Sphingosylphosphorylcholine is a Melanogenic Stimulator for Human Melanocytes

As lysosphingolipids have multiple bio-modulator functions in various types of cells, we measured the biological effects of sphingosylphosphorylcholine (SPC) on cultured human melanocytes to determine whether these lysosphingolipids have the potential to activate these cells. The addition of SPC to cultured human melanocytes significantly stimulated DNA synthesis assessed by [3H]thymidine and melanogenesis assessed by the release of [3H]H2O (tyrosinase activity), the incorporation of [14C]thiouracil (melanin synthesis) and dopa-oxidase activity. Reverse transcription-polymerase chain reaction of RNA isolated from human melanocytes exposed to SPC revealed an upregulation of mRNA transcripts for tyrosinase, microphthalmia-associated transcription factor-M, endothelin B receptor and the stem cell factor receptor, c-kit. An increase in expression of tyrosinase and c-kit proteins was also demonstrated by Western blot analysis. This stimulation of melanogenesis by SPC was associated with a marked increase in the phosphorylation of extracellular signal-regulated kinase 1/2. These results suggest that SPC may be a melanogenic stimulator of human melanocytes inducing the coordinated upregulated expression of various melanogenic molecules, including c-kit.

Synthesis and antiproliferative activity of alkylphosphocholines

Alkylphosphocholines (APC) with one or more methylene groups in the alkyl chain replaced by oxygen atoms or carbonyl groups, or both have been assembled modularly using omega-diols as central building blocks. Out of 25 new compounds of this kind, 11 were evaluated for their antiproliferative activity on four cell lines and compared with miltefosine to evaluate their hemolytic activity (HA) and cytotoxicity on non-tumoral cells (MT2), used as markers of adverse effects. Compound 13 was more active on cancer cell lines than on non-tumoral cells and the data were similar for MTT and thymidine incorporation assays. It had less HA than miltefosine. Compound 13 could therefore be a candidate for the preparation of compounds with higher cytotoxicity on cancer cells and lower general toxicity.

Reactivation and aging kinetics of human acetylcholinesterase inhibited by organophosphonylcholines

A great number of structurally different organophosphorus compounds (OPs) was synthesized in the past decades to be used as pesticides or chemical warfare agents. Methyl-fluorophosphonylcholines were found to be highly toxic OPs and the acetylcholinesterase (AChE) reactivator pralidoxime was shown to be unable to reactivate inhibited AChE. In the course of the development of more effective AChE reactivators, we have determined the reactivation rate constants of various oximes with human AChE inhibited by methylfluorophosphonylcholine (MFPCh), methylfluoro-beta-phosphonylcholine (MFP beta Ch) and methylfluorophosphonylhomocholine (MFPhCh). In addition, we investigated the potential influence of aging phenomena on the oxime efficacy. Human AChE inhibited by MFPCh, MFP beta Ch or MFPhCh was extremely resistant towards reactivation by oximes. Nevertheless, the newer compounds, HLö 7 and HI 6, were substantially more potent reactivators than obidoxime and pralidoxime. The low oxime efficacy was not due to rapid aging since no decrease in reactivatability was found over 96 h at 37 degrees C. Within this period a substantial spontaneous reactivation was observed, with MFPCh >MFP beta Ch >MFPhCh, which did not follow pseudo-first-order kinetics. In conclusion, the unexpected results, i.e., high resistance of inhibited AChE towards oxime reactivation and aging, and much lower resistance towards spontaneous reactivation, calls for further experiments at a molecular level for a better understanding of the interactions among AChE, its inhibitors and reactivators.

Perifosine, a novel alkylphospholipid, inhibits protein kinase B activation

Perifosine is a novel p.o. bioavailable alkylphospholipid. Perifosine has displayed significant antiproliferative activity in vitro and in vivo in several human tumor model systems and has recently entered phase I clinical trials. Recent studies have identified that perifosine could cause cell cycle arrest with induction of p21(WAF1/CIP1) in a p53-independent fashion; however, the basis for that effect is not known. Structurally, perifosine resembles naturally occurring phospholipids. Therefore, we hypothesized that perifosine might perturb pathways related to phospholipids modulated by growth factor action. We demonstrate here that perifosine causes dose-dependent inhibition of protein kinase B/Akt phosphorylation and thus activation at concentrations causing growth inhibition of PC-3 prostate carcinoma cells. Only the myristoylated form of Akt (MYR-Akt), which bypasses the requirement for pleckstrin homology (PH) domain-mediated membrane recruitment, abrogated perifosine-mediated decrease of Akt phosphorylation and cell growth inhibition by perifosine. We demonstrate further that perifosine decreases the plasma membrane localization of Akt, and this is substantially relieved by MYR-Akt along with relief of downstream drug effect on induction of p21(WAF1/CIP1). Perifosine does not directly affect phosphoinositide 3-kinase (PI3K), phosphoinositide-dependent kinase 1, or Akt activity at concentrations inhibiting Akt phosphorylation and membrane localization. Our results demonstrate that Akt is an important cellular target of perifosine action. In addition, these studies show that the membrane translocation of certain PH domain-containing molecules can be greatly perturbed by the alkylphospholipid class of drugs and imply further that the PI3K/Akt pathway contributes to regulation of p21(WAF1/CIP1) expression.

Physiological coagulation can be maintained in extracorporeal circulation by means of shed blood separation and coating

OBJECTIVE

Conventional extracorporeal circulation results in an activation of coagulation cascades. Coating of extracorporeal circulation tubes as well as avoidance of shed blood recirculation have been shown to reduce these phenomena. We evaluated a new shed blood separation system (AVANT D 970) utilizing a coated cardiopulmonary bypass tube system (PHISIO).

METHODS

Forty patients (62 +/- 10 years) underwent isolated coronary revascularization. Four groups (n = 10/group) were defined: no extracorporeal circulation, conventional uncoated extracorporeal circulation, uncoated extracorporeal circulation with shed blood separation, and coated extracorporeal circulation with shed blood separation. Thrombin-antithrombin complex and free Hb were analyzed and statistically compared.

RESULTS

Conventional extracorporeal circulation exhibited the highest intraoperative activation of coagulation (thrombin-antithrombin complex: extracorporeal circulation, 31.1 +/- 15.8 microg/L; uncoated extracorporeal circulation with shed blood separation, 15.3 +/- 7.8 microg/L; coated extracorporeal circulation with shed blood separation, 8.1 +/- 4.8 microg/L; no extracorporeal circulation, 2.4 +/- 0.6 microg/L; P <.05 extracorporeal circulation vs all others) and red blood cell damage (free Hb: extracorporeal circulation, 16.8 +/- 11.4 micromol/L; uncoated extracorporeal circulation with shed blood separation, 10.3 +/- 3.5 micromol/L; coated extracorporeal circulation with shed blood separation, 6.8 +/- 2.9 micromol/L; no extracorporeal circulation, 3.4 +/- 1.1 micromol/L; P <.05 extracorporeal circulation vs no extracorporeal circulation, coated extracorporeal circulation with shed blood separation). Coated extracorporeal circulation with shed blood separation showed only slight activation and cell trauma, which did not differ significantly from no extracorporeal circulation.

CONCLUSIONS

Combination of coating and avoidance of shed blood recirculation maintained physiological coagulation levels and markedly reduced red blood cell trauma in extracorporeal circulation procedures. These combined modalities may therefore offer an alternative for off-pump procedures in patients with contraindications for conventional extracorporeal circulation.

Sphingosylphosphorylcholine regulates keratin network architecture and visco-elastic properties of human cancer cells

Sphingosylphosphorylcholine (SPC) is a naturally occurring bioactive lipid that is present in high density lipoproteins (HDL) particles and found at increased levels in blood and malignant ascites of patients with ovarian cancer. Here, we show that incubation of human epithelial tumour cells with SPC induces a perinuclear reorganization of intact keratin 8-18 filaments. This effect is specific for SPC, largely independent of F-actin and microtubules, and is accompanied by keratin phosphorylation. In vivo visco-elastic probing of single cancer cells demonstrates that SPC increases cellular elasticity. Accordingly, SPC stimulates migration of cells through size-limited pores in a more potent manner than lysophosphatidic acid (LPA). LPA induces actin stress fibre formation, but does not reorganize keratins in cancer cells and hence increases cellular stiffness. We propose that reorganization of keratin by SPC may facilitate biological phenomena that require a high degree of elasticity, such as squeezing of cells through membranous pores during metastasis.

