Role of Indoxyl Sulfate as a Predisposing Factor for Atrial Fibrillation in Renal Dysfunction.
ABSTRACT: Renal dysfunction is a major risk factor for atrial fibrillation (AF). The uremic toxin indoxyl sulfate may contribute to the progression of cardiac fibrosis and AF substrate in renal dysfunction.Male Sprague-Dawley rats were assigned randomly to the following groups: 5/6 nephrectomy (5/6Nx) with vehicle, 5/6Nx with AST-120, sham procedure with vehicle, and sham procedure with AST-120. Vehicle and AST-120 were administered for 4 weeks. Serum levels of IS were significantly increased in 5/6Nx groups. Expression of malondialdehyde, an indicator of oxidative stress, was upregulated in the left atrium of 5/6Nx groups and was accompanied by an increase in expression of NADPH oxidase 2 and 4. Monocyte-mediated inflammatory signals such as CD68, monocyte chemoattractant protein 1, and vascular cell adhesion molecule 1 were also upregulated in 5/6Nx groups. Interstitial fibrosis was promoted heterogeneously, and expression of profibrotic indicators such as transforming growth factor β1, α-smooth muscle actin, and collagen type 1 was upregulated in left atrium tissue of 5/6Nx groups. In cultured atrial fibroblasts, incubation with IS upregulated expression of the markers of oxidative stress, inflammation, and profibrotic factors. These results suggest the direct effects of IS on the progression of AF substrate. AF was consistently and invariably induced by atrial extrastimuli in 5/6Nx groups in electrophysiological experiments. AST-120 treatment significantly alleviated renal dysfunction-induced oxidative stress, inflammation, and atrial fibrosis and, consequently, attenuated AF inducibility.Indoxyl sulfate facilitates atrial fibrosis and AF and thus is a novel therapeutic target for prevention of renal dysfunction-induced AF.
Project description:AIM:To investigate the effects of rhubarb enema treatment using a 5/6 nephrectomized rat model and study its mechanisms. METHODS:Twenty-eight Sprague Dawley rats were divided into three groups: sham operation group (n = 8), 5/6 nephrectomized (5/6Nx) (n = 10), and 5/6Nx with rhubarb enema treatment (n = 10). The rhubarb enema was continuous for 1.0 month. Serum creatinine, serum indoxyl sulfate (IS) level, renal pathology, tubulointerstitial fibrosis, and renal oxidative stress were assessed. RESULTS:5/6Nx rats showed increasing levels of serum creatinine and severe pathological lesions. Their serum creatinine levels obviously decreased after rhubarb enema treatment (P < 0.05 vs 5/6Nx group). The administration of rhubarb enema attenuated the histopathological changes in 5/6Nx rats. In addition, 5/6Nx rats showed an enhanced extent of tubulointerstitial fibrosis compared with sham rats, and administration of rhubarb enema to 5/6Nx rats ameliorated tubulointerstitial fibrosis. 5/6Nx rats showed increased serum levels of IS, renal oxidative stress, and NF-?B compared with sham rats, whereas administration of rhubarb enema to 5/6Nx rats decreased serum levels of IS, renal oxidative stress, and NF-?B levels. CONCLUSION:Rhubarb enema treatment ameliorates tubulointerstitial fibrosis in the kidneys of 5/6Nx rats, most likely by alleviating IS overload and reducing kidney oxidative stress and inflammatory injury.
Project description:Current therapies are less effective for treating sustained/permanent versus paroxysmal atrial fibrillation (AF). We and others have previously shown that histone deacetylase (HDAC) inhibition reverses structural and electrical atrial remodeling in mice with inducible, paroxysmal-like AF. Here, we hypothesize an important, specific role for class I HDACs in determining structural atrial alterations during sustained AF. The class I HDAC inhibitor N-acetyldinaline [4-(acetylamino)-N-(2-amino-phenyl) benzamide] (CI-994) was administered for 2 weeks (1 mg/kg/day) to Hopx transgenic mice with atrial remodeling and inducible AF and to dogs with atrial tachypacing-induced sustained AF. Class I HDAC inhibition prevented atrial fibrosis and arrhythmia inducibility in mice. Dogs were divided into three groups: 1) sinus rhythm, 2) sustained AF plus vehicle, and 3) sustained AF plus CI-994. In group 3, the time in AF over 2 weeks was reduced by 30% compared with group 2, along with attenuated atrial fibrosis and intra-atrial adipocyte infiltration. Moreover, group 2 dogs had higher atrial and serum inflammatory cytokines, adipokines, and atrial immune cells and adipocytes compared with groups 1 and 3. On the other hand, groups 2 and 3 displayed similar left atrial size, ventricular function, and mitral regurgitation. Importantly, the same histologic alterations found in dogs with sustained AF and reversed by CI-994 were also present in atrial tissue from transplanted patients with chronic AF. This is the first evidence that, in sustained AF, class I HDAC inhibition can reduce the total time of fibrillation, atrial fibrosis, intra-atrial adipocytes, and immune cell infiltration without significant effects on cardiac function.
