Dyscholesterolemia Protects Against Ischemia-Induced Ventricular Arrhythmias

Electrocontractile remodeling of isolated cardiomyocytes induced during early-stage hypercholesterolemia

Hypercholesterolemia is one of the most important risk factors for cardiovascular diseases. However, it is mostly associated with vascular dysfunction and atherosclerotic lesions, while evidence of direct effects of hypercholesterolemia on cardiomyocytes and heart function is still incomplete and controversial. In this study, we assessed the direct effects of hypercholesterolemia on heart function and the electro-contractile properties of isolated cardiomyocytes. After 5 weeks, male Swiss mice fed with AIN-93 diet added with 1.25% cholesterol (CHO), developed an increase in total serum cholesterol levels and cardiomyocytes cholesterol content. These changes led to altered electrocardiographic records, with a shortening of the QT interval. Isolated cardiomyocytes displayed a shortening of the action potential duration with increased rate of depolarization, which was explained by increased IK, reduced ICa.L and altered INa voltage-dependent inactivation. Also, reduced diastolic [Ca2+]i was found with preserved adrenergic response and cellular contraction function. However, contraction of isolated hearts is impaired in isolated CHO hearts, before and after ischemia/reperfusion, although CHO heart was less susceptible to arrhythmic contractions. Overall, our results demonstrate that early hypercholesterolemia-driven increase in cellular cholesterol content is associated with direct modulation of the heart and cardiomyocytes' excitability, Ca2+ handling, and contraction.

Transcriptome analysis of effects of Tecrl deficiency on cardiometabolic and calcium regulation in cardiac tissue

Catecholaminergic polymorphic ventricular tachycardia (CPVT) is a hereditary heart disease characterized by bidirectional or polymorphic ventricular tachycardia and an increased risk of sudden cardiac death. Although trans-2,3-enoyl-CoA reductase like (TECRL) is a newly reported pathogenic gene leading to CPVT that can influence intracellular calcium regulation, the unidentified mechanism underlying the pathogenesis of TECRL deficiency-mediated CPVT remains mainly elusive. In the present study, Tecrl knockout (KO) mice were established and the differentially expressed genes (DEGs) were investigated by RNA-sequencing from the heart tissues. In addition, 857 DEGs were identified in Tecrl KO mice. Subsequently, a weighted gene co-expression network analysis was conducted to discern the pivotal pathways implicated in the Tecrl-mediated regulatory network. Moreover, pathway mapping analyses demonstrated that essential metabolism-related pathways were significantly enriched, notably the fatty acid metabolic process and calcium regulation. Collectively, the data suggested a synergistic relationship between Tecrl deficiency and cardiometabolic and calcium regulation during the development of CPVT. Therefore, further studies on the potential function of TECRL in cardiac tissues would be beneficial to elucidate the pathogenesis of CPVT.

Association between remnant cholesterol and incident atherosclerotic cardiovascular disease, heart failure, and atrial fibrillation

BACKGROUND

It remains unclear if remnant cholesterol is associated with atherosclerotic cardiovascular disease (ASCVD) (myocardial infarction, angina pectoris and stroke), heart failure (HF), and atrial fibrillation (AF) under primary prevention settings.

OBJECTIVE

We aimed to clarify this issue among a general population without a history of ASCVD, HF or AF.

METHODS

Analyses were conducted with a nationwide health claims database collected in the JMDC Claims Database between 2005 and 2022 (n = 1,313,722; median age, 42 years; 54.6% men). We assessed the associations between remnant cholesterol calculated as total cholesterol minus HDL cholesterol minus LDL cholesterol and composite CVD outcomes, including, ASCVD, HF, and AF using Cox proportional hazard model, dividing the individuals into tertiles of remnant cholesterol (T1-T3).

