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Biomedical subjects

P M Williams

Publications and source records attributed to P M Williams.

At least 19 recordsLinked to original sources
PubMed2006

Stochastic elastohydrodynamics of a microcantilever oscillating near a wall.

We consider the thermally driven motion of a microcantilever in a fluid environment near a wall, a configuration characteristic of the atomic force microscope. A theoretical model is presented which accounts for hydrodynamic interactions between the cantilever and wall over a wide range of frequencies and which exploits the fluctuation-dissipation theorem to capture the Brownian dynamics of the coupled fluid-cantilever system. Model predictions are tested against experimental thermal spectra for a cantilever in air and water. The model shows how, in a liquid environment, the effects of non-delta-correlated Brownian forcing appear in the power spectrum, particularly at low frequencies. The model also predicts accurately changes in the spectrum in liquid arising through hydrodynamic wall effects, which we show are strongly mediated by the angle at which the cantilever is tilted relative to the wall.

Journal Article↗
PubMed2006

Audit of hepatitis C antibody requests made by a genito-urinary department.

Requests for hepatitis C antibodies (HCV Ab) made by the Oxford Department of Genito-urinary (GU) Medicine were audited against national guidelines to determine how the service performed and to develop locally applicable standards. This resulted in more effective screening and cost savings.

Female Urogenital Diseases↗
PubMed2005

Immune response in silico (IRIS): immune-specific genes identified from a compendium of microarray expression data.

Immune cell-specific expression is one indication of the importance of a gene's role in the immune response. We have compiled a compendium of microarray expression data for virtually all human genes from six key immune cell types and their activated and differentiated states. Immune Response In Silico (IRIS) is a collection of genes that have been selected for specific expression in immune cells. The expression pattern of IRIS genes recapitulates the phylogeny of immune cells in terms of the lineages of their differentiation. Gene Ontology assignments for IRIS genes reveal significant involvement in inflammation and immunity. Genes encoding CD antigens, cytokines, integrins and many other gene families playing key roles in the immune response are highly represented. IRIS also includes proteins of unknown function and expressed sequence tags that may not represent genes. The predicted cellular localization of IRIS proteins is evenly distributed between cell surface and intracellular compartments, indicating that immune specificity is important at many points in the signaling pathways of the immune response. IRIS provides a resource for further investigation into the function of the immune system and immune diseases.

Gene Expression Profiling↗
PubMed2004

Direct atomic force microscopy observations of monovalent ion induced binding of DNA to mica.

Multivalent ions in solution are known to mediate attraction between two like-charged molecules. Such attraction has proved useful in atomic force microscopy (AFM) where DNA may be immobilized to a mica surface facilitating direct imaging in liquid. Theories of DNA immobilization suggest that either 'salt bridging' or fluctuation in the positions of counter ions about both the mica surface and DNA backbone secure DNA to the mica substrate. Whilst both theoretical and experimental evidence suggest that immobilization is possible in the presence of divalent ions, very few studies identify that such immobilization is possible with monovalent ions. Here we present direct AFM evidence of DNA immobilized to mica in the presence of only monovalent ions. Our data depict E. coli plasmid pBR322 adsorbed onto the negatively charged mica both after short (10 min) and long (24 h) incubation periods. These data suggest the need to re-explore current theories of like-charge attraction to include the possibility of monovalent interactions. We suggest that this DNA immobilization strategy may offer the potential to image natural processes with limited immobilization forces and hence enable maximum conformational freedom of the immobilized biomolecule.

Aluminum Silicates↗
PubMed2003

Electrostatic interactions observed when imaging proteins with the atomic force microscope.

The atomic force microscope (AFM) is now an established and valuable tool for the study of biological macromolecules in aqueous environments. In this paper we form a patterned boundary via the microcontact printing of individually isolated proteins, covalently attached to a solid support. We use this boundary to investigate electrostatic interactions that can occur between an AFM tip and a protein surface during imaging in solution. The observed height variations of the protein film are found to be a combination of not only structural considerations and thickness of the protein film, but also the repulsive contribution from electrostatic interactions between the AFM tip and the sample. These variations in measured heights of the protein surface can be described by Derjaguin, Landau, Verway, Overbeek (DLVO) theory. Our experimental results show that height measurements can be manipulated either negatively or positively by adjusting the pH and concentration of the electrolyte buffer that is utilised.

