Biomedical subjects

R H Notter

Publications and source records attributed to R H Notter.

At least 37 records · Page 2Linked to original sources

PubMed1995

Bilayer characteristics of a diether phosphonolipid analog of the major lung surfactant glycerophospholipid dipalmitoyl phosphatidylcholine.

Thermal and lyotropic phase behavior was studied by X-ray diffraction and differential scanning calorimetry for a diether phosphonolipid analog (DEPN-8) of the major lung surfactant glycerophospholipid dipalmitoyl phosphatidylcholine (DPPC). DEPN-8 differs in an ether, rather than an ester, bond at the acyl chain-backbone linkage and a headgroup phosphonate (isosteric methylene substitution) versus phosphate constituent. Analysis of lamellar diffraction maxima demonstrated that at high relative humidity (98%) and temperatures below the liquid crystal phase transition (approximately 45 degrees C), DEPN-8 formed interdigitated bilayers with a characteristic periodicity of 41.9-46.5 A. At low humidity the gel phase DEPN-8 bilayers were characteristic of a normal L beta phase with a periodicity equivalent to DPPC (57-59 A). Above the liquid crystal thermal phase transition, bilayer spacing for both DEPN-8 and DPPC was 51-52 A, characteristic of the L alpha phase. Complete assessments of both lamellar and in-plane X-ray scattering used to construct electron density profiles and structure-factor plots for DEPN-8 defined more fully the interdigitated bilayer state at high humidity and low temperature. Compared to DPPC, it is energetically favorable for DEPN-8 to form interdigitated bilayers under conditions of excess water and low temperature. The flexible character of the ether bonds in DEPN-8 allows increased hydrophobic interactions between acyl chains, without generating a steric penalty from the increased packing density of the molecules. Additionally, the ether bond and the phosphonate moiety may allow for more energetically favorable interactions between the choline portion of the headgroup and water. The DEPN-8 ether linkage may also contribute to the improved adsorption and film respreading found previously for this phosphonolipid compared to DPPC.

1,2-Dipalmitoylphosphatidylcholine↗

PubMed1995

Dynamic surface activity of films of lung surfactant phospholipids, hydrophobic proteins, and neutral lipids.

Surface pressure-area (pi-A) isotherms during dynamic cycling were measured for films of dipalmitoyl phosphatidylcholine (DPPC) and column-separated fractions of calf lung surfactant extract (CLSE). Emphasis was on defining the relative importance of lung surfactant phospholipids (PPL), neutral lipids (N), and hydrophobic proteins (SP) in facilitating dynamic respreading and surface tension lowering within the interfacial film itself. Solvent-spread films in a Wilhelmy balance were studied at 23 degrees and 37 degrees C over a range of cycling rates for initial concentrations giving both monomolecular and surface-excess films. A striking finding was that PPL films containing the complete mix of surfactant phospholipids had greatly improved dynamic respreading compared to DPPC, particularly in surface excess films (30 and 15 Angstrum 2/molecule). Hydrophobic SP gave an additional increase in dynamic respreading in SP&PL compared to PPL films for initial concentrations of 60, 30, and 15 Anstrum 2/molecule. Neutral lipids also improved respreading slightly in N&PL versus PPL films, but maximum surface pressures in N&PL films at 37 degrees C were consistently the lowest of any surfactant subfraction. Spread films of SP&PL at 60 and 30 Angstrum 2/molecule had lower maximum pressures than PPL, but maximum pressures were slightly larger for SP&PL films at high initial concentration (15 Anstrum 2/molecule). Supplementary oscillating bubble studies involving both adsorption and film dynamics at rapid cycling rate (20 cycles/min) showed that dispersions of CLSE and SP&PL lowered surface tension to < 1 mN/m, while PPL and N&PL had elevated minimums of 21 mN/m. These results show that secondary surfactant phospholipids in addition to DPPC are important in the film behavior of pulmonary surfactant, giving improved respreading and overall pi-A isotherms very different from disaturated phospholipids. Hydrophobic SP also increase respreading in the interfacial film, in addition to their known action in increasing surfactant adsorption. SP may also improve film stability at high interfacial concentrations of phospholipid, although they were destabilizing in more dilute films. Neutral lipids contributed minor increases in surfactant respreading, but were consistently detrimental to surface tension lowering.

1,2-Dipalmitoylphosphatidylcholine↗

PubMed1994

Changes in subphase aggregates in rabbits injured by free fatty acid.

