Decreased passive stiffness of cardiac myocytes and cardiac tissue from copper-deficient rat hearts

Copper Preserves Vasculature Structure and Function by Protecting Endothelial Cells from Apoptosis in Ischemic Myocardium

The present study was undertaken to investigate whether Cu protects vasculatures from ischemic injury in the heart. C57/B6 mice were introduced to myocardial ischemia (MI) by permanent ligation of the left anterior descending (LAD) coronary artery. Two hours post-LAD ligation, mice were intravenously injected with a Cu-albumin (Cu-alb) solution, or saline as control. At 1, 4, or 7 days post-MI, hearts were collected for further analysis. A dramatic decrease in CD31-positive endothelial cells concomitantly with abundant apoptosis, along with obstruction of blood flow, was observed in ischemic myocardium 1 day post-MI. The early Cu-alb treatment protected CD31-positive cells from apoptosis, along with a preservation of micro-vessels and a decrease in infarct size. This early vasculature preservation ensured myocardial blood perfusion and protected cardiac contractile function until 28 days post-MI. This strategy of Cu-alb treatment immediately following MI would help develop a therapeutic approach for acute heart attack patients in a clinical setting.

Stem cell therapy restores viscoelastic properties of myocardium in rat model of hypertension

Extensive remodeling of the myocardium is seen in a variety of cardiovascular diseases, including systemic hypertension. Stem cell therapy has been proposed to improve the clinical outcomes of hypertension, and we hypothesized that changes in mechanical properties of the myocardium would accompany the progression of disease and the results of treatment conditions. Using spontaneously hypertensive rats (SHR) as a model of hypertension, we treated 13-week-old hypertensive rats with a single injection of adipose-derived stem cells (ADSC) isolated from a normotensive control. We indented the isolated ventricles of control, untreated sham-injected SHR, and ADSC-treated SHR hearts with a custom cantilever-based system and fit the resulting data to a standard linear solid model. SHR animals had higher blood pressure (198.4±25.9mmHg) and lower ejection fraction (69.9±4.2%) than age-matched control animals (109.0±1.6mmHg, 88.2±1.3%), and increased viscoelastic properties accompanied these clinical changes (right ventricle effective stiffness, SHR: 21.97±5.10kPa, Control: 13.14±3.48kPa). ADSC-treated animals saw improvement in clinical parameters compared to the untreated SHR group, which was also accompanied by a significant restoration of viscoelastic properties of the myocardium (ACSD-treated SHR: 9.77±6.96kPa).

Cardioprotective effects of lysyl oxidase inhibition against volume overload-induced extracellular matrix remodeling

A hallmark of heart failure (HF) is adverse extracellular matrix (ECM) remodeling, which is regulated by the collagen cross-linking enzyme, lysyl oxidase (LOX). In this study, we evaluate the efficacy of LOX inhibition to prevent adverse left ventricular (LV) remodeling and dysfunction using an experimental model of HF. Sprague-Dawley rats were subjected to surgically induced volume overload (VO) by creation of aortocaval fistula (ACF). A LOX inhibitor, beta-aminopropionitrile (BAPN; 100 mg/kg/day), was administered to rats with ACF or sham surgery at eight weeks postsurgery. Echocardiography was used to assess progressive alterations in cardiac ventricular structure and function. Left ventricular (LV) catheterization was used to assess alterations in contractility, stiffness, LV pressure and volume, and other indices of cardiac function. The LV ECM alterations were assessed by: (a) histological staining of collagen, (b) protein expression of collagen types I and III, (c) hydroxyproline assay, and (d) cross-linking assay. LOX inhibition attenuated VO-induced increases in cardiac stress, and attenuated increases in interstitial myocardial collagen, total collagen, and protein levels of collagens I and III. Both echocardiography and catheterization measurements indicated improved cardiac function post-VO in BAPN treated rats vs. untreated. Inhibition of LOX attenuated VO-induced decreases in LV stiffness and cardiac function. Overall, our data indicate that LOX inhibition was cardioprotective in the volume overloaded heart.

