Biomedical subjects

B Wong

Publications and source records attributed to B Wong.

At least 55 records · Page 3Linked to original sources

PubMed1998

Determinants of DNA binding and bending by the Saccharomyces cerevisiae high mobility group protein NHP6A that are important for its biological activities. Role of the unique N terminus and putative intercalating methionine.

The non-histone proteins 6A/B (NHP6A/B) of Saccharomyces cerevisiae are high mobility group proteins that bind and severely bend DNA of mixed sequence. They exhibit high affinity for linear DNA and even higher affinity for microcircular DNA. The 16-amino acid basic segment located N-terminal to the high mobility group domain is required for stable complex formation on both linear and microcircular DNA. Although mutants lacking the N terminus are able to promote microcircle formation and Hin invertasome assembly at high protein concentrations, they are unable to form stable complexes with DNA, co-activate transcription, and complement the growth defect of Deltanhp6a/b mutants. A basic patch between amino acids 13 and 16 is critical for these activities, and a second basic patch between residues 8 and 10 is required for the formation of monomeric complexes with linear DNA. Mutational analysis suggests that proline 18 may direct the path of the N-terminal arm to facilitate DNA binding, whereas the conserved proline at position 21, tyrosine 28, and phenylalanine 31 function to maintain the tertiary structure of the high mobility group domain. Methionine 29, which may intercalate into DNA, is essential for NHP6A-induced microcircle formation of 75-bp but not 98-bp fragments in vitro, and for full growth complementation of Deltanhp6a/b mutants in vivo.

Amino Acid Sequence↗

PubMed1998

Pharyngoesophageal reconstruction with the ulnar forearm flap.

OBJECTIVE: To evaluate the use of a generous fasciocutaneous ulnar forearm free flap in pharyngoesophageal reconstruction. DESIGN: Tertiary referral center. SETTING: Private practice. PATIENTS: From September 1, 1991, to October 30, 1996, 20 ulnar forearm free flaps were used to reconstruct the pharyngoesophagus in 19 patients after surgery for squamous cell carcinoma. There were 13 circumferential defects and 7 near-circumferential defects (<2 cm of mucosa remaining). The reconstructions were performed primarily (at the time of tumor resection) in 16 cases and secondarily in 4 cases. INTERVENTION: A generous fasciocutaneous ulnar forearm flap with a minimum dimension of 9 x 22 cm was harvested to reconstruct the pharyngoesophagus. A 2-layer closure was performed in flap tailoring and proximal (pharynx to flap) and distal (flap to esophagus) anastomoses to minimize the risk of leakage. Also, portions of the flap were used to monitor flap viability, to cover cervical vessels, to obliterate dead space, and as skin coverage when the skin flaps were deficient. RESULTS: Nineteen of the 20 flaps transferred were successful. Swallow function was restored in 18 cases, and voice was rehabilitated in all the patients using either tracheoesophageal puncture and a voice device or an electrolarynx device. There was 1 perioperative mortality. Three fistulas occurred, all of which healed with nonsurgical treatment. One stricture developed that required intermittent dilatation. The donor site morbidity was minor. CONCLUSIONS: This versatile technique achieves excellent results with a decreased complication rate compared with other methods currently available in pharyngoesophageal reconstruction.

Adult↗

PubMed1998

Effects of spacing and repetition on amnesic patients' performance during perceptual identification, stem completion, and category exemplar production.

The effects of repetition and spacing of repetitions on amnesic patients' implicit task performance was studied. Amnesic patients and control participants performed a perceptual identification task, a word-stem completion task, and a category exemplar production task after the presentation of target words repeated within a list. Repetition proved to have no effect on perceptual identification or on word-stem completion, but it did play a role in category exemplar production. As expected, the amnesic patients demonstrated normal performance on the perceptual identification and word-stem completion tasks. However, on category exemplar production, the amnesic patients' performance was significantly below that of the control participants, and the 2 groups differentially responded to repetition. The normal control participants' spontaneous ability to analyze semantic features of words led to unconscious priming of the category and its links to the exemplars after only one presentation of a word. Amnesic patients, on the other hand, seemed to rely more on the fluency produced by multiple presentations.

Aged↗

PubMed1998

The prevalence of diabetes and associated coronary risk factors in urban and rural older Mexican populations.