RESULTS

The mean follow-up duration was 3.0 years. In total, 43,755 events were recorded. Remnant cholesterol was significantly associated with composite CVD outcomes after adjustments (T3 vs T1: hazard ratio [HR]; 1.07, 95% confidence interval [CI]: 1.04-1.10, p-trend<0.001). Remnant cholesterol was associated with myocardial infarction (T3 vs T1:HR: 1.20, 95% CI: 1.06-1.34, p-trend=0.002), angina pectoris (T3 vs T1:HR: 1.09, 95% CI: 1.05-1.14, p-trend<0.001), stroke (T3 vs T1:HR: 1.08, 95% CI: 1.02-1.14, p-trend=0.007), and HF (T3 vs T1:HR: 1.08, 95% CI: 1.04-1.12, p-trend<0.001), while we found a marginal inverse association between remnant cholesterol and AF (T3 vs T1:HR: 0.92, 95% CI: 0.86-1.00, p-trend=0.054).

CONCLUSION

Remnant cholesterol was positively associated with ASCVD and HF, while we found a marginal inverse association between remnant cholesterol and AF.

Meta-analysis of the Current Research on the Relationship Between Blood Lipid Levels and the Occurrence of Atrial Fibrillation

BACKGROUND

There is still debate in the literature about the relationship between lipid profile and the occurrence of atrial fibrillation (AF). In order to assess the association between blood lipid profiles and incidence of AF, this review was conducted to perform a meta-analysis of all available studies.

METHODS

This review analysed all studies up to 28 February 2023 in PubMed, Google Scholar, and the Cochrane Library that included data regarding blood lipid levels and incidence of AF. For the purpose of calculating pooled estimates, the hazard ratios were extracted from all studies.

RESULTS

Fourteen studies including 19 cohorts with 3,990,484 patients were included in this meta-analysis. An elevation of one standard deviation in total cholesterol (TC) level was associated with an 8% reduction (HR=0.92, 0.88-0.96; p<0.01) in the risk of developing AF. Although increased low-density lipoprotein cholesterol levels were associated with a 7% reduction in the development of AF (HR=0.93, 0.87-1.00; p=0.04), there was high heterogeneity in the random effects model (I2=92%). Changes in high-density lipoprotein cholesterol and triglyceride levels were not found to be associated with AF risk in the pooled analysis. Dose-response meta-analysis showed that TC was inversely linearly associated with the risk of AF (p<0.001).

CONCLUSIONS

Higher TC levels were shown to be independently attributed to an increased risk of AF in individuals without cardiovascular disease. There was no association between the incidence of AF and triglyceride, high-density lipoprotein cholesterol, or low-density lipoprotein cholesterol blood levels.

Association between cardiovascular risk factors and atrial fibrillation

Background

The most prevalent sustained arrhythmia in medical practice, atrial fibrillation (AF) is closely associated with a high risk of cardiovascular disease. Nevertheless, the risk of AF associated with cardiovascular risk factors has not been well elucidated. We pooled all published studies to provide a better depiction of the relationship among cardiovascular risk factors with AF.

Methods

Studies were searched in the MEDLINE, Web of Science, and EMBASE databases since initiation until January 15, 2022. Prospective cohort studies assessing the relationship a minimum of single cardiovascular risk factors to AF incidence were included if they contained adequate data for obtaining relative risks (RR) and 95% confidence intervals (CI). Random-effects models were utilized to perform independent meta-analyses on each cardiovascular risk factor. PROSPERO registry number: CRD42022310882.

Results

A total of 17,098,955 individuals and 738,843 incident cases were reported for data from 101 studies included in the analysis. In all, the risk of AF was 1.39 (95% CI, 1.30-1.49) for obesity, 1.27 (95% CI, 1.22-1.32) per 5 kg/m2 for increase in body mass index, 1.19 (95% CI, 1.10-1.28) for former smokers, 1.23 (95% CI, 1.09-1.38) for current smokers, 1.31 (95% CI, 1.23-1.39) for diabetes mellitus, 1.68 (95% CI, 1.51-1.87) for hypertension, and 1.12 (95% CI, 0.95-1.32) for dyslipidemia.

Interpretation

Adverse cardiovascular risk factors correlate with an increased risk of AF, yet dyslipidemia does not increase the risk of AF in the general population, potentially providing new insights for AF screening strategies among patients with these risk factors.

Systematic Review Registration

https://www.crd.york.ac.uk/PROSPERO/, PROSPERO identifier (CRD42022310882).

