Atrial fibrillation is associated with hematopoietic tissue activation and arterial inflammation

Dissecting and Visualizing the Functional Diversity of Cardiac Macrophages

Cardiac macrophages represent a functionally diverse population of cells involved in cardiac homeostasis, repair, and remodeling. With recent advancements in single-cell technologies, it is possible to elucidate specific macrophage subsets based on transcriptional signatures and cell surface protein expression to gain a deep understanding of macrophage diversity in the heart. The use of fate-mapping technologies and parabiosis studies have provided insight into the ontogeny and dynamics of macrophages identifying subsets derived from embryonic and adult definitive hematopoietic progenitors that include tissue-resident and bone marrow monocyte-derived macrophages, respectively. Within the heart, these subsets have distinct tissue niches and functional roles in the setting of homeostasis and disease, with cardiac resident macrophages representing a protective cell population while bone marrow monocyte-derived cardiac macrophages have a context-dependent effect, triggering both proinflammatory tissue injury, but also promoting reparative functions. With the increased understanding of the clinical relevance of cardiac macrophage subsets, there has been an increasing need to detect and measure cardiac macrophage compositions in living animals and patients. New molecular tracers compatible with positron emission tomography/computerized tomography and positron emission tomography/ magnetic resonance imaging have enabled investigators to noninvasively and serially visualize cardiac macrophage subsets within the heart to define associations with disease and measure treatment responses. Today, advancements within this thriving field are poised to fuel an era of clinical translation.

Disordered GPR43/NLRP3 expression in peripheral leukocytes of patients with atrial fibrillation is associated with intestinal short chain fatty acids levels

BACKGROUND

Atrial fibrillation (AF) is associated with circulating inflammation. Short-chain fatty acids (SCFAs) derived from gut microbiota (GM) regulate leukocyte function and inhibit the release of inflammatory cytokines, which are partly mediated by the G-protein-coupled receptor 43 (GPR43) signaling. This study aimed to investigate the expression of GPR43/NOD-like receptors family pyrin domain containing 3 (NLRP3) in leukocytes and the interaction with intestinal SCFAs levels in AF patients.

METHODS

Expressions of GPR43 and NLRP3 mRNA in peripheral blood leukocytes from 23 AF patients and 25 non-AF controls were detected by quantitative reverse transcription-polymerase chain reaction (qRT-PCR). Expressions of leukocyte GPR43 and NLRP3 protein were evaluated by western blot analysis. The levels of plasma IL-1β were measured by enzyme-linked immunosorbent assay (ELISA). The fecal SCFAs levels based on GC/MS metabolome of corresponding 21 controls and 14 AF patients were acquired from our published dataset. To evaluate the expression of NLRP3 and GPR43 and the release of IL-1β, human THP-1 cells were stimulated with or without SCFAs (acetate, propionate, and butyrate), lipopolysaccharide (LPS), and nigericin in vitro, respectively.

RESULTS

Compared to the controls, the mRNA expression in peripheral leukocytes was significantly reduced in AF patients (P = 0.011) coupled with the increase in downstream leukocyte NLRP3 mRNA expression (P = 0.007) and plasma IL-1β levels (P < 0.001), consistent with changes in GPR43 and NLRP3 protein expression. Furthermore, leukocyte GPR43 mRNA levels were positively correlated with fecal GM-derived acetic acid (P = 0.046) and negatively correlated with NLRP3 mRNA expression (P = 0.024). In contrast to the negative correlation between left atrial diameter (LAD) and GPR43 (P = 0.008), LAD was positively correlated with the leukocyte NLRP3 mRNA levels (P = 0.024). Subsequent mediation analysis showed that 68.88% of the total effect of intestinal acetic acid on AF might be mediated by leukocyte GPR43/NLRP3. The constructed GPR43-NLRP3 score might have a predictive potential for AF detection (AUC = 0.81, P < 0.001). Moreover, SCFAs treatment increased GPR43 expression and remarkably reduced LPS/nigericin-induced NLRP3 expression and IL-1β release in human THP-1 cells in vitro.

