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Biomedical subjects

E Evans

Publications and source records attributed to E Evans.

At least 55 records · Page 3Linked to original sources
PubMed1996

Biomembrane templates for nanoscale conduits and networks.

Long nanotubes of fluid-lipid bilayers can be used to create templates for photochemical polymerization into solid-phase conduits and networks. Each nanotube is pulled from a micropipette-held feeder vesicle by mechanical retraction of the vesicle after molecular bonding to a rigid substrate. The caliber of the tube is controlled precisely in a range from 20 to 200 nanometers merely by setting the suction pressure in the micropipette. Branched conduits can be formed by coalescing separate nanotubes drawn serially from the feeder vesicle surface. Single nanotubes and nanotube junctions can be linked together between bonding sites on a surface to create a functionalized network. After assembly, the templates can be stabilized by photoinitiated radical cross-linking of macromonomers contained in the aqueous solution confined by the lipid bilayer boundary.

Biophysical Phenomena↗
PubMed1995

Characterization and chromosomal localization of ELANH2, the gene encoding human monocyte/neutrophil elastase inhibitor.

Human monocyte/neutrophil elastase inhibitor (HEI) is a protease inhibitor of the serpin superfamily that rapidly inactivates neutrophil elastase, proteinase-3, and possibly cathepsin-G in vitro and, by regulating these potent proteases, is thought to prevent tissue damage at inflammatory sites. The HEI gene (ELANH2) was characterized by amplifying intron regions using cDNA-specific primers. Intron positions of ELANH2 were found to be homologous to intron positions in the genes for the serpin molecules chicken ovalbumin and human plasminogen activator inhibitor-2 (PLANH2). Because serpin superfamily genes in general have widely different organizational patterns, the shared organization of these genes strengthens the evidence that they form a subgroup or family, the "ovalbumin-related serpin" ("Ov-serpin") family. By amplifying DNA of a somatic cell hybrid panel, ELANH2 was unambiguously localized to chromosome 6. The use of a panel of radiation and somatic cell hybrids specific for chromosome 6 refined the localization of ELANH2 to the short arm telomeric of D6S89, F13A, and D6S202 at 6p24-pter. Another Ov-serpin gene PI6 (placental thrombin inhibitor) was colocalized to the same region, thus defining an Ov-serpin locus on chromosome 6 in addition to the previously defined PLANH2-containing Ov-serpin locus on chromosome 18.

Base Sequence↗
PubMed1995

Sensitive force technique to probe molecular adhesion and structural linkages at biological interfaces.

Adhesion and cytoskeletal structure are intimately related in biological cell function. Even with the vast amount of biological and biochemical data that exist, little is known at the molecular level about physical mechanisms involved in attachments between cells or about consequences of adhesion on the material structure. To expose physical actions at soft biological interfaces, we have combined an ultrasensitive transducer and reflection interference microscopy to image submicroscopic displacements of probe contact with a test surface under minuscule forces. The transducer is a cell-size membrane capsule pressurized by micropipette suction where displacement normal to the membrane under tension is proportional to the applied force. Pressure control of the tension tunes the sensitivity in operation over four orders of magnitude through a range of force from 0.01 pN up to the strength of covalent bonds (approximately 1000 pN)! As the surface probe, a microscopic bead is biochemically glued to the transducer with a densely-bound ligand that is indifferent to the test surface. Movements of the probe under applied force are resolved down to an accuracy of approximately 5 nm from the interference fringe pattern created by light reflected from the bead. With this arrangement, we show that local mechanical compliance of a cell surface can be measured at a displacement resolution set by structural fluctuations. When desired, a second ligand is bound sparsely to the probe for focal adhesion to specific receptors in the test surface. We demonstrate that monitoring fluctuations in probe position at low transducer stiffness enhances detection of molecular adhesion and activation of cytoskeletal structure. Subsequent loading of an attachment tests mechanical response of the receptor-substrate linkage throughout the force-driven process of detachment.

Animals↗
PubMed1995

Biofilm-related infections in ophthalmology.

