Pharmacology of caspase inhibitors in rabbit cardiomyocytes subjected to metabolic inhibition and recovery.

Protection of ischemic myocardium is an important unmet need in reperfusion therapy of acute myocardial infarction. Myocardial ischemia and reperfusion induce necrosis and apoptosis in cardiomyocytes. Caspase processing and activation are critical steps in most receptor and nonreceptor pathways of apoptosis. Caspase inhibitors have been shown to reduce ischemia reperfusion injury in cardiac muscle. Information about dose response and time of administration are needed to optimize the design of preclinical studies. We used isolated adult rabbit cardiomyocytes subjected to metabolic inhibition (MI) and recovery to examine the role of caspases and caspase inhibitors, the dose response, and the timing of administration. In vitro inhibitory concentrations (Ki) were determined for purified caspases. Cardiomyocytes subjected to MI were treated with peptidomimetic fluoromethyl ketone inhibitors of caspases before or during MI, or at recovery. Caspase inhibitors were most effective when added before MI and included throughout recovery, but were partially protective if added after MI. The optimal concentration of the inhibitors tested was approximately 10 microM. Protection was sustained when cells were allowed to recover for 4 or 24 h. These results suggest that caspase activation is an important component of myocyte injury mediated by MI and recovery. Low doses of caspase inhibitors were identified that reduce injury in this model system, and further investigations using in vivo models are warranted.

Apoptosis in myocardial ischemia-reperfusion.

The signal transduction pathways by which ischemia-reperfusion leads to apoptosis may involve the JNK pathway, ceramide generation, and inhibition of protective PKC pathways. The biochemical events associated with apoptosis include mitochondrial inactivation, cytochrome c dislocation, caspase activation, and cytoplasmic acidification. Through the concerted efforts of multiple classes of enzymes, apoptosis is accomplished, resulting in the death of a cell in which potentially transforming oncogenes have been degraded and inflammatory contents are contained within the plasma membrane until the fragments can be ingested by phagocytes. This non-inflammatory mode of cell death permits tissue remodeling with minimal scar formation, and so is preferable to necrotic cell death. The distinction between apoptosis and necrosis, which implies different mechanisms of cell death, is blurred in the case of a pathologic insult such as ischemia-reperfusion. It is suggested that it is more useful to view cell death in the context of whether or not it can be prevented.

Effect of vacuolar proton ATPase on pHi, Ca2+, and apoptosis in neonatal cardiomyocytes during metabolic inhibition/recovery.

Recently, we found that vacuolar proton ATPase (VPATPase) operates in cardiomyocytes as a complementary proton-extruding mechanism. Its activity was increased by preconditioning with resultant attenuation of intracellular acidification during ischemia. In this study, we examined whether VPATPase-mediated proton efflux during metabolic inhibition/recovery may spare Na+ overload via Na+-H+ exchange, attenuate Na+-Ca2+ exchange, and decrease apoptosis. Neonatal rat cardiomyocytes were subjected to 2- to 3-hour metabolic inhibition with cyanide and 2-deoxyglucose and 24-hour recovery. The effect of VPATPase inhibition by 50 nmol/L bafilomycin A1 on apoptosis, pHi, and [Ca2+]i was studied by flow cytometry with propidium iodide, seminaphthorhodafluor (SNARF)-1-AM, and indo-1-AM staining, respectively. VPATPase inhibition increased the amount of apoptosis measured after 24 hours of recovery and abrogated the protective effect of inhibition of Na+-H+ exchange by (5-N-ethyl-N-isopropyl)amiloride (EIPA). Dual blockade of VPATPase and Na+-H+ exchange was additive in effect with EIPA on pHi during metabolic inhibition/recovery and recovery from the acid challenge with sodium propionate. VPATPase blockade increased the rate of accumulation of intracellular Ca2+ at the beginning of metabolic inhibition and abrogated the delaying effect of EIPA on intracellular Ca2+ accumulation. These results indicate that VPATPase plays an important accessory role in cardiomyocyte protection by reducing acidosis and Na+-H+ exchange-induced Ca2+ overload.

