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David Thomas

Publications and source records attributed to David Thomas.

53 records · Page 3Linked to original sources
PubMed2003

Properties of the demarcation membrane system in living rat megakaryocytes.

The demarcation membrane system (DMS) is the precursor of platelet cell membranes yet little is known of its properties in living megakaryocytes. Using confocal microscopy, we now demonstrate that demarcation membranes in freshly isolated rat marrow megakaryocytes are rapidly stained by styryl membrane indicators such as di-8-ANEPPS and FM 2-10, confirming that they are invaginations of the plasma membrane and readily accessible from the extracellular space. Two-photon excitation of an extracellular indicator displayed the extensive nature of the channels formed by the DMS throughout the extranuclear volume. Under whole-cell patch clamp, the DMS is electrophysiologically contiguous with the peripheral plasma membrane such that a single capacitative component can account for the biophysical properties of all surface-connected membranes in the majority of recordings. Megakaryocyte capacitances were in the range of 64-694 pF, equivalent to 500-5500 platelets (mean value 1850). Based upon calculations for a spherical geometry, the DMS results in a 4- to 14-fold (average 8.1-fold) increase in specific membrane capacitance expressed per unit spherical surface area. This indicates a level of plasma membrane invagination comparable with mammalian skeletal muscle. Whole-cell capacitance measurements and confocal imaging of membrane-impermeant fluorescent indicators therefore represent novel approaches to monitor the DMS during megakaryocytopoiesis and thrombopoiesis.

Animals↗
PubMed2003

Overexpression, purification, and characterization of recombinant Ca-ATPase regulators for high-resolution solution and solid-state NMR studies.

Phospholamban (PLB) and Sarcolipin (SLN) are integral membrane proteins that regulate muscle contractility via direct interaction with the Ca-ATPase in cardiac and skeletal muscle, respectively. The molecular details of these protein-protein interactions are as yet undetermined. Solution and solid-state NMR spectroscopies have proven to be effective tools for deciphering such regulatory mechanisms to a high degree of resolution; however, large quantities of pure recombinant protein are required for these studies. Thus, recombinant PLB and SLN production in Escherichia coli was optimized for use in NMR experiments. Fusions of PLB and SLN to maltose binding protein (MBP) were constructed and optimal conditions for protein expression and purification were screened. This facilitated the large-scale production of highly pure protein. To confirm their functionality, the biological activities of recombinant PLB and SLN were compared to those of their synthetic counterparts. The regulation of Ca-ATPase activity by recombinant PLB and SLN was indistinguishable from the regulation by synthetic proteins, demonstrating the functional integrity of the recombinant constructs and ensuring the biological relevance of our future structural studies. Finally, NMR spectroscopic conditions were established and optimized for use in investigations of the mechanism of Ca-ATPase regulation by PLB and SLN.

Amino Acid Sequence↗
PubMed2003

Immunotactoid glomerulopathy in an HIV-positive African-American man.

The authors report the first case of immunotactoid glomerulopathy (ITG) in a human immunodeficiency virus (HIV)-positive, hepatitis B- and C-negative African-American man who presented with hematuria and proteinuria. His initial presentation was compatible with HIV associated nephropathy, but on renal biopsy he was found to have ITG. He has been treated with highly active antiretroviral therapy and an angiotensin-converting enzyme inhibitor, but his proteinuria has not responded after 4 months of treatment. This case emphasizes the diverse glomerular lesions seen in HIV-positive patients and supports the use of renal biopsy to establish a diagnosis.

Adult↗
PubMed2003

The man behind the eponyms: Richard L Sutton: periadenitis mucosa necrotica recurrens (Sutton's ulcer) and leukoderma acquisitum centrifugum-Sutton's (halo) nevus.

Richard L. Sutton described what he termed "periadenitis mucosa necrotica recurrens," now known as major aphthosis or Sutton's ulcer in 1911. He described "leukoderma acquisitum centrifugum" (halo nevus, Sutton's nevus) in 1916. Here, we summarize the 2 publications by Sutton, trace his life story, and comment briefly on these 2 diseases.

Eponyms↗
PubMed2003

The men behind the eponym: Francis E. Senear, Barney Usher, and the Senear-Usher syndrome.

This historical review will summarize the report of Francis Senear and Barney Usher on a disease that they called pemphigus erythematodes and which later became pemphigus erythematosus (the Senear-Usher syndrome). It will then outline the lives of these two men. Finally, it will review the literature on that condition and relate the views of various authorities as to whether pemphigus erythematosus is merely pemphigus foliaceus, a variant of pemphigus foliaceus, a syndrome combining features of lupus erythematosus and pemphigus or whether pemphigus erythematosus (Senear-Usher syndrome) is a distinct and separate disease.

Dermatology↗
PubMed2003

A study on the mineral depletion of the foods available to us as a nation over the period 1940 to 1991.

