Increased synthesis of phospholipid during phagocytosis

Mitochondrial Dysfunction in Advanced Liver Disease: Emerging Concepts

Mitochondria are entrusted with the challenging task of providing energy through the generation of ATP, the universal cellular currency, thereby being highly flexible to different acute and chronic nutrient demands of the cell. The fact that mitochondrial diseases (genetic disorders caused by mutations in the nuclear or mitochondrial genome) manifest through a remarkable clinical variation of symptoms in affected individuals underlines the far-reaching implications of mitochondrial dysfunction. The study of mitochondrial function in genetic or non-genetic diseases therefore requires a multi-angled approach. Taking into account that the liver is among the organs richest in mitochondria, it stands to reason that in the process of unravelling the pathogenesis of liver-related diseases, researchers give special focus to characterizing mitochondrial function. However, mitochondrial dysfunction is not a uniformly defined term. It can refer to a decline in energy production, increase in reactive oxygen species and so forth. Therefore, any study on mitochondrial dysfunction first needs to define the dysfunction to be investigated. Here, we review the alterations of mitochondrial function in liver cirrhosis with emphasis on acutely decompensated liver cirrhosis and acute-on-chronic liver failure (ACLF), the latter being a form of acute decompensation characterized by a generalized state of systemic hyperinflammation/immunosuppression and high mortality rate. The studies that we discuss were either carried out in liver tissue itself of these patients, or in circulating leukocytes, whose mitochondrial alterations might reflect tissue and organ mitochondrial dysfunction. In addition, we present different methodological approaches that can be of utility to address the diverse aspects of hepatocyte and leukocyte mitochondrial function in liver disease. They include assays to measure metabolic fluxes using the comparatively novel Biolog’s MitoPlates in a 96-well format as well as assessment of mitochondrial respiration by high-resolution respirometry using Oroboros’ O2k-technology and Agilent Seahorse XF technology.

Untargeted lipidomics uncovers lipid signatures that distinguish severe from moderate forms of acutely decompensated cirrhosis

BACKGROUND & AIMS

Acute decompensation (AD) of cirrhosis is a heterogeneous clinical entity associated with moderate mortality. In some patients, this condition develops quickly into the more deadly acute-on-chronic liver failure (ACLF), in which other organs such as the kidneys or brain fail. The aim of this study was to characterize the blood lipidome in a large series of patients with cirrhosis and identify specific signatures associated with AD and ACLF development.

METHODS

Serum untargeted lipidomics was performed in 561 patients with AD (518 without and 43 with ACLF) (discovery cohort) and in 265 patients with AD (128 without and 137 with ACLF) in whom serum samples were available to perform repeated measurements during the 28-day follow-up (validation cohort). Analyses were also performed in 78 patients with AD included in a therapeutic albumin trial (43 patients with compensated cirrhosis and 29 healthy individuals).

RESULTS

The circulating lipid landscape associated with cirrhosis was characterized by a generalized suppression, which was more manifest during AD and in non-surviving patients. By computing discriminating accuracy and the variable importance projection score for each of the 223 annotated lipids, we identified a sphingomyelin fingerprint specific for AD of cirrhosis and a distinct cholesteryl ester and lysophosphatidylcholine fingerprint for ACLF. Liver dysfunction and infections were the principal net contributors to these fingerprints, which were dynamic and interchangeable between patients with AD whose condition worsened to ACLF and those who improved. Notably, blood lysophosphatidylcholine levels increased in these patients after albumin therapy.

CONCLUSIONS

Our findings provide insights into the lipid landscape associated with decompensation of cirrhosis and ACLF progression and identify unique non-invasive diagnostic biomarkers of advanced cirrhosis.

LAY SUMMARY

Analysis of lipids in blood from patients with advanced cirrhosis reveals a general suppression of their levels in the circulation of these patients. A specific group of lipids known as sphingomyelins are useful to distinguish between patients with compensated and decompensated cirrhosis. Another group of lipids designated cholesteryl esters further distinguishes patients with decompensated cirrhosis who are at risk of developing organ failures.

