Cyclic phosphatidic acid is produced by autotaxin in blood

Association between plasma lysophosphatidic acid levels and bronchopulmonary dysplasia in extremely preterm infants: A prospective study

BACKGROUND

Lysophosphatidic acid (LPA) is implicated in bronchopulmonary dysplasia (BPD) pathogenesis, but clinical evidence is lacking. This study aimed to investigate LPA levels in preterm infants with and without BPD and explore LPA as a biomarker for predicting BPD occurrence.

METHODS

Premature infants with a gestational age of <28 weeks or a birth weight of <1000 g were enrolled. Blood samples were collected at postnatal day (PD) 7, 28, and postmenstrual age (PMA) 36 weeks, and plasma LPA levels were measured using a commercial ELISA kit. Receiver operating characteristic curve (ROC) curve analysis determined the PD 28 cutoff for LPA, and multivariable regression analyzed LPA's independent contribution to BPD and exploratory outcomes.

RESULT

Among the 91 infants enrolled in this study, 35 were classified into the non-BPD group and 56 into the BPD group. Infants with BPD had higher plasma LPA levels at PD 28 (6.467 vs. 4.226 μg/mL, p = 0.034) and PMA 36 weeks (2.330 vs. 1.636 μg/mL, p = 0.001). PD 28 LPA level of 6.132 μg/mL was the cutoff for predicting BPD development. Higher PD 28 LPA levels (≥6.132 μg/mL) independently associated with BPD occurrence (OR 3.307, 95% CI 1.032-10.597, p = 0.044). Higher LPA levels correlated with longer oxygen therapy durations [regression coefficients (β) 0.147, 95% CI 0.643-16.133, p = .034].

CONCLUSIONS

Infants with BPD had higher plasma LPA levels at PD 28 and PMA 36 weeks. Higher PD 28 LPA levels independently associated with an increased BPD risk.

A Review of Cyclic Phosphatidic Acid and Other Potential Therapeutic Targets for Treating Osteoarthritis

Osteoarthritis (OA), a chronic degenerative joint disease, is the most common form of arthritis. OA occurs when the protective cartilage that cushions the ends of bones gradually breaks down. This leads to the rubbing of bones against each other, resulting in pain and stiffness. Cyclic phosphatidic acid (cPA) shows promise as a treatment for OA. In this article, we review the most recent findings regarding the biological functions of cPA signaling in mammalian systems, specifically in relation to OA. cPA is a naturally occurring phospholipid mediator with unique cyclic phosphate rings at the sn-2 and sn-3 positions in the glycerol backbone. cPA promotes various responses, including cell proliferation, migration, and survival. cPA possesses physiological activities that are distinct from those elicited by lysophosphatidic acid; however, its biochemical origin has rarely been studied. Although there is currently no cure for OA, advances in medical research may lead to new therapies or strategies in the future, and cPA has potential therapeutic applications.

GDE7 produces cyclic phosphatidic acid in the ER lumen functioning as a lysophospholipid mediator

Cyclic phosphatidic acid (cPA) is a lipid mediator, which regulates adipogenic differentiation and glucose homeostasis by suppressing nuclear peroxisome proliferator-activated receptor γ (PPARγ). Glycerophosphodiesterase 7 (GDE7) is a Ca2+-dependent lysophospholipase D that localizes in the endoplasmic reticulum. Although mouse GDE7 catalyzes cPA production in a cell-free system, it is unknown whether GDE7 generates cPA in living cells. Here, we demonstrate that human GDE7 possesses cPA-producing activity in living cells as well as in a cell-free system. Furthermore, the active site of human GDE7 is directed towards the luminal side of the endoplasmic reticulum. Mutagenesis revealed that amino acid residues F227 and Y238 are important for catalytic activity. GDE7 suppresses the PPARγ pathway in human mammary MCF-7 and mouse preadipocyte 3T3-L1 cells, suggesting that cPA functions as an intracellular lipid mediator. These findings lead to a better understanding of the biological role of GDE7 and its product, cPA.

Astrocytic Neuroimmunological Roles Interacting with Microglial Cells in Neurodegenerative Diseases

Both astrocytic and microglial functions have been extensively investigated in healthy subjects and neurodegenerative diseases. For astrocytes, not only various sub-types were identified but phagocytic activity was also clarified recently and is making dramatic progress. In this review paper, we mostly focus on the functional role of astrocytes in the extracellular matrix and on interactions between reactive astrocytes and reactive microglia in normal states and in neurodegenerative diseases, because the authors feel it is necessary to elucidate the mechanisms among activated glial cells in the pathology of neurological diseases in order to pave the way for drug discovery. Finally, we will review cyclic phosphatidic acid (cPA), a naturally occurring phospholipid mediator that induces a variety of biological activities in the brain both in vivo and in vitro. We propose that cPA may serve as a novel therapeutic molecule for the treatment of brain injury and neuroinflammation.

Lysophosphatidylcholine: Potential Target for the Treatment of Chronic Pain

The bioactive lipid lysophosphatidylcholine (LPC), a major phospholipid component of oxidized low-density lipoprotein (Ox-LDL), originates from the cleavage of phosphatidylcholine by phospholipase A2 (PLA2) and is catabolized to other substances by different enzymatic pathways. LPC exerts pleiotropic effects mediated by its receptors, G protein-coupled signaling receptors, Toll-like receptors, and ion channels to activate several second messengers. Lysophosphatidylcholine (LPC) is increasingly considered a key marker/factor positively in pathological states, especially inflammation and atherosclerosis development. Current studies have indicated that the injury of nervous tissues promotes oxidative stress and lipid peroxidation, as well as excessive accumulation of LPC, enhancing the membrane hyperexcitability to induce chronic pain, which may be recognized as one of the hallmarks of chronic pain. However, findings from lipidomic studies of LPC have been lacking in the context of chronic pain. In this review, we focus in some detail on LPC sources, biochemical pathways, and the signal-transduction system. Moreover, we outline the detection methods of LPC for accurate analysis of each individual LPC species and reveal the pathophysiological implication of LPC in chronic pain, which makes it an interesting target for biomarkers and the development of medicine regarding chronic pain.

