Search PubMed⌕ Search

Biomedical subjects

R Brown

Publications and source records attributed to R Brown.

At least 73 records · Page 4Linked to original sources
PubMed2002

Aberrant DNA methylation in cancer: potential clinical interventions.

DNA methylation, the addition of a methyl group to the carbon-5 position of cytosine residues, is the only common covalent modification of human DNA and occurs almost exclusively at cytosines that are followed immediately by a guanine (so-called CpG dinucleotides). The bulk of the genome displays a clear depletion of CpG dinucleotides, and those that are present are nearly always methylated. By contrast, small stretches of DNA, known as CpG islands, are comparatively rich in CpG nucleotides and are nearly always free of methylation. These CpG islands are frequently located within the promoter regions of human genes, and methylation within the islands has been shown to be associated with transcriptional inactivation of the corresponding gene. Alterations in DNA methylation might be pivotal in the development of most cancers. In recent years, it has become apparent that the pattern of DNA methylation observed in cancer generally shows a dramatic shift compared with that of normal tissue. Although cancers often exhibit clear reductions throughout their genomes in the levels of DNA methylation, this goes hand-in-hand with increased methylation at the CpG islands. Such changes in methylation have a central role in tumourigenesis; in particular, methylation of CpG islands has been shown to be important in transcriptional repression of numerous genes that function to prevent tumour growth or development. Studies of DNA methylation in cancer have thus opened up new opportunities for diagnosis, prognosis and ultimately treatment of human tumours.

Animals↗
PubMed2002

Nitric oxide modulates and adenosine mediates the tubuloglomerular feedback mechanism.

The tubuloglomerular feedback (TGF) mechanism is an important regulator of the glomerular filtration rate (GFR) and urine excretion rate. It operates by sensing the distal delivery of fluid at the macula densa site and adjusting the tone of the glomerular arterioles to control GFR. We found evidence that nitric oxide is an important modulator of the setting of the sensitivity of the TGF mechanism. Studies on adenosine A1 receptor deficient mice have shown that these animals lack the TGF response and have an increased renin release. These findings show the important role of adenosine as a mediator of the signal for the TGF mechanism and as an inhibitor of renin release.

Adenosine↗
PubMed2002

Detection of toxin production in Clostridium difficile strains by three different methods.

OBJECTIVE: To compare two immunoassays for detection of toxins produced in vitro by isolates of Clostridium difficile with the standard tissue culture assay, to help in the diagnosis of C. difficile-associated diarrhoea. METHODS: Toxin production was investigated in 42 strains of C. difficile of various serotypes, ribotypes and S-protein types. These included strains from our laboratory collection, strains freshly isolated from stool specimens of patients suspected of suffering from C. difficile-associated disease or of carrying it asymptomatically, and one reference strain (NCTC 11223). Toxin was assayed by (i) a rapid slide immunoassay (C. difficile toxin A test, Clearview, Oxoid), (ii) an enzyme-linked microplate immunoassay (C. difficile toxin A/B test, Techlab), and (iii) a tissue culture assay. The rapid slide assay and the enzyme immunoassay were performed according to the manufacturers' recommendations. The tissue culture assay was performed using Vero cells. RESULTS: Thirty of the 42 strains (71%) were shown to be positive for toxin A by the slide immunoassay and 34 of the strains (81%) were found to be toxin A/B producers by the enzyme immunoassay. The same 34 strains that were positive in the enzyme immunoassay also produced toxin B (cytotoxin) in the tissue culture assay. The sensitivity, specificity, and positive and negative predictive values for the rapid slide immunoassay method were calculated to be 88.2%, 100.0%, 100.0% and 66.7%, respectively, when compared to tissue culture assay results as the reference method. These values for the enzyme immunoassay method were all 100.0%. In this study eight strains were found to be non-toxin-producing by all methods. It is possible that there were four strains that only produced toxin B (A- B+), and were missed by the rapid A-only assay. CONCLUSIONS: We can recommend the use of the Techlab A + B enzyme immunoassay for the detection of toxin production by C. difficile strains because of its high sensitivity and specificity, its ease of use, and its capability of detecting both A- and B-type toxins.

