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Biomedical subjects

B J Benson

Publications and source records attributed to B J Benson.

At least 37 records · Page 2Linked to original sources
PubMed1987

Low molecular weight human pulmonary surfactant protein (SP5): isolation, characterization, and cDNA and amino acid sequences.

Pulmonary surfactant is a lipid-protein complex that promotes alveolar stability by lowering the surface tension at the air-fluid interface in the peripheral air spaces. A group of hydrophobic surfactant-associated proteins has been shown to be essential for rapid surface film formation by surfactant phospholipids. We have purified a hydrophobic surfactant protein of approximately 5 kDa that we term SP5 from bronchopulmonary lavage fluid from a patient with alveolar proteinosis and shown that it promotes rapid surface film formation by simple mixtures of phospholipids. We have derived the full amino acid sequence of human SP5 from the nucleotide sequence of cDNAs identified with oligonucleotide probes based on the NH2-terminal sequence of SP5. SP5 isolated from surfactant is a fragment of a much larger precursor protein (21 kDa). The precursor contains an extremely hydrophobic region of 34 amino acids that comprises most of the mature SP5. This hydrophobicity explains the unusual solubility characteristics of SP5 and the fact that it is lipid-associated when isolated from lung.

Amino Acid Sequence↗
PubMed1987

The coding sequence for the 32,000-dalton pulmonary surfactant-associated protein A is located on chromosome 10 and identifies two separate restriction-fragment-length polymorphisms.

The primary protein component of human pulmonary surfactant is a 32,000-dalton glycoprotein called surfactant-associated protein A. This protein is important for normal lung function, and its expression is developmentally regulated. Using a mapping panel of somatic-cell hybrids, we have localized the coding sequence for pulmonary surfactant-associated protein A to chromosome 10. Additionally, this sequence identifies two separate MspI restriction-fragment-length polymorphisms. Since there is a relative lack of polymorphic markers for chromosome 10, this sequence may be useful in linkage analysis.

Animals↗
PubMed1985

Effects of a surfactant-associated protein and calcium ions on the structure and surface activity of lung surfactant lipids.

Previous studies have demonstrated that lung-specific proteins are associated with surfactant lipids, particularly the highly surface active subfraction known as tubular myelin. We have isolated a surfactant-associated protein complex with molecular weight components of 36 000, 32 000, and 28 000 and reassembled it with protein-free lung surfactant lipids prepared as small unilamellar liposomes. The effects of divalent cations on the structure and surface activity of this protein-lipid mixture were investigated by following (1) the state of lipid dispersion by changes in turbidity and by electron microscopy and (2) the ability of the surfactant lipids to form a surface film from an aqueous subphase at 37 degrees C. The protein complex markedly increased the rate of Ca2+-induced surfactant-lipid aggregation. Electron microscopy demonstrated transformation of the small unilamellar liposomes (median diameter 440 A) into large aggregates. The threshold Ca2+ concentration required for rapid lipid aggregation was reduced from 13 to 0.5 mM by the protein complex. This protein-facilitated lipid aggregation did not occur if Mg2+ was the only divalent cation present. Similarly, 5 mM Ca2+ but not 5 mM Mg2+ improved the ability of the protein-lipid mixture to form a surface film at 37 degrees C. Extensive aggregation of the surfactant lipids without protein by 20 mM Ca2+ or 20 mM Mg2+ did not promote rapid surface film formation. These results add to the growing evidence that specific Ca2+-protein-lipid interactions are important in determining both the structure and function of extracellular lung surfactant fractions.

Animals↗
PubMed1985

Patient response to surgical and nonsurgical treatment for internal derangement of the temporomandibular joint.

One hundred thirty-six patients who had been diagnosed as having internal derangements of the temporomandibular joint by history, clinical examination, and arthrotomography were retrospectively evaluated. Fifty-two patients had been treated by nonsurgical and 84 by surgical methods. A case review was conducted and a self-administered survey was distributed to patients to assess response to treatment. The results indicated that for a majority of the patients surgery had significantly reduced TMJ symptoms. Patients who had been treated nonsurgically also reported fewer symptoms following treatment, but the improvement was not as great as that of the surgical group.

