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Biomedical subjects

L Regan

Publications and source records attributed to L Regan.

At least 73 records · Page 4Linked to original sources
PubMed2000

The risks associated with pregnancy in women aged 35 years or older.

The obstetric risks of adverse outcome during pregnancy in women aged > or =35 years were quantified using a retrospective analysis of data from 385 120 singleton pregnancies in the North West Thames Region, UK, between 1988 and 1997. A comparison of pregnancy outcome was made on the basis of maternal age at delivery: 18-34 years (n = 336 462), 35-40 years (n = 41 327) and women aged > 40 years (n = 7331). Women aged <18 years (n = 5246) were excluded from the study. Data are presented as percentages of 18-34 year old women, 35-40 year old and > 40 year old women, with adjusted odds ratios (OR) according to age group. Pregnant women aged 35-40 years were at increased risk of: gestational diabetes, OR = 2.63 [99% confidence interval (CI) 2.40-2.89]; placenta praevia = 1.93 (1.58-2.35); breech presentation = 1.37 (1.28-1.47); operative vaginal delivery = 1.5 (1.43-1.57); elective Caesarean section = 1.77 (1.68-1.87); emergency Caesarean section = 1.59 (1.52-1.67); postpartum haemorrhage = 1.14 (1.09-1.19); delivery before 32 weeks gestation = 1.41 (1.24-1.61); birthweight below the 5th centile = 1.28 (1.20-1. 36); and stillbirth = 1.41 (1.17-1.70). Women aged >40 years had higher OR for the same risks. Pregnant women aged >/=35 years are at increased risk of complications in pregnancy compared with younger women.

Adult↗
PubMed2000

Polycystic ovaries and recurrent miscarriage--a reappraisal.

The prevalence of polycystic ovaries (PCO) was established amongst 2199 consecutive women (median age 33 years; range 19-46) with a history of recurrent miscarriage (median 3; 3-14). A diagnosis of PCO was made if the ovarian volume was enlarged (>9 ml), there were >/=10 cysts of 2-8 mm in diameter in one plane and there was increased density of the stroma. In a cohort study, the prospective pregnancy outcome of 486 of the women scanned who were antiphospholipid antibody negative and who received no pharmacological treatment during their next pregnancy was studied. The prevalence of PCO was 40.7% (895/2199). The livebirth rate was similar amongst women with PCO (60.9%; 142/233) compared to that amongst women with normal ovarian morphology (58.5%; 148/253; not significant). Neither an elevated serum luteinizing hormone concentration (>10 IU/l) nor an elevated serum testosterone concentration (>3 nmol/l) was associated with an increased miscarriage rate. Polycystic ovarian morphology is not predictive of pregnancy loss amongst ovulatory women with recurrent miscarriage conceiving spontaneously. The search for a specific endocrine abnormality that can divide women with PCO into those with a good and those with a poorer prognosis for a future successful pregnancy continues.

Abortion, Habitual↗
PubMed2000

Prospective pregnancy outcome in untreated recurrent miscarriers with thyroid autoantibodies.

The purpose of this study was to determine the prevalence of thyroid antibodies in women with recurrent miscarriage and to observe whether their presence was predictive of future pregnancy outcome. A total of 870 consecutive, non-pregnant women with a history of three or more pregnancy losses and normal parental karyotypes were investigated for the presence of thyroglobulin antibodies (TgAb) and for thyroid microsomal antibodies (TmAb). Thyroid antibodies were found in 162 (19%) women. TgAb only were found in eight women (5%); TmAb only in 98 (60%) and both TgAb and TmAb were found in 56 (35%). Thirteen women had a history of thyroid disease and a further 15 women were found to have abnormal thyroid function. All 28 were excluded from the pregnancy outcome study. Among the remaining 134 thyroid antibody positive women, 36 women were not tested and normal thyroid stimulating hormone results were obtained for 98. In the group proven euthyroid, 14 of 24 untreated pregnancies resulted in live births (58%). Among the 710 thyroid antibody negative women, 47 of 81 untreated pregnancies resulted in live births (58%). The future risk of pregnancy loss in women with unexplained recurrent miscarriage is not affected by their thyroid antibody status.

Abortion, Habitual↗
PubMed2000

Interstitial thermo-ablation under MRI guidance for the treatment of fibroids.

