Myocardial remodeling: cellular and extracellular events and targets.

The focus of this review is on translational studies utilizing large-animal models and clinical studies that provide fundamental insight into cellular and extracellular pathways contributing to post-myocardial infarction (MI) left ventricle (LV) remodeling. Specifically, both large-animal and clinical studies have examined the potential role of endogenous and exogenous stem cells to alter the course of LV remodeling. Interestingly, there have been alterations in LV remodeling with stem cell treatment despite a lack of long-term cell engraftment. The translation of the full potential of stem cell treatments to clinical studies has yet to be realized. The modulation of proteolytic pathways that contribute to the post-MI remodeling process has also been examined. On the basis of recent large-animal studies, there appears to be a relationship between stem cell treatment post-MI and the modification of proteolytic pathways, generating the hypothesis that stem cells leave an echo effect that moderates LV remodeling.

Targeted regional injection of biocomposite microspheres alters post-myocardial infarction remodeling and matrix proteolytic pathways.

BACKGROUND: Although localized delivery of biocomposite materials, such as calcium hydroxyapatite (CHAM), have been demonstrated to potentially attenuate adverse left ventricular (LV) remodeling after myocardial infarction (MI), the underlying biological mechanisms for this effect remain unclear. This study tested the hypothesis that targeted CHAM injections would alter proteolytic pathways (matrix metalloproteinases [MMPs] and tissue inhibitors of MMPs [TIMPs]) and would be associated with parameters of post-MI LV remodeling. METHODS AND RESULTS: MI was induced in adult sheep followed by 20 targeted injections of a total volume of 1.3 mL (n=6) or 2.6 mL of CHAM (n=5) or saline (n=13) and LV end-diastolic volume (EDV) and MMP/TIMP profiles in the MI region were measured at 8 weeks after MI. LV EDV decreased with 2.6 mL CHAM versus MI only (105.4 ± 7.5 versus 80.6 ± 4.2 respectively, P<0.05) but not with 1.3 mL CHAM (94.5 ± 5.0, P=0.32). However, MI thickness increased by 2-fold in both CHAM groups compared with MI only (P<0.05). MMP-13 increased 40-fold in the MI only group (P<0.05) but fell by >6-fold in both CHAM groups (P<0.05). MMP-7 increased approximately 1.5-fold in the MI only group (P<0.05) but decreased to referent control values in both CHAM groups in the MI region (P<0.05). Collagen content was reduced by approximately 30% in the CHAM groups compared with MI only (P<0.05). CONCLUSIONS: Differential effects on LV remodeling and MMP/TIMP profiles occurred with CHAM. Thus, targeted injection of a biocomposite material can favorably affect the post-MI remodeling process and therefore holds promise as a treatment strategy in and of itself, or as a matrix with potentially synergistic effects with localized pharmacological or cellular therapies.

Continuous localized monitoring of plasmin activity identifies differential and regional effects of the serine protease inhibitor aprotinin: relevance to antifibrinolytic therapy.

BACKGROUND: Antifibrinolytic therapy, such as the use of the serine protease inhibitor aprotinin, was a mainstay for hemostasis after cardiac surgery. However, aprotinin was empirically dosed, and although the pharmacological target was the inhibition of plasmin activity (PLact), this was never monitored, off-target effects occurred, and led to withdrawn from clinical use. The present study developed a validated fluorogenic microdialysis method to continuously measure PLact and tested the hypothesis that standardized clinical empirical aprotinin dosing would impart differential and regional effects on PLact. METHODS/RESULTS: Pigs (30 kg) were instrumented with microdialysis probes to continuously measure PLact in myocardial, kidney, and skeletal muscle compartments (deltoid) and then randomized to high-dose aprotinin administration (2 mKIU load/0.5 mKIU/hr infusion; n = 7), low-dose aprotinin administration (1 mKIU load/0.250 mKIU/hr infusion; n = 6). PLact was compared with time-matched vehicle (n = 4), and PLact was also measured in plasma by an in vitro fluorogenic method. Aprotinin suppressed PLact in the myocardium and kidney at both high and low doses, indicative that both doses exceeded a minimal concentration necessary for PLact inhibition. However, differential effects of aprotinin on PLact were observed in the skeletal muscle, indicative of different compartmentalization of aprotinin. CONCLUSIONS: Using a large animal model and a continuous method to monitor regional PLact, these unique results demonstrated that an empirical aprotinin dosing protocol causes maximal and rapid suppression in the myocardium and kidney and in turn would likely increase the probability of off-target effects and adverse events. Furthermore, this proof of principle study demonstrated that continuous monitoring of determinants of fibrinolysis might provide a novel approach for managing fibrinolytic therapy.

