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Biomedical subjects

N J Gross

Publications and source records attributed to N J Gross.

At least 19 recordsLinked to original sources
PubMed2000

Is dipalmitoylphosphatidylcholine a substrate for convertase?

Convertase has homology with carboxylesterases, but its substrate(s) is not known. Accordingly, we determined whether dipalmitoylphosphatidylcholine (DPPC), the major phospholipid in surfactant, was a substrate for convertase. We measured [(3)H]choline release during cycling of the heavy subtype containing [(3)H]choline-labeled DPPC with convertase, phospholipases A(2), B, C, and D, liver esterase, and elastase. Cycling with liver esterase or peanut or cabbage phospholipase D produced the characteristic profile of heavy and light peaks observed on cycling with convertase. In contrast, phospholipases A(2), B, and C and yeast phospholipase D produced a broad band of radioactivity across the gradient without distinct peaks. [(3)H]choline was released when natural surfactant containing [(3)H]choline-labeled DPPC was cycled with yeast phospholipase D but not with convertase or peanut and cabbage phospholipases D. Similarly, yeast phospholipase D hydrolyzed [(3)H]choline from [(3)H]choline-labeled DPPC after incubation in vitro, whereas convertase, liver esterase, or peanut and cabbage phospholipases D did not. Thus convertase, liver esterase, and plant phospholipases D did not hydrolyze choline from DPPC either on cycling or during incubation with enzyme in vitro. In conclusion, conversion of heavy to light subtype of surfactant by convertase may require a phospholipase D type hydrolysis of phospholipids, but the substrate in this reaction is not DPPC.

1,2-Dipalmitoylphosphatidylcholine↗
PubMed1999

Effect of systemic glucocorticoids on exacerbations of chronic obstructive pulmonary disease. Department of Veterans Affairs Cooperative Study Group.

BACKGROUND AND METHODS: Although their clinical efficacy is unclear and they may cause serious adverse effects, systemic glucocorticoids are a standard treatment for patients hospitalized with exacerbations of chronic obstructive pulmonary disease (COPD). We conducted a double-blind, randomized trial of systemic glucocorticoids (given for two or eight weeks) or placebo in addition to other therapies, for exacerbations of COPD. Most other care was standardized over the six-month period of follow-up. The primary end point was treatment failure, defined as death from any cause or the need for intubation and mechanical ventilation, readmission to the hospital for COPD, or intensification of drug therapy. RESULTS: Of 1840 potential study participants at 25 Veterans Affairs medical centers, 271 were eligible for participation and were enrolled; 80 received an eight-week course of glucocorticoid therapy, 80 received a two-week course, and 111 received placebo. About half the potential participants were ineligible because they had received systemic glucocorticoids in the previous 30 days. Rates of treatment failure were significantly higher in the placebo group than in the two glucocorticoid groups combined at 30 days (33 percent vs. 23 percent, P=0.04) and at 90 days (48 percent vs. 37 percent, P=0.04). Systemic glucocorticoids (in both groups combined) were associated with a shorter initial hospital stay (8.5 days, vs. 9.7 days for placebo, P=0.03) and with a forced expiratory volume in one second that was about 0.10 liter higher than that in the placebo group by the first day after enrollment. Significant treatment benefits were no longer evident at six months. The eight-week regimen of therapy was not superior to the two-week regimen. The patients who received glucocorticoid therapy were more likely to have hyperglycemia requiring therapy than those who received placebo (15 percent vs. 4 percent, P=0.002). CONCLUSIONS: Treatment with systemic glucocorticoids results in moderate improvement in clinical outcomes among patients hospitalized for exacerbations of COPD. The maximal benefit is obtained during the first two weeks of therapy. Hyperglycemia of sufficient severity to warrant treatment is the most frequent complication.

Administration, Oral↗
PubMed1999

Influence of phospholipid composition on the properties of reconstituted surfactants.

The influence of phospholipids on the ultrastructure and metabolism of reconstituted surfactants has not been well defined. The aim of this study was to determine if changes in the phospholipid composition of reconstituted surfactants altered their biophysical properties, ultrastructure, and conversion to light subtype by cycling. We prepared various surfactants containing radiolabeled dipalmitoylphosphatidylcholine ([14C]DPPC). The addition of phosphatidylglycerol (PG) or dipalmitoylphosphatidic acid (PA) to DPPC increased conversion to light subtype. In contrast, the addition of dipalmitoylphosphatidylglycerol (DPPG) to DPPC markedly reduced conversion to light subtype on cycling. DPPC and DPPC+PG produced large liposomes ( approximately 1,000 nm), whereas DPPC+PA or DPPC+DPPG formed multilamellar membranes. Mixtures of DPPC and PA were highly surface active in vitro, whereas the surface activity of DPPC+DPPG was similar to that of DPPC. In conclusion, the ultrastructure, metabolism, and surface active properties of DPPC+PG mixtures were influenced markedly by alterations in the fatty acid composition or polar head group of PG.