Characterization of recombinant murine GDE4 and GDE7, enzymes producing lysophosphatidic acid and/or cyclic phosphatidic acid

GDE4 and GDE7 are membrane-bound enzymes that exhibit lysophospholipase D (lysoPLD) activities. We found that GDE7 produced not only lysophosphatidic acid (LPA) but also cyclic phosphatidic acid (cPA) from lysophospholipids by a transphosphatidylation reaction. In contrast, GDE4 produced only LPA. The analysis of substrate specificity showed that 1-alkyl-lysophosphospholipids were preferred substrates for both enzymes rather than 1-alkyl-lysophospholipids and 1-alkenyl-lysophospholipids. Among the various lysophospholipids with different polar head groups that were tested, lysophosphatidylglycerol and lysophosphatidylserine were preferred substrates for GDE4 and GDE7, respectively. The detailed analysis of the dependency of the enzyme activities of GDE4 and GDE7 on divalent cations suggested multiple divalent cations were bound in the active sites of both enzymes. Taken together, these results suggest the possibility that GDE7 functions as a cPA-producing enzyme in the body.

2-Carba-lysophosphatidic acid is a novel β-lysophosphatidic acid analogue with high potential for lysophosphatidic acid receptor activation and autotaxin inhibition

Cyclic phosphatidic acid (cPA) is a naturally occurring phospholipid mediator that, along with its chemically stabilized analogue 2-carba-cyclic phosphatidic acid (2ccPA), induces various biological activities in vitro and in vivo. Although cPA is similar to lysophosphatidic acid (LPA) in structure and synthetic pathway, some of cPA biological functions apparently differ from those reported for LPA. We previously investigated the pharmacokinetic profile of 2ccPA, which was found to be rapidly degraded, especially in acidic conditions, yielding an unidentified compound. Thus, not only cPA but also its degradation compound may contribute to the biological activity of cPA, at least for 2ccPA. In this study, we determined the structure and examined the biological activities of 2-carba-lysophosphatidic acid (2carbaLPA) as a 2ccPA degradation compound, which is a type of β-LPA analogue. Similar to LPA and cPA, 2carbaLPA induced the phosphorylation of the extracellular signal-regulated kinase and showed potent agonism for all known LPA receptors (LPA_1–6) in the transforming growth factor-α (TGFα) shedding assay, in particular for LPA₃ and LPA₄. 2carbaLPA inhibited the lysophospholipase D activity of autotaxin (ATX) in vitro similar to other cPA analogues, such as 2ccPA, 3-carba-cPA, and 3-carba-LPA (α-LPA analogue). Our study shows that 2carbaLPA is a novel β-LPA analogue with high potential for the activation of some LPA receptors and ATX inhibition.

Evaluation of the pharmacokinetics of 2-carba-cyclic phosphatidic acid by liquid chromatography-triple quadrupole mass spectrometry

Cyclic phosphatidic acid (cPA) is a lysophospholipid mediator that suppresses cancer metastasis and osteoarthritis. It also has neuroprotective roles in diseases such as multiple sclerosis and delayed neuronal death following transient ischemia. In order to take advantage of the properties of cPA for the development of new therapeutic strategies, we have synthesized several cPA derivatives and discovered 2-carba-cPA (2ccPA) as a promising candidate. To develop 2ccPA as a therapeutic agent, we investigated the pharmacokinetic profile of 2ccPA by liquid chromatography-triple quadrupole mass spectrometry in this study. When 2ccPA was administered intraperitoneally to mice at a dose of 1.6 mg/kg, the half-life of 2ccPA in plasma was 16 min. The 2ccPA, dosed intraperitoneally to mice at 16 mg/kg, distributed to each organ including brain at 20 min after dosing. It was found that 2ccPA was stable in neutral or alkaline conditions (e.g., intestine) but unstable in acidic conditions (e.g., stomach). When 2ccPA was orally administrated to rats as a gastro-resistant form using an enterosoluble capsule, plasma 2ccPA levels peaked at 2 h, slowly declined thereafter and persistently detected even at 10 h after administration. Here, we present the findings on the effect of the continuous release of 2ccPA from the capsule to reduce the lysophospholipase D activity and also decrease plasma levels of lysophosphatidic acid in rat. These findings will be useful in further studies for evaluating the application of 2ccPA in several disorders.

2-carba cyclic phosphatidic acid suppresses inflammation via regulation of microglial polarisation in the stab-wounded mouse cerebral cortex

Traumatic brain injury (TBI) is caused by physical damage to the brain and it induces blood-brain barrier (BBB) breakdown and inflammation. To diminish the sequelae of TBI, it is important to decrease haemorrhage and alleviate inflammation. In this study, we aimed to determine the effects of 2-carba-cyclic phosphatidic acid (2ccPA) on the repair mechanisms after a stab wound injury as a murine TBI model. The administration of 2ccPA suppressed serum immunoglobulin extravasation after the injury. To elucidate the effects of 2ccPA on inflammation resulting from TBI, we analysed the mRNA expression of inflammatory cytokines. We found that 2ccPA prevents a TBI-induced increase in the mRNA expression of Il-1β, Il-6, Tnf-α and Tgf-β1. In addition, 2ccPA reduces the elevation of Iba1 levels. These data suggest that 2ccPA attenuates the inflammation after a stab wound injury via the modulation of pro-inflammatory cytokines release from microglial cells. Therefore, we focused on the function of 2ccPA in microglial polarisation towards M1 or M2 phenotypes. The administration of 2ccPA decreased the number of M1 and increased the number of M2 type microglial cells, indicating that 2ccPA modulates the microglial polarisation and shifts them towards M2 phenotype. These data suggest that 2ccPA treatment suppresses the extent of BBB breakdown and inflammation after TBI.

