Influence of a neoglycolipid and its PEO-lipid moiety on the organization of phospholipid monolayers.

The surface properties of the neoglycolipid (GlcNAcE(3)G(28)) and of its PEO-lipid (E(3)G(28)) moiety mixed with phospholipids (dipalmitoylphosphatidylcholine, DPPC; distearoylphosphatidylcholine, DSPC; diarachidoylphosphatidylcholine, DAPC; and dibehenoylphosphatidylcholine, DBPC) were studied in Langmuir monolayers at various mixture compositions and surface pressures. The pi-A isotherms of the pure compounds revealed that because of the presence of the sugar group in its molecule, GlcNAcE(3)G(28) collapsed at a higher surface pressure and occupied a larger molecular area than the PEO-lipid moiety. It was also observed that the presence of the PEO-lipid (E(3)G(28)) in the mixtures triggered a strong alteration of both phospholipid pi-A isotherm profiles and surface diffraction spectra, an indication that the disordering of the initially structured phospholipid monolayers took place. Unlike E(3)G(28), GlcNAcE(3)G(28) did not disorganize phospholipid monolayers but generated a partial segregation of the film-forming components. The calculated excess free energies of mixing (DeltaG(exc)) for GlcNAcE(3)G(28)-phospholipid mixtures enabled us to predict the stability of such systems.

Native and Hydrophobically Modified Human Immunoglobulin G at the Air/Water Interface.

The adsorption of human immunoglobulin G (IgG) at the air/water interface was monitored both by the in situ radiotracer technique using [(14)C] labeled IgG and by surface tension measurements. The results reveal that adsorption of IgG from single protein systems displays bimodality due to molecular rearrangements at the interface. Above the threshold value of 1.5x10(-2) mg/ml solution concentration, adsorbed IgG molecules reoriented from the side-on to the end-on configuration. The existence of a lag time which did not appear in Gamma=f(t) curves, was observed in Pi=f(t) relationships at low protein concentrations and was due to the limits of the surface pressure technique to detect protein adsorption. The adsorption of native IgG was also carried out in the presence of a hydrophobized IgG obtained by grafting capryloyl residues to its lysine groups by reaction with N-hydroxysuccinimide ester of caprylic acid, which yielded 19 covalently bound alkyl chains to the IgG molecule (19C(8)-IgG). This modified IgG exhibited enhanced adsorption at the air/water interface, as manifested by its increased adsorption efficiency relative to the native protein. Sequential and competitive adsorption experiments from binary mixtures of native IgG and 19C(8)-IgG clearly demonstrate that the displacement of the native protein from the air/water interface strongly depended on the manner of how 19C(8)-IgG and native IgG competed with each other. When the two proteins competed simultaneously, 19C(8)-IgG predominantly occupied the available area but when native IgG was adsorbed first, for 2 h, the sequentially adsorbed 19C(8)-IgG was incapable of substantially displacing it from the interface. Copyright 2001 Academic Press.

Molecular organization of the human serotonin transporter at the air/water interface.

The serotonin transporter (SERT) is the target of several important antidepressant and psychostimulant drugs. It has been shown that under defined conditions, the transporter spread at the air/water interface was able to bind its specific ligands. In this paper, the interfacial organization of the protein has been assessed from dynamic surface pressure and ellipsometric measurements. For areas comprising between 10,400 and 7,100 A(2)/molecule, ellipsometric measurements reveal an important change in the thickness of the SERT film. This change was attributed to the reorientation of the transporter molecules from a horizontal to their natural predictive transmembrane orientation. The thickness of the SERT film at 7,100 A(2)/molecule was found to be approximately equal to 84 A and coincided well with the theoretical value estimated from the calculations based on the dimensions of alpha-helices containing membrane proteins. These data suggest that the three-dimensional arrangement of the SERT may be represented as a box with lengths d(z)=83--85 A and d(y) or d(x)=41--47 A.

Fucosyled neoglycolipids: synthesis and interaction with a phospholipid.

The interfacial behavior of the neoglycolipids formed of Guerbet alcohol (G(28)) bound to a triethylene glycol spacer (E(3)) and to a sugar moiety (alpha- and beta-fucose) spread at the air/water interface has been studied under dynamic conditions of compression. Although the alpha (alpha-FucE3G28)- and beta-fucose (beta-FucE3G28) derivatives possessed the same chemical structure, the positioning of the sugar moiety relative to the whole molecule had a significant influence on the organization of neoglycolipid molecules in the spread monolayers. Thus, beta-fucose molecules exhibited higher compressibilities and larger molecular areas than a alpha/beta (84/16%) mixture (alpha(84)-FucE3G28). The comparison of the compressional behavior of the fucose derivatives with that of Guerbet alcohol in the absence and in the presence of the triethylene glycol spacer shows that the presence of the E(3) chain is necessary to stabilize the lipid at the interface and that the incorporation of a sugar moiety into the molecule resulted in an important expansion of a monolayer. Despite their different interfacial behaviors, the two sugar derivatives formed ideal mixtures when cospread at the air/water interface. Conversely, in the presence of a phospholipid, such as DMPC, repulsive interactions were observed and appeared to be stronger for DMPC/alpha(84)-FucE3G28 mixed monolayers. The membrane fluidity of DMPC liposomes bearing the studied amphiphilic molecules was assessed by fluorescence depolarization measurements. The results reveal that whereas G(28) was deeply inserted into the liposome bilayers, the presence of a E(3) chain and of a sugar moiety in these bilayers induced a transfer of the amphiphilic derivatives from the hydrophobic core towards polar headgroups of phospholipid molecules.

