The obligate role of protein kinase C in mediating clinically accessible cardiac preconditioning

HMGB1 preconditioning: therapeutic application for a danger signal?

High mobility group box 1 (HMGB1) is a nuclear factor released extracellularly as a late mediator of lethality in sepsis and as an early mediator of inflammation following injury. In contrast to the proinflammatory role of HMGB1, recent evidence suggests beneficial applications of HMGB1 in injury states. One such application is the use of HMGB1 as a preconditioning stimulus. Preconditioning is a phenomenon whereby a low level of stressful stimuli confers protection against subsequent injury. Preconditioning has been demonstrated in multiple species, can be induced by various stimuli, and is applicable in different organ systems. Only with the recent introduction of the concept of endogenous molecules, such as HMGB1, as signals and mediators for inflammation during injury states has the use of endogenous molecules been investigated for this use. This review will focus on the use of endogenous molecules, specifically HMGB1, as a preconditioning stimulus and its mechanism of protection, as well as other protective applications for HMGB1.

Protein kinase C-epsilon coimmunoprecipitates with cytochrome oxidase subunit IV and is associated with improved cytochrome-c oxidase activity and cardioprotection

We have utilized an in situ rat coronary ligation model to establish a PKC-epsilon cytochrome oxidase subunit IV (COIV) coimmunoprecipitation in myocardium exposed to ischemic preconditioning (PC). Ischemia-reperfusion (I/R) damage and PC protection were confirmed using tetrazolium-based staining methods and serum levels of cardiac troponin I. Homogenates prepared from the regions at risk (RAR) and not at risk (RNAR) for I/R injury were fractionated into cell-soluble (S), 600 g low-speed centrifugation (L), Percoll/Optiprep density gradient-purified mitochondrial (M), and 100,000 g particulate (P) fractions. COIV immunoreactivity and cytochrome-c oxidase activity measurements estimated the percentages of cellular mitochondria in S, L, M, and P fractions to be 0, 55, 29, and 16%, respectively. We observed 18, 3, and 3% of PKC-delta, -epsilon, and -zeta isozymes in the M fraction under basal conditions. Following PC, we observed a 61% increase in PKC-epsilon levels in the RAR M fraction compared with the RNAR M fraction. In RAR mitochondria, we also observed a 2.8-fold increase in PKC-epsilon serine 729 phosphoimmunoreactivity (autophosphorylation), indicating the presence of activated PKC-epsilon in mitochondria following PC. PC administered before prolonged I/R induced a 1.9-fold increase in the coimmunoprecipitation of COIV, with anti-PKC-epsilon antisera and a twofold enhancement of cytochrome-c oxidase activity. Our results suggest that PKC-epsilon may interact with COIV as a component of the cardioprotection in PC. Induction of this interaction may provide a novel therapeutic target for protecting the heart from I/R damage.

Protein kinase Cepsilon interacts with cytochrome c oxidase subunit IV and enhances cytochrome c oxidase activity in neonatal cardiac myocyte preconditioning

We have previously identified a phorbol ester-induced PKCepsilon (protein kinase Cepsilon) interaction with the ( approximately 18 kDa) COIV [CO (cytochrome c oxidase) subunit IV] in NCMs (neonatal cardiac myocytes). Since PKCepsilon has been implicated as a key mediator of cardiac PC (preconditioning), we examined whether hypoxic PC could induce PKCepsilon-COIV interactions. Similar to our recent study with phorbol esters [Ogbi, Chew, Pohl, Stuchlik, Ogbi and Johnson (2004) Biochem. J. 382, 923-932], we observed a time-dependent increase in the in vitro phosphorylation of an approx. 18 kDa protein in particulate cell fractions isolated from NCMs subjected to 1-60 min of hypoxia. Introduction of a PKCepsilon-selective translocation inhibitor into cells attenuated this in vitro phosphorylation. Furthermore, when mitochondria isolated from NCMs exposed to 30 min of hypoxia were subjected to immunoprecipitation analyses using PKCepsilon-selective antisera, we observed an 11.1-fold increase in PKCepsilon-COIV co-precipitation. In addition, we observed up to 4-fold increases in CO activity after brief NCM hypoxia exposures that were also attenuated by introducing a PKCepsilon-selective translocation inhibitor into the cells. Finally, in Western-blot analyses, we observed a >2-fold PC-induced protection of COIV levels after 9 h index hypoxia. Our studies suggest that a PKCepsilon-COIV interaction and an enhancement of CO activity occur in NCM hypoxic PC. We therefore propose novel mechanisms of PKCepsilon-mediated PC involving enhanced energetics, decreased mitochondrial reactive oxygen species production and the preservation of COIV levels.

Preconditioning: Gender Effects1

Preconditioning is injury induced protection from subsequent injury. During preconditioning protective cellular responses to injury are up regulated resulting in acute and delayed defense against further damage. Several studies indicate that females experience a protective advantage after acute insult compared to males. Despite evidence of gender differences in acute injury, relatively few studies have evaluated whether there are sex differences in preconditioning. Variations in patients' pre-morbid preconditioning status may explain outcome variations that are not apparent in small animal studies. This review discusses the differences in response to acute injury experienced by males and females, the basic mechanisms of preconditioning, and the sex differences in the mechanisms of preconditioning.

