Neuroprotective effect of plasmalogens on AlCl3-induced Alzheimer's disease zebrafish via acting on the regulatory network of ferroptosis, apoptosis and synaptic neurotransmission release with oxidative stress as the center

Plasmalogens (Pls) are considered to play a potential role in the treatment of neurodegenerative diseases. In the present study, an Alzheimer's disease (AD) model of zebrafish induced by AlCl3 was established to investigate whether the marine-derived Pls could alleviate cognitive impairments of AD zebrafish. Behavioral tests were carried out to assess the athletic ability. The transcriptional profiles of zebrafish in the control, AD model and AD_PLS group were compared and analyzed to determine the potential mechanisms of dietary Pls on AD. The study found that Pls could reverse athletic impairment in the AD zebrafish model, and the expression levels of genes related to ferroptosis, synaptic dysfunction and apoptosis were significantly altered between experimental groups. Further analysis showed that all of these genes were associated with oxidative stress (OS). These data suggest that healthy protective role of marine-derived Pls on AD zebrafish may result from inhibition of ferroptosis and neuronal apoptosis, restoring synaptic neurotransmission release, and reducing neuroinflammation. Among them, Oxidative stress is acted as the center to connect different regulation pathways. This study provides evidence to support the essential roles of OS in pathogenesis of AD, and the application of Pls in relieving AD.

EPA-enriched ethanolamine plasmalogen and EPA-enriched phosphatidylethanolamine enhance BDNF/TrkB/CREB signaling and inhibit neuronal apoptosis in vitro and in vivo

Our previous study showed that EPA-enriched ethanolamine plasmalogen (EPA-pPE) exerted more significant effects than EPA-enriched phosphatidylethanolamine (EPA-PE) in improving learning and memory deficit. However, the results of the mechanism study were not consistent with the improved cognitive function, which suggested that other signaling pathways might be involved. In the present study, primary cultured hippocampal neurons and cognitive deficiency rats were used to compare the effects of EPA-pPE and EPA-PE on brain-derived neurotrophic factor (BDNF)/tropomyosin receptor kinase B (TrkB)/cAMP response element-binding protein (CREB) signaling and neuronal apoptosis. The in vitro experiment showed that both EPA-pPE and EPA-PE could relieve cell death and improve the cellular morphology of neurons via upregulating anti-apoptotic proteins and downregulating pro-apoptotic proteins. The in vivo experiment showed that EPA-pPE exerted more significant effects than EPA-PE in improving the number of neuronal Nissl bodies, increasing the branching of dendrites and dendritic spine density in cortical neurons, as well as improving the expression of synaptic vesicle-related proteins synaptophysin (SYN) and PSD95 via BDNF/TrkB/CREB signaling. These results indicated that EPA-pPE exerted neuroprotection at least partly through inhibiting neuronal apoptosis and enhancing the BDNF/TrkB/CREB pathway, which suggests that EPA-enriched plasmalogen can be explored as a potential therapeutic agent in long-term Alzheimer's disease therapy.

Biological Functions of Plasmalogens

Plasmalogens (Pls) are one kind of phospholipids enriched in the brain and other organs. These lipids were thought to be involved in the membrane bilayer formation and anti-oxidant function. However, extensive studies revealed that Pls exhibit various beneficial biological activities including prevention of neuroinflammation, improvement of cognitive function, and inhibition of neuronal cell death. The biological activities of Pls were associated with the changes in cellular signaling and gene expression. Membrane-bound GPCRs were identified as possible receptors of Pls, suggesting that Pls might function as ligands or hormones. Aging, stress, and inflammatory stimuli reduced the Pls contents in cells, and addition of Pls inhibited inflammatory processes, which could suggest that reduction of Pls might be one of the risk factors for the diseases associated with inflammation. Oral ingestion of Pls showed promising health benefits among Alzheimer's disease (AD) patients, suggesting that Pls might have therapeutic potential in other neurodegenerative diseases.

Choline and Ethanolamine Plasmalogens Prevent Lead-Induced Cytotoxicity and Lipid Oxidation in HepG2 Cells

Plasmalogens derived from dietary phospholipids are considered to be potential protectors against oxidation-related disorders, while lead (Pb) is an environmental contaminant worldwide and is known to induce oxidative stress. However, the protective and antilipid oxidative effects of individual plasmalogen species against Pb damage have received little attention. In this study, six plasmalogen species (with either choline or ethanolamine as the headgroup and p16:0/18:1, p16:0/18:2, or p16:0/20:5 as the side chains) were evaluated in human hepatoma cells. Plasmalogen species showed a remarkable recovery in cell viability as well as elimination of reactive oxygen species and suppressed the accumulation of phosphatidylcholine hydroperoxides (from 63.6 ± 1.8% to 80.3 ± 2.9%) and phosphatidylethanolamine hydroperoxides (from 25.7 ± 9.3% to 76.1 ± 3.7%). Moreover, plasmalogens significantly upregulated the gene expression levels of a series of antioxidant enzymes that are regulated via the Nrf-2-dependent pathway. This study suggested that choline and ethanolamine plasmalogens could prevent Pb-induced cytotoxicity and lipid oxidation in HepG2 cells.

Ether lipids and their elusive function in the nervous system: a role for plasmalogens: An Editorial Highlight for 'Reduced muscle strength in ether lipid-deficient mice is accompanied by altered development and function of the neuromuscular junction' on page 569

In this editorial, we highlight the recent work of Dorninger et al. that demonstrates a reduction in plasmalogens in the motor end plate is associated with a reduction in motor end plate function. This reduction in function is illuminated in reduced muscle function in these mice, corresponding with the reduction in acetylcholine release and in its receptor density observed in these mice.

Plasmalogen precursor mitigates striatal dopamine loss in MPTP mice

Ethanolamine plasmalogens (PlsEtn) are a class of glycerophospholipids characterized by a vinyl-ether bond at the sn-1 position that play an important role in the structure and function of membranes. Previous reports have suggested a link between reduced blood and brain PlsEtn levels and Parkinson's disease (PD). We recently reported that the DHA containing plasmalogen precursor PPI-1011 protected striatal dopamine (DA) against MPTP toxicity in mice. In this paper, we further investigate the specificity requirements of the lipid side chains by testing the oleic acid-containing plasmalogen precursor PPI-1025. Male mice were treated for 10days with daily oral administration of PPI-1025 (10, 50 or 200mg/kg). On day 5 mice received MPTP and were sacrificed on Day 11. Treatment with PPI-1025 prevented MPTP-induced decrease of DA and serotonin, as well as their metabolites. In addition, PPI-1025 treatment prevented the MPTP-induced decrease of the striatal dopamine transporter (DAT) and vesicular monoamine transporter 2 (VMAT2) specific binding. Significant positive correlations were measured between striatal DA concentrations and DAT or VMAT2 specific binding, as well as with serum plasmalogen concentrations. The neuroprotective effect of PPI-1025 displayed a bell-curve dose-dependency losing effect at the highest dose tested. The similar protective response of oleic and docosahexaenoic acid (DHA)-containing plasmalogen precursors suggests that the neuroprotection observed is not only due to DHA but to the oleic substituent and the plasmalogen backbone.

