Downregulation of peroxisome proliferator-activated receptor-gamma expression in hypertensive atrial fibrillation

Adipose Triglyceride Lipase Deficiency Aggravates Angiotensin II-Induced Atrial Fibrillation by Reducing Peroxisome Proliferator-Activated Receptor α Activation in Mice

Atrial fibrillation (AF) is a main risk factor for cerebrovascular diseases but lacks precision therapy. Adipose triglyceride lipase (ATGL) is a key enzyme involved in the intracellular degradation of triacylglycerol and plays an important role in lipid and energy metabolism. However, the role of ATGL in the regulation of AF remains unclear. In this study, AF was induced by infusion of angiotensin II (Ang II, 2000 ng/kg/min) for 3 weeks in male ATGL knockout (KO) mice and age-matched C57BL/6 wild-type mice. The atrial volume was measured by echocardiography. Atrial fibrosis, inflammatory cells, and superoxide production were detected by histologic examinations. The results showed that ATGL expression was significantly downregulated in the atrial tissue of the Ang II-infused mice. Moreover, Ang II-induced increase in the inducibility and duration of AF, atrial dilation, fibrosis, inflammation, and oxidative stress in wild-type mice were markedly accelerated in ATGL KO mice; however, these effects were dramatically reversed in the ATGL KO mice administered with peroxisome proliferator-activated receptor (PPAR)-α agonist clofibric acid. Mechanistically, Ang II downregulated ATGL expression and inhibited PPAR-α activity, activated multiple signaling pathways (inhibiting kappa B kinase α/β-nuclear factor-κB, nicotinamide adenine dinucleotide phosphate oxidase, and transforming growth factor-β1/SMAD2/3) and reducing Kv1.5, Cx40, and Cx43 expression, thereby contributing to atrial structural and electrical remodeling and subsequent AF. In summary, our results indicate that ATGL KO enhances AF inducibility, possibly through inhibiting PPAR-α activation and suggest that activating ATGL might be a new therapeutic option for treating hypertensive AF.

Electroimmunology and cardiac arrhythmia

Conduction disorders and arrhythmias remain difficult to treat and are increasingly prevalent owing to the increasing age and body mass of the general population, because both are risk factors for arrhythmia. Many of the underlying conditions that give rise to arrhythmia - including atrial fibrillation and ventricular arrhythmia, which frequently occur in patients with acute myocardial ischaemia or heart failure - can have an inflammatory component. In the past, inflammation was viewed mostly as an epiphenomenon associated with arrhythmia; however, the recently discovered inflammatory and non-canonical functions of cardiac immune cells indicate that leukocytes can be arrhythmogenic either by altering tissue composition or by interacting with cardiomyocytes; for example, by changing their phenotype or perhaps even by directly interfering with conduction. In this Review, we discuss the electrophysiological properties of leukocytes and how these cells relate to conduction in the heart. Given the thematic parallels, we also summarize the interactions between immune cells and neural systems that influence information transfer, extrapolating findings from the field of neuroscience to the heart and defining common themes. We aim to bridge the knowledge gap between electrophysiology and immunology, to promote conceptual connections between these two fields and to explore promising opportunities for future research.

Effect of fish oil on circulating asymmetric dimethylarginine and adiponectin in overweight or obese patients with atrial fibrillation

Obesity and adipose-derived peptides might be involved in the pathogenesis of atrial fibrillation (AF). Adiponectin plays a major role in the modulation of several metabolic pathways, and asymmetric dimethylarginine (ADMA) has been suggested to be predictive of AF and associated adverse events. The aim of this study was to investigate the effect of fish oil supplementation on circulating adiponectin and ADMA in overweight or obese patients with persistent AF. In this randomized, double-blind, placebo-controlled trial, 80 overweight or obese (body mass index (BMI) ≥ 25 kg/m2) patients with persistent AF were randomly assigned to two groups to receive either 2 g/day fish oil or placebo, for 8 weeks. Serum levels of adiponectin and ADMA, and anthropometric indexes were measured. This study showed that serum adiponectin concentrations increased significantly following fish oil supplementation compared with the placebo group (13.15 ± 7.33 vs. 11.88 ± 6.94 µg/ml; p = .026). A significant reduction was also observed in serum ADMA levels in the fish oil compared with the placebo group following the intervention (0.6 ± 0.13 vs. 0.72 ± 0.15 µmol/L; p = .001). The changes in serum adiponectin and ADMA concentrations remained significant after adjustments for baseline values, age, sex, and changes of BMI and waist circumference (p = .011 and p = .001, respectively). In conclusion,  8 weeks supplementation with fish oil increased serum adiponectin and decreased ADMA concentrations in overweight or obese patients with persistent AF. As adiponectin and ADMA are suggested to be involved in many pathways associated with AF, the current findings might be promising in the clinical management of this disease, an issue that needs further investigations.