Magnesium blocks the loss of protein kinase C, leads to a transient translocation of PKCα and PKCε, and improves recovery after anoxia in rat hippocampal slices

Magnesium is a potent neuroprotective agent against damage to synaptic transmission during cerebral anoxia and reoxygenation. We investigated the mechanisms of anoxic transmission damage and magnesium neuroprotection by examining the response of PKC isoforms to an anoxic insult in the rat hippocampal slice model. A 2-min anoxic period, which resulted in almost complete recovery of synaptic function, did not result in PKC downregulation. In contrast, inducing long-term damage with 10-min anoxia resulted in the downregulation of the conventional PKCs betaI, betaII and gamma immediately after the insult and after 1-h reoxygenation. There was additional loss of PKC(alpha) and PKC(epsilon) after 1-h reoxygenation. Magnesium treatment improved the recovery of synaptic transmission, blocked the loss of PKC and resulted in a transient translocation of PKC(alpha) and PKC(epsilon) to the membrane fraction. Selective downregulation of cPKCs and PKC(epsilon) correlated with permanent damage to synaptic transmission while translocation of PKC(alpha) and PKC(epsilon) correlated with preservation of synaptic function. The mechanisms of magnesium neuroprotection may include altering the PKC response to an anoxic insult.

Preconditioning: evolution of basic mechanisms to potential therapeutic strategies

Preconditioning describes the phenomenon by which a traumatic or stressful stimulus confers protection against subsequent injury. Originally recognized in dog heart subjected to ischemic challenges, preconditioning has been demonstrated in multiple species, can be induced by various stimuli, and is applicable in different organ systems. Tremendous progress has been made elucidating the signal transduction cascade of preconditioning. Preconditioning represents a potent tissue-protective condition, and mechanistic understanding may allow safe clinical application. This review recalls the history of preconditioning and how it relates to the history of the investigation of endogenous adaptation; summarizes the current mechanistic understanding of acute preconditioning; outlines the signal transduction cascade leading to the development of delayed preconditioning; discusses preconditioning in noncardiac tissue; and explores the potential of using preconditioning clinically.

Attenuation of liver ischemia-reperfusion-induced atrial dysfunction by external pacing but not by isoproterenol

Remote ischemia–reperfusion detrimentally affects myocardial function by initially interfering with the rate of contraction. We investigated the usefulness of isoproterenol versus external electrical pacing in attenuating secondary functional damage of isolated Wistar rat atria. Atrial strips (n = 10/group) were bathed within oxygenated Krebs–Henseleit solution that exited from isolated livers that had been either perfused normally (controls) or underwent no flow (ischemia) for 2 h. In addition to one noninterventional ischemia-exposed strip group, a second group was externally paced at a fixed rate (55 pulses·min–1, 6 V) and a third "ischemia" group was treated with isoproterenol (0.1 mM), both interventions commencing upon the strips' exposure to the hepatic effluents. Control strips displayed unaltered contraction rate and systolic-generated tension during the 2-h exposure. Nontreated strips exposed to ischemic reperfusate experienced bradycardia compared with baseline values (7 ± 2 vs. 50 ± 12 beats·min–1, p < 0.05), followed <1-min later by a fall in the generated tension (11 ± 4 vs. 20 ± 6 mmHg, p < 0.05). The paced-ischemic strips displayed unaltered rate and force of contraction, whereas the addition of isoproterenol did not prevent deterioration in the rate and force of contraction (8 ± 3 beats·min–1, 12 ± 4 mmHg, respectively; p < 0.05 vs. baseline control ischemia-paced strips). Thus, external electrical pacing prevented liver ischemia–reperfusion-induced atrial strips' bradycardia and loss of contractility, while isoproterenol did not.Key words: ischemia, reperfusion, liver, atrium, dysfunction, isoproterenol, pacing.

Myocardial adenosine does not correlate with the protection mediated by ischaemic or pharmacological preconditioning in rat heart

