Induction of type-IIA secretory phospholipase A2 in animal models of acute lung injury

The aim of this study was to evaluate the presence of type-II secretory phospholipase A2 (sPLA2-IIA) in alveolar space and its possible role in the destruction of surfactant in three rat models of acute lung injury. Alveolar instillation of either lipopolysaccaride or live Pseudomonas aeruginosa resulted in a significant increase in lung oedema and in a decrease in static compliance of the respiratory system together with alveolar-neutrophil influx as compared with healthy control rats. The upregulation of messenger ribonucleic acid and sPLA2-IIA by the lung was evident. This was associated with surfactant degradation and a decrease in large:small ratio of surfactant aggregates in bacteria-instilled rats. A negative correlation between compliance and sPLA2-IIA activity in bronchoalveolar lavage fluid was shown. By contrast, during alpha naphthylthiourea-induced injury, neither alveolar-neutrophil influx nor increase in sPLA2-IIA activity was observed. Additional experiments in rats treated with a specific inhibitor of type-II secretory phospholipase A2 activity (3 acetamine-1-benzyl-2 ethylindolyl-5 oxy; propane phosphonic acid (LY311727)) demonstrated no improvement in physiological parameters despite a biochemical effect, suggesting that its activity is only one of the multiple factors involved in the pathophysiology of lung injury.

Hypoxia enhances Ecto-5'-Nucleotidase activity and cell surface expression in endothelial cells: role of membrane lipids

Extracellular adenosine production by the glycosyl-phosphatidyl-inositol-anchored Ecto-5'-Nucleotidase plays an important role in the defense against hypoxia, particularly in the intravascular space. The present study was designed in order to elucidate the mechanisms underlying hypoxia-induced stimulation of Ecto-5'-Nucleotidase in endothelial cells. For this purpose, aortic endothelial cells (SVARECs) were submitted to hypoxic gas mixture. Hypoxia (0% O2 for 18 hours) induced a 2-fold increase of Ecto-5'-Nucleotidase activity (Vmax 19.78+/-0.53 versus 8.82+/-1.12 nmol/mg protein per min), whereas mRNA abundance and total amount of the protein were unmodified. By contrast, hypoxia enhanced cell surface expression of Ecto-5'-Nucleotidase, as evidenced both by biotinylation and immunostaining. This effect was accompanied by a decrease of Ecto-5'-Nucleotidase endocytosis, without modification of Ecto-5'-Nucleotidase association with detergent-resistant membranes. Finally, whereas cholesterol content was unmodified, hypoxia induced a time-dependent increase of saturated fatty acids in SVARECs, which was reversed by reoxygenation, in parallel to Ecto-5'-Nucleotidase stimulation. Incubation of normoxic cells with palmitic acid enhanced Ecto-5'-Nucleotidase activity and cell surface expression. In conclusion, hypoxia enhances cell surface expression of Ecto-5'-Nucleotidase in endothelial cells. This effect could be supported by a decrease of Ecto-5'-Nucleotidase endocytosis through modification of plasma membrane fatty acid composition.

Bimodal regulatory effect of melittin and phospholipase A2-activating protein on human type II secretory phospholipase A2

Melittin and phospholipase A2-activating protein (PLAP) are known as efficient activators of secretory phospholipase A2(sPLA2) types I, II, and III when phospholipid liposomes are used as substrate. The present study demonstrates that both peptides can either inhibit or activate sPLA2 depending on the peptide/phospholipid ratio when erythrocyte membranes serve as a biologically relevant substrate. Low concentrations of melittin and PLAP were observed to inhibit sPLA2-triggered release of fatty acids from erythrocyte membranes. The inhibition was reversed at melittin concentrations above 1 microM. PLAP-induced inhibition of sPLA2 persisted steadily throughout the used concentration range (0-150 nM). The two peptides induced a dose-dependent activation of sPLA2 at low concentrations, followed by inhibition when model membranes were used as substrate. This opposite modulatory effect on biological membranes and model membranes is discussed with respect to different mechanisms the interaction of the regulatory peptides with the enzyme molecules and the substrate vesicles.

