Phospholipase D is activated by phorbol ester but not CSF-1 in murine bone marrow-derived macrophages

Phospholipase D activity was measured in murine bone marrow-derived macrophages (BMM) treated with either colony stimulating factor-1 (CSF-1) or phorbol myristyl acetate (PMA) by measuring formation of phosphatidylbutanol (PtBut) in cells preloaded with n-butanol. Addition of 10(-7) M PMA for 15 min stimulated the amount of PtBut formed in growth arrested cells by 3-4 fold whereas no stimulation was observed with 5000 units mL-1 CSF-1 for 0.5, 2 or 15 min. Protein kinase C activity was determined in growth-arrested BMM by phosphorylation of Myristoylated Alanine-Rich C Kinase Substrate (MARCKS). PMA stimulation for 5 min increased protein kinase C activity 5-6 fold whereas CSF-1 treatment for 5 min or 15 min did not. Contrary to earlier reports, CSF-1 did not stimulate diradyl glycerol formation in BMM. These results show that stimulation of protein kinase C and the activation of phospholipase D are not involved in the early events of CSF-1-stimulated signal transduction pathways in BMM.

Identification of molecular species of glycerophospholipids and sphingomyelin using electrospray mass spectrometry

This paper describes the use of positive and negative ion electrospray mass spectrometry (MS) and MS/MS (tandem mass spectrometry) to identify glycerophospholipid and ceramide headgroups and their alkyl, alkenyl and acyl constituents. Molecular ion adducts were the primary products formed by positive ionization, occurring as [M+H]+, [M+Na]+, [M+K]+, [M+formate]+, or [M+acetate]+, depending upon the class of glycerophospholipid and the presence or absence of these ionization-promoting species. Similar (negatively charged) ions corresponding to the loss of the groups listed above were formed in negative ion MS. Positive ion electrospray MS/MS provides information on the nature of the headgroup, with the formation of an ion corresponding to the headgroup itself, or the loss of the headgroup from the molecular ion H+ or Na+ adduct. Acyl constituents are identified during negative ion MS/MS from the formation of their RCOO- ions. The nature of alkyl or alkenyl substituents in glycerophosphoethanolamine (PE) molecular species can be identified from residual ions following the loss of ethanolamine plus loss of the acyl moiety in the sn-2 position, and cyclization of a phosphate oxygen with C-2 of glycerol. In glycerophosphoinositol (PI) species, it appears that an RCO- ion is formed during negative ion MS/MS, possibly to steric interference from the bulky phosphoinositol headgroup that prevents cyclization (and subsequent stabilization) of the ion described for PE species. Positive and negative ion electrospray MS spectra for molecular species of commercial preparations of PE, PI, phosphatidylserine (PS), glycerophosphocholine (PC) and sphingomyelin (SM) produced similar profiles. For phospholipids occurring as Na+ adducts, concentrations above ca. 1 ng/microliter produced significant quantities of both [M+H]+ and [M+Na]+ ions for those molecular species present in the largest quantities, complicating interpretation of the spectra. Complete profiles of molecular species were obtained from as little as 10 picograms of material. Major components of PE were identified from 0.1 picogram total lipid. Using single ion monitoring of the Na+ adduct of beta-acetyl-gamma-O-hexadecyl L-alpha-phosphatidylcholine, 10 femtograms of material was detected. A mixture of 1 nanogram each of PE, PI, PS, and PC was readily resolved into individual molecular species, with little apparent loss of resolution or preferential ionization. Electrospray MS did not provide information on the position (sn-1 or sn-2) of fatty acids, and was not capable of differentiating in all instances between alkyl-acyl and alkenyl-acyl substituents without prior separation of these lipid subclasses.(ABSTRACT TRUNCATED AT 400 WORDS)

Phospholipase-D activation can be negatively regulated through the action of protein kinase C

Transient activation of COS-1 cell phospholipase-D (PLD) in response to the protein kinase C (PKC) agonist tetradecanoyl phorbol acetate (TPA) was demonstrated by monitoring the ethanol-dependent accumulation of phosphatidylethanol (PtdEth). Transfection of COS-1 cells with PKC-alpha (wild type and constitutively activated mutants) produced no detectable ptdEth on incubation of transfected cells in the presence of ethanol. However, the response of transfected cells to subsequent TPA stimulation was inhibited, consistent with a role for the PKC-alpha in the suppression of PLD activity.