Animals↗
PubMed2002

Low-dose (550 cGy), single-exposure total body irradiation and cyclophosphamide: consistent, durable engraftment of related-donor peripheral blood stem cells with low treatment-related mortality and fatal organ toxicity.

On the basis of observations of dog models and from earlier studies with humans, we hypothesized that a low-dose (550 cGy) TBI-based conditioning regimen would result in sustained engraftment of HLA-matched sibling peripheral blood stem cells (PBSC) with low treatment-related mortality (TRM) and low serious organ toxicity if the TBI was given as a single dose and at a high dose rate. The regimen included 550 cGy TBI administered as a single dose at 30 cGy/min and cyclophosphamide. Cyclosporine was given as GVHD prophylaxis. Twenty-seven good-risk (acute leukemia in first remission and chronic-phase chronic myelogenous leukemia) and 53 poor-risk (other) patients were accrued. Complete donor engraftment occurred in 93% to 100% of evaluable patients at each scheduled assessment and was durable through 4 years. Mixed chimerism (50% to 98% donor) was observed in 9 patients (11%). Without further intervention, all patients had complete donor engraftment on subsequent assessments. Graft failure did not occur. TRM through at least 2 years was 7% in the good-risk and 19% in the poor-risk diagnostic groups. Grade 4 (fatal) organ toxicity occurred in only 2 patients (2.5%). Other causes of TRM included infection and GVHD. Median follow-up for the surviving patients was 1234 days (range, 780-1632 days). Current status includes 39 patients (49%) alive and in complete remission, 2 alive in relapse, and 39 dead. Relapse occurred in 15% of the good-risk group and 45% of the poor-risk group. The Kaplan-Meier estimates of 3-year disease-free and overall survival of the good-risk group were 77% and 85%, respectively, and of the poor-risk group were 34% and 36%, respectively. Low-dose (550 cGy), single-exposure TBI given at a high dose rate with cyclophosphamide resulted in consistent durable engraftment of HLA-matched sibling PBSC with a low risk of fatal organ toxicity and TRM.

Adolescent↗
PubMed2002

Malignant hyperthermia associated with exercise-induced rhabdomyolysis or congenital abnormalities and a novel RYR1 mutation in New Zealand and Australian pedigrees.

Malignant hyperthermia (MH) is rarely associated with specific myopathies or musculoskeletal abnormalities. Three clinical investigations of MH associated with either non-specific myopathies or congenital disorders in three separate families are presented. Two of these cases also show evidence of exercise-induced rhabdomyolysis. In each case MH susceptibility was confirmed by in vitro contracture testing of quadriceps muscle. DNA sequence analysis of each kindred revealed the presence of a common novel mutation that results in an arginine401-cysteine substitution in the skeletal muscle ryanodine receptor gene (RYR1). Haplotype analysis using chromosome 19q markers indicated that the three families are likely to be unrelated, providing confirmation that the MH/central core disease region 1 of RYR1 is a mutation hot spot.

Amino Acid Sequence↗
PubMed2001

10-year experience of injuries sustained during clearance of anti-personnel mines.

Clearance of anti-personnel mines and unexploded ordnance in countries recovering from war usually continues long after conflict has ceased. We prospectively recorded 92 traumatic injuries sustained by 73 mineclearers working in seven countries over a period of 10 years. 15% of injuries were fatal, with an incidence of 116 injuries per 100000 workers per year. Limb injury occurred in 59% of cases, with an overall amputation rate of 30%. 44% of injuries were sustained by workers handling a mine, resulting in severe upper limb and facial injuries. The incidence of facial injuries fell after the introduction of visors.

Adult↗
PubMed2001

Hydrocarbon carcinogens induce p53 activity in normal mouse tissue.

Previous studies led to the suggestion that a sub class of hydrocarbon carcinogens have the capacity of damage DNA and evade normal cellular defence mechanisms. To examine the ability of hydrocarbon carcinogens to induce p53 transcriptional activity in normal tissues, we have used transgenic mice in which LacZ transgene is driven by a p53 response element. We demonstrate that transcriptionally active p53 is induced in normal tissue after exposure to putative stealth carcinogens in an identical manner to non-stealth agents.

Animals↗
PubMed2001

Purified poloxamer 188 for treatment of acute vaso-occlusive crisis of sickle cell disease: A randomized controlled trial.