Ligand-dependent inhibition of B16 melanoma cell migration and invasion via endogenous S1P2 G protein-coupled receptor. Requirement of inhibition of cellular RAC activity

We investigated mechanisms for inhibition of B16 melanoma cell migration and invasion by sphingosine-1-phosphate (S1P), which is the ligand for the Edg family G protein-coupled receptors and also implicated as an intracellular second messenger. S1P, dihydro-S1P, and sphingosylphosphorylcholine inhibited B16 cell migration and invasion with the relative potencies expected as S1P2 receptor agonists. The S1P2-selective antagonist JTE013 completely abolished the responses to these agonists. In addition, JTE013 abrogated the inhibition by sphingosine, which is the S1P precursor but not an agonist for S1P receptors, indicating that the sphingosine effects were mediated via S1P2 stimulation, most likely by S1P that was converted from sphingosine. S1P induced inhibition and activation, respectively, of Rac and RhoA in B16 cells, which were abrogated by JTE013. Adenovirus-mediated expression of N17Rac mimicked S1P inhibition of migration, whereas C3 toxin pretreatment, but not Rho kinase inhibitors, reversed the S1P inhibition. Overexpression of S1P2 sensitized, and that of either S1P1 or S1P3 desensitized, B16 cells to S1P inhibition of Rac and migration. In JTE013-pretreated, S1P3-overexpressing B16 cells, S1P stimulated cellular RhoA but failed to inhibit either Rac or migration, indicating that RhoA stimulation itself is not sufficient for inhibition of migration. These results provide compelling evidence that endogenously expressed S1P2 negatively regulates cell motility and invasion through ligand-dependent reciprocal regulation of cellular Rac and RhoA activities. In the presence of JTE013, S1P instead stimulated Rac and migration in B16 cells that overexpress either S1P1 or S1P3, unveiling counteractions between S1P2 and S1P1 or S1P3 chemotactic receptor.

Leishmania donovani resistance to miltefosine involves a defective inward translocation of the drug

Miltefosine (hexadecylphosphocholine [HePC]) is the first drug approved for the oral treatment of visceral leishmaniasis. As part of a study on the mechanisms of action of this drug and on the rates of resistance to this drug, we have been working in vitro with an Leishmania donovani line that was previously shown to be 15-fold more resistant to HePC. We have studied the accumulation of [(14)C]HePC by L. donovani promastigotes and have found a drastic reduction (>95%) in the ability of the resistant line to internalize the drug. Binding of HePC to the plasma membrane and drug efflux from preloaded cells were similar in both drug-sensitive and -resistant lines, and no [(14)C]HePC metabolism was evident in either line. Resistant parasites were also unable to take up other short-chain phospholipid analogs, independently of their polar head group, even though endocytosis remained unaltered. Finally, HePC uptake was temperature and energy dependent and sensitive to the thiol-reactive agent N-ethylmaleimide. We propose that inward translocation of a short-chain phospholipid across the plasma membrane may exist in Leishmania promastigotes and that such activity is defective in the resistant line.

Alkylphosphocholines inhibit proliferation of human retinal pigment epithelial cells

PURPOSE

To investigate the effect and mechanism of action of alkylphosphocholines (APCs) on proliferation of human retinal pigment epithelium (RPE) cells and RPE-mediated collagen matrix contraction in vitro.

METHODS

Cultured RPE cells of five human donors were treated with four APCs in the presence of fetal calf serum. Proliferation was assessed by the tetrazolium dye-reduction (MTT) assay and by counting the number of cells dividing in culture. The effect of APCs on RPE-mediated matrix contraction was determined in three-dimensional collagen gels. Cell viability was tested by the trypan blue exclusion assay. As a possible mechanism of APC action, protein kinase C (PKC) activity was quantified by scintillation counting of (32)P-labeled phosphate transferred to a PKC-specific substrate.

