Addition Of SP-B Research Articles

Effect of platelet size in a soft nanocomposite: Physical gelation and yielding

We investigated the role of the platelet size in the viscoelasticity of a soft solid nanocomposite, which consisted of exfoliated clay in a liquid polymer matrix. The internal connectivity of the nanocomposite reduced significantly when made up of smaller platelets. This expresses itself in a lowering of the modulus and an increase in relaxation times. Sample preparation played a critical role in these experimental findings. Two liquid polybutadienes served as matrix fluids, a nonfunctionalized polybutadiene (PB), which is a noninteracting liquid, and a carboxyl terminated polybutadiene (sPB), which caused the clay to exfoliate. Unexfoliated clay particles were suspended in PB and treated to high-intensity chaotic flow in a planetary mixer for size reduction. The size-reduced clay particles were exfoliated through the addition of sPB followed by annealing at an elevated temperature. The exfoliated clay in the 50/50 PB/sPB blend formed a percolating network, a physical gel. The resulting soft solid was cha...

Effect of Electron Beam Irradiation on the Polypropylene/Syndiotactic 1,2-Polybutadiene Blends: Radiation Stabilization of Polypropylene

The effect of electron beam irradiation on polypropylene (PP), syndiotactic 1,2-polybutadiene (sPB) and their blends were studied. They were irradiated with the doses of 20 kGy, 60 kGy, 80 kGy and 100 kGy. Scanning electron microscopy and mechanical test were carried out to characterize the irradiated samples. When PP/sPB blends were irradiated, a part of PP macroradicals created by irradiation acts either as crosslinking agent making the PP and sPB crosslink or it is grafted onto sPB in the interface, which results in the interfacial adhesion stronger between PP and sPB compared with unirradiated PP/sPB blends. Significant improvement of mechanical properties has been obtained by the addition of sPB in the PP matrix when irradiated. The presence of sPB obviously decreases the PP sensitivity to radiation effects.

Effect of Hydrophobic Surfactant Proteins SP-B and SP-C on the Phase and Morphology of Protein Deficient Native Surfactant Films

We present alterations in the phase, morphology and mechanical properties of a native replacement surfactant film induced either by the presence or absence of surfactant specific proteins SP-B and SP-C. Using Langmuir isotherms and fluorescence microscopy, the individual lipid-protein interactions in a complicated native surfactant system are explored. The surface tension lowering property of SurvantaTM, a native surfactant, is significantly compromised in the absence of the proteins, as is the ability of the film to undergo reversible collapse. A lack of proteins also causes the characteristic shoulder, prevalent at ∼ 40 mN/m in most lung surfactant mixtures, to disappear. A lack of this characteristic shoulder illustrates the inability of the film to undergo reversible squeeze out by forming “surface associated surfactant reservoirs”. Addition of SP-B causes an increase in the amount of surfactant material adsorbed from the sub-phase. Further it increases the monolayer stability and the compressibility modulus of the protein deficient film. SP-B is therefore responsible for helping the film achieve a high enough surface pressure during compression, as well as quick re-absorption of material during expansion. SP-C plays a dominant role in the formation of bilayer patches containing unsaturated lipids. SP-C also changes the mechanisms of monolayer collapse, and the film collapses via the formation of reversible collapse cracks. However, it is only in the presence of both SP-B and SP-C that the monolayer films are able to perform all the biophysical functions necessary for the proper working of the lung surfactant. These observations provide conclusive evidence showing that both SP-B and SP-C have distinct biophysical functions in the lung surfactant system, making them equally necessary for the long term survival of air-breathing mammals.

Perturbation of DPPC/POPG bilayers by the N-terminal helix of lung surfactant protein SP-B: a 2H NMR study