Project description:Celiac disease (CD), a serious autoimmune disorder that occurs in people who are genetically predisposed, is induced by dietary gluten intake and affects primarily the small intestine. Many studies have identified an increased risk of cardiovascular problems in patients with CD. Moreover, these patients are susceptible to certain liver diseases, as well as fibrosis.The aim of this study was to assess the presence of fibrosis using the De Ritis ratio, determining its effect on the electromechanical features of the left atrium and its susceptibility to atrial fibrillation (AF) in patients with CD.A total of 97 patients diagnosed with CD by antibody test and biopsy were included in this prospective study. Two groups were created from these patients, a fibrosis-prone (FP) group and a non-fibrosis-prone (NFP) group, according to the cut-off value, as defined in previously published reports, for the AST/ALT ratio. Electrocardiographic and echocardiographic examinations were performed as part of the study.There were no differences in the baseline characteristics and conventional echocardiographic parameters of the defined groups. However, the patients in the FP group, as compared to those in the NFP group, had significantly increased PWD (56.68±6.48 ms vs. 37.49±6.22 ms, P<0.001). Additionally, significantly higher interatrial (60.50±13.05 ms vs. 29.40±11.55 ms, P<0.001), intra-left atrial (44.18±14.12 ms vs. 21.02±11.99 ms, P<0.001), and intra-right atrial (15.61±8.91 ms vs. 8.38±4.50 ms, P<0.001) EMD was found among the patients in the FP group compared to that of the NFP group.It is believed that the susceptibility to AF cited in previous studies may be related to fibrosis. Our study is the first to examine the possible effects of fibrosis on AF susceptibility in patients with CD, whereby we propose a new biomarker for prediction of AF susceptibility of these patients.
Project description:Atrial fibrosis, one of the most striking features in the pathology of atrial fibrillation (AF), is promoted by local and systemic inflammation. Electrophilic fatty acid nitroalkenes, endogenously generated by both metabolic and inflammatory reactions, are anti-inflammatory mediators that in synthetic form may be useful as drug candidates. Herein we investigate whether an exemplary nitro-fatty acid can limit atrial fibrosis and AF.Wild-type C57BL6/J mice were treated for 2 weeks with angiotensin II (AngII) and vehicle or nitro-oleic acid (10-nitro-octadec-9-enoic acid, OA-NO2, 6 mg/kg body weight) via subcutaneous osmotic minipumps. OA-NO2 significantly inhibited atrial fibrosis and depressed vulnerability for AF during right atrial electrophysiological stimulation to levels observed for AngII-naive animals. Left atrial epicardial mapping studies demonstrated preservation of conduction homogeneity by OA-NO2. The protection from fibrotic remodelling was mediated by suppression of Smad2-dependent myofibroblast transdifferentiation and inhibition of Nox2-dependent atrial superoxide formation.OA-NO2 potently inhibits atrial fibrosis and subsequent AF. Nitro-fatty acids and possibly other lipid electrophiles thus emerge as potential therapeutic agents for AF, either by increasing endogenous levels through dietary modulation or by administration as synthetic drugs.
Project description:Atrial fibrillation (AF) contributes significantly to morbidity and mortality in elderly patients and has been correlated with enhanced age-dependent atrial fibrosis. Reversal of atrial fibrosis has been proposed as therapeutic strategy to suppress AF.To test the ability of relaxin to reverse age-dependent atrial fibrosis and suppress AF.Aged F-344 rats (24 months old) were treated with subcutaneous infusion of vehicle or relaxin (0.4 mg/kg/day) for 2 weeks. Rat hearts were excised, perfused on a Langendorff apparatus, and stained with voltage and Ca(2+) indicator dyes. Optical mapping and programmed electrical stimulation was used to test arrhythmia vulnerability and changes in electrophysiological characteristics. Changes in protein expression and Na(+) current density (INa) were measured by tissue immunofluorescence and whole-cell patch clamp technique.In aged rats, sustained AF was readily induced with a premature pulse (n = 7/8) and relaxin treatment suppressed sustained AF by a premature impulse or burst pacing (n = 1/6) (P < .01). Relaxin significantly increased atrial action potential conduction velocity and decreased atrial fibrosis. Relaxin treatment increased Nav1.5 expression (n = 6; 36% ± 10%) and decreased total collagen and collagen I (n = 5-6; 55%-66% ± 15%) in aged atria (P < .05) and decreased collagen I and III and TGF-?1 mRNA (P < .05). Voltage-clamp experiments demonstrated that relaxin treatment (100 nM for 2 days) increased atrial INa by 46% ± 4% (n = 12-13/group, P < .02).Relaxin suppresses AF through an increase in atrial conduction velocity by decreasing atrial fibrosis and increasing INa. These data provide compelling evidence that relaxin may serve as an effective therapy to manage AF in geriatric patients by reversing fibrosis and modulating cardiac ionic currents.
