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Biomedical subjects

D R Hall

Publications and source records attributed to D R Hall.

At least 55 records · Page 3Linked to original sources
PubMed2000

Is the prophylactic administration of magnesium sulphate in women with pre-eclampsia indicated prior to labour?

OBJECTIVE: To determine whether prophylactic magnesium sulphate is necessary to prevent eclampsia and associated complications among women with pre-eclampsia prior to labour. DESIGN: Case series. SETTING: Tertiary referral centre. POPULATION: Three hundred and eighteen women with pre-eclampsia (blood pressure > or = 140/90 mmHg and > or = 2+ proteinuria) who were not in labour or for planned induction thereof and had not received magnesium sulphate during transfer. METHODS: Clinical evaluation of the pregnant women with careful blood pressure control. Magnesium sulphate was withheld even in the presence of imminent eclampsia. During labour, the option of magnesium sulphate prophylaxis was left to the clinician, but magnesium sulphate was administered in cases of eclampsia. MAIN OUTCOME MEASURES: Eclampsia and related complications. RESULTS: Five women (1.5%) developed eclampsia, although none developed related complications. Women presented at an early gestational age (mean 30 weeks), with high blood pressure, often suffering from headaches. Twenty pregnancies were terminated prior to viability, of which half were terminated for maternal reasons. Ten intrauterine deaths occurred. Most often fetal distress (38.6%) initiated the delivery process, which was mainly by caesarean section (68.5%). With the exception of epigastric discomfort, symptoms and signs of imminent eclampsia decreased after admission. Blood pressure values were significantly lower at delivery although biochemistry results deteriorated from admission to delivery. CONCLUSION: In women with pre-eclampsia prior to labour, where blood pressure control was carefully applied but magnesium sulphate not given, the eclampsia rate was low and eclampsia did not appear to worsen the existing prognosis for mother or fetus.

Adult↗
PubMed2000

Expectant management of early onset, severe pre-eclampsia: maternal outcome.

OBJECTIVE: To evaluate the safety and outcome of women undergoing expectant management of early onset, severe pre-eclampsia. DESIGN: Prospective case series extending over a five-year period. SETTING: Tygerberg Hospital, a tertiary referral centre. POPULATION: All women (n = 340) presenting with early onset, severe pre-eclampsia, where both the mother and the fetus were otherwise stable. METHODS: Frequent clinical and biochemical monitoring of maternal status, together with careful blood pressure control, in a high care obstetric ward. MAIN OUTCOME MEASURES: Major maternal complications and prolongation of gestation. RESULTS: Multigravid women constituted 67% of the group. Antenatal biochemistry was reassuring with some expected, but not severe, deteriorations. Twenty-seven percent of women experienced a major complication, but few had poor outcomes. No maternal deaths occurred. Most major complications resolved quickly, necessitating only three admissions (0.8%) to the intensive care unit. One woman required dialysis. Pregnancies were prolonged by a mean (median) number of 11 days (9) before delivery, with more time being gained at earlier gestations. The postpartum inpatient stay (89% < or =7 days, bearing in mind that 82% of women were delivered by caesarean section) was not extended. CONCLUSION: Careful noninvasive management of early onset, severe pre-eclampsia in a tertiary centre can diminish and limit the impact of serious maternal complications. Valuable time to prolong the pregnancy and improve neonatal outcome is thereby gained.

Adolescent↗
PubMed2000

Expectant management of early onset, severe pre-eclampsia: perinatal outcome.

