Abstract-The matrix metalloproteinases (MMPs) are an endogenous family of proteolytic enzymes implicated to contribute to LV remodeling. However, broad-spectrum MMP inhibition (MMPi), particularly inhibition of interstitial collagenase (MMP-1), may not be clinically applicable. This study examined the effects of selective MMPi (sparing MMP-1) in a model of developing congestive heart failure. Pigs were randomly assigned to 3 groups: (1) rapid pacing for 3 weeks (240 bpm, nϭ10); (2) selective MMPi (20 mg/kg per day-PO;PGE7113313) and rapid pacing (nϭ12); and (3) controls (nϭ10 Key Words: left ventricular systolic function Ⅲ myocardial stiffness Ⅲ myocardial structure Ⅲ matrix metalloproteinases Ⅲ heart failure A structural milestone in the progression of congestive heart failure (CHF) is alterations in left ventricular (LV) geometry, commonly referred to as myocardial remodeling. The myocardial extracellular matrix contributes to the maintenance of LV geometry, structural alignment of adjoining myocytes, as well as modulating transmembrane signaling pathways. A family of enzymes that contributes to extracellular collagen degradation and tissue remodeling is the matrix metalloproteinases (MMPs). 1-3 Increased expression and activity of MMPs within the LV myocardium occurs in both patients and animals with CHF. 4 -8 Orally active nonselective MMP inhibitors, termed as broad spectrum MMP inhibitors, have been used in several animal models of CHF and demonstrated to attenuate the LV remodeling process. 7-9 Therefore, modulating MMP activity represents a potential therapeutic target in the context of LV remodeling and CHF. However, long-term inhibition of all MMP species will likely interfere with normal tissue remodeling processes and can give rise to undesirable systemic effects. 10 -12 Thus, selective targeting of MMP species that contribute to pathological myocardial remodeling in developing CHF will likely hold greater therapeutic potential. Whereas a number of MMP species are expressed within the human myocardium, not all MMPs are upregulated in end-stage CHF. 6,13,14 Specifically, the abundance of interstitial collagenase-1, or MMP-1, is significantly reduced in patients with cardiomyopathic disease. 6 However, it remains unknown whether inhibition of MMP-1 is a fundamental requirement in order to alter the myocardial remodeling process during the initiation and development of CHF. Accordingly, the overall goal of this study was to institute selective MMP inhibition that would effectively spare MMP-1 inhibition in an animal model of developing CHF. Materials and Methods Selective MMP InhibitionPast studies have demonstrated that several classes of MMPs are increased in CHF including the interstitial collagenase MMP-13, stromelysins such as MMP-3, and the gelatinases such as MMP-2 and MMP-9. 4 -8,14 In order to identify an MMP inhibition dosage regimen that would provide acceptable plasma profiles with respect to inhibition of these species but effectively spare MMP-1 inhibition, pharmacokinetic studies were p...

Transient left ventricular (LV) dysfunction can occur after cardioplegic arrest. The contributory mechanisms for this phenomenon are not completely understood. We tested the hypothesis that exposure of LV myocytes to endothelin (ET) during simulated cardioplegic arrest would have direct effects on contractile processes with subsequent reperfusion. LV porcine myocytes were randomly assigned to three groups: 1) CONTROL: normothermic (37 degrees C) cell media (n = 204); 2) Cardioplegia: simulated cardioplegic arrest (K(+) 24 mEq/L, 4 degrees C x 2 h) followed by reperfusion and rewarming with cell media (n = 164); and 3) Cardioplegia/ ET: simulated cardioplegic arrest in the presence of ET (200 pM) followed by reperfusion with cell media containing ET (n = 171). Myocyte contractility was measured by computer-assisted video microscopy. In a subset of experiments, myocyte intracellular calcium was determined after Fluo-3 (Molecular Probes, Eugene, OR) loading by digital fluorescence image analysis. Myocyte shortening velocity was reduced after cardioplegic arrest compared with controls (52 +/- 2 vs 84 +/- 3 microm/s, respectively; P < 0.05) and was further reduced with cardioplegic arrest and ET exposure (43 +/- 2 microm/s, P < 0.05). Intracellular calcium was significantly increased in myocytes exposed to cardioplegia compared with normothermic control myocytes and was further augmented by cardioplegia with ET supplementation (P < 0.05). Exposure of the LV myocyte to ET during cardioplegic arrest directly contributed to contractile dysfunction after reperfusion. Moreover, alterations in intracellular calcium may play a role in potentiating the myocyte contractile dysfunction associated with ET exposure during cardioplegic arrest.

Although this pilot study identified differences in the downstream distribution of embolic particles when the antireflux catheter was used, further investigation is needed to determine if these findings are reproducible in a larger patient cohort and, if so, whether they are associated with any clinical impact.

The improved LV pump function that occurred with GHS treatment in this model of CHF was most likely a result of favorable effects on LV myocardial remodeling and contractile processes. On the basis of these results, further studies are warranted to determine the potential role of GH secretagogues in the treatment of CHF.