PubMed Health⌕ Search

Biomedical subjects

L J Thomas

Publications and source records attributed to L J Thomas.

At least 19 recordsLinked to original sources
PubMed2001

Digoxin to facilitate late second-trimester abortion: a randomized, masked, placebo-controlled trial.

OBJECTIVE: To examine the efficacy of digoxin for decreasing operative time, difficulty, and pain of late second-trimester surgical abortions. METHODS: We performed a randomized, double-masked, placebo-controlled trial of intra-amniotic digoxin for second-trimester dilation and evacuation (D&E) involving 126 consecutive women at an inner-city public hospital. Eligible women had gestational ages of 20-23.1 weeks, spoke English or Spanish, and were at least 16 years old. Digoxin (1 mg) or saline was injected intra-amniotically 24 hours before the procedure, at cervical laminaria insertion. The primary outcome was procedure duration. Sample size was based on 80% power to detect a difference of 3.5 minutes between groups. RESULTS: The two groups were similar in demographic factors, obstetric histories, and gestational duration. The average gestational length was 22.5 weeks. There was no difference in procedure duration (mean +/- standard deviation) between groups (placebo 14.7 +/- 7.0, digoxin 15.4 +/- 8.0). There were no differences in blood loss estimated by surgeons, pain scores, procedure difficulty scores, or complications between groups. Vomiting was significantly more common in those who received digoxin (placebo 3.1%, digoxin 16.1%). Most subjects (91%) reported that they preferred their fetuses were dead before the abortions. CONCLUSION: Although digoxin did not increase efficacy of late second-trimester abortion, patient preference might justify its use.

Abortifacient Agents↗
PubMed2001

Carboxyhemoglobin levels in patients with sickle-cell anemia: relationship to hemolytic and vasoocclusive severity.

BACKGROUND: When carbon monoxide binds to hemoglobin, it increases the affinity of hemoglobin for oxygen and shifts the oxygen dissociation curve to the left. The resulting decrease in sickling tendency could have clinical benefit, and carbon monoxide has been suggested as a treatment for sickle-cell disease. Furthermore, in sickle-cell disease, as in other hemolytic diseases, endogenous carbon monoxide production is increased because of increased heme catabolism. METHODS: In the present study, we measured carboxyhemoglobin levels in sickle-cell patients and compared them with estimates of the hemolytic and the vasoocclusive severity of the disease. RESULTS: Significant correlation was found between carboxyhemoglobin (HbCO) levels and hematocrit, reticulocyte count, unconjugated bilirubin level, and percentage of irreversibly sickled cells. However, there was no significant correlation between carboxyhemoglobin levels and measures of the vaso-occlusive severity of the disease. CONCLUSIONS: The correlations between HbCO levels and measures of hemolytic severity are best explained by the known relationship between hemoglobin catabolism and CO production. The lack of correlation with vaso-occlusive severity may be due to the complex changes involved and the difficulty of quantifying vasoocclusive severity.

Adult↗
PubMed2000

Characterization of N-linked oligosaccharides bearing sialyl lewis x moieties on an alternatively glycosylated form of soluble complement receptor type 1 (sCR1).

We sought to produce a complement inhibitory protein possessing oligosaccharides specifically modified to contain the sialyl Lewis x (sLe(x)) moiety. This modified glycoprotein could combine anti-complement activity with the ability to inhibit selectin-mediated interactions and concentrate this activity to sites of activated endothelium where selectins are upregulated. Soluble complement receptor type 1 (sCR1), previously shown to be effective in inhibiting the complement cascade, was produced in a cell line capable of adding fucose to N-linked oligosaccharides in the alpha1-3 linkage, which is necessary for sLe(x) glycosylation. The glycoprotein purified from these cells was designated sCR1sLe(x), and may prove to be more effective than sCR1 in some clinical applications. Detailed analysis and characterization of sCR1sLe(x) was performed to confirm that the N-linked oligosaccharides possessed sLe(x) moieties and also to determine the extent of sLe(x) glycosylation. The glycoproteins were characterized by oligosaccharide profiling, sequencing, linkage analysis and quantified by differential enzymic digestion, using fluorophore-assisted carbