Begoña López

Myocardial Fibrosis as an Early Manifestation of Hypertrophic Cardiomyopathy

BACKGROUND Myocardial fibrosis is a hallmark of hypertrophic cardiomyopathy and a proposed substrate for arrhythmias and heart failure. In animal models, profibrotic genetic pathways are activated early, before hypertrophic remodeling. Data showing early profibrotic responses to sarcomere-gene mutations in patients with hypertrophic cardiomyopathy are lacking. METHODS We used echocardiography, cardiac magnetic resonance imaging (MRI), and serum biomarkers of collagen metabolism, hemodynamic stress, and myocardial injury to evaluate subjects with hypertrophic cardiomyopathy and a confirmed genotype. RESULTS The study involved 38 subjects with pathogenic sarcomere mutations and overt hypertrophic cardiomyopathy, 39 subjects with mutations but no left ventricular hypertrophy, and 30 controls who did not have mutations. Levels of serum C-terminal propeptide of type I procollagen (PICP) were significantly higher in mutation carriers without left ventricular hypertrophy and in subjects with overt hypertrophic cardiomyopathy than in controls (31% and 69% higher, respectively; P<0.001). The ratio of PICP to C-terminal telopeptide of type I collagen was increased only in subjects with overt hypertrophic cardiomyopathy, suggesting that collagen synthesis exceeds degradation. Cardiac MRI studies showed late gadolinium enhancement, indicating myocardial fibrosis, in 71% of subjects with overt hypertrophic cardiomyopathy but in none of the mutation carriers without left ventricular hypertrophy. CONCLUSIONS Elevated levels of serum PICP indicated increased myocardial collagen synthesis in sarcomere-mutation carriers without overt disease. This profibrotic state preceded the development of left ventricular hypertrophy or fibrosis visible on MRI. (Funded by the National Institutes of Health and others.)

Serum Carboxy-Terminal Propeptide of Procollagen Type I Is a Marker of Myocardial Fibrosis in Hypertensive Heart Disease

BACKGROUND This study was designed to investigate whether the serum concentration of the carboxy-terminal propeptide of procollagen type I (PIP), a marker of collagen type I synthesis, is related to myocardial fibrosis in hypertensive patients. METHODS AND RESULTS The study was performed in 26 patients with essential hypertension in which ischemic cardiomyopathy was excluded after a complete medical workup. Right septal endomyocardial biopsies were performed in hypertensive patients to quantify collagen content. Collagen volume fraction (CVF) was determined on picrosirius red-stained sections with an automated image analysis system. The serum concentration of PIP was measured by specific radioimmunoassay. Compared with normotensives, both serum PIP and CVF were increased (P<0.001) in hypertensives. A direct correlation was found between CVF and serum PIP (r=0.471, P<0.02) in all hypertensives. Histological analysis revealed the presence of 2 subgroups of patients: 8 with severe fibrosis and 18 with nonsevere fibrosis. Serum PIP was higher (P<0.05) in patients with severe fibrosis than in patients with nonsevere fibrosis. Using receiver operating characteristic curves, we observed that a cutoff of 127 microg/L for PIP provided 78% specificity and 75% sensitivity for predicting severe fibrosis with a relative risk of 4.80 (95% CI, 1.19 to 19.30). CONCLUSIONS These results show a strong correlation between myocardial collagen content and the serum concentration of PIP in essential hypertension. Although preliminary, these findings suggest that the determination of PIP may be an easy and reliable method for the screening and diagnosis of severe myocardial fibrosis associated with arterial hypertension.

Different effects of antihypertensive therapies based on losartan or atenolol on ultrasound and biochemical markers of myocardial fibrosis: results of a randomized trial.

Background—In hypertensive left ventricular hypertrophy (LVH), myocardial texture is altered by a disproportionate increase in fibrosis, but there is insufficient clinical evidence whether antihypertensive therapy or individual agents can induce regression of myocardial fibrosis. Methods and Results—We compared the effects of an angiotensin II receptor antagonist with a &bgr;-blocker on myocardial collagen volume (assessed by echoreflectivity and serum collagen markers) in 219 hypertensive patients with echocardiographically documented LVH. Patients were allocated randomly to receive losartan 50 to 100 mg/d (n=111) or atenolol 50 to 100 mg/d (n=99) with or without hydrochlorothiazide 12.5 to 25 mg/d for 36 weeks. Echoreflectivity analysis was conducted on ultrasound tracings of the midapex septum with specifically designed and validated software. A color histogram of reflecting echoes was obtained, and its spread (broadband [BB], previously shown to correlate directly with collagen volume fraction on endomyocardial biopsies) was used as the primary outcome measure. Mean color scale and serum markers of collagen synthesis (PIP, PIIIP) or degradation (CITP) were secondary outcome variables. Echoreflectivity analysis proved feasible in 106 patients (losartan 52, atenolol 54). Losartan reduced BB over 36 weeks (from 114.5 to 104.3 color levels, P<0.02), whereas atenolol treatment was associated with an increase in BB (from 109.0 to 113.6 color levels, P=NS), the difference between treatments being −12.8 color levels (95% CI −23.6 to −2.0, P=0.02). Secondary end points (mean color scale and collagen markers) also changed in the direction of decreased collagen in patients receiving losartan, but differences between groups were not statistically significant. Conclusions—In hypertensive patients with LVH, losartan decreases myocardial collagen content, whereas atenolol does not. The difference between the 2 treatments is statistically significant.

