Effects of a heat shock protein inducer on the atrial fibrillation substrate caused by acute atrial ischaemia

Aims Heat shock proteins (HSPs) are a set of endogenous cytoprotective factors activated by various pathological conditions. This study addressed the effects of geranylgeranylacetone (GGA), an orally active HSP inducer, on the atrial fibrillation (AF) substrate associated with acute atria( ischaemia (AI). Methods and results Four groups of mongrel dogs were studied: (1) a group subjected to AI without GGA (AI-CTL, n = 13 dogs); (2) dogs that underwent AI after GGA pretreatment (120 mg/kg/day; AI-GGA, n 12); (3) dogs receiving GGA pretreatment without AI in = 5); (4) control dogs for tissue sampling (n = 5). Isolated right Al was produced by occluding a right atrial (RA) coronary-artery branch. AI reduced ischaemic-zone conduction velocity (CV, from 94 +/- 3 to 46 +/- 5 cm/s; P <0.01) and increased maximum local phase delays (1395, from 1.6 +/- 0.1 to 4.6 +/- 0.6 ms/mm; P <0.01), conduction heterogeneity index (CHI, from 0.7 +/- 0.1 to 2.9 +/- 0.5; P <0.01), and the mean duration of burst pacing-induced AF (DAF, from 44 +/- 18 to 890 +/- 323 s; P <0.01) in AI-CTL dogs. GGA pretreatment attenuated ischaemia-induced conduction abnormalities (CV, 77 +/- 8 cm/s; P95, 2.1 +/- 0.4 ms/mm; CHI, 1.1 +/- 0.2; all P <0.01 vs. AI-CTL) and DAF (328 +/- 249 s; P <0.01) in AI-GGA dogs. GGA treatment alone, without ischaemia, did not alter DAF or conduction indices. Al slightly prolonged atrial refractory period, an effect also prevented by GGA. GGA significantly increased HSP70 protein expression in RA tissues of ischaemic hearts. Conclusions GGA prevents ischaemia-induced atrial conduction abnormalities and suppresses ischaemia-related AF These results suggest that HSP induction might be a useful new anti-AF intervention for patients with coronary artery disease

Effects of simvastatin on the development of the atrial fibrillation substrate in dogs with congestive heart failure

Background: Congestive heart failure (CHF) is a common cause of atrial fibrillation (AF). Oxidative stress and inflammation (profibrotic) and peroxisome proliferator-activated receptor-alpha (PPAR-alpha, antifibrotic) factors may be involved in CHF-related remodeling. We evaluated the effects of simvastatin (antioxidant, anti-inflammatory) and fenofibrate (PPAR-alpha activator) on CHF-related atrial remodeling. Methods and results: Dogs were subjected to 2-week ventricular tachypacing (VTP) in the absence and presence of simvastatin (20 or 80 mg/day) or fenofibrate. Induced AF duration (DAF) was increased by VTP from 36 +/- 14 (non-paced controls) to 1005 +/- 257 s (p Conclusions: CHF-induced atrial structural remodeling and AF promotion are attenuated by simvastatin, but not fenofibrate. Statin-induced inhibition of profibrotic atrial fibroblast responses and attenuation of left-ventricular dysfunction may contribute to preventing the CHF-induced fibrotic AF substrate. (c) 2007 European Society of Cardiology. Published by Elsevier B.V. All rights reserved

Heat shock proteins as molecular targets for intervention in atrial fibrillation

Atrial fibrillation (AF) is the most common sustained clinical tachyarrhythmia. AF is a progressive condition as demonstrated by the finding that maintenance of normal rhythm and contractile function becomes more difficult the longer AF exists. AF causes cellular stress, which induces atrial. remodelling, involving reduction in the expression of L-type Ca2+ channels and structural changes (myolysis), finally resulting in contractile dysfunction. Heat shock proteins (HSPs) comprise a family of proteins involved in the protection against different forms of cellular stress. Their classical function is the prevention of toxic protein aggregation by binding to (partially) unfolded proteins. Recent investigations reveal that HSPs prevent atrial. remodelling and attenuate the promotion of AF in both cellular and animal experimental models. Furthermore, studies in humans suggest a protective role for HSPs against progression from paroxysmal AF to chronic, persistent AF. Therefore, manipulation of the HSP system may offer novel therapeutic approaches for the prevention of atrial remodelling. Such approaches may contribute to the maintenance or restoration of tissue integrity and contractile function. Ultimately, this concept may offer an additional treatment strategy to delay progression towards chronic AF and/or improve the outcome of cardioversion

Contrasting gene expression profiles in two canine models of atrial fibrillation.

International audienceGene-expression changes in atrial fibrillation patients reflect both underlying heart-disease substrates and changes because of atrial fibrillation-induced atrial-tachycardia remodeling. These are difficult to separate in clinical investigations. This study assessed time-dependent mRNA expression-changes in canine models of atrial-tachycardia remodeling and congestive heart failure. Five experimental groups (5 dogs/group) were submitted to atrial (ATP, 400 bpm x 24 hours, 1 or 6 weeks) or ventricular (VTP, 240 bpm x 24 hours or 2 weeks) tachypacing. The expression of approximately 21,700 transcripts was analyzed by microarray in isolated left-atrial cardiomyocytes and (for 18 genes) by real-time RT-PCR. Protein-expression changes were assessed by Western blot. In VTP, a large number of significant mRNA-expression changes occurred after both 24 hours (2209) and 2 weeks (2720). In ATP, fewer changes occurred at 24 hours (242) and fewer still (87) at 1 week, with no statistically-significant alterations at 6 weeks. Expression changes in VTP varied over time in complex ways. Extracellular matrix-related transcripts were strongly upregulated by VTP consistent with its pathophysiology, with 8 collagen-genes upregulated >10-fold, fibrillin-1 8-fold and MMP2 4.5-fold at 2 weeks (time of fibrosis) but unchanged at 24 hours. Other extracellular matrix genes (eg, fibronectin, lysine oxidase-like 2) increased at both time-points ( approximately 10, approximately 5-fold respectively). In ATP, mRNA-changes almost exclusively represented downregulation and were quantitatively smaller. This study shows that VTP-induced congestive heart failure and ATP produce qualitatively different temporally-evolving patterns of gene-expression change, and that specific transcriptomal responses associated with atrial fibrillation versus underlying heart disease substrates must be considered in assessing gene-expression changes in man