Mechanisms of the "No-Reflow" Phenomenon After Acute Myocardial Infarction: Potential Role of Pericytes

Pericytes contract during myocardial ischemia resulting in capillary constriction and no reflow. Reversing pericyte contraction pharmacologically reduces no reflow and infarct size. These findings open up an entire new venue of research aimed at altering pericyte function in myocardial ischemia and infarction.

Role of ranolazine in heart failure: From cellular to clinic perspective

Ranolazine was approved by the US Food and Drug Administration as an antianginal drug in 2006, and has been used since in certain groups of patients with stable angina. The therapeutic action of ranolazine was initially attributed to inhibitory effects on fatty acids metabolism. As investigations went on, however, it developed that the main beneficial effects of ranolazine arise from its action on the late sodium current in the heart. Since late sodium currents were discovered to be involved in various heart pathologies such as ischemia, arrhythmias, systolic and diastolic dysfunctions, and all these conditions are associated with heart failure, ranolazine has in some way been tested either directly or indirectly on heart failure in numerous experimental and clinical studies. As the heart continuously remodels following any sort of severe injury, the inhibition by ranolazine of the underlying mechanisms of cardiac remodeling including ion disturbances, oxidative stress, inflammation, apoptosis, fibrosis, metabolic dysregulation, and neurohormonal impairment are discussed, along with unresolved issues. A projection of pathologies targeted by ranolazine from cellular level to clinical is provided in this review.

Ligustrazine Attenuates Myocardial Injury Induced by Coronary Microembolization in Rats by Activating the PI3K/Akt Pathway

Background/Aims

Coronary microembolization- (CME-) induced myocardial injury and progressive cardiac dysfunction are mainly caused due to CME-induced myocardial local inflammatory response and myocardial apoptosis. Ligustrazine plays an important protective role in multiple cardiovascular diseases, but its role and the protection mechanism in CME is unclear. This study hypothesized that ligustrazine attenuates CME-induced myocardial injury in rats. This study also explored the mechanism underlying this attenuation.

Methods

Forty SD rats were randomly divided into CME group, ligustrazine group, ligustrazine+LY294002 (ligustrazine+LY) group, and sham group (ten rats in each). In each group, the cardiac function, apoptotic index, serum c-troponin I (cTnI) level, inflammation [interleukin-1β (IL-1β) and tumor necrosis factor-alpha (TNF-α)], and oxidative stress [nitric oxide (NO), superoxide dismutase (SOD), and malondialdehyde (MDA)] were determined. Western blotting was used to detect the proteins which are present in the PI3K/Akt pathway.

Results

Ligustrazine improved cardiac dysfunction induced by CME, increased serum NO and SOD activities, and decreased the serum level in IL-1β, MDA, cTnI, and TNF-α. Moreover, ligustrazine inhibited myocardial apoptosis, which is perhaps caused by the upregulated Bcl-2, the downregulated cleaved caspase-3 and Bax, and the increased protein level in endothelial nitric oxide synthase and phosphorylated Akt. These effects, however, were reduced if ligustrazine was coadministered with LY294002.

Conclusions

Ligustrazine attenuates CME-induced myocardial injury. The effects associated with this attenuation may be achieved by activating the myocardium PI3K/Akt signaling pathway.

No-reflow phenomenon in the heart and brain

The no-reflow phenomenon refers to the observation that when an organ is made ischemic by occlusion of a large artery supplying it, restoration of patency in that artery does not restore perfusion to the microvasculature supplying the parenchyma of that organ. This has been observed after prolonged arterial occlusions in the heart (30–90 min), brain, skin, and kidney. In experimental models, zones of no reflow in the heart are characterized by ultrastructural microvascular damage, including focal endothelial swelling obstructing the lumen of small vessels. Blood elements such as neutrophil plugs, platelets, and stacking of erythrocytes have also been implicated. No reflow is associated with poor healing of the myocardial infarction. In patients, no reflow is associated with a poor clinical outcome independent of infarct size, suggesting that therapy for no reflow may be an important approach to improving outcome for ST elevation myocardial infarction. No reflow occurs after reperfusion of experimental cerebral ischemia and may be observed after only 5-min episodes of ischemia. Aggregation of blood elements may play a greater role than in cardiac no reflow. No reflow in the brain may involve cortical spreading depression with disturbed local vascular control and high, vasculotonic levels of extracellular K+ concentration, postischemic swelling in endothelial cells and abutting end feet of pericytes, pericyte contraction and death, interstitial edema with collapse of cerebral capillaries, and inflammatory reaction. New guidelines suggesting that reperfusion for stroke may be considered as late as 24 h after the onset of symptoms suggest that clinicians may be seeing more no reflow in the future.