Adolescent↗
PubMed1985

Structural and functional aspects of protein: phospholipid interactions in surfactant.

Lung surfactant lipids require the presence of a specific protein and calcium ions in order to form surface films rapidly at air-water interfaces. Film formation is a necessary first step in maintenance of low surface tensions in the lung. We have studied some of the factors involved with the lipid-protein interactions in reassembled complexes as well as in isolated lung surfactant. For both of these systems, removal of apoprotein or calcium ions results in impaired surface spreading. Increasing the amounts of this apoprotein relative to phospholipid results in increased lipid-protein association, increased vesicle aggregation, and increased monolayer film formation at the air-water interface in the surface balance.

Animals↗
PubMed1984

Protein composition of rabbit alveolar surfactant subfractions.

The goal of this investigation was to characterize the proteins in subfractions of alveolar surfactant obtained by lung lavage and separated by differential centrifugation. It was previously demonstrated that the material in the more sedimentable fraction, which was enriched in tubular-myelin and was surface-active may be a precursor to the less sedimentable, vesicular, inactive material [1]. Separation of the proteins by polyacrylamide gel electrophoresis showed that the more sedimentable subfractions and rabbit surfactant isolated by conventional methods contained proteins with molecular weights comparable to those previously reported for alveolar surface active material (approximately 36 000 and 10 000). The less sedimentable subfractions contained less of these proteins. Immunoblots with anti-dog surfactant apoprotein antibodies, which cross-react with rabbit proteins, supported these observations. Immunoblots also showed that all of the subfractions contained serum proteins and secretory IgA, with the less sedimentable subfractions containing more secretory IgA. These results suggested that changes in protein composition may accompany functional changes in surfactant in the alveoli.

Animals↗
PubMed1984

Role of calcium ions the structure and function of pulmonary surfactant.

Pulmonary surfactant isolated by centrifugation in buffers containing ions contains at least three different morphologic structures. The presence of one of these, tubular myelin, is dependent on calcium ions, since chelation of the calcium ions causes disruption of this structure. Addition of EDTA also decreases the ability of the surfactant to absorb rapidly to air-water interfaces and lower surface tension. Titration with calcium ions (2.5 or 5 mM) restores rapid surface adsorption and restores the tubular myelin structural forms. Magnesium ions cannot substitute for calcium ions in these processes. The reversibility of structure and function induced by calcium ions and EDTA is also accompanied by reversible isopycnic density shifts probably related to aggregation and disaggregation of the lipid-protein complex with calcium ions and EDTA, respectively.

Animals↗
PubMed1984

Role of apoprotein and calcium ions in surfactant function.

Pulmonary surfactant isolated in the presence of calcium ions contains substantial amounts of the morphologic structure, tubular myelin. Chelation of these calcium ions results in disruption of this structure and attendant loss of surface adsorption. Reassembly studies indicate that ability of the lipids to rapidly form surface films is dependent on the presence of a specific surfactant protein in addition to the calcium ions. The formation of this surface-active complex (apoprotein-lipid-calcium ions) is accompanied by aggregation of the lipid. This increase in aggregation may have important implications in the mechanism of surfactant function.

Adsorption↗
PubMed1983

Changes in phospholipid composition of lung surfactant during development in the fetal lamb.

The lung surfactant isolated from pulmonary fluid of fetal sheep changes both in amount and composition during gestation. Total phosphatidylcholine (PC) and its most surface-active components, disaturated PC, are present at very low levels 3-4 weeks prior to term and rise to adult levels 3-4 days before birth. The acidic phospholipids appear with a different time course. Phosphatidylserine reaches elevated levels about 21 days before birth. Phosphatidylinositol begins to increase at about 130 days of gestation. Phosphatidylglycerol is not a component (less than 1%) of the surfactant in this fetal lung fluid. At term, phosphatidylinositol is the major acidic phospholipid found in these fluids.

