Search PubMed⌕ Search

Biomedical subjects

D P O'Brien

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

At least 73 records · Page 4Linked to original sources
PubMed1994

The extent of vitamin K deficiency in patients with cholestatic jaundice: a preliminary communication.

Eleven patients with cholestatic jaundice had measurements of plasma vitamin K1 performed. Seven of these 11 (64%) had subnormal levels. The prothrombin time (PT) was prolonged in three of 15 patients with cholestasis (20%), the patient with the longest PT had the lowest vitamin K1 level. A single intramuscular (im) dose of 10 mg vitamin K1 lowered the PT in 9/15 patients (includes correcting the three prolonged PTs). The initial mean plasma vitamin K1 level rose 24 h later, to a mean plasma level which was 33 times the upper limit of the normal physiological range. These preliminary results suggest that a majority of patients presenting with cholestatic jaundice have low tissue reserves of vitamin K1, and that guidelines for vitamin K1 therapy in patients with cholestatic jaundice should be revised.

Adult↗
PubMed1994

Factor VIII S373L: mutation at P1' site confers thrombin cleavage resistance, causing mild haemophilia A.

A novel CRM+ mutation, factor VIII position 373 serine to leucine substitution (FVIII 373-Leu) was identified during a survey of Factor VIII (FVIII) mutations. We have purified the variant protein from the patient's plasma in order to allow further characterisation of the molecule. The CRM+ plasma contained 120% Factor VIII antigen (FVIII:Ag) and 6% Factor VIII coagulant activity (FVIII:C). After purification the mutant FVIII was subjected to thrombin proteolysis, and was thereby activated 5.6-fold compared with 7-fold for wild type molecule. Subsequently, spontaneous inactivation of the mutant was much slower than noted for wild type FVIII. Western blot analysis using monoclonal antibodies demonstrated that thrombin cleavage of FVIII 373-Leu at positions 740 and 1689 were normal but that cleavage at position 372 was completely absent. Crystallographic coordinates of the active site of thrombin complexed to fibrinopeptide A were used to explore possible mechanistic reasons for the failure of thrombin to cleave the mutant FVIII at position 372. Steric hindrance between the mutant side chain and the side chain of the P1 residue was apparent. We conclude that the functional defect of FVIII 373-Leu results from the inability of thrombin to cleave the mutant at position 372-373, and propose that this is due to steric hindrance by the side chain of leucine 373, preventing correct formation of the enzyme substrate complex.

Antibodies, Monoclonal↗
PubMed1994

The corneal quilt: a protective device designed to reduce intraoperative retinal phototoxicity.

The corneal quilt is a simple, safe, inexpensive, and effective device designed to decrease the risk of intraoperative retinal phototoxicity from the operating microscope. Retinal injury is a well documented hazard, especially during prolonged procedures. The corneal quilt can be easily used as an adjunct to other methods designed to protect the retina from excessive incident light. In this study, we fashioned an approximately 6- x 5-millimeter semi-transparent corneal occluder from the nonadhesive portion of a 3M Steridrape. We determined spectrophotometrically that the corneal quilt reduced the transmission not only of visible light, but of ultraviolet and blue wavelengths as well, the wavelengths known to be the most phototoxic to the retina. However, no data were obtained actually demonstrating the degree to which light is scattered after transmission through the corneal quilt.

Bandages↗
PubMed1993

Synthesis and characterization of wild-type and variant gamma-carboxyglutamic acid-containing domains of factor VII.

Synthetic peptides corresponding to portions of the wild-type and variant sequences of the human factor VII gamma-carboxyglutamic acid (Gla)-containing domain have been prepared by direct peptide synthesis using the Fmoc-based protection strategy. Peptides were purified by ion-exchange and reversed-phase chromatography and characterized as the correct products. A peptide comprising residues 1-49 (GP 1-49) inhibited the activation of factor X (FX) by soluble tissue factor (sTF) and recombinant activated factor VII (rFVIIa). In the absence of phospholipid, no inhibition by this peptide was observed. GP 1-49 did not inhibit the hydrolysis of a peptidyl substrate by rFVIIa in the presence of either sTF or relipidated TF apoprotein in the presence or absence of phospholipid. A similar peptide (residues 1-38, GP 1-38) that did not contain the aromatic stack region was also inhibitory. Two variant peptides, one identical to GP 1-49 but lacking the N-terminal alanine residue (GP 2-49) and one identical to GP 1-38 but with an arginine to alanine substitution at position 9 (GP 1-38 R9A), showed substantially reduced inhibitory activity. Kinetic analysis of the inhibition of Xa generation by GP 1-49 revealed a noncompetitive mode of inhibition, probably via a substrate-depletion mechanism. GP 1-49 does not inhibit by preventing FX binding to phospholipid surfaces. This indicates that the N-terminal residues of the FVII Gla domain are important for the structural integrity of the peptide, and implicates the Gla domain per se in a direct interaction with phospholipid-bound FX.