RESULTS

All APCs inhibited RPE proliferation and RPE-mediated collagen matrix contraction in a dose-dependent manner in vitro. The antiproliferative and anticontractile effect of APCs increased with elongation of the fatty acid chain beyond C20. IC(50)s of all APCs varied between 8.5 micro M (erucyl-phosphocholine, C22:1-PC), 9.0 micro M (Z)-12-heneicosenyl-phosphocholine, C21:1-PC), 11.0 micro M (Z)-10-eicosenyl-phosphocholine, C20:1-PC), and 26.5 micro M (oleyl-phosphocholine, C18:1-PC). Trypan blue staining revealed a toxicity below 5% for all APCs within the concentration interval tested. PKC activity was significantly reduced by all four APCs, with C22:1-PC being the most effective.

CONCLUSIONS

APCs inhibit proliferation of RPE cells and RPE-mediated matrix contraction in vitro at nontoxic concentrations. This effect seems to be exerted through inhibition of PKC activity. Therefore, APCs are promising candidates for treatment of RPE-mediated proliferative processes such as proliferative vitreoretinopathy.

Modulation of spontaneous transmitter release from the frog neuromuscular junction by interacting intracellular Ca(2+) stores: critical role for nicotinic acid-adenine dinucleotide phosphate (NAADP)

Nicotinic acid-adenine dinucleotide phosphate (NAADP) is a recently described potent intracellular Ca(2+)-mobilizing messenger active in a wide range of diverse cell types. In the present study, we have investigated the interaction of NAADP with other Ca(2+)-mobilizing messengers in the release of transmitter at the frog neuromuscular junction. We show, for the first time, that NAADP enhances neurosecretion in response to inositol 1,4,5-trisphosphate (IP(3)), cADP-ribose (cADPR) and sphingosine 1-phosphate (S1P), but not sphingosylphosphorylcholine. Thapsigargin was without effect on transmitter release in response to NAADP, but blocked the responses to subsequent application of IP(3), cADPR and S1P and their potentiation by NAADP. Asynchronous neurotransmitter release may therefore involve functional coupling of endoplasmic reticulum Ca(2+) stores with distinct Ca(2+) stores targeted by NAADP.

Cell adhesion behavior of chitosan surface modified by bonding 2-methacryloyloxyethyl phosphorylcholine

2-Methacryloyloxyethyl phosphorylcholine (MPC)-bonded chitosan was prepared by Michael addition of MPC to the amino groups of chitosan. The modified surfaces were characterized by static contact angle and electron spectroscopy for chemical analysis (ESCA). The water contact angle of chitosan decreased with the MPC bonding and the rate of decrease depended on the amount of MPC bonding. ESCA analysis results proved that MPC had been bonded on the chitosan surface and the chitosan modified directly by MPC had a much higher concentration of MPC on the surface compared with that of MPC on chitosan modified indirectly by MPC. Cell adhesion tests indicated that a low concentration of MPC bonded chitosan was more favorable to cell adhesion while a high concentration of MPC bonded chitosan inhibited cell attachment.

Extra- and intracellular sphingosylphosphorylcholine promote spontaneous transmitter release from frog motor nerve endings

Similar to phosphatidylinositol bisphosphate, sphingomyelin breakdown generates several lipids, including sphingosylphosphorylcholine (SPC), that are putative signaling molecules. The present study was undertaken to evaluate the involvement of SPC in transmitter release process. Intracellular recordings were made from isolated frog sciatic-sartorius nerve-muscle preparations, and the effects of SPC on neurosecretion in the form of miniature endplate potentials (MEPPs) were assessed. Extracellular application of SPC mixture (D,L-SPC) at 1, 10, and 25 microM increased the MEPP frequency by 68, 96, and 127%, respectively. D-erythro-SPC (dissolved in dimethyl sulfoxide but not coupled to bovine serum albumin), but not L-threo-SPC, was active extracellular; the former (at 10 microM) increased the MEPP frequency by 143%. D-erythro-SPC treatment did not significantly change the median amplitude or frequency-distribution of MEPPs. Intracellular delivery via liposomes, in which 10, 100, or 1000 microM SPC mixture was entrapped in liposomal aqueous phase, induced a concentration-dependent increase in MEPP frequency of 45, 91, and 100%, respectively. D-erythro-SPC and L-threo-SPC at the concentration of 100 microM increased the MEPP frequency by 117 and 67%, respectively, or 91 and 61%, respectively, when coupled to bovine serum albumin. Pretreatment with thapsigargin significantly reduced but did not abolish the effects of extracellular D-erythro-SPC (10 microM) or liposomes containing 100 microM D-erythro-SPC. Liposomes filled with 100 microM D-myo-inositol 1,4,5-trisphosphate (IP3) enhanced the MEPP frequency to the same magnitude as 100 microM D-erythro-SPC entrapped in liposomes. However, administration of 100 microM D-erythro-SPC and IP3 entrapped in the same liposomes enhanced the MEPP frequency by 70%, which was less than that produced by these two compounds alone. The result provides the first electrophysiological evidence that SPC can modulate transmitter release by an extra- or intracellular action at the frog motor nerve ending.