Cholesterol favors phase separation of sphingomyelin

The phase behavior of mixed lipid dispersions representing the inner leaflet of the cell membrane has been characterized by X-ray diffraction. Aqueous dispersions of phosphatidylethanolamine:phosphatidylserine (4:1 mole/mole) have a heterogeneous structure comprising an inverted hexagonal phase H(II) and a lamellar phase. Both phases coexist in the temperature range 20-45 degrees C. The fluid-to-gel mid-transition temperature of the lamellar phase assigned to phosphatidylserine is decreased from 27 to 24 degrees C in the presence of calcium. Addition of sphingomyelin to phosphatidylethanolamine/phosphatidylserine prevents phase separation of the hexagonal H(II) phase of phosphatidylethanolamine but the ternary mixture phase separates into two lamellar phases of periodcity 6.2 and 5.6 nm, respectively. The 6.2-nm periodicity is assigned to the gel phase enriched in sphingomyelin of molecular species comprising predominantly long saturated hydrocarbon chains because it undergoes a gel-to-fluid phase transition above 40 degrees C. The coexisting fluid phase we assign to phosphatidylethanolamine and phosphatidylserine and low melting point molecular species of sphingomyelin which suppresses the tendency of phosphatidylethanolamine to phase-separate into hexagonal H(II) structure. There is evidence for considerable hysteresis in the separation of lamellar fluid and gel phases during cooling. The addition of cholesterol prevents phase separation of the gel phase of high melting point sphingomyelin in mixtures with phosphatidylserine and phosphatidylethanolamine. In the quaternary mixture the lamellar fluid phase, however, is phase separated into two lamellar phases of periodicities of 6.3 and 5.6 nm (20 degrees C), respectively. The lamellar phase of periodicity 5.6 nm is assigned to a phase enriched in aminoglycerophospholipids and the periodicity 6.3 nm to a liquid-ordered phase formed from cholesterol and high melting point molecular species of sphingomyelin characterized previously by ESR. Substituting 7-dehydrocholesterol for cholesterol did not result in evidence for lamellar phase separation in the mixture within the temperature range 20-40 degrees C. The specificity of cholesterol in creation of liquid-ordered lamellar phase is inferred.

N-terminal and C-terminal plasma membrane anchoring modulate differently agonist-induced activation of cytosolic phospholipase A2

The 85 kDa cytosolic phospholipase A2 (cPLA2) plays a key role in liberating arachidonic acid from the sn-2 position of membrane phospholipids. When activated by extracellular stimuli, cPLA2 undergoes calcium-dependent translocation from cytosol to membrane sites which are still a matter of debate. In order to evaluate the effect of plasma membrane association on cPLA2 activation, we constructed chimeras of cPLA2 constitutively targeted to the plasma membrane by the N-terminal targeting sequence of the protein tyrosine kinase Lck (Lck-cPLA2) or the C-terminal targeting signal of K-Ras4B (cPLA2-Ras). Constitutive expression of these chimeras in Chinese hamster ovary cells overproducing the alpha2B adrenergic receptor (CHO-2B cells) did not affect the basal release of [3H]arachidonic acid, indicating that constitutive association of cPLA2 with cellular membranes did not ensure the hydrolysis of membrane phospholipids. However, Lck-cPLA2 increased [3H]arachidonic acid release in response to receptor stimulation and to increased intracellular calcium, whereas cPLA2-Ras inhibited it, compared with parental CHO-2B cells and CHO-2B cells producing comparable amounts of recombinant wild-type cPLA2. The lack of stimulation of cPLA2-Ras was not due to a decreased enzymatic activity as measured using an exogenous substrate, or to a decreased phosphorylation of the protein. These results show that the plasma membrane is a suitable site for cPLA2 activation when orientated correctly.

[Physical arrangement of membrane lipids susceptible to being used in the process of cell sorting of proteins]

