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Biomedical subjects

Michael Roberts

Publications and source records attributed to Michael Roberts.

15 recordsLinked to original sources
PubMed2006

Characterization of methods for determining sterilization efficacy and reuse efficiency of oxygen biosensor multiwell plates.

High-throughput screening (HTS) assays based upon fluorometric detection of oxygen consumption in microtiter plates were primarily developed for applications in drug discovery and ecotoxicology but have recently been adopted for use in microbial community-level physiological profiling assays (CLPP). The widespread use of oxygen biosensor systems for CLPP applications has, however, been hindered by the relatively high cost of oxygen biosensor reagent systems and limited access to microplate fluorometer instrumentation platforms. The ability to recycle and reuse oxygen biosensor system plates would expand their utilization for CLPP assays and other research applications in microbial ecology. Here, the efficacy and cost effectiveness of multiple procedures for sterilization of Oxygen Biosensor System (OBS; BD Biosciences) plates for reuse was evaluated. OBS plates were sterilized using ethylene oxide, ultraviolet radiation, and bleach treatments, then evaluated for biosensor response and plate life-cycle performance. Of the sterilization methods tested, ethylene oxide sterilization was most effective based on its low cost, high sterilization efficacy, and minimal impact upon OBS plate response.

Biosensing Techniques↗
PubMed2005

Uptake and metabolism of ginsenoside Rh2 and its aglycon protopanaxadiol by Caco-2 cells.

The uptake and metabolism profiles of ginsenoside Rh2 and its aglycon protopanaxadiol (ppd) were studied in the human epithelial Caco-2 cell line. High-performance liquid chromatography-mass spectrometry was applied to determine Rh2 and its aglycon ppd concentration in the cells at different pH, temperature, concentration levels and in the presence or absence of inhibitors. Rh2 uptake was time and concentration dependent, and its uptake rates were reduced by metabolic inhibitors and influenced by low temperature, thus indicating that the absorption process was energy-dependent. Drug uptake was maximal when the extracellular pH was 7.0 for Rh2 and 8.0 for ppd. Rh2 kinetic analysis showed that a non-saturable component (Kd 0.17 nmol x h(-1) x mg(-1) protein) and an active transport system with a Km of 3.95 micromol x l(-1) and a Vmax of 4.78 nmol x h(-1) x mg(-1)protein were responsible for the drug uptake. Kinetic analysis of ppd showed a non-saturable component (Kd 0.78 nmol x h(-1) x mg(-1) protein). It was suggested that active extrusion of P-glycoprotein and drug degradation in the intestine may influence Rh2 bioavailability.

Caco-2 Cells↗
PubMed2005

Unidirectional inversion of ibuprofen in Caco-2 cells: developing a suitable model for presystemic chiral inversion study.

Intestinal chiral inversion of ibuprofen is still lacking direct evidence. In a preliminary experiment, ibuprofen was found to undergo inversion in Caco-2 cells. This investigation was thus conducted to determine the characteristics and influence of some biochemical factors on the chiral inversion of ibuprofen in Caco-2 cells. The effects of substrate concentration (2.5-40 microg/ml), cell density (0.5-2 x 10(6) cells/well), content of serum (0-20%), coexistence of S ibuprofen (corresponding doses), sodium azide (10 mM), exogenous Coenzyme A (CoA) (0.1-0.4 mM), and palmitic acid (5-25 microM) on inversion were examined. A stereoselective HPLC method based on the Chromasil-CHI-TBB column was developed for quantitative analysis of the drug in cell culture medium. The inversion ratio (F(i)) and elimination rate constant were calculated as the indexes of inversion extent. Inversion of ibuprofen in Caco-2 cells was found to be both dose and cell density dependent, indicating saturable characteristics. Addition of serum significantly inhibited the inversion, to an extent of 2.7 fold decrease at 20% content. Preexistence of S enantiomer exerted a significant inhibitory effect (p<0.01 for all tests). Sodium azide decreased the inversion ratio from 0.43 to 0.32 (p<0.01). Exogenous CoA and palmitic acid significantly promoted the inversion at all tested doses (p<0.01 for all tests). This research provided strong evidence to the capacity and capability of intestinal chiral inversion. Although long incubation times up to 120 h were required, Caco-2 cells should be a suitable model for chiral inversion research of 2-APAs considering the human-resourced and well-defined characteristics from the present study.