The Relationship between Blood Lipids and Risk of Atrial Fibrillation: Univariable and Multivariable Mendelian Randomization Analysis

We performed univariable and multivariable Mendelian randomization (MR) analysis to evaluate the association between blood lipids and risk of atrial fibrillation (AF), including low-density lipoprotein cholesterol (LDL-C), high-density lipoprotein cholesterol (HDL-C), triglyceride (TG), Apolipoprotein A1, and Apolipoprotein B.

METHODS

Data on the single nucleotide polymorphisms (SNPs) related to blood lipids were obtained from the UK Biobank study with more than 300,000 subjects of White British European ancestry, and data for AF were from the latest meta-analysis of Genome-wide association study (GWASs) with six independent cohorts with more than 1,000,000 subjects of European ancestry. The univariable MR analysis was conducted to explore whether genetic evidence of individual lipid-related traits was significantly associated with AF risks and multivariable MR analysis with three models was performed to assess the independent effects of lipid-related traits.

RESULTS

The IVW estimate showed that genetically predicted LDL-C (OR: 1.016, 95% CI: 0.962-1.073, p = 0.560), HDL-C (OR: 0.951, 95% CI: 0.895-1.010, p = 0.102), TG (OR: 0.961, 95% CI: 0.889-1.038, p = 0.313), Apolipoprotein A1 (OR: 0.978, 95% CI: 0.933-1.025, p = 0.356), and Apolipoprotein B (OR: 1.008, 95% CI: 0.959-1.070, p = 0.794) were not causally associated with the risk of AF. Sample mode (OR: 0.852, 95% CI: 0.731-0.993, p = 0.043) and weighted mode (OR: 0.907, 95% CI: 0.841-0.979, p = 0.013) showed that a 1-unit increase in TG (mmol/L) was causally associated with a 14.8% and 9.3% relative decrease in AF risk, respectively. The multivariable MR analysis with model 1, 2, and 3 indicated that TG, LDL-C, HDL-C, Apolipoprotein A1, and Apolipoprotein B were not associated with the lower risk for AF.

CONCLUSIONS

Our multivariable Mendelian randomization analysis (MVMR) finding suggested no genetic evidence of lipid traits was significantly associated with AF risk. Furthermore, more work is warranted to confirm the potential association between lipid traits and AF risks.

Novel cholesterol-dependent regulation of cardiac KATP subunit expression revealed using histone deacetylase inhibitors

We recently discovered that the histone deacetylase inhibitor, trichostatin A (TSA), increases expression of the sulfonylurea receptor 2 (SUR2; Abcc9) subunit of the ATP-sensitive K+ (KATP ) channel in HL-1 cardiomyocytes. Interestingly, the increase in SUR2 was abolished with exogenous cholesterol, suggesting that cholesterol may regulate channel expression. In the present study, we tested the hypothesis that TSA increases SUR2 by depleting cholesterol and activating the sterol response element binding protein (SREBP) family of transcription factors. Treatment of HL-1 cardiomyocytes with TSA (30 ng/ml) caused a time-dependent increase in SUR2 mRNA expression that correlates with the time course of cholesterol depletion assessed by filipin staining. Consistent with the cholesterol-dependent regulation of SREBP increasing SUR2 mRNA expression, we observe a significant increase in SREBP cleavage and translocation to the nucleus following TSA treatment that is inhibited by exogenous cholesterol. Further supporting the role of SREBP in mediating the effect of TSA on KATP subunit expression, SREBP1 significantly increased luciferase reporter gene expression driven by the upstream SUR2 promoter. Lastly, HL-1 cardiomyocytes treated with the SREBP inhibitor PF429242 significantly suppresses the effect of TSA on SUR2 gene expression. These results demonstrate that SREBP is an important regulator of KATP channel expression and suggest a novel method by which hypercholesterolemia may exert negative effects on the cardiovascular system, namely, by suppressing expression of the KATP channel.

