Dipyridamole with low-dose aspirin augments the infarct size-limiting effects of simvastatin

Why Not Dipyridamole: a Review of Current Guidelines and Re-evaluation of Utility in the Modern Era

Dipyridamole is an old anti-platelet and coronary vasodilator agent that inhibits platelet phosphodiesterase and increases interstitial adenosine levels. Its use in coronary artery disease (CAD) has fallen out of practice in the modern era with the advent of new anti-platelet agents, and most modern guidelines on the management of CAD either neglect to comment on its utility or outright recommend against it. The majority of the studies used in these guidelines are outdated and took place in an era when high doses of aspirin were used and statins were not widely utilized. There is growing evidence in rat models of dipyridamole's synergy with statins through adenosine modulation resulting in significant myocardial protection against ischemia-reperfusion injury and limitation of infract size. The data in human studies are limited but show a similar potential synergy between dipyridamole and statins. It would thus be prudent to reconsider the recommendations against the use of dipyridamole in CAD and to re-evaluate its possible role and potential benefits through well-designed randomized trials combining it with statins, low-dose aspirin, and/or other anti-platelet agents.

Effects of atorvastatin on sevoflurane postconditioning in in vivo rabbit hearts

OBJECTIVES

Myocardial ischemia-reperfusion injury is a phenomenon that promotes myocardial damage when the blood supply returns to the tissue after a period of ischemia. Anesthetic postconditioning involves myocardial protection against myocardial I/R injury. The effects of atorvastatin (ATV) on sevoflurane postconditioning against myocardial ischemia-reperfusion injury have not been thoroughly studied. The present study aimed to investigate if ATV interacts synergistically with sevoflurane postconditioning against myocardial infarction in rabbit hearts in vivo.

METHODS

Twenty-eight male rabbits underwent 30 min of left anterior descending coronary artery occlusion that was followed by reperfusion for 180 min under ketamine/xylazine (K/X) anesthesia. Rabbits were randomly assigned to four groups that included Group K/X (under K/X anesthesia only), Group POST (sevoflurane exposure at initial reperfusion), Group ATV (ATV 5 mg/kg/day administered before ischemia), and Group ATV + POST (POST intervention with atorvastatin administered once daily for 3 days). At the end of reperfusion, the myocardial infarct size and the area at risk were both measured.

RESULTS

The mean infarct sizes in the POST, ATV, and ATV + POST groups were significantly smaller compared to those in the K/X group. Furthermore, the mean infarct size in Group ATV + POST was significantly smaller than was that in Group POST and significantly smaller compared to that in Group ATV.

CONCLUSION

The combination of sevoflurane postconditioning and pre-administration of ATV further reduced the myocardial infarction size compared to that observed with sevoflurane postconditioning alone or ATV alone. Our data suggest that sevoflurane postconditioning and ATV may function additively to enhance cardioprotection.

Rational Application of β-Hydroxybutyrate Attenuates Ischemic Stroke by Suppressing Oxidative Stress and Mitochondrial-Dependent Apoptosis via Activation of the Erk/CREB/eNOS Pathway

Stroke is one of the leading causes of disability and death. Increasing evidence indicates that β-hydroxybutyrate (BHB) exerts beneficial effects in treating stroke, but the underlying mechanism remains largely unknown. In this study, we injected different doses of BHB into the lateral ventricle in middle cerebral artery occlusion (MCAO) model rats and neuronal cells were treated with different doses of BHB followed by oxygen-glucose deprivation (OGD). We found that a moderate dose of BHB enhanced mitochondrial complex I respiratory chain complex I activity, reduced oxidative stress, inhibited mitochondrial apoptosis, improved neurological scores, and reduced infarct volume after ischemia. We further showed that the effects of BHB were achieved by upregulating the dedicated BHB transporter SMCT1 and activating the Erk/CREB/eNOS pathway. These results provide us with a foundation for a novel understanding of the neuroprotective effects of BHB in stroke.

miR-134-5p inhibition reduces infarct-induced cardiomyocyte apoptosis via Creb1 upregulation

BACKGROUND

Following the recent discovery that microRNA-134-5p (miR-134-5p) is elevated in the early stages of acute myocardial infarction (AMI), we examined the specific role of miR-134-5p in cardiomyocytes during AMI.

