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D P O'Brien

Publications and source records attributed to D P O'Brien.

At least 55 records · Page 3Linked to original sources
PubMed1996

Octamer independent activation of transcription from the kappa immunoglobulin germline promoter.

Previous analyses of immunoglobulin V region promoters has led to the discovery of a common octamer motif which is functionally important in the tissue-specific and developmentally regulated transcriptional activation of immunoglobulin genes. The germline promoters (Ko) located upstream of the J region gene segments of the kappa locus also contain an octamer motif (containing a single base pair mutation and referred to as the variant octamer) which has been shown previously to bind Oct-1 and Oct-2 transcription factors in vitro. To further elucidate the role of this variant octamer motif in the regulation of germline transcription from the unrearranged kappa locus, we have quantitated the relative binding affinity of Oct-1 and Oct-2 for the variant octamer motif and determined the functional role of this octamer motif in transcriptional activation. We find that, although the variant octamer motif binds Oct-1 and Oct-2 in vitro with 5-fold lower affinity than the consensus octamer motif, mutation of the variant octamer motif to either a consensus octamer or non-octamer motif has no effect on transcriptional activation from the germline promoter. We also find significant differences in activation of germline and V region promoters by kappa enhancers. Our results suggest that the germline promoters and V region promoters differ in their dependence on octamer for activation and respond differently to enhancer activation. These findings have important implications in regulation of germline transcription as well as concomitant activation of the V-J recombination of the kappa light chain locus.

Animals↗
PubMed1996

Medical care of the neurosurgical patient.

Proper medical care before and after surgery play an important role in the overall care of patients requiring neurosurgery and will have an impact on the neurological recovery. Prevention of spinal cord destruction resulting from the cascade of events which occur secondary to central nervous system trauma is a critical part of a patient's preoperative care. High doses of methylprednisolone sodium succinate given within the first 8 hours of trauma are currently recommended to provide protection to neural tissue after trauma. Other promising drugs for patients with spinal trauma, such as 21-aminosteroids and GM-1 gangliosides, may become available in the near future. Knowledge of potential complications after surgery and methods to prevent complications from occurring is an important part of the postoperative care of neurosurgical patients. This includes management of micturition and defecation dysfunction, management of postoperative pain, physical therapy to speed recovery, and providing good supportive care to the recumbent patient.

Animals↗
PubMed1996

Decreased production of IL-2 and IFN-gamma by stimulated splenocytes from mice bearing plasma cell tumors is associated with alteration of DNA-binding factors.

We have previously demonstrated that polyclonally stimulated splenocytes as well as enriched T cells from mice bearing plasma cell tumors (PCT) show decreased production of the Th1-associated cytokines, IL-2 and IFN-gamma. This observed loss of IL-2 and IFN-gamma production could be attributed to possible alterations in various factors required for T cell activation and cytokine production. We find that B7 co-stimulatory molecules and IL-2R are up-regulated normally on splenocytes from PCT mice. Concanavalin A (Con A) stimulation of splenocytes from PCT mice in the presence of immobilized anti-CD28 antibody does not enhance proliferation. Exogenous rIL-2 addition to cultures of splenocytes from PCT mice also does not enhance proliferative responses or cytokine production. Furthermore, we do not observe inhibition of normal splenocyte proliferation and IL-2 production in the presence of splenocytes from PCT mice, suggesting that the appearance of suppressor cells cannot account for the decreased responses by splenocytes from PCT mice. Also, IL-2 mRNA levels are decreased in stimulated splenocytes from PCT mice, suggesting that there may be an alteration of transcription factors required for activation of IL-2. Therefore, we have evaluated the DNA-binding activity of transcription factors involved in activation of IL-2 and IFN-gamma gene transcription. We find that binding activities of AP-1, Oct-1 and Oct-2 transcription factors in stimulated splenocytes from PCT mice are similar to normal splenocytes. However, the binding activities of NF-kappa B complexes and factors that bind to the proximal conserved element in the IFN-gamma promoter are dramatically altered in splenocytes from PCT mice. These results suggest that PCT induce changes in certain transcription factors that are important for anti-tumor responses, including T cell proliferative responses and Th1-associated cytokine production.