Granulocyte colony-stimulating factor upregulates the vacuolar proton ATPase in human neutrophils.

We have previously shown that granulocyte colony-stimulating factor (G-CSF ) delays spontaneous neutrophil apoptosis through activation of the vacuolar proton ATPase (v-ATPase). We have now examined the regulation of the v-ATPase in neutrophils exposed to G-CSF in vitro. When neutrophils were cultivated in the absence of G-CSF, the 57-kD cytosolic B subunit of the v-ATPase disappeared within 1 to 2 hours, its loss preceding the nuclear changes of apoptosis and coinciding with the onset of acidification. By contrast, in neutrophils cultured for 2 hours in the presence of G-CSF, the amount of the 57-kD subunit was similar to that in freshly isolated neutrophils. However, inhibition of protein synthesis with cycloheximide and actinomycin D led to loss of the 57-kD subunit even in the presence of G-CSF. These results indicated that ongoing protein synthesis was required to maintain the v-ATPase, and further suggested that G-CSF acted, at least in part, by maintaining synthesis of the 57-kD cytosolic subunit. G-CSF also promoted the translocation of the 57-and 33-kD cytosolic v-ATPase subunits to the membrane. Our findings suggested two coordinate mechanisms by which the activity of the v-ATPase could be increased by G-CSF: the synthesis of cytosolic v-ATPase subunits and their translocation to the membrane.

Preconditioning rabbit cardiomyocytes: role of pH, vacuolar proton ATPase, and apoptosis.

Ischemic preconditioning signals through protein kinase C (PKC) to protect against myocardial infarction. This protection is characterized by diminished intracellular acidification. Acidification is also a feature of apoptosis, and several agents act to prevent apoptosis by preventing acidification through activation of ion channels and pumps to promote cytoplasmic alkalinization. We characterized metabolic inhibition, recovery, and preconditioning through a PKC-dependent pathway in cardiomyocytes isolated from adult rabbit hearts. Preconditioning reduced loss of viability assessed by morphology and reduced DNA nicking. Blockade of the vacuolar proton ATPase (VPATPase) prevented the effect of preconditioning to reduce metabolic inhibition-induced acidosis, loss of viability, and DNA nicking. The beneficial effect of Na+/H+ exchange inhibition, which is thought to be effective through reduced intracellular Na+ and Ca++, was also abrogated by VPATPase blockade, suggesting that acidification even in the absence of Na+/H+ exchange may lead to cell death. We conclude that a target of PKC in mediating preconditioning is activation of the VPATPase with resultant attenuation of intracellular acidification during metabolic inhibition. Inhibition of the "death protease," interleukin-1-beta converting enzyme or related enzymes, also protected against the injury that followed metabolic inhibition. This observation, coupled with the detection of DNA nicking in cells subjected to metabolic inhibition, suggests that apoptotic cell death may be preventable in this model of ischemia/reperfusion injury.

Effects of induced tolerance to bacterial lipopolysaccharide on myocardial infarct size in rats.

