Role of opioid delta1 receptors, mitochondrial K(ATP) channels, and protein kinase C during cardiocyte apoptosis

The roles of PKC-δ and PKC-ε in myocardial ischemia/reperfusion injury

Ischemia and reperfusion (I/R) cause a reduction in arterial blood supply to tissues, followed by the restoration of perfusion and consequent reoxygenation. The reestablishment of blood flow triggers further damage to ischemic tissue through reactive oxygen species (ROS) accumulation, interference with cellular ion homeostasis, opening of mitochondrial permeability transition pores (mPTPs) and promotion of cell death (apoptosis or necrosis). PKC-δ and PKC-ε, belonging to a family of serine/threonine kinases, have been demonstrated to play important roles during I/R injury in cardiovascular diseases. However, the cardioprotective mechanisms of PKC-δ and PKC-ε in I/R injury have not been elaborated until now. This article discusses the roles of PKC-δ and PKC-ε during myocardial I/R in redox regulation (redox signaling and oxidative stress), cell death (apoptosis and necrosis), Ca²⁺ overload, and mitochondrial dysfunction.

Cardioprotective Exercise and Pharmacologic Interventions as Complementary Antidotes to Cardiovascular Disease

Exercise and pharmacologic therapies to prevent and treat cardiovascular disease have advanced largely through independent efforts. Understanding of first-line drug therapies, findings from preclinical animal studies, and the need for research initiatives related to complementary cardioprotective exercise-pharma interventions are reviewed from the premise that contemporary cardioprotective therapies must include adjunctive exercise and lifestyle interventions in addition to pharmacologic agents.

Prospects for Creation of Cardioprotective and Antiarrhythmic Drugs Based on Opioid Receptor Agonists

It has now been demonstrated that the μ, δ1 , δ2 , and κ1 opioid receptor (OR) agonists represent the most promising group of opioids for the creation of drugs enhancing cardiac tolerance to the detrimental effects of ischemia/reperfusion (I/R). Opioids are able to prevent necrosis and apoptosis of cardiomyocytes during I/R and improve cardiac contractility in the reperfusion period. The OR agonists exert an infarct-reducing effect with prophylactic administration and prevent reperfusion-induced cardiomyocyte death when ischemic injury of heart has already occurred; that is, opioids can mimic preconditioning and postconditioning phenomena. Furthermore, opioids are also effective in preventing ischemia-induced arrhythmias.

Myocardial apoptosis and infarction after ischemia/reperfusion are attenuated by kappa-opioid receptor agonist

BACKGROUND AND AIMS

It remains unclear whether U50488H (a selective kappa-opioid receptor agonist) produces anti-apoptotic effect during ischemia and reperfusion (I/R). Therefore, the effect of U50488H on myocardial apoptosis was investigated in the present study.

METHODS

Rats were subjected to 45min coronary artery occlusion and 180min of reperfusion. U50488H (1.5mg/kg IV) was given prior to occlusion. Nor-Binaltorphimine (nor-BNI) (2mg/kg IV), a selective kappa-opioid receptor antagonist, was given 10min prior to U50488H. Cardiac apoptosis was evaluated by terminal deoxynucleotidyl transferase mediated dUTP-biotin nick end labeling (TUNEL) assay and in situ identification of nuclear DNA fragmentation.

RESULTS

The ultrastructure injury of myocardium, myocardial infarct size, and plasma CK and LDH were reduced significantly with administration of U50488H before I/R, whereas the effects of U50488H were abolished by nor-BNI. DNA fragments were visualized by agarose electrophoresis, and clear DNA ladder formation was observed in myocardial tissue from hearts subjected to I/R. Administration of U50488H before ischemia exerted a significant anti-apoptotic effect as evidenced by markedly weaker DNA ladder formation. TUNEL staining showed U50488H treatment before I/R significantly reduced the percentage of apoptotic cells, which was blocked by 5-HD, a mitochondrial k(ATP) channel blocker. In accordance, U50488H treatment significantly inhibited I/R-induced elevated activities of caspase-3 and caspase-9. U50488H also produced an increase in Bcl-2 and a decrease in Bax protein expression in the I/R heart, and the anti-apoptotic effects of U50488H were all blocked by nor-BNI.

CONCLUSIONS

U50488H reduces myocardial necrosis and apoptosis after I/R and activation of kappa-opioid receptor may mediate a role in U50488H-induced myocardial protection.

