Recent studies have focused their attention on the role of the proinflammatory cytokine tumor necrosis factor (TNF) in the development of heart failure. First recognized as an endotoxin-induced serum factor that caused necrosis of tumors and cachexia, it is now recognized that TNF participates in the pathophysiology of a group of inflammatory diseases including rheumatoid arthritis and Crohn's disease. The normal heart does not express TNF; however, the failing heart produces robust quantities. Furthermore, there is a direct relationship between the level of TNF expression and the severity of disease. In addition, both in vivo and in vitro studies demonstrate that TNF effects cellular and biochemical changes that mirror those seen in patients with congestive heart failure. Furthermore, in animal models, the development of the heart failure phenotype can be abrogated at least in part by anticytokine therapy. Based on information from experimental studies, investigators are now evaluating the clinical efficacy of novel anticytokine and anti-TNF strategies in patients with heart failure; one such strategy is the use of a recombinantly produced chimeric TNF alpha soluble receptor. Thus, in view of the emerging importance of proinflammatory cytokines in the pathogenesis of heart disease, we review the biology of TNF, its role in inflammatory diseases, the effects of TNF on the physiology of the heart and the development of clinical strategies that target the cytokine pathways.

Myocardial fibrosis due to maladaptive extracellular matrix remodeling contributes to dysfunction of the failing heart. Further elucidation of the mechanism by which myocardial fibrosis and dilatation can be prevented or even reversed remains of great interest as a potential means to limit myocardial remodeling and dysfunction. Matrix metalloproteinases (MMPs) are the driving force behind extracellular matrix degradation during remodeling and are increased in the failing human heart. MMPs are regulated by a variety of growth factors, cytokines, and matrix fragments such as matrikines. In the present report, we discuss the regulation of MMPs, the role of MMPs in the development of cardiac fibrosis, and the modulation of MMP activity using gene transfer and knockout technologies. We also present recent findings from our laboratory on the regulation of the extracellular MMP inducer (EMMPRIN), MMPs, and transforming growth factor-beta(1) in the failing human heart before and after left ventricular assist device support, as well as the possibility of preventing ventricular fibrosis using different anti-MMP strategies. Several studies suggest that such modulation of MMP activity can alter ventricular remodeling, myocardial dysfunction, and the progression of heart failure. It is therefore suggested that the interplay of MMPs and their regulators is important in the development of the heart failure phenotype, and myocardial fibrosis in heart failure may be modified by modulating MMP activity.

These studies demonstrated a selective downregulation of TIMPs along with upregulation of MMP-9 and gelatinolytic activity in the failing hearts, alterations that favor matrix degradation and turnover. These findings might be of pathophysiological significance and might suggest new therapeutic targets for limiting the ventricular remodeling and dilatation process characteristic of the failing human heart.

Background-Left ventricular assist device (LVAD) support of the failing heart induces salutary changes in myocardial structure and function. Matrix metalloproteinases (MMPs) are increased in the failing heart and are induced by stretch in cardiac cells in vitro. We hypothesized that mechanical unloading may affect LV plasticity by regulating MMPs and their substrates. Methods and Results-LV samples were collected from patients with dilated cardiomyopathy (DCM, nϭ14) or ischemic cardiomyopathy (ICM, nϭ16) at the time of implantation of the LVAD and again during cardiac transplantation. MMP-1, -3, and -9 were measured by ELISA, MMP-2 and -9 gelatinolytic activity by gelatin zymography, and tissue inhibitors of metalloproteinases (TIMPs) by Western blot. Total soluble and insoluble collagens were separated by pepsin solubilization, and the contents were determined by quantification of hydroxyproline. The undenatured soluble collagen was measured by Sircol collagen assay. The results showed that MMP-1 and -9 were decreased, whereas TIMP-1 and -3 were increased, but there was no change in MMP-2 and -3 and TIMP-2 and -4 after LVAD support. The undenatured collagen was increased, with the ratio of undenatured to total soluble collagens increased in ICM and that of insoluble to total soluble collagens increased in DCM after LVAD support. Conclusions-The reduced MMPs and increased TIMPs and ratios of undenatured to total soluble collagens and insolubleto total soluble collagens after LVAD support suggest that reduced MMP activity diminished damage to the matrix. These changes may contribute to the functional recovery and LV plasticity after LVAD support. Key Words: collagen Ⅲ metalloproteinases Ⅲ remodeling Ⅲ heart-assist device Ⅲ heart failure L eft ventricular assist devices (LVADs) provide mechanical support for the failing heart and serve as a bridge to cardiac transplantation, with the potential to be a destiny therapy for heart failure. [1][2][3] Recent reports demonstrate that LVAD support may be associated with adaptive remodeling of the ventricular myocardium, including reduced LV mass, wall thickness, and myocyte diameter; changes in LV pressure-volume relationships; and reversal of LV chamber dilation and molecular remodeling of proteins involved in Ca 2ϩ cycling. [3][4][5][6][7][8][9][10] In addition, LVAD support has been associated with salutary changes in cardiomyocyte function. Indeed, a small subgroup of patients can be successfully weaned from LVAD after recovery of ventricular function. 6,[11][12][13][14] Although it has been suggested that these beneficial changes are attributed to chronic unloading of the ventricular myocardium, the molecular mechanisms that play a role in LVAD-induced myocardial plasticity and LV remodeling remain undefined. See p 1089We hypothesized that the myocardial remodeling that occurs with LVAD unloading might be attributable to alterations in the components of the extracellular matrix, and specifically in the activity of matrix metalloproteinases (MMPs) and the physical pr...