1,2-Dipalmitoylphosphatidylcholine↗
PubMed1999

Effects of salmeterol on arterial blood gases in patients with stable chronic obstructive pulmonary disease. Comparison with albuterol and ipratropium.

Administration of beta-adrenergic agonist bronchodilators to patients with airways obstruction commonly results in transient decreases in Pa(O(2)) levels despite bronchodilation, an effect that has been attributed to these drugs' pulmonary vasodilator action. We compared the acute effects on gas exchange of salmeterol with those of albuterol and the anticholinergic agent ipratropium in 20 patients with stable chronic obstructive pulmonary disease (COPD). Each agent was given in recommended dosage on separate days in a double-blind, crossover format, and the patients' arterial blood gases (ABGs) were measured at baseline and at intervals to 120 min. Small but statistically significant declines in Pa(O(2)), the primary outcome variable, were found after administration of both salmeterol and albuterol. The decline in PaO2 after salmeterol was of lesser magnitude but was more prolonged than that after albuterol, the greatest mean change being -2.74 +/- 0.89 mm Hg (mean +/- SEM) at 30 min after salmeterol, and -3.45 +/- 0.92 mm Hg at 20 min after albuterol. Following ipratropium, the corresponding change was -1.32 +/- 0.85 mm Hg at 20 min. These declines, which were almost entirely attributable to increases in the alveolar-arterial difference in oxygen tension Delta(A-a)DO2 tended to be more marked in subjects with higher baseline PaO2 values. No subject experienced a decline in PaO2 to levels below 59 mm Hg. There were no significant differences among the three drugs studied. We conclude that despite small decreases in PaO2 after each of the three drugs, the declines were small transient, and of doubtful clinical significance.

Administration, Inhalation↗
PubMed1999

Efficacy of salmeterol xinafoate in the treatment of COPD.

STUDY OBJECTIVES: To examine and compare the efficacy and safety of salmeterol xinafoate, a long-acting inhaled beta2-adrenergic agonist, with inhaled ipratropium bromide and inhaled placebo in patients with COPD. DESIGN: A stratified, randomized, double-blind, double-dummy, placebo-controlled, parallel group clinical trial. SETTING: Multiple sites at clinics and university medical centers throughout the United States. PATIENTS: Four hundred eleven symptomatic patients with COPD with FEV1 < or = 65% predicted and no clinically significant concurrent disease. INTERVENTIONS: Comparison of inhaled salmeterol (42 microg twice daily), inhaled ipratropium bromide (36 microg four times a day), and inhaled placebo (2 puffs four times a day) over 12 weeks. RESULTS: Salmeterol xinafoate was significantly (p < 0.0001) better than placebo and ipratropium in improving lung function at the recommended doses over the 12-week trial. Both salmeterol and ipratropium reduced dyspnea related to activities of daily living compared with placebo; this improvement was associated with reduced use of supplemental albuterol. Analyses of time to first COPD exacerbation revealed salmeterol to be superior to placebo and ipratropium (p < 0.05). Adverse effects were similar among the three treatments. CONCLUSIONS: These collective data support the use of salmeterol as first-line bronchodilator therapy for the long-term treatment of airflow obstruction in patients with COPD.

Administration, Inhalation↗
PubMed1998

Protein-lipid interactions and enzyme requirements for light subtype generation on cycling reconstituted surfactant.

Surfactant convertase is required for conversion of heavy density (H) natural surfactant to light density (L) subtype during cycling in vitro, a technique that reproduces surfactant metabolism. To study mechanisms of H to L conversion, we prepared liposomes of dipalmitoylphosphatidylcholine (DPPC) and phosphatidylglycerol (PG), or the phospholipids (PL) in combination with either surfactant protein A (SP-A), surfactant protein B (SP-B), or both SP-A and SP-B. Phospholipids alone showed time-dependent conversion from heavy to light subtype on cycling in the absence of convertase, which was decreased by adding SP-B, but not SP-A, to phospholipids (p < 0.01 for PL+SP-B, or PL+SP-A+SP-B vs. PL, or PL+SP-A). The ultrastructure, surface activity, buoyant density, and L subtype generation on cycling PL+SP-A+SP-B with partially purified convertase or with phospholipase D were similar to those of natural TM. In conclusion, a reconstituted surfactant mimics the behavior of natural surfactant on cycling, and reveals that interaction of SP-B with phospholipids decreases L subtype generation. In addition, esterase/ phospholipase D activity is required for conversion of heavy to light subtype on cycling.