Rabbits treated with intravenous free fatty acid suffer an acute lung injury. Material obtained from these lungs by bronchoalveolar lavage (BAL) has dramatically impaired ability to lower surface tension in vitro despite normal levels of surfactant phospholipids. Although large quantities of surface-active inhibitors are present in BAL, their effects are not sufficient to explain the magnitude of surfactant inactivation. This study determines if alterations in the surfactant aggregates can explain the loss of surfactant function in fatty acid lung injury. In injured animals, the larger, most active surfactant particles recovered by centrifugal pelleting were found to be decreased in amount. The remaining large particles had reduced surface activity compared with control aggregates. In addition, large particles in injured animals had a higher density than control animals on sucrose gradients following equilibrium centrifugation. Interaction with serum components present in the injured BAL could explain these higher densities. The ability of the injured BAL to lower surface tension was improved by supplementation with normal levels of particles from injured lungs. Supplementation of injured BAL with control large aggregates improved activity further and restored the ability to lower surface tension to < 1 mN/m. Therefore both the decreased amount and activity of large surfactant aggregates in injured animals contributed significantly to the observed inactivation of surfactant. Diminished surfactant function from alteration in surfactant aggregates is a mechanism common to other forms of acute lung injury, and the design of therapies with exogenous surfactants in injured lungs will need to consider strategies that restore surfactant function towards normal.

Animals↗

PubMed1994

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.

Animals↗

PubMed1994

Separation of subfractions of the hydrophobic components of calf lung surfactant.

This study reports the biochemical separation of the hydrophobic constituents of calf lung surfactant into separate fractions from which specific components are excluded. Gel permeation chromatography on LH-20 with acidified chloroform-methanol separated the constituents of calf lung surfactant extract (CLSE) into fractions containing purified phospholipids (PPL), the neutral lipids and phospholipids (N&PL), or the hydrophobic surfactant proteins (SP)-B and -C together with the phospholipids (SP&PL). Extraction of acid to prevent phospholipid degradation after separation reduced recovery of the apoproteins in SP&PL. This fraction was therefore supplemented with protein purified separately to attain the initial levels present in CLSE. Biochemical analyses confirmed that the resulting preparations had the expected composition not only of protein, neutral lipids and phospholipids, but also of the phospholipid head groups. In addition to these fractions obtained with acidified solvent, elution of CLSE with chloroform-methanol without acid yielded the zwitterionic phospholipids substantially depleted of anionic phosphatidylglycerol and phosphatidylinositol. Limited interfacial measurements also demonstrated that the process of separation did not alter the fundamental surface characteristics of the surfactant constituents. Recombined CLSE (rCLSE) reconstituted from all of the separated components had surface activity indistinguishable from the original CLSE. The individual fractions of surfactant components also had average molecular areas at the air-liquid interface which agreed with predictions based on their biochemical composition. These well defined preparations of the hydrophobic constituents of pulmonary surfactant provide the basis for future studies to establish the role of individual components in the function of this complex surface active material.

Animals↗

PubMed1993

Approximations in the measurement of surface tension on the oscillating bubble surfactometer.

This paper examines two factors, shape deformation and surface viscosity, that affect measurements of surface tension of lung surfactants with the oscillating bubble surfactometer. At lower surface tensions, the compressed bubble in this apparatus becomes deformed to an oblate ellipsoid that cannot be analyzed rigorously using the simplified (spherical) Laplace equation to calculate surface tension from interfacial pressure drop. However, for the small air bubbles present in this apparatus, analysis with more general equations for ellipsoids of revolution shows that deformation effects are limited to extremely low surface tensions, and the absolute error from the spherical approximation is minimal in practice. In contrast, this was not the case for the effects of surface dilational viscosity in oscillating bubble calculations. Direct measurements and values from the literature indicated that the surface dilational viscosities of lung surfactant, dipalmitoyl phosphatidylcholine, and palmitic acid were sufficient to give substantial errors if their effects on interfacial pressure drop were neglected during dynamic cycling. Surface tension calculations at maximum and minimum radii on the oscillating bubble apparatus remain accurate, because the time derivative of radius becomes zero and viscous effects vanish. However, surface tensions determined at points other than these extremes of bubble size should be interpreted with caution.

1,2-Dipalmitoylphosphatidylcholine↗

PubMed1992

High-frequency jet ventilation and surfactant treatment of newborns with severe respiratory failure.

