Dipalmitoylphosphatidylcholine Films Research Articles

Formation of ring calcium oxalate patterns induced by domains in DPPC Langmuir–Blodgett films

The ring patterns of calcium oxalate crystals were induced by domains in Langmuir–Blodgett (LB) films of dipalmitoylphosphatidylcholine (DPPC). The result was explained by the defects at the ring boundaries of liquid condensed (LC) and liquid expanded (LE) phases of LB film. These boundaries could provide less free energy and much more nucleating sites for COM crystals.

Effects of albumin and erythrocyte membranes on spread monolayers of lung surfactant lipids

Dipalmitoyl phosphatidylcholine (DPPC), one of the main constituents of lung surfactant is mainly responsible for reduction of surface tension to near 0 mN/m during expiration, resisting alveolar collapse. Other unsaturated phospholipids like palmitoyloleoyl phosphatidylglycerol (PG), palmitoyloleoyl phosphatidylcholine (POPC) and neutral lipids help in adsorption of lung surfactant to the air–aqueous interface. Lung surfactant lipids may interact with plasma proteins and hematological agents flooding the alveoli in diseased states. In this study, we evaluated the effects of albumin and erythrocyte membranes on spread films of DPPC alone and mixtures of DPPC with each of PG, POPC, palmitoyloleoyl phosphatidylethanolamine (PE), cholesterol (CHOL) and palmitic acid (PA) in 9:1 molar ratios. Surface tension–area isotherms were recorded using a Langmuir–Blodgett (LB) trough at 37 °C with 0.9% saline as the sub-phase. In the presence of erythrocyte membranes, DPPC and DPPC + PA monolayers reached minimum surface tensions of 7.3 ± 0.9 and 9.6 ± 1.4 mN/m, respectively. Other lipid combinations reached significantly higher minimum surface tensions >18 mN/m in presence of membranes (Newman Keul's test, p < 0.05). The relative susceptibility to membrane inhibition was [(DPPC + PG, 7:3) = (DPPC + PG, 9:1) = (DPPC + POPC) = (DPPC + PE) = (DPPC + CHOL)] > [(DPPC + PA) = (DPPC)]. The differential response was more pronounced in case of albumin with DPPC and DPPC + PA monolayers reaching minimum surface tensions less than 2.4 mN/m in presence of albumin, whereas DPPC + PG and DPPC + POPC reached minimum surface tensions of around 20 mN/m in presence of albumin. Descending order of susceptibility of the spread monolayers of lipid mixtures to albumin destabilization was as follows: [(DPPC + PG, 7:3) = (DPPC + PG, 9:1) = (DPPC + POPC)] > [(DPPC + PE) = (DPPC + CHOL)] > [(DPPC + PA) = (DPPC)] The increase in minimum surface tension in presence of albumin and erythrocyte membranes was accompanied by sudden increases in compressibility at surface tensions of 15–30 mN/m. This suggests a monolayer destabilization and could be indicative of phase transitions in the mixed lipid films due to the presence of the hydrophobic constituents of erythrocyte membranes.

Lung surfactant dysfunction in tuberculosis: Effect of mycobacterial tubercular lipids on dipalmitoylphosphatidylcholine surface activity