A biofilm is a functional consortium of microorganisms organised within an extensive exopolymer matrix. Organisms within a biofilm are difficult to eradicate by conventional antimicrobial therapy and can cause indolent infections. This paper reviews the pathophysiology of biofilms and their application of ophthalmology. Under certain environmental conditions such as nutrient limitation, some bacteria may secrete and reside in an exopolysaccharide glycocalyx polymer. This confers relative protection from humoral and cellular immunity, antibiotics and surfactants. Biofilms occur in natural aquatic ecosystems, on ship hulls, in pipelines and on the surface of biomaterials. They cause clinical infections of prosthetic hip joints, heart valves and catheters. Biofilm formation may occur rapidly on contact lenses and their cases and hence contribute to the pathogenesis of keratitis. Formation of biofilms is also implicated in delayed post-operative endophthalmitis and crystalline keratopathy. Bacteria within biofilms are 20-1000 times less sensitive to antibiotic than free-living planktonic organisms. Existing experimental methods for modifying biofilm include the use of macrolide antibiotics that specifically impair biofilm production, and the use of enzymes to digest it. These may have clinical applications, as potential adjunctive therapies to antibiotic treatment, for these resistant infections. In conclusion, biofilm is an important cause of infections associated with biomaterials. Novel strategies are needed to deal with these.

Biofilms↗
PubMed1995

The vaccinia virus D5 protein, which is required for DNA replication, is a nucleic acid-independent nucleoside triphosphatase.

The vaccinia virus D5 gene encodes a 90-kDa protein that is transiently expressed at early times after infection. Temperature-sensitive mutants with lesions in the D5 gene exhibit a fast-stop DNA- phenotype and are also impaired in homologous recombination. Here we report the overexpression of the D5 protein within the context of a vaccinia virus infection and its purification to apparent homogeneity. The purified protein has an intrinsic nucleoside triphosphatase activity which is independent of, and not stimulated by, any common nucleic acid cofactors. All eight common ribo- and deoxyribonucleoside triphosphates are hydrolyzed to the diphosphate form in the presence of a divalent cation. Implications for the role of D5 in viral DNA replication are addressed.

Acid Anhydride Hydrolases↗
PubMed1995

Integrating nursing research and practice: Part II-A Delphi study of nursing practice priorities for research-based solutions.

Reading formal research reports and developing the art of critical analysis and evaluation are essential skills for nurses in practice. Here is an opportunity to begin developing these skills as Catherine Cooney, Susan Stebbings, Margaret Roxburgh, Janice Mayo, Niqui Keen, Ellen Evans and Therese Meehan report a survey done by nurses in Northland. Feedback through letters to the editor would be welcomed.

Delphi Technique↗
PubMed1994

Comparison of weight-based dosages of enteric-coated microtablet enzyme preparations in patients with cystic fibrosis.

Twenty-one stable hospitalized cystic fibrosis patients with malabsorption syndrome participated in an open-label crossover clinical trial to evaluate the efficacy of two-period dosing regimens of a pancreatic microtablet enzyme preparation in the treatment of steatorrhea. Standard dosing consisted of 500 U lipase/kg body weight/meal, 250 U lipase/kg body weight/snack; high dosing consisted of 1,500 U lipase/kg body weight/meal, 750 U lipase/kg body weight/snack. Doses were determined by units of lipase/kg body weight to provide dosing consistency among patients of varying size. Each patient was on a regular diet of approximately 100 g of fat per day. Two separate, 72-h stool collections were performed between markers. A significant difference in mean percentage fat absorbed between the standard dose and the high dose was found (86% versus 91%, p < 0.05). Subjects were then stratified into two groups, based on the grams of fecal fat eliminated (GFFE) as follows: Group 1 with < or = 7 GFFE/24 h on both dosages (n = 7) and Group 2 with > 7 GFFE/24 h on either dose (n = 14). A significant difference (p < 0.05) between Group 1 (96%) and Group 2 (88%) was noted in the percentage fat absorbed while on the high dose. Fat absorption improved from 81% to 88%, (p < 0.05) in Group 2. During the study period, the adverse reactions of constipation or elevated serum uric acid levels were not observed. The increased doses of pancreatic enzymes resulted in improved correction of steatorrhea.

Absorption↗
PubMed1994

Iron chelator, exopolysaccharide and protease production in Staphylococcus epidermidis: a comparative study of the effects of specific growth rate in biofilm and planktonic culture.