OBJECTIVE: To evaluate the perinatal outcome of expectant management of early onset, severe pre-eclampsia. DESIGN: Prospective case series extending over a five-year period. SETTING: Tertiary referral centre. POPULATION: All women (n = 340) presenting with early onset, severe pre-eclampsia, where both mother and the fetus were otherwise stable. METHODS: Frequent clinical and biochemical monitoring of maternal status with careful blood pressure control. Fetal surveillance included six-hourly heart rate monitoring, weekly Doppler and ultrasound evaluation of the fetus every two weeks. All examinations were carried out in a high care obstetric ward. MAIN OUTCOME MEASURES: Prolongation of gestation, perinatal mortality rate, neonatal survival and major complications. RESULTS: A mean of 11 days were gained by expectant management. The perinatal mortality rate was 24/1,000 (> or = 1,000 g/7 days) with a neonatal survival rate of 94%. Multivariate analysis showed only gestational age at delivery to be significantly associated with neonatal outcome. Chief contributors to neonatal mortality and morbidity were pulmonary complications and sepsis. Three pregnancies (0.8%) were terminated prior to viability and only two (0.5%) intrauterine deaths occurred, both due to placental abruption. Most women (81.5%) were delivered by caesarean section with fetal distress the most common reason for delivery. Neonatal intensive care was necessary in 40.7% of cases, with these babies staying a median of six days in intensive care. CONCLUSION: Expectant management of early onset, severe pre-eclampsia and careful neonatal care led to high perinatal and neonatal survival rates. It also allowed the judicious use of neonatal intensive care facilities. Neonatal sepsis remains a cause for concern.

Antihypertensive Agents↗
PubMed2000

Nifedipine or prazosin as a second agent to control early severe hypertension in pregnancy: a randomised controlled trial.

OBJECTIVE: To determine whether nifedipine or prazosin is the more appropriate second-line antihypertensive agent in pregnancy. DESIGN: Randomised controlled trial. SETTING: Tygerberg Hospital, a tertiary referral centre. POPULATION: Women with early, severe pre-eclampsia or hypertension in pregnancy, whose blood pressure could not be adequately controlled by methyldopa 2 g/day, but were otherwise stable. METHODS: Nifedipine or prazosin were given and increased as necessary in a stepwise fashion. Once the maximum dose was reached, the other drug was added in a crossover pattern. Failure to control blood pressure, or the onset of maternal/fetal complications were indications for delivery. Patients reaching a minimum gestation of 34 weeks without complications were delivered electively. MAIN OUTCOME MEASURES: Antenatal days gained; major maternal complications and perinatal survival. RESULTS: Days gained on the second antihypertensive agent did not differ significantly (P = 0.9), while more days were gained using nifedipine as the crossover 'third agent' (P = 0.01). In the nifedipine group better renal function was recorded, but more cases with isolated low platelet counts occurred. More cases of pulmonary oedema as well as more nonviable mid-trimester and third trimester intrauterine deaths occurred in the prazosin group. CONCLUSION: Nifedipine and prazosin as second agents allowed comparable amounts of time to be gained, although this changed when used as crossover third-line agents. The efficacy and safety of nifedipine in this study are consistent with the results of other studies. A greater number of intrauterine deaths occurred in the prazosin group.

Antihypertensive Agents↗
PubMed1999

Reassessment of the calibration constant for the IAsys biosensor.

A magnitude of 50 are s ng-1 mm2 has been determined for the calibration constant relating biosensor response to the amount of protein bound to the sensor surface of an IAsys cuvette. These studies entailed enzymatic assessment of the extent of lactate dehydrogenase depletion in the liquid phase arising from enzyme binding to a carboxymethyldextran-coated sensor surface, and also estimation of a maximum biosensor response for the electrostatic interaction of ovalbumin with an aminosilane-coated sensor surface. The latter results required correction for contributions to biosensor response resulting from changes in the refractive index of the liquid phase effected by high protein concentrations.

Biosensing Techniques↗
PubMed1999

The crystal structure of Escherichia coli class II fructose-1, 6-bisphosphate aldolase in complex with phosphoglycolohydroxamate reveals details of mechanism and specificity.

