Neutrophil-induced myocardial cell damage and active oxygen metabolites

New insights in to the treatment of myocardial infarction

This study investigated the effects of the L-17 compound of the group of substituted 5R1, 6H2-1,3,4-thiadiazine-2-amines on the inflammatory cellular infiltration and myocardial remodelling which occurs after acute myocardial infarction (MI) in rats. The study is based upon recent clinical and experimental work which demonstrated the role of local and systemic inflammatory reactions in postinfarction remodelling. Acute MI in rats was induced by left coronary artery coagulation. Animals were sacrificed on day one, five and seven after MI induction. The myocardiumal samples were taken from all parts of the heart and examined by histology. This included areas of infarction, infraction and areas that were peri-infarctiom and left ventricular areas distant from the damaged tissues. Serum activity of creatine phosphokinase (CPK), aspartate aminotransferase (AST), isoenzymes 1 and 2 and lactate dehydrogenase (LDH1-2) were investigated on the same three days, before and in the process of MI development was investigated (at days 1, 5 and 7). The L-17 compound to not only decreased the area of initial infarction but also changed the pattern of inflammatory reaction in the affected myocardium fundamentally. Laboratory studies of effects of L-17 compound on the development and course of experimental MI showed that administration decreased blood AST and CPK levels significantly and provided useful the data about the correlation between the activity of these enzymes and the dimensions of the significantly necrotic area. In this model of experimental MI the use of the L-17 compound induced led to the replacement of the exudative destructive inflammation that is seen under standard conditions with a more cellular "productive" pattern of inflammation, with associated reduction in initial necrosis area and the, decrease in myocardial ischaemia and reperfusion injury may account for the accelerated repair process.

Linear furanocoumarin protects rat myocardium against lipidperoxidation and membrane damage during experimental myocardial injury

The antioxidant activity and the membrane effects of linear furanocoumarin marmesinin isolated from Aegle marmelose was evaluated during experimental myocardial injury. Isoproterenol (150 mg kg(-1) intraperitonially twice at an interval of 24 h) caused increase in the levels of serum marker enzymes via creatinekinase (CK), creatinekinase-MB (CK-MB) isoenzyme, lactatedehydrogenase (LDH) and lactatedehydrogenase isoenzyme (LDH1). It also produced electrocardiographic changes such as increased heart rate, reduced R amplitude and ST elevation. Marmesinin at a dose of 200 mg kg(-1), when administered orally, demonstrated a decrease in serum enzyme levels and restored the electrocardiographic changes towards normalcy. Myocardial injury was accompanied by the disintegration of lipidperoxides and the impairment of natural scavengers. Marmesinin oral treatment for 2 days before and during isoproterenol administration decreased the effect of lipidperoxidation. It was also shown to have a membrane stabilizing action by inhibiting the release of beta-glucuronidase from the subcellular fractions. Thus, linear furanocoumarin marmesinin could have the protective effect against the damage caused by experimental myocardial injury.

Complement and polymorphonuclear leukocyte activation each play a role in determining myocardial ischemia-reperfusion injury

Cobra venom factor (CVF) transiently activates polymorphonuclear leukocytes (PMN) by complement activation, followed by rapid complement depletion and gradual reversal of PMN activation. Utilizing these sequential changes caused by CVF, the individual and combined effects of complement and PMNs on myocardial infarct size (IS) were investigated. Rats were treated with CVF, and/or anti-PMNs. Complement was depleted, but circulating PMNs were being activated at 4h after CVF administration, and at 36h after, complement was depleted, but PMNs were in a near basal condition. Under anesthesia, the rats had a 30-min coronary occlusion followed by 6h of reperfusion. The IS was assessed by tetrazolium staining. CVF, as well as anti-PMNs, reduced myeloperoxidase (MPO) activity in the risk area and the reduced MPO resulted in a reduced IS, which was also the effect of anti-PMNs, but complement depletion by CVF, during which circulating PMNs were activated, failed to reduce the IS despite low MPO activity. These results suggest that complement and the condition of PMNs each play a role in determining the IS, and ischemic reperfusion injury might be produced even by relatively low myocardial MPO activity.

