Thrombin and its receptor enhance ST-segment elevation in acute myocardial infarction by activating the KATP channel

Guidelines for in vivo mouse models of myocardial infarction

Despite significant improvements in reperfusion strategies, acute coronary syndromes all too often culminate in a myocardial infarction (MI). The consequent MI can, in turn, lead to remodeling of the left ventricle (LV), the development of LV dysfunction, and ultimately progression to heart failure (HF). Accordingly, an improved understanding of the underlying mechanisms of MI remodeling and progression to HF is necessary. One common approach to examine MI pathology is with murine models that recapitulate components of the clinical context of acute coronary syndrome and subsequent MI. We evaluated the different approaches used to produce MI in mouse models and identified opportunities to consolidate methods, recognizing that reperfused and nonreperfused MI yield different responses. The overall goal in compiling this consensus statement is to unify best practices regarding mouse MI models to improve interpretation and allow comparative examination across studies and laboratories. These guidelines will help to establish rigor and reproducibility and provide increased potential for clinical translation.

Detection of Acute Myocardial Infarction in a Pig Model Using the SAN-Atrial-AVN-His (SAAH) Electrocardiogram (ECG), Model PHS-A10, an Automated and Integrated Signals Recognition System

BACKGROUND The aim of this study was to compare the use of the standard 12-lead electrocardiogram (ECG) with the SAN-Atrial-AVN-His (SAAH) ECG (Model PHS-A10), a new automated and integrated signals recognition system that detects micro-waveforms within the P, QRS, and T-wave, in a pig model of acute myocardial infarction (MI). MATERIAL AND METHODS Six medium-sized domestic Chinese pigs underwent general anesthesia, and an angioplasty balloon was placed and dilated for 120 minutes in the first diagonal coronary artery arising from the left anterior descending (LAD) coronary artery. A standard ECG and a SAAH ECG (Model PHS-A10) were used to evaluate: 1) the number of wavelets in ST-T segment in lead V5; 2) the duration of the repolarization initial (Ri), or duration of the wavelets starting from the J-point to the endpoint of the wavelets in the ST interval; 3) the duration of the repolarization terminal (Rt), of the wavelets, starting from the endpoint of the wavelets in the ST interval to the cross-point of the T-wave and baseline; 4) the ratio Ri: Rt. RESULTS Following coronary artery occlusion, duration of Ri and Ri/Rt increased, and Rt decreased, which was detected by the SAAH ECG (Model PHS-A10) within 12 seconds, compared with standard ECG that detected ST segment depression at 24 seconds following coronary artery occlusion. CONCLUSIONS The findings from this preliminary study in a pig model of acute MI support the need for clinical studies to evaluate the SAAH ECG (Model PHS-A10) for the early detection of acute MI.

Lipid signaling to membrane proteins: From second messengers to membrane domains and adapter-free endocytosis

Hilgemann et al. explain how lipid signaling to membrane proteins involves a hierarchy of mechanisms from lipid binding to membrane domain coalescence.

Lipids influence powerfully the function of ion channels and transporters in two well-documented ways. A few lipids act as bona fide second messengers by binding to specific sites that control channel and transporter gating. Other lipids act nonspecifically by modifying the physical environment of channels and transporters, in particular the protein–membrane interface. In this short review, we first consider lipid signaling from this traditional viewpoint, highlighting innumerable Journal of General Physiology publications that have contributed to our present understanding. We then switch to our own emerging view that much important lipid signaling occurs via the formation of membrane domains that influence the function of channels and transporters within them, promote selected protein–protein interactions, and control the turnover of surface membrane.

Effects of thrombin and thrombin receptor activation on cardiac function after acute myocardial infarction

Thrombin and thrombin receptor activation impact cardiomyocyte contraction and ventricular remodeling. However, there is some controversy regarding their effects in cardiac function, especially in cardiac dysfunction after acute myocardial infarction (AMI). A rat AMI model was created by left coronary artery ligation (LCA). Cardiac functional parameters, including the maximum left ventricular (LV) systolic pressure (LVSPmax), LV end-diastolic pressure (LVEDP), and the rise and fall rates in LV pressure (dp/dt max and dp/dt min, respectively), were measured. Hirudin decreased cardiac function within 120 minutes after AMI, whereas treatment with thrombin receptor-activating peptide (TRAP) reversed this hirudin-induced decrease in cardiac function. The mRNA and protein expression levels of inositol 1,4,5-trisphosphate receptor (IP3R) subtypes in infarct area tissues were analyzed by reverse transcription-polymerase chain reaction and immunoreaction. Hirudin decreased the expression levels of IP3R-1, -2, and -3 in the infarct area for up to 40 minutes after AMI, whereas TRAP treatment reversed these hirudin-induced effects. Treatment with the IP3R antagonist 2-aminoethoxydiphenyl borate (2.5 mg/kg) eliminated the effect of TRAP on the hirudin-induced decrease in cardiac function after AMI. Finally, TRAP increased the maximum binding capacity of the three IP3R subtypes, but only enhanced the affinity of IP3R-2. Thrombin and thrombin receptor activation improved cardiac function after AMI by an IP3R-mediated pathway, probably through the IP3R-2 subtype.