The Prevalence, Risk Factors and Clinical Correlates of QTc Prolongation in Chinese Hospitalized Patients With Chronic Schizophrenia

Background: The QTc interval may be significantly prolonged in schizophrenia patients taking antipsychotics. Few studies have addressed QTc prolongation (QTP) in Chinese patients. Objectives: This study was designed to evaluate the prevalence of QTP and its clinical correlates in Chinese hospitalized patients with chronic schizophrenia. Methods: A total of 436 inpatients and 291 normal controls matched with age and sex were included. QTc prolongation was defined as 2 standard deviations (SD) above the mean value of normal controls. Positive and Negative Syndrome Scale (PANSS) and its five-factor model were used to evaluate psychopathological symptoms. Results: QTc interval was significantly longer in patients than in normal controls. The prevalence of QTP is 8.26% in Chinese hospitalized patients with chronic schizophrenia. More women than men displayed QTP. Compared with patients without QTP, the patients with QTP had significantly higher concrete/disorganized subscore, lower low density lipoprotein (LDL) and lower total protein (TP). Furthermore, binary logistic regression analysis showed that higher number of hospitalizations, higher concrete/disorganized subscore and lower LDL were risk factors for QTP. Correlation analysis indicated significant association between QTc interval and the following variables: sex, age, duration of illness, the number of hospitalizations, PANSS total score, fasting blood glucose (FPG). Finally, a multiple regression analysis showed that older age, antipsychotic polypharmacy, higher PANSS total score, and lower LDL were risk factors for QTP. Among them, LDL seemed to be a protective factor for QTP. Conclusions: QTc interval was longer in schizophrenia patients than in normal controls. The prevalence of QTP is 8.26% in Chinese hospitalized patients with chronic schizophrenia. Some clinical characteristics were risk factors for QTP. And LDL seemed to be a protective factor for QTP.

Admission Low-Density Lipoprotein Cholesterol Stratified by Circulating CD14++CD16+ Monocytes and Risk for Recurrent Cardiovascular Events Following ST Elevation Myocardial Infarction: Lipid Paradox Revised

Lower level of low-density lipoprotein cholesterol (LDL-C) is paradoxically associated with increased mortality in ST elevation myocardial infarction (STEMI) patients. The underlying mechanism remains unclear. In a cohort of 220 de novo STEMI patients receiving timely primary percutaneous coronary intervention, admission LDL-C was negatively associated with circulating CD14++CD16+ monocyte counts. Moreover, admission LDL-C < 85 mg/dL was associated with increased risk for major adverse cardiovascular events (MACE) during a median follow-up of 2.7 years. After categorizing the patients according to the cutoff values of 85 mg/dL for LDL-C and the median for CD14++CD16+ monocytes, low LDL-C-associated MACE risk was only observed in those with high CD14++CD16+ monocyte counts (low LDL-C/high CD14++CD16+ monocytes vs. low LDL-C/low CD14++CD16+ monocytes: hazard ratio 5.38, 95% confidence interval 1.52 to 19.06, P = 0.009). This work provided the proof-of-principle evidence indicating a role of CD14++CD16+ monocytes in risk stratification of STEMI patients presenting with low LDL-C level. Graphical abstract.

Lipid levels and risk of new-onset atrial fibrillation: A systematic review and dose-response meta-analysis

Lipid levels are closely associated with health, but whether lipid levels are associated with atrial fibrillation (AF) remains controversial. We thought that blood lipid levels may influence new-onset AF. Here, we used a meta-analysis to examine the overall association between lipid levels and new-onset AF. PubMed and EMBASE databases were searched up to 20 December 2019. We conducted a systematic review and quantitative meta-analysis of prospective studies to clarify the association between lipid levels and the risk of new-onset AF. Sixteen articles with data on 4 032 638 participants and 42 825 cases of AF were included in this meta-analysis. The summary relative risk (RR) for a 1 mmol/L increment in total cholesterol (TC) was 0.95 (95% CI 0.93-0.96, I² = 74.6%, n = 13). Subgroup analyses showed that follow-up time is a source of heterogeneity; for low-density lipoprotein cholesterol (LDL-C), RR was 0.95 (95% CI 0.92-0.97, I² = 71.5%, n = 10). Subgroup analyses indicated that adjusting for heart failure explains the source of heterogeneity; for high-density lipoprotein cholesterol (HDL-C), RR was 0.97 (95% CI 0.96-0.99, I² = 26.1%, n = 11); for triglycerides (TGs), RR was 1.00 (95% CI 0.96-1.03, I² = 81.1%, n = 8). Subgroup analysis showed that gender, age, follow-up time, and adjustment for heart failure are sources of heterogeneity. Higher levels of TC, LDL-C, and HDL-C were associated with lower risk of new-onset AF. TG levels were not associated with new-onset AF in all subjects.