Plasmalogen phospholipids protect internodal myelin from oxidative damage

Reactive oxygen species (ROS) are implicated in a range of degenerative conditions, including aging, neurodegenerative diseases, and neurological disorders. Myelin is a lipid-rich multilamellar sheath that facilitates rapid nerve conduction in vertebrates. Given the high energetic demands and low antioxidant capacity of the cells that elaborate the sheaths, myelin is considered intrinsically vulnerable to oxidative damage, raising the question whether additional mechanisms prevent structural damage. We characterized the structural and biochemical basis of ROS-mediated myelin damage in murine tissues from both central nervous system (CNS) and peripheral nervous system (PNS). To determine whether ROS can cause structural damage to the internodal myelin, whole sciatic and optic nerves were incubated ex vivo with a hydroxyl radical-generating system consisting of copper (Cu), hydrogen peroxide (HP), and ortho-phenanthroline (OP). Quantitative assessment of unfixed tissue by X-ray diffraction revealed irreversible compaction of myelin membrane stacking in both sciatic and optic nerves. Incubation in the presence of the hydroxyl radical scavenger sodium formate prevented this damage, implicating hydroxyl radical species. Myelin membranes are particularly enriched in plasmalogens, a class of ether-linked phospholipids proposed to have antioxidant properties. Myelin in sciatic nerve from plasmalogen-deficient (Pex7 knockout) mice was significantly more vulnerable to Cu/OP/HP-mediated ROS-induced compaction than myelin from WT mice. Our results directly support the role of plasmalogens as endogenous antioxidants providing a defense that protects ROS-vulnerable myelin.

Involvement of plasmalogens in post-natal retinal vascular development

Objective

Proper development of retinal blood vessels is essential to ensure sufficient oxygen and nutrient supplies to the retina. It was shown that polyunsaturated fatty acids (PUFAs) could modulate factors involved in tissue vascularization. A congenital deficiency in ether-phospholipids, also termed “plasmalogens”, was shown to lead to abnormal ocular vascularization. Because plasmalogens are considered to be reservoirs of PUFAs, we wished to improve our understanding of the mechanisms by which plasmalogens regulate retinal vascular development and whether the release of PUFAs by calcium-independent phospholipase A2 (iPLA2) could be involved.

Methods and Results

By characterizing the cellular and molecular steps of retinal vascular development in a mouse model of plasmalogen deficiency, we demonstrated that plasmalogens modulate angiogenic processes during the early phases of retinal vascularization. They influence glial activity and primary astrocyte template formation, endothelial cell proliferation and retinal vessel outgrowth, and impact the expression of the genes involved in angiogenesis in the retina. These early defects led to a disorganized and dysfunctional retinal vascular network at adult age. By comparing these data to those obtained on a mouse model of retinal iPLA2 inhibition, we suggest that these processes may be mediated by PUFAs released from plasmalogens and further signalling through the angiopoietin/tie pathways.

Conclusions

These data suggest that plasmalogens play a crucial role in retinal vascularization processes.

Plasmalogens rescue neuronal cell death through an activation of AKT and ERK survival signaling

Neuronal cells are susceptible to many stresses, which will cause the apoptosis and neurodegenerative diseases. The precise molecular mechanism behind the neuronal protection against these apoptotic stimuli is necessary for drug discovery. In the present study, we have found that plasmalogens (Pls), which are glycerophospholipids containing vinyl ether linkage at sn-1 position, can protect the neuronal cell death upon serum deprivation. Interestingly, caspse-9, but not caspase-8 and caspase-12, was cleaved upon the serum starvation in Neuro-2A cells. Pls treatments effectively reduced the activation of caspase-9. Furthermore, cellular signaling experiments showed that Pls enhanced phosphorylation of the phosphoinositide 3-kinase (PI3K)-dependent serine/threonine-specific protein kinase AKT and extracellular-signal-regulated kinases ERK1/2. PI3K/AKT inhibitor LY294002 and MAPK/ERK kinase (MEK) inhibitor U0126 treatments study clearly indicated that Pls-mediated cell survival was dependent on the activation of these kinases. In addition, Pls also inhibited primary mouse hippocampal neuronal cell death induced by nutrient deprivation, which was associated with the inhibition of caspase-9 and caspase-3 cleavages. It was reported that Pls content decreased in the brain of the Alzheimer’s patients, which indicated that the reduction of Pls content could endanger neurons. The present findings, taken together, suggest that Pls have an anti-apoptotic action in the brain. Further studies on precise mechanisms of Pls-mediated protection against cell death may lead us to establish a novel therapeutic approach to cure neurodegenerative disorders.

Choline plasmalogens isolated from swine liver inhibit hepatoma cell proliferation associated with caveolin-1/Akt signaling

Plasmalogens play multiple roles in the structures of biological membranes, cell membrane lipid homeostasis and human diseases. We report the isolation and identification of choline plasmalogens (ChoPlas) from swine liver by high performance thin layer chromatography (HPTLC) and high performance liquid chromatography (HPLC)/MS. The growth and viability of hepatoma cells (CBRH7919, HepG2 and SMMC7721) was determined following ChoPlas treatment comparing with that of human normal immortal cell lines (HL7702). Result indicated that ChoPlas inhibited hepatoma cell proliferation with an optimal concentration and time of 25 μmol/L and 24 h. To better understand the mechanism of the ChoPlas-induced inhibition of hepatoma cell proliferation, Caveolin-1 and PI3K/Akt pathway signals, including total Akt, phospho-Akt(pAkt) and Bcl-2 expression in CBRH7919 cells, were determined by western blot. ChoPlas treatment increased Caveolin-1 expression and reduced the expression of phospho-Akt (pAkt) and Bcl-2, downstream targets of the PI3K/Akt pathway. Further cell cycle analysis showed that ChoPlas treatment induced G1 and G1/S phase transition cell cycle arrest. The expression of essential cell cycle regulatory proteins involved in the G1 and G1/S phase transitions, cyclin D, CDK4, cyclin E and CDK2, were also analyzed by western blot. ChoPlas reduced CDK4, cyclin E and CDK2 expression. Taken together, the results indicate that swine liver-derived natural ChoPlas inhibits hepatoma cell proliferation associated with Caveolin-1 and PI3K/Akt signals.