Molecular Mechanisms of Lipid Metabolism Disorders in Infectious Exacerbations of Chronic Obstructive Pulmonary Disease

Exacerbations largely determine the character of the progression and prognosis of chronic obstructive pulmonary disease (COPD). Exacerbations are connected with changes in the microbiological landscape in the bronchi due to a violation of their immune homeostasis. Many metabolic and immune processes involved in COPD progression are associated with bacterial colonization of the bronchi. The objective of this review is the analysis of the molecular mechanisms of lipid metabolism and immune response disorders in the lungs in COPD exacerbations. The complex role of lipid metabolism disorders in the pathogenesis of some infections is only beginning to be understood, however, there are already fewer and fewer doubts even now about its significance both in the pathogenesis of infectious exacerbations of COPD and in general in the progression of the disease. It is shown that the lipid rafts of the plasma membranes of cells are involved in many processes related to the detection of pathogens, signal transduction, the penetration of pathogens into the cell. Smoking disrupts the normally proceeded processes of lipid metabolism in the lungs, which is a part of the COPD pathogenesis.

Genes Involved in Energy Metabolism Are Differentially Expressed During the Day-Night Cycle in Murine Retinal Pigment Epithelium

Purpose

The functional interaction between photoreceptors and retinal pigment epithelium (RPE) cells is essential for vision. Phagocytosis of photoreceptor outer segments (POSs) by the RPE follows a circadian pattern; however, it remains unknown whether other RPE processes follow a daily rhythm. Therefore, our aim was to identify RPE processes following a daily rhythm.

Methods

Murine RPE was isolated at Zeitgeber time (ZT) 0, 2, 4, 9, 14, and 19 (n = 5 per time point), after which RNA was isolated and sequenced. Genes with a significant difference in expression between time points (P < 0.05) were subjected to EnrichR pathway analysis to identify daily rhythmic processes.

Results

Pathway enrichment revealed 13 significantly enriched KEGG pathways (P < 0.01), including the metabolic pathway (P = 0.002821). Analysis of the metabolic pathway differentially expressed genes revealed that genes involved in adenosine triphosphate production, glycolysis, glycogenolysis, and glycerophospholipid were low at ZT0 (light onset) and high at ZT19 (night). Genes involved in fatty acid degradation and cholesterol synthesis were high at light onset and low at night.

Conclusions

Our transcriptome data suggest that the highest energy demand of RPE cells is at night, whereas POS phagocytosis and degradation take place in the morning. Furthermore, we identified genes involved in fatty acid and glycerophospholipid synthesis that are upregulated at night, possibly playing a role in generating building blocks for membrane synthesis.

Quantitative analysis of phospholipids and demonstration of plasmalogen in human neutrophil subcellular fractions by high-performance liquid chromatography

The subcellular distribution of phospholipids in unstimulated neutrophils was investigated by high-performance liquid chromatography of lipid extracts of granule and plasma membranes obtained from Percoll density gradients. The mobile phase contained acetonitrile:methanol:85% phosphoric acid (131:3:0.8 v/v/v). Post-nuclear supernatants contained 2.3 micrograms lipid phosphorus/mg protein. Phosphatidylinositol, phosphatidylserine, phosphatidylethanolamine and phosphatidylcholine were demonstrated in azurophil granules, specific granules and in a combined fraction of secretory granules and plasma membranes. Separate estimates of each phospholipid class by peak areas obtained by high-performance liquid chromatography showed that secretory granules and plasma membranes contained most of the phosphatidylinositol and phosphatidylcholine (p less than 0.005 vs peaks areas obtained in azurophil and specific granules), whereas a major part of the phosphatidylethanolamine was located in the specific granules (p less than 0.005 vs peak areas obtained in azurophil granules, and plasma membrane and secretory granules). High-performance liquid chromatography proved to be a useful principle for the demonstration of plasmalogen because the acidic solvent caused hydrolysis of phosphatidalethanolamine, which was recovered as lysophosphatidylethanolamine. Additionally, sphingomyelin was demonstrated in all subfractions by thin-layer chromatography.

Metabolic basis of asthma. A united hypothesis

Asthma is a heterogenous disease triggered by a large number of different stimuli. This article presents a theory of the metabolic mechanisms of asthma. The theory is based on the growing understanding of the activity of lysophosphatidylcholine (LPC). Since the effect of LPC on cell membranes, membrane bound enzymes and the various types of cells involved in the pathogenesis of asthma, this may represent a unifying link between the various types of asthma.

