Advanced technique of myocardial no-reflow quantification using indocyanine green.

The post-ischemic no-reflow phenomenon after primary percutaneous coronary intervention (PCI) is observed in more than half of subjects and is defined as the absence or marked slowing of distal coronary blood flow despite removal of the arterial occlusion. To visualize no-reflow in experimental studies, the fluorescent dye thioflavin S (ThS) is often used, which allows for the estimation of the size of microvascular obstruction by staining the endothelial lining of vessels. Based on the ability of indocyanine green (ICG) to be retained in tissues with increased vascular permeability, we proposed the possibility of using it to assess not only the severity of microvascular obstruction but also the degree of vascular permeability in the zone of myocardial infarction. The aim of our study was to investigate the possibility of using ICG to visualize no-reflow zones after ischemia-reperfusion injury of rat myocardium. Using dual ICG and ThS staining and the FLUM multispectral fluorescence organoscope, we recorded ICG and ThS fluorescence within the zone of myocardial necrosis, identifying ICG-negative zones whose size correlated with the size of the no-reflow zones detected by ThS. It is also shown that the contrast change between the no-reflow zone and nonischemic myocardium reflects the severity of blood stasis, indicating that ICG-negative zones are no-reflow zones. The described method can be an addition or alternative to the traditional method of measuring the size of no-reflow zones in the experiment.

Ultra-High-Resolution Electrocardiography Enables Earlier Detection of Transmural and Subendocardial Myocardial Ischemia Compared to Conventional Electrocardiography.

The sensitivity of exercise ECG is marginally sufficient for the detection of mild reduction of coronary blood flow in patients with early coronary atherosclerosis. Here, we describe the application of a new technique of ECG registration/analysis-ultra-high-resolution ECG (UHR ECG)-for early detection of myocardial ischemia (MIS). The utility of UHR ECG vs. conventional ECG (C ECG) was tested in anesthetized rats and pigs. Transmural MIS was induced in rats by the ligation of the left coronary artery (CA). In pigs, subendocardial ischemia of a variable extent was produced by stepwise inflation of a balloon within the right CA, causing a 25-100% reduction of its lumen. In rats, a reduction in power spectral density (PSD) in the high-frequency (HF) channel of UHR ECG was registered at 60 s after ischemia (power 0.81 ± 0.14 vs. 1.25 ± 0.12 mW at baseline, p < 0.01). This was not accompanied by any ST segment elevation on C ECG. In pigs, PSD in the HF channel of UHR ECG was significantly decreased at a 25% reduction of CA lumen, while the ST segment on C ECG remained unchanged. In conclusion, UHR ECG enabled earlier detection of transmural MIS compared to C ECG. PSD in the HF channel of UHR ECG demonstrated greater sensitivity in the settings of subendocardial ischemia.

Effect of sleeve gastrectomy, Roux-en-Y gastric bypass, and ileal transposition on myocardial ischaemia-reperfusion injury in non-obese non-diabetic rats.

Bariatric surgery (BS) improves outcomes in patients with myocardial infarction (MI). Here we tested the hypothesis that BS-mediated reduction in fatal MI could be attributed to its infarct-limiting effect. Wistar rats were randomized into five groups: control (CON), sham (SHAM), Roux-en-Y gastric bypass (RYGB), sleeve gastrectomy (SG), and ileotransposition (IT). Ten weeks later, animals were subjected to 30-min myocardial ischemia plus 120-min reperfusion. Infarct size (IS) and no-reflow area were determined histochemically. Fasting plasma levels of glucagon-like peptide-1 (GLP-1), leptin, ghrelin, and insulin were measured using ELISA. Compared with SHAM, RYGB and SG reduced IS by 22% (p = 0.011) and 10% (p = 0.027), and no-reflow by 38% (p = 0.01) and 32% (p = 0.004), respectively. IT failed to reduce IS and no-reflow. GLP-1 level was increased in the SG and RYGB groups compared with CON. In both the SG and RYGB, leptin level was decreased compared with CON and SHAM. In the SG group, ghrelin level was lower than that in the CON and SHAM. Insulin levels were not different between groups. In conclusion, RYGB and SG increased myocardial tolerance to ischemia-reperfusion injury of non-obese, non-diabetic rats, and their infarct-limiting effect is associated with decreased leptin and ghrelin levels and increased GLP-1 level.

Intracellular Development of Resident Cardiac Stem Cells: An Overlooked Phenomenon in Myocardial Self-Renewal and Regeneration.