OBJECTIVES: Induced tolerance to bacterial lipopolysaccharide (LPS) by pretreatment with sublethal doses of LPS has been shown to reduce the inflammatory response of monocytes, circulating PMNs and PMN adhesion to endothelial cells in response to subsequent stimuli, and also to increase cellular and organ tolerance to stress by other mechanisms. Therefore, we undertook to determine whether or not LPS desensitization is associated with reduced myocardial infarct size at 3 days after reperfusion following coronary occlusion. METHODS: Rats were randomized to either daily intraperitoneal LPS injections to provide LPS tolerance, or to equal volumes of saline (controls). In both groups at day 7 nontransmural infarction was produced by a 45 min coronary occlusion followed by 3 days of reperfusion during which LPS injections were continued. Histologic infarct size was assessed as percent of the left ventricle and as a percent of the risk zone (determined by fluorescent microspheres). RESULTS: Myocardial infarct size as percent of the left ventricle and of the risk zone were significantly reduced in the LPS-tolerant group (n = 14) compared to control rats (n = 12), the latter being reduced by 37% (33.6 +/- 18.4 vs. 54.1 +/- 8.6% of the risk zone, P < 0.002). The percentages of activated circulating PMN after LPS desensitization and saline pretreatment were not different prior to coronary occlusion (at 7 days), but 3 days after coronary occlusion and reperfusion the percent of activated PMNs in the treated group was markedly reduced compared to controls (2.9 +/- 1.6 vs. 11.4 +/- 7.2%, respectively, P < 0.02). CONCLUSIONS: LPS desensitization in rats for 1 week prior to coronary occlusion inhibited activation of circulating PMNs 3 days after reperfusion following 45 min of coronary occlusion. LPS also is well-known to induce heat stress proteins and may affect other protective mechanisms. These actions are associated with a significant reduction in myocardial infarct size in LPS-tolerant animals compared to untreated controls.

The acid deoxyribonuclease of neutrophils: a possible participant in apoptosis-associated genome destruction.

Human neutrophils are terminally differentiated cells that spontaneously undergo apoptosis in tissue culture. Apoptosis in these cells can be delayed by culture in the presence of granulocyte colony-stimulating factor or other inflammatory mediators. Neutrophils were found to contain an acid endonuclease that appeared to be responsible for the internucleosomal DNA cleavage that accompanies apoptosis. As measured by a plasmid nicking assay, this endonuclease had a molecular weight (M(r)) of 35,000, a pH optimum of 5.5, and a threshold for activity of pH 6.6 to 6.8. It was weakly inhibited by divalent cations (Ca2+, Mg2+, and Zn2+) and more strongly inhibited by aurintricarboxylic acid and N-bromosuccinimide. DNA from neutrophils treated with nigericin in buffers of defined pH displayed nucleosomal ladders whose prominence varied with pH in a manner that paralleled the pH dependence of the plasmid cleavage assays, consistent with internucleosomal DNA cleavage by the acid endonuclease. We have previously shown that neutrophils undergo acidification to a pH value as low as 6.0 during apoptosis; we suggest that this endonuclease may be responsible for the DNA cleavage seen in apoptotic neutrophils.

Cell acidification in apoptosis: granulocyte colony-stimulating factor delays programmed cell death in neutrophils by up-regulating the vacuolar H(+)-ATPase.

Neutrophils in tissue culture spontaneously undergo programmed cell death (apoptosis), a process characterized by well-defined morphological alterations affecting the cell nucleus. We found that these morphological changes were preceded by intracellular acidification and that acidification and the apoptotic changes in nuclear morphology were both delayed by granulocyte colony-stimulating factor (G-CSF). Among the agents that defend neutrophils against intracellular acidification is a vacuolar H(+)-ATPase that pumps protons out of the cytosol. When this proton pump was inhibited by bafilomycin A1, G-CSF no longer protected the neutrophils against apoptosis. We conclude that G-CSF delays apoptosis in neutrophils by up-regulating the cells' vacuolar H(+)-ATPase and that intracellular acidification is an early event in the apoptosis program.

Reperfusion injury induces apoptosis in rabbit cardiomyocytes.

The most effective way to limit myocardial ischemic necrosis is reperfusion, but reperfusion itself may result in tissue injury, which has been difficult to separate from ischemic injury. This report identifies elements of apoptosis (programmed cell death) in myocytes as a response to reperfusion but not ischemia. The hallmark of apoptosis, nucleosomal ladders of DNA fragments (approximately 200 base pairs), was detected in ischemic/reperfused rabbit myocardial tissue but not in normal or ischemic-only rabbit hearts. Granulocytopenia did not prevent nucleosomal DNA cleavage. In situ nick end labeling demonstrated DNA fragmentation predominantly in myocytes. The pattern of nuclear chromatin condensation was distinctly different in reperfused than in persistently ischemic tissue by transmission electron microscopy. Apoptosis may be a specific feature of reperfusion injury in cardiac myocytes, leading to late cell death.

