Lipid abnormalities in myocardial cell injury

Identifying the role of cytochrome c in post-resuscitation pathophysiology

Cytochrome c, an electron carrier that normally resides in the mitochondrial intermembrane space, may translocate to the cytosol under ischemic and hypoxic conditions and contribute to mitochondrial permeability transition pore opening. In addition, reperfusion of brain tissue following ischemia initiates a cell death cascade that includes cytochrome c-mediated induction of apoptosis. Further studies are needed to determine the contribution of cytochrome c in the regulation of cell death, as well as its value as an in vivo prognostic marker after cardiac arrest and resuscitation.

Examination of physiological function and biochemical disorders in a rat model of prolonged asphyxia-induced cardiac arrest followed by cardio pulmonary bypass resuscitation

Background

Cardiac arrest induces whole body ischemia, which causes damage to multiple organs particularly the heart and the brain. There is clinical and preclinical evidence that neurological injury is responsible for high mortality and morbidity of patients even after successful cardiopulmonary resuscitation. A better understanding of the metabolic alterations in the brain during ischemia will enable the development of better targeted resuscitation protocols that repair the ischemic damage and minimize the additional damage caused by reperfusion.

Method

A validated whole body model of rodent arrest followed by resuscitation was utilized; animals were randomized into three groups: control, 30 minute asphyxial arrest, or 30 minutes asphyxial arrest followed by 60 min cardiopulmonary bypass (CPB) resuscitation. Blood gases and hemodynamics were monitored during the procedures. An untargeted metabolic survey of heart and brain tissues following cardiac arrest and after CPB resuscitation was conducted to better define the alterations associated with each condition.

Results

After 30 min cardiac arrest and 60 min CPB, the rats exhibited no observable brain function and weakened heart function in a physiological assessment. Heart and brain tissues harvested following 30 min ischemia had significant changes in the concentration of metabolites in lipid and carbohydrate metabolism. In addition, the brain had increased lysophospholipid content. CPB resuscitation significantly normalized metabolite concentrations in the heart tissue, but not in the brain tissue.

Conclusion

The observation that metabolic alterations are seen primarily during cardiac arrest suggests that the events of ischemia are the major cause of neurological damage in our rat model of asphyxia-CPB resuscitation. Impaired glycolysis and increased lysophospholipids observed only in the brain suggest that altered energy metabolism and phospholipid degradation may be a central mechanism in unresuscitatable brain damage.

Postresuscitation myocardial dysfunction in a dog

OBJECTIVE

To describe a clinical case of postresuscitation myocardial dysfunction in a dog.

CASE SUMMARY

An 11-month-old, 2.37 kg female spayed Chihuahua was referred for management post CPR after suffering cardiopulmonary arrest. Postresuscitation a gallop rhythm was identified and an echocardiogram revealed severe left ventricular dilation and severely impaired myocardial contractility with a mild eccentric jet of mitral regurgitation on color Doppler interrogation. The primary differentials were idiopathic or nutritional dilated cardiomyopathy, end-stage myocarditis, or postresuscitation myocardial dysfunction. Echocardiogram was repeated 48 hours later and showed normal left ventricular dimensions and contractility assessed as consistent with postresuscitation myocardial dysfunction.

NEW OR UNIQUE INFORMATION PROVIDED

Postresuscitation myocardial dysfunction is a common complication of CPR in human medicine and is associated with a worse outcome. This is the first clinical report of postresuscitation myocardial dysfunction in a dog.

Redox-mediated programed death of myocardial cells after cardiac arrest and cardiopulmonary resuscitation

Besides the fact that prolonged whole-body ischemia causes tissue and organ injury during cardiac arrest, additional damage occurs after the restoration of spontaneous circulation, during which the reperfusion activates a host of intracellular responses. These responses may lead to an increased threshold of oxidant-mediated injury and redox-mediated programed cell death in the stunned myocardium. The aim of this article is to summarize the major intracellular responses occurring from the onset of cardiac arrest until the post-resuscitation period that may lead to redox-mediated programed death of myocardial cells.

