Methanolysis of sphingomyelin. Toward an epimerization-free methodology for the preparation of D-erythro-sphingosylphosphocholine

It is well known that acid hydrolysis of natural sphingomyelin in aqueous methanol or 1-butanol at refluxing temperature is accompanied by epimerization at the C-3 position of the long-chain base. An improved procedure for the hydrolysis of commercially available, naturally occurring sphingomyelin is described. Prolonged exposure (3;-4 days) of sphingomyelin to freshly prepared 0.5 M anhydrous methanolic hydrogen chloride (generated by trapping the gas evolved from the reaction of concentrated sulfuric acid with solid sodium chloride in anhydrous methanol) at 50 degrees C resulted in cleavage of the amide side chain. The extent of epimerization of the allylic alcohol stereocenter was quantified by integration of the C-5 signal of the (13)C nuclear magnetic resonance spectrum of lysosphingomyelin. The method described here is superior to the traditional acid hydrolysis methods because it provides the product as a approximately 10:1 ratio of d-erythro/l-threo epimers; in contrast, a ratio of approximately 1. 3:1 was obtained by the previous methods. We also report that use of dichloromethane as a cosolvent with N,N-dimethylformamide in the reaction of lysosphingomyelin with an activated fatty acid reduced the time required for completion of the N-acylation reaction.

Phosphorylcholine-containing polyurethanes for the control of protein adsorption and cell attachment via photoimmobilized laminin oligopeptides

In this study, we synthesized a biomaterial whose surface inhibits non-specific protein and cell attachment. The polymer was designed to mimic the external cell plasma membrane properties through the introduction of particular chemical constituents of the cell membrane: phospholipid polar headgroups. This was done by copolymerizing phosphorylcholine (PC) groups into a polyurethane polymer backbone (PCPUR). Peptides known to induce specific cell attachment were subsequently bound to the surface of this copolymer in a photoadressible manner to obtain surfaces that allowed the attachment of cells in a specific pattern. Two polymers with different phosphorylcholine concentrations were synthesized and their bulk and surface properties were characterized through differential scanning calorimetry, wettability measurements, angle-resolved X-ray photoelectron spectroscopy and time-of-flight secondary ion mass spectrometry. Protein and lipid adsorption investigation using optical waveguide light mode spectroscopy showed that the irreversible adsorption of both proteins and lipids is drastically reduced as a result of simultaneous contributions of the PC groups, molecular mobility and strong hydrophilicity of the polymers. Consequently, this leads to a marked reduction in the cellular attachment response, which further decreases with increasing PC concentration. Finally, when the polymer surface was photo-derivatized, attachment of the neural NG108-15 cell line occurred only on the areas of the PCPUR where the laminin CDPGYIGSR peptide sequence was photoimmobilized. Cell attachment was nevertheless found to be non-specific with respect to the peptide sequence used and reasons for such results are therefore discussed.

Non-HPLC separation of water-soluble choline metabolites by two-dimensional high voltage electrophoresis and thin layer chromatography

In cholinergic neurons choline is directed to three main pathways; (1) conversion to phosphorylcholine (PCh) and cytidine diphosphate choline (CDP-choline) for the synthesis of phosphatidylcholine, (2) acylation to the neurotransmitter acetylcholine and (3) oxidation to betaine for the formation of methionine. Thus, the distribution of choline among the different metabolites is important for a better understanding of the regulation of these pathways in neurons. A non-HPLC method for the simultaneous separation of five choline metabolites found in neurons is described. High voltage electrophoresis (HVE) was combined with thin layer chromatography (TLC) to separate choline, PCh, CDP-choline, acetylcholine and betaine. This method is useful in studying the distribution of choline among its different metabolites in radiotracer experiments. Aqueous metabolites from leukemia inhibitory factor treated LA-N-2 cells labeled with [methyl-3H]choline were separated by HVE followed by TLC in the same dimension. Although the separation appeared to be complete, some 'tailing' by PCh significantly elevated the radioactivity measured in CDP-choline. This tailing of PCh was confirmed by subjecting radiolabeled PCh alone to this multiple separation method. Contamination of CDP-choline by PCh was eliminated by subjecting the samples to HVE followed by TLC in the second dimension. This two-dimensional approach was consistently reproducible and achieved excellent resolution of all five metabolites. In addition, this technique also resolved a sixth choline-containing metabolite, glycerophosphorylcholine (GPC), a breakdown product of phosphatidylcholine.

