Dabigatran and Thrombin Modulate Electrophysiological Characteristics of Pulmonary Vein and Left Atrium

The role of senescence in the pathogenesis of atrial fibrillation: A target process for health improvement and drug development

Cellular senescence is a state of growth arrest that occurs after cells encounter various stresses. Senescence contributes to tumour suppression, embryonic development, and wound healing. It impacts on the pathology of various diseases by secreting inflammatory chemokines, immune modulators and other bioactive factors. These secretory biosignatures ultimately cause inflammation, tissue fibrosis, immunosenescence and many ageing-related diseases such as atrial fibrillation (AF). Because the molecular mechanisms underpinning AF development remain unclear, current treatments are suboptimal and have serious side effects. In this review, we summarize recent results describing the role of senescence in AF. We propose that senescence factors induce AF and have a causative role. Hence, targeting senescence and its secretory phenotype may attenuate AF.

Trastuzumab increases pulmonary vein arrhythmogenesis through modulating pulmonary vein electrical and conduction properties via phosphatidylinositol 3-kinase signaling

Objective(s):

Drug-induced atrial fibrillation (AF) is considered an adverse effect of chemotherapeutic drugs. AF is a crucial risk factor for stroke, heart failure, myocardial infarction, and mortality. Pulmonary veins (PVs) are considered triggers inducing AF, and the sinoatrial node (SAN) may modulate PV activity and participate in AF genesis. AF was associated with early discontinuation of trastuzumab in patients with breast cancer. However, whether trastuzumab directly modulates the electrophysiological characteristics of PV and SAN remains unclear.

Materials and Methods:

ECG and conventional microelectrode system were used to record rabbit heart rhythm in vivo and electrical activities in vitro from isolated SAN, PV, and SAN-PV preparations.

Results:

Trastuzumab reduced the beating rate in isolated PV and SAN preparations at 1, 10, and 30 μM (particularly in isolated SAN preparations) and induced burst firings in isolated PV preparations at 10 μΜ. In addition, trastuzumab (10 μM) induced SAN-PV conduction block and burst firings, which were blocked by wortmannin (a PI3K inhibitor, 100 nM). Similarly, ECG recordings showed that acute intravenous administration of trastuzumab (10 mg/kg) reduced rabbit heart rates.

Conclusion:

Trastuzumab increased PV arrhythmogenesis through interfering with PI3K signaling, which may contribute to the genesis of AF.

Pharmacological Inhibition of Serine Proteases to Reduce Cardiac Inflammation and Fibrosis in Atrial Fibrillation

Systemic inflammation correlates with an increased risk of atrial fibrillation (AF) and thrombogenesis. Systemic inflammation alters vessel permeability, allowing inflammatory and immune cell migration toward target organs, including the heart. Among inflammatory cells infiltrating the atria, macrophages and mast cell have recently attracted the interest of basic researchers due to the pathogenic mechanisms triggered by their activation. This chemotactic invasion is likely implicated in short- and long-term changes in cardiac cell-to-cell communication and in triggering fibrous tissue accumulation in the atrial myocardium and electrophysiological re-arrangements of atrial cardiomyocytes, thus favoring the onset and progression of AF. Serine proteases are a large and heterogeneous class of proteases involved in several processes that are important for cardiac function and are involved in cardiac diseases, such as (i) coagulation, (ii) fibrinolysis, (iii) extracellular matrix degradation, (iv) activation of receptors (i.e., protease-activated receptors [PPARs]), and (v) modulation of the activity of endogenous signals. The recognition of serine proteases substrates and their involvement in inflammatory/profibrotic mechanisms allowed the identification of novel cardio-protective mechanisms for commonly used drugs that inhibit serine proteases. The aim of this review is to summarize knowledge on the role of inflammation and fibrosis as determinants of AF. Moreover, we will recapitulate current findings on the role of serine proteases in the pathogenesis of AF and the possible beneficial effects of drugs inhibiting serine proteases in reducing the risk of AF through decrease of cardiac inflammation and fibrosis. These drugs include thrombin and factor Xa inhibitors (used as oral anticoagulants), dipeptidyl-peptidase 4 (DPP4) inhibitors, used for type-2 diabetes, as well as novel experimental inhibitors of mast cell chymases.

