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Biomedical subjects

C R Robertson

Publications and source records attributed to C R Robertson.

At least 19 recordsLinked to original sources
PubMed1999

Two-dimensional streptavidin crystals: macropatterns and micro-organization.

Two dimensional crystals of streptavidin grown on lipid monolayers can be viewed as model systems for the study of phase transitions and morphology. These crystals form a variety of macroscopic morphologies associated with different microscopic crystal structures. Observed morphologies are similar to those found in two-dimensional lipid systems, and growth of the protein arrays is somewhat analogous. Such solid state physical processes as nucleation, transformation between crystal phases, crystal phase coexistence, and roughening have been observed in the streptavidin system. In this review, we highlight observations that cause streptavidin to remain an interesting model system exhibiting a variety of intriguing phenomena.

Crystallization↗
PubMed1998

Prying open the door to the tobacco industry's secrets about nicotine: the Minnesota Tobacco Trial.

In 1994 the state of Minnesota filed suit against the tobacco industry. This trial is now history, but its legacy will carry on into the 21st century because of the revelations contained in the millions of pages of previously secret internal tobacco industry documents made public in the trial. In this article, we review representative documents relating to nicotine addiction, low-tar, low-nicotine cigarettes, and cigarette design and nicotine manipulation in cigarette manufacture. These documents reveal that for decades, the industry knew and internally acknowledged that nicotine is an addictive drug and cigarettes are the ultimate nicotine delivery device; that nicotine addiction can be perpetuated and even enhanced through cigarette design alterations and manipulations; and that "health-conscious" smokers could be captured by low-tar, low-nicotine products, all the while ensuring the marketplace viability of their products. Appreciation of tobacco industry strategies over the past decades is essential to formulate an appropriate legislative and public policy response. We propose key elements for such legislation and urge no legal or financial immunity for the tobacco industry.

Behavior Control↗
PubMed1995

Absorption spectra indicate conformational alteration of myoglobin adsorbed on polydimethylsiloxane.

To assess the effects of adsorption on protein structure, ultraviolet optical absorption spectra of myoglobin (Mb) bound to polydimethylsiloxane (PDMS) were measured. A flow cell, which enabled adsorption under controlled hydrodynamic conditions, was used in conjunction with a conventional spectrophotometer to obtain the spectra. Adsorption to PDMS reduced significantly the absorbance in the Soret region of the Mb spectrum, whereas the spectrum in the region near 280 nm was essentially unaffected. This result showed that disruption of the native structure of Mb occurs following interaction with PDMS. Furthermore, the change in the absorption spectrum may indicate loss of heme from the heme pocket of the adsorbed protein. Mb structure was altered from its solution configuration within fifteen min of contact with the surface. Exchange of adsorbed Mb with Mb in solution had little or no effect on the absorption spectrum of the surface-confined protein, indicating that exchange occurs only between conformationally altered species or between native species.

Adsorption↗
PubMed1994

Changing concepts in pathophysiology of the vasculitides.

Vasculitis is a clinicopathologic process that involves inflammation and necrosis of blood vessels, resulting in a wide range of clinical diseases. The pathogenesis of vasculitis has been attributed to immunologic mechanisms, including immune complexes, cellular immunity, and humoral immunity, with numerous inciting events such as infection, drugs, malignancy, or toxins. Inflammatory cytokine production and adhesion molecule activation or upregulation are important determinants of the pathogenic inflammatory responses noted in vasculitis. Endothelial cells may be targeted by anti-endothelial cell antibodies and are central targets of numerous proinflammatory cytokines in vasculitis pathogenesis. Finally, antineutrophil cytoplasmic antibodies (ANCA) and T-cell responses to the protein targets of ANCA may play a role in vessel damage in ANCA-associated vasculitis.

Antibodies, Antineutrophil Cytoplasmic↗
PubMed1993

Interleukin-8 and development of adult respiratory distress syndrome in at-risk patient groups.

Neutrophils have been implicated in the pathogenesis of the adult respiratory distress syndrome (ARDS). We have measured concentrations of the neutrophil attractant interleukin-8 in blood and bronchoalveolar lavage fluid (BAL) from patients at risk of ARDS. We studied 29 patients from three groups at risk of developing ARDS: multiple trauma (n = 16), perforated bowel (n = 6), and pancreatitis (n = 7). ARDS developed in 7 of these patients. Interleukin-8 in BAL and blood samples taken on initial hospital presentation was measured by a sandwich enzyme-linked immunosorbent assay. The mean BAL interleukin-8 concentration was significantly higher for the patients who subsequently progressed to ARDS than for the non-ARDS group (3.06 [SE 2.64] vs 0.053 [0.010] ng/mL, p = 0.0006). There was no difference between the groups in plasma interleukin-8 (6.23 [2.60] vs 5.12 [2.22] ng/mL, p = 0.31). Immunocytochemistry suggested that the alveolar macrophage is an important source of interleukin-8 at this early stage in ARDS development. This study provides evidence of a relation between the presence of interleukin-8 in early BAL samples and the development of ARDS. The early appearance of interleukin-8 in BAL of patients at risk of ARDS may be an important prognostic indicator for the development of the disorder and reinforces the likely importance of neutrophils and the effects of their accumulation and activation in the pathogenesis of many cases of ARDS.