METHODS

To study miR-134-5p's role in the context of AMI, we used a combination of in vitro experiments in H₂O₂-treated or hypoxic cardiomyocyte cell cultures as well as in vivo experiments in a murine model of AMI.

RESULTS

H₂O₂- and hypoxia-induced cardiomyocyte injury upregulated miR-134-5p expression. miR-134-5p overexpression increased cardiomyocyte apoptosis, whereas miR-134-5p inhibition reduced cardiomyocyte apoptosis. We discovered that the transcription factor cAMP-responsive element binding protein 1 (Creb1) is a functional target of miR-134-5p responsible for regulating cardiomyocyte apoptosis. In vivo AMI resulted in the upregulation and downregulation of miR-134-5p and Creb1 in the infarct area, respectively. Circulating miR-134-5p levels were also increased at days 1 and 2 post-AMI. Modulation of myocardial miR-124-5p expression by intramyocardial injection of antagomiR-134-5p or agomiR-134-5p significantly affected cardiomyocyte apoptosis, infarct size, and cardiac function in vivo.

CONCLUSIONS

miR-134-5p/Creb1 axis dysregulation plays a role in hypoxia- or oxidative stress-induced cardiomyocyte apoptosis as well as AMI. Circulating miR-134-5p may show promise as a biomarker for AMI or post-AMI cardiac dysfunction. Manipulating the miR-134-5p/Creb1 axis through either inhibition of miR-134-5p or overexpression of Creb1 may show promise as a novel therapeutic strategy to attenuate cardiac dysfunction following AMI.

Ticagrelor Does Not Protect Isolated Rat Hearts, Thus Clouding Its Proposed Cardioprotective Role Through ENT 1 in Heart Tissue

P2Y₁₂ receptor-blocking drugs given at reperfusion offer protection against myocardial infarction in animal models of transient coronary occlusion. Two recent reports concluded that ticagrelor was more cardioprotective than clopidogrel and attributed this to ticagrelor's unique ability to raise tissue adenosine by blocking the equilibrative nucleoside transporter 1. Indeed, an adenosine receptor blocker attenuated ticagrelor's protection. The related P2Y₁₂ inhibitor cangrelor, which does not block the transporter, protects hearts only when platelets are in the perfusate, while adenosine is known to protect equally in situ blood-perfused and crystalloid-perfused isolated hearts. We, therefore, tested whether ticagrelor liberates a sufficient amount of adenosine to protect a Krebs buffer-perfused isolated rat heart subjected to 40 minutes of global ischemia followed by 2 hours of reperfusion. In untreated hearts, 77.6% ± 4.0% of the ventricle was infarcted as measured by triphenyltetrazolium staining. Ischemically preconditioned hearts had only 32.7% ± 3.6% infarction ( P < .001 vs untreated), indicating that our model could be protected by preconditioning which is known to involve adenosine. Strikingly, hearts treated with 10 μmol/L ticagrelor in the buffer throughout the reperfusion period had 77.5% ± 2.4% infarction comparable to unprotected controls ( P = NS vs untreated). These data strongly suggest that ticagrelor was unable to release sufficient adenosine from the crystalloid-perfused rat heart to protect it against infarction. Our previous studies have found no difference in the anti-infarct potency among clopidogrel, cangrelor, and ticagrelor in open-chest rats and rabbits, and surprisingly adenosine receptor antagonists block protection from all 3 drugs. We have no explanation why ticagrelor is more protective in the pig than clopidogrel but suspect a species or perhaps a treatment schedule difference that may or may not involve adenosine.

Ticagrelor and Rosuvastatin Have Additive Cardioprotective Effects via Adenosine

BACKGROUND

Ticagrelor inhibits the equilibrative-nucleoside-transporter-1 and thereby, adenosine cell re-uptake. Ticagrelor limits infarct size (IS) in non-diabetic rats and the effect is adenosine-dependent. Statins, via ecto-5'-nucleotidase activation, also increase adenosine levels and limit IS.

HYPOTHESIS

Ticagrelor and rosuvastatin have additive effects on myocardial adenosine levels, and therefore, on IS and post-reperfusion activation of the NLRP3-inflammasome.

