Changes in fatty acid metabolism after erythrocyte peroxidation: stimulation of a membrane repair process

Plasma membrane wounding and repair in pulmonary diseases

Various pathophysiological conditions such as surfactant dysfunction, mechanical ventilation, inflammation, pathogen products, environmental exposures, and gastric acid aspiration stress lung cells, and the compromise of plasma membranes occurs as a result. The mechanisms necessary for cells to repair plasma membrane defects have been extensively investigated in the last two decades, and some of these key repair mechanisms are also shown to occur following lung cell injury. Because it was theorized that lung wounding and repair are involved in the pathogenesis of acute respiratory distress syndrome (ARDS) and idiopathic pulmonary fibrosis (IPF), in this review, we summarized the experimental evidence of lung cell injury in these two devastating syndromes and discuss relevant genetic, physical, and biological injury mechanisms, as well as mechanisms used by lung cells for cell survival and membrane repair. Finally, we discuss relevant signaling pathways that may be activated by chronic or repeated lung cell injury as an extension of our cell injury and repair focus in this review. We hope that a holistic view of injurious stimuli relevant for ARDS and IPF could lead to updated experimental models. In addition, parallel discussion of membrane repair mechanisms in lung cells and injury-activated signaling pathways would encourage research to bridge gaps in current knowledge. Indeed, deep understanding of lung cell wounding and repair, and discovery of relevant repair moieties for lung cells, should inspire the development of new therapies that are likely preventive and broadly effective for targeting injurious pulmonary diseases.

Methods for imaging and detecting modification of proteins by reactive lipid species

Products of lipid peroxidation are generated in a wide range of pathologies associated with oxidative stress and inflammation. Many oxidized lipids contain reactive functional groups that can modify proteins, change their structure and function, and affect cell signaling. However, intracellular localization and protein adducts of reactive lipids have been difficult to detect, and the methods of detection rely largely on antibodies raised against specific lipid-protein adducts. As an alternative approach to monitoring oxidized lipids in cultured cells, we have tagged the lipid peroxidation substrate arachidonic acid and an electrophilic lipid, 15-deoxy-Delta(12,14)-prostaglandin-J2 (15d-PGJ2), with either biotin or the fluorophore BODIPY. Tagged arachidonic acid can be used in combination with conditions of oxidant stress or inflammation to assess the subcellular localization and protein modification by oxidized lipids generated in situ. Furthermore, we show that reactive lipid oxidation products such as 15d-PGJ2 can also be labeled and used in fluorescence and Western blotting applications. This article describes the synthesis, purification, and selected application of these tagged lipids in vitro.

Lipid hydroperoxide-induced peroxidation and turnover of endothelial cell phospholipids

The effects of lipid peroxidation on rabbit aortic endothelial cell phospholipid turnover was studied using linoleic acid hydroperoxide (LOOH). Following treatments with 20-40 microM LOOH, cells prelabeled with either arachidonic acid (20:4) or oleic acid (18:1) showed a movement of these fatty acids out of the phospholipids and into neutral lipid and free fatty acid pools. There was also a release of radioactive free fatty acids and phospholipids into the media, which was significantly increased as compared to cells maintained under standard culture conditions. Fatty acid uptake and distribution among phospholipid pools was also affected by LOOH treatment where incorporation of 20:4 and 18:1 into phosphatidylcholine (PC) decreased, while uptake into phosphatidylinositol (PI) increased after 1 h of incubation with 40 microM LOOH. These effects were also inhibited by vitamin E. In cells prelabeled with 20:4 or 18:1 under conditions where approximately 99% of the fatty acids were incorporated into neutral and phospholipid pools, LOOH treatment produced a decrease in radioactivity associated with PC, while the specific activity of PI increased. The extent of these changes was greater for 20:4 than 18:1, but in each case the effects were inhibited by vitamin E. The temporal pattern of uptake for labeled choline and inositol after LOOH treatments paralleled those found for fatty acid incorporation. These cell responses indicate that induction of lipid peroxidation produces rapid fatty acid release and phospholipid turnover involving repair as well as de novo synthesis. The implications of these effects on turnover of specific phospholipids and cell responses to oxidative stress are discussed.

