Search PubMed⌕ Search

Biomedical subjects

B Chan

Publications and source records attributed to B Chan.

At least 91 records · Page 5Linked to original sources
PubMed1993

Organizational and administrative factors influencing the adoption of consortia programs by rural hospitals.

This study was designed to assess the effects of various hospital and environmental characteristics on the involvement of rural hospitals in forming and governing consortia and adopting consortia programs. The study focused on the 127 hospitals that are members of the nine rural consortia developed by grants from the Robert Wood Johnson Foundation during 1989 under its Hospital-Based Rural Hospital Consortia Program. Hospital involvement in the formation and governance of the consortia was found to be far less than expected for these grass-roots organizations. Only 38 percent of the administrators said that their hospitals were involved in developing the consortia, and 44 percent said that they played a role in determining the program menu. Governing board and medical staff involvement was even more limited. Program adoption rates were found to be related to both the types of programs offered by the consortia and the characteristics of the hospitals. In general, greater involvement of physicians and governing board members in hospital decisions was found to enhance program adoption rates, but the influence varied by type of involvement in the hospital and program content.

Chief Executive Officers, Hospital↗
PubMed1992

Structural and functional characterisation of recombinant human haemoglobin A expressed in Saccharomyces cerevisiae.

Recombinant human HbA, produced by co-expressing alpha-globin and beta-globin chains in the yeast Saccharomyces cerevisiae, has been characterised extensively both physically and functionally. Structural studies using N-terminal sequence analysis, peptide mapping, amino acid composition analysis and electrospray MS demonstrated that the recombinant protein was identical to standard HbA purified from erythrocytes. The functional properties of the recombinant protein were assessed using equilibrium and kinetic measurements of oxygen and carbon monoxide binding. The oxygen-binding studies demonstrated that the yeast-derived HbA behaved as a fully functional, cooperative tetramer (Hill coefficient, 2.9), exhibited a normal Bohr effect and response to phosphate, and displayed a rate of oxygen dissociation identical to that of the native human molecule. The recombinant protein also showed the same characteristics of carbon monoxide combination as the standard protein. These studies demonstrate that yeast provides an ideal system for the production of Hb for structural and functional analysis and a potentially useful source of HbA for formulation into a Hb-based oxygen carrier.

Amino Acids↗
PubMed1991

Denervation of transplanted porcine lung causes airway obstruction.

Lung transplantation can be complicated by a form of small airway obstruction known as bronchiolitis obliterans. We tested the hypothesis that lung denervation causes small airway obstruction in young pigs (10 +/- 1 weeks). Control pigs had an innervated native lobe, and study pigs had either a denervated native lobe or a denervated transplant lobe. Transplanted pigs received standard immunosuppression. At 10 weeks we measured isolated left lobe pulmonary mechanics. Dynamic resistance in both study groups was significantly higher than in the lobectomy group, whereas dynamic compliance in both study groups was significantly lower than in the lobectomy group. No significant difference in resistance or compliance was noted between the transplant and reimplant groups. Histologic changes consistent with rejection were noted in the transplant lobes. We conclude that the small airway obstruction noted in this model is due to operative denervation rather than to immunosuppression or rejection.

Animals↗
PubMed1990

The organization of open complexes between Escherichia coli RNA polymerase and DNA fragments carrying promoters either with or without consensus -35 region sequences.