The role of plasmalogen in the oxidative stability of neutral lipids and phospholipids

The role of ethanolamine plasmalogen extracted from bovine brain (BBEP) in maintaining oxidative stability of bulk soybean oil and liposome made with egg phospholipids (PL) was studied. In a purified soybean oil (PSO), the addition of 200 and 1000 ppm of BBEP promoted lipid oxidation at rates of 0.037 and 0.071 (all rates in ln (PV) h(-1), and PV stands for peroxide value), whereas soy lecithin (SL) added in the same amount showed a trend similar to the PSO blank, which had an oxidation rate of 0.025. The PSO with BBEP was susceptible to cupric ion catalyzed oxidation, in that the oil was oxidized much more quickly than the PSO with SL and cupric ion. In commercial soybean oil (CSO) with the presence of tocopherols, SL at 1000 ppm acted synergistically as an antioxidant with the natural tocopherols, but addition of BBEP accelerated lipid oxidation, as evidenced by the oxidative stability index (OSI) test. In the egg PL liposome, the BBEP caused a fast breakdown of the lipid hydroperoxides and consequently promoted more thiobarbituric acid reactive substance (TBARS) formation. The PL oxidation in the presence of copper in the liposome was not affected by the BBEP, which indicates that the hypothesis of ethanolamine plasmalogen (EthPm) chelating cupric ion as the antioxidation mechanism was not supported. The addition of cumene hydroperoxide to the egg PL liposome promoted lipid oxidation, as indicated by a fast development of PV and TBARS. However, the result with cumene hydroperoxide failed to differentiate the effect of BBEP and SL and their concentration on lipid oxidation. On the basis of the observations from this study, we conclude that EthPm is not an antioxidant but rather a pro-oxidant in a bulk lipid system, and it has no significant antioxidant effect for PL oxidation in the liposome.

Synthesis and antioxidant properties of an unnatural plasmalogen analogue bearing a trans O-vinyl ether linkage

To assess the antioxidant behavior of trans-1, we first synthesized trans-allyl ether 4 by opening an (S)-glycidol derivative with an (E)-alk-2-en-ol, and then produced the unnatural E-enol ether 1 by a stereoselective iridium(I)-catalyzed olefin isomerization. Natural cis-1 was preferentially degraded by HOCl and was more protective than trans-1 against lipid peroxidation induced by a free-radical initiator, demonstrating that the geometry of the 1'-alkenyloxy bond participates in the antioxidant defensive role of 1.

Conjugated Dienes as Prohaptens in Contact Allergy: In Vivo and in Vitro Studies of Structure−Activity Relationships, Sensitizing Capacity, and Metabolic Activation

There is a great interest in developing in vitro/in silico methods for the prediction of contact allergenic activity. However, many proposed methods do not take the activation of prohaptens to sensitizers by skin metabolism into account. As a consequence, consumer products containing potent sensitizers could be marketed. To identify prohaptens, studies regarding their structure-activity relationships and the mechanisms of their activation must be conducted. In the present investigation, we have studied the structure-activity relationships for alkene prohaptens. A series of seven alkenes (1-7), all of the same basic structure but with variation in the number and position(s) of the double bond(s), were designed and screened for sensitizing capacity using the murine local lymph node assay. Compounds 1-7 were also incubated with liver microsomes in the presence of glutathione to trap and identify reactive metabolites. The metabolic conversion of three alkenes (9-11) to epoxides (12-15) was also studied along with comparison of their sensitizing capacity. Our results show that conjugated dienes in or in conjunction with a six-membered ring are prohaptens that can be metabolically activated to epoxides and conjugated with GSH. Related alkenes containing isolated double bonds and an acyclic conjugated diene were shown to be weak or nonsensitizers. For the first time, the naturally occurring monoterpenes alpha-phellandrene, beta-phellandrene, and alpha-terpinene were demonstrated to be prohaptens able to induce contact allergy. The difference in sensitizing capacity of conjugated dienes as compared to alkenes with isolated double bonds was found to be due to the high reactivity and sensitizing capacity of the allylic epoxides metabolically formed from conjugated dienes. We recommend that these structure-activity relationship rules are incorporated into in silico predictive databases and propose that the prediction of contact allergenic activity of suspected prohaptens is based on assessment of susceptibility to metabolic activation and chemical reactivity of potential metabolites.

A novel antioxidant action of ethanolamine plasmalogens in lowering the oxidizability of membranes

We have demonstrated a novel antioxidant action of ethanolamine plasmalogens both in protecting cholesterol from oxidation by free radicals and in lowering the oxidizability of membranes, along with the action of scavenging radicals, by the oxygen-uptake method using large unilamellar vesicles and the water-soluble azo-radical initiator, AAPH [2,2´-azobis-(2-amidino-propane) dihydrochloride].

Plasmalogens protect unsaturated lipids against UV-induced oxidation in monolayer

Oxidative stress results from the attack by free radicals of several cellular targets (proteins, DNA and lipids). The cell equilibrium is a direct consequence of the pro-/antioxidant balance. In order to understand the physiological processes involved in oxidative stress, we followed oxidation of unsaturated lipids using a biomimetic system: Langmuir monolayers. The oxidation mode chosen was UV-irradiation and the lipid model was a polyunsaturated phospholipid: 1,2-dilinoleoyl-sn-glycero-3-phosphocholine (DLPC). The monomolecular film technique was used to measure membrane rheology before and after UV-irradiation. We showed that the UV-irradiation of a DLPC monomolecular film led to a molecular area and surface elasticity modulus decrease that attests to the apparition of new molecular species at the air-water interface. The antioxidant effect of a synthetic plasmalogen (1-O-(1'-(Z)-hexadecenyl)-2-O-oleoyl-sn-glycero-3-phosphocholine or P(PLM)OPE) was tested on the oxidation of DLPC. Indeed, for about 25% mol P(PLM)OPE in mixed DLPC/P(PLM)OPE monolayers, a complete inhibition of the molecular area and the surface elasticity modulus decreases was observed in our experimental conditions. Lower P(PLM)OPE quantities delayed but did not prevent the DLPC oxidation in mixed monolayers.

Eosinophil peroxidase-derived reactive brominating species target the vinyl ether bond of plasmalogens generating a novel chemoattractant, alpha-bromo fatty aldehyde

Plasmalogens are a subclass of glycerophospholipids that are enriched in the plasma membrane of many mammalian cells. The vinyl ether bond of plasmalogens renders them susceptible to oxidation. Accordingly, it was hypothesized that reactive brominating species, a unique oxidant formed at the sites of eosinophil activation, such as in asthma, might selectively target plasmalogens for oxidation. Here we show that reactive brominating species produced by the eosinophil peroxidase system of activated eosinophils attack the vinyl ether bond of plasmalogens. Reactive brominating species produced by eosinophil peroxidase target the vinyl ether bond of plasmalogens resulting in the production of a neutral lipid and lysophosphatidylcholine. Chromatographic and mass spectrometric analyses of this neutral lipid demonstrated that it was 2-bromohexadecanal (2-BrHDA). Reactive brominating species produced by eosinophil peroxidase attacked the plasmalogen vinyl ether bond at acidic pH. Bromide was the preferred substrate for eosinophil peroxidase, and chloride was not appreciably used even at a 1000-fold molar excess. Furthermore, 2-BrHDA production elicited by eosinophil peroxidase-derived reactive brominating species in the presence of 100 microM NaBr doubled with the addition of 100 mM NaCl. The potential physiological significance of this pathway was suggested by the demonstration that 2-BrHDA was produced by phorbol myristate acetate-stimulated eosinophils and by the demonstration that 2-BrHDA is a phagocyte chemoattractant. Taken together, the present studies demonstrate the targeting of the vinyl ether bond of plasmalogens by the reactive brominating species produced by eosinophil peroxidase and by activated eosinophils, resulting in the production of brominated fatty aldehydes.