In 1927 a study at King's College, University of London, of the chemical composition of foods was initiated by Dr McCance to assist with diabetic dietary guidance. The study evolved and was then broadened to determine all the important organic and mineral constituents of foods, it was financed by the Medical Research Council and eventually published in 1940. Over the next 51 years subsequent editions reflected changing national dietary habits and food laws as well as advances in analytical procedures. The most recent (5th Edition) published in 1991 has comprehensively analysed 14 different categories of foods and beverages. In order to provide some insight into any variation in the quality of the foods available to us as a nation between 1940 and 1991 it was possible to compare and contrast the mineral content of 27 varieties of vegetable, 17 varieties of fruit, 10 cuts of meat and some milk and cheese products. The results demonstrate that there has been a significant loss of minerals and trace elements in these foods over that period of time. It is suggested that the results of this study cannot be taken in isolation from recent dietary, environmental and disease trends. These trends are briefly mentioned and suggestions are made as to how the deterioration in the micronutrient quality of our food intake may be arrested and reversed.

Dairy Products↗
PubMed2003

Evaluation of a pilot hands-on course in surgical dentistry for primary care dental practitioners in Oxfordshire.

OBJECTIVES: To evaluate the impact of a course in surgical dentistry on the confidence of 32 general dental practitioners, each of whom attended a one-day hands-on course. DESIGN: Questionnaire survey. SETTING: General dental practitioners attending a course on surgical dentistry, which was run over a day, for eight participants per day. RESULTS: The course was rated highly by participants. The hands-on component was particularly well received. Confidence scores increased for several surgical procedures, particularly for removal of impacted teeth and for apicectomies of single-rooted teeth. There were concomitant decreases in the proportion of participants who said that they would refer patients requiring these surgical procedures. Confidence scores remained low for complex procedures such as molar apicectomies. However, it would be appropriate to refer these cases for specialist care. CONCLUSIONS: The results of this pilot study indicated that a course in surgical dentistry was successful in increasing the confidence of a small group of general dental practitioners. More research is needed to determine whether this is the most effective way of helping practitioners maintain and improve skills and confidence in surgical dentistry.

Apicoectomy↗
PubMed2003

Removal of endotoxin by reverse phase HPLC abolishes anti-endothelial cell activity of bacterially expressed plasminogen kringle 5.

The success of recombinant protein expression/purification in Escherichia coli depends on a high-fidelity system rendering purified proteins free of confounding contaminants such as endotoxin. Here we report on the expression and purification of a cryptic plasminogen-derived domain, kringle 5, which was previously reported to specifically inhibit endothelial cell growth and, therefore, angiogenesis. Using a histidine (HIS)-tag expression and Ni(+)-NTA agarose purification system identical to previous reports, we found that our purified recombinant kringle 5 did inhibit endothelial cell growth, but this activity could not be eradicated by heat denaturing or proteolysis of kringle 5 with various proteases. This led us to suspect the presence of a contaminant in the purified samples. Quantitative endotoxin testing using a limulus amoebocyte lysate assay revealed that all samples purified by Ni(+)-NTA agarose alone harbored high concentrations of endotoxin that could not be removed by additional purification on anion exchange chromatography. Finally, when kringle 5 was rendered endotoxin-free by purification on reverse phase high-performance liquid chromatography (HPLC), there was a complete loss of endothelial cell growth inhibitory activity. These results strongly suggest that endotoxin-free recombinant kringle 5 may not possess anti-angiogenic activity and demonstrates that, especially in angiogenesis type assays, endotoxin contamination can lead to a misinterpretation of results.

Animals↗
PubMed2003

Contraindicated antiretroviral drug combinations.

The proper implementation of combination antiretroviral treatment regimens is fundamental to successful therapeutic outcomes for patients with HIV/AIDS. Unfortunately, some patients are still being prescribed contraindicated antiretroviral regimens that include: 1. stavudine plus zidovudine; 2. Invirase plus two nucleoside analog reverse transcriptase inhibitors (NRTIS); 3. zalcitabine plus didanosine; 4. zalcitabine plus stavudine; and, 5. zalcitabine plus lamivudine. Inappropriate regimens such as these either have limited effectiveness or potential severe toxicity.

Anti-Retroviral Agents↗
PubMed2002

Lack of behavior change after disclosure of hepatitis C virus infection among young injection drug users in Baltimore, Maryland.

We evaluated behavior change after disclosure of a positive hepatitis C virus (HCV) antibody test result among a cohort of young injection drug users (IDUs). Participants underwent semiannual interviews, human immunodeficiency virus (HIV) and HCV antibody testing, and pretest and posttest counseling. We used chi(2) statistics to study changes in the frequencies of high-risk behaviors from baseline to a 6-month follow-up visit among 46 IDUs who had a positive HCV test result and among 60 IDUs who did not have a positive HCV test result or who were unaware of their test result. No significant differences were detected between the 2 groups. Both groups continued to share syringes, needles, and other injection paraphernalia. These findings suggest that young IDUs may not be aware of the risk of HCV infection and highlight the urgent need for post-HCV test guidelines and behavioral interventions to reduce ongoing high-risk behavior that perpetuates the risk of HCV transmission.