Changes in erythrocyte membrane phospholipid composition induced by physical training and physical exercise

The effects were investigated of physical training and exercise on lipids of the erythrocyte membrane of healthy students. Membrane cholesterol and phospholipids were analysed simultaneously by thin-layer chromatography with a flame ionization detector and the fatty acid composition was determined by gas chromatography. Physically trained students had similar physical characteristics to control students but a significantly higher aerobic capacity, estimated as the maximal oxygen uptake and anaerobic threshold. Of the phospholipids examined, only the content of membrane phosphatidylserine was significantly lower in the trained group. Fatty acid analysis showed that the amount of docosahexaenoic acid in membrane phosphatidylserine was lower in the trained group. There was no significant difference between the fatty acid compositions of membrane phosphatidylcholine in the two groups. Maximal exercise decreased membrane phosphatidylserine in the control group but not in the trained group. It also significantly decreased the relative amounts of unsaturated fatty acids in both phosphatidylcholine and phosphatidylserine in the untrained group. Maximal oxygen uptake was negatively correlated with the amount of erythrocyte membrane phosphatidylserine. These results would indicate that both physical training and acute exercise decrease phosphatidylserine and polyunsaturated fatty acids in erythrocyte membranes, possibly due to lipid peroxidation, suggesting limited enhancement of erythrocyte defense mechanisms in adaptation to chronic oxidative stress.

Inhibition of arachidonic acid incorporation into erythrocyte phospholipids by peracetic acid and other peroxides. Role of arachidonoyl-CoA: 1-palmitoyl-sn-glycero-3-phosphocholine acyl transferase

To explore possible mechanisms of the arachidonic acid deficiency of the red blood cell membrane in alcoholics, we compared the effect of ethanol and its oxidized products, acetaldehyde and peracetic acid, with other peroxides on the accumulation of [14C]arachidonate into RBC membrane lipids in vitro. Incubation of erythrocytes with 50 mM ethanol or 3 mM acetaldehyde had no effect on arachidonate incorporation. Pretreatment of erythrocytes with 10 mM hydrogen peroxide, 0.1 mM cumene hydroperoxide or 0.1 mM t-butyl hydroperoxide had little effect on [14C]arachidonate incorporation in the absence of azide. However, pretreatment of cells with N-ethylmaleimide, 0.1 mM peracetic acid or performic acid, with or without azide, inhibited arachidonate incorporation into phospholipids but not neutral lipids. In chase experiments, peracetate also inhibited transfer of arachidonate from neutral lipids to phospholipids. To investigate a possible site of this inhibition of arachidonate transfer into phospholipids by percarboxylic acids, we assayed a repair enzyme, arachidonoyl CoA: 1-palmitoyl-sn-glycero-3-phosphocholine acyl transferase (EC 2.3.1.23). As in intact cells, phospholipid biosynthesis was inhibited more by N-ethylmalemide and peracetic acid than by hydrogen peroxide, cumene hydroperoxide, and t-butyl hydroperoxide. Peracetic acid was the only active inhibitor among ethanol and its oxidized products studied and may deserve further examination in ethanol toxicity.

Comparison of the protective effect of various flavonoids against lipid peroxidation of erythrocyte membranes (induced by cumene hydroperoxide)

An experimental model system was designed to test the antioxidant effects of various pharmacologic compounds. Cumene hydroperoxide induces in vitro the peroxidation of erythrocyte membrane and the subsequent formation of malonaldehyde and fluorescent lipid-soluble products. The protective effect of various flavonoids was compared to that of butylated hydroxytoluene (BHT). Protective effect was evaluated by the inhibition of peroxidation product formation. In this experimental system, quercetin and catechin showed a protective effect against lipid peroxidation as high as that of BHT. Morin, rutin, trihydroxyethylrutin, and naringin were active but to a lesser degree, whereas flavone was devoid of antioxidant activity.

t-Butyl hydroperoxide alters fatty acid incorporation into erythrocyte membrane phospholipid

Because the ability of cells to replace oxidized fatty acids in membrane phospholipids via deacylation and reacylation in situ may be an important determinant of the ability of cells to tolerate oxidative stress, incorporation of exogenous fatty acid into phospholipid by human erythrocytes has been examined following exposure of the cells to t-butyl hydroperoxide. Exposure of human erythrocytes to t-butyl hydroperoxide (0.5-1.0 mM) results in oxidation of glutathione, formation of malonyldialdehyde, and oxidation of hemoglobin to methemoglobin. Under these conditions, incorporation of exogenous [9,10-3H]oleic acid into phosphatidylethanolamine is enhanced while incorporation of [9,10-3H]oleic acid into phosphatidylcholine is decreased. These effects of t-butyl hydroperoxide on [9,10-3H]oleic acid incorporation are not affected by dissipating transmembrane gradients for calcium and potassium. When malonyldialdehyde production is inhibited by addition of ascorbic acid, t-butyl hydroperoxide still decreases [9,10-3H]oleic acid incorporation into phosphatidylcholine but no stimulation of [9,10-3H]oleic acid incorporation into phosphatidylethanolamine occurs. In cells pre-treated with NaNO2 to convert hemoglobin to methemoglobin, t-butyl hydroperoxide reduces [9,10-3H]oleic acid incorporation into phosphatidylcholine by erythrocytes but does not stimulate [9,10-3H]oleic acid incorporation into phosphatidylethanolamine. Under these conditions oxidation of erythrocyte glutathione and formation of malonyldialdehyde still occur. These results indicate that membrane phospholipid fatty acid turnover is altered under conditions where peroxidation of membrane phospholipid fatty acids occurs and suggest that the oxidation state of hemoglobin influences this response.