1. We tested the hypothesis that ischaemic preconditioning of the rat heart activates cardiovascular adenosine formation to provide enhanced cardioprotection. 2. Rat isolated perfused hearts were either non-preconditioned, preconditioned with 5 min ischaemia or treated for 5 min with the alpha1-adrenoceptor agonist phenylephrine (50 micro mol/L) before being subjected to 30 min sustained ischaemia followed by 30 min reperfusion. Isolated cardiomyocytes were either non-preconditioned, subjected to 10 min simulated ischaemia or treated for 10 min with phenylephrine (50 micro mol/L) before being subjected to 30 min simulated ischaemia. Functional recovery of hearts and cell viability were used as indices of the effects of ischaemia. 3. Myocardial adenosine, as well as intracellular pH, was determined at the end of the preconditioning period and at 10, 20 and 30 min of sustained ischaemia. Intracellular pH was also determined during the reperfusion. 4. Ischaemic or pharmacological preconditioning with phenylephrine correlated with an improved functional recovery of perfused hearts during reperfusion and increased cell viability during ischaemia. 5. In perfused hearts, ischaemic preconditioning resulted in increased adenosine production in the myocardium during the following sustained ischaemia. However, in isolated cardiomyocytes, adenosine levels during sustained ischaemia were lower in ischaemically preconditioned cells compared with the respective non-preconditioned cardiomyocytes. 6. The increase in adenosine production was not observed in hearts preconditioned with phenylephrine instead of transient ischaemia. Similarly, pharmacological preconditioning resulted in decreased adenosine levels during sustained ischaemia in isolated cardiomyocytes. 7. Intracellular pH was preserved during ischaemia to the same extent in both ischaemically or pharmacologically preconditioned hearts and cardiomyocytes, indicating that less acidosis during ischaemia is related to protection. 8. Taken together, the results suggest that cardioprotection does not necessarily correlate with increased adenosine production. Thus, adenosine concentration is not crucial to the beneficial effects of preconditioning in rat heart.

Ischemic preconditioning: fact or fantasy?

Fifteen years ago, an experimental effort to magnify a myocardial infarction, with preinfarction episodes of transient ischemia, proved paradoxically protective. In the ensuing years, surgeons have learned to discriminate a biochemical/metabolic/functional spectrum of cardiac states ranging from healthy myocardium to "stunned" or "hibernating" heart to the modes of "apoptotic" or "necrotic" cardiomyocyte death. It is now clear that "protective cardiac preconditioning" influences all of these cardiac states. The cellular mechanisms of preconditioning (PC) are now sufficiently understood to permit clinical application. Ligation of adrenergic, adenosine, bradykinin or opioid receptors involves signaling via both tyrosine and calcium-dependent protein kinases (PKC), which activate mitochondrial ATP-dependent potassium channels. Subsequently, the release of oxygen radicals induces nuclear translocation of transcriptional regulators, which transform the cardiomyocyte into a more resilient cell. Although preconditioning was initially recognized as protecting only against infarction, PC also limits postischemic dysrhythmias and enhances contractile function. Phase I (safety) and phase II (efficacy) clinical trials now persuasively support pharmacological preconditioning as a safe mode of preventing postcardiac surgical complications. Indeed, preconditioning is currently being proposed as adjunctive to hypothermic perfusates in protecting against the obligate organ ischemia during transplantation.

Heat shock prevents simulated ischemia-induced apoptosis in renal tubular cells via a PKC-dependent mechanism

Heat shock produces cellular tolerance to a variety of adverse conditions; however, the protective effect of heat shock on renal cell ischemic injury remains unclear. Protein kinase C (PKC) has been implicated in the signaling mechanisms of acute preconditioning, yet it remains unknown whether PKC mediates heat shock-induced delayed preconditioning in renal cells. To study this, renal tubular cells (LLC-PK1) were exposed to thermal stress (43 degrees C) for 1 h and heat shock protein (HSP) 72 induction was confirmed by Western blot analysis. Cells were subjected to simulated ischemia 24 h after thermal stress, and the effect of heat shock (delayed preconditioning) on ischemia-induced apoptosis (terminal deoxynucleotidyl transferase dUTP nick-end labeling) and B cell lymphoma 2 (Bcl(2)) expression (Western) was determined. Subsequently, the effect of PKC inhibition on HSP72 induction and heat stress-induced ischemic tolerance was evaluated. Thermal stress induced HSP72 production, increased Bcl(2) expression, and prevented simulated ischemia-induced renal tubular cell apoptosis. PKC inhibition abolished thermal induction of HSP72 and prevented heat stress-induced ischemic tolerance. These data demonstrate that thermal stress protects renal tubular cells from simulated ischemia-induced apoptosis through a PKC-dependent mechanism.

Role of adenosine and glycogen in ischemic preconditioning of rat hearts

We tested whether ischemic preconditioning of the rat heart is mediated by reduced glycogenolysis during ischemia, an event triggered by adenosine A1 receptor activation. Rat hearts (n=40) were studied with [31P] and [13C] nuclear magnetic resonance (NMR) spectroscopy, using the Langendorff perfusion technique (5.5 mM [1-13C]glucose, 10 U/l insulin). In parallel experiments, hearts (n=43) were freeze-clamped at different time-points throughout the protocol. They were subjected to either ischemic preconditioning (PC), PC in the presence of 50 microM adenosine receptor antagonist, 8-(p-sulfophenyl)-theophylline (SPT), or intermittent infusion of 0.25 microM adenosine A1 receptor agonist, 2-chloro-N6-cyclopentyladenosine (CCPA). After 30 min ischemia and reperfusion, recovery of heart ratexpressure product was improved in hearts treated with preconditioning (33+/-13%) or CCPA (58+/-14%) compared with the SPT and ischemic control (IC) groups, which both failed to recover (P<0.05). CCPA administration induced a 58% increase in pre-ischemic [13C]glycogen (P<0.05 vs. all groups). In the PC and SPT groups, [13C]glycogen decreased by 25 and 47%, respectively (P<0.05) due to the short bouts of ischemia, resulting in lower pre-ischemic glycogen compared to ischemic control and CCPA hearts (P<0.05). The rate of [13C]glycogen utilization during the first 15 min of ischemia (in micromol/min g wwt) was not statistically different between IC (0.42+/-0.03), PC (0.30+/-0.04), and CCPA (0.38+/-0.05) hearts, but was reduced in SPT hearts (0.24+/-0.05; P<0.05). Total glycogen depletion during 30-min ischemia was reduced in PC hearts (0.61 mg/g wwt) compared to IC (1.84 mg/g wwt) and CCPA (1.75 mg/g wwt) hearts; SPT did not block reduced glycogenolysis during ischemia in PC hearts (0.77 mg/g wwt vs. IC). This study adds further strong evidence that in rat hearts, adenosine is involved in ischemic preconditioning. However, protection is unrelated to pre-ischemic glycogen levels and glycogenolysis during ischemia.