The structure of a class II fructose-1,6-bisphosphate aldolase in complex with the substrate analogue and inhibitor phosphoglycolohydroxamate (PGH) has been determined using X-ray diffraction terms to a resolution of 2.0 A (1 A=0.1 nm). The crystals are trigonal, space group P3121 with a=b=78.24 A, c=289.69 A. The asymmetric unit is a homodimer of (alpha/beta)8 barrels and the model has refined to give R-work 19.2 %, R-free (based on 5 % of the data) 23.0 %. PGH resembles the ene-diolate transition state of the physiological substrate dihydroxyacetone phosphate. It is well ordered and bound in a deep polar cavity at the C-terminal end of the (alpha/beta)8 barrel, where it chelates the catalytic zinc ion using hydroxyl and enolate oxygen atoms. Trigonal bipyramidal coordination of the zinc ion is completed by three histidine residues. The complex network of hydrogen bonds at the catalytic centre is required to organise the position of key functional groups and metal ion ligands. A well-defined monovalent cation-binding site is observed following significant re-organisation of loop structures. This assists the formation of a phosphate-binding site on one side of the barrel that tethers PGH in the catalytic site. The positions of functional groups of substrate and putative interactions with key amino acid residues are identified. Knowledge of the complex structure complements the results of spectroscopic and site-directed mutagenesis studies, and contributes to our understanding of the mechanism and substrate specificity of this family of enzymes. A reaction mechanism distinct from that proposed for other class II aldolases is discussed. The results suggest that the class II aldolases should be sub-divided into two groups on the basis of both distinct folds and mechanism.

Binding Sites↗
PubMed1999

The high-resolution crystal structure of the molybdate-dependent transcriptional regulator (ModE) from Escherichia coli: a novel combination of domain folds.

The molybdate-dependent transcriptional regulator (ModE) from Escherichia coli functions as a sensor of molybdate concentration and a regulator for transcription of operons involved in the uptake and utilization of the essential element, molybdenum. We have determined the structure of ModE using multi-wavelength anomalous dispersion. Selenomethionyl and native ModE models are refined to 1. 75 and 2.1 A, respectively and describe the architecture and structural detail of a complete transcriptional regulator. ModE is a homodimer and each subunit comprises N- and C-terminal domains. The N-terminal domain carries a winged helix-turn-helix motif for binding to DNA and is primarily responsible for ModE dimerization. The C-terminal domain contains the molybdate-binding site and residues implicated in binding the oxyanion are identified. This domain is divided into sub-domains a and b which have similar folds, although the organization of secondary structure elements varies. The sub-domain fold is related to the oligomer binding-fold and similar to that of the subunits of several toxins which are involved in extensive protein-protein interactions. This suggests a role for the C-terminal domain in the formation of the ModE-protein-DNA complexes necessary to regulate transcription. Modelling of ModE interacting with DNA suggests that a large distortion of DNA is not necessary for complex formation.

Amino Acid Sequence↗
PubMed1999

Two crystal forms of ModE, the molybdate-dependent transcriptional regulator from Escherichia coli.

The molybdenum-responsive ModE regulatory protein from Escherichia coli has been purified and used in crystallization trials. Two crystal forms have been observed. Form I is tetragonal, P41212 (or enantiomorph), with a = b = 72.3, c = 246.2 A and diffracts to medium resolution. Form II is orthorhombic, P21212, with a = 82.8, b = 127.9, c = 64.0 A and diffraction has been observed beyond 2.8 A resolution. Structural analysis, in combination with ongoing biochemical characterization, will assist the elucidation of the structure-activity relationship in regulating the uptake of molybdate in bacteria.

Bacterial Proteins↗
PubMed1998

Crystallization and preliminary X-ray diffraction studies of 6-phosphogluconate dehydrogenase from Lactococcus lactis.

6-Phosphogluconate dehydrogenase is one of the seven enzymes involved in the pentose phosphate pathway. Crystals of a mammalian and a protozoan enzyme have been obtained previously and structures determined. It is reported here that a bacterial 6-phosphogluconate dehydrogenase, from Lactococcus lactis, has been purified and used in crystallization trials. Large prisms suitable for a detailed structural analysis have been obtained and characterized as orthorhombic, space group F222, with a = 70.4, b = 105.7, c = 474.6 A. Diffraction has been observed to 2.2 A resolution using synchrotron radiation. Structural analysis, in combination with ongoing biochemical characterization, will assist the elucidation of the structure-activity relationships of this enzyme.