In pulmonary tuberculosis, Mycobacterium tuberculosis bacteria reside in the alveoli and are in close proximity with the alveolar surfactant. Mycolic acid in its free form and as cord factor, constitute the major lipids of the mycobacterial cell wall. They can detach from the bacteria easily and are known to be moderately surface active. We hypothesize that these surface-active mycobacterial cell wall lipids could interact with the pulmonary surfactant and result in lung surfactant dysfunction. In this study, the major phospholipid of the lung surfactant, dipalmitoylphosphatidylcholine (DPPC) and binary mixtures of DPPC:phosphatidylglycerol (PG) in 9:1 and 7:3 ratios were modelled as lung surfactant monolayers and the inhibitory potential of mycolic acid and cord factor on the surface activity of DPPC and DPPC:PG mixtures was evaluated using Langmuir monolayers. The mycobacterial lipids caused common profile changes in all the isotherms: increase in minimum surface tension, compressibility and percentage area change required for change in surface tension from 30 to 10 mN/m. Higher minimum surface tension values were achieved in the presence of mycolic acid (18.2 ± 0.7 mN/m) and cord factor (13.28 ± 1.2 mN/m) as compared to 0 mN/m, achieved by pure DPPC film. Similarly higher values of compressibility (0.375 ± 0.005 m/mN for mycolic acid:DPPC and 0.197 ± 0.003 m/mN for cord factor:DPPC monolayers) were obtained in presence of mycolic acid and cord factor. Thus, mycolic acid and cord factor were said to be inhibitory towards lung surfactant phospholipids. Higher surface tension and compressibility values in presence of tubercular lipids are suggestive of an unstable and fluid surfactant film, which will fail to achieve low surface tensions and can contribute to alveolar collapse in patients suffering from pulmonary tuberculosis. In conclusion a biophysical inhibition of lung surfactant may play a role in the pathogenesis of tuberculosis and may serve as a target for the development of new drug loaded surfactants for this condition.

Mixed monolayers of Bauhinia monandra and Concanavalin A lectins with phospholipids, part II

Isotherms of surface pressure and surface potential versus mean molecular area for dibehenoylphosphatidylcholine (DBPC), dipalmitoylphosphatidylcholine (DPPC), dipalmitoylphosphatidylethanolamine (DPPE), and dioleoylphosphatidylcholine (DOPC) monolayers were shown to be greatly modified when these lipids were cospread with either Bauhinia monandra (BmoLL) or Concanavalin A (Con A) lectins. For the binary films of DBPC, DPPC, and DPPE cospread with each of these two lectins, there was both a displacement of the Π – A and Δ V – A isotherms toward higher molecular areas relative to pure lipids and an increase in the maximum surface potential values relative to the Δ V – A relationships observed for the corresponding single-lectin systems. Both effects can be understood in terms of the occurrence of an explicit interaction between the lipids and the lectins. The plots of the corresponding compressibilities versus molecular areas reveal that, for all lipids but DOPC, the extent of this interaction was always larger for BmoLL than for Con A. The DPPC and DPPE mixed films with BmoLL differed in compressibility. Owing to the small DPPE polar headgroup, the DPPE–BmoLL film was much more incompressible than the DPPC–BmoLL mixed monolayer. However, for the DOPC–BmoLL and DOPC–Con A mixed films there was no evidence that an interaction between the lectins and the lipid took place, a fact attributed to the unsaturated character in the DOPC aliphatic chains, which leads to an expanded Π – A isotherm.

Influence of a Fluorescent Probe on the Nanostructure of Phospholipid Membranes: Dipalmitoylphosphatidylcholine Interfacial Monolayers

Monolayers of dipalmitoylphosphatidylcholine (DPPC), both in the absence and in the presence of 1% (mol/mol) of a fluorescent phospholipid probe, have been spread at the air-liquid interface of a surface balance, compressed up to pressures in the liquid-expanded/liquid-condensed plateau of the isotherm, transferred onto mica supports, and analyzed by scanning force microscopy (SFM). Supported DPPC films showed micrometer-sized condensed domains with morphology and size that were entirely analogous to those observed in situ at the air-liquid interface by epifluorescence microscopy. The analysis by SFM, however, allowed the study and comparison of monolayers in the absence and in the presence of the fluorescent marker. This analysis revealed that the presence of dye reduced by 10-20% the total amount of the liquid-condensed phase in the DPPC films. The presence of the dye also decreased the mechanical stability of the film and increased the time required for the monolayer to equilibrate. The resolution of SFM permitted the determination that the structures of both the liquid-expanded and the liquid-condensed regions of DPPC films were heterogeneous at the nanometer scale. Liquid-condensed DPPC microdomains contained nanoholes covering 4-8% of their area whereas 60-80% of the surface detected as liquid-expanded by fluorescence microscopy consisted of a condensed-like framework of nanodomains. The total area, the shape of the nanodomains, and their interconnectivity were affected by the presence of the probe, suggesting that care must be taken when studying the structure, especially at the nanometer scale, and properties of model lipid films in the presence of extrinsic probes.