Anti-Inflammatory Agents, Non-Steroidal↗
PubMed2005

Communicating effectively with patients suspected of having bulimia nervosa.

BACKGROUND: The dental team often is confronted with the clinical appearance of erosion affecting the hard and soft oral tissues. An investigative process often is needed to determine the cause of such erosion, because factors other than eating disorders may be involved. The authors present a protocol that should be considered in the assessment of dental erosion. Guidelines provide direction for the clinician toward opening a dialogue with a patient when the suspected cause of erosion is an eating disorder. TYPES OF STUDIES REVIEWED: The authors review publications related to the causes of dental erosion and the patterns that are involved with both chemical and mechanical destruction of oral tissues. They also discuss the oral-tissue effects related to eating disorders. The authors stress the importance of assisting parents in obtaining adequate treatment for pediatric patients. RESULTS: Cases of eating disorders among female college students, athletes, preadolescent children and men are well-documented. However, dental staff members often do not feel comfortable beginning a dialogue with patients who are suspected of having an eating disorder. This article focuses on the proper protocol for approaching such patients and beginning a dialogue. In addition, the authors provide suggestions for limiting further erosive damage to the tissues. They also discuss other causes of erosion that should be considered when assessing any type of oral erosion. CLINICAL IMPLICATIONS: The dental team is in a prime position to assist patients who have eating disorders. Timely treatment by mental health and other medical professionals is crucial. The authors suggest a dialogue for approaching these patients and offer educational material to reduce further tissue destruction.

Adolescent↗
PubMed2004

Characterization of anion channels in the plasma membrane of Arabidopsis epidermal root cells and the identification of a citrate-permeable channel induced by phosphate starvation.

Organic-acid secretion from higher plant roots into the rhizosphere plays an important role in nutrient acquisition and metal detoxification. In this study we report the electrophysiological characterization of anion channels in Arabidopsis (Arabidopsis thaliana) root epidermal cells and show that anion channels represent a pathway for citrate efflux to the soil solution. Plants were grown in nutrient-replete conditions and the patch clamp technique was applied to protoplasts isolated from the root epidermal cells of the elongation zone and young root hairs. Using SO4(2-) as the dominant anion in the pipette, voltage-dependent whole-cell inward currents were activated at membrane potentials positive of -180 mV exhibiting a maximum peak inward current (I(peak)) at approximately -130 mV. These currents reversed at potentials close to the equilibrium potential for SO4(2-), indicating that the inward currents represented SO4(2-) efflux. Replacing intracellular SO4(2-) with Cl- or NO3(-) resulted in inward currents exhibiting similar properties to the SO4(2-) efflux currents, suggesting that these channels were also permeable to a range of inorganic anions; however when intracellular SO4(2-) was replaced with citrate or malate, no inward currents were ever observed. Outside-out patches were used to characterize a 12.4-picoSiemens channel responsible for these whole-cell currents. Citrate efflux from Arabidopsis roots is induced by phosphate starvation. Thus, we investigated anion channel activity from root epidermal protoplasts isolated from Arabidopsis plants deprived of phosphate for up to 7 d after being grown for 10 d on phosphate-replete media (1.25 mm). In contrast to phosphate-replete plants, protoplasts from phosphate-starved roots exhibited depolarization-activated voltage-dependent citrate and malate efflux currents. Furthermore, phosphate starvation did not regulate inorganic anion efflux, suggesting that citrate efflux is probably mediated by novel anion channel activity, which could have a role in phosphate acquisition.

Arabidopsis↗
PubMed2004

Reducing storage requirements for biological sequence comparison.