Algorithms↗
PubMed2002

Non-invasive assessment of selective 5-HT(1B/1D)-receptor agonist-induced peripheral vascular effects in humans: comparison of different techniques.

OBJECTIVE: To compare the sensitivity of three non-invasive techniques for detecting serotonin (5-HT)(1B/1D)-receptor agonist-induced peripheral vascular effects in humans: the measurement of (1) systolic (SBP) and diastolic (DBP) blood pressures, (2) dorsal hand vein (DHV) diameter and (3) toe-arm systolic blood pressure gradient (DeltaSBP(toe-arm)). METHODS: A double-blind, placebo-controlled, three-way, cross-over study was performed in 12 healthy male volunteers. According to a randomly assigned allocation schedule, subjects were administered sumatriptan 3 mg, sumatriptan 6 mg or placebo subcutaneously. Measurements were performed at baseline, every 5 min for 30 min and at 40 min and 60 min after drug administration. SBP and DBP were recorded using a semi-automated oscillometric device. DHV diameter was measured using a linear variable differential transformer. DeltaSBP(toe-arm) was calculated after measuring toe and arm SBP with a strain-gauge technique. Sensitivity was evaluated with responsiveness statistics. RESULTS: Based on weighted mean and compared with placebo, sumatriptan 3 mg and 6 mg increased SBP by 3.3 mmHg ( P=0.023) and 6.4 mmHg ( P<0.001) and DBP by 5.0 mmHg ( P=0.006) and 7.5 mmHg ( P<0.001), respectively. Sumatriptan 3 mg and 6 mg decreased DHV diameter by 36% ( P=0.015) and 40% ( P=0.005), respectively. DeltaSBP(toe-arm) did not change. Peak changes were observed within 10-15 min after drug administration. The rank order of responsiveness was: BP > DHV diameter > DeltaSBP(toe-arm.) CONCLUSIONS: Clinically relevant doses of subcutaneous sumatriptan increased blood pressure and decreased DHV diameter without affecting DeltaSBP(toe-arm). The increase in blood pressure appeared to be dose dependent. Compared with DHV diameter and DeltaSBP(toe-arm), blood pressure measurement appeared to be the most sensitive technique for detecting selective 5-HT(1B/1D)-receptor agonist-induced peripheral vascular effects in humans.

Adult↗
PubMed2002

Interactions of 3T3 fibroblasts and endothelial cells with defined pore features.

The colonization of biodegradable polymer scaffolds with cell populations has been established as the foundation for the engineering of a number of tissues, including cartilage, liver, and bone. Within these scaffolds, the cells encounter a porous environment in which they must migrate across the convoluted polymer surface to generate a homogenous cell distribution. Predicting the interactions between cells and pores is important if scaffold characteristics are to be optimized. Therefore, we investigated the behavior of two model cell types over a range of defined pore features. These pore features range from 5 to 90 microm in diameter and have been fabricated by photolithographic techniques. Quantitatively, the behavior of the cells is dependent on three factors: 1) percentage cell coverage of the surface; 2) pore size; and 3) cell type. Fibroblast cells displayed a co-operative pattern of cell spreading in which pores with diameters greater than the cell dimensions were bridged by groups of cells using their neighbors as supports. Endothelial cells were unable to use neighbors as support structures and failed to bridge pores greater than the cell diameter.

3T3 Cells↗
PubMed2001

Effects of early angiotensin-converting enzyme inhibition on cardiac gene expression after acute myocardial infarction.