Adolescent↗
PubMed1992

Patterns of heavy and light chain utilization in the antibody response to single-stranded bacterial DNA in normal human subjects and patients with systemic lupus erythematosus.

Although anti-DNA antibodies are generally considered to be specific markers for systemic lupus erythematosus (SLE), antibodies binding DNA from certain bacterial species can be found in the sera of normal subjects. To characterize the immunochemical properties of these antibodies, the IgG subclass and light chain profile of antibodies to single-stranded micrococcal DNA (MC DNA) in the sera of normal subjects and patients with SLE was determined. The anti-MC DNA response in normal sera was predominantly of the IgG2 subclass with a marked predominance of kappa light chains. In contrast, anti-MC DNA antibodies in SLE sera exhibited all IgG subclasses with a predominance of the IgG1 subclass and both kappa and lambda light chains were represented. These results suggest that antibodies to bacterial DNA in the sera of normal subjects and patients with SLE differ in patterns of immunoglobulin gene expression; the restricted response of normal subjects may be related to the binding to a discrete DNA determinant.

Antibody Formation↗
PubMed1992

Immunochemical properties of anti-DNA antibodies in the sera of patients with Escherichia coli bacteremia.

To assess the role of infection in anti-DNA antibody production, the DNA-binding activity of sera from patients with Escherichia coli bacteremia was analyzed. Among 8 patients with bacteremia documented by blood culture, 5 demonstrated increased levels of antibodies to single-stranded DNA from E. coli as measured by enzyme-linked immunosorbent assay. Sera from these patients also reacted with single-stranded DNA from other bacterial and mammalian species as well as certain synthetic polynucleotides including poly-dT and poly-dC. The isotype distribution of these antibodies and their avidity as assessed by competition enzyme-linked immunosorbent assay resembled, moreover, responses of patients with systemic lupus erythematosus. These results suggest that, during the course of infection with E. coli, some patients may produce antibodies with immunochemical properties similar to those arising in systemic lupus erythematosus.

Aged↗
PubMed1991

Performance of the polypropylene fiber tailstring on the Copper 7 intrauterine device.

New and used polypropylene tailstrings from the Copper 7 (Cu-7) intrauterine device were examined by a combination of analytical techniques. Optical microscopy, scanning acoustic and electron microscopy, x-ray diffraction, energy dispersive x-ray analysis, and chemical etching were employed to elucidate both the surface and interior morphology of new Cu-7 tailstrings. Tailstrings removed from women following varying periods of use were investigated with optical microscopy, scanning and transmission electron microscopy. In addition, a subset of the used tailstrings were cultured to identify the types of microorganisms associated with them. Our findings show that unused Cu-7 tailstrings are in various stages of degradation owing to a combination of factors which include the high-draw ratio employed during manufacturing, the method of packaging, and the use of a particulate colourant. Furthermore, it is evident that used Cu-7 tailstrings undergo major deterioration while in situ because of the unfavorable interactions between the highly drawn polypropylene and the physiological environment. These results indicate that the polypropylene tailstrings as manufactured for use with the Cu-7 IUD fail to meet accepted design criteria for biomedical implants.

Bacterial Infections↗
PubMed1991

Metabolic behavior of immobilized aggregates of Escherichia coli under conditions of varying mechanical stress.

Experiments were conducted on immobilized aggregates of Escherichia coli cells. Mechanical stress was applied by forcing a convective stream of nutrient medium through the aggregate. It was shown to be possible to maintain uniform exponential growth with this convective supply of nutrients. Analysis of effluent from the system allowed investigation of metabolic responses unambiguously attributable to mechanical stress. A reversible increase in catabolic activity was observed after an increase in mechanical stress. Changes in the level of catabolism were accompanied by an alteration in the total acid yield on glucose and in the spectrum of organic acids produced during glucose fermentation. The behavior observed here was likely due to an osmoregulatory response induced by the mechanically stressed bacteria to counteract changes in shape.

Acids↗
PubMed1990

Surface diffusion of interacting proteins. Effect of concentration on the lateral mobility of adsorbed bovine serum albumin.