Reduced adhesion of blood cells to biodegradable polymers by introducing phosphorylcholine moieties

Aliphatic polyesters are believed to be good biocompatible polymers for tissue engineering because of their biodegradability and nontoxicity of the degradated products. However, it is necessary to reduce the nonspecific protein adsorption for the application of biodegradable polymers to drug delivery systems or antiadhesive membranes. We hypothesized that novel biodegradable polymers could be synthesized by introducing phosphorylcholine moieties into aliphatic polyesters. The L-lactide was polymerized in the presence of L-alpha-glycelophosphorylcholine (LGPC) using stannous octate as the catalyst. The molecular weight and crystallinity of poly(L-lactide) (PLLA)-based phospholipid polymers (PLLA-PC) decreased with an increase in the composition of the LGPC unit in the PLLA-PC. The hydrolysis of the PLLA-PC was evaluated by soaking the polymer membranes in a phosphate buffer solution. The rate of weight loss was increased with increasing the LGPC units in PLLA-PC. The surface analysis of the membranes using an X-ray photoelectron microscope showed the composition of phosphorylcoline groups on the surface. The amount of adsorbed protein and adherent blood cell on the polymer surface was decreased with introducing LGPC unit. PLLA-PC is a promising biodegradable polymer having blood compatibility and antiadhesive property.

Effects of detergents on the secondary structures of prion protein peptides as studied by CD spectroscopy

Pathogenic prion proteins (PrP(Sc)) are thought to be produced by alpha-helical to beta-sheet conformational changes in the normal cellular prion proteins (PrP(C)) located solely in the caveolar compartments. In order to inquire into the possible conformational changes due to the influences of hydrophobic environments within caveolae, the secondary structures of prion protein peptides were studied in various kinds of detergents by CD spectra. The peptides studied were PrP(129-154) and PrP(192-213); the former is supposed to assume beta-sheets and the latter alpha-helices, in PrP(Sc). The secondary structure analyses for the CD spectra revealed that in buffer solutions, both PrP(129-154) and PrP(192-213) mainly adopted random-coils (approximately 60%), followed by beta-sheets (30%-40%). PrP(129-154) showed no changes in the secondary structures even in various kinds of detergents such as octyl-beta-D-glucopyranoside (OG), octy-beta-D-maltopyranoside (OM). sodium dodecyl sulfate (SDS), Zwittergent 3-14 (ZW) and dodecylphosphocholine (DPC). In contrast, PrP(192-213) changed its secondary structure depending on the concentration of the detergents. SDS, ZW, OG and OM increased the alpha-helical content, and decreased the beta-sheet and random-coil contents. DPC also increased the alpha-helical content, but to a lesser extent than did SDS, ZW, OG or OM. These results indicate that PrP(129-154) has a propensity to adopt predominantly beta-sheets. On the other hand, PrP(192-213) has a rather fickle propensity and varies its secondary structure depending on the environmental conditions. It is considered that the hydrophobic environments provided by these detergents may mimic those provided by gangliosides in caveolae, the head groups of which consist of oligosaccharide chains containing sialic acids. It is concluded that PrP(C) could be converted into a nascent PrP(Sc) having a transient PrP(Sc) like structureunder the hydrophobic environments produced by gangliosides.