The phospholipid composition of extracellular herpes simplex virions differs from that of host cell nuclei

Enveloped viruses of eukaryotes obtain their membrane by budding through a cellular membrane. Therefore, most frequently the lipid composition of the virion envelope reflects that of the membrane where budding took place. In the case of herpes simplex viruses, nucleocapsids assemble in the nucleus and bud through the inner nuclear membrane. The pathway from the perinuclear space to the extracellular medium is as yet poorly understood. Here we demonstrate that the phospholipid composition of extracellular herpes simplex virions differs from that of nuclei isolated from the infected cells. The viral membrane contains threefold higher concentrations of sphingomyelin and phosphatidylserine. These lipids are typically enriched in the Golgi apparatus and plasma membrane. The data are in agreement with a model in which herpes simplex virus, after budding through the inner nuclear membrane, loses its envelope by fusing with the outer nuclear membrane and obtains a new membrane by budding into a compartment late in the exocytotic pathway, very likely the Golgi apparatus or membranes derived from it. Alternatively, because the perinuclear space is continuous with the ER lumen, the virus after its first budding may be transported through the exocytotic pathway without ever leaving the lumen of the subsequent compartments. In that case, either the virions, while budding through the nuclear membrane select for sphingomyelin and phosphatidylserine, or the original lipids of the viral envelope are exchanged for lipids of an exocytotic membrane, most likely by a transient membrane continuity between the virion and the vesicle by which it is surrounded. Light particles, virus-like particles that lack capsid and DNA but contain tegument and envelope proteins, displayed the same lipid composition as complete herpes simplex virions, suggesting that they also acquired their envelope from a Golgi membrane.

Phospholipase D activity of human amnion cells stimulated with phorbol ester and bradykinin

We investigated the activity of phospholipase D (PLD) in human amnion cells labeled with [3H]oleate. The PLD activity was detected as signal-induced synthesis of phosphatidic acid (PA) and in the presence of ethanol, phosphatidylethanol (PEt). The PLD was shown to be activated by phorbol, 12-myristate, 13-acetate (PMA), calcium ionophore A23187, oxytocin, bombesin and bradykinin, but not by platelet-activating factor (PAF) and epidermal growth factor (EGF). The amniotic PLD thus appeared to be activated by a variety of agonists but with a certain specificity to stimulators. We examined the mode of the PLD activation using PMA (20 nM) and bradykinin (1 microM) as model stimulators. PMA and bradykinin elicited a rapid and sustained response with the peaks of PA-labeling attained at 5 and < 1 min after stimulation, respectively. In both cases, there was a concomitant rise of diacylglycerol (DG), and the PA accumulation was suppressed by ethanol at the expense of labeling of PEt. The PA synthesis caused by the two stimulators was similarly inhibited by staurosporine and by a chronic treatment with PMA (100 nM for 24 h), suggesting that the activation of PLD is linked to the action of protein kinase C. With the cells labeled with radioactive choline and ethanolamine, we found that the amniotic PLD hydrolyzed almost equally phosphatidylcholine and phosphatidylethanolamine. Although bradykinin and PMA stimulated cellular PLD to a comparable extent, prostaglandin (PG)E2 release was not stimulated by bradykinin in contrast to the marked effect by PMA. Further work is thus needed to clarify the significance of the novel PLD signaling pathway in the function of amnion cells.

Unilateral nephrectomy selectively stimulates phospholipase D in the remaining kidney

The activation of phospholipase D in the kidney could be detected in vivo in rats treated with ethanol by the accumulation of phosphatidylethanol. Unilateral nephrectomy stimulated the activity of phospholipase D in the remaining kidney as indicated by an increase in the level of phosphatidylethanol. A significant increase in phosphatidylethanol level was observed as early as 5 min after contralateral nephrectomy and peak accumulation (200% of control) was observed after 15 min. The phosphatidylethanol level decreased again to the basal level after 2 h. The accumulation of phosphatidylethanol was specific for kidney and the product was localized primarily in the cortex. Phospholipase D activity in kidney cortical slices from untreated rats was stimulated in vitro by plasma obtained from unilaterally nephrectomized rats, indicating that circulating factors in the plasma are responsible for the activation of phospholipase D. The phospholipase D activation by plasma from uninephrectomized animals was selectively inhibited by the tyrosine kinase inhibitor genistein, but not by the protein kinase C inhibitor H7. It is concluded that phospholipase D activity is stimulated as an early signal transduction event in compensatory kidney growth.