Acid Phosphatase↗
PubMed1983

Subfractionation of lung surfactant. Implications for metabolism and surface activity.

Because previous studies have suggested that lung surfactant is not a simple compartment of homogeneous material, we subfractionated lamellar bodies and components of alveolar lavage from male New Zealand white rabbits, according to differences in sedimentability. We recovered two lamellar body populations at different densities in discontinuous sucrose density gradients; we separated six subfractions of alveolar lavage by differential centrifugation. To determine whether or not precursor-product relationships existed among the subfractions, we injected radioactive palmitate intravenously, killed the rabbits 1-72 h later, and measured phospholipid specific activities. The two populations of lamellar bodies had similar phospholipid composition, fatty acyl composition of phosphatidylcholine and phosphatidylglycerol, and surface activity. Light lamellar bodies had a higher ratio of phospholipid to protein, and labelled with tracer later in time than dense ones. For alveolar lavage subfractions, later labelling with tracer, lower adsorption rate and lower total protein and phosphatidylglycerol content seemed to correlate with decreasing average density and particle size as well as with the disappearance of tubular myelin structure and appearance of predominantly vesicular structure. The subfractions appear to be in a metabolic sequence in which heavier, more dense material is a precursor to lighter, less dense material. The results suggest that subfractions of surfactant are extensively recycled.

Animals↗
PubMed1982

Secretion of surfactant by primary cultures of alveolar type II cells isolated from rats.

Pulmonary surfactant conventionally is prepared from material obtained by endobronchial lavage. Although it has been assumed that the components of surfactant are secreted by alveolar type II cells, direct proof of this assumption has not been available. Furthermore, it is possible that the final material obtained by lavage has been modified after secretion or altered during the isolation procedure. It has been shown previously that type II cells, after 1 day in primary culture, secrete saturated phosphatidylcholine, one of the lipid components of surfactant. Because saturated phosphatidylcholine is not unique to surfactant and because type II cells in culture lose differentiated characteristics over the first several days in culture, it has not previously been established how closely the secretory products of cultures of type II cells resemble surfactant as obtained by endobronchial lavage. We therefore studied the morphologic, physical and chemical characteristics of the material that type II cells secrete under basal conditions and after stimulation with terbutaline or 12-O-tetradecanoyl-13-phorbol acetate. The secreted material resembled surfactant obtained by lavage; it was similar morphologically to the lamellar material and tubular myelin seen in the fluid-filled alveoli of fetal rats, it lowered surface tension to 5 mN per meter, and it contained the 72000 dalton apolipoprotein of surfactant (as measured by the 'rocket' immunoelectrophoresis technique). When cells were incubated for 22 h with [1-(14)C]acetate, the distribution of radioactivity in the secreted material was very similar to the phospholipid composition of rat surfactant. We conclude that the material secreted by alveolar type II cells after 1 day in primary culture is similar to surfactant obtained by endobronchial lavage.

Animals↗
PubMed1981

Isolation of a major apolipoprotein of canine and murine pulmonary surfactant. Biochemical and immunochemical characteristics.

We studied some of the biochemical and immunochemical properties of a major apolipoprotein in isolated pulmonary surfactant from dog and rat lungs. These apolipoproteins were purified by DEAE-cellulose chromatography in buffers containing Triton X-100. Purity of the apolipoproteins was assessed by both fused rocket and crossed immunoelectrophoreses. In addition, the apolipoproteins showed one band with an apparent molecular weight of 72 000-73 000 on SDS-polyacrylamide gel electrophoresis. These proteins are composed of two polypeptide chains of 36 000 daltons. When subjected to isoelectric focusing, the major component of the apolipoprotein had an isoelectric point of about 4.4, with very minor components near 4.6. Even though the apolipoproteins of both species had very similar amino acid compositions, including a relatively high glycine content, no immunologic cross-reactivity was observed. Rocket immunoelectrophoretic analysis of several preparations of dog and rat surfactant using the respective purified apolipoproteins as standards indicated that the apolipoprotein constituted 56.9% +/- 4.6. (S.D., n = 3) and 42.1% +/- 2.1 (S.D., n = 2) of the total protein in dog and rat surfactant, respectively.