SP-B(8-25) is a synthetic peptide comprising the N-terminal helix of the essential lung surfactant protein SP-B. Rat lung oxygenation studies have shown that SP-B(8-25) retains some of the function of full-length SP-B. We have used deuterium nuclear magnetic resonance ((2)H-NMR) to examine the influence of SP-B(8-25) on the mixing properties of saturated PC and unsaturated PG lipids in model mixed lipid bilayers containing dipalmitoylphosphatidylcholine (DPPC) and palmitoyl-oleoyl-phosphatidylglycerol (POPG), in a molar ratio of 7:3. In the absence of the peptide, (2)H-NMR spectra of DPPC/POPG mixtures, with one or the other lipid component deuterated, indicate coexistence of large liquid crystal and gel domains over a range of about 10 degrees C through the liquid crystal to gel transition of the bilayer. Addition of SP-B(8-25) has little effect on the width of the transition but the spectra through the transition range cannot be resolved into distinct liquid crystal and gel spectral components suggesting that the peptide interferes with the tendency of the DPPC and POPG lipid components in this mixture to phase separate near the bilayer transition temperature. Quadrupole echo decay observations suggest that the peptide may also reduce differences in the correlation times for local reorientation of the two lipids. These observations suggest that SP-B(8-25) promotes a more thorough mixing of saturated PC and unsaturated PG components and may be relevant to understanding the behaviour of lung surfactant material under conditions of lateral compression which might be expected to enhance the propensity for saturated and unsaturated surfactant lipid components to segregate.

Pulmonary surfactant inhibits cationic liposome-mediated gene delivery to respiratory epithelial cells in vitro.

Cationic lipid-mediated transfection of the alveolar epithelium in vivo will require exposure of plasmid DNA and cationic lipids to endogenous surfactant lipids and proteins in the alveolar space. Effects of pulmonary surfactant and of surfactant constituents on transfection in vitro of two respiratory epithelial cell lines (MLE-15 and H441) with a plasmid encoding the luciferase reporter gene were studied using two cationic lipid formulations: 1,2-dimyristyloxypropyl-3-dimethyl-hydroxyethyl ammonium bromide/cholesterol (DMRIE/C) and 1,2-dioleoyl-3-trimethylammonium propane/dioleoyl phosphatidylethanolamine (DOTAP/DOPE). Gene expression, as assessed by luciferase activity, decreased as increasing concentrations of natural surfactant were added to cationic lipid-DNA complexes. Incorporation of phospholipids DOPC/DOPG or surfactant proteins SP-B or SP-C in the cationic lipid formulation inhibited transfection. A fluorescent lipid mixing assay was used to determine the effects of surfactant proteins SP-B and SP-C on mixing between cationic lipid-DNA complexes and surfactant lipid vesicles. Mixing between DOPC/DOPG vesicles and cationic lipid-DNA complexes in the absence of added proteins amounted to 10-20%. Addition of SP-B or SP-C increased the mixing of DOPC/DOPG vesicles with DOTAP/DOPE-DNA complexes, but not DMRIEC-DNA complexes. These results demonstrate that pulmonary surfactant lipids and proteins inhibit transfection with cationic lipid-DNA complexes in vitro, and may therefore represent a barrier to gene transfer in the lung.

In vivo function of surfactants containing phosphatidylcholine analogs.

Increased phospholipase A2 activity demonstrated in some forms of lung injury may contribute to surfactant dysfunction. Phospholipase A2-resistant analogs of dipalmitoylphosphatidylcholine (DPPC) with surfactant properties might therefore be useful lipid components of treatment surfactants for certain lung injuries. The in vivo function of surfactants containing DPPC or the phospholipase-resistant analogs dihexadecylphosphatidylcholine (DEPC) or dihexadecylphosphonotidylcholine (DEPnC), with or without surfactant proteins B and C (SP-B+C), was thus evaluated in preterm rabbits (27 days' gestation). Rabbits randomly received one of seven surfactants (DPPC, DEPC, DEPnC, DPPC+SP-B+C, DEPC+SP-B+C, DEPnC+SP-B+C, or lipid extract surfactant [LES]) or 0.45% NaCl (control) and were ventilated for 30 min. Lipid-only surfactants decreased ventilatory pressures (peak inspiratory pressures minus positive end-expiratory pressure) relative to control (p < 0.05). Addition of SP-B+C further decreased ventilatory pressures to levels similar to LES (p < 0.01 versus control, lipid-only surfactants). Lung dynamic compliances and postventilation pressure-volume curves improved in the following order: LES, SP-B+C lipid surfactants > lipid-only surfactants > control (p < 0.05). All surfactant preparations decreased intravascular 125I-albumin recoveries in the lungs relative to control (p < 0.01 for all surfactants versus control). These results indicate that DEPC and DEPnC were as effective as DPPC as lipid components of synthetic surfactants. And like DPPC, the analogs interacted with isolated SP-B+C and improved in vivo function to levels comparable to LES.