Adolescent↗
PubMed2002

Generation of conditional lethal Candida albicans mutants by inducible deletion of essential genes.

The yeast Candida albicans is the most important fungal pathogen of humans and a model organism for studying fungal virulence. Sequencing of the C. albicans genome will soon be completed, allowing systematic approaches to analyse gene function. However, techniques to define and characterize essential genes in this permanently diploid yeast are limited. We have developed an efficient method to create conditional lethal C. albicans null mutants by inducible, FLP-mediated gene deletion. Both wild-type alleles of the CDC42 or the BEM1 gene were deleted in strains that carried an additional copy of the respective gene that could be excised from the genome by the site-specific recombinase FLP. Expression of a C. albicans-adapted FLP gene under the control of an inducible promoter generated cell populations consisting of > or = 99.9% null mutants. Upon plating, these cells were unable to form colonies, demonstrating that CDC42 and BEM1 are essential genes in C. albicans. The cdc42 null mutants failed to produce buds and hyphae and grew as large, round cells instead, suggesting that they lacked the ability to produce polarized cell growth. However, the cells still responded to hyphal inducing signals by aggregating and expressing hypha-specific genes, behaviours typical of the mycelial growth form of C. albicans. Budding cells and germ tubes of bem1 null mutants exhibited morphological abnormalities, demonstrating that BEM1 is essential for normal growth of both yeast and hyphae. Inducible, FLP-mediated gene deletion provides a powerful approach to generate conditional lethal C. albicans mutants and allows the functional analysis of essential genes.

Candida albicans↗
PubMedDate not supplied

Promoting organ donation to Hispanics: the role of the media and medicine.

This study assesses the impact of a paid media advertising campaign employing Spanish language, culturally sensitive television and radio spots airing on major Hispanic stations in southern California. An advertising tracking study with a baseline and three postintervention telephone surveys was conducted from 2001 through 2003 among 500 randomly selected self-identified, primarily Spanish language dominant adult Hispanics. Measures of organ donation attitudes and behaviors (decision and declared intent to donate organs) improved significantly (P < .05) in 2001 and 2002, then leveled off or declined in 2003. Among the reasons given for not making a decision to donate was fear that medical personnel might withhold care from identified organ donors, suggesting lack of knowledge and distrust of the health care system. Few respondents talked to health care professionals or contacted the organ procurement agency for information either before or after the campaign. Findings from this study indicate a need for ongoing public education in the Hispanic community about organ transplantation and donation. Health professionals need to become more engaged in encouraging Hispanic patients to learn about organ transplantation and donation, and to inform their families that they have made the personal decision to donate.

Adult↗
PubMedDate not supplied

Pharmacokinetics of the antimalarial drug, AQ-13, in rats and cynomolgus macaques.

The purpose of this study was to evaluate the bioavailability and pharmacokinetics of a new antimalarial drug, AQ-13, a structural analog of chloroquine (CQ) that is active against CQ-resistant Plasmodium species, in rats and cynomolgus macaques. Sprague-Dawley rats (n = 4/sex) were administered a single dose of AQ-13 intravenously (i.v.) (10 mg/kg) or orally (20 or 102 mg/kg). Blood and plasma samples were collected at several timepoints. AQ-13 achieved C(max) after oral administration at approximately 3 to 4 h and could be detected in blood for 2 to 5 days after oral administration. The ratio of area under the curve (AUC) values at the high and low dose for AQ-13 deviated from an expected ratio of 5.0, indicating nonlinear kinetics. A metabolite peak was noted in the chromatograms that was identified as monodesethyl AQ-13. Oral bioavailability of AQ-13 was good, approximately 70%. The pharmacokinetics of AQ-13 was also determined in cynomolgus macaques after single (i.v., 10 mg/kg; oral, 20 or 100 mg/kg) and multiple doses (oral loading dose of 50, 100, or 200 mg/kg on first day followed by oral maintenance dose of 25, 50, or 100 mg/kg, respectively, for 6 days). The AUC and C(max) values following single oral dose administration were not dose proportional; the C(max) value for AQ-13 was 15-fold higher following an oral dose of 100 mg/kg compared to 20 mg/kg. Monodesethyl AQ-13 was a significant metabolite formed by cynomolgus macaques and the corresponding C(max) values for this metabolite increased only 3.8-fold over the dose range, suggesting that the formation of monodesethyl AQ-13 is saturable in this species. The bioavailability of AQ-13 in cynomolgus macaques following oral administration was 23.8% for the 20-mg/kg group and 47.6% for the 100-mg/kg group. Following repeat dose administration, high concentrations of monodesethyl AQ-13 were observed in the blood by day 4, exceeding the AQ-13 blood concentrations through day 22. Saturation of metabolic pathways and reduced metabolite elimination after higher doses are suggested to play a key role in AQ-13 pharmacokinetics in macaques. In summary, the pharmacokinetic profile and metabolism of AQ-13 are very similar to that reported in the literature for chloroquine, suggesting that this new agent is a promising candidate for further development for the treatment of chloroquine-resistant malaria.

Administration, Oral↗