Twenty-eight newborn infants (birthweight, 2.4 +/- 1.1 kg; gestational age, 34.6 +/- 6.1 weeks) with respiratory distress syndrome (RDS), meconium aspiration syndrome, or pneumonia who deteriorated in spite of optimal conventional mechanical ventilation (CMV) and exogenous surfactant therapy were treated with high-frequency jet ventilation (HFJV) and continued surfactant therapy. For enrollment, infants had to have a limited response to surfactant therapy and conventional ventilation, and meet clinical criteria that confirmed clinical deterioration and severity of illness. Study infants had received exogenous calf lung surfactant extract (CLSE) and conventional ventilation prior to the start of HFJV at 46.3 +/- 8.2 hours of age. Patients initially responded to HFJV alone with significant improvement in several respiratory variables, but deteriorated subsequently and receive additional doses of exogenous surfactant on HFJV. Exogenous surfactant and HFJV resulted in significant and sustained improvement in several respiratory variables. Only ten patients deteriorated to meet criteria for a second surfactant dose on HFJV, and two patients received a third dose. Twenty-five of the 28 patients studied survived (89%). No patients received extracorporeal membrane oxygenation or were discharged home on oxygen. The results of this pilot study suggest that the combination of HFJV and exogenous surfactant replacement may be effective in treating infants with more severe respiratory failure, and indicate the need for more extensive controlled investigations.

Gestational Age↗

PubMed1992

Inhibition of pulmonary surfactant by oleic acid: mechanisms and characteristics.

The inhibitory effects of oleic acid (OA) on the surface activity of pulmonary surfactant were characterized by use of the oscillating bubble surfactometer, the Wilhelmy balance, and excised rat lungs. Oscillating bubble studies showed that OA prevented lavaged calf surfactant [0.5 mM phospholipid (PL)] from lowering surface tension below 15 mN/m at or above a molar ratio of OA/PL = 0.5. In contrast to inhibition of surfactant by plasma proteins, increasing the surfactant concentration did not eliminate inhibition by oleic acid, which occurred at OA/PL greater than 0.67 on the oscillating bubble even at surfactant concentrations of 1.5 and 12 mM PL. Studies of surfactant adsorption showed that preformed films of OA had little effect on the adsorption of pulmonary surfactant. Wilhelmy balance studies showed that OA did interfere with the ability of spread films of surfactant to reach low surface tensions during dynamic compression. Further balance experiments with binary films of OA and dipalmitoyl phosphatidylcholine showed that these compounds were miscible in surface films. Together these findings suggested that OA inhibited pulmonary surfactant activity by disrupting the rigid interfacial film responsible for the generation of very low surface tension during dynamic compression. Mechanical studies in excised rat lungs showed that instillation of OA gave altered deflation pressure-volume characteristics with decreased quasi-static compliance, indicating disruption of pulmonary surfactant function in situ. This alteration of mechanics occurred without major changes in the composition of lavaged PLs or in the tissue compliance of the lungs defined by mechanical measurements during inflation-deflation with saline.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1992

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)

1,2-Dipalmitoylphosphatidylcholine↗

PubMed1991

Chemical synthesis and surface activity of lung surfactant phospholipid analogs. II. Racemic N-substituted diether phosphonolipids.

A series of racemic 16:0 disaturated N-substituted diether phosphonolipid analogs of glycerophospholipids have been synthesized and purified. Isosteric methylene substitution at three of the four ester sites (carboxyl, phosphate) of conventional glycerophospholipids enhanced the hydrophobicity of analog compounds compared with dipalmitoyl phosphatidylcholine (DPPC), the major glycerophospholipid component of lung surfactant. Further substitutions at the nitrogen headgroup also contributed to hydrophobicity/hydrophilicity characteristics, as well as allowing graded variations in headgroup size among the members of the diether phosphonolipid analog series. Interfacial property studies showed that these compounds had significant differences in surface activity characteristics compared with DPPC, including increased adsorption and respreading facility, plus an enhanced ability to generate low surface tension (less than 1 to 4 mN/m) on an oscillating bubble apparatus at 37 degrees C. In addition, pressure-volume mechanical studies in surfactant-deficient excised rat lungs showed that the diether phosphonate analog of DPPC could partially restore pressure-volume characteristics toward normal, both as a pure component and in binary mixtures with palmitoyl-oleoyl phosphatidylglycerol. These findings suggest that selected analog compounds, synthesized with relatively small structural modifications from biologic glycerophospholipids, may have eventual applications as components of synthetic exogenous lung surfactants. Of more immediate importance, analog molecules with defined structural variations are convenient molecular probes for developing structure-surface activity correlates for phospholipid-like surfactants and for investigating the specificity of interactions between glycerophospholipids and other compounds such as proteins.