Bacterial Proteins↗
PubMed1998

Potential of biosensor technology for the characterization of interactions by quantitative affinity chromatography.

This review places the characterization of interactions by biosensor technology in the broader context of their study by quantitative affinity chromatography. The general reluctance to consider biosensor-based characterization as a form of quantitative affinity chromatography on the grounds of a difference in aims of the two techniques reflects a mistaken belief that BIAcore and IAsys studies characterize the kinetics of the chemical reaction responsible for biospecific adsorption of a soluble reactant to an immobilized form of its affinity partner. It now transpires that the association and dissociation rate constants thereby determined refer to thermodynamic characterization of biospecific adsorption in terms of a single-phase model in which affinity sites are distributed uniformly throughout the liquid-phase volume accessible to the partitioning reactant--the model used for characterization of biospecific adsorption by quantitative affinity chromatography. In that light the most important attribute of biosensor technology is its potential for thermodynamic characterization of biospecific adsorption by virtue of its ability to monitor complex formation directly; and hence its potential for the characterization of interactions with affinities that are too strong for study by forms of quantitative affinity chromatography that monitor complex formation on the basis of reactant depletion from the liquid phase. Kinetic as well as thermodynamic analyses of biosensor data are described for attainment of that potential.

Biosensing Techniques↗
PubMed1997

Theoretical and experimental considerations of the pseudo-first-order approximation in conventional kinetic analysis of IAsys biosensor data.

The validity of the conventional interpretation of IAsys biosensor profiles in terms of pseudo-first-order kinetic behavior is subjected to closer scrutiny by its application to simulated data for low- and high-affinity interactions between ligate and immobilized ligand. As might reasonably have been expected, analysis of the simulated data for the low-affinity system (association equilibrium constant of 10(5) M-1) in such terms returned the input association and dissociation rate constants (10(3) M-1 s-1 and 10(-2) s-1, respectively)-a consequence of essential compliance with the assumed constancy of ligate concentration in the liquid phase. For the high-affinity interaction (ka = 10(5) M-1 s-1, kd = 10(-2) s-1, KAX = 10(7) M-1) the ligate concentration was depleted by up to 35%, and hence its assumed constancy was clearly an untenable approximation. Whereas no symptomatic evidence of such violation (apart from the return of incorrect estimates of ka and kd) was evident from pseudo-first-order kinetic analysis of the adsorption profiles, the corresponding analysis of desorption profiles was more informative in that the data deviated demonstrably from pseudo-first-order kinetic behavior. A second-order kinetic analysis was therefore developed and shown to be applicable to adsorption and desorption profiles, irrespective of the validity or otherwise of the pseudo-first-order kinetic approximation. Experimental results obtained for the interaction of histidine-rich glycoprotein with immobilized IgG were then used to illustrate various features of the pseudo-first-order and second-order kinetic analyses, and to determine from the second-order analysis an association equilibrium constant of 2 x 10(8) M-1, which is 20-fold greater than the value obtained by interpretation of the profiles in terms of pseudo-first-order kinetic behavior.

Adsorption↗
PubMed1997

Use of a resonant mirror biosensor to characterize the interaction of carboxypeptidase A with an elicited monoclonal antibody.

The binding of apocarboxypeptidase A to an immobilized form of its elicited monoclonal antibody has been used to explore the potential of a biosensor instrument (IAsys) based on resonant mirror technology for the quantitative characterization of antibody-antigen interactions. Advantage has been taken of the stirred cuvette design of the IAsys instrument to develop a stepwise titration procedure for thermodynamic characterization of the interaction, an association equilibrium constant of 3.3 (+/-0.9) x 10(7) M-1 having been obtained under the conditions studied (0.1 M Tris/HCl-0.5 M NaCl, pH 7.5, 21 degrees C). In a test of the feasibility of subjecting the time course of biosensor response to conventional pseudo-first-order kinetic analysis, nonconformity of results with such description was encountered at high and low concentrations of apocarboxypeptidase A. Whereas the deviations from Langmuirian kinetic behavior at high antigen concentrations undoubtedly stem from the same sources as those already encountered in studies with the BIA-core biosensor instrument, the deviations at the other concentration extreme occur in a range in which the assumed constancy of free antigen concentration in the liquid phase is becoming a poor approximation. An alternative approach in such circumstances has been tested in which prior thermodynamic characterization is a prerequisite for rate constant evaluation by means of a second-order kinetic analysis. Finally, the effect of soluble anticarboxypeptidase A on the pseudo-first-order kinetics of the biosensor response has been used to illustrate a simple kinetic procedure for evaluating the affinity constant for the antibody-antigen interaction in solution, a value of 1.9 (+/-0.2) x 10(8) M-1 being obtained by such means.