Quantitative determination of cyclic phosphatidic acid and its carba analog in mouse organs and plasma using LC-MS/MS

Cyclic phosphatidic acid (cPA), an analog of lysophosphatidic acid, is involved in the regulation of many cellular processes. A sensitive and specific method to quantify the molecular species of cPA is important for studying the physiological and pathophysiological roles of cPA. Here, we developed a liquid chromatography-tandem mass spectrometry (LC-MS/MS)-based quantification method for the simultaneous detection of cPA species having various fatty acids (16:0, 18:0, 18:1, and 18:2) as well as 2-carba-cPA, a chemically synthesized analog of cPA. Chromatography was performed using a reversed-phase C18 column. cPA species were detected using a triple quadrupole mass spectrometer. cPA 17:0 was used as an internal standard. Intra- and interday precision values (CV%) were within 10%. The linear range of detection for each cPA species was 0.01 μg/mL to 5 μg/mL, with correlation coefficients of 0.998 or higher. The developed method was applied to the quantification of cPA species in mouse plasma and organs. The concentrations of cPA 16:0, 18:0, and 18:1 were revealed to be significantly reduced in the brains of cuprizone-treated mice, a model of multiple sclerosis, compared with control mice. These findings could be important for understanding the roles of cPA in the neurodegenerative processes associated with multiple sclerosis.

2-O-Carba-oleoyl cyclic phosphatidic acid induces glial proliferation through the activation of lysophosphatidic acid receptor

Lysophosphatidic acid (LPA) and cyclic phosphatidic acid (cPA) are one of the lipid mediators regulating cell proliferation and differentiation through the activation of LPA receptors. An LPA receptor-mediated signal is important for the development of the central nervous system, while it has been demonstrated that LPA caused microglial activation and astroglial dysfunction. Previously, we have reported that cPA and carba analog of cPA, 2-O-carba-cPA (2ccPA), protected neural damage caused by transient ischemia. However, little is known about the target cell of cPA/2ccPA in the central nervous systems. Here, we examined the effect of 2ccPA on glial proliferation and differentiation using the primary astrocytes and oligodendrocyte precursor cells (OPCs) cultures. 2ccPA increased the DNA synthesis of astrocytes and OPCs, but it did not reduce the formazan production in the mitochondria. Further, 2ccPA increased the cell number and cell survival against oxidative stress. The inhibition of LPA receptors by ki16425 abolished 2ccPA-induced DNA synthesis. Extracellular signal-regulated kinase (ERK) was activated by 2ccPA, which contributed to the astroglial DNA synthesis. These results suggest that 2ccPA is a beneficial regulator of glial population through the activation of LPA receptor without reduction of mitochondrial activity.

Autotaxin, Pruritus and Primary Biliary Cholangitis (PBC)

Autotaxin (ATX) is a 125-kD type II ectonucleotide pyrophosphatase/phosphodiesterase (ENPP2 or NPP2) originally discovered as an unknown "autocrine motility factor" in human melanoma cells. In addition to its pyrophosphatase/phosphodiesterase activities ATX has lysophospholipase D (lysoPLD) activity, catalyzing the conversion of lysophosphatidylcholine (LPC) into lysophosphatidic acid (LPA). ATX is the only ENPP family member with lysoPLD activity and it produces most of the LPA in circulation. In support of this, ATX heterozygous mice have 50% of normal LPA plasma levels. The ATX-LPA signaling axis plays an important role in both normal physiology and disease pathogenesis and recently has been linked to pruritus in chronic cholestatic liver diseases, including primary biliary cholangitis (PBC). Several lines of evidence have suggested that a circulating puritogen is responsible, but the identification of the molecule has yet to be definitively identified. In contrast, plasma ATX activity is strongly associated with pruritus in PBC, suggesting a targetable molecule for treatment. We review herein the biochemistry of ATX and the rationale for its role in pruritus.

Cyclic phosphatidic acid treatment suppress cuprizone-induced demyelination and motor dysfunction in mice

Multiple sclerosis is a chronic demyelinating disease of the central nervous system leading to progressive cognitive and motor dysfunction, which is characterized by neuroinflammation, demyelination, astrogliosis, loss of oligodendrocytes, and axonal pathologies. Cyclic phosphatidic acid (cPA) is a naturally occurring phospholipid mediator with a unique cyclic phosphate ring structure at the sn-2 and sn-3 positions of the glycerol backbone. cPA elicits a neurotrophin-like action and protects hippocampal neurons from ischemia-induced delayed neuronal death. In this study, we investigated the effects of cPA on cuprizone-induced demyelination, which is a model of multiple sclerosis. Mice were fed a diet containing 0.2% cuprizone for 5 weeks, which induces severe demyelination, astrocyte and microglial activation, and motor dysfunction. Simultaneous administration of cPA effectively attenuated cuprizone-induced demyelination, glial activation, and motor dysfunction. These data indicate that cPA may be a useful treatment to reduce the extent of demyelination and the severity of motor dysfunction in multiple sclerosis. cPA is a potential lead compound in the development of drugs for the treatment of this devastating disease.

Phospholipase D toxins of brown spider venom convert lysophosphatidylcholine and sphingomyelin to cyclic phosphates

Venoms of brown spiders in the genus Loxosceles contain phospholipase D enzyme toxins that can cause severe dermonecrosis and even death in humans. These toxins cleave the substrates sphingomyelin and lysophosphatidylcholine in mammalian tissues, releasing the choline head group. The other products of substrate cleavage have previously been reported to be monoester phospholipids, which would result from substrate hydrolysis. Using (31)P NMR and mass spectrometry we demonstrate that recombinant toxins, as well as whole venoms from diverse Loxosceles species, exclusively catalyze transphosphatidylation rather than hydrolysis, forming cyclic phosphate products from both major substrates. Cyclic phosphates have vastly different biological properties from their monoester counterparts, and they may be relevant to the pathology of brown spider envenomation.