Mesenchymal cell transplantation and myocardial remodeling after myocardial infarction.

BACKGROUND: Targeted delivery of mesenchymal precursor cells (MPCs) can modify left ventricular (LV) cellular and extracellular remodeling after myocardial infarction (MI). However, whether and to what degree LV remodeling may be affected by MPC injection post-MI, and whether these effects are concentration-dependent, remain unknown. METHODS AND RESULTS: Allogeneic MPCs were expanded from sheep bone marrow, and direct intramyocardial injection was performed within the borderzone region 1 hour after MI induction (coronary ligation) in sheep at the following concentrations: 25x10(6) (25 M, n=7), 75x10(6) (75 M, n=7), 225x10(6) (225 M, n=10), 450x10(6) (450 M, n=8), and MPC free media only (MI Only, n=14). LV end diastolic volume increased in all groups but was attenuated in the 25 and 75 M groups. Collagen content within the borderzone region was increased in the MI Only, 225, and 450 M groups, whereas plasma ICTP, an index of collagen degradation, was highest in the 25 M group. Within the borderzone region matrix metalloproteinases (MMPs) and MMP tissue inhibitors (TIMPs) also changed in a MPC concentration-dependent manner. For example, borderzone levels of MMP-9 were highest in the 25 M group when compared to the MI Only and other MPC treatment group values. CONCLUSIONS: MPC injection altered collagen dynamics, MMP, and TIMP levels in a concentration-dependent manner, and thereby influenced indices of post-MI LV remodeling. However, the greatest effects with respect to post-MI remodeling were identified at lower MPC concentrations, thus suggesting a therapeutic threshold exists for this particular cell therapy.

Heterogeneity in MT1-MMP activity with ischemia-reperfusion and previous myocardial infarction: relation to regional myocardial function.

After a myocardial infarction (MI), an episode of ischemia-reperfusion (I/R) can result in a greater impairment of left ventricular (LV) regional function (LVRF) than that caused by an initial I/R episode in the absence of MI. Membrane type-I matrix metalloproteinase (MT1-MMP) proteolytically processes the myocardial matrix and is upregulated in LV failure. This study tested the central hypothesis that a differential induction of MT1-MMP occurs and is related to LVRF after I/R in the context of a previous MI. Pigs with a previous MI [3 wk postligation of the left circumflex artery (LCx)] or no MI were randomized to undergo I/R [60-min/120-min left anterior descending coronary artery (LAD) occlusion] or no I/R as follows: no MI and no I/R (n = 6), no MI and I/R (n = 8), MI and no I/R (n = 8), and MI and I/R (n = 8). Baseline LVRF (regional stroke work, sonomicrometry) was lower in the LAD region in the MI group compared with no MI (103 ± 12 vs. 188 ± 26 mmHg·mm, P < 0.05) and remained lower with peak ischemia (35 ± 8 vs. 88 ± 17 mmHg·mm, P < 0.05). Using a novel interstitial microdialysis method, MT1-MMP was directly measured and was over threefold higher in the LCx region and over twofold higher in the LAD region in the MI group compared with the no MI group at baseline. MT1-MMP fluorogenic activity was persistently elevated in the LCx region in the MI and I/R group but remained unchanged in the LAD region. In contrast, no changes in MT1-MMP occurred in the LCx region in the no MI and I/R group but increased in the LAD region. MT1-MMP mRNA was increased by over threefold in the MI region in the MI and I/R group. In conclusion, these findings demonstrate that a heterogeneous response in MT1-MMP activity likely contributes to regional dysfunction with I/R and that a subsequent episode of I/R activates a proteolytic cascade within the MI region that may contribute to a continued adverse remodeling process.