Ethanolamine plasmalogen and cholesterol reduce the total membrane oxidizability measured by the oxygen uptake method

To investigate the effects of ethanolamine plasmalogen, phosphatidylethanolamine, cholesterol, and alpha-tocopherol on the oxidizability of membranes, various large unilamellar vesicles (LUVs) including these lipids and antioxidant were examined for their total membrane oxidizabilities, evaluated as R(p)/R(i)(1/2) value (where R(p) is rate of oxygen consumption and R(i)(1/2) is the square root of rate of chain initiation) by the oxygen uptake method with water-soluble radical initiator and inhibitor. Incorporation of bovine brain ethanolamine plasmalogen (BBEP) into vesicles as well as cholesterol led to lower the total membrane oxidizability dose-dependently. The effect of BBEP was more efficient in the presence of cholesterol in vesicles. On the other hand, diacyl counterpart, egg yolk phosphatidylethanolamine, and a typical radical scavenger, alpha-tocopherol, had no effect on the membrane oxidizability. Alpha-tocopherol only prolonged an induction period dose-dependently in the present oxidizing system, suggesting a novel antioxidant mechanism of ethanolamine plasmalogens besides the action of scavenging radicals.

Ethanolamine plasmalogens prevent the oxidation of cholesterol by reducing the oxidizability of cholesterol in phospholipid bilayers

The aims of the present study are to establish an appropriate system for assessing the oxidizability of cholesterol (CH) in phospholipid (PL) bilayers, and to explore the effect of ethanolamine plasmalogens on the oxidizability of CH with the system, through comparing with those of choline plasmalogens, phosphatidylethanolamine, and antioxidant alpha-tocopherol (Toc). Investigation of the effects of oxidants, vesicle lamellar forms, saturation level, and constituent ratio of PLs in vesicles on CH oxidation revealed the suitability of a system comprising unilamellar vesicles and the water-soluble radical initiator 2,2'-azobis (2-amidino-propane) dihydrochloride (AAPH). As CH oxidation in the system was found to follow the rate law for autoxidation without significant interference from oxidizable PLs, the oxidizability of CH in PL bilayers could be experimentally determined from the equation: k (p)/(2k (t))(1/2)=R (p)/[LH]R(i)(1/2) by measuring the rate of CH oxidation. It was found with this system that bovine brain ethanolamine plasmalogen (BBEP), bovine heart choline plasmalogen, and egg yolk phosphatidylethanolamine lower the oxidizability of CH in bilayers. Comparison of the dose-dependent effects of each PL demonstrated the greatest ability of BBEP to reduce the oxidizability. A time course study of CH oxidation suggested a novel mechanism of BBEP for lowering the oxidizability of CH besides the action of scavenging radicals.

Effect of cholesterol and surfactant protein B on the viscosity of phospholipid mixtures

Low viscosity of the surface of alveolar fluid is mandatory for undisturbed surfactant function. Based on the known reduction of the viscosity of surfactant-like phospholipid (PL-) mixtures by plasmalogens, the effect of cholesterol and surfactant protein (SP-) B on surface viscosity of these lipid mixtures has been studied. Surface viscosity at the corresponding surface tension was measured with the oscillating drop surfactometer. We found that the viscosity was lowest in cholesterol-, followed by plasmalogen- and SP-B containing samples. Addition of SP-B to a plasmalogen-containing PL-mixture caused a further decrease in viscosity. However, in cholesterol containing mixtures, addition of SP-B led to a significant increase in viscosity, and the effect was reversed by further addition of plasmalogens. We conclude that SP-B, plasmalogens and cholesterol all affect the surface viscosity, thus synergistically regulate monolayer stability. This suggests that they are all needed in vivo for fine tuning of surface properties of pulmonary surfactant.

Effect of ethanol amine plasmalogens on Fe-induced peroxidation of arachidonic acid in dipalmitoylphosphatidylcholine vesicles

We have investigated the influence of ethanolamine plasmalogens on iron-induced oxidation of arachidonic acid in dipalmitoylphosphatidylcholine (DPPC) vesicles. Lipoperoxidation was induced by the addition of 50 microM FeSO4 and studied above (50 degrees C) and below (15 degrees C) the gel-to liquid transition temperature of the vesicles, at two different pH values (7.4 or 6.4). The extent of peroxidation was measured as thiobarbituric reactive product formed and the influence exerted by ethanolamine plasmalogens (PEPL) in this process was compared to that of dipalmitoylphosphatidylethanolamine (DPPE) and diacylphosphatidylethanolamines (DAPE). The extent of peroxidation of arachidonic acid embedded in DPPC vesicles was similar at the two temperatures and greater at 50 degrees C under acidic conditions. However, the peroxidative process was significantly decreased at 50 degrees C in the presence of PEPL, but not of DPPE or DAPE and the inhibitory effect was enhanced at pH 6.4. The possibility that a different phase distribution of the phospholipids, namely a transition from a lamellar to a hexagonal phase, may play a role in the scavenger effect of ethanolamine plasmalogens is discussed.

Oxidation of plasmalogens produces highly effective modulators of macrophage function

Model derivatives of plasmalogens and chemically synthesized oxidative degradation products as found e.g. during oxidation of low density lipoproteins show strong effects on phagocytosis induced secretion of reactive oxygen species of macrophages which was measured by luminol-enhanced chemiluminescence. Whereas a plasmalogen epoxide showed enhancing effects in submicromolar range, inhibition was found with higher concentrations as well as with alpha-hydroxyaldehydes. The substances showed only little effects on the non-cellular ROS-dependent chemiluminescence of the reaction between hydrogen peroxide and opsonized zymosan and no cytotoxic effects under the assay conditions used. These results show that oxidative modification and degradation of plasmalogens occuring also under pathophysiological situations in vivo produces effective modulators of macrophage function which could be important; e.g. during inflammation or atherogenesis.

