Effects of platelet-activating factor and related lipids on dielaidoylphosphatidylethanolamine by DSC, FTIR and NMR

MicroRNA-935 Inhibits Proliferation and Invasion of Osteosarcoma Cells by Directly Targeting High Mobility Group Box 1

Numerous studies have suggested that microRNAs (miRNAs) are dysregulated in osteosarcoma (OS), implicating miRNAs in OS initiation and progression. Therefore, knowledge of aberrantly expressed miRNAs in OS may provide novel mechanistic insights into the tumorigenesis and tumor development of OS and facilitate therapeutic methods for patients with this aggressive bone neoplasm. In this study, data obtained from reverse transcription quantitative polymerase chain reaction (RT-qPCR) revealed that miR-935 was significantly decreased in OS tissues and cell lines. Restoration expression of miR-935 obviously restricted proliferation and invasion of OS cells. In addition, high-mobility group box 1 (HMGB1) was predicted to be a putative target of miR-935. Subsequent dual-luciferase reporter assay, RT-qPCR, and Western blot analysis confirmed that miR-935 could directly target the 3′-untranslated region of HMGB1 and negatively regulated HMGB1 expression in OS cells. Furthermore, a significant negative association was found between miR-935 and HMGB1 mRNA expression in OS tissues. Rescue experiments showed that recovery of HMGB1 expression partially rescued miR-935-induced suppression of cell proliferation and invasion in OS. These results provide the first evidence for the suppressive roles of miR-935 in OS by directly targeting HMGB1, suggesting that miR-935 may be a potential candidate for the treatment of patients with this disease.

MicroRNA-200c inhibits epithelial-mesenchymal transition, invasion, and migration of lung cancer by targeting HMGB1

MicroRNAs (miRs) play critical roles in cancer development, proliferation, epithelial-mesenchymal transition (EMT), invasion, and migration through regulating the expression of oncogenes and tumour suppressor genes. Previous studies have indicated that miR-200c acts as a tumour suppressor in various cancers by downregulating high-mobility group box 1 (HMGB1) and thereby suppressing EMT and metastasis. In addition, miR-200c was reported to be downregulated and correlated with poor outcomes in non-small cell lung cancer (NSCLC). However, its functional role in HMGB1 regulation in NSCLC is still unclear. This study aimed to clarify whether miR-200c acts as a tumour suppressor in NSCLC by downregulating HMGB1, which is associated with EMT, invasion, cytoskeleton rearrangement, and migration in vitro and in vivo. In order to demonstrate HMGB1 downregulation by miR-200c, the NSCLC cell line A549 was transfected with miR-200c mimic or inhibitor. The mimic significantly reduced HMGB1 expression and suppressed EMT, invasion, and migration, while the inhibitor generated the opposite effects. Additionally, using xenograft mouse models, we confirmed that HMGB1 overexpression increased tumour EMT. In summary, our results demonstrated that miR-200c could suppress EMT, invasion, and migration of NSCLC cells by downregulating HMGB1.

Sphingosine-1-phosphate as an amphipathic metabolite: its properties in aqueous and membrane environments

Sphingosine-1-phosphate (S1P) is currently considered to be an important signaling molecule in cell metabolism. We studied a number of relevant biophysical properties of S1P, using mainly Langmuir balance, differential scanning calorimetry, (31)P-NMR, and infrared (IR) spectroscopy. We found that, at variance with other, structurally related sphingolipids that are very hydrophobic, S1P may occur in either an aqueous dispersion or a bilayer environment. S1P behaves in aqueous media as a soluble amphiphile, with a critical micelle concentration of approximately 12 muM. Micelles give rise to larger aggregates (in the micrometer size range) at and above a 1 mM concentration. The aggregates display a thermotropic transition at approximately 60 degrees C, presumably due to the formation of smaller structures at the higher temperatures. S1P can also be studied in mixtures with phospholipids. Studies with dielaidoylphosphatidylethanolamine (DEPE) or deuterated dipalmitoylphosphatidylcholine (DPPC) show that S1P modifies the gel-fluid transition of the glycerophospholipids, shifting it to lower temperatures and decreasing the transition enthalpy. Low (<10 mol %) concentrations of S1P also have a clear effect on the lamellar-to-inverted hexagonal transition of DEPE, i.e., they increase the transition temperature and stabilize the lamellar versus the inverted hexagonal phase. IR spectroscopy of natural S1P mixed with deuterated DPPC allows the independent observation of transitions in each molecule, and demonstrates the existence of molecular interactions between S1P and the phospholipid at the polar headgroup level that lead to increased hydration of the carbonyl group. The combination of calorimetric, IR, and NMR data allowed the construction of a temperature-composition diagram ("partial phase diagram") to facilitate a comparative study of the properties of S1P and other related lipids (ceramide and sphingosine) in membranes. In conclusion, two important differences between S1P and ceramide are that S1P stabilizes the lipid bilayer structure, and physiologically relevant concentrations of S1P can exist dispersed in the cytosol.