The role of phosphatidylcholine and choline metabolites to cell proliferation and survival

The reorganization of metabolic pathways in cancer facilitates the flux of carbon and reducing equivalents into anabolic pathways at the expense of oxidative phosphorylation. This provides rapidly dividing cells with the necessary precursors for membrane, protein and nucleic acid synthesis. A fundamental metabolic perturbation in cancer is the enhanced synthesis of fatty acids by channeling glucose and/or glutamine into cytosolic acetyl-CoA and upregulation of key biosynthetic genes. This lipogenic phenotype also extends to the production of complex lipids involved in membrane synthesis and lipid-based signaling. Cancer cells display sensitivity to ablation of fatty acid synthesis possibly as a result of diminished capacity to synthesize complex lipids involved in signaling or growth pathways. Evidence has accrued that phosphatidylcholine, the major phospholipid component of eukaryotic membranes, as well as choline metabolites derived from its synthesis and catabolism, contribute to both proliferative growth and programmed cell death. This review will detail our current understanding of how coordinated changes in substrate availability, gene expression and enzyme activity lead to altered phosphatidylcholine synthesis in cancer, and how these changes contribute directly or indirectly to malignant growth. Conversely, apoptosis targets key steps in phosphatidylcholine synthesis and degradation that are linked to disruption of cell cycle regulation, reinforcing the central role that phosphatidylcholine and its metabolites in determining cell fate.

Lysophosphatidic acid in atherosclerotic diseases

Lysophosphatidic acid (LPA) is a potent bioactive phospholipid. As many other biological active lipids, LPA is an autacoid: it is formed locally on demand, and it acts locally near its site of synthesis. LPA has a plethora of biological activities on blood cells (platelets, monocytes) and cells of the vessel wall (endothelial cells, smooth muscle cells, macrophages) that are all key players in atherosclerotic and atherothrombotic processes. The specific cellular actions of LPA are determined by its multifaceted molecular structures, the expression of multiple G-protein coupled LPA receptors at the cell surface and their diverse coupling to intracellular signalling pathways. Numerous studies have now shown that LPA has thrombogenic and atherogenic actions. Here, we aim to provide a comprehensive, yet concise, thoughtful and critical review of this exciting research area and to pinpoint potential pharmacological targets for inhibiting thrombogenic and atherogenic activities of LPA. We hope that the review will serve to accelerate knowledge of basic and clinical science, and to foster drug development in the field of LPA and atherosclerotic/atherothrombotic diseases.

Decrease in circulating autotaxin by oral administration of prednisolone

BACKGROUND

Autotaxin (ATX), secreted mainly from adipose tissue, functions as a lysophospholipase D (lysoPLD) to hydrolyze lysophosphatidylcholine (LPC) into lysophosphatidic acid (LPA). ATX-LPA signaling is implicated in a wide range of physiological and pathophysiological processes including immune response.

METHODS

The present study measured serum ATX antigen levels in patients with various autoimmune diseases using a recently developed automated enzyme immunoassay. In addition, serum lysoPLD activity was assessed by measuring choline liberation from the substrate LPC. Moreover, the effect of prednisolone (PSL) on mRNA expression of ATX was evaluated using cultured adipose tissue from mice.

RESULTS

Decreased serum ATX antigen levels were observed after the initiation of treatment with PSL. The decreased levels recovered during tapering of PSL dose in a dose-dependent manner without exacerbation of disease activity. Moreover, decreased ATX mRNA expression in PSL-treated cultured murine adipose tissue suggested that the effect of PSL on serum ATX may have resulted from changes in adipose tissue ATX expression.

CONCLUSIONS

Our results suggest that measurement of serum ATX antigen level may be clinically useful for the assessment of steroid treatment effect and drug compliance with steroids. Furthermore, our findings provide many novel insights into the biosynthesis, physiological functions, pathological roles, and clinical significance of circulating ATX.

Cellular function and molecular structure of ecto-nucleotidases

Ecto-nucleotidases play a pivotal role in purinergic signal transmission. They hydrolyze extracellular nucleotides and thus can control their availability at purinergic P2 receptors. They generate extracellular nucleosides for cellular reuptake and salvage via nucleoside transporters of the plasma membrane. The extracellular adenosine formed acts as an agonist of purinergic P1 receptors. They also can produce and hydrolyze extracellular inorganic pyrophosphate that is of major relevance in the control of bone mineralization. This review discusses and compares four major groups of ecto-nucleotidases: the ecto-nucleoside triphosphate diphosphohydrolases, ecto-5'-nucleotidase, ecto-nucleotide pyrophosphatase/phosphodiesterases, and alkaline phosphatases. Only recently and based on crystal structures, detailed information regarding the spatial structures and catalytic mechanisms has become available for members of these four ecto-nucleotidase families. This permits detailed predictions of their catalytic mechanisms and a comparison between the individual enzyme groups. The review focuses on the principal biochemical, cell biological, catalytic, and structural properties of the enzymes and provides brief reference to tissue distribution, and physiological and pathophysiological functions.

The chemical synthesis of metabolically stabilized 2-OMe-LPA analogues and preliminary studies of their inhibitory activity toward autotaxin

The chemical synthesis of five new metabolically stabilized 2-OMe-LPA analogues (1a-e) possessing different fatty acid residues has been performed by phosphorylation of corresponding 1-O-acyl-2-OMe-glycerols which were prepared by multistep process from racemic glycidol. The now analogues were subjected to biological characterization as autotaxin inhibitors using the FRET-based, synthetic ATX substrate FS-3. Among tested compounds 1-O-oleoyl-2-OMe-LPA (1e) appeared to be the most potent, showing ATX inhibitory activity similar to that of unmodified 1-O-oleoyl-LPA. Parallel testing showed, that similar trend was also observed for corresponding 1-O-acyl-2-OMe-phosphorothioates (2a-e, synthesized as described by us previously). 1-O-oleoyl-2-OMe-LPA (1e) was found to be resistant toward alkaline phosphatase as opposed to unmodified 1-O-oleoyl-LPA.