Myocardial ischemia and reperfusion injury

Myocardial ischemic injury results from severe impairment of coronary blood supply and produces a spectrum of clinical syndromes. As a result of intensive investigation over decades, a detailed understanding is now available of the complexity of the response of the myocardium to an ischemic insult. Myocardial ischemia results in a characteristic pattern of metabolic and ultrastructural changes that lead to irreversible injury. Recent studies have explored the relationship of myocardial ischemic injury to the major modes of cell death, namely, oncosis and apoptosis. The evidence indicates that apoptotic and oncotic mechanisms can proceed together in ischemic myocytes with oncotic mechanisms and morphology dominating the end stage of irreversible injury. Myocardial infarcts evolve as a wavefront of necrosis, extending from subendocardium to subepicardium over a 3- to 4-hour period. A number of processes can profoundly influence the evolution of myocardial ischemic injury. Timely reperfusion produces major effects on ischemic myocardium, including a component of reperfusion injury and a greater amount of salvage of myocardium. Preconditioning by several short bouts of coronary occlusion and reperfusion can temporarily salvage significant amounts of myocardium and extend the window of myocardial viability. Ongoing research into the mechanisms involved in reperfusion and preconditioning is yielding new insights into basic myocardial pathobiology.

The effect of enalapril and verapamil on the left ventricular hypertrophy and the left ventricular cardiomyocyte numerical density in rats submitted to nitric oxide inhibition

Forty male Wistar rats were separated into four groups of ten rats each (control and other three groups that have received nitric oxide (NO) synthesis inhibitor L-NAME) but the last two groups have concomitantly received antihypertensive drugs (Enalapril and Verapamil). After 40 days of experimentation, the heart and the ventricles were measured. The optical disector was used for the calculation of numerical density of the cardiomyocytes (Nv[c]). The left ventricular myocytes number (N[c]) was calculated as the product of Nv[c] and the left ventricular myocardium volume (LVMV) that was determined by using the Scherle's method. In the L-NAME group the blood pressure (BP) had a significant weekly increment. In the enalapril and the verapamil groups, BP increased in the first two weeks, but decreased in the following weeks. The LVMV increased in the L-NAME rats and decreased in the enalapril and verapamil animals. The Nv[c] and N[c] decreased in the L-NAME rats but the verapamil and enalapril treatments maintained the Nv[c] close to the control group. In conclusion, the left ventricular hypertrophy and the significant decrease of the left ventricular cardiomyocyte number caused by the NO synthesis inhibition are efficiently prevented with the use of enalapril and verapamil.

Lipolysis is an important determinant of isoproterenol-induced myocardial necrosis

The cardiotoxic effect of isoproterenol (ISO) is associated with, and possibly due to, calcium overload. Prior work suggests that calcium entry into cardiac myocytes after ISO administration occurs in two phases: an early rapid phase, followed by a slow phase beginning about 1 hour after ISO injection, leading to a peak myocardial calcium level after about 4 hours. We have tested the relationship of these phases to myocardial necrosis (MN) by determining the time after ISO administration at which the commitment to MN occurs. This was done by administration of propranolol at various times before and after ISO. In addition, since ISO induces lipolysis, and lipids can be toxic, experiments were conducted to determine if adrenergically-activated lipolysis could play a significant role in ISO-MN. We found that propranolol protected the myocardium equally well when administered anytime within 2 hours of ISO injection, but had no effect when given 4 hours after ISO. This showed that metabolic events taking place more than two hours after ISO injection are required for ISO-MN. As expected from prior work, there was a small and consistent amount of propranolol-resistant ISO-MN. Lipolysis, assessed by measuring serum glycerol levels, increased to tenfold above base line at one hour after ISO administration and returned to near basal levels at 4 hours. Potentiation of lipolysis by intravenous injections of phospholipase A2 (PLA2) or lipoprotein lipase (LPL) to rats treated with ISO substantially augmented MN. Propranolol completely blocked the increase in necrosis produced by PLA2 when given with ISO. Lipases induced only minimal necrosis in the absence of ISO. Administration of adenosine (an anti-lipolytic agent), oxfenicine (an inhibitor of mitochondrial palmitoyl carnitine transferase), or vitamin C (an anti-oxidant) resulted in a 55-60% reduction in MN. These results suggest that critical necrosis-determining events occur between 2 and 4 hours after ISO administration and imply a relationship between ISO-induced lipolysis, calcium influx, and ISO-MN. We hypothesize that importance of lipolysis as a determinant of ISO-MN is related to the generation of free fatty acids, their oxidized/metabolic products, or direct damage to plasma membrane.