Mechanisms underlying direct actions of hyperlipidemia on myocardium: an updated review

Hyperlipidemia is a common metabolic disorder and one of risk factors for cardiovascular disease. Clinical studies have shown that hyperlipidemia increases the risk of non-ischemic heart failure, while decreasing serum lipids can reverse heart dysfunction. Apart from indirectly affecting the function of the heart by promoting the development of atherosclerosis, hyperlipidemia also affects the systolic function and cardiac electrophysiological response of the heart directly, which may be related to gradual accumulation of cardiac lipids and consequent systemic oxidative stress, proinflammatory state and mitochondrial dysfunction. However, the mechanism underlying direct effects of hyperlipidemia on the heart are not fully understood. In this review, we provide an updated summary of recent experimental and clinical studies that focus on elucidating the mechanisms of the action of hyperlipidemia on cardiac function, the relationship between heart failure and serum lipids, and protective effects of lipid-lowering drugs on the heart. The exciting progress in this field supports the prospect of guiding early protection of the heart to benefit the patients with chronic hyperlipidemia and familial hyperlipidemia.

LongShengZhi capsule inhibits doxorubicin-induced heart failure by anti-oxidative stress

Heart failure is a major cause of morbidity and mortality worldwide. LongShengZhi capsule (LSZ), a traditional Chinese medicine, is used for treatment of patients with vascular diseases. Herein we investigated the effect of LSZ treatment on doxorubicin (DOX)-induced heart failure in mice. C57BL/6 mice randomly in 3 groups received following treatment: Control group, mice were fed normal chow; DOX group, mice were intraperitoneally injected DOX to induce heart failure and fed normal chow; and LSZ group, mice were injected DOX and fed normal chow containing LSZ. DOX induced heart failure as evidenced by increased serum creatine kinase, lactic dehydrogenase and α-hydroxybutyrate dehydrogenase, and cardiac fibrosis. However, LSZ treatment substantially inhibited DOX-induced heart failure parameters. Mechanistically, LSZ reduced collagen content and fibrosis by inhibiting expression of collagen type I α1 (COL1α1), COL1α2, α-smooth muscle actin and transforming growth factor β1. In addition, DOX-induced cell apoptosis was inhibited by LSZ, coupled with reduced caspase 3 activity and mRNA expression. LSZ decreased inflammatory cytokine levels. More importantly, LSZ decreased oxidative stress by inducing expression of anti-oxidative stress enzymes including superoxide dismutase 1 (SOD1), SOD2, catalase and glutathione peroxidase 1 through activation of forkhead box O3A and sirtuin 3. In conclusion, our study demonstrates that LSZ reduces heart failure by reducing production of reactive oxygen species and inhibiting inflammation/apoptosis. Our study also suggests the potential application of LSZ for heart failure treatment.

Blood lipid profiles and risk of atrial fibrillation: A systematic review and meta-analysis of cohort studies

BACKGROUND

There is an increasing body of evidence associating traditional cardiovascular risk factors with atrial fibrillation (AF), but the relationship between blood lipid profiles and the risk of AF remains controversial.

OBJECTIVE

This study aimed to conduct a systemic review and meta-analysis of large cohort studies to evaluate the relationship between blood lipid profiles and incident AF.

METHODS

PubMed and Embase were searched up to January 31, 2019, for cohort studies that reported the relationship between blood lipid levels and incident AF. The hazard ratios or odds ratios of the highest vs lowest categories of lipid levels were extracted to calculate pooled estimates. Sensitivity analysis and meta-regression were performed to explore potential sources of heterogeneity.

RESULTS

Eleven studies were included in the meta-analysis, including 9 studies for total cholesterol (TC), 5 for low-density lipoprotein cholesterol (LDL-C), 8 for high-density lipoprotein cholesterol (HDL-C), and 8 for triglyceride. Serum TC and LDL-C levels were inversely related to AF risk (relative risk [RR] = 0.81, 95% confidence interval [CI]: 0.72-0.92; RR = 0.79, 95% CI: 0.70-0.88, respectively). Likewise, elevated HDL-C levels were associated with a reduced AF risk (RR = 0.86, 95% CI: 0.76-0.97), whereas no significant association was observed between triglyceride levels and incident AF (RR = 1.02, 95% CI: 0.90-1.17).

