Biomedical subjects

J Szebeni

Publications and source records attributed to J Szebeni.

46 records · Page 3Linked to original sources

PubMed1988

Factors influencing the in vitro stability of artificial red blood cells based on hemoglobin-containing liposomes.

The effects of membrane phospholipid composition, surface charge and cholesterol content on the deteriorating interactions between hemoglobin (Hb) and phospholipid bilayers were studied. Hb was either encapsulated in multilamellar liposomes (hemosomes), or incubated with small unilamellar vesicles (SUV). Negatively charged phospholipids increased the rate of oxyHb decay in unsaturated lipid hemosomes. This effect was not linked to Hb-induced lipid peroxidation, since the latter process was inhibited in hemosomes with negative surface charge. Cholesterol decreased both the negative-charge elicited fall in oxyHb-level, and Hb-induced lipid peroxidation. In hemosomes prepared from synthetic, saturated phospholipids, negative surface charge (phosphatidic acid) elicited drastic denaturation (bleaching) of Hb, which effect was completely prevented by cholesterol. The experiments with SUV prepared from unsaturated lipids indicated intercalation of Hb into the bilayer due to hydrophobic interaction. This process was decreased by membrane cholesterol. Negative surface charge of the vesicles, through an electrostatic interaction with the positively charged heme, resulted in the displacement of heme relative to globin. This process was also decreased by cholesterol. With saturated, negatively charged SUV, the penetration of Hb into the bilayer was smaller, but the ionic interaction between the acidic lipids and the heme led to the detachment of the letter from globin. Cholesterol in such membrane increased the intercalation of Hb into the membrane, and at the same time completely prevented the loss of heme. The latter observations suggest that the fluid phase of the membrane favours the hydrophobic interaction with the protein, whereas the gel state promotes the partition of the heme into the bilayer. It is suggested that the effects of cholesterol are indirect, mediated by changes in membrane fluidity. By highlighting potentially harmful reactions between Hb and phospholipid bilayers, our findings may help the design of in-vitro stable hemosomes.

Blood Substitutes↗

PubMed1988

The effect of zinc on iron-induced lipid peroxidation in different lipid systems including liposomes and micelles.

The effect of zinc on FeSO4/ascorbic acid-induced lipid peroxidation was measured by the thiobarbituric acid assay in various lipid systems including small unilamellar liposomes prepared from egg phosphatidylcholine (EPC), ionic micelles prepared from arachidonic acid (C20:4), non-ionic monocomponent micelles prepared from EPC-derived, methylated fatty acids, and an eicosatetrene emulsion. With the exception of C20:4 micelles, zinc inhibited lipid peroxidation in each of the above systems in a similar dose-related fashion, with 0.5 mM zinc having maximal effect. Gas-chromatographic fatty acid analysis too indicated a protective effect of zinc against FeCl3-induced lipid peroxidation in soybean PC vesicles, which do not contain C20:4 moieties. These findings, in particular the inhibition of lipid peroxidation in eicosatetrene emulsion, suggest that the presence of uncharged polar head groups, or packing of lipid molecules into ordered self-assemblages (membranes and micelles) have no critical influence on the antioxidant effect of zinc. The results with Fe2+ are compatible with the concept that zinc interferes with the formation of Fe2+-oxygen-enoic complexes. This mechanism, however, cannot account for the inhibition by zinc of the Fe#+-induced lipid peroxidation, suggesting the involvement of other types of zinc effects in these systems.

Ascorbic Acid↗

PubMed1986

Inhibition of ethanol induced ethane exhalation by carcinogenic pretreatment of rats 12 months earlier.

The exhalation of ethane was used as a measure of in vivo lipid peroxidation in rats treated with the hepatocarcinogen diethylnitrosamine followed by 2-acetylaminofluorene (AAF), and carbon tetrachloride, and subsequently fed a liquid diet containing 7% ethanol for 12 months. The other groups consisted of animals treated with methylbenzylnitrosamine (MBN), an esophageal carcinogen, or non-carcinogen pretreated animals with or without 7% ethanol feeding. Ethane production was increased in rats consuming ethanol irrespective of their pretreatment with MBN. In sharp contrast, the ethanol-induced increase of ethane production was absent in rats given the hepatocarcinogenic regime. Our results strengthen recent observations indicating decreased susceptibility of tumor cells to lipid peroxidation. In addition, they confirm the debated concept that there is increased lipid peroxidation following ethanol consumption.

2-Acetylaminofluorene↗

PubMed1986

Lipid peroxidation in hemoglobin-containing liposomes. Effects of membrane phospholipid composition and cholesterol content.

