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Biomedical subjects

M P Hughes

Publications and source records attributed to M P Hughes.

16 recordsLinked to original sources
PubMed2005

Parallel measurements of drug actions on Erythrocytes by dielectrophoresis, using a three-dimensional electrode design.

A type of well-based assay that uses a laminated three-dimensional electrode design to characterise the effects of different drugs on red blood cells using dielectrophoresis is presented. The capability of the system to determine the effects of chemical agents on the electrophysiology of red blood cells is demonstrated using saponin and valinomycin as two examples of drugs that can penetrate the cell membrane and therefore change the dielectric properties of the cell. Light intensity changes are measured in the well over a period of time at various frequencies and the dielectric properties of the cells determined using an ellipsoidal multi-shell model. It is shown that the laminated electrode permits a high degree of automation and thus a high number of parallel experiments, which reduces both the time and effort needed to examine differences between populations of red blood cells. The technique is directly compatible with the industry-standard 1536 well-plate analysis technique.

Biological Assay↗
PubMed2003

Surface-enhanced resonance Raman scattering of black inkjet dyes in solution and in situ printed onto paper.

Understanding the changes that occur when dyes are absorbed onto paper is crucial for the design of new inkjet dyes. This problem is particularly difficult for black dyes that have complex chromophores, and as a result, spectroscopic information on electronic and structural changes can be of importance. Surface-enhanced resonance Raman scattering (SERRS) and electronic structure calculations were used to probe in situ changes in the chromophore in black di-azo dyes printed onto paper. The data indicate that the low-energy chromophore is due mainly to the hydrazone group and the high-energy chromophore to both the azo and hydrazone groups. A comparison of SERRS from the dyes adsorbed onto silver particles in suspension and from the dyes on paper demonstrated a broadening of the chromophore into the red for both dyes and evidence of a structural change in one dye.

Azo Compounds↗
PubMed2001

Selenium deficiency is associated with shedding of HIV-1--infected cells in the female genital tract.

OBJECTIVE: To assess the relation between selenium deficiency and vaginal or cervical shedding of HIV-1-infected cells. DESIGN: Cross-sectional study of 318 HIV-1 seropositive women in Mombasa, Kenya. METHODS: Vaginal and cervical swab specimens were tested for the presence of HIV-1 DNA by polymerase chain reaction. Multivariate logistic regression models, adjusting for CD4 count and vitamin A deficiency, were used. RESULTS: Selenium deficiency (defined as levels <85 microg/L) was observed in 11% of the study population. In unstratified multivariate analyses, there was no significant association between selenium deficiency and vaginal or cervical shedding. In stratified analyses, however, significant associations became apparent after excluding women with predictors of shedding with strong local effects on the genital tract mucosa. Among women who did not use oral contraceptives and who did not have vaginal candidiasis, selenium deficiency was significantly associated with vaginal shedding (adjusted odds ratio [AOR] 2.9, 95% confidence interval [CI] 1.0--8.8, p =.05). Effect modification was also observed in the relation between selenium deficiency and cervical shedding, with a significant association seen among those women who were not using oral contraceptive pills or depot medroxyprogesterone acetate and who did not have Neisseria gonorrhoeae infection (AOR 2.8, 95% CI 1.1--7.0, p =.02). CONCLUSIONS: We found selenium deficiency to be associated with a nearly threefold higher likelihood of genital mucosal shedding of HIV-1--infected cells, suggesting that deficiency may increase the infectiousness of women with HIV-1. Nutritional interventions to prevent HIV-1 transmission warrant investigation.

Adolescent↗
PubMed2001

Dielectrophoretic manipulation and characterization of herpes simplex virus-1 capsids.

The dielectrophoretic behaviour of the capsids of herpes simplex virus type-1 has been measured over a range of conductivities of KCl solutions, with and without the addition of mannitol. The dielectrophoretic response of the capsids was recorded by measuring the frequency corresponding to zero dielectrophoretic force. The data were analysed using a multi-shelled model, and the permittivity and conductivity of the particles estimated. The capsid was modelled as a porous protein shell through which suspending medium passes, an inner chamber containing suspending medium in equilibrium with the outside, and a central core of protein (the scaffold). Capsids suspended in KCl without mannitol exhibited a different behaviour to those suspended in KCl with mannitol.

Biophysical Phenomena↗
PubMed2001

Predictors of serum selenium in cigarette smokers and the lack of association with lung and prostate cancer risk.