Temporally and regionally disparate differences in plasmin activity by tranexamic acid.

BACKGROUND: A major complication associated with cardiac surgery is excessive and prolonged bleeding in the perioperative period. Improving coagulation by inhibiting fibrinolysis, primarily through inhibition of plasmin activity (PLact) with antifibrinolytics such as tranexamic acid (TXA), has been a pharmacological mainstay in cardiac surgical patients. Despite its almost ubiquitous use, the temporal and regional modulation of PLact profiles by TXA remains unexplored. Accordingly, we developed a fluorogenic-microdialysis system to measure in vivo dynamic changes in PLact after TXA administration in a large animal model. METHODS: Pigs (25-35 kg) were randomly assigned to receive TXA (30 mg/kg, diluted into 50 mL normal saline; n = 9) or vehicle (50 mL normal saline; n = 7). Microdialysis probes were placed in the liver, myocardium, kidney, and quadriceps muscle compartments. The microdialysate infusion contained a validated plasmin-specific fluorogenic peptide. The fluorescence emission (standard fluorogenic units [SFU]) of the interstitial fluid collected from the microdialysis probes, which directly reflects PLact, was determined at steady-state baseline and 30, 60, 90, and 120 min after TXA/vehicle infusion. Plasma PLact was determined at the same time points using the same fluorogenic substrate approach. RESULTS: TXA reduced plasma PLact at 30 min after infusion by >110 SFU compared with vehicle values (P < 0.05). Specifically, there was a decrease in liver PLact at 90 and 120 min after TXA infusion of >150 SFU (P < 0.05) and 175 SFU (P < 0.05), respectively. The decrease in liver PLact occurred 60 min after the maximal decrease in plasma PLact. In contrast, kidney, heart, and quadriceps PLact transiently increased followed by an overall decrease at 120 min. CONCLUSIONS: Using a large animal model and in vivo microdialysis measurements of PLact, the unique findings from this study were 2-fold. First, TXA induced temporally distinct PLact profiles within the plasma and selected interstitial compartments. Second, TXA caused region-specific changes in PLact profiles. These temporal and regional differences in the effects of TXA may have important therapeutic considerations when managing fibrinolysis in the perioperative period.

Management of common bile duct injury during partial gastrectomy.

Injury to the common bile duct (CBD) during upper gastrointestinal surgery for peptic ulcer disease is a serious complication with an underestimated prevalence in light of the few cases reported in the surgical literature. Three cases of CBD injury were referred to a multidisciplinary specialized gastrointestinal unit for management over a 4-year period. Anomalous anatomy, adhesions, and potential duodenal shortening secondary to contracture all predispose the biliary ducts to intraoperative injury. The axial nature of the blood supply to the extrahepatic ducts and the tendency of bile itself to cause rapid collagen turnover and fibrosis, combined with the inflammation and subsequent fibrosis to the surrounding tissues caused by bile leakage, give the bile ducts a high propensity for stricture formation. Frequently presenting symptoms of CBD injury immediately after surgery include jaundice, elevated bilirubin values, elevated t-tube drainage, and symptoms of sepsis. The most common complaints noted in patients who present in a delayed manner are symptoms of cholangitis. Even when injuries are rapidly identified and corrected, the potential for lasting negative impact on quality of life is great in many cases. When CBD injury occurs, the pancreatic duodenal union can be concomitantly disrupted.

Influence of salinity and fish species on PAH uptake from dispersed crude oil.

The use of chemical oil dispersants to minimize spill impacts causes a transient increase in hydrocarbon concentrations in water, which increases the risk to aquatic species if toxic components become more bioavailable. The risk of effects depends on the extent to which dispersants enhance the exposure to toxic components, such as polycyclic aromatic hydrocarbons (PAH). Increased salinities can reduce the solubility of PAH and the efficiency of oil dispersants. This study measured changes in the induction of CYP1A enzymes of fish to demonstrate the effect of salinity on PAH availability. Freshwater rainbow trout and euryhaline mummichog were exposed to water accommodated fractions (WAF), and chemically-enhanced water accommodated fractions (CEWAF) at 0 per thousand, 15 per thousand, and 30 per thousand salinity. For both species, PAH exposure decreased as salinity increased whereas dispersant effectiveness decreased only at the highest salinity. Hence, risks to fish of PAH from dispersed oil will be greatest in coastal waters where salinities are low.