Effect of Pulmonary Surfactant Protein SP-B on the Micro- and Nanostructure of Phospholipid Films

Monolayers of dipalmitoylphosphatidylcholine (DPPC) and DPPC/dipalmitoylphosphatidylglycerol (DPPG) (7:3, w/w) in the absence or in the presence of 2, 5, 10, or 20 weight percent of porcine surfactant protein SP-B were spread at the air-liquid interface of a surface balance, compressed up to surface pressures in the liquid-expanded/liquid-condensed (LE-LC) plateau of the isotherm, transferred onto mica supports, and analyzed by scanning force microscopy. In the absence of protein, the films showed micrometer-sized condensed domains with morphology and size that were analogous to those observed in situ at the air-liquid interface by epifluorescence microscopy. Scanning force microscopy permits examination of the coexisting phases at a higher resolution than previously achieved with fluorescent microscopy. Both LE and LC regions of DPPC films were heterogeneous in nature. LC microdomains contained numerous expanded-like islands whereas regions apparently liquid-expanded were covered by a condensed-like framework of interconnected nanodomains. Presence of increasing amounts of pulmonary surfactant protein SP-B affected the distribution of the LE and LC regions of DPPC and DPPC/DPPG films both at the microscopic and the nanoscopic level. The condensed microdomains became more numerous but their size decreased, resulting in an overall reduction of the amount of total LC phase in both DPPC and DPPC/DPPG films. At the nanoscopic level, SP-B also caused a marked reduction of the size of the condensed-like nanodomains in the LE phase and an increase in the length of the LE/LC interface. SP-B promotes a fine nanoscopic framework of lipid and lipid-protein nanodomains that is associated with a substantial mechanical resistance to film deformation and rupture as observed during film transference and manipulation. The effect of SP-B on the nanoscopic structure of the lipid films was greater in DPPC/DPPG than in pure DPPC films, indicating additional contributions of electrostatic lipid-protein interactions. The alterations of the nanoscopic structures of phospholipid films by SP-B provide the structural framework for the protein simultaneously sustaining structural stability as well as dynamical flexibility in surfactant films at the extreme conditions imposed by the respiratory mechanics. SP-B also formed segregated two-dimensional clusters that were associated with the boundaries between LC microdomains and the LE regions of DPPC and DPPC/DPPG films. The presence of these clusters at protein-to-lipid proportions above 2% by weight suggests that the concentration of SP-B in the surfactant lipid-protein complexes may be close to the solubility limit of the protein in the lipid films.

Oxidation of Ascorbic Acid by Rutin at a Glassy Carbon Electrode Modified with Lipid Films

A stable film was prepared by casting dipalmitoylphosphatidylcholine (DPPC) and rutin onto the surface of a glassy carbon (GC) electrode. The electrochemistry behavior of rutin in the DPPC film was investigated. The modified electrode coated with rutin shows a quasi-reversible reduction-oxidation peak on the cyclic voltammogram in phosphate buffer (pH 7.4). This model of biological membrane was not only used to provide biological environment but also to investigate the oxidation of ascorbic acid by rutin. The DPPC-rutin modified electrode behaves as electrocatalytic oxidation to ascorbic acid. The oxidation peak current of ascorbic acid increases drastically and the peak potential of 4 x 10(-4) mol L-1 ascorbic acid shifts negatively about 100 mV compared with that obtained at a bare glassy carbon electrode. The catalytic current increased linearly with the ascorbic acid concentration in the range of 2 x 10(-4) mol L-1 and 1.4 x 10(-3) mol L-1 at a scan rate of 50 mV s(-1).

