The NAD ⁺ precursor nicotinamide improves diastolic dysfunction caused by aging, hypertension, or metabolic syndrome in rodents.

Rationale: Atrial fibrillation (AF) and heart failure often coexist, but their interaction is poorly understood. Clinical data indicate that the arrhythmic component of AF may contribute to left ventricular (LV) dysfunction. Objective: This study investigates the effects and molecular mechanisms of AF on the human LV. Methods and Results: Ventricular myocardium from patients with aortic stenosis and preserved LV function with sinus rhythm or rate-controlled AF was studied. LV myocardium from patients with sinus rhythm and patients with AF showed no differences in fibrosis. In functional studies, systolic Ca ²⁺ transient amplitude of LV cardiomyocytes was reduced in patients with AF, while diastolic Ca ²⁺ levels and Ca ²⁺ transient kinetics were not statistically different. These results were confirmed in LV cardiomyocytes from nonfailing donors with sinus rhythm or AF. Moreover, normofrequent AF was simulated in vitro using arrhythmic or rhythmic pacing (both at 60 bpm). After 24 hours of AF-simulation, human LV cardiomyocytes from nonfailing donors showed an impaired Ca ²⁺ transient amplitude. For a standardized investigation of AF-simulation, human iPSC-cardiomyocytes were tested. Seven days of AF-simulation caused reduced systolic Ca ²⁺ transient amplitude and sarcoplasmic reticulum Ca ²⁺ load likely because of an increased diastolic sarcoplasmic reticulum Ca ²⁺ leak. Moreover, cytosolic Na ⁺ concentration was elevated and action potential duration was prolonged after AF-simulation. We detected an increased late Na ⁺ current as a potential trigger for the detrimentally altered Ca ²⁺ /Na ⁺ -interplay. Mechanistically, reactive oxygen species were higher in the LV of patients with AF. CaMKII (Ca ²⁺ /calmodulin-dependent protein kinase IIδc) was found to be more oxidized at Met281/282 in the LV of patients with AF leading to an increased CaMKII activity and consequent increased RyR2 phosphorylation. CaMKII inhibition and ROS scavenging ameliorated impaired systolic Ca ²⁺ handling after AF-simulation. Conclusions: AF causes distinct functional and molecular remodeling of the human LV. This translational study provides the first mechanistic characterization and the potential negative impact of AF in the absence of tachycardia on the human ventricle.

Lipid abnormalities may have an effect on clinical outcomes of patients on dialysis. Recent studies have indicated that HDL dysfunction is a hallmark of ESRD. In this study, we compared HDL composition and metrics of HDL functionality in patients undergoing hemodialysis (HD) or peritoneal dialysis (PD) with those in healthy controls. We detected a marked suppression of several metrics of HDL functionality in patients on HD or PD. Compositional analysis revealed that HDL from both dialysis groups shifted toward a more proinflammatory phenotype with profound alterations in the lipid moiety and protein composition. With regard to function, cholesterol efflux and anti-inflammatory and antiapoptotic functions seemed to be more severely suppressed in patients on HD, whereas HDL-associated paraoxonase activity was lowest in patients on PD. Quantification of enzyme activities involved in HDL metabolism suggested that HDL particle maturation and remodeling are altered in patients on HD or PD. In summary, our study provides mechanistic insights into the formation of dysfunctional HDL in patients with ESRD who are on HD or PD.

Background—: A hallmark of heart failure is impaired cytoplasmic Ca ²⁺ handling of cardiomyocytes. It remains unknown whether specific alterations in nuclear Ca ²⁺ handling via altered excitation-transcription coupling contribute to the development and progression of heart failure. Methods and Results—: Using tissue and isolated cardiomyocytes from nonfailing and failing human hearts, as well as mouse and rabbit models of hypertrophy and heart failure, we provide compelling evidence for structural and functional changes of the nuclear envelope and nuclear Ca ²⁺ handling in cardiomyocytes as remodeling progresses. Increased nuclear size and less frequent intrusions of the nuclear envelope into the nuclear lumen indicated altered nuclear structure that could have functional consequences. In the (peri)nuclear compartment, there was also reduced expression of Ca ²⁺ pumps and ryanodine receptors, increased expression of inositol-1,4,5-trisphosphate receptors, and differential orientation among these Ca ²⁺ transporters. These changes were associated with altered nucleoplasmic Ca ²⁺ handling in cardiomyocytes from hypertrophied and failing hearts, reflected as increased diastolic Ca ²⁺ levels with diminished and prolonged nuclear Ca ²⁺ transients and slowed intranuclear Ca ²⁺ diffusion. Altered nucleoplasmic Ca ²⁺ levels were translated to higher activation of nuclear Ca ²⁺ /calmodulin-dependent protein kinase II and nuclear export of histone deacetylases. Importantly, the nuclear Ca ²⁺ alterations occurred early during hypertrophy and preceded the cytoplasmic Ca ²⁺ changes that are typical of heart failure. Conclusions—: During cardiac remodeling, early changes of cardiomyocyte nuclei cause altered nuclear Ca ²⁺ signaling implicated in hypertrophic gene program activation. Normalization of nuclear Ca ²⁺ regulation may therefore be a novel therapeutic approach to prevent adverse cardiac remodeling.