Comparison of patients with central sleep apnea. With and without Cheyne-Stokes respiration.

This study was designed to determine the impact of central sleep apnea with or without Cheyne-Stokes respiration (CSR) on morbidity and mortality. Central sleep apnea was found in 77 male general medical ward in-patients. Cheyne-Stokes respiration was found in 49 of the 77 men; in 15 men, CSR was severe, ie, > or = 25 percent of the night spent in CSR, in 34 men CSR was mild (1 to 25 percent CSR). Twenty-eight men had central sleep apnea but no CSR. An additional 31 patients had no sleep apnea and no CSR. The patients with severe CSR had more central apneas, more, but shorter desaturations, more awakenings and more wake time during the night, but spent more time in bed than those with no CSR or no apnea. Radiographic evidence was consistent with an association of CSR and heart failure. In addition, patients with severe CSR were at almost twice the risk of dying compared with those with no apnea and had a shorter survival time. Nevertheless, we could not confirm that CSR was an independent predictor of elevated mortality risk, implying that some other factors specific to severe CSR predispose these patients to shorter survival time.

Harnessing nature's own cardiac defense mechanism with acadesine, an adenosine regulating agent: importance of the endothelium.

Although the effects of adenosine on the heart, including the clinical suppression of cardiac arrhythmias, have been recognized for more than half a century, it is only in the last decade that the therapeutic potential of adenosine has been recognized. Research related to the clinical application of adenosine has concentrated on two areas. The first came directly from early observations about the use of adenosine in treating cardiac arrhythmias, in particular supraventricular tachycardias. The second relates to the use of adenosine to protect the heart from the deleterious consequences of myocardial ischemia and reperfusion. This review will focus on the latter cardioprotective properties of adenosine, particularly those shown by a novel group of drugs termed adenosine regulating agents, the prototype of which is acadesine (Protara).

Spatial and temporal correlation between leukocyte behavior and cell injury in postischemic rat skeletal muscle microcirculation.

BACKGROUND: Although leukocyte adhesion and capillary plugging are postulated to play a role in postischemic tissue injury, there is only limited evidence demonstrating the relationship between tissue leukocyte accumulation and cell injury in terms of their temporal sequence and spatial distribution. EXPERIMENTAL DESIGN: This study was designed to study in vivo neutrophil behavior and its correlation with cell injury in postischemic skeletal muscle microcirculation. The microcirculation of the rat spinotrapezius muscle was observed in vivo using dual-color digital microfluorography to simultaneously visualize leukocyte traffic and cell death (irreversible nuclear damage) on the basis of carboxyfluorescein diacetate succinimidyl ester and propidium iodide, respectively. A 1-hour period of hemorrhagic hypotension (40 mm Hg) followed by reperfusion was carried out to induce muscle injury. RESULTS: Hypotension was followed by an increase in leukocyte recruitment in two different ways: capillary obstruction and venular adhesion. Upon reperfusion, a majority of the leukocytes were initially dispersed from the muscle capillaries and venules, but then the number of leukocytes plugging capillaries and adherent to venules increased again in a time-dependent manner. The number of leukocytes obstructing capillaries was closely correlated with the postischemic systemic blood pressure. The cell injury became detectable initially at the end of the hypotensive period and then increased explosively after reperfusion before a significant leukocyte accumulation. Reperfusion-induced early nuclear injury was seen predominantly in reperfused capillaries without plugging leukocytes. A majority of the initially damaged nuclei were those of myocytes in the pericapillary space, but no nuclei of capillary endothelium was involved. Sodium (-)-8-(3-methoxy-4-phenylsulfinylphenyl) pyrazolo [1,5-a]-1,3,5-triazine-4-olate monohydrate, a novel inhibitor of xanthine oxidase, significantly attenuated the early increase in muscle injury and subsequent venular leukocyte adhesion after reperfusion. CONCLUSIONS: These results suggest the involvement of an endothelium-dependent mechanism involving xanthine oxidase in postischemic irreversible myocyte injury. It is conceivable that leukocytes adherent to venules as well as those plugging capillaries play only minor roles in the initial mechanism of reperfusion injury.