Interfacial behaviour and mechanical properties of spread lung surfactant protein/lipid layers

The surface behaviour of spread dipalmitoyl phosphatidyl choline (DPPC), lung surfactant protein C (SP-C), and their mixtures were characterised using a captive bubble surfactometer. The surface tension was determined by using axisymmetric bubble shape analysis. Surface dilatational rheological behaviour was characterised by sinusoidal oscillation of the bubble volume and at frequencies 0.006–0.025 Hz. The π/ A isotherms of DPPC, SP-C, and their mixtures were described with a generalised equation of state. Monolayer cycling of mixed DPPC/SP-C layers yields isotherms with a plateau in the range of 50–53 mN/m. When the surface pressure becomes higher SP-C is squeezed out of the film, but it re-enters the film upon expansion. Surface dilatational elasticities of DPPC films had a maximum at about 30 mN/m. At higher surface pressures, the films became brittle and the elasticity decreased. A slightly pronounced maximum was found at a surface pressure exceeding 55 mN/m. The dilatational viscosity had two distinct maxima, corresponding with those in the elasticity curves, i.e. one before the minimum area demand, and one in the range of over-compression. This was explained by the formation of a second ordered complex structure in the range of film over-compression. SP-C films show continuously increasing dilatational elasticities and viscosities with a maximum at f≈0.02 Hz. Mixed monolayers, DPPC+2 mol% SP-C, had dilatational elasticities increasing with surface pressure. In contrast to DPPC alone, an elasticity maximum appeared in the range of the squeeze out plateau. The dilatational viscosity had two distinct maxima as observed for DPPC, whereas the maximum before the squeeze out plateau is very broad like that of SP-C. The viscosity decreased for frequencies higher 0.02 Hz favouring elastic properties of the film. Our data provide experimental evidence that SP-C mixed with DPPC yield higher elasticities and viscosities as compared with films formed by the single components. This behaviour is likely to support breathing cycles, especially for the turn from inspiration to expiration and vice versa.

Electrocatalytic oxidation of NADH by rutin in biomembrane-like films on glassy carbon electrode

Stable lipid film was made by casting dipalmitoylphosphatidylcholine (DPPC) and rutin onto the surface of a glassy carbon (GC) electrode. The electrochemical behavior of rutin in the DPPC film was studied. The modified electrode coated with rutin gave quasi-reversible reduction-oxidation peak on cyclic voltammogram in the phosphate buffer (pH 7.4). The peak current did not decrease apparently after stored at 4°C for 8 hours in refrigerator. This model of biological membrane was used to investigate the oxidation of dihydronicotinamide adenine dinucleotide (NADH) by rutin. Rutin in the film acts as a mediator. The modified electrode shows a great enhancement and the anodic peak potential was reduced by about 220 mV in the oxidation of 5×10 −3 mol L −1 NADH compared with that obtained at a bare glassy carbon electrode.

Imaging Phospholipid Arrangement in Pultonary Surfactant Using Atomic Force Microscopy

Lung surfactant stabilizes the pulmonary air-water interface, by enriching this interface with films of amphipathic phospholipids. These films reduce the surface tension of the air-water interface to very low values (∼ 1 mN/m) at end expiration and prevents alveolar collapse. Surfactant contains mainly phospholipids (90%), and small amounts of associated proteins. Among the phospholipids, saturated dipalmitoylphosphatidylcholine (DPPC) and monounsaturated phosphatidylcholine are the main surfactant components, although significant amounts of other lipids are also present (1). DPPC is the only component of surfactant which exists in gel phase at physiological temperature, films of which can reduce the air-water surface tension to low values. DPPC films can undergo a fluid to gel transition with increase in the molecular packing leading to superstructures or domains (2). However it is not clear how the molecules of surfactant pack at the air-water interface to form highly compact films, and if DPPC phase segregate in such films.

