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Biomedical subjects

D Bentley

Publications and source records attributed to D Bentley.

At least 19 recordsLinked to original sources
PubMed2005

Common VKORC1 and GGCX polymorphisms associated with warfarin dose.

We report a novel combination of factors that explains almost 60% of variable response to warfarin. Warfarin is a widely used anticoagulant, which acts through interference with vitamin K epoxide reductase that is encoded by VKORC1. In the next step of the vitamin K cycle, gamma-glutamyl carboxylase encoded by GGCX uses reduced vitamin K to activate clotting factors. We genotyped 201 warfarin-treated patients for common polymorphisms in VKORC1 and GGCX. All the five VKORC1 single-nucleotide polymorphisms covary significantly with warfarin dose, and explain 29-30% of variance in dose. Thus, VKORC1 has a larger impact than cytochrome P450 2C9, which explains 12% of variance in dose. In addition, one GGCX SNP showed a small but significant effect on warfarin dose. Incorrect dosage, especially during the initial phase of treatment, carries a high risk of either severe bleeding or failure to prevent thromboembolism. Genotype-based dose predictions may in future enable personalised drug treatment from the start of warfarin therapy.

Adult↗
PubMed2005

Specificity of VO2MAX and the ventilatory threshold in free swimming and cycle ergometry: comparison between triathletes and swimmers.

OBJECTIVES: To compare maximal heart rate (HRmax), maximal oxygen consumption (VO2MAX), and the ventilatory threshold (VT; %VO2MAX) during cycle ergometry and free swimming between swimmers and triathletes. METHODS: Nine swimmers and ten triathletes completed an incremental swimming and cycling test to exhaustion. Whole body metabolic responses were determined in each test. RESULTS: The swimmers exhibited a significantly higher VO2MAX in swimming than in cycling (58.4 (5.6) v 51.3 (5.1) ml/kg/min), whereas the opposite was found in the triathletes (53.0 (6.7) v 68.2 (6.8) ml/kg/min). HRmax was significantly different in the maximal cycling and swimming tests for the triathletes (188.6 (7.5) v 174.8 (9.0) beats/min). In the maximal swimming test, HRmax was significantly higher in the swimmers than in the triathletes (174.8 (9.0) v 184.6 (9.7) beats/min). No significant differences were found for VT measured in swimming and cycling in the triathletes and swimmers. CONCLUSION: This study confirms that the exercise testing mode affects the VO2MAX value, and that swimmers have very specific training adaptations even compared with triathletes. This may be a function of acute physiological responses combined with the specialist training status of the different athletes influencing maximal cardiac output or oxygen extraction. In contrast, the different training regimens do not seem to influence the VT, as this variable did not differ between the two testing modes in either group.

Adolescent↗
PubMed2002

The components of the "critical quartet" log Kow values assessed by four commercial software packages.

Partition coefficient (log Kow) values of 103 compounds in four different solvent-water systems (alkane-water, octanol-water, chloroform-water and propylene glycol dipelargonate (PGDP)-water--the "critical quartet") were published by Leahy et al. (1992). J. Chem. Soc. Perkin Trans. 2, pp. 723-731. They used the Abraham LSER (linear solvation energy relationship) descriptors to model the log Kow values in the four systems. The calculation of Abraham LSER descriptors has now been computerized in the ABSOLV program, and we have used ABSOLV, and three other commercial software packages (HYBOT-PLUS, Molecular Modeling Pro and QsarIS) that calculate descriptors of similar classes, to model partitioning in the four solvent-water systems. Stepwise regression selected broadly similar types of descriptor from each software package to model logKow values in each solvent-water system. Overall, HYBOT-PLUS gave the best results. The rĵle of the various classes of descriptor (size, polarity, polarizability, hydrogen bonding) in modeling partitioning in the four different solvent-water systems is discussed.

Forecasting↗
PubMed2001

Regulation of the stem cell leukemia (SCL) gene: a tale of two fishes.

