Search PubMed⌕ Search

Biomedical subjects

K R Chien

Publications and source records attributed to K R Chien.

At least 163 records · Page 9Linked to original sources
PubMed1985

Phospholipid alterations and membrane injury during myocardial ischemia.

Several independent studies have demonstrated that there is a degradation of membrane phospholipids during myocardial ischemia. At present, most of the data support the initial activation of a phospholipase A pathway of phospholipid degradation. The extent of total phospholipid degradation is in the nanomole per gram wet weight quantity, as opposed to ischemic liver, in which the extent of phospholipid depletion approaches the micromole per gram wet weight level. However, in vitro studies suggest that calcium permeability properties and other myocardial cell membrane functions are sensitive to nanomole levels of phospholipid degradation. Clearly, further work is necessary in intact cell and heart preparations to correlate the degradation of phospholipid with the development of irreversible membrane injury during ATP depletion and hypoxia.

Animals↗
PubMed1985

Mechanisms of accumulation of arachidonic acid in cultured myocardial cells during ATP depletion.

Previous studies have suggested that the accumulation of free arachidonic acid may be of major importance in the pathophysiology of myocardial ischemia. The purpose of the present study was to determine if the release of arachidonic acid from myocardial cells was more dependent on the extent of ATP depletion than on the inhibition of fatty acid oxidation. In addition, these studies were designed to determine if arachidonic acid release only occurred when ATP was depleted beyond a critical threshold level. To examine the relationship between arachidonic acid release and ATP depletion, cultured myocardial cells from neonatal rat hearts were labeled with [3H]arachidonate and [14C]palmitate. In response to ATP depletion with various metabolic inhibitors, [3H]arachidonic acid and [14C]palmitic acid were released from phospholipids. Phosphatidylcholine, phosphatidylethanolamine, and phosphatidic acid were the major esterified sources of the arachidonate. The release of both fatty acids was related to the extent of ATP depletion and not whether a glycolytic or respiratory inhibitor was utilized. Various combinations and doses of metabolic inhibitors were used, and experimental conditions that produced a greater than 75% decrease in ATP content were associated with the accumulation of arachidonic acid. These results suggest that an ATP-dependent step may be linked to the accumulation of arachidonic acid during myocardial ATP depletion. It is suggested that myocardial cells may release arachidonic acid directly in response to ATP depletion.

Adenosine Triphosphate↗
PubMed1985

Characterization of a potentially reversible increase in beta-adrenergic receptors in isolated, neonatal rat cardiac myocytes with impaired energy metabolism.

Previous studies have reported that the numbers of beta- and alpha-adrenergic receptors increase in ischemic myocardium. In vivo studies have raised questions regarding the mechanisms involved in the adrenergic receptor alterations and the consequences of these alterations. The purpose of this study was to evaluate potential relationships among beta-adrenergic receptor changes, high energy phosphate reduction, and severity of cell injury in cultured neonatal rat myocytes treated with metabolic inhibitors. The potential for reversal of the receptor changes also was addressed. Binding parameters were measured using [125I]iodocyanopindolol. After 4 hours incubation in potassium cyanide and 2-deoxyglucose, there was a 43% increase in beta-adrenergic receptor number, 41% decrease in adenosine triphosphate, and minimal morphological change in myocytes. Twenty-four hours after removal of the inhibitors, myocytes exhibited a return to normal of the receptor number and adenosine triphosphate level. Iodoacetate treatment for up to 3 hours resulted in marked reduction in adenosine triphosphate and increasing severity of cell injury. The number of beta-adrenergic receptors was unchanged at 1.2 hours, increased at 1.5-2 hours, and decreased at 3 hours. Thus: beta-adrenergic receptor density increases during relatively early stages of injury in metabolically impaired myocytes with reduced adenosine triphosphate levels and decreases subsequently, after the myocytes become irreversibly injured; the increased beta-adrenergic receptor density in moderately injured myocytes can be reversed upon removal of the injurious agent and restoration of the cellular adenosine triphosphate level; and changes in catecholamines mediated by an intact nervous system are not required for an increase in beta-adrenergic receptor density in the setting of impaired energy metabolism.

Adenosine Triphosphate↗
PubMed1985

Release of arachidonate from membrane phospholipids in cultured neonatal rat myocardial cells during adenosine triphosphate depletion. Correlation with the progression of cell injury.

