Chronic Matrix Metalloproteinase Inhibition Following Myocardial Infarction in Mice: Differential Effects on Short and Long-Term Survival

Recovery of left ventricular function following in vivo reexpression of cardiac myosin binding protein C

The loss of cardiac myosin binding protein C (cMyBP-C) results in left ventricular dilation, cardiac hypertrophy, and impaired ventricular function in both constitutive and conditional cMyBP-C knockout (MYBPC3 null) mice. It remains unclear whether the structural and functional phenotypes expressed in the MYBPC3 null mouse are reversible, which is an important question, since reduced expression of cMyBP-C is an important cause of hypertrophic cardiomyopathy in humans. To investigate this question, we generated a cardiac-specific transgenic mouse model using a Tet-Off inducible system to permit the controlled expression of WT cMyBP-C on the MYBPC3 null background. Functional Tet-Off mice expressing WT cMyBP-C (FT-WT) were generated by crossing tetracycline transactivator mice with responder mice carrying the WT cMyBP-C transgene. Prior to dietary doxycycline administration, cMyBP-C was expressed at normal levels in FT-WT myocardium, which exhibited similar levels of steady-state force and in vivo left ventricular function as WT mice. Introduction of dietary doxycycline for four weeks resulted in a partial knockdown of cMyBP-C expression and commensurate impairment of systolic and diastolic function to levels approaching those observed in MYBPC 3 null mice. Subsequent withdrawal of doxycycline from the diet resulted in the reexpression of cMyBP-C to levels comparable to those observed in WT mice, along with near-complete recovery of in vivo ventricular function. These results show that the cardiac phenotypes associated with MYBPC3 null mice are reversible. Our work also validates the use of the Tet-Off inducible system as a means to study the mechanisms underlying hypertrophic cardiomyopathy.

Tollip Negatively Regulates Vascular Smooth Muscle Cell-Mediated Neointima Formation by Suppressing Akt-Dependent Signaling

BACKGROUND

Tollip, a well-established endogenous modulator of Toll-like receptor signaling, is involved in cardiovascular diseases. The aim of this study was to investigate the role of Tollip in neointima formation and its associated mechanisms.

METHODS AND RESULTS

In this study, transient increases in Tollip expression were observed in platelet-derived growth factor-BB-treated vascular smooth muscle cells and following vascular injury in mice. We then applied loss-of-function and gain-of-function approaches to elucidate the effects of Tollip on neointima formation. While exaggerated neointima formation was observed in Tollip-deficient murine neointima formation models, Tollip overexpression alleviated vascular injury-induced neointima formation by preventing vascular smooth muscle cell proliferation, dedifferentiation, and migration. Mechanistically, we demonstrated that Tollip overexpression may exert a protective role in the vasculature by suppressing Akt-dependent signaling, which was further confirmed in rescue experiments using the Akt-specific inhibitor (AKTI).

CONCLUSIONS

Our findings indicate that Tollip protects against neointima formation by negatively regulating vascular smooth muscle cell proliferation, dedifferentiation, and migration in an Akt-dependent manner. Upregulation of Tollip may be a promising strategy for treating vascular remodeling-related diseases.

Guidelines for measuring cardiac physiology in mice

Cardiovascular disease is a leading cause of death, and translational research is needed to understand better mechanisms whereby the left ventricle responds to injury. Mouse models of heart disease have provided valuable insights into mechanisms that occur during cardiac aging and in response to a variety of pathologies. The assessment of cardiovascular physiological responses to injury or insult is an important and necessary component of this research. With increasing consideration for rigor and reproducibility, the goal of this guidelines review is to provide best-practice information regarding how to measure accurately cardiac physiology in animal models. In this article, we define guidelines for the measurement of cardiac physiology in mice, as the most commonly used animal model in cardiovascular research.

Listen to this article’s corresponding podcast at http://ajpheart.podbean.com/e/guidelines-for-measuring-cardiac-physiology-in-mice/.

Early changes of left ventricular filling pattern after reperfused ST-elevation myocardial infarction and doxycycline therapy: Insights from the TIPTOP trial

AIM

Metalloproteinases inhibition by doxycycline reduces cardiac protein degradation at extracellular and intracellular level in the experimental model ischemia/reperfusion injury. Since both extracellular cardiac matrix and titin filaments inside the cardiomyocyte are responsible for the myocardial stiffness, we hypothesized that doxycycline could favorably act on left ventricular (LV) filling pressures in patients after reperfused acute ST-elevation myocardial infarction (STEMI).

