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Biomedical subjects

L R Brown

Publications and source records attributed to L R Brown.

At least 55 records · Page 3Linked to original sources
PubMed1993

Thymoma.

Thymomas and thymic carcinomas are thymic epithelial tumors that constitute approximately 15% of all mediastinal masses. From 28 to 66% of thymomas cause chest symptoms as the initial manifestation; the rest are discovered on routine chest roentgenograms or during investigations prompted by the presence of a paraneoplastic syndrome. Forty percent of patients with thymoma have one or more paraneoplastic syndromes, including myasthenia gravis, pure red cell aplasia, and hypogammaglobulinemia. Extrathymic malignant lesions develop in up to 20% of patients. Traditional histologic classifications have not accurately predicted tumor behavior; a recently developed classification based on cellular differentiation toward thymic medullary or cortical epithelium may correlate better with prognosis. Nevertheless, the prognosis is best predicted by stage of the tumor determined intraoperatively and is poorer in patients with incomplete resection than in those with complete resection of the thymoma. In addition to surgical intervention, irradiation and chemotherapy have important roles in the management of thymomas, particularly in advanced stages. In this article, the clinical manifestations, diagnosis, pathologic features, staging, and treatment of thymomas are reviewed, and the prognosis of affected patients is discussed.

Humans↗
PubMed1993

A new asymmetric screen-film combination for conventional chest radiography: evaluation in 50 patients.

OBJECTIVE: A new asymmetric screen-film combination for conventional chest radiography was evaluated by four thoracic radiologists. MATERIALS AND METHODS: Fifty chest radiographs obtained with a new asymmetric screen-film combination were compared with radiographs obtained in the same patients during the same breath-hold with a conventional system. Patients referred from the oncology service were studied because of the increased prevalence of abnormal findings on chest radiographs in this population. The differences in the quality of the images were assessed by four chest radiologists who used a direct-comparison technique. Eleven anatomic shadows that are normal on chest radiographs were assessed. Fifty abnormal findings also were compared. RESULTS: The image quality of the new asymmetric screen-film combination was judged to be superior to that of the conventional system for normal anatomy and abnormal findings (p < or = .003). CONCLUSION: The new asymmetric film consistently showed more clinically useful detail in the mediastinum and in the lung projected over the diaphragm and heart. The radiation dose was about 30% less with the new screen-film system.

Evaluation Studies as Topic↗
PubMed1992

Nuclear magnetic resonance solution structure of the alpha-neurotoxin from the black mamba (Dendroaspis polylepis polylepis).

The three-dimensional structure in solution of the alpha-neurotoxin from the black mamba (Dendroaspis polylepis polylepis) has been determined by nuclear magnetic resonance spectroscopy. A high quality structure for this 60-residue protein was obtained from 656 NOE distance constraints and 143 dihedral angle constraints, using the distance geometry program DIANA for the structure calculation and AMBER for restrained energy minimization. For a group of 20 conformers used to represent the solution structure, the average root-mean-square deviation value calculated for the polypeptide backbone heavy atoms relative to the mean structure was 0.45 A. The protein consists of a core region from which three finger-like loops extend outwards. It includes a short, two-stranded antiparallel beta-sheet of residues 1-5 and 13-17, a three-stranded antiparallel beta-sheet involving residues 23-31, 34-42 and 51-55, and four disulfide bridges in the core region. There is also extensive non-regular hydrogen bonding between the carboxy-terminal tail of the polypeptide chain and the rest of the core region. Comparison with the crystal structure of erabutoxin-b indicates that the structure of alpha-neurotoxin is quite similar to other neurotoxin structures, but that local structural differences are seen in regions thought to be important for binding of neurotoxins to the acetylcholine receptor. For two regions of the alpha-neurotoxin structure there is evidence for an equilibrium between multiple conformations, which might be related to conformational rearrangements upon binding to the receptor. Overall, the alpha-neurotoxin presents itself as a protein with a stable core and flexible surface areas that interact with the acetylcholine receptor in such a way that high affinity binding is achieved by conformational rearrangements of the deformable regions of the neurotoxin structure.

Amides↗
PubMed1992

Solitary pulmonary nodule: CT evaluation of enhancement with iodinated contrast material--a preliminary report.