Thrombin Induces Angiotensin II-Mediated Senescence in Atrial Endothelial Cells: Impact on Pro-Remodeling Patterns

BACKGROUND

Besides its well-known functions in hemostasis, thrombin plays a role in various non-hemostatic biological and pathophysiologic processes. We examined the potential of thrombin to promote premature atrial endothelial cells (ECs) senescence.

METHODS AND RESULTS

Primary ECs were isolated from porcine atrial tissue. Endothelial senescence was assessed by measuring beta-galactosidase (SA-β-gal) activity using flow cytometry, oxidative stress using the redox-sensitive probe dihydroethidium, protein level by Western blot, and matrix metalloproteinases (MMPs) activity using zymography. Atrial endothelial senescence was induced by thrombin at clinically relevant concentrations. Thrombin induced the up-regulation of p53, a key regulator in cellular senescence and of p21 and p16, two cyclin-dependent kinase inhibitors. Nicotinamide adenine dinucleotide phosphate NADPH oxidase, cyclooxygenases and the mitochondrial respiration complex contributed to oxidative stress and senescence. Enhanced expression levels of vascular cell adhesion molecule (VCAM)-1, tissue factor, transforming growth factor (TGF)-β and MMP-2 and 9 characterized the senescence-associated secretory phenotype of atrial ECs. In addition, the pro-senescence endothelial response to thrombin was associated with an overexpression of both angiotensin converting enzyme and AT1 receptors and was inhibited by perindoprilat and losartan.

CONCLUSIONS

Thrombin promotes premature ageing and senescence of atrial ECs and may pave the way to deleterious remodeling of atrial tissue by a local up-regulation of the angiotensin system and by promoting pro-inflammatory, pro-thrombotic, pro-fibrotic and pro-remodeling responses. Hence, targeting thrombin and/or angiotensin systems may efficiently prevent atrial endothelial senescence.

Straight to the heart: Pleiotropic antiarrhythmic actions of oral anticoagulants

Mechanistic understanding of atrial fibrillation (AF) pathophysiology and the complex bidirectional relationship with thromboembolic risk remains limited. Oral anticoagulation is a mainstay of AF management. An emerging concept is that anticoagulants may themselves have potential pleiotropic disease-modifying effects. We here review the available evidence for hemostasis-independent actions of the oral anticoagulants on electrical and structural remodeling, and the inflammatory component of the vulnerable substrate.

Thrombin induces protease-activated receptor 1 signaling and activation of human atrial fibroblasts and dabigatran prevents these effects

BACKGROUND

Data with animal cells and models suggest that thrombin activates cardiac fibroblasts (Fib) to myofibroblasts (myoFib) via protease-activated receptor 1 (PAR1) cleavage, and in this way promotes adverse atrial remodeling and, thereby, atrial fibrillation (AF).

OBJECTIVE

Here, we explored the effects of thrombin on human atrial Fib and whether they are antagonized by the clinically available direct thrombin inhibitor, dabigatran.

METHODS

Fib isolated from atrial appendages of patients without AF undergoing elective cardiac surgery were evaluated for PAR expression and treated with thrombin with or without dabigatran. PAR1 cleavage, downstream signaling and myoFib markers were investigated by immunofluorescence and Western blot. Collagen synthesis, activity of matrix metalloprotease (MMP)-2 and proliferation were assessed by Picro-Sirius red staining, gelatinolytic zymography and BrdU incorporation, respectively. Fib function was studied as capability to contract a collagen gel and stimulate the chemotaxis of peripheral blood monocytes from healthy volunteers.

RESULTS

Primary human atrial Fib expressed PAR1, while levels of the other PARs were very low. Thrombin triggered PAR1 cleavage and phosphorylation of ERK1/2, p38 and Akt, elicited a switch to myoFib enriched for αSMA, fibronectin and type I collagen, and induced paracrine/autocrine transforming growth factor beta-1, cyclooxygenase-2, endothelin-1 and chemokine (C-C motif) ligand 2 (CCL2); conversely, MMP-2 activity decreased. Thrombin-primed cells displayed enhanced proliferation, formed discrete collagen-containing cellular nodules, and stimulated the contraction of a collagen gel. Furthermore, their conditioned medium caused monocytes to migrate. All these effects were prevented by dabigatran.

CONCLUSION

These results with human cells complete the knowledge about thrombin actions on cardiac Fib and strengthen the translational potential of the emerging paradigm that pharmacological blockade of thrombin may counteract molecular and cellular events underlying AF.