Platelet-activating factor modulates phospholipid acylation in human neutrophils

The present study showed that platelet-activating factor (1-O-hexadecyl-2-acetyl-sn-glycero-3-phosphocholine, PAF), but not lysoPAF (1-O-hexadecyl-sn-glycero-3-phosphocholine) rapidly (within 15 sec) stimulated the incorporation of both [1-14C]arachidonate and [1-14C]docosahexaenoate into phosphatidylinositol (PI) and phosphatidylcholine (PC) in human neutrophils. Concomitantly, it inhibited the formation of labeled phosphatidic acid from both fatty acids. The magnitude of stimulation (percentage of control) was greater in PI than in PC for the incorporation of arachidonate and vice versa for the incorporation of docosahexaenoate. It reached a maximum at 10(-7) M and started to decline at 10(-6) M. Extracellular Ca2+ was not essential for the action of PAF on phospholipid acylation. The distribution of labeled arachidonate in the molecular species of PC was not altered by PAF after 1 min incubation, suggesting that the increased formation of arachidonyl-PC during the early stage of neutrophil-PAF interaction was not originated from the added PAF. No measurable changes in the mass of each phospholipid were detected in neutrophils challenged by PAF from 15 sec to 2 min. The data suggest that the increased incorporation of extracellular fatty acids into PI and PC elicited by PAF may be secondary to increased deacylation of these phospholipids, and the magnitude of stimulation reflects the specificity of acyltransferase catalyzing the acylation of lysoPI and lysoPC by fatty acyl-CoA.

Synthesis of the dipalmitoyl species of diacyl glycerophosphocholine by rabbit alveolar macrophages

The distribution of radioactivity among the molecular species of diacyl glycerophosphocholine of rabbit alveolar macrophages was determined after incubation with [3H]glycerol and 1-[14C]palmitoyl-sn-glycero-3-phosphocholine. The highest percentage of radioactivity of [3H]glycerol was found in the dipalmitoyl species (35% of the total) followed by the 1-palmitoyl-2-linoleoyl (23.6%) and 1-stearoyl-2-linoleoyl plus 1-palmitoyl-2-oleoyl species (19.7%) during the first 30 min incubation. The radioactivity of the dipalmitoyl species reached a maximum at 120 min incubation and decreased thereafter, although the radioactivities of other molecular species still increased. In contrast to the [3H]glycerol labeling, only 4% of the total radioactivity in diacyl glycerophosphocholine derived from 1-[14C]palmitoyl glycerophosphocholine was found in the dipalmitoyl species; 80% of the radioactivity was located in the 1-palmitoyl-2-arachidonoyl species at 10 min incubation. The present results indicate that the dipalmitoyl species of diacyl glycerophosphocholine are synthesized predominantly via a de novo pathway and not the deacylation-reacylation pathway in rabbit alveolar macrophages.

Incorporation of [3H]palmitate and [14C]choline into disaturated phosphatidylcholines in rat alveolar macrophages

We studied the synthesis of disaturated phosphatidylcholines in rat alveolar macrophages and, in some cases, compared it with that which occurs in isolated alveolar type II cells. Alveolar macrophages suspended in phosphate-buffered medium incorporate palmitate, choline and glycerol into disaturated phosphatidylcholines. The time-course for incorporation of palmitate into disaturated phosphatidylcholines is linear for 20-30 min and reaches a maximum in 2-3 h. Incorporation is dependent on extracellular palmitate with a Vmax (at 1 mM) of 1.53 nmol palmitate incorporated into disaturated phosphatidylcholines per 5 X 10(5) cells per 2 h and a K 1/2 of 0.19 mM palmitate. Exposure of the cells to zymosan particles increases incorporation of palmitate disaturated phosphatidylcholines by almost 2-fold, while cholinergic and beta-adrenergic agonists have no effect. On a per cell basis, alveolar macrophages incorporate only one-third to one-half as much palmitate into disaturated phosphatidylcholines as do type II cells isolated by centrifugal elutriation. The following results suggest there is extensive remodeling of disaturated phosphatidylcholines in alveolar macrophages: (1) palmitate- and choline-labeled disaturated phosphatidylcholines are catabolized by the cells; (2) the products of catabolism are palmitate and water-soluble choline products; (3) addition of unlabeled palmitate and choline to the medium enhances catabolism of the labeled phospholipid. Addition of oleate also enhances catabolism, suggesting that modification of phospholipids is not specific for the saturated variety. Some of the recently labeled disaturated phosphatidylcholines is released from alveolar macrophages into the extracellular space. Several possible functions of alveolar macrophage disaturated phosphatidylcholines are discussed.

Composition and metabolism of phospholipids of human leukocytes

Human mononuclear (MN) and polymorphonuclear (PMN) leukocytes were analyzed for their phospholipid, triglyceride, cholesterol and fatty acid content. The phospholipid/cholesterol ratio was 1.24 for both cells. MN cells contain more phosphatidylcholine (PC), but less phosphatidylserine (PS), Phosphatidylethanolamine (PE) and sphingomyelin (SPH) than PMN cells when expressed as percent of total phospholipid. When expressed on the basis of lipid content per cell, MN cells contain less PS, PE and SPH but more triglyceride than PMN cells. PMN cells incorporate palmitic, stearic, linoleic and linolenic acids into their phospholipids, triglycerides or cholesterol esters. The incorporation into triglycerides was highest for all fatty acids. Of the phospholipids, the incorporation was highest into PC. Labeled fatty acids also were found in proteins which had been delipidized by exhaustive extraction with organic solvents. These represent tightly or covalently bound fatty acids. The incorporation [3H] palmitic acid into this protein fraction is stimulated by insulin.

