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Biomedical subjects

E B Brown

Publications and source records attributed to E B Brown.

At least 19 recordsLinked to original sources
PubMed2000

Glycoprotein IIb-IIIa-liposomes bind fibrinogen but do not undergo fibrinogen-mediated aggregation.

Although platelet cross-bridging is mediated primarily by the binding of fibrinogen to its activated membrane receptor, glycoprotein (GP) IIb-IIIa*, such an interaction may not be sufficient to support the aggregation process. As this question could potentially be answered by reconstituting GPIIb-IIIa* into a non-platelet environment such as liposomes, a protocol was developed for the generation of large lipid vesicles containing purified GPIIb-IIIa*. Flow cytometric techniques confirmed that the receptor was present in the lipid bilayer and were used to evaluate the characteristics of fibrinogen binding to the liposomes, which like fibrinogen-platelet interactions exhibited specificity, saturability, time dependence and calcium dependence. No fibrinogen-specific aggregation of GPIIb-IIIa* liposomes with stir or shear was observed, as determined by flow cytometric cell counting and microscopic examination of particles. In contrast, activated platelets rapidly bound Fg and rapidly formed large aggregates. The Fg associated with GPIIb-IIIa* in liposomes was 'normally' recognized by two fluorescently labelled antibodies: 4A5, which interacts with the Fg gamma chain C-terminus (residues 400-411) required for Fg-mediated cross-bridging of activated platelets in platelet aggregation (Shiba E, Lindon JN, Kushner L, Matsueda GR, Hawiger J, Kloczewiak M, Kudryk B, Salzman EW. Antibody-detectable changes in fibrinogen adsorption affecting platelet activation on polymer surfaces. Am J Physiol 1991; 260: C965-74), and anti-Fg-RIBS-I, which associates with an epitope on Fg (residues 373-385) expressed upon binding to GPIIb-IIIa. These data suggest that the Fg gamma-terminus is sterically accessible for particle cross-bridging and that an identical conformational change occurs for receptor-bound Fg on both liposomes and platelets. It thus appears that cellular elements aside from GPIIb-IIIa, such as cytoskeletal proteins proposed to be necessary for receptor 'anchoring', play a necessary role in flow-associated platelet aggregation.

Acetates↗
PubMed1999

Measurement of molecular diffusion in solution by multiphoton fluorescence photobleaching recovery.

Multiphoton fluorescence photobleaching recovery (MP-FPR) is a technique for measuring the three-dimensional (3D) mobility of fluorescent molecules with 3D spatial resolution of a few microns. A brief, intense flash of mode-locked laser light pulses excites fluorescent molecules via multiphoton excitation in an ellipsoidal focal volume and photobleaches a fraction. Because multiphoton excitation of fluorophores is intrinsically confined to the high-intensity focal volume of the illuminating beam, the bleached region is restricted to a known, three-dimensionally defined volume. Fluorescence in this focal volume is measured with multiphoton excitation, using the attenuated laser beam to measure fluorescence recovery as fresh unbleached dye diffuses in. The time course of the fluorescence recovery signal after photobleaching can be analyzed to determine the diffusion coefficient of the fluorescent species. The mathematical formulas used to fit MP-FPR recovery curves and the techniques needed to properly utilize them to acquire the diffusion coefficients of fluorescently labeled molecules within cells are presented here. MP-FPR is demonstrated on calcein in RBL-2H3 cells, using an anomalous subdiffusion model, as well as in aqueous solutions of wild-type green fluorescent protein, yielding a diffusion coefficient of 8.7 x 10(-7) cm(2)s(-1) in excellent agreement with the results of other techniques.

Cell Line↗
PubMed1999

Photolysis of caged calcium in femtoliter volumes using two-photon excitation.

A new technique for the determination of the two-photon uncaging action cross section (deltau) of photolyzable calcium cages is described. This technique is potentially applicable to other caged species that can be chelated by a fluorescent indicator dye, as well as caged fluorescent compounds. The two-photon action cross sections of three calcium cages, DM-nitrophen, NP-EGTA, and azid-1, are studied in the range of excitation wavelengths between 700 and 800 nm. Azid-1 has a maximum deltau of approximately 1.4 GM at 700 nm, DM-nitrophen has a maximum deltau of approximately 0.013 GM at 730 nm, and NP-EGTA has no measurable uncaging yield. The equations necessary to predict the amount of cage photolyzed and the temporal behavior of the liberated calcium distribution under a variety of conditions are derived. These equations predict that by using 700-nm light from a Ti:sapphire laser focused with a 1.3-NA objective, essentially all of the azid-1 within the two-photon focal volume would be photolyzed with a 10-micros pulse train of approximately 7 mW average power. The initially localized distributions of free calcium will dissipate rapidly because of diffusion of free calcium and uptake by buffers. In buffer-free cytoplasm, the elevation of the calcium concentration at the center of the focal volume is expected to last for approximately 165 micros.