Women with symptomatic uterine fibroids are increasingly seeking alternatives to open surgery. The combination of high resolution magnetic resonance imaging and the application of laser heat permit percutaneous treatment of fibroids under local anaesthetic. This article reviews the technique of interstitial thermo-ablation and other current minimally invasive therapies for symptomatic fibroids.

Adult↗
PubMed2000

The role of backbone conformational heat capacity in protein stability: temperature dependent dynamics of the B1 domain of Streptococcal protein G.

The contributions of backbone NH group dynamics to the conformational heat capacity of the B1 domain of Streptococcal protein G have been estimated from the temperature dependence of 15N NMR-derived order parameters. Longitudinal (R1) and transverse (R2) relaxation rates, transverse cross-relaxation rates (eta(xy)), and steady state [1H]-15N nuclear Overhauser effects were measured at temperatures of 0, 10, 20, 30, 40, and 50 degrees C for 89-100% of the backbone secondary amide nitrogen nuclei in the B1 domain. The ratio R2/eta(xy) was used to identify nuclei for which conformational exchange makes a significant contribution to R2. Relaxation data were fit to the extended model-free dynamics formalism, incorporating an axially symmetric molecular rotational diffusion tensor. The temperature dependence of the order parameter (S2) was used to calculate the contribution of each NH group to conformational heat capacity (Cp) and a characteristic temperature (T*), representing the density of conformational energy states accessible to each NH group. The heat capacities of the secondary structure regions of the B1 domain are significantly higher than those of comparable regions of other proteins, whereas the heat capacities of less structured regions are similar to those in other proteins. The higher local heat capacities are estimated to contribute up to approximately 0.8 kJ/mol K to the total heat capacity of the B1 domain, without which the denaturation temperature would be approximately 9 degrees C lower (78 degrees C rather than 87 degrees C). Thus, variation of backbone conformational heat capacity of native proteins may be a novel mechanism that contributes to high temperature stabilization of proteins.

Bacterial Proteins↗
PubMed2000

Understanding the sequence determinants of conformational switching using protein design.

An important goal of protein design is to understand the forces that stabilize a particular fold in preference to alternative folds. Here, we describe an extension of earlier studies in which we successfully designed a stable, native-like helical protein that is 50% identical in sequence to a predominantly beta-sheet protein, the B1 domain of Streptococcal IgG-binding protein G. We report the characteristics of a series of variants of our original design that have even higher sequence identity to the B1 domain. Their properties illustrate the extent to which protein stability and conformation can be modulated through careful manipulation of key amino acid residues. Our results have implications for understanding conformational change phenomena of central biological importance and in probing the malleability of the sequence/structure relationship.

Amino Acid Sequence↗
PubMed2000

Prevalence of hepatitis C among pregnant women attending an inner London obstetric department: uptake and acceptability of named antenatal testing.

OBJECTIVE: To examine the value of universal antenatal screening for hepatitis C virus (HCV) infection among an inner London population, with regard to prevalence, uptake, and acceptability of testing, and identification of new cases. DESIGN: Serum analysis for antibodies against HCV in pregnant women following informed consent ("opt out" policy). Samples positive for HCV antibodies were tested for the presence of HCV RNA by polymerase chain reaction. Information on hepatitis C was provided for all women. Acceptability of antenatal HCV testing and identification of risk factors for infection were assessed through the use of questionnaires randomly distributed among a cohort of 300 pregnant women. SETTING: Antenatal clinics at St Mary's Hospital, London, serving a multiethnic population. SUBJECTS: A total of 4825 pregnant women booking for antenatal care between November 1997 and April 1999. RESULTS: The overall prevalence of anti-HCV was 0.8% and HCV viraemia was 0.6%. Ninety eight per cent of samples (n=4729) were tested; 0.2% of women had a false positive result. In 207 women who completed a questionnaire regarding our testing policy, 84% made a positive decision to be tested for anti-HCV and 92% said that HCV testing should be offered to all pregnant women. The majority (22/32-69%) of HCV infected women were newly diagnosed and although HCV positive women were significantly more likely to have a history of drug abuse, most (16/22-73%) new cases had no identified risk factors for HCV infection at booking. CONCLUSION: The prevalence of anti-HCV in an inner London multiethnic antenatal population is high (0.8%). Routine screening for HCV is acceptable to pregnant women. The majority of women diagnosed during their current pregnancy would not have been identified as HCV infected by epidemiological risk factors at the time of booking.