Langmuir Films of Pure Antibiotic Ionophores and of Mixtures with Phospholipid at Different Temperatures

New results are presented concerning insertion of two antibiotic ionophores Lasalocid and Monensin as sodium salts (LAS-Na, MON-Na) in biomimetic membranes. Langmuir films of Dipalmitoylphosphatidylcholine (DPPC) have been used as model systems. Evolution of the compression isotherms has been investigated below the gel - liquid crystal phase transition, between the ambiant and temperatures approching physiological conditions, not only for the pure antibiotics but also for the antibiotic - lipid mixtures, the molecular ratio ρ antibi-otic/lipid equal to 0.1. In the mixed films with LAS-Na, the antibiotic molecule is well maintained by the film also when raising the temperature, whereas MON-Na is expelled above the low pressure region. The results are discussed and compared with effects produced in model systems of bilayers submitted to similar temperature variations.

Interactions of pulmonary surfactant protein SP-A with monolayers of dipalmitoylphosphatidylcholine and cholesterol: roles of SP-A domains

Pulmonary surfactant protein A (SP-A) is an oligomeric glycoprotein that binds dipalmitoylphosphatidylcholine (DPPC). Interactions of rat SP-A and recombinant SP-As with pure and binary monolayers of DPPC and cholesterol were studied using a rhomboid surface balance at 37°C. A marked inflection at equilibrium surface tension (23 mN/m) in surface tension-area isotherm of a pure DPPC film was abolished by rat SP-A. The inflection was decreased and shifted to 18 mN/m with wild-type recombinant SP-A (SP-Ahyp). Both rat SP-A and SP-Ahyp decreased surface area reduction required for pure DPPC films to reach near zero surface tension from 30 to 25%. SP-Ahyp,E195Q,R197D, mutated in carbohydrate recognition domain (CRD) known to be essential for SP-A–vesicle interactions, conveyed a detrimental effect on DPPC surface activity. SP-AΔG8-P80, with deletion of collagen-like domain, had little effect. Both SP-Ahyp,C6S (Ser substitution for Cys6) and SP-Ahyp,ΔN1-A7 (N-terminal segment deletion) which appear mainly as monomers on non-reducing SDS-PAGE analysis, increased required surface area reduction for minimal surface tension. All SP-As reduced collapse surface tension of a pure cholesterol film from 27 to 23 mN/m in the presence of Ca2+. When mixed films were formed by successive spreading of DPPC/SP-A/cholesterol, rat SP-A, SP-Ahyp, or SP-AΔG8-P80 blocked the interaction of cholesterol with DPPC; SP-Ahyp,E195Q,R197D could not impede the interaction; SP-Ahyp,C6S or SP-Ahyp,ΔN1-A7 only partially blocked the interaction, and cholesterol appeared to stabilize SP-Ahyp,C6S–DPPC association. These results demonstrate the importance of CRD and N-terminal dependent oligomerization in SP-A–phospholipid associations. The findings further indicate that SP-A–cholesterol interactions differ from SP-A–DPPC interactions and may be nonspecific.—Yu, S-H., F. X. McCormack, D. R. Voelker, and F. Possmayer. Interactions of pulmonary surfactant protein SP-A with monolayers of dipalmitoylphosphatidylcholine and cholesterol: roles of SP-A domains. J. Lipid Res. 1999. 40: 920–929.

Interactions of cyclosporin A with phospholipid membranes: effect of cholesterol.

