Impact of early pericardial fluid chymase activation after cardiac surgery.

Introduction: Chymase is a highly destructive serine protease rapidly neutralized in the circulation by protease inhibitors. Here we test whether pericardial fluid (PCF) chymase activation and other inflammatory biomarkers determine intensive care unit length of stay, and explore mechanisms of chymase delivery by extracellular vesicles to the heart.

Methods: PCF was collected from adult patients (17 on-pump; 13 off-pump) 4 h after cardiac surgery.

Mitochondrial haplotype modulates genome expression and mitochondrial structure/function in cardiomyocytes following volume overload.

Mitochondrial DNA (mtDNA) haplotype regulates mitochondrial structure/function and reactive oxygen species in aortocaval fistula (ACF) in mice. Here, we unravel the mitochondrial haplotype effects on cardiomyocyte mitochondrial ultrastructure and transcriptome response to ACF in vivo. Phenotypic responses and quantitative transmission electron microscopy (TEM) and RNA sequence at 3 days were determined after sham surgery or ACF in vivo in cardiomyocytes from wild-type (WT) C57BL/6J (C57:C57) and C3H/HeN (C3H:C3H) and mitochondrial nuclear exchange mice (C57:C3H or C3H:C57).

Interstitial Collagen Loss, Myocardial Remodeling, and Function in Primary Mitral Regurgitation.

Interstitial collagen loss and cardiomyocyte ultrastructural damage accounts for left ventricular (LV) sphericity and decrease in LV twist and circumferential strain. Normal LV diastolic function belies significantly abnormal left atrial (LA) function and early LV diastolic untwist rate. This underscores the complex interplay of LV and LA myocardial remodeling and function in the pathophysiology of primary mitral regurgitation.

Plasma Exosome Hemoglobin Released During Surgery Is Associated With Cardiac Injury in Animal Model.

Background: Patients with valvular heart disease require cardiopulmonary bypass and cardiac arrest. Here, we test the hypothesis that exosomal hemoglobin formed during cardiopulmonary bypass mediates acute cardiac injury in humans and in an animal model system.

Methods: Plasma exosomes were collected from arterial blood at baseline and 30 minutes after aortic cross-clamp release in 20 patients with primary mitral regurgitation and 7 with aortic stenosis.

Chronic cardiac structural damage, diastolic and systolic dysfunction following acute myocardial injury due to bromine exposure in rats.

Accidental bromine spills are common and its large industrial stores risk potential terrorist attacks. The mechanisms of bromine toxicity and effective therapeutic strategies are unknown. Our studies demonstrate that inhaled bromine causes deleterious cardiac manifestations.

Chymase uptake by cardiomyocytes results in myosin degradation in cardiac volume overload.

Background: Volume overload (VO) of isolated mitral regurgitation (MR) or aortocaval fistula (ACF) is associated with extracellular matrix degradation and cardiomyocyte myofibrillar and desmin breakdown. Left ventricular (LV) chymase activity is increased in VO and recent studies demonstrate chymase presence within cardiomyocytes. Here we test the hypothesis that chymase within the cardiomyocyte coincides with myosin and desmin breakdown in VO.

Bromine inhalation mimics ischemia-reperfusion cardiomyocyte injury and calpain activation in rats.

Halogens are widely used, highly toxic chemicals that pose a potential threat to humans because of their abundance. Halogens such as bromine (Br) cause severe pulmonary and systemic injuries; however, the mechanisms of their toxicity are largely unknown. Here, we demonstrated that Br and reactive brominated species produced in the lung and released in blood reach the heart and cause acute cardiac ultrastructural damage and dysfunction in rats.

Desmin loss and mitochondrial damage precede left ventricular systolic failure in volume overload heart failure.

Heart failure due to chronic volume overload (VO) in rats and humans is characterized by disorganization of the cardiomyocyte desmin/mitochondrial network. Here, we tested the hypothesis that desmin breakdown is an early and continuous process throughout VO. Male Sprague-Dawley rats had aortocaval fistula (ACF) or sham surgery and were examined 24 h and 4 and 12 wk later.

Disruption of desmin-mitochondrial architecture in patients with regurgitant mitral valves and preserved ventricular function.

Objective: Recent studies have demonstrated improved outcomes in patients receiving early surgery for degenerative mitral regurgitation (MR) rather than adhering to conventional guidelines for surgical intervention. However, studies providing a mechanistic basis for these findings are limited.