The growth rate of Staphylococcus epidermidis was controlled for populations growing as a biofilm and perfused with supplemented, simple-salts medium. Production of iron chelators, extracellular protease and exopolysaccharide (EPS) by these populations was assessed as a function of specific growth rate and compared to that by planktonic populations grown in the same medium within a chemostat. Perfused biofilms increased their iron chelator and protease production with increasing growth rate. Chemostat populations decreased their production of iron chelators with increasing growth rate, whilst showing much enhanced production of proteases at intermediate growth rates (mu 0.15-0.25 h-1). Production of iron chelator and protease was generally 2-50 times higher by biofilms than by planktonic populations. EPS production was low and relatively unaffected by growth rate for the chemostat cultures (about 0.2 micrograms per unit cell mass) but high for the attached biofilms, particularly at slow growth rates (about 4 micrograms per unit cell mass). EPS production within the biofilms decreased markedly with increasing growth rate. At growth rates of 0.35 h-1 and above, the levels of EPS for biofilms and planktonic populations were equivalent. The results of this study clearly indicate that growth as a biofilm markedly influences extracellular virulence factor production by S. epidermidis.

Animals↗
PubMed1994

The effects of Tenidap on cytokine induced proliferation of human synovial fibroblasts in vitro.

OBJECTIVES: Tenidap, a new anti-rheumatic agent, is a lipoxygenase and cyclooxygenase inhibitor, and is reported to inhibit the production and action of interleukin 1 (IL-1). Since eicosanoids, IL-1, and other cytokines may influence the growth of fibroblasts in the joint synovium the study was carried out to determine the effects of Tenidap on cytokine induced proliferation of these cells in vitro. METHODS: Cell cultures derived from patients with a variety of rheumatic diseases were cultured in different concentrations of Tenidap sodium, with or without IL-1, tumour necrosis factor alpha (TNF), IL-6, basic fibroblast growth factor (bFGF), or transforming growth factor beta (TGF beta). Cell proliferation was measured using a crystal violet colourimetric assay. Prostaglandin E2 levels in culture supernatants were measured by radioimmunoassay. RESULTS: Tenidap at concentrations above 10 micrograms/ml inhibited cell growth, while at 1.25-5 micrograms/ml there was a small but significant increase in proliferation compared with controls. A further increase in growth was obtained when cells were incubated with Tenidap+IL-1, TNF or bFGF, and this was significantly higher than in the presence of any cytokine alone. Stimulation of IL-1 induced growth by Tenidap was reduced by addition of high levels of exogenous PGE2 (100 ng/ml) although growth was still higher than in IL-1 alone. CONCLUSIONS: Depending on concentration, Tenidap may inhibit or stimulate synovial fibroblast growth. Our results suggest that augmentation of growth by low concentrations cannot be explained by inhibition of PGE2 production alone. Tenidap may directly stimulate cell growth or may block other fibroblast factors which are involved in control of cytokine induced proliferation.

Cell Division↗
PubMed1993

New physical concepts for cell amoeboid motion.

Amoeboid motion of cells is an essential mechanism in the function of many biological organisms (e.g., the regiment of scavenger cells in the immune defense system of animals). This process involves rapid chemical polymerization (with numerous protein constituents) to create a musclelike contractile network that advances the cell over the surface. Significant progress has been made in the biology and biochemistry of motile cells, but the physical dynamics of cell spreading and contraction are not well understood. The reason is that general approaches are formulated from complex mass, momentum, and chemical reaction equations for multiphase-multicomponent flow with the nontrivial difficulty of moving boundaries. However, there are strong clues to the dynamics that allow bold steps to be taken in simplifying the physics of motion. First, amoeboid cells often exhibit exceptional kinematics, i.e., steady advance and retraction of local fixed-shape patterns. Second, recent evidence has shown that cell projections "grow" by polymerization along the advancing boundary of the cell. Together, these characteristics represent a local growth process pinned to the interfacial contour of a contractile network. As such, the moving boundary becomes tractable, but subtle features of the motion lead to specific requirements for the chemical nature of the boundary polymerization process. To demonstrate these features, simple examples for limiting conditions of substrate interaction (i.e., "strong" and "weak" adhesion) are compared with data from experimental studies of yeast particle engulfment by blood granulocytes and actin network dynamics in fishscale keratocytes.