Project description:<h4>Aims</h4>Left-atrial (LA) fibrosis is an important feature of many atrial fibrillation (AF) substrates. The JAK-STAT system contributes to cardiac remodelling, but its role in AF is unknown. Here we investigated JAK-STAT changes in an AF-model and their potential contributions to LA-fibrosis.<h4>Methods and results</h4>LA-remodelling was studied in dogs with heart failure (HF) induced by ventricular tachypacing (VTP, 240 bpm), and in mice with left-ventricular (LV) dysfunction due to myocardial infarction (MI). The selective STAT-3 inhibitor S3I-201 was administered to fibroblasts in vitro or mice in vivo (10?mg/kg/d, osmotic mini-pump). HF-dogs developed LA-selective fibrosis and AF-susceptibility at 1-week VTP. The mRNA-expression of platelet-derived growth factor (PDGF, a JAK-STAT activator) isoforms A, C and D, as well as JAK2, increased in LA fibroblasts from 1-week VTP. HF upregulated protein-expression of PDGF-receptor-? and phosphorylated (activated) signal transducer and activator of transcription 3 (STAT3) in LA. PDGF-AB stimulation of LA fibroblasts increased PDGFR-?, STAT3 and phosphorylated-STAT3 expression, as well as collagen-1 and fibronectin-1 protein secretion (by 1.6- to 20-fold), with smaller changes in LV fibroblasts. Phosphorylated-STAT3 and collagen upregulation were suppressed by the JAK2 inhibitor AG-490, PDGF receptor inhibitor AG1296 and STAT3-inhibitor SI3-201. In vivo S3I-201 treatment of MI-mice attenuated LA-fibrosis, LA-dilation and P-wave duration changes versus vehicle-control.<h4>Conclusions</h4>HF activates the LA JAK-STAT system and enhances PDGF-signalling. JAK-STAT inhibition reduces the profibrotic effects of PDGF stimulation on canine fibroblasts in vitro while attenuating in vivo LA-fibrosis and remodelling in post-MI mice, suggesting that the JAK/STAT pathway contributes to LA-fibrogenesis and might be a potential target for LA-fibrosis prevention.
Project description:Atrial fibrillation (AF) commonly occurs after surgery and is associated with atrial remodeling. TRPV4 is functionally expressed in the heart, and its activation affects cardiac structure and functions. We hypothesized that TRPV4 blockade alleviates atrial remodeling and reduces AF induction in sterile pericarditis (SP) rats. TRPV4 antagonist GSK2193874 or vehicle was orally administered 1 day before pericardiotomy. AF susceptibility and atrial function were assessed using in vivo electrophysiology, ex vivo optical mapping, patch clamp, and molecular biology on day 3 after surgery. TRPV4 expression increased in the atria of SP rats and patients with AF. GSK2193874 significantly reduced AF vulnerability in vivo and the frequency of atrial ectopy and AF with a reentrant pattern ex vivo. Mechanistically, GSK2193874 reversed the abnormal action potential duration (APD) prolongation in atrial myocytes through the regulation of voltage-gated K+ currents (IK); reduced the activation of atrial fibroblasts by inhibiting P38, AKT, and STAT3 pathways; and alleviated the infiltration of immune cells. Our results reveal that TRPV4 blockade prevented abnormal changes in atrial myocyte electrophysiology and ameliorated atrial fibrosis and inflammation in SP rats; therefore, it might be a promising strategy to treat AF, particularly postoperative AF.