Cardiac Arrhythmias in Autoimmune Diseases

Autoimmune diseases (ADs) affect approximately 10% of the world's population. Because ADs are frequently systemic disorders, cardiac involvement is common. In this review we focus on typical arrhythmias and their pathogenesis, arrhythmia-associated mortality, and possible treatment options among selected ADs (sarcoidosis, systemic lupus erythematosus, scleroderma, type 1 diabetes, Graves' disease, rheumatoid arthritis, ankylosing spondylitis [AS], psoriasis, celiac disease [CD], and inflammatory bowel disease [IBD]). Rhythm disorders have different underlying pathophysiologies; myocardial inflammation and fibrosis seem to be the most important factors. Inflammatory processes and oxidative stress lead to cardiomyocyte necrosis, with subsequent electrical and structural remodeling. Furthermore, chronic inflammation is the pathophysiological basis linking AD to autonomic dysfunction, including sympathetic overactivation and a decline in parasympathetic function. Autoantibody-mediated inhibitory effects of cellular events (i.e., potassium or L-type calcium currents, M₂muscarinic cholinergic or β₁-adrenergic receptor signaling) can also lead to cardiac arrhythmia. Drug-induced arrhythmias, caused, for example, by corticosteroids, methotrexate, chloroquine, are also observed among AD patients. The most common arrhythmia in most AD presentations is atrial arrhythmia (primarily atrial fibrillation), expect for sarcoidosis and scleroderma, which are characterized by a higher burden of ventricular arrhythmia. Arrhythmia-associated mortality is highest among patients with sarcoidosis and lowest among those with AS; there are scant data related to mortality in patients with psoriasis, CD, and IBD.

Integrative analysis of transcriptome-wide association study data and mRNA expression profiles identified candidate genes and pathways associated with atrial fibrillation

Atrial fibrillation (AF) is the most common sustained cardiac arrhythmia characterized by extensive structural, contractile and electrophysiological remodeling. The genetic basis of AF remained elusive until now. Transcriptome-wide association study (TWAS) was conducted by FUSION tool using gene expression weights of 7 tissues combined with a large-scale genome-wide association study (GWAS) dataset of AF, totally involving 8180 AF cases and 28,612 controls. Significant genes identified by TWAS were then subjected to gene ontology (GO) and pathway enrichment analysis. The genome-wide mRNA gene expression profiling of AF was compared with the results of TWAS to detect common genes shared by TWAS and mRNA expression profiling of AF. TWAS detected a group of candidate genes with P_TWAS values < 0.05 across the seven tissues for AF, such as CMAH (P_TWAS = 3.15 × 10^-25 for whole blood), INCENP (P_TWAS = 1.77 × 10^-22 for artery aorta), CMAHP (P_TWAS = 4.57 × 10^-20 for artery aorta). Pathway enrichment analysis identified multiple candidate pathways, such as protein K48-linked ubiquitination (P value = 0.0124), positive regulation of leukocyte chemotaxis (P value = 0.0046) and fatty acid degradation (P value = 0.0295). Further comparing the GO results of TWAS and mRNA expression profiling, 2 common GO terms were identified, including actin binding (P_TWAS = 0.0446, P_mRNA = 7.00 × 10^-4) and extracellular matrix (P_TWAS = 0.0037, P_mRNA = 3.00 × 10^-6). We detected multiple novel candidate genes, GO terms and pathways for AF, providing novel clues for understanding the genetic mechanism of AF.

