Aron T. Goldberg

A Matrix Metalloproteinase Induction/Activation System Exists in the Human Left Ventricular Myocardium and Is Upregulated in Heart Failure

BackgroundMatrix metalloproteinases (MMPs) contribute to matrix remodeling in disease states such as tumor metastases. Extracellular matrix metalloproteinase inducer (EMMPRIN) has been reported to increase MMP expression, and membrane-type MMP or MT1-MMP has been implicated to activate MMPs. The present study examined whether and to what degree EMMPRIN and MT1-MMP were expressed in human left ventricular (LV) myocardium as well as the association with MMP activity and expression in dilated cardiomyopathy (DCM). Methods and ResultsLV myocardial zymographic MMP activity increased by >2-fold with both nonischemic DCM (n=21) and ischemic DCM (n=16) compared with normal (n=13). LV myocardial abundance of MMP-9 was increased with both forms of DCM. MMP-2 and MMP-3 were increased with nonischemic DCM. MMP-1 levels were decreased with both forms of DCM. EMMPRIN increased by >250% and MT1-MMP increased by >1000% with both forms of DCM. ConclusionsIncreased LV myocardial MMP activity and selective upregulation of MMPs with nonischemic and ischemic forms of DCM occurred. Moreover, a local MMP induction/activation system was identified in isolated normal human LV myocytes that was upregulated with DCM. The control of MMP activation and expression in the failing human LV myocardium represents a new and potentially significant therapeutic target for this disease process.

Endothelin receptor pathway in human left ventricular myocytes: relation to contractility

BACKGROUND Increased synthesis and release of the potent bioactive peptide endothelin-1 (ET-1) occurs during and after cardiac surgery. However, the cellular and molecular basis for the effects of ET-1 on human left ventricular (LV) myocyte contractility remains unknown. METHODS LV myocyte contractility was examined from myocardial biopsies taken from patients (n = 30) undergoing elective coronary artery bypass. LV myocytes (n = 997, > 30/patient) were isolated using microtrituration and contractility examined by videomicroscopy at baseline and after ET-1 exposure (200 pmol/L). In additional studies, myocytes were pretreated to inhibit either protein kinase C (PKC) (chelerythrine, 1 micromol/L), the sodium/hydrogen (Na/H) exchanger (EIPA, 1 micromol/L), both PKC and the Na/H exchanger, or the ET(A) receptor (BQ-123, 1 micromol/L), followed with ET-1 exposure. RESULTS Basal myocyte shortening increased 37.8 +/- 6.3% with ET-1 (p < 0.05). Na/H exchanger, PKC, and dual inhibition all eliminated the effects of ET-1. Furthermore, ET(A) inhibition demonstrated that ET-1 effects on myocyte contractility were mediated through the ET(A) receptor subtype. CONCLUSIONS ET-1 directly influences human LV myocyte contractility, which is mediated through the ET(A) receptor and requires intracellular activation of PKC and stimulation of the Na/H exchanger.

Effects of adenosine receptor subtype A1 on ventricular and renal function.

The adenosine subtype 1 (A 1 ) receptor, which may influence cardiac function and modulate renal function, may have particular relevance in congestive heart failure (CHF). However, the effects of A 1 receptor inhibition in the setting of CHF are poorly defined. Systemic hemodynamics and indices of renal function were measured in pigs with pacing-induced CHF at 240 bpm for 3 weeks (n = 10) before and after A 1 receptor blockade with 100 &mgr;g of BG9719 (1,3-dipropyl-8-[2-(5,6-epoxynorbornyl)]xanthene) or in CHF pigs after infusion of vehicle only (n = 10). Heart rate, mean aortic pressure, and left ventricular peak pressure increased following A 1 blockade in the CHF group, consistent with an adenosine inhibitory effect. However, cardiac output and global measures of vascular resistance did not significantly change following A 1 blockade. Urine output increased twofold and sodium clearance increased threefold following A 1 blockade (p < 0.05). Creatinine clearance increased following A 1 blockade (127 ± 17 vs. 62 ± 7 ml/min, p < 0.05). Selective A 1 receptor blockade improved glomerular filtration rate and induced a natriuresis and diuresis in a model of CHF without adverse effects on cardiac function. These unique results suggest that renal A 1 receptor activation may contribute to the reduced renal function associated with CHF.

Myocardial Bradykinin Following Acute Angiotensin-Converting Enzyme Inhibition, AT1 Receptor Blockade, or Combined Inhibition in Congestive Heart Failure

Background: The present study examined the effects of acute angiotensin-converting enzyme inhibition (ACEI), AT, receptor blockade (AT, block), or combined treatment on in vitro and in vivo bradykinin (BK) levels. Methods: BK levels were measured in isolated porcine myocyte preparations (n = 13) in the presence of exogenous BK (10-8 M); with an ACEI (benezaprilat; 0.1 mM) and BK; an AT, block (valsartan; 10-5 M) and BK; and combined treatment and BK. In a second study, myocardial microdialysis was used to measure porcine interstitial BK levels in both normal (n = 14) and pacing-induced congestive heart failure (CHF) (240 beats/min, 3 weeks, n = 16) under the following conditions: baseline, following ACEI (benezaprilat, 0.0625 mg/kg) or AT, block (valsartan, 0. I mg/kg), and a combined treatment (benezaprilat, 0.0625 mg/kg; valsartan, 0.1 mg/kg). Results: In the left ventricular myocyte study, BK levels increased over 93% with all treatments compared to untreated values (P < 0.05). In the in vivo study, basal interstitial BK values were lower in the CHF group than in controls (2.64 ± 0.57 vs 5.91 + 1.4 nM, respectively, P < 0.05). Following acute infusion of the ACEI, BK levels in the CHF state increased from baseline (57% ± 22; P < 0.05). Following combined ACEIIAT, block, BK levels increased from baseline in both control (42% ± 11) and CHF groups (60% ± 22; P < 0.05 for both). Conclusion: These findings suggest that ACEI, or combined ACEI/AT, block increased BK at the level of the myocyte and potentiated BK levels in the CHF myocardial interstitium.

Bradykinin degradation and relation to myocyte contractility.

Background: Past studies have demonstrated that exogenous bradykinin (BK) causes vasodilation and increases coronary blood flow, effects that may be beneficial in the setting of cardiac disease states. An important pathway for BK degradation is through angiotensin-converting enzyme (ACE), which results in the formation of a degradative peptide, BK(1-7). The goal of this study was to examine the effects of BK, BK(1-7), and the potential modulation of BK by ACE inhibition on myocyte contractility. Methods and Results: Contractile function was examined in isolated adult porcine (n = 15) left ventricular (LV) myocyte preparations in the presence or absence of BK (10-8 mol/L), BK(1-7) (10-8 mol/L), and with pretreatment by ACE inhibition (benazaprilat). Myocyte velocity of shortening fell by over 15% in the presence of BK and by 8% with BK(1-7) ( P < .05 vs basal). ACE inhibition blunted the negative effect of BK on myocyte velocity of shortening by over 60% (P < .05). Furthermore, robust ACE activity coupled with significant BK degradation was demonstrated in LV-isolated myocyte preparations, and BK proteolysis was influenced by ACE inhibition. Conclusion: These results suggest that BK has a direct effect on LV myocyte contractility, and that this effect may be mediated by proteolysis of BK at the level of the LV myocyte sarcolemma.