1,2-Dipalmitoylphosphatidylcholine↗

PubMed1991

A comparison of surfactant as immediate prophylaxis and as rescue therapy in newborns of less than 30 weeks' gestation.

BACKGROUND: Exogenous pulmonary surfactants are administered into the trachea either to prevent respiratory distress syndrome in premature infants or to treat it. In a randomized, multicenter trial, we compared the results of surfactant therapy initiated as prophylaxis with the results of rescue therapy with surfactant. METHODS: Before birth, 479 infants with an estimated gestational age of less than 30 weeks were randomly assigned to receive surfactant as prophylaxis (n = 235) or rescue therapy (n = 244). The infants in the prophylaxis group received a 90-mg intratracheal dose of an exogenous calf-lung surfactant extract at the time of delivery, whereas the infants in the rescue-therapy group received 90 mg of the surfactant several hours after delivery if the fractional inspiratory oxygen concentration was at least 0.40 or if the mean airway pressure was at least 0.686 kPa (7 cm of water), or both. Infants in both groups received additional doses of surfactant at intervals of 12 to 24 hours if these criteria were met. RESULTS: The proportion of infants surviving until discharge to their homes was significantly higher in the prophylaxis group than in the rescue-therapy group (88 vs. 80 percent, P = 0.028). This difference was due primarily to the longer survival of very premature infants (less than or equal to 26 weeks' gestation) in the prophylaxis group than in the rescue-therapy group (75 vs. 54 percent, P = 0.006). According to proportional-hazards regression analysis, the distribution of survival times was better for all infants in the prophylaxis group (P = 0.007) and for the subgroup of infants in the prophylaxis group who were delivered at 26 weeks' gestation or earlier (P = 0.0048). Infants in the prophylaxis group who were delivered at 26 weeks' gestation or earlier had a lower incidence of pneumothorax than similar infants in the rescue-therapy group (7 vs. 18 percent, P = 0.03). CONCLUSIONS: We found a significant advantage to the administration of the initial dose of surfactant as prophylaxis rather than as rescue therapy in very premature infants.

Clinical Protocols↗

PubMed1991

Surfactant treatment of full-term newborns with respiratory failure.

Surfactant inactivation has been shown to be a significant factor in animal models of lung injury and may also be important in some forms of respiratory failure in full-term newborns. Fourteen full-term newborns with respiratory failure associated with pneumonia (7 patients) and meconium aspiration syndrome (7 patients) were treated with 90 mg/kg of a calf lung surfactant extract, given intratracheally up to every 6 hours for a maximum of four doses. The group mean fraction of inspired oxygen (FI02) before treatment was 0.99 +/- 0.01 SEM, and the mean airway pressure (MAP) was 14.6 +/- 1.0 cm H2O. Patients showed significant improvement in oxygenation after initial surfactant treatment, with the arterial-alveolar oxygenation ratio (a/A ratio) rising from 0.09 +/- 0.01 before surfactant treatment to 0.22 +/- 0.05 by 15 minutes (P = .03) and remaining improved for 6 hours. The oxygenation index, incorporating MAP as well as oxygen variables, also improved significantly from 26.2 +/- 3.1 to 11.2 +/- 1.7 at 15 minutes (P less than .001), with improvement sustained for more than 6 hours. Chest radiographs were blindly scored from 0 (normal) to 5 (severe opacification), and these improved with marginal significance after initial surfactant treatment (from 2.9 +/- 0.2 to 2.5 +/- 0.2, P = .05).(ABSTRACT TRUNCATED AT 250 WORDS)

Humans↗

PubMed1990

Relationships among surfactant fraction lipids, proteins and biophysical properties in the developing rat lung.