Interrelationship between diabetes mellitus and heart failure: the role of peroxisome proliferator-activated receptors in left ventricle performance

Heart failure (HF) is a common cardiac syndrome, whose pathophysiology involves complex mechanisms, some of which remain unknown. Diabetes mellitus (DM) constitutes not only a glucose metabolic disorder accompanied by insulin resistance but also a risk factor for cardiovascular disease and HF. During the last years though emerging data set up, a bidirectional interrelationship between these two entities. In the case of DM impaired calcium homeostasis, free fatty acid metabolism, redox state, and advance glycation end products may accelerate cardiac dysfunction. On the other hand, when HF exists, hypoperfusion of the liver and pancreas, b-blocker and diuretic treatment, and autonomic nervous system dysfunction may cause impairment of glucose metabolism. These molecular pathways may be used as therapeutic targets for novel antidiabetic agents. Peroxisome proliferator-activated receptors (PPARs) not only improve insulin resistance and glucose and lipid metabolism but also manifest a diversity of actions directly or indirectly associated with systolic or diastolic performance of left ventricle and symptoms of HF. Interestingly, they may beneficially affect remodeling of the left ventricle, fibrosis, and diastolic performance but they may cause impaired water handing, sodium retention, and decompensation of HF which should be taken into consideration in the management of patients with DM. In this review article, we present the pathophysiological data linking HF with DM and we focus on the molecular mechanisms of PPARs agonists in left ventricle systolic and diastolic performance providing useful insights in the molecular mechanism of this class of metabolically active regiments.

Cardiolipotoxicity, Inflammation, and Arrhythmias: Role for Interleukin-6 Molecular Mechanisms

Fatty acid infiltration of the myocardium, acquired in metabolic disorders (obesity, type-2 diabetes, insulin resistance, and hyperglycemia) is critically associated with the development of lipotoxic cardiomyopathy. According to a recent Presidential Advisory from the American Heart Association published in 2017, the current average dietary intake of saturated free-fatty acid (SFFA) in the US is 11–12%, which is significantly above the recommended <10%. Increased levels of circulating SFFAs (or lipotoxicity) may represent an unappreciated link that underlies increased vulnerability to cardiac dysfunction. Thus, an important objective is to identify novel targets that will inform pharmacological and genetic interventions for cardiomyopathies acquired through excessive consumption of diets rich in SFFAs. However, the molecular mechanisms involved are poorly understood. The increasing epidemic of metabolic disorders strongly implies an undeniable and critical need to further investigate SFFA mechanisms. A rapidly emerging and promising target for modulation by lipotoxicity is cytokine secretion and activation of pro-inflammatory signaling pathways. This objective can be advanced through fundamental mechanisms of cardiac electrical remodeling. In this review, we discuss cardiac ion channel modulation by SFFAs. We further highlight the contribution of downstream signaling pathways involving toll-like receptors and pathological increases in pro-inflammatory cytokines. Our expectation is that if we understand pathological remodeling of major cardiac ion channels from a perspective of lipotoxicity and inflammation, we may be able to develop safer and more effective therapies that will be beneficial to patients.

Single and persistent elevation of C-reactive protein levels and the risk of atrial fibrillation in a general population: The Ansan-Ansung Cohort of the Korean Genome and Epidemiology Study

BACKGROUND

Inflammation has been reported to cause atrial fibrillation (AF). However, it remains unclear whether C-reactive protein (CRP) levels predict AF. We investigated whether there was an association between serum CRP levels and the development of AF.

METHODS

A total of 10,030 subjects aged between 40 and 69 years were enrolled and followed biennially over a 12-year period in the Ansan-Ansung cohort study. Serum CRP levels were measured at baseline and high-sensitivity CRP (hsCRP) levels were measured at every revisit. AF was identified using 12-lead standard electrocardiography. Inverse probability of treatment weighting was applied to balance the confounders of AF development between groups.

RESULTS

Serum CRP levels were higher in subjects with AF at baseline and those with new-onset AF than in those without AF. Cox-regression analysis showed that high CRP levels (>3 mg/L) and intermediate CRP levels (1-3 mg/L) at baseline were not associated with a higher risk of new-onset AF compared with low CRP levels (<1 mg/L) after adjustments for covariates. The weighted incidences of AF also did not differ according to the CRP levels. In contrast, persistent elevation of CRP or hsCRP levels (≥1 mg/L at all visits) was associated with a higher risk of AF compared with nonpersistent elevation of CRP or hsCRP levels after adjustment for covariates in both unweighted and weighted cohorts.

