Oxidant Stress and Damage in Post-Ischemic Mouse Hearts: Effects of Adenosine

Effect of dietary arginine to lysine ratios on productive performance, meat quality, plasma and muscle metabolomics profile in fast-growing broiler chickens

Background

Due to the important functions of arginine in poultry, it should be questioned whether the currently adopted dietary Arg:Lys ratios are sufficient to meet the modern broiler requirement in arginine. The present study aimed, therefore, to evaluate the effects of the dietary supplementation of L-arginine in a commercial broiler diet on productive performance, breast meat quality attributes, incidence and severity of breast muscle myopathies and foot pad dermatitis (FPD), and plasma and muscle metabolomics profile in fast-growing broilers.

Results

A total of 1,170 1-day-old Ross 308 male chicks was divided into two experimental groups of 9 replicates each fed either a commercial basal diet (CON, digestible Arg:Lys ratio of 1.05, 1.05, 1.06 and 1.07 in each feeding phase, respectively) or the same basal diet supplemented on-top with crystalline L-arginine (ARG, digestible Arg:Lys ratio of 1.15, 1.15, 1.16 and 1.17, respectively). Productive parameters were determined at the end of each feeding phase (12, 22, 33, 43 d). At slaughter (43 d), incidence and severity of FPD and breast myopathies were assessed, while plasma and breast muscle samples were collected and analyzed by proton nuclear magnetic resonance-spectroscopy. The dietary supplementation of arginine significantly reduced cumulative feed conversion ratio compared to the control diet at 12 d (1.352 vs. 1.401, P < 0.05), 22 d (1.398 vs. 1.420; P < 0.01) and 33 d (1.494 vs. 1.524; P < 0.05), and also tended to improve it in the overall period of trial (1.646 vs. 1.675; P = 0.09). Body weight was significantly increased in ARG compared to CON group at 33 d (1,884 vs. 1,829 g; P < 0.05). No significant effect was observed on meat quality attributes, breast myopathies and FPD occurrence. ARG birds showed significantly higher plasma concentration of arginine and leucine, and lower of acetoacetate, glutamate, adenosine and proline. Arginine and acetate concentrations were higher, whereas acetone and inosine levels were lower in the breast of ARG birds (P < 0.05).

Conclusions

Taken together, these data showed that increased digestible Arg:Lys ratio had positive effects on feed efficiency in broiler chickens probably via modulation of metabolites that play key roles in energy and protein metabolism.

A hypoxic episode during cardiogenesis downregulates the adenosinergic system and alters the myocardial anoxic tolerance

To what extent hypoxia alters the adenosine (ADO) system and impacts on cardiac function during embryogenesis is not known. Ectonucleoside triphosphate diphosphohydrolase (CD39), ecto-5'-nucleotidase (CD73), adenosine kinase (AdK), adenosine deaminase (ADA), equilibrative (ENT1,3,4), and concentrative (CNT3) transporters and ADO receptors A1, A2A, A2B, and A3 constitute the adenosinergic system. During the first 4 days of development chick embryos were exposed in ovo to normoxia followed or not followed by 6 h hypoxia. ADO and glycogen content and mRNA expression of the genes were determined in the atria, ventricle, and outflow tract of the normoxic (N) and hypoxic (H) hearts. Electrocardiogram and ventricular shortening of the N and H hearts were recorded ex vivo throughout anoxia/reoxygenation ± ADO. Under basal conditions, CD39, CD73, ADK, ADA, ENT1,3,4, CNT3, and ADO receptors were differentially expressed in the atria, ventricle, and outflow tract. In H hearts ADO level doubled, glycogen decreased, and mRNA expression of all the investigated genes was downregulated by hypoxia, except for A2A and A3 receptors. The most rapid and marked downregulation was found for ADA in atria. H hearts were arrhythmic and more vulnerable to anoxia-reoxygenation than N hearts. Despite downregulation of the genes, exposure of isolated hearts to ADO 1) preserved glycogen through activation of A1 receptor and Akt-GSK3β-GS pathway, 2) prolonged activity and improved conduction under anoxia, and 3) restored QT interval in H hearts. Thus hypoxia-induced downregulation of the adenosinergic system can be regarded as a coping response, limiting the detrimental accumulation of ADO without interfering with ADO signaling.