OBJECTIVE: To determine the prevalence of diabetes and examine its association with food intake, anthropometric and metabolic variables, and other coronary risk factors in urban and rural older Mexican populations. DESIGN: A cross-sectional study. SETTING: Three Mexican communities (urban areas of medium and low income and a rural area). PARTICIPANTS: A total of 121 men and 223 women aged 60 years and older and 93 men and 180 women aged 35 to 59 years were selected randomly for inclusion in the survey, which was derived from the CRONOS study (Cross-Cultural Research on Nutrition in the Older Adult Study Group) promoted by the European Economic Community. MEASUREMENTS: A personal interview assessed demographic information, personal medical history, and functional status, and a 24-hour diet recall was obtained. A physical examination included anthropometric and blood pressure measurements. A fasting blood sample was obtained for measurements of lipids, insulin, and glucose. RESULTS: Diabetes prevalence was higher in men than in women for all age groups: 16.7% versus 9.5% in younger adults and 30.8% versus 22.8% in older adults. For all age groups, diabetes was more highly prevalent in urban communities. Using a multivariate stepwise logistic regression, variables associated independently with diabetes in older individuals were: gender (male sex: OR = 2.1; P < .009); diminished carbohydrate intake in the diet (OR = 0.77; P < .03); central distribution of adiposity (OR = 1.9; P < .03); and functional disability (OR = 2.3; P < .01). This relationship was not observed with living area, income, education, fiber and alcohol intake, body mass index, or age. Individuals 80 years and older had a diminished atherogenic risk profile. Diabetes in older people was associated significantly with hypertriglyceridemia, impaired functional status, and an increased prevalence of ischemic heart disease; in younger adults diabetes was associated with low density lipoprotein (LDL) hypercholesterolemia, hypertriglyceridemia, and a proportionally higher fat intake. CONCLUSION: This survey confirms the high prevalence of diabetes in the older Mexican population - particularly in men and in individuals living in urban areas - associated with an increased prevalence of other coronary risk factors. Diabetes was associated with higher fat, low carbohydrate, low fiber diets and increased prevalence of central distribution of adiposity. In the older subjects, diabetes was associated significantly with hypertriglyceridemia, impaired functional status, and increased prevalence of ischemic heart disease. A bias produced by early mortality and a survivorship effect must be considered in studies of older individuals. The health situation in the older Mexican population presents a complex problem that needs correct diagnosis and better strategies to benefit those segments of the population at increased risk.

Age Distribution↗

PubMed1998

Cryptococcus neoformans: virulence and host defences.

Cryptococcus neoformans represents a model organism for the study of virulence and the host response. In this discussion, there is a focus on the genetic, molecular, and biochemical aspects of C. neoformans as it interacts with the host. Investigations into direct and indirect virulence phenotypes are now possible. The molecular aspects of two major virulence factors, capsule and melanin, are characterized. Yeast polyol metabolism through mannitol is examined as a potential biochemical pathway for virulence. The concept of C. neoformans differentially expressed genes within the host or in response to certain environmental cues can be used indirectly to identify potential virulence genes. However, despite significant progress in molecular pathogenesis with C. neoformans, the future of research in this area will require a certain critical mass of investigators to help share in the developmental costs which continue to occur.

Cryptococcosis↗

PubMed1997

T cell receptor signals enhance susceptibility to Fas-mediated apoptosis.

Fas(CD95) and its ligand (FasL) interaction plays a pivotal role in T cell receptor (TCR)-mediated apoptosis. However, the susceptibility of T cells to Fas-mediated apoptosis is tightly regulated during immune responses, a regulation which is thought to maintain the antigen-specificity of T cell apoptosis. Here we show that TCR stimulation enhances the induction of Fas-mediated apoptosis. In addition, using a mutant T cell hybridoma with impaired FasL expression, we show that the synergy provided by TCR stimulation can be mimicked by activators of PKC but not calcium influx. This effect cannot be inhibited by actinomycin D, suggesting that TCR stimulation leads to the alteration in preexisting signaling molecules to enhance Fas-mediated apoptosis. Our results therefore provide a mechanism of how Fas-FasL interactions lead to T cell death in an antigen-specific manner via repetitive antigen stimulation.

Animals↗

PubMed1997

Stability of propafenone hydrochloride in i.v. solutions.