The authors hypothesized that the degree of contrast material enhancement of a pulmonary nodule, measured with computed tomography (CT), may indicate the likelihood of malignancy. Fifty-two patients with uncalcified solitary pulmonary nodules (diameter, 6-30 mm) were studied. Five single serial thin-section CT scans were obtained at 1-minute intervals after injection of 100 mL of nonionic contrast material. Twenty-two patients were excluded because the diagnosis was not clearly established: The observation period was less than 2 years, or the examination was technically inadequate. Malignant nodules were identified in 23 of the 30 remaining patients, and benign nodules were identified in seven. Within the first 2 minutes after the injection, all the malignant nodules had enhanced by 20 HU or greater (only one benign nodule had that degree of enhancement). The authors conclude that the degree of contrast material enhancement of pulmonary nodules as measured with CT may indicate the likelihood of malignancy.

Adult↗
PubMed1992

Benign giant-cell tumor of bone with pulmonary metastases: clinical findings and radiologic appearance of metastases in 13 cases.

Tumors that metastasize are considered "malignant" by definition. However, benign giant-cell tumor of bone is an exception because of the potential for histologically benign pulmonary metastases, a fact seldom emphasized in the radiologic literature. We therefore report our experience with 13 cases of pulmonary metastasis among 475 patients (prevalence, 3%) in whom benign giant-cell tumor of bone was diagnosed before 1990 at our institution. Five (38%) of the 13 primary bone tumors were located in the distal radius. Local recurrence at the site of the primary bone tumor tumor occurred in seven patients (54%) before pulmonary metastases developed. The mean interval from the diagnosis of the primary bone tumor to the onset of pulmonary metastasis was 3.8 years, with a maximum of 10.7 years. Fifty-four percent of the patients (7/13) had pulmonary metastases 3 years after diagnosis of the primary bone lesion, and 92% (12/13) had pulmonary metastases 7.5 years after diagnosis. Overall mortality rate directly due to giant-cell tumor and its metastases was 23%. On chest radiographs and CT scans, pulmonary metastases appeared as rounded, nodular opacities of homogeneous density, ranging from 0.5 cm to 8.0 cm in diameter. Peripheral regions of the lungs were involved in 85% of the cases and basilar regions in 62%. Our study shows that benign giant-cell tumor of bone can produce pulmonary metastases, that metastases most often occurred with recurrent local disease and distal radial lesions, that the prognosis was relatively favorable, and that such metastases had no distinguishing radiologic features.

Adult↗
PubMed1991

Recognition of the influenza hemagglutinin by class II MHC-restricted T lymphocytes and antibodies. I. Site definition and implications for antigen presentation and T lymphocyte recognition.

We have identified the site encompassing residues 126-145 on the A/Japan/57 influenza hemagglutinin molecule that is recognized in association with HLA-DRw11 by a clonal population of human, influenza specific, CD4+ cytolytic T lymphocytes. The critical core sequence of the T cell determinant spans hemagglutinin residues 129-140 and overlaps a putative antibody binding site. Hemagglutinins of influenza field strains that are not recognized by the T cell clones contain sequence alterations within the 129-140 target site of the CD4+ T cells. Functional analyses, with synthetic peptides, of the contribution of each of the residues within the sequence toward the capacity of the antigenic fragment to associate with both the restriction element and the TCR revealed a continuous linear array of residues necessary for MHC binding and/or Ag receptor engagement. At least one residue, the lysine at position 134, was shown to be critical for both DRw11 association and TCR recognition. The significance of these findings for recognition of glycoproteins by human CD4+ T cells is discussed.

Amino Acid Sequence↗
PubMed1991

Physicochemical characterization of dodecylphosphocholine/palmitoyllysophosphatidic acid/myelin basic protein complexes.

The stoichiometry of dodecylphosphocholine/palmitoyllysophosphatidic acid/myelin basic protein complexes and the location of the protein in the micelles have been investigated by electron paramagnetic resonance, ultracentrifugation, small-angle X-ray scattering, 31P, 13C, and 1H nuclear magnetic resonance spectroscopy, and electron microscopy. Ultracentrifugation measurements indicated that well-defined complexes are formed by association of one protein molecule with approximately 133 detergent molecules. The spin-labels 5-, 12-, and 16-doxylstearate have been incorporated into detergent/protein aggregates. Electron paramagnetic resonance spectral parameters and 13C and 1H nuclear magnetic resonance relaxation times showed that the addition of myelin basic protein does not affect the environment and location of the labels or the organization of the micelles. Previous results suggesting that the protein lies primarily near the surface of the micelles have been confirmed by comparing 13C spectra of the detergents with and without protein with spectra of detergent/protein aggregates containing the spin labels. Electron micrographs of the complexes taken by using the freeze-fracture technique revealed the presence of particles with an estimated radius about three times the radius of the micelles measured by small-angle X-ray scattering. The structural integrity of the complexes appears to be based on intramolecular protein interactions as well as protein-detergent interactions.