Acetates↗
PubMed1997

Tolerance intervals for assessing individual bioequivalence.

Evaluation of equivalence of two formulations of a drug typically entails the comparison of average bioavailabilities. Recently, however, authors have become aware that this may be insufficient to assess individual bioequivalence, that is, interchangeability of formulations on an individual basis. This paper outlines a tolerance interval procedure to assess individual bioequivalence based on a model that includes a subject by formulation interaction. We give methods for several higher-order cross-over designs along with examples.

Chemistry, Pharmaceutical↗
PubMed1996

Multiphoton-excited fluorescence of fluorogen-labeled neurotransmitters.

Fluorescence detection of fluorogen-labeled neurotransmitters is demonstrated using 100 fs pulses from a titanium-sapphire mode-locked laser to achieve molecular excitation by simultaneous absorption of two and three photons of near-IR radiation. Two-photon excitation spectra are determined for the naphthalene-2,3 dicarboxaldehyde derivative of glycine and the fluorescamine derivative of leucine enkephalin, with the peak excitation cross section (o2) approximately equal to 1 x 10(-50) cm4 s/photon for both species. Three-photon-excitation fluorescence is demonstrated for o-phthaldialdehyde-labeled glutamate using excitation wavelengths between 965 and 1012 nm. The three-photon excitation cross section (o3) remains nearly constant in this wavelength range, with an absolute value of approximately 10(-84)-10(-85) cm6 s2/photon 2. Rapid cycling of analytes through the fluorescent excited state and detection that is free from background caused by Rayleigh and Raman scatter combine to make multiphoton-excited fluorescence a highly sensitive approach for detecting trace amounts of neurotransmitters. Measurements of two-photon-excited fluorescence of fluorescamine-labeled bradykinin and analysis of multiphoton-excited background reveal the potential of this method to detect fewer than 1000 neurotransmitter molecules.

Fluorescent Dyes↗
PubMed1991

Comparison of dual photon and dual energy X-ray bone densitometers in a clinic setting.

In clinical practice, decisions must be made about whether and how to convert to newer technologies. To address this issue, two separate studies were conducted. We evaluated the relationships between results of lumbar spine measurements using two dual photon absorptiometry (DPA1 and DPA2) instruments and one dual energy X-ray (DXA) instrument with the same subjects (49 volunteers), and also in 65 patients who were measured on the DPA1 and DXA machines. Second, we measured the lumbar spine and the proximal femur in three groups of 12 female volunteers three times on one instrument within 1 week. We purposely simulated a busy clinic setting with different technologists, older radioactive sources, and a heterogeneous patient group. The comparison study indicated a significant difference between the mean bone density values reported by the machines, but the results were highly correlated (R2 = 0.89-0.96). The short-term precision errors (coefficients of variation) differed among the instruments, ranging from 1.3% (DXA of the spine) to 5.1% (DPA1 of the spine), and in the femoral neck, 2.3% and 2.4% (DXA and DPA1, respectively) versus 3.5% by DPA2. This study emphasizes the differences between instruments, the potential for greater error in busy clinic environments, and the apparent superiority of dual energy X-ray absorptiometry under these less than ideal conditions.

Absorptiometry, Photon↗
PubMed1991

Correlations between vertebral regional bone mineral density (rBMD) and whole bone fracture load.

To assess the significance of regional quantitative computed tomography measurements of bone density with respect to mechanical strength in the human lumbar spine, 58 vertebrae (from 12 males, 10 females) were scanned in vitro with multiple-thin-slice quantitative computed tomography and then compressed to fracture. With computer graphics, 18 specific regions of physical density and 10 combination averages of density were identified within each vertebral body. To ensure the statistical independence of data, the individual vertebral specimens were assigned to one of three groups (T11-L1, L2-L3, or L4-L5). Use of best-subsets procedures resulted in regression models to predict fracture strength. These models used specific regional density values and often the age and sex of the donors. The correlation coefficients that resulted from the multiple regression models ranged from r = 0.88 to r = 0.95. When the density values were multiplied by the minimum cross-sectional area of the vertebral body, similar regional density averages were selected, and the predictive values were slightly improved (r = 0.94-0.97). The heterogeneity of the density samples (measured as standard deviation) in multiple regression fashion also produced strong correlation coefficients (r = 0.88-0.94). The bone density in an anterior cylinder of the midplane region, the location measured most often in quantitative computed tomography densitometry, was strongly correlated (r = 0.85) to fracture load for the T12-L1 group (N = 20), but was not significant for the other two groups of vertebrae. The cancellous bone density from the female data was not found to be significantly different from the male data set.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1990

Risk of systemic reactions in patients taking beta-blocker drugs receiving allergen immunotherapy injections.