Epidemiological studies have suggested that low levels of selenium are associated with a higher incidence of both lung and prostate cancer. We analyzed the selenium serum concentration in 356 Carotene and Retinol Efficacy Trial (CARET) participants who later developed lung cancer and 356 matched controls and in 235 prostate cancer cases and 456 matched controls. Serum samples were obtained a mean of 4.7 years before diagnosis for both tumor types. Controls were matched to cases by year of randomization, age, smoking status, treatment arm, exposure population (asbestos workers or cigarette smokers), and year of blood draw. In the control population (n = 820), significant predictors of low serum selenium concentration were current smoking status and East Coast locations of the study center. Overall, there was no significant difference in mean serum selenium in lung cancer cases versus controls (11.91 microg/dl versus 11.77 microg/dl) or prostate cancer cases versus controls (11.48 microg/dl versus 11.43 microg/dl). No statistically significant trend in odds ratio was seen across quartiles of serum selenium for lung cancer (P = 0.49) or prostate cancer (P = 0.69). In a subpopulation of 174 prostate cancer patients who had clinical and pathological staging material reviewed, there was no association between serum selenium and Gleason score or clinical or pathological stage. In the CARET population of current and former smokers consuming an ad libitum diet, the serum concentration of selenium was not a risk factor for either lung cancer or prostate cancer.

Age Distribution↗
PubMed1999

Detection of domoic acid in northern anchovies and California sea lions associated with an unusual mortality event.

The occurrence of an unusual mortality event involving California sea lions (Zalophus californianus) along the central California coast in May 1998 was recently reported. The potent neurotoxin domoic acid (DA), produced naturally by the diatom Pseudo-nitzschia australis and transmitted to the sea lions via planktivorous northern anchovies (Engraulis mordax), was identified as the probable causative agent. Details of DA analyses for anchovy tissues and sea lion feces are described. Domoic acid levels were estimated in anchovy samples by HPLC-UV, and in sea lion feces using the same method as well as a microplate receptor binding assay, with absolute confirmation by tandem mass spectrometry. The highest DA concentrations in anchovies occurred in the viscera (223 +/- 5 microg DA g(-1)), exceeding values in the body tissues by seven-fold and suggesting minimal bioaccumulation of DA in anchovy tissue. HPLC values for DA in sea lion fecal material (ranging from 152 to 136.5 microg DA g(-1)) required correction for interference from an unidentified compound. Inter-laboratory comparisons of HPLC data showed close quantitative agreement. Fecal DA activity determined using the receptor binding assay corresponded with HPLC values to within a factor of two. Finally, our detection of P. australis frustules, via scanning electron microscopy, in both anchovy viscera and fecal material from sea lions exhibiting seizures provides corroborating evidence that this toxic algal species was involved in this unusual sea lion mortality event.

Animals↗
PubMed1999

Separation of submicron bioparticles by dielectrophoresis.

Submicron particles such as latex spheres and viruses can be manipulated and characterized using dielectrophoresis. By the use of appropriate microelectrode arrays, particles can be trapped or moved between regions of high or low electric fields. The magnitude and direction of the dielectrophoretic force on the particle depends on its dielectric properties, so that a heterogeneous mixture of particles can be separated to produce a more homogeneous population. In this paper the controlled separation of submicron bioparticles is demonstrated. With electrode arrays fabricated using direct write electron beam lithography, it is shown that different types of submicron latex spheres can be spatially separated. The separation occurs as a result of differences in magnitude and/or direction of the dielectrophoretic force on different populations of particles. These differences arise mainly because the surface properties of submicron particles dominate their dielectrophoretic behavior. It is also demonstrated that tobacco mosaic virus and herpes simplex virus can be manipulated and spatially separated in a microelectrode array.

Electric Conductivity↗
PubMed1998

Manipulation of herpes simplex virus type 1 by dielectrophoresis.

The frequency-dependent dielectrophoretic behaviour of an enveloped mammalian virus, herpes simplex virus type 1 is described. It is demonstrated that over the range 10 kHz-20 MHz, these viral particles, when suspended in an aqueous medium of conductivity 5 mS m(-1), can be manipulated by both positive and negative dielectrophoresis using microfabricated electrode arrays. The observed transition from positive to negative dielectrophoresis at frequencies around 4.5 MHz is in qualitative agreement with a simple model of the virus as a conducting particle surrounded by an insulating membrane.

Biophysics↗
PubMed1998

Computer-aided analysis of conditions for optimizing practical electrorotation.

Previous studies have indicated that the variations in torque induced in particles in electrorotation electrode arrays are sufficiently large to cause errors in electrorotation measurements. In order to avoid this, experimenters usually study particles bounded by an arbitrary region near the centre of the electrodes. By simulating the time-dependent electric field for polynomial electrodes, we have assessed the variation in torque across the centre of the array. By considering both the variation in applied torque and the dielectrophoretic force in the electrode chamber, the optimal conditions for electrorotation experiments have been determined. Further to this, by comparing the torque variation across the electrode chamber for a number of common electrode designs, a comparison of the suitability of each electrode design for multiparticle electrorotation analysis has been made.