Importance of Hydrophobic Apoproteins as Constituents of Clinical Exogenous Surfactants

The biophysical properties and physiologic effects of a series of clinical exogenous pulmonary surfactants was compared to determine the importance of the hydrophobic apoproteins (SP-B and C) as constituents of these preparations. The three exogenous surfactants studied, calf lung surfactant extract (CLSE), Survanta (Surfactant-TA), and Exosurf, all contain dipalmitoyl phosphatidylcholine (DPPC) as their major constituent. CLSE and Survanta also contain 1 to 2% of SP-B,C but Exosurf has the additives hexadecanol and tyloxapol instead to enhance the activity of DPPC. In adsorption experiments, CLSE reached a final surface tension of 22 mN/m, and Survanta and Exosurf reached 28 and 38 mN/m, respectively. Addition of 1% by weight of an apoprotein isolate containing both SP-B and C to Exosurf slightly improved its adsorption. In oscillating bubble studies, CLSE and Survanta decreased surface tension to low values of less than 1 and 2 mN/m, respectively, but Exosurf achieved a minimum value of only 29 mN/m. Addition of SP-B,C to Exosurf improved this minimum to 1 mN/m and approached the behavior of mixtures of synthetic DPPC with SP-B,C. In both adsorption and pulsating bubble experiments, the minimum surface tensions found for Exosurf were almost identical to those generated by tyloxapol alone. In studies of physiologic activity, 20 mg of CLSE or Survanta restored the pressure-volume mechanics of lavaged, surfactant-deficient excised rat lungs to 95 and 50%, respectively, of normal prelavage levels. Instillation of Exosurf (37.5 mg) produced a minimal improvement of only 10% compared to 70% for mixtures containing 1% SP-B,C with either Exosurf or DPPC.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of surfactant-associated protein SP-B synthetic analogs on the structure and surface activity of model membrane bilayers

The effect of several synthetic peptides based on the sequence of human pulmonary surfactant-associated protein B (SPB) on the molecular packing of model membrane lipids (7:1 dipalmitoyl phosphatidylcholine (DPPC)/dipalmitoyl phosphatidylglycerol (DPPG)) was studied using fluorescence anisotropy. This information was then correlated with complementary biophysical data obtained on both a modified Wilhelmy-Langmuir balance and a pulsating bubble surfactometer. The SP-B peptides examined in these studies are synthetic human SP-B Phe1-Ser78 (SP-B 1-78, full-length sequence), synthetic human SP-B Phe1-Thr60 (SP-B 1-60), synthetic human SP-B Phe1-Ala20 (SP-B 1-20), synthetic human SP-B Ala20-Thr60 (SP-B 20-60), synthetic human SP-B Leu27-Ser78 (SP-B 27-78), synthetic human SP-B Leu40-Thr60 (SP-B 40-60) and synthetic human SP-B Tyr53-Ser78 (SP-B 53-78). trans-parinaric acid was utilized to detect changes in ordering of lipids within the interior upon incorporation of synthetic SP-B peptide, whereas 1-hexadecanoyl-2-[N-(7-nitro-2-benzoxa-1,3-diazol-4-yl)-a min ohexanoyl] phosphatidylcholine (6-NBD-PC) and 1-acyl-2-[N-(7-nitro-2-benzoxa-1,3-diazol-4-yl)aminohexanoyl ] phosphatidylglycerol (6-NBD-PG) were utilized to determine alterations in lipid order at the surface of the model membrane bilayer. With the exception of SP-B 40-60, which corresponds to the most hydrophobic segment of the full-length SP-B, none of the other peptide significantly perturbed the interior bilayer as determined by fluorescence anisotropy of trans-parinaric acid. Incorporation of any of the peptides with the exception of SP-B 40-60, resulted in an increase in anisotropy of NBD-PC. The most significant enhancements resulted from the addition of SP-B 1-78, SP-B 1-20, SP-B 27-78 or SP-B 53-78. The magnitude of anisotropy increase with these peptides is similar to that observed with an equivalent molar ratio of native SP-B isolated from a bovine source. These observations suggest that these four synthetic peptides have the structural and compositional characteristics required for surface ordering of the membrane bilayer in a manner similar to that observed with native SP-B, thereby facilitating the surfactant-like properties of phospholipid mixtures.