BACKGROUND: ACE inhibition after myocardial infarction (MI) has been shown to have beneficial effects on cardiac anatomy and function. The purpose of this study was to examine the effects of ACE inhibition on cardiac gene expression after MI. METHODS AND RESULTS: Rats were randomized to receive captopril or no treatment 1 day after MI. Eight weeks later, cardiac function and hemodynamics were measured by use of indwelling catheters and perivascular flow probes. Myocardial gene expression was assessed with DNA microarrays and real-time reverse transcription-polymerase chain reaction. The ratios of heart and left ventricular weights to body weight were significantly increased by MI and normalized by captopril. Cardiac index and stroke volume index were lower in the untreated MI group than in sham controls but were normal in the MI+captopril group. Thirty-seven genes were found to be differentially expressed between the untreated MI group and sham controls; 31 were induced and 6 repressed. Captopril partially or completely inhibited changes in 10 of the genes. The 37 genes clustered into 11 functional groups, and 6 had >/=1 genes whose expression was modified by ACE inhibition. CONCLUSIONS: ACE inhibition after MI inhibits cardiac hypertrophy, preserves cardiac function, and attenuates changes in myocardial gene expression. Gene expression profiling reveals, however, that some elements of the pathophysiology may be unaffected by the treatment and be targets for new therapies.

Acute Disease↗
PubMed2001

Single-nucleotide polymorphism alleles in the insulin receptor gene are associated with typical migraine.

We have identified a migraine locus on chromosome 19p13.3/2 using linkage and association analysis. We isolated 48 single-nucleotide polymorphisms within the locus, of which we genotyped 24 in a Caucasian population comprising 827 unrelated cases and 765 controls. Five single-nucleotide polymorphisms within the insulin receptor gene showed significant association with migraine. This association was independently replicated in a case-control population collected separately. We used experiments with insulin receptor RNA and protein to investigate functionality for the migraine-associated single-nucleotide polymorphisms. We suggest possible functions for the insulin receptor in migraine pathogenesis.

Alleles↗
PubMed2001

Force-induced melting of a short DNA double helix.

The dynamic behaviour of DNA is of fundamental importance to many cellular processes. One principal characteristic, central to transcription and replication, is the ability of the duplex to "melt". It has recently been shown that dynamic force spectroscopy provides information about the energetics of biomolecular dissociation. We have employed this technique to investigate the unbinding of single dodecanucleotide molecules. To separate the duplex to single-stranded DNA, forces ranging from 17 to 40 pN were required over a range of loading rates. Interpretation of the dependence of melting force on loading rate revealed that the energy barrier to rupture is between 9 and 13 kcal mol-1 in height and situated 0.58 nm from an intermediate structural state. Thermal melting studies show that, prior to dissociation, the oligonucleotide underwent a transition which required between 7 and 11 kcal mol-1 in energy. Through combined dynamic force spectroscopy and thermal melting studies we show the derivation of an energy landscape to dissociate a 12-mer duplex. Until very recently, this type of information was only accessible by computational analysis. Additionally, the force spectroscopy data allow an estimation of the kinetics of duplex formation and melting.

Base Sequence↗
PubMed2001

Synthesis and characterisation of a degradable poly(lactic acid)-poly(ethylene glycol) copolymer with biotinylated end groups.

Poly(lactic acid)-poly(ethylene glycol)-biotin (PLA-PEG-biotin) is a degradable polymer with protein resistant properties that can undergo rapid surface engineering in aqueous media to create biomimetic surfaces. Surface engineering of this polymer is dependent on biomolecular interactions between the biotin end group and the protein avidin. Given the vigorous conditions of synthesis, it is essential that the manufacture of the polymer does not alter the biotin structure or its molecular recognition. Equally, it is important that the incorporation of biotin does not adversely affect the physicochemical properties of the polymer. (1)H NMR provides evidence of biotin attachment and structural integrity. (1)H NMR, gel permeation chromatography (GPC), and differential scanning calorimetry (DSC) analysis shows there is no significant effect on bulk properties induced by the biotin end group. Surface plasmon resonance (SPR) and fluorescent spectroscopy studies using the 2-(4'-hydroxyazobenzene) benzoic acid (HABA)/avidin complex show that the biotin moieties binding capabilities are not impaired by the synthesis.

Avidin↗
PubMed2001

An in situ dissolution study of aspirin crystal planes (100) and (001) by atomic force microscopy.