Transcription initiation at the Escherichia coli galP1 promoter does not depend on specific nucleotide sequences in the -35 region. Footprint analysis of transcriptionally competent complexes between E. coli RNA polymerase and DNA fragments carrying galP1 shows that RNA polymerase protects sequences as far upstream as -55, whereas sequences around the -35 region are exposed. In contrast, with galP1 derivatives carrying -35 region sequences resembling the consensus, RNA polymerase protects bases as far as -45, and the -35 region is fully protected. Taken together, our data suggest that the overall architecture of RNA polymerase-promoter complexes can vary according to whether or not consensus -35 region sequences are present; in the absence of these sequences, open complex formation requires distortion of the promoter DNA. However, the unwinding of promoter DNA around the transcription start is not affected by the nature of the -35 region sequence. With a galP1 derivative carrying point mutations in the spacer region that greatly reduce promoter activity, the protection of bases by RNA polymerase around the -10 sequence and transcription start site is reduced. In contrast, protection of the region upstream of -25 is unaffected by the spacer mutations, although sequences from -46 to -54 become hypersensitive to attack by potassium permanganate, indicating severe distortion or kinking of this zone. We suggest that, with this galP1 derivative, RNA polymerase is blocked in a complex that is an intermediate on the path to open complex formation.

Base Sequence↗
PubMed1990

Unwinding of duplex DNA during transcription initiation at the Escherichia coli galactose operon overlapping promoters.

We have used potassium permanganate as a probe to detect DNA duplex unwinding in vitro, in open complexes between E. coli RNA polymerase and DNa fragments carrying the E. coli galactose operon regulatory region. This zone contains 3 overlapping promoters which specify transcription initiation at 3 distinct startpoints. We have used mutant gal derivatives carrying different single point mutations, each of which allows initiation from only one of the 3 start sites. This has allowed us to compare duplex unwinding in open complexes at the 3 different promoters, and to show that the extent of the unwinding is similar in each case. Further, the pattern of DNA modification by potassium permanganate suggests a model for discrimination between the upper and lower strands. Finally, we show that DNA modification by potassium permanganate at the gal promoters is the same in vivo as in vitro.

Base Sequence↗
PubMed1990

Comparison of promoter activities in Escherichia coli and Pseudomonas aeruginosa: use of a new broad-host-range promoter-probe plasmid.

The broad-host-range plasmid, pRW2, is a derivative of pRK 2501 carrying the Escherichia coli lac operon without a promoter, downstream of a polylinker sequence. We have cloned a number of DNA fragments carrying promoters into this plasmid and measured promoter activity in both E. coli and Pseudomonas aeruginosa. Promoters carrying consensus -10 and -35 sequences were active in both backgrounds and the dependence of activity on the nucleotide sequence of the 35 region was the same in both cases. We also measured the activity of two promoters at which transcription in E. coli was totally dependent on the E. coli activators CRP and FNR: both promoters were found to be active in P. aeruginosa.

Base Sequence↗
PubMed1989

Recognition of nucleotide sequences at the Escherichia coli galactose operon P1 promoter by RNA polymerase.

Specific nucleotide (nt) sequences in the -35 region are not essential for galP1 promoter activity, whereas nt sequences in the spacer region are needed for transcription initiation: a G:C base pair at nt -14 and sequences upstream from this position are necessary. In the absence of these sequences, transcription initiation is dependent on the insertion of oligodeoxyribonucleotides carrying -35 region consensus hexamer sequences. Additionally, for maximal promoter activity, specific sequences just upstream from nt -49 are required. Because galP1 carries no sequence resembling the -35 region consensus hexamer, we propose that recognition by RNA polymerase proceeds via an unusual mechanism involving contacts upstream from the -10 hexamer, distortion of the spacer region and a contact upstream from nt -49.

Base Sequence↗
PubMed1989

Macrophage/monocyte receptor for nonenzymatically glycosylated protein is upregulated by cachectin/tumor necrosis factor.