Surface-active properties of the antitumour ether lipid 1-O-octadecyl-2-O-methyl-rac-glycero-3-phosphocholine (edelfosine)

The surface activity and interaction with lipid monolayers and bilayers of the antitumour ether lipid 1-O-octadecyl-2-O-methyl-rac-glycero-3-phosphocholine (edelfosine) have been studied. Edelfosine is a surface-active soluble amphiphile, with critical micellar concentrations at 3.5 microM and 19 microM in water. When the air-water interface is occupied by a phospholipid, edelfosine becomes inserted in the phospholipid monolayer, increasing surface pressure. This increase is dose-dependent, and reaches a plateau at ca. 2 microM edelfosine bulk concentration. The ether lipid can become inserted in phospholipid monolayers with initial surface pressures of up to 33 mN/m, which ensures its capacity to become inserted into cell membranes. Upon interaction with phospholipid vesicles, edelfosine exhibits a weak detergent activity, causing release of vesicle contents to a low extent (<5%), and a small proportion of lipid solubilization. The weak detergent properties of edelfosine can be related to its very low critical micellar concentrations. Its high affinity for lipid monolayers combined with low lytic properties support the use of edelfosine as a clinical drug. The surface-active properties of edelfosine are similar to those of other "single-chain" lipids, e.g. lysophosphatidylcholine, palmitoylcarnitine, or N-acetylsphingosine.

Effects of the anti-neoplastic agent ET-18-OCH3 and some analogs on the biophysical properties of model membranes

The effect of 1-O-octadecyl-2-O-methyl-sn-glycero-3-phosphocholine (ET-18-OCH(3), edelfosine), and six other analog asymmetric phosholipids on the physical properties of 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) model membranes was studied using differential scanning calorimetry (DSC), (31)P-nuclear magnetic resonance ((31)P NMR) and X-ray diffraction. DSC data revealed that, at concentrations of 40mol% and higher, a new type of mixtures with higher T(c) and narrower transitions appeared with all the asymmetric lipids studied. At very high concentrations of these lipids (50-80 mol%), destabilization was observed in the systems probably because of the formation of micelles or small vesicles. In all cases, the asymmetric lipids at concentrations of 40 mol% induced the formation of interdigitated structures in the lamellar gel phase, as deduced from X-ray diffraction. The asymmetric phospholipids were also added to 1,2-dielaidoyl-sn-glycero-3-phosphoethanolamine (DEPE) model membranes and DSC data revealed that the lipids primarily affected transition from the lamellar gel (L(beta)) to the lamellar liquid crystalline (L(alpha)) phase in two aspects: the transition temperature was reduced, and the transition itself became broader and smaller. The lamellar liquid crystalline (L(alpha)) to inverted hexagonal phase (H(II)) transition was also affected, as detected by DSC and (31)P NMR data. Increasing concentrations of the asymmetric lipids reduced the formation of inverted hexagonal phases, which were completely inhibited in the case of ET-18-OCH(3). Since these compounds have been shown to have important biological actions through the plasma membrane, these results may help to understand the mechanism of action of these compounds. In addition these asymmetric lipids were tested for their capacity to induce cell apoptosis, and only ET-18-OCH(3) was found to have a clear effect, thus suggesting that the apoptotic effect is not exerted through changes in the biophysical properties of model membranes.

