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D J Mason

Publications and source records attributed to D J Mason.

At least 19 recordsLinked to original sources
PubMed2004

Determination of naturally-occurring formaldehyde in raw and cooked Shiitake mushrooms by spectrophotometry and liquid chromatography-mass spectrometry.

The initial objective was to check samples of Shiitake mushrooms for potential contamination with formaldehyde. A small number of UK retail samples were analysed using a spectrophotometric method and were found to produce formaldehyde concentrations ranging from 110-240 mg kg(-1). A more specific method, based on a derivative that could be measured and characterized by LC-MS, confirmed these results. A secondary objective tested the hypothesis that the formaldehyde might be of natural origin. Samples of UK and Chinese Shiitake, verified as being produced without any formaldehyde treatments, were found to produce similar levels of formaldehyde ranging from 100-320 mg kg(-1). Frying for 6 min significantly reduced formaldehyde concentrations, whereas storage for up to 10 days had no effect on the concentrations. The relatively harsh analytical conditions used may have produced some of the formaldehyde measured during extraction, from a number of chemical precursors.

Cooking↗
PubMed2004

The role of glutamate transporters in bone cell signalling.

The amino acid L-glutamate mediates signals at excitatory synapses in the CNS where its effects are controlled by co-ordinated activities of various types of glutamate receptor and transporter. This signalling mechanism has proved to be far more ubiquitous with many different cell types responding to glutamate. The glutamate transporter GLAST-1 was the first component of this pathway identified in bone where its expression was found to be mechanoresponsive in osteocytes. There is now a wealth of evidence supporting a role for this signalling mechanism in bone. Osteoblasts can release glutamate in a regulated manner and express functional glutamate receptors that influence their differentiation and osteogenic activity. Likewise, osteoclasts express functional glutamate receptors that influence their bone resorbing capacity. This article considers the various functions of glutamate transporters in this signalling pathway, and the evidence supporting an important role of glutamate signalling in regulating bone cell activities.

Animals↗
PubMed2002

The effect of thymosin beta4 on articular cartilage chondrocyte matrix metalloproteinase expression.

Mechanical loading is paramount in regulating both the anabolic and catabolic activities of articular cartilage chondrocytes, essential for the matrix to retain its functional integrity. We have identified thymosin beta(4) as a putative mechanically regulated gene that may mediate load-enhanced synthesis and activation of matrix metalloproteinases (MMPs) 2 and 9 in articular cartilage. The objective of this study was to confirm the mechanical regulation of thymosin beta(4) and determine its effect on cartilage chondrocyte MMP production. Thymosin beta(4) mRNA expression, analysed by quantitative PCR, revealed a significant 20-fold increase in cartilage loaded for 10 min which was still evident after 30 min of loading. Treatment of primary chondrocytes with 2 and 4 micro x ml(-1) thymosin beta(4) peptide for 4 h significantly increased pro-MMP 9 expression and activation. We postulate a functional role for load-induced thymosin beta(4) in modulating the cytoskeletal organization of articular cartilage chondrocytes to affect MMP expression.

Animals↗
PubMed2002

Tumour necrosis factor alpha up-regulates protein kinase R (PKR)-activating protein (PACT) and increases phosphorylation of PKR and eukaryotic initiation factor 2-alpha in articular chondrocytes.

Our previous analysis of the genes regulated in cartilage at the onset of spontaneous osteoarthritis in the guinea pig knee revealed up-regulation of the gene for protein kinase R (PKR)-activating protein (PACT), which encodes the cellular activator of the protein kinase, PKR. PACT and PKR are upstream components of a number of signal transduction and gene transcription pathways used by pro-inflammatory cytokines. We have investigated the role of PACT and PKR in articular cartilage degradation using cytokine treatment of bovine primary chondrocytes and cartilage explants. Tumour necrosis factor alpha increased expression of PACT protein after 3 h of treatment. Furthermore, increased phosphorylation of PKR and eukaryotic initiation factor 2-alpha was observed. The known role of PKR in cytokine-induced signalling pathways, together with our data showing cytokine regulation of PACT and PKR in chondrocytes, reveals a novel mechanism of cartilage degradation that may be important in the pathogenesis of arthritic diseases.

Animals↗
PubMed2002

The glutamate transporter GLAST-1 (EAAT-1) is expressed in the plasma membrane of osteocytes and is responsive to extracellular glutamate concentration.

