Development and biological evaluation of fluorophosphonate-modified hydroxyapatite for orthopaedic applications

There is an incentive to functionalise hydroxyapatite (HA) for orthopaedic implant use with bioactive agents to encourage superior integration of the implants into host bone. One such agent is (3S) 1-fluoro-3-hydroxy-4-(oleoyloxy) butyl-1-phosphonate (FHBP), a phosphatase-resistant lysophosphatidic acid (LPA) analogue. We investigated the effect of an FHBP-HA coating on the maturation of human (MG63) osteoblast-like cells. Optimal coating conditions were identified and cell maturation on modified and unmodified, control HA surfaces was assessed. Stress tests were performed to evaluate coating survivorship after exposure to mechanical and thermal insults that are routinely encountered in the clinical environment. MG63 maturation was found to be three times greater on FHBP-modified HA compared to controls (p < 0.0001). There was no significant loss of coating bioactivity after autoclaving (P = 0.9813) although functionality declined by 67% after mechanical cleaning and reuse (p < 0.0001). The bioactivity of modified disks was significantly greater than that of controls following storage for up to six months (p < 0.001). Herein we demonstrate that HA can be functionalised with FHBP in a facile, scalable manner and that this novel surface has the capacity to enhance osteoblast maturation. Improving the biological performance of HA in a bone regenerative setting could be realised through the simple conjugation of bioactive LPA species in the future. Depicted is a stylised summary of hydroxyapatite (HA) surface modification using an analogue of lysophosphatidic acid, FHBP. a HA surfaces are simply steeped in an aqueous solution of 2 μM FHBP. b The polar head group of some FHBP molecules react with available hydroxyl residues at the mineral surfaces forming robust HA-O-P bonds leaving acyl chain extensions perpendicular to the HA surface. These fatty acyl chains provide points of integration for other FHBP molecules to facilitate their self-assembly. This final surface finish enhanced the human osteoblast maturation response to calcitriol, the active vitamin D3 metabolite.

Ceramide and S1P Signaling in Embryonic Stem Cell Differentiation

Bioactive sphingolipids are important regulators for stem cell survival and differentiation. Most recently, we have coined the term "morphogenetic lipids" for sphingolipids that regulate stem cells during embryonic and postnatal development. The sphingolipid ceramide and its derivative, sphingosine-1-phosphate (S1P), can act synergistically as well as antagonistically on embryonic stem (ES) cell differentiation. We show here simple as well as state-of-the-art methods to analyze sphingolipids in differentiating ES cells and discuss new protocols to use ceramide and S1P analogs for the guided differentiation of mouse ES cells toward neuronal and glial lineage.

Harnessing Sphingosine-1-Phosphate Signaling and Nanotopographical Cues To Regulate Skeletal Muscle Maturation and Vascularization

Despite possessing substantial regenerative capacity, skeletal muscle can suffer from loss of function due to catastrophic traumatic injury or degenerative disease. In such cases, engineered tissue grafts hold the potential to restore function and improve patient quality of life. Requirements for successful integration of engineered tissue grafts with the host musculature include cell alignment that mimics host tissue architecture and directional functionality, as well as vascularization to ensure tissue survival. Here, we have developed biomimetic nanopatterned poly(lactic-co-glycolic acid) substrates conjugated with sphingosine-1-phosphate (S1P), a potent angiogenic and myogenic factor, to enhance myoblast and endothelial maturation. Primary muscle cells cultured on these functionalized S1P nanopatterned substrates developed a highly aligned and elongated morphology and exhibited higher expression levels of myosin heavy chain, in addition to genes characteristic of mature skeletal muscle. We also found that S1P enhanced angiogenic potential in these cultures, as evidenced by elevated expression of endothelial-related genes. Computational analyses of live-cell videos showed a significantly improved functionality of tissues cultured on S1P-functionalized nanopatterns as indicated by greater myotube contraction displacements and velocities. In summary, our study demonstrates that biomimetic nanotopography and S1P can be combined to synergistically regulate the maturation and vascularization of engineered skeletal muscles.