Phospholipase A2 and arachidonic acid: a common link in the generation of the eosinophil chemotactic factor (ECF) from human PMN by various stimuli

An eosinophil chemotactic factor (ECF) of low molecular weight can be generated and released from human polymorphonuclear neutrophils by the calcium ionophore, phagocytosis of zymosan particles, arachidonic acid, and phospholipase A2. Since the activation of cells by the ionophore and during the phagocytic event leads to phospholipid turnover, with the subsequent generation of arachidonic acid, it is reasonable that phospholipase A2 represents the common link for ECF production. The kinetics of ECF release by phospholipase A2 is similar to the pattern observed with the various stimuli. After a rapid rise in activity a decline occurred at later times of secretion, suggesting a mechanism of inactivation. During subcellular fractionation of cells an ECF-generating component was enriched in the 200,00 g supernatant fraction, which represents the cytosol. Addition of arachidonic acid or phospholipase A2 induced ECF generation. On gel filtration analysis the ECF-generating component revealed a molecular weight of about 80,000 daltons. It is suggested that this component represents a lipoxygenase.

Hydrolysis of membrane phospholipids by phospholipases of rat liver lysosomes

(1) The hydrolysis of (32)P- or myo-[2-(3)H]inositol-labelled rat liver microsomal phospholipids by rat liver lysosomal enzymes has been studied. (2) The relative rates of hydrolysis of phospholipids at pH4.5 are: sphingomyelin>phosphatidylethanolamine>phosphatidylcholine> phosphatidylinositol. (3) The predominant products of phosphatidylcholine and phosphatidylethanolamine hydrolysis are their corresponding lyso-compounds, indicating a slow rate of total deacylation. (4) Ca(2+) inhibits the hydrolysis of all phospholipids, though only appreciably at high (>5mm) concentration. The hydrolysis of sphingomyelin is considerably less sensitive to Ca(2+) than that of glycerophospholipids. (5) Analysis of the water-soluble products of phosphatidylinositol hydrolysis (by using myo-[(3)H]inositol-labelled microsomal fraction as a substrate) produced evidence that more than 95% of the product is phosphoinositol, which was derived by direct cleavage from phosphatidylinositol, rather than by hydrolysis of glycerophosphoinositol. (6) This production of phosphoinositol, allied with negligible lysophosphatidylinositol formation and a detectable accumulation of diacylglycerol, indicates that lysosomes hydrolyse membrane phosphatidylinositol almost exclusively in a phospholipase C-like manner. (7) Comparisons are drawn between the hydrolysis by lysosomal enzymes of membrane substrates and that of pure phospholipid substrates, and also the possible role of phosphatidylinositol-specific lysosomal phospholipase C in cellular phosphatidylinositol catabolism is discussed.

The use of a phospholipase A-less Escherichia coli mutant to establish the action of granulocyte phospholipase A on bacterial phospholipids during killing by a highly purified granulocyte fraction

Phospholipase A2 present in a highly purified, potently bactericidal, fraction from rabbit graulocytes produces net bacterial phospholipid degradation during killing of a phospholipase A-less strain of Escherichia coli. In the wild-type parent strain phospholipid breakdown is caused not only by the action of phospholipase A2 but also by phospholipase A1, indicating activation of the most prominent phospholipase of E. coli. This activation occurs as soon as the bacteria are exposed to the granulocyte fraction. Phospholipid breakdown by both phospholipases A is dose dependent but reaches a plateau after 30-60 min and at higher concentrations of the fraction. Phospholipid degradation is accompanied in both strains by an increase in permeability to actinomycin D that is also dose dependent. Even though net hydrolysis of phospholipids is greater in the parent strain than in the mutant, the increase in permeability is the same in the two strains. The addition of 0.04 M Mg2+, after the effects on phospholipids and permeability have become manifest, initiates in both strains the restoration of insensitivity to actinomycin D, the net resynthesis of phospholipids, and the disappearance of monoacylphosphatides and the partial disappearance of free fatty acids that had accumulated. Loss of ability to multiply is not reversed by Mg2+ in either strain. Less than 5 micrograms of granulocyte fraction causes loss of viability of from 90 to 99% of 1 X 10(8) microorganisms of both strains. However, at lower concentrations the parent strain is considerably more sensitive to the bactericidal effect of the granulocyte fraction than the mutant strain.