Inhibition of peroxyl radical-mediated lipid oxidation by plasmalogen phospholipids and alpha-tocopherol

The recently discovered peroxyl radical scavenging properties of plasmalogen phospholipids led us to evaluate their potential interactions with alpha-tocopherol. The oxidative decay of plasmalogen phospholipids and of polyunsaturated fatty acids as induced by peroxyl radicals (generated from 2,2'-azobis-2-amidinopropane hydrochloride; AAPH) was studied in micelles using 1H-NMR and chemical analyses. In comparison with alpha-tocopherol, a 20- to 25-fold higher concentration of plasmalogen phospholipids was needed to induce a similar inhibition of peroxyl radical-mediated oxidation of polyunsaturated fatty acids. Plasmalogen phospholipids and alpha-tocopherol protected each other from oxidative degradation. In low-density lipoproteins (LDL) and micelles supplemented with plasmalogen phospholipids plus alpha-tocopherol, the peroxyl radical-promoted oxidation was additively diminished. The differences in the capacities to inhibit oxidation processes induced by peroxyl radicals between the plasmalogen phospholipids and alpha-tocopherol were less pronounced in the LDL particles than in the micelles. In conclusion, plasmalogen phospholipids and alpha-tocopherol apparently compete for the interaction with the peroxyl radicals. Oxidation processes induced by peroxyl radicals are inhibited in an additive manner in the presence of the two radical scavengers. The contribution of the plasmalogen phospholipids to the protection against peroxyl radical promoted oxidation in vivo is expected to be at least as important as that of alpha-tocopherol.

The selective activation of the cardiac sarcolemmal sodium-calcium exchanger by plasmalogenic phosphatidic acid produced by phospholipase D

Since plasmalogens are the predominant phospholipid of cardiac sarcolemma, the activation of the sodium-calcium exchanger by either plasmenylethanolamine or plasmalogenic phosphatidic acid generated by phospholipase D was explored. Sodium-calcium exchange activity was 7-fold greater in proteoliposomes comprised of plasmenylethanolamine compared to proteoliposomes comprised of only plasmenylcholine. Phospholipase D treatment of proteoliposomes resulted in 1 mol % conversion of plasmenylcholine or phosphatidylcholine to their respective phosphatidic acid molecular species with a concomitant 8-fold or 2-fold activation of sodium-calcium exchange activity, respectfully. Thus, phospholipase D-mediated hydrolysis of plasmalogens to phosphatidic acid may be an important mechanism for the regulation of the sodium-calcium exchanger.

Plasmalogens effectively reduce the surface tension of surfactant-like phospholipid mixtures

The alkenyl-acyl subclass of phosphatidylethanolamine (PtdEtn) and phosphatidylcholine (plasmalogens) are minor components of alveolar surfactant. Plasmalogens promote and stabilize hexagonal structures of phospholipids. In another study (W.R. Perkins, R.B. Dause, R.A. Parente, S.R. Michey, K.C. Neuman, S.M. Gruner, T.F. Taraschi, and A.S. Janoff. Science 273: 330-332, 1996), it was shown that polymorphic phase behavior may have an important role in the effective functioning of pulmonary surfactant. Therefore, we hypothesized that surface properties of phospholipid mixtures that contain plasmalogens are superior to plasmalogen-free mixtures. The effect of plasmalogens on surface tension of surfactant-like phospholipid mixtures (70 mol% dipalmitoyl phosphatidylcholine, 10 mol% phosphatidylglycerol, and 20 mol% PtdEtn) was measured. Using the pulsating bubble surfactometer, we show that an increasing amount of ethanolamine plasmalogens [plasmenylethanolamine (PlsEtn) results in reduction of surface tension (0 mol% PlsEtn 44.7 +/- 1.7, 2 mol% 33.5 +/- 1.7, 4 mol% 36 +/- 3.1, 6 mol% 26.2 +/- 2.9, and 8 mol% 22.2 +/- 0.3 mN/m). By means of the captive bubble surfactometer, minimal surface tension reached with 8 mol% PlsEtn was even lower (3.8 +/- 0.7 mN/m). With regard to morphological studies (B. Fringes, K. Gorgas, and A. Reith. Eur. J. Cell Biol. 46: 136-143, 1988), clofibrate treatment of rats might increase the plasmalogen content of alveolar surfactant. However, in the present study, we could not show that synthesis and secretion of plasmalogens are affected by clofibrate treatment.

Modification of heart sarcolemmal phosphoinositide pathway by lysophosphatidylcholine

Although lysophosphatidylcholine (lyso-PtdCho) accumulates in the sarcolemmal (SL) membrane and alters its function during myocardial ischemia and diabetic cardiomyopathy, the effects of lyso-PtdCho on SL signalling processes have not yet been investigated. The present study was carried out to examine the actions of lyso-PtdCho on the rat heart SL membrane enzymes involved in the phosphoinositide pathway. Different lyso-PtdCho species (10 to 200 microM) inhibited the activities of both phosphatidylinositol kinase and phosphatidylinositol-4-phosphate kinase in the SL membrane in a concentration-dependent manner. The inhibitory potency of lyso-PtdCho compounds for phosphatidylinositol kinase was lyso-PtdCho plasmalogen > 1-oleoyl-lyso-PtdCho > 1-stearoyl-lyso-PtdCho > 1-palmitoyl-lyso-PtdCho, and that for phosphatidylinositol-4-phosphate kinase was lyso-PtdCho plasmalogen > 1-oleoyl-lyso-PtdCho > 1-palmitoyl-lyso-PtdCho > 1-stearoyl-lyso-PtdCho. The inhibitory effect of lyso-PtdCho on phosphatidylinositol-4-phosphate kinase was greater than that on phosphatidylinositol kinase. Lyso-PtdCho structural analogues, such as phosphatidylcholine, lysophosphatidic acid, lysophosphatidylethanolamine, L-alpha-glycerophosphate, oleate and phosphorylcholine, did not affect the phosphoinositide kinases, suggesting that the intact structure of lyso-PtdCho was required for the inhibition of the kinases. The detrimental action of lyso-PtdCho on PtdIns kinase was potentiated by acidosis. Unlike Ca2+, ATP (0.1 and 4 mM) increased lyso-PtdCho-induced deactivation of the kinases. Both enzyme activities were found to be depressed in the ischemic-reperfused or diabetic hearts. None of the tested lyso-PtdCho species altered phosphatidylinositol-4,5-bisphosphate (PtdIns(4,5)P2) hydrolysis by SL phospholipase C. These results indicate that accumulation of lyso-PtdCho in the SL membrane under pathological conditions may diminish the availability of the PtdIns(4,5)P2 substrate for the production of second messengers by receptor-linked phospholipase C.