Biogenesis, transport and remodeling of lysophospholipids in Gram-negative bacteria

Lysophospholipids (LPLs) are metabolic intermediates in bacterial phospholipid turnover. Distinct from their diacyl counterparts, these inverted cone-shaped molecules share physical characteristics of detergents, enabling modification of local membrane properties such as curvature. The functions of LPLs as cellular growth factors or potent lipid mediators have been extensively demonstrated in eukaryotic cells but are still undefined in bacteria. In the envelope of Gram-negative bacteria, LPLs are derived from multiple endogenous and exogenous sources. Although several flippases that move non-glycerophospholipids across the bacterial inner membrane were characterized, lysophospholipid transporter LplT appears to be the first example of a bacterial protein capable of facilitating rapid retrograde translocation of lyso forms of glycerophospholipids across the cytoplasmic membrane in Gram-negative bacteria. LplT transports lyso forms of the three bacterial membrane phospholipids with comparable efficiency, but excludes other lysolipid species. Once a LPL is flipped by LplT to the cytoplasmic side of the inner membrane, its diacyl form is effectively regenerated by the action of a peripheral enzyme, acyl-ACP synthetase/LPL acyltransferase (Aas). LplT-Aas also mediates a novel cardiolipin remodeling by converting its two lyso derivatives, diacyl or deacylated cardiolipin, to a triacyl form. This coupled remodeling system provides a unique bacterial membrane phospholipid repair mechanism. Strict selectivity of LplT for lyso lipids allows this system to fulfill efficient lipid repair in an environment containing mostly diacyl phospholipids. A rocker-switch model engaged by a pair of symmetric ion-locks may facilitate alternating substrate access to drive LPL flipping into bacterial cells. This article is part of a Special Issue entitled: Bacterial Lipids edited by Russell E. Bishop.

Concerted regulation of npc2 binding to endosomal/lysosomal membranes by bis(monoacylglycero)phosphate and sphingomyelin

Niemann-Pick Protein C2 (npc2) is a small soluble protein critical for cholesterol transport within and from the lysosome and the late endosome. Intriguingly, npc2-mediated cholesterol transport has been shown to be modulated by lipids, yet the molecular mechanism of npc2-membrane interactions has remained elusive. Here, based on an extensive set of atomistic simulations and free energy calculations, we clarify the mechanism and energetics of npc2-membrane binding and characterize the roles of physiologically relevant key lipids associated with the binding process. Our results capture in atomistic detail two competitively favorable membrane binding orientations of npc2 with a low interconversion barrier. The first binding mode (Prone) places the cholesterol binding pocket in direct contact with the membrane and is characterized by membrane insertion of a loop (V59-M60-G61-I62-P63-V64-P65). This mode is associated with cholesterol uptake and release. On the other hand, the second mode (Supine) places the cholesterol binding pocket away from the membrane surface, but has overall higher membrane binding affinity. We determined that bis(monoacylglycero)phosphate (bmp) is specifically required for strong membrane binding in Prone mode, and that it cannot be substituted by other anionic lipids. Meanwhile, sphingomyelin counteracts bmp by hindering Prone mode without affecting Supine mode. Our results provide concrete evidence that lipids modulate npc2-mediated cholesterol transport either by favoring or disfavoring Prone mode and that they impose this by modulating the accessibility of bmp for interacting with npc2. Overall, we provide a mechanism by which npc2-mediated cholesterol transport is controlled by the membrane composition and how npc2-lipid interactions can regulate the transport rate.

