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BackgroundSmall-conductance Ca2+-activated K+ (SK)-channel inhibitors have antiarrhythmic effects in animal models of atrial fibrillation (AF), presenting a potential novel antiarrhythmic option. However, the regulation of SK-channels in human atrial cardiomyocytes and its modification in patients with AF are poorly understood and were the object of this study.MethodsApamin-sensitive SK-channel current (ISK) and action potentials were recorded in human right-atrial cardiomyocytes from sinus rhythm control (Ctl) patients or patients with (long-standing persistent) chronic AF (cAF).ResultsISK was significantly higher, and apamin caused larger action potential prolongation in cAF- versus Ctl-cardiomyocytes. Sensitivity analyses in an in silico human atrial cardiomyocyte model identified IK1 and ISK as major regulators of repolarization. Increased ISK in cAF was not associated with increases in mRNA/protein levels of SK-channel subunits in either right- or left-atrial tissue homogenates or right-atrial cardiomyocytes, but the abundance of SK2 at the sarcolemma was larger in cAF versus Ctl in both tissue-slices and cardiomyocytes. Latrunculin-A and primaquine (anterograde and retrograde protein-trafficking inhibitors) eliminated the differences in SK2 membrane levels and ISK between Ctl- and cAF-cardiomyocytes. In addition, the phosphatase-inhibitor okadaic acid reduced ISK amplitude and abolished the difference between Ctl- and cAF-cardiomyocytes, indicating that reduced calmodulin-Thr80 phosphorylation due to increased protein phosphatase-2A levels in the SK-channel complex likely contribute to the greater ISK in cAF-cardiomyocytes. Finally, rapid electrical activation (5 Hz, 10 minutes) of Ctl-cardiomyocytes promoted SK2 membrane-localization, increased ISK and reduced action potential duration, effects greatly attenuated by apamin. Latrunculin-A or primaquine prevented the 5-Hz-induced ISK-upregulation.ConclusionsISK is upregulated in patients with cAF due to enhanced channel function, mediated by phosphatase-2A-dependent calmodulin-Thr80 dephosphorylation and tachycardia-dependent enhanced trafficking and targeting of SK-channel subunits to the sarcolemma. The observed AF-associated increases in ISK, which promote reentry-stabilizing action potential duration shortening, suggest an important role for SK-channels in AF auto-promotion and provide a rationale for pursuing the antiarrhythmic effects of SK-channel inhibition in humans.

RationaleThe mechanisms underlying atrial fibrillation (AF), the most common clinical arrhythmia, are poorly understood. Nucleoplasmic Ca2+ regulates gene expression, but the nature and significance of nuclear Ca2+-changes in AF are largely unknown.ObjectiveTo elucidate mechanisms by which AF alters atrial-cardiomyocyte nuclear Ca2+ ([Ca2+]Nuc) and CaMKII (Ca2+/calmodulin-dependent protein kinase-II)-related signaling.Methods and resultsAtrial cardiomyocytes were isolated from control and AF dogs (kept in AF by atrial tachypacing [600 bpm × 1 week]). [Ca2+]Nuc and cytosolic [Ca2+] ([Ca2+]Cyto) were recorded via confocal microscopy. Diastolic [Ca2+]Nuc was greater than [Ca2+]Cyto under control conditions, while resting [Ca2+]Nuc was similar to [Ca2+]Cyto; both diastolic and resting [Ca2+]Nuc increased with AF. IP3R (Inositol-trisphosphate receptor) stimulation produced larger [Ca2+]Nuc increases in AF versus control cardiomyocytes, and IP3R-blockade suppressed the AF-related [Ca2+]Nuc differences. AF upregulated nuclear protein expression of IP3R1 (IP3R-type 1) and of phosphorylated CaMKII (immunohistochemistry and immunoblot) while decreasing the nuclear/cytosolic expression ratio for HDAC4 (histone deacetylase type-4). Isolated atrial cardiomyocytes tachypaced at 3 Hz for 24 hours mimicked AF-type [Ca2+]Nuc changes and L-type calcium current decreases versus 1-Hz-paced cardiomyocytes; these changes were prevented by IP3R knockdown with short-interfering RNA directed against IP3R1. Nuclear/cytosolic HDAC4 expression ratio was decreased by 3-Hz pacing, while nuclear CaMKII phosphorylation was increased. Either CaMKII-inhibition (by autocamtide-2-related peptide) or IP3R-knockdown prevented the CaMKII-hyperphosphorylation and nuclear-to-cytosolic HDAC4 shift caused by 3-Hz pacing. In human atrial cardiomyocytes from AF patients, nuclear IP3R1-expression was significantly increased, with decreased nuclear/nonnuclear HDAC4 ratio. MicroRNA-26a was predicted to target ITPR1 (confirmed by luciferase assay) and was downregulated in AF atrial cardiomyocytes; microRNA-26a silencing reproduced AF-induced IP3R1 upregulation and nuclear diastolic Ca2+-loading.ConclusionsAF increases atrial-cardiomyocyte nucleoplasmic [Ca2+] by IP3R1-upregulation involving miR-26a, leading to enhanced IP3R1-CaMKII-HDAC4 signaling and L-type calcium current downregulation. Graphic Abstract: A graphic abstract is available for this article.