Animals↗
PubMed1998

Molecular cloning, characterization, and differential expression pattern of mouse lung surfactant convertase.

We recently reported the purification and partial amino acid sequence of "surfactant convertase," a 72-kDa glycoprotein involved in the extracellular metabolism of lung surfactant (S. Krishnasamy, N. J. Gross, A. L. Teng, R. M. Schultz, and R. Dhand. Biochem. Biophys. Res. Commun. 235: 180-184, 1997). We report here the isolation of a cDNA clone encoding putative convertase from a mouse lung cDNA library. The cDNA spans a 1,836-bp sequence, with an open reading frame encoding 536 amino acid residues in the mature protein and an 18-amino acid signal peptide at the NH2 terminus. The deduced amino acid sequence matches the four partial amino acid sequences (68 residues) that were previously obtained from the purified protein. The deduced amino acid sequence contains an 18-amino acid residue signal peptide, a serine active site consensus sequence, a histidine consensus sequence, five potential N-linked glycosylation sites, and a COOH-terminal secretory-type sequence His-Thr-Glu-His-Lys. Primer-extension analysis revealed that transcription starts 29 nucleotides upstream from the start codon. Northern blot analysis of RNA isolated from various mouse organs showed that convertase is expressed in lung, kidney, and liver as a 1,800-nucleotide-long transcript. The nucleotide and amino acid sequences of putative convertase are 98% homologous with mouse liver carboxylesterase. It thus may be the first member of the carboxylesterase family (EC 3.1.1.1) to be expressed in lung parenchyma and the first with a known physiological function.

Amino Acid Sequence↗
PubMed1997

Lung "surfactant convertase" is a member of the carboxylesterase family.

The extracellular conversion of lung surfactant from tubular myelin to the small vesicular form has previously been shown to require a serine-active enzyme called "surfactant convertase." In the present study, a 72kD serine-active enzyme previously identified in mouse lung alveolar lavage and having convertase activity was partially sequenced. Sixty-eight residues obtained from amino acid sequencing of this protein show that it is a new member of the mouse carboxylesterase family (EC 3.1.1.1). The 72kD lung protein also has esterase activity. A commercial esterase of the same family was able to reproduce surfactant convertase bioactivity in vitro, unlike several serine proteinases previously tested. We conclude that surfactant convertase is a carboxylesterase which mediates a biochemical step in the extracellular metabolism of surfactant.

Amino Acid Sequence↗
PubMed1997

Surfactant convertase action is not essential for surfactant film formation.

A serine-active enzyme, "surfactant convertase", is required for the conversion of surfactant from the tubular myelin (TM) form to the small vesicular (SV) form. This transformation involves at least two steps, the conversion of TM to a surface-active film at the air-fluid interface and the reorientation of the film into the surface-inactive SV form; we asked if convertase was required for the first of these steps. Rat and mouse TMs were pretreated with diisopropyl fluorophosphate (DFP) to inactivate endogenous convertase activity or with vehicle and then were analyzed for their ability to lower surface tension in vitro as an index of the conversion of TM to a surface film. DFP pretreatment did not alter the ability of TM preparations to lower surface tension, as assessed by pulsating bubble, and it did not affect the behavior of TM in a surface balance. In an experiment designed to test the ability of TM to feed a surface film to exhaustion, TMs that had been pretreated with DFP or vehicle performed similarly. These experiments show that convertase activity is not required for the conversion of TM to a monolayer and suggest, instead, that convertase acts at a post surface film stage.

Animals↗
PubMed1996

Management of chronic obstructive pulmonary disease.

Chronic obstructive pulmonary disease is the fourth leading cause of death in the United States, affecting approximately 10% of all adults. Several articles published during the past year contributed significantly to our understanding of the complicated management of this disease. New information concerning bronchodilators, antibiotic therapy, mechanical ventilation, pulmonary rehabilitation, nutrition, and lung transplantation will help physicians further refine the care delivered to these patients.