Phosphorylcholine and poly(D,L-lactic acid) containing copolymers as substrates for cell adhesion

Fibroblast cell culture was performed to evaluate cell adhesion and cell morphology on novel hydrolyzable copolymers composed of poly(D,L-lactic acid) (PDLA) macromonomer, 2-methacryloyloxyethyl phosphorylcholine (MPC), and n-butyl methacrylate. The copolymers were used as cell culture materials for regulating the interaction between the cells and the polymer surface. The results of X-ray photoelectron spectroscopy (XPS) confirmed that the PDLA chains and MPC units were present in the copolymer coating on PET films. Cell adhesion and morphology of adherent cells on coatings of the copolymers were studied. The number of cells on the surface increased with the PDLA content of the copolymer. As for the cell morphology, a round shape was observed on copolymers containing MPC units. These findings suggest that the cells recognize the PDLA and MPC units on the surface via changes in protein adsorption and/or conformation, and that the numbers of adhering cells and the cell morphology can be regulated by the composition of the copolymer.

[New drugs for treatment of parasitic infections]

In this review we have summarized published data on two new compounds, which can represent important antiparasitic drugs in the near future, nitazoxanide for treatment of intestinal parasitic infections including cryptosporidiosis and miltefosine for oral treatment of visceral leishmaniasis.

Ca2+ and voltage dependence of cardiac ryanodine receptor channel block by sphingosylphosphorylcholine

The effect of sphingosylphosphorylcholine (SPC) on the cytoplasmic Ca(2+) and voltage dependence of channel gating by cardiac ryanodine receptors (RyR) was examined in lipid bilayer experiments. Micromolar concentrations of the lysosphingolipid SPC added to cis solutions rapidly and reversibly decreased the single-channel open probability (P(o)) of reconstituted RyR channels. The SPC-induced decrease in P(o) was marked by an increase in mean closed time and burst-like channel gating. Gating kinetics during intraburst periods were unchanged from those observed in the absence of the sphingolipid, although SPC induced a long-lived closed state that appeared to explain the observed decrease in channel P(o). SPC effects were observed over a broad range of cis [Ca(2+)] but were not competitive with Ca(2+). Interestingly, the sphingolipid-induced, long-lived closed state displayed voltage-dependent kinetics, even though other channel gating kinetics were not sensitive to voltage. Assuming SPC effects represent channel blockade, these results suggest that the blocking rate is independent of voltage whereas the unblocking rate is voltage dependent. Together, these results suggest that SPC binds directly to the cytoplasmic side of the RyR protein in a location in or near the membrane dielectric, but distinct from cytoplasmic Ca(2+) binding sites on the protein.

Anti-cancer alkyl-lysophospholipids inhibit the phosphatidylinositol 3-kinase-Akt/PKB survival pathway

Synthetic alkyl-lysophospholipids (ALPs) represent a new class of anti-tumor agents that target cell membranes and induce apoptosis. However, the exact mechanisms by which ALPs exert these effects remain unclear. Here, we investigated in the epithelial carcinoma cell lines A431 and HeLa the effect of three clinically relevant ALPs [Et-18-OCH3 (Edelfosine), HePC (Miltefosine) and D-21266 (Perifosine)] on the phosphatidylinositol 3-kinase (PI3K)-Akt/PKB survival pathway. We found that growth factor-induced Akt/PKB activation in these cells is dependent on PI3K and that all three ALPs inhibited this pathway in a dose-dependent manner. We further showed that inhibition of the PI3K-Akt/PKB pathway by wortmannin or ALPs is associated with activation of the pro-apoptotic SAPK/JNK pathway. Inhibition of the PI3K-Akt/PKB survival pathway represents a novel mode of action of ALPs that may significantly contribute to the induction of apoptosis.

Role of phospholipase C-beta in the modulation of epithelial tight junction permeability