METHODS AND RESULTS

Seventy-three of 110 patients of the TIPTOP trial underwent a 2D-Echo-Doppler on admission, and at pre-discharge and at 6-month after a primary PCI for STEMI and LV dysfunction. From admission to pre-discharge, LV filling changed from a high filling pressure (HFP) to a normal filling pressure (NFP) pattern in 91% of the doxycycline-group, and in 67% of the control-group. Conversely, 1% of the doxycycline-group, and 37% of the control-group changed the LV filling from NFP to HFP pattern. Overall, a pre-discharge HFP pattern was present in 4 patients (11%) of the doxycycline-group and in 13 patients (36%) of the control-group (p=0.025). The evaluation of metalloproteinases and their tissue inhibitors plasma concentrations provide possible favorable action of doxycycline. On the multivariate analyses, troponine I peak (p=0.026), doxycycline (p=0.033), and on admission to pre-discharge LVEF changes (p=0.044) were found to be associated with pre-discharge HFP pattern. Independently of their baseline LV filling behavior, the 6-month remodeling was less in patients with pre-discharge NFP pattern than in patients with HFP pattern.

CONCLUSIONS

In patients with STEMI and LV dysfunction doxycycline can favorably modulate the LV filling pattern early after primary PCI.

Pharmacological reasons that may explain why randomized clinical trials have failed in acute heart failure syndromes

Acute heart failure (AHF) represents a clinical challenge as it encloses a heterogeneous group of syndromes (AHFS) with different pathophysiology, clinical presentations, prognosis and response to therapy. In the last 25years multiple therapeutic targets have been identified and numerous new drugs were evaluated but, up to now, all failed to demonstrate a consistent benefit on clinical outcomes. Moreover, a repeated finding has been the poor correlation between the encouraging results of preclinical and early clinical trials and the lack of effect on outcomes observed in phase III trials. We review several possible pharmacological reasons that may explain the lack of success to develop new drugs and the pharmacological challenges to overcome in the future to develop new more effective and safer drugs for the treatment of AHFS.

Pathophysiology of Myocardial Infarction

Myocardial infarction is defined as sudden ischemic death of myocardial tissue. In the clinical context, myocardial infarction is usually due to thrombotic occlusion of a coronary vessel caused by rupture of a vulnerable plaque. Ischemia induces profound metabolic and ionic perturbations in the affected myocardium and causes rapid depression of systolic function. Prolonged myocardial ischemia activates a "wavefront" of cardiomyocyte death that extends from the subendocardium to the subepicardium. Mitochondrial alterations are prominently involved in apoptosis and necrosis of cardiomyocytes in the infarcted heart. The adult mammalian heart has negligible regenerative capacity, thus the infarcted myocardium heals through formation of a scar. Infarct healing is dependent on an inflammatory cascade, triggered by alarmins released by dying cells. Clearance of dead cells and matrix debris by infiltrating phagocytes activates anti-inflammatory pathways leading to suppression of cytokine and chemokine signaling. Activation of the renin-angiotensin-aldosterone system and release of transforming growth factor-β induce conversion of fibroblasts into myofibroblasts, promoting deposition of extracellular matrix proteins. Infarct healing is intertwined with geometric remodeling of the chamber, characterized by dilation, hypertrophy of viable segments, and progressive dysfunction. This review manuscript describes the molecular signals and cellular effectors implicated in injury, repair, and remodeling of the infarcted heart, the mechanistic basis of the most common complications associated with myocardial infarction, and the pathophysiologic effects of established treatment strategies. Moreover, we discuss the implications of pathophysiological insights in design and implementation of new promising therapeutic approaches for patients with myocardial infarction.

Matrix metalloproteinases and their tissue inhibitor after reperfused ST-elevation myocardial infarction treated with doxycycline. Insights from the TIPTOP trial

BACKGROUND

The TIPTOP (Early Short-term Doxycycline Therapy In Patients with Acute Myocardial Infarction and Left Ventricular Dysfunction to Prevent The Ominous Progression to Adverse Remodelling) trial demonstrated that a timely, short-term therapy with doxycycline is able to reduce LV dilation, and both infarct size and severity in patients treated with primary percutaneous intervention (pPCI) for a first ST-elevation myocardial infarction (STEMI) and left ventricular (LV) dysfunction. In this secondary, pre-defined analysis of the TIPTOP trial we evaluated the relationship between doxycycline and plasma levels of matrix metalloproteinases (MMPs) and their tissue inhibitors (TIMPs).

METHODS

In 106 of the 110 (96%) patients enrolled in the TIPTOP trial, plasma MMPs and TIMPs were measured at baseline, and at post-STEMI days 1, 7, 30 and 180. To evaluate the remodeling process, 2D-Echo studies were performed at baseline and at 6months. A (99m)Tc-SPECT was performed to evaluate the 6-month infarct size and severity.