Detection of immiscible lipid domains in biological membranes offers an alternative support to protein sorting. Liquid ordered domains ("rafts") comprising cholesterol and saturated sphingolipids incorporate saturated glycosyl-phosphatidylinositol (GPI)-anchored or acylated (palmitoyl- and myristoyl-) proteins or particular transmembrane protein sequences. These lipid domains can be isolated in the form of Detergent resistant membranes (DRM) from biological plasma membrane preparations. Caveolae appear to be a differentiated fraction of plasma membranes comprising such numerous cross-linked microdomains associated with caveolin in different cell types. While the biological relevance of such membrane domains is evidenced in vivo by co-patching of proteins sharing the identical affinity for sphingolipids and by the disruption of co-patching following cell cholesterol depletion, only a few physical studies confort the principle of membrane heterogeneity. Results are now presented where cholesterol addition in a tertiary lipid mixture forces outphase-separation, as a realistic model where the lipid segregation can promote protein sorting to the segregated Lo phase. A lipid mixture comprising phosphatidylserine, phosphatidylethanolamine and sphingomyelin of natural origin in the ratio (1/4/3: mole/mole) has been rendered neatly heterogeneous after the addition of cholesterol (27 mole%). Xray diffraction (Small angle Xray scattering) showed the splitting of two neatly resolved lamellar diffractions in the presence of cholesterol. Above 37 degrees C the heterogeneity was traceable by a broadened diffraction spot up to the complete get-to-liquid transition of sphingomyelin at temperatures > 40 degrees C where the spot became again symmetrical and narrow. The large temperature range where the immiscible lamellar phases are detected, the specific requirement for cholesterol association with sphingomyelin, the positive influence of calcium and the reversibility of domain formation support the occurrence for such domains at the inner side of the plasma membrane whereon lipids-bound proteins concentrate.

Interleukin 1beta induces type II-secreted phospholipase A(2) gene in vascular smooth muscle cells by a nuclear factor kappaB and peroxisome proliferator-activated receptor-mediated process

Type II-secreted phospholipase A(2) (type II-sPLA(2)) is expressed in smooth muscle cells during atherosclerosis or in response to interleukin-1beta. The present study shows that the induction of type II-sPLA(2) gene by interleukin-1beta requires activation of the NFkappaB pathway and cytosolic PLA(2)/PPARgamma pathway, which are both necessary to achieve the transcriptional process. Interleukin-1beta induced type II-sPLA(2) gene dose- and time-dependently and increased the binding of NFkappaB to a specific site of type II-sPLA(2) promoter. This effect was abolished by proteinase inhibitors that block the proteasome machinery and NFkappaB nuclear translocation. Type II-sPLA(2) induction was also obtained by free arachidonic acid and was blocked by either AACOCF(3), a specific cytosolic-PLA(2) inhibitor, PD98059, a mitogen-activated protein kinase kinase inhibitor which prevents cytosolic PLA(2) activation, or nordihydroguaiaretic acid, a lipoxygenase inhibitor, but not by the cyclooxygenase inhibitor indomethacin, suggesting a role for a lipoxygenase product. Type II-sPLA(2) induction was obtained after treatment of the cells by 15-deoxy-Delta(12,14)-dehydroprostaglandin J(2), carbaprostacyclin, and 9-hydroxyoctadecadienoic acid, which are ligands of peroxisome proliferator-activated receptor (PPAR) gamma, whereas PPARalpha ligands were ineffective. Interleukin-1beta as well as PPARgamma-ligands stimulated the activity of a reporter gene containing PPARgamma-binding sites in its promoter. Binding of both NFkappaB and PPARgamma to their promoter is required to stimulate the transcriptional process since inhibitors of each class block interleukin-1beta-induced type II-sPLA(2) gene activation. We therefore suggest that NFkappaB and PPARgamma cooperate at the enhanceosome-coactivator level to turn on transcription of the proinflammatory type II-sPLA(2) gene.

Generation of lyso-phospholipids from surfactant in acute lung injury is mediated by type-II phospholipase A2 and inhibited by a direct surfactant protein A-phospholipase A2 protein interaction

Lyso-phospholipids exert a major injurious effect on lung cell membranes during Acute Respiratory Distress Syndrome (ARDS), but the mechanisms leading to their in vivo generation are still unknown. Intratracheal administration of LPS to guinea pigs induced the secretion of type II secretory phospholipase A2 (sPLA2-II) accompanied by a marked increase in fatty acid and lyso-phosphatidylcholine (lyso-PC) levels in the bronchoalveolar lavage fluid (BALF). Administration of LY311727, a specific sPLA2-II inhibitor, reduced by 60% the mass of free fatty acid and lyso-PC content in BALF. Gas chromatography/mass spectrometry analysis revealed that palmitic acid and palmitoyl-2-lyso-PC were the predominant lipid derivatives released in BALF. A similar pattern was observed after the intratracheal administration of recombinant guinea pig (r-GP) sPLA2-II and was accompanied by a 50-60% loss of surfactant phospholipid content, suggesting that surfactant is a major lung target of sPLA2-II. In confirmation, r-GP sPLA2-II was able to hydrolyze surfactant phospholipids in vitro. This hydrolysis was inhibited by surfactant protein A (SP-A) through a direct and selective protein-protein interaction between SP-A and sPLA2-II. Hence, our study reports an in vivo direct causal relationship between sPLA2-II and early surfactant degradation and a new process of regulation for sPLA2-II activity. Anti-sPLA2-II strategy may represent a novel therapeutic approach in lung injury, such as ARDS.