Amino Acids↗
PubMed1981

Immunocytochemical localization and identification of the major surfactant protein in adult rat lung.

We investigated the cellular and subcellular sites of metabolism of the 72,000 dalton protein of pulmonary surfactant in order to provide insights into mechanisms of synthesis, intracellular assembly, and intraalveolar metabolism of this phospholipid-rich secretory product. Surfactant (approximately 90% lipid, 10% protein by weight) was purified by density gradient centrifugation of material obtained by lavaging rat lungs. The purified material was used to generate an antiserum from which a specific antibody was obtained by affinity chromatography. A horseradish peroxidase-labeled Fab was used to localize the antigen in rat lung. The antibody labeled the rough endoplasmic reticulum and Golgi apparatus of type II cells only. Some multivesicular bodies in type II cells were also labeled, but whether the antigen was present in lamellar bodies was uncertain. Phagosomes of alveolar macrophages were labeled as were similar inclusions in type I cells. Using indirect immunocytochemistry we determined that the labeling of alveolar cell surfaces does not represent the presence of a continuous layer of secreted surfactant. These results suggest that only the type II cell synthesizes surfactant protein and than mainly alveolar macrophages participate in its catabolism. The initial intracellular site of the association of protein with lipid may be multivesicular bodies as suggested previously by others.

Animals↗
PubMed1980

Properties of an acid phosphatase in pulmonary surfactant.

Lung surfactant, a lipid-protein complex purified from dog lungs, contains a highly active phosphomonoesterase associated with it. This phosphatase is quite specific for the hydrolysis of phosphatidic acid and 1-acyl-2-lysophosphatidic acid. The enzyme possesses many of the characteristics of the microsomal enzyme, phosphatidate phosphohydrolase (EC 3.1.3.4). In addition, we have shown that this enzyme will also convert phosphatidylglycerol phosphate [1-(3-sn-phosphatidyl)-sn-glycerol-1-P] to phosphatidylglycerol [1-(3-sn-phosphatidyl)-sn-glycerol] and Pi. The phosphatidylglycerol phosphate was made available to the surfactant enzyme in a coupled assay by hydrolysis of cardiolipin [1-(3-sn-phosphatidyl)-3-(3-sn-phosphatidyl)-sn-glycerol] by stereospecific cleavage with phospholipase C (phosphatidylcholine cholinephosphohydrolase, EC 3.1.4.3) from Bacillus cereus. This enzyme has been previously shown to generate the naturally occurring isomer of phosphatidylglycerol phosphate because it has specificity for the 3-(3-sn-phosphatidyl) group of cardiolipin. Other properties of the surfactant enzyme are discussed in relation to its presence in lung surface active material.

Acid Phosphatase↗
PubMed1980

Transplacental stimulation of lung development in the fetal rabbit by 3,5-dimethyl-3'-isopropyl-L-thyronine.