Alkanes are not innocuous vehicles for hydrophobic reagents in membrane studies

Alkanes (C6-C16) are often used as vehicles for hydrophobic reagents, e.g. long-chain ceramides, in cell biology studies. It is generally understood that they are inert solvents, particularly when added in small volumes. However, simple calculations show that, under standard experimental conditions in cell studies, alkane: phospholipid molar ratios in excess of 1000:1 may be found. Even at much smaller ratios (close to 1:1) our studies with liposomes show that alkanes induce vesicle aggregation. Differential scanning calorimetry shows marked changes in both the gel-fluid and the lamellar-hexagonal transitions. Alkanes inhibit bacterial sphingomyelinase when acting on large unilamellar vesicles, and activate bacterial phospholipase C under the same conditions. Thus, the use of alkanes in cell studies requires strict control experiments to avoid artefactual results.

Different effects of long- and short-chain ceramides on the gel-fluid and lamellar-hexagonal transitions of phospholipids: a calorimetric, NMR, and x-ray diffraction study

The effects on dielaidoylphosphatidylethanolamine (DEPE) bilayers of ceramides containing different N-acyl chains have been studied by differential scanning calorimetry small angle x-ray diffraction and (31)P-NMR spectroscopy. N-palmitoyl (Cer16), N-hexanoyl (Cer6), and N-acetyl (Cer2) sphingosines have been used. Both the gel-fluid and the lamellar-inverted hexagonal transitions of DEPE have been examined in the presence of the various ceramides in the 0-25 mol % concentration range. Pure hydrated ceramides exhibit cooperative endothermic order-disorder transitions at 93 degrees C (Cer16), 60 degrees C (Cer6), and 54 degrees C (Cer2). In DEPE bilayers, Cer16 does not mix with the phospholipid in the gel phase, giving rise to high-melting ceramide-rich domains. Cer16 favors the lamellar-hexagonal transition of DEPE, decreasing the transition temperature. Cer2, on the other hand, is soluble in the gel phase of DEPE, decreasing the gel-fluid and increasing the lamellar-hexagonal transition temperatures, thus effectively stabilizing the lamellar fluid phase. In addition, Cer2 was peculiar in that no equilibrium could be reached for the Cer2-DEPE mixture above 60 degrees C, the lamellar-hexagonal transition shifting with time to temperatures beyond the instrumental range. The properties of Cer6 are intermediate between those of the other two, this ceramide decreasing both the gel-fluid and lamellar-hexagonal transition temperatures. Temperature-composition diagrams have been constructed for the mixtures of DEPE with each of the three ceramides. The different behavior of the long- and short-chain ceramides can be rationalized in terms of their different molecular geometries, Cer16 favoring negative curvature in the monolayers, thus inverted phases, and the opposite being true of the micelle-forming Cer2. These differences may be at the origin of the different physiological effects that are sometimes observed for the long- and short-chain ceramides.

An index of lipid phase diagrams

There is a growing awareness of the utility of lipid phase behavior data in studies of membrane-related phenomena. Such miscibility information is commonly reported in the form of temperature-composition (T-C) phase diagrams. The current index is a conduit to the relevant literature. It lists lipid phase diagrams, their components and conditions of measurement, and complete bibliographic information. The main focus of the index is on lipids of membrane origin where water is the dispersing medium. However, it also includes records on acylglycerols, fatty acids, cationic lipids, and detergent-containing systems. The miscibility of synthetic and natural lipids with other lipids, with water, and with biomolecules (proteins, nucleic acids, carbohydrates, etc.) and non-biological materials (drugs, anesthetics, organic solvents, etc.) is within the purview of the index. There are 2188 phase diagram records in the index, the bulk (81%) of which refers to binary (two-component) T-C phase diagrams. The remainder is made up of more complex (ternary, quaternary) systems, pressure-T phase diagrams, and other more exotic miscibility studies. The index covers the period from 1965 through to July, 2001.