False Positive Reactions↗
PubMed1999

Sidechain interactions in parallel beta sheets: the energetics of cross-strand pairings.

BACKGROUND: Both backbone hydrogen bonding and interactions between sidechains stabilize beta sheets. Cross-strand interactions are the closest contacts between the sidechains of a beta sheet. Here we investigate the energetics of cross-strand interactions using a variant of the B1 domain of immunoglobulin G (IgG) binding protein G (beta1) as our model system. RESULTS: Pairwise mutations of polar and nonpolar residues were made at a solvent-exposed site between the two central parallel beta strands of beta1. Both stabilizing and destabilizing interactions were measured. The greatest stabilizations were observed for charge-charge interactions. Our experimental study of sidechain interactions correlates with statistical preferences: residue pairs for which we measure stabilizing interaction energies occur together frequently, whereas destabilizing pairs are rarely observed together. CONCLUSIONS: Sidechain interactions modulate the stability of beta sheets. We propose that cross-strand sidechain interactions specify correct strand register and ordering through the energetic benefit of optimally arranged pairings.

Calorimetry↗
PubMed1999

Inhibition of spontaneous receptor phosphorylation by residues in a putative alpha-helix in the KIT intracellular juxtamembrane region.

KIT receptor kinase activity is repressed, prior to stem cell factor binding, by unknown structural constraints. Using site-directed mutagenesis, we examined the role of KIT intracellular juxtamembrane residues Met-552 through Ile-563 in controlling receptor autophosphorylation. Alanine substitution for Tyr-553, Trp-557, Val-559, or Val-560, all sitting along the hydrophobic side of an amphipathic alpha-helix (Tyr-553-Ile-563) predicted by the Chou-Fasman algorithm, resulted in substantially increased spontaneous receptor phosphorylation, revealing inhibitory roles for these residues. Alanine substitution for other residues, most of which are on the hydrophilic side of the helix, caused no or slightly increased basal receptor phosphorylation. Converting Tyr-553 or Trp-557 to phenylalanine generated slight or no elevation, respectively, in basal KIT phosphorylation, indicating that the phenyl ring of Tyr-553 and the hydrophobicity of Trp-557 are critical for the inhibition. Although alanine substitution for Lys-558 had no effect on receptor phosphorylation, its substitution with proline produced high spontaneous receptor phosphorylation, suggesting that the predicted alpha-helical conformation is involved in the inhibition. A synthetic peptide comprising Tyr-553 through Ile-563 showed circular dichroism spectra characteristic of alpha-helix, supporting the structural prediction. Thus, the KIT intracellular juxtamembrane region contains important residues which, in a putative alpha-helical conformation, exert inhibitory control on the kinase activity of ligand-unoccupied receptor.

Amino Acid Sequence↗
PubMed1999

Using loop length variants to dissect the folding pathway of a four-helix-bundle protein.

Rop is a four-helix-bundle protein formed by the association of two helix-loop-helix monomers. The short helix-connecting loop was replaced with a series of polyglycine linkers of increasing length. These mutant proteins all appear to fold via the same general mechanism as that of the wild-type protein, even at the longest loop lengths. Replacement of the wild-type two-residue loop (Asp-Ala) with a (Gly-Gly) linker accelerates both unfolding and refolding rates. These changes in folding and unfolding kinetics likely indicate an alteration in the energy of the transition state. As the length of the glycine linker is further increased, the unfolding rate increases while the refolding rates decrease. The influence of loop length is not limited to these rates, but also impacts upon the stability of the folding intermediate. These dependences underscore the importance of loop closure and help refine the model for Rop's folding, implicating a dimeric intermediate involving hairpin formation. These observations show that loop alteration may be useful as a general technique for dissecting protein folding pathways.

Escherichia coli↗
PubMed1999

Regulation of Hsp90 ATPase activity by tetratricopeptide repeat (TPR)-domain co-chaperones.