The stability of propafenone hydrochloride in i.v. solutions was studied. Solutions of propafenone hydrochloride 2, 1, and 0.5 mg/mL in 5% dextrose injection and in 5% dextrose and 0.2% sodium chloride injection were prepared. Portions of each type of solution were transferred to 10-mL polypropylene syringes and to 150-mL polyvinyl chloride (PVC) bags. Syringes and bags were stored at 20.5-22.5 degrees C under fluorescent light. Two 0.5-mL samples were drawn from each container at 0, 6, 12, 24, 36, and 48 hours and frozen in polystyrene tubes at -20 degrees C until assayed. Propafenone concentrations were determined by high-performance liquid chromatography. All samples of propafenone hydrochloride 2 mg/mL in 5% dextrose and 0.2% sodium chloride injection taken from PVC bags precipitated when thawed. For the remaining solutions, the mean decrease from the initial concentration was < 10% regardless of diluent, container type, and initial concentration. Propafenone hydrochloride 1 and 0.5 mg/mL in 5% dextrose injection or in 5% dextrose and 0.2% sodium chloride injection was stable for 48 hours at 20.5-22.5 degrees C when stored in polypropylene syringes or PVC bags. Propafenone hydrochloride 2 mg/mL in 5% dextrose injection was stable for 48 hours when stored in syringes or bags, but in 5% dextrose and 0.2% sodium chloride injection was stable in syringes only.

Anti-Arrhythmia Agents↗

PubMed1997

A regulatory role for TRAF1 in antigen-induced apoptosis of T cells.

Tumor necrosis factor receptor (TNFR)-associated factor 2 (TRAF2) and TRAF1 were found as components of the TNFR2 signaling complex, which exerts multiple biological effects on cells such as cell proliferation, cytokine production, and cell death. In the TNFR2-mediated signaling pathways, TRAF2 works as a mediator for activation signals such as NF-kappaB, but the role of TRAF1 has not been previously determined. Here we show in transgenic mice that TRAF1 overexpression inhibits antigen-induced apoptosis of CD8(+) T lymphocytes. Our results demonstrate a biological role for TRAF1 as a regulator of apoptotic signals and also support the hypothesis that the combination of TRAF proteins in a given cell type determines distinct biological effects triggered by members of the TNF receptor superfamily.

Animals↗

PubMed1997

Identifying the molecular control of T-cell death; on the hunt for killer genes.

Apoptosis, the series of morphological changes which result from a cell-suicide program, has fascinated biologists in recent years. Identifying apoptosis regulatory and effector genes to elucidate the molecular mechanisms of programmed cell death has been a challenging but successful endeavor. However, our knowledge of this process is far from complete. The discovery of 'death genes' has provided insight into the homeostatic mechanisms regulating the immune system including the clonal deletion of self-reactive and activated lymphocytes. Notably, apoptosis induced by T-cell receptor (TCR) stimulation is the critical event which drives negative selection of thymocytes and peripheral T cells. Differential display, differential screening and subtractive hybridization have provided the technical backbone for the isolation of genes whose expression is specific for apoptotic cells. However, the genes identified by these techniques only correlate with the apoptotic phenotype and their expression may be the result of non-apoptotic pathways also affected by the death-inducing agent. Here, we review what is known about the molecular mechanisms of TCR-triggered apoptosis and discuss techniques used to isolate and characterize death regulatory molecules. In addition, we present a novel approach utilizing somatic cell genetics to clone genes involved in TCR-triggered apoptosis.

Apoptosis↗

PubMed1997

Pathways leading to cell death in T cells.

Antigen-induced apoptosis of T cells is a highly regulated process which plays a key role in the elimination of self-reactive T cells and, thus, in the prevention of autoimmunity. It has recently become apparent that members of the tumor necrosis factor (TNF) and TNF receptor (TNFR) superfamily regulate antigen-induced T-cell death. Studies characterizing genes which control TNF/TNFR superfamily expression and how TNF/TNFR signal transducers activate cell death machinery, such as caspases, have begun to reveal the molecular control of antigen-induced T-cell death.

Animals↗

PubMed1997

Expression of bacterial mtlD in Saccharomyces cerevisiae results in mannitol synthesis and protects a glycerol-defective mutant from high-salt and oxidative stress.

Polyols, or polyhydroxy alcohols, are produced by many fungi. Saccharomyces cerevisiae produces large amounts of glycerol, and several fungi that cause serious human infections produce D-arabinitol and mannitol. Glycerol functions as an intracellular osmolyte in S. cerevisiae, but the functions of D-arabinitol and mannitol in pathogenic fungi are not yet known. To investigate the functions of mannitol, we constructed a new mannitol biosynthetic pathway in S. cerevisiae. S. cerevisiae transformed with multicopy plasmids encoding the mannitol-1-phosphate dehydrogenase of Escherichia coli produced mannitol, whereas S. cerevisiae transformed with control plasmids did not. Although mannitol production had no obvious phenotypic effects in wild-type S. cerevisiae, it restored the ability of a glycerol-defective, osmosensitive osg1-1 mutant to grow in the presence of high NaCl concentrations. Moreover, osg1-1 mutants producing mannitol were more resistant to killing by oxidants produced by a cell-free H2O2-FeSO4-NaI system than were controls. These results indicate that mannitol can (i) function as an intracellular osmolyte in S. cerevisiae, (ii) substitute for glycerol as the principal intracellular osmolyte in S. cerevisiae, and (iii) protect S. cerevisiae from oxidative damage by scavenging toxic oxygen intermediates.