At present, the approaches aimed at increasing myocardial regeneration after infarction are not available. The key question is the identity of cells capable of producing functional cardiac myocytes (CMs), replenishing those lost during ischemia. With identification of resident cardiac stem cells (CSCs), it has been supposed that this cell population may be crucial for myocardial self-renewal and regeneration. In the last few years, the focus has been shifted towards another concept, implying that new CMs are produced by dedifferentiation and proliferation of mature CMs. The observation that CSCs can undergo development inside immature cardiac cells by formation of "cell-in-cell structures" (CICSs) has enabled us to conclude that encapsulated CICSs are implicated in mammalian cardiomyogenesis over the entire lifespan. Earlier we demonstrated that new CMs are produced through formation of CSC-derived transitory amplifying cells (TACs) either in the CM colonies or inside encapsulated CICSs. In this study, we described the phenomenon of CSC penetration into mature CMs, resulting in the formation of vacuole-like CICSs (or non-encapsulated CICSs) containing proliferating CSCs with subsequent differentiation of CSC progeny into TACs and their release. In addition, we compared the phenotypes of TACs derived from encapsulated and non-encapsulated CICSs developing in immature and mature CMs, respectively.

Effects of three types of bariatric interventions on myocardial infarct size and vascular function in rats with type 2 diabetes mellitus.

AIMS: The effects of three types of bariatric interventions on myocardial infarct size were tested in the rat model of type 2 diabetes mellitus (T2DM). We also evaluated the effects of bariatric surgery on no-reflow phenomenon and vascular dysfunction caused by T2DM. MAIN METHODS: Rats with T2DM were assigned into groups: without surgery, sham-operated, ileal transposition, Roux-en-Y gastric bypass, and sleeve gastrectomy. Oral glucose tolerance, glucagon-like peptide-1, and insulin levels were measured. Six weeks after surgery, the animals were subjected to myocardial ischemia-reperfusion followed by histochemical determination of infarct size (IS), no-reflow zone, and blood stasis area size. Vascular dysfunction was characterized using wire myography. KEY FINDINGS: All bariatric surgery types caused significant reductions in animal body weight and resulted in T2DM compensation. All bariatric interventions partially normalized glucagon-like peptide-1 responses attenuated by T2DM. IS was significantly smaller in animals with T2DM. Bariatric surgery provided no additional IS limitation compared with T2DM alone. Bariatric surgeries reversed T2DM-induced enhanced contractile responses of the mesenteric artery to 5-hydroxytryptamine. Sleeve gastrectomy normalized decreased nitric oxide synthase contribution to the endothelium-dependent vasodilatation in T2DM. SIGNIFICANCE: T2DM resulted in a reduction of infarct size and no-reflow zone size. Bariatric surgery provided no additional infarct-limiting effect, but it normalized T2DM-induced augmented vascular contractility and reversed decreased contribution of nitric oxide to endothelium-dependent vasodilatation typical of T2DM. All taken together, we suggest that this type of surgery may have a beneficial effect on T2DM-induced cardiovascular diseases.

Neurohumoral, cardiac and inflammatory markers in the evaluation of heart failure severity and progression.

Heart failure is common in adult population, accounting for substantial morbidity and mortality worldwide. The main risk factors for heart failure are coronary artery disease, hypertension, obesity, diabetes mellitus, chronic pulmonary diseases, family history of cardiovascular diseases, cardiotoxic therapy. The main factor associated with poor outcome of these patients is constant progression of heart failure. In the current review we present evidence on the role of established and candidate neurohumoral biomarkers for heart failure progression management and diagnostics. A growing number of biomarkers have been proposed as potentially useful in heart failure patients, but not one of them still resembles the characteristics of the "ideal biomarker." A single marker will hardly perform well for screening, diagnostic, prognostic, and therapeutic management purposes. Moreover, the pathophysiological and clinical significance of biomarkers may depend on the presentation, stage, and severity of the disease. The authors cover main classification of heart failure phenotypes, based on the measurement of left ventricular ejection fraction, including heart failure with preserved ejection fraction, heart failure with reduced ejection fraction, and the recently proposed category heart failure with mid-range ejection fraction. One could envisage specific sets of biomarker with different performances in heart failure progression with different left ventricular ejection fraction especially as concerns prediction of the future course of the disease and of left ventricular adverse/reverse remodeling. This article is intended to provide an overview of basic and additional mechanisms of heart failure progression will contribute to a more comprehensive knowledge of the disease pathogenesis.