RESULTS

Doxycycline therapy was independently related to higher plasma TIMP-2 levels at day 7 (p<0.05). Plasma TIMP-2 levels above the median value at day 7 were correlated with the 6-month smaller infarct size (3% [0%-16%] vs. 12% [0%-30%], p=0.002) and severity (0.55 [0.44-0.64] vs. 0.45 [0.29-0.60], p=0.002), and LV dilation (-1ml/m(2) [from -7ml/m(2) to 9ml/m(2)] vs. 3ml/m(2) [from -2ml/m(2) to 19ml/m(2)], p=0.04), compared to their counterpart.

CONCLUSIONS

In this clinical setting, doxycycline therapy results in higher plasma levels of TIMP-2 which, in turn, inversely correlate with 6month infarct size and severity as well as LV dilation.

Angiotensin II type 1 receptor expression in astrocytes is upregulated leading to increased mortality in mice with myocardial infarction-induced heart failure

Enhanced central sympathetic outflow worsens left ventricular (LV) remodeling and prognosis in heart failure after myocardial infarction (MI). Previous studies suggested that activation of brain angiotensin II type 1 receptors (AT1R) in the brain stem leads to sympathoexcitation due to neuronal AT1R upregulation. Recent studies, however, revealed the importance of astrocytes for modulating neuronal activity, but whether changes in astrocytes influence central sympathetic outflow in heart failure is unknown. In the normal state, AT1R are only weakly expressed in astrocytes. We hypothesized that AT1R in astrocytes are upregulated in heart failure and modulate the activity of adjacent neurons, leading to enhanced sympathetic outflow. In the present study, by targeting deletion of astrocyte-specific AT1R, we investigated whether AT1R in astrocytes have a key role in enhancing central sympathetic outflow, and thereby influencing LV remodeling process and the prognosis of MI-induced heart failure. Using the Cre-LoxP system, we generated glial fibrillary acidic protein (GFAP)-specific AT1R knockout (GFAP/AT1RKO) mice. Urinary norepinephrine excretion for 24 h, as an indicator of sympathoexcitation, was significantly lower in GFAP/AT1RKO-MI mice than in control-MI mice. LV size and heart weight after MI were significantly smaller in GFAP/AT1RKO mice than in control mice. Prognosis was significantly improved in GFAP/AT1RKO-MI mice compared with control-MI mice. Our findings indicated that AT1R expression was upregulated in brain stem astrocytes in MI-induced heart failure, which worsened LV remodeling and prognosis via sympathoexcitation. Thus, in addition to neuronal AT1R, AT1R in astrocytes appear to have a key role in enhancing central sympathetic outflow in heart failure.

Targeted overexpression of tissue inhibitor of matrix metalloproteinase-4 modifies post-myocardial infarction remodeling in mice

RATIONALE

Myocardial infarction (MI) causes an imbalance between matrix metalloproteinases and tissue inhibitors of matrix metalloproteinases (TIMPs) and is associated with adverse left ventricular (LV) remodeling. A uniform reduction in TIMP-4 post-MI has been observed.

OBJECTIVE

To examine post-MI remodeling with cardiac-restricted overexpression of TIMP-4, either through a transgenic or viral delivery approach.

METHODS AND RESULTS

MI was induced in mice and then randomized to targeted injection of an adenoviral construct (10 μL; 8×10(9) plaque forming units/mL) encoding green fluorescent protein (GFP) and the full-length human TIMP-4 (Ad-GFP-TIMP4) or GFP. A transgenic construct with cardiac-restricted overexpression TIMP-4 (hTIMP-4exp) was used in a parallel set of studies. LV end-diastolic volume, an index of LV remodeling, increased by >60% from baseline at 5 days post-MI and by >100% at 21 days post-MI in the Ad-GFP only group. However, LV dilation was reduced by ≈50% in both the Ad-GFP-TIMP4 and hTIMP-4exp groups at these post-MI time points. LV ejection fraction was improved with either Ad-GFP-TIMP-4 or hTIMP-4exp. Fibrillar collagen expression and content were increased within the MI region with both TIMP-4 interventions, suggestive of matrix stabilization.

CONCLUSIONS

This study is the first to demonstrate that selective myocardial targeting for TIMP-4 induction through either a viral or transgenic approach favorably altered the course of adverse LV remodeling post-MI. Thus, localized induction of endogenous matrix metalloproteinase inhibitors, such as TIMP-4, holds promise as a means to interrupt the progression of post-MI remodeling.