Early repolarization increases the occurrence of sustained ventricular tachyarrhythmias and sudden death in the chronic phase of an acute myocardial infarction

BACKGROUND

We recently showed that the presence of early repolarization (ER) increases the risk of ventricular fibrillation occurrences in the early phase of acute myocardial infarction (AMI). This study aimed to clarify whether an association exists between ER and occurrences of ventricular tachyarrhythmias or sudden death in the chronic phase of AMI.

METHODS AND RESULTS

This study retrospectively enrolled 1131 patients (67±12 years; 862 men) with AMIs surviving 14 days post-AMI. The primary end point was the occurrence of sustained ventricular tachyarrhythmias or sudden death >14 days after the AMI onset. We evaluated the presence of ER from the predischarge ECG (mean 10±3 days post-AMI). ER was defined as an elevation of the terminal portion of the QRS complex of >0.1 mV in inferior or lateral leads. After a median follow-up of 26.2 months, 26 patients had an episode of ventricular tachyarrhythmias or sudden death. A multivariable Cox regression analysis revealed the presence of ER (hazard ratio, 5.37; 95% confidence interval, 2.27-12.69; P<0.001), Killip class on admission of >I (hazard ratio, 2.75; 95% confidence interval, 1.24-6.07; P=0.013), and a left ventricular ejection fraction of <35% (hazard ratio, 11.83; 95% confidence interval, 5.16-27.13; P<0.001) were significantly associated with event occurrences. As features of the ER pattern, ER in the inferior leads, high-amplitude ER, a notched morphology, and ER without ST-segment elevation were associated with an increased risk of event occurrences.

CONCLUSIONS

ER observed at a mean of 10 days post-AMI may be a marker for a subsequent risk of ventricular tachyarrhythmias or sudden death.

Potent cardioprotection from ischemia-reperfusion injury by a two-domain fusion protein comprising annexin V and Kunitz protease inhibitor

BACKGROUND

Considerable evidence suggests that coagulation proteases (tissue factor [TF]/activated factor VII [FVIIa]/FXa/thrombin) and their target protease activated receptors (PAR-1/PAR-2) play important roles in myocardial ischemia-reperfusion (I-R) injury. We hypothesized that localized inhibition of TF/FVIIa on the membrane surfaces of ischemic cells could effectively block coagulation cascade and subsequent PAR-1/PAR-2 cell signaling, thereby protecting the myocardium from I-R injury.

OBJECTIVES

We recently developed an annexin V-Kunitz inhibitor fusion protein (ANV-6L15) that could specifically bind to anionic phospholipids on the membrane surfaces of apoptotic cells and efficiently inhibit the membrane-anchored TF/FVIIa. In this study, we investigated the cardioprotective effect of ANV-6L15 in a rat cardiac I-R model in comparison with that of hirudin.

METHODS

Left coronary artery occlusion was maintained for 45 min followed by 4 h of reperfusion in anesthetized Sprague-Dawley rats. One minute before or 2 min after coronary ligation, rats received an intravenous bolus injection of ANV-6L15 (2.5-250 μg kg(-1) ), vehicle, or hirudin via bolus injection and continuous infusion.

RESULTS AND CONCLUSIONS

ANV-6L15 dose-dependently reduced infarct size by up to 87% and decreased plasma levels of cardiac troponin I, tumor necrosis factor-α, and soluble intercellular adhesion molecule-1, by up to 97%, 96%, and 66%, respectively, with little impact on the coagulation parameters. ANV-6L15 also ameliorated hemodynamic derangements, attenuated neutrophil infiltration and reduced Terminal deoxynucleotidyl transferase dUTP nick end labeling-positive apoptotic cardiomyocytes. Hirudin was less efficacious even at supraclinical dose. ANV-6L15 confers exceptionally potent cardioprotection and is a promising drug candidate for the prevention of myocardial I-R injury.