Rationale : Synchronized release of Ca ²⁺ into the cytosol during each cardiac cycle determines cardiomyocyte contraction. Objective:: We investigated synchrony of cytosolic [Ca ²⁺ ] decay during diastole and the impact of cardiac remodeling. Methods and Results:: Local cytosolic [Ca ²⁺ ] transients (1-µm intervals) were recorded in murine, porcine, and human ventricular single cardiomyocytes. We identified intracellular regions of slow (slowCaR) and fast (fastCaR) [Ca ²⁺ ] decay based on the local time constants of decay (TAU _local ). The SD of TAU _local as a measure of dyssynchrony was not related to the amplitude or the timing of local Ca ²⁺ release. Stimulation of sarcoplasmic reticulum Ca ²⁺ ATPase with forskolin or istaroxime accelerated and its inhibition with cyclopiazonic acid slowed TAU _local significantly more in slowCaR, thus altering the relationship between SD of TAU _local and global [Ca ²⁺ ] decay (TAU _global ). Na ⁺ /Ca ²⁺ exchanger inhibitor SEA0400 prolonged TAU _local similarly in slowCaR and fastCaR. FastCaR were associated with increased mitochondrial density and were more sensitive to the mitochondrial Ca ²⁺ uniporter blocker Ru360. Variation in TAU _local was higher in pig and human cardiomyocytes and higher with increased stimulation frequency (2 Hz). TAU _local correlated with local sarcomere relengthening. In mice with myocardial hypertrophy after transverse aortic constriction, in pigs with chronic myocardial ischemia, and in end-stage human heart failure, variation in TAU _local was increased and related to cardiomyocyte hypertrophy and increased mitochondrial density. Conclusions:: In cardiomyocytes, cytosolic [Ca ²⁺ ] decay is regulated locally and related to local sarcomere relengthening. Dyssynchronous intracellular [Ca ²⁺ ] decay in cardiac remodeling and end-stage heart failure suggests a novel mechanism of cellular contractile dysfunction.

Aims The sarcoplasmic reticulum (SR) Ca²⁺ leak is an important pathomechanism in heart failure (HF). It has been suggested that Ca²⁺/calmodulin‐dependent protein kinase II (CaMKII) is only relevant for the induction of the SR Ca²⁺ leak in non‐ischaemic but not in ischaemic HF. Therefore, we investigated CaMKII and its targets as well as the functional effects of CaMKII inhibition in human ischaemic cardiomyopathy (ICM, n = 37) and dilated cardiomyopathy (DCM, n = 40). Methods and results Western blots showed a significantly increased expression (by 54 ± 9%) and autophosphorylation at Thr286 (by 129 ± 29%, P < 0.05 each) of CaMKII in HF compared with healthy myocardium. However, no significant difference could be detected in ICM compared with DCM as to the expression and autophosphorylation of CaMKII nor the phosphorylation of the target sites ryanodine receptor 2 (RyR2)‐S2809, RyR2‐S2815, and phospholamban‐Thr17. Isolated human cardiomyocytes (CMs) of patients with DCM and ICM showed a similar frequency of diastolic Ca²⁺ sparks (confocal microscopy) as well as of major arrhythmic events (Ca²⁺ waves, spontaneous Ca²⁺ transients). Despite a slightly smaller size of Ca²⁺ sparks in DCM (P < 0.01), the calculated SR Ca²⁺ leak [Ca²⁺ spark frequecy (CaSpF) × amplitude × width × duration] did not differ between CMs of ICM vs. DCM. Importantly, CaMKII inhibition by autocamide‐2‐related inhibitory peptide (AIP, 1 µmol/L) reduced the SR Ca²⁺ leak by ∼80% in both aetiologies (P < 0.05 each) and effectively decreased the ratio of arrhythmic cells (P < 0.05). Conclusion Functional and molecular measures of the SR Ca²⁺ leak are comparable in human ICM and DCM. CaMKII is equally responsible for the induction of the ‘RyR2 leakiness’ in both pathologies. Thus, CaMKII inhibition as a therapeutic measure may not be restricted to patients suffering from DCM but rather may be beneficial for the majority of HF patients.