Assessment of the cytoprotective role of adenosine in an in vitro cellular model of myocardial ischemia

Cardiac Thyrotropin-releasing Hormone Inhibition Improves Ventricular Function and Reduces Hypertrophy and Fibrosis After Myocardial Infarction in Rats

BACKGROUND

Cardiac thyrotropin-releasing hormone (TRH) is a tripeptide with still unknown functions. We demonstrated that the left ventricle (LV) TRH system is hyperactivated in spontaneously hypertensive rats and its inhibition prevented cardiac hypertrophy and fibrosis. Therefore, we evaluated whether in vivo cardiac TRH inhibition could improve myocardial function and attenuate ventricular remodeling in a rat model of myocardial infarction (MI).

METHODS AND RESULTS

In Wistar rats, MI was induced by a permanent left anterior descending coronary artery ligation. A coronary injection of a specific small interfering RNA against TRH was applied simultaneously. The control group received a scrambled small interfering RNA. Cardiac remodeling variables were evaluated one week later. In MI rats, TRH inhibition decreased LV end-diastolic (1.049 ± 0.102 mL vs 1.339 ± 0.102 mL, P < .05), and end-systolic volumes (0.282 ± 0.043 mL vs 0.515 ± 0.037 mL, P < .001), and increased LV ejection fraction (71.89 ± 2.80% vs 65.69 ± 2.85%, P < .05). Although both MI groups presented similar infarct size, small interfering RNA against TRH treatment attenuated the cardiac hypertrophy index and myocardial interstitial collagen deposition in the peri-infarct myocardium. These effects were accompanied by attenuation in the rise of transforming growth factor-β, collagen I, and collagen III, as well as the fetal genes (atrial natriuretic peptide, B-type natriuretic peptide, and beta myosin heavy chain) expression in the peri-infarct region. In addition, the expression of Hif1α and vascular endothelial growth factor significantly increased compared with all groups.

CONCLUSIONS

Cardiac TRH inhibition improves LV systolic function and attenuates ventricular remodeling after MI. These novel findings support the idea that TRH inhibition may serve as a new therapeutic strategy against the progression of heart failure.

Translation of nanomedicines from lab to industrial scale synthesis: The case of squalene-adenosine nanoparticles

A large variety of nanoparticle-based delivery systems have become increasingly important for diagnostic and/or therapeutic applications. Yet, the numerous physical and chemical parameters that influence both the biological and colloidal properties of nanoparticles remain poorly understood. This complicates the ability to reliably produce and deliver well-defined nanocarriers which often leads to inconsistencies, conflicts in the published literature and, ultimately, poor translation to the clinics. A critical issue lies in the challenge of scaling-up nanomaterial synthesis and formulation from the lab to industrial scale while maintaining control over their diverse properties. Studying these phenomena early on in the development of a therapeutic agent often requires partnerships between the public and private sectors which are hard to establish. In this study, through the particular case of squalene-adenosine nanoparticles, we reported on the challenges encountered in the process of scaling-up nanomedicines synthesis. Here, squalene (the carrier) was functionalized and conjugated to adenosine (the active drug moiety) at an industrial scale in order to obtain large quantities of biocompatible and biodegradable nanoparticles. After assessing nanoparticle batch-to-batch consistency, we demonstrated that the presence of squalene analogs resulting from industrial scale-up may influence several features such as size, surface charge, protein adsorption, cytotoxicity and crystal structure. These analogs were isolated, characterized by multiple stage mass spectrometry, and their influence on nanoparticle properties further evaluated. We showed that slight variations in the chemical profile of the nanocarrier's constitutive material can have a tremendous impact on the reproducibility of nanoparticle properties. In a context where several generics of approved nanoformulated drugs are set to enter the market in the coming years, characterizing and solving these issues is an important step in the pharmaceutical development of nanomedicines.