Synthesis of azidophospholipids and labeling of lysophosphatidylcholine acyltransferase from developing soybean cotyledons

A photoreactive substrate analog of lysophosphatidylcholine (LPC), 1-([(4-azidosalicyl)-12-amino)]dodecanoyl-sn-glycerol-3-phospho cholin e (azido-LPC) was synthesized. Fast atom bombardment mass spectrometry was employed to confirm the structures of azido-LPC and its intermediates. Azido-LPC was used to label putative acyl-CoA:LPC acyltransferase from microsomal membranes of developing soybean cotyledons. The synthesized substrate analog acts as a substrate for the target acyltransferases and phospholipases in the dark. When the microsomal membranes were incubated with the acyl acceptor analog and immediately photolyzed, LPC acyltransferase was irreversibly inhibited. Photoinactivation of the enzyme by the photoprobe decreased in the presence of LPC. Microsomal membranes were photolyzed with 125I-labeled azido-LPC and analyzed by SDS-PAGE followed by autoradiography. These revealed that the analog preferentially labeled 54- and 114-kDa polypeptides. Substrate protected the labeling of both the polypeptides. In our earlier report, the same polypeptides were also labeled with photoreactive acyl-CoA analogs, suggesting that these polypeptides could be putative LPC acyltransferase(s). These results demonstrated that the photoreactive phospholipid analog could be a powerful tool to label acyltransferases involved in lipid biosynthesis.

Calcium-dependent binding of rabbit C-reactive protein to supported lipid monolayers containing exposed phosphorylcholine group

The interaction of rabbit C-reactive protein (rCRP) with a supported monolayer containing a phosphorylcholine moiety was studied. Three types of phospholipids were synthesized, each containing a insertion spacer of eight, six, or three atoms between the phosphorylcholine group and hydrophobic tail. By varying the length of the insertion spacer, we can vary the extension of the phosphorylcholine group from the membrane surface. By varying the monolayer composition, we can control the lateral distance between the exposed phosphorylcholine groups. Using the surface plasmon resonance technique (SPR), we demonstrated that the calcium-dependent binding of rCRP to the model membrane is governed not only by the ability of the ligand to access the binding pocket fully (spacer length), but also by lateral hindrance within the two-dimensional plane of the membrane. The value of the apparent binding constant was estimated by theoretical analysis, which is obviously dependent on the composition of the lipid mixture, and a maximum of (9.9 +/- 1.5) x 10(6) M-1 was obtained.

Synthesis, structure and surface dynamics of phosphorycholine functional biomimicking polymers

2-Acryloyloxyethyl phosphorylcholine (APC) was synthesised and copolymerised with methyl methacrylate (MMA) and methyl acrylate (MA) to lead to a PC functional terpolymer. Bulk and solution properties were assessed through elemental analysis, DSC and 1H-NMR. The possibility of chain transfer was discussed. Surface properties were investigated by ToF-SIMS and XPS as well as in vitro assays to assess the non-fouling characteristic of the terpolymer. It was found that a low PC concentration generates an amphiphile terpolymer and is responsible for the organisation of the bulk into a microphase separated morphology with enriched PC domains dispersed in a (MMA-MA) matrix. The presence of PC micelles in non-polar solvent could also be deduced from the analysis of the polymer structure behaviour in solution. Finally, surface reorganisation of the terpolymer was shown to be highly dependent upon the affinities of the PC group for its environment and owing to surface compliance, a low PC content was already sufficient to strongly reduce cell attachment.

Synthesis of DL-alpha-tocopherol-ligated phospholipids

A three-step synthesis of DL-alpha-tocopheryl-6-O-phosphorylcholine and its -6-O-phosphorylethanolamine homologue is described. The reaction pathway involves the conversion of DL-alpha-tocopherol to the corresponding 2-bromoethyl phosphate, hydrolytic cleavage of the remaining phosphorochloridate bond and treatment of the diester intermediate formed with either aqueous trimethylamine or ammonia to give the aminated target derivatives in good overall yields (61-67%). The compounds represent new models of ligated lipid mediators in which a vitamin E-unit is covalently bonded to a naturally occurring phospholipid fragment.

Neutrophil adhesion on phosphorylcholine-containing polyurethanes

Polyurethanes have been synthesized using glycerophosphorylcholine (GPC) as a chain extender. By altering the ratio of GPC to butanediol (BD), a series of polymers was obtained composed of different contents of phosphorylcholine. Bulk and surface characterization of the polymers was carried out. Differential scanning calorimetry and dynamic mechanical analysis showed that the polymer with the highest phosphorylcholine content (PU-GPC-20) had the lowest soft segment Tg and the highest tensile strength and Young's modulus among the polymers studied. This is due to the high degree of microphase separation in PU-GPC-20 as a result of by ionic aggregation and hydrogen bonding from the zwitterionic phosphorylcholine moiety. PU-GPC-20 contained approximately 20 wt%, of glycerophosphorylcholine. Dynamic contact angle analysis showed that these polymers, especially the ones with high phosphorylcholine content, rearranged themselves to minimize their interfacial tension upon contacting an aqueous environment. Under shear rates of from 20 to 120 s(-1), neutrophils did not adhere to PU-GPC-20. Under similar conditions neutrophil adhesion was observed only at 20 s(-1) on PU-GPC-10, PU-GPC-5 and on the control polyurethane (PU-base). Cell spreading was observed on the control polyurethane but not on any of the other surfaces. The incorporation of phosphorylcholine into the polyurethane backbone effectively reduced neutrophil adhesion and thus potentially could result in lower inflammatory and foreign body responses.