Methods: Left ventricular (LV) myocardium from 22 patients undergoing mitral valve repair for American Heart Association class I indications was evaluated for desmin, the voltage-dependent anion channel, α-B-crystallin, and α, β-unsaturated aldehyde 4-hydroxynonenal by fluorescence microscopy.

Increased fibroblast chymase production mediates procollagen autophagic digestion in volume overload.

Background: Previous work has identified mast cells as the major source of chymase largely associated with a profibrotic phenotype. We recently reported increased fibroblast autophagic procollagen degradation in a rat model of pure volume overload (VO). Here we demonstrate a connection between increased fibroblast chymase production and autophagic digestion of procollagen in the pure VO of aortocaval fistula (ACF) in the rat.

Volume overload induces autophagic degradation of procollagen in cardiac fibroblasts.

In a pure volume overloaded (VO) heart, interstitial collagen loss is degraded by matrix metalloproteinases (MMPs) that leads to left ventricular (LV) dilatation and heart failure. Cardiac fibroblasts are the primary source of extracellular matrix proteins that connect cardiomyocytes. The goal of this study was to determine how VO affects intracellular procollagen in cardiac fibroblasts.

Chymase mediates injury and mitochondrial damage in cardiomyocytes during acute ischemia/reperfusion in the dog.

Cardiac ischemia and reperfusion (I/R) injury occurs because the acute increase in oxidative/inflammatory stress during reperfusion culminates in the death of cardiomyocytes. Currently, there is no drug utilized clinically that attenuates I/R injury in patients. Previous studies have demonstrated degranulation of mast cell contents into the interstitium after I/R.

Whole-genome profiling highlights the molecular complexity underlying eccentric cardiac hypertrophy.

Objectives: Heart failure is typically preceded by myocardial hypertrophy and remodeling, which can be concentric due to pressure overload (PO), or eccentric because of volume overload (VO). The molecular mechanisms that underlie these differing patterns of hypertrophy are distinct and have yet to be fully elucidated. Thus, the goal of this work is to identify novel therapeutic targets for cardiovascular conditions marked by hypertrophy that have previously been resistant to medical treatment, such as a pure VO.

Increased sarcolipin expression and adrenergic drive in humans with preserved left ventricular ejection fraction and chronic isolated mitral regurgitation.

Background: There is currently no therapy proven to attenuate left ventricular (LV) dilatation and dysfunction in volume overload induced by isolated mitral regurgitation (MR). To better understand molecular signatures underlying isolated MR, we performed LV gene expression analyses and overlaid regulated genes into ingenuity pathway analysis in patients with isolated MR.

Methods And Results: Gene arrays from LV tissue of 35 patients, taken at the time of surgical repair for isolated MR, were compared with 13 normal controls.

Cardiac kallikrein-kinin system is upregulated in chronic volume overload and mediates an inflammatory induced collagen loss.

Background: The clinical problem of a "pure volume overload" as in isolated mitral or aortic regurgitation currently has no documented medical therapy that attenuates collagen loss and the resultant left ventricular (LV) dilatation and failure. Here, we identify a potential mechanism related to upregulation of the kallikrein-kinin system in the volume overload of aortocaval fistula (ACF) in the rat.

Methodology/principal Findings: LV interstitial fluid (ISF) collection, hemodynamics, and echocardiography were performed in age-matched shams and 4 and 15 wk ACF rats.

Cardiac O-GlcNAcylation blunts autophagic signaling in the diabetic heart.

Aims: Increased O-linked attachment of β-N-acetylglucosamine (O-GlcNAc) to proteins has been implicated in the adverse effects of diabetes on the heart, although this has typically been based on models of severe hyperglycemia. Diabetes has also been associated with dysregulation of autophagy, a critical cell survival process; however, little is known regarding autophagy in the diabetic heart or whether this is influenced by O-GlcNAcylation or hemodynamic stress.

Main Methods: Young male rats were assigned to control (12% kcal fat/19% protein/69% carbohydrate), high fat diet (60/19/21%) and type 2 diabetic (high fat diet+low dose streptozotocin) groups for 8 weeks, followed by sham or pressure overload surgeries; animals were sacrificed 8 weeks after surgery.

Dynamic molecular and histopathological changes in the extracellular matrix and inflammation in the transition to heart failure in isolated volume overload.