Intracellular ATP concentration contributes to the cytotoxic and cytoprotective effects of adenosine

Extracellular adenosine (Ade) interacts with cells by two pathways: by activating cell surface receptors at nanomolar/micromolar concentrations; and by interfering with the homeostasis of the intracellular nucleotide pool at millimolar concentrations. Ade shows both cytotoxic and cytoprotective effects; however, the underlying mechanisms remain unclear. In the present study, the effects of adenosine-mediated ATP on cell viability were investigated. Adenosine treatment was found to be cytoprotective in the low intracellular ATP state, but cytotoxic under the normal ATP state. Adenosine-mediated cytotoxicity and cytoprotection rely on adenosine-derived ATP formation, but not via the adenosine receptor pathway. Ade enhanced proteasome inhibition-induced cell death mediated by ATP generation. These data provide a new pathway by which adenosine exerts dual biological effects on cell viability, suggesting an important role for adenosine as an ATP precursor besides the adenosine receptor pathway.

Cardioprotection induced by adenosine A1 receptor agonists in a cardiac cell ischemia model involves cooperative activation of adenosine A2A and A2B receptors by endogenous adenosine

Extracellular adenosine concentrations increase within the heart during ischemia, and any exogenous adenosine receptor agonists therefore work in the context of significant local agonist concentrations. We evaluated the interactions between A1, A2A, A2B, and A3 receptors in the presence and absence of adenosine deaminase (ADA, which is used to remove endogenous adenosine) in a cardiac cell ischemia model. Simulated ischemia (SI) was induced by incubating H9c2(2-1) cells in SI medium for 12 hours in 100% N2 gas before assessment of necrosis using propidium iodide (5 microM) or apoptosis using AnnexinV-PE flow cytometry. N6-Cyclopentyladenosine (CPA; 10(-7)M) and N6-(3-iodobenzyl) adenosine-5'-N-methyluronamide (IB-MECA; 10(-7)M) reduced the proportion of nonviable cells to 30.87 +/- 2.49% and 35.18 +/- 10.30%, respectively (% of SI group). In the presence of ADA, the protective effect of CPA was reduced (62.82 +/- 3.52% nonviable), whereas the efficacy of IB-MECA was unchanged (35.81 +/- 3.84% nonviable; P < 0.05, n = 3-5, SI vs. SI + ADA). The protective effects of CPA and IB-MECA were abrogated in the presence of their respective antagonists DPCPX (8-cyclopentyl-1,3-dipropylxanthine) and MRS1191 [3-ethyl-5-benzyl-2-methyl-4-phenylethynyl-6-phenyl-1,4-(+/-)-dihydropyridine-3,5-dicarboxylate], whereas A2A and A2B agonists had no significant effect. CPA-mediated protection was abrogated in the presence of both A2A (ZM241385, 4-(2-[7-amino-2-(2-furyl)[1,2,4]triazolo[2,3-a][1,3,5]triazin-5-lamino]ethyl)phenol; 50 nM) and A2B (MRS1754, 8-[4-[((4-cyanophenyl)carbamoylmethyl)oxy]phenyl]-1,3-di(n-propyl)xanthine; 200 nM) antagonists (n = 3-5, P < 0.05). In the absence of endogenous adenosine, significant protection was observed with CPA in presence of CGS21680 (4-[2-[[6-amino-9-(N-ethyl-b-D-ribofuranuronamidosyl)-9H-purin-2-yl]amino]ethyl]benzenepropanoic acid) or LUF5834 [2-amino-4-(4-hydroxyphenyl)-6-(1H-imidazol-2-ylmethylsulfanyl)pyridine-3,5-dicarbonitrile] (P < 0.05 vs. SI + ADA + CPA). Apoptosis (14.35 +/- 0.15% of cells in SI + ADA group; P < 0.05 vs. control) was not significantly reduced by CPA or IB-MECA. In conclusion, endogenous adenosine makes a significant contribution to A1 agonist-mediated prevention of necrosis in this SI model by cooperative interactions with both A2A and A2B receptors but does not play a role in A3 agonist-mediated protection.

Signaling pathways of cardioprotective ischemic preconditioning

BACKGROUND

Ischemia/reperfusion (I/R) injury is a major contributory factor to cardiac dysfunction and infarct size that determines patient prognosis after acute myocardial infarction. During the last 20 years, since the appearance of the first publication on ischemic preconditioning (IP), our knowledge of this phenomenon has increased exponentially.