Animals↗
PubMed1991

Antibody recognition of an immunogenic influenza hemagglutinin-human leukocyte antigen class II complex.

The A/Japan/57 influenza hemagglutin (HA) peptide HA 128-145, when bound by human histocompatibility leukocyte antigen-DRw11 cells, is recognized by the human CD4+ T cell clone V1. A rabbit antiserum has been raised against HA 128-145 which recognizes not only the free peptide, but also the HA 128-145/DRw11 complex on a solid matrix, in solution, or on the surface of viable cells. The detection of these complexes on viable cells was shown to be class II specific, DRw11 restricted, and commensurate with the level of DRw11 expression. The identity of DRw11 as the cell surface molecule binding HA 128-145 was confirmed by immunoprecipitation, sodium dodecyl sulfate-polyacrylamide gel electrophoresis, and tryptic peptide mapping. Using this antiserum HA 128-145/DRw11 complexes could be detected on the cell surface as soon as 30 min after the peptide was added, and increased up to 24 h. Dissociation kinetics showed these complexes were long-lived, with a half-life of approximately 14 h. This anti-HA peptide antiserum represents the first direct means of studying antigenic peptide-human leukocyte antigen class II complexes on the surface of living cells without the addition of a non-amino acid moiety to the peptide. The properties of this antiserum thus provide the potential to study naturally processed antigenic peptides as well as the mechanism of processing itself in a physiologically relevant system.

Amino Acid Sequence↗
PubMed1991

Roentgenologic features of pulmonary blastomycosis.

In 35 cases of pulmonary blastomycosis, the roentgenologic features were as follows: consolidation 26%, mass 31%, intermediate-sized nodules 6%, miliary pattern 11%, solitary cavity 9%, fibrotic and cavitary changes 6%, interstitial pattern 6%, diffuse alveolar involvement 3%, and mixed alveolar and interstitial infiltrate 3%. All symptomatic cases of consolidation were acute (symptoms for less than 1 month), and most were in young patients (mean age, 34 years). Consolidation constituted 58% of the acute cases in this series. Two of the nine cases of consolidation were asymptomatic epidemic cases detected by screening. A pulmonary mass was the most common initial manifestation in this series; it tended to occur in patients with chronic symptoms (more than 1 month). The mass was considered suggestive enough of bronchogenic carcinoma to necessitate resection in 55% of cases. The military form of pulmonary blastomycosis occurred in older patients with disseminated disease. Fibrotic and cavitary disease was chronic in nature. The presence of intermediate-sized nodules elsewhere in the lung proved to be a helpful diagnostic finding in several patients with consolidation, mass, or cavitary disease. Hilar adenopathy, postinfectious calcification, chest wall invasion, and pleural effusion occurred infrequently or not at all in this series.

Adolescent↗
PubMed1991

Masses of the anterior mediastinum: CT and MR imaging.

CT and MR imaging allow earlier diagnosis and more specific characterization of anterior mediastinal masses than is possible with plain film radiographs. This review describes state-of-the-art CT and MR imaging of the anterior mediastinum. After a discussion of CT and MR imaging and indications for their use, normal and abnormal CT and MR findings in the anterior mediastinum are reviewed. Abnormalities include benign and malignant neoplasms, cysts, and mediastinal thyroid. Several masses such as thymolipomas, goiters, cysts, and lymphangiomas often do not require removal and now can be diagnosed with reasonable accuracy when imaging results are combined with clinical history. Detection, diagnosis, staging, and follow-up of malignant anterior mediastinal masses are important and have been improved with CT and MR imaging.

Humans↗
PubMed1990

Interactions of myelin basic protein with mixed dodecylphosphocholine/palmitoyllysophosphatidic acid micelles.