The effect of thyroid hormone on maturation of fetal rabbit lung was studied with maternal treatment using 3,5-dimethyl-3'-isopropyl-L-thyronine (DIMIT), a synthetic analogue of triiodothyronine. To investigate the in vivo kinetics and distribution of DIMIT, we prepared [3H]DIMIT and injected both pregnant rats (18-21 d gestation) and rabbits (25 d gestation). In the rat, maximal concentrations of radioactivity in maternal plasma, fetal plasma, and amniotic fluid occurred within 10 min, 1-2 h, and 4-6 h, respectively, after intramuscular injection. After 7 h the concentration of radioactivity in fetal plasma was 163 and 71% of the maternal level in rats and rabbits, respectively, indicating that DIMIT readily crosses the placenta. We treated pregnant rabbits for 1-2 d with DIMIT in doses of 0.5-3 mg/kg per d and examined the fetuses at 26 and 27 d gestation. Treatment did not affect fetal growth or viability. In fetal liver, DIMIT increased the activity of NADPH cytochromeac reductase by 64% and decreased the glycogen content by 73% compared to controls. The rate of choline incorporation by lung minces increased in dose-dependent manner to a maximum of +104% at 3 mg/kg DIMIT; this does stimulated by 38% the activity of lung phosphatidic acid phosphatase (PAPase), a corticosteroid-responsive enzyme, but there was no increase in tissue PAPase activity at most lower doses of DIMIT that enhanced choline incorporation. Treated lungs had 38% less glycogen tha controls, but there was no effect on tissue levels of DNA, protein, or phospholipid. DIMIT treatment increased the amount of total phospholipid (+163%). saturated phosphatidylcholine (+330%), and PAPase activity (+134%) in lung lavage fluid. The DIMIT effects on both choline incorporation by lung minces and phospholipid content of lavage fluid were substantially greater than what had occurred with an optimal dose of betamethasone. DIMIT also increased corticosteroid binding capacity in fetal plasma and produced a dose-dependent increase (maximal threefold) in total and free corticoids of both maternal and fetal plasma. It is estimated that elevated endogenous corticoids probably account for less than one-third of the increases in phospholipid synthesis and secretion observed at the higher doses of DIMIT. These data indicate that administration of DIMIT to pregnant rabbits accelertes maturation of the surfactant system in fetal lung. The magnitude of the effects on phospholipid synthesis and secretion, along with the minimal effect of PAPase activity in fetal lung tissue, suggest that thyroid hormones affect different biochemical processes from those influenced by glucocorticoids.

Adrenal Cortex Hormones↗
PubMed1980

Canine surface active material and pulmonary lymphocyte function. Studies with mixed-lymphocyte culture.

Canine bronchoalveolar cells, obtained by lavage, were enriched for lymphocytes by adsorption to plastic or by filtration over nylon wool and tested for their ability to function in the mixed lymphocyte culture (MLC) reaction. Pulmonary lymphocytes were markedly hyporesponsive to stimulation with allogeneic cells in vitro: their responses rarely exceeded 10% of those of blood lymphocytes obtained simultaneously from the same donor. However, pulmonary lymphocytes did function as stimulating cells, inducing allogeneic blood lymphocytes to proliferate in MLC. The failure of pulmonary lymphocytes to respond in MLC, coupled with their ability to stimulate clearly, distinguishes these cells from circulating blood lymphocytes. The effect of canine surface active material (SAM), a lipoprotein unique to the lung, on the function of blood lymphocytes in MLC was studied. A transient exposure to SAM in vitro profoundly suppressed blood lymphocyte responses to allogenic stimulation, but had only a minor effect on their function as stimulator cells in MLC. Thus, exposure to SAM in vitro converts normal blood lymphocytes into cells whose function mimics that of pulmonary lymphocytes. These results suggest that exposure of pulmonary lymphocytes to SAM in vivo may contribute to their abnormal immune reactivity in vitro.

Animals↗
PubMed1980

Identification of the immunosuppressive components of canine pulmonary surface active material.

Pulmonary surface active material (SAM), purified from canine lung lavage fluids, is a phospholipid-rich lipoprotein with potent immunosuppressive activity. Experiments were performed to identify those components of SAM that were responsible for this immunosuppressive effect. Results indicated that the lipid, and not the protein, fraction of SAM was immunosuppressive. Two phospholipids, phosphatidylglycerol and phosphatidylcholine, were identified as the predominant immunosuppressive components of the SAM-lipid fraction. lymphocyte proliferation in response to mitogenic or allogeneic stimulation was suppressed by intact SAM, SAM-lipid, phosphatidylglycerol, and phosphatidylcholine. Each of these preparations inhibited RNA, protein and DNA synthesis by mitogen-stimulated lymphocytes. Antioxidants consistently failed to diminish the immunosuppressive properties of SAM or its lipid components. The mechanism of this immunosuppressive action of SAM and its phospholipid components remains undefined. Our data indicate, however, that it is unlikely to be due either to cytotoxicity or to an artifact of lipid oxidation in vitro.

Animals↗