The effect of aldosterone on phospholipid and phosphoinositide metabolism in rat submandibular gland

It is well known that aldosterone stimulates Na+ transport in epithelia, including rat submandibular salivary gland. Aldosterone affects cells by causing nuclear-directed synthesis of aldosterone-induced protein. That protein then exerts its effect by: (1) phospholipid remodelling of the cell membrane (increasing permeability to Na+); (2) stimulating the Na+ pump; or (3) increasing ATP production by mitochondria. The purpose of this study was to determine if aldosterone stimulates membrane phospholipid or phosphoinositide turnover in the rat salivary gland and duct. Paired salivary glands were removed from 12 rats and main salivary-gland excretory ducts were removed from 16 rats. One-half of each group was treated with aldosterone (10(-6) M) while being incubated in Ringer's containing [32P]-orthophosphate for 2 h at 37 degrees C. The other half (controls) received no aldosterone during incubation. Phospholipids were extracted, separated and detected by thin-layer chromatography, autoradiography, and quantified by liquid scintillation counting. Results were expressed in dis/min (microM PO4)-1(h)-1. The turnover of membrane phospholipid fractions or percentage fractions was not changed significantly by aldosterone (p > 0.10). Paired submandibular salivary glands were also removed from 12 more rats and main submandibular excretory ducts from 18 rats. Tissue was incubated in 2 ml of Ringer's solution containing [3H]-myo-inositol for 2 h at 37 degrees C. Tissue was then placed in Ringer's containing LiCl and the experimental groups were challenged with aldosterone for 20 min at 37 degrees C. The tissues were then homogenized, and the inositol phosphate fractions quantified by column chromatography and liquid scintillation counting.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of differentiation on the phospholipid and phospholipid fatty acid composition of N1E-115 neuroblastoma cells

The effects of differentiation on the phospholipid and phospholipid fatty acid composition of N1E-115 neuroblastoma cells were determined. The cellular lipids were extracted on days 0, 3 and 7, following the addition of 1.2% dimethylsulfoxide to induce cellular differentiation. Proportions of ethanolamine glycerophospholipids (EtnGpl), phosphatidylinositol (PtdIns) and sphingomyelin (CerPCho) were significantly elevated following differentiation. The mole percentage of choline glycerophospholipids (ChoGpl) decreased with differentiation. The plasmalogens, both choline and ethanolamine, increased by 1.3- and 2.3-fold, respectively, during differentiation. The fatty acid composition of the phospholipid classes was also altered. PtdIns and ChoGpl had decreased proportions of polyenoic fatty acids, while these proportions were increased in EtnGpl. Both ChoGpl and EtnGpl had increased n-3/n-6 series fatty acid ratios, but this ratio was decreased in PtdIns. The mole percentage of arachidonic acid was significantly decreased in both PtdIns and ChoGpl, but elevated in EtnGpl and may be a result of the increase in ethanolamine plasmalogen. Thus, differentiation did not increase the overall mole percentage of polyenoic FA in the cells nor increase the n-6 series fatty acid proportions. We speculate plasmalogens may have a role in the differentiation process or in maintaining the cell in the differentiated state.

Elongation predominates over desaturation in the metabolism of 18:3n-3 and 20:5n-3 in turbot (Scophthalmus maximus) brain astroglial cells in primary culture

The origin of docosahexaenoic acid (DHA, 22:6n-3) that accumulates in turbot brain during development was investigated by studying the incorporation and metabolism via the desaturase/elongase pathways of [1-14C]-labelled polyunsaturated fatty acids (PUFA) in primary cultures of brain astrocytic glial cells. There was little specificity evident in the total incorporation of PUFAs into the turbot astrocytes. However, specificity was apparent in the distribution of the various PUFAs among the individual lipid classes. In particular, there was very specific incorporation of [14C]arachidonic acid (AA, 20:4n-6) into phosphatidylinositol balanced by a lower incorporation of this acid into total diradyl glycerophosphocholines. [14C]-Linolenic acid (LNA, 18:3n-3) and [14C]eicosapentaenoic acid (EPA, 20:5n-3) were metabolized via the desaturase/elongase pathways to a significantly greater extent than [14C]linoleic acid (18:2n-6) and [14C]AA. The turbot astrocytes expressed very little delta 5 desaturase activity and only low levels of delta 4 desaturation activity. Although the percentages were small, approximately 4-5 times as much labelled DHA was produced from [14C]EPA compared with [14C]LNA. However, it was concluded that very little DHA in the turbot brain could result from the metabolism of LNA and EPA in astrocytic glial cells.