Proteins of extracellular matrix undergo over time multiple reactions with glucose to form advanced glycosylation endproducts (AGEs) which are highly active in protein crosslinking, and have been implicated in tissue damage associated with aging and diabetes. A macrophage/monocyte receptor for AGE moieties mediates the uptake of AGE-modified proteins by a process that also induces cachectin/tumor necrosis factor (TNF) and IL-1 secretion. Reasoning that cytokines might regulate this AGE-receptor system, we have evaluated the effect of cachectin/TNF, IL-1, and IFN-gamma on AGE-protein processing. We report that cachectin/TNF induced a severalfold enhancement of binding, endocytosis, and degradation of AGE-BSA by both murine peritoneal macrophages and human blood monocytes in vitro, and that cachectin/TNF enhanced the rate of disappearance of AGE-modified red blood cells in vivo. IL-1 and IFN-gamma alone did not increase AGE processing, but IFN-gamma consistently enhanced cachectin/TNF-induced changes in AGE-receptor kinetics. Similar effects were induced by AGE-BSA and FFI-BSA, a chemically synthesized AGE, when used as macrophage stimulants, possibly via cachectin/TNF induction. All upregulatory responses were blocked by anticachectin/TNF monoclonal antibody. These data suggest that AGE-induced cachectin/TNF, in addition to influencing tissue regeneration and remodelling, may also normally regulate the disposal of tissue damaging AGE-proteins through an autocrine upregulation.

Animals↗
PubMed1988

Alterations in the binding site of the cyclic AMP receptor protein at the Escherichia coli galactose operon regulatory region.

Gene manipulation techniques have been used to alter the binding site for the cyclic AMP-cyclic AMP receptor protein complex (cAMP-CRP) at the regulatory region of the Escherichia coli galactose (gal) operon. The effects of these changes on CRP-dependent stimulation of expression from the galP1 promoter in vivo have been measured, and gel binding assays have been used to measure the affinity of cAMP-CRP for the modified sites. Firstly we have deleted progressively longer sequences from upstream of the gal CRP site in order to locate the functional limit of the site. A deletion to -49, removing the first base that corresponds to the consensus sequence for a CRP binding site, is sufficient to reduce CRP binding and block CRP-dependent stimulation of P1. Secondly, we used synthetic oligonucleotides to invert the asymmetric nucleotide sequence at the gal CRP binding site or to make the sequence symmetric. Inversion of the site has little effect on CRP binding, the architecture of open complexes at P1 revealed by DNAase I footprinting, or the stimulation of transcription from P1. Making the site symmetric increases the affinity for CRP by over 50-fold and leads to increased transcription from P1, whilst hardly altering the DNAase I footprint of open complexes. Our results confirm that the strength of binding of CRP depends on the nature of the site and show that it is this that principally accounts for differences in CRP-dependent stimulation of transcription.

Base Sequence↗
PubMed1988

Changes in circulating alphafetoprotein and human chorionic gonadotrophin following chorionic villus sampling.

Chorionic villus sampling (CVS) is rapidly becoming established as a routine procedure for first-trimester fetal diagnosis. The technique can result in fetomaternal haemorrhage and this might sensitize Rhesus-negative mothers and on occasion lead to spontaneous abortion. Serial sampling indicates that there is a rapid rise in alphafetoprotein (AFP) levels following CVS; however, this is not reflected by raised levels at 16-18 weeks and does not influence the subsequent pregnancy outcome. Unlike AFP, alterations in hCG levels are small and variable. Anti-D prophylaxis for non-sensitized Rhesus negative mothers should be given after CVS and the procedure may be contra-indicated in patients who are already sensitized.

Chorionic Gonadotropin↗
PubMed1988

Functional analysis of different sequence elements in the Escherichia coli galactose operon P2 promoter.

Starting with a DNA fragment containing the galactose operon P2 promoter, we made a series of deletions that progressively replaced DNA sequences upstream of the transcription startpoint and determined their effects on P2 activity. The results show that specific sequences upstream of -32 are not important. Removal of the sequence 5'-CACA-3' from -32 to -28 reduces P2 activity by 50%: longer deletions to -16 further reduce activity but do not remove the information specifying the transcription startpoint. DNA sequences between -32 and -16 at gal P2 assist the isomerization of RNA polymerase from closed to open complexes rather than contributing to the initial binding of RNA polymerase. The activity of gal P2 in the absence of -35 region sequences is dependent on the sequence TG just upstream of the -10 hexamer, TATACT: a mutation at -14 changing the TG sequence to TT totally inactivates P2. However, P2 activity can be restored if the consensus -35 region sequence TTGACA is cloned 17 bp upstream of the -10 hexamer. Thus, for transcription initiation, the -10 hexamer, TATACT, must 'cooperate' with upstream sequences that may be located either around -35 or -14.