CONCLUSIONS

Our meta-analysis of large cohort studies found an inverse relationship between serum TC, LDL-C, and HDL-C levels and AF risk, although there was no significant association between TG levels and incident AF. Future studies regarding AF risk stratification may take these blood lipids into consideration, and further efforts are needed to investigate the potential mechanisms.

Association Between HDL Cholesterol and QTc Interval: A Population-Based Epidemiological Study

Previous experimental studies showed that increasing high-density lipoprotein cholesterol (HDL) cholesterol shortens cardiac ventricular repolarization and the QT interval corrected for heart rate (QTc). However, little is known about the epidemiological relationship between HDL and QTc. The potential antiarrhythmic effect of HDL cholesterol remains a speculative hypothesis. In this cross-sectional population based study in adults living in the Italian-speaking part of Switzerland, we aimed to explore the association between HDL cholesterol and the QTc interval in the general population. A total of 1202 subjects were screened. electrocardiogram (ECG) recordings, measurements of lipid parameters and other laboratory tests were performed. QTc was corrected using Bazett’s (QTc_Baz) and Framingham (QTc_Fram) formulas. HDL was categorized according to percentile distributions: <25th (HDL-1; ≤1.39 mmol/L); 25th–<50th (HDL-2; 1.40–1.69 mmol/L); 50th–<75th (HDL-3; 1.69–1.99 mmol/L); and ≥75th (HDL-4; ≥2.0 mmol/L). After exclusion procedures, data of 1085 subjects were analyzed. Compared with the HDL reference group (HDL-1), HDL-2 and HDL-3 were associated with a reduction of QTc_Baz and QTc_Fram duration in crude (HDL-2, QTc_Baz/QTc_Fram: β-11.306/–10.186, SE 4.625/4.016; p = 0.016/0.012; HDL-3, β-12.347/–12.048, SE 4.875/4.233, p = 0.012/<0.001) and adjusted (HDL-2: β-11.697/–10.908, SE 4.333/4.151, p < 0.001/0.010; HDL-3 β-11.786/–11.002, SE 4.719/4.521, p = 0.014/0.016) linear regression models in women. In adjusted logistic regression models higher HDL, were also associated with lower risk of prolonged QTc_Baz/QTc_Fram (HDL-2: OR 0.16/0.17, CI 0.03–0.83/0.47–0.65; HDL-3: OR 0.10/0.14, CI 0.10–0.64/0.03–0.63) in women. Restricted cubic spline analysis confirmed a non linear association (p < 0.001). The present findings indicate an epidemiological association between HDL cholesterol and QTc duration. To draw firm conclusions, further investigations in other populations and with a prospective cohort design are needed.

Integrative analyses of myocardial lipidome and proteome implicate mitochondrial dysfunction in lethal ventricular tachyarrhythmia (LVTA) induced by acute myocardial ischemia (AMI)

Lethal ventricular tachyarrhythmia (LVTA) is the most prevalent electrophysiological event leading to sudden cardiac death (SCD). In this study, the myocardial lipidome and proteome were analysed in rats experiencing LVTA as a consequence of acute myocardial ischemia (AMI). Results showed that 257 lipid species and 814 myocardial proteins were disrupted during LVTA. Cardiolipin (CL), phosphatidylcholine (PC), phosphatidylethanolamine (PE), ceramide (Cer), lysophosphatidylethanolamine (LPE), lysophosphatidylcholine (LPC), phosphatidylglycerol (PG), and lysophosphatidylserine (LPS) were down-regulated; whereas sphingosine (SO) and diacylglycerol (DG) were up-regulated. Enrichment analysis of these proteins suggested mitochondrial dysfunction. Most of the differential lipids showed a high degree of interaction with the core differentially expressed proteins. Seven lipid pathways, including DG → PE, PE → LPE, PA → DG, PC → DG, PE → PA, Cer → SM, and LPE → LPC, were active during the process. Activation of LPE → PE could be partially confirmed by proteomic results. CL (72:7), PE (42:4), and LPE (P-18:0) jointly represent a promising diagnostic markers for LVTA. Collectively, we discovered marked disturbances of the lipidome and proteome in the myocardia of LVTA rats, mainly involving dysfunction of the mitochondrial respiratory chain.