CONCLUSION

A high CRP level at a single measurement was not associated with the risk of AF, whereas persistently elevated CRP levels independently predicted the development of AF.

Data Linking Diabetes Mellitus and Atrial Fibrillation-How Strong Is the Evidence? From Epidemiology and Pathophysiology to Therapeutic Implications

According to estimates, around 5% of the world population has hazel eyes. And there are about as many people with diabetes mellitus (DM). Red hair occurs naturally in up to 2% of the human population. And about as many people are estimated to have atrial fibrillation (AF). If a hazel eyed person with red hair does not surprise us, should a diabetic patient with AF? Accumulating epidemiologic data suggest, however, that the DM-AF association may be more than a simple coincidence. But, how strong is this evidence? Experimental studies bring evidence for a DM-induced atrial proarrhythmic remodelling. But how relevant are these data for the clinical setting? In this review, we aim to provide a critical analysis of the existing clinical and experimental, epidemiologic, and mechanistic data that bridge DM and AF, we emphasize a number of questions that remain to be answered, and we identify hotspots for future research. The therapeutic implications of the DM-AF coexistence are also discussed, with a focus on rhythm control and on conventional and DM-specific upstream therapies for AF management.

Interleukin-1 in monocyte activation phenotypes in systemic juvenile idiopathic arthritis: Observations from a clinical trial of rilonacept, an interleukin-1 inhibitor

Systemic juvenile idiopathic arthritis (sJIA) is a childhood rheumatic disease of unknown origin. Dysregulated innate immunity is implicated in disease pathology. We investigated if IL-1 inhibition affects circulating cytokines and monocyte gene expression. CD14+ monocytes from patients in the RAPPORT trial were analyzed by RT-PCR for expression of IL1B and transcription factors associated with monocyte activation. Serum IL-1ra decreased with treatment, and IL-18BP transiently increased. Serum levels of IL-1β, IL-6, IL-10 and IL-18 were unchanged. IRF5 and STAT6 were decreased, and PPARG was increased, independent of clinical response, and may represent a skew toward a PPARG-driven M2-like phenotype. IL1B expression was decreased in early clinical responders. A transient increase in STAT1, and a decrease in SOCS1 preceded the reduction in IL1B in early clinical responders. Changes in IL1B/STAT1/SOCS1 could be associated with crosstalk between IL-1 and IFN pathways in sJIA. These transcriptional changes might be useful as drug response biomarkers.

Interplay between the renin-angiotensin system, the canonical WNT/β-catenin pathway and PPARγ in hypertension

PURPOSE OF REVIEW

Heterogeneous causes can determinate hypertension.

RECENT FINDINGS

The renin-angiotensin system (RAS) has a major role in the pathophysiology of blood pressure. Angiotensin II and aldosterone are overexpressed during hypertension and lead to hypertension development and its cardiovascular complications. In several tissues, the overactivation of the canonical WNT/β-catenin pathway leads to inactivation of peroxisome proliferator-activated receptor gamma (PPARγ), while PPARγ stimulation induces a decrease of the canonical WNT/β-catenin pathway. In hypertension, the WNT/β-catenin pathway is upregulated, whereas PPARγ is decreased. The WNT/β-catenin pathway and RAS regulate positively each other during hypertension, whereas PPARγ agonists can decrease the expression of both the WNT/β-catenin pathway and RAS. We focus this review on the hypothesis of an opposite interplay between PPARγ and both the canonical WNT/β-catenin pathway and RAS in regulating the molecular mechanism underlying hypertension. The interactions between PPARγ and the canonical WNT/β-catenin pathway through the regulation of the renin-angiotensin system in hypertension may be an interesting way to better understand the actions and the effects of PPARγ agonists as antihypertensive drugs.

Effects of atorvastatin on atrial remodeling in a rabbit model of atrial fibrillation produced by rapid atrial pacing

Background

Accumulating evidence suggests that myeloperoxidase (MPO) is involved in atrial remodeling of atrial fibrillation (AF). Statins could reduce the MPO levels in patients with cardiovascular diseases. This study evaluated the effects of atorvastatin on MPO level and atrial remodeling in a rabbit model of pacing-induced AF.