Bench to bedside: tumor necrosis factor-alpha: from inflammation to resuscitation

Proinflammatory mediators such as tumor necrosis factor-alpha (TNF) have been implicated in the pathophysiology in a number of acute disease states. Tumor necrosis factor-alpha can contribute to cell death, apoptosis, and organ dysfunction. Tumor necrosis factor-alpha can be generated with sepsis or ischemia-reperfusion by activation of cell mitogen-activated protein kinases and nuclear factor kappa B, leading to TNF production. A number of strategies to modulate TNF have been recently explored, including factors directed toward mitogen-activated protein kinases, TNF transcription, anti-inflammatory ligands, heat shock proteins, and TNF-binding proteins. However, TNF may also play an important role in the adaptive response to injury and inflammation. Control of the deleterious effects of TNF and other proinflammatory cytokines represents a realistic goal for clinical emergency medicine. The purpose of this article is to provide a background of relevance to emergency medicine academicians on the production and regulation of TNF, the acute effects of TNF on pathophysiology, and the rationale for therapeutic interventions directed toward TNF and the clinical experience with these strategies.

Exogenous calcium preconditions myocardium from patients taking oral sulfonylurea agents

We have previously reported that atrial trabeculae from patients taking oral sulfonylurea hypoglycemic agents cannot be preconditioned by transient ischemia, which may, in part, explain the increased cardiovascular mortality historically associated with the use of these agents (J. C. Cleveland et al., 1997, Circulation 96, 29-32). Recently, we reported that clinically accessible and acceptable exogenous Ca(2+) pretreatment protects human atrial trabeculae from subsequent ischemia (B. S. Cain et al., 1998, Ann. Thoracic Surg. 65, 1065-1070). It remains unknown whether this preconditioning strategy could confer protection to trabeculae from patients taking oral sulfonylurea drugs. We therefore hypothesized that exogenous Ca(2+) confers ischemic protection to trabeculae from patients taking oral sulfonylureas. Human atrial trabeculae were suspended in organ baths and field stimulated at 1 Hz, and force development was recorded. Following 90 min equilibration, trabeculae from patients taking oral sulfonylurea agents (n = 6 patients) were subjected to ischemia/reperfusion (I/R; 45/120 min) with or without Ca(2+) (1 mM increase x 5 min) 10 min prior to I/R. I/R decreased postischemic human myocardial contractility in trabeculae from patients on oral hypoglycemics to 15.3 +/- 2.0% baseline developed force (%BDF). Ca(2+) pretreatment increased postischemic human myocardial developed force to 35.3 +/- 2.9 %BDF in these patients (P < 0.05 vs I/R, ANOVA and Bonferroni/Dunn). We conclude that atrial muscle from patients taking oral hypoglycemic agents can be preconditioned with exogenous Ca(2+). This therapy may offer a clinically relevant means to precondition the myocardium of diabetics taking oral hypoglycemic agents prior to clinical interventions such as coronary angioplasty or cardiac bypass.

Calcium preconditioning, but not ischemic preconditioning, bypasses the adenosine triphosphate-dependent potassium (KATP) channel

BACKGROUND

Recent evidence has implicated the KATP channel as an important mediator of ischemic preconditioning (IPC). Indeed, patients taking oral sulfonylurea hypoglycemic agents (i.e., KATP channel inhibitors) for treatment of diabetes mellitus are resistant to the otherwise profoundly protective effects of IPC. Unfortunately, many cardiopulmonary bypass patients, who may benefit from IPC, are chronically exposed to these agents. Calcium preconditioning (CPC) is a potent form of similar myocardial protection which may or may not utilize the KATP channel in its mechanism of protection. The purpose of this study was to determine whether CPC may bypass the KATP channel in its mechanism of action. If so, CPC may offer an alternative to IPC in patients chronically exposed to these agents.