Protective effect of lycopene on cardiac function and myocardial fibrosis after acute myocardial infarction in rats via the modulation of p38 and MMP-9

Extracellular matrix (ECM) plays an important role in maintaining the left ventricular geometry and ventricular function, and the inhibition of ECM remodeling has therapeutic benefits that could alleviate the progression of ventricular remodeling. Recent studies have indicated that lycopene has cardioprotective effects. In this study, a rat myocardial infarction (MI) model was established by left anterior descending coronary artery ligation. After the operation, the rats received lycopene or saline. After 28 days, the rats underwent echocardiography detection and were sacrificed. Myocardial fibrosis was observed by Masson staining. Type I collagen, MMP-9, and MAPK protein expression were detected in the ischemic zone surrounding the MI by western blot. Treatment with lycopene increased the EF from 45.2 ± 3.12 % to 51.1 ± 4.63, and it decreased the LVEDd from 6.52 ± 0.37 mm to 6.18 ± 0.41 mm and the LVESd from 4.29 ± 0.63 to 3.94 ± 0.37 at 28 days post-myocardial infarction. Lycopene attenuated the MI-induced increase in MMP-9 and type I collagen expression, and inhibited p38 activation. Moreover, lycopene decreased the collagen volume fraction in the peri-infarcted zone. The data indicated that lycopene improved the cardiac function and ventricular remodeling by inhibiting p38 activation and MMP-9 expression.

Early short-term doxycycline therapy in patients with acute myocardial infarction and left ventricular dysfunction to prevent the ominous progression to adverse remodelling: the TIPTOP trial

AIMS

Experimental studies suggest that doxycycline attenuates post-infarction remodelling and exerts protective effects on myocardial ischaemia/reperfusion injury. However, the effects of the drug in the clinical setting are unknown. The aim of this study was to examine the effect of doxycycline on left ventricular (LV) remodelling in patients with acute ST-segment elevation myocardial infarction (STEMI) and LV dysfunction.

METHODS AND RESULTS

Open-label, randomized, phase II trial. Immediately after primary percutaneous coronary intervention, patients with STEMI and LV ejection fraction < 40% were randomly assigned to doxycycline (100 mg b.i.d. for 7 days) in addition to standard therapy, or to standard care. The echo LV end-diastolic volumes index (LVEDVi) was determined at baseline and 6 months. (99m)Tc-Sestamibi-single-photon emission computed tomography infarct size and severity were assessed at 6 months. We calculated a sample size of 110 patients, assuming that doxycycline may reduce the increase in the LVEDVi from baseline to 6 months > 50% compared with the standard therapy (statistical power > 80% with a type I error = 0.05). The 6-month changes in %LVEDVi were significant smaller in the doxycycline group than in the control group [0.4% (IQR: -16.0 to 14.2%) vs.13.4% (IQR: -7.9 to 29.3%); P = 0.012], as well as infarct size [5.5% (IQR: 0 to 18.8%) vs. 10.4% (IQR: 0.3 to 29.9%) P = 0.052], and infarct severity [0.53 (IQR: 0.43-0.62) vs. 0.44 (IQR: 0.29-0.60), P = 0.014], respectively.

CONCLUSION

In patients with acute STEMI and LV dysfunction, doxycycline reduces the adverse LV remodelling for comparable definite myocardial infarct size (NCT00469261).

Inhibiting matrix metalloproteinase by cell-based timp-3 gene transfer effectively treats acute and chronic ischemic cardiomyopathy

After a myocardial infarction (MI), an increase in the cardiac ratio of matrix metalloproteinases (MMPs) relative to their inhibitors (TIMPs) causes extracellular matrix modulation that leads to ventricular dilatation and congestive heart failure. Cell therapy can mitigate these effects. In this study, we tested whether increasing MMP inhibition via cell-based gene transfer of Timp-3 further preserved ventricular morphometry and cardiac function in a rat model of MI. We also measured the effect of treatment timing. We generated MI (coronary artery ligation) in adult rats. Three or 14 days later, we implanted medium (control) or vascular smooth muscle cells transfected with empty vector (VSMCs) or Timp-3 (C-TIMP-3) into the peri-infarct region (n = 15-24/group). We assessed MMP-2 and -9 expression and activity, TIMP-3, and TNF-α expression, cell apoptosis, infarct size and thickness, ventricular morphometry, and cardiac function (by echocardiography). Relative to medium, VSMCs delivered at either time point significantly reduced cardiac expression and activity of MMP-2 and -9, reduced expression of TNF-α, and increased expression of TIMP-3. Cell therapy also reduced apoptosis and scar area, increased infarct thickness, preserved ventricular structure, and reduced functional loss. All these effects were augmented by C-TIMP-3 treatment. Survival and cardiac function were significantly greater when VSMCs or C-TIMP-3 were delivered at 3 (vs. 14) days after MI. Upregulating post-MI cardiac TIMP-3 expression via cell-based gene therapy contributed additional regulation of MMP, TIMP, and TNF-α levels, thereby boosting the structural and functional effects of VSMCs transplanted at 3 or 14 days after an MI in rats. Early treatment may be superior to late, though both are effective.