Animals↗
PubMed1993

Synchrony of cell spreading and contraction force as phagocytes engulf large pathogens.

A simple micromechanical method has been used to directly measure the force of contraction in single mammalian phagocytes (blood granulocytes) during engulfment of large yeast pathogens. Both the time course of cell spreading over the yeast particle and increase in cell body contractile force were quantitated at three temperatures in the range of 23-35 degrees C. The surprising feature of the phagocyte response was that engulfment and cell body contraction occurred in a serial sequence: i.e., the phagocyte spread rapidly over the particle at a steady rate with no detectable cell body contraction; when spreading stopped, contraction force in the cell body then rose steadily to a plateau level that remained stationary until the next sequence of spreading and contraction. Both spreading and contraction exhibited abrupt start/stop kinetics. Also impressive, the cell contraction force stimulated by phagocytosis was quite large (approximately 10(-8) N)-two orders of magnitude larger than the force necessary to deform passive phagocytes to the same extent. If distributed uniformly over the cell cross section, the contraction force is equivalent to an average contractile stress of approximately 10(3) N/m2 (0.01 Atm). These physical measurements in situ set critical requirements for the mechanism of force generation in granulocytes, imply that a major increase in network cross-linking accompanies build-up in contractile force and that subsequent network dissolution is necessary for locomotion.

Biomechanical Phenomena↗
PubMed1993

Thermally-induced cutaneous vasodilatation in aging.

A decrease in heat-induced cutaneous vasodilatation has been implicated as the cause of increased heat stress in the elderly. We used laser Doppler techniques to study the skin blood flow response to local heat in 82 healthy volunteers. There were 39 young volunteers, mean age 29 +/- 1, and 43 elderly volunteers, mean age 76 +/- 1. There was minimal difference in skin blood flow at 35 degrees C between the two groups. In contrast, skin blood flow at 44 degrees C was significantly lower in the older subjects at nutritively perfused sites, such as the knee and elbow. However, there was no difference between the young and old groups in skin blood flow at the finger or toe pulp, sites with primarily arteriovenous anastomotic (AVA) flow. In the older subjects, the two components of skin blood flow, microvascular volume (VOL) and red blood cell velocity (VEL), were both decreased at 44 degrees C at nutritive sites, but not at AVA sites. Regression analysis demonstrated a linear fall in blood flow, VOL, and VEL with advancing age at nutritive sites at 44 degrees C. We conclude that thermally-induced cutaneous blood flow is reduced in older persons at nutritive capillary sites, but not at AVA sites.

Adult↗
PubMed1993

Differences in neuropsychological correlates between normals and those experiencing "Old Hag Attacks".

240 university students were given The Cognitive Laterality Battery as well as a questionnaire, the answers to which were used to identify those who had experienced an "Old Hag Attack." This refers to a hypnagogic sleep disorder in which there is paralysis and, quite often, terrifying hallucinations. Those suffering from this disorder showed a statistically significantly different profile of scores from normal subjects on The Cognitive Laterality Battery. The implications of this finding for existing theories concerning "Old Hag Attacks" are discussed.

Auditory Perception↗
PubMed1993

Microscopic-physical determinants in biological adhesion.

Adhesion processes in biology are dynamic events and seldom "ideal" in character. Adhesion embodies both initiation, and subsequent separation ("fracture"), of contact. With few exceptions in vivo, active cell motility is the universal process by which cells spread on other cells and artificial substrates. Although colloidal attraction is ever present, it is usually too weak (because of steric hindrance and local electrostatic repulsion) to overcome mechanical stiffness of the cell membrane and cortical cytoskeleton in order to advance contact. Cells simply "stick" at a few points where they touch with little affinity (adhesion energy) to promote contact. On the other hand, after cell contact has been made (either by active spreading or mechanical impingement), separation is often opposed by tenacious intersurface attachments, and a large mechanical force (e.g., membrane tension) is required to "peel" the contact apart. The physical determinants of biological cell adhesion are complex because of "strong coupling" between cellular biochemistry, structure, and interface bonding at the microscopic level.

Animals↗