Escherichia coli↗

PubMed1997

Three-dimensional kinematics and limb kinetic energy of running cockroaches.

We tested the hypothesis that fast-running hexapeds must generate high levels of kinetic energy to cycle their limbs rapidly compared with bipeds and quadrupeds. We used high-speed video analysis to determine the three-dimensional movements of the limbs and bodies of cockroaches (Blaberus discoidalis) running on a motorized treadmill at 21 cm s-1 using an alternating tripod gait. We combined these kinematic data with morphological data to calculate the mechanical energy produced to move the limbs relative to the overall center of mass and the mechanical energy generated to rotate the body (head + thorax + abdomen) about the overall center of mass. The kinetic energy involved in moving the limbs was 8 microJ stride-1 (a power output of 21 mW kg-1, which was only approximately 13% of the external mechanical energy generated to lift and accelerate the overall center of mass at this speed. Pitch, yaw and roll rotational movements of the body were modest (less than +/- 7 degrees), and the mechanical energy required for these rotations was surprisingly small (1.7 microJ stride-1 for pitch, 0.5 microJ stride-1 for yaw and 0.4 microJ stride-1 for roll) as was the power (4.2, 1.2 and 1.1 mW kg-1, respectively). Compared at the same absolute forward speed, the mass-specific kinetic energy generated by the trotting hexaped to swing its limbs was approximately half of that predicted from data on much larger two- and four-legged animals. Compared at an equivalent speed (mid-trotting speed), limb kinetic energy was a smaller fraction of total mechanical energy for cockroaches than for large bipedal runners and hoppers and for quadrupedal trotters. Cockroaches operate at relatively high stride frequencies, but distribute ground reaction forces over a greater number of relatively small legs. The relatively small leg mass and inertia of hexapeds may allow relatively high leg cycling frequencies without exceptionally high internal mechanical energy generation.

Animals↗

PubMed1996

Development of a manganese dioxide solid-phase reactor for oxidation of toxins associated with paralytic shellfish poisoning.

Using manganese dioxide as a solid-phase oxidant, a post-column HPLC reactor for paralytic shellfish poison toxins was constructed and evaluated. Operating parameters such as reaction temperature and pH, flow-rate, reactor column size, and MnO2 particle size were studied. Based on a 3:1 signal-to-noise ratio the limits of detection for the non-hydroxylated toxins were in the sub-nanogram range, while the hydroxylated toxins were ten times less detectable. The limit of detection for saxitoxin was about 0.1 ng per injection. The repeatability of replicate injections was < or = 10% (relative standard deviation). The system was used to analyze extracts of shellfish and plankton yielding results that were in agreement with those obtained by established analytical methods. Extracts of shellfish contaminated at the regulatory limit of 0.8 microgram/g were successfully analyzed.

Animals↗

PubMed1996

High-performance liquid chromatographic method for the determination of mycophenolate mofetil in human plasma.

A method for the quantification of mycophenolate mofetil (MMF, CellCept) in plasma using solid-phase extraction and HPLC is described here. A solution of internal standard is added to a 0.5-ml plasma aliquot. The resulting sample is treated with water and dilute HCl and applied to a C18 solid-phase extraction column. After a water wash, the MMF and internal standard are eluted with methanol-0.1 M citrate-phosphate buffer, pH 2.6 (80:20, v/v). A 20-microliters aliquot of the eluate is injected onto a C18 column (5 microns particle size, 150 x 4.6 mm I.D.) and eluted at ambient temperature with acetonitrile-0.05 M citrate-phosphate buffer, pH 3.6, containing 0.02 M heptanesulfonic acid (41:59, v/v). Quantification is achieved by UV detection at 254 nm. The method is reproducible, accurate and specific for MMF. Using 0.5 ml of plasma for analysis, the quantification limit is 0.400 microgram/ml and the range is 0.400-20 micrograms/ml. Based on the stability profile of MMF in plasma, it is recommended that blood samples collected following intravenous infusion be immediately stored on ice and that plasma be prepared rapidly, immediately stored frozen at -80 degrees C and analyzed within four months of collection.

Chromatography, High Pressure Liquid↗

PubMed1996

Oxidative killing of Cryptococcus neoformans by human neutrophils. Evidence that fungal mannitol protects by scavenging reactive oxygen intermediates.