Delayed oxidative degradation of polyunsaturated diacyl phospholipids in the presence of plasmalogen phospholipids in vitro

The oxidative degradation of plasmalogen (alkenylacyl) phospholipids was analysed in the absence and the presence of polyunsaturated ester phospholipids by 1H-NMR and by chemical determination. Brain lysoplasmenylethanolamine (lyso-P-PE), brain P-PE and erythrocyte P-PE, containing an increasing number of intrachain double bonds at sn2, were oxidized with 2,2'-azobis-(2-amidinopropane hydrochloride) (AAPH; 2 or 10 mM) in Triton X-100 micelles (detergent/phospholipid 1:5, mol/mol). The formation of two peroxyl radicals was accompanied by the degradation of approx. one molecule of brain lyso-P-PE. On oxidation of brain P-PE or erythrocyte P-PE (320 nmol) with 2 mM AAPH, the (alpha-vinyl) methine 1H signal of the enol ether decreased more rapidly than the methine proton peak of intrachain double bonds. The rate of enol ether degradation increased in the order: erythrocyte P-PE>brain P-PE>brain lyso-P-PE. The disappearance of the polyunsaturated ester phospholipids 1-palmitoyl-2-arachidonoyl phosphatidylcholine (16:0/20:4-PC) and 1-palmitoyl-2-linoleoyl phosphatidylcholine (16:0/18:2-PC) (100 nmol), as induced by 10 mM AAPH, was nearly completely inhibited by the plasmalogens (25 nmol) in the first 30 and 60 min of incubation respectively, and was delayed at later time points. Plasmalogens and vitamin E (4-25 nmol) mitigated the decreases in 16:0/[3H]20:4-PC (100 nmol) induced by 2 mM AAPH in a similar manner. The initial rate of degradation of intrachain double bonds of 16:0/20:4-PC and 16:0/18:2-PC (320 nmol; 2 mM AAPH) was decreased by 59% and 81% respectively in the presence of 80 nmol of brain lyso-P-PE. In conclusion, plasmalogens markedly delay the oxidative degradation of intrachain double bonds under in vitro conditions. Interactions of enol ether double bonds with initiating peroxyl radicals as well as with products generated by prior oxidation of polyunsaturated fatty acids are proposed to be responsible for this capacity of plasmalogens. Furthermore, the products of enol ether oxidation apparently do not propagate the oxidation of polyunsaturated fatty acids.

Delay of copper-catalyzed oxidation of low density lipoprotein by in vitro enrichment with choline or ethanolamine plasmalogens

Low density lipoprotein (LDL) isolated from human serum of different donors was enriched with plasmalogens and their diacyl analogs in order to investigate a possible effect of these phospholipids on the rate of lipid peroxidation in this lipoprotein. LDL was incubated with either vesicles of choline plasmalogen or phosphatidylcholine in presence of lipoprotein- deficient serum, or with liposomes of ethanolamine plasmalogen or phosphatidylethanolamine together with the non-specific phospholipid transfer protein isolated from beef liver. After re-isolation of LDL by ultracentrifugation, a dose-dependent incorporation of the exogenous phospholipids was obtained. Enrichment of LDL with choline plasmalogen resulted in a delay of the copper-catalyzed oxidation of LDL from five different donors. LDL from two donors was also enriched with diacylglycerophosphocholine which led to a delay of oxidation, but the protective effect was smaller than with choline plasmalogen. Enrichment of LDL from two additional donors with ethanolamine plasmalogen resulted in the strongest protection against oxidation, whereas, diacylglycerophospho-ethanolamine had little effect. The delay of the copper-catalyzed LDL oxidation may be due to a direct antioxidative action of the plasmalogens, which are partially degraded during the lag phase of oxidation, or to an indirect effect caused by alteration of the LDL surface in the presence of an excess of glycerophospholipids.

Inhibitory effect of ethanolamine plasmalogen on iron- and copper-dependent lipid peroxidation

The effect of ethanolamine plasmalogen (EtnPm) on lipid peroxidation was investigated in liposomal suspension of egg yolk phosphatidylcholine. EtnPm inhibited iron- and copper-dependent peroxidation in the presence of preformed hydroperoxides, although it was not effective for radical initiator mediated lipid peroxidation. EtnPm resulted in complete binding of iron to liposomal lipids, suggesting that EtnPm exerts its inhibitory effect on lipid peroxidation through inhibiting preformed peroxide decomposition by trapping transition metal ions.

Plasmalogen phospholipids as potential protectors against lipid peroxidation of low density lipoproteins

A phospholipid subgroup with potential antioxidant properties, the plasmalogen (1-alkenyl, 2-acyl-) fraction, was determined to constitute about 4.5% of total LDL phospholipids. In vitro oxidation of LDL by 2,2'-azobis-(2-amidinopropane hydrochloride) (AAPH, 0.5-10mM) or 5 microM copper induced a selective reduction of plasmalogen subgroups in phosphatidylcholine and phosphatidylethanolamine by 15%-35% within 30 min. Under the same experimental conditions alpha tocopherol (vitamin E) levels were lowered by 5%-40%, indicating a comparable sensitivity of plasmalogen phospholipids and alpha tocopherol towards oxidative attack by AAPH and copper. In vitro enrichment of LDL with 1-alkenyl, 2-lyso-phosphatidylcholine increased the lag phase of formation of conjugated double bonds induced by oxidation of the particles with copper. Incorporation of the lyso plasmalogen did not affect the maximal contents of conjugated dienes in copper oxidized LDL. Due to their relatively high concentration in LDL, their pronounced sensitivity towards oxidation and their capacity to increase the oxidative resistance of the particles, plasmalogen phospholipids may play a significant role in the defense of LDL particles against oxidative stress.

Role of cytosolic calcium-independent plasmalogen-selective phospholipase A2 in hypoxic injury to rabbit proximal tubules

Although the activation of calcium-independent phospholipase A2 (PLA2) enzymes has been described in the heart, the pathogenetic role of this enzyme(s) in hypoxic cell injury has not been previously examined in any tissue. Therefore, we characterized the time course of activation of calcium-independent PLA2 using both plasmalogen and diacylglycerophospholipid substrates during hypoxia in rabbit proximal tubules and examined whether inhibition of calcium-independent PLA2 activity is associated with a cytoprotective effect. Subjecting rabbit proximal tubules to hypoxia for 5 min resulted in at least a threefold increase in cytosolic calcium-independent PLA2, which was selective for plasmalogen substrates (control 444 +/- 69 vs hypoxia 1,675 +/- 194 pmol.mg protein-1.min-1, n = 5). In contrast, no changes in PLA2 activity were observed in the presence of 4 mM EGTA in the membrane fraction using plasmenylcholine substrates. 20 min of hypoxia resulted in an increase in arachidonate from 3 +/- 1 to 28 +/- 4 ng/mg protein and lactate dehydrogenase release from 7.5 +/- 2% to 38 +/- 5%, n = 4. Pretreatment of proximal tubules with 10 microM Compound I, a specific inhibitor of calcium-independent PLA2, resulted in reduction in the magnitude of both hypoxia-induced arachidonic acid release (11 +/- 3 ng/mg protein) and lactate dehydrogenase release (18 +/- 4%). Our data indicate that a significant fraction of PLA2 activity in the proximal tubule is calcium-independent and selective for plasmalogen substrates. Furthermore, the activation of this enzyme plays an important role in the pathogenesis of membrane injury during hypoxia in the proximal tubule.