Biological Safety and Biodistribution of Chitosan Nanoparticles.

: The effect of unmodified chitosan nanoparticles with a size of ~100 nm and a weakly positive charge on blood coagulation, metabolic activity of cultured cardiomyocytes, general toxicity, biodistribution, and reactive changes in rat organs in response to their single intravenous administration at doses of 1, 2, and 4 mg/kg was studied. Chitosan nanoparticles (CNPs) have a small cytotoxic effect and have a weak antiplatelet and anticoagulant effect. Intravenous administration of CNPs does not cause significant hemodynamic changes, and 30 min after the CNPs administration, they mainly accumulate in the liver and lungs, without causing hemolysis and leukocytosis. The toxicity of chitosan nanoparticles was manifested in a dose-dependent short-term delay in weight gain with subsequent recovery, while in the 2-week observation period no signs of pain and distress were observed in rats. Granulomas found in the lungs and liver indicate slow biodegradation of chitosan nanoparticles. In general, the obtained results indicate a good tolerance of intravenous administration of an unmodified chitosan suspension in the studied dose range.

Cardiomyocyte-Specific Snrk Prevents Inflammation in the Heart.

Background The SNRK (sucrose-nonfermenting-related kinase) enzyme is critical for cardiac function. However, the underlying cause for heart failure observed in Snrk cardiac conditional knockout mouse is unknown. Methods and Results Previously, 6-month adult mice knocked out for Snrk in cardiomyocytes (CMs) displayed left ventricular dysfunction. Here, 4-month adult mice, on angiotensin II (Ang II) infusion, show rapid decline in cardiac systolic function, which leads to heart failure and death in 2 weeks. These mice showed increased expression of nuclear factor κ light chain enhancer of activated B cells (NF-κB), inflammatory signaling proteins, proinflammatory proteins in the heart, and fibrosis. Interestingly, under Ang II infusion, mice knocked out for Snrk in endothelial cells did not show significant systolic or diastolic dysfunction. Although an NF-κB inflammation signaling pathway was increased in Snrk knockout endothelial cells, this did not lead to fibrosis or mortality. In hearts of adult mice knocked out for Snrk in CMs, we also observed NF-κB pathway activation in CMs, and an increased presence of Mac2+ macrophages was observed in basal and Ang II-infused states. In vitro analysis of Snrk knockdown HL-1 CMs revealed similar upregulation of the NF-κB signaling proteins and proinflammatory proteins that was exacerbated on Ang II treatment. The Ang II-induced NF-κB pathway-mediated proinflammatory effects were mediated in part through protein kinase B or AKT, wherein AKT inhibition restored the proinflammatory signaling protein levels to baseline in Snrk knockdown HL-1 CMs. Conclusions During heart failure, SNRK acts as a cardiomyocyte-specific repressor of cardiac inflammation and fibrosis.

Synthesis of N-succinyl- and N-glutaryl-chitosan derivatives and their antioxidant, antiplatelet, and anticoagulant activity.

The effects of temperature, reactant ratio, pH, and reaction time were studied on the polymers formed by the reactions of succinic and glutaric anhydrides with chitosan under both homogeneous and heterogeneous conditions. As a result, protocols were developed for the synthesis of succinyl- and glutaryl-chitosan derivatives (SC and GC, respectively) with a specific degree of substitution. The polymers were characterized by NMR spectroscopy, including two-dimensional NMR techniques, that confirms N-substitution of chitosan under reaction conditions used. SC and GC both show pronounced and similar antioxidant activity, which slightly increases with an increase in the degree of substitution. Both SC and GC showed antiplatelet and anticoagulant activity. The platelet aggregation is suppressed more strongly in the experiments with GC than with SC, although the latter exhibits a more pronounced anticoagulant activity.

In vivo visualization and ex vivo quantification of experimental myocardial infarction by indocyanine green fluorescence imaging.

The fluorophore indocyanine green accumulates in areas of ischemia-reperfusion injury due to an increase in vascular permeability and extravasation of the dye. The aim of the study was to validate an indocyanine green-based technique of in vivo visualization of myocardial infarction. A further aim was to quantify infarct size ex vivo and compare this technique with the standard triphenyltetrazolium chloride staining. Wistar rats were subjected to regional myocardial ischemia (30 minutes) followed by reperfusion (n = 7). Indocyanine green (0.25 mg/mL in 1 mL of normal saline) was infused intravenously for 10 minutes starting from the 25th minute of ischemia. Video registration in the near-infrared fluorescence was performed. Epicardial fluorescence of indocyanine green corresponded to the injured area after 30 minutes of reperfusion. Infarct size was similar when determined ex vivo using traditional triphenyltetrazolium chloride assay and indocyanine green fluorescent labeling. Intravital visualization of irreversible injury can be done directly by fluorescence on the surface of the heart. This technique may also be an alternative for ex vivo measurements of infarct size.