* Injectable Graft Substitute Active on Bone Tissue Regeneration

With the aim to obtain an injectable bioactive scaffold that can accelerate bone formation in sinus lift augmentation, in bony void and fracture repair, we have developed a three-dimensional (3D) jelly collagen containing lysophosphatidic acid (LPA) and 1α,25-dihydroxyvitamin D3 (1,25D3). Using an in vitro 3D culture model of bone fracture, we show that the contraction of the collagen gel is mediated by Rho-kinase activation in osteoblasts. The gel contraction showed dependence on cell concentration and was increased by LPA, which favored apposition and fastening of bone fragments approach. LPA was shown to act through actin cytoskeleton reorganization and myosin light chain phosphorylation of human primary osteoblasts (hOB). Moreover, LPA conferred osteoconductive properties as evidenced by the induction of proliferation, differentiation, and migration of hOB. The addition of 1,25D3 did not enhance cell-mediated gel contraction, but stimulated the maturation of hOB in vitro through the production of extracellular matrix of higher quality. On the basis of these observations, the collagen gel enriched with LPA and 1,25D3 described herein can be considered an injectable natural scaffold that allows the migration of cells from the side of bone defect and a promising candidate to accelerate bone growth and fracture healing.

Genotypic Variation in Wheat Flour Lysophospholipids

Lysophospholipids (LPLs) are the most abundant polar lipids in wheat endosperm and naturally complex with amylose, affecting starch physicochemical properties. We analyzed LPLs in wheat flour from 58 cultivars which differ by grain hardness using liquid chromatography mass spectrometry (LCMS). There were significant differences in LPL content between cultivars, demonstrating that genotype rather than environment contributes most to the total variance in wheat endosperm LPLs. Polar lipids such as LPLs may play a role in grain hardness through their interaction with puroindoline proteins, however, no strong correlation between kernel hardness and LPLs was detected. This may reflect the location of LPLs within the starch granule as opposed to the puroindoline proteins outside starch granules. LPLs may have an indirect relationship with kernel hardness as they could share the same origin as polar lipids that interact with puroindoline on the starch granule surface.

Mildly oxidized HDL decrease agonist-induced platelet aggregation and release of pro-coagulant platelet extracellular vesicles

Stored platelet concentrates (PLCs) for therapeutic purpose, develop a platelet storage lesion (PSL), characterized by impaired platelet (PLT) viability and function, platelet extracellular vesicle (PL-EV) release and profound lipidomic changes. Whereas oxidized low-density lipoprotein (oxLDL) activates PLTs and promotes atherosclerosis, effects linked to oxidized high-density lipoprotein (oxHDL) are poorly characterized. PLCs from blood donors were treated with native (nHDL) or mildly oxidized HDL (moxHDL) for 5days under blood banking conditions. Flow cytometry, nanoparticle tracking analysis (NTA), aggregometry, immunoblot analysis and mass spectrometry were carried out to analyze PL-EV and platelet exosomes (PL-EX) release, PLT aggregation, protein expression, and PLT and plasma lipid composition. In comparison to total nHDL, moxHDL significantly decreased PL-EV release by -36% after 5days of PLT storage and partially reversed agonist-induced PLT aggregation. PL-EV release positively correlated with PLT aggregation. MoxHDL improved PLT membrane lipid homeostasis through enhanced uptake of lysophospholipids and their remodeling to corresponding phospholipid species. This also appeared for sphingomyelin (SM) and d18:0/d18:1 sphingosine-1-phosphate (S1P) at the expense of ceramide (Cer) and hexosylceramide (HexCer) leading to reduced Cer/S1P ratio as PLT-viability indicator. This membrane remodeling was associated with increased content of CD36 and maturation of scavenger receptor-B1 (SR-B1) protein in secreted PL-EVs. MoxHDL, more potently than nHDL, improves PLT-membrane lipid homeostasis, partially antagonizes PL-EV release and agonist-induced PLT aggregation. Altogether, this may be the result of more efficient phospho- and sphingolipid remodeling mediated by CD36 and SR-B1 in the absence of ABCA1 on PLTs. As in vitro supplement in PLCs, moxHDL has the potential to improve PLC quality and to prolong storage.