The present study utilized a cultured myocardial cell model to evaluate the relationship between the release of arachidonate from membrane phospholipids, and the progression of cell injury during ATP depletion. High-energy phosphate depletion was induced by incubating cultured neonatal rat myocardial cells with various combinations of metabolic inhibitors (deoxyglucose, oligomycin, cyanide, and iodoacetate). Phospholipid degradation was assessed by the release of radiolabeled arachidonate from membrane phospholipids. In this model, the current study demonstrates that (a) cultured myocardial cells display a time-dependent progression of cell injury during ATP depletion; (b) the morphologic patterns of mild and severe cell injury in the cultured cells are similar to those found in intact ischemic canine myocardial models; (c) cultured myocardial cells release arachidonate from membrane phospholipids during ATP depletion; and (d) using two separate combinations of metabolic inhibitors, there is a correlation between the release of arachidonate, the development of severe cellular and sarcolemmal damage, the release of creatine kinase into the extracellular medium, and the loss of the ability of the myocardial cells to regenerate ATP when the metabolic inhibitors are removed. Thus, the present results suggest that during ATP depletion, in cultured neonatal rat myocardial cells, the release of arachidonate from myocardial membrane phospholipids is linked to the development of membrane defects and the associated loss of cell viability.

Adenosine Triphosphate↗
PubMed1984

Accumulation of unesterified arachidonic acid in ischemic canine myocardium. Relationship to a phosphatidylcholine deacylation-reacylation cycle and the depletion of membrane phospholipids.

Studies in ischemic canine left ventricle have shown that the depletion of membrane phospholipids is a critical event in the development of a sarcolemmal calcium permeability defect and associated irreversible myocyte injury. The mechanism of phospholipid loss is unclear, but may be due to the activation of endogenous phospholipases. Since arachidonic acid is a fatty acid found almost entirely in phospholipid, increases in arachidonate provide evidence for increased phospholipase activity. The present study was designed to examine the temporal relationship of the accumulation of free arachidonate with the onset of phospholipid depletion during fixed ligation of the left anterior descending coronary artery in canine myocardium. The following results were demonstrated in ischemic canine myocardium: (1) the accumulation of unesterified arachidonate is minimal during 10-30 minutes of ischemia, but is significantly increased after prolonging the duration of ischemia to 1-3 hours; (2) significant increases in arachidonate precede the development of a significant decrease in total phospholipid content; (3) the decrease in the arachidonate content of phosphatidylcholine is accompanied by similar decreases in all of the fatty acyl moieties; (4) the arachidonate content of lysophosphatidylcholine and diacylglycerol are unchanged during myocardial ischemia; (5) there is evidence of a deacylation-reacylation cycle in phosphatidylcholine prior to the accumulation of free arachidonate; (6) the fatty acyl specificity of the lysophosphatidylcholine acyltransferase corresponds to the pattern of fatty acyl remodeling of phosphatidylcholine during early myocardial ischemia. These data suggest that the accumulation of arachidonate may be a more sensitive measure of phospholipid degradation than the decrease in total phospholipid content in ischemic canine myocardium. It is postulated that the defective reacylation of arachidonate into phosphatidylcholine may contribute to the net loss of membrane phospholipid during myocardial ischemia.

1-Acylglycerophosphocholine O-Acyltransferase↗
PubMed1983

Fatty acylcarnitine accumulation and membrane injury in ischemic canine myocardium.

Although previous work has shown that long chain fatty acylcarnitine derivatives accumulate in ischemic canine myocardium, their role in the production of irreversible injury and associated sarcolemmal membrane injury is undefined. The present study examines the temporal and topographic relationship of the accumulation of long chain acylcarnitine with the uptake of technetium pyrophosphate and tissue calcium content during ligation of the left anterior descending coronary artery (LAD) in canine myocardium. After 60 minutes of fixed LAD ligation, there was no significant increase in long chain acylcarnitine content in the ischemic subendocardium compared with the corresponding nonischemic value. However, the ischemic subendocardium was irreversibly injured at this time, as assessed by a 4-fold increase in tissue calcium content and a 20-fold increase in technetium-99m pyrophosphate uptake after reperfusion. The ischemic subepicardium showed a 41% increase in long chain acylcarnitine content compared with the corresponding nonischemic subepicardium. However, the ischemic subepicardium contained only 50% of the calcium content and 10% of the technetium-99m pyrophosphate uptake found in the ischemic subendocardium. It is concluded that increases in fatty acylcarnitine can be dissociated from the development of irreversible ischemic injury during fixed LAD occlusion in ischemic canine myocardium.

Animals↗
PubMed1983

Influence of chlorpromazine on lysosomal alterations during myocardial ischaemia.