Lysophosphatidic acids are new substrates for the phosphatase domain of soluble epoxide hydrolase

Soluble epoxide hydrolase (sEH) is a bifunctional enzyme that has a C-terminus epoxide hydrolase domain and an N-terminus phosphatase domain. The endogenous substrates of epoxide hydrolase are known to be epoxyeicosatrienoic acids, but the endogenous substrates of the phosphatase activity are not well understood. In this study, to explore the substrates of sEH, we investigated the inhibition of the phosphatase activity of sEH toward 4-methylumbelliferyl phosphate by using lecithin and its hydrolyzed products. Although lecithin itself did not inhibit the phosphatase activity, the hydrolyzed lecithin significantly inhibited it, suggesting that lysophospholipid or fatty acid can inhibit it. Next, we investigated the inhibition of phosphatase activity by lysophosphatidyl choline, palmitoyl lysophosphatidic acid, monopalmitoyl glycerol, and palmitic acid. Palmitoyl lysophosphatidic acid and fatty acid efficiently inhibited phosphatase activity, suggesting that lysophosphatidic acids (LPAs) are substrates for the phosphatase activity of sEH. As expected, palmitoyl, stearoyl, oleoyl, and arachidonoyl LPAs were efficiently dephosphorylated by sEH (Km, 3-7 μM; Vmax, 150-193 nmol/min/mg). These results suggest that LPAs are substrates of sEH, which may regulate physiological functions of cells via their metabolism.

Identification and biochemical characterization of a novel autotaxin isoform, ATXδ, with a four-amino acid deletion

Autotaxin (ATX) is lysophospholipase D, which converts lysophospholipids such as lysophosphatidylcholine (LPC) to lysophosphatidic acid (LPA), a bioactive lipid mediator with multiple biological roles. ATX is present in high concentrations in various biological fluids and is responsible for LPA production in these fluids. The plasma ATX level is altered in some patho-physiological conditions. Three splicing isoforms of ATX have been reported so far (ATXα, β and γ). In this study, we identified and characterized ATXδ, a novel alternative splice variant of ATX, which has a four-amino acid deletion in the L2 linker region of ATXβ. ATXδ was found to be the second major isoform following ATXβ and fully active. ATXβ and ATXδ showed similar divalent cation sensitivity and cell motility-stimulating activity. ATXβ and ATXδ are present in wide range of organism from fish to mammals. Among them, only ATXδ was found in Gallus gallus and Xenopus laevis, suggesting the indispensable role of the isoform. ATXδ was expressed in various human tissues with different expression patterns from that of ATXβ. These results show that ATXδ is a second major ATX isoform sharing similar biochemical characters with the major isoform, ATXβ, and is a potential biomarker.

Autotaxin regulates vascular development via multiple lysophosphatidic acid (LPA) receptors in zebrafish

Autotaxin (ATX) is a multifunctional ecto-type phosphodiesterase that converts lysophospholipids, such as lysophosphatidylcholine, to lysophosphatidic acid (LPA) by its lysophospholipase D activity. LPA is a lipid mediator with diverse biological functions, most of which are mediated by G protein-coupled receptors specific to LPA (LPA1-6). Recent studies on ATX knock-out mice revealed that ATX has an essential role in embryonic blood vessel formation. However, the underlying molecular mechanisms remain to be solved. A data base search revealed that ATX and LPA receptors are conserved in wide range of vertebrates from fishes to mammals. Here we analyzed zebrafish ATX (zATX) and LPA receptors both biochemically and functionally. zATX, like mammalian ATX, showed lysophospholipase D activity to produce LPA. In addition, all zebrafish LPA receptors except for LPA5a and LPA5b were found to respond to LPA. Knockdown of zATX in zebrafish embryos by injecting morpholino antisense oligonucleotides (MOs) specific to zATX caused abnormal blood vessel formation, which has not been observed in other morphant embryos or mutants with vascular defects reported previously. In ATX morphant embryos, the segmental arteries sprouted normally from the dorsal aorta but stalled in midcourse, resulting in aberrant vascular connection around the horizontal myoseptum. Similar vascular defects were not observed in embryos in which each single LPA receptor was attenuated by using MOs. Interestingly, similar vascular defects were observed when both LPA1 and LPA4 functions were attenuated by using MOs and/or a selective LPA receptor antagonist, Ki16425. These results demonstrate that the ATX-LPA-LPAR axis is a critical regulator of embryonic vascular development that is conserved in vertebrates.

Benzyl and naphthalene methylphosphonic acid inhibitors of autotaxin with anti-invasive and anti-metastatic activity

Autotaxin (ATX, NPP2) is a member of the nucleotide pyrophosphate phosphodiesterase enzyme family. ATX catalyzes the hydrolytic cleavage of lysophosphatidylcholine (LPC) by lysophospholipase D activity, which leads to generation of the growth-factor-like lipid mediator lysophosphatidic acid (LPA). ATX is highly upregulated in metastatic and chemotherapy-resistant carcinomas and represents a potential target to mediate cancer invasion and metastasis. Herein we report the synthesis and pharmacological characterization of ATX inhibitors based on the 4-tetradecanoylaminobenzylphosphonic acid scaffold, which was previously found to lack sufficient stability in cellular systems. The new 4-substituted benzylphosphonic acid and 6-substituted naphthalen-2-ylmethylphosphonic acid analogues block ATX activity with K(i) values in the low micromolar to nanomolar range against FS3, LPC, and nucleotide substrates through a mixed-mode inhibition mechanism. None of the compounds tested inhibit the activity of related enzymes (NPP6 and NPP7). In addition, the compounds were evaluated as agonists or antagonists of seven LPA receptor (LPAR) subtypes. Analogues 22 and 30 b, the two most potent ATX inhibitors, inhibit the invasion of MM1 hepatoma cells across murine mesothelial and human vascular endothelial monolayers in vitro in a dose-dependent manner. The average terminal half-life for compound 22 is 10±5.4 h and it causes a long-lasting decrease in plasma LPA levels. Compounds 22 and 30 b significantly decrease lung metastasis of B16-F10 syngeneic mouse melanoma in a post-inoculation treatment paradigm. The 4-substituted benzylphosphonic acids and 6-substituted naphthalen-2-ylmethylphosphonic acids described herein represent new lead compounds that effectively inhibit the ATX-LPA-LPAR axis both in vitro and in vivo.