METHODS

Isolated rat hearts (n = 6-8/group) were perfused (Langendorff) and received KATP channel inhibition (glibenclamide) or saline vehicle 10 min prior to either a CPC or IPC preconditioning stimulus or neither (ischemia and reperfusion, I/R). Hearts were subjected to global warm I/R (20 min/40 min). Postischemic myocardial functional recovery was determined by measuring developed pressure (DP), coronary flow (CF), and compliance (end diastolic pressure, EDP) with a MacLab pressure digitizer.

RESULTS

Both CPC and IPC stimuli protected myocardium against postischemic dysfunction (P < 0.05 vs I/R; ANOVA with Bonferroni/Dunn): DP increased from 52 +/- 4 (I/R) to 79 +/- 2 and 83 +/- 4 mmHg; CF increased from 11 +/- 0.7 to 17 +/- 2 and 16 +/- 1 ml/min; and EDP decreased (compliance improved) from 50 +/- 7 to 27 +/- 5 and 31 +/- 7 mmHg. However, KATP channel inhibition abolished protection in hearts preconditioned with IPC (P < 0.05 vs IPC alone), but not in those preconditioned with CPC (P > 0.05 vs CPC alone).

CONCLUSIONS

(1) Both IPC and CPC provide similar myocardial protection; (2) IPC and CPC operate via different mechanisms; i.e., IPC utilizes the KATP channel whereas CPC does not; and (3) CPC may offer a means of bypassing the deleterious effects of KATP channel inhibition in diabetic patients chronically exposed to oral sulfonylurea hypoglycemic agents.

Tumor necrosis factor-alpha and interleukin-1beta synergistically depress human myocardial function

OBJECTIVE

Proinflammatory cytokines such as tumor necrosis factor (TNF)-alpha and interleukin (IL)-1beta have been implicated in the pathogenesis of myocardial dysfunction in ischemia-reperfusion injury, sepsis, chronic heart failure, viral myocarditis, and cardiac allograft rejection. Although circulating TNF-alpha and IL-1beta are both often elevated in septic shock, it remains unknown whether TNF-alpha or IL-1beta are the factors induced during sepsis that directly depress human myocardial function, and if so, whether the combination synergistically depresses myocardial function. Furthermore, the mechanism(s) by which these cytokines induce human myocardial depression remain unknown. We hypothesized the following: a) TNF-alpha and IL-1beta directly depress human myocardial function; b) together, TNF-alpha and IL-1beta act synergistically to depress human myocardial function; and c) inhibition of ceramidase or nitric oxide synthase attenuates myocardial depression induced by TNF-alpha or IL-1beta by limiting proximal cytokine signaling or production of myocardial nitric oxide (NO).

DESIGN

Prospective, randomized, controlled study.

SETTING

Experimental laboratory in a university hospital.

SUBJECTS

Freshly obtained human myocardial trabeculae.

INTERVENTIONS

Human atrial trabeculae were obtained at the time of cardiac surgery, suspended in organ baths, and field simulated at 1 Hz, and the developed force was recorded. After a 90-min equilibration, TNF-alpha (1.25, 12.5, 125, or 250 pg/mL for 20 mins), IL-1beta (6.25, 12.5, 50, or 200 pg/mL for 20 mins), or TNF-alpha (1.25 pg/mL) plus IL-1beta (6.25 pg/mL) were added to the bath, and function was measured for the subsequent 100 mins after the 20-min exposure. To assess the roles of the sphingomyelin and NO pathways in TNF-alpha and IL-1beta cross-signaling, the ceramidase inhibitor N-oleoyl ethanolamine (1 microM) or the NO synthase inhibitor N(G)-monomethyl-L-arginine (10 microM) was added before TNF-alpha (125 pg/mL) or IL-1beta (50 pg/mL).

MEASUREMENTS AND MAIN RESULTS

TNF-alpha and IL-1beta each depressed human myocardial function in a dose-dependent fashion (maximally depressing to 16.2 + 1.9% baseline developed force for TNF-alpha and 25.7 + 6.3% baseline developed force for IL-1beta), affecting systolic relatively more than diastolic performance (each p < .05). However, when combined, TNF-alpha and IL-1beta at concentrations that did not individually result in depression (p > .05 vs. control) resulted in contractile depression (p < .05 vs. control). Inhibition of myocardial sphingosine or NO release abolished the myocardial depressive effects of either TNF-alpha or IL-1beta.

CONCLUSIONS

TNF-alpha and IL-1beta separately and synergistically depress human myocardial function. Sphingosine likely participates in the TNF-alpha and IL-1beta signal leading to human myocardial functional depression. Therapeutic strategies to reduce production or signaling of either TNF-alpha or IL-1beta may limit myocardial dysfunction in sepsis.

p38 MAPK inhibition decreases TNF-alpha production and enhances postischemic human myocardial function

INTRODUCTION

TNF-alpha is a proinflammatory cytokine implicated in myocardial dysfunction following ischemia/reperfusion (I/R). I/R results in myocardial production of TNF-alpha and TNF-alpha suppresses myocardial contractility. p38 mitogen-activated protein kinase (MAPK) is a redox-sensitive protein kinase involved in intracellular signaling leading to TNF-alpha production. It remains unknown if the human heart produces TNF-alpha after I/R and, if so, whether p38 MAPK is involved.