Tumor necrosis factor-alpha and interleukin-1 beta regulate the expression of TIMPs and disintegrin metalloproteinase, which may in turn contribute to the increased matrix degradation in cardiac cells. Since heart failure in humans is characterized by both re-expression of myocardial cytokines and remodeling of the extracellular matrix, those in vitro results suggest a potential role for those cytokines in the regulation of extracellular matrix remodeling and therefore in the transition to the end-stage heart failure phenotype.

. MMP inhibition modulates TNF-␣ transgenic mouse phenotype early in the development of heart failure. Am J Physiol Heart Circ Physiol 282: H983-H989, 2002; 10.1152/ajpheart.00233. 2002.-Myocardial extracellular matrix remodeling regulated by matrix metalloproteinases (MMPs) is implicated in the progression of heart failure. We hypothesized that MMP inhibition may modulate extracellular matrix remodeling and prevent the progression of heart failure. The effects of the MMP inhibitor BB-94 (also known as batimastat) on MMP expression, collagen expression, collagen deposition, collagen denaturation, and left ventricular structure and function in transgenic mice with cardiac-restricted overexpression of tumor necrosis factor-␣ (TNF-␣) (TNF1.6) were assessed. The results showed that BB-94 reduced the expression of collagens, increased insoluble collagen and the ratio of undenatured to total soluble collagen, and prevented myocardial hypertrophy and diastolic dysfunction in young TNF1.6 mice. Furthermore, the treatment significantly improved cumulative survival of TNF1.6 mice. However, MMP inhibition did not have salutary effects on ventricular size and function in old mice with established heart failure. The results suggest that MMP activation may play a critical role in changes of myocardial function through the remodeling of extracellular matrix, and MMP inhibition may serve as a potential therapeutic strategy for heart failure, albeit within a narrow window during the development of heart failure. metalloendopeptidases; ventricular remodeling; extracellular matrix; collagen MATRIX METALLOPROTEINASES (MMPs, EC 3.4.24) are a family of functionally related zinc-containing proteinases that are capable of degrading all the components of the extracellular matrix (ECM). The collagenous matrix provides the support essential for maintaining alignment of myofibrils within the myocyte as well as for maintaining myocyte alignment within the myocardium (2, 7). Denatured collagens do not function as a structural support for myofibrils and myocytes. Activation of MMPs may result in fibrillar collagen denaturation, collagen degradation, and the synthesis of new fibrous tissue. As the initial step of collagen degradation and structural reformation, collagen denaturation may be a result of excessive exposure to active MMPs (18). Therefore, activated MMPs may play an important role in cardiac ECM remodeling that accompanies the development of heart failure (6,19,35). Indeed, elevation of MMP activity has been previously identified in the failing hearts of both animal models and humans (5,16,32,35,36). ECM remodeling, which contributes to left ventricular remodeling and dilation (9, 10), is a cumulative result of matrix protein synthesis, denaturation, degradation, and structural reformation. The process of ECM remodeling is not only a change in the amount but also a change in the quality of matrix proteins (17,22,40).Previous studies from our laboratory demonstrated a robust increase in MMP-2 and MMP-9 gelatinolytic activity, exten...

. Overexpression of tumor necrosis factor-␣ increases production of hydroxyl radical in murine myocardium.

Background-Recent studies suggest that mutations in cardiac mitochondrial DNA (mtDNA) may contribute to the development of dilated cardiomyopathy. The mechanisms that regulate those mutations, however, remain undefined. Thus, we studied cardiac mtDNA repair mechanisms, mtDNA damage, and mitochondrial structure and function in mice with heart failure secondary to overexpression of TNF-␣ (TNF1.6 mice). Methods and Results-We studied mtDNA repair by measuring the uracil DNA glycosylase (mtUDG) and base excision repair activities. mtDNA damage was assessed by Southern blot of Fpg protein-digested mtDNA. Mitochondrial ultrastructural changes were examined by electron microscopy, and function by cytochrome c oxidase and succinate dehydrogenase activity assays. The results showed that both mtUDG and base excision repair activities were significantly reduced in TNF1.6 mouse heart. Fpg-sensitive sites were markedly increased in TNF1.6 mouse cardiac mtDNA, suggesting increased mtDNA damage. Mitochondrial function as demonstrated by cardiac cytochrome c oxidase activity was also markedly reduced. Cardiac ATP content was not changed, however, suggesting a shift from oxidative phosphorylation to glycolysis, as shown by increased LDH and ALT activities and lactate/pyruvate ratio. Ultrastructurally, the TNF1.6 mouse cardiac mitochondria became irregular in shape and smaller, and the cristae were decreased and appeared disorganized, with breaks. Conclusions-These results suggest that mtDNA mutations and mitochondrial structural and functional alterations in TNF-␣-induced heart failure may be associated with reduced mtDNA repair activity, and the pathophysiological effects of TNF-␣ on the heart may be mediated, at least in part, through these changes in mitochondria.