Base Sequence↗
PubMed1987

RNA polymerase makes important contacts upstream from base pair -49 at the Escherichia coli galactose operon P1 promoter.

A G:C to T:A transversion at bp position -19 in the gal operon promoter region relieves the dependence of galP1 promoter activity on the cAMP-CRP complex. Deletion analysis shows that expression from the promoter is decreased on replacement of the sequence between 49 and 54 bp upstream from the P1 start point. Moreover, protection experiments show that RNA polymerase interacts with this region in open complexes at P1. We propose that this contact is necessary for optimal P1 activity; point mutations in the gal promoter region can alter DNA flexibility and hence the strength of this contact; CRP factor activates P1 transcription by favouring formation of this contact; and the gal repressor blocks P1 activity by binding to this zone.

Base Sequence↗
PubMed1987

A novel whole blood capillary technic for measuring the prothrombin time.

The prothrombin time (PT) is frequently performed to monitor anticoagulant therapy. Although relatively simple to perform, it requires venipuncture and laboratory resources for sample handling and analysis. A recently developed capillary whole blood device that uses fingerstick samples was evaluated. Paired capillary whole blood and reference plasma PTs were performed in 858 samples from 732 subjects. The PT for normal volunteers (n = 193) was 11.8 +/- 0.9 seconds with the use of the new instrument and 12.1 +/- 0.5 seconds with the use of the reference method. In samples from 539 patients receiving anticoagulants, the correlation coefficient between the two methods was 0.96. Venous whole blood without anticoagulant and capillary whole blood gave equivalent results, which suggests that the fingersticks do not effect the quality of the specimen. Variation in hematocrit between 23.4% (0.34) and 53.8% (0.538) did not alter the performance of the instrument. The new instrument is easy to use and may allow testing by nonlaboratory personnel and patients. It obviates the need for venipuncture, provides immediate results, and appears to be comparable in accuracy to current reference methods.

Anticoagulants↗
PubMed1986

Mutations that reduce expression from the P2 promoter of the Escherichia coli galactose operon.

We describe the isolation and characterisation of twelve different mutations that reduce gene expression from the galP2 promoter, starting with a gal regulatory region with a mutation that inactivated galP1, the cAMP-CRP-dependent promoter. Seven of the new mutations reduce the initiation of transcription at P2 whereas the others reduce translation initiation of the first gal operon gene, galE. Two of the mutations affecting translation fall in the galE initiation codon and the Shine-Dalgarno sequence. Mutations that allow the formation of a stem-loop structure in the messenger including this sequence also reduce translation. A deletion of 11 bp, upstream of the Shine-Dalgarno sequence, almost totally prevents translation. Although none of the point mutations that reduced transcription initiation at P2 fall in the -35 region, we repeatedly isolated insertions in this zone. The point mutations all fell around the -10 region: the strongest effects were found with mutations that altered the sequence away from the consensus that has been established for Escherichia coli promoters. The effects of the two strongest P2 mutations were investigated in the absence of the P1 mutation used for their isolation. One mutation, a T:A to C:G transition at -12, inactivates both P2 and P1. In contrast the other, a T:A to G:C transversion at -19, specifically inactivates P2, but leaves P1 partially active even in the absence of cAMP-CRP. The implications of this are discussed in the context of how cAMP-CRP controls the balance between transcription from P2 and P1 at the gal operon regulatory region.

Base Sequence↗
PubMed1985

Effect of vagal blockade on food- and hormone-stimulated release of pancreatic polypeptide and motilin in dogs.