Oxidant-induced arachidonic acid release and impairment of fatty acid acylation in vascular smooth muscle cells

Oxidative damage, which plays a major role in the early stages of atherosclerosis, is associated with arachidonic acid (AA) release in vascular smooth muscle cells (VSMC) as in other cell types. In this study, H2O2 was used to investigate mechanisms of AA release from VSMC on oxidative stress. Cell treatment with H2O2 inhibited AA incorporation in an inverse relationship to prolonged H2O2-induced AA release. Identical kinetics of inhibition of AA incorporation and AA release were observed after cell treatment with AlF4-, a process not involving phospholipase A2 (PLA2) activation as recently described (A. Cane, M. Breton, G. Béréziat, and O. Colard. Biochem. Pharmacol. 53: 327-337, 1997). AA release was not specific, since oleic acid also increased in the extracellular medium of cells treated with H2O2 or AlF4- as measured by gas chromatography-mass spectrometry. In contrast, AA and oleic acid cell content decreased after cell treatment. Oleoyl and arachidonoyl acyl-CoA synthases and acyltransferases, assayed using a cell-free system, were not significantly modified. In contrast, a good correlation was observed between decreases in AA acylation and cell ATP content. The decrease in ATP content is only partially accounted for by mitochondrial damage as assayed by rhodamine 123 assay. We conclude that oxidant-induced arachidonate release results from impairment of fatty acid esterification and that ATP availability is probably responsible for free AA accumulation on oxidative stress by preventing its reesterification and/or transmembrane transport.

Modulation of human type II secretory phospholipase A2 by sphingomyelin and annexin VI

Conjectural results have been reported on the capacity of inflammatory secreted phospholipase A2 (sPLA2) to hydrolyse mammalian membrane phospholipids. Development of an assay based on the release of non-esterified fatty acids by the enzyme acting on the organized phospholipid mixture constituting the membrane matrix has led to the identification of two prominent effectors, sphingomyelin (SPH) and annexin. Recombinant human type II sPLA2 hydrolyses red-cell membrane phospholipids with a marked preference for the inner leaflet. This preference is apparently related to the high content of SPH in the outer leaflet, which inhibits sPLA2. This inhibition by SPH is specific for sPLA2. Cholesterol counteracts the inhibition of sPLA2 by SPH, suggesting that the SPH-to-cholesterol ratio accounts in vivo for the variable susceptibility of cell membranes to sPLA2. Different effects were observed of the presence of the non-hydrolysable D-alpha-dipalmitoyl phosphatidylcholine (D-DPPC), which renders the membranes rigid but does not inhibit sPLA2. Annexin VI was shown, along with other annexins, to inhibit sPLA2 activity by sequestering the phospholipid substrate. The present study has provided the first evidence that annexin VI, in concentrations that inhibit hydrolysis of purified phospholipid substrates, stimulated the hydrolysis of membrane phospholipids by sPLA2. The activation requires the presence of membrane proteins. The effect is specific for type II sPLA2 and is not reproducible with type I PLA2. The activation by annexin VI of sPLA2 acting on red cell membranes results in the preferential release of polyunsaturated fatty acids. It suggests that type II sPLA2, in conjunction with annexin VI, might be involved in the final step of endocytosis and/or exocytosis providing the free polyunsaturated fatty acids acting synergistically to cause membrane fusion.