METHODS

Diabetic ZDF rats received via oral gavage; water (control), ticagrelor (150 mg/kg/d), prasugrel (7.5 mg/kg/d), rosuvastatin (5 mg/kg/d), ticagrelor + rosuvastatin and prasugrel + rosuvastatin for 3d. On day 4, rats underwent 30 min coronary artery occlusion and 24 h of reperfusion. Two additional groups received, ticagrelor + rosuvastatin or water in combination with CGS15943 (CGS, an adenosine receptor antagonist, 10 mg/kg i.p. 1 h before ischemia).

RESULTS

Both ticagrelor and rosuvastatin increased myocardial adenosine levels with an additive effect of the combination whereas prasugrel had no effect. Similarly, both ticagrelor and rosuvastatin significantly reduced IS with an additive effect of the combination whereas prasugrel had no effect. The effect on IS was adenosine dependent as CGS15943 reversed the effect of ticagrelor + rosuvastatin. The ischemia-reperfusion injury increased myocardial mRNA levels of NLRP3, ASC, IL-1β and IL-6. Ticagrelor and rosuvastatin, but not prasugrel, significantly decreased these pro-inflammatory mediators with a trend to an additive effect of the combination. The combination also increased the levels of anti-inflammatory 15-epilipoxin A₄.

CONCLUSIONS

Ticagrelor and rosuvastatin when given in combination have an additive effect on local myocardial adenosine levels in the setting of ischemia reperfusion. This translates into an additive cardioprotective effect mediated by adenosine-induced effects including downregulation of pro- but upregulation of anti-inflammatory mediators.

Statin-Induced Cardioprotection Against Ischemia-Reperfusion Injury: Potential Drug-Drug Interactions. Lesson to be Learnt by Translating Results from Animal Models to the Clinical Settings

Numerous interventions have been shown to limit myocardial infarct size in animal models; however, most of these interventions have failed to have a significant effect in clinical trials. One potential explanation for the lack of efficacy in the clinical setting is that in bench models, a single intervention is studied without the background of other interventions or modalities. This is in contrast to the clinical setting in which new medications are added to the "standard of care" treatment that by now includes a growing number of medications. Drug-drug interaction may lead to alteration, dampening, augmenting or masking the effects of the intended intervention. We use the well described model of statin-induced myocardial protection to demonstrate potential interactions with agents which are commonly concomitantly used in patients with stable coronary artery disease and/or acute coronary syndromes. These interactions could potentially explain the reduced efficacy of statins in the clinical trials compared to the animal models. In particular, caffeine and aspirin could attenuate the infarct size limiting effects of statins; morphine could delay the onset of protection or mask the protective effect in patients with ST elevation myocardial infarction, whereas other anti-platelet agents (dipyridamole, cilostazol and ticagrelor) may augment (or mask) the effect due to their favorable effects on adenosine cell reuptake and intracellular cAMP levels. We recommend that after characterizing the effects of new modalities in single intervention bench research, studies should be repeated in the background of standard-of-care medications to assure that the magnitude of the effect is not altered before proceeding with clinical trials.

Time to Give Up on Cardioprotection?

The mortality from acute myocardial infarction (AMI) remains significant, and the prevalence of post-myocardial infarction heart failure is increasing. Therefore, cardioprotection beyond timely reperfusion is needed. Conditioning procedures are the most powerful cardioprotective interventions in animal experiments. However, ischemic preconditioning cannot be used to reduce infarct size in patients with AMI because its occurrence is not predictable; several studies in patients undergoing surgical coronary revascularization report reduced release of creatine kinase and troponin. Ischemic postconditioning reduces infarct size in most, but not all, studies in patients undergoing interventional reperfusion of AMI, but may require direct stenting and exclusion of patients with >6 hours of symptom onset to protect. Remote ischemic conditioning reduces infarct size in patients undergoing interventional reperfusion of AMI, elective percutaneous or surgical coronary revascularization, and other cardiovascular surgery in many, but not in all, studies. Adequate dose-finding phase II studies do not exist. There are only 2 phase III trials, both on remote ischemic conditioning in patients undergoing cardiovascular surgery, both with neutral results in terms of infarct size and clinical outcome, but also both with major problems in trial design. We discuss the difficulties in translation of cardioprotection from animal experiments and proof-of-concept trials to clinical practice. Given that most studies on ischemic postconditioning and all studies on remote ischemic preconditioning in patients with AMI reported reduced infarct size, it would be premature to give up on cardioprotection.