The glutamate/aspartate transporter GLAST-1 is expressed in bone in vivo and also exists as a splice variant (GLAST-1a) in which exon 3 is excluded. Since GLAST-1 expression is regulated in bone in response to osteogenic mechanical stimuli in vivo and binding of glutamate to receptors on osteoblasts increases osteoblast number and activity in vitro, control of extracellular glutamate concentrations may be critical for balanced bone remodelling. To determine whether GLAST isoforms may act to regulate extracellular glutamate concentration in bone we investigated whether their pattern or level of expression is responsive to glutamate concentration in bone cells. GLAST-1a mRNA is expressed at lower levels than GLAST-1 mRNA in all cells examined. The GLAST-1a/GLAST-1 mRNA ratio is greater in MLO-Y4 osteocytes than in SaOS-2 osteoblast-like cells, although this does vary in SaOS-2 cells in response to extracellular glutamate concentration. Transfection of MLO-Y4 cells with green fluorescent protein (GFP)-tagged GLAST isoforms revealed a plasma membrane localization of GLAST-1, consistent with its transporter function, whereas GLAST-1a appeared to be expressed within internal vesicles. Interestingly, low extracellular glutamate concentrations redistributed GLAST-1-GFP into a similar internal expression pattern. Regulation of the expression and distribution of GLAST-1 by extracellular glutamate in bone cells indicates that it may regulate glutamate signalling in bone, consistent with its operation in the central nervous system.

Animals↗
PubMed2002

Glutamate transporters in bone.

In the central nervous system Na(+)-dependent glutamate transporters bind extracellular glutamate and transport it into cells surrounding the synapse, terminating excitatory signals. These glutamate transporters also function as ion channels. The glutamate transporter, GLAST-1, is expressed in the plasma membrane of osteoblasts and osteocytes and is the same molecular weight as in brain. Thus in bone cells GLAST-1 may transport glutamate or operate as a glutamate gated ion channel. A splice variant, GLAST-1a, is also expressed in bone. Hydropathy and Western blot analysis suggest GLAST-1a adopts a reversed orientation within the cell membrane. Sodium and potassium ion gradients drive glutamate transport but glycosylation, oxidation and phosphorylation modulate transporter activity. Reversal of GLAST-1a would alter these modifications varying its transport activity under the same ionic gradients. The significance of GLAST-1/1a in bone in vivo is unknown. GLAST-1 knockout mice show no major disruption of skeletal development but have not been investigated in detail. Glutamate affects both osteoclast and osteoblast biology and the regulation of GLAST-1 by mechanical loading in bone suggests a role for glutamate transporters in osteogenesis. Differential regulation and modification of GLAST variants may provide an intricate mechanism controlling extracellular glutamate levels and thus its downstream signalling effects in bone.

Journal Article↗
PubMed2001

Up-regulation of matrix metalloproteinase expression and activation following cyclical compressive loading of articular cartilage in vitro.

Osteoarthritis (OA) results in articular cartilage degeneration and subchondral bone remodeling. Excessive or abnormal loading of the joint may contribute to matrix destruction by creating an imbalance between proteinases and their inhibitors. This study investigates whether cyclical loading regulates expression and/or activation of metalloproteinases 2 and 9 (MMPs) in articular cartilage explants. Gelatin zymography, reverse zymography, and MMP activity assays of mechanically loaded bovine cartilage explants (0.5 MPa, 1 Hz, 3 h) showed increased expression and activation of MMPs 2 and 9, whereas expression of the tissue inhibitors of MMPs was unaffected. This shows, for the first time that mechanical loading can influence tissue homeostasis generating an imbalance of proteinases and their inhibitors inducing turnover and/or catabolic events in cartilage.

Animals↗
PubMed2001

Hand stand.

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Guideline Adherence↗
PubMed2001

An apple a day.

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Female↗
PubMed2001

Places of healing?

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Attitude of Health Personnel↗
PubMed2001

Assessment of lithium dilution cardiac output as a technique for measurement of cardiac output in dogs.