Mathematically engineered stromal cell-derived factor-1α stem cell cytokine analog enhances mechanical properties of infarcted myocardium

OBJECTIVE

The biomechanical response to a myocardial infarction consists of ventricular remodeling that leads to dilatation, loss of contractile function, abnormal stress patterns, and ultimately heart failure. We hypothesized that intramyocardial injection of our previously designed pro-angiogenic chemokine, an engineered stromal cell-derived factor-1α analog (ESA), improves mechanical properties of the heart after infarction.

METHODS

Male rats (n = 54) underwent either sham surgery (n = 17) with no coronary artery ligation or ligation of the left anterior descending artery (n = 37). The rats in the myocardial infarction group were then randomized to receive either saline (0.1 mL, n = 18) or ESA (6 μg/kg, n = 19) injected into the myocardium at 4 predetermined spots around the border zone. Echocardiograms were performed preoperatively and before the terminal surgery. After 4 weeks, the hearts were explanted and longitudinally sectioned. Uniaxial tensile testing was completed using an Instron 5543 Microtester. Optical strain was evaluated using custom image acquisition software, Digi-Velpo, and analyzed in MATLAB.

RESULTS

Compared with the saline control group at 4 weeks, the ESA-injected hearts had a greater ejection fraction (71.8% ± 9.0% vs 55.3% ± 12.6%, P = .0004), smaller end-diastolic left ventricular internal dimension (0.686 ± 0.110 cm vs 0.763 ± 0.160 cm, P = .04), greater cardiac output (36 ± 11.6 mL/min vs 26.9 ± 7.3 mL/min, P = .05), and a lower tensile modulus (251 ± 56 kPa vs 301 ± 81 kPa, P = .04). The tensile modulus for the sham group was 195 ± 56 kPa, indicating ESA injection results in a less stiff ventricle.

CONCLUSIONS

Direct injection of ESA alters the biomechanical response to myocardial infarction, improving the mechanical properties in the postinfarct heart.

Viscoelastic characteristics of contracted collagen gels populated with rat fibroblasts or cardiomyocytes

The viscoelastic characteristics of contracted collagen gels populated with rat fibroblasts or cardiomyocytes were investigated by uniaxial tensile testing. Rat type I collagen-Dulbecco's modified Eagle's medium solution (each 2 ml in volume, 0.5 mg/ml collagen concentration) containing 2.0 million rat fibroblasts or cardiomyocytes were cast in a circular shape. After gelation and culture for 10 days the contracted gels were first stretched to a tensile strain of approximately 0.20 at 4.6 × 10(-3)/s strain rate, and then the strain was kept unchanged for 3 min. The tensile stress in the gels was recorded. The results were regressed against the equations of the Kelvin viscoelastic model. It was found that the two elastic coefficients in the model were 6.5 ± 1.7 and 10.2 ± 3.2 kPa, respectively, for gels with cardiomyocytes and 5.1 ± 1.6 and 4.5 ± 0.9 kPa for those with fibroblasts; the values for gels with cardiomyocytes were significantly higher than those for gels with fibroblasts. The viscous coefficient was 169.6 ± 60.7 kPa s for the cardiomyocytes and 143.6 ± 44.7 kPa s for the fibroblasts. The relaxation time constant for gels with cardiomyocytes was 19.6 ± 10.6 s, significantly smaller than for gels with fibroblasts (36.4 ± 13.3 s). This study is the first to obtain viscoelastic data for living cell-contracted collagen gels. These data show that the viscous effect has a vital effect on the mechanical behavior of the gels and cannot be neglected in the culture and function of artificial substitutes based on contracted collagen gels. Furthermore, the data may imply that viscous coefficient of the gels might be closely related to collagen density rather than to cross linking among collagen fibrils.

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.