Stimulation of neutrophil activation during coronary artery bypass grafting: comparison of crystalloid and blood cardioplegia

BACKGROUND

During myocardial ischemia, activation of polymorphonuclear neutrophils (PMNs) results in the production of free oxygen radicals, which increase myocardial injury. It has been shown that PMNs also produce nitric oxide. It is not clear whether PMNs become activated as a result of their direct contact with ischemic/reperfused myocardium or if PMN activation and free oxygen radical production are effects of specific stimuli released during coronary artery bypass grafting (CABG). The aim of the current study was to evaluate plasma-mediated neutrophil stimulation and production of superoxide anion (O2) and nitric oxide in patients undergoing CABG, and to verify whether crystalloid and blood cardioplegia can modify such stimulation.

METHODS

Coronary sinus, peripheral arterial, and venous plasma samples were collected from 50 patients who underwent CABG and were divided into 2 equal groups which received either crystalloid or blood cardioplegia: directly before myocardial ischemia and aortic cross-clamping; at the beginning of reperfusion after aortic clamp release; and 30 minutes after reperfusion. O2 and nitric oxide production by PMN was evaluated by standard methods.

RESULTS

There was a significant (p < 0.05) increase in O2 production by PMN incubated with plasma obtained from the coronary sinus immediately after reperfusion in patients receiving crystalloid cardioplegia compared to blood cardioplegia. No difference was observed in plasma stimulation of nitric oxide production by PMN in the 2 groups of patients at different times during the procedure.

CONCLUSIONS

Cardioplegia may affect release of neutrophil-oriented stimuli from ischemic myocardium and modify neutrophil activation during coronary artery bypass grafting.

N2O-induced hypoxia as a model of hypoxic stress of rat myocardium. An ultrastructural-morphometric study

A model system consisting of a hypoxia chamber combined with a commercial narcosis apparatus adapted to small animals was used to perform a controlled acute isobaric hypoxia on rats with N2O/O2. Ultrathin sections from the left ventricular wall were analysed qualitatively and quantitatively using a computer-aided morphometric program. Compared with the control the cardiomyocytes exhibited a significant increase of volume densities of cytoplasmic vacuoles, lipid drops, sarcoplasmic reticulum, mitochondria, and degenerated intramitochondrial areas. Hypoxic alterations of microvessels consisted mainly in localized endothelial swelling and perivascular edema, protrusions of the luminal surface and moderate mitochondrial alterations similar to those of cardiomyocytes. Further, the number of plasmalemmal vesicles decreased, and the number of vacuoles increased significantly. The results were confirmed by quantitative histochemistry performed by our group in a parallel study. The model can be recommended for studies concerning protective interventions in hypoxia experiments.

Inducible nitric oxide synthase augments injury elicited by oxidative stress in rat cardiac myocytes

The effects of nitric oxide (NO) produced by cardiac inducible NO synthase (iNOS) on myocardial injury after oxidative stress were examined: Interleukin-1 beta induced cultured rat neonatal cardiac myocytes to express iNOS. After induction of iNOS, L-arginine enhanced NO production in a concentration-dependent manner. Glutathione peroxidase (GPX) activity in myocytes was attenuated by elevated iNOS activity and by an NO donor, S-nitroso-N-acetyl-penicillamine (SNAP). Although NO production by iNOS did not induce myocardial injury, NO augmented release of lactate dehydrogenase from myocyte cultures after addition of H2O2 (0.1 mM, 1 h). Inhibition of iNOS with N omega-nitro-L-arginine methyl ester ameliorated the effects of NO-enhancing treatments on myocardial injury and GPX activity. SNAP augmented the myocardial injury induced by H2O2. Inhibition of GPX activity with antisense oligodeoxyribonucleotide for GPX mRNA increased myocardial injury by H2O2. Results suggest that the induction of cardiac iNOS promotes myocardial injury due to oxidative stress via inactivation of the intrinsic antioxidant enzyme, GPX.

Neutrophil mediated myocardial injury

1. Activated polymorphonuclear neutrophils (PMN) were shown to exacerbate ischemic myocardial injury and their activation is modulated by complement system, platelet activating factor, arachidonic acid metabolites, adenosine and nitric oxide. 2. Mechanisms of injurious PMN effect on ischemic myocardium are related to both mechanical and biochemical processes. 3. Activated PMN aggregate and adhere to endothelium that results in capillary plugging and subsequent impairment of coronary blood flow as well as participating in the development of endothelial cell edema. 4. PMN-related biochemical damage of ischemic myocardium is a result of the release of cytotoxic free oxygen radicals and proteolytic enzymes as well as vasoconstrictor leukotriene B4 and leukotoxin.