Pyloric stenosis after gastroschisis closure.

Hypertrophic pyloric stenosis is a very common surgical problem in infants. It occurs most often in otherwise well babies with normal gestation and birth history. Rarely, pyloric stenosis has been described in babies with history of prior abdominal surgery. Below we discuss the management of hypertrophic pyloric stenosis in a child who remained hospitalized, recovering from repair of a congenital abdominal wall defect.

Progressive induction of left ventricular pressure overload in a large animal model elicits myocardial remodeling and a unique matrix signature.

OBJECTIVE: Patients with severe left ventricular pressure overload secondary to aortic stenosis can present with signs and symptoms of heart failure despite normal left ventricular ejection fraction. This process occurs, at least in part, as a result of left ventricular pressure overload-induced extracellular matrix remodeling that promulgates increased left ventricular stiffness and impaired diastolic function. However, the determinants that drive extracellular matrix remodeling in this form of left ventricular pressure overload remain to be fully defined. METHODS: Left ventricular pressure overload was induced in mature pigs (n = 15) by progressive ascending aortic cuff inflation (once per week for 4 weeks), whereby left ventricular mass, left ventricular ejection fraction, and regional myocardial stiffness (rK(m)) were compared with referent controls (n = 12). Determinants of extracellular matrix remodeling were assessed by measuring levels of mRNA expression for fibrillar collagens, matrix metalloproteinases, and tissue inhibitors of matrix metalloproteinase 1 and 4. RESULTS: With left ventricular pressure overload, left ventricular mass and rK(m) increased by 2- and 3-fold, respectively, compared with control, with no change in left ventricular ejection fraction. Left ventricular myocardial collagen increased approximately 2-fold, which was accompanied by reduced solubility (ie, increased cross-linking) with left ventricular pressure overload, but mRNA expression for fibrillar collagen and matrix metalloproteinases remained relatively unchanged. In contrast, a robust increase in mRNA expression for tissue inhibitors of matrix metalloproteinase-1 and 4 occurred with left ventricular pressure overload. CONCLUSIONS: In a progressive model of left ventricular pressure overload, which recapitulates the phenotype of aortic stenosis, increased extracellular matrix accumulation and subsequently increased myocardial stiffness were not due to increased fibrillar collagen expression but rather to determinants of post-translational control that included increased collagen stability (thereby resistant to matrix metalloproteinase degradation) and increased endogenous matrix metalloproteinase inhibition. Targeting these extracellular matrix post-translational events with left ventricular pressure overload may hold both diagnostic and therapeutic relevance.

Hemodynamics and myocardial blood flow patterns after placement of a cardiac passive restraint device in a model of dilated cardiomyopathy.

BACKGROUND: The present study examined a cardiac passive restraint device which applies epicardial pressure (HeartNet Implant; Paracor Medical, Inc, Sunnyvale, Calif) in a clinically relevant model of dilated cardiomyopathy to determine effects on hemodynamic and myocardial blood flow patterns. METHODS: Dilated cardiomyopatht was established in 10 pigs (3 weeks of atrial pacing, 240 beats/min). Hemodynamic parameters and regional left ventricular blood flow were measured under baseline conditions and after acute placement of the HeartNet Implant. Measurements were repeated after adenosine infusion, allowing maximal coronary vasodilation and coronary flow reserve to be determined. RESULTS: Left ventricular dilation and systolic dysfunction occurred relative to baseline as measured by echocardiography. Left ventricular end-diastolic dimension increased and left ventricular fractional shortening decreased (3.8 ± 0.1 vs 6.1 ± 0.2 cm and 31.6% ± 0.5% vs 16.2% ± 2.1%, both P < .05, respectively), consistent with the dilated cardiomyopathy phenotype. The HeartNet Implant was successfully deployed without arrhythmias and a computed median mid-left ventricular epicardial pressure of 1.4 mm Hg was applied by the HeartNet Implant throughout the cardiac cycle. Acute HeartNet placement did not adversely affect steady state hemodynamics. With the HeartNet Implant in place, coronary reserve was significantly blunted. CONCLUSIONS: In a large animal model of dilated cardiomyopathy, the cardiac passive restraint device did not appear to adversely affect basal resting myocardial blood flow. However, after acute HeartNet Implant placement, left ventricular maximal coronary reserve was blunted. These unique results suggest that cardiac passive restraint devices that apply epicardial transmural pressure can alter myocardial blood flow patterns in a model of dilated cardiomyopathy. Whether this blunting of coronary reserve holds clinical relevance with chronic passive restraint device placement remains unestablished.