RBM20 Mutations Induce an Arrhythmogenic Dilated Cardiomyopathy Related to Disturbed Calcium Handling

Background:

Mutations in RBM20 (RNA-binding motif protein 20) cause a clinically aggressive form of dilated cardiomyopathy, with an increased risk of malignant ventricular arrhythmias. RBM20 is a splicing factor that targets multiple pivotal cardiac genes, such as Titin (TTN) and CAMK2D (calcium/calmodulin-dependent kinase II delta). Aberrant TTN splicing is thought to be the main determinant of RBM20-induced dilated cardiomyopathy, but is not likely to explain the increased risk of arrhythmias. Here, we investigated the extent to which RBM20 mutation carriers have an increased risk of arrhythmias and explore the underlying molecular mechanism.

Methods:

We compared clinical characteristics of RBM20 and TTN mutation carriers and used our previously generated Rbm20 knockout (KO) mice to investigate downstream effects of Rbm20-dependent splicing. Cellular electrophysiology and Ca 2+ measurements were performed on isolated cardiomyocytes from Rbm20 KO mice to determine the intracellular consequences of reduced Rbm20 levels.

Results:

Sustained ventricular arrhythmias were more frequent in human RBM20 mutation carriers than in TTN mutation carriers (44% versus 5%, respectively, P =0.006). Splicing events that affected Ca 2+ - and ion-handling genes were enriched in Rbm20 KO mice, most notably in the genes CamkIIδ and RyR2. Aberrant splicing of CamkIIδ in Rbm20 KO mice resulted in a remarkable shift of CamkIIδ toward the δ-A isoform that is known to activate the L-type Ca 2+ current ( I Ca,L ). In line with this, we found an increased I Ca,L , intracellular Ca 2+ overload and increased sarcoplasmic reticulum Ca 2+ content in Rbm20 KO myocytes. In addition, not only complete loss of Rbm20, but also heterozygous loss of Rbm20 increased spontaneous sarcoplasmic reticulum Ca 2+ releases, which could be attenuated by treatment with the I Ca,L antagonist verapamil.

Conclusions:

We show that loss of Rbm20 disturbs Ca 2+ handling and leads to more proarrhythmic Ca 2+ releases from the sarcoplasmic reticulum. Patients that carry a pathogenic RBM20 mutation have more ventricular arrhythmias despite a similar left ventricular function, in comparison with patients with a TTN mutation. Our experimental data suggest that RBM20 mutation carriers may benefit from treatment with an I Ca,L blocker to reduce their arrhythmia burden.

Human electronegative low-density lipoprotein modulates cardiac repolarization via LOX-1-mediated alteration of sarcolemmal ion channels

Dyslipidemia is associated with greater risk of ventricular tachyarrhythmias in patients with cardiovascular diseases. We aimed to examine whether the most electronegative subfraction of low-density lipoprotein (LDL), L5, is correlated with QTc prolongation in patients with coronary artery disease (CAD) and investigate the effects of human L5 on the electrophysiological properties of cardiomyocytes in relation to the lectin-like oxidized LDL receptor (LOX-1). L5 was isolated from the plasma of 40 patients with angiography documented CAD and 13 patients with no CAD to correlate the QTc interval respectively. The mean concentration of L5 was higher and correlated with QTc in patients with CAD compared to controls. To examine the direct effect of L5 on QTc, mice were intravenously injected with L5 or L1. L5-injected wild-type but not LOX-1^−/− mice showed longer QTc compared to L1-injected animals in vivo with corresponding longer action potential duration (APD) in cardiomyocytes incubated with L5 in vitro. The APD prolongation was mediated by an increase of L-type calcium current and a decrease of transient outward potassium current. We show that L5 was positively correlated with QTc prolongation in patients with ischemic heart disease. L5 can modulate cardiac repolarization via LOX-1-mediated alteration sarcolemmal ionic currents.