Cloning, chromosomal mapping, and expression of a novel human secretory phospholipase A2

Secretory phospholipases A2 (sPLA2s) represent a rapidly expanding family of structurally related enzymes found in mammals as well as in insect and snake venoms. In this report, a cDNA coding for a novel sPLA2 has been isolated from human fetal lung, and its gene has been mapped to chromosome 16p13.1-p12. The mature sPLA2 protein has a molecular mass of 13.6 kDa, is acidic (pI 5.3), and made up of 123 amino acids. Key structural features of the sPLA2 include: (i) a long prepropeptide ending with an arginine doublet, (ii) 16 cysteines located at positions that are characteristic of both group I and group II sPLA2s, (iii) a C-terminal extension typical of group II sPLA2s, (iv) and the absence of elapid and pancreatic loops that are characteristic of group I sPLA2s. Based on these structural properties, this sPLA2 appears as a first member of a new group of sPLA2s, called group X. A 1.5-kilobase transcript coding for the human group X (hGX) sPLA2 was found in spleen, thymus, and peripheral blood leukocytes, while a less abundant 0.8-kilobase transcript was detected in the pancreas, lung, and colon. When the hGX sPLA2 cDNA was expressed in COS cells, sPLA2 activity preferentially accumulated in the culture medium, indicating that hGX sPLA2 is an actively secreted enzyme. It is maximally active at physiological pH and with 10 mM Ca2+. hGX sPLA2 prefers phosphatidylethanolamine and phosphatidylcholine liposomes to those of phosphatidylserine.

Alterations in rat alveolar surfactant system induced by treatment with carbicron (O-[(2-butenoic acid)-N,N-dimethylamide-3-yl]-O,O-dimethylphosphate)

1. Intoxication of rats with carbicron (O-([2-butenoic acid)-N,N-dimethylamide-3-yl]-O,O-dimethylphosphate) induced a reduction of the total phospholipids and phosphatidylcholine in lung alveolar surfactant. 2. The lipid transfer protein activity was inhibited due to carbicron treatment. 3. No alterations were observed in phospholipase A2 activity in the alveolar surfactant of intoxicated animals. The structural order parameter (SDPH) of bilayer liposomes, prepared from surfactant phospholipids of carbicron-treated rats also remained unchanged.

Influence of immobilization stress on the phospholipid composition of alveolar surfactant and lungs in rats

The influence of immobilization stress on the lipid composition of alveolar surfactant and lungs in rats immobilized for 12 and 24 hours, the effects of phospholipase A2, and lipid transfer activity in alveolar surfactant were investigated. The results indicate that alveolar surfactant phospholipids underwent more significant alterations compared to lung phospholipids. Furthermore, phospholipase A2 and lipid transfer activity were reduced in alveolar surfactant of immobilized rats. The reported data suggest that the lower lipid transfer activity might be responsible for the reduced phospholipids in the surfactant system.

Changes in the phospholipid composition and phospholipid asymmetry of ram sperm plasma membranes after cryopreservation

The changes in the phospholipid composition of spermatozoa plasma membranes after freezing were determined by thin-layer chromatography. The results showed an augmentation of the diphosphatidylglycerol and a diminution of phosphatidylglycerol, phosphatidylserine, and phosphatidylethanolamine in sperm plasma membranes after freezing. In intact sperm cells we observed an elevation of the sphingomyelin and phosphatidylinositol levels and a diminution of the phosphatidylethanolamine and diphosphatidylglycerol levels. The effect of freezing on the phospholipid distribution between the inner and outer monolayers of the plasma membrane was also studied using exogenous phospholipases and trinitrobenzene sulfonate. The most important change we observed after freezing, was the translocation of diphosphatidylglycerol from the inner to the outer monolayer of the plasma membrane.

Phosphatidylcholine and phosphatidylethanolamine derivatives, membrane fluidity and changes in the lipolytic activity of ram spermatozoa plasma membranes during cryoconservation

1. A decrease of the alkenyl-acyl derivatives and an increase of the diacyl derivatives of PC and PE were observed after cryoconservation. 2. A diminution of membrane-bound phospholipase A2 activity was observed after cryoconservation. The activity of neutral sphingomyelinase remained unchanged. 3. The enrichment of plasma membranes with DPPC as well as the addition of the cryoprotector of Nagase-Niwa were observed to protect the membranes from fluidization.