HYPOTHESIS

p38 MAPK inhibition enhances human myocardial post-I/R contractile function by inhibition of myocardial TNF-alpha production.

METHODS

Human atrial trabeculae were suspended in organ baths, field simulated at 1 Hz, and force development was recorded. Following a 90-min equilibration, trabeculae were exposed to a p38 MAPK inhibitor (SB 203580, 1 microM) or vehicle (each n = 6) prior to simulated ischemia (45 min hypoxia, substrate-free, rapid pacing at 3 Hz) followed by 120 min reoxygenation. Myocardial TNF-alpha levels were measured by ELISA at end reoxygenation.

RESULTS

I/R increased human myocardial TNF-alpha levels from 26.9 +/- 9.3 to 83.9 +/- 19.2 pg/g wet tissue (P < 0.05 perfusion vs I/R; ANOVA Bonferroni/Dunn), while p38 MAPK inhibition decreased post-I/R myocardial TNF-alpha levels to 32.3 +/- 8.0 pg/g wet tissue (P > 0.05 p38 MAPK inhibition vs I/R). p38 MAPK inhibition improved postischemic force development from 18.5 +/- 2.1 to 37.0 +/- 2.0% baseline developed force (%BDF; P < 0.05 I/R vs p38 MAPK inhibition).

CONCLUSIONS

(1) The human heart produces TNF-alpha after I/R, (2) p38 MAPK mediates myocardial I/R-induced TNF-alpha production, (3) p38 MAPK inhibition limits functional impairment after I/R, and (4) inhibition of ischemia-induced TNF-alpha production may represent a potent therapeutic strategy for improving myocardial function after angioplasty, coronary bypass, or heart transplantation.

Human SERCA2a levels correlate inversely with age in senescent human myocardium

OBJECTIVES

This study sought to characterize functional impairment after simulated ischemia-reperfusion (I/R) or Ca2+ bolus in senescent human myocardium and to determine if age-related alterations in myocardial concentrations of SERCA2a, phospholamban, or calsequestrin participate in senescent myocardial dysfunction.

BACKGROUND

Candidates for elective cardiac interventions are aging, and an association between age and impairment of relaxation has been reported in experimental animals. Function of the sarcoplasmic reticulum resulting in diastolic dysfunction could be dysregulated at the level of cytosolic Ca2+ uptake by SERCA2a, its inhibitory subunit (phospholamban), or at the level of Ca2+ binding by calsequestrin.

METHODS

Human atrial trabeculae from 17 patients (45-75 years old) were suspended in organ baths, field simulated at 1 Hz, and force development was recorded during I/R (45/120 min). Trabeculae from an additional 12 patients (53-73 years old) were exposed to Ca2+ bolus (2-3 mmol/L bath concentration). Maximum +/- dF/dt and the time constant of force decay (tau) were measured before and after I/R or Ca2+ bolus and related to age. SERCA2a, phospholamban, and calsequestrin from 12 patients (39-77 years old) were assessed by immunoblot.

RESULTS

Functional results indicated that maximum +/-dF/dt and tau were prolonged in senescent (>60 years) human myocardium after I/R (p < 0.05). Calcium bolus increased the maximum +/-dF/dt and decreased tau in younger, but not older patients (p < 0.05). SERCA2a and the ratio of SERCA2a to either phospholamban or calsequestrin were decreased in senescent human myocardium (p < 0.05).

CONCLUSIONS

Senescent human myocardium exhibits decreased myocardial SERCA2a content with age, which may, in part, explain impaired myocardial function after either I/R or Ca2+ exposure.

Postischemic function and protein kinase C signal transduction

BACKGROUND

The protective effects of myocardial preconditioning may occur by way of multiple mechanisms, with G-protein-mediated protein kinase C (PKC) translocation as a final common pathway. In this study we investigate the pharmacologic induction of preconditioning, by PKC translocation, using PKC agonists/antagonists to reveal its effects on contractile function after myocardial ischemia.

METHODS

Langendorff-perfused rabbit hearts received: (1) control; (2) dimethyl sulfoxide (vehicle); (3) acetylcholine (0.55 mmol/L; PKC agonist); (4) 1,2-s,n-dioctanoylglycerol (DOG; 22 mmol/L; PKC agonist); (5) chelerythrine (0.8 mmol/L; PKC antagonist); or (6) DOG-chelerythrine followed by a 2-hour ischemic period, using modified St. Thomas cardioplegia and a 45-minute reperfusion period. The period of ischemia was chosen so as to allow for improvement by appropriate agonists. To observe metabolic changes, tissue nucleotides and nucleosides were measured. Membrane and cytosolic fractions of PKC were determined by an anti-PKC antibody directed against the PKC delta isozyme. Lactate levels and myocardial pH were measured.