Remote vs. local ischaemic preconditioning in the rat heart: infarct limitation, suppression of ischaemic arrhythmia and the role of reactive oxygen species.

The unmet clinical need for myocardial salvage during ischaemia-reperfusion injury requires the development of new techniques for myocardial protection. In this study the protective effect of different local ischaemic preconditioning (LIPC) and remote ischaemic preconditioning (RIPC) protocols was compared in the rat model of myocardial ischaemia-reperfusion, using infarct size and ischaemic tachyarrhythmias as end-points. In addition, the hypothesis that there is involvement of reactive oxygen species (ROS) in the protective signalling by RIPC was tested, again in comparison with LIPC. The animals were subjected to 30-min coronary occlusion and 90-min reperfusion. RIPC protocol included either transient infrarenal aortic occlusion (for 5, 15 and 30 min followed by 15-min reperfusion) or 15-min mesenteric artery occlusion with 15-min reperfusion. Ventricular tachyarrhythmias during test ischaemia were quantified according to Lambeth Conventions. It was found that the infarct-limiting effect of RIPC critically depends on the duration of a single episode of remote ischaemia, which fails to protect the heart from infarction when it is too short or, instead, too prolonged. It was also shown that RIPC is ineffective in reducing the incidence and severity of ischaemia-induced ventricular tachyarrhythmias. According to our data, the infarct-limiting effect of LIPC could be partially eliminated by the administration of ROS scavenger N-2-mercaptopropionylglycine (90 mg/kg), whereas the same effect of RIPC seems to be independent of ROS signalling.

Silicon-containing nanocarriers for targeted drug delivery: synthesis, physicochemical properties and acute toxicity.

Silicon-containing nanoparticles (NPs) are considered promising drug carriers for targeted drug delivery. In this study, we investigated the physical and chemical properties of silicon-containing NPs, including silica and organomodified silica NPs (SiO2NPs and OrSiO2NPs, respectively), with different surface modifications, with the aim of increasing drug-loading efficiency. In addition, we described the original synthesis methods of different sizes of OrSiO2NPs, as well as new hybrid OrSiO2NPs with a silica core (SiO2 + OrSiO2NPs). Animal experiments revealed that the silicon-containing NPs investigated were non-toxic, as evidenced by a lack of hemodynamic response after intravenous administration. Bioelimination studies showed rapid renal excretion of OrSiO2NPs. In drug release kinetics studies, adenosine was immobilized on SiO2NPs using three different approaches: physical adsorption, ionic, and covalent bonding. We observed that the rate of adenosine desorption critically depended on the type of immobilization; therefore, adenosine release kinetics can be adjusted by SiO2NP surface modification technique. Adsorption of adenosine on SiO2 + OrSiO2NPs resulted in a significant attenuation of adenosine-induced hypotension and bradycardia.

Protease-activated receptor 1 inhibition by SCH79797 attenuates left ventricular remodeling and profibrotic activities of cardiac fibroblasts.

PURPOSE: Fibroblast activity promotes adverse left ventricular (LV) remodeling that underlies the development of ischemic cardiomyopathy. Transforming growth factor-ß (TGF-ß) is a potent stimulus for fibrosis, and the extracellular signal-regulated kinases(ERK) 1/2 pathway also contributes to the fibrotic response. The thrombin receptor, protease-activated receptor 1 (PAR1), has been shown to play an important role in the excessive fibrosis in different tissues. The aim of this study was to investigate the influence of a PAR1 inhibitor, SCH79797, on cardiac fibrosis, tissue stiffness and postinfarction remodeling, and effects of PAR1 inhibition on thrombin-induced TGF-ß and (ERK) 1/2 activities in cardiac fibroblasts. METHODS: We used a rat model of myocardial ischemia-reperfusion injury, isolated cardiac fibroblasts, and 3-dimensional (3D) cardiac tissue models fabricated to ascertain the contribution of PAR1 activation on cardiac fibrosis and LV remodeling. RESULTS: The PAR1 inhibitor attenuated LV dilation and improved LV systolic function of the reperfused myocardium at 28 days. This improvement was associated with a nonsignificant decrease in scar size (%LV) from 23 ± % in the control group (n = 10) to 16% ± 5.5% in the treated group (n = 9; P = .052). In the short term, the PAR1 inhibitor did not rescue infarct size or LV systolic function after 3 days. The PAR1 inhibition abolished thrombin-mediated ERK1/2 phosphorylation, TGF-ß and type I procollagen production, matrix metalloproteinase-2/9 activation, myofibroblasts transformation in vitro, and abrogated the remodeling of 3D tissues induced by chronic thrombin treatment. CONCLUSION: These studies suggest PAR1 inhibition initiated after ischemic injury attenuates adverse LV remodeling through late-stage antifibrotic events.