PURPOSE: To observe in situ and on individual aspirin crystal faces the comparative rates and processes of dissolution of the dominant faces. METHODS: The kinetics of the dissolution rate of two aspirin crystal planes (001) and (100) under 0.05M HCl are studied in situ at room temperature using Atomic Force Microscopy. The dissolution process of each crystal plane was followed by observed changes in topographic features. RESULTS: The results revealed that crystal plane (001) dissolves by receding step edges, and has a dissolution rate of 0.45 nm s(-1). Conversely. plane (100) displays crystal terrace sinking at an average rate of 2.93 nm s(-1). Calculated intrinsic dissolution values (g s(-1) cm(-2)) for planes (001) and (100) are 1.37 x 10(-7) gs(-1) cm(-2) and 8.36 x 10(-7) gs(-1) cm(-2), respectively. CONCLUSIONS: These values indicate that the rate of flux of material from plane (100) is approximately six times greater than that from plane (001), under 0.05M HCl. Interpretation of the data, based upon intrinsic dissolution rates and dissolution rate velocities, correlate with reported variations in the dissolution behavior of commercial aspirin products. These observations illustrate the suitability of the technique for characterizing the dissolution behavior of crystalline drugs.

Aspirin↗
PubMed2001

Molecular patterning on carbon based surfaces through photobiotin activation.

We have demonstrated the site-specific adhesion of photobiotin as a method of producing protein micropatterns. These patterns were created by the selective UV irradiation of a thin film of deposited photobiotin. The UV activated areas of photobiotin were then developed using fluorescently labelled avidin. The size of pattern produced is an order of magnitude smaller than those previously reported by this method. The patterns were characterised, using atomic force microscopy (AFM) to determine their microstructure. It was found that the AFM could discriminate between the areas of protein immobilised to the surface through the activated photobiotin, and the bare substrate surface where the inactivated photobiotin had been removed during the washing process. The potential of these patterns as sensing surfaces is demonstrated through the creation of a spatially patterned immunosensing surface. In this case, a biotinylated antibody was bound to the surface and the pattern developed using a second antibody specific to the immobilised biotinylated antibody. This technique could thus provide a simple and efficient method of producing high density immunoassay systems.

Journal Article↗
PubMed2001

Investigation of microcontact transfer of proteins from a selectively plasma treated elastomer stamp by fluorescence microscopy and force microscopy.

Selective plasma treatment of the recessed regions of the elastomer stamps is shown to alter the resultant protein patterns. Fluorescence microscopy is demonstrated to be an excellent tool to discriminate between regions of microcontact printed fluorescent dye-labelled albumin in polystyrene. Atomic force microscopy and shear force microscopy are used to provide high-resolution images of the patterned protein layers. The formation and characteristics of the patterns formed by these alternative strategies is discussed.

Animals↗
PubMed2000

Observation of DNA-polymer condensate formation in real time at a molecular level.

Dynamic real time assembly of toroidal and rod-like DNA condensates has been visualised using atomic force microscopy. Imaging has been conducted in an aqueous environment allowing the visualisation of hydrated, pegylated-polymer DNA condensates undergoing dynamic structural movement and conformational change. A major hurdle in the field of gene delivery is cellular transfection and the subsequent transfer of condensed genetic material to the cell nucleus. An increased understanding of the process of DNA condensation will aid the development and optimisation of gene delivery vectors.

Cations↗
PubMed2000

Surface characterization of aspirin crystal planes by dynamic chemical force microscopy.

Tapping mode (TM) atomic force microscopy (AFM) has been applied in a novel fashion to characterize and distinguish the (001) and (100) surfaces of individual aspirin crystals. The surface characterization was achieved by amplitude-phase, distance (a-p,d) measurements employing gold-coated AFM probes functionalized with self-assembled monolayers (SAM). Experiments using model probes coated with -CH3 and -COOH terminated SAMs have been performed on the two aspirin crystal planes (001) and (100). Results indicate that the hydrophobic -CH3 terminated AFM probes had a greater degree of interaction with the crystal plane (001), whereas the -COOH terminated AFM probes had a larger interaction with the crystal plane (100). Interpretation of these data, based upon the chemistries of the probes, correlates with current understanding of the crystal surface chemistry derived from X-ray diffraction data and dissolution rate studies.

Anti-Inflammatory Agents, Non-Steroidal↗