MOTIVATION: Comparison of nucleic acid and protein sequences is a fundamental tool of modern bioinformatics. A dominant method of such string matching is the 'seed-and-extend' approach, in which occurrences of short subsequences called 'seeds' are used to search for potentially longer matches in a large database of sequences. Each such potential match is then checked to see if it extends beyond the seed. To be effective, the seed-and-extend approach needs to catalogue seeds from virtually every substring in the database of search strings. Projects such as mammalian genome assemblies and large-scale protein matching, however, have such large sequence databases that the resulting list of seeds cannot be stored in RAM on a single computer. This significantly slows the matching process. RESULTS: We present a simple and elegant method in which only a small fraction of seeds, called 'minimizers', needs to be stored. Using minimizers can speed up string-matching computations by a large factor while missing only a small fraction of the matches found using all seeds.

Algorithms↗
PubMed2004

A preprocessor for shotgun assembly of large genomes.

The whole-genome shotgun (WGS) assembly technique has been remarkably successful in efforts to determine the sequence of bases that make up a genome. WGS assembly begins with a large collection of short fragments that have been selected at random from a genome. The sequence of bases at each end of the fragment is determined, albeit imprecisely, resulting in a sequence of letters called a "read." Each letter in a read is assigned a quality value, which estimates the probability that a sequencing error occurred in determining that letter. Reads are typically cut off after about 500 letters, where sequencing errors become endemic. We report on a set of procedures that (1) corrects most of the sequencing errors, (2) changes quality values accordingly, and (3) produces a list of "overlaps," i.e., pairs of reads that plausibly come from overlapping parts of the genome. Our procedures, which we call collectively the "UMD Overlapper," can be run iteratively and as a preprocessor for other assemblers. We tested the UMD Overlapper on Celera's Drosophila reads. When we replaced Celera's overlap procedures in the front end of their assembler, it was able to produce a significantly improved genome.

Animals↗
PubMed2003

Does the admitting officer system reduce the time taken to arrange an emergency admission to hospital?

AIM: Communication is an important feature of admitting acutely ill patients to hospital in both New Zealand and Australia. The mechanisms used to facilitate communication between the general practitioner (GP) and the admitting hospital differ between the two countries. The relative effectiveness of each of these systems has never been formally studied. Our aim was to compare the efficiency of the admitting officer system for arranging hospital admissions (used in Australia) with that of direct referral by the GP to the specialist registrar (the system used in New Zealand). METHODS: Five metropolitan hospitals of comparable size from each country were selected and the time taken to contact the relevant doctor in order to arrange admission of an acutely ill patient was documented. RESULTS: A total of 120 contact attempts were made, 60 in each country. The total time taken to contact the admitting doctor in order to arrange an emergency assessment for a patient was significantly longer in New Zealand than it was in Australia (p <0.05). CONCLUSIONS: When arranging an emergency patient assessment for a patient in the community, the total time taken to contact the appropriate doctor is less in Australia, where the admitting officer system is used, than it is in New Zealand, using the specialist registrar system. Consideration should be given by acute hospitals in New Zealand to streamlining their communications processes in order to minimise delays to referring doctors and their patients.

Australia↗
PubMed2003

Involvement of helices at the dimer interface in ClC-1 common gating.

ClC-1 is a dimeric, double-pored chloride channel that is present in skeletal muscle. Mutations of this channel can result in the condition myotonia, a muscle disorder involving increased muscle stiffness. It has been shown that the dominant form of myotonia often results from mutations that affect the so-called slow, or common, gating process of the ClC-1 channel. Mutations causing dominant myotonia are seen to cluster at the interface of the ClC-1 channel monomers. This study has investigated the role of the H, I, P, and Q helices, which lie on this interface, as well as the G helix, which is situated immediately behind the H and I helices, on ClC-1 gating. 11 mutant ClC-1 channels (T268M, C277S, C278S, S289A, T310M, S312A, V321S, T539A, S541A, M559T, and S572V) were produced using site-directed mutagenesis, and gating properties of these channels were investigated using electrophysiological techniques. Six of the seven mutations in G, H, and I, and two of the four mutations in P and Q, caused shifts of the ClC-1 open probability. In the majority of cases this was due to alterations in the common gating process, with only three of the mutants displaying any change in fast gating. Many of the mutant channels also showed alterations in the kinetics of the common gating process, particularly at positive potentials. The changes observed in common gating were caused by changes in the opening rate (e.g. T310M), the closing rate (e.g. C277S), or both rates. These results indicate that mutations in the helices forming the dimer interface are able to alter the ClC-1 common gating process by changing the energy of the open and/or closed channel states, and hence altering transition rates between these states.