Baicalein protects chicken embryonic cardiomyocyte against hypoxia-reoxygenation injury via mu- and delta- but not kappa-opioid receptor signaling

Baicalein, a pure compound derived from Scutellaria baicalensis Georgi, protected cells from lethal damage in an ischemia-reperfusion model. This study was aimed to investigate the role of opioid receptors in mediating cardioprotection by baicalein against hypoxia-reoxygenation injury. By using chick cardiomyocyte as in vitro model, baicalein was added to the perfusate during 1 h-hypoxia followed by 1 h-reoxygenation. Cell viability was assessed by propidium iodide uptake, while apoptosis was assessed by TUNEL and Hoechst 33342 staining. The expression of opioid receptors mRNA in chicken embryonic myocardium was determined by RT-PCR. Opioid receptor antagonists, protein kinase C inhibitors, and KATP channel blockers were used to determine the presumed signal transduction pathways. The results showed that baicalein (0.1 approximately 5 microM) concentration dependently reduced hypoxia-reoxygenation-induced myocardial death and apoptosis. The cardioprotective effect of baicalein (1 microM) was blocked by pretreatment of nonspecific opioid receptor antagonist (naloxone), opioid mu-receptor (beta-funaltrexamine) and delta-receptor (7-Benzylidenenaltrexone) antagonists, protein kinase C inhibitors (H7 and chelerythrine), and KATP channel blockers (glibenclamide and 5-hydroxydecanoate). Finally, RT-PCR analysis successfully demonstrated the presence of opioid receptors mRNA in chicken embryonic cardiomyocytes. We conclude that the cardioprotective effect of baicalein is mediated via mu-, delta- but not kappa-opioid receptor and their related signal transduction pathways, such as protein kinase C and the KATP channel.

deltaPKC participates in the endoplasmic reticulum stress-induced response in cultured cardiac myocytes and ischemic heart

The cellular response to excessive endoplasmic reticulum (ER) stress includes the activation of signaling pathways, which lead to apoptotic cell death. Here we show that treatment of cultured cardiac myocytes with tunicamycin, an agent that induces ER stress, causes the rapid translocation of deltaPKC to the ER. We further demonstrate that inhibition of deltaPKC using the deltaPKC-specific antagonist peptide, deltaV1-1, reduces tunicamycin-induced apoptotic cell death, and inhibits expression of specific ER stress response markers such as CHOP, GRP78 and phosphorylation of JNK. The physiological importance of deltaPKC in this event is further supported by our findings that the ER stress response is also induced in hearts subjected to ischemia and reperfusion injury and that this response also involves deltaPKC translocation to the ER. We found that the levels of the ER chaperone, GRP78, the spliced XBP-1 and the phosphorylation of JNK are all increased following ischemia and reperfusion and that deltaPKC inhibition by deltaV1-1 blocks these events. Therefore, ischemia-reperfusion injury induces ER stress in the myocardium in a mechanism that requires deltaPKC activity. Taken together, our data show for the first time that deltaPKC activation plays a critical role in the ER stress-mediated response and the resultant cell death.

Ischemia reperfusion injury, preconditioning and critical illness

The purpose of this review is to describe in more detail ischemia reperfusion injury and preconditioning, and to speculate on the potential role of preconditioning in the care of critically ill patients. Current hemodynamic treatment of hypotension and hypoperfusion in critically ill patients is directed at ensuring essential organ perfusion by maintaining intravascular volume and cardiac output, and ensuring adequate oxygen delivery by maintaining arterial oxygen partial pressure and hemoglobin levels. However, morbidity and mortality remain high and new approaches to critically ill patients are required. Treatments are needed that can protect against organ ischemia during periods of low blood flow. In recent years, there has been a growing appreciation of the importance of ischemia reperfusion injury. Ischemia associated with reperfusion may result in greater injury than ischemia alone. Ischemic preconditioning is used to describe the protective effect of short periods of ischemia to an organ or tissue against longer periods of ischemia. Although first described in the myocardium, there is now evidence that this phenomenon occurs in a wide variety of organs and tissues, including the brain and other nervous tissue such as the retina and spinal cord, liver, stomach, intestines, kidney, and the lungs. Preconditioning therapy may offer a new avenue of treatment in critically ill patients. Both traditional preconditioning methods and pharmacologic agents that mimic or induce such preconditioning may be used in the future. Clinical trials of pharmacologic agents are underway in patients with coronary artery disease. Further trials of such methods and agents are needed in critically ill patients suffering from sepsis or multiorgan system failure.