Biochemical and ultrastructural aspects of the inhibited phagocytosis by neutrophil granulocytes in acute brain-damaged patients

In a study of 60 head-injured patients inhibition of phagocytosis by neutrophil granulocytes was observed over a period of up to 5 weeks. This inhibition of phagocytosis could be correlated with the severity of head injury as well as with the state of unconsciousness at the time of the investigation. No correlation was found between neutrophil granulocyte counts and the inhibition of phagocytosis. A good correlation could be demonstrated between the level of lumbar CSF 5-HIAA and the inhibition of phagocytosis. After in vitro incubation with albumin the cells showed a recovery of phagocytosis. Electron micrographs of the cells showed ultrastructural appearances suggesting a changed permeability of the plasma membrane and, in addition, alterations in the cytoplasmic region beneath the plasma membrane. It is suggested that head injury may influence the pituitary-adrenal system and the autonomic nervous system, giving changes of neutrophil function and of neurotransmitter metabolism; these changes may represent an adaptation mechanism.

Phospholipid metabolism and lysosomal enzyme secretion by leukocytes. Effects of dibutyryl cyclic adenosine 3':5'-monophosphate and ATP

The effects of dibutyryl cyclic adenosine 3':5'-monophosphate and ATP on isotope incorporation into phospholipids and the release of beta-glucuronidase into the extracellular medium were studied in polymorphonuclear leukocytes from guinea pig peritoneal exudates. Exogenous dibutyryl cyclic adenosine 3':5'-monophosphate (0.1--1.0 mM) reduced beta-glucoronidase release induced by cytochalasin B in the absence of inert particles. It selectively inhibited 32Pi incorporation into phosphatidic acid and the phosphoinositides and the incorporation of myo-[2-3H]inositol into the phosphoinositides. Added ATP (0.1--1.0 MM), but not other nucleotides, was found to potentiate beta-glucuronidase release provoked by cytochasin B, but it impaired the labeling of the phosphoinositides by myo-[2-3H]inositol. The mechanism of the inhibition the isotope incarparation into these acidic phospholipids by the two mucleotides has not been defined. Dibutyryl cyclic adenosine 3':5'-monophosphate at 2--4 mM concentration was not found to appreciably alter the incorporation of [gamma-32P]ATP into phosphatidic acid, phosphatidylinositol, diphosphoinositide, and triphosphoinositide.

Enzymes of phospholipid synthesis in Bacillus Calmette-Guerin induced rabbit alveolar macrophage. Characterization and localization of cytidine diphosphocholine phosphotransferase and monoacylphospholipid acyltransferase

The rabbit alveolar macrophage is capable of renewing its plasma membrane by at least two metabolic pathways. It contains (1) a monoacylphospholipid acyltransferase, which catalyzes the synthesis of diacylphospholipids by recycling monoacylphospholipids produced by the action of phospholipases and (2) a cytidine diphosphocholine phosphotransferase (CDPcholine phosphotransferase), which catalyzes the last step in the synthesis de novo of diacylglycerophosphocholine. These activities have been characterized in the cell homogenate with respect to time, protein, pH optimum (for CDPcholine phosphotransferase), substrate specificity (for monoacylphospholipid acyltransferase) and cation requirement ( for CDPcholine phosphotransferase). Monoacylphospholipid acyltransferase activity is localized solely in the endoplasmic reticulum. On the other hand, the CDPcholine phosphotransferase activity can be measured in the endoplasmic reticulum and in the plasma membrane, characterized by both differential and gradient sedimentation techniques. In addition to the normal route of phospholipid synthesis in the endoplasmic reticulum, the rabbit alveolar macrophage may thus possess the capacity for in situ synthesis of phospholipids of plasma membrane as a mechanism for membrane renewal following phagocytosis.