CONCLUSIONS

Disrupted interactions between GPR43 and NLRP3 expression in peripheral blood leukocytes, associated with reduced intestinal GM-derived SCFAs, especially acetic acid, may be involved in AF development and left atrial enlargement by enhancing circulating inflammation.

Series of myocardial FDG uptake requiring considerations of myocardial abnormalities in FDG-PET/CT

Distinct from cardiac PET performed with preparation to control physiological FDG uptake in the myocardium, standard FDG-PET/CT performed with 4-6 h of fasting will show variation in myocardial FDG uptake. For this reason, important signs of myocardial and pericardial abnormality revealed by myocardial FDG uptake tend to be overlooked. However, recognition of possible underlying disease will support further patient management to avoid complications due to the disease. This review demonstrates the mechanism of FDG uptake in the myocardium, discusses the factors affecting uptake, and provides notable image findings that may suggest underlying disease.

New methodological approaches to atrial fibrillation drug discovery

INTRODUCTION

Atrial fibrillation (AF) is the most common arrhythmia encountered in clinical practice and rhythm control using pharmacological agents is required in selected patients. Nonetheless, current medication is only modestly efficacious and associated with significant cardiovascular and systemic side effects. More efficacious and safe drugs are required to restore and maintain sinus rhythm in patients with AF.

AREAS COVERED

In this review, several potential drug targets are discussed including trans-membrane ion channels, intracellular calcium signaling, gap junction signaling, atrial inflammation and fibrosis, and the autonomic nervous system. New tools and methodologies for AF drug development are also reviewed including gene therapy, genome-guided therapy, stem cell technologies, tissue engineering, and optogenetics.

EXPERT OPINION

In recent decades, there has been an increased understanding of the underlying pathogenesis of AF. As a result, there is a gradual paradigm shift from focusing only on trans-membrane ion channel inhibition to developing therapeutic agents that target other underlying arrhythmogenic mechanisms. Gene therapy and genome-guided therapy are emerging as novel treatments for AF with some success in proof-of-concept studies. Recent advances in stem cell technology, tissue engineering, and optogenetics may allow more effective in-vitro drug screening than conventional methodologies.

Factors relevant to atrial 18F-fluorodeoxyglucose uptake in atrial fibrillation

BACKGROUND

This retrospective study was designed to explore the factors relevant to increased atrial 18F-fluorodeoxyglucose (FDG) uptake in patients with atrial fibrillation (AF) who had undergone routine whole-body positron emission tomography/computed tomography (PET/CT) imaging.

METHODS AND RESULTS

Forty-eight consecutive AF patients (32 persistent, 16 paroxysmal) were identified from our routine FDG PET/CT database. Twenty-two control subjects were selected to establish the normal range of FDG uptake (maximum standardized uptake value, SUVmax) in target tissues. A target-to-background ratio (TBR) was calculated to determine abnormal uptake in the atrium and atrial appendage (AA). Univariate comparisons and multivariate regression analyses were conducted to explore the factors associated with the increased FDG accumulation in the atrium and AA. Seventeen AF patients, all with persistent AF, had increased atrial FDG uptake. Most of them (14, or 82.4%) had increased uptake in the right atrium. Eleven AF patients, 9 with persistent AF, had increased uptake in the AA, and bilateral AAs were equally involved. Multivariate logistic regression analyses identified that female gender, persistent AF, and activity in epicardial adipose tissue (EAT) were independent factors predicting the increased activity of the atrium; also, SUVmax of the left ventricle was found for the AA. In addition, multivariate linear regression analyses showed that EAT activity was the only independent variable linearly correlated with the activity of the atrium and AA.

CONCLUSIONS

Atrial uptake was present in persistent AF and localized mainly in the right atrium, whereas bilateral AAs could be equally involved. Multiple factors contributed to the increased activity in atrium; in particular, the EAT activity was independently correlated with the activity of the atrium and AA.