Targeted imaging of the spatial and temporal variation of matrix metalloproteinase activity in a porcine model of postinfarct remodeling: relationship to myocardial dysfunction

BACKGROUND

Matrix metalloproteinases (MMPs) are known to modulate left ventricular (LV) remodeling after a myocardial infarction (MI). However, the temporal and spatial variation of MMP activation and their relationship to mechanical dysfunction after MI remain undefined.

METHODS AND RESULTS

MI was surgically induced in pigs (n = 23) and cine magnetic resonance (MR) and dual-isotope hybrid single-photon emission CT (SPECT)/CT imaging obtained using thallium-201 and a technetium-99m-labeled MMP targeted tracer ((99m)Tc-RP805) at 1, 2, and 4 weeks post-MI along with controls (n = 5). Regional myocardial strain was computed from MR images and related to MMP zymography and ex vivo myocardial (99m)Tc-RP805 retention. MMP activation as assessed by in vivo and ex vivo (99m)Tc-RP805 imaging and retention studies was increased nearly 4-fold within the infarct region at 1 week post-MI and remained elevated up to 1 month post-MI. The post-MI change in LV end-diastolic volumes was correlated with MMP activity (y = 31.34e(0.48x), P = 0.04). MMP activity was increased within the border and remote regions early post-MI, but declined over 1 month. There was a high concordance between regional (99m)Tc-RP805 uptake and ex vivo MMP-2 activity.

CONCLUSIONS

A novel, multimodality, noninvasive hybrid SPECT/CT imaging approach was validated and applied for in vivo evaluation of MMP activation in combination with cine MR analysis of LV deformation. Increased (99m)Tc-RP805 retention was seen throughout the heart early post-MI and was not purely a reciprocal of thallium-201 perfusion. The (99m)Tc-RP805 SPECT/CT imaging may provide unique information regarding regional myocardial MMP activation and predict late post-MI LV remodeling.

Improvement of cardiac function in the failing rat heart after transfer of skeletal myoblasts engineered to overexpress placental growth factor

BACKGROUND

Transplant of skeletal myoblasts is an attractive alternative to repair irreversibly damaged myocardium in ischemic heart failure. We investigated whether transplant of myoblasts overexpressing placental growth factor would stimulate angiogenesis and enhance myoblast survival in a rat heart failure model.

METHODS

Three weeks after myocardial infarction, Sprague-Dawley rats in heart failure received intramyocardial injections of Ringer solution (control) or autologous myoblasts, unmodified or transfected with placental growth factor expression plasmid. Sham-operated animals served as noninfarct controls. Cardiac function was assessed by echocardiography to 86 days after engraftment. Immunocytochemistry and fluorescence imaging were used to investigate vessel formation, grafted myoblast survival, infarct wall thickness, and infarct size. Quantitative real-time reverse transcriptase polymerase chain reaction and Western blotting measured tissue messenger RNA and protein expressions.

RESULTS

Left ventricular function significantly improved with time, and fractional shortening on day 86 was significantly enhanced in transfected myoblast group relative to control (P < .01) and unmodified myoblast (P < .05) groups. Vascular density (P < .01) and myoblast survival (P < .05) were enhanced in rats treated with transfected myoblasts relative to other groups (P < .05). Mean fraction of fibrotic scar tissue was decreased in unmodified and transfected myoblast groups relative to controls on day 86 (P < .05), and left ventricular wall thickness was significantly increased in transfected myoblast group relative to other groups (P < .05).

CONCLUSIONS

Intramyocardial injections of autologous myoblasts overexpressing placental growth factor improved cardiac function, attenuated adverse cardiac remodeling, induced angiogenesis, and probably enhanced survival of grafted myoblasts.

