, Nedd4-2 also increased the rate of degradation of the cell surface pool of cleaved αENaC. Together the data indicate that Nedd4-2 reduces ENaC surface expression by altering its trafficking at two distinct sites in the endocytic pathway, inducing endocytosis of cleaved channels and targeting them for degradation.

Hrs Controls Sorting of the Epithelial Na+ Channel between Endosomal Degradation and Recycling Pathways

Epithelial Na+ absorption is regulated by Nedd4-2, an E3 ubiquitin ligase that reduces expression of the epithelial Na+ channel (ENaC) at the cell surface. Defects in this regulation cause Liddle syndrome, an inherited form of hypertension. Previous work found that Nedd4-2 functions through two distinct effects on trafficking, enhancing both ENaC endocytosis and ENaC degradation in lysosomes. To investigate the mechanism by which Nedd4-2 targets ENaC to lysosomes, we tested the role of hepatocyte growth factor-regulated tyrosine kinase substrate (Hrs), a component of the endosomal sorting complexes required for transport (ESCRT)-0 complex. We found that α-, β-, and γENaC each interact with Hrs. These interactions were enhanced by Nedd4-2 and were dependent on the catalytic function of Nedd4-2 as well as its WW domains. Mutation of ENaC PY motifs, responsible for inherited hypertension (Liddle syndrome), decreased Hrs binding to ENaC. Moreover, binding of ENaC to Hrs was reduced by dexamethasone/serum- and glucocorticoid-inducible kinase and cAMP, which are signaling pathways that inhibit Nedd4-2. Nedd4-2 bound to Hrs and catalyzed Hrs ubiquitination but did not alter Hrs protein levels. Expression of a dominant negative Hrs lacking its ubiquitin-interacting motif (Hrs-ΔUIM) increased ENaC surface expression and current. This occurred through reduced degradation of the cell surface pool of proteolytically activated ENaC, which enhanced its recycling to the cell surface. In contrast, Hrs-ΔUIM had no effect on degradation of uncleaved inactive channels. The data support a model in which Nedd4-2 induces binding of ENaC to Hrs, which mediates the sorting decision between ENaC degradation and recycling.

Incidence and Electrophysiologic Properties of Dissociated Pulmonary Vein Activity Following Pulmonary Vein Isolation During Catheter Ablation of Atrial Fibrillation

Dissociated PV Activity During AF Ablation. Introduction: Pulmonary veins (PV) play an important role in the arrhythmogenesis of atrial fibrillation (AF). Catheter‐based PV isolation is one of the primary treatments for symptomatic drug refractory AF. Following electrical isolation, isolated rhythms in the PV are encountered. The aim of this study was to assess the frequency of postisolation PV activity and classify the different rhythms observed.

Effect of Race on Outcomes (Stroke and Death) in Patients >65 Years With Atrial Fibrillation

Atrial fibrillation (AF) is associated with stroke and death. We sought to determine whether there are any racial differences in the outcomes of death and stroke in patients with AF. We used Medicare administrative data from January 1, 2010, to December 31, 2011, to identify 517,941 patients with newly diagnosed AF. Of these, 452,986 patients (87%) were non-Hispanic white, 36,425 (7%) were black, and 28,530 (6%) were Hispanic. The association between race and outcomes of death and stroke were measured using Cox proportional hazard models. Over a median follow-up period of 20.3 months, blacks had a significantly higher hazard of death (hazard ratio [HR] = 1.46; 95% confidence interval [CI] 1.43 to 1.48; p <0.001) and stroke (HR = 1.66; 95% CI 1.57 to 1.75; p <0.001), compared with white patients. After controlling for pre-existing co-morbidities, the higher hazard of death in blacks was eliminated (HR 0.95; 95% CI 0.93 to 0.96; p <0.001) and the relative hazard of stroke was reduced (HR = 1.46; 95% CI 1.38 to 1.55; p <0.001). Similarly, Hispanics had a higher risk of death (HR = 1.11; 95% CI 1.09 to 1.14; p <0.001) and stroke (HR = 1.21; 95% CI 1.13 to 1.29; p <0.001) compared with whites. The relative hazard of death was lower in Hispanics (HR 0.82; 95% CI 0.80 to 0.84; p <0.001) compared with whites, after controlling for pre-existing co-morbidities, and the relative hazard of stroke was also attenuated (HR = 1.11; 95% CI 1.03 to 1.18; p <0.001). In conclusion, in patients >65 years with newly diagnosed AF, the risks of death and stroke are higher in blacks and Hispanics compared with whites. The increased risk was eliminated or significantly reduced after adjusting for pre-existing co-morbidities. AF may be a marker for underlying co-morbidities in black and Hispanic patients who may be at a higher mortality risk.