Intracoronary versus intravenous effects of cocaine on coronary flow and ventricular function.

BACKGROUND: Cocaine use has been associated with cardiomyopathy and ischemic coronary syndromes. However, the pathophysiological mechanisms responsible for these syndromes are not clear and have been suggested to involve direct effects of cocaine on myocyte contractility and coronary resistance as well as indirect effects via altered autonomic tone, secondary mediators, and myocardial metabolism. We sought to distinguish direct from indirect effects of cocaine on ventricular function and coronary resistance by comparison of the administration of intracoronary cocaine (0.12 to 0.36 mg/min constant infusion) with intravenous cocaine (5 mg/kg bolus infusion) in an in vivo anesthetized pig preparation. METHODS AND RESULTS: To control for changes in coronary resistance secondary to autoregulation and myocardial metabolism, the left anterior descending coronary artery was perfused at constant coronary pressure and the interventricular vein was cannulated for coronary venous oxygen saturation measurement. Coronary blood flow, regional percent segment shortening, myocardial oxygen consumption, and serum cocaine concentrations were measured. Intracoronary cocaine produced a dose-dependent decrease in percent segment shortening in the absence of significant changes in coronary flow or systemic hemodynamics. In contrast, intravenous cocaine had mild biphasic effects on coronary resistance with an initial brief vasodilation (30.0 +/- 5% increase in flow from control) followed by more prolonged vasoconstriction (17.0 +/- 3.3% decrease in flow from control), which were independent of autoregulation or myocardial metabolism. In addition, intravenous cocaine caused an early 48% decrease in percent segment shortening, at which time the measured cocaine concentration was 20.1 micrograms/mL blood. This was comparable to the intracoronary cocaine concentration of 17.1 micrograms/mL blood, which produced a similar 48% decrease in percent segment shortening. CONCLUSIONS: We conclude that the effects of acute cocaine exposure on ventricular function are predominantly direct but of brief duration and therefore probably not clinically relevant. The effects of cocaine on coronary tone are predominantly indirect and biphasic, with early vasodilation followed by mild and more prolonged vasoconstriction. In the absence of coronary stenosis or ventricular hypertrophy, this small amount of vasoconstriction is unlikely to cause ischemia.

Severe neutrophil depletion by leucocyte filters or cytotoxic drug does not improve recovery of contractile function in stunned porcine myocardium.

OBJECTIVE: The contribution of neutrophils to myocardial injury during stunning remains controversial because of conflicting results in neutropenic animals. The goal of this study was to compare the recovery of function in stunned myocardium using two distinct methods for inducing neutropenia in pigs. METHODS: Three groups of pigs were studied: control (n = 6), and made neutropenic by either Leukopak blood filters (n = 7), or cyclophosphamide (n = 7, 50 mg.kg-1 intravenously 4 d prior to study). In anaesthetised open chest pigs, with the heart paced at 110 beats.min-1, the left anterior descending coronary artery was perfused with an extracorporeal circuit at controlled coronary pressure (CP) and the regional coronary blood flow was measured. Systolic wall thickening was determined by sonomicrometry in the left anterior descending and circumflex coronary artery regions. The protocol consisted of 15 min of low flow ischaemia (CP = 40 mm Hg), followed by a staged reperfusion over 10 min back to baseline (CP = 90 mm Hg), and continued for 2 h. Blood filtration was initiated prior to ischaemia and stopped after 90 min reperfusion. RESULTS: In both treated groups during ischaemia and the initial 60 min of reperfusion the neutrophil count was severely depleted to < 5% compared to the control group. Aortic pressure, coronary blood flow during ischaemia, area at risk, and systolic wall thickening in the circumflex region were similar between groups. Recovery of systolic wall thickening in the left anterior descending region after reperfusion was equivalent in all three groups. In the filter group, arrhythmias during ischaemia and reperfusion were significantly less. CONCLUSION: As assessed in the pig model of myocardial stunning and using two different methods, severe neutropenia does not reduce the depression of contractile function.