Cardioprotection against experimental myocardial ischemic injury using cornin

Phosphorylated-cyclic adenosine monophosphate response element-binding protein (Phospho-CREB) has an important role in the pathogenesis of myocardial ischemia. We isolated the iridoid glycoside cornin from the fruit of Verbena officinalis L, investigated its effects against myocardial ischemia and reperfusion (I/R) injury in vivo, and elucidated its potential mechanism in vitro. Effects of cornin on cell viability, as well as expression of phospho-CREB and phospho-Akt in hypoxic H9c2 cells in vitro, and myocardial I/R injury in vivo, were investigated. Cornin attenuated hypoxia-induced cytotoxicity significantly in H9c2 cells in a concentration-dependent manner. Treatment of H9c2 cells with cornin (10 µM) blocked the reduction of expression of phospho-CREB and phospho-Akt in a hypoxic condition. Treatment of rats with cornin (30 mg/kg, iv) protected them from myocardial I/R injury as indicated by a decrease in infarct volume, improvement in hemodynamics, and reduction of severity of myocardial damage. Cornin treatment also attenuated the reduction of expression of phospho-CREB and phospho-Akt in ischemic myocardial tissue. These data suggest that cornin exerts protective effects due to an increase in expression of phospho-CREB and phospho-Akt.

Simvastatin attenuates oleic acid-induced oxidative stress through CREB-dependent induction of heme oxygenase-1 in renal proximal tubule cells

BACKGROUND

Statins elicit antioxidant effects independently of their lipid-lowering properties. Heme oxygenase-1 (HO-1) induction may be a part of these pleiotropic effects, which are insufficiently described in the kidney. We hypothesize that simvastatin (SIM) transcriptionally activates HO-1 that protects renal proximal tubule cells from lipotoxic injury.

METHODS

Impact of SIM on 100 μmol/l oleic acid (OA)-mediated reactive oxygen species (ROS) production and consequent oxidative stress (4-hydroxynonenal (HNE) content) as well as cell injury/apoptosis (lactate dehydrogenase (LDH) release, caspase-3 activation) were determined in cultured renal proximal tubule (NRK52E) cells. Effect of SIM on the HO-1 promoter and its enhancer elements (antioxidant response element (ARE), CCAAT, AP1, and cAMP response element (CRE)) was also determined in reporter luciferase assays. Dominant-negative (dnMEK, M1CREB) and pharmacologic (H89) approaches were used to inhibit activation of extracellular signal regulated kinase (ERK), CREB, and protein kinase A (PKA), respectively.

RESULTS

SIM dose-dependently activated the HO-1 promoter that was essential for protection against OA-dependent ROS production/oxidative stress and LDH release/caspase-3 activation. We found that the HO-1 promoter was induced through ERK and PKA-dependent activation of the CRE by SIM.

CONCLUSION

SIM may protect the kidney from adverse effects of circulating fatty acids by upregulating the antioxidant HO-1, aside from its well-described lipid-lowering effects.

Interaction of risk factors, comorbidities, and comedications with ischemia/reperfusion injury and cardioprotection by preconditioning, postconditioning, and remote conditioning