Relationship between circulating miRNA-30e and no-reflow phenomenon in STEMI patients undergoing primary coronary intervention

To investigate the relationship between miRNA-30e level in circulation and no-reflow phenomenon in patients with acute ST-segment elevation myocardial infarction (STEMI) during primary percutaneous coronary intervention (pPCI). A total of 255 consecutive patients with STEMI undergoing pPCI were enrolled in this study. These patients were divided into two groups according to the occurrence of reflow during pPCI, namely normal-reflow group with 214 cases and no-reflow group with 41 cases. The plasma levels of miRNA-30e were quantified using real-time quantitative polymerase chain reaction. The plasma levels of miRNA-30e were significantly lower in the no-reflow group as compared to the normal-reflow group (p < .05). Also, miRNA-30e was positively correlated with left ventricular ejection fraction (LVEF) and negatively correlated with hs-CRP levels (p < .05). Multivariate logistic regression analyses indicated that the plasma level of miRNA-30e (OR = 0.732, 95% CI 0.674-0.851, p = .034), hs-CRP (OR = 1.353, 95% CI 1.129-1.635, p = .012) and Killip class ≥2 at admission (OR = 1.263, 95% CI 1.023-1.532, p = .027), were independent risk factors for no-reflow during pPCI. When plasma miRNA-30e level was used as the test variable, the area under the curve was 0.914 (p < .05) by ROC curve analysis. Lower miRNA-30e levels at admission are associated with no-reflow in STEMI patients undergoing pPCI and may play an important role in the pathogenesis of no-reflow. Plasma miRNA-30e level was an independent predictor of no-reflow during pPCI in patients with STEMI. Therefore, early detection of plasma miRNA-30e level can be a preliminary assessment for risk of no-reflow during pPCI.

No-Reflow Phenomenon: Maintaining Vascular Integrity

The no-reflow phenomenon relates to the inability to reperfuse regions of the myocardium after ischemia, despite removal of the large epicardial coronary artery occlusion. The mechanism involves microvascular obstruction. In experimental studies, using markers for flow (thioflavin S, carbon black, microspheres), perfusion defects associated with no-reflow demonstrated ultrastructural evidence of localized endothelial swelling and blebs that appeared to obstruct flow. In humans no-reflow is more complicated due to the microemboli of atherosclerotic debris and thrombi generated by percutaneous coronary intervention. The no-reflow zone expands during the first few hours of reperfusion suggesting an element of reperfusion injury. In animal models, extensive no-reflow was associated with worse infarct expansion. The phenomenon of no-reflow following reperfusion therapy for myocardial infarction in humans has been demonstrated by magnetic resonance imaging, echo contrast agents, thallium, technecium-99m-labeled albumin microspheres, Thrombolysis In Myocardial Infarction (TIMI) scores, and myocardial blush grade. Patients exhibiting no-reflow following reperfusion therapy for myocardial infarction have greater left ventricular dilation and remodeling, more congestive heart failure, shock, and reduced survival. Certain vasodilators (adenosine, nitroprusside, nicorandil, and calcium blockers) are used acutely in the catheterization laboratory and appear to improve no-reflow, but systematic studies on therapy for no-reflow are needed. There is now clinical evidence that no-reflow is a strong predictor of long-term mortality that is independent of and beyond that provided by infarct size. Identifying and treating no-reflow may have important benefits including enhancing delivery of nutrients and cells required for healing and reducing infarct expansion and ventricular remodeling, which ultimately may reduce congestive heart failure and mortality.

Novel regulation of cardiac Na pump via phospholemman

As the only quantitatively significant Na efflux pathway from cardiac cells, the Na/K ATPase (Na pump) is the primary regulator of intracellular Na. The transmembrane Na gradient it establishes is essential for normal electrical excitability, numerous coupled-transport processes and, as the driving force for Na/Ca exchange, thus setting cardiac Ca load and contractility. As Na influx varies with electrical excitation, heart rate and pathology, the dynamic regulation of Na efflux is essential. It is now widely recognized that phospholemman, a 72 amino acid accessory protein which forms part of the Na pump complex, is the key nexus linking cellular signaling to pump regulation. Phospholemman is the target of a variety of post-translational modifications (including phosphorylation, palmitoylation and glutathionation) and these can dynamically alter the activity of the Na pump. This review summarizes our current understanding of the multiple regulatory mechanisms that converge on phospholemman and govern NA pump activity in the heart. The corrected Fig. 4 is reproduced below. The publisher would like to apologize for any inconvenience caused. [corrected].