Cell Line↗
PubMed2002

Adrenoceptor and local modulator control of cutaneous blood flow in thermal stress.

Blood flow to the skin is controlled by body temperatures in two ways: core and mean skin temperature combine in the central nervous system to form a reflex mechanism that controls the frequency of activity in sympathetic nerves to the cutaneous blood vessels; and local mechanisms independent of reflex effects control contractile response to the sympathetic transmitter norepinephrine (NE) at different temperatures. Cutaneous vessels differ in responsiveness to NE across temperatures: in limbs and tails, the superficial vessels constrict more strongly to NE when cooled, while the deep vessels show weaker responses to NE when cooled. This allows the limb to dissipate heat when warm and to conserve heat when cool. The mechanism for this difference in thermal response of deep and superficial vessels is not completely known, but may relate to differences in the adrenoceptors on which NE acts, and/or to the actions of locally produced substances that modulate the responses to NE in different ways at different temperatures. This paper discusses the alpha1- and alpha2-adrenoceptors involved in contraction of deep and superficial cutaneous vessels and also describes the roles of the local modulator nitric oxide, which interacts with adrenoceptors to affect cutaneous blood flow.

Animals↗
PubMed2002

NMDA receptor antagonists impair memory for nonspatial, socially transmitted food preference.

Rats avoid unfamiliar foods and learn to prefer those that they smell on the breath of conspecifics. Hippocampal lesions produce rapid forgetting of this socially acquired memory. The authors report that NMDA receptor antagonists impair this memory. Rats given CPP were trained in the social transmission of food preference task. Normal rats showed robust memory 72 hr later. CPP-injected rats performed normally 24 hr, but randomly 72 hr, after training. Spatial context was irrelevant: Rats trained and tested in different rooms performed the same as rats trained and tested in 1 room. MK801 and intrahippocampal injections of APV produced amnestic effects similar to CPP. Thus, NMDA receptor activation is crucial for the persistence of socially acquired, hippocampus-dependent, nonspatial memory.

Animals↗
PubMed2002

The bioavailability and pharmacokinetics of subcutaneous, nebulized and oral morphine-6-glucuronide.

AIMS: Morphine-6-glucuronide (M6G), one of the active metabolites of morphine, has attracted considerable interest as a potent opioid analgesic with an apparently superior therapeutic index. To date studies have used the intravenous route, which is generally unacceptable in the treatment of cancer related pain. The aim of this study was to define the pharmacokinetics, toxicity and cardio-respiratory effects of three alternative routes of administration of M6G. METHODS: Ten healthy volunteers participated in an open randomized study. Subjects received M6G 2 mg as an intravenous bolus, 20 mg orally, 2 mg subcutaneously and 4 mg by the nebulized route. Pulse, blood pressure, respiratory rate and peak flow rate were monitored and subjective toxicity recorded on rating and visual analogue scales. RESULTS: After i.v. M6G the mean (+/- s.d.) AUC(0,infinity) standardized to a dose of 1 mg was 223 +/- 57 nmol l(-1) h, mean elimination half-life was 1.7 +/- 0.7 h and the mean clearance was 157 +/- 46 ml min(-1). These parameters were virtually identical after subcutaneous administration which had a bioavailability (F(0,infinity)) of 102 +/- 35% (90% CI 82, 117%) and t(max) of 0.5 +/- 0.2 h. The mean bioavailability of nebulized M6G was 6 +/- 2% (90% CI 4, 7%) with a t(max) of 1.2 +/- 0.8 h. Following oral M6G two plasma M6G peaks were seen in 7 of the 10 subjects, the first with a t(max) of 3.1 (+/- 0.9) h. The second peak had a t(max) of 13.4 (+/-5.0) h, started approximately 4 h after dosing, and was associated with the detection of plasma M3G and morphine, suggesting that M6G was significantly hydrolysed in the gut to morphine, which was then glucuronidated following absorption. Although the overall mean bioavailability was 11 +/- 3% (90% CI 9, 12%), confining the analysis to data from the first peak suggested a bioavailability of directly absorbed M6G of only 4 +/- 4%. Apart from a characteristic dysphoria following intravenous and subcutaneous M6G, there was no significant toxicity. CONCLUSIONS: With the minimal toxicity reported in this and previous studies, subcutaneous infusion of M6G may potentially provide clinically useful analgesia for advanced cancer pain. Nebulized M6G is not significantly absorbed via the lungs, and if opiates are shown to have a local effect in the lung, reducing the sensation of breathlessness, then nebulized administration is likely to minimize systemic effects. Oral M6G has poor bioavailability, but is significantly hydrolysed in the gut to morphine, which is subsequently glucuronidated following absorption. This circuitous route accounts for the majority of systemically available M6G after oral administration.