Ligand interaction with the purified serotonin transporter in solution and at the air/water interface.

The purified serotonin transporter (SERT) was spread at the air/water interface and the effects both of its surface density and of the temperature on its interfacial behavior were studied. The recorded isotherms evidenced the existence of a stable monolayer undergoing a lengthy rearrangement. SERT/ligand interactions appeared to be dependent on the nature of the studied molecules. Whereas an unrelated drug (chlorcyclizine) did not bind to the spread SERT, it interacted with its specific ligands. Compared to heterocyclic drugs, for which binding appeared to be concentration-dependent, a 'two-site' mechanism was evidenced for pinoline and imipramine.

Chemically Modified Glucose Oxidase with Enhanced Hydrophobicity: Adsorption at Polystyrene, Silica, and Silica Coated by Lipid Monolayers.

Covalent modification of glucose oxidase from Aspergillus niger by the palmitic acid ester of N-hydroxysuccinimide at a molar ratio ester:protein of 56:1 results in the formation of the enzyme derivative with 11 attached palmitic chains. Surface hydrophobicity measurements by a fluorescent probe, 8-anilino-1-naphthalenesulfonate, indicate a drastic increase in the hydrophobicity index of glucose oxidase after such a modification. The modified glucose oxidase displays a much higher adsorption affinity for hydrophilic (silica) as well as for hydrophobic (silica coated by phosphatidyl choline and cholesterol monolayers and polystyrene latex beads) surfaces, and forms more compact surface layers compared to the native glucose oxidase. Such a difference results from a spontaneous formation of micelle-like aggregates (clusters) of the hydrophobized enzyme molecules (average size 500 nm), which come into contact with a surface. A possible structure of the glucose oxidase surface layers and the nature of the forces determining the adsorption of the enzyme on various adsorbents are discussed. Copyright 1999 Academic Press.

Drug-Cyclodextrin Association Constants Determined by Surface Tension and Surface Pressure Measurements.

The complexation reaction between the amphiphilic peptide antibiotic polymyxin B and naturally occurring cyclodextrins, used as potential drug carriers, was quantitatively evaluated from surface tension measurements at various drug concentrations. The association constant, Ka, of polymyxin B:beta-cyclodextrin inclusion complex formation of 1:1 stoichiometry was determined from the change in the drug interfacial activity upon the addition of beta-cyclodextrin at the excess solution concentration (10(-3) M). The obtained Ka value is discussed in terms of molecular matching of the host cyclodextrin cavity and the guest drug molecule. Copyright 1999 Academic Press.

Drug-Cyclodextrin Association Constants Determined by Surface Tension and Surface Pressure Measurements.

The compression of water-insoluble drug monolayers spread on the aqueous subphase containing cyclodextrins (CD) led to a shift of surface pressure (pi)-area (A) isotherms toward smaller molecular areas with respect to the pi-A isotherms on the pure water subphase. The displacement of the compression isotherm obtained for the retinol spread on the beta-CD containing aqueous subphase was used to quantify the depletion process and to determine the drug-CD association constants. The proposed method appeared to be sensitive enough to account for extremely low amounts of sequestered drug molecules. The obtained values of the association constants Ka ranged from about 1.4.10(-2) to 36 m2/mol. The magnitudes of these constants are discussed in terms of drug bioavailability and of the stoichiometry of retinol-beta-cyclodextrin inclusion complex which was shown to have a 1:1 correspondence. Copyright 1999 Academic Press.

Penetration of Glucose Oxidase and of the Hydrophobically Modified Enzyme into Phospholipid and Cholesterol Monolayers.