Pre-, post-, and remote conditioning of the myocardium are well described adaptive responses that markedly enhance the ability of the heart to withstand a prolonged ischemia/reperfusion insult and provide therapeutic paradigms for cardioprotection. Nevertheless, more than 25 years after the discovery of ischemic preconditioning, we still do not have established cardioprotective drugs on the market. Most experimental studies on cardioprotection are still undertaken in animal models, in which ischemia/reperfusion is imposed in the absence of cardiovascular risk factors. However, ischemic heart disease in humans is a complex disorder caused by, or associated with, cardiovascular risk factors and comorbidities, including hypertension, hyperlipidemia, diabetes, insulin resistance, heart failure, altered coronary circulation, and aging. These risk factors induce fundamental alterations in cellular signaling cascades that affect the development of ischemia/reperfusion injury per se and responses to cardioprotective interventions. Moreover, some of the medications used to treat these risk factors, including statins, nitrates, and antidiabetic drugs, may impact cardioprotection by modifying cellular signaling. The aim of this article is to review the recent evidence that cardiovascular risk factors and their medication may modify the response to cardioprotective interventions. We emphasize the critical need to take into account the presence of cardiovascular risk factors and concomitant medications when designing preclinical studies for the identification and validation of cardioprotective drug targets and clinical studies. This will hopefully maximize the success rate of developing rational approaches to effective cardioprotective therapies for the majority of patients with multiple risk factors.

Ticagrelor Protects the Heart Against Reperfusion Injury and Improves Remodeling After Myocardial Infarction

Objective—

In addition to P2Y 12 receptor antagonism, ticagrelor inhibits adenosine cell uptake. Prior data show that 7-day pretreatment with ticagrelor limits infarct size. We explored the acute effects of ticagrelor and clopidogrel on infarct size and potential long-term effects on heart function.

Approach and Results—

Rats underwent 30-minute ischemia per 24-hour reperfusion. (1) Ticagrelor (10 or 30 mg/kg) or clopidogrel (12.5 mg/kg) was given via intraperitoneal injection 5 minutes before reperfusion. (2) Rats received ticagrelor acute (intraperitoneal; 30 mg/kg), chronic (oral; 300 mg/kg per day) for 4 weeks starting 1 day after reperfusion or the combination (acute+chronic). Another group received clopidogrel (intraperitoneal [12.5 mg/kg]+oral [62.5 mg/kg per day]) for 4 weeks. (1) Ticagrelor dose-dependently reduced infarct size, 10 mg/kg (31.5%±1.8%; P <0.001) and 30 mg/kg (21.4%±2.6%; P <0.001) versus control (45.3±1.7%), whereas clopidogrel had no effect (42.4%±2.6%). Ticagrelor, but not clopidogrel, increased myocardial adenosine levels, increased phosphorylation of Akt, endothelial NO synthase, and extracellular-signal-regulated kinase 1/2 4 hours after reperfusion and decreased apoptosis. (2) After 4 weeks, left ventricular ejection fraction was reduced in the vehicle-treated group (44.8%±3.5%) versus sham (77.6%±0.9%). All ticagrelor treatments improved left ventricular ejection fraction, acute (69.5%±1.6%), chronic (69.2%±1.0%), and acute+chronic (76.3%±1.2%), whereas clopidogrel had no effect (37.4%±3.7%). Ticagrelor, but not clopidogrel, attenuated fibrosis and decreased collagen-III mRNA levels 4 weeks after ischemia/reperfusion. Ticagrelor, but not clopidogrel, attenuated the increase in proinflammatory tumor necrosis factor-α, interleukin-1β, and interleukin-18, and increased anti-inflammatory 15-epi-lipoxin-A 4 levels.

Conclusions—

Ticagrelor, but not clopidogrel, administered just before reperfusion protects against reperfusion injury. This acute treatment or chronic ticagrelor for 4 weeks or their combination improved heart function, whereas clopidogrel, despite achieving a similar degree of platelet inhibition, had no effect.

Chronic Treatment With Ticagrelor Limits Myocardial Infarct Size

Objective—

In a phase III clinical trial (PLATelet inhibition and patient Outcomes, PLATO), ticagrelor provided better clinical outcomes than clopidogrel in patients with acute coronary syndromes. In addition to P2Y 12 -receptor antagonism, ticagrelor prevents cell uptake of adenosine and has proven able to augment adenosine effects. Adenosine protects the heart against ischemia–reperfusion injury. We compared the effects of clopidogrel and ticagrelor on myocardial infarct size (IS).