Identification of Crucial Amino Acid Residues Involved in Agonist Signaling at the GPR55 Receptor

GPR55 is a newly deorphanized class A G-protein-coupled receptor that has been implicated in inflammatory pain, neuropathic pain, metabolic disorder, bone development, and cancer. Few potent GPR55 ligands have been identified to date. This is largely due to an absence of information about salient features of GPR55, such as residues important for signaling and residues implicated in the GPR55 signaling cascade. The goal of this work was to identify residues that are key for the signaling of the GPR55 endogenous ligand, l-α-lysophosphatidylinositol (LPI), as well as the signaling of the GPR55 agonist, ML184 {CID 2440433, 3-[4-(2,3-dimethylphenyl)piperazine-1-carbonyl]-N,N-dimethyl-4-pyrrolidin-1-ylbenzenesulfonamide}. Serum response element (SRE) and serum response factor (SRF) luciferase assays were used as readouts for studying LPI and ML184 signaling at the GPR55 mutants. A GPR55 R* model based on the recent δ-opioid receptor (DOR) crystal structure was used to interpret the resultant mutation data. Two residues were found to be crucial for agonist signaling at GPR55, K2.60 and E3.29, suggesting that these residues form the primary interaction site for ML184 and LPI at GPR55. Y3.32F, H(170)F, and F6.55A/L mutation results suggested that these residues are part of the orthosteric binding site for ML184, while Y3.32F and H(170)F mutation results suggest that these two residues are part of the LPI binding pocket. Y3.32L, M3.36A, and F6.48A mutation results suggest the importance of a Y3.32/M3.36/F6.48 cluster in the GPR55 signaling cascade. C(10)A and C(260)A mutations suggest that these residues form a second disulfide bridge in the extracellular domain of GPR55, occluding ligand extracellular entry in the TMH1-TMH7 region of GPR55. Taken together, these results provide the first set of discrete information about GPR55 residues important for LPI and ML184 signaling and for GPR55 activation. This information should aid in the rational design of next-generation GPR55 ligands and the creation of the first high-affinity GPR55 radioligand, a tool that is sorely needed in the field.

Characterization of the Anticoagulant and Antithrombotic Properties of the Sphingosine 1-Phosphate Mimetic FTY720

Sphingosine 1-phosphate (S1P) is a highly active lysophospholipid implicated in various cardiocerebrovascular events such as coagulation, myocardial infarction and stroke. However, as the functional S1P receptor antagonist, whether the S1P mimetic FTY720 can modulate coagulation and/or thrombotic formation remains largely unknown. We investigated the effects of FTY720 on adenosine diphosphate (ADP)-induced platelet aggregation, coagulation parameters and thrombus formation in rats. Pretreatment with FTY720 (2.5 mg/kg) inhibited platelet aggregation induced by ADP, elongated the thrombin time and decreased the fibrinogen levels. However, FTY720 produced no significant effects on the arteriovenous bypass thrombus formation or the FeCl3-induced thrombus formation in the inferior vena cava and the common carotid artery. Our data suggest that FTY720 can exert an inhibitory effect on platelet aggregation and coagulation-related parameters. These characteristics of FTY720 could be useful as an adjunct in the treatment of ischemic diseases such as ischemic stroke and myocardial infarction.

Role of Membrane Lipids in the Regulation of Erythrocytic Oxygen-Transport Function in Cardiovascular Diseases

The composition and condition of membrane lipids, the morphology of erythrocytes, and hemoglobin distribution were explored with the help of laser interference microscopy (LIM) and Raman spectroscopy. It is shown that patients with cardiovascular diseases (CVD) have significant changes in the composition of their phospholipids and the fatty acids of membrane lipids. Furthermore, the microviscosity of the membranes and morphology of the erythrocytes are altered causing disordered oxygen transport by hemoglobin. Basic therapy carried out with the use of antiaggregants, statins, antianginals, beta-blockers, and calcium antagonists does not help to recover the morphofunctional properties of erythrocytes. Based on the results the authors assume that, for the relief of the ischemic crisis and further therapeutic treatment, it is necessary to include, in addition to cardiovascular disease medicines, medication that increases the ability of erythrocytes' hemoglobin to transport oxygen to the tissues. We assume that the use of LIM and Raman spectroscopy is advisable for early diagnosis of changes in the structure and functional state of erythrocytes when cardiovascular diseases develop.