Evaluation of intracoronary adenosine to prevent periprocedural myonecrosis in elective percutaneous coronary intervention (from the PREVENT-ICARUS Trial)

Great interest has focused on pharmacotherapy to prevent periprocedural myocardial injury during elective percutaneous coronary intervention (PCI). The aim of the present trial was to investigate the benefits of preprocedural intracoronary administration of high-dose adenosine during elective PCI. This was a single-center, double-blind, randomized trial of patients undergoing elective PCI. The patients were randomized (1:1) by sealed envelops to intracoronary adenosine (120 μg for the right coronary artery and 180 μg for the left coronary artery) or placebo. The primary study end point was a periprocedural increase in troponin I >3 times the upper limit of normal. The secondary study end points were (1) the corrected Thrombolysis In Myocardial Infarction frame count; (2) troponin I release >10 times the upper limit of normal; (3) creatine kinase-MB mass release ≥3 times the upper limit of normal; and (4) the combined cumulative incidence of in-hospital death, periprocedural myocardial infarction, and in-hospital urgent target vessel revascularization. The safety end point was the occurrence of bradycardia and ventricular arrhythmias during study drug administration. From November 2009 to September 2010, we randomized 260 patients who were undergoing elective PCI to intracoronary adenosine (n = 130) or placebo (n = 130). A greater prevalence of calcified lesions was observed in the adenosine group (p = 0.002). In contrast, a greater prevalence of type C lesions (p = 0.091), chronic occlusions (p = 0.015), worse preprocedural Thrombolysis In Myocardial Infarction flow (p = 0.038), and more severely stenotic lesions (p = 0.005) were observed in the placebo group. No difference was found in the primary (67.7% vs 70%, p = 0.69) or secondary end points. No serious side effects were observed with adenosine. In conclusion, our randomized trial showed that preprocedural intracoronary administration of a single high-dose bolus of adenosine does not provide any benefit in terms of periprocedural myonecrosis in patients undergoing elective PCI.

Therapeutic potential of adenosine analogues and conjugates

This review summarizes current knowledge of adenosine analogues and conjugates with promising therapeutic properties. Adenosine is a signaling molecule that triggers numerous physiological responses. It acts through the adenosine receptors (ARs), belonging to the family of G-protein-coupled receptors and widely distributed throughout the body. Moreover, adenosine is involved in key biochemical processes as a part of ATP, the universal energy currency. Thus, compounds that are analogues of adenosine and its conjugates have been extensively studied as potential therapeutics. Many inhibitors of ARs are in clinical trials as promising agents in treatment of inflammation, type 2 diabetes, arrhythmia and as vasodilators used in the myocardial perfusion imaging (MPI) stress test. Furthermore, adenosine analogues revealed high efficacy as enzyme inhibitors, tested for antitrypanosomal action and as bivalent ligands and adenosine-oligoarginine conjugates as inhibitors of protein kinases.

The synthetic polyphenol tert-butyl-bisphenol inhibits myoglobin-induced dysfunction in cultured kidney epithelial cells

Abstract Rhabdomyolysis caused by severe burn releases extracellular myoglobin (Mb) that accumulates in the kidney and urine (maximum [Mb] approximately 50 microM) (termed myoglobinuria). Extracellular Mb can be a pro-oxidant. This study cultured Madin-Darby-canine-kidney-Type-II (MDCK II) cells in the presence of Mb and tested whether supplementation with a synthetic tert-butyl-polyphenol (tert-butyl-bisphenol; t-BP) protects these renal cells from dysfunction. In the absence of t-BP, cells exposed to 0-100 microM Mb for 24 h showed a dose-dependent decrease in ATP and the total thiol (TSH) redox status without loss of viability. Gene expression of superoxide dismutases-1/2, haemoxygenase-1 and tumour necrosis factor increased and receptor-mediated endocytosis of transferrin and monolayer permeability decreased significantly. Supplementation with t-BP before Mb-insult maintained ATP and the TSH redox status, diminished antioxidant/pro-inflammatory gene responses, enhanced monolayer permissiveness and restored transferrin uptake. Overall, bolstering the total antioxidant capacity of the kidney may protect against oxidative stress induced by experimental myoglobinuria.

