Attenuation of apoptosis in vitro and ischemia/reperfusion injury in vivo in mouse skeletal muscle by P2Y6 receptor activation.

Activation of the G(q)-coupled P2Y(6) receptor heterologously expressed in astrocytes significantly attenuates apoptosis induced by tumor necrosis factor alpha (TNFalpha). We have extended the analysis of P2Y(6) receptor-induced cytoprotection to mouse skeletal muscle cells endogenously expressing this receptor. The endogenous P2Y(6) receptor agonist UDP and synthetic agonist MRS2693 protected C2C12 skeletal muscle cells against apoptosis in a concentration-dependent manner (0.

Regulation of death and survival in astrocytes by ADP activating P2Y1 and P2Y12 receptors.

ADP is the endogenous agonist for both P2Y(1) and P2Y(12) receptors, which are important therapeutic targets. It was previously demonstrated that ADP and a synthetic agonist, 2-methylthioadenosine 5'-diphosphate (2MeSADP), can induce apoptosis by activating the human P2Y(1) receptor heterologously expressed in astrocytoma cells. However, it was not known whether the P2Y(12) receptor behaved similarly.

NUCLEOSIDE PRODRUGS OF A ADENOSINE RECEPTOR AGONISTS AND ANTAGONISTS.

9-(β-D-Ribosfuranosyluronamide)adenine derivatives that are selective agonists and antagonists of the A adenosine receptor (AR) have been derivatized as prodrugs for delivery. The free hydroxy groups at the 2' and 3' positions of the agonists 2-chloro- -(3-iodobenzyl)-9-(-methyl-(β-D-ribosfuranosyluronamide)adenine , the corresponding 4'-thio nucleoside , and antagonists and (5'-,-dimethylamides related to and , respectively) were derivatized through simple acylation reactions. The prodrug derivatives were tested in radioligand binding assays at ARs and in a functional assay of adenylate cyclase at the AAR and found to be considerably less active than the parent drugs.

Leptin protects the cardiac myocyte cultures from hypoxic damage.

Leptin, a circulating hormone mainly produced by adipose tissue, regulates fatty acid metabolism and causes multiple systemic biological actions even the regulation of cardiovascular function. It is previously known that leptin is a hypoxia-inducible hormone, that hypoxic conditions increase the expression of this peptide in various tissues such as placenta, pancreas and also in the heart. Since leptin receptors are present in the heart, we hypothesized that whether leptin was a protector response for tissues especially for the heart against the deleterious effects of hypoxia.

Role of adenosine A1 and A3 receptors in regulation of cardiomyocyte homeostasis after mitochondrial respiratory chain injury.

Activation of either the A(1) or the A(3) adenosine receptor (A(1)R or A(3)R, respectively) elicits delayed cardioprotection against infarction, ischemia, and hypoxia. Mitochondrial contribution to the progression of cardiomyocyte injury is well known; however, the protective effects of adenosine receptor activation in cardiac cells with a respiratory chain deficiency are poorly elucidated. The aim of our study was to further define the role of A(1)R and A(3)R activation on functional tolerance after inhibition of the terminal link of the mitochondrial respiratory chain with sodium azide, in a state of normoxia or hypoxia, compared with the effects of the mitochondrial ATP-sensitive K(+) channel opener diazoxide.

Enhanced connexin-43 and alpha-sarcomeric actin expression in cultured heart myocytes exposed to triiodo-L-thyronine.

This study examined whether triiodo-L-thyronine (T3) affects the expression of the major intercellular channel protein, connexin-43, and contractile protein alpha-sarcomeric actin. Cultured cardiomyocytes from newborn rats were treated on day three in culture with 10 or 100 nM T3 and examined 48 and 72 h thereafter. Treated and untreated cells were examined by immunofluorescence and electron microscopy.

2-Substituted adenosine derivatives: affinity and efficacy at four subtypes of human adenosine receptors.

The affinity and efficacy at four subtypes (A(1), A(2A), A(2B) and A(3)) of human adenosine receptors (ARs) of a wide range of 2-substituted adenosine derivatives were evaluated using radioligand binding assays and a cyclic AMP functional assay in intact CHO cells stably expressing these receptors. Similar to previous studies of the N(6)-position, several 2-substituents were found to be critical structural determinants for the A(3)AR activation. The following adenosine 2-ethers were moderately potent partial agonists (K(i), nM): benzyl (117), 3-chlorobenzyl (72), 2-(3-chlorophenyl)ethyl (41), and 2-(2-naphthyl)ethyl (130).

Diisothiocyanate derivatives as potent, insurmountable antagonists of P2Y6 nucleotide receptors.

The physiological role of the P2Y(6) nucleotide receptor may involve cardiovascular, immune and digestive functions based on the receptor tissue distribution, and selective antagonists for this receptor are lacking. We have synthesized a series of symmetric aryl diisothiocyanate derivatives and examined their ability to inhibit phospholipase C (PLC) activity induced by activation of five subtypes of recombinant P2Y receptors. Several derivatives were more potent at inhibiting action of UDP at both human and rat P2Y(6) receptors expressed in 1321N1 human astrocytes than activation of human P2Y(1), P2Y(2), P2Y(4) and P2Y(11) receptors.

Glycogen metabolism in rat heart muscle cultures after hypoxia.

Elevated glycogen levels in heart have been shown to have cardioprotective effects against ischemic injury. We have therefore established a model for elevating glycogen content in primary rat cardiac cells grown in culture and examined potential mechanisms for the elevation (glycogen supercompensation). Glycogen was depleted by exposing the cells to hypoxia for 2 h in the absence of glucose in the medium.

Mechanism of glycogen supercompensation in rat skeletal muscle cultures.

A model to study glycogen supercompensation (the significant increase in glycogen content above basal level) in primary rat skeletal muscle culture was established. Glycogen was completely depleted in differentiated myotubes by 2 h of electrical stimulation or exposure to hypoxia during incubation in medium devoid of glucose. Thereafter, cells were incubated in medium containing glucose, and glycogen supercompensation was clearly observed in treated myotubes after 72 h.

Insights into the cardioprotective function of adenosine A(1) and A(3) receptors.

Objectives: Cardioprotection (delaying of irreversible damage in hypoxia or prevention of doxorubicin [DOX] toxicity) is achieved by increasing the energy supply, or decreasing the energy demand in the cell and may be regulated through adenosine (ADO) receptor (AR) signalling. The aim of this study was to define of the protective role of ADO A(1)R and A(3)R against these two different kinds of stress conditions via direct action on isolated cardiomyocytes. Effects of A(1) and A(3) adenosine receptors were assessed by comparing morphological-functional tolerance, cellular energy state and contribution of the mitochondrial K(ATP) channels during development of hypoxia and DOX cytotoxicity.

Cardiomyocyte resistance to doxorubicin mediated by A(3) adenosine receptor.

Recently, we reported that the activation of A(3) adenosine receptor (A(3)R) in newborn cultured cardiomyocytes by highly selective agonist Cl-IB-MECA (2-chloro-N(6)-(3-iodobenzyl)adenosine-5'-N-methyluronamide) induces protection against the anthracycline antibiotic doxorubicin (DOX) cardiotoxicity. The present study was undertaken to further characterize the cardioprotective action of A(3)R activation by revealing the structural changes in cardiomyocytes elicited upon exposure to DOX. Morphological observations (ultrastructural and immunocytochemical) indicate that after DOX treatment, the cardiomyocytes undergo destructive alterations, and protective action of A(3)R is not connected with its anti-apoptotic activity.