Lung development is associated with increases in specific phospholipids and proteins that function as critical pulmonary surfactant components. Attempts to characterize the pattern of surfactant development in fetal rat lungs have been hampered by the lack of a micromethod which will permit quantitative isolation of surface active components from small tissue specimens. As part of studies designed to elucidate the metabolic regulation of lung development in the rat, we developed sucrose density gradient centrifugation procedures to separate pulmonary phospholipids and proteins into a presumed surfactant (S) fraction and a residual (R) fraction. Electron microscopy of S pellets from mature fetuses identified predominant lamellar bodies and minimal contamination; incubation with 5 mM CaCl2 induced the appearance of tubular myelin figures, implying functional potential. This was confirmed by demonstrating low surface tension (less than 1 dyn/cm) in S, but not R, fractions at term gestation (21.5 days) and in 1-day-old neonatal lung isolates, based on dynamic measurements using the oscillating bubble technique. Surface activity was also high in the S pellets from fetuses at 20.5 days of gestation; however, at 19.5 days, minimum surface tension values of at least 19 dyne/cm were seen. These results correlated directly with biochemical analyses which indicated striking increases in three surfactant-associated proteins (SP-A, SP-B, and SP-C) after 19.5 days of gestation; a finding in agreement with previously reported data on the developmental increase of disaturated phosphatidylcholine in fetal rat lung. We conclude that isolation of S fraction components is valuable for demonstrating maturation of the fetal rat lung and may provide a useful tool for the study of regulatory mechanisms influencing surfactant production and function.

Animals↗

PubMed1990

Hydrophobic homopolymeric peptides enhance the biophysical activity of synthetic lung phospholipids.

The effects of homopolymeric amino acids (molecular weight 2300 to 14,000) on the surface activity of dipalmitoyl phosphatidylcholine (DPPC) and DPPC/egg-phosphatidylglycerol (PG) were characterized by adsorption and dynamic surface tension lowering measurements at 37 degrees C. Homopolyamino acids studied included poly-L-leucine (poly-Leu) and poly-L-valine (poly-Val), since Leu and Val are known to be prominent in the structure of hydrophobic lung surfactant apoprotein SP-B and SP-C. In addition, several other homopolyamino acids with varying hydrophobicity index were also investigated, including poly-L-phenylalanine (poly-Phe), poly-L-serine (poly-Ser), poly-L-lysine (poly-Lys) and poly-L-glutamic acid (poly-Glu). Results showed that hydrophobic poly-Leu and poly-Phe at 1 and 10 weight percent greatly increased the adsorption facility of DPPC and DPPC/PG mixtures, with maximum surface pressures (up to 49 mN/m) near the equilibrium limit for phospholipid systems. In oscillating bubble studies, 1% mixture of poly-Leu or poly-Phe with DPPC or 8:2 DPPC/PG lowered surface tension into the range (near 1 mN/m) associated with active lung surfactant. In contrast, mixtures of DPPC and DPPC/PG with the more hydrophilic peptides poly-Ser, poly-Lys and poly-Glu showed little or no enhancement of surface activity over the phospholipids alone. Mixtures of poly-Val and phospholipids did not combine well with the simple co-sonication procedure used, and also exhibited little improvement in surface activity.(ABSTRACT TRUNCATED AT 250 WORDS)

1,2-Dipalmitoylphosphatidylcholine↗

PubMed1990

Enhancement of biophysical activity of lung surfactant extracts and phospholipid-apoprotein mixtures by surfactant protein A.

The effects of surfactant protein (SP)-A on the dynamic surface tension lowering and resistance to inhibition of dispersions of calf lung surfactant extract (CLSE) and mixtures of synthetic phospholipids combined with SP-B,C hydrophobic apoproteins were studied at 37 degrees C and rapid cycling rate (20 cycles/min). Addition of SP-A to CLSE, which already contains SP-B and -C, gave a slight improvement in the time course of surface tension lowering on an oscillating bubble apparatus in the absence of inhibitory protein molecules such as albumin or hemoglobin. However, when these proteins were present at concentrations of 10-50 mg/ml, SP-A substantially improved the resistance of CLSE to their inhibitory effects. The beneficial effect of SP-A required the presence of Ca2+ ions, and disappeared when EDTA was substituted for this divalent cation in the subphase. The effect was also retained when SP-A was heated to 50 degrees C prior to addition to CLSE, but was abolished by heating SP-A to 99 degrees C. Additional studies showed that similar improvements in resistance to inhibition were found when SP-A was added to synthetic mixtures of dipalmitoyl phosphatidylcholine (DPPC):egg phosphatidylglycerol (PG) (80:20 by weight) reconstituted with 1% SP-B or SP-B and -C, but not to phospholipid mixtures containing only SP-C. The requirements for SP-B and calcium for the beneficial effects of SP-A on surface activity suggest that the formation of ordered, larger phospholipid-apoprotein aggregates may be involved in the process. The finding that SP-A enhances the ability of CLSE and other surfactant mixtures containing SP-B to resist inhibition is an advantage that will need to be weighed against other factors such as increased antigenicity and heat sensitivity in therapeutic applications in surfactant replacement therapy.

