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Relaxin suppresses atrial fibrillation by reversing fibrosis and myocyte hypertrophy and increasing conduction velocity and sodium current in spontaneously hypertensive rat hearts.

ABSTRACT: 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.

SUBMITTER: Parikh A

PROVIDER: S-EPMC3774019 | biostudies-literature | 2013 Jul

REPOSITORIES: biostudies-literature

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Relaxin suppresses atrial fibrillation by reversing fibrosis and myocyte hypertrophy and increasing conduction velocity and sodium current in spontaneously hypertensive rat hearts.

Parikh Ashish A Patel Divyang D McTiernan Charles F CF Xiang Wenyu W Haney Jamie J Yang Lei L Lin Bo B Kaplan Aaron D AD Bett Glenna C L GC Rasmusson Randall L RL Shroff Sanjeev G SG Schwartzman David D Salama Guy G

Circulation research 20130607 3

<h4>Rationale</h4>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.<h4>Objective</h4>To evaluate the efficacy of the antifibrotic hormone relaxin (RLX) in suppressing AF in spontaneously hypertensive rats (SHR).<h4>Methods and results</h4>Normotensive Wistar-Kyoto (W ...[more]

PMID: 23748429

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Project description:Full Title: Transition from Compensated Hypertrophy to Systolic Heart Failure in the Spontaneously Hypertensive Rat: Structure, Function, and Transcript Analysis Gene expression changes and left ventricular remodeling associated with the transition to systolic heart failure (HF) were determined in the spontaneously hypertensive rat (SHR). By combining transcriptomics of left ventricles from six SHR with HF with changes in function and structure we aimed to better understand the molecular events underlying the onset of systolic HF compared to six age-matched, SHR with compensated hypertrophy. Left ventricle (LV) ejection fraction was depressed (82±4 to 52±3 %) in compensated vs. failing animals. Systolic blood pressure decreased and LV end-diastolic and systolic volume increased with HF. Failing SHR hearts also demonstrated increases in left and right ventricular mass relative to non-failing SHRs. LV papillary muscle force development and shortening velocity decreased, β-adrenergic responsiveness was depressed, myocardial stiffness and myocardial fibrosis increased with HF relative to non-failing animals. Initial micro-array analysis revealed that 1,431 transcripts were differentially expressed with HF compared to non-failing SHR (p<0.05). Of the identified transcripts, lipopolysaccharide binding protein, the most highly expressed transcript with HF, was negatively correlated to myocardial force while elevated expression of the collagen cross-linking enzyme lysyl oxidase correlated positively with muscle stiffness. Besides these individual transcripts, gene set enrichment analysis (GSEA) identified multiple enriched pathways with HF, most prominent of the altered signaling pathways involved TGF-β and insulin signaling. GESA analysis additionally identified altered gene sets involving inflammation, oxidative stress, cell degradation and cell death, among others (all p<0.01). In contrast to diastolic HF where few transcripts are reported to be altered, our data indicate multiple genes and pathways involved in a variety of biological processes characterize the onset of systolic HF, consistent with many functional and structural changes present in the failing hypertensive heart.

Project description:BackgroundQuantifying dose-dependent ultra-early edema and ultrastructural changes in the myocyte after drug delivery is important for the development of new mixed calcium channel blockers (CCBs).Materials and methodsArterial cannulation was used to measure mean arterial pressure in real time; simultaneously, magnetic resonance imaging proton density mapping was used to quantify edema 5-55 min after the delivery of L-type CCBs, T- and L-type CCBs, and solvent to a spontaneously hypertensive rat model. Transmission electron microscopy was used to show ultrastructural changes in the myocyte.ResultsAnalysis of variance showed significant differences among the three groups in mean arterial pressure reduction (F = 246.36, P = 5.75E-25), ultra-early level of edema (ULE) (F = 175.49, P = 5.62E-22), and dose-dependent level of edema (DLE) (F = 199.48, P = 4.28E-23). Compared with the solvent's mean arterial pressure reduction (2.65±6.56±1.64), ULE (1.16±0.09±0.02), and DLE (0.0010±0.0001±0.0000), post hoc tests showed that T- and L-type CCBs had better mean arterial pressure reduction (90.67±11.58±2.90, P = 1.06E-24 vs. 68.34±15.19±3.80, P = 1.76E-12), lower ULE (1.53±0.14±0.04, P = 4.74E-9 vs. 2.08±0.18±0.04, P = 2.68E-22), and lower DLE (0.0025±0.0004±0.0001, P = 1.14E-11 vs. 0.0047±0.0008±0.0002, P = 2.10E-11) than L- type CCBs. Transmission electron microscopy showed that T- and L-type CCBs caused fewer ultrastructural changes in the myocytes after drug delivery than L-type CCBs.ConclusionT- and L-type CCBs produced less ultra-early and dose-dependent edema, fewer ultrastructural changes in the myocyte, and a greater antihypertensive effect. Proton density mapping combined with arterial cannulation and transmission electron microscopy allowed for quantification of ultra-early and dose-dependent edema, antihypertensive efficacy, and ultrastructural changes in the myocyte. This is important for the evaluation of induced vasodilatory edema.

Dataset Information

Relaxin suppresses atrial fibrillation by reversing fibrosis and myocyte hypertrophy and increasing conduction velocity and sodium current in spontaneously hypertensive rat hearts.

Publications

Relaxin suppresses atrial fibrillation by reversing fibrosis and myocyte hypertrophy and increasing conduction velocity and sodium current in spontaneously hypertensive rat hearts.

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