The interactions of myelin basic protein and peptides derived from it with detergent micelles of lysophosphatidylglycerol, lysophosphatidylserine, palmitoyllysophosphatidic acid, and sodium lauryl sulfate, and with mixed micelles of the neutral detergent dodecylphosphocholine and the negatively charged detergent palmitoyllysophosphatidic acid, were investigated by 1H NMR spectroscopy and circular dichroic spectropolarimetry. The results with single detergents suggested that there are discrete interaction sites in the protein molecule for neutral and anionic detergent micelles and that at least some of these sites are different for each type of detergent. The data on the binding of the protein and peptides to mixed detergent micelles suggested that intramolecular interactions in the intact protein and in one of the longer peptides limited the formation of helices and also that a balance between hydrophobic and ionic forces is achieved in the interactions of the peptides with the detergents. At high detergent/protein molar ratios, hydrophobic interactions appeared to be favored.

Animals↗
PubMed1990

Influence of dietary fats and vitamin E on plasma and hepatic vitamin A and beta-carotene levels in rats fed excess beta-carotene.

Effects of different dietary lipids and excess vitamin E on plasma and hepatic concentrations of beta-carotene were evaluated in rats fed diets containing a large excess (0.2%) of beta-carotene. Male weanling Wistar Kyoto rats were fed beta-carotene-supplemented diets containing various dietary lipids as follows: Group I, a saturated fat (coconut oil); Group II, a monounsaturated fat (olive oil); Group III, a polyunsaturated fat rich in omega-6 fatty acids (safflower oil); Group IV, same as Group III plus vitamin E; and Group V, a polyunsaturated fat rich in omega-3 fatty acids (menhaden oil). All diets contained 2% safflower oil to provide sufficient amounts of linoleic acid (an essential fatty acid). Rats were killed after six weeks of feeding the various diets, and the concentrations of beta-carotene and vitamin A were determined in plasma and liver. Plasma vitamin A levels were not altered by any of the dietary lipids or by an excess of vitamin E. The concentrations of beta-carotene in plasma were the lowest in rats fed the diet containing menhaden oil. The feeding of the diet containing an excess of vitamin E also resulted in a significant decrease in plasma beta-carotene concentration. Similarly, the hepatic beta-carotene concentration was also reduced to about one-half in rats fed the diet containing an excess of vitamin E. Liver beta-carotene concentration was higher in Groups II and III than in the other three dietary groups. Hepatic vitamin A concentrations were also affected by the type of dietary fat.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1990

Class II glass ionomer/silver cermet restorations and their effect on interproximal growth of mutans streptococci.

The release of fluoride from glass ionomer materials is one of the most important features of this newly implemented material, and the remineralization effects of this phenomenon have been documented (Hicks and Silverstone 1986). This paper examines the effects of glass ionomer/silver cermet restorations on the plaque levels of interproximal mutans streptococci. Fifteen patients with Class II lesions in primary molars were selected for study. Interproximal plaque samples were obtained from each of the lesion sites and from one caries-free site approximal to a primary molar. One lesion was restored with composite resin to serve as a treated control to the glass ionomer/silver cermet (Ketac Silver, ESPE/Premier Sales Corp., Norristown, Pennsylvania) test site. A sound (unaltered) interproximal site served as the untreated control site. Plaque samples were collected before and at one week, one month, and three months post-treatment. Samples were serially diluted to enable colony counts of mutans streptococci. One week post-treatment counts showed that the glass ionomer/silver cermet restorations significantly reduced (P less than 0.05) the approximal plaque levels of mutans streptococci. Conversely, the untreated and treated control sites did not exhibit reductions in approximal plaque levels of mutans streptococci. These results indicate that glass ionomer restorations may be inhibitory to the growth of mutans streptococci in dental plaque approximal to this restorative material in the primary dentition.

Cermet Cements↗
PubMed1990

Conventional radiography of the hilum and mediastinum in bronchogenic carcinoma.

Knowledge of normal and abnormal hilar and mediastinal anatomy as depicted by chest radiography is important for the practicing radiologist. This article is an illustrated review of some of the alterations of normal anatomy that can indicate signs of metastatic spread of bronchogenic carcinoma. Thorough analysis of conventional radiographs with recognition of normal variants and detection of abnormal alterations will expedite or obviate certain therapeutic options in patients with bronchogenic carcinoma.

Carcinoma, Bronchogenic↗