Autotaxin as a novel serum marker of liver fibrosis

BACKGROUND

The clinical significance of autotaxin (ATX), a key enzyme for the production of the bioactive lysophospholipid lysophosphatidic acid remains unknown. Serum ATX enzymatic activity reportedly increases in parallel with liver fibrosis and exhibits a gender difference.

METHODS

Serum ATX antigen level, measured easier than the activity, was evaluated as a marker of liver fibrosis in 2 cohorts of chronic liver disease caused by hepatitis C virus.

RESULTS

In the first cohort, serum ATX level correlated significantly with liver fibrosis stage and was the best parameter for prediction of cirrhosis with an area under the receiver operating characteristic curve (AUROC) of 0.756 in male and 0.760 in female, when compared with serum hyaluronic acid and aminotransferase-to-platelet ratio index, an established marker of liver fibrosis. In another cohort, serum ATX level correlated significantly with liver stiffness, a novel reliable marker of liver fibrosis, being the second-best parameter in male (AUROC, 0.799) and in female (AUROC, 0.876) for prediction of significant fibrosis, and the best parameter in male (AUROC, 0.863) and the third-best parameter in female (AUROC, 0.872) for prediction of cirrhosis, both of which were judged by liver stiffness.

CONCLUSIONS

Serum ATX level may be a novel marker of liver fibrosis.

Lysophosphatidic acid is a lipid mediator with wide range of biological activities. Biosynthetic pathways and mechanism of action

Lysophosphatidic acid (LPA) is a lipid mediator required for maintaining homeostasis of numerous physiological functions and also involved in development of some pathological processes through interactions with G protein-coupled receptors. Recently many data have appeared about the role of this phospholipid in humans, but pathways of LPA biosynthesis and mechanisms of its action remain unclear. This review presents modern concepts about biosynthesis, reception, and biological activity of LPA in humans. Natural and synthetic LPA analogs are considered in the view of their possible use in pharmacology as agonists and/or antagonists of G protein-coupled receptors of LPA.

Crystal structure of autotaxin and insight into GPCR activation by lipid mediators

Autotaxin (ATX, also known as Enpp2) is a secreted lysophospholipase D that hydrolyzes lysophosphatidylcholine to generate lysophosphatidic acid (LPA), a lipid mediator that activates G protein-coupled receptors to evoke various cellular responses. Here, we report the crystal structures of mouse ATX alone and in complex with LPAs with different acyl-chain lengths and saturations. These structures reveal that the multidomain architecture helps to maintain the structural rigidity of the lipid-binding pocket, which accommodates the respective LPA molecules in distinct conformations. They indicate that a loop region in the catalytic domain is a major determinant for the substrate specificity of the Enpp family enzymes. Furthermore, along with biochemical and biological data, these structures suggest that the produced LPAs are delivered from the active site to cognate G protein-coupled receptors through a hydrophobic channel.

Synthesis and pharmacological evaluation of the stereoisomers of 3-carba cyclic-phosphatidic acid

Cyclic phosphatidic acid (CPA) is a naturally occurring analog of lysophosphatidic acid (LPA) in which the sn-2 hydroxy group forms a five-membered ring with the sn-3 phosphate. Here, we describe the synthesis of R-3-CCPA and S-3-CCPA along with their pharmacological properties as inhibitors of lysophospholipase D/autotaxin, agonists of the LPA(5) GPCR, and blockers of lung metastasis of B16-F10 melanoma cells in a C57BL/6 mouse model. S-3CCPA was significantly more efficacious in the activation of LPA(5) compared to the R-stereoisomer. In contrast, no stereoselective differences were found between the two isomers toward the inhibition of autotaxin or lung metastasis of B16-F10 melanoma cells in vivo. These results extend the potential utility of these compounds as potential lead compounds warranting evaluation as cancer therapeutics.

Large scale purification and characterization of recombinant human autotaxin/lysophospholipase D from mammalian cells

We utilized a mammalian expression system to purify and characterize autotaxin (ATX)/lysophospholipase D, an enzyme present in the blood responsible for biosynthesis of lysophosphatidic acid. The human ATX cDNA encoding amino acids 29-915 was cloned downstream of a secretion signal of CD5. At the carboxyl terminus was a thrombin cleavage site followed by the constant domain (Fc) of IgG to facilitate protein purification. The ATX-Fc fusion protein was expressed in HEK293 cells and isolated from conditioned medium of a stable clone by affinity chromatography with Protein A sepharose followed by cleavage with thrombin. The untagged ATX protein was further purified to essential homogeneity by gel filtration chromatography with a yield of approximately 5 mg/liter medium. The purified ATX protein was enzymatically active and biologically functional, offering a useful tool for further biological and structural studies of this important enzyme.

Effects of cyclic phosphatidic acid on delayed neuronal death following transient ischemia in rat hippocampal CA1

Cyclic phosphatidic acid (cPA) is a lipid mediator that elicits a neurotrophin-like action in embryonic hippocampal neurons in vitro. In this study, we investigated the effects of cPA and 2-O-carba-oleoyl-cPA (2ccPA), a metabolically stabilized cPA derivative, on ischemia-induced delayed neuronal death in the rat hippocampal CA1 region. Transient occlusion for 8 min of bilateral carotid arteries besides permanent ligation of bilateral vertebral arteries was performed and morphological changes of the neurons were examined histologically 5 days after occlusion. cPA or 2ccPA was continuously administered for 5 days by means of an osmotic pump that was implanted subcutaneously before occlusion. Five days after occlusion, delayed neuronal death occurred in approximately 85% of the CA1 hippocampal neurons in the 0.2-2% bovine serum albumin vehicle control group. However, administration of cPA significantly increased the number of undamaged neurons in a dose-dependent manner. At the most effective concentration (18 μg/kg/5d), the number of undamaged neurons was increased to 4 times of that in the vehicle control group. 2ccPA also showed a neuroprotective effect, but it was less potent than that of natural cPA. These results indicate that systemic administration of both cPA and 2ccPA can protect neurons from ischemia-induced delayed neuronal death in the hippocampus.