The dual role of implantable loop recorder in patients with potentially arrhythmic symptoms: a retrospective single-center study.

Background: Unexplained and potentially arrhythmic symptoms often lead to electrophysiology referral for evaluation. Implantable loop recorder (ILR) correlation of the symptom to the rhythm can secure a definitive arrhythmic diagnosis after a standard, yet nondiagnostic workup.

Catheter ablation targeting complex fractionated atrial electrograms for the control of atrial fibrillation.

Purpose of review Catheter ablation of persistent atrial fibrillation has a lower success rate than for paroxysmal atrial fibrillation, due to structural, electrical and anatomical remodeling of the left atrium. Ablation strategies targeting complex fractionated atrial electrograms (CFAEs) are commonly employed to identify and eliminate the substrate responsible for atrial fibrillation maintenance in persistent cases. This review discusses the pathophysiology as well as the role of targeting CFAEs in catheter ablation of atrial fibrillation. Recent findings As our understanding regarding the origin and role of CFAEs in atrial fibrillation continues to evolve, there have been multiple recent studies looking at pathophysiology, distribution and significance of CFAEs in atrial fibrillation. In addition, different ablation strategies targeting CFAEs have been compared with the standard pulmonary vein isolation in persistent as well as paroxysmal atrial fibrillation. Recent meta-analysis studies have striven to identify atrial fibrillation patients who would benefit from CFAE ablation. Summary Whereas CFAE ablation in addition to standard pulmonary vein isolation improves outcomes in patients with persistent atrial fibrillation, there is no benefit of CFAE ablation in paroxysmal atrial fibrillation. Further studies are required to define and identify CFAEs more accurately, in a standardized manner, to enhance the success of catheter ablation and freedom from atrial fibrillation.

Direct oral anticoagulant use in nonvalvular atrial fibrillation with valvular heart disease: a systematic review

Direct oral anticoagulants (DOACs) are indicated for stroke prevention in patients with nonvalvular atrial fibrillation (NVAF), which, according to the American College of Cardiology/American Heart Association/Heart Rhythm Society atrial fibrillation (AF) guidelines, excludes patients with rheumatic mitral stenosis, a mechanical or bioprosthetic heart valve, or mitral valve repair. However, the data regarding use of DOACs in AF patients with other types of valvular heart disease (VHD) are unclear. We aimed to summarize and evaluate the literature regarding the safety and efficacy of DOAC use in NVAF patients with other types of VHD. After an extensive literature search, a total of 1 prospective controlled trial, 4 subanalyses, and 1 abstract were identified. Efficacy of the DOAC agents in NVAF patients with VHD mirrored the overall trial results. Bleeding risk was significantly increased in VHD patients treated with rivaroxaban, but not for dabigatran or apixaban. Of the bioprosthetic valve patients enrolled in the Apixaban for Reduction in Stroke and Other Thromboembolic Events in Atrial Fibrillation (ARISTOTLE) trial, no safety or efficacy concerns were identified. In conclusion, subanalyses of DOAC landmark AF trials revealed that dabigatran, rivaroxaban, and apixaban may be safely used in AF patients with certain types of VHD: aortic stenosis, aortic regurgitation, and mitral regurgitation. More evidence is needed before routinely recommending these agents for patients with bioprosthetic valves or mild mitral stenosis. Patients with moderate to severe mitral stenosis or mechanical valves should continue to receive warfarin, as these patients were excluded from all landmark AF trials.