The effects of phospholipid-oxidation state and vesicle composition on lipid peroxidation in hemolysate-containing liposomes (hemosomes) were studied by the thiobarbituric acid assay. Liposomes (hemosomes) were prepared from egg phosphatidylcholine (PC) with either low (PC0.08) or high (PC0.66) oxidation indices reflecting low and high conjugated diene/lipid hydroperoxy contents. Thiobarbituric acid reactivity was negligible over 6 h at 38 degrees C in buffer-containing (control) liposomes prepared from PC0.08, whereas it was slightly increased in those prepared from PC0.66. Encapsulated hemolysate had no effect in PC0.08 liposomes, but significantly increased thiobarbituric acid reactivity in those prepared from PC0.66. Inclusion of either phosphatidylethanolamine or phosphatidylinositol in the membrane further increased lipid peroxidation in hemosomes prepared from PC0.66, whereas phosphatidic acid and phosphatidylserine were inhibitory. Inclusion of cholesterol in the membrane had no effect in PC0.66 hemosomes, but significantly inhibited lipid peroxidation in the presence of phosphatidylethanolamine or phosphatidylinositol. The effects of phosphatidic acid and cholesterol were dose-dependent. Co-incorporation of cholesterol and phosphatidic acid or phosphatidylserine in the membrane resulted in almost complete elimination of hemoglobin (Hb)-induced lipid peroxidation. Lysophosphatidic acid had similar effect as phosphatidic acid, whereas lysophosphatidylserine exerted inhibition only in the presence of phosphatidylethanolamine. The rate of lipid peroxidation showed no correlation with the amount of encapsulated Hb, neither with the oxidation indices nor the polyunsaturated fatty acid contents of negatively charged phospholipids. The above findings suggest a possible role for the high cholesterol content and preferential localization of phosphatidylserine in the inner bilayer leaflet of erythrocyte membrane in protecting against Hb-induced lipid peroxidation in the membrane.

Animals↗

PubMed1986

Plasma fatty acid pattern including diene-conjugated linoleic acid in ethanol users and patients with ethanol-related liver disease.

The level of conjugated dienes (CD) in the serum, conjugated linoleic acid isomer in the phospholipid fraction [18:2(9, 11)], and the fatty acid profile in both the serum and in the separated lipid classes were analyzed in current and previous alcohol abusers and in patients with alcoholic liver disease. None of the subjects consumed alcohol for at least 2-3 days prior to blood collection for analysis of lipids. There was no significant difference in CD or in the absolute level of 18:2(9, 11) among the groups, whereas the 18:2(9, 11)/18:2(9, 12) molar ratio was significantly elevated in patients with liver disease. Fatty acid analysis of the whole plasma extract showed that the absolute level of arachidonic acid increased from 4.8 +/- 3.5 mg/dl (n = 9) in lifelong abstainers to 13.4 +/- 4.0 (n = 8) in current ethanol abusers, and its relative level (related to the total fatty acids) from 1.73 +/- 1.34 to 4.55 +/- 1.01 in the same groups. An increased proportion of linoleic acid in the triglyceride and phospholipid fractions from current abusers and patients with liver disease was also found; the percentage of 18:2 in phospholipids increased from 5.4 +/- 5.0 (n = 8) in lifelong abstainers to 14.3 +/- 3.9 (n = 8) in current abusers and 12.7 +/- 2.2 (n = 10) in patients with liver disease. The percentage of 16:0 was significantly lower in the phospholipids of current abusers as compared to lifelong abstainers.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗

PubMed1985

Encapsulation of hemoglobin in phospholipid liposomes: characterization and stability.

Hemoglobin is encapsulated in liposomes of different lipid composition. The resulting dispersion consists primarily of multilamellar liposomes (hemosomes) of a wide particle size distribution (diameter ranging mainly between 0.1 and 1 micron). The encapsulation efficiency is significantly larger with liposomes containing negatively charged lipids as compared to liposomes made of phosphatidylcholine. The integrity of the phospholipid bilayer is maintained in the presence of hemoglobin. The reaction rate of CO binding to encapsulated hemoglobin is reduced compared to that of free hemoglobin, but it is still greater than that observed in red blood cells. Hemoglobin encapsulated in liposomes made from negatively charged phospholipids is less stable than hemoglobin entrapped in isoelectric phosphatidylcholine. The instability of hemoglobin is due to the protein interacting with the negatively charged lipid bilayer. This interaction leads in turn to hemoglobin denaturation, possibly involving the dissociation of the heme group from the heme-globin complex. The nature of the negatively charged phospholipid is important in promoting the interaction with hemoglobin, the effect being in the order phosphatidic acid greater than phosphatidylinositol congruent to phosphatidylglycerol greater than phosphatidylserine. The presence of equimolar amounts of cholesterol in the phospholipid bilayer has a stabilizing effect on hemoglobin. This effect is pronounced with saturated phospholipids, but it is also observed, though to a lesser extent, with unsaturated ones, indicating that the bilayer fluidity has a modulating effect. The presence of cholesterol possibly interferes with secondary interactions following the binding of hemoglobin to the negatively charged lipid bilayer.

Hemoglobins↗

PubMed1984

Oxidative interactions between haemoglobin and membrane lipid. A liposome model.