Approach and Results—

Rats received oral ticagrelor (0, 75, 150, or 300 mg/kg/d) or clopidogrel (30 or 90 mg/kg/d) for 7 days and underwent 30-minute coronary artery ligation and 24-hour reperfusion. Area at risk was assessed by blue dye and IS by 2,3,5-triphenyl-tetrazolium-chloride. Cyclooxygenase-2 (COX2) enzyme activity was assessed by ELISA and expression by real-time polymerase chain reaction. Mechanism responsible was explored using adenosine-receptor antagonist (CGS15943, an A 2A /A 1 antagonist) or cyclooxygenase inhibition by either aspirin (5, 10, or 25 mg/kg) or specific cyclooxygenase-1 (SC560) or COX2 (SC5815) inhibitors. Ticagrelor, dose-dependently, reduced IS, whereas clopidogrel had no effect. Adenosine-receptor antagonism blocked the ticagrelor effect and COX2 inhibition by SC5815, or high-dose aspirin attenuated the IS-limiting effect of ticagrelor, whereas cyclooxygenase-1 inhibition or low-dose aspirin had no effect. Ticagrelor, but not clopidogrel, upregulated COX2 expression and activity. Also this effect was blocked by adenosine-receptor antagonism. Ticagrelor, but not clopidogrel, increased Akt and endothelial nitric oxide synthase phosphorylation.

Conclusions—

Ticagrelor, but not clopidogrel, reduces myocardial IS. The protective effect of ticagrelor was dependent on adenosine-receptor activation with downstream upregulation of endothelial nitric oxide synthase and COX2 activity.

Classical and pleiotropic actions of dipyridamole: Not enough light to illuminate the dark tunnel?

Dipyridamole is a platelet inhibitor indicated for the secondary prevention of transient ischemic attack. It inhibits the enzyme phosphodiesterase, elevates cAMP and cGMP levels and prevents platelet aggregation. Dipyridamole inhibits the cellular uptake of adenosine into red blood cells, platelets and endothelial cells that results in increased extracellular availability of adenosine, leading to modulation of cardiovascular function. The antiplatelet action of dipyridamole might offer therapeutic benefits in secondary stroke prevention in combination with aspirin. Inflammation and oxidative stress play an important role in atherosclerosis and thrombosis development, leading to stroke progression. Studies demonstrated anti-inflammatory, anti-oxidant and anti-proliferative actions of dipyridamole. These pleiotropic potentials of dipyridamole might contribute to improved therapeutic outcomes when used with aspirin in preventing secondary stroke. Dipyridamole was documented as a coronary vasodilator 5 decades ago. The therapeutic failure of dipyridamole as a coronary vasodilator is linked with induction of 'coronary steal' phenomenon in which by dilating resistance vessels in non-ischemic zone, dipyridamole diverts the already reduced blood flow away from the area of ischemic myocardium. Dipyridamole at high-dose could cause a marked 'coronary steal' effect. Dipyridamole, however, at low-dose could have a minimal hemodynamic effect. Low-dose dipyridamole treatment has a therapeutic potential in partially preventing diabetes mellitus-induced experimental vascular endothelial and renal abnormalities by enhancing endothelial nitric oxide signals and inducing renovascular reduction of oxidative stress. In spite of plenteous research on dipyridamole's use in clinics, its precise clinical application is still obscure. This review sheds lights on pleiotropic pharmacological actions and therapeutic potentials of dipyridamole.

Adenosine-mediated effects of ticagrelor: evidence and potential clinical relevance

This review constitutes a critical evaluation of recent publications that have described an additional mode of action of the P2Y12 receptor antagonist ticagrelor. The effect is mediated by inhibition of the adenosine transporter ENT1 (type 1 equilibrative nucleoside transporter), which provides protection for adenosine from intracellular metabolism, thus increasing its concentration and biological activity, particularly at sites of ischemia and tissue injury where it is formed. Understanding the mode of action of ticagrelor is of particular interest given that its clinical profile, both in terms of efficacy and adverse events, differs from that of thienopyridine P2Y12 antagonists.

Platelet P2Y₁₂ blockers confer direct postconditioning-like protection in reperfused rabbit hearts

BACKGROUND

Blockade of platelet activation during primary percutaneous intervention for acute myocardial infarction is standard care to minimize stent thrombosis. To determine whether antiplatelet agents offer any direct cardioprotective effect, we tested whether they could modify infarction in a rabbit model of ischemia/reperfusion caused by reversible ligation of a coronary artery.