Phospholipid-transfer proteins in human liver and primary liver carcinoma

Investigations have been carried out on phospholipid-transfer activity of the cytosol and the phospholipid composition of subcellular membranes from human liver and primary liver carcinoma. In both human liver and primary liver carcinoma cytosolic fractions, the transfer activity for phosphatidylcholine (PC), phosphatidylethanolamine (PE) and sphingomyelin has been observed for the first time. The transfer rate of PC and PE in normal human liver was almost equal, whereas sphingomyelin-transfer activity was much slower. In carcinoma cells, the transfer activity for PE and PC was significantly enhanced, while sphingomyelin transfer remained unchanged. Comparative investigations with HepG2 cultured cells have revealed a high PE-transfer activity in this cell line. Parallel with the phospholipid-transfer activity modifications in neoplasic cells, changes in the phospholipid composition of microsomes and mitochondria have been observed. The content of PC and PE in hepatocarcinoma cells was decreased in microsomes, while in the mitochondria it was increased. The possible role of the phospholipid-transfer proteins in the maintenance of membrane composition and structure is discussed.

Rat liver microsomal phospholipase A2 and membrane fluidity

The influence of the physical state and the lipid composition on microsomal membrane-bound phospholipase A2 activity has been investigated. It was established that the decrease of membrane fluidity expressed by the alterations of the steady-state fluorescent anisotropy (rs) and the structural order parameter for DPH (SDPH) leads to augmentation of phospholipase A2 specific activity. Phosphatidylinositol is the only phospholipid having a specific activating effect on microsomal membrane-bound phospholipase A2.

Sensitivity of 5'-nucleotidase and phospholipase A2 towards liver plasma membranes modifications

The changes in the phospholipid and fatty acid composition of liver plasma membranes isolated from rats, fed two different diets, containing either saturated or unsaturated fatty acids, were investigated. We established that dietary treatment can considerably modify the fatty acid as well as the phospholipid composition of liver plasma membranes. Lipid transfer proteins were used for enrichment of liver plasma membranes with sphingomyelin, dioleoylphosphatidylcholine, dipalmitoylphosphatidylcholine, and phosphatidylinositol. A marked sphingomyelin and membrane fluidity dependence of the membrane-bound 5'-nucleotidase and phospholipase A2 was observed.

Insulin effect on some biochemical and biophysical characteristics of lung surfactant

The incorporation of [14C]palmitic acid into rat alveolar wash total phospholipids and phospholipid fractions has been followed for 6, 8, 10 and 12 hr after insulin administration, indicating a considerable enhancement. The fatty acid profiles of phosphatidylcholines, phosphatidylethanolamines and phosphatidylglycerols were found changed after the hormone administration. Eight hours post insulin treatment the precursor incorporation was highest in all phospholipid fractions studied, as well as the contribution of long chain fatty acids. Dynamic monolayer studies of the lung wash lipid extracts indicated a maximally expanded lipid film corresponding to the highly unsaturated phospholipids present.

Maternal diabetes mellitus and changes in neonatal rat lung and alveolar surfactant phospholipids

We investigated the extent of the influence of maternal diabetes on the phospholipid composition and exchange activity of the neonatal lung alveolar surfactant. The results show that each phospholipid fraction (as well as the total phospholipid content) of the surfactant of neonates with diabetic mothers are decreased to about 30% of the control values. Phosphatidylcholine and phosphatidylglycerol, which are the most important surface active phospholipid fractions, were decreased to 27% and 34% respectively. In lung tissue of the neonates with diabetic mothers, all phospholipid fractions were increased. We found that the phosphatidylcholine-exchange activity in the alveolar surfactant does not exist in neonates with diabetic mothers. This inhibited phospholipid-exchange activity may be the reason for the decrease in the surfactant phospholipids and their increase in the lungs of neonates with diabetic mothers. The cholesterol content in the surfactant of such neonates decreased by almost half in comparison with the controls, while in lung tissue it remained unchanged. Producing an experimental respiratory distress syndrome could permit to study more deeply the causes which provoke it and the accompanying metabolic changes.

Phospholipid composition of subcellular fractions and phospholipid-exchange activity in chicken liver and MC-29 hepatoma

The phospholipid composition of mitochondria, microsomes and plasma membranes from liver and MC-29 hepatoma from White Leghorn chickens has been investigated. It was established that all mitochondria and microsome phospholipid fractions obtained from MC-29 hepatoma are increased strongly compared to those from liver. The sphingomyelin augmentation was particularly great. In hepatoma plasma membranes only the sphingomyelin quantity was increased. Sphingomyelin- and phosphatidylcholine-exchange activities were observed in avian liver for the first time. These two activities were increased in MC-29 hepatoma cells. Three phospholipid-exchange proteins have been established in chicken liver 105000 X g supernatant. One of them specifically transports phosphatidylcholine, the second one is non-specific for phosphatidylcholine and sphingomyelin, and the third one is specific only for sphingomyelin. In hepatoma cells only a non-specific phosphatidylcholine- and sphingomyelin-exchange protein was found.