Cyclosporin A (CsA) is a highly hydrophobic drug used to prevent graft rejection after organ transplantation. Interactions of CsA with phosphatidylcholine as well as with binary mixtures containing phosphatidylcholine and cholesterol were investigated by measuring the penetration of CsA into lipid monolayers at an air/water interface, by differential scanning calorimetry, and by imaging with fluorescence microscopy the effects of CsA on the lateral distribution of a fluorescent probe, 1-palmitoyl-2-(N-4-nitrobenz-2-oxa-1, 3-diazol)aminocaproyl-phosphocholine, in monolayers. Film penetration studies revealed the association of CsA with lipids to be a biphasic process. Cholesterol diminished the intercalation of CsA into the monolayer at surface pressures of >19 mN/m. CsA broadened the main transition of dimyristoylphosphatidylcholine (DMPC)/beta-cholesterol (10:1, mol/mol) multilamellar vesicles. The behavior of the transition enthalpy was more complex; the behavior of DMPC/beta-cholesterol multilamellar vesicles in the XCsA of 0 to 0.1 showed at most ratios a increase, but several well distinct dips were observed. The results are interpreted in terms of regular structures in tertiary alloy. Influence of CsA on lateral organization could be verified for lipid domains observed by fluorescence microscopy of lipid monolayers. More specifically, CsA altered the distribution of 1-palmitoyl-2-(N-4-nitrobenz-2-oxa-1, 3-diazol)aminocaproyl-phosphocholine in a dipalmitoylphosphatidylcholine film and in DPPC/beta-cholesterol (88:10, mol/mol) mixtures in a manner that suggests that CsA partitions into the boundaries between fluid and gel domains. To our knowledge, this constitutes the first demonstration of a change in lipid domain morphology to be induced by a drug molecule.

Phase Transitions in Films of Lung Surfactant at the Air-Water Interface

Pulmonary surfactant maintains a putative surface-active film at the air-alveolar fluid interface and prevents lung collapse at low volumes. Porcine lung surfactant extracts (LSE) were studied in spread and adsorbed films at 23 ± 1°C using epifluorescence microscopy combined with surface balance techniques. By incorporating small amounts of fluorescent probe 1-palmitoyl-2-nitrobenzoxadiazole dodecanoyl phosphatidylcholine (NBD-PC) in LSE films the expanded (fluid) to condensed (gel-like) phase transition was studied under different compression rates and ionic conditions. Films spread from solvent and adsorbed from vesicles both showed condensed (probe-excluding) domains dispersed in a background of expanded (probe-including) phase, and the appearance of the films was similar at similar surface pressure. In quasistatically compressed LSE films the appearance of condensed domains occurred at a surface pressure ( π) of 13 mN/m. Such domains increased in size and amounts as π was increased to 35 mN/m, and their amounts appeared to decrease to 4% upon further compression to 45 mN/m. Above π of 45 mN/m the LSE films had the appearance of filamentous materials of finely divided dark and light regions, and such features persisted up to a π near 68 mN/m. Some of the condensed domains had typical kidney bean shapes, and their distribution was similar to those seen previously in films of dipalmitoylphosphatidylcholine (DPPC), the major component of surfactant. Rapid cyclic compression and expansion of LSE films resulted in features that indicated a possible small (5%) loss of fluid components from such films or an increase in condensation efficiency over 10 cycles. Calcium (5 mM) in the subphase of LSE films altered the domain distribution, decreasing the size and increasing the number and total amount of condensed phase domains. Calcium also caused an increase in the value of π at which the maximum amount of independent condensed phase domains were observed to 45 mN/m. It also induced formation of large amounts of novel, nearly circular domains containing probe above π of 50 mN/m, these domains being different in appearance than any seen at lower pressures with calcium or higher pressures in the absence of calcium. Surfactant protein-A (SP-A) adsorbed from the subphase onto solvent-spread LSE films, and aggregated condensed domains in presence of calcium. This study indicates that spread or adsorbed lung surfactant films can undergo expanded to condensed, and possibly other, phase transitions at the air-water interface as lateral packing density increases. These phase transitions are affected by divalent cations and SP-A in the subphase, and possibly by loss of material from the surface upon cyclic compression and expansion.

