Blaine C. White

Iron chelation prevents tissue injury following ischemia

Abstract Damage to a tissue following ischemia appears top occur during its reperfusion with oxygenated blood. This damage is apparently oxidative in nature and is generally considered to be the result of excessive superoxide (O2− and hydrogen peroxide (H2O2) production. Since neither O2− nor H2O2 cause oxidative damage in the absence of iron, we proposed that the oxidative processes are caused by the released of iron during reperfusion. The damage caused by the iron is exacerbated by hypoperfusion and the loss of calcium homeostasis. Our hypothesis is supported by the finding of significant levels of low molecular weight, chelatable iron in tissues during reperfusion following ischemia. The tissue damage can be ameliorated by techniques that increase the rate of reperfusion (open chest direct heart massage for the cardiac arrest model) and the administration of an iron chelator plus a calcium antagonist. Animals treated in this manner appear to completely recover from 15 minutes of cardiac arrest.

Ischemia, resuscitation, and reperfusion: mechanisms of tissue injury and prospects for protection.

Since its introduction in 1960, CPR has evolved into a complex program involving not only the medical community but also the lay public. Currently, program activities include instruction of the lay public in basic life support techniques, development and deployment of emergency medical systems, recommendations for drug protocols for advanced cardiac life support and, most recently, introduction of new methods for tissue protection following resuscitation. After 25 years of experience, we are beginning to understand the pathophysiology of tissue ischemia during cardiac arrest and the interventions required to improve chances of survival and quality of life of the cardiac arrest victim. Recent data in the literature suggest that modification of certain interventions in the resuscitation program may be needed. The poor neurologic outcomes with prolonged standard CPR show that it is not protective after 4 to 6 minutes of cardiac arrest. Modifications to this technique, including SVC-CPR or IAC-CPR, have not been shown to increase resuscitability or hospital discharge rates. Human studies of open-chest cardiac massage are needed to evaluate this option. Defibrillation is the definitive treatment for ventricular fibrillation. Greater emphasis should be placed on the earliest possible delivery of this treatment modality. Computerized defibrillators may provide greater and earlier access to defibrillation in the homes of patients at high risk of ventricular fibrillation. They may also be applicable by untrained public service personnel (police and firemen), individuals in geographically inaccessible areas (aircraft), or emergency medical technicians in rural areas where skill retention is a significant problem. Calcium has no proved benefit in cardiac resuscitation. There is biochemical evidence that it may be harmful in brain resuscitation. Its use in resuscitation should be discontinued. The dose of epinephrine currently advocated in the ACLS protocols may be inadequate to increase aortic diastolic pressure and coronary and cerebral perfusion pressures and thus aid resuscitation. Animal studies indicate that substantial increases in the current dosage are needed to achieve these effects. Human studies are needed to verify these results. A role for calcium antagonists in the treatment of postarrest encephalopathy has been demonstrated in animals and is currently undergoing clinical trials. Iron-dependent lipid peroxidative cell membrane injury may be important in the pathogenesis of postarrest encephalopathy. Animal studies suggest that the iron chelator deferoxamine may have a significant therapeutic role in the treatment of postarrest encephalopathy.

Post resuscitation iron delocalization and malondialdehyde production in the brain following prolonged cardiac arrest

Assays for brain tissue malondialdehyde (MDA) and low molecular weight chelated (LMWC) iron were used to examine samples of the cerebral cortex obtained from dogs 2 h after resuscitation from a 15-min cardiac arrest. The effect of post-resuscitation treatment with lidoflazine and/or desferrioxamine was similarly examined. Non-ischemic brain samples had LMWC iron levels (in nmol/100 mg tissue) of 12.32 + 2.60 and MDA levels (in nmol/100 mg tissue) of 8.46 + 1.35. Animals subjected to cardiac arrest and resuscitation and standard intensive care (SIC) had LMWC iron levels of 37.04 + 4.58 (p less than .01 against non-ischemic controls) and MDA levels of 12.24 + 1.9 (p less than .05 against non-ischemic controls). All treatment interventions significantly reduced the LMWC iron (p less than .05), but only treatment with desferrioxamine alone significantly reduced MDA (p less than .05), although a trend toward reduction of the MDA was also evident in animals treated with both desferrioxamine and lidoflazine. LMWC iron levels are increased in the post-ischemic brain, and this increase may be related to lipid peroxidation in the brain following resuscitation from cardiac arrest. These changes are probably pathologic and are amenable to pharmacologic intervention.

Postischemic tissue injury by iron-mediated free radical lipid peroxidation

Cell damage initiated during ischemia matures during reperfusion. Mechanisms involved during reperfusion include the effects of arachidonic acid and its oxidative products prostaglandins and leukotrienes, reperfusion tissue calcium overloading, and damage to membranes by lipid peroxidation. Lipid peroxidation occurs by oxygen radical mechanisms that require a metal with more than one ionic state (transitional metal) for catalysis. We have shown that cellular iron is delocalized from the large molecules where it is normally stored to smaller chemical species during postischemic reperfusion. Postischemic lipid peroxidation is inhibited by the iron chelator deferoxamine. Intervention in the reperfusion injury of membranes by chelation of transitional metals is a new and promising therapeutic possibility for protection of the heart and brain.

Brain injury by ischemic anoxia: Hypothesis extension — A tale of two ions?