Animals↗
PubMed1996

Antithrombotic actions of the thrombin inhibitor, argatroban, in a canine model of coronary cyclic flow: comparison with heparin.

1. The antithrombotic action of argatroban, a synthetic thrombin inhibitor, was studied in a canine model of coronary cyclic flow having some of the characteristics of acute unstable angina. Heparin was studied as a reference anticoagulant. 2. Localized endothelial damage was induced in the circumflex coronary artery of anaesthetized open-chest foxhounds and a critical stenosis was applied by use of a Lexan constrictor placed around the artery at the site of endothelial damage. An electro-magnetic flow probe was placed distal to the lesion, and cyclic flow variations (CFVs) were observed, as thrombi formed at the site of the arterial lesion and were dislodged. Test compounds were administered by i.v. infusion commencing 1 h after the appearance of CFVs, and maintained for 1 h. On termination of the treatments, coronary flow was observed for a further 60 min. A series of blood samples were taken at predetermined times throughout each experiment in order to determine the coagulation parameters, thrombin time (TT) activated partial thromboplastin time (aPTT) and for the determination of fibrinopeptide A (FpA) levels before, during and post-treatment. 3. Argatroban and heparin showed antithrombotic effects in this model. Argatroban dose-dependently increased the minimum coronary flow at the nadir of the CFVs from 5.4 +/- 1.7 to 9.1 +/- 2.1 ml min-1 (30 micrograms kg-1 min-1, P = 0.041) and from 2.9 +/- 0.9 to 16.3 +/- 4.5 ml min-1 (100 micrograms kg-1 min-1, P = 0.023, n = 8 dogs at each dose level). Heparin (5 and 15 iu kg-1 min-1) also increased minimum flow, but the increase was not statistically significant at the 5% level, although the P value in animals treated with 15 iu kg-1 min-1 (P = 0.0521, n = 6 dogs) fell just outside this limit. Although neither compound significantly decreased the overall CFV frequency, argatroban (100 micrograms kg-1 min-1) significantly (P < 0.01) decreased the number of large amplitude CFVs (minimum coronary flow < 10 ml min-1) by 63%, and heparin (15 iu kg-1 min-1) caused a 50% decrease in this parameter (P < 0.05). 4. The thrombin times were increased by a factor greater than 10 during antithrombotic treatment, irrespective of the compound or doses used. Heparin treatment induced 17 and > 30 fold increases in aPTT at 5 and 15 iu kg-1 min-1 respectively. However, argatroban produced only 2 and 3 fold increases in aPTT at 30 and 100 micrograms kg-1 min-1, despite significant antithrombotic effects. FpA levels were reduced in the presence of both argatroban and heparin. 5. These data show that, when administered as an intravenous infusion, argatroban is a potent antithrombotic agent in a canine model of coronary cyclic flow.

Angina, Unstable↗
PubMed1996

Neurosurgery for the elderly: facts and figures.

A retrospective audit of all patients admitted to a national neurosurgical unit, aged 65 years or over, was reviewed. Details of clinical presentation, investigations, management and functional outcome were recorded. Our findings confirm that elderly patients constitute a major proportion of the neurosurgical workload and this has major medical and socio-economic implications.

Aged↗
PubMed1996

Morphophysiologic characterization of peripheral neuropathy in zinc-deficient guinea pigs.