Phosphatidic acid stimulates the rolipram-sensitive cyclic nucleotide phosphodiesterase from rat thymocytes

The role of phospholipid metabolites in the modulation of cyclic AMP degradation during the early response of rat thymic lymphocytes to mitogenic stimulation was investigated by measuring their in vitro effect on the activity of five different cyclic nucleotide phosphodiesterase forms separated from thymocyte cytosol by means of an HPLC technique. Arachidonic acid was found to markedly inhibit four of the enzyme forms, with IC50 ranging from 14 to 60 microM, while its hydroperoxy and hydroxy derivatives proved inefficient. Dioctanoylglycerol, a biologically active diacylglycerol, was weakly inhibitory while phosphatidic acid, the diacylglycerol phosphorylated derivative, markedly stimulated the two cyclic-AMP-specific type-IV forms identified in thymocyte cytosol, by 50 and 70%. In intact cells labelled with tritiated arachidonate, the mitogenic lectin concanavalin A induced a rapid 4-5-fold increase in radiolabelled phosphatidic acid which peaked at 1 min, and remained elevated for at least 30 min. These observations suggest that phosphatidic acid formed during the mitogenic stimulation of T-cells might be responsible for an early activation of cyclic AMP degradation with, as a consequence, a lowering of cyclic AMP level, which is reported to be necessary for the occurrence of the first steps of mitogenesis.

Molecular species analysis of phospholipids from Trypanosoma brucei bloodstream and procyclic forms

We present a quantitative description of the molecular species composition of the major phospholipid classes in bloodstream and procyclic forms of Trypanosoma brucei. Phospholipid classes were resolved by 2-dimensional thin-layer chromatography. Diradylglycerols were released from individual phospholipid classes by phospholipases C, converted into benzoate derivatives and separated into diacyl, alkylacyl and alk-1-enylacyl subclasses. Individual molecular species were quantitated and identified by HPLC and the assignments were confirmed by mass spectrometry. Comparison of the diacyl species of PC, PE and PI in bloodstream trypanosomes showed major differences in the relative amounts of individual molecular species between the different classes but not striking changes in the degree of saturation or overall chain length. In contrast, in procyclic trypanosomes the relative amounts of diacyl molecular species with polyunsaturated fatty acyl chains decreased in the order of PC > PE >> PI. Also, the alkylacyl and alk-1-enylacyl subclasses of PC and PE in bloodstream trypanosomes comprised a single molecular species, 18:0 18:2. Such exclusivity was not observed in procyclic trypanosomes among the same phospholipid subclasses, although 18:0 18:2 was the predominant species. Almost all the PI of bloodstream forms contained one 18:0 acyl species, which is consistent with the composition of the PI used for glycosylphosphatidylinositol synthesis.

Bradykinin stimulates phospholipase D in primary cultures of guinea-pig tracheal smooth muscle

Conditions were established for the primary culture of guinea-pig tracheal smooth muscle cells, the identity of which was confirmed by the presence of smooth muscle alpha-actin by western blotting. Cells were preincubated with [3H]palmitate which was incorporated, almost exclusively, into phosphatidylcholine. When these cells were stimulated by either bradykinin or phorbol 12-myristate 13-acetate (PMA), in the presence of butan-1-ol, the non-metabolizable product [3H]phosphatidylbutanol ([3H]PtdBut) accumulated by virtue of the phosphatidyltransferase activity of phospholipase D. The activation of phospholipase D by bradykinin was inhibited by 86 +/- 11% (N = 3 experiments) in the presence of the protein kinase C inhibitor, staurosporine (1 microM) and by 88 +/- 11% (N = 3 experiments) in cells that had been chronically treated with PMA to down-regulate their protein kinase C. PMA-stimulated phospholipase D was similarly affected (92 +/- 2% inhibited by staurosporine, 87 +/- 6% inhibited by protein kinase C down-regulation). Removal of extracellular Ca2+ markedly reduced the bradykinin-stimulated phospholipase D response (by 73 +/- 10%, N = 3 experiments) but had only a limited effect upon PMA-stimulated phospholipase D activity (by 23 +/- 6%, N = 3 experiments). [AIF4](-)-stimulation of the cells also resulted in the activation of phospholipase D, indicating the involvement of a G-protein. However, this was not Gi since pertussis-toxin pretreatment of the cells failed to abolish either bradykinin-stimulated inositol (1,4,5)trisphosphate formation or [3H]PtdBut accumulation. Western blotting revealed the presence of Gq/G11 which couples to the inositol lipid-directed phospholipase C. Indomethacin (10 microM) was without effect upon bradykinin-stimulated phospholipase D activity, suggesting that the bradykinin effects were not mediated indirectly by cyclooxygenase products. The role of phospholipase D activation in tracheal smooth muscle may be to, indirectly, produce diacylglycerol for the activation of protein kinase C which has been implicated in sustained contraction. However, the immediate product of phospholipase D, phosphatidate, has been proposed to have a number of second messenger roles and may itself, by an undefined mechanism, be involved in the sustained contraction of airway smooth muscle.