L-theanine administration results in neuroprotection and prevents glutamate receptor agonist-mediated injury in the rat model of cerebral ischemia-reperfusion.

While the neuroprotective effect of green tea (Camellia sinensis) might be explained by the presence of amino acid L-theanine in the tea leaves, it is not known whether postischemic administration of L-theanine could also provide neuroprotection. In the present study, we investigated the neuroprotective effect of L-theanine (1 and 4 mg/kg) administered at 3, 12, and 24 h after reperfusion in the rat model of stroke. We also studied the effect of L-theanine on brain injury caused by exogenous administration of N-methyl-D-aspartate and α-amino-3-hydroxy-5-methyl-isoxazole-4-propionate/kainate receptor agonists during reperfusion. Rats were subjected to 30-min middle cerebral artery occlusion followed by 48-h reperfusion. Neurological deficit and infarct size were determined at the end of reperfusion. At 3 and 12 h, but not at 24 h of reperfusion, L-theanine substantially reduced the size of brain infarct. Neurological status was improved when L-theanine was administered 3, 12, and 24 h after reperfusion. Repeated intrastriatal injections of L-theanine at a total dose of 800 µg/kg during reperfusion prevented brain injury caused by glutamate receptor agonists. In conclusion, L-theanine at reperfusion exerts neuroprotective effect in the in vivo rat model of stroke. Local treatment with L-theanine at reperfusion prevents glutamate receptor agonist-mediated brain injury.

cPLA2 is protective against COX inhibitor-induced intestinal damage.

Cytosolic phospholipase A(2) (cPLA(2)) is the rate-limiting enzyme responsible for the generation of prostaglandins (PGs), which are bioactive lipids that play critical roles in maintaining gastrointestinal (GI) homeostasis. There has been a long-standing association between administration of cyclooxygenase (COX) inhibitors and GI toxicity. GI injury is thought to be induced by suppressed production of GI-protective PGs as well as direct injury to enterocytes. The present study sought to determine how pan-suppression of PG production via a genetic deletion of cPLA(2) impacts the susceptibility to COX inhibitor-induced GI injury. A panel of COX inhibitors including celecoxib, rofecoxib, sulindac, and aspirin were administered via diet to cPLA(2)(-/-) and cPLA(2)(+/+) littermates. Administration of celecoxib, rofecoxib, and sulindac, but not aspirin, resulted in acute lethality (within 2 weeks) in cPLA(2)(-/-) mice, but not in wild-type littermates. Histomorphological analysis revealed severe GI damage following celecoxib exposure associated with acute bacteremia and sepsis. Intestinal PG levels were reduced equivalently in both genotypes following celecoxib exposure, indicating that PG production was not likely responsible for the differential sensitivity. Gene expression profiling in the small intestines of mice identified drug-related changes among a panel of genes including those involved in mitochondrial function in cPLA(2)(-/-) mice. Further analysis of enterocytic mitochondria showed abnormal morphology as well as impaired ATP production in the intestines from celecoxib-exposed cPLA(2)(-/-) mice. Our data demonstrate that cPLA(2) appears to be an important component in conferring protection against COX inhibitor-induced enteropathy, which may be mediated through affects on enterocytic mitochondria.

Targeted drug delivery into reversibly injured myocardium with silica nanoparticles: surface functionalization, natural biodistribution, and acute toxicity.