Comparison of 1-O-alkyl-, 1-O-alk-1'-enyl-, and 1-O-acyl-2-acetyl-sn-glycero-3-phosphoethanolamines and -3-phosphocholines as agonists of the platelet-activating factor family

Four naturally occurring platelet-activating factor (PAF) analogs, 1-alk-1'-enyl-2-acetyl-sn-glycero-3-phosphocholine, 1-hexadecanoyl-2-acetyl-sn-glycero-3-phosphocholine, 1-octadecanoyl-2-acetyl-sn-glycero-3-phosphocholine, and 1-alkyl-2-acetyl-sn-glycero-3-phosphoethanolamine, stimulated human neutrophils (PMN) to mobilize Ca2+, degranulate, and produce superoxide anion. They were, respectively, 5-, 300-, 500-, and 4000-fold weaker than PAF in each assay; inhibited PMN-binding of [3H]PAF at concentrations paralleling their biological potencies; and showed sensitivity to the inhibitory effects of PAF antagonists. PAF and the analogs, moreover, desensitized PMN responses to each other but not to leukotriene B4 and actually increased (or primed) PMN responses to N-formyl-MET-LEU-PHE. Finally, 5-hydroxyeicosatetraenoate-enhanced PMN responses to PAF and the analogs without enhancing the actions of other stimuli. It stereospecifically raised each analog's potency by as much as 100-fold and converted a fifth natural analog, 1-alk-1'-enyl-2-acetyl-sn-glycero-3-phosphoethanolamine from inactive to a weak stimulator of PMN. PAF and its analogs thus represent a structurally diverse family of cell-derived phospholipids which can activate, prime, and desensitize neutrophils by using a common, apparently PAF receptor-dependent mechanism.

The rapid and reversible activation of a calcium-independent plasmalogen-selective phospholipase A2 during myocardial ischemia

Recent studies have demonstrated the existence of two members of a novel family of calcium-independent plasmalogen-selective phospholipases A2 in mammalian myocardium (Wolf, R. A., and R. W. Gross. 1985. J. Biol. Chem. 260:7295-7303; and Hazen, S. L., D. A. Ford, and R. W. Gross. 1991. J. Biol. Chem. 266:5629-5633). To examine the potential role of these calcium-independent phospholipases A2 in mediating membrane dysfunction during early myocardial ischemia, the temporal course of alterations in phospholipase A2 activity during global ischemia in Langendorf perfused rabbit hearts was quantified and compared with traditionally accepted markers of myocytic ischemic injury and anaerobic metabolism. We now report that membrane-associated calcium-independent plasmalogen-selective phospholipase A2 activity increased over 400% during 2 min of global ischemia (P less than 0.01), was near maximally activated (greater than 10-fold) after only 5 min of ischemia, and remained activated throughout the entire ischemic interval examined (2-60 min). Activation of membrane-associated plasmalogen-selective phospholipase A2 after 5 min of myocardial ischemia was rapidly reversible during reperfusion of ischemic tissue. Both the activation of phospholipase A2 and its reversibility during reperfusion were temporally correlated to alterations in myocytic anaerobic metabolism. Furthermore, activation of membrane-associated phospholipase A2 was essentially complete before electron microscopic evidence of cellular damage. Collectively, these results identify dynamic alterations in calcium-independent plasmalogen-selective phospholipase A2 activity during myocardial ischemia which precede irreversible cellular injury and demonstrate that activation of plasmalogen-selective phospholipase A2 is amongst the earliest biochemical alterations in ischemic myocardium.

Activation of myocardial protein kinase C by plasmalogenic diglycerides

Recently, we have demonstrated that myocardial sarcolemma is predominantly comprised of plasmalogen molecular species and that the plasmalogen metabolite 1-O-alk-1'-enyl-2-acyl-sn-glycerol (AAG) accumulates during myocardial ischemia despite substantial decreases in 1,2-diacyl-sn-glycerol (DAG) content. To elucidate the physiological significance of AAG accumulation during myocardial ischemia, rabbit myocardial protein kinase C was partially purified by DE-52 and high-performance hydroxylapatite chromatographies, and the potency of AAG as an activator of myocardial protein kinase C was assessed. Both AAG and 1-O-alkyl-2-acyl-sn-glycerol are potent activators of myocardial protein kinase C with obligatory requirements for physiological increments in free Ca2+ concentration. In contrast, a substantial amount of myocardial protein kinase C activity elicited by DAG was calcium independent. Concentration dependence of ATP for protein kinase C-mediated phosphorylation was identical utilizing either ether-linked diglycerides or DAG as activators, with maximal phosphorylation manifest at ATP concentrations two orders of magnitude less than those found in ischemic myocardium. Thus accumulation of AAG in ischemic myocardium in conjunction with increases in intracellular free Ca2+ concentration may synergistically activate protein kinase C and therefore modulate phosphorylation of proteins in specific subcellular loci.

A possible role for plasmalogens in protecting animal cells against photosensitized killing

Chinese hamster ovary (CHO) cells incorporate 12-(1'-pyrene) dodecanoic acid (P12) into membrane lipids. Exposure of P12-labeled cells to long wavelength ultraviolet light causes cell killing, presumably because excitation of the pyrene moiety (a photosensitizer) leads to the generation of reactive oxygen species. Cytotoxicity is dependent upon the concentration of P12 used to label the cells, and time of UV exposure, and the presence of oxygen during irradiation. CHO mutant cells deficient in plasmalogen biosynthesis and peroxisome assembly (Zoeller, R.A., and Raetz, C.R.H. (1986) Proc. Natl. Acad. Sci. U.S.A. 83, 5170-5174) are several orders of magnitude more sensitive to P12/UV treatment than wild-type cells, permitting direct selection of one wild-type cell in 1 X 10(4) mutant cells. A major factor responsible for the P12/UV hypersensitivity of these mutants appears to be the absence of plasmalogens. Supplementation of the mutants with 1-O-hexadecyl-sn-glycerol restores plasmalogen levels and nearly normal resistance to P12/UV treatment, whereas the biogenesis of peroxisomes is not restored. The P12/UV hypersensitivity of the plasmalogen-deficient mutants, together with the selective, P12/UV-induced decomposition of plasmalogens in wild-type cells, documented in the accompanying manuscript, suggest that the vinyl ether linkage of plasmalogens plays a direct role in protecting animal cell membranes against certain oxidative stresses.