The understanding of the pathophysiology of cerebral ischemic anoxia depends on elucidation of cellular neuronal changes during this event and under conditions of cardiopulmonary resuscitation. Current knowledge of these metabolic developments is reviewed, and a hypothesis of the role of iron in this situation is presented.

Cardiac arrest and resuscitation: Brain iron delocalization during reperfusion

We hypothesize that brain injury from cardiac arrest occurs during reperfusion and is in part mediated by iron-dependent lipid peroxidation. We conducted a study to examine the time course of brain iron delocalization and lipid peroxidation in an animal model of cardiac arrest and resuscitation. Assays for brain tissue iron in low-molecular-weight species (LMWS iron) used the o-phenanthroline test on an ultrafiltered (molecular weight P P

Blood flow in the cerebral cortex during cardiac resuscitation in dogs

Regional cerebral cortical blood flow (rCCBF) in 15 large dogs was determined using the double thermistor dilution method during standard closed-chest massage (CCM), CCM with an epinephrine infusion at 30 micrograms/kg/min (CCM + Epi), and open-chest cardiac massage (OCCM). As a percentage of prearrest flow values, the rCCBF was 9.8% with CCM, 35% with CCM + Epi, and 156% with OCCM. The rCCBF was reduced significantly with CCM (P less than .005) and CCM + Epi (P less than .01). OCCM generated flows indistinguishable from prearrest values. The use of high-dose epinephrine significantly increased the rCCBF during CCM. The implications for intact neurologic resuscitation of these reductions in rCCBF with CCM are important.

Myocardial tissue iron delocalization and evidence for lipid peroxidation after two hours of ischemia

Ischemic tissue injury has been proposed to be in part due to oxygen-radical-mediated lipid peroxidation. In vitro studies of such reactions show that they are thermodynamically unfavorable unless catalyzed by transitional metals such as iron in low molecular weight species (LMWS iron), ie, the iron-ADP complex. This study tests for iron delocalization into a LMWS pool during myocardial ischemia and for increased tissue malondialdehyde (MDA), a product of lipid peroxidation. Anesthesia was induced in eight dogs (weighing 20 to 30 kg) with ketamine and maintained by ventilation with 1% halothane. The left anterior descending coronary artery was ligated in four animals, and the circumflex coronary artery was ligated in the other four. Two hours after ligation, the animals were sacrificed by a central venous injection of KCl. Tissue samples were immediately taken from the ischemic zone and from the corresponding nonischemic zone. MDA was determined by the thiobarbituric acid assay. LMWS iron was determined on a tissue ultrafiltrate by the o-phenanthroline assay. Statistical data analysis used the matched-pair two-tailed t test. LMWS iron was 18.3 nM/100 mg in ischemic tissue versus 13.1 nM/100 mg in nonischemic tissue (t = 4.14; P less than .01). MDA was 0.91 nM/100 mg in ischemic tissue versus 0.83 nM/100 mg in nonischemic tissue (t = 7.27; P less than .005). We conclude that there is a significant increase in tissue LMWS iron and in MDA after two hours of regional myocardial ischemia. This iron might be the catalyst for maturation of tissue injury during reperfusion as observed by other investigators.(ABSTRACT TRUNCATED AT 250 WORDS)

Perfusion of the cerebral cortex by use of abdominal counterpulsation during cardiopulmonary resuscitation.

Perfusion of the cerebral cortex (rCCBF) during resuscitation from cardiac arrest was studied using 24 large dogs and three different resuscitation models. Conventional cardiopulmonary resuscitation (CPR) was compared with interposed abdominal compression CPR (IAC-CPR) and with IAC-CPR together with infusion of epinephrine. Conventional CPR produced a mean rCCBF of only 11% (0.057 +/- 0.07 ml/min/g) normal perfusion (0.54 +/- 0.14 ml/min/g). Even without epinephrine, IAC-CPR produced mean rCCBF equal to 51% (0.27 +/- 0.17 ml/min/g) of normal. With epinephrine, IAC-CPR produced rCCBF (0.93 +/- 0.49 ml/min/g) statistically indistinguishable from normal. Both models of IAC-CPR were significantly superior to conventional CPR in perfusion of the cerebral cortex.

Effect of flunarizine on global brain ischemia in the dog: A quantitative morphologic assessment

The effects of flunarizine, a calcium antagonist, were evaluated in an experimental model of global brain ischemia produced by 15 min of cardiac arrest followed by resuscitation and reperfusion. One group of dogs received flunarizine (0.1 mg/kg intravenously during a 10-min period) at the onset of resuscitation. Another group of dogs underwent cardiac arrest, resuscitation, and reperfusion but did not receive flunarizine. A third group served as nonischemic control. In situ-fixed brains of all animals (nonischemic controls and the postischemic dogs after 8 h of reperfusion) were examined for anoxic ischemic injury. Quantitation of the ischemic neurons was carried out in parietal cortex, hippocampus, and cerebellum by using an image analysis system. Significant difference in the number of necrotic neurons between the flunarizine-treated group and the ischemic controls was noted in the hippocampus only; the mean percentage of necrotic neurons in the two groups being 14.8 +/- 9.6 and 29.3 +/- 12.1, respectively (P less than 0.05). These results indicate that flunarizine has an ameliorating effect on neuronal injury in the hippocampus that follows cardiac arrest in this experimental model of global brain ischemia. However, flunarizine was not found to be effective in reducing the ischemic neuronal damage in the cortex or the cerebellum.