Ligation of the circumflex artery of anaesthetised, open-chest rabbits caused a progressive increase in nonsedimentable cathepsin D activity in severely ischaemic myocardium and an anatomical redistribution of the enzyme from lysosomes into the cytosol, along with progressive ultrastructural signs of cellular damage and necrosis. Chlorpromazine pretreatment (15 mg X kg-1 intravenously) reduced the increase in nonsedimentable cathepsin D activity slightly, but no appreciable protective effect on the anatomical redistribution of the enzyme or the development of ultrastructural signs of necrosis could be detected. It is concluded that in this experimental model of myocardial infarction, high concentrations of chlorpromazine have a mild stabilising action on lysosomes, but the drug has minimal if any effect in protecting the heart from ischaemic damage.

Animals↗
PubMed1983

In vivo esterification of a synthetic 125I-labeled fatty acid into cardiac glycerolipids.

Recent studies have demonstrated that fatty acids can be successfully utilized as myocardial imaging agents. 125I-paraphenylpentadecanoic acid (IPPA), a synthetic fatty acid, accumulates within the myocardium and can be visualized by conventional gamma scintigraphy. To determine if IPPA was incorporated into cardiac lipids in a pattern similar to palmitate, IPPA was purified by liquid chromatography, bound to fat-free albumin, and administered by intravenous injection to male Sprague-Dawley rats. After 2.5, 5, 10, and 30 min, the hearts were excised and the lipids were extracted in chloroform-methanol. The uptake of IPPA into the myocardium reached a maximal value after 2.5 min, and 95% of the 125I was found in the cardiac lipid fraction after chromatographic separation. Over 65% of the IPPA was found in cardiac triglycerides, whereas approximately 10% was present in membrane phospholipids (predominantly phosphatidylcholine and phosphatidylethanolamine). This pattern of IPPA incorporation is similar to that reported for intravenously administered [3H]palmitate. The rate of turnover of IPPA present in the triglyceride fraction was threefold faster than the rate of the IPPA which was incorporated into membrane lipids. At all time periods examined, the methanol-water soluble end products of IPPA oxidation did not account for more than 5% of the total IPPA present within the myocardium. The present study indicates that IPPA is incorporated primarily into triglycerides and other cardiac lipids in a pattern similar to palmitate.

Animals↗
PubMed1983

Induction of a reversible cardiac lipidosis by a dietary long-chain fatty acid (erucic acid). Relationship to lipid accumulation in border zones of myocardial infarcts.

Previous studies have demonstrated that cardiac myocytes in the border zone of acute myocardial infarction become markedly overloaded with neutral lipid during the transition from reversible to irreversible injury. To examine directly the role of these changes in neutral lipid metabolism in the development of irreversible cellular injury and associated increases in tissue Ca2+ content, the authors fed rats large amounts of a fatty acid (erucic acid) that is poorly oxidized by the heart and that subsequently accumulates as neutral lipid. Rats fed a high erucic acid (C22:1) diet in the form of 20% rapeseed oil for 3-5 days had a fourfold increase in triglyceride (49.5 +/- 3.8 SEM mg/g wet wt versus 13.6 +/- 13, n = 4) and a 60% increase in long-chain acyl CoA content (166.0 +/- 21.9 versus 91.5 +/- 9.0 nM/g wet wt, n = 4), compared with controls. However, there was no change in long-chain acyl carnitine or total phospholipid content. Histochemical studies showed accumulation of numerous lipid droplets in the myocytes, and electron microscopy revealed localization of lipid vesicles in direct contact with mitochondria, thus mimicking the lipid-laden cells in the border zone regions of acute myocardial infarcts. The acute lipidosis was reversible with either continued feeding of erucic acid for several weeks or conversion to a normal diet. It was not associated with an increased tissue Ca2+ content, nor with cell necrosis. However, continued erucic acid intake for 3 months was associated with focal myocardial degeneration and loss of myocytes. These results suggest that acute increases in neutral lipids, as found in the border zone of acute myocardial infarction, may not be the cause of progression to irreversible damage during acute myocardial injury, but that the persistent presence of similar lipid material over months may result in focal myocardial degeneration.

Animals↗
PubMed1981

Myocardial ischemia: the pathogenesis of irreversible cell injury in ischemia.