Lipids favoring inverted phase enhance the ability of aerolysin to permeabilize liposome bilayers

Channel formation by the bacterial toxin aerolysin follows oligomerization of the protein to produce heptamers that are capable of inserting into lipid bilayers. How insertion occurs is not understood, not only for aerolysin but also for other proteins that can penetrate membranes. We have studied aerolysin channel formation by measuring dye leakage from large unilamellar egg phosphatidylcholine vesicles containing varying amounts of other lipids. The rate of leakage was enhanced in a dose-dependent manner by the presence of phosphatidylethanolamine, diacylglycerol, cholesterol, or hexadecane, all of which are known to favor a lamellar-to-inverted hexagonal (L-H) phase transition. Phosphatidylethanolamine molecular species with low L-H transition temperatures had the largest effects on aerolysin activity. In contrast, the presence in the egg phosphatidylcholine liposomes of lipids that are known to stabilize the lamellar phase, such as sphingomyelin and saturated phosphatidylcholines, reduced the rate of channel formation, as did the presence of lysophosphatidylcholine, which favors positive membrane curvature. When two different lipids that favor hexagonal phase were present with egg PC in the liposomes, their stimulatory effects were additive. Phosphatidylethanolamine and lysophosphatidylcholine canceled each other's effect on channel formation.

Phases and phase transitions of the phosphatidylcholines

LIPIDAT (http://www.lipidat.chemistry.ohio-state.edu) is an Internet accessible, computerized relational database providing access to the wealth of information scattered throughout the literature concerning synthetic and biologically derived polar lipid polymorphic and mesomorphic phase behavior and molecular structures. Here, a review of the data subset referring to phosphatidylcholines is presented together with an analysis of these data. This subset represents ca. 60% of all LIPIDAT records. It includes data collected over a 43-year period and consists of 12,208 records obtained from 1573 articles in 106 different journals. An analysis of the data in the subset identifies trends in phosphatidylcholine phase behavior reflecting changes in lipid chain length, unsaturation (number, isomeric type and position of double bonds), asymmetry and branching, type of chain-glycerol linkage (ester, ether, amide), position of chain attachment to the glycerol backbone (1,2- vs. 1,3-) and head group modification. Also included is a summary of the data concerning the effect of pressure, pH, stereochemical purity, and different additives such as salts, saccharides, amino acids and alcohols, on phosphatidylcholine phase behavior. Information on the phase behavior of biologically derived phosphatidylcholines is also presented. This review includes 651 references.

Effect of long-chain acyl-CoAs and acylcarnitines on gel-fluid and lamellar-hexagonal phospholipid phase transitions

The effect of a series of long-chain acyl-CoAs and acylcarnitines has been tested by differential scanning calorimetry on the gel-fluid transition of saturated phosphatidylcholines and of dietai-doylphosphatidylethanolamine (DEPE), and on the lamellar-Hexagonal transition of DEPE. Both series of acylderivatives have similar effects (the acylcarnitines being more potent): a decrease in the gel-fluid transition enthalpy and an increase in the gel-fluid transition width. Mixtures of dipalmitoylphosphatidylcholine with palmitoyl-CoA or palmitoylcarnitine (i.e. when all three hydrocarbon chains are 16C in length) display a peculiar behaviour, in that the main endotherm remains unchanged until a high proportion of palmitoylderivative is present, then it collapses suddenly. The disappearance of the gel-fluid main endotherm in the presence of palmitoylcarnitine is due to the fragmentation of the bilayer below the cooperative unit size of the phospholipid, while the same effect is caused by palmitoyl-CoA through the interaction of the coenzyme A polar moiety with the lipid-water interface, the overall bilayer structure being maintained. The effect of both series of compounds on the lamellar to inverted hexagonal phase transition of DEPE is also similar: they both stabilize the lamellar phase, increase the transition temperature and smear out the transition endotherm. Their behaviour may be rationalized considering that they are compounds with a bulky polar head, relative to their single hydrophobic chain, that would favour a positive curvature in the monolayer, while the inverted hexagonal phase requires a negative curvature.