Scanning force microscopy characterization of thin lipid films on a substrate

The surface morphology and frictional property of self-assembled domains of ultrathin organic films adsorbed on a solid substrate have been studied by a commercially available scanning probe microscopy with an operation mode of simultaneous atomic force microscopy and lateral force microscopy measurements. Two lipid film systems have been studied; one is a film system formed from synthetic dialkyl lipid, N, N-dioctadecylsuccinamic acid, and the other is films formed from biological phospholipids such as dipalmitoylphosphatidylcholine (DPPC), phosphatidylcholine, and phosphatidylethanolamine. The characteristic self-assembled domain structures as well as the local friction behaviors of the lipid films are presented. A preliminary result is also shown which suggests the hydrophobic alkyl tail groups appeared on multilamellar surfaces of DPPC film can be distinguished from the other hydrophilic polar headgroups.

Differential activity and lack of synergy of lung surfactant proteins SP-B and SP-C in interactions with phospholipids.

This study shows that the hydrophobic lung surfactant proteins (SP)-B and SP-C are not synergistic in enhancing functionally relevant surface behaviors in films and dispersions with phospholipids, and that SP-B is more effective than SP-C in facilitating surface activity. Purified bovine SP-B, SP. C, or SP-B/C (1/1 by wt) were combined with chroma tographically purified calf lung surfactant phospholipids (PPL), or with dipalmitoyl phosphatidylcholine (DPPC) or complex phospholipid mixtures containing 75% or 50% DPPC (75% SPL or 50% SPL). Adsorption was consistently better in corresponding mixtures of phospholipids plus SP-B versus SP-C, but was not improved further by substitution of SP-B/C for SP-B. Interfacial films of DPPC or SPL plus 1.3% SP-B or 1.3% SP-C had improved respreading compared to phospholipids alone (Wilhelmy balance, 23 degrees C and 37 degrees C), but substitution of mixed SP-B/C for either pure apoprotein did not increase respreading further. Surface-excess films of phospholipids plus SP-B had higher maximum surface pressures, or maintained a high maximum pressure through more consecutive compressions, than corresponding films with SP-C. Dispersions of phospholipids plus 1.3% SP-B or mixed (1/1) SP-B/C (2.6%) rapidly lowered surface tension to < 1 mN/m in oscillating bubble studies (20 cpm, 37 degrees C), while corresponding dispersions containing SP-C reduced surface tension more slowly or reached higher minima. Mixtures of 50% SPL with SP-B versus SP-C were also better able to resist inhibition by serum albumin in bubble and adsorption studies, and inhibition resistance was not significantly improved in mixtures containing 2.6% SP-B/C (1/1) versus 1.3% SP-B. The lack of synergy in hydrophobic apoprotein function, coupled with the greater effectiveness of SP-B in improving phospholipid adsorption, dynamic surface activity, and inhibition resistance, suggests that mixtures of phospholipids plus SP-B or related peptides may be particularly relevant its clinical exogenous surfactants.

Calcium ions and interactions of pulmonary surfactant proteins SP-B and SP-C with phospholipids in spread monolayers at the air/water interface

Spread monolayers containing hydrophobic pulmonary surfactant protein, SP-B or SP-C, or SP-B/SP-C ( 2:1, w w ), alone or mixed with dipalmitoylphosphatidylcholine (DPPC) or dipalmitoylphosphatidylglycerol (DPPG), were formed on saline subphases containing calcium ions. Surface pressure-area characteristics of the films of the proteins were not affected by the presence of Ca 2+ in the subphase. Calcium ions did not alter the surface properties of the binary and ternary films of DPPC plus either SP-B, or SP-C, or SP-B/SP-C (2:1, w w . Surface pressure-area isotherms for the spread films of DPPG plus hydrophobic surfactant protein were Ca 2+-dependent. The exclusion pressures of SP-B, SP-C and SP-B/SP-C ( 2:1, w w ) from protein-DPPG films in the presence of calcium were lower than the exclusion pressures in the absence of Ca 2+. The divalent cation appeared to suppress the ability of SP-C and SP-B/SP-C (2:1, w/w) to remove phospholipid during: squeeze-out from their mixed films with DPPG. The effects of Ca 2+ on the monolayers of DPPG plus hydrophobic surfactant proteins were consistent with calcium producing diminished lipid-protein interactions, possibly resulting from Ca 2+-induced changes in the ionization state and molecular packing of DPPG.