RESULTS AND CONCLUSION

Basic scientific experiments and preliminary clinical trials in humans suggest that IP confers resistance to subsequent sustained ischemic insults not only in the regional tissue but also in distant organs (remote ischemic preconditioning), which may provide a simple, cost-effective means of reducing the risk of perioperative myocardial ischemia. The mechanism may be humoral, neural, or a combination of both, and involves adenosine, bradykinin, protein kinases and K(ATP) channels, although the precise end-effector remains unclear. This review describes different signaling pathways involved in acute ischemic preconditioning in detail.

[Development of cardiac physiopathological models from cultured cardiomyocytes]

The cultures of neonatal rat cardiomyocytes represent a very useful tool for the observation and the understanding of the cellular aspects of the electrophysiological, contractile, morphological, metabolic and molecular properties of the myocardium. This model is characterized by a homogeneous population of cardiac muscular cells and by vast possibilities of control of the chemical and physical environment of the cells, allowing the in vitro mimicry of a wide range of cardiac pathological situations. The cardiomyocyte cultures are thus suited to very varied experimental protocols, allowing multiparametric analysis of the cardiocellular effects of different stress such as hypoxia-reoxygenation, of ischemia-reperfusion, of the free radical attack and of thermal shock. These investigations can be combined with the study of the effects and of the cytotoxicity of pharmacological agents, not limited to the putatively cardioactive drugs. The present review proposes an outline of the procedures for the isolation, the culture and the use of neonatal cardiomyocytes. To illustrate the potentialities of this preparation, we describe more specifically the protocols and the various consequences at the cellular scale of an in vitro model of myocardial ischemia reperfusion.

Acute adenosinergic cardioprotection in ischemic-reperfused hearts

Cells of the cardiovascular system generate and release purine nucleoside adenosine in increasing quantities when constituent cells are "stressed" or subjected to injurious stimuli. This increased adenosine can interact with surface receptors in myocardial, vascular, fibroblast, and inflammatory cells to modulate cellular function and phenotype. Additionally, adenosine is rapidly reincorporated back into 5'-AMP to maintain the adenine nucleotide pool. Via these receptor-dependent and independent (metabolic) paths, adenosine can substantially modify the acute response to ischemic insult, in addition to generating a more sustained ischemia-tolerant phenotype (preconditioning). However, the molecular basis for acute adenosinergic cardioprotection remains incompletely understood and may well differ from more widely studied preconditioning. Here we review current knowledge and some controversies regarding acute cardioprotection via adenosine and adenosine receptor activation.

Specific electromechanical responses of cardiomyocytes to individual and combined components of ischemia

The main factors of myocardial ischemia are hypoxia, substrate deprivation, acidosis, and high extracellular potassium concentration ([K+]e), but the influence of each of these factors has not yet been evaluated in a cardiomyocyte (CM) culture system. Electromechanical responses to the individual and combined components of ischemia were studied in CM cultured from newborn rat ventricles. Action potentials (APs) were recorded using glass microelectrodes and contractions were monitored photometrically. Glucose-free hypoxia initially reduced AP duration, amplitude, and rate and altered excitation-contraction coupling, but AP upstroke velocity (Vmax) remained unaffected. Early afterdepolarizations appeared, leading to bursts of high-rate triggered impulses before the complete arrest of electromechanical activity after 120 min. Acidosis reduced Vmax whereas AP amplitude and rate were moderately decreased. Combining acidosis and substrate-free hypoxia also decreased Vmax but attenuated the effects of substrate-free hypoxia on APs and delayed the cessation of the electrical activity (180 min). Raising [K+]e reduced the maximal diastolic potential and Vmax. Total ischemia (substrate deletion, hypoxia, acidosis, and high [K+]e) decreased AP amplitude and Vmax without changing AP duration. Moreover, delayed afterdepolarizations appeared, initiating triggered activity. Ultimately, 120 min of total ischemia blocked APs and contractions. To conclude, glucose-free hypoxia caused severe functional defects, acidosis delayed the changes induced by substrate-free hypoxia, and total ischemia induced specific dysfunctions differing from those caused by the former conditions. Heart-cell cultures thus represent a valuable tool to scrutinize the individual and combined components of ischemia on CMs.