The effect of two synthetic phospholipids on cell proliferation and phosphatidylcholine biosynthesis in Madin-Darby canine kidney cells

The concentration-dependent effects of two different synthetic phospholipids on cell proliferation and phosphatidylcholine biosynthesis were compared in Madin-Darby canine kidney (MDCK) cells. The alkyllysophospholipid 1-O-octadecyl-2-O-methyl-sn-glycero-3-phosphocholine and the alkylphosphocholine, hexadecylphosphocholine, inhibited cell proliferation with half-inhibitory concentrations (IC50) of 75 and 135 mumol/L, respectively. The agents also inhibited phosphatidylcholine biosynthesis in confluent and proliferating MDCK cells. The IC50 of 1-O-octadecyl-2-O-methyl-sn-glycero-3-phosphocholine was 40 mumol/L in confluent cells and 20 mumol/L in proliferating cells, whereas the IC50 of hexadecylphosphocholine was higher in both experimental systems (67 mumol/L in confluent cells and 40 mumol/L in proliferating cells). Further experiments revealed that the effect of both agents on phosphatidylcholine biosynthesis was reversible and that the inhibition was mediated by translocation of the rate-limiting enzyme of this pathway, CTP:phosphocholine cytidylyltransferase (EC 2.7.7.15), from membranes to the cytosol, where it is inactive. The present findings suggest that the inhibition of phosphatidylcholine biosynthesis by both synthetic phospholipids might be related, in part, to their antiproliferative effects.

Hemocompatibility on graft copolymers composed of poly(2-methacryloyloxyethyl phosphorylcholine) side chain and poly(n-butyl methacrylate) backbone

To improve the hemocompatibility on hydrophobic biomedical materials by a simple coating technique, graft copolymers composed of a hydrophilic side chain with phospholipid polar groups and a hydrophobic backbone were synthesized. The hydrophilic chain had phospholipid polar groups, poly[2-methacryloyloxyethyl phosphorylcholine (MPC)], and the hydrophobic backbone was poly[n-butyl methacrylate (BMA)]. Because the graft copolymers obtained could dissolve in ethanol, they could be used as a coating material. When the poly(MPC-graft-BMA) was coated onto a poly(BMA) membrane, the composition of the MPC units on the surface was maintained in the bulk graft copolymer even after immersion in water. Protein adsorption on the membrane coated with the graft copolymer from human plasma detected by a gold-colloid labeled immunoassay was drastically decreased compared with that on glass and the original membrane. Moreover, blood cell adhesion, activation, and aggregation on the membrane after contact with human citrated whole blood were suppressed by the coating of the graft copolymer. These results clearly show that the poly(MPC-graft-BMA) is a suitable material for improving hemocompatibility on the biomedical devices because of its protein adsorption and cell adhesion resistant properties.

Metabolism and neurite promoting effect of exogenous sphingosylphosphocholine in cultured murine neuroblastoma cells

Exogenous sphingosylphosphocholine analogues and naturally occurring sphingomyelin stimulated the neurite outgrowth in cultured murine neuroblastoma cell lines, NS-20Y, Neuro2a, and N1E-115, whereas exogenous sphinganine at a non-cytotoxic concentration inhibited the neurite outgrowth in NS-20Y and Neuro2a cells. The effect of sphingosylphosphocholine on the neurite outgrowth was reversible, indicating that the extended neurites needed to be maintained by continuous stimulation. The uptake and metabolism of the exogenous [3-3H]sphingosylphosphocholine in pulse and chase experiments suggested that the radioactive ceramide and sphingomyelin, which were detected as major metabolic products, were in a precursor/product relationship. It is thus assumed that the exogenous sphingosylphosphocholine taken up by the cells is first degraded into phosphocholine and sphingosine, of which the latter is rapidly acylated to ceramide then converted to sphingomyelin by phosphocholine transfer. Metabolism of sphingosylphosphocholine through sphingomyelin synthesis in the cells may be associated with neurite outgrowth.