Catalytic Mechanism of Eukaryotic Neutral Ceramidase

Neutral ceramidases are key enzymes of sphingolipid metabolism that hydrolyze the fatty acyl/sphingosine amide linkage of ceramide at neutral pH. In this issue of Structure, Airola et al. (2015) present the first crystal structure of human nCDase and show how complexation with phosphate supports a new catalytic mechanism for Zn-dependent amidases while providing a structurally based explanation for ceramide specificity.

Near-Infrared Fluorogenic Probes with Polarity-Sensitive Emission for in Vivo Imaging of an Ovarian Cancer Biomarker

Lysophosphatidic acid (LPA, cutoff values ≥ 1.5 μM) is an effective biomarker for early stage ovarian cancer. The development of selective probes for LPA detection is therefore critical for early clinical diagnosis. Although current methods have been developed for the detection of LPA in solution, they cannot be used for tracking LPA in vivo. Here, we report a near-infrared (NIR) fluorescent probe that can selectively respond to LPA based on polarity-sensitive emission at a very low detection limit of 0.5 μM in situ. This probe exhibits a marked increase of fluorescence at 720 nm upon binding to LPA, allowing the direct visualization of LPA in vitro and in vivo without interference from other biomolecules. Moreover, the probe containing two arginine-glycine-aspartic acid units can be efficiently taken up by cancer cells based on an αvβ3 integrin receptor targeting mechanism. It also exhibits excellent biocompatibility and high pH stability in live cells and in vivo. Confocal laser scanning microscopy and flow cytometric imaging of SKOV-3 cells have confirmed that our probe can be used to image LPA in live cells. In particular, its NIR turn-on fluorescence can be used to effectively monitor LPA imaging in a SKOV-3 tumor-bearing mouse model. Our probe may pave the way for the detection of cancer-related biomarkers and even for early stage cancer diagnosis.

Fluorophosphonate-functionalised titanium via a pre-adsorbed alkane phosphonic acid: a novel dual action surface finish for bone regenerative applications

Enhancing vitamin D-induced human osteoblast (hOB) maturation at bone biomaterial surfaces is likely to improve prosthesis integration with resultant reductions in the need for revision arthroplasty consequent to aseptic loosening. Biomaterials that are less appealing to microorganisms implicated in implant failures through infection are also highly desirable. However, finding surfaces that enhance hOB maturation to active vitamin D yet deter bacteria remain elusive. In addressing this, we have sought to bio-functionalise titanium (Ti) with lysophosphatidic acid (LPA) and related, phosphatase-resistant, LPA analogues. The impetus for this follows our discovery that LPA co-operates with active vitamin D3 metabolites to secure hOB maturation in vitro including cells grown upon Ti. LPA has also been found, by others, to inhibit virulence factor production and biofilm formation of the human opportunistic pathogen Pseudomonas aeruginosa. Collectively, selected LPA species might offer potential dual-action surface finishes for contemporary bone biomaterials. In attaching a phosphatase-resistant LPA analogue to Ti we took advantage of the affinity of alkane phosphonic acids for TiO2. Herein, we provide evidence for the facile development of a dual-action Ti surface for potential orthopaedic and dental applications. Successful conjugation of an LPA analogue (3S)1-fluoro-3-hydroxy-4-(oleoyloxy)butyl-1-phosphonate (FHBP) to the Ti surface was supported through physiochemical characterisation using x-ray photoelectron spectroscopy and secondary ion mass spectrometry. hOB maturation to active vitamin D3 was enhanced for cells grown on FHBP-Ti whilst these same surfaces exhibited clear antiadherent properties towards a clinical isolate of Staphylococcus aureus.