To learn whether patients taking beta-blocker (BB) drugs were at increased risk of having systemic reactions (SRs) from allergen immunotherapy, we prospectively studied 56,105 injection visits in 3178 patients during a 1-year interval. A total of 166 SRs occurred in 144 patients (4.5% of all patients) or 3.0 SRs occurred per 1000 injection visits. Sixty-eight patients were taking BB drugs throughout the year, and only one patient had an SR. By chance, 3.08 patients were expected to have had SRs. We conclude that BB drugs did not increase the frequency of SRs in the patients studied who were receiving immunotherapy (p greater than 0.95). Patients taking BB drugs may still be at increased risk, however, from more severe SRs or their SRs may be more refractory to therapy.

Adrenergic beta-Antagonists↗
PubMed1989

Tungiasis: report of one case and review of the 14 reported cases in the United States.

Tungiasis is a cutaneous parasitic infestation by the fertilized female sand flea Tunga penetrans. It is prevalent in tropical Africa and in Central and South America. Despite increasing air travel to and from these countries, surprisingly the disease is rarely reported in the United States. This report describes another case of tungiasis and reviews the 14 previously reported cases in the United States. Clinical features, differential diagnosis, treatment, and prophylaxis of tungiasis are discussed.

Adult↗
PubMed1989

Iron metabolism: a 40-year overview.

The study of iron metabolism during the past 40 years is summarized. The status of hematology in general, and of the Hematology Division at Washington University in particular, is retrospectively reviewed. From a baseline of accepted information in 1950, the major areas of iron metabolism in humans are examined and significant additions to the fund of knowledge are identified. Progress in most areas is characterized by slow accretion of knowledge rather than by true conceptual breakthroughs.

Food, Fortified↗
PubMed1986

Electron microscopy of the low pH structure of influenza virus haemagglutinin.

Influenza virus haemagglutinin mediates infection of cells by fusion of viral and endosomal membranes, triggered by low pH which induces a conformational change in the protein. We report studies of this change by electron microscopy, neutron scattering, sedimentation and photon correlation on X-31 (H3N2) haemagglutinin, both intact and bromelain cleaved, in various assemblies. HAs in all preparations showed a thinning at low pH, and a marked elongation which was removed on tryptic digestion, revealing altered features in the remaining stem portion of the molecule. A tentative model of the change is proposed, with reference to the known X-ray structure at neutral pH, in which major changes occur in the stem tertiary structure, while the top portion is only affected in its quaternary structure.

Animals↗
PubMed1983

Electron microscopic evidence for the axial rotation and inter-domain flexibility of the Fab regions of immunoglobulin G.

The Fab arms of immunoglobulin G (IgG) have long been known to hinge about their joint with the Fc subunit. Using monoclonal antibodies bound to influenza haemagglutinin (HA) as position markers, we now show that these arms can also rotate about their long axis with respect to Fc. We also show that when two IgGs are bound cyclically with two HA molecules, the arms can bend between the variable and constant domains to accommodate bond angle constraint.

Antigen-Antibody Complex↗
PubMed1983

Tissue effects of iron deficiency in the rat.

Measurements of succinate dehydrogenase and mitochondrial glycerol-3-phosphate dehydrogenase activities, iron, cytochrome c and myoglobin, were made on various hind-leg muscles, fast-twitch red and white muscle and heart and liver of male Wistar rats fed an iron-deficient diet on weaning. Rats fed the same diet and given 20 mg iron intraperitoneally as iron-dextran (Imferon) served as controls. For iron-repletion studies anemic rats (hemoglobin less than 7 g/dl) were given a single injection of 10 mg iron (Imferon) and the time course of change in the above parameters was followed up to 22 days after injection. The iron concentration of most iron-deficient muscles dropped to approx. 35% of control, the heart to 60% and liver to 13%. On repletion, the iron concentration of all tissues increase significantly by 4 days. While the levels of cytochrome c and myoglobin approximated the iron levels in muscle, they did not change significantly in the heart. Succinate dehydrogenase activity dropped profoundly in muscle, to 10-30% of control; on repletion, the activity increased significantly. Mitochondrial glycerol-3-phosphate dehydrogenase activity showed only small changes in iron-deficient tissues.

Anemia, Hypochromic↗
PubMed1983

Electron microscopy of influenza haemagglutinin-monoclonal antibody complexes.

The molecular locations of antibody binding sites on the haemagglutinin of influenza virus X-31 were investigated by electron microscopy of haemagglutinin-monoclonal antibody complexes. Evidence was obtained for different sites of binding of different antibodies and direct correspondence was observed between these sites and the locations of antigenic sites A, B, and E (D. C. Wiley, I. A. Wilson, and J. J. Skehel (1981). Nature (London) 289, 373-378) defined by determining the amino acids recognized by the specific antibodies.

Amino Acids↗