Role of lysyl oxidase in myocardial fibrosis: from basic science to clinical aspects.

Because of its dynamic nature, the composition and structure of the myocardial collagen network can be reversibly modified to adapt to transient cardiac injuries. In response to persistent injury, however, irreversible, maladaptive changes of the network occur leading to fibrosis, mostly characterized by the excessive interstitial and perivascular deposition of collagen types I and III fibers. It is now becoming apparent that myocardial fibrosis directly contributes to adverse myocardial remodeling and the resulting alterations of left ventricular (LV) anatomy and function present in the major types of cardiac diseases. The enzyme lysyl oxidase (LOX) is a copper-dependent extracellular enzyme that catalyzes lysine-derived cross-links in collagen and elastin. LOX-mediated cross-linking of collagen types I and III fibrils leads to the formation of stiff collagen types I and III fibers and their subsequent tissue deposition. Evidence from experimental and clinical studies shows that the excess of LOX is associated with an increased collagen cross-linking and stiffness. It is thus conceivable that LOX upregulation and/or overactivity could underlie myocardial fibrosis and altered LV mechanics and contribute to the compromise of LV function in cardiac diseases. This review will consider the molecular aspects related to the regulation and actions of LOX, namely, in the context of collagen synthesis. In addition, it will address the information related to the role of myocardial LOX in heart failure and the potential benefits of controlling its expression and function.

Mechanisms of disease: pathologic structural remodeling is more than adaptive hypertrophy in hypertensive heart disease.

Changes in the composition of cardiac tissue develop in arterial hypertension and lead to structural remodeling of the myocardium. Structural remodeling is the consequence of a number of pathologic processes, mediated by mechanical, neurohormonal and cytokine routes, occurring in the cardiomyocyte and the noncardiomyocyte compartments of the heart. One of these processes is related to the disruption of the equilibrium between the synthesis and degradation of collagen type I and III molecules, which results in an excessive accumulation of collagen type I and III fibers in the interstitium and the perivascular regions of the myocardium. The clinical relevance of ventricular fibrosis is that it might contribute to the increased cardiac risk of patients with hypertensive heart disease. This review focuses on the mechanisms of hypertensive ventricular fibrosis and its clinical consequences. In addition, we discuss the noninvasive methods for the diagnosis of cardiac fibrosis and the therapeutic strategies aimed to promote its reduction.

Clinical aspects of hypertensive myocardial fibrosis

Myocardial fibrosis is one of the histologic constituents of myocardial remodeling present in hypertensive patients with hypertensive heart disease. In fact, an exaggerated interstitial and perivascular accumulation of fibrillar collagens type I and type III has been found in the myocardium of patients with arterial hypertension and left ventricular hypertrophy. Hypertensive myocardial fibrosis has been shown to facilitate abnormalities of cardiac function, coronary reserve, and electrical activity that adversely affect the clinical outcome of hypertensive patients. Therefore, development of noninvasive tools for the monitoring of myocardial fibrosis and pharmacological strategies aimed to promote the regression of fibrosis could be of particular relevance in the clinical treatment of patients with hypertensive heart disease.

T1 measurements identify extracellular volume expansion in hypertrophic cardiomyopathy sarcomere mutation carriers with and without left ventricular hypertrophy.