LC-MS based metabolomics identification of novel biomarkers of tobacco smoke-induced chronic bronchitis

Tobacco smoke (TS) is a major causative agent to lead to chronic bronchitis (CB). However the mechanisms of CB induced by TS are unclear. In this report, rats were exposed to different concentrations of TS and the metabolic features of CB were characterized by using a nontargeted metabolic profiling method based on liquid chromatography-mass spectrometry (LC-MS) to detect the altered metabolic patterns in serum from CB rats and investigate the mechanisms of CB. 11 potential biomarkers were identified in serum of rats. Among them, the levels of lysophosphatidylethanolamine (18:1), lysophosphatidic acid (18:1), lysophosphatidylethanolamine (18:0), lysophosphatidylethanolamine (16:0), lysophosphatidylethanolamine (20:4), docosahexaenoic acid, 5-hydroxyindoleacetic acid and 5'-carboxy-γ-tocopherol were higher in TS group compared to control group. Conversely, the levels of 4-imidazolone-5-propionic acid, 12-hydroxyeicosatetraenoic acid and uridine were lower in TS group. The results indicated that the mechanism of CB was related to amino acid metabolism and lipid metabolism, particularly lipid metabolism. In addition, lysophosphatidylethanolamines were proved to be important mediators, which could be used as biomarkers to diagnose CB. These results also suggested that metabolomics was suitable for diagnosing CB and elucidating the possible metabolic pathways of TS-induced CB.

New drug delivery system for liver sinusoidal endothelial cells for ischemia-reperfusion injury

AIM: To investigate the cytoprotective effects in hepatic ischemia-reperfusion injury, we developed a new formulation of hyaluronic acid (HA) and sphingosine 1-phophate.

METHODS: We divided Sprague-Dawley rats into 4 groups: control, HA, sphingosine 1-phosphate (S1P), and HA-S1P. After the administration of each agent, we subjected the rat livers to total ischemia followed by reperfusion. After reperfusion, we performed the following investigations: alanine aminotransferase (ALT), histological findings, TdT-mediated dUTP-biotin nick end labeling (TUNEL) staining, and transmission electron microscopy (TEM). We also investigated the expression of proteins associated with apoptosis, hepatoprotection, and S1P accumulation.

RESULTS: S1P accumulated in the HA-S1P group livers more than S1P group livers. Serum ALT levels, TUNEL-positive hepatocytes, and expression of cleaved caspase-3 expression, were significantly decreased in the HA-S1P group. TEM revealed that the liver sinusoidal endothelial cell (LSEC) lining was preserved in the HA-S1P group. Moreover, the HA-S1P group showed a greater increase in the HO-1 protein levels compared to the S1P group.

CONCLUSION: Our results suggest that HA-S1P exhibits cytoprotective effects in the liver through the inhibition of LSEC apoptosis. HA-S1P is an effective agent for hepatic ischemia/reperfusion injury.

Dual Action of Lysophosphatidate-Functionalised Titanium: Interactions with Human (MG63) Osteoblasts and Methicillin Resistant Staphylococcus aureus

Titanium (Ti) is a widely used material for surgical implants; total joint replacements (TJRs), screws and plates for fixing bones and dental implants are forged from Ti. Whilst Ti integrates well into host tissue approximately 10% of TJRs will fail in the lifetime of the patient through a process known as aseptic loosening. These failures necessitate revision arthroplasties which are more complicated and costly than the initial procedure. Finding ways of enhancing early (osseo)integration of TJRs is therefore highly desirable and continues to represent a research priority in current biomaterial design. One way of realising improvements in implant quality is to coat the Ti surface with small biological agents known to support human osteoblast formation and maturation at Ti surfaces. Lysophosphatidic acid (LPA) and certain LPA analogues offer potential solutions as Ti coatings in reducing aseptic loosening. Herein we present evidence for the successful bio-functionalisation of Ti using LPA. This modified Ti surface heightened the maturation of human osteoblasts, as supported by increased expression of alkaline phosphatase. These functionalised surfaces also deterred the attachment and growth of Staphylococcus aureus, a bacterium often associated with implant failures through sepsis. Collectively we provide evidence for the fabrication of a dual-action Ti surface finish, a highly desirable feature towards the development of next-generation implantable devices.

