Narsimha R Nayini

Brain iron delocalization and lipid peroxidation following cardiac arrest

Brain injury after cardiac arrest and resuscitation may occur, in part, by oxygen radical mechanisms. The availability of a transition metal, such as iron, is essential for in vitro initiation of this type of reaction. The brain has significant stores of iron bound in large proteins. We conducted this study to determine whether iron availability is enhanced in the canine brain following resuscitation from 15 minutes of cardiac arrest, and whether this iron is associated with the appearance of products of radical-mediated lipid peroxidation (LP) after two hours of reperfusion. Examination of the data by the method of multivariate analysis revealed significant increases in the low molecular weight species (LMWS) iron (300% of nonischemic controls, P less than .01), malondialdehyde (MDA), a lipid peroxidation degradation product (145% of nonischemic controls, P less than .01), and conjugated dienes (CD) (204% of nonischemic controls, P = .07). Therapy with deferoxamine (50 mg/kg IV immediately post resuscitation) produced a reduction in MDA and CD to levels statistically indistinguishable from nonischemic controls. We conclude that brain tissue iron is delocalized from normal storage forms to a LMWS pool after two hours of reperfusion following resuscitation from a 15-minute cardiac arrest, and that this is associated with increased products of LP. The increase in LP products is blocked by treatment with deferoxamine.

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.

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

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)

Natural course of iron delocalization and lipid peroxidation during the first eight hours following a 15-minute cardiac arrest in dogs

Lipid peroxidation is thought to be a major contributing factor in neurological injury following cardiac arrest. Because iron availability is a prerequisite for lipid peroxidation, this experiment was designed to examine the natural time course of iron release, lipid peroxidation, and cerebral polyunsaturated fatty acid content following a 15-minute cardiac arrest in dogs. Large mongrel dogs were anesthetized with ketamine and halothane and divided into three groups of five each. In two groups, cardiac arrest was induced with KCl. After 15 minutes of cardiac arrest, the dogs were resuscitated by five minutes of internal cardiac massage, epinephrine, bicarbonate, and internal defibrillation. All ten dogs were resuscitated and supported by a standard intensive care protocol until tissue harvest. A 3-g portion of parietal cerebral cortex was obtained from the nonischemic dogs (n = 5), or at two hours (n = 5), or eight hours (n = 5) after resuscitation. Total tissue iron was measured by an atomic emission spectrometer; low molecular weight species (LMWS) iron by the o-phenanthroline test on an ultrafiltered sample; and lipid peroxidation by both the thiobarbituric acid test (TBARS) and determination of the tissue content of lipid double bonds, calculated by first fractionating the lipids by gas-liquid chromatography and then measuring the double bonds in each fraction by spectrometry and summing the results. Univariate ANOVA demonstrated all variables except total tissue iron to have significance at P less than .02. At two hours of reperfusion, LMWS iron and TBARS were significantly elevated above nonischemic control levels.(ABSTRACT TRUNCATED AT 250 WORDS)

Ultrastructural and ionic studies in global ischemic dog brain

SummaryA time course of tissue ionic changes, and their relation to ultrastructural findings during reperfusion following a 15-min global ischemic brain insult was studied in a dog model. Parietal cortex was analyzed for Ca, Na, K, Mg and Fe in controls and after 10 min, 2, 4, and 8 h of reperfusion. After 8 h of reperfusion, the mean values (μmol/g tissue wet wt.) for Ca (control=1.43, 8 h=2.76) and Na (control 60.4, 8 h=107.4) doubled and K (control=90.4, 8 h=48.5) decreased to half that of the control. Ultrastructural studies and subcellular localization of calcium in parietal cortex of in situ-fixed brains after 8 h showed cortical neurons with clumping of nuclear chromatin, dilatation of endoplasmic reticulum and disruption of plasma membranes. Large amounts of electron-dense precipitates of calcium were present within dilated astrocytic processes, synaptic vesicles, cytoplasm of edematous dendrites and mitochondria. Cortical neurons from postischemic dogs without reperfusion showed only slight chromatin clumping and edema of astrocytic processes, but no calcium accumulation. The large ionic shifts noted between 4 and 8 h of reperfusion, indicate a progressive inability of the cells to maintain normal transmembrane gradients of these ions and may reflect a membrane destructive process, as demonstrated ultrastructurally at 8 h. Enhanced calcium entry into the neuron during reperfusion appears to be a part of the cytotoxic mechanism leading to neuronal necrosis.

Effect on biochemical markers of brain injury of therapy with deferoxamine or superoxide dismutase following cardiac arrest

Iron-mediated lipid peroxidation by oxygen radical mechanisms is thought to be a contributing factor to neurological injury during reperfusion following resuscitation from cardiac arrest. This study was designed to examine and compare the effects of an iron chelator (deferoxamine) and superoxide dismutase (SOD) on brain lipid peroxidation and tissue ions after eight hours of reperfusion following a 15-minute cardiac arrest. This sampling time was chosen because other work with this model has shown severe ionic and ultrastructural derangement at this point. Twenty-three dogs were anesthetized with ketamine and halothane and divided into four groups. Six dogs were nonischemic controls (group I). In the remaining dogs, a 15-minute cardiac arrest was induced with KCl. Resuscitation was begun with internal cardiac massage and artificial ventilation. After five minutes of artificial perfusion, internal defibrillation was performed to restart the heart. All dogs were resuscitated and supported by a standard intensive care (SIC) protocol for eight hours. Six resuscitated dogs served as SIC controls (group II). Six were treated with deferoxamine, 200 mg/kg loading dose and 100 mg/kg/h maintenance drip (group III), and five were treated with SOD, 1,000,000 units bolus and 500,000 units/h drip (group IV). All drugs were administered intravenously immediately postresuscitation. At eight hours postresuscitation, a 3-g portion of parietal cerebral cortex was obtained through a trephine hole. The sample was assayed for tissue malondialdehyde (MDA) by the thiobarbituric acid test, the double bond content of the tissue lipids (lipid unsaturation index, LUSI), and total tissue content of K and Na.(ABSTRACT TRUNCATED AT 250 WORDS)

Brain cortex tissue Ca, Mg, Fe, Na, and K following resuscitation from cardiac arrest in dogs

Recent evidence suggests that ultimate neurologic injury following cardiac arrest and resuscitation may be largely determined by biochemical events occurring during reperfusion. To test this hypothesis and further characterize the time course of some of these events, we examined tissue samples from the parietal cortex for their total content of calcium (Ca), magnesium (Mg), iron (Fe), sodium (Na), and potassium (K) after 10 minutes, two hours, four hours, and eight hours of reperfusion following a 15-minute cardiac arrest in dogs. After 10 minutes of reperfusion, there were relatively small, but significant, increases in the total tissue content of Ca and Na, as compared to nonischemic controls. All values had returned to normal at two hours and remained normal at four hours of reperfusion. However, at eight hours of reperfusion, Ca and Na content approximately doubled and K content was reduced by half. There were no significant changes at any time in the tissue content of Fe or Mg. We conclude that with between four and eight hours of reperfusion following a 15-minute cardiac arrest, a major defect occurs in many cells of the cortex with respect to their ability to control ionic balances of Ca, Na, and K. This might be explained either by failure of the energy-dependent ionic pumps or by more generalized damage to the membrane permeability barrier by a process such as lipid peroxidation.