The stem cell leukemia (SCL) gene encodes a tissue-specific basic helix-loop-helix (bHLH) protein with a pivotal role in hemopoiesis and vasculogenesis. Several enhancers have been identified within the murine SCL locus that direct reporter gene expression to subdomains of the normal SCL expression pattern, and long-range sequence comparisons of the human and murine SCL loci have identified additional candidate enhancers. To facilitate the characterization of regulatory elements, we have sequenced and analyzed 33 kb of the SCL genomic locus from the pufferfish Fugu rubripes, a species with a highly compact genome. Although the pattern of SCL expression is highly conserved from mammals to teleost fish, the genes flanking pufferfish SCL were unrelated to those known to flank both avian and mammalian SCL genes. These data suggest that SCL regulatory elements are confined to the region between the upstream and downstream flanking genes, a region of 65 kb in human and 8.5 kb in pufferfish. Consistent with this hypothesis, the entire 33-kb pufferfish SCL locus directed appropriate expression to hemopoietic and neural tissue in transgenic zebrafish embryos, as did a 10.4-kb fragment containing the SCL gene and extending to the 5' and 3' flanking genes. These results demonstrate the power of combining the compact genome of the pufferfish with the advantages that zebrafish provide for studies of gene regulation during development. Furthermore, the pufferfish SCL locus provides a powerful tool for the manipulation of hemopoiesis and vasculogenesis in vivo.

Amino Acid Sequence↗
PubMed2001

Initial sequencing and analysis of the human genome.

The human genome holds an extraordinary trove of information about human development, physiology, medicine and evolution. Here we report the results of an international collaboration to produce and make freely available a draft sequence of the human genome. We also present an initial analysis of the data, describing some of the insights that can be gleaned from the sequence.

Animals↗
PubMed2001

A SNP resource for human chromosome 22: extracting dense clusters of SNPs from the genomic sequence.

The recent publication of the complete sequence of human chromosome 22 provides a platform from which to investigate genomic sequence variation. We report the identification and characterization of 12,267 potential variants (SNPs and other small insertions/deletions) of human chromosome 22, discovered in the overlaps of 460 clones used for the chromosome sequencing. We found, on average, 1 potential variant every 1.07 kb and approximately 18% of the potential variants involve insertions/deletions. The SNPs have been positioned both relative to each other, and to genes, predicted genes, repeat sequences, other genetic markers, and the 2730 SNPs previously identified on the chromosome. A subset of the SNPs were verified experimentally using either PCR-RFLP or genomic Invader assays. These experiments confirmed 92% of the potential variants in a panel of 92 individuals. [Details of the SNPs and RFLP assays can be found at http://www.sanger.ac.uk and in dbSNP.]

Base Composition↗
PubMed2000

Dynamic association of capping enzymes with transcribing RNA polymerase II.

The C-terminal heptad repeat domain (CTD) of RNA polymerase II (pol II) is proposed to target pre-mRNA processing enzymes to nascent pol II transcripts, but this idea has not been directly tested in vivo. In vitro, the yeast mRNA capping enzymes Ceg1 and Abd1 bind specifically to the phosphorylated CTD. Here we show that yeast capping enzymes cross-link in vivo to the 5' ends of transcribed genes and that this localization requires the CTD. Both the extent of CTD phosphorylation at Ser 5 of the heptad repeat and the binding of capping enzymes decreased as polymerase moved from the 5' to the 3' ends of the ACT1, ENO2, TEF1, GAL1, and GAL10 genes. Ceg1 is released early in elongation, but Abd1 can travel with transcribing pol II as far as the 3' end of a gene. The CTD kinase, Kin28, is required for binding, and the CTD phosphatase, Fcp1, is required for dissociation of capping enzymes from the elongation complex. CTD phosphorylation and dephosphorylation therefore control the association of capping enzymes with pol II as it transcribes a gene.

Cyclin-Dependent Kinases↗
PubMed2000

Genomic sequence and transcriptional profile of the boundary between pericentromeric satellites and genes on human chromosome arm 10q.