Project description:Renal denervation (RD) was reported to reduce the susceptibility of atrial fibrillation (AF), but the underlying mechanism has not been well understood. This study was performed to investigate the effect of RD on the inducibility of AF in a rabbit model for atrial fibrosis and to explore the potential mechanisms. Thirty-five rabbits were randomly assigned into sham-operated group (n = 12), abdominal aortic constriction (AAC) group (n = 12) and AAC with RD (AAC-RD) group (n = 11). The incidence of AF induced by burst pacing in atriums was determined. Blood was collected to measure the levels of rennin, angiotensin II and aldosterone. Atrial samples were preserved to evaluate protein and gene expression of collagen, connective tissue growth factor (CTGF) and transforming growth factor-?1 (TGF-?1). Our data suggested cardiac structure remodeling and atrial fibrosis were successfully induced by AAC. Compared with the AAC group, the AAC-RD rabbits had smaller ascending aortic diameter and left ventricular end-systolic diameter. For burst pacing at the left atrium (LA), AF was induced in two of the 12 rabbits in the sham-operated group, 10 of the 12 rabbits in the AAC group, and 2 of the 11 rabbits in the AAC-RD group, with great difference among the three groups (P = 0.001). The percentage of LA burst stimulations with induced AF achieved 47.2% in the AAC group, which was higher than those in both the AAC-RD (12.1%) and the Sham-operated (5.6%) groups. Significantly increasing intercellular space in the AAC group (P<0.001) compared with the sham-operated rabbits. RD clearly decreased the volume fraction of collagen in LA and right atrium compared with that of the AAC group (P< 0.01). AAC-induced elevation of collagen I, CTGF and TGF-?1 was suppressed by RD. In conclusion, RD suppressed the inducibility of AF in a rabbit model for pressure associated atrial fibrosis, potentially by modulating renin-angiotensin-aldosterone system and decreasing pro-fibrotic factors.
Project description:<h4>Background</h4>Although microRNA (miRNA) regulates initiation and/or progression of atrial fibrillation (AF) in canine AF models, the underlying mechanism in humans remains unclear. We speculated that certain miRNAs in atrial tissue are related to AF, and evaluated the relationship of miRNA expression in human atrial tissue in cardiac surgery patients.<h4>Methods</h4>Right atrial tissues from 29 patients undergoing cardiovascular surgery were divided into 3 groups [A: chronic AF or unsuccessful maze, n=6; B: successful maze, n=10; C: sinus rhythm (SR) n=13]. miRNA expression was determined using high density microarrays and with Reverse transcriptase-polymerase chain reaction (RT-PCR). Fibrosis was examined using Masson trichrome staining.<h4>Results</h4>miRNA microarray analysis showed elevated miRNA-21, miRNA-23b, miRNA-199b, and miRNA-208b in AF as compared to SR groups. RT-PCR showed elevated miRNA-21 (1.9-fold) and miRNA-208b (4.2-fold) in AF as compared to the SR groups. miRNA-21 expression increased from Group C to A (A: 2.1-fold, B: 1.8-fold, C: 1.0-fold). Fibrosis increased from C to A (A: 43.0±12.9%, B: 21.3±6.1%, C: 11.9±3.1%). Percent fibrosis and miRNA-21 expression were correlated (r=0.508, p<0.05). The plasma levels of miRNA-21 in AF patients was significantly decreased as compared to the healthy volunteers (p<0.05).<h4>Conclusion</h4>The expression of miRNA-21 in human atrial tissue was found to be related to atrial fibrosis and might affect AF occurrence, indicating its usefulness as a biomarker for cardiac surgery management.
Project description:Atrial fibrillation (AF) contributes significantly to morbidity and mortality in elderly and hypertensive patients and has been correlated to enhanced atrial fibrosis. Despite a lack of direct evidence that fibrosis causes AF, reversal of fibrosis is considered a plausible therapy.To evaluate the efficacy of the antifibrotic hormone relaxin (RLX) in suppressing AF in spontaneously hypertensive rats (SHR).Normotensive Wistar-Kyoto (WKY) and SHR were treated for 2 weeks with vehicle (WKY+V and SHR+V) or RLX (0.4 mg/kg per day, SHR+RLX) using implantable mini-pumps. Hearts were perfused, mapped optically to analyze action potential durations, intracellular Ca²? transients, and restitution kinetics, and tested for AF vulnerability. SHR hearts had slower conduction velocity (CV; P<0.01 versus WKY), steeper CV restitution kinetics, greater collagen deposition, higher levels of transcripts for transforming growth factor-?, metalloproteinase-2, metalloproteinase-9, collagen I/III, and reduced connexin 43 phosphorylation (P<0.05 versus WKY). Programmed stimulation triggered sustained AF in SHR (n=5/5) and SHR+V (n=4/4), but not in WKY (n=0/5) and SHR+RLX (n=1/8; P<0.01). RLX treatment reversed the transcripts for fibrosis, flattened CV restitution kinetics, reduced action potential duration at 90% recovery to baseline, increased CV (P<0.01), and reversed atrial hypertrophy (P<0.05). Independent of antifibrotic actions, RLX (0.1 µmol/L) increased Na? current density, INa (?2-fold in 48 hours) in human cardiomyocytes derived from inducible pluripotent stem cells (n=18/18; P<0.01).RLX treatment suppressed AF in SHR hearts by increasing CV from a combination of reversal of fibrosis and hypertrophy and by increasing INa. The study provides compelling evidence that RLX may provide a novel therapy to manage AF in humans by reversing fibrosis and hypertrophy and by modulating cardiac ionic currents.