Ghrelin inhibits post-infarct myocardial remodeling and improves cardiac function through anti-inflammation effect

Ghrelin is a novel growth hormone-releasing peptide, which has been shown to exert beneficial cardiac effects on chronic heart failure (CHF) recently. In this study, we attempted to investigate the mechanisms for the effect of ghrelin on ventricular remodeling following acute myocardial infarction (MI). Ligation of a coronary artery was used to create an MI in rats. One week after MI, ghrelin (100 microg/kg) or saline was injected subcutaneously twice a day for 4 weeks. When compared to sham groups, ghrelin administration significantly decreased left ventricular (LV) remodeling in post-MI rats, as indicated by increased LV maximum rate of pressure, LV fractional shortening and scar thickness; and decreased LV end-diastolic pressure, LV end-systolic diameter, LV end-diastolic diameter and cardiocytocytes apoptosis. Moreover, ghrelin inhibited the inflammatory response, as shown by decreased mRNA and protein levels of interleukin (IL)-1beta and tumor necrosis factor-alpha (TNF-alpha). Subsequently, the expression of matrix metalloproteinase (MMP)-2 and MMP-9 were also inhibited by ghrelin injection. Ghrelin alleviates LV dysfunction and ventricular remodeling in post-MI rats. This suggests that the beneficial effects of ghrelin on CHF may result from an inhibition of the inflammatory response.

Relation of high concentrations of plasma carboxy-terminal telopeptide of collagen type I with outcome in acute myocardial infarction

Acute myocardial infarction (AMI) is associated with matrix metalloproteinase activation. The plasma concentrations of carboxy-terminal telopeptide of collagen type I (CITP) reflect collagen type I degradation due to matrix metalloproteinase activation. We assessed the role of CITP as an early marker of outcome in AMI. Plasma CITP was measured 72 hours after hospital admission in 432 patients presenting with AMI. The 2 composite end points of the study (death, resuscitated cardiac arrest, recurrent AMI or ischemia, and heart failure or stroke; and death, resuscitated cardiac arrest, or heart failure) and mortality were assessed at 1 year in 4 patient groups stratified by the CITP quartiles. Patients with ST-segment elevation MI represented 75.7% of the population. In-hospital percutaneous coronary intervention was performed in 70.4% of the patients. The mean left ventricular ejection fraction was 53.9 +/- 12.5%. At 1 year of follow-up, high levels of CITP were associated with the occurrence of both composite end points and mortality (p <0.01 for all). Stepwise logistic regression analysis identified CITP as an independent predictor of both composite end points (odds ratio 2.14, 95% confidence interval 1.34 to 3.42, p = 0.001; and odds ratio 3.19, 95% confidence interval 1.50 to 6.81, p = 0.003), along with the Killip class and brain natriuretic peptide levels. In conclusion, high hospital levels of CITP, a marker of collagen degradation and ventricular remodeling, are associated with late mortality and other serious clinical events after AMI.

Extracellular matrix remodeling during the progression of volume overload-induced heart failure

Volume overload-induced heart failure results in progressive left ventricular remodeling characterized by chamber dilation, eccentric cardiac myocyte hypertrophy and changes in extracellular matrix (ECM) remodeling changes. The ECM matrix scaffold is an important determinant of the structural integrity of the myocardium and actively participates in force transmission across the LV wall. In response to this hemodynamic overload, the ECM undergoes a distinct pattern of remodeling that differs from pressure overload. Once thought to be a static entity, the ECM is now regarded to be a highly adaptive structure that is dynamically regulated by mechanical stress, neurohormonal activation, inflammation and oxidative stress, that result in alterations in collagen and other matrix components and a net change in matrix metalloproteinase (MMP) expression and activation. These changes dictate overall ECM turnover during volume overload hear failure progression. This review will discuss the cellular and molecular mechanisms that dictate the temporal patterns of ECM remodeling during heart disease progression.

Cell-based gene therapy modifies matrix remodeling after a myocardial infarction in tissue inhibitor of matrix metalloproteinase-3-deficient mice

OBJECTIVE

Cell-based gene therapy can enhance the effects of cell transplantation by temporally and spatially regulating the release of the gene product. The purpose of this study was to evaluate transient matrix metalloproteinase inhibition by implanting cells genetically modified to overexpress a natural tissue inhibitor of matrix metalloproteinases (tissue inhibitor of matrix metalloproteinase-3) into the hearts of mutant (tissue inhibitor of matrix metalloproteinase-3-deficient) mice that exhibit an exaggerated response to myocardial infarction. Following a myocardial infarction, tissue inhibitor of matrix metalloproteinase-3-deficient mice undergo accelerated cardiac dilatation and matrix disruption due to uninhibited matrix metalloproteinase activity. This preliminary proof of concept study assessed the potential for cell-based gene therapy to reduce matrix remodeling in the remote myocardium and facilitate functional recovery.