CONTEXT: Sickle cell disease (SCD) can cause severe painful episodes that are often thought to be caused by vaso-occlusion. The current therapy for these uncomplicated painful episodes includes hydration, oxygen, and analgesics. Purified poloxamer 188 may increase tissue oxygenation and thereby reduce inflammation, pain, and the overall duration of such painful episodes in patients with SCD. OBJECTIVE: To compare the duration of painful episodes in patients with SCD treated with purified poloxamer 188 to that of similar episodes experienced by patients who receive a placebo. DESIGN AND SETTING: Randomized, double-blind, placebo-controlled, intention-to-treat trial conducted between March 1998 and October 1999 in 40 medical centers in the United States. PARTICIPANTS: Two hundred fifty-five patients with SCD (aged 9-53 years) who had a painful episode sufficiently severe to require hospitalization and narcotic analgesics. INTERVENTION: Patients were randomly assigned to receive an intravenous infusion of purified poloxamer 188, 100 mg/kg for 1 hour followed by 30 mg/kg per hour for 47 hours (n = 127), or a matching volume of saline placebo (n = 128). MAIN OUTCOME MEASURE: Duration of the painful episode, from randomization to crisis resolution. RESULTS: Mean (SD) duration of the painful episodes was 141 (42) hours in the placebo group compared with 133 (41) hours in those treated with purified poloxamer 188, a 9-hour reduction (P =.04). Subset analyses indicated an even more pronounced purified poloxamer 188 effect in children aged 15 years or younger (21 hours; P =.01) and in patients who were receiving hydroxyurea (16 hours; P =.02). Finally, the proportion of patients achieving crisis resolution was increased by purified poloxamer 188 (65/126 [52%] vs 45/123 [37%]; P =.02). Similar results were observed in children aged 15 years or younger (22/37 [60%] vs 10/36 [28%]; P =.009) and in patients who were also receiving hydroxyurea (12/26 [46%] vs 4/28 [14%]; P =.02). CONCLUSIONS: A decrease in the duration of painful episodes and an increase in the proportion of patients who achieved resolution of the symptoms were observed when the purified poloxamer 188-treated patients were compared with the patients receiving placebo. However, the difference between these groups was significant but relatively small. In subgroup analysis, a more significant effect on both parameters was observed in children and in patients who were receiving concomitant hydroxyurea. It is important to confirm both of these observations in further prospective trials.

Adolescent↗
PubMed2001

Purging of autologous peripheral-blood stem cells using CD34 selection does not improve overall or progression-free survival after high-dose chemotherapy for multiple myeloma: results of a multicenter randomized controlled trial.

PURPOSE: Although high-dose chemotherapy supported by autologous peripheral-blood progenitor-cell (PBPC) transplantation improves response rates and survival for patients with multiple myeloma, all patients eventually develop progressive disease after transplantation. It has been hypothesized that depletion of malignant plasma cells from autografts may improve outcome by reducing infused cells contributing to relapse. PATIENTS AND METHODS: A randomized phase III study using the CEPRATE SC System (Cellpro, Bothell, WA) to enrich CD34(+) autograft cells and passively purge malignant plasma cells was completed in 190 myeloma patients randomized to receive an autograft of CD34-selected or unselected PBPCs. RESULTS: After CD34 selection, tumor burden was reduced by 1.6 to 6.0 logs (median, 3.1), with 54% of CD34-enriched products having no detectable tumor. Median time to count recovery, number of transfusions, transplantation-related mortality, and days in hospital were equivalent between the two transplantation arms. With a median follow-up of 37 months, 33 patients (36%) in the selected and 34 patients (35%) in the unselected arm had died (P =.784). Median overall survival in the selected arm was reached at 50 months and is not reached at this time in the unselected arm (P =.78). Median disease-free survival was 100 versus 104 weeks (P =.82), with 67% of patients in the selected arm and 66% of patients in the unselected arm relapsing. CONCLUSION: This phase III trial demonstrates that although CD34 selection significantly reduces myeloma cell contamination in PBPC collections, no improvement in disease-free or overall survival was achieved.

Adult↗
PubMed2001

Polyglutamine expansions cause decreased CRE-mediated transcription and early gene expression changes prior to cell death in an inducible cell model of Huntington's disease.