Polymorphonuclear neutrophils (PMN) kill Cryptococcus neoformans (Cn) by oxidative mechanisms, but the roles of various reactive oxygen intermediates (ROIs) are not known. We used a mannitol low-producing Cn mutant (Cn MLP) and its wild-type parent (Cn H99) to examine the role of ROIs distal to H2O2 in PMN killing and to determine whether mannitol produced by Cn protects the fungus against ROIs. At PMN:Cn cell ratios of 1:1, 10:1, and 100:1, PMN killed significantly more Cn MLP than Cn H99 cells after 2 and 4 h (p less than 0.05). Superoxide dismutase and the hydroxyl radical (OH.) scavengers mannitol and DMSO inhibited killing of both strains (p less than 0.05), but catalase did not. Cn H99 and Cn MLP stimulated PMN to produce similar amounts of O2- and H2O2. In contrast, Cn MLP stimulated greater luminol-dependent chemiluminescence than did Cn H99 (p less than 0.05). Finally, H2O2 alone killed similar numbers of Cn H99 and Cn MLP cells, but oxidants generated by FeSO4 (1 microM), H2O2 (10 microM), and iodide (1 to 3 microM) killed significantly more Cn MLP than Cn H99 cells in 1 h (p less than 0.05). Mannitol, DMSO, and catalase completely inhibited killing of both Cn strains by this cellfree system, but superoxide dismutase did not. These results suggest that 1) distal ROIs such as OH. and HOCI are key effector molecules against Cn, and 2) mannitol produced by Cn may protect against oxidative killing by scavenging distal ROIs.

Cell-Free System↗

PubMed1996

Manual and automated (robotic) high-performance liquid chromatography methods for the determination of mycophenolic acid and its glucuronide conjugate in human plasma.

A manual and an automated (Zymark PyTechnology robot) HPLC method for simultaneous determination of plasma mycophenolic acid (MPA) and its glucuronide conjugate (MPAG) are described here. Both methods are reproducible and accurate, and both are equivalent in all respects, including quantification limits (MPA, 0.100 microgram/ml; MPAG, 4.00 micrograms/ml), range (using 0.05-0.5 ml of plasma: MPA, 0.0500-20.0 micrograms/aliquot; MPAG, 2.00-200 micrograms/aliquot), precision, and accuracy. MPA and MPAG were stable under the conditions used with both methods. Results from aliquots of paired control samples, analyzed by the manual method over three years at six analytical laboratories, showed excellent agreement in precision and accuracy.

Chromatography, High Pressure Liquid↗

PubMed1996

Comparison of metalworking fluid mist exposures from machining with different levels of machine enclosure.

This research investigated the efficacy of machine enclosures in reducing employee exposures to metalworking fluid mist. Four hundred fifty-five personal samples from automotive machining and grinding operations collected over six years were divided into three groups based on the type and extent of enclosure and local exhaust ventilation. The sample groups were (1) machining equipment with original equipment manufacturer (OEM) total enclosures and local exhaust ventilation, (2) machining equipment with partial or retrofit enclosures and local exhaust ventilation, and (3) machining equipment with little or no enclosure. The results of the Mann Whitney U test of the three data sets indicated that the employees operating equipment with OEM enclosures had significantly lower exposures than employees operating equipment that had either of the other two control methods. There was no difference between the exposures of operators of equipment with retrofit enclosures compared to operators of equipment without enclosures. The median exposure for operators of equipment with OEM enclosures was 0.21 mg/m3, about half that found with the other two control methods. Each of the data sets was compared to exposure criteria; 100% of the exposures associated with OEM enclosures were below 1.0 mg/m3, and 90% of the exposures were below 0.5 mg/m3. The other two methods were not as effective as OEM in reducing exposure to below these criteria. These results indicate that OEM enclosures provide the most effective control of metalworking fluid mist exposure.

Aerosols↗

PubMed1996

Identification of a Cryptococcus neoformans gene that directs expression of the cryptic Saccharomyces cerevisiae mannitol dehydrogenase gene.

The Mtl gene from Cryptococcus neoformans, which confers the ability of Saccharomyces cerevisiae Sc4l YJO to grow on mannitol with substantial NAD-dependent mannitol dehydrogenase activity, was identified. Purifications and characterizations of this enzyme show that it is found in polyploid strain BB1, and the peptide sequence of the enzyme helped identify the saccharomyces gene encoding this mannitol dehydrogenase activity. On the other hand, the Mtl gene of C. neoformans encodes a 346-amino-acid protein which is not mannitol dehydrogenase but a regulatory element which is active in a heterologous fungus.

Aldehyde Reductase↗