Insulin effect on lung subcellular fraction phospholipids and cholesterol

Lung subcellular fraction (microsomes, mitochondria, 105 000 X g supernatant and plasma membranes) were isolated from normal and insulin treated rats. Phospholipid and cholesterol contents were determined, phosphatidylcholines and phosphatidyl-ethanolamines separated and their fatty acid profiles assayed. Teh investigations carried out indicated that insulin influenced the phospholipid content of all fractions. Cholesterol levels in the 105 000 X g supernatant and especially in the plasma membrane fraction were raised significantly. Insulin administration increased the contribution of the unsaturated long chain fatty acids in both phospholipids studied. The results are discussed in relation to stimulated lipid biosynthesis and to lipid fluidity, of which fatty acyl unsaturation and cholesterol level are main parameters.

[Effect of hyperoxia on triacylglycerol lipase activity of the rat lung (author's transl)]

An investigation of acid and neutral triacylglycerol lipases in rat lung tissue has been carried out. The effect of high oxygen concentration in the inspired gas mixture on the activities of the two triacylglycerol lipases has been studied. Hyperoxia had a strong inhibitory effect on both enzymes, the degree of inhibition being dependent on the duration of exposure. Dibutyryl-3',5' AMP and NaF restored completely the activities of the inhibited triacylglycerol lipases, while adrenaline and caffeine had no effect. The possible mechanisms of the effects of oxygen on lung triacylglycerol lipases are discussed.

[Effect of prolonged hyperoxia on rabbit lung lipids and their fatty acid content (author's transl)]

The effect of a 36-hour hyperoxia (60 % oxygen) on rabbit lung lipids has been investigated. It has been established that hyperoxia leads to the increase of all lipid fractions in lung tissue and alveolar surfactant, phospholipid and cholesterol being most significantly affected. It has also been found that hyperoxia leads to the decrease of palmitic acid and to the increase of linoleic and arachidonic acids almost in all lipid fractions. Marked changes in the positional distribution of fatty acids in alveolar surfactant phosphatidylcholine have also been observed. The possible mechanisms of the effect of oxygen on lung lipid metabolism have been discussed, and the consequences ensuing from it which could affect the structural organization of membranes have been evaluated.

Positional distribution of fatty acids in rabbit lung phospholipids and triacylglycerols and effect of prolonged hyperoxy

Investigations have been carried out for the determination of the effect of high oxygen concentration in inspired gas mixutre on the positional distribution of fatty acids in rabbit lung phospholipids and triacylglycerols. The following results were obtained: 1. In the phosphatidylcholine fraction, the high oxygen concentration caused a quantitative increase of palmitic acid (16 : 0) at the alpha-position, and of myristic (14 : 0), heptadecenic (17 : 1) and arachidonic (20 : 4) acids at the beta-position. 2. In t-e phosphatidylethanolamine fraction, the high oxygen concentration caused an increase of oleic acid (18 : 1) at the alpha-position, and of palmitoleic (16 : 1) and heptadecenic (17 : 1) acids at the beta-position. 3. In the triacylglycerol fraction such changes were not observed. In connection with these effects of oxygen, its possible influence on membrane structures in the lung has been discussed.

In vitro effect of insulin and adrenaline on lung triglyceride-lipase activity in rats

The in vitro effect of insulin and adrenaline on the activity of lung triglyceride-lipases (alkaline and acid) has been investigated. Insulin inhibited strongly both triglyceride-lipases. Only caffein almost eliminated the inhibitory action of insulin, while adrenaline and dibutyryl cyclic adenosine monophosphate did not exhibit such an effect. It was assumed that the inhibition of lung triglyceride-lipases by insulin was effected through the activation of phosphodiesterases. On the other hand since adrenaline markedly activated lung triglyceride-lipases, this action was assumed to be carried out via the activation of lung adenylate cyclase and the increase of cyclic adenosine monophosphate.