Huntington's disease (HD) is one of 10 known diseases caused by a (CAG)(n) trinucleotide repeat expansion that is translated into an abnormally long polyglutamine tract. We have developed stable inducible neuronal (PC12) cell lines that express huntingtin exon 1 with varying CAG repeat lengths under doxycycline (dox) control. The expression of expanded repeats is associated with aggregate formation, caspase-dependent cell death and decreased neurite outgrowth. Post-mitotic cells expressing mutant alleles were more prone to cell death compared with identical cycling cells. To determine early metabolic changes induced by this mutation in cell models, we studied changes in gene expression after 18 h dox induction, using Affymetrix arrays, cDNA filters and adapter-tagged competitive PCR (ATAC-PCR). At this time point there were low rates of inclusion formation, no evidence of mitochondrial compromise and no excess cell death in the lines expressing expanded compared with wild-type repeats. The expression profiles suggest novel targets for the HD mutation and were compatible with impaired cAMP response element (CRE)-mediated transcription, which we confirmed using CRE-luciferase reporter assays. Reduced CRE-mediated transcription may contribute to the loss of neurite outgrowth and cell death in polyglutamine diseases, as these phenotypes were partially rescued by treating cells with cAMP or forskolin.

Animals↗
PubMed2001

The stability of gold iodides in the gas phase and the solid state.

The stability of gold iodides in the oxidation state +I and +III is investigated at the ab initio and density functional level using relativistic and nonrelativistic energy-adjusted pseudopotentials for gold and iodine. The calculations reveal that relativistic effects stabilize the higher oxidation state of gold as expected, that is Au2I6 is thermodynamically stable at the relativistic level, whilst at the nonrelativistic level the complex of two iodine molecules weakly bound to both gold atoms in Au2I2 is energetically preferred. The rather low stability of AuI3 with respect to dissociation into AuI and I2 will make it difficult to isolate this species in the solid state as (possibly) Au2I6 or detect it by matrix-isolation techniques. The monomer AuI3 is Jahn-Teller distorted from the ideal trigonal planar (D3h) form, but adopts a Y-shaped structure (in contrast to AuF3 and AuCl3), and in the nonrelativistic case can be described as I2 weakly bound to AuI. Relativistic effects turn AuI3 from a static Jahn-Teller system to a dynamic one. For the yet undetected gas-phase species AuI accurate coupled-cluster calculations for the potential energy curve are used to predict vibrational-rotational constants. Solid-state density functional calculations are performed for AuI and Au2I6 in order to predict cohesive energies.

Journal Article↗
PubMed2001

Differences in the human and mouse amino-terminal leader peptides of ornithine transcarbamylase affect mitochondrial import and efficacy of adenoviral vectors.

Mouse models of ornithine transcarbamylase (OTC) deficiency are being used to test the efficacy of viral vectors as possible vehicles for gene therapy. However, it has been demonstrated that virus containing the human OTC cDNA failed to express functional OTC enzyme in the recipient animals. Because functional OTC is assembled as a homotrimer in the mitochondria, there are at least two possible explanations for these results. Either endogenous mutant protein coassembles with the human OTC and has a "dominant-negative effect," or the human version of the protein is not appropriately imported or processed in the mouse mitochondria. To test the importance of processing, which in rodents is thought to depend on the leader peptide, adenoviral vectors containing chimeric OTC cDNAs were prepared. These vectors were evaluated in the OTC-deficient sparse fur mouse models. Although comparable levels of transgene expression were observed in all groups of mice, the only mice that had high levels of OTC activity and mitochondrial OTC immunoreactivity were those mice injected with the vectors containing the mouse leader peptide (mouse OTC and a mouse-human chimera of OTC). To address possible dominant-negative effects, adenoviruses containing mutant human or mouse OTC cDNAs were prepared and evaluated in cell lines or normal C3H mice, respectively. No inhibition of normal OTC activity was observed in either model system. Together, these studies provide no evidence of a dominant-negative effect and suggest that the human and rodent enzymes responsible for transporting of OTC and possibly other mitochondrial proteins have different specificity.

Adenoviridae↗
PubMed2001

A role for mismatch repair in control of DNA ploidy following DNA damage.