Observation of chiral domain morphology in a phospholipid Langmuir-Blodgett monolayer by atomic force microscopy

Using atomic force microscopy, we directly observe monolayer Langmuir-Blodgett (LB) films of dipalmitoylphosphatidylcholine (DPPC) deposited onto a solid substrate. Under specified deposition conditions, we find that the lipid monolayers form two-dimensional chiral morphologies, most with 2-,3-, 4- or 6-fold rotation symmetry, which is directly related to the enantiomorphic configuration of the lipids composing the monolayer. In addition, the high resolution AFM images also reveal the fine structure of the domains in the two-phase coexistence region as well as within a single sollid phase domain, which cannot be identified by optical microscopic techniques.

Pulmonary surfactant proteins SP-B and SP-C in spread monolayers at the air-water interface: III. Proteins SP-B plus SP-C with phospholipids in spread monolayers

Spread binary monolayers of surfactant-associated proteins SP-B and SP-C were formed at the air-water interface. Surface pressure measurements showed no interactions between the hydrophobic proteins. The effects of a mixture of SP-B plus SP-C (2:1, w/w) on the properties of monolayers of dipalmitoylphosphatidylcholine (DPPC), dipalmitoylphosphatidylglycerol (DPPG), and DPPC:DPPG (7:3, mol:mol) were studied. During compression of ternary and quaternary films, containing less than 0.4 mol% or 5 weight% total protein, the proteins were not squeezed out and appeared to remain associated with the film until collapse at surface pressures of about 65-70 mN.m-1. At initial concentrations of total protein of about 0.9 mol% or 10 weight%, exclusion of protein-lipid complexes was observed at 40-50 mN.m-1. Larger amounts of phospholipid were removed by proteins from (SP-B:SP-C)/DPPG films than from (SP-B:SP-C)/DPPC ones. Separate squeeze-out of SP-B (or SP-B plus DPPC) at about 40 mN.m-1, followed by exclusion of SP-C (or SP-C plus DPPC) at about 50 mN.m-1, was observed in (SP-B:SP-C)/DPPC films. This led to a conclusion that there was independent behavior of SP-B and SP-C in (SP-B:SP-C)/DPPC monolayers. The quaternary (SP-B:SP-C)/(DPPC:DPPG) films showed qualitatively similar process of squeeze-out of the proteins. In the ternary mixtures of SP-B plus SP-C with DPPG separate exclusion of SP-B was not detected; rather, the data was consistent with exclusion of a (SP-B:SP-C)/DPPG complex at about 50 mN.m-1. The results imply possible interactions between SP-B and SP-C and the acidic phospholipid.

Mixed monolayers of dipalmitoylphosphatidylcholine with Azone or oleic acid at the air-water interface

The surface pressure-area characteristics of the skin penetration enhancers Azone ( N-dodecylazacycloheptanone) and oleic acid have been recorded as compression isotherms at 25 ° C of the pure films and in mixed monolayers with dipalmitoylphosphatidylcholine (DPPC). Holding the pure films at constant surface pressures revealed a slow dissolution of the Azone monolayers into the aqueous subphase compared with a negligible loss from the oleic acid and DPPC films. The mean area/molecule in the oleic acid mixtures followed the simple additivity rule but large expansions were evident in the case of the Azone mixtures. Both enhancers gradually reduced and finally abolished the liquid-expanded to liquid-condensed (LE/LC) phase transition of DPPC with increasing mole fraction and Azone was the more effective in this respect. Collapse pressures of the mixed films indicated miscibility of the components with evidence for the existence of an Azone-rich surface phase at high mole fractions. These results indicate the very clear differences in the effects exerted upon lipid packing by these two enhancers and the importance of the Azone head-group conformation to its activity. It is therefore likely that similar differences occur when these molecules interact with the lipid lamellae of the stratum corneum. The miscibility of lipids and enhancers is also a significant consideration in determining transport characteristics across the epidermis.