Cytoprotective Effects of Lysophospholipids from Sea Cucumber Holothuria atra

Lysophospholipids are important signaling molecules in animals and metazoan cells. They are widely distributed among marine invertebrates, where their physiological roles are unknown. Sea cucumbers produce unique lysophospholipids. In this study, two lysophospholipids were detected in Holothuria atra for the first time, lyso-platelet activating factor and lysophosphatidylcholine, with nuclear magnetic resonance and liquid chromatography-time-of-flight mass spectrometric analyses. The lipid fraction of H. atra contained lyso-platelet activating factor and lysophosphatidylcholine, and inhibited H2O2-induced apoptosis in the macrophage cell line J774A.1. The antioxidant activity of the lysophospholipid-containing lipid fraction of H. atra was confirmed with the oxygen radical absorbance capacity method. Our results suggest that the lysophospholipids from H. atra are potential therapeutic agents for the inflammation induced by oxidative stress.

Structural Basis for Ceramide Recognition and Hydrolysis by Human Neutral Ceramidase

Neutral ceramidase (nCDase) catalyzes conversion of the apoptosis-associated lipid ceramide to sphingosine, the precursor for the proliferative factor sphingosine-1-phosphate. As an enzyme regulating the balance of ceramide and sphingosine-1-phosphate, nCDase is emerging as a therapeutic target for cancer. Here, we present the 2.6-Å crystal structure of human nCDase in complex with phosphate that reveals a striking, 20-Å deep, hydrophobic active site pocket stabilized by a eukaryotic-specific subdomain not present in bacterial ceramidases. Utilizing flexible ligand docking, we predict a likely binding mode for ceramide that superimposes closely with the crystallographically observed transition state analog phosphate. Our results suggest that nCDase uses a new catalytic strategy for Zn(2+)-dependent amidases, and generates ceramide specificity by sterically excluding sphingolipids with bulky headgroups and specifically recognizing the small hydroxyl head group of ceramide. Together, these data provide a foundation to aid drug development and establish common themes for how proteins recognize the bioactive lipid ceramide.

Effect of lysophosphatidic acid receptor inhibition on bone changes in ovariectomized mice

Pharmacological inhibition of signaling through lysophosphatidic acid (LPA) receptors reduces bone erosions in an experimental model of arthritis by mechanisms involving reduced osteoclast differentiation and bone resorption and increased differentiation of osteoblasts and bone mineralization. These results led us to hypothesize that LPA receptor inhibition would be beneficial in osteoporosis. Our aim was to test this hypothesis with the LPA receptor antagonist, Ki16425, in ovariectomized mice, a model of postmenopausal osteoporosis. Ovariectomized mice treated with Ki16425 showed bone loss similar to that observed in the controls. Osteoblast markers, Alpl, Bglap and Col1a1, were increased at the mRNA level but no changes were detected in serum. No additional difference was observed in the Ki16425-treated mice relative to the ovariectomized controls with regard to osteoclast function markers or assays of matrix mineralization or osteoclast differentiation. Thus, pharmacological inhibition of LPA receptor was not beneficial for preventing bone loss in ovariectomized mice, indicating that its favorable effect on bone remodeling is less general than hypothesized.