Preparation of inside-out vesicles from erythrocyte membranes inactivates the pathway for oleic acid incorporation into phospholipid

The pathway for membrane phospholipid fatty acid turnover in situ may be important in the regulation of the composition and turnover of the lipid microenvironment of membrane proteins. This pathway has been characterized further by studying the activation and incorporation of [9,10(n)-3H]oleic acid and transesterification of [1-14C]oleoyl-CoA into membrane phospholipids by isolated erythrocyte membrane ghosts and inside-out vesicles derived from these ghosts. Erythrocyte ghosts and sealed vesicles of defined orientation prepared from them have been widely employed in studies of the function of membrane proteins, particularly those which mediate the transport of ions and sugars. Preparation of inside-out vesicles from ghosts by exposure to alkaline hypotonic conditions results in elution of some membrane proteins but no loss of membrane phospholipid. Compared to ghosts, the ability of inside-out vesicles to activate and incorporate [9,10(n)-3H]oleic acid into phospholipid is diminished by over 90% and the ability of inside-out vesicles to transesterify [1-14C]oleoyl-CoA to phospholipid is diminished by over 50%. These findings indicate that exposure of erythrocyte membranes to the alkaline hypotonic conditions required for inside-out vesicle preparation results in loss or inactivation of both acyl-CoA ligase and acyl-CoA-lysophospholipid acyltransferase activities. This lability of the enzymes for in situ phospholipid fatty acid turnover should be considered in the design and interpretation of studies concerned with elucidation of the relationship between phospholipid fatty acid turnover and the regulation of membrane protein function in this membrane preparation.

Red cell membrane lipid peroxidation and hemolysis secondary to phototherapy

The exposure of red cells to phototherapy light in the presence of a sensitizer (bilirubin) resulted in oxidative injury to the red cell membrane as manifested by a significant increase in the concentration of the products of lipid peroxidation (TBA reactants and diene conjugation) in the membrane and hemolysis. To induce a photo-oxidized membrane injury, the sensitizer (bilirubin) has to be membrane bound. Thus, by altering the availability of free bilirubin in the red cell suspension through changes in the molar concentration ratio of bilirubin to albumin, one is able to regulate the occurrence and extent of the oxidative red cell membrane injury. The clinical implications of these findings are discussed.

Macrophage oxidative burst (OB) and related cytotoxicity--II. Differential sensitivity of erythrocytes from various animals to OB dependent lysis

Red blood cells (RBCs) from various animals, when exposed to oxidative burst (OB)-stimulated mouse macrophages, showed differences in sensitivity to OB dependent lysis. The increasing order of sensitivity was: mouse, hamster, rabbit, guinea pig, sheep and human RBCs. The degree of OB dependent hemolysis did not correlate with either the capacity of the various cells to degrade H2O2 or their osmotic fragility. The relative sensitivity of the various RBCs to OB products generated by macrophages concurred with their sensitivity to H2O2 generated by an enzymatic system. The differential sensitivity may be correlated with the sphingomyelin content of the cells.

Minireview. Roles of turnover and repair of macromolecules and supramolecular structural components

Macromolecules and supramolecular structural components that are incorrectly synthesized or are damaged by radiation or by reactive chemicals are either repaired or selectively degraded and resynthesized. In addition, turnover rates for macromolecules and supramolecular structures can be elevated by alternation of fasting and feeding periods and can be influenced by metabolic regulatory mechanisms which are governed by steady-state concentrations of labile macromolecules.

Calcium potentiates the peroxidation of erythrocyte membrane lipids

To explore the possible role of intracellular calcium in membrane lipid peroxidation, we subjected red cells to conditions designed to increase intracellular calcium levels and then measured lipid peroxidation after exposure to a peroxidant threat. Human erythrocytes were pretreated for 3 h with either very high levels of CaCl2, or with low levels in the presence of the ionophore A23187. The erythrocytes were subsequently exposed to a peroxide-generating system consisting of xanthine and xanthine oxidase, or H2O2 for 1 h at 37 degrees C. As measured by a malonyldialdehyde assay, the calcium-treated cell showed up to a 2-fold increase in lipid peroxidation in comparison to untreated cells. In experiments with the ionophore, calcium concentration-dependent effects were detected at levels as low as 10 microM and were maximal at 50 microM. A significant loss of phosphatidylserine and phosphatidylethanolamine was observed in calcium- and peroxide-treated erythrocytes. This potentiation of membrane lipid peroxidation and lipid loss could be prevented by either lipid antioxidants or EGTA. The present study shows that pretreatment of erythrocytes with calcium increases their sensitivity to lipid peroxidation. This suggests that increased calcium concentration may be a factor in the potentiation of membrane lipid peroxidation of erythrocytes known to have increased calcium levels such as sickled and senescent red cells.