Surface components of chylomicrons from rats fed glyceryl or alkyl esters of fatty acids: minor components

The lipid class, fatty acid and molecular species composition of the minor polar surface components of rat lymph chylomicrons were determined during absorption of menhaden oil and corn oil or of the corresponding fatty acid ethyl esters. In addition to the previously reported minor polar lipids (sphingomyelin, phosphatidylserine, phosphatidylinositol, phosphatidic acid and lysophosphatidylcholine), we identified phosphatidylglycerol, dimethylphosphatidylethanolamine, ceramide and cholesteryl sulfate in the chylomicrons from both oil and ester feeding. The dietary fatty acids were found to be incorporated to a variable extent into the different phospholipid classes, the proportions of which remained the same during both types of feeding. No evidence was obtained for the presence of the minor glycerophospholipids characteristic of the lysosomal membranes (e.g., bis-phosphatidic, lysobisphosphatidic and semilysobis-phosphatidic acids), although special efforts were made to identify them. These results indicate that the chylomicrons arising from the monoacylglycerol and phosphatidic acid pathways of triacylglycerol biosynthesis become enveloped in closely similar monolayers of phospholipids. Hence, all triacylglycerols may be secreted from the villus cells via a common mechanism as suggested by the previously demonstrated convergence (at the 2-monoacylglycerol stage) of the monoacylglycerol and the phosphatidic acid pathways of mucosal triacylglycerol formation [Yang, Y.L., and Kuksis, A. (1991) J. Lipid Res. 32, 1173-1186].

Effects of orally administered cytidine 5'-diphosphate choline on brain phospholipid content

Cytidine, as cytidine 5'-diphosphate choline (CDP-choline), is important for the synthesis of phosphatidylcholine in cell membranes. To investigate whether exogenous CDP-choline could affect brain phospholipid composition, we supplemented the diet of mice with this drug (500 mg/kg/day) for 27 months in 3-month-old mice and for 90, 42, and 3 days in 12-month-old mice, and measured their levels of phosphatidylcholine (PC), phosphatidylethanolamine (PE), phosphatidylserine (PS), and the content of phosphatidylinositol plus phosphatidic acid in the cerebral cortex. After 27 months of treatment, PC and PE increased significantly by 19% (P < 0.05) and by 20% (P < 0.01), respectively. PS levels increased by 18% (not statistically significant). Similar elevations in PC and PE levels were obtained when older mice were treated for only 3 months (P < 0.05). No changes were observed with shorter treatment periods. These results suggest that chronic administration of CDP-choline can have effects on brain phospholipid composition that may underlie its reported utility in various neurologic disorders.

Lipid peroxidation, phosphoinositide turnover and protein kinase C activation in human platelets treated with anthracyclines and their complexes with Fe(III)

The effects of the antitumor drugs daunorubicin, doxorubicin and their complexes with Fe(III) on phosphoinositide hydrolysis, lipid peroxidation and protein kinase C (PKC) activation were measured in intact human platelets. Doxorubicin and the Fe(III) complexes of both doxorubicin and daunorubicin quickly induced lipid peroxidation [as measured by the thiobarbituric acid (TBA) assay], phosphorylation of the 40 K substance of PKC, and increased levels of phosphatidic acid and inositol phosphates. Fe(III) alone or complexed to acetohydroxamic acid induced high levels of TBA-reactive material but did not affect either PKC activation or phosphoinositide turnover. In contrast, daunorubicin, which was ineffective per se, inhibited all these doxorubicin- and anthracyclines/Fe(III)-induced biochemical events. We suggest that phosphoinositide hydrolysis determined by anthracyclines, and consequently PKC activation, could be due to lipid peroxidation, thus triggering the activity of phospholipase C.

Lipids of the earthworm Lumbricus terrestris

The lipid composition of the earthworm Lumbricus terrestris has been reexamined under conditions intended to avoid enzymatic and chemical alterations during storage, extraction, and fractionation procedures. The simple lipids included aliphatic hydrocarbons, steryl esters, glycerides, and at least nine different sterols, all thought to be derived from the diet. Free fatty acids, previously considered to be major components of worm lipids, comprised only 0.3% of the total lipid weight. Phospholipids included (in order of relative abundance) phosphatidylcholine, phosphatidylethanolamine, phosphatidylserine, and phosphatidylinositol, as well as sphingomyelin. Glycolipids included cerebrosides and sulfatides containing both glucose and galactose, and gangliosides containing glucosamine and sialic acid. The fatty acid compositions of these lipid classes appeared to be a mixture of what are considered typical plant, bacterial, and animal acids. Several fatty acids found in the worms, including cis-vaccenic and eicosapentaenoic acids, were essentially absent from the dietary components, and it is concluded that these acids were synthesized in the worms. The earthworm derives much of its lipid adventitiously, but exerts at least some control over its tissue lipid composition.