Dabigatran Use in the Real World A Multihospital System Experience

Dabigatran etexilate, an oral direct thrombin inhibitor, was approved by the Food and Drug Administration to reduce the risk of stroke and systemic embolism in patients with nonvalvular atrial fibrillation based on the outcomes of the Randomized Evaluation of Long-term anticoagulant therapY (RE-LY) study. Although this study provides robust data on the efficacy and safety of dabigatran, there may be differences in the drug use and outcomes in routine clinical practice following drug approval. In this retrospective chart review study, we describe the use of dabigatran in 160 patients in 4 adult hospitals (1 academic and 3 community), including appropriate prescribing for indication, starting dose, concomitant anticoagulant and antiplatelet use, and clinical outcomes such as bleeding, myocardial infarction, and stroke. The study revealed appropriate indication of nonvalvular atrial fibrillation in 145 (91%) of the 160 patients. The dose of dabigatran was appropriate in 90% of the patients, with the most common cause of inappropriate dosing due to perceived bleeding risk. Over a follow-up period of 6 months, bleeding complications were noted in 6 patients still taking dabigatran, 5 of which were gastrointestinal bleeding. Our study underscores the importance of prescriber education regarding the appropriate indication, dosage, and safety of dabigatran with active participation of pharmacists in this process.

Novel oral anticoagulants for the prevention and treatment of thromboembolism

Over the last 5 years, new oral anticoagulant options, including dabigatran, rivaroxaban and apixaban, have become available. Prior to this, vitamin K antagonists were the sole oral anticoagulants, which have been in use for more than 60 years. These novel agents have been studied in a variety of patient populations, including atrial fibrillation, acute coronary syndrome, treatment of venous thromboembolism and thromboprophylaxis. Compared with standard care, these agents have largely been found to be noninferior or superior for efficacy end points, with similar or improved rates of bleeding. As a result, these agents have become attractive alternatives to vitamin K antagonists for the prevention and treatment of thromboembolic disease. This article provides a summary of clinical trial data to help clinicians determine which agent is most appropriate for a given patient.

Marijuana, bigeminal premature ventricular contractions and sluggish coronary flow: Are they related?

Premature ventricular contractions (PVCs) and slow coronary flow phenomenon (SCFP) are primarily separate entities. Each one of them has different characteristics and a diverse spectrum of presentation. However, and despite many suggested theories, a comprehensive understanding of the etiology of both of them is still a matter of debate. PVCs, which can be triggered by consuming cannabis (marijuana), and through decreasing the diastolic time (DT), can affect the slow blood flow found in SCFP even more and worsen the clinical picture in patients who have PVCs and SCFP. In this paper, we present a patient who uses marijuana and has PVCs and SCFP, try to address different aspects of PVCs and SCFP, pinpoint any suspected interaction between both of them and the role of marijuana in this context. <Learning objective: (i) PVCs are extra abnormal heartbeats arising in one of the ventricles and disrupting the normal rhythm of the heart. (ii) PVCs are very common and occur in a broad spectrum of the population including those with and without underlying heart disease. (iii) SCFP is an angiographic finding characterized by delayed progression of the contrast injected inside large coronary arteries without any significant CAD. (iv) It has an incidence of 1% among patients who undergo coronary angiography, especially those presenting with acute coronary syndrome. (v) PVCs, which can be triggered by consuming cannabis (marijuana), and throughout decreasing the DT, can affect the slow blood flow found in SCFP even more and worsen the clinical picture in patients who have PVCs and SCFP.>.