Cells made ischemic rapidly manifest many distinct structural and functional alterations as a consequence of the depletion of their energy stores. In attempting to determine which of these are causally related to the eventual cell death, the authors have emphasized the relationship to the reversibility of the ischemic injury. Two phenomena have consistently characterized irreversibly in contrast to reversibly injured ischemic cells: the inability to restore mitochondrial function and evidence of plasma membrane damage. Studies in the authors' laboratory are reviewed that have focused on the pathogenesis, biochemical nature, and the relationship to irreversible cell injury of both of these alterations. A number of mitochondrial abnormalities are related to changes in long-chain acyl-CoA metabolism with inhibition of adenine nucleotide translocation and potentiation of a Ca2+-dependent increase in the permeability of the inner mitochondrial membrane. These changes are reversible upon reoxygenation only when the large increase in intracellular Ca2+ content that accompanies the phospholipid depletion from other cellular membranes is prevented. This disorder in phospholipid metabolism is felt to be the critical lesion that produces irreversible cell injury in ischemia. It affects the endoplasmic and sarcoplasmic reticular membranes of liver and myocardial cells, respectively, and probably the plasma membranes of both. It is prevented by pretreatment with chlorpromazine. An activation of endogenous phospholipases by an elevated, cytosolic free Ca2+ ion concentration is suggested as the mechanism underlying this phospholipid disturbance. The central role of intracellular Ca2+ in the initiation and functional consequences of ischemic cell injury are emphasized.

Animals↗
PubMed1979

Ischemic myocardial cell injury. Prevention by chlorpromazine of an accelerated phospholipid degradation and associated membrane dysfunction.

Ligation of the left coronary artery of an adult rat heart results in the reproducible ischemic cell death of the entire free wall of the left ventricular myocardium. The time course of the development of the cellular changes is biphasic. The subendocardial and subepicardial cells die within the first few hours. The main mass of free-wall myocardium reacts more slowly, with morphologic evidence of irreversible cell injury developing after 12 hours. Measurement of the increases in total free wall Ca++ reflected this biphasic pattern. There was a rapid 3-fold rise in total Ca++ during the first 4 hours. Between 4 and 12 hours the Ca++ was constant. Between 12 and 30 hours there was a second increase that reached a level some 8-10 times the control value. Treatment with chlorpromazine before and subsequent to surgery prevented the appearance of ischemic cell death in the main portion of the free-wall myocardium for at least 24 hours without affecting the reaction of the subepicardial and subendocardial cells. Chlorpromazine also inhibited the second phase of Ca++ accumulation. An accelerated degradation of phospholipids was observed with a 33% decrease in total phospholipids by 12 hours. Phosphatidylethanolamine was reduced by 50% and phosphatidylcholine by 25% without increases in the corresponding lysophospholipids. Chlorpromazine prevented the accelerated degradation and consequent loss of phospholipid. Isolated sarcoplasmic reticulum showed a time-dependent loss of phospholipid with a parallel loss of active Ca++ uptake that reach 60% with a total lipid depletion from these membranes of 33% by 12 hours. Twelve-hour ischemic sarcoplasmic reticulum exhibited a 6--7-fold increase in passive permeability to Ca++. Chlorpromazine protected against the loss of phospholipids, the inhibition of Ca++ uptake, and the increased Ca++ permeability of the sarcoplasmic reticulum. These observations indicate that rat myocardial cells react to lethal doses of ischemia in a manner similar to the reaction of liver cells described previously. In both cases the evidence implies that a disturbance in phospholipid metabolism and its associated membrane dysfunction is the critical alteration that produces irreversible cell injury in ischemia.

Animals↗
PubMed1978

Irreversible ischemic cell injury. Prevention by chlorpromazine of the aggregation of the intramembranous particles of rat liver plasma membranes.

Ischemic rat liver tissue has been shown previously to exhibit a markedly accelerated rate of phospholipid degradation, producing a loss of almost one half the total cellular phospholipid with 3 hours of ischemia. Pretreatment of the rats with chlorpromazine completely prevented the disturbed phospholipid metabolism at the same time that it prevented the cell death associated with as much as 3 hours of ischemia. Lipid-depleted microsomal membranes were shown previously to manifest alterations in their structure and function. The present report documents that similar structural alterations are evident in ischemic liver cell plasma membranes. The technique of freeze-fracture electron microscopy was used to examine the morphology of ischemic liver cell plasma membranes. Freeze-fracture replicas of whole tissue fragments exhibited a diffuse aggregation of the intramembranous particles in the P face of the plasma membranes. The incidence of this change correlated with the duration of ischemia. Pretreatment of the rats with chlorpromazine (20 mg/kg) for 30 minutes before inducing ischemia prevented the aggregation of the membrane-associated particles. These findings establish the existence of plasma membrane alterations in ischemic liver cells. The time course of these changes, their prevention by chlorpromazine, and their similarity to the previously described structural alterations in the microsomal membranes suggest that they are related to the loss of liver cell phospholipid. The data in the present report support the hypothesis that an accelerated phospholipid degradation and its resultant membrane dysfunction are the critical alterations that produce irreversible liver cell injury and, ultimately, cell death in ischemia.

Animals↗