The effects of dietary n-3/n-6 ratio on brain development in the mouse: a dose response study with long-chain n-3 fatty acids

This study examines the effects of the ratio of n-3/n-6 fatty acids (FA) on brain development in mice when long-chain n-3 FA are supplied in the diet. From conception until 12 days after birth, B6D2F1 mice were fed liquid diets, each providing 10% of energy from olive oil, and a further 10% from different combinations of free FA concentrates derived from safflower oil (18:2n-6), and fish oil (20:5n-3 and 22:6n-3). The range of dietary n-3/n-6 ratios was 0, 0.25, 0.5, 1.0, 2.0 and 4.0, with an n-6 content of greater than 1.5% of energy in all diets, and similar levels of total polyunsaturated fatty acids (PUFA). In an additional group of ratio 0.5, 18:2n-6 was partially replaced by its delta 6 desaturation product, 18:3n-6. Biochemical analyses were conducted on 12-day-old pup brains, as well as on samples of maternal milk. No obvious effects on overall pup growth and development were observed, apart from a smaller litter size at ratio 1. Co-variance analysis indicated that increasing the n-3/n-6 ratio was associated with slightly smaller brains, relative to body weight. We found that 18:2n-6 and 20:5n-3 were the predominant n-6 and n-3 FA in the milk; in the brain these were 20:4n-6 and 22:6n-3, respectively. Increasing dietary n-3/n-6 ratios generally resulted in an increase in n-3 FA, with a corresponding decrease in n-6 FA.(ABSTRACT TRUNCATED AT 250 WORDS)

Lipid bilayer in genetic hypertension

Membrane microviscosity, phospholipid composition, and turnover were measured in cultured vascular smooth muscle cells isolated from mesenteric arteries of stroke-prone spontaneously hypertensive and age-matched, normotensive Wistar-Kyoto rats. Membrane microviscosity, measured with fluorescence polarization, revealed greater microviscosity (lower fluidity) of the membranes isolated from smooth muscle cells from hypertensive as compared with those isolated from normotensive rats (p less than 0.01). Preincubation of membranes from hypertensive rats with 5 mM calcium reduced membrane microviscosity in "core" and in "surface" regions of the bilayer toward values observed in Wistar-Kyoto rats. Phospholipid composition did not differ between intact aortas and cultured mesenteric cells or between those tissues obtained from normotensive and from hypertensive rats. The total lipid-associated radioactivity was significantly lower in cells from stroke-prone spontaneously hypertensive rats than in those from Wistar-Kyoto controls (p less than 0.01). Phosphatidylcholine incorporated 70% and phosphatidylinositol 16% of total lipid-associated radioactivity, with no difference between cells from hypertensive and normotensive animals. Turnover of phosphatidylethanolamine was greater in cells from Wistar-Kyoto rats (p = 0.02), whereas turnover of phosphatidylserine was greater in cells from stroke-prone spontaneously hypertensive rats (p = 0.04). The greater microviscosity of the lipid bilayer in hypertension is a generalized defect of the matrix in which the transport proteins function. We hypothesize that this defect is responsible for the multiple abnormalities of membrane transport systems that have been described in genetic hypertension.

An original method for rapid serial determination of phospholipid biosynthesis. Applications to mammalian lymphocytic cells and a lower eucaryote, Plasmodium falciparum

A rapid, convenient, and efficient method is presented to measure phosphatidylcholine, phosphatidylethanolamine, and phosphatidylinositol biosynthesis from [3H]choline, [3H]ethanolamine, and [3H]inositol, respectively. After incubation of the cells in 96-multi-well dishes with the appropriate radioactive precursor, cells were lysed with water and the water-insoluble materials, particularly cellular membranes which contain the bulk of phospholipids, were serially collected on glass-fiber papers using a cell harvester. The method was first applied to human lymphocytic cell lines then adapted to Plasmodium falciparum-infected human erythrocytes which in both cases allowed recovery of more than 90% of the newly biosynthesized phospholipids. With this quick method, adapted to short incubation periods (less than 5 h), we were able to determine optimal conditions such as the best medium (RPMI devoid of serum, thus avoiding interference from endogenous precursors, notably choline present in significant quantities in serum) and the lowest specific activity to be used for each radioactive precursor and the minimum quantity of cells. This method could be adapted to other cell systems, provided that the precursors are specific to phospholipids and that the bulk of biosynthesized phospholipids are present as membrane components. Finally, by this method the activity of effectors of phospholipid metabolism can be tested on a large scale, thus allowing rapid screening of original molecules specifically affecting cellular phospholipid metabolism.