Aiming drug discovery at lysophosphatidic acid targets

Lysophosphatidic acid (LPA, 1-radyl-2-hydroxy-sn-glycero-3-phosphate) is the prototype member of a family of lipid mediators and second messengers. LPA and its naturally occurring analogues interact with G protein-coupled receptors on the cell surface and a nuclear hormone receptor within the cell. In addition, there are several enzymes that utilize LPA as a substrate or generate it as a product and are under its regulatory control. LPA is present in biological fluids, and attempts have been made to link changes in its concentration and molecular composition to specific disease conditions. Through their many targets, members of the LPA family regulate cell survival, apoptosis, motility, shape, differentiation, gene transcription, malignant transformation and more. The present review depicts arbitrary aspects of the physiological and pathophysiological actions of LPA and attempts to link them with select targets. Many of us are now convinced that therapies targeting LPA biosynthesis and signalling are feasible for the treatment of devastating human diseases such as cancer, fibrosis and degenerative conditions. However, successful targeting of the pathways associated with this pleiotropic lipid will depend on the future development of as yet undeveloped pharmacons.

Autotaxin--an LPA producing enzyme with diverse functions

Autotaxin (ATX) is an ecto-enzyme responsible for lysophosphatidic acid (LPA) production in blood. ATX is present in various biological fluids such as cerebrospinal and seminal fluids and accounts for bulk LPA production in these fluids. ATX is a member of the nucleotide pyrophosphatase/phosphodiesterase (NPP) family and was originally isolated from conditioned medium of melanoma cells as an autocrine motility stimulating factor. LPA, a second-generation lipid mediator, binds to its cognate G protein-coupled receptors through which it exerts a number of biological functions including influencing cell motility and proliferation stimulating activity. Some of the biological roles of LPA can be mediated by ATX. However, there are other LPA-producing pathways independent of ATX. The accumulating evidences for physiological and pathological functions of ATX strongly support that ATX is an important therapeutic target. This review summarizes the historical aspects, structural basis, pathophysiological functions identified in mice studies and clinical relevance discovered by measuring the blood ATX level in human. The general features and functions of each NPP family member will be also briefly reviewed. The presence of the ATX gene in other model organisms and recently developed ATX inhibitors, both of which will be definitely useful for further functional analysis of ATX, will also be mentioned.

Biological roles of lysophosphatidic acid signaling through its production by autotaxin

Lysophosphatidic acid (LPA) exhibits a wide variety of biological functions as a bio-active lysophospholipid through G-protein-coupled receptors specific to LPA. Currently at least six LPA receptors are identified, named LPA(1) to LPA(6), while the existence of other LPA receptors has been suggested. From studies on knockout mice and hereditary diseases of these LPA receptors, it is now clear that LPA is involved in various biological processes including brain development and embryo implantation, as well as patho-physiological conditions including neuropathic pain and pulmonary and renal fibrosis. Unlike sphingosine 1-phosphate, a structurally similar bio-active lysophospholipid to LPA and produced intracellularly, LPA is produced by multiple extracellular degradative routes. A plasma enzyme called autotaxin (ATX) is responsible for the most of LPA production in our bodies. ATX converts lysophospholipids such as lysophosphatidylcholine to LPA by its lysophospholipase D activity. Recent studies on ATX have revealed new aspects of LPA. In this review, we highlight recent advances in our understanding of LPA functions and several aspects of ATX, including its activity, expression, structure, biochemical properties, the mechanism by which it stimulates cell motility and its pahto-physiological function through LPA production.

A novel enzyme immunoassay for the determination of phosphatidylserine-specific phospholipase A(1) in human serum samples

BACKGROUND

The bioactive lipid lysophosphatidylserine (LPS) is postulated to induce important biological responses and to be produced by phosphatidylserine-specific phospholipase A(1) (PS-PLA(1)). To evaluate the functional roles of LPS in vivo, a facile assay method for PS-PLA(1) has been awaited.

METHODS

Recombinant human PS-PLA(1) was produced using a baculovirus system, and anti-human PS-PLA(1) monoclonal antibodies were generated. Two clones were then selected for a 2-site immunoassay. The resulting PS-PLA(1) assay reagent was applied to a commercial automated immunoassay analyzer.

RESULTS

Satisfactory results were obtained for the within-run and between-run precision, interference, detection limit, and linearity of this PS-PLA(1) assay. The mean+/-SD of the serum PS-PLA(1) antigen concentration in the 191 healthy subjects was 33.8+/-16.6microg/l, and the central 95th percentile reference interval for the serum PS-PLA(1) antigen concentration was 13.8-74.1microg/l. The concentration was significantly (p<0.001) higher among men (13.8-80.6microg/l) than among women (12.1-68.8microg/l). We did not find a correlation between PS-PLA(1) and existing laboratory tests.

CONCLUSIONS

The present PS-PLA(1) assay method can be applied to clinical laboratory testing, and further studies are warranted to establish its clinical significance.

Autotaxin

Autotaxin is a protein of approximately 900 amino acids discovered in the early 1990s. Over the past 15 years, a strong association between cancer cells and autotaxin production has been observed. Recent publications indicate that autotaxin and the capacity of cancer to metastasise are intimately linked. The discovery of new molecular targets in pharmacology is a mixture of pure luck, hard work and industrial strategy. Despite a crucial and desperate need for new therapeutic tools, many targets are approached in oncology, but only a few are validated and end up at the patient bed. Outside the busy domain of kinases, few targets have been discovered that can be useful in treating cancer, particularly metastatic processes. The fortuitous relationship between autotaxin and lysophosphatidic acid renders the results of observations made in the diabetes/obesity context considerably important. The literature provides observations that may aid in redesigning experiments to validate autotaxin as a potential oncology target.