Chromosome instability in T-cells cultured in the presence of pancuronium or fentanyl

BACKGROUND

Genomic instability is recognized as a cause of cellular apoptosis and certain drugs that exhibit a proapoptotic effect are also able to induce chromosome damage. Since we found in recent experiments that drugs such as pancuronium and fentanyl exerted an apoptogenic effect on T cells, we studied the capacity of those agents to promote chromosome instability, i.e. chromosome aberrations (CA) and telomeric associations (tas) in peripheral blood lymphocytes.

METHODS

Lymphocytes from healthy donors were cultured with pancuronium or fentanyl, using two different concentrations for each drug: 20 and 200 ng/ml for pancuronium and 10 and 30 ng/ml for fentanyl, respectively. Cells were exposed to each concentration of these drugs either for 24 or 48 h. The higher concentration chosen was the same at which we detected the proapoptotic effect in our previous works. Cytogenetic analysis was performed by means of a standard technique and chromosome aberrations or telomeric associations were blindly evaluated by two independent observers.

RESULTS

The chromosome aberrations we observed in treated cells were not significantly different from control lymphocytes. However, an unusual rate of telomeric associations (P < 0.001) was detected in cells exposed to both pancuronium and fentanyl, at each concentration tested and at each exposure time of the study.

CONCLUSIONS

Fentanyl and pancuronium do not have a direct clastogenic effect on T cultures, but at the same concentrations at which we demonstrated their apoptogenic power, these drugs are able to increase genomic instability through inducing an elevated rate of telomeric associations. Such a capacity could exploit in peripheral T cells the same mitochondrion-mediated signal pathway of apoptosis death.

Apoptogenic Effect of Fentanyl on Freshly Isolated Peripheral Blood Lymphocytes

BACKGROUND

Opioids may trigger the apoptotic death of widely ranging cell types, and apoptosis contributes to the immune deficiency of critically ill patients and subjects experiencing surgical trauma. There is evidence that an altered mitochondrial membrane potential constitutes an early and irreversible step in the death-signaling pathway of apoptosis. This study investigated whether fentanyl, a opioid widely used in the management of these patients, may induce apoptosis of T cells by altering their mitochondrial membrane potential.

METHODS

Peripheral blood lymphocytes were cultured in the presence of 30 ng fentanyl for 60 (time 1), 90 (time 2), and 120 (time 3) minutes, respectively. The cells then were processed for assessment of mitochondrial membrane potential by means of flow cytometry and confocal scanning microscopy. Furthermore, production of reactive oxygen species, expression of the Fas-Fas L pro-apoptotic pathway, and apoptosis frequency were measured by means of flow cytometry. Control cells were incubated for the same times in the complete culture medium without the drug.

RESULTS

Flow cytometry analysis showed a significantly increased rate (p < 0.05) of lymphocytes with disrupted mitochondrial membrane potential after incubation with fentanyl for 90 and 120 minutes, as compared with both control cells and lymphocytes cultured in the presence of fentanyl for 60 minutes. In addition, as early as 60 minutes after exposure to fentanyl, cells displayed a disrupted mitochondrial membrane potential when this was assayed by means of confocal laser scanning. These findings were associated with increased production of reactive oxygen species. The frequency of apoptotic lymphocytes was markedly increased (p < 0.05) after 120 minutes of incubation, as compared with untreated cells and cells exposed to fentanyl for only 60 and 90 minutes. Expression of Fas-FasL was not substantially affected by exposure to fentanyl.

CONCLUSIONS

Fentanyl may induce a time-dependent apoptosis of lymphocytes by altering their mitochondrial redox metabolism.

Protein kinase Cepsilon and the antiadrenergic action of adenosine in rat ventricular myocytes

Adenosine-induced antiadrenergic effects in the heart are mediated by adenosine A(1) receptors (A(1)R). The role of PKCepsilon in the antiadrenergic action of adenosine was explored with adult rat ventricular myocytes in which PKCepsilon was overexpressed. Myocytes were transfected with a pEGFP-N1 vector in the presence or absence of a PKCepsilon construct and compared with normal myocytes. The extent of myocyte shortening elicited by electrical stimulation of quiescent normal and transfected myocytes was recorded with video imaging. PKCepsilon was found localized primarily in transverse tubules. The A(1)R agonist chlorocyclopentyladenosine (CCPA) at 1 microM rendered an enhanced localization of PKCepsilon in the t-tubular system. The beta-adrenergic agonist isoproterenol (Iso; 0.4 microM) elicited a 29-36% increase in myocyte shortening in all three groups. Although CCPA significantly reduced the Iso-produced increase in shortening in all three groups, the reduction caused by CCPA was greatest with PKCepsilon overexpression. The CCPA reduction of the Iso-elicited shortening was eliminated in the presence of a PKCepsilon inhibitory peptide. These results suggest that the translocation of PKCepsilon to the t-tubular system plays an important role in A(1)R-mediated antiadrenergic actions in the heart.