Nucleoside/nucleobase transport and metabolism by microvascular endothelial cells isolated from ENT1−/− mice

Nucleoside and nucleobase uptake is integral to mammalian cell function, and its disruption has significant effects on the cardiovasculature. The predominant transporters in this regard are the equilibrative nucleoside transporter subtypes 1 (ENT1) and 2 (ENT2). To examine the role of ENT1 in more detail, we have assessed the mechanisms by which microvascular endothelial cells (MVECs) from ENT1−/− mice transport and metabolize nucleosides and nucleobases. Wild-type murine MVECs express mainly the ENT1 subtype with only trace levels of ENT2. These cells also have a Na+-independent equilibrative nucleobase transport mechanism for hypoxanthine (ENBT1). In the ENT1−/− cells, there is no change in ENT2 or ENBT1, resulting in a very low level of nucleoside uptake in these cells, but a high capacity for nucleobase accumulation. Whereas there were no significant changes in nucleoside transporter subtype expression, there was a dramatic increase in adenosine deaminase and adenosine A2a receptors (both transcript and protein) in the ENT1−/− tissues compared with WT. These changes in adenosine deaminase and A2a receptors likely reflect adaptive cellular mechanisms in response to reduced adenosine flux across the membranes of ENT1−/− cells. Our study also revealed that mouse MVECs have a nucleoside/nucleobase transport profile that is more similar to human MVECs than to rat MVECs. Thus mouse MVECs from transgenic animals may prove to be a useful preclinical model for studies of the effects of purine metabolite modifiers on vascular function.

Endogenous adenosine selectively modulates oxidant stress via the A1 receptor in ischemic hearts

We tested the impact of A1 adenosine receptor (AR) deletion on injury and oxidant damage in mouse hearts subjected to 25-min ischemia/45-min reperfusion (I/R). Wild-type hearts recovered approximately 50% of contractile function and released 8.2 +/- 0.7 IU/g of lactate dehydrogenase (LDH). A1AR deletion worsened dysfunction and LDH efflux (15.2 +/- 2.6 IU/g). Tissue cholesterol and native cholesteryl esters were unchanged, whereas cholesteryl ester-derived lipid hydroperoxides and hydroxides (CE-O(O)H; a marker of lipid oxidation) increased threefold, and alpha-tocopherylquinone [alpha-TQ; oxidation product of alpha-tocopherol (alpha-TOH)] increased sixfold. Elevations in alpha-TQ were augmented by two- to threefold by A1AR deletion, whereas CE-O(O)H was unaltered. A(1)AR deletion also decreased glutathione redox status ([GSH]/[GSSG + GSH]) and enhanced expression of the antioxidant response element heme oxygenase-1 (HO-1) during I/R: fourfold elevations in HO-1 mRNA and activity were doubled by A1AR deletion. Broad-spectrum AR agonism (10 microM 2-chloroadenosine; 2-CAD) countered effects of A1AR deletion on oxidant damage, HO-1, and tissue injury, indicating that additional ARs (A(2A), A(2B), and/or A3) can mediate similar actions. These data reveal that local adenosine engages A1ARs during I/R to limit oxidant damage and enhance outcome selectively. Control of alpha-TOH/alpha-TQ levels may contribute to A1AR-dependent cardioprotection.

Physiology of Nucleoside Transporters: Back to the Future

Nucleoside transporters (NTs) are integral membrane proteins responsible for mediating and facilitating the flux of nucleosides and nucleobases across cellular membranes. NTs are also responsible for the uptake of nucleoside analog drugs used in the treatment of cancer and viral infections, and they are the target of certain compounds used in the treatment of some types of cardiovascular disease. The important role of NTs as drug transporters and therapeutic targets has necessarily led to intense interest into their structure and function and the relationship between these proteins and drug efficacy. In contrast, we still know relatively little about the fundamental physiology of NTs. In this review, we discuss various aspects of the physiology of NTs in mammalian systems, particularly noting tissues and cells where there has been little recent research. Our central thesis is reference back to some of the older literature, combined with current findings, will provide direction for future research into NT physiology that will lead to a fuller understanding of the role of these intriguing proteins in the everyday lives of cells, tissues, organs, and whole animals.