Label-free detection and identification of protein ligands captured by receptors in a polymerized planar lipid bilayer using MALDI-TOF MS.

Matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) mass spectrometry (MS) coupled with affinity capture is a well-established method to extract biological analytes from complex samples followed by label-free detection and identification. Many bioanalytes of interest bind to membrane-associated receptors; however, the matrices and high-vacuum conditions inherent to MALDI-TOF MS make it largely incompatible with the use of artificial lipid membranes with incorporated receptors as platforms for detection of captured proteins and peptides. Here we show that cross-linking polymerization of a planar supported lipid bilayer (PSLB) provides the stability needed for MALDI-TOF MS analysis of proteins captured by receptors embedded in the membrane. PSLBs composed of poly(bis-sorbylphosphatidylcholine) (poly(bis-SorbPC)) and doped with the ganglioside receptors GM1 and GD1a were used for affinity capture of the B subunits of cholera toxin, heat-labile enterotoxin, and pertussis toxin. The three toxins were captured simultaneously, then detected and identified by MS on the basis of differences in their molecular weights. Poly(bis-SorbPC) PSLBs are inherently resistant to nonspecific protein adsorption, which allowed selective toxin detection to be achieved in complex matrices (bovine serum and shrimp extract). Using GM1-cholera toxin subunit B as a model receptor-ligand pair, we estimated the minimal detectable concentration of toxin to be 4 nM. On-plate tryptic digestion of bound cholera toxin subunit B followed by MS/MS analysis of digested peptides was performed successfully, demonstrating the feasibility of using the PSLB-based affinity capture platform for identification of unknown, membrane-associated proteins. Overall, this work demonstrates that combining a poly(lipid) affinity capture platform with MALDI-TOF MS detection is a viable approach for capture and proteomic characterization of membrane-associated proteins in a label-free manner.

In vitro assessment of macrophage attachment and phenotype on polymerized phospholipid bilayers.

Phosphatidyl choline (PC)-based materials have been found to be resistant to nonspecific protein adhesion in vitro. In this study, a PC-based planar supported phospholipid bilayer composed of 1,2-bis[10-(2',4'-hexadienoyloxy)decanoyl]-sn-glycero-3-phosphocholine (bis-SorbPC or BSPC) was generated on piranha-treated silicon wafers by vesicle deposition. The bilayer was polymerized with redox initiation forming a stable 4-nm thick coating. Polymerized lipid bilayers (PLBs) were characterized and tested for uniformity, with ellipsometry and contact angle. Cellular adhesion and morphological changes in RAW 264.7 macrophages were investigated in vitro on PLBs and compared to bare silicon controls. Fluorescent and scanning electron microscopy were used to observe changes in cellular morphology. The PLBs showed much lower cellular adhesion than bare silicon controls. Of the cells that attached to the PLBs, a very low percentage showed the same morphological expressions seen on the controls. It is hypothesized that proteins adsorb to the defects in the PLBs, caused by incomplete polymerization, and this mediates the observed minimal cellular attachment and morphological changes. © 2011 Wiley Periodicals, Inc. J Biomed Mater Res Part A: , 2011.

Stable, ligand-doped, poly(bis-SorbPC) lipid bilayer arrays for protein binding and detection.

A continuous-flow microspotter was used to generate planar arrays of stabilized bilayers composed of the polymerizable lipid bis-SorbPC and dopant lipids bearing ligands for proteins. Fluorescence microscopy was used to determine the uniformity of the bilayers and to detect protein binding. After UV-initiated polymerization, poly(lipid) bilayer microarrays were air-stable. Cholera toxin subunit b (CTb) bound to an array of poly(lipid) bilayers doped with GM(1), and the extent of binding was correlated to the mole percentage of GM(1) in each spot. A poly(lipid) bilayer array composed of spots doped with GM(1) and spots doped with biotin-DOPE specifically bound CTb and streptavidin to the respective spots from a dissolved mixture of the two proteins. Poly(bis-SorbPC)/GM(1) arrays retained specific CTb binding capacity after multiple regenerations with a protein denaturing solution and also after exposure to air. In addition, these arrays are stable in vacuum, which allows the use of MALDI-TOF mass spectrometry to detect specifically bound CTb. This work demonstrates the considerable potential of poly(lipid) bilayer arrays for high-throughput binding assays and lipidomics studies.

Diagnostic value of post-bronchodilator pulmonary function testing to distinguish between stable, moderate to severe COPD and asthma.