Erythrocyte membrane lipid reorganization during the sickling process

In order to study possible alterations in membrane lipids during sickling, we have measured the difference in susceptibility to lipid peroxidation, binding of trinitrobenzenesulfonic acid (TNBS) to aminophospholipids, and fatty acid uptake in cells containing sickle haemoglobin under aerobic and anaerobic conditions. We have also examined TNBS binding in irreversibly sickled cells in an attempt to evaluate the permanent effects of any such alterations. We found that when erythrocytes were sickled by deoxygenation, the susceptibility to lipid peroxidation and binding of TNBS to aminophospholipids was markedly increased, while normal control cells showed no change. These effects appeared to be specific for the sickled state rather than a nonspecific consequence of cell age or the concentration of sickle haemoglobin within the cell. In contrast, fatty acid incorporation into membrane phospholipids, representing potential lipid renewal, was decreased in the sickled state. Cell fractions enriched in irreversibly sickled cells showed increased TNBS labelling in air and only modest rises with anoxia. Taken together, these data imply a rearrangement of membrane lipids during the sickling process and suggest a permanent reorganization of membrane lipids in the irreversibly sickled cell.

[Changes of erythrocyte membrane lipids in ethanol induced hyperlipidemia (Zieve's syndrome) (author's transl)]

In 11 patients with alcohol-induced hyperlipemia, of whom 6 showed a Zieve Syndrome increased phospholipids, triglycerides and total cholesterol were found in the red cells stromal. The gasliquid chromatographic analysis of the phospholipid fatty acids showed increased contents of saturated and monounsaturated fatty acids C 16-C 18 smaller contents of longchain highly unsaturated fatty acids. The changes in the fatty acid pattern mainly occurred in patients with Zieve Syndrome and could be important for the mechanism of the hemolytic anemia. Theses findings could be in connexion with vitamin E deficiency.

Role of dietary iron and fat on vitamin E deficiency anemia of infancy

Thirty-five infants weighing less than 1500 g at birth were fed four commercial formulas (A-D) varying in polyunsaturated fatty acid composition (32 per cent linoleic acid in A and B and 12 per cent linoleic acid in C and D) and in iron content (smaller than 1.0 in A and B; 12 to 12 mg per liter in B and D). Infants receiving formula B showed significantly lower hemoglobins (p smaller than 0.01) and higher reticulocyte counts (p smaller than 0.005) than infants fed the other three formulas. Infants receiving the two formulas with higher concentrations of unsaturated fatty acids (A and B) showed significantly greater hydrogen-peroxide-induced hemolysis (p smaller than 0.001) than those given diets containing lower amounts. Infants in groups A and B also had lower serum tocopherol concentrations. Infant red-cell membranes are altered by the increased amounts of polyunsaturated fatty acids and iron in the diet. It appears that the development of vitamin E deficiency anemia occurs in infants receiving iron supplementation.

Remodeling of granulocyte membrane fatty acids during phagocytosis

During phagocytosis, new phospholipid is synthesized from triglyceride fatty acid and may be utilized to form the membranes of phagocytic vesicles. In addition, hydrogen peroxide, which can peroxidize unsaturated fatty acids, is generated. Since both of these processes could change membrane fatty acid composition during the conversion of cytoplasmic granules and plasma membranes to phagosomes, the lipid compositions of these structures were examined. Phagocytic vesicles were prepared by density gradient centrifugation of polystyrene latex particles after phagocytosis. Granule and plasma membrane fractions were isolated by density gradient and differential centrifugation. Phospholipids and fatty acids were analyzed by thin-layer chromatography and gas-liquid chromatography. While whole cells, granules, plasma membranes, and phagosomes were all similar in phospholipid composition, phagosome fatty acids were significantly more saturated than those of the other fractions. This was primarily due to reduced oleic and arachidonic acids and increased palmitic acid in the phagocytic vesicle lipids. Plasma membrane was also more saturated in comparison to whole cells and granules. However, this difference was not sufficient to explain the marked comparative saturation of the phagosomes. The observed increase in fatty acid saturation in these lipids may have been induced by a combination of either peroxidative destruction of polyunsaturated fatty acids or phospholipase activity, coupled with reacylation mechanisms favoring saturated fatty acids.