The results presented in this study establish an association between phospholipase C-beta (PLC-beta) and tight junction permeability across Madin-Darby canine kidney (MDCK) cell monolayers, an in vitro model for epithelial tissue. These results further show that PLC-beta modulates tight junction permeability by affecting actin filament organization. Hexadecylphosphocholine (HPC) inhibited PLC-beta and increased tight junction permeability in MDCK cells. Interestingly, the analogs of HPC, a series of alkylphosphocholines containing various lengths of linear alkyl chains, inhibited PLC-beta and increased tight junction permeability with a wide range of potency. The potency of alkylphosphocholines as enhancers of tight junction permeability significantly correlated (p < 0.05) with their potency as PLC-beta inhibitors. U73122, a steroid derivative that is structurally unrelated to alkylphosphocholines, inhibited PLC-beta and increased tight junction permeability with potencies that fit into the correlation observed for the alkylphosphocholine series. U73122 and HPC induced disorganization of actin filaments in MDCK cell monolayers. The potencies to cause disorganization of actin filaments were consistent with the potencies of these agents as inhibitors of PLC-beta and enhancers of tight junction permeability. Furthermore, ATP, an activator of PLC-beta, attenuated U73122-induced increase in tight junction permeability as well as disorganization of actin filaments. These results provide strong evidence that PLC-beta inhibition leads to increased tight junction permeability across MDCK cell monolayers through disorganization of actin filaments.

Sphingosylphosphorylcholine, a naturally occurring lipid mediator, inhibits human platelet function

1 The lysophospholipids, lysophosphatidic acid and sphingosine 1-phosphate, have been reported to activate platelets. Here we examined effects of the naturally occurring related sphingosylphosphorylcholine (SPC) on human platelet function. 2 Platelet activation was determined as aggregation, elevation of intracellular Ca(2+) concentrations, surface expression of P-selectin, GP 53, and GP IIb/IIIa neoepitope PAC-1, and of fibrinogen binding to the platelet surface. 3 Platelets were activated by ADP (5 and 20 micro M), the thrombin receptor-activating peptide TRAP-6 (5 and 20 micro M), the thromboxane A(2) mimetic U-46619 (1 micro M) and collagen (20 and 50 micro g ml(-1)) but not by SPC (up to 20 micro M). 4 SPC concentration-dependently (IC(50) approximately 1-10 micro M) inhibited activation of washed human platelets in response to all of the above agonists, with almost complete inhibition occurring at 20 micro M SPC. 5 The SPC stereoisomers, D-erythro SPC and L-threo SPC, exhibited similar concentration-response curves in inhibiting 20 micro M ADP-induced platelet aggregation, suggesting that SPC did not act via specific lysophospholipid receptors. 6 Although SPC slightly activated platelet protein kinase A (as assessed by VASP phosphorylation), this effect could not explain the marked platelet inhibition. Possible protein kinase C inhibition also did not explain the inhibition of platelet activation by SPC. On the other hand, SPC suppressed agonist-induced Ca(2+) mobilization and phospholipase C stimulation. 7 These results indicate that the lysophospholipid SPC is an effective inhibitor of human platelet activation, apparently primarily by uncoupling agonist-activated receptors from their effectors.

Antiprotozoal activities of phospholipid analogues

The antiprotozoal activity of phospholipid analogues, originally developed as anti-cancer drugs, has been determined in the past decade. The most susceptible parasites are Leishmania spp. and Trypanosoma cruzi with activity also shown against Trypanosoma brucei spp., Entamoeba histolytica and Acanthamoeba spp. Miltefosine, an alkylphosphocholine, was registered for the oral treatment of visceral leishmaniasis (VL) in India in March 2002. This review will focus on the biological activities of phospholipid analogues. Biochemical and molecular targets and mechanism(s) of action have been studied extensively in tumor cells but have not been determined in protozoa.

Role of the G-protein-coupled receptor GPR12 as high-affinity receptor for sphingosylphosphorylcholine and its expression and function in brain development

Lysophospholipids are bioactive molecules influencing numerous cellular processes such as proliferation, differentiation, and motility. As extracellular ligands, they interact with specific members of the G-protein-coupled receptor family. We show in this paper that the lysophospholipid sphingosylphosphorylcholine is a high-affinity ligand for the orphan G-protein-coupled receptor GPR12. Heterologous expression of GPR12 in Chinese hamster ovary cells and in frog oocytes revealed a high-affinity interaction with sphingosylphosphorylcholine in the nanomolar range. Blockade of its action by pertussis toxin was taken as evidence that GPR12 is coupled to an inhibitory G-protein. In the adult mouse brain, GPR12 was expressed in the limbic system. During mouse embryonal development, GPR12 transcripts were detected in the CNS, especially in areas where neuronal differentiation occurs. Consistent with this we found that cultures of embryonal cerebral cortical neurons responded to sphingosylphosphorylcholine with an increase in synaptic contacts. The GPR12-expressing hippocampal cell line HT22 reacted to sphingosylphophorylcholine with an increase in cell proliferation and cell clustering. Other receptors known to interact at nanomolar concentrations with sphingosylphosphorycholine were expressed neither in the developing cerebral cortex nor in the HT22 cell line. We therefore hypothesize that sphingosylphosphorylcholine, most likely by interaction with GPR12, has positive effects on the differentiation and maturation of postmitotic neurons and that it may also influence the proliferation of neuronal precursor cells.