Administration, Inhalation↗
PubMed2002

The future of Duchenne muscular dystrophy gene therapy: shrinking the dystrophin gene.

Duchenne muscular dystrophy is a debilitating muscle-wasting disease caused by mutations in the dystrophin gene - one of the largest genes identified thus far - and which ultimately results in premature death. With no current treatment available, the hopes of many sufferers lie in the establishment of an effective gene therapy. The adeno-associated virus is now emerging as a premium gene transfer vector eliciting minimal immune response from the host and allowing for long-term gene expression. It is the scope of this review to examine the recent efforts that have been made to develop ultra-truncated versions of the dystrophin gene that retain functionality, yet can still be cloned into recombinant adeno-associated viral vectors and other low-capacity vector systems.

Adenoviridae↗
PubMedDate not supplied

Biomechanical analysis of allograft bone treated with a novel tissue sterilization process.

BACKGROUND CONTEXT: Several methods to sterilize allograft bone exist, including gamma irradiation and freeze-drying, which can alter the mechanical properties of the graft. Efforts are under way to develop a method for processing osseous allograft that maintains structural integrity. Herein is presented one such method. PURPOSE: To analyze the mechanical properties, compared with nontreated controls, of a novel sterilization process for allograft cortical bone. STUDY DESIGN/SETTING: A controlled biomechanical evaluation of allograft bone under various types of loading after a novel sterilization treatment. PATIENT SAMPLE: Not applicable; basic science. OUTCOME MEASURES: The load to failure was recorded for both the study and control groups, and statistical analysis of these results was performed. Significance level (alpha) and power (beta) were set to 0.05 and 0.90, respectively. Single-factor analysis of variance (ANOVA) was used to detect significant differences between the treated and untreated groups. A post-experimental power analysis was performed for each of the response variables. METHODS: Cortical tibia and femur samples from seven cadaveric donors (mean age 68.7 years) were treated with Biocleanse and compared with untreated samples with regard to density and strength. All samples were loaded to failure under diametral and biaxial compression, shear, and three-point bending. RESULTS: Statistical analysis was done on the density and failure stress for all modes of loading. ANOVA did not indicate a significant (p>.05) effect of treatment on the density except for the axial and biaxial specimens (p<.05). ANOVA analysis of failure stress demonstrated no significant differences (p>.05) between cortical bone treated with Biocleanse and untreated specimens under all four types of mechanical loading. Post-experimental power analysis revealed power to be greater than 0.9 for each test. CONCLUSIONS: Sterilization of allograft bone with Biocleanse does not significantly alter the mechanical properties when compared with untreated samples. The effect of this sterilization process on the osteoconductive and osteoinductive properties of allograft bone must be determined.

Aged↗