Pathophysiology of myocardial injury and remodeling: implications for molecular imaging.

Despite advances in reperfusion therapy, acute coronary syndromes can still result in myocardial injury and subsequent myocardial infarction (MI). Molecular, cellular, and interstitial events antecedent to the acute MI culminate in deleterious changes in the size, shape, and function of the left ventricle (LV), collectively termed LV remodeling. Three distinct anatomic and physiologic LV regions can be described after MI: the infarct, border zone, and remote regions. Given the complexity of post-MI remodeling, imaging modalities must be equally diverse to elucidate this process. The focus of this review will first be on cardiovascular MRI of the anatomic and pathophysiologic LV regions of greatest interest with regard to the natural history of the post-MI remodeling process. This review will then examine imaging modalities that provide translational and molecular insight into burgeoning treatment fields for the attenuation of post-MI remodeling, such as cardiac restraint devices and stem cell therapy.

Interstitial plasmin activity with epsilon aminocaproic acid: temporal and regional heterogeneity.

BACKGROUND: Epsilon aminocaproic acid (EACA) is used in cardiac surgery to modulate plasmin activity (PLact). The present study developed a fluorogenic-microdialysis system to measure in vivo region specific temporal changes in PLact after EACA administration. METHODS: Pigs (25 to 35 kg) received EACA (75 mg/kg, n = 7) or saline in which microdialysis probes were placed in the liver, myocardium, kidney, and quadricep muscle. The microdialysate contained a plasmin-specific fluorogenic peptide and fluorescence emission, which directly reflected PLact, determined at baseline, 30, 60, 90, and 120 minutes after EACA/vehicle infusion. RESULTS: Epsilon aminocaproic acid caused significant decreases in liver and quadricep PLact at 60, 90, 120 minutes, and at 30, 60, and 120 minutes, respectively (p < 0.05). In contrast, EACA induced significant biphasic changes in heart and kidney PLact profiles with initial increases followed by decreases at 90 and 120 minutes (p < 0.05). The peak EACA interstitial concentrations for all compartments occurred at 30 minutes after infusion, and were fivefold higher in the renal compartment and fourfold higher in the myocardium, when compared with the liver or muscle (p < 0.05). CONCLUSIONS: Using a large animal model and in vivo microdialysis measurements of plasmin activity, the unique findings from this study were twofold. First, EACA induced temporally distinct plasmin activity profiles within the plasma and interstitial compartments. Second, EACA caused region-specific changes in plasmin activity profiles. These temporal and regional heterogeneic effects of EACA may have important therapeutic considerations when managing fibrinolysis in the perioperative period.

Large animal models of heart failure: a critical link in the translation of basic science to clinical practice.

Congestive heart failure (HF) is a clinical syndrome, with hallmarks of fatigue and dyspnea, that continues to be highly prevalent and morbid. Because of the growing burden of HF as the population ages, the need to develop new pharmacological treatments and therapeutic interventions is of paramount importance. Common pathophysiologic features of HF include changes in left ventricle structure, function, and neurohormonal activation. The recapitulation of the HF phenotype in large animal models can allow for the translation of basic science discoveries into clinical therapies. Models of myocardial infarction/ischemia, ischemic cardiomyopathy, ventricular pressure and volume overload, and pacing-induced dilated cardiomyopathy have been created in dogs, pigs, and sheep for the investigation of HF and potential therapies. Large animal models recapitulating the clinical HF phenotype and translating basic science to clinical applications have successfully traveled the journey from bench to bedside. Undoubtedly, large animal models of HF will continue to play a crucial role in the elucidation of biological pathways involved in HF and the development and refinement of HF therapies.