Signal transduction mechanisms in the ischemic and reperfused myocardium

The cellular mechanisms regulating myocardial dysfunction during ischemia and subsequent reperfusion are complex. As can be determined from this review, it is clear that signal transduction pathways are altered during these conditions, which may explain, in part, the pathophysiology of ischemia and reperfusion. With respect to beta-adrenoceptor signal transduction, adaptive changes during ischemia and reperfusion ensure that this critical pathway for the regulation of cardiac function remains intact. Additionally, although the relative contribution of alpha 1-adrenoceptors to the regulation of cardiac function is minimal in normal myocardium, these receptors clearly exacerbate conditions associated with the generation of arrhythmias during reperfusion. It is likely that this enhancement of arrhythmogenesis is related to the activation of NHE by a PKC-dependent mechanisms. The importance of non-receptor-mediated signal transduction as a mediator of ischemia and reperfusion injury has long been established with respect to products of membrane lipid breakdown. As discussed, recent evidence now suggests that other compounds formed during ischemia and reperfusion, such as reactive oxygen species and NO, are also linked to cellular second messenger systems. In conclusion, as signal transduction is critical for normal myocardial function, signal transduction pathways are of even more importance during ischemia and reperfusion. There is an increasing interest in the role of non-receptor-mediated signal transduction as a mediator of ischemia and reperfusion injury and it is hoped that these pathways may represent new levels for therapeutic intervention.

Cytoskeletal alterations in cultured cardiomyocytes following exposure to the lipid peroxidation product, 4-hydroxynonenal

Damage to the cardiac myocyte sarcolemma following any of several pathological insults such as ischemia (anoxia) alone or followed by reperfusion (reoxygenation), is most apparent as progressive sarcolemmal blebbing, an event attributed by many investigators to a disruption in the underlying cytoskeletal scaffolding. Scanning electron microscopic observation of tissue cultured rat neonatal cardiomyocytes indicates that exposure of these cells to the toxic aldehyde 4-hydroxynonenal (4-HNE), a free radical-induced, lipid peroxidation product, results in the appearance of sarcolemmal blebs, whose ultimate rupture leads to cell death. Indirect immunofluorescent localization of a number of cytoskeletal components following exposure to 4-HNE reveals damage to several, but not all, key cytoskeletal elements, most notably microtubules, vinculin-containing costameres, and intermediate filaments. The exact mechanism underlying the selective disruption of these proteins cannot be ascertained at this time. Colocalization of actin indicated that whereas elements of the cytoskeleton were disrupted by increasing length of exposure to 4-HNE, neither the striated appearance of the myofibrils nor the lateral register of neighboring myofibrils was altered. Monitoring systolic and diastolic levels of intracellular calcium ([Ca2+]i) indicated that increases in [Ca2+]i occurred after considerable cytoskeletal changes had already taken place, suggesting that damage to the cytoskeleton, at least in early phases of exposure to 4-HNE, does not involve Ca(2+)-dependent proteases. However, 4-HNE-induced cytoskeletal alterations coincide with the appearance of, and therefore suggest linkage to, sarcolemmal blebs in cardiac myocytes. Although free radicals produced by reperfusion or reoxygenation of ischemic tissue have been implicated in cellular damage, these studies represent the first evidence linking cardiomyocyte sarcolemmal damage to cytoskeletal disruption produced by a free radical product.