Reduction of atrial fibrillation burden by pulmonary vein isolation leads to a decrease of CD11b expression on inflammatory cells

Aims

It is hypothesized that inflammation could promote structural and electrical remodelling processes in atrial fibrillation (AF). Atrial infiltration of monocytes and granulocytes has been shown to be dependent on CD11b expression. The aim of this study was to investigate whether treatment of AF by pulmonary vein isolation (PVI) may lead to reduced inflammation, as indicated by a decrease of CD11b expression on monocytes and granulocytes.

Methods and results

Flow-cytometric quantification analysis and determination of systemic inflammatory markers of peripheral blood were performed in 75 patients undergoing PVI 1 day before and 6 months after PVI. The extent of activation of monocytes and granulocytes was measured by quantifying the cell adhesion molecule CD11b. The mean expression of CD11b on monocytes (20.9 ± 2.5 vs. 10.2 ± 1.4; P < 0.001) and granulocytes (13.9 ± 1.6 vs. 6.8 ± 0.5; P < 0.001), as well as the relative count of CD11b-positive monocytes (P < 0.05) and CD11b-positive granulocytes (P < 0.01) were significantly reduced when comparing the identical patients before and 6 months after PVI. Systemic inflammatory parameters showed only a declining tendency after 6 months. Patients with unsuccessful PVI and ongoing AF on the day of follow-up showed no decrease in CD11b expression.

Conclusions

A significant reduction of CD11b expression on monocytes and granulocytes, as a sign of reduced cellular inflammation, was achieved by treatment of AF using PVI. These data strongly support that AF is not only a consequence of but also a cause for inflammatory processes, which, in turn, may contribute to atrial remodelling.

Prediction of New-Onset and Recurrent Atrial Fibrillation by Complete Blood Count Tests: A Comprehensive Systematic Review with Meta-Analysis

BACKGROUND Atrial fibrillation (AF) is one of the most critical and frequent arrhythmias precipitating morbidities and mortalities. The complete blood count (CBC) test is an important blood test in clinical practice and is routinely used in the workup of cardiovascular diseases. This systematic review with meta-analysis aimed to determine the strength of evidence for evaluating the association of hematological parameters in the CBC test with new-onset and recurrent AF. MATERIAL AND METHODS We conducted a meta-analysis of observational studies evaluating hematologic parameters in patients with new-onset AF and recurrent AF. A comprehensive subgroup analysis was performed to explore potential sources of heterogeneity. RESULTS The literature search of all major databases retrieved 2150 studies. After screening, 70 studies were analyzed in the meta-analysis on new-onset AF and 23 studies on recurrent AF. Pooled analysis on new-onset AF showed platelet count (PC) (weighted mean difference (WMD)=WMD of -26.39×10^9/L and p<0.001), mean platelet volume (MPV) (WMD=0.42 FL and p<0.001), white blood cell (WBC) (WMD=-0.005×10^9/L and p=0.83), neutrophil to lymphocyte ratio (NLR) (WMD=0.89 and p<0.001), and red blood cell distribution width (RDW) (WMD=0.61% and p<0.001) as associated factors. Pooled analysis on recurrent AF revealed PC (WMD=-2.71×109/L and p=0.59), WBC (WMD=0.20×10^9/L (95% CI: 0.08 to 0.32; p=0.002), NLR (WMD=0.37 and p<0.001), and RDW (WMD=0.28% and p<0.001). CONCLUSIONS Hematological parameters have significant ability to predict occurrence and recurrence of AF. Therefore, emphasizing the potential predictive role of hematological parameters for new-onset and recurrent AF, we recommend adding the CBC test to the diagnostic modalities of AF in clinical practice.

Normalization of Testosterone Levels After Testosterone Replacement Therapy Is Associated With Decreased Incidence of Atrial Fibrillation

Background

Atrial fibrillation (AF) is the most common cardiac dysrhythmia associated with significant morbidity and mortality. Several small studies have reported that low serum total testosterone (TT) levels were associated with a higher incidence of AF. In contrast, it is also reported that anabolic steroid use is associated with an increase in the risk of AF. To date, no study has explored the effect of testosterone normalization on new incidence of AF after testosterone replacement therapy (TRT) in patients with low testosterone.