RESULTS

The PKC agonists DOG and acetylcholine showed the greatest recovery of developed pressure (68% +/- 2%, 60% +/- 9%, respectively). Although pH, lactate, and nucleotide levels were similar between groups at all times, myocyte PKC translocation demonstrated 25% of PKC delta isoforms on cell membrane sites during baseline, which shifted to 67% delta 17% with unprotected ischemia. DOG mimicked this shift with 58% delta 12% of PKC delta isoforms on membranes, which was also blocked by chelerythrine to 35% +/- 7%.

CONCLUSIONS

These data demonstrate that PKC translocation results in improved postischemic function, not by alteration of energetics or metabolism, and deserves further investigation.

Adenosine reduces cardiac TNF-alpha production and human myocardial injury following ischemia-reperfusion

Myocardial tumor necrosis factor-alpha (TNF-alpha) is an autocrine contributor to myocardial dysfunction and cardiomyocyte death in ischemia-reperfusion injury (I/R), sepsis, chronic heart failure, and cardiac allograft rejection. Cardiac resident macrophages and cardiomyocytes themselves produce TNF-alpha. In this regard, adenosine (ADO) has been reported to reduce macrophage TNF-alpha production. Our purposes were to determine whether (1) I/R induces rat myocardial TNF-alpha production; (2) ADO decreases ischemia-induced rat myocardial TNF-alpha production; (3) ADO functionally protects human myocardium against I/R; and (4) TNF-alpha-binding protein (TNFBP; p55) confers similar protection when substituted for ADO pretreatment. To study this, human atrial trabeculae were obtained during cardiac surgery and suspended in organ baths, paced at 1 Hz, and force development was recorded during I/R (45/120 min) with or without ADO pretreatment (125 microM x 10 min), or TNFBP (1 microgram/ml) during I/R. Isolated rat hearts were perfused using the Langendorff method undergoing I/R (20/40 min) with or without ADO pretreatment (125 microM x 2 min) and rat myocardial expression of TNF-alpha was assessed by ELISA. Results demonstrated that I/R increased rat myocardial TNF-alpha levels from 324 +/- 36 to 902 +/- 77 pg/g (P < 0.05; ANOVA and Bonferroni/Dunn) and decreased human myocardial developed force (DF) to 18 +/- 2% of baseline (%BDF; P < 0.05). ADO pretreatment decreased ischemia-induced rat myocardial TNF-alpha production (356 +/- 107 pg/g; P < 0.05) and increased postischemic DF of human myocardium to 39 +/- 3% BDF (P < 0.05. Further substantiating the link between ischemia-induced TNF-alpha production and injury, TNFBP administration similarly improved post-I/R function of human myocardium (55 +/- 5% BDF; P < 0.05 vs. I/R alone). We conclude that (1) I/R induces rat myocardial TNF-alpha production; (2) ADO pretreatment decreases I/R-induced rat myocardial TNF-alpha production; (3) ADO improves human myocardial function; (4) TNFBP confers similar protection; and (5) inhibition/neutralization of TNF-alpha represents a novel strategy for protecting human myocardium against ischemia and reperfusion injury.

Therapeutic antidysrhythmic and functional protection in human atria

Approximately 30% of patients suffer supraventricular dysrhythmias after cardiac bypass. While the heart can be constructively preconditioned to maintain function against subsequent ischemic insult using a variety of stimuli across many species, preconditioning in experimental animals is associated with decreased postischemic reperfusion cardiac dysrhythmias. This mode of therapeutic preconditioning has not been previously examined in human atrial myocardium. We therefore hypothesized that preconditioning provides both antidysrhythmic and functional protection to human atria. To study this, human atrial trabeculae were suspended in organ baths, paced at 1 Hz, while force development and ectopy were recorded before and after simulated ischemia. The study consisted of five groups: (1) control trabeculae (n = 12), (2) trabeculae exposed to dysrhythmogenic stimuli (phenylephrine 50 microM and isoproterenol 25 microM (n = 8)), (3) trabeculae exposed to ischemia-reperfusion (I/R) injury and then drug stimulated (n = 10), (4) trabeculae preconditioned with adenosine (ADO 125 microM) then drug stimulated (n = 10), and (5) trabeculae preconditioned with ischemic preconditioning (IPC) then drug stimulated (n = 6) each at end reoxygenation. Differences between groups were assessed using X2 analysis and ANOVA (Bonferroni/Dunn). Results demonstrated that human atrial trabeculae did not exhibit dysrhythmia at baseline or when stimulated with alpha and beta agonists. After I/R, control trabeculae exhibited stimulated reperfusion dysrhythmia, while trabeculae preconditioned with either ADO or transient ischemia exhibited decreased stimulated dysrhythmia (each P < 0.05 vs. I/R). Functionally, I/R decreased developed force (DF) to 16 +/- 2% of baseline (%BDF) while ADO pretreatment increased postischemic DF to 41 +/- 3% BDF (P < 0.05 vs. I/R) while IPC increased DF to 49 +/- 3% BDF (P < 0.05 vs. I/R). We conclude that (1) human atrial trabeculae can ve functionally preconditioned with either ADO or IPC, and (2) protective preconditioning/ cardioprotection does extend to dysrhythmia control and is therapeutically accessible in human atrial myocardium.