Amino Acid Sequence↗

PubMed1990

Biophysical inhibition of synthetic lung surfactants.

The biophysical activity and inhibition of a series of synthetic surfactant mixtures was studied and correlated with physiological effectiveness in restoring pressure-volume (P-V) mechanics of excised lungs. Results showed that several simple mixtures of dipalmitoyl phosphatidylcholine (DPPC) with fatty acids or diacylglycerols could be formulated to give good adsorption facility and dynamic surface tension lowering to less than 1 mN/m in pulsating bubble measurements at 37 degrees C. However, although biophysical activity approached that of natural lung surfactant (LS) and a related surfactant extract (CLSE) under normal conditions, surface properties were sharply inhibited by relatively small amounts of the plasma protein albumin (2 mg/ml) with minimum surface tensions greater than 30 nM/m even at high surfactant concentrations (5-20 mg lipids/ml). This sensitivity to biophysical inhibition was markedly increased compared to LS and CLSE, and had direct consequences for physiological efficacy: in spite of initially high activity, synthetic surfactants did not exert beneficial effects on P-V mechanics when instilled into surfactant-deficient excised rat lungs. Endogenous protein material was shown to be present upon surfactant recovery by lavage, and bubble measurements confirmed surface activity well below pre-instillation levels. Moreover, full biophysical activity was restored when lavage fluid was extracted to separate the synthetic surfactants from endogenous inhibitors. These results show that it is important to define relative sensitivity to biophysical inhibition in the development of effective lung surfactant substitutes. In addition, the existence of inhibition effects can generate an apparent lack of correspondence between initial biophysical activity and ultimate physiological actions of exogenous surfactant mixtures.

1,2-Dipalmitoylphosphatidylcholine↗

PubMed1990

Changes in gene expression in hyperoxia-induced neonatal lung injury.

Exposure to high concentrations of oxygen (hyperoxia) can result in lung injury. The biochemical basis of this injury is poorly understood, but it is likely to include alterations in gene expression. Hyperoxia-induced (H-I) cDNAs have been molecularly cloned (Horowitz et al. J. Biol. Chem. 264: 7092-7095, 1989) from the lungs of an adult rabbit exposed to toxic levels of oxygen. One of them (H-I 1) was identified as encoding the tissue inhibitor of metalloproteinases (TIMP), a key regulatory protein of extracellular matrix turnover. Here we identify another clone (H-I 3) as encoding pulmonary surfactant apoprotein A (SP-A). We also show that in neonatal rabbits exposed to 100% oxygen for 96 h, the mRNAs corresponding to TIMP, SP-A, and another H-I gene are increased. These studies have begun to explore specific changes in gene expression associated with neonatal hyperoxic lung injury.

Animals↗

PubMed1990

Altered function of pulmonary surfactant in fatty acid lung injury.

To determine whether acute fatty acid lung injury impairs pulmonary surfactant function, we studied anesthetized ventilated rabbits given oleic acid (55 mg/kg iv, n = 11) or an equivalent volume of saline (n = 8). Measurements of pulmonary mechanics indicated a decrease in dynamic compliance within 5 min of injury and a decrease in lung volume that was disproportionately large at low pressures, consistent with diminished surfactant activity in vivo. Bronchoalveolar lavage fluid obtained 1 h after injury had significantly increased erythrocytes and total leukocytes, largely polymorphonuclear cells. The phospholipid content and composition of the cell-free fraction had only minor changes from those of controls, but the protein content was increased 35-fold. Measurements of lavage surface activity in vitro showed an increase in average minimum surface tension from 1.3 +/- 0.4 (SE) dyn/cm in controls to 20.2 +/- 3.9 dyn/cm in injured animals. The alterations in static pressure-volume curves and decrease in lavage surface activity suggest a severe alteration of surfactant function in this form of lung injury that occurs despite the presence of normal amounts of surfactant phospholipids.

Animals↗