Methods

Eighteen rabbits were randomly divided into sham, control and atorvastatin groups. Rabbits in the control and atorvastatin groups were subjected to rapid atrial pacing (RAP) at 600 bpm for 3 weeks, and treated with placebo or atorvastatin (2.5 mg/kg/d), respectively. Rabbits in the sham group did not receive RAP. After 3 weeks of pacing, atrial structural and functional changes were assessed by echocardiography, atrial effective refractory period (AERP) and AF inducibility were measured by atrial electrophysiological examination, and histological changes were evaluated by Masson trichrome-staining. The L-type calcium channel α1c (Cav1.2), collagen I and III, MPO, matrix metalloproteinase (MMP)-2 and MMP-9 were analyzed by real time polymerase chain reaction and/or western blot.

Results

All rabbits were found to have maintained sinus rhythm after 3 weeks of RAP. Atrial burst stimulation induced sustained AF (>30 min) in 5, 4, and no rabbits in the control, atorvastatin, and sham groups, respectively. The AERP shortened and Cav1.2 mRNA level decreased in the control group, but these changes were suppressed in the atorvastatin group. Obvious left atrial enlargement and dysfunction was found in both control and atorvastatin groups. Compared with the control group, these echocardiograhic indices of left atrium did not differ in the atorvastatin group. Prominent atrial fibrosis and increased levels of collagen I and III were observed in the control group but not in the atorvastatin group. The mRNA and protein levels of MPO, MMP-2 and MMP-9 significantly increased in the control group, but these changes were prevented in the atorvastatin group.

Conclusion

Treatment with atorvastatin prevented atrial remodeling in a rabbit model of RAP-induced AF. The reduction of levels of atrial MPO, MMP-2 and MMP-9 may contribute to the prevention of atorvastatin on atrial remodeling.

Peroxisome Proliferator-Activated Receptor-γ Is Critical to Cardiac Fibrosis

Peroxisome proliferator-activated receptor-γ (PPARγ) is a ligand-activated transcription factor belonging to the nuclear receptor superfamily, which plays a central role in regulating lipid and glucose metabolism. However, accumulating evidence demonstrates that PPARγ agonists have potential to reduce inflammation, influence the balance of immune cells, suppress oxidative stress, and improve endothelial function, which are all involved in the cellular and molecular mechanisms of cardiac fibrosis. Thus, in this review we discuss the role of PPARγ in various cardiovascular conditions associated with cardiac fibrosis, including diabetes mellitus, hypertension, myocardial infarction, heart failure, ischemia/reperfusion injury, atrial fibrillation, and several other cardiovascular disease (CVD) conditions, and summarize the developmental status of PPARγ agonists for the clinical management of CVD.

Atrial fibrillation in patients with diabetes: molecular mechanisms and therapeutic perspectives

Atrial fibrillation (AF) remains the most frequent sustained cardiac arrhythmia worldwide and its incidence increases with ageing, cardiovascular risk factors and comorbidities. Prevalence of diabetes mellitus (DM) is growing fast and is assuming pandemic proportions mostly due to overnutrition and sedentary habits. Experimental and clinical evidences suggest that DM and AF are strongly interconnected. The present review addresses in detail new molecular pathways implicated in the etiology of AF and their relevance for mechanism-based therapeutic strategies in this setting. Advances in risk stratification, drug therapy (i.e., novel anticoagulants) and catheter ablation are also described.

Stimulation of ICa by basal PKA activity is facilitated by caveolin-3 in cardiac ventricular myocytes