METHODS AND RESULTS

The P2Y₁₂ (adenosine diphosphate) receptor blocker cangrelor administered shortly before reperfusion in rabbits undergoing 30-minute regional ischemia/3-hour reperfusion reduced infarction from 38% of ischemic zone in control hearts to only 19%. Protection was dose dependent and correlated with the degree of inhibition of platelet aggregation. Protection was comparable to that seen with ischemic postconditioning (IPOC). Cangrelor protection, but not its inhibition of platelet aggregation, was abolished by the same signaling inhibitors that block protection from IPOC suggesting protection resulted from protective signaling rather than anticoagulation. As with IPOC, protection was lost when cangrelor administration was delayed until 10 minutes after reperfusion and no added protection was seen when cangrelor and IPOC were combined. These findings suggest both IPOC and cangrelor may protect by the same mechanism. No protection was seen when cangrelor was used in crystalloid-perfused isolated hearts indicating some component in whole blood is required for protection. Clopidogrel had a very slow onset of action requiring 2 days of treatment before platelets were inhibited, and only then the hearts were protected. Signaling inhibitors given just prior to reperfusion blocked clopidogrel's protection. Neither aspirin nor heparin was protective.

CONCLUSIONS

Clopidogrel and cangrelor protected rabbit hearts against infarction. The mechanism appears to involve signal transduction during reperfusion rather than inhibition of intravascular coagulation. We hypothesize that both drugs protect by activating IPOC's protective signaling to prevent reperfusion injury. If true, patients receiving P2Y₁₂ inhibitors before percutaneous intervention may already be postconditioned thus explaining failure of recent clinical trials of postconditioning drugs.

Current therapeutic strategies to mitigate the eNOS dysfunction in ischaemic stroke

Impairment of endothelial nitric oxide synthase (eNOS) activity is implicated in the pathogenesis of endothelial dysfunction in many diseases including ischaemic stroke. The modulation of eNOS during and/or following ischaemic injury often represents a futile compensatory mechanism due to a significant decrease in nitric oxide (NO) bioavailability coupled with dramatic increases in the levels of reactive oxygen species that further neutralise NO. However, applications of a number of therapeutic agents alone or in combination have been shown to augment eNOS activity under a variety of pathological conditions by potentiating the expression and/or activity of Akt/eNOS/NO pathway components. The list of these therapeutic agents include NO donors, statins, angiotensin-converting enzyme inhibitors, calcium channel blockers, phosphodiesterase-3 inhibitors, aspirin, dipyridamole and ellagic acid. While most of these compounds exhibit anti-platelet properties and are able to up-regulate eNOS expression in endothelial cells and platelets, others suppress eNOS uncoupling and tetrahydrobiopterin (an eNOS stabiliser) oxidation. As the number of therapeutic molecules that modulate the expression and activity of eNOS increases, further detailed research is required to reveal their mode of action in preventing and/or reversing the endothelial dysfunction.

Protecting against ischemia-reperfusion injury: antiplatelet drugs, statins, and their potential interactions

Statins and antiplatelet agents are currently used as therapeutic agents for patients with acute myocardial infarction. Statins limit myocardial infarct size by activating phosphatidylinositol-3-kinase (PI3K), ecto-5'-nucleotidase, Akt/endothelial nitric oxide synthase (eNOS), and the downstream effectors inducible nitric oxide synthase (iNOS) and cyclooxygenase-2 (COX-2). Inhibition of PI3K, adenosine receptors, eNOS, iNOS, or COX-2 abrogates the protective effects of statins. At >5 mg/kg, aspirin attenuates the myocardial infarct-size-limiting effect of statins. In contrast, the combination of low-dose atoravastatin with either the phosphodiesterase-III inhibitor cilostazol or the adenosine reuptake inhibitor dipyridamole synergistically limits infarct size. Low-dose aspirin with dipyridamole started during ischemia augmented the infarct-size-limiting effects of simvastatin. In contrast, high-dose aspirin blocked the protective effect of simvastatin. The combination of dipyridamole with low-dose aspirin and simvastatin resulted in the smallest infarct size. According to the most current data available, we believe that antiplatelet regimens may require modification for patients who are receiving statins.