Lysophosphatidic acid signaling in airway epithelium: role in airway inflammation and remodeling

Lysophosphatidic acid (LPA), a potent bioactive phospholipid, induces diverse cellular responses, including cell proliferation, migration, and cytokine release. LPA can be generated intracellularly and extracellularly through multiple synthetic pathways by action of various enzymes, such as phospholipase A(1/2) (PLA(1/2)), phospholipase D (PLD), acylglycerol kinase (AGK), and lysophospholipase D (lysoPLD). Metabolism of LPA is regulated by a family of lipid phosphate phosphatases (LPPs). Significant amounts of LPA have been detected in various biological fluids, including serum, saliva, and bronchoalveolar lavage fluid (BALF). The most significant effects of LPA appear to be through activation of the G-protein-coupled receptors (GPCRs), termed LPA(1-6). LPA regulates gene expression through activation of several transcriptional factors, such as nuclear factor-kappaB (NF-kappaB), AP-1, and C/EBPbeta. In addition to GPCRs, cross-talk between LPA receptors and receptor tyrosine kinases (RTKs) partly regulates LPA-induced intracellular signaling and cellular responses. Airway epithelial cells participate in innate immunity through the release of cytokines, chemokines, lipid mediators, other inflammatory mediators and an increase in barrier function in response to a variety of inhaled stimuli. Expression of LPA receptors has been demonstrated in airway epithelial cells. This review summarizes our recent observations of the role of LPA/LPA-Rs in regulation of airway epithelium, especially in relation to the secretion of pro- and anti-inflammatory mediators and regulation of airway barrier function.

Therapeutic potential of autotaxin/lysophospholipase d inhibitors

Lysophosphatidic acids (LPAs) are structurally simple lipid phosphate esters with a widely appreciated role as extracellular signaling molecules. LPA binds to selective cell surface receptors to promote cell growth, survival, motility and differentiation. Studies using LPA receptor knockout mice and experimental therapeutics targeting these receptors identify roles for LPA signaling in processes that include cardiovascular disease and function, angiogenesis, reproduction, cancer progression and neuropathic pain. These studies identify considerable functional redundancy between these receptors and raise the possibility that additional lysophosphatidic acid receptors remain to be identified. LPA is present in the blood and other biological fluids at physiologically relevant concentrations and can likely be rapidly generated and degraded in different locations, for example at sites of inflammation, vascular injury and thrombosis or in the tumor micro environment. Recent work identifies a secreted enzyme, autotaxin (ATX), as the key component of an extracellular pathway for generation of lysophosphatidic acid by lysophospholipase D catalyzed hydrolysis of lysophospholipid substrates. In contrast to the apparently redundant functions of LPA receptors, studies using ATX knock out and transgenic mice indicate that this enzyme is uniquely required for LPA signaling during early development and serves as the primary determinant of circulating LPA levels in adult animals. Accordingly, pharmacological inhibition of ATX may be a viable and potentially effective way to interfere with LPA signaling in the cardiovascular system and possibly other settings such as tumor metastasis for therapeutic benefit. In this review we provide an update on recent advances in defining roles for LPA signaling in major disease processes and discuss recent progress in understanding the regulation and function of autotaxin focusing on strategies for the identification and initial evaluation of small molecule autotaxin inhibitors.

Cyclic phosphatidic acid - a unique bioactive phospholipid

Cyclic phosphatidic acid (CPA) is a naturally occurring analog of the growth factor-like phospholipid mediator, lysophosphatidic acid (LPA). The sn-2 hydroxy group of CPA forms a 5-membered ring with the sn-3 phosphate. CPA affects numerous cellular functions, including anti-mitogenic regulation of the cell cycle, induction of stress fiber formation, inhibition of tumor cell invasion and metastasis, and regulation of differentiation and survival of neuronal cells. Interestingly, many of these cellular responses caused by CPA oppose those of LPA despite the activation of apparently overlapping receptor populations. Since the early 1990s, studies on CPA actions gradually developed, and we are now beginning to understand the importance of this lipid. In this review, we focus on the current knowledge about CPA, including enzymatic formation of CPA, unique biological activities and biological targets of CPA, and we also explore metabolically stabilized CPA analogs.

Targeting platelets for prevention and treatment of cardiovascular disease

Platelets play an important role in the development of thrombosis, atherosclerosis, hypertension, heart attack and stroke. As a result, pharmacologic interventions that influence platelet functions, such as adhesion, aggregation and the release of different factors, are considered useful for the prevention and treatment of cardiovascular disease. Although classical anti-platelet agents have proven beneficial effects for the treatment of some specific cardiovascular diseases, there are limitations for their use as these drugs target platelet function directly. In contrast, newly developed anti-platelet agents have broad applications for the treatment of cardiovascular disease as they not only influence platelet function but are also considered to affect cardiac and vascular smooth muscle cell functions. Natural food products and nutraceutical agents also appear to modify cardiovascular abnormalities by affecting various platelet functions; however, the mechanisms of their actions remain to be investigated. Accordingly, this article is focused to discuss emerging pharmacologic, nutritional and nutraceutical interventions that may influence the prevention or progression of a broad range of cardiovascular diseases.

Quantitative determination of cyclic phosphatidic acid in human serum by LC/ESI/MS/MS

An LC/ESI/MS/MS method for cyclic phosphatidic acid (cPA) quantification in serum is established in the present report. The limit of quantitation of the assay reaches low nanomolar level in human serum and the CV% are within 10%. Using this method, we successfully quantify the levels of two cPA species, 16:0 and 18:1, in human serum. We find that the concentrations of 16:0 cPA in the serum of normal subjects and post-surgery ovarian cancer patients are significantly higher than its corresponding concentration in pre-surgery ovarian cancer patients, supporting the observation that cPA has anti-cancer activity. Another discovery is that the addition of strong acids (such as hydrochloric acid) in human serum may lead to the production of artificial cPA. Therefore, strong acids should be avoided in the extraction of cPA present in a complex matrix. Based on this observation, a new lipid extraction method was developed and used to extract cPA. The extraction recovery is close to 80%, guaranteeing an accurate quantification of cPA by LC/ESI/MS/MS can be performed.