PAR1 contribution in acute electrophysiological properties of oral anticoagulants in rabbit pulmonary vein sleeve preparations

Whether oral anticoagulants, vitamin K antagonists (VKAs), and nonvitamin K oral anticoagulant (NOACs) frequently prescribed to atrial fibrillation (AF) patients, do themselves have a pro- or anti-arrhythmic effect have never been addressed. Transmembrane action potentials were recorded in an acute rabbit model of superfused pulmonary veins (PVs) sleeves preparations using standard microelectrode technique. Fluindione 10 μm (n = 6) increased the AP (action potential) duration (APD), induced a significantly V_max depression (from 95 ± 14 to 53 ± 5 V/s, P < 0.05), and 2 : 1 blocks during rapid atrial pacing thus evoking class I anti-arrhythmic properties, and prevented spontaneous trigger APs. Apixaban 10 μm (n = 6) increased the APD, significantly prolonged the effective refractory period (from 56.3 ± 4.2 to 72.0 ± 8.6 ms, P < 0.05), and prevented triggered APs occurrence. Fluindione and apixaban effects were suppressed with the addition of the protease-activated receptors 1 (PAR 1) agonist SFLLR-NH₂ . Warfarin 10 μm (n = 6) significantly abbreviated the early refractory period (from 56.3 ± 4.2 to 45.0 ± 2.2 ms, P < 0.05) and increased triggered APs occurrence that were successfully prevented by nifedipine but not by the addition of the protease-activated receptors 1 agonist SFLLR-NH₂ . In this acute rabbit PVs model, VKAs and NOACs, at physiological concentrations, exhibited very different pharmacological properties that influence PVs electrophysiology, implying PAR1, with fluindione and apixaban which exhibited more anti-arrhythmic properties, whereas warfarin exhibited more pro-arrhythmic properties.

Epigallocatechin-3-gallate modulates arrhythmogenic activity and calcium homeostasis of left atrium

BACKGROUND

Atrial fibrillation (AF) is the commonest sustained arrhythmia, and increases the risk of stroke, heart failure, and mortality. Calcium (Ca²⁺) overload and oxidative stress are thought to participate in the pathogenesis of AF. Epigallocatechin-3-gallate (EGCG) has an antioxidative effect and been shown to be beneficial in promoting cardiovascular health. However, it is not clear if EGCG directly modulates the electrophysiological characteristics and Ca²⁺ homeostasis of the left atrium (LA).

METHODS AND RESULTS

Conventional microelectrodes, whole-cell patch-clamp, and Fluo-3 fluorometric ratio technique were performed using the isolated rabbit LA preparations or isolated single LA cardiomyocytes before and after EGCG treatment. EGCG (0.01, 0.1, 1, and 10μM) which concentration-dependently decreased the APD₂₀ by 13±8%, 25±5%, 31±6%, and 37±5%, APD₅₀ by 9±8%, 22±6%, 32±7%, and 40±4%, and APD₉₀ by 2±12%, 9±8%, 24±10%, and 34±5% in LA preparations. EGCG (0.1μM) decreased the late sodium (Na⁺) current, L-type Ca²⁺ current, nickel-sensitive Na⁺-Ca²⁺ exchanger current, and transient outward current, but did not change the Na⁺ current and ultra-rapid delayed rectifier potassium current in LA cardiomyocytes. EGCG decreased intracellular Ca²⁺ transient and sarcoplasmic reticulum Ca²⁺ content in LA cardiomyocytes. Furthermore, EGCG decreased isoproterenol (ISO, 1μM)-induced burst firing. KT5823 (1μM) or KN93 (1μM) decreased the incidences of ISO-induced LA burst firing, which became lower with EGCG treatment. H89 (10μM) and KN92 (1μM) did not suppress the incidence of ISO-induced LA burst firing. However, EGCG decreased the incidences of ISO-induced LA burst firing in the presence of H89 or KN92.

CONCLUSION

EGCG directly regulates LA electrophysiological characteristics and Ca²⁺ homeostasis, and suppresses ISO-induced atrial arrhythmogenesis through inhibiting Ca²⁺/calmodulin or cGMP-dependent protein kinases.