Tumor necrosis factor in the heart

The heart is a tumor necrosis factor (TNF)-producing organ. Both myocardial macrophages and cardiac myocytes themselves synthesize TNF. Accumulating evidence indicates that myocardial TNF is an autocrine contributor to myocardial dysfunction and cardiomyocyte death in ischemia-reperfusion injury, sepsis, chronic heart failure, viral myocarditis, and cardiac allograft rejection. Indeed, locally (vs. systemically) produced TNF contributes to postischemic myocardial dysfunction via direct depression of contractility and induction of myocyte apoptosis. Lipopolysaccharide or ischemia-reperfusion activates myocardial P38 mitogen-activated protein (MAP) kinase and nuclear factor kappa B, which lead to TNF production. TNF depresses myocardial function by nitric oxide (NO)-dependent and NO-independent (sphingosine dependent) mechanisms. TNF activation of TNF receptor 1 or Fas may induce cardiac myocyte apoptosis. MAP kinases and TNF transcription factors are feasible targets for anti-TNF (i.e., cardioprotective) strategies. Endogenous anti-inflammatory ligands, which trigger the gp130 signaling cascade, heat shock proteins, and TNF-binding proteins, also control TNF production and activity. Thus modulation of TNF in cardiovascular disease represents a realistic goal for clinical medicine.

Adaptive and maladaptive mechanisms of cellular priming

OBJECTIVE

The mechanisms of cellular priming resulting in both adaptive and maladaptive responses to subsequent injury and strategies for manipulating this priming to constructive therapeutic advantage are explored.

BACKGROUND DATA

A cell is prepared or educated by an initial insult (priming stimulus). Investigations in both laboratory animals and humans indicate that cells, organs, and perhaps even whole patients respond differently to a proximal second insult ("second hit") by virtue of this prior environmental history. The opportunity to achieve the primed state appears to be conserved across almost all cell types. The initial stimulus transmits a message to the cellular machinery that influences the cell's response to a subsequent challenge. This response may result in an exaggerated inflammatory response in the case of the neutrophil (an often maladaptive process) or an improved tolerance to injury by the myocyte (adaptive response). Our global hypothesis is that cellular priming is a conserved, receptor-dependent process that invokes common intracellular targets across multiple cell types. We further postulate that these targets create a language based on the transient phosphorylation and dephosphorylation of intracellular enzymes that is therapeutically accessible.

CONCLUSIONS

Priming is a conserved, receptor-dependent process transduced by means of intracellular targets across multiple cell types. The potential therapeutic strategies outlined involve the receptor-mediated manipulation of cellular events. These events are transmitted through an intracellular language that instructs the cell regarding its behavior in response to subsequent stimulation. Understanding these intracellular events represents a realistic goal of priming and preconditioning biology and will likely lead to clinical control of the primed state.

Mechanisms of cardiac preconditioning: ten years after the discovery of ischemic preconditioning

Cardiac preconditioning describes the phenomenon by which transient ischemia induces myocardial protection against subsequent ischemia and reperfusion injury. Ten years have passed since the original description of this potent cardiac protective strategy and within this period tremendous progress has been made elucidating the mechanisms of preconditioning. Mechanistic understanding may allow safe clinical application. This review (1) recalls the history of preconditioning and how it relates to the history of the investigation of endogenous adaptation; (2) summarizes the current mechanistic understanding of early preconditioning; (3) compares and contrasts the mechanisms of early versus delayed preconditioning; (4) suggests potential anti-inflammatory aspects of preconditioning; (5) examines limitations in laboratory models of preconditioning; and (6) explores the potential of using preconditioning clinically.

Protein kinase C isoform diversity in preconditioning

Protein kinase C (PKC) appears to be a common intracellular effector and signal collector during cardiac preconditioning; however, it remains unknown whether agonists that activate different PKC isoforms are also linked to select aspects of myocardial protection. Using agonists that are known to activate unique combinations of PKC isoforms, we interrogated the relationship between isoform activation and the different aspects (pH, function, and viability) of endogenous myocardial protection. To study this, isolated rat hearts were subjected to ischemia-reperfusion (I/R) (20 min/40 min), without (control = Ctrl) or with receptor-dependent [phenylephrine (PE), 50 microM; adenosine (ADO), 125 microM] or -independent [phorbol myristate acetate (PMA), 100 nM] activation of PKC. Function, pH, and viability were assessed by rate pressure product (%RPP) and coronary flow (CF; ml/min), by 31P NMR, and by CF creatine kinase (CK; U/liter) leak, respectively. PMA, which activates PKC delta but not eta, resulted in intracellular pH (pHi) and viability protection, but did not protect against postischemic myocardial stunning. ADO, which activates PKC eta but not delta, protects against stunning, but not acidosis or necrosis. PE, which activates PKC delta and eta, provided global myocardial protection against necrosis, acidosis, and stunning. Different PKC isoforms may be linked to distinct aspects of myocardial protection. Targeted activation of PKC isoforms may allow precise mechanistic application of preconditioning-like myocardial protection.