The organization of centromeric heterochromatin has been established in a number of eucaryotes but remains poorly defined in human. Here we present 1025 kb of contiguous human genomic sequence which links pericentromeric satellites to the RET proto-oncogene in 10q11.2 and is presumed to span the transition from centric heterochromatin to euchromatin on this chromosome arm. Two distinct domains can be defined within the sequence. The proximal approximately 240 kb consists of arrays of satellites and other tandem repeats separated by tracts of complex sequence which have evolved by pericentromeric-directed duplication. Analysis of 32 human paralogues of these sequences indicates that most terminate at or within repeat arrays, implicating these repeats in the interchromosomal duplication process. Corroborative PCR-based analyses establish a genome-wide correlation between the distribution of these paralogues and the distribution of satellite families present in 10q11. In contrast, the distal approximately 780 kb contains few tandem repeats and is largely chromosome specific. However, a minimum of three independent intrachromosomal duplication events have resulted in >370 kb of this sequence sharing >90% identity with sequences on 10p. Using computer-based analyses and RT-PCR we confirm the presence of three genes within the sequence, ZNF11/33B, KIAA0187 and RET, in addition to five transcripts of unknown structure. All of these transcribed sequences map distal to the satellite arrays. The boundary between satellite-rich interchromosomally duplicated DNA and chromosome-specific DNA therefore appears to define a transition from pericentromeric heterochromatin to euchromatin on the long arm of this chromosome.

Centromere↗
PubMed1999

Hybrid (BDBB) interferon-alpha: preformulation studies.

A number of techniques, including RP-HPLC, HP-SEC and SDS-PAGE have been used in the delineation of degradative mechanisms of recombinant hybrid (BDBB) interferon-alpha (IFN-alpha) in the solution phase. Different degradation profiles are found according to medium pH. At pH 4.0 the major routes of degradation are via chemical transformation of the monomeric protein to a species which retains antiviral activity, and by self-proteolytic hydrolysis. At pH 7.6, methionine-oxidation is the major chemical degradative process. Protein aggregation is also a significant route of degradation at the higher pH. The results have assisted in a targeted preformulation screen of potentially stabilising excipients and possible parenteral solution dosage forms have been identified. Preliminary 'real-time' storage data confirm excellent chemical and physical stability of IFN-alpha in vehicles formulated at pH 7.6 or, especially, pH 4.0 under the proposed shelf conditions.

Chemistry, Pharmaceutical↗
PubMed1999

Induction of filopodia by direct local elevation of intracellular calcium ion concentration.

In neuronal growth cones, cycles of filopodial protrusion and retraction are important in growth cone translocation and steering. Alteration in intracellular calcium ion concentration has been shown by several indirect methods to be critically involved in the regulation of filopodial activity. Here, we investigate whether direct elevation of [Ca2+]i, which is restricted in time and space and is isolated from earlier steps in intracellular signaling pathways, can initiate filopodial protrusion. We raised [Ca2+]i level transiently in small areas of nascent axons near growth cones in situ by localized photolysis of caged Ca2+ compounds. After photolysis, [Ca2+]i increased from approximately 60 nM to approximately 1 microM within the illuminated zone, and then returned to resting level in approximately 10-15 s. New filopodia arose in this area within 1-5 min, and persisted for approximately 15 min. Elevation of calcium concentration within a single filopodium induced new branch filopodia. In neurons coinjected with rhodamine-phalloidin, F-actin was observed in dynamic cortical patches along nascent axons; after photolysis, new filopodia often emerged from these patches. These results indicate that local transient [Ca2+]i elevation is sufficient to induce new filopodia from nascent axons or from existing filopodia.

Actins↗
PubMed1999

Coupling RNA polymerase II transcription with pre-mRNA processing.

How are transcription and processing of mRNA precursors co-ordinated? The past two years has witnessed exciting insights into the mechanism which targets the mRNA processing machinery to RNA polymerase II (pol II) transcription complexes and closely integrates processing with transcription. Protein-protein contacts have been discovered between the pol II transcription machinery and RNA processing factors; furthermore, a unique domain of pol II has been identified that not only recruits processing factors but also controls their activity.

Animals↗
PubMed1999

CE marking--what does it really mean?

Compliance with the Medical Devices Directive (93/42/EEC) became compulsory for all medical devices placed on the European market in June 1998. Under the directive, manufacturers are required to fulfil a number of requirements leading to the placing of the CE mark on their devices. However, many questions still remain. Not all manufacturers are aware of their responsibilities and not all purchasers are aware of the true meaning of the CE mark. It is vital to understand the purpose of the regulations, the definition of 'medical device', the importance of complying with the manufacturer's intended purpose and instructions, the role of quality systems and clinical investigations in the compliance process, and the decisions which may be made by the manufacturers. It is also important to realise that whilst the directive, if correctly applied and enforced, brings benefits to the medical industry and patients, it is not a substitute for professional judgement in the purchasing process.

Consumer Product Safety↗