Evidence for mitochondrial K+ channels and their role in cardioprotection

Twenty years after the discovery of sarcolemmal ATP-sensitive K+ channels and 12 years after the discovery of mitochondrial K(ATP) (mitoK(ATP)) channels, progress has been remarkable, but many questions remain. In the case of the former, detailed structural information is available, and it is well accepted that the channel couples bioenergetics to cellular electrical excitability; however, in the heart, a clear physiological or pathophysiological role has yet to be defined. For mitoK(ATP), structural information is lacking, but there is abundant evidence linking the opening of the channel to protection against ischemia-reperfusion injury or apoptosis. This review updates recent progress in understanding the physiological role of mitoK(ATP) and highlights outstanding questions and controversies, with the intent of stimulating additional investigation on this topic.

Delta-opioid receptor activation mimics ischemic preconditioning in the canine heart

The role of delta-opioid receptors in mediating ischemic preconditioning (IPC) in rats, rabbits, and pigs has been well-established; however, no studies have been performed in dogs. Therefore, the purpose of the present study was to determine if activation of delta-opioid receptors can mimic the cardioprotective effects of IPC in the canine heart and to determine if a nonselective opioid receptor antagonist could block IPC. All dogs were subjected to 60 minutes of left anterior descending (LAD) coronary artery occlusion and 3 hours of reperfusion. Ischemic preconditioning was produced by one 5-minute period of ischemia 10 minutes before LAD coronary artery occlusion. Infarct size (IS) expressed as a percent of the area at risk (AAR; IS/AAR) was determined by triphenyltetrazolium staining. Two selective delta-opioid receptor (DOR) agonists, TAN-67 and BW373U86, were administered by intracoronary infusion for 30 minutes before LAD occlusion and the opioid receptor antagonist naloxone was administered 30 minutes before IPC. Both TAN-67 and BW373U86 produced significant reductions in IS/AAR similar to that of IPC (control: 28+/-2.1; TAN: 12.3+/-2.2; IPC: 9.3+/-3.0: BW: 11.7+/-2.6). Naloxone attenuated the effect of IPC (control: 28+/-2.1; naloxone: 18.2+/-4.5). These results suggest that opioid receptors are important in IPC in dogs, and stimulation of delta-opioid receptors with selective agonists can mimic the cardioprotective effects of IPC and may have therapeutic potential.

The basic biology of apoptosis and its implications for cardiac function and viability

Apoptosis or programed cell death is a continuous process of destruction of nonfunctional cells. It is a physiologic process whereby the body disposes of unwanted cells by self-destruction and is our utmost defense against damaged cells. There are several pathways leading to programed cell death. Apoptosis is seen in failing, infarcted, and hibernating human hearts, and during open heart surgery. Apoptosis appears to be induced by myocardial ischemia-reperfusion injury and this is reduced by ischemic preconditioning. Antiapoptotic interventions may be a future target for myocardial protection.

Receptor crosstalk. Implications for cardiovascular function, disease and therapy

There are at least three well-defined signalling cascades engaged directly in the physiological regulation of cardiac circulatory function: the beta1-adrenoceptors that control the cardiac contractile apparatus, the renin-angiotensin-aldosterone system involved in regulating blood pressure and the natriuretic peptides contributing at least to the factors determining circulating volume. Apart from these pathways, other cardiac receptor systems, particularly the alpha1-adrenoceptors, adenosine, endothelin and opioid receptors, whose physiological role may not be immediately evident, are also important with respect to regulating cardiovascular function especially in disease. These and the majority of other cardiovascular receptors identified to date belong to the guanine nucleotide binding (G) protein-coupled receptor families that mediate signalling by coupling primarily to three G proteins, the stimulatory (Gs), inhibitory (Gi) and Gq/11 proteins to stimulate the adenylate cyclases and phospholipases, activating a small but diverse subset of effectors and ion channels. These receptor pathways are engaged in crosstalk utilizing second messengers and protein kinases as checkpoints and hubs for diverting, converging, sieving and directing the G protein-mediated messages resulting in different signalling products. Besides, the heart itself is endowed with the means to harmonize these signalling mechanisms and to fend off potentially fatal consequences of functional loss of the essential signalling pathways via compensatory reserve pathways, or by inducing some adaptive mechanisms to be turned on, if and when required. This receptor crosstalk constitutes the underlying basis for sustaining a coherently functional circulatory entity comprising mechanisms controlling the contractile apparatus, blood pressure and circulating volume, both in normal physiology and in disease.