Zinc-deficient guinea pigs develop a peripheral neuropathy characterized by abnormal posture and gait, hyperesthesia, slowed motor nerve conduction velocity (MNCV), and decreased sciatic nerve Na,K-ATPase activity. This study was designed to further investigate longitudinally the morphophysiologic features of the neuropathy. Weanling guinea pigs were fed a low-zinc (<1 mg/kg) diet ad libitum (-ZnAL), an adequate-zinc (100 mg/kg) diet ad libitum (+ZnAL), or the adequate diet restricted in intake ((+ZnRF). Electrophysiologic, morphologic, and biochemical parameters of peripheral nerves were examined at 2.5, 4.0, and 5.5 weeks. Serum zinc was significantly lower by 2.5 weeks and growth rate reduced by 4 weeks in -ZnAL animals. Postural abnormalities were first obvious at 4 weeks, although MNCVs were significantly slower in zinc-deficient animals at all time intervals. The conduction of sensory impulses, as measured by spinal cord somatosensory evoked potentials (sSSEP), was significantly slower in the -ZnAL animals at 5.5 weeks. Examination of teased preparations and histologic sections of sciatic nerves at 5.5 weeks revealed no degenerative lesions or differences in density of myelinated fibers (MF). The size frequency distribution of MF in all groups was unimodal, with a trend toward smaller myelinated nerve fibers in -ZnAL and +ZnRF animals. Sciatic nerve Na,K-ATPase activity in the -ZnAL animals was significantly reduced after 4 weeks of zinc deprivation. At 5.5 weeks, nerve concentrations of myo-inositol, glucose, fructose, and sorbitol were significantly decreased in -ZnAL animals compared with the +ZnRF and +ZnAL controls. The peripheral neuropathy associated with acute zinc deficiency is a parenchymatous axonal disorder characterized by slowed motor and sensory nerve impulse conduction and reduction in nerve Na,K-ATPase activity and nerve concentrations of simple sugars and their metabolites.

Animals↗
PubMed1996

Inhibition by Argatroban, a specific thrombin inhibitor, of platelet activation by fibrin clot-associated thrombin.

Clot-associated thrombin retains amidolytic activity, and is resistant to inhibition by heparin, but not to low molecular weight thrombin inhibitors. We show that clot-associated thrombin induces platelet aggregation, is resistant to heparin:antithrombin III, less so to recombinant hirudin (rHV2Lys47) but not to argatroban, an active-site directed thrombin inhibitor. Fibrin clots prepared with human fibrinogen and thrombin were used to aggregate rabbit washed platelets assessed by single platelet counting, thromboxane B2 (TXB2) immunoassay and scanning electron microscopy. Fibrin clots decreased platelet counts, and released TXB2. Electron microscopy showed platelet aggregates on the clot surface. Argatroban concentration-dependently inhibited such aggregation with IC50s of 21 nM and 13 nM versus aggregation and TXB2 release respectively. The IC50s of Argatroban against fluid-phase thrombin producing similar aggregation were 12 nM (aggregation) and 33 nM (TXB2). rHV2Lys47 was less active against clot-induced aggregation (IC50 = 1.8 nM) than against fluid-phase thrombin (IC50 = 0.06 nM). Heparin had an IC50 of 0.02 mU/ml against aggregation induced by fluid-phase thrombin, but much greater concentrations are required to inhibit clot-induced aggregation (IC50 = 48 mU/ml). These data provide a basis for the superiority of direct-acting thrombin inhibitors over heparin in platelet rich thrombi.

Animals↗
PubMed1996

Evolving strategies in immunosuppressive therapy: the Emory experience.

We have reviewed our experience with various immunosuppression regimens over the past 11 years in 2,065 renal transplant recipients. Patients received triple-drug maintenance therapy with CsA, imuran and prednisone following either no induction therapy or treatment with polyclonal (PCA) or monoclonal (MCA) antibody. The most recent immunosuppressive regimen has included CsA, MMF, and prednisone without induction therapy. We observed that those patients receiving PCA had a better graft survival 5 years after transplantation than recipients with MCA induction or those receiving standard triple drug therapy without induction. Patients receiving MMF experienced superior one-year graft survival compared with those receiving induction with PCA, MCA or standard triple drug therapy. A similar one-year graft survival rate for both Black and White recipients was observed in the MMF group and raises the possibility of achieving improved long-term graft survival in Black recipients with a MMF-based immunosuppression strategy. Our experience indicates that excellent short-term graft survival can be achieved with an immunosuppressive protocol of MMF, CsA and prednisone without induction. Graft survival in MMF-treated recipients was equal to or superior to that which we previously achieved with induction therapy.

Antilymphocyte Serum↗
PubMed1995

Factor VIIa and the extracellular domains of human tissue factor form a compact complex: a study by X-ray and neutron solution scattering.