Antibodies, Monoclonal↗
PubMed1997

Studies of protein interactions by biosensor technology: an alternative approach to the analysis of sensorgrams deviating from pseudo-first-order kinetic behavior.

A procedure for evaluating the thermodynamic equilibrium constant by kinetic analysis of sensorgrams which deviate from the pseudo-first-order kinetic behavior predicted for 1:1 interactions between ligate and affinity sites on the sensor surface is described. This analysis employs quantitative expressions that are used in conventional kinetic characterization of protein interactions by biosensor technology, but with the equilibrium sensorgram response fixed at a predetermined magnitude. Simulated sensorgrams for situations in which the aberrant kinetic behavior reflects (i) heterogeneity of affinity sites and (ii) isomerization of the complex between ligate and affinity sites are used to explore the feasibility of the approach. Its application is then illustrated with BIAcore studies of the interaction between the Fab fragment of an anti-paraquat monoclonal antibody and immobilized antigen in the form of a paraquat analog attached covalently to the sensor surface. Studies with an extremely high degree of antigen substitution on the sensor surface yielded sensorgrams that deviated markedly from pseudo-first-order kinetic behavior. However, they yielded the same binding constant (3 x 10(6) M-1) as the value deduced by conventional analysis of sensorgrams that conformed with pseudo-first-order kinetics because of a much lower concentration of immobilized antigen on the sensor surface. Such identity of binding constants eliminates heterogeneity of immobilized paraquat sites as the likely source of the aberrant kinetic behavior.

Antibodies, Monoclonal↗
PubMed1996

Demonstration of an upper limit to the range of association rate constants amenable to study by biosensor technology based on surface plasmon resonance.

Numerical simulation of BIAcore sensorgrams has highlighted the need for concern about an assumption, inherent in current determinations of rate constants for macromolecular interactions, that the concentration of solute in the flowing phase remains constant at its injected value. This assumption is shown to be valid for systems with effective association rate constants equal to or less than 10 M(-1) values characteristic of antibody interactions with protein antigens. However, the assumption loses validity when the effective association rate constant is raised to 10 M' . The basic correctness of the latter prediction is verified by an experimental study of the interaction between soybean trypsin inhibitor and immobilized -trypsin, a system with comparable reaction kinetics.

Animals↗
PubMed1996

Maternal factors contributing to asphyxia neonatorum.

The objective was to identify maternal risk factors for birth asphyxia, and took the form of a retrospective study over 3 years of 15,964 deliveries. The antenatal and intrapartum course of 68 mothers who delivered babies with birth asphyxia was studied. Babies < 34 weeks/< or = 2000 g at birth were excluded. A 5-min Apgar score < 6 was regarded as abnormal. The incidence of asphyxia neonatorum was 4.6/1000. Most mothers (76 per cent), resided locally, booked (91 per cent), and had satisfactory antenatal clinic attendance (average seven visits). The distribution showed a disproportionately large number of grand multiparas (10 per cent). Labour was characterized by prolonged first (49 per cent) and second (36 per cent) stages with a high incidence of meconium in the amniotic fluid (47 per cent). Most deliveries (53 per cent) were by caesarian section of which 44 per cent were performed for fetal distress. Meconium aspiration was common (34 per cent). High risk signs in labour can be recognized. The judicious use of the partogram, fetal scalp blood pH, and amino-infusion are encouraged.

Asphyxia Neonatorum↗