Alkylphospholipids reversibly open epithelial tight junctions

Alkylphospholipids, such as the antitumor ether lipid 1-O-octadecyl-2-O-methylglycero-3-phosphocholine, modulate cancer cell invasion through changes in the adherens junction E-cadherin complex, a major organizer of epithelia. We wanted to know whether alkylphospholipids would also change tight junctions, molecular complexes that seal cell-to-cell contacts in polarised epithelia. Therefore, human colorectal cancer cell layers T84 were established in two-compartment culture chambers and the functional integrity of tight junctions was evaluated through their transepithelial electrical resistance. Incorporation of alkylphospholipids causes a rapid and reversible decrease of transepithelial electrical resistance. This decrease is due to an increased paracellular permeability and is temperature-independent. Unlike methyl-beta-cyclodextrin, alkyl-phospholipids do not specifically displace lipids from raft-like membrane domains. Nevertheless, alkylphospholipids change the detergent-solubility of zonula occludens-protein and occludin. Our data, together with the literature, indicate that non-toxic doses of alkylphospholipids affect more than one cell-cell adhesion complex, probably through their incorporation into the plasma membrane lipid bilayer.

Sphingosylphosphorylcholine stimulates cellular fibronectin expression through upregulation of IL-6 in cultured human dermal fibroblasts

Sphingosylphosphorylcholine (SPC) has been reported to stimulate wound healing by its potent mitogenic effect. Fibronectin (FN) is a cell-adhesion protein that plays an important role in cell migration and collagen deposition during wound healing. In order to elucidate further the mechanism involved in the accelerated wound healing stimulated by SPC, we studied the role of SPC in FN production in cultured human dermal fibroblasts. We demonstrated that SPC dose- and time-dependently enhanced the expression of FN in human dermal fibroblast at the protein and mRNA levels. IL-6 is known to stimulate the production of FN in fibroblasts. SPC also markedly induced IL-6 production in cultured human dermal fibroblasts in a dose- and time-dependent manner. We also demonstrated that FN mRNA expression in human dermal fibroblasts was upregulated 4 h after IL-6 treatment. Moreover, pretreatment with neutralizing anti-IL-6 antibodies partially blocked the upregulation of FN mRNA expression induced by SPC in human dermal fibroblasts. These results indicate that SPC may stimulate FN synthesis through IL-6 production in cultured human dermal fibroblasts.

Eicosanoids in insect immunity: bacterial infection stimulates hemocytic phospholipase A2 activity in tobacco hornworms

Intracellular phospholipase A(2) (PLA(2)) is responsible for releasing arachidonic acid from cellular phospholipids, and is thought to be the first step in eicosanoid biosynthesis. Intracellular PLA(2)s have been characterized in fat body and hemocytes from tobacco hornworms, Manduca sexta. Here we show that bacterial challenge stimulated increased PLA(2) activity in isolated hemocyte preparations, relative to control hemocyte preparations that were challenged with water. The increased activity was detected as early as 15 s post-challenge and lasted for at least 1 h. The increased activity depended on a minimum bacterial challenge dose, and was inhibited in reactions conducted in the presence of oleyoxyethylphosphorylcholine, a site-specific PLA(2) inhibitor. In independent experiments with serum prepared from whole hemolymph, we found no PLA(2) activity was secreted into serum during the first 24 h following bacterial infection. We infer that a hemocytic intracellular PLA(2) activity is increased immediately an infection is detected. The significance of this enzyme lies in its role in launching the biosynthesis of eicosanoids, which mediate cellular immune reactions to bacterial infection.