Surface diffusion of bovine serum albumin absorbed from aqueous solution to poly(methylmethacrylate) surfaces is significantly hindered by protein-protein lateral interactions. The long-time self diffusion coefficient measured by fluorescence recovery after pattern photobleaching decreases by approximately one order of magnitude as the surface area fraction occupied by protein increases from 0.10 to 0.69. Qualitative features of the surface concentration dependence of the self diffusion coefficient can be described by several recent models for lateral diffusion of interacting species. The mobile fraction is independent of the surface concentration, and both the self diffusion coefficient and the mobile fraction are constant between 15 min and 7 h of adsorption.

Adsorption↗
PubMed1988

Adsorption of the protein antigen myoglobin affects the binding of conformation-specific monoclonal antibodies.

Five monoclonal antibodies against sperm whale myoglobin have been used to investigate the physical state of the antigen adsorbed onto a polydimethylsiloxane surface. The binding of each antibody is sensitive to the antigen's conformation in solution while the locations of the antigenic sites on the myoglobin molecule for three of the antibodies have been determined (Berzofsky, J.A., G.K. Buckenmeyer, G. Hicks, F.R.N. Gurd, R.J. Feldmann, and J. Minna. 1982. J. Biol. Chem. 257:3189-3198). The binding of the fluorescein isothiocyanate-labeled IgG and Fab antibodies to previously adsorbed myoglobin has been observed using total internal reflection fluorescence. Three of the antibodies bind specifically to surface-adsorbed myoglobin with affinities at least 50% relative to myoglobin in solution whereas two of the antibodies show affinities for the surface-adsorbed myoglobin diminished by at least two orders of magnitude relative to myoglobin in solution. The specific loss of certain antigenic determinants on the adsorbed myoglobin, coupled with the retention of others, indicates a nonrandom adsorption of the myoglobin molecules.

Adsorption↗
PubMed1988

Product inhibition of immobilized Escherichia coli arising from mass transfer limitation.

Mass transfer-limited removal of metabolic products led to product-inhibited growth of Escherichia coli that was immobilized in a model system. Comparison of the growth kinetics of immobilized and free-living cells revealed no further physiological differences between cells in these two modes of existence beyond those manifested in the local concentrations of substrate and product. Bacteria were retained on a microporous membrane in a dense, planar aggregate and were grown anaerobically on a glucose-based minimal medium. Radioisotope labeling of the immobilized cell mass with 35S was used to determine growth kinetic parameters. Growth rates in the immobilized cell layer were measured by an autoradiographic technique which allowed comparison of the size of the growing region with the rate of cell convection caused by growth. Immobilized cell growth rates and growth yields ranged from near maximal (0.56 h-1 and 39 g of dry cell weight/mol of glucose, respectively) to substantially reduced (0.15 h-1 and 15 g/mol). The depression of these kinetic parameters was attributed to product inhibition arising from mass transfer-limited removal of acidic waste products from the cell mass. A simple one-dimensional reaction-diffusion model, which incorporated data on the product-inhibited growth kinetics of free-living cells collected in a product-limited chemostat, satisfactorily predicted product inhibition of immobilized cell growth.

Autoradiography↗
PubMed1987

Mass transfer limitations in gel beads containing growing immobilized cells.

Immobilized-cell aggregates have traditionally been approximated as effective continua within which the catalytic activity of the cells is homogeneously distributed. Chang & Park (1985), however, recently modelled the immobilized cells as discrete inclusions within a support matrix. With some modification, this theory is applicable to the analysis of microbial colonies growing within gel beads, and indicates that predictions obtained using the traditional approach may be significantly in error.

Cell Aggregation↗
PubMed1987

The medullary microcirculation.

Like other regional circulations, the medullary circulation supplies oxygen and other primary substrates to the medulla and removes carbon dioxide and other waste metabolites. It also acts as a countercurrent exchanger and simultaneously removes water reabsorbed from the renal tubule to preserve mass balance. Our present understanding of how the medulla serves both these functions at the same time is illustrated in Figure 3. Blood leaves the efferent arteriole with an elevated plasma protein concentration as a consequence of glomerular filtration, and flows down descending vasa recta within a vascular bundle. The increased interstitial osmotic-concentration coupled with a finite capillary reflection coefficient for small solutes causes additional water to be extracted so that at the termination of descending vasa recta, the plasma protein concentration exceeds that in the systemic circulation by approximately twofold. Solute, urea more than sodium chloride, also enters descending vasa recta. As blood flows through the interconnecting capillary plexus and up ascending vasa recta, transcapillary oncotic and osmotic pressure differences combine to cause capillary uptake of fluid. There is also simultaneous loss of urea such that the medullary trapping of urea is very effective. Countercurrent exchange of sodium chloride, however, appears to be less efficient and as a consequence, not only water but sodium chloride is removed from the medulla. Antidiuretic hormone reduces medullary blood flow, both directly by its vasoconstrictor (V1-receptor mediated) effect and indirectly by its antidiuretic (V2-receptor mediated) effects. Prostaglandins are able to enhance medullary blood flow by counteracting vasoconstrictive influences.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