Role of nitric-oxide synthase, free radicals, and protein kinase C delta in opioid-induced cardioprotection

Opioids generate free radicals that mediate protection in isolated cultured cardiomyocytes. We hypothesize that the nature of these radicals is nitric oxide, and that nitric oxide activates the protein kinase C (PKC) delta isoform. Through this signal transduction pathway, opiates protect cardiomyocytes during hypoxia and reoxygenation. Cell viability was quantified in chick embryonic ventricular myocytes with propidium iodide. Oxygen radicals were quantified using a molecular probe, 2',7'-dichlorofluorescin diacetate (DCFH-DA). After a 10-min infusion of the opioid delta receptor agonist BW373U86 (BW; 2 or 20 pM) and a 10-min drug-free period, cells were subjected to hypoxia for 1 h followed by reoxygenation for 3 h. BW produced a concentration-dependent reduction in cardiomyocyte death (2 pM, 35.3 +/- 3.9%, n = 5; 20 pM, 21.5 +/- 4.0%, n = 8, p < 0.05 versus controls) and attenuated oxidant stress compared with controls (43.3 +/- 4.2%, n = 8). The increase in DCFH-DA oxidation with BW before hypoxia was abolished by the specific nitric-oxide synthase inhibitors nitro-L-arginine methyl ester (L-NAME) or N(G)-monomethyl-L-arginine (L-NMMA) (100 microM each). L-NAME or L-NMMA blocked the protective effects of BW. BW selectively increased the activity of PKC delta isoform in the particulate fraction, and its protection was abolished by the selective PKC delta inhibitor rottlerin (1 microM). Similar to BW, infusion with 5 microM of the nitric oxide donor S-nitroso-N-acetylpenicillamine (SNAP) reduced cardiomyocyte death (24.6 +/- 3.7, n = 8), and this protection was blocked by chelerythrine or rottlerin. Chelerythrine and rottlerin had no effect on BW-generated oxygen radicals before hypoxia, but they abolished the protection of SNAP. The nature of DCFH oxidation produced by opioid delta receptor stimulation is nitric oxide. Nitric oxide mediates cardioprotection via activating PKC delta in isolated myocytes.

H(2)O(2) opens mitochondrial K(ATP) channels and inhibits GABA receptors via protein kinase C-epsilon in cardiomyocytes

Oxygen radicals and protein kinase C (PKC) mediate ischemic preconditioning. Using a cultured chick embryonic cardiomyocyte model of hypoxia and reoxygenation, we found that the oxygen radicals generated by ischemic preconditioning were H(2)O(2). Like preconditioning, H(2)O(2) selectively activated the epsilon-isoform of PKC in the particulate compartment and increased cell viability after 1 h of hypoxia and 3 h of reoxygenation. The glutathione peroxidase ebselen (converting H(2)O(2) to H(2)O) and the superoxide dismutase inhibitor diethyldithiocarbamic acid abolished the increased H(2)O(2) and the protection of preconditioning. PKC activation with phorbol 12-myristate 13-acetate increased cell survival; the protection of preconditioning was blocked by epsilonV(1-2), a selective PKC-epsilon antagonist. Similar to preconditioning, the protection of PKC activation was abolished by mitochondrial K(ATP) channel blockade with 5-hydroxydecanoate or by GABA receptor stimulation with midazolam or diazepam. In addition, PKC, mitochondrial ATP-sensitive K(+) (K(ATP)) channels, and GABA receptors had no effects on H(2)O(2) generated by ischemic preconditioning before prolonged hypoxia and reoxygenation. We conclude that H(2)O(2) opens mitochondrial K(ATP) channels and inhibits GABA receptors via activating PKC-epsilon. Through this signal transduction, preconditioning protects ischemic cardiomyocytes.