Copper, oxidative stress, and human health

Copper (Cu), a redox active metal, is an essential nutrient for all species studied to date. During the past decade, there has been increasing interest in the concept that marginal deficits of this element can contribute to the development and progression of a number of disease states including cardiovascular disease and diabetes. Deficits of this nutrient during pregnancy can result in gross structural malformations in the conceptus, and persistent neurological and immunological abnormalities in the offspring. Excessive amounts of Cu in the body can also pose a risk. Acute Cu toxicity can result in a number of pathologies, and in severe cases, death. Chronic Cu toxicity can result in liver disease and severe neurological defects. The concept that elevated ceruloplasmin is a risk factor for certain diseases is discussed. In this paper, we will review recent literature on the potential causes of Cu deficiency and Cu toxicity, and the pathological consequences associated with the above. Finally, we will review some of the potential biochemical lesions that might underlie these pathologies. Given that oxidative stress is a characteristic of Cu deficiency, the role of Cu in the oxidative defense system will receive special attention. The concept that excess Cu may be a precipitating factor in Alzheimer's disease is discussed.

Binding of copper(II) ions to the polyproline II helices of PEVK modules of the giant elastic protein titin as revealed by ESI-MS, CD, and NMR

Titin, a family of giant elastic proteins, constitutes an elastic sarcomere matrix in striated muscle. In the I-band region of the sarcomere, the titin PEVK segment acts as a molecular spring to generate elasticity as well as sites of adhesion with parallel thin filaments. Previously, we reported that PEVK consists of tandem repeats of 28 residue modules and that the "polyproline II-coil" motif is the fundamental conformational motif of the PEVK module. In order to characterize the factors that may affect and alter the PPII-coil conformational motifs, we have initiated a systematic study of the interaction with divalent cations (Cu2+, Ca2+, Zn2+, and Ni2+) and a conformational profile of PEVK peptides (a representative 28-mer peptide PR: PEPPKEVVPEKKAPVAPPKKPEVPPVKV and its subfragments PR1: kvPEPPKEVVPE, PR2: VPEKKAPVAPPK, PR3: KPEVPPVKV). UV-Vis absorption difference spectra and CD spectra showed that Cu2+ bound to PR1 with high affinity (20 microM), while its binding to PR2 and PR3 as well as the binding of other cations to all four peptides were of lower affinity (>100 microM). Conformational studies by CD revealed that Cu2+ binding to PR1 resulted in a polyproline II to turn transition up to a 1:2 PR1/Cu2+ ratio and a coil to turn transition at higher Cu2+ concentration. ESI-MS provided the stoichiometry of PEVK peptide-Cu2+ complexes at both low and high ion strength, confirming the specific high affinity binding of Cu2+ to PR1 and PR. Furthermore, NMR and ESI-MS/MS fragmentation analysis elucidated the binding sites of the PEVK peptide-Cu2+ complexes at (-2)KVPE2, 8VPE10, 13APV15, and 22EVP24. A potential application of Cu2+ binding in peptide sequencing by mass spectrometry was also revealed. We conclude that Cu2+ binds and bends PEVK peptides to a beta-turn-like structure at specific sites. The specific targeting of Cu2+ towards PPII is likely to be of significant value in elucidating the roles of PPII in titin elasticity as well as in interactions of proline-rich proteins.