Biochemical changes in knee joint articular cartilage after cemented prosthetic hip hemiarthroplasty in dogs

Biochemical changes in the distal femoral articular cartilage (knee joint) after cemented prosthetic replacement of the femoral head were determined. Femurs from dogs (n = 10) that had undergone cobalt-chromium prosthetic hip hemiarthroplasty (6-8 months postoperatively) were analyzed for articular cartilage lipids in the distal femur. The quantity of phosphatidylserine increased from 0.59 +/- 0.14 mg (uninvolved) to 1.52 +/- 0.23 mg (hemiarthroplasty) lipid phosphorus/100 g tissue, and the quantity of arachidonic acid in the articular cartilage increased from 0.23 +/- 0.07 mg (uninvolved) to 2.07 +/- 0.29 mg/100 g tissue (hemiarthroplasty). Likewise, hydroxyproline content was higher in the recipient femurs (77.4 +/- 1.58 micrograms/mg cartilage) versus uninvolved femurs (71.8 +/- 1.03 micrograms/mg cartilage); the activity of acid phosphatase was greater in the recipient distal femoral cartilage as compared with the uninvolved femur, 0.07 +/- 0.01 and 0.06 +/- 0.02 mol hydrolyzed per kilogram per hour, respectively, and the hexosamine content was lower in the recipient femur knee cartilage versus knee cartilage from uninvolved femurs, 54.5 +/- 1.51 and 63.1 +/- 1.37 micrograms/mg cartilage, respectively. These biochemical changes may suggest degeneration of the knee joint articular cartilage after cemented hip hemiarthroplasty.

Apparent convergence (at 2-monoacylglycerol level) of phosphatidic acid and 2-monoacylglycerol pathways of synthesis of chylomicron triacylglycerols

Dietary fats are converted into chylomicron triacylglycerols via the 2-monoacylglycerol and phosphatidic acid pathways of acylglycerol formation. In view of the known positional and fatty acid specificity of the acyltransferases, the triacylglycerol structures resulting from the two pathways would be expected to differ, but this has not been demonstrated. We have performed stereospecific analyses on the chylomicron triacylglycerols from rats fed menhaden oil and the corresponding fatty acid alkyl esters, which would be expected to be assimilated via the monoacylglycerol and the phosphatidic acid pathways, respectively. The results show a remarkable similarity between the two triacylglycerol types in the fatty acid composition of the sn-1 and sn-3 positions, along with marked differences in the composition of the sn-2 positions. The triacylglycerols from rats fed oil retained about 85% of the original fatty acids in the sn-2 position, including a high proportion of the long chain polyunsaturates (e.g., 5-7% 20:5 and 4-5% 22:6). The triacylglycerols from rats fed the alkyl ester contained large amounts of endogenous fatty acids in the sn-2 position (e.g., 18% 16:1, 14% 18:1, 14% 18:2, and 2.5% 20:4), which approximated the composition of the sn-2 position of the presumed phosphatidic acid intermediates. The sn-1 position contained a much higher proportion of polyunsatured fatty acids (e.g., 12-13% 20:5, 5-6% 22:6) than the sn-2 position (e.g. 2-3% 20:5, 0-0.6% 22:6) of triacylglycerols from rats fed the ester. We conclude that the chylomicron triacylglycerols arising via the 2-monoacylglycerol and the phosphatidic acid pathways differ mainly in the composition of the fatty acids in the sn-2 position. The similarity in the acids of the sn-1 and sn-3 positions of the chylomicron triacylglycerols from rats fed oil or ester is consistent with a hydrolysis of the acylglycerol products of the phosphatidic acid pathway to 2-monoacylglycerols prior to reconversion to triacylglycerols via the monoacylglycerol pathway and secretion as chylomicrons.