Adenosine and Opioid Receptors Do Not Trigger the Cardioprotective Effect of Mild Hypothermia

Mild hypothermia (32°C-34°C) exerts a potent cardioprotection in animal models of myocardial infarction. Recently, it has been proposed that this beneficial effect is related to survival signaling. We, therefore, hypothesized that the well-known cardioprotective pathways dependent on adenosine and/or opioid receptors could be the trigger of hypothermia-induced salvage. Open-chest rabbits were accordingly exposed to 30 minutes of coronary artery occlusion (CAO) under normothermic (NT) or hypothermic ([HT] 32°C) conditions. In the latter, hypothermia was induced by total liquid ventilation with temperature-controlled perfluorocarbons in order to effect ultrafast cooling and to accurately control cardiac temperature. After 4 hours of reperfusion, infarct and no-reflow zone sizes were assessed and quantified as a percentage of the risk zone. In animals experiencing HT ischemia, the infarct size was dramatically reduced as compared to NT animals (9% ± 3% vs 55% ± 2% of the risk zone, respectively). Importantly, administration of opioid and adenosine receptor antagonists (naloxone [6 mg/kg iv] and 8-( p-sulfophenyl) theophylline [20 mg/kg iv], respectively) did not alter the infarct size or affect the cardioprotective effect of hypothermia. Doses of these 2 antagonists were appropriately chosen since they blunted infarct size reduction induced by selective opioid or adenosine receptor stimulation with morphine (0.3 mg/kg iv) or N6-cyclopentyladenosine ([CPA] 100 μg/kg iv), respectively. Therefore, the cardioprotective effect of mild hypothermia is not triggered by either opioid or adenosine receptor activation, suggesting the involvement of other cardioprotective pathways.

Antifibrillatory effect of ranolazine during severe coronary stenosis in the intact porcine model

BACKGROUND

Clinical evidence suggests that the antianginal agent ranolazine has antiarrhythmic properties, but its effects on vulnerability to ventricular fibrillation (VF) and T-wave alternans (TWA) during coronary artery stenosis have not been measured.

OBJECTIVE

We investigated whether the antiarrhythmic effect of ranolazine during acute coronary stenosis could be quantified by measuring VF threshold and TWA magnitude.

METHODS

Electrode catheters placed in the left ventricular apex were used to determine VF threshold during ventricular pacing at 130 beats/min, and TWA was quantified from epicardial electrograms using modified moving average method (N = 18). Left anterior descending coronary flow was reduced with a balloon occluder by 75% for 10 minutes. The I(Kr) blocker E-4031 was used to distinguish effects of late I(Na) and I(Kr) inhibition by ranolazine.

RESULTS

Before stenosis, ranolazine and E-4031 increased VF threshold from 32 ± 4 mA to 46 ± 4 mA (mean ± SEM), P = .02, and from 33 ± 5 mA to 40 ± 9 mA, P = .02, respectively. During stenosis, ranolazine increased VF threshold from 19 ± 2 mA to 33 ± 3 mA (P = .02), whereas E-4031 decreased VF threshold from 21 ± 3 mA to 15 ± 3 mA (P = .02). The ischemia-induced increase in TWA was suppressed by ranolazine but not by E-4031, consistent with effects of these agents on VF threshold.

CONCLUSION

Ranolazine exerts significant antifibrillatory effects during coronary stenosis through direct effects on cardiac electrical properties independent of coronary flow. Ranolazine's antifibrillatory action during myocardial ischemia does not appear to be mediated by blockade of I(Kr) but rather by inhibition of late I(Na). TWA changes paralleled vulnerability to VF as indicated by VF threshold testing.