The in vivo function of the heat shock protein 90 (Hsp90) molecular chaperone is dependent on the binding and hydrolysis of ATP, and on interactions with a variety of co-chaperones containing tetratricopeptide repeat (TPR) domains. We have now analysed the interaction of the yeast TPR-domain co-chaperones Sti1 and Cpr6 with yeast Hsp90 by isothermal titration calorimetry, circular dichroism spectroscopy and analytical ultracentrifugation, and determined the effect of their binding on the inherent ATPase activity of Hsp90. Sti1 and Cpr6 both bind with sub-micromolar affinity, with Sti1 binding accompanied by a large conformational change. Two co-chaperone molecules bind per Hsp90 dimer, and Sti1 itself is found to be a dimer in free solution. The inherent ATPase activity of Hsp90 is completely inhibited by binding of Sti1, but is not affected by Cpr6, although Cpr6 can reactivate the ATPase activity by displacing Sti1 from Hsp90. Bound Sti1 makes direct contact with, and blocks access to the ATP-binding site in the N-terminal domain of Hsp90. These results reveal an important role for TPR-domain co-chaperones as regulators of the ATPase activity of Hsp90, showing that the ATP-dependent step in Hsp90-mediated protein folding occurs after the binding of the folding client protein, and suggesting that ATP hydrolysis triggers client-protein release.

Adenosine Triphosphatases↗
PubMed1999

Protein redesign.

It has been demonstrated that, for a number of proteins, it is possible to dramatically alter the connectivities between elements of secondary structure. Remarkably large loop insertions are tolerated and many redesigns have generated proteins that successfully fold to stable, active structures. Some redesigns have been entirely the choice of the investigators, whereas others have incorporated a randomization and selection step to identify optimal sequences. These studies have provided basic guidelines for the rational manipulation of protein structure and stability, they have allowed the dissection of folding pathways and they have generated proteins with the potential for practical therapeutic applications.

Bacterial Proteins↗
PubMed1999

Secondary ligands enhance affinity at a designed metal-binding site.

BACKGROUND: Specific interactions of metal ions with proteins are central to all life processes. The varied functions enabled by this cooperation are a consequence of strict control of the binding-site environment, particularly the number, type and geometry of metal-coordinating sidechains. Attempts to mimic these characteristics in the de novo design of metal-binding sites have thus far concentrated primarily on metal recruitment and not on affecting site function through systematic fine-tuning of the metal environment. RESULTS: A designed tetrahedral Zn(II)-binding site in a variant of the B1 domain of IgG-binding protein G has been expanded by introducing 'secondary ligands'. These interactions were engineered to stabilize the positions of the metal-coordinating histidine residues while retaining the desired coordination geometry. Each mutation increased the protein's affinity for metal, and combining two secondary ligands demonstrated that these enhancements are additive. These results mimic the effects of altering similar interactions observed in the native Zn(II)-binding site of carbonic anhydrase. In the B1 system, this enhanced affinity for metal is observed despite a substantial decrease in protein secondary structure. CONCLUSIONS: The intended effects of secondary ligand addition on metal affinity were observed in each mutant and demonstrated to be additive. Addition of metal also stabilized the protein's structure, partially offsetting the destabilizing effect of the mutations. These results represent a successful first attempt at designing an extended metal-binding site environment and illustrate the importance of including secondary interactions in the design of metal-binding sites.

Bacterial Proteins↗
PubMed1999

Glucose production by the human placenta in vivo.

The human placenta transports glucose by facilitated diffusion down a concentration gradient from mother to fetus. It has previously been considered incapable of glucose synthesis. However, recent work has demonstrated the presence in placental tissue of glucose-6-phosphatase, which is required for the final step in the synthesis of glucose. Following continuous intravenous infusion into the maternal circulation of the stable isotope, 6,6-(2)H(2)glucose, during elective caesarean section, we have observed isotope dilution in the umbilical vein, without further dilution in the umbilical artery. Using a mathematical model containing maternal, placental and fetal compartments, the data were compatible with the release of glucose by the placenta. We conclude that the human placenta at term can produce glucose.

Adult↗
PubMed1999

Endometrial CD56+ natural killer cells in women with recurrent miscarriage: a histomorphometric study.

Endometrial natural killer (NK) cells were compared in luteal-phase endometrial samples from women with recurrent miscarriage and from normal subjects. Cryostat sections were labelled using a monoclonal antibody to CD56 using an avidin-biotin complex method and a morphometric study performed. Increased mean numbers of CD56+ cells were documented in the endometrium of women with recurrent early miscarriage only. These findings suggest a possible role for NK cells in the pathogenesis of recurrent early pregnancy loss.

Abortion, Habitual↗