Congestive heart failure in copper-deficient mice

Copper Deficiency (CuD) leads to hypertrophic cardiomyopathy in various experimental models. The morphological, electrophysiological, and molecular aspects of this hypertrophy have been under investigation for a long time. However the transition from compensated hypertrophy to decompensated heart failure has not been investigated in the study of CuD. We set out to investigate the contractile and hemodynamic parameters of the CuD mouse heart and to determine whether heart failure follows hypertrophy in the CuD heart. Dams of FVB mice were fed CuD or copper-adequate (CuA) diet starting from the third day post delivery and the weanling pups were fed the same diet for a total period of 5 weeks (pre- and postweanling). At week 4, the functional parameters of the heart were analyzed using a surgical technique for catheterizing the left ventricle. A significant decrease in left ventricle systolic pressure was observed with no significant change in heart rate, and more importantly contractility as measured by the maximal rate of left ventricular pressure rise (+dP/dt) and decline (-dP/dt) were significantly depressed in the CuD mice. However, left ventricle end diastolic pressure was elevated, and relaxation was impaired in the CuD animals; the duration of relaxation was prolonged. In addition to significant changes in the basal level of cardiac function, CuD hearts had a blunted response to the stimulation of the beta-adrenergic agonist isoproterenol. Furthermore, morphological analysis revealed increased collagen accumulation in the CuD hearts along with lipid deposition. This study shows that CuD leads to systolic and diastolic dysfunction in association with histopathological changes, which are indices commonly used to diagnose congestive heart failure.

Multitrack system for superfusing isolated cardiac myocytes

A new system for studying mechanical activity of freshly isolated cardiac myocytes from up to four experimental groups simultaneously is described. Suspensions of cardiac myocytes isolated from adult rat hearts were drawn into microhematocrit capillary tubes, which were then mounted in parallel fashion between two four-channel tubing manifolds placed on the movable stage of an inverted microscope. Within a few minutes, cells settled and attached to the bottom of the tubes and then could be superfused with various test solutions. The system allowed for electrical field stimulation, rapid changes in bathing solutions, control of temperature, and simulation of ischemia and reperfusion with measurements of the effects of such interventions on both populations of cells (low power survey) and individual myocytes (high power). Myocyte responses to these various interventions are described. The primary advantage of this system is the ability to conduct experiments on cardiac myocytes isolated concurrently from multiple experimental groups at the same time and under identical conditions.

Viscoelastic properties of pressure overload hypertrophied myocardium: effect of serine protease treatment

To determine whether and to what extent one component of the extracellular matrix, fibrillar collagen, contributes causally to abnormalities in viscoelasticity, collagen was acutely degraded by activation of endogenous matrix metalloproteinases (MMPs) with the serine protease plasmin. Papillary muscles were isolated from normal cats and cats with right ventricular pressure overload hypertrophy (POH) induced by pulmonary artery banding. Plasmin treatment caused MMP activation, collagen degradation, decreased the elastic stiffness constant, and decreased the viscosity constant in both normal and POH muscles. Thus, whereas many mechanisms may contribute to the abnormalities in myocardial viscoelasticity in the POH myocardium, changes in fibrillar collagen appear to play a predominant role.

Isolated ventricular myocytes from copper-deficient rat hearts exhibit enhanced contractile function

Dietary copper deficiency leads to cardiac hypertrophy, cardiac fibrosis, derangement of myofibrils, and impaired cardiac contractile and electrophysiological function. The purpose of this study was to determine whether impaired cardiac function from copper deficiency is due to depressed contractile function at the single myocyte level. Male Sprague-Dawley rats were fed diets that were either copper adequate (5.59-6.05 microg copper/g body wt; n = 11) or copper deficient (0.29-0.34 microg copper/g body wt; n = 11) for 5 wk. Ventricular myocytes were dispersed and mechanical properties were evaluated using the SoftEdge video-based edge-detection system. Intracellular Ca2+ transients were examined using fura 2-acetoxymethyl ester. Myocytes were electrically stimulated to contract at 0.5 Hz. Properties evaluated included peak shortening (PS), time to peak shortening (TPS), time to 90% relengthening (TR90), and maximal velocities of shortening and relengthening (+/-dL/dt). Myocytes from the copper-deficient rat hearts exhibited significantly enhanced PS values associated with shortened TR90 measurements compared with those from copper-adequate rat hearts. The +/-dL/dt values were enhanced and the intracellular Ca2+ transient decay rate was depressed in myocytes from copper-deficient rats. These data indicate that impaired cardiac contractile function that is seen in copper-deficient whole hearts might not be due to depressed cardiac contractile function at the single cell level but rather to other mechanisms such as cardiac fibrosis.