Regulation of the phosphoinositide cycle by Na+/H+ exchange and intracellular pH in human platelets

We have found that thrombin-induced activation of protein kinase C (PKC) in platelets, measured by phosphorylation of the 47 kDa protein, is synergistically enhanced by the amiloride analogue ethylisopropylamiloride (EIA), a specific inhibitor of Na+/H+ exchange. This EIA effect was further synergistically enhanced by lowering intracellular pH (pHi) with either nigericin or sodium propionate, and reversed by raising pHi with monensin or ammonium chloride. The synergistic enhancement of thrombin-activated PKC by EIA plus nigericin was not observed when PKC was directly activated by phorbol esters. EIA and EIA plus nigericin caused a 3- to 6-fold increase in thrombin-induced diacylglycerol (DAG), but not phosphatidic acid (PA), production. EIA and nigericin also caused a marked increase in thrombin-induced breakdown and inhibition of resynthesis of phosphatidylinositol 4,5-bisphosphate (PIP2). In summary, we have presented evidence that inhibition of Na+/H+ exchange causes primarily a H(+)-mediated interruption of the phosphoinositide cycle in activated platelets, including the accumulation of DAG associated with the enhancement of PKC activation, the inhibition of conversion of DAG to PA, and increased PIP2 breakdown. These data suggest a model in which Na+/H+ and pHi play an important regulatory role in permitting the phosphoinositide cycle to proceed in thrombin-activated platelets.

[Lung maturation during artificial placentation and mechanical lung distension]

An new method of lung maturation during artificial placentation was evaluated during a series of 15 animal experiments in premature lambs (gestational age 125-132 days). Perfusion circuit with interposition of a membrane lung was connected with the umbilical vessels. Extracorporeal CO2-removal (ECCO2-R) and apneic oxygenation were provided during lung distension. The ultramicroscopic pattern approved a maturation of the lung during the procedure showing development of lamellar bodies and surfactant secretion into the alveolar space. The biochemical analysis of the tracheal fluid showed a significant increase of both PC and PG concentrations (3.225 +/- 1.112 mg/100g to 24.228 +/- 3.36 mg/100 g respectively 0.249 +/- 0.11 mg/100 g of 0.622 +/- 0.09 mg/100 g. The biophysical function of the lung was also improved as was shown by a significant increase of the statistical compliance. We conclude that artificial placentation and lung distension might be a new mode of prophylaxis for respiratory distress syndrome in critically immature babies.

Assays for investigations of signal transduction mechanisms involving phospholipase D: mass measurements of phosphatidate, phosphatidylethanol, and diacylglycerol in cultured cells

With the intent of achieving a better understanding of agonist-induced phospholipase D activity, we have developed simple, rapid assays for quantitating the mass of phosphatidate, phosphatidylethanol, and diacylglycerol. Crude lipid extracts of cultured cells are used; preliminary sample cleanup or derivatization procedures are not necessary. The assays resolve the particular lipids by short-bed/continuous-development thin-layer chromatography. Quantitative assessments are derived from photodensitometric analysis of charred lipid spots. The assays may be employed for as little as 45 pmol of diacylglycerol and 50 pmol of phosphatidate or phosphatidylethanol. The newly developed assays are compared to other procedures for quantitating lipid mediators. The utility of the assays is illustrated in experiments that use a variety of cultured cells to demonstrate the agonist activation of the phospholipase D pathway. In addition, experiments designed to screen various agonists for signal-response coupling to phospholipase D are described.

Application of liquid chromatography-thermospray mass spectrometry in the analysis of glycerophospholipid molecular species

We report the application of high-performance liquid chromatographic (HPLC) separation with ultraviolet detection and direct, on-line, structural analyses by mass spectrometry of glycerobenzoate derivatives from complex mixtures of phospholipid molecular species. Individual phospholipids were resolved from total lipid extracts by thin-layer chromatography (TLC). Diradylglycerols were released from phospholipids by phospholipase-C treatment, converted to diradyl glycerobenzoates and subsequently separated by TLC into subclasses (alk-1-enylacyl, alkylacyl and diacyl types). The molecular species within each subclass were resolved by HPLC with an octadecyl reversed-phase column in acetonitrile-isopropanol (80:20, v/v). Individual peaks were quantitated at the picomole level by measuring absorbance at 230 nm. After post-column addition of methanol-0.2 M ammonium acetate (50:50, v/v), peaks were introduced through the thermospray interface into a VG Masslab 30-250 quadrupole mass spectrometer. Molecular species showed as base peaks the salt adducts of the molecular ion which permitted easy deduction of the overall fatty acyl composition. In addition, the diglyceride fragment of each species was found at [MH - 122]+ and two fragments formed by the loss of the fatty acyl groups (R) in the sn-1 or sn-2 position were found at [M - R1]+ and [M - R2]+, respectively. Since preferential release of either fatty acyl group was observed in positional isomers, the ratio of the intensity of these fragments gave information on the position of the fatty acyl groups in the individual HPLC peaks. We show that the use of on-line mass spectrometry, however, provides easy identification of all molecular species present in a complex phospholipid mixture, even when more than one molecular species is contained in an HPLC peak.