Vagal control of food- and hormone-stimulated release of pancreatic polypeptide (PP) and motilin was investigated in four conscious dogs by examining the effect of cryogenic vagosympathetic blockade. The postprandial PP response of 189 +/- 7 pM was totally, although reversibly, inhibited to 58 +/- 11 pM with the vagi blocked. Similarly, bombesin-, CCK-OP-, or neurotensin-stimulated PP release was abolished. Although the PP response to intraduodenal perfusion of an elemental diet was also reduced by blockade, the 52 +/- 15% inhibition was less than observed with the meal. In contrast to PP, plasma motilin fell after the meal from a fasting level of 128 +/- 16 pM to a nadir of 52 +/- 7 pM. Vagal blockade reversed this decline as plasma motilin rose to a peak of 121 +/- 18 pM with a pattern resembling the motilin response in the interdigestive state. This motilin increment during blockade was inhibited by atropine and by infusion of porcine PP. Plasma motilin also fell with the elemental diet, but this response was not affected by blockade. During infusion of bombesin, plasma motilin rose by 60 +/- 9 pM; vagal blockade augmented this increment twofold. Thus, the PP response to a meal and to hormonal stimulation is controlled by a vagal cholinergic excitatory pathway. However, intestinal release of PP is mediated in part by the vagus and in part by a vagally independent mechanism which may be neural or hormonal. Alternatively, vagal noncholinergic inhibition is a major mechanism modulating the motilin response after oral food but motilin release exclusively from intestinal nutriments is mediated by nonvagal, noncholinergic mechanisms.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1985

The role of vagal integrity in gastrin releasing peptide stimulated gastroenteropancreatic hormone release and gastric acid secretion.

The role of the vagus nerve in the control of gastrin releasing peptide (GRP) stimulated gastroenteropancreatic hormone release and gastric acid secretion was investigated in four conscious gastric fistula dogs using a technique of bilateral cryogenic vagal blockade. A 90-min infusion of GRP at a dose of 400 pmol X kg-1. h-1 produced significant elevations in plasma levels of gastrin, motilin, GIP, enteroglucagon, insulin, pancreatic glucagon, pancreatic polypeptide and VIP. Vagal blockade reversibly inhibited the rise of plasma PP and significantly blunted the elevation of plasma VIP. However, the GRP stimulated response of the other hormones investigated was not modified by vagal blockade. Similarly, the substantial secretion of gastric acid observed with GRP was not influenced by vagal blockade. Thus GRP acts predominantly via mechanisms which are independent of vagal integrity, findings that are in support of a major role for the local neuromodulation of hormone release and gastric acid secretion.

Animals↗
PubMed1985

Simultaneous or sequential expression of lymphoid and myeloid phenotypes in acute leukemia.

Acute mixed myeloid-lymphoid leukemia is uncommon. We report four cases in which myeloid and lymphoid cell markers were observed simultaneously or sequentially when 94 patients with acute leukemia were phenotyped according to the French-American-British (FAB) classification system, with cytochemical stains, and with immunologically defined differentiation markers (identified by monoclonal antibodies and antiterminal deoxynucleotidyl transferase [TdT]). In one case, conversion from acute lymphoblastic leukemia to acute myeloid leukemia was noted (FAB L1, TdT+ to FAB M4, Auer rods, TdT-). In another patient, two distinct populations of myeloid and lymphoid blast cells were observed simultaneously (TdT-, LeuM1+/TdT+, LeuM1-). In two additional patients, acute leukemia was characterized by the expression of both lymphoid and myeloid markers on the same cell (TdT+/Leu M1+, B4+/Leu M1+ and greater than or equal to 70% TdT+, T11+, My9+). The Philadelphia (Ph1) chromosome was negative in all cases, though other chromosomal abnormalities were noted in three out of four cases. Malignant transformation of a pluripotential stem cell for both lymphoid and myeloid lineages, with or without the Ph1 chromosome marker, could explain the coexistence of distinct populations of lymphoblasts and myeloblasts in acute leukemia. Acute leukemia with a biphenotypic profile may reflect genome depression accompanying neoplasia.

Adult↗