Methods and Results

Using data from the Veterans Administrations Corporate Data Warehouse, we identified a national cohort of 76 639 veterans with low TT levels and divided them into 3 groups. Group 1 had TRT resulting in normalization of TT levels (normalized TRT), group 2 had TRT without normalization of TT levels (nonnormalized TRT), and group 3 did not receive TRT (no TRT). Propensity score–weighted stabilized inverse probability of treatment weighting Cox proportional hazard methods were used for analysis of the data from these groups to determine the association between post‐TRT levels of TT and the incidence of AF. Group 1 (40 856 patients, median age 66 years) had significantly lower risk of AF than group 2 (23 939 patients, median age 65 years; hazard ratio 0.90, 95% CI 0.81–0.99, P=0.0255) and group 3 (11 853 patients, median age 67 years; hazard ratio 0.79, 95% CI 0.70–0.89, P=0.0001). There was no statistical difference between groups 2 and 3 (hazard ratio 0.89, 95% CI 0.78– 1.0009, P=0.0675) in incidence of AF.

Conclusions

These novel results suggest that normalization of TT levels after TRT is associated with a significant decrease in the incidence of AF.

Presence of atrial fibrillation is associated with liver stiffness in an elderly Finnish population

Background

Chronic liver injury from different etiologies drives liver fibrosis. However, little is known about the associated factors, systemic factors in particular. Recently, non-alcoholic fatty liver disease (NAFLD) and atrial fibrillation have been shown to be associated with each other. Thereby, we aimed to study the association between atrial fibrillation and liver stiffness.

Study

Extensive clinical measurements including echocardiography of the heart, transient elastography (TE) of the liver and the presence of atrial fibrillation were determined in elderly Finnish study subjects (n = 76, mean age 73 years) from OPERA (Oulu Project Elucidating the Risk of Atherosclerosis) study cohort. Half of the study subjects had non-alcoholic fatty liver disease, whereas others did not have any known hepatic morbidity. The present study was cross-sectional by nature.

Results

The subjects with atrial fibrillation had higher TE values (with atrial fibrillation TE = 9.3kPa, without atrial fibrillation TE = 6.3kPa, p = 0.018). When the cohort was divided to four subgroups (those without NAFLD or atrial fibrillation, with NAFLD but without atrial fibrillation, with both conditions, and with atrial fibrillation but without NAFLD), the TE value was the highest in the subjects with both conditions (5.3kPa, 7.4kPa, 10.8kPa and 7.8kPa, respectively, p = 0.019). Moreover, the higher the TE value, the more prevalent atrial fibrillation was (the atrial fibrillation prevalence by tertiles of TE 27% / 36% / 77%, p = 0.001). Likewise, the greater the TE value, the greater the left atrial diameter, a collateral of atrial fibrillation (left atrial diameters by tertiles of TE 39mm / 45mm / 48mm, p<0.001) was. All these p-values for continuous variables remained statistically significant even after adjustment for common clinically relevant risk factors.

Conclusions

There is an association between atrial fibrillation and liver stiffness. This novel association may have multiple explanations and mechanistic links, which are discussed here and need further studies, prospective studies in particular.

The cardiosplenic axis: another obscure pathophysiological function of the spleen and its investigation using molecular imaging

Splenic pathophysiology has been relatively unstudied, but recently, the spleen has received more attention as a result of the discovery of the 'cardiosplenic axis'. This term describes a role that the spleen plays in the progression of atherosclerosis following acute myocardial infarction. Human studies of this axis have largely used fluorine-18-fluorodeoxyglucose (F-FDG) PET/CT to quantify peri-infarction inflammation, arterial wall inflammation and splenic metabolic activity. Most of these studies have quantified arterial wall inflammation and splenic metabolic activity using the standardized uptake value, but this is a semiquantitative measurement with several drawbacks, including overestimation of metabolic activity in overweight individuals and a dependence on blood glucose levels. A better approach to the measurement of metabolic activity using F-FDG is to measure tissue F-FDG clearance from dynamic imaging and Patlak-Rutland graphical analysis. This is the preferred approach for future human studies of the cardiosplenic axis that will be required to better define the nature of the spleen's role.