Ranolazine, an antianginal agent, markedly reduces ventricular arrhythmias induced by ischemia and ischemia-reperfusion

We tested the effect of the antianginal agent ranolazine on ventricular arrhythmias in an ischemic model using two protocols. In protocol 1, anesthetized rats received either vehicle or ranolazine (10 mg/kg, iv bolus) and were subjected to 5 min of left coronary artery (LCA) occlusion and 5 min of reperfusion with electrocardiogram and blood pressure monitoring. In p rotocol 2, rats received either vehicle or three doses of ranolazine (iv bolus followed by infusion) and 20 min of LCA occlusion. With protocol 1, ventricular tachycardia (VT) occurred in 9/12 (75%) vehicle-treated rats and 1/11 (9%) ranolazine-treated rats during reperfusion ( P = 0.003). Sustained VT occurred in 5/12 (42%) vehicle-treated but 0/11 in ranolazine-treated rats ( P = 0.037). The median number of episodes of VT during reperfusion in vehicle and ranolazine groups was 5.5 and 0, respectively ( P = 0.0006); median duration of VT was 22.2 and 0 s in vehicle and ranolazine rats, respectively ( P = 0.0006). With p rotocol 2, mortality in the vehicle group was 42 vs. 17% ( P = 0.371), 10% ( P = 0.162) and 0% ( P = 0.0373) with ranolazine at plasma concentrations of 2, 4, and 8 μM, respectively. Ranolazine significantly reduced the incidence of ventricular fibrillation [67% in controls vs. 42% ( P = 0.414), 30% ( P = 0.198) and 8% ( P = 0.0094) in ranolazine at 2, 4, and 8 μM, respectively]. Median number (2.5 vs. 0; P = 0.0431) of sustained VT episodes, incidence of sustained VT (83 vs. 33%, P = 0.0361), and the duration of VT per animal (159 vs. 19 s; P = 0.0410) were also significantly reduced by ranolazine at 8 μM. Ranolazine markedly reduced ischemia-reperfusion induced ventricular arrhythmias. Ranolazine demonstrated promising anti-arrhythmic properties that warrant further investigation.

Nonanticoagulant heparin reduces myocyte Na+ and Ca2+ loading during simulated ischemia and decreases reperfusion injury

Heparin desulfated at the 2-O and 3-O positions (ODSH) decreases canine myocardial reperfusion injury. We hypothesized that this occurs from effects on ion channels rather than solely from anti-inflammatory activities, as previously proposed. We studied closed-chest pigs with balloon left anterior descending coronary artery occlusion (75-min) and reperfusion (3-h). ODSH effects on [Na(+)](i) (Na Green) and [Ca(2+)](i) (Fluo-3) were measured by flow cytometry in rabbit ventricular myocytes after 45-min of simulated ischemia [metabolic inhibition with 2 mM cyanide, 0 glucose, 37 degrees C, pacing at 0.5 Hz; i.e., pacing-metabolic inhibition (PMI)]. Na(+)/Ca(2+) exchange (NCX) activity and Na(+) channel function were assessed by voltage clamping. ODSH (15 mg/kg) 5 min before reperfusion significantly decreased myocardial necrosis, but neutrophil influx into reperfused myocardium was not consistently reduced. ODSH (100 microg/ml) reduced [Na(+)](i) and [Ca(2+)](i) during PMI. The NCX inhibitor KB-R7943 (10 microM) or the late Na(+) current (I(Na-L)) inhibitor ranolazine (10 microM) reduced [Ca(2+)](i) during PMI and prevented effects of ODSH on Ca(2+) loading. ODSH also reduced the increase in Na(+) loading in paced myocytes caused by 10 nM sea anemone toxin II, a selective activator of I(Na-L). ODSH directly stimulated NCX and reduced I(Na-L). These results suggest that in the intact heart ODSH reduces Na(+) influx during early reperfusion, when I(Na-L) is activated by a burst of reactive oxygen production. This reduces Na(+) overload and thus Ca(2+) influx via NCX. Stimulation of Ca(2+) extrusion via NCX later after reperfusion may also reduce myocyte Ca(2+) loading and decrease infarct size.

Phospholemman: its role in normal cardiac physiology and potential as a druggable target in disease

Phospholemman (PLM) is a member of the FXYD ('fix-it') family of proteins many of which have now been identified as tissue-specific regulators of the Na/K ATPase. PLM (FXYD1) is the primary sarcolemmal substrate for PKC and PKA in the heart. We have recently identified PLM as a novel accessory protein that forms part of the cardiac Na/K ATPase pump complex. PLM regulates Na/K pump activity in a way analogous to the regulation of SERCA by phospholamban-that is un-phosphorylated PLM exerts a tonic inhibition on the Na/K pump, while phosphorylated PLM relieves this inhibition and stimulates pump activity. This process is likely to be fundamentally important in the normal physiological regulation of the cell particularly at high heart rates and, as briefly reviewed in this article, is also likely to offer novel therapeutic targets for the treatment of diseases such as cardiac hypertrophy and heart failure.