The relationship between haemoglobin and membrane oxidation was studied using liposomes containing haemoglobin (haemosomes) as a red cell model. Rapid oxidation occurred in haemosomes formed from purified haemoglobin and unsaturated lipid (egg phosphatidylcholines). After 3 h at 37 degrees C most of the haemoglobin was oxidized, predominantly to methaemoglobin with some haemichrome formation. The oxidation of haemoglobin was paralleled by membrane lipid peroxidation as measured by thiobarbituric acid reactivity. These changes were largely abolished by using freshly prepared haemolysate instead of purified haemoglobin, or when haemosomes were prepared with saturated phosphatidylcholines. In haemosomes consisting of fresh haemolysate and saturated phosphatidylcholine, the rate of haemoglobin oxidation at 37 degrees C corresponded to that of non-encapsulated haemolysate, and after 4 months storage at 4 degrees C 45% of oxyhaemoglobin was oxidized. In haemosomes prepared from purified haemoglobin and egg lecithin, alpha-tocopherol, catalase and ascorbate each protected against both haemoglobin oxidation and lipid peroxidation. Superoxide dismutase or reduced glutathione had no effect. In unsaturated-lipid haemosomes containing haemolysate, the rate of haemoglobin oxidation increased when catalase was inhibited or reduced glutathione was depleted, but after long term incubation only concurrent catalase-inhibition and glutathione depletion could increase thiobarbituric acid reactivity. These results demonstrate a close interdependence between haemoglobin oxidation and lipid peroxidation, and show that constituents of haemolysate strongly protect against both processes. H2O2 appears to be an important mediator, with its removal by either catalase or the glutathione/glutathione peroxidase system protecting against both oxidative changes.

Catalase↗

PubMed1984

Oxidation and denaturation of hemoglobin encapsulated in liposomes.

A study was made of the in vitro stability of hemoglobin-containing liposomes ('hemosomes') prepared from phosphatidylcholines, equimolar cholesterol and red cell lysate by the hand-shaking and ether-injection methods. Absorption spectra indicated hemichrome formation in 'hemosomes' prepared by the ether-injection technique, and increased oxidation of hemoglobin in hand-shaken 'hemosomes'. The denaturation of hemoglobin in ether-injection 'hemoglobin' was increased if the initial methemoglobin content of the hemolysate, or the temperature of preparation was elevated. It was slower if liposomes were prepared under either N2 or CO, or if the radical scavenger 1,3-diphenylisobenzofuran was added with the ether. Egg phosphatidylcholine and synthetic saturated phospholipids gave the same results. With hand-shaken 'hemosomes' the oxidized product was primarily methemoglobin, and oxidation could be inhibited by using saturated phosphatidylcholines instead of egg phosphatidylcholine. Lysophosphatidylcholine levels were higher and arachidonic acid levels lower in egg phosphatidylcholine 'hemosomes' than in equivalent liposomes containing no hemolysate. The 'hemosome' seems to be a suitable model for the study of hemoglobin-lipid membrane interactions and the resulting hemoglobin denaturation process.

Freeze Fracturing↗

PubMed1981

The Ca2+-sensitive K+ transport in inside-out red cell membrane vesicles.

Ca2+-sensitive K+ transport ("Gárdos-effect") was investigated in inside-out red cell membrane vesicles (IOVs) by measuring the effect of Ca2+ and other agents on the 86Rb+ (K+-analogue) influx. 50 micro M-5 mM Ca2+ stimulated the 86Rb+ influx as compared to the effect of 1 mM EDTA. Mg2+ and chlorpromazine inhibited the effect of Ca2+, oligomycin and quinine were without effect. The permeability increase of K+, elicited by Ca2+ in IOVs, corresponded to that of intact cells. The effect of Ca2+ was not specific to K+ with respect to Na+. The Ca2+-sensitive K+ channels saturated about 5-10 mM KCl in the medium. The results indicate that IOVs the Ca2+-sensitive K+ transport has altered characteristics as compared to that of intact cells and resealed ghosts. However, in contrast to the suggestion of other investigators, it was found that some features of this phenomenon are still preserved in IOVs.

Biological Transport↗

PubMedDate not supplied

Role of complement activation in hypersensitivity reactions to doxil and hynic PEG liposomes: experimental and clinical studies.

Pegylated liposomal doxorubicin (Doxil) and 99mTc-HYNIC PEG liposomes (HPL) were reported earlier to cause hypersensitivity reactions (HSRs) in a substantial percentage of patients treated i.v. with these formulations. Here we report that (1) Doxil, HPL, pegylated phosphatidylethanolamine (PEG-PE)-containing empty liposomes matched with Doxil and HPL in size and lipid composition, and phosphatidylglycerol (PG)-containing negatively charged vesicles were potent C activators in human serum in vitro, whereas small neutral liposomes caused no C activation. (2) Doxil and other size-matched PEG-PE and/or PG-containing liposomes also caused massive cardiopulmonary distress with anaphylactoid shock in pigs via C activation, whereas equivalent neutral liposomes caused no hemodynamic changes. (3) A clinical study showed more frequent and greater C activation in patients displaying HSR than in non-reactive patients. These data suggest that liposome-induced HSRs in susceptible individuals may be due to C activation, which, in turn, is due to the presence of negatively charged PEG-PE in these vesicles.

Animals↗