The penetrant ability of the native glucose oxidase, GOx, and of the hydrophobically modified enzyme GO(mod) realized by grafting to its lysine residues alkyl C16 chains, into phosphatidylcholine dibehenoyl (DBPC), phosphatidylcholine dipalmitoyl (DPPC), phosphatidyl-ethanolamine dipalmitoyl (DPPE), phosphatidyl-serine dipalmitoyl (DPPS), and cholesterol (CHOL) monolayers was assessed by surface pressure measurements at constant area by enzyme injection to the aqueous phase beneath spread monolayers. As revealed by the magnitude of surface pressure increments (DeltaPi), both the quantities and the rates of penetration of the enzymes into these monolayers were lipid chemical nature and enzyme concentration dependent. When compared with GOx, GO(mod) displayed an enhanced penetrant ability into all the studied monolayers that resulted in rapidly attained DeltaPi plateau values, characteristic of stable systems. The influence of lipid hydrocarbon chain length and of the polar headgroup charge on the efficiency and effectiveness of GOx and GO(mod) penetration into these monolayers is discussed. Copyright 1999 Academic Press.

Adsorption of Hydrophobized Glucose Oxidase at Solution/Air Interface

The modification of glucose oxidase by palmitic acid ester of N -hydroxysuccinimide leads to the formation of a new hydrophobized enzyme with five covalently bound C16 groups. Such a modification was shown not to alter noticeably the native structure of the enzyme. The modified glucose oxidase displays enhanced surface activity at the water/air interface in comparison with the native enzyme. The maximum reduction of surface tension at all concentrations studied was higher for the modified glucose oxidase than for the native one. The modified enzyme also displayed a much steeper rise of the surface potential with time and a much more rapid attainment of the saturation plateau than the unmodified enzyme.

Liposomes bearing platelet proteins: a model for surface functions studies.

An improved procedure for the direct transfer of membrane proteins from human platelets to liposomes involving the treatment of platelets with linolenic acid was developed. The transfer of platelet proteins to liposomes prepared from the mixture of L-alpha-dimyristoyl-phosphatidylcholine/sphingomyelin in the molar ratio 80/20 appeared to be significantly enhanced compared with liposomes prepared from the same components mixed in other ratios. A wide range of platelet proteins was transferred, the most important being GPIb (170 kDa), GPIIb/IIIa (135 and 110 kDa). GPIV (90 kDa), GPIX (24 kDa) and the serotonin transporter (68 kDa). The recognition interactions between these proteoliposomes and specific protein antibodies clearly indicate that the non-invasive procedure used in this study ensured the reproducible transfer of platelet proteins without essentially altering their original conformation. The obtained results reveal also that the affinity of proteoliposomes to bind paroxetin was virtually the same as that of the native serotonin transporter. These results provide an indication of the possible use of such proteoliposomes as models to study at the molecular level the interaction of these proteins with their ligands.

Competitive adsorption of albumin against collagen at solution-air and solution-polyethylene interfaces.

The adsorption of human serum albumin (HSA) from the binary mixtures with collagen was monitored at solution-air and solution-polyethylene interfaces by the in situ measurements. The results clearly demonstrate that on both interfaces albumin is the only adsorbing protein within a large collagen solution concentration range. At the albumin concentration equal to 0.005 mg/mL, the presence of collagen in solution results in the enhancement of albumin adsorption at solution-air interface relative to its adsorption from the single protein system. The same phenomenon is manifested at the solution-polyethylene interface, although the increase in albumin adsorption at this interface occurs at the albumin concentration equal to 0.01 mg/mL. These results are attributed to the lowering in the solution-air and solution-polyethylene interfacial tensions, and thus to the increase in the spreading characteristics of albumin in the presence of collagen molecules. The desorption experiments carried out with a buffer solution on polyethylene surfaces reveal the irreversibility of adsorbed albumin from both the single and the binary mixtures with collagen. When after 20 h of adsorption from the solutions containing albumin only, collagen was added to these solutions or when the samples after that period of time were first rinsed with a buffer and then with a collagen solution, the amounts of albumin remaining at the surfaces were in both cases reduced by one-half.

Physico-chemical surface characterization of hyaluronic acid derivatives as a new class of biomaterials.

Three hyaluronic acid derivatives with different types and/or percentages of esterification, were analyzed by means of static contact angle measurements, SEM, ESCA, ATR/FT-IR, WAXS, DSC and TGA. The physico-chemical characterization of the three different samples, in both dry and wet state, was provided in terms of surface and bulk properties. ESCA and infrared analyses showed that the surface composition of all samples differs from that of the bulk. The hydrophilic-hydrophobic character of the samples changed according to the chemical composition as shown by ESCA and contact angle measurements. Both infrared and contact angle measurements reveal that surface restructuring occurred upon hydration for all the samples and the greater the hydrophilic character of the sample, the greater and faster the restructuring phenomenon. A clear picture of the different types of chemical groups has been established at different depth for the three materials.

[Stabilization and function of liposomes]. / Stabilisation et fonctionnalisation des liposomes.