Direct Thrombin Inhibitors Prevent Left Atrial Remodeling Associated With Heart Failure in Rats

The present study tested the hypothesis that thrombin participates in formation of left atrial remodeling and that direct oral anticoagulants, such as direct thrombin inhibitors (DTIs), can prevent its progression. In a rat model of heart failure associated with left atrial dilation, we found that chronic treatment with DTIs reduces the atrial remodeling and the duration of atrial fibrillation (AF) episodes induced by burst pacing by inhibiting myocardial hypertrophy and fibrosis. In addition to the prevention of thromboembolism complicating AF, DTIs may be of interest to slow down the progression of the arrhythmogenic substrate.

Gap junction modifiers regulate electrical activities of the sinoatrial node and pulmonary vein: Therapeutic implications in atrial arrhythmogenesis

BACKGROUND

Gap junction (GJ) dysfunctions predispose cardiac tissues to various arrhythmias. Sinoatrial node (SAN) and pulmonary veins (PVs) are closely related atrial dysrhythmia. This study evaluated whether GJ modifications modulate SAN and PVs electrical activities.

METHODS

Conventional microelectrodes were used to record action potentials in isolated rabbit SAN, PVs, and connected PV-SAN tissue preparations before and after heptanol (GJ inhibitor) and PQ1 (GJ enhancer) administration with and without isoproterenol. A whole-cell patch clamp was used to record the electrical activities before and after heptanol in single SAN and PV cardiomyocytes.

RESULTS

Heptanol (1, 3, and 10μM) reduced the spontaneous beating rates of isolated SAN preparations but not PVs. Heptanol (10μM) decelerated the SAN leading rhythm in the PV-SAN preparations and induced PV burst firings without (3 of 6, 50%) and with (6 of 6, 100%) isoproterenol (1μM). Heptanol (10μM) also reduced the spontaneous beating rates in single SAN cardiomyocyte, but not PV cardiomyocyte, with a decreased pacemaker current. PQ1 (50 and 500nM) treatment did not change the spontaneous beating rates in isolated SAN and PV preparations. In the connected PV-SAN preparations, PQ1 (500nM) did not induce any PV firing even having additional isoproterenol treatment (1μM). Moreover, PQ1 (500nM) prevented heptanol-induced electrical changes in SAN and PVs preparations.

CONCLUSION

GJ dysfunction modulates SAN and PV electrical activity, which may contribute to atrial arrhythmogenesis. GJ enhancer has a therapeutic potential in SAN dysfunction and atrial arrhythmogenesis.

Selective and non-selective non-steroidal anti-inflammatory drugs differentially regulate pulmonary vein and atrial arrhythmogenesis

BACKGROUND

Non-steroidal anti-inflammatory drugs (NSAIDs) increase the risk of atrial fibrillation (AF). This study investigated whether selective and non-selective NSAIDs differentially regulate the arrhythmogenesis of pulmonary veins and atria.

METHODS

Conventional microelectrodes were used to record action potentials (APs) in isolated rabbit PVs, sinoatrial node (SAN), left atrium (LA), and right atrium (RA) preparations before and after celecoxib or indomethacin administration. A whole-cell patch clamp was used to record the sodium-calcium exchanger (NCX) current, L-type calcium current (ICa-L), and late sodium current (INa-late) before and after celecoxib administration in isolated PV cardiomyocytes.

RESULTS

Celecoxib (0.3, 1, and 3 μM) reduced PV spontaneous beating rates, and induced delayed afterdepolarizations and burst firings in four of eight PV preparations (50%, p<0.05). Celecoxib also reduced SAN beating rates and decreased AP durations (APDs) in RA and LA, but did not change the resting membrane potential. Indomethacin (0.3, 1, 3, and 10 μM) changed neither the PV or SAN beating rates nor RA APDs, but it reduced LA APDs. Celecoxib (3 μM) significantly increased the NCX current and decreased the ICa-L, but did not change the INa-late. Ranolazine (10 μM) suppressed celecoxib (3 μM)-induced PV burst firings in 6 (86%, p<0.05) of 7 PVs. KB-R7943 (10 μM) suppressed celecoxib (3 μM)-induced PV burst firings in 5 (71%, p<0.05) of 7 PVs.

CONCLUSIONS

Selective and non-selective NSAIDs differentially modulate PV and atrial electrophysiological characteristics. Celecoxib increased PV triggered activity through enhancement of the NCX current, which contributed to its arrhythmogenesis.