Introduction Atrial fibrillation (AF) is the most commonly diagnosed cardiac arrhythmia, with a high prevalence worldwide (1, 2). AF significantly affects the quality of life, as it is associated with [...], Chronic kidney disease (CKD) is associated with a higher risk of atrial fibrillation (AF). The mechanistic link between CKD and AF remains elusive. IL-1[beta], a main effector of NLR family pyrin domain-containing 3 (NLRP3) inflammasome activation, is a key modulator of conditions associated with inflammation, such as AF and CKD. Circulating IL-1[beta] levels were elevated patients with CKD who had AF (versus patients with CKD in sinus rhythm). Moreover, NLRP3 activity was enhanced in atria of patients with CKD. To elucidate the role of NLRP3/IL- 1[beta] signaling in the pathogenesis of CKD-induced AF, [Nlrp3.sup.-/-] and WT mice were subjected to a 2-stage subtotal nephrectomy protocol to induce CKD. Four weeks after surgery, IL-1[beta] levels in serum and atrial tissue were increased in WT CKD (WT-CKD) mice versus sham-operated WT (WT-sham) mice. The increased susceptibility to pacing-induced AF and the longer AF duration in WT-CKD mice were associated with an abbreviated atrial effective refractory period, enlarged atria, and atrial fibrosis. Genetic inhibition of NLRP3 in [Nlrp3.sup.-/-] mice or neutralizing anti-IL- 1[beta] antibodies effectively reduced IL- 1[beta] levels, normalized left atrial dimensions, and reduced fibrosis and the incidence of AF. These data suggest that CKD creates a substrate for AF development by activating the NLRP3 inflammasome in atria, which is associated with structural and electrical remodeling. Neutralizing IL-1[beta] antibodies may be beneficial in preventing CKD-induced AF.

Background/Objectives: Coronary artery bypass surgery (CABG) with multiple arterial grafting (MAG) has shown potential to improve patient survival compared to single arterial bypass grafting. Whether this superiority in survival also exists in diabetics is uncertain. We therefore aimed to compare short and long-term outcomes of MAG in diabetic versus non-diabetic patients. Methods: In this retrospective study, we investigated short- and long-term clinical outcomes of diabetic (n = 256) and non-diabetic (n = 800) patients undergoing CABG with MAG between January 1999 and December 2019 at our institution. Results: Diabetics had a significantly higher EuroScore II (1.37 ± 2.4 vs. 0.88 ± 1.58, p < 0.0001) and underwent significantly less bilateral internal thoracic artery (BITA) grafting (51.95% vs. 67.75%; p < 0.0001) compared to non-diabetics. The incidence of postoperative adverse events, such as pneumonia, stroke, and sepsis, did not differ between the two groups. However, diabetics suffered significantly more often from post-cardiotomy cardiogenic shock, renal failure requiring dialysis, and sternal wound infections over the entire follow-up period. Non-diabetics had a significantly higher median survival time of 19.6 years compared to 14.54 years found in diabetic patients (p < 0.0001). Conclusions: Among patients undergoing MAG, diabetic individuals were found to have a significantly lower overall median survival. This emphasizes the importance of diabetes as a risk factor in choosing individual surgical strategies. [ABSTRACT FROM AUTHOR]

Background and Objectives: The use of temporary left ventricular assist devices (tLVADs) for patients suffering from cardiogenic shock (CS) is becoming more common. This study examines the indications and outcomes of microaxial flow pumps (Impella®, Abiomed Inc., Danvers, MA, USA) when cannulated through the axillary artery in patients with severe CS, with a particular focus on acute phase reactions and hemolytic responses. Materials and Methods: This single-center, retrospective cohort involved patients who received microaxial Impella implantation via the axillary artery from 2020 to 2022 (n = 47). Results: Among the patients, 66% (N = 31 cases) were treated with the Impella 5.5, 25.5% (N = 12 cases) with the Impella 5.0, and 8.5% (N = 4 cases) with the Impella CP. Additionally, 28% were managed using the ECMELLA concept. The mean length of time for Impella support was 8 days. The overall 30-day survival rate was 78%, with no significant differences observed between the ECMELLA group and the various Impella types. At 30 days post-therapy, 47% of survivors no longer required mechanical support, while 26% were upgraded to a durable LVAD. Interleukin-6 (IL-6) levels were significantly lower in patients receiving Impella 5.5 (n = 17 vs. 12) immediately following implantation (p = 0.03) compared with those with smaller devices. Haptoglobin levels were significantly higher in the Impella 5.5 group (n = 17 vs. 11, p = 0.02), with overall lower rates of hemolysis (45.1%, p < 0.01). Conclusions: The mortality rate in critical CS appears reduced with axillary artery implantation of Impella devices relative to existing literature. A full-flow microaxial pump (Impella 5.5) seems advantageous regarding systemic inflammatory response syndrome (SIRS) and acute hemolysis, indicated by lower IL-6 and higher haptoglobin levels, compared with smaller Impella devices. A tailored escalation/de-escalation concept using axillary access for different mAFP types appears feasible and safe. [ABSTRACT FROM AUTHOR]

Sphingosine has been previously shown to kill many strains of pathogenic bacteria including Pseudomonas aeruginosa, Staphyloccus aureus , Acinetobacter, and atypical mycobacteria. However, these studies were performed on isolated or extracellular bacteria and it is unknown whether sphingosine also targets intracellular bacteria. Here, we demonstrate that exogenously-added sphingosine directly binds to extracellular P. aeruginosa and S. aureus , but also targets and binds to intracellular bacteria. Intracellular sphingosine and bacteria were identified by sequential immunostainings. We further show that exogenously-added sphingosine also kills intracellular P. aeruginosa and S. aureus using modified gentamycin assays. Intracellular killing of P. aeruginosa and S. aureus by sphingosine is not mediated by improved phagosomal-lysosomal fusion. In summary, our data indicate that sphingosine binds to and most likely also directly kills extra- and intracellular P. aeruginosa and S. aureus. [ABSTRACT FROM AUTHOR]