Many reports have shown a link between mismatch repair (MMR) deficiency and loss of normal cell cycle control, particularly loss of G2 arrest. However almost all of these studies utilized transformed cell lines, and thus the involvement of other genes in this phenotype cannot be excluded. We have examined the effects of cisplatin treatment on primary embryo fibroblasts (MEFs) derived from mice in which the MMR gene Msh2 had been inactivated (Msh2(-/-)). This analysis determined that both primary Msh2(-/-) and wild type (WT) fibroblasts exhibited an essentially identical G2 arrest following cisplatin treatment. Similarly, we observed a cisplatin-induced G2 arrest in immortalized MMR deficient (Mlh1(-/-) and Pms2(-/-)) and WT MEFs. p53 deficient primary MEFs (p53(-/-)) exhibited both a clear G2 arrest and an increase in cells with a DNA content of 8N in response to cisplatin. When the Msh2 and p53 defects were combined (p53(-/-)/Msh2(-/-)) the G2 arrest was essentially identical to the p53(-/-) fibroblasts. However, the p53(-/-)/Msh2(-/-) fibroblasts demonstrated a further increase in cells with an 8N DNA content, above that seen in the p53(-/-) fibroblasts. These results suggest that loss of MMR on its own is not enough to overcome G2 arrest following exposure to cisplatin but does play a role in preventing polyploidization, or aberrant DNA reduplication, in the absence of functional p53.

Animals↗
PubMed2001

Identification of a novel stretch-responsive skeletal muscle gene (Smpx).

Skeletal muscle is able to respond to a range of stimuli, including stretch and increased load, by increasing in diameter and length in the absence of myofiber division. This type of cellular growth (hypertrophy) is a highly complex process involving division of muscle precursor cells (myoblasts) and their fusion to existing muscle fibers as well as increased protein synthesis and decreased protein degradation. Underlying the alterations in protein levels are increases in a range of specific mRNAs including those coding for structural proteins and proteins that regulate the hypertrophic process. Seven days of passive stretch in vivo of tibialis anterior (TA) muscle has been shown to elicit muscle hypertrophy. We have identified a cDNA corresponding to an mRNA that exhibits increased expression in response to 7 days of passive stretch imposed on TA muscles in vivo. This 944-bp novel murine transcript is expressed primarily in cardiac and skeletal muscle and to a lesser extent in brain. Translation of the transcript revealed an open reading frame of 85 amino acids encoding a nuclear localization signal and two overlapping casein kinase II phosphorylation sites. This gene has been called "small muscle protein (X chromosome)" (Smpx; HGMW-approved human gene symbol SMPX) and we hypothesize that it plays a role in skeletal muscle hypertrophy.

Amino Acid Sequence↗
PubMed2001

Discussing adjuvant cancer therapy.

PURPOSE: To document the adequacy of patient information in oncology consultations concerning adjuvant therapy and explore predictors of physician communication patterns, treatment decisions, patient information recall, and satisfaction. PATIENTS AND METHODS: Retrospective analysis of audiotapes and verbatim transcripts of 101 initial adjuvant therapy consultations with medical and radiation oncologists was undertaken. Content analysis, data on communication patterns, treatment decisions, patient anxiety, satisfaction, and information recall were collected. Predictors of physician communication, treatment decisions, recall, and satisfaction with the consultation were identified. RESULTS: The majority of patients were well informed of their prognosis, benefits and risks of therapy, and alternative management options. Only half were asked about preferences for information or decision-making involvement. Predictors of information detail given include patient sex, age, occupation, and education. Radiation and medical oncologists express prognosis and treatment benefit using similar phrases. When offered the chance to delay decision-making, most patients do so (P <.01). Final treatment decisions appear to be influenced by the presentation of choice in treatment options by the oncologist and whether the treatment decision was made during the initial consultation (P <.01). Information recall was not influenced by communication factors. Patients receiving less detailed information had slightly higher satisfaction with the consultation (P =.03). More anxious patients tended to be less satisfied (P =.07). CONCLUSION: The optimal way to discuss adjuvant therapy is undefined. More emphasis can be placed on soliciting patient preferences for information and decision-making involvement and tailoring both to the needs of the individual patient. Providing choice in treatment and delaying decision-making may affect the patient's treatment decision.

Adult↗