Palmitic acid-1-14C incorporation and turnover in lung phospholipids of rats treated with chlorphentermine, RMI 10.393 and Ro 4-4318

The effects of 3 lipidosis-inducing drugs on the incorporation and turnover of palmitic acid-1-14C in lung phospholipids was studied. In rats treated with 1 dose of chlorphentermine or RMI 10.393, the incorporation of palmitate-1-14C into most lung phospholipid fractions was moderately decreased, but markedly lowered after 1 dose of Ro 4-4318. Eight doses of chlorphentermine and RMI 10.393 strongly inhibited the incorporation of palmitate-1-14C into lung phospholipids, whereas with 8 doses of Ro 4-4318 the incorporation was highly increased. Thirty hours after the last of 3 injections of the labeled palmitic acid the turnover of most lung phospholipids was considerably lower in chlorphentermine- and RMI 10.393-treated rats than in controls. Ro 4-4318, however, induced a highly increased turnover of most phospholipids. After 54 h, this effect had practically disappeared. Our studies showed that phospholipid storage after treatment with chlorphentermine and RMI 10.393 is mainly due to decreased degradation of phospholipids, whereas increased synthesis accounts for the effect of Ro 4-4318.

Reversible envelope effects during and after killing of Escherichia coli w by a highly-purified rabbit polymorpho-nuclear leukocyte fraction

The effects of a highly-purified, potently bactericidal fraction from rabbit polymorphonuclear leukocytes on the envelope of Escherichia coli (W) have been examined. This leukocyte fraction has equally enriched bactericidal, permeability-increasing and phospholipase A2 activities, and is essentially devoid of lysozyme, myeloperoxidase and protease activities (Weiss, J., Franson, R.C., Beckerdite, S., Schmeidler, K. and Elsbach, P. (1975) J. Clin. Invest. 55, 33-42). Rapid killing of E. coli by this fraction is accompanied by two almost immediate alterations in the bacterial envelope: (1) a discrete increase in envelope permeability (measured by inhibition of bacterial leucine incorporation by normally impermeant actinomycin D), and, (2) hydrolysis of 14C-labeled fatty acid-prelabeled E. coli phospholipids. Both envelope effects are promptly reversed during further incubation at 37 degrees C, But not at 0 degrees C, with 40 mM Mg2+. Reversal is also produced by Ca2+ (40 mM) and trypsin (200 mug/ml), but 200 mM K+ causes only partial recovery and Na+ and hyperosmolar sucrose are ineffective. Upon addition of Mg2+, phospholipid degradation ceases abruptly and the labeled products of hydrolysis (free fatty acids and lysocompounds) disappear with a corresponding reaccumulation of radioactive diacylphosphatides. The time course of resynthesis of phospholipids coincides with that of restoration of the permeability barrier. Higher concentrations of the leukocyte fraction and prolonged incubation increase both the extent of phospholipid degradation and the time required for reversal of both envelope effects. These findings suggest that both the initiation of the increased permeability and its reversal are linked to respectively the breakdown and resynthesis of major E. coli membrane phospholipids, and thus depend on the fact that the biochemical apparatus of E. coli remains capable of biosynthesis despite loss of viability. Treatment of E. coli, exposed to the leukocyte fraction, with albumin results in extracellular sequestration of the products of hydrolysis and also restores the permeability barrier to actinomycin D, suggesting that the accumulation of lytic products of lipid hydrolysis within the bacterial envelope, rather than the loss of phospholipids per se, causes increased permeability Whereas the effects on the envelope are reversible as long as 2 h after nearly complete loss of ability to multiply by E. coli, the effect on bacterial multiplication is irreversible within 5 min.

Regulation of guanylate and adenylate cyclase activities by lysolecithin

The guanylate cyclase activity [GTP pyrophosphate-lyase (cyclizing), EC 4.6.1.2] in membrane preparations from 3T3 mouse fibroblasts is stimulated approximately 5-fold by lysolecithin at concentrations of 100 mug/ml and above.

Effects of human and rabbit serum on viability, permeability, and envelope lipids of Serratia marcescens

The major action of serum on gram-negative organisms is thought to be on the microbial envelope. We compared the effects of normal human and rabbit serum on the envelope lipids of two strains of Serratia marcescens, one sensitive and one resistant to the bactericidal effects of serum. During killing by either serum, the sensitive strain underwent rapid permeability changes coincident with degradation of microbial phospholipids. The resistant strain exhibited none of these effects. The phospholipid degradation that accompanies killing of the sensitive strain by serum could be caused by phospholipases present in serum or by Serratia's own phospholipid-splitting enzymes. The results indicate that phospholipid breakdown is caused by activation of bacterial of bacterial phospholipases and not by serum phospholipases. This conclusion is based upon the following findings.(i1 Although rabbit serum phospholipase A was at least 10 times more active than human serum phospholipase A, phospholipid degradation in the sensitive Serratia strain was comparable during (equally rapid) killing by human or rabbit serum. (ii) Heat treatment (56 C) of both sera eliminated bactericidal activity as well as microbial lipid degradation but abolished phospholipase activity of human serum only. (iii) Virtually complete removal of phospholipase A activity from human serum by adsorption onto autoclaved Micrococcus lysodeikticus had no effect on the extent of phospholipid hydrolysis or on bactericidal activity. Activation by serum of endogenous phospholipase activity in S. marcescens was accompanied by enhanced incorporation of lipid precursors into bacterial lipids. No evidence was found for increased turnover of protein or ribonucleic acid during killing by serum.