The four-domain structure of human factor VIIa and the two-domain structure of tissue factor form a tight complex to initiate blood coagulation. By solution scattering, the mean X-ray and neutron radii of gyration RG (which determine macro-molecular elongation) were found to be 3.25 nm, 2.13 nm and 3.14 nm (+/- 0.13 nm) for factor VIIa, the extracellular region of tissue factor and their complex in that order. The mean cross-sectional radii of gyration RXS were 1.33 nm, 0.56 nm and 1.42 nm (+/- 0.13 nm) in that order. The mean lengths were 10.3 nm, 7.7 nm and 10.2 nm in that order. The data show that, in solution, the free proteins have extended domain structures, and the complex is formed by a compact side-by-side alignment of the two proteins along their long axes. The high binding affinity of tissue factor for factor VIIa may thus be accounted for by the occurrence of many intermolecular contacts in the complex.

Animals↗
PubMed1995

Intracranial metastases from pituitary adenoma.

Two patients with histologically benign pituitary adenomas subsequently underwent resections of a frontal and a cerebellar tumour each of which had histological appearances identical to those of classic pituitary adenomas. The frontal tumour was immunoreactive for prolactin, and the cerebellar metastasis was immunoreactive for thyrotropin and gonadotrophins. There was no evidence of residual or recurrent intrasellar pituitary adenoma, nor was there a connection between the frontal or cerebellar masses and the sella turcica. Extracranial tumours have not developed. Both tumours fulfil criteria for diagnosis of pituitary carcinoma. These rare tumours are reviewed with emphasis on diagnosis and management.

Adenoma↗
PubMed1995

Ureteral obstruction due to calculi in the early postoperative period in renal cadaveric transplantation: a case report and discussion of ureteral obstruction in the renal transplant patient.

We report a case of obstruction secondary to multiple ureteral calculi on postoperative day 3 after cadaveric renal transplantation. Treatment consisted of ureterolithotomy with stenting of the ureteroneocystotomy and convalescence was otherwise unremarkable. Obstructive complications of the ureter after renal transplantation are reviewed.

Adult↗
PubMed1994

Surface plasmon resonance studies of the interaction between factor VII and tissue factor. Demonstration of defective tissue factor binding in a variant FVII molecule (FVII-R79Q).

The blood coagulation cascade is initiated when vessel injury allows factor VII (FVII) to form a complex with tissue factor (TF). Complete deficiency of FVII causes a lethal bleeding diathesis, but individuals with moderately reduced FVII levels are often asymptomatic. Some of these individuals have circulating partially functional FVII, as a result of point missense mutations in critical parts of the molecule. One such mutation has been reported at position 79 in the first epidermal growth factor-like (EGF) domain of FVII, where an arginine residue has been replaced by glutamine. There is controversy as to whether or not this mutation reduces the affinity of the FVII/TF interaction compared to wild-type FVII. To address this problem, we have expressed recombinant FVII-R79Q and subjected it to detailed biochemical analysis. One-stage FVII:C assays show the variant FVII to have reduced activity with respect to the wild type. Rates of autoactivation and activation by FXa to the two-chain molecule were identical for wild-type and variant FVII. The Vmax for FX activation was lower for the mutant as measured using an amidolytic assay for FX activity. In contrast, the Km for FX was lower for the variant than the wild-type molecule. Peptidyl substrate hydrolysis was virtually identical for both variant and normal FVIIa in the presence and absence of TF. The variant has reduced affinity for TF as measured by surface plasmon resonance. FVII-R79Q has an association rate constant (kassoc) one-fifth of that of normal FVII, but a similar kdiss, resulting in a decrease in the affinity of the enzyme for its cofactor.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1994

Crystal structure of the extracellular region of human tissue factor.

Tissue factor is a cell-surface glycoprotein receptor which initiates the blood coagulation cascade after vessel injury by interacting with blood clotting factor VII/VIIa and which is implicated in various pathological processes. When bound to tissue factor, factor VII is readily converted to the active protease factor VIIa by trace amounts of factors Xa, IXa or VIIa. Human tissue factor consists of 263 residues, the first 219 of which comprise the extracellular region. We have determined the crystal structure of the extracellular region at a resolution of 2.2 A. Tissue factor consists of two immunoglobulin-like domains associated through an extensive, novel, interdomain interface region. The binding site for factor VII lies at the interface region and involves residues from domain 1 and an extended loop (binding 'finger') of domain 2. This is the first reported structure of a representative of the class 2 cytokine receptor family, which also includes interferon-alpha, interferon-gamma (refs 2, 3) and interleukin-10 (ref. 4) receptors.