METHODS

Anesthetized tissue inhibitor of matrix metalloproteinase-3-deficient mice were subjected to coronary ligation followed by intramyocardial injection of vector-transfected bone marrow stromal cells, bone marrow stromal cells overexpressing tissue inhibitor of matrix metalloproteinase-3, or medium. Functional, morphologic, histologic, and biochemical studies were performed 0, 3, 7, and 28 days later.

RESULTS

Bone marrow stromal cells and bone marrow stromal cells overexpressing tissue inhibitor of matrix metalloproteinase-3 significantly decreased scar expansion and ventricular dilatation 28 days after coronary ligation and increased regional capillary density to day 7. Only bone marrow stromal cells overexpressing tissue inhibitor of matrix metalloproteinase-3 reduced early matrix metalloproteinase activities and tumor necrosis factor alpha levels relative to medium injection. Bone marrow stromal cells overexpressing tissue inhibitor of matrix metalloproteinase-3 were also more effective than bone marrow stromal cells in preventing progressive cardiac dysfunction, preserving remote myocardial collagen content and structure, and reducing border zone apoptosis for at least 28 days after implantation.

CONCLUSIONS

Tissue inhibitor of matrix metalloproteinase-3 overexpression enhanced the effects of bone marrow stromal cells transplanted early after a myocardial infarction in tissue inhibitor of matrix metalloproteinase-3-deficient mice by contributing regulated matrix metalloproteinase inhibition to preserve matrix collagen and improve functional recovery.

Potential novel pharmacological therapies for myocardial remodelling

Left ventricular (LV) remodelling remains an important treatment target in patients after myocardial infarction (MI) and chronic heart failure (CHF). Accumulating evidence has supported the concept that beneficial effects of current pharmacological treatment strategies to improve the prognosis in these patients, such as angiotensin-converting enzyme (ACE) inhibition, angiotensin type 1 receptor blocker therapy, and beta-blocker therapy, are related, at least in part, to their effects on LV remodelling and dysfunction. However, despite modern reperfusion therapy after MI and optimized treatment of patients with CHF, LV remodelling is observed in a substantial proportion of patients and is associated with an adverse clinical outcome. These observations call for novel therapeutic strategies to prevent or even reverse cardiac remodelling. Recent insights from experimental studies have provided new targets for interventions to prevent or reverse LV remodelling, i.e. reduced endothelial nitric oxide (NO) synthase-derived NO availability, activation of cardiac and leukocyte-dependent oxidant stress pathways, inflammatory pathway activation, matrix-metalloproteinase activation, or stem cell transfer and delivery of novel paracrine factors. An important challenge in translating these observations from preclinical studies into clinical treatment strategies relates to the fact that clinical studies are designed on top of established pharmacological therapy, whereas most experimental studies have tested novel interventions without concomitant drug regimens such as ACE inhibitors or beta-blockers. Therefore, animal studies may overestimate the effect of potential novel treatment strategies on LV remodelling and dysfunction, since established pharmacological therapies may act, in part, via identical or similar signalling pathways. Nevertheless, preclinical studies provide essential information for identifying potential novel targets, and their potential drawbacks, and are required for developing novel clinical treatment strategies to prevent or reverse LV remodelling and dysfunction.

The design of inhibitors for medicinally relevant metalloproteins

A number of metalloproteins are important medicinal targets for conditions ranging from pathogenic infections to cancer. Many but not all of these metalloproteins contain a zinc(II) ion in the protein active site. Small-molecule inhibitors of these metalloproteins are designed to bind directly to the active site metal ions. In this review several metalloproteins of interest are discussed, including matrix metalloproteinases (MMPs), histone deacetylases (HDACs), anthrax lethal factor (LF), and others. Different strategies that have been employed to design effective inhibitors against these proteins are described, with an effort to highlight the strengths and drawbacks of each approach. An emphasis is placed on examining the bioinorganic chemistry of these metal active sites and how a better understanding of the coordination chemistry in these systems may lead to improved inhibitors. It is hoped that this review will help inspire medicinal, biological, and inorganic chemists to tackle this important problem by considering all aspects of metalloprotein inhibitor design.