Background— Myocardial fibrosis is a hallmark of hypertrophic cardiomyopathy (HCM) and a potential substrate for arrhythmias and heart failure. Sarcomere mutations seem to induce profibrotic changes before left ventricular hypertrophy (LVH) develops. To further evaluate these processes, we used cardiac magnetic resonance with T1 measurements on a genotyped HCM population to quantify myocardial extracellular volume (ECV). Methods and Results— Sarcomere mutation carriers with LVH (G+/LVH+, n=37) and without LVH (G+/LVH−, n=29), patients with HCM without mutations (sarcomere-negative HCM, n=11), and healthy controls (n=11) underwent contrast cardiac magnetic resonance, measuring T1 times pre- and postgadolinium infusion. Concurrent echocardiography and serum biomarkers of collagen synthesis, hemodynamic stress, and myocardial injury were also available in a subset. Compared with controls, ECV was increased in patients with overt HCM, as well as G+/LVH− mutation carriers (ECV=0.36±0.01, 0.33±0.01, 0.27±0.01 in G+/LVH+, G+/LVH−, controls, respectively; P⩽0.001 for all comparisons). ECV correlated with N-terminal probrain natriuretic peptide levels (r=0.58; P<0.001) and global E’ velocity (r=−0.48; P<0.001). Late gadolinium enhancement was present in >60% of overt patients with HCM but absent from G+/LVH− subjects. Both ECV and late gadolinium enhancement were more extensive in sarcomeric HCM than sarcomere-negative HCM. Conclusions— Myocardial ECV is increased in HCM sarcomere mutation carriers even in the absence of LVH. These data provide additional support that fibrotic remodeling is triggered early in disease pathogenesis. Quantifying ECV may help characterize the development of myocardial fibrosis in HCM and ultimately assist in developing novel disease-modifying therapy, targeting interstitial fibrosis.

Myocardial Titin Hypophosphorylation Importantly Contributes to Heart Failure With Preserved Ejection Fraction in a Rat Metabolic Risk Model

Background—Obesity and diabetes mellitus are important metabolic risk factors and frequent comorbidities in heart failure with preserved ejection fraction. They contribute to myocardial diastolic dysfunction (DD) through collagen deposition or titin modification. The relative importance for myocardial DD of collagen deposition and titin modification was investigated in obese, diabetic ZSF1 rats after heart failure with preserved ejection fraction development at 20 weeks. Methods and Results—Four groups of rats (Wistar-Kyoto, n=11; lean ZSF1, n=11; obese ZSF1, n=11, and obese ZSF1 with high-fat diet, n=11) were followed up for 20 weeks with repeat metabolic, renal, and echocardiographic evaluations and hemodynamically assessed at euthanization. Myocardial collagen, collagen cross-linking, titin isoforms, and phosphorylation were also determined. Resting tension (Fpassive)–sarcomere length relations were obtained in small muscle strips before and after KCl–KI treatment, which unanchors titin and allows contributions of titin and extracellular matrix to Fpassive to be discerned. At 20 weeks, the lean ZSF1 group was hypertensive, whereas both obese ZSF1 groups were hypertensive and diabetic. Only the obese ZSF1 groups had developed heart failure with preserved ejection fraction, which was evident from increased lung weight, preserved left ventricular ejection fraction, and left ventricular DD. The underlying myocardial DD was obvious from high muscle strip stiffness, which was largely (±80%) attributable to titin hypophosphorylation. The latter occurred specifically at the S3991 site of the elastic N2Bus segment and at the S12884 site of the PEVK segment. Conclusions—Obese ZSF1 rats developed heart failure with preserved ejection fraction during a 20-week time span. Titin hypophosphorylation importantly contributed to the underlying myocardial DD.

New Targets to Treat the Structural Remodeling of the Myocardium

Classical therapy of heart failure is based on treatment of its pre-disposing/triggering factors and of the neurohumoral activation secondary to the deterioration of cardiac function. A new view is emerging that proposes the direct intervention on the pathological structural remodeling of the myocardium as part of heart failure therapy. In fact, in conditions of chronic injury, the cardiomyocytic and the noncardiomyocytic components of the myocardium undergo a series of structural lesions (i.e., cardiomyocyte growth and death, inflammation, alterations of collagen matrix, and microvascular rarefaction) that are governed by a complex interplay of mechanisms. Our increasing knowledge of the role of these mechanisms in remodeling enables us not only to better understand how our more successful therapies work but also to explore novel therapies for the future. In this paper, we will examine recent insights from experimental and pilot clinical studies that have provided new targets for interventions to prevent or reverse inflammation, alterations of collagen matrix, and cardiomyocyte death.

Cardiomyocyte apoptosis in hypertensive cardiomyopathy

It is widely accepted that there are two principal forms of cell death; namely, necrosis and apoptosis. According to the classical view, necrosis is the major mechanism of cardiomyocyte death in cardiac diseases. However, in the past few years observations have been made showing that cardiomyocyte apoptosis occurs in diverse conditions and that apoptosis may be a contributing cause of the loss and functional abnormalities of cardiomyocytes with important pathophysiological consequences. In this regard, although a number of formal proofs are pending, it is conceivable that cardiomyocyte apoptosis may be an important variable in the clinical evolution of hypertensive cardiomyopathy. This review summarizes recent evidence demonstrating that cardiomyocyte apoptosis is abnormally stimulated in the heart of animals and humans with arterial hypertension. In addition, the potential mechanisms of cardiomyocyte apoptosis in hypertension and its detrimental impact on cardiac function will be addressed. Finally, the perspectives of strategies aimed to detect and modulate apoptosis of cardiomyocytes in hypertensive cardiomyopathy will be considered.