Calcium diphosphatidate membrane traversal is inhibited by common phospholipids and cholesterol but not by plasmalogen

Phosphatidate-mediated Ca2+ membrane traversal is inhibited by phospholipids (PL) such a phosphatidylcholine (PC), phosphatidylinositol (PI), phosphatidylserine (PS), sphingomyelin and lysoPC, but not by PC-plasmalogen. Kinetics of Ca2+ traversal through a 'passive' bilayer consisting of OH-blocked cholesterol show competition between PC and phosphatidic acid (PA); it appears likely that a Ca(PA.PC) complex is formed which is not a transmembrane ionophore but will reduce the amount of phosphatidic acid available for the formation of the ionophore, Ca(PA)2. PS and PI may inhibit Ca2+-traversal in the same manner by forming Ca(PA.PL) complexes. We suggest that PC-plasmalogen, with one of the Ca2+-chelating ester CO groups missing, cannot engage in calcium cages, i.e., Ca(PA.PL) complexes, and thus does not interfere with Ca(PA)2 formation. Double-reciprocal plotting of Ca2+ traversal rates in cholesterol-containing liposomes vs. calcium concentration suggests that cholesterol inhibits Ca2+ traversal by competing with Ca2+ for PA. The inhibition does not seem to be caused by a restructuring or dehydration of the membrane 'hydrogen belts' affected by cholesterol; most probably, it is due to hydrogen bonding of the cholesterol-OH group to a CO group of PA; this reduces the amount of PA available for the calcium ferry. The inhibition by sphingomyelin and lysoPC may also be explained by their OH group interacting with PA via hydrogen bonding. The pH dependence of Ca2+ traversal suggests that H[Ca(PA)2]- can serve as Ca2+ cross-membrane ferry but that at physiological pH, [Ca(PA)2]2- is the predominant ionophore. In conclusion, the results indicate that Ca2+ traversal is strongly dependent on the structure of the hydrogen belts, i.e., the membrane strata occupied by hydrogen bond acceptors (CO of phospholipids) and donors (OH of cholesterol, sphingosine), and that lipid hydrogen belt structures may regulate storage and passage of Ca2+.

The effect of isoprenaline on the phospholipid content of the compact and spongious musculature of the carp ventricular myocardium

1. After a single injection of 40 mg kg-1 of isoprenaline to the carp, lysophospholipids appear in the tissue of the heart ventricle, ethanolamine plasmalogens increase and choline plasmalogens decrease; phosphatidylinositol is lowered in the spongious layer only. 2. Daily administration of 5 mg kg-1 of the drug leads, after 5 doses, to a dramatic decrease of the diphosphatidylglycerol content; during the subsequent 5 and 10 doses a return to normal values occurs. Shifts in plasmalogens are similar to those found after a single high dose. Some other phospholipids change significantly. 3. All changes reveal that the spongious musculature is more sensitive to the drug than the compact one.

Endothelium-dependent vasorelaxation induced by Cn-acetal plasmalogens

In this study the effects of the synthetic acetal plasmalogens (AP) C17-AP, C13-AP, C9-AP on isolated rabbit aorta were investigated with emphasis on their putative relationship with endothelium-dependent relaxing factor (EDRF). The various AP were obtained by total synthesis from the related fatty acid chlorides. In isolated rabbit aorta precontracted with phenylephrine (PE, 10(-7) M), C17-AP (greater than 10(-6) M) and C13-AP (greater than 10(-5) M) exerted an endothelium-dependent relaxation (EDR). In contrast, C9-AP was totally devoid of effect. Given 30 or 45 min before PE, C17-AP (greater than 10(-6) M) and C13-AP (greater than 10(-5) M) abolished the carbachol-induced ERD; moreover, following preincubation with C17-AP, enhanced contraction was obtained with carbachol. Similar effects were obtained with preincubation of aortas with both AA(10(-4) M) and A 23 187 (10(-8) M). Conversely preincubation of aortas with carbachol (3X 10(-6) M) and ATP (3 X 10(-5) M) did not significantly modify the carbachol-induced EDR. Atropine (3 X 10(-7) M) did not affect the relaxation induced by C17-AP and C13-AP. The in vivo effects are correlated with the in vitro actions of acetal plasmalogens: C17-AP and C13-AP but not C9-AP, given iv (5 mg/kg) induced a pronounced but transient hypotension which lasted 2-3 min and which was followed by a persistent hypertensive state. Atropine (0.5 and 1 mg/kg; iv) given 5 min before C17-AP inhibited the secondary hypertensive phase. These results show that C17-AP and C13-AP should be added to the list of compounds capable of releasing EDRF.

Cytotoxic ether phospholipids. Different affinities to lysophosphocholine acyltransferases in sensitive and resistant cells

Alkyllysophospholipids (ALP) which are 1-O-alkyl analogs of the cell membrane component 1-acyl-sn-glycero-3-phosphocholine (1-acyl-GPC) represent a family of new antitumor drugs. Susceptibility of cells to ALP is correlated to a selective inhibition of fatty acid incorporation into 1,2-diacyl-sn-glycero-3-phosphocholine in intact cells. This report examines oleoyl-CoA-1-acyl-GPC acyl-transferase activities in cell-free systems of ALP-sensitive methylcholanthrene-induced fibrosarcoma cells (MethA cells) and ALP-resistant bone marrow-derived murine macrophages (BMM phi). The specific activities for the oleoyl-CoA-1-acyl-GPC acyltransferases were 1.05 +/- 0.06 nmol X mg-1 X min-1 and 2.98 +/- 0.27 nmol X mg-1 X min-1, respectively. The kinetic parameters for 1-palmitoyl-GPC were Km = 16.6 microM, Vmax = 4.3 nmol X mg-1 X min-1 (BMM phi) and Km = 7.6 microM, Vmax = 2.0 nmol X mg-1 X min-1 (MethA cells). In the presence of 1-O-octadecyl-2-O-methyl racemic glycero-3-phosphocholine (ET-18-OCH3), one of the most potent cytotoxic ALP, the acyltransferase was dose dependently inhibited in MethA cells with a 50% inhibition concentration at 40 micrograms/ml. The BMM phi-acyltransferase was not affected up to 80 micrograms of ET-18-OCH3/ml. The kinetic parameters (Km' = 15.4 microM, Vmax' = 2.2 nmol X mg-1 X min-1) suggest that ET-18-OCH3 is a competitive inhibitor in MethA cells. Inhibitor constants for ET-18-OCH3, calculated from Dixon plots, were found to be 423 microM (BMM phi) and 13 microM (MethA cells) indicating a 33-fold larger affinity of ET-18-OCH3 to the MethA cells than to the BMM phi acyltransferase. From these data we assume that the inhibition of oleic acid incorporation into cellular phosphocholine during the antineoplastic action of ALP may be due to different affinities of the inhibitor to the 1-acyl-GPC acyltransferases in different cell types.

Plasmenylethanolamine: growth factor for cholesterol-reducing Eubacterium

A plasmalogen, plasmenylethanolamine, is required for in vitro growth of strains of Eubacterium which convert cholesterol to coprostanol. Plasmenylethanolamine was isolated from calf brain by selective saponification of lipid fractions separated by thin-layer or column chromatography. Cholesterol-containing thioglycolate broth plus purified plasmenylethanolamine or its 2-lyso derivative supported growth of Eubacterium ATCC 21408 and a cholesterol-reducing Eubacterium isolated from baboon feces. Plasmenylethanolamine obtained from commercial sources also supported growth of these organisms, but none of a number of other pure lipids would support growth. Metabolism of the alkenyl ether group of plasmenylethanolamine occurred during growth.