OBJECTIVES: To determine agreement of cardiac output measured by use of lithium dilution cardiac output (LiDCO) and thermodilution cardiac output (TDCO) techniques in dogs and to determine agreement of low- and high-dose LiDCO with TDCO. ANIMALS: 10 dogs (7 males, 3 females). PROCEDURE: Cardiac output was measured in anesthetized dogs by use of LiDCO and TDCO techniques. Four rates of cardiac output were induced by occlusion of the caudal vena cava, changes in depth of anesthesia, or administration of dobutamine. Lithium dilution cardiac output was performed, using 2 doses of lithium chloride (low and high dose). Each rate of cardiac output allowed 4 comparisons between LiDCO and TDCO. RESULTS: 160 comparisons were determined of which 68 were excluded. The remaining 92 comparisons had values ranging from 1.10 to 12.80 L/min. Intraclass correlation coefficient (ICC) between low-dose LiDCO and TDCO was 0.9898 and between high-dose LiDCO and TDCO was 0.9896. When all LiDCO determinations were pooled, ICC was 0.9894. For determinations of cardiac output < 5.0 L/min, ICC was 0.9730. Mean +/- SD of the differences of TDCO minus LiDCO for all measurements was -0.084+/-0.465 L/min, and mean of TDCO minus LiDCO for cardiac outputs < 5.0 L/min was -0.002+/-0.245 L/min. CONCLUSIONS AND CLINICAL RELEVANCE: The LiDCO technique is a suitable substitute for TDCO to measure cardiac output in dogs. Use of LiDCO eliminates the need for catheterization of a pulmonary artery and could increase use of cardiac output monitoring, which may improve management of cardiovascularly unstable animals.

Anesthesia↗
PubMed2000

Flow cytometric monitoring of antibiotic-induced injury in Escherichia coli using cell-impermeant fluorescent probes.

Three fluorescent nucleic acid binding dyes-propidium iodide, TO-PRO-1, and SYTOX green-were evaluated, and their abilities to distinguish between bacterial cells with and without an intact cytoplasmic membrane were compared. Each dye was readily able to discriminate between healthy and permeabilized cells of Escherichia coli, although SYTOX green showed a greater enhancement in fluorescence intensity on staining-compromised, as opposed to healthy, cells in log-phase growth, than either PI or TO-PRO-1. Flow cytometric analysis of E. coli stained with these dyes after exposing them to several antimicrobial agents showed that all three dyes were able to detect antimicrobial action. Notably, however, the intensity of the cell-associated fluorescence was related to the mechanism of action of the antimicrobial agent. Large changes in fluorescence intensity were observed for all the dyes subsequent to beta-lactam antibiotic action, but smaller changes (or no change) were seen subsequent to exposure to antimicrobials acting directly or indirectly on nucleic acid synthesis. Furthermore, cell-associated fluorescence did not relate to loss of viability as determined by plate counts. Despite offering much insight into antimicrobial mechanisms of action, these fundamental problems become relevant to the development of rapid antimicrobial susceptibility tests if colony formation is used as the standard.

Anti-Bacterial Agents↗
PubMed2000

Flow cytometric investigation of filamentation, membrane patency, and membrane potential in Escherichia coli following ciprofloxacin exposure.

Ninety-eight percent of the cells in a population of Escherichia coli in log-phase growth lost colony-forming ability after being exposed for 3 h to the quinolone antibiotic ciprofloxacin at four times the MIC in nutrient broth, a concentration easily reached in vivo. Flow cytometric analysis, however, demonstrated that only 68% of this bacterial population had lost membrane potential, as judged by the membrane potential-sensitive dye bis-(1,3-dibutylbarbituric acid) trimethine oxonol [DiBAC(4)(3)], and only 30% could no longer exclude the nucleic acid-binding dye propidium iodide (PI), reflecting lost membrane integrity, efflux mechanisms, or both. Subsequent removal of ciprofloxacin and resuspension in nutrient broth resulted in renewed cell division after 2 h, with a calculated postantibiotic effect (PAE) time of 57 min. The proportion of DiBAC- and PI-fluorescent cells in this recovering population remained stable for more than 4 h after antibiotic removal. Eighty percent of cells present at drug removal were filamentous. Their number subsequently decreased with time, and the increase in particle count seen at the end of the PAE resulted from the division of short cells. Exposure to ciprofloxacin in the presence of the protein synthesis inhibitor chloramphenicol increased colony-forming ability to 60% of starting population numbers. In contrast to ciprofloxacin alone, this antibiotic combination resulted in insignificant filamentation and no dye uptake. Subsequent drug removal and resuspension in nutrient broth resulted in the appearance of filaments within 1 h, with 69% of the population forming filaments at 3 h. Dye uptake was also seen, with 20% of the population fluorescing with either dye after 4 h. We were unable to relate dye uptake to the viable count. Cell division resumed 240 min after removal of both drugs, yielding a PAE calculated at 186 min. Inhibition of protein synthesis with chloramphenicol prevented ciprofloxacin-induced changes in bacterial morphology, cell membrane potential, and ability to exclude nucleic acid-binding dye. These changes persisted beyond the end of the classically defined PAE and were not a definite indicator of cell death as defined by loss of colony formation, which related at least in part to filamentation.

Anti-Infective Agents↗