Amino Acid Sequence↗
PubMed1994

Fatal cerebral coenurosis in a cat.

A 6-year-old cat that was laterally recumbent and panting was evaluated because of a 10-day history of progressive neurologic abnormalities. Despite aggressive treatment, the cat died on the day of admission. At necropsy, a 1.5-cm-diameter, fluid-filled cyst was found in the white matter of the left cerebrum. The cyst was identified as a coenurus of Taenia serialis, on the basis of the cyst wall, distribution of scolices, and the shape and dimensions of rostellar hooks. Scolices were found in varying stages of ontogeny, ranging from undifferentiated to nearly mature. Taenia serialis has a canid-lagomorph life cycle, with cats being accidental intermediate hosts. However, the potential exists for rare zoonotic transmission and subsequent serious disease in human beings and other accidental intermediate hosts.

Animals↗
PubMed1994

High-level production of human blood coagulation factors VII and XI using a new mammalian expression vector.

Recombinant human proteins are generally recovered in low yields from mammalian tissue culture following transfection with commercially available vectors. We have constructed a novel vector containing both the neomycin-resistance-encoding gene (neo) as a dominant selectable marker, and the dihydrofolate reductase-encoding gene (DHFR) to enable amplification of transfected DNA followed by stable expression in mammalian cell lines. Levels of 5 micrograms/ml of the coagulation proteins, factor VII (FVII) and factor XI (FXI), have been achieved in serum-free media. N-terminal sequencing of the purified proteins, and of their separated chains after proteolytic activation, demonstrated correct processing of the recombinant products. In addition, the ratios of clotting activity to antigen for each are close to unity, and the recombinant and plasma-derived proteins had identical mobilities upon electrophoresis in the presence of SDS. The vector described will be of use for the synthesis of recombinant proteins, both wild-type and variants produced by site-directed mutagenesis, especially where complex post-translational modification of the protein makes it essential to use mammalian cells.

Animals↗
PubMed1994

Propositional reasoning by mental models? Simple to refute in principle and in practice.

Two experiments compared the predictions of mental-models theory with a mental-logic theory. Results show that people do not make fallacious inferences predicted by mental-models theory but not predicted by mental-logic theory and that people routinely make many valid inferences predicted by mental-logic theory that should be too difficult on mental-models theory. Thus, the mental-logic theory accounts better for the data. A difference between the two theories concerning predictions about the order in which inferences are made was also investigated. The data clearly favor the mental-logic theory. It is argued that the mental-logic theory provides the more plausible description of the actual psychological processes in propositional reasoning.

Cognition↗
PubMed1994

Simple method for comparing reliability of two serum tumour markers in breast carcinoma.

AIMS: To compare the two breast tumour markers, CA15-3 and mucinous-like carcinoma associated antigen (MCA), using Receiver Operating Characteristic (ROC) curve analysis. METHODS: One hundred and ninety six patients "presenting" with breast carcinoma had serum CA15-3 and MCA concentrations measured. RESULTS: Using these markers as indicators of stage IV disease at the recommended laboratory level, true positive rates (TPR) and false positive rates (FPR) were obtained as follows: CA15-3 TPR = 75%, FPR = 7.4%, MCA TPR = 80%, FPR = 59.1%. By increasing the CA15-3 cutoff level to 45 U/ml, a TPR and FPR of 75% and 0.6%, respectively were obtained. By increasing the MCA cutoff level to 23 U/ml, a TPR and FPR of 65% and 2.3%, respectively, were obtained. CONCLUSIONS: Using ROC curve analysis shows that CA15-3 is a superior indicator of metastatic breast disease than MCA at recommended laboratory levels, and by altering the cutoff points, the specificity and sensitivity for both these markers can be improved.

Antigens, Neoplasm↗