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.

Effects of phagocytosis by rabbit granulocytes on macromolecular synthesis and degradation in different species of bacteria

Phagocytosis and killing of gram-positive Bacillus megaterium and Micrococcus lysodeikticus by granulocytes in vitro is associated with almost immediate cessation of bacterial protein synthesis. By contrast, protein synthesis by Escherichia coli continues after ingestion and killing. After preincubation of E. coli with intact granulocytes for 15 min, when 95% or more of the bacteria can no longer multiply, induction of beta-galactosidase proceeds at rates about half of control values. With disrupted granulocytes, which kill E. coli as rapidly as intact cells, the rate of induction of beta-galactosidase does not fall until after 30 min of preincubation. We attribute the different effects of phagocytosis on the biochemical apparatus of these microorganisms to the different fates of their envelopes. Specifically labeled protein, ribonucleic acid, deoxyribonucleic acid, and lipid of all three species of bacteria and peptidoglycan of E. coli are apparently incompletely degraded during phagocytosis. However, the cell walls of M. lysodeikticus and B. megaterium undergo rapid and almost complete degradation. The resulting structural disintegration of these gram-positive microorganisms must cause extensive biochemical disorganization as well. Our evidence indicates that the E. coli envelope, on the other hand, retains sufficient structural organization to preserve integrated biochemical function for at least 1 h after the bacteria have lost the ability to multiply.

Lipids of alveolar macrophages, polymorphonuclear leukocytes, and their phagocytic vesicles

Phagocytic vesicles were isolated from rabbit alveolar macrophages and guinea pig polymorphonuclear leukocytes that had ingested emulsified paraffin oil. Phospholipids and their fatty acids were determined in whole cells and in the phagocytic vesicle and pellet fractions separated from them. The cholesterol-to-phospholipid ratios in the vesicle fractions were distinctly higher than those of the respective whole cells or pellet fractions. The vesicle fractions also had higher phospholipid-to-protein ratios than did the whole cells. The phospholipids of the phagocytic vesicle fraction from macrophages contained relatively more sphingomyelin, lyso-(bis)phosphatidic acid, and phosphatidylserine and less lecithin, phosphatidylethanolamine, and phosphatidylinositol than did the whole cells or pellet fractions. The phospholipids of phagocytic vesicles from polymorphonuclear leukocytes contained significantly more phosphatidylinositol than did the pellet fractions. Lyso(bis)phosphatidic acid, which constituted 15% of the phospholipid in rabbit alveolar macrophages and 25% of that in their phagocytic vesicles, contained almost 60% oleic acid and 20% linoleic acid. This lipid was not detected in rabbit peritoneal macrophages or in rat alveolar macrophages.The polyunsaturated fatty acids of leukocyte phospholipids were chiefly linoleic, whereas in macrophages arachidonic accounted for almost 20% of the total fatty acids. The macrophages produced malondialdehyde when ingesting polystyrene beads or emulsified paraffin oil, from which it was inferred that peroxidation of endogenous lipid can occur during phagocytosis. Polymorphonuclear leukocytes in which less than 3% of phospholipid fatty acids were arachidonic did not produce malondialdehyde during phagocytosis of these inert particles, but did when ingesting an emulsion containing linolenate, thus providing evidence for peroxidation of ingested lipid. Isolated phagocytic vesicles from alveolar macrophages contained lipid peroxides and generated malondialdehyde when incubated with ADP, FeCl(3), and NADH.

The appearance of lecithin- 32 P, synthesized from lysolecithin- 32 P, in phagosomes of polymorphonuclear leukocytes

Rabbit polymorphonuclear leukocytes ingesting paraffin oil particles stabilized with albumin, converted more lysolecithin-(32)P (added to the medium as an albumin complex) to cellular lecithin than did control cells. Almost all of the increment in leukocyte lecithin-(32)P is found in association with the isolated phagocytic vacuoles. About half of lecithin-(32)P of granulocytes incubated first with lysolecithin-(32)P and then reincubated with paraffin particles in a nonradioactive medium is transferred from a sedimentable (presumably membrane) fraction to the phagosomes. Isolated phagosomes or granules by themselves are capable of acylating lysolecithin. The main source of lysolecithin-(32)P for synthesis of cellular lecithin-(32)P, however, appears to be extracellular rather than lysolecithin-(32)P within the cytoplasm or the phagocytic vacuole. We interpret our findings therefore as indicating that lecithin-(32)P in the phagosomes derives chiefly from the outer membrane.