1-Carboxyglutamic Acid↗
PubMed1993

Crystallization and preliminary X-ray analysis of human tissue factor extracellular domain.

The extracellular domain (residues 1 to 220) of human tissue factor has been cloned and expressed in Escherichia coli and purified to isoelectric homogeneity. Single crystals suitable for X-ray analysis have been obtained by vapour diffusion. They belong to the tetragonal space group P4(1)2(1)2 or P4(3)2(1)2 with a = b = 45.2 A, c = 231.5 A, contain one molecule per asymmetric unit and diffract to 2.6 A resolution. Native and derivative data sets have been collected to 3.6 and 3.9 A, respectively.

Crystallography, X-Ray↗
PubMed1993

Structural requirements for the interaction between tissue factor and factor VII: characterization of chymotrypsin-derived tissue factor polypeptides.

Tissue Factor (TF) is the cellular receptor for coagulation Factor VII/VIIa (FVII/VIIa). TF binds to FVIIa and promotes the rapid activation of the zymogen substrates Factors IX and X (FIX and FX) to the respective serine proteinases. In order to probe structure-function relationships in TF, we have subjected the truncated membrane-bound variant, TF 1-243, to proteolytic digestion in SDS-containing gels. Three major polypeptide fragments were generated by proteolysis of TF 1-243 with chymotrypsin, producing cleavages C-terminal to residues 34, 76 and 103. All three polypeptides, TF 35-243, 77-243 and 104-243, bound biotinylated human FVII in a highly specific ligand blot assay. High-performance electrophoretic chromatography was used to isolated chymotrypsin-derived fragments of TF. These purified fragments bound FVII in ligand blots, and two of the three polypeptides exhibited much reduced, but significant, procoagulant activity in a chromogenic assay for the generation of Factor Xa in the presence of FVIIa and Ca2+. The smallest chymotrypsin-derived TF polypeptide, TF 104-243, showed reduced binding of FVII in ligand blot analyses, inhibited the activity of the full-length molecule, but had no procoagulant activity. These data suggest that a part of the binding site for FVII is contained within the TF sequence 104-243. The sequence TF 1-34 either contains a part of the FVII-binding domain or its removal leads to dysfunctional folding, disrupting binding sites elsewhere in the molecule.

Amino Acid Sequence↗
PubMed1993

The relationship between factor VII coagulant activity and factor XII activation induced in plasma by endogenous or exogenously added contact surface.

The contribution of various enzymes in the activation of factor VII, determined from the increase in factor VII coagulant activity (VIIc), was investigated following the exposure of citrated plasma to low temperature. The contact system of coagulation was initiated either by the contact surface present in certain plasmas (i.e. plasma from women in late pregnancy) or by micellar stearate added to plasma diluted with an equal volume of buffer (plasma from normal healthy subjects or from women in late pregnancy). With either of the contact surfaces, increase of VIIc and the concentration of enzymes derived from factor XII (XIIa) depended on the potency of the contact surface. The stearate-induced VIIc in diluted plasmas from women in late pregnancy or from normal subjects was inhibited by 60-70% in the presence of anti-factor IX monoclonal antibody. VIIc was not increased in XII-deficient plasma following the addition of stearate. The addition of purified human factor XII to this plasma restored the increase in VIIc and the activation of factor XII. In factor IX-deficient plasma, the stearate-induced increase in VIIc was only 38% of that seen in normal plasma and was restored by the addition of purified factor IX. Similarly in factor XI-deficient plasma, the stearate-induced increase in VIIc and the factor XII activation were 48% and 69% of that found in normal plasma. The addition of EDTA (2 mM) did not alter the extent of factor XII activation induced by contact surface, but it did inhibit the rise in VIIc. It is concluded that in the presence of contact surface the activation of factor XII and the sequential activation of factor XI and of factor IX results in the activation of factor VII. Activated factor IX is responsible for the major part of the factor VII activation whereas the rest may be through the direct activation by XIIa.