Simplified methods for the synthesis of 2-hexadecanoylthio-1-ethylphosphorylcholine and for the determination of phospholipase A2 activity

A simple and straight forward method was developed for the synthesis of 2-hexadecanoylthio-1-ethyl phosphorylcholine (HEPC). The new procedure, which used p-toulenesulfonate instead of 2-bromoethyl phosphorylcholine, not only reduced the reaction time but also allowed the reaction to proceed under mild conditions. Using HEPC as a substrate, we have also developed a microplate assay for measuring phospholipase A2 activity which is rapid and will be useful for analyzing a large number of samples in a very short time. The applicability of this assay method for assessing phospholipases A2 from two different sources and determining their kinetic constants is also demonstrated. This method can also be extended for measuring lipases and lysophospholipases using a suitable thioester. Thus, both synthesis and assay methods will be useful in basic and applied research on phospholipases and related enzymes.

Synthesis of alkylphosphonates, a new class of antineoplastic agents

Three different phosphonate analogues of hexadecylphosphocholine, a representative of a new class of antineoplastic agents, were synthesized. The structures of the newly synthesized compounds have been devised to contain only one cleavage point for either phospholipase C or phospholipase D. These structural features should allow an examination of the importance of these enzymes for the antineoplastic activities of alkylphosphocholines.

Identification of a naturally occurring methyl-ester of phosphate, methyl-phosphorylcholine (methyl-2-(N,N,N trimethylamino) ethyl phosphate), in the eggs of the sea urchin S. purpuratus

A novel metabolite of choline, phosphorylcholine methyl ester, has been identified in the eggs of S. purpuratus wherein it is present at approximately 1 mM concentration. To the best of our knowledge, this is the first instance of a phosphoryl-methyl-ester to be observed in nature. The compound appears to be species specific, since it has not been observed in other species such as L. pictus and P. depressus. In S. purpuratus its distribution is confined to the ovary, eggs and embryos, and is absent from young animals following metamorphosis.

Biomembranes as models for polymer surfaces. II. The syntheses of reactive species for covalent coupling of phosphorylcholine to polymer surfaces

We have proposed previously that the biocompatibility of biomaterial surfaces might be improved by mimicking the phospholipid components which are present on the external faces of cellular plasma membranes. This approach may have particular relevance to the generation of haemocompatible surfaces, since the distributional asymmetry of phospholipids in the plasma membranes of blood cells is critical to the maintenance of haemostasis. The simplest feature common to the external faces of essentially all the mammalian plasma membranes investigated so far is the high content of the electrically neutral, but zwitterionic, phosphorylcholine. The present communication describes the syntheses of a group of novel reactive species capable of covalently linking phosphorylcholine to a variety of polymer surfaces.

[Synthesis and biological activity of some lysing and fusogenically active phosphocholine derivatives]

2-Hexadecylglycerophosphocholine (1) and its 1-O-methyl, 1-O-ethyl and 1-O-benzyl (4) derivatives as well as some n-alkanol phosphocholines were synthetized and tested for haemolytic activity. Most potent (LD50 approximately equal to 5.10(-6) mol/l) were 1 and the hexadecanol and octadecanol phosphocholines (7 and 8). 1, 4 and 7 were tested for fusogenic activity against vegetable protoplasts. When used at sublytic concentrations (0.01 - 0.05 mmol), these compounds were as efficient as polyethylene glycol.

Synthesis of enzyme-inhibitory phospholipid analogs. III. A facile synthesis of N-acylaminoethylphosphorylcholines

A facile and efficient synthesis of N-aceylaminoethylphosphorylcholines, a series of inhibitory substrate analogs of phospholipase A2, is described. The procedure consists of a three-step sequence including: (1) N-acylation of ethanolamine with fatty acid chloride, followed by (2) phosphorylation of the alcohol function using 2-chloro-2-oxo-1,3,2-dioxaphospholane and (3) nucleophilic ring opening of the cyclic phosphate triester (IV) with anhydrous trimethylamine. The resulting isosteric amide analogs of glycol-lecithins have been isolated in high yields. The synthesis is illustrated by the preparation of the compounds containing palmitoyl, stearoyl and lauroyl fatty acid side-chains. The N-acylaminoethylphosphorylcholines have been shown to function as reversible phospholipase A2 inhibitors. They are likely to become a new series of useful substrate analogs and an attractive replacement for the n-alkylphosphorylcholines commonly used as single-chain-carrying phospholipase inhibitors.

Inhibition of lecithin:cholesterol acyltransferase in human plasma by dicarboxylic lecithins

The effect of dicarboxylic lecithins on the lecithin:cholesterol acyltransferase [LCAT] activity was studied with a partially purified preparation [approximately 24-fold]. The presence of dicarboxylic lecithins is followed by the inhibition of LCAT. The inhibition is proportional to the concentration of glutaryl-lecithin and is about 50% with 0.16 mM glutaryl-lecithin. For a higher concentration, the inhibition is total. The inhibition of LCAT activity was of a mixed type. It can be explained by a combination of competitive inhibition and interaction of glutaryl-lecithin with phospholipid, which changes the physical properties of lipid, making it less available for conversion into cholesteryl ester.