Synthesis of dipalmitoyl lecithin by alveolar macrophages

A reliable, relatively simple method for isolation and quantification of disaturated lecithins is described. In rabbit lung, 34% of the lecithins were disaturated, in alveolar macrophages, 19%. More than 95% of the fatty acids of the disaturated lecithins from lung and alveolar macrophages was palmitic. Hence, the disaturated lecithins from these sources were essentially all dipalmitoyl lecithin. Both heterophils and alveolar macrophages incorporated (14)C-labeled choline and palmitate into disaturated lecithins. Liver slices in which only about 1% of the lecithins were disaturated incorporated very little of these precursors into this fraction. Of the palmitate incorporated in vitro into disaturated lecithins by alveolar macrophages, heterophils, and lung slices, 37% was in the 1 position. In disaturated lecithins isolated from pulmonary lavage fluid, alveolar macrophages, and lung of rabbit 8-12 hr after a single intravenous injection of palmitic-1-(14)C acid, 45% of the (14)C was in position 1. At earlier times, from 20-240 min after injection, the distribution of (14)C was similar in the samples from lung, but in those from alveolar macrophages and lavage fluid, the percentage in position 1 was slightly lower.Glycerol-U-(14)C was incorporated into disaturated lecithins by alveolar macrophages and by lung slices in vitro. Both tissues incorporated very little label from ethanolamine or from methyl-labeled methionine into this fraction. All of the data are consistent with the view that alveolar macrophages synthesize dipalmitoyl lecithin via the cytidine diphosphate-choline pathway.

Effect of phagocytosis on membrane transport of nonelectrolytes

The activities of specific transport systems were determined before and after large portions of the surface membrane had been interiorized by phagocytosis of inert particles. In five separate transport systems in rabbit polymorphonuclear leukocytes (adenosine and two adenine transport systems) and alveolar macrophages (adenosine and lysine transport systems), the rate of transport was unaffected even after an estimated 35-50% of the membrane had been internalized. Studies of the kinetics of lysine and adenosine transport, exchange diffusion of lysine transport in alveolar macrophages, and the specificities of adenine transport in polymorphonuclear leukocytes indicate that the nature of the membrane transport systems is not altered by phagocytosis. Therefore the constancy of transport indicates that the number of carriers remains the same before and after phagocytosis. It was also shown that this constancy of transport did not depend on the introduction into the surface of new transport sites during phagocytosis. Therefore transport sites are preserved on the surface during the internalization of membrane which accompanies phagocytosis. The results are best explained by the concept that the membrane is mosaic in character with geographically separate transport and phagocytic sites.

Lipids of Acanthamoeba castellanii. Composition and effects of phagocytosis on incorporation of radioactive precursors

The lipids of Acanthamoeba castellanii (Neff) consist of 52% neutral lipids and 48% polar lipids. Triglycerides account for 75% and free sterols for 17% of the neutral lipids. The major phospholipids are phosphatidylcholine (45%), phosphatidylethanolamine (33%), phosphatidylserine (10%), a phosphoinositide (6%), and diphosphatidylglycerol (4%). The phosphoinositide is unique in that it contains fatty acids, aldehyde, inositol, and phosphate in the ratio of 1.4:0.5:1.1, but it contains no glycerol. Sphingomyelin, cerebrosides, psychosine, and glycoglycerides were not detected, but small amounts of unidentified long chain bases and sugars are present. The rates of uptake of palmitate-1-(14)C and of its incorporation into glycerides and phospholipids were not affected by the phagocytosis of polystyrene latex beads. Although phagocytosis usually decreased the uptake by amebas of phosphate-(32)P, serine-U-(14)C, and inositol-2-(3)H, their subsequent incroporation into phospholipids was not demonstrably stimulated or inhibited by phagocytosis. Phagocytosis did seem to increase the incorporation into ameba phospholipids of phosphatidylcholine-1 ,2-(14)C but not that of phosphatidylethanolamine-1 ,2-(14)C. These experiments, in which the incorporation of radioactive precursors into total cell lipids was measured, do not, of course, eliminate the possibility that localized effects may occur.

Activation and release of lysosomal enzymes from isolated leukocytic granules by liposomes. A proposed model for degranulation in polymorphonuclear leukocytes

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