Antibodies, Monoclonal↗
PubMed1993

Comparison of fine-needle aspiration biopsy, Doppler ultrasound, and radionuclide scintigraphy in the diagnosis of acute allograft dysfunction in renal transplant recipients: sensitivity, specificity, and cost analysis.

150 episodes of allograft dysfunction in 128 renal transplant recipients, 77 due to acute rejection, 32 secondary to acute-on-chronic rejection, 33 due to either prerenal factors, acute tubular necrosis, or ciclosporin A nephrotoxicity, and 8 secondary to multiple causes, were evaluated by fine-needle aspiration biopsy (FNAB), Doppler ultrasound (DUS), and radionuclide scintigraphy (RS), each performed within a 24-hour period and prior to any specific therapeutic intervention. Tests were interpreted by appropriate specialists in a large transplant center without access to clinical information. The final diagnosis was based primarily upon response to therapeutic maneuvers with histological (core biopsy) confirmation in 123 episodes. RS was the most sensitive (70%) test for the diagnosis of acute rejection during the early posttransplant period, exceeding both FNAB (52%) and DUS (43%). The predictive accuracy of either FNAB, DUS, RS, or core biopsy in the detection of a steroid-responsive component to acute rejection when superimposed upon chronic rejection was low at approximately 50%. When the underlying cause of renal dysfunction was either prerenal, acute tubular necrosis, or ciclosporin A nephrotoxicity, FNAB, DUS, and RS each gave an erroneous diagnosis of acute rejection in about 50% of the episodes. Cost analysis revealed that core biopsy was the most expensive test, but only 9% more than RS, with FNAB the least costly. In conclusion, the lack of ideal sensitivity and specificity combined with the expense of present-day FNAB, DUS, RS, and core biopsy in the diagnosis of a therapeutically reversible component to acute-on-chronic rejection and of FNAB, DUS, and RS in the diagnosis of acute rejection during the early posttransplant period should prompt research into ways to improve their diagnostic yield or alternate modalities.

Acute Disease↗
PubMed1993

Prospective evaluation of one surgeon's first 100 cases of endocapsular phacoemulsification cataract surgery.

In this series of one surgeon's first 100 cases of endocapsular phacoemulsification cataract surgery (EPECS), believed to be the first truly prospective study of its kind, 86% of patients achieved corrected vision of 6/6 to 6/4; 96% achieved vision of 6/12 or better; and excluding those with pre-existing pathology, 99% achieved 6/12. Posterior capsular rupture occurred in 11 cases, with vitrectomy being required in eight cases. Detailed analysis of the 100 cases is provided.

Adult↗
PubMed1992

Inactivation of factor VIII by factor IXa.

Factor VIII (FVIII) is the nonproteolytic cofactor for FIXa in the tenase complex of blood coagulation. FVIII is proteolytically activated by thrombin and FXa in vitro to form a heterotrimer with full procoagulant activity. Activated protein C inactivates thrombin-activated FVIII through cleavage adjacent to position Arg 336 in the cofactor. We have investigated the interaction of FIXa and FVIII and subjected FVIII polypeptides to N-terminal amino acid sequence analysis. Contrary to previous reports, we were unable to demonstrate the activation of FVIII by FIXa. Incubation of these two proteins at equimolar or close to equimolar concentrations resulted in the inactivation of FVIII, coincident with cleavage of the FVIII heavy chain adjacent to Arg 336 and the light chain adjacent to Arg 1719. These cleavages were detected in the presence or absence of thrombin, indicating that FIXa does not stabilize thrombin-activated FVIIIa. APC cleaved FVIII at the same position in the heavy chain, and simultaneous incubation of FVIII, APC, and FIXa did not result in stabilization of the cofactor. We conclude that FIXa does not play a role in the stabilization or activation of FVIII.

Amino Acid Sequence↗
PubMed1992

Spinal epidermoid cyst and cauda equina syndrome in a teenage girl.

A sixteen year old girl presented with a four year history of hip pain followed subsequently by back pain radiating down her left leg, progressive urgency of micturition, urinary incontinence, a feeling of bladder fullness and incomplete bladder emptying, faecal impaction and finally, numbness in both of her buttocks. A diagnosis of Cauda Equina Syndrome was suspected on the history and the clinical examination. A plain X-ray of her lumbar spine revealed evidence of a slow growing mass within the vertebral canal at the level of L3. A Magnetic Resonance Imaging (MRI) scan confirmed an intradural space occupying lesion at the same level. This lesion was surgically removed and histological examination revealed a benign epidermoid cyst.