The structure of nerve growth factor in complex with lysophosphatidylinositol

Nerve growth factor (NGF) is an important protein that is involved in a variety of physiological processes in cell survival, differentiation, proliferation and maintenance. The previously reported crystal structure of mouse NGF (mNGF) in complex with lysophosphatidylserine (LysoPS) showed that mNGF can bind LysoPS at its dimeric interface. To expand the understanding of the structural basis for specific lipid recognition by NGF, the crystal structure of mNGF complexed with lysophosphatidylinositol (13:0 LysoPI) was solved. Interestingly, in addition to Lys88, which interacts with the head glycerol group and the phosphate group of LysoPI, as seen in the mNGF-LysoPS structure, two additional residues, Tyr52 and Arg50, were found to assist in lipid binding by forming hydrogen bonds to the inositol moiety of the LysoPI molecule. The results suggest a specific recognition mechanism of inositol group-containing lipids by NGF, which may help in the design of bioactive compounds that can be delivered by NGF.

The YhhN protein of Legionella pneumophila is a Lysoplasmalogenase

Lysoplasmalogenase catalyzes hydrolytic cleavage of the vinyl-ether bond of lysoplasmalogen to yield fatty aldehyde and glycerophospho-ethanolamine or glycerophospho-choline. We recently purified lysoplasmalogenase from rat liver microsomes and identified the protein as TMEM86B, an integral membrane protein that is a member of the YhhN family found in numerous species of eukaryotes and bacteria. To test the hypothesis that bacterial YhhN proteins also function as lysoplasmalogenase enzymes, we cloned the Lpg1991 gene of Legionella pneumophila, which encodes a 216 amino acid YhhN protein (LpYhhN), and expressed it in Escherichia coli as a C-terminal-GFP-His8-fusion. Membranes were solubilized and the fusion protein was purified by nickel-affinity chromatography, cleaved with Tobacco Etch Virus protease, and subjected to a reverse nickel column to purify the un-tagged LpYhhN. Both the fusion protein and un-tagged LpYhhN exhibit robust lysoplasmalogenase activity, cleaving the vinyl-ether bond of lysoplasmalogen with a Vmax of 12 µmol/min/mg protein and a Km of 45 μM. LpYhhN has no activity on diradyl plasmalogen, 1-alkenyl-glycerol, and monoacylglycerophospho-ethanolamine or monoacylglycerophospho-choline; the pH optimum is 6.5-7.0. These properties are very similar to mammalian TMEM86B. Sequence analysis suggests that YhhN proteins contain eight transmembrane helices, an N-in/C-in topology, and about 5 highly conserved amino acid residues that may form an active site. This work is the first to demonstrate a function for a bacterial YhhN protein, as a vinyl ether bond hydrolase specific for lysoplasmalogen. Since L. pneumophila does not contain endogenous plasmalogens, we hypothesize that LpYhhN may serve to protect the bacterium from lysis by lysoplasmalogen derived from plasmalogens of the host.

Spiroguanidine rhodamines as fluorogenic probes for lysophosphatidic acid

Direct determination of total lysophosphatidic acid (LPA) was accomplished using newly developed spiroguanidines derived from rhodamine B as universal fluorogenic probes. Optimum conditions for the quantitative analysis of total LPA were investigated. The linear range for the determination of total LPA is up to 5 μM with a limit of detection of 0.512 μM.

[Lipid and fatty acid profiles of Pseudomonas aurantiaca DNA-bound lipids determined by mass spectrometry]

An approach used on investigation of the lipid composition of loosely (fraction 1) and tightly (fraction 2) DNA-bound lipids of Pseudomonas aurantiaca cells by electrospray ionization using mass spectrometry (ESI-LC-MS) was used for determination of the lipidom of a prokaryotic cell. Free fatty acids C16:0, C18:1 (fraction 1), C14:0, C16:0, and C18:2 (fraction 2) were detected. Both fractions of DNA-bound lipids were characterized by the presence of phosphatidylglycerol, phosphatidylserine, and lyso-phosphatidylinositol. The alcohol-soluble fraction 1 could also contain phosphatidylcholine and phosphatidylinositol, while fraction 2 probably contained triacylglycerides. Compared to gas chromatography, ESI-LC-MS provides new possibilities for investigation of the nucleoid lipidome, providing for more detailed investigation of DNA-bound lipids in bacterial cells.