Left ventricular (LV) volume overload (VO) causes eccentric remodeling with inflammatory cell infiltration and extracellular matrix (ECM) degradation, for which there is currently no proven therapy. To uncover new pathways that connect inflammation and ECM homeostasis with cellular dysfunction, we determined the cardiac transciptome in subacute, compensated, and decompensated stages based on in vivo hemodynamics and echocardiography in the rat with aortocaval fistula (ACF). LV dilatation at 5 wk was associated with a normal LV end-diastolic dimension-to-posterior wall thickness ratio (LVEDD/PWT; compensated), whereas the early 2-wk (subacute) and late 15-wk (decompensated) ACF groups had significant increases in LVEDD/PWT.

Loss of interstitial collagen causes structural and functional alterations of cardiomyocyte subsarcolemmal mitochondria in acute volume overload.

Volume overload (VO) caused by aortocaval fistula (ACF) is associated with oxidative/inflammatory stress. The resulting inflammation, matrix metalloproteinase (MMP) activation, and collagen degradation is thought to play a pivotal role in left ventricular (LV) dilatation and failure. Since mitochondria are also targets for inflammation and oxidative stress, we hypothesized that there would be bioenergetic dysfunction with acute VO.

Chymase inhibition prevents fibronectin and myofibrillar loss and improves cardiomyocyte function and LV torsion angle in dogs with isolated mitral regurgitation.

Background: The left ventricular (LV) dilatation of isolated mitral regurgitation (MR) is associated with an increase in chymase and a decrease in interstitial collagen and extracellular matrix. In addition to profibrotic effects, chymase has significant antifibrotic actions because it activates matrix metalloproteinases and kallikrein and degrades fibronectin. Thus, we hypothesize that chymase inhibitor (CI) will attenuate extracellular matrix loss and LV remodeling in MR.

Mast cell stabilization decreases cardiomyocyte and LV function in dogs with isolated mitral regurgitation.

Background: Mast cells are increased in isolated mitral regurgitation (MR) in the dog and may mediate extracellular matrix loss and left ventricular (LV) dilatation. We tested the hypothesis that mast cell stabilization would attenuate LV remodeling and improve function in the MR dog.

Methods And Results: MR was induced in adult dogs randomized to no treatment (MR, n = 5) or to the mast cell stabilizer, ketotifen (MR + MCS, n = 4) for 4 months.

Mast cell chymase limits the cardiac efficacy of Ang I-converting enzyme inhibitor therapy in rodents.

Ang I-converting enzyme (ACE) inhibitors are widely believed to suppress the deleterious cardiac effects of Ang II by inhibiting locally generated Ang II. However, the recent demonstration that chymase, an Ang II-forming enzyme stored in mast cell granules, is present in the heart has added uncertainty to this view. As discussed here, using microdialysis probes tethered to the heart of conscious mice, we have shown that chronic ACE inhibitor treatment did not suppress Ang II levels in the LV interstitial fluid (ISF) despite marked inhibition of ACE.

Increased oxidative stress and cardiomyocyte myofibrillar degeneration in patients with chronic isolated mitral regurgitation and ejection fraction >60%.

Objectives: This study assessed myocardial damage in patients with chronic isolated mitral regurgitation (MR) and left ventricular ejection fraction (LVEF) >60%.

Background: Typically, MR patients have decreased LVEF after mitral valve (MV) repair despite normal pre-operative LVEF.

Methods: Twenty-seven patients with isolated MR had left ventricular (LV) biopsies taken at time of MV repair.

Tumor necrosis factor-alpha produced in cardiomyocytes mediates a predominant myocardial inflammatory response to stretch in early volume overload.

Acute stretch caused by volume overload (VO) of aorto-caval fistula (ACF) induces a variety of myocardial responses including mast cell accumulation, matrix metalloproteinase (MMP) activation, and collagen degradation, all of which are critical in dictating long-term left ventricle (LV) outcome to VO. Meanwhile, these responses can be part of myocardial inflammation dictated by tumor necrosis factor-alpha (TNF-alpha), which is elevated after acute ACF. However, it is unknown whether TNF-alpha mediates a major myocardial inflammatory response to stretch in early VO.

Microarray identifies extensive downregulation of noncollagen extracellular matrix and profibrotic growth factor genes in chronic isolated mitral regurgitation in the dog.

Background: The volume overload of isolated mitral regurgitation (MR) in the dog results in left ventricular (LV) dilatation and interstitial collagen loss. To better understand the mechanism of collagen loss, we performed a gene array and overlaid regulated genes into ingenuity pathway analysis.

Methods And Results: Gene arrays from LV tissue were compared in 4 dogs before and 4 months after MR.