OBJECTIVE: The GOLD guidelines suggest that the presence of a post-bronchodilator forced expiratory volume in one second (FEV1) < 80% of the predicted value in combination with a FEV1/forced vital capacity (FVC) < 70% confirms the diagnosis of COPD. Limited data exist regarding the accuracy of these criteria to distinguish between COPD and asthma. The aim of this study therefore was to investigate the diagnostic value of post-bronchodilator lung function parameters in obstructive lung disease. METHODS: The pulmonary function tests of 43 (22 = COPD, 21 = asthma) patients with similar baseline characteristics were evaluated (baseline FEV were 55.7% +/- 7.6%, and 59.3% +/- 8.4% predicted for COPD and asthma, respectively). Bronchodilator responsiveness (BDR) was calculated according to three recognized pulmonary function test criteria. RESULTS: The first criteria, post-bronchodilator FEV1 < 80% of the predicted value in combination with a post-bronchodilator FEV1/FVC ratio of < 70%, had an accuracy of 70% to diagnose COPD. This combination was very sensitive (100%) in diagnosing COPD, but it was not specific (38%). The second BDR criteria, defined as an increase of < 12% and 200 mL of initial FEV1 and criterion number 3, an increase of < 9% of predicted FEV1, were less sensitive (55% and 59%, respectively), but more specific (81% and 76% respectively) to diagnose COPD. Our findings suggest that the current recommended spirometric indices are not optimal in differentiating between COPD and asthma.

Patterned protein films on poly(lipid) bilayers by microcontact printing.

The use of polymerized lipid bilayers as substrates for microcontact printing (muCP) of protein films was investigated. We have previously shown that vesicle fusion of bis-SorbPC, a dienoate lipid, on glass and silica substrates, followed by redox-initiated radical polymerization, produces a planar supported lipid bilayer (PSLB) that is ultrastable(1a) [Ross, E. E.; Rozanski, L. J.; Spratt, T.; Liu, S.; O'Brien, D. F.; Saavedra, S. S. Langmuir 2003, 19, 1752] and highly resistant to nonspecific adsorption of dissolved proteins [Ross, E. E.; Spratt, T.; Liu, S.; Rozanski, L. J.; O'Brien, D. F.; Saavedra, S. S. Langmuir 2003, 19, 1766].(1b) Here we demonstrate that muCP of bovine serum albumin (BSA) onto a dried poly(bis-SorbPC) PSLB from a poly(dimethylsiloxane) (PDMS) stamp produces a layer of strongly adsorbed protein, comparable in surface coverage to films printed on glass surfaces. Immobilization of proteins on poly(PSLB)s has potential applications in biosensing, and this work shows that direct muCP of proteins is a technically simple approach to create immobilized monolayers, as well as multilayers of different proteins.

A randomized, double-blind, double-dummy, parallel-group, multicenter, dose-reduction trial of the minimal effective doses of budesonide and fluticasone dry-powder inhalers in adults with mild to moderate asthma.

BACKGROUND: Inhaled corticosteroids are established first-line anti-inflammatory treatment for asthma. Clinical trials comparing inhaled corticosteroids must take into consideration that because of their excellent effect at low doses, they typically induce a near-maximal response in asthma patients. OBJECTIVE: The aim of the present dose-response study was to estimate the minimal effective doses (MEDs) of budesonide and of fluticasone propionate via dry-powder inhaler in adults with mild to moderate asthma. METHODS: This was a randomized, double-blind, double-dummy, parallel-group, multicenter, dose-reduction trial performed in adults to compare these 2 inhaled corticosteroids. After a 4- to 6-week run-in period with beclomethasone dipropionate 2000 pg/d, patients fulfilling defined criteria for asthma control were randomly allocated to treatment with budesonide or fluticasone, both administered BID at a total of 800 pg/d. At 5-week intervals, the dose was reduced to 400 and then 200 pg/d (200 and 100 pg BID) if asthma control was maintained according to further defined criteria. The MED was defined as the last dose level before deterioration of asthma control. RESULTS: Subjects were 197 asthmatic patients with a mean age of 40.6 years in the budesonide group and 41.5 years in the fluticasone group. In both groups, baseline mean forced expiratory volume in 1 second (FEV(1)) was 79.4% of the predicted normal volume and baseline mean FEV(1) reversibility was 22.3%. The median MED for both groups was 400 microg/d, with no detectable difference in dis-tributions. The budesonide-to-fluticasone ratio for the geometric mean MED was 123% (95% CI, 99-153 [not significant]). No statistically significant differences regarding lung function, symptom scores, or rescue medication usage were found between the treatment groups during the first treatment period. Adverse-event profiles were similar in both groups, and no unexpected adverse events were considered to be caused by the study drugs. CONCLUSION: This effect-controlled study did not detect a statistically significant difference between the MEDs for budesonide and fluticasone via dry-powder inhaler in adults with mild to moderate asthma.