Liposomes stability can be improved by covering them with polysaccharide derivatives. The anchoring mechanism of these derivatives into the lipid membrane has been studied and explained. In order to improve liposome specificity, protein transfer from erythrocytes and platelets into liposome membrane has been carried out. The effect of a newly developed phospholipid, DDPC, on the efficiency and the selectivity of protein transfer is reported.

Role of phospholipid lining on respiratory mucus clearance by cough.

Phospholipid lining, present at the respiratory mucus-mucosa interface, may have an important role in the protective function of the airways by its abhesive properties and may also facilitate mucus transport. To mimic respiratory mucus-mucosa interface, monolayers of three different forms of phosphatidylglycerol (PG) have been deposited on glass slides by the Langmuir-Blodgett technique. Mucus adhesion and clearance by cough of mucus on these PG-coated or noncoated surfaces have been analyzed and compared, using frog respiratory mucus as "normal" mucus. Among the three PG types studied, the phosphatidylglycerol distearoyl, which is the phospholipid with the longest saturated fatty acid chain, was found to significantly improve the mucus cough clearance by decreasing the mucus work of adhesion compared with the noncoated surfaces. On the other hand, phosphatidylglycerol dipalmitoyl did not improve mucus cough clearance although it decreased mucus adhesion, and phosphatidylglycerol dioleyl did not improve either mucus cough clearance or mucus adhesion.

Wettability of polymers by mucin aqueous solutions.

The wettability of poly(methyl methacrylate) and polyethylene by water and aqueous mucin solutions have been studied by sessile drop and under-water captive air bubble contact angles, respectively. From the sessile drop and octane under-water contact angles the polymer-water interfaces have been characterized in terms of works of adhesion and acid-base (polar) interactions. A large water-air contact angle hysteresis observed with poly(methyl methacrylate) surfaces has been attributed to side-chain beta relaxations of polymer ester methyl groups. The wettabilities of the polymers by mucin aqueous solutions have been studied as a function of protein concentration and related to the surface tensions. A positive slope of adhesion tension vs surface tension line, characteristic of polar surfaces, was found with poly(methyl methacrylate). By contrast, a change in the slope, explained as a change in mucin relative adsorption densities at solid/liquid and solid/vapour interfaces, was observed with polyethylene. This adhesion tension behavior appeared to be in agreement with previous data we have published concerning the quantity and state of mucin which are adsorbed to polymers characterized by different surface properties.

Complete denture retention. Part II: Wettability studies on various acrylic resin denture base materials.

The objective of this study was to characterize in vitro selected acrylic resin denture base materials by water-contact angle measurements. The sessile drop method and the underwater-bubble method were used. The results obtained from these measurements are discussed in terms of contact angle and polymer-water work of adhesion hysteresis. On polished heat-polymerized samples this hysteresis results from the reorientation of superficial polymer chains. The combined effect of increased sample roughness and of the entrapment of water droplets in the pores of material gives rise to the highest contact-angle hysteresis observed on sand-abraded samples. On the basis of physical analysis of the mechanism involved in complete denture retention, developed in Part I of this work, it is believed that the sand-abraded material is the most convenient for the retention of the complete denture.

[Insulin-phospholipid interactions. A study in monolayers by measuring surface potential]. / Interactions phospholipides-insuline. Etude en couches monomoléculaires par des mesures de potentiel de surface.

Surface potential (delta V) measurements were performed to assess information on insulin penetration/interaction with dipalmitoylphosphatidylcholine (DPPC) monolayers spread at the water-air interface. The results reveal existence of the threshold surface density value of spread lipid molecules (7.5 x 10(13) molecules/cm2) above which none penetration of insulin molecules occurs. Surface potential data clearly indicate also that insulin penetration/interaction with DPPC monolayers is enhanced in the presence of the second studied constituent of these monolayers in the order DPPC + stearylamine greater than DPPC + cholesteryl betainate greater than DPPC + cholesterol greater than DPPC. The results clearly indicate the existence of two types of phospholipid-insulin interactions namely: adsorption and penetration.

Monolayer studies on poly(isobutylcyanoacrylate)-ampicillin association.

Surface pressure-area isotherms (pi-A) of poly(isobutylcyanoacrylate) monolayers with or without glucose and dextran as polymerization adjuvants used in the preparation of nanoparticles have been derived from measurements made at the air-water interface with the subphase pH at 2.7, 5.5 or 8.8. The isotherms were characteristic of the expanded type of polymer monolayer curves, yielding unusually low limiting area values compared with those of other known poly(acrylate) derivatives. This behaviour may be explained by the folding of polar moieties of the polymer groups in the water subphase. Ampicillin incorporated during preparation of nanoparticles had a negligible effect on the general behaviour of adjuvant-free monolayers, but a significant one on the adjuvant-loaded polymer monolayer system which showed an increase in surface area throughout the compression cycle, as compared with the surface area of the adjuvant-free polymer system although the collapse pressure was practically the same at 67 mN m-1.