Adult↗
PubMed1996

Effects of radiation on the lung.

Since the beginning of the twentieth century, radiation has been employed as a tool to cure or palliate malignancy. Unfortunately, soon after its discovery, the harmful effects of radiation were recognized as well. As our understanding of the physiologic responses to radiation increases, we can refine the routes of delivery and dosages of radiation administered. The use of three-dimensional treatment planning and the manipulation of the biochemical response with drugs and synthesized cytokines offers promise in curtailing the undesirable effects of irradiation. Side effects will be minimized and benefits maximized with further technologic developments that will more accurately control the delivery of and response to radiation.

Animals↗
PubMed1995

The role of alpha 1-antitrypsin in the control of extracellular surfactant metabolism.

Alveolar surfactant exists in several structural forms that are believed to be secular products of the secreted form, lamellar bodies. The conversion of tubular myelin to the small vesicular form appears to require the action of a novel serine protease, surfactant convertase. As the in vitro activity of this enzyme is quite sensitive to inhibition by the serine protease inhibitor alpha 1-antitrypsin, a normal constituent of the alveolar fluid lining layer, we explored the possibility that the alveolar level of alpha 1-antitrypsin might affect the rate of subtype conversion in vivo. When the alveolar alpha 1-antitrypsin level was augmented by tracheal instillation of exogenous alpha 1-antitrypsin, the newly synthesized surfactant phospholipids of spontaneously breathing mice accumulated in the heavy subtype, and virtually none was found in the light subtype form up to 72 h later. An in vivo turnover study suggested that when the alveolar alpha 1-antitrypsin level was raised by the same means, the flux of surfactant through the light (small vesicular) compartment was virtually shut off, despite the availability of abundant amounts of its precursor, heavy subtype (tubular myelin). Finally, mouse lungs that were lavaged to remove resident surfactant and mechanically ventilated for 1-5 h released surfactant that progressed through heavy and light subtype compartments as in vivo. But in mice whose lung alpha 1-antitrypsin might affect the metabolism of alveolar surfactant in addition to its well-known role in lung defense.

Animals↗
PubMed1992

Requirements for extracellular metabolism of pulmonary surfactant: tentative identification of serine protease.

Pulmonary alveolar surfactant is secreted by the alveolar epithelium in the form of lamellar bodylike structures that evolve sequentially into tubular myelin and vesicular forms that can be separated by centrifugation. Using an in vitro procedure by which the extracellular metabolism of pulmonary surfactant can be mimicked, namely cyclic variation in surface area, we previously reported that serine protease activity, which we called "convertase," was required for the conversion of tubular myelin to the vesicular form. In the present studies we explored the biochemical requirements of this activity and sought the enzyme in alveolar products. Convertase activity has unusual requirements; in addition to being dependent on repetitive variations in surface area (cycling), it requires the presence of a high g fraction of lung secretions that is heat stable and not inhibitable by diisopropyl fluorophosphate (DFP) or alpha 1-antitrypsin, both typical serine protease inhibitors. The enzyme does not require calcium ions and has a pH optimum of 7.4. Convertase appears to be a component of surfactant itself because the ability of purified surfactant to convert to the vesicular form on cycling is impaired by pretreating it with DFP. A protein of Mr 75,000 that reacts with DFP and is heat sensitive was found in alveolar lavage, lamellar body preparations, and lung homogenate. It copurifies with lung surfactant in sucrose gradients. A similar DFP-reactive protein was observed in stable human neoplastic peripheral airway cell lines that express type II properties, suggesting that it may be a product of type II cells. We tentatively conclude that surfactant convertase is a 75,000 serine protease that is closely associated with surfactant phospholipid and that may be a product of alveolar type II cells.

Animals↗
PubMed1991

The influence of anticholinergic agents on treatment for bronchitis and emphysema.

Recent studies have shown that anticholinergic therapy is more effective than the most potent beta-adrenergic agents for chronic obstructive pulmonary disease. In the 3 years since it has been available to physicians in the United States, the quaternary anticholinergic drug ipratropium bromide (Atrovent) has had a considerable influence on clinical practice and the management of patients who have this disease. However, knowledge in this area is still incomplete. Questions remain as to the long-term effects of anticholinergic agents on the airways and, perhaps more important, on the natural progression of chronic obstructive pulmonary disease. Studies currently in progress will help determine the effect of prolonged therapy with anticholinergic agents on the progression and morbidity of lung disease.

Bronchitis↗