Computer Simulation↗
PubMed1996

Accuracy of mortality data for interstitial lung diseases in New Mexico, USA.

BACKGROUND: The sensitivity and accuracy of death certificates and mortality data as sources of population based data on the occurrence of interstitial lung diseases has received limited attention. To determine the usefulness of these data sources, death certificates and mortality data from patients in New Mexico were examined. METHODS: Patients with an interstitial lung disease were identified from a population based registry. For subjects who had died, diagnostic information from their death certificates and from mortality data was compared with the clinical diagnoses made before death. RESULTS: Of 385 patients with a clinical diagnosis of an interstitial lung disease, 134 died between October 1988 and August 1994. Death certificates were obtained for 96% of these patients. An interstitial lung disease was listed somewhere on the death certificate for only 46% of the patients, and as an immediate cause of death for only 15%. For the patients with an interstitial lung disease listed somewhere on the death certificate the overall concordance between the diagnoses before death and those on the death certificate was 76%. Mortality data for the State of New Mexico showed a diagnosis of interstitial lung disease to be the assigned cause of death for only 22% of the patients. The overall agreement between the diagnoses made before death and those of the state mortality data was only 21%. CONCLUSIONS: These results suggest that death certificates and state mortality data are neither sensitive nor accurate for describing the occurrence of interstitial lung diseases. This finding may partly explain the apparently low mortality rates from idiopathic pulmonary fibrosis in the USA compared with other countries.

Adult↗
PubMed1995

Non-uniform spatial distributions of both the magnitude and phase of AC electric fields determine dielectrophoretic forces.

It is well known that the conventional dielectrophoretic force acting on a polarised particle in a non-uniform AC electric field is proportional to the in-phase component of the induced dipole moment and the non-uniformity of the field strength. In contrast, the travelling-wave-dielectrophoretic force that acts on a particle subjected to a travelling electric field is proportional to the out-of-phase component of the induced dipole moment. We derive a theory that unifies the description and interpretation of conventional dielectrophoretic and travelling-wave-dielectrophoretic forces. We show that a particle in a non-uniform AC electric field experiences a dielectrophoretic force due to spatial non-uniformities of the magnitude and the phase of the field interacting, respectively, with the in-phase and out-of-phase components of the induced dipole moment. The theory is used to explain the translational effects observed for particles in the presence of standing, travelling and rotating fields in several experimental electrode configurations. The good agreement found between the experimental observations and the theoretical predictions validate the theory.

Cell Movement↗
PubMed1991

Extrauterine findings of ectopic pregnancy of transvaginal US: importance of echogenic fluid.

Transvaginal ultrasound (US) studies of 232 consecutive patients with positive serum pregnancy tests who were considered to be at risk for ectopic pregnancy were prospectively evaluated to determine the significance of various extrauterine findings, including echogenic fluid in the cul-de-sac. All patients were found to have a surgically proved ectopic gestation (group 1, 68 patients [29.3%]), reliable evidence of intrauterine pregnancy at initial transvaginal US (group 2, 83 patients [35.8%]), or no evidence of pregnancy at initial transvaginal US, but subsequent proof of an intrauterine pregnancy (group 3, 81 patients [34.9%]). Adnexal findings were demonstrated in 45 (66%) group 1 patients, including a living extrauterine embryo in 10 (15%), an extrauterine gestational sac in 21 (31%), and an adnexal mass in 14 (21%). Intraperitoneal fluid was detected in 43 (63%) group 1 patients and in 81 (31%) group 3 patients. Echogenic fluid was the only abnormal finding at US in 10 (15%) group 1 patients and added confidence to the diagnosis of ectopic pregnancy in many others. Echogenic fluid correlated with hemoperitoneum at the time of surgery. The presence of echogenic fluid indicates a high risk for ectopic pregnancy in women referred with this clinical indication.

Female↗
PubMedDate not supplied

Measurement of bacterial flagellar thrust by negative dielectrophoresis.

The force produced by the flagella of the bacterium Salmonella typhimurium has been measured using negative dielectrophoretic methods. The bacteria are held in a force funnel, produced using a nonuniform electric field. When the motor force is balanced against an opposing negative dielectrophoretic force the bacteria become motionless. Numerical simulations have been used to estimate the electric field gradient in the electrodes. Together with experimental observations of bacterial motion the data gives a value of the force produced by the bacterial motor to be 0.37 pN.

Electrodes↗