The clinical outcome of patients with ischemic heart disease can be significantly improved with the implementation of targeted drug delivery into the ischemic myocardium. In this paper, we present our original findings relevant to the problem of therapeutic heart targeting with use of nanoparticles. Experimental approaches included fabrication of carbon and silica nanoparticles, their characterization and surface modification. The acute hemodynamic effects of nanoparticle formulation as well as nanoparticle biodistribution were studied in male Wistar rats. Carbon and silica nanoparticles are nontoxic materials that can be used as carriers for heart-targeted drug delivery. Concepts of passive and active targeting can be applied to the development of targeted drug delivery to the ischemic myocardial cells. Provided that ischemic heart-targeted drug delivery can be proved to be safe and efficient, the results of this research may contribute to the development of new technologies in the pharmaceutical industry.

Role of P2X purinergic receptors in the rescue of ischemic heart failure.

Evidence is accumulating to support the presence of P2X purinergic receptors in the heart. However, the biological role of this receptor remains to be defined. The objectives here were to determine the role of cardiac P2X receptors in modulating the progression of post-myocardial infarction ischemic heart failure and to investigate the underlying mechanism. The P2X4 receptor (P2X4R) is an important subunit of native cardiac P2X receptors, and the cardiac-specific transgenic overexpression of P2X4R (Tg) was developed as a model. Left anterior descending artery ligation resulted in similar infarct size between Tg and wild-type (WT) mice (P > 0.1). However, Tg mice showed an enhanced cardiac contractile performance at 7 days, 1 mo, and 2 mo after infarction and an increased survival at 1 and 2 mo after infarction (P < 0.01). The enhanced intact heart function was manifested by a greater global left ventricular developed pressure and rate of contraction of left ventricular pressure in vitro and by a significantly increased fractional shortening and systolic thickening in the noninfarcted region in vivo (P < 0.05). The salutary effects on the ischemic heart failure phenotype were seen in both sexes and were not the result of any difference in infarct size in Tg versus WT hearts. An enhanced contractile function of the noninfarcted area in the Tg heart was likely an important rescuing mechanism. The cardiac P2X receptor is a novel target to treat post-myocardial infarction ischemic heart failure.

P2X purinergic receptor-mediated ionic current in cardiac myocytes of calsequestrin model of cardiomyopathy: implications for the treatment of heart failure.

P2X purinergic receptors, activated by extracellular ATP, mediate a number of cardiac cellular effects and may be important under pathophysiological conditions. The objective of the present study was to characterize the P2X receptor-mediated ionic current and determine its role in heart failure using the calsequestrin (CSQ) model of cardiomyopathy. Membrane currents under voltage clamp were determined in myocytes from both wild-type (WT) and CSQ mice. The P2X agonist 2-methylthio-ATP (2-meSATP) induced an inward current that was greater in magnitude in CSQ than in WT ventricular cells. The novel agonist, MRS-2339, an N-methanocarba derivative of 2-chloro-AMP relatively resistant to nucleotidase, induced a current in the CSQ myocyte similar to that by 2-meSATP. When administered via a miniosmotic pump (Alzet), it significantly increased longevity compared with vehicle-injected mice (log rank test, P = 0.02). The improvement in survival was associated with decreases in the heart weight-to-body weight ratio and in cardiac myocyte cross-sectional area [MRS-2339-treated mice: 281 +/- 15.4 (SE) mum(2), n = 6 mice vs. vehicle-treated mice: 358 +/- 27.8 mum(2), n = 6 mice, P < 0.05]. MRS-2339 had no vasodilator effect in mouse aorta ring preparations, indicating that its salutary effect in heart failure is not because of any vascular unloading. The cardiac P2X current is upregulated in the CSQ heart failure myocytes. Chronic administration of a nucleotidase-resistant agonist confers a beneficial effect in the CSQ model of heart failure, apparently via an activation of the cardiac P2X receptor. Cardiac P2X receptors represent a novel and potentially important therapeutic target for the treatment of heart failure.

Semi-rational design of (north)-methanocarba nucleosides as dual acting A(1) and A(3) adenosine receptor agonists: novel prototypes for cardioprotection.

Ring-constrained adenosine analogues have been designed to act as dual agonists at tissue-protective A(1) and A(3) adenosine receptors (ARs). 9-Ribosides transformed into the ring-constrained (N)-methanocarba-2-chloro-5'-uronamides consistently lost affinity at A(1)/A(2A)ARs and gained at A(3)AR. Among 9-riboside derivatives, only N(6)-cyclopentyl and 7-norbornyl moieties were extrapolated for mixed A(1)/A(3) selectivity and rat/human A(3)AR equipotency. Consequently, 2 was balanced in affinity and potency at A(1)/A(3)ARs as envisioned and dramatically protected in an intact heart model of global ischemia and reperfusion.