Chronic doxycycline exposure accelerates left ventricular hypertrophy and progression to heart failure in mice after thoracic aorta constriction

Tetracycline is a powerful tool for controlling the expression of specific transgenes (TGs) in various tissues, including heart. In these mouse systems, TG expression is repressed/enhanced by adding doxycycline (Dox) to the diet. However, Dox has been shown to attenuate matrix metalloproteinase (MMP) expression and activity in various tissues, and MMP inactivation mitigates left ventricular (LV) remodeling in animal models of heart failure. Therefore, we examined the influence of Dox on LV remodeling and MMP expression in mice after transverse aortic constriction (TAC). One month after TAC, cardiac hypertrophy (99% vs. 67%) and the proportion of mice exhibiting congestive heart failure (CHF, 74% vs. 32%) were higher in the TAC + Dox group than in the TAC group (P < 0.05). These differences were no longer seen 2 mo after TAC, although LV was more severely dilated in TAC + Dox mice than in TAC mice (P < 0.05). One month after TAC, the increase in brain natriuretic peptide and beta-myosin heavy chain mRNA levels was 1.6 and 1.7 times higher, respectively, in TAC + Dox mice than in TAC mice (P < 0.01). MMP-2 gelatin zymographic activity increased 1.9- and 2.4-fold in TAC and TAC + Dox mice, respectively (P < 0.01 and P < 0.05 relative to respective sham-operated animals), but the difference between TAC + Dox and TAC mice did not reach statistical significance. Dox did not significantly alter TAC-associated perivascular and interstitial myocardial fibrosis. These findings demonstrate that Dox accelerates the onset of cardiac hypertrophy and the progression to CHF following TAC in mice. Accordingly, care should be taken when designing and interpreting studies based on TG mouse models of LV hypertrophy using the tetracycline-regulated (tet)-on/tet-off system.

Oral treatment with probucol in a pharmacological dose has no beneficial effects on mortality in chronic ischemic heart failure after large myocardial infarction in rats

Cardiac remodeling after myocardial infarction is in part triggered and maintained by reactive oxygen species. Antioxidants such as probucol have shown positive short-term effects on these cardiac interstitial changes in different experimental models after intraperitoneal administration or after per-oral administration with a long pre-treatment period or in high doses. In this study, the long-term effects on mortality and cardiac remodeling were examined after induction of a large myocardial infarction in a clinical daily-life-like setting. Male Lewis rats were randomized to the study groups. Large anterolateral myocardial infarctions were induced or sham operations performed. The oral treatment was started after 48 h either with probucol or placebo after myocardial infarction and with placebo after sham operation. Induction of large myocardial infarctions led to changes of the left ventricular stiffness constants, a dilatation of the left ventricle and an increased interstitial fibrosis in the remote non-infarcted part. These changes were in tendency, but not significantly, reversed after treatment with probucol. The 6-month survival rates were 53.1% in the group probucol-myocardial infarction, 43.2% in the group placebo-myocardial infarction and 100% in the group after sham operation. There were no significant differences at Kaplan-Meier analysis between the groups after myocardial infarctions. Oral treatment with the antioxidant probucol started after myocardial infarction in a pharmacological dose does not have favourable effects on the long-term mortality in the chronic ischemic heart failure model in the rat.

Adenosine inhibits matrix metalloproteinase-9 secretion by neutrophils: implication of A2a receptor and cAMP/PKA/Ca2+ pathway

Matrix metalloproteinases (MMPs), and in particular MMP-9 secreted by neutrophils, are capable of degrading the matrix components of the heart and are thought to be the driving force behind myocardial matrix remodeling after infarction. Adenosine, a naturally produced nucleoside, has been shown to have cardioprotective effects and to inhibit secretion of various cytokines. The aim of our study was to determine the effect of adenosine on the secretion of MMP-9 by neutrophils. Neutrophils were isolated from healthy volunteers through Ficoll and Dextran sedimentation. Neutrophils were activated by N-formylmethionyl-leucyl-phenylalanine (fMLP) in the presence or absence of adenosine or adenosine analogs. Zymography and enzyme linked immunosorbent assay were used to measure MMP-9 secretion. Adenosine (1 micromol/L) decreased the fMLP-induced MMP-9 secretion by 30+/-2% (n=8, P<0.001). The effect was dose-dependent and was not specific to fMLP because adenosine also inhibited MMP-9 secretion by LPS- or H(2)O(2)-stimulated neutrophils. The effect of adenosine was mimicked by the adenosine A2a receptor agonist CGS21680 and was inhibited by both the A2a antagonist SCH5826 and A2a RNA silencing. The A3 agonist IB-MECA moderately decreased fMLP-induced MMP-9 secretion. Agonists and antagonists of the other types of adenosine receptors had no significant effect. Adenosine increased intracellular cAMP concentration and accelerated the return to baseline of the intracytoplasmic calcium peak. The inhibition of MMP-9 secretion by adenosine, as well as the calcium effect, was prevented by the protein kinase A inhibitor H-89. In conclusion, we show here that adenosine inhibits MMP-9 secretion by neutrophils. Our results suggest that this effect implies the A2a receptor and is mediated through the cAMP/PKA/Ca(2+) pathway. Therefore, adenosine may represent a new approach to prevent matrix degradation and remodeling after myocardial injury.