L-type Ca channels (LTCC), which play a key role in cardiac excitation–contraction coupling, are located predominantly at the transverse (t-) tubules in ventricular myocytes. Caveolae and the protein caveolin-3 (Cav-3) are also present at the t-tubules and have been implicated in localizing a number of signaling molecules, including protein kinase A (PKA) and β₂-adrenoceptors. The present study investigated whether disruption of Cav-3 binding to its endogenous binding partners influenced LTCC activity. Ventricular myocytes were isolated from male Wistar rats and LTCC current (I_Ca) recorded using the whole-cell patch-clamp technique. Incubation of myocytes with a membrane-permeable peptide representing the scaffolding domain of Cav-3 (C3SD) reduced basal I_Ca amplitude in intact, but not detubulated, myocytes, and attenuated the stimulatory effects of the β₂-adrenergic agonist zinterol on I_Ca. The PKA inhibitor H-89 also reduced basal I_Ca; however, the inhibitory effects of C3SD and H-89 on basal I_Ca amplitude were not summative. Under control conditions, myocytes stained with antibody against phosphorylated LTCC (pLTCC) displayed a striated pattern, presumably reflecting localization at the t-tubules. Both C3SD and H-89 reduced pLTCC staining at the z-lines but did not affect staining of total LTCC or Cav-3. These data are consistent with the idea that the effects of C3SD and H-89 share a common pathway, which involves PKA and is maximally inhibited by H-89, and suggest that Cav-3 plays an important role in mediating stimulation of I_Ca at the t-tubules via PKA-induced phosphorylation under basal conditions, and in response to β₂-adrenoceptor stimulation.

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Basal L type calcium current was reduced by interfering with caveolin-3 binding.

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L type calcium current is tonically regulated by PKA phosphorylation.

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Interfering with caveolin-3 binding reduced beta2 adrenergic stimulation of I_Ca.

A pilot study of circulating PPAR-γ receptor protein in elderly patients with atrial fibrillation

INTRODUCTION

The present study aimed to investigate the relationship between serum peroxisome proliferator-activated receptor-γ (PPAR-γ) protein concentration and inflammatory markers in elderly patients with atrial fibrillation (AF).

MATERIAL AND METHODS

We enrolled a total of 73 elderly patients: 45 with AF as the test group and 28 in sinus rhythm as a control group. We assayed serum PPAR-γ receptor protein, high-sensitivity C-reactive protein (hs-CRP), interleukin-6 (IL-6), and tumour necrosis factor-α (TNF-α). The study protocol and written informed consent were approved by the Ethics Committee of Clinical Research, Peking University First Hospital.

RESULTS

The concentration of PPAR-γ receptor protein was lower in AF patients than that in the control group (p < 0.01), and the concentrations of hs-CRP, IL-6, and TNF-α were higher than those in the control group (all p < 0.01). The PPAR-γ level was negatively correlated with hs-CRP, IL-6, and left atrium diameter (LAD) level (all p < 0.05). On logistic regression analysis, PPAR-γ, hs-CRP, TNF-α and LAD level were associated with AF.

CONCLUSIONS

Elderly patients with AF show an inflammatory state and atrial remodeling. The PPAR-γ receptor protein concentration is inversely linked with inflammation in AF. As an important transcription factor regulating inflammatory gene expression, PPAR-γ may take part in the pathogenesis of AF.

Inflammatory cytokines and atrial fibrillation: current and prospective views

Atrial fibrillation (AF) is the most common sustained arrhythmia and a challenging clinical problem encountered in daily clinical practice. There is an increasing body of evidence linking inflammation to a broad spectrum of cardiovascular conditions including AF. Historical evidence supports an association between AF and inflammation and is consistent with the association of AF with inflammatory conditions of the heart, such as myocarditis and pericarditis. AF has been associated with myocardial oxidative stress, and antioxidant agents have demonstrated antiarrhythmic benefit in humans. Increased plasma interleukin (IL)-6, C-reactive protein (CRP), and plasma viscosity support the existence of an inflammatory state among "typical" populations with chronic AF. These indexes of inflammation are related to the prothrombotic state and may be linked to the clinical characteristics of the patients (underlying vascular disease and comorbidities), rather than simply to the presence of AF itself. It has been suggested that inflammation may have a role in the development of atrial arrhythmias after cardiac surgery, and that a genetic predisposition to develop postoperative complications exists. Cytokines can have a prognostic significance; IL-6 levels, CRP, and other cytokines may have prognostic value in AF. Cytokine lowering therapies, statins, angiotensin converting enzyme inhibitors and other anti-inflammatory agents may have a role in the treatment of AF. The present article provides an overview of the evidence linking inflammatory cytokines to AF and their therapeutic and prognostic implications.