Role of cardiac mast cells in complement C5a-induced myocardial ischemia.

Activated complement component C5a causes myocardial ischemia mediated by thromboxane (Tx) A2 and leukotrienes C4/D4. Blood cells are not involved in either the mediator release or the myocardial effects of C5a, suggesting that a C5a-sensitive, cardiac resident inflammatory cell is responsible. The goals of this study were to determine whether 1) cardiac mast cell activation accompanies the C5a response, 2) inhibition of mast cell degranulation inhibits the response, and 3) histamine release plays a role in the C5a-induced myocardial ischemia. The left anterior descending coronary artery (LAD) of open-chest pigs (n = 13) was perfused with arterial blood at constant pressure (95 mmHg). Coronary blood flow (CBF) was measured (in-line flowmeter) and regional function [percent segment shortening (%SS)] determined with sonomicrometry. A coronary vein was cannulated for measurement of plasma TxB2 and histamine (a marker of mast cell degranulation). Intracoronary C5a (500 ng) decreased coronary blood flow (45% of preinfusion levels) and LAD %SS (65% of preinfusion) and was accompanied by increases in coronary venous TxB2 (delta 63.3 ng/ml) and histamine (delta 200 nM). Mast cell inhibition with lodoxamide (2 mg/kg iv, n = 8) attenuated the C5a-induced fall in CBF (14 vs. 53% decrease, P < 0.01) and %SS (10 vs. 38% decrease, P < 0.01) and also reduced the C5a-induced increase in both coronary venous histamine (delta 26 vs. 278 nM, P < 0.05) and TxB2 (delta 0.34 vs. 63.3 ng/ml, P < 0.01). However, histamine H1 (pyrilamine) and H2 (ranitidine) receptor blockade had no effect on the C5a-induced fall in CBF or LAD %SS.(ABSTRACT TRUNCATED AT 250 WORDS)

Complement C5a-mediated myocardial ischemia and neutrophil sequestration: two independent phenomena.

The intracoronary infusion of complement C5a causes a decrease in coronary blood flow and contractile dysfunction mediated by thromboxane (TxA2) and leukotrienes. Although these effects are accompanied by polymorphonuclear leukocyte (PMN) sequestration, the role of PMNs and the source of these eicosanoids remain unknown. To assess the contribution of PMNs to the C5a-induced myocardial ischemic response, the left anterior descending (LAD) coronary artery of pigs (n = 13) was cannulated and pump perfused at constant pressure with either normal arterial blood or neutropenic arterial blood (PMN count 0.02 x 10(3) cells/microliters) obtained from animals treated with cyclophosphamide (50 mg/kg iv, given 4 days before). The coronary vein draining the LAD region was cannulated for measurement of leukocyte count and TxB2 levels. Two groups of animals were studied: group 1 (n = 7) neutropenic animals were instrumented and normal animals served as blood donors and group 2 (n = 6) normal animals were instrumented and neutropenic animals served as blood donors. The myocardial response to intracoronary C5a (500 ng) was determined in each animal during coronary perfusion with normal arterial blood and also with neutropenic arterial blood. During perfusion with normal arterial blood, C5a decreased coronary flow to 52.3% and contractile function to 58.8% of preinfusion values. This was accompanied by a transient myocardial accumulation of PMNs (arterial-coronary venous gradient of 5.4 x 10(3) cells/microliters) and increased TxB2 levels in coronary venous blood (from 0.31 to 17.5 ng/ml).(ABSTRACT TRUNCATED AT 250 WORDS)