Differential expression of B-type natriuretic peptide between left and right ventricles, with particular regard to sudden cardiac death

The aim of the present study was to investigate the differential expression of B-type natriuretic peptide (BNP) between the left and right ventricle (RV) in sudden cardiac death (SCD). A total of 26 forensic autopsy cases of sudden death (survival time <30 min, postmortem interval <48 h or frozen within 6 h following death) in the present institute were examined. The cases consisted of acute ischemic heart disease (AIHD, n=15) with/without apparent myocardial necrosis as a sign of infarction (acute myocardial infarction, n=6; ischemic heart disease, IHD, n=9), and arrhythmogenic right ventricular cardiomyopathy (ARVC/D, n=5), in addition to traffic accidents and high falls without any pre existing heart disease as control (C, total n=6). BNP was investigated in all cases by the colloidal gold method, hematoxylin-eosin staining, immunohistochemistry (IHC) and the molecular pathological method. The IHC results demonstrated that a positive BNP immunostaining was detected in all groups; however, there was no difference between different causes of death. Pericardial N-terminal (NT)-proBNP concentration was significantly increased in deaths resulting from AIHD and ARVC/D compared with control group. The relative quantification of BNP mRNA demonstrated that relative expression levels of BNP mRNA were significantly increased in the left ventricle (LV) in the AIHD group, and in the RV of the ARVC/D group. The relative quantification difference and ratio of BNP mRNA between LV and RV demonstrated a significantly greater value in the AIHD group compared with control group. BNP mRNA in myocardium and NT-proBNP concentration in pericardial fluid were elevated in SCD patients, and left ventricular dysfunction predominated in AIHD patients, whereas right ventricular dysfunction predominated in ARVC/D patients. The results of the present study suggest the possible use of molecular pathology of BNP for the determination of terminal cardiac function in SCD and analysis of its fatal mechanism in forensic practice.

Common lipid features of lethal ventricular tarchyarrhythmias (LVTAs) induced by myocardial infarction and myocardial ion channel diseases

Lethal ventricular tachyarrhythmia (LVTA) is the most prevalent electrophysiological underpinning of sudden cardiac death (SCD), a condition that occurs in response to multiple pathophysiological abnormalities. The aim of this study was to identify common lipid features of LVTA that were induced by distinct pathophysiological conditions, thereby facilitating the discovery of novel SCD therapeutic targets. Two rat LVTA-SCD models were established to mimic myocardial infarction (MI) and myocardial ion channel diseases. Myocardial and serum specimens were analyzed using ultra-performance liquid chromatography-mass spectrometry (UPLC-MS)-based lipidomics. The lipid profiles of the myocardial and serum specimens were similar between the models. Eleven myocardial lipid classes were altered, including downregulations of: cardiolipin, ceramide, phosphatidylinositol, phosphatidylethanolamine, triacylglycerol, diacylglycerol, phosphatidylglycerol, lysophosphatidylethanolamine and phosphatidylserine, and upregulations of: lysophosphatidylcholine and phosphatidic acid. Serum concentrations of triacylglycerol, lysophosphatidylcholine, phosphatidylethanolamine and phosphatidylinositol were also altered. Alterations of lipids in paired myocardia and sera were closely correlated. Cardiolipin 70:5, cardiolipin 74:9 and ceramide d34:2 were tested as potential biomarkers of LVTA. The results indicate that there are common LVTA lipid profiles induced by MI and myocardial ion channel diseases, potentially offering novel LVTA-SCD therapeutic targets.

The pro- or antiarrhythmic actions of polyunsaturated fatty acids and of cholesterol

In this review, the pro- and anti-arrhythmic effects of a diet rich in fish oil fatty acids and of hypercholesterolemia will be discussed in relation to two major mechanisms of arrhythmogenesis (triggered activity and re-entry). Whereas a diet rich in fish oil is pro-arrhythmic in relation to re-entry based arrhythmias (as occur in acute myocardial ischemia) and anti-arrhythmic in relation to triggered activity based arrhythmias (as occur in heart failure), the reverse is true for hypercholesterolemia. Changing the lipid composition of cardiomyocytes likely has powerful pro- or anti-arrhythmic consequences, depending on the mechanism of arrhythmias, and has corresponding therapeutic potential.