Adolescent↗
PubMed1992

CA15-3: a reliable indicator of metastatic bone disease in breast cancer patients.

Carcinoma of the breast is the most common malignancy in women and is frequently associated with metastatic bone disease and its associated osteolytic morbidity and mortality. Traditional radiological methods for mass screening bony secondaries are not cost-effective. We examined the value of the tumour marker 'CA15-3' as an alternative to conventional isotope bone scintigraphy. A total of 218 patients with breast cancer was evaluated over a 4-year period. Venous CA15-3 levels were obtained at 3-monthly intervals and bone scintigraphy annually or if the patient developed locomotor symptoms or exhibited elevated CA15-3 levels. Of these patients, 33 with metastatic breast carcinoma had an elevated tumour marker level at the time of diagnosis of their metastases; bone metastases alone = 15/17 (88%), soft tissue metastases alone = 2/6 (33%), simultaneous bony and soft tissue metastases = 7/10 (70%). The preponderance of an elevated CA15-3 in metastatic bone disease, be it in isolation or in combination with non-bone metastases, yields a sensitivity, specificity and positive predictive value of 81.5%, 66% and 92%, respectively. Although 22 of the 27 patients had an elevated CA15-3 at the time of diagnosis of their bone metastases, the remaining five patients (with tumour marker levels in the normal range) showed a similar, albeit a delayed, increase (median = 3 months). Thus, all metastatic bone disease patients demonstrated elevated marker levels. We recommend CA15-3 as a simple, reliable and inexpensive screening method for detecting bone metastases in the patient with breast carcinoma.

Antigens, Neoplasm↗
PubMed1991

Purification and characterization of factor VII 304-Gln: a variant molecule with reduced activity isolated from a clinically unaffected male.

Factor VII (FVII) is the plasma serine protease zymogen which, on binding to its cellular receptor tissue factor (TF), initiates blood coagulation. A 47-year-old man with no clinical bleeding tendency was found to have undetectable plasma FVII activity when tested in a one-stage assay using rabbit brain TF, but 0.3 U/mL using recombinant human TF and 1.04 U/mL FVII antigen. Variant FVII purified from his plasma showed an identical migration on sodium dodecyl sulfate-polyacrylamide gel electrophoresis to wild-type zymogen. By enzyme kinetic analysis the Km of the variant using FX as a substrate was 12-fold higher than that of normal FVII. Also, the variant FVII was unable to compete with wild-type FVII for limited rabbit TF binding sites. A ligand blot procedure was used to directly demonstrate reduced binding of recombinant human TF to the variant FVII compared with normal FVII. Genetic analysis of leukocyte DNA showed a G to A mutation in the propositus' gene at codon 304 that results in the substitution of a glutamine for an arginine residue in the catalytic domain of the protease. We conclude that this region of the FVII molecule is important for its function.

Amino Acid Sequence↗
PubMed1991

Atrial natriuretic factor does not improve the outcome of cadaveric renal transplantation.

Atrial natriuretic factor (ANF) ameliorates renal damage in animal models of acute ischemic renal failure. Consequently, ANF could blunt acute tubular necrosis related to ischemia that occurs frequently in cadaveric renal transplants. Ten pairs of cadaveric kidneys were transplanted into 20 recipients. Paired recipients received either alpha-human ANF (hANF) or vehicle alone in a prospective, double-blind protocol. Upon revascularization of the allograft, either hANF or vehicle was administered intravenously as a 50-micrograms bolus, followed by a 4-h infusion (0.1 microgram/kg/min). Glomerular filtration rate ([125I]iothalamate clearance) was measured between 4 and 7 days posttransplant and again between 14 and 21 days posttransplant. Serum creatinine was measured daily when patients were in the hospital, then twice weekly as patients were examined in the outpatient clinic. Between the groups, there was no significant difference in age of the recipients or donors, cold ischemia time, or histocompatibility leukocyte antigen match. Infusion of hANF had no adverse effects. When subjects receiving hANF were compared with those treated with vehicle alone, there were no significant differences in serum creatinine or glomerular filtration rate. Three hANF and four vehicle recipients required dialysis postoperatively. At 1 month posttransplant, 19 of 20 patients had functioning allografts; an allograft from one hANF recipient never functioned. It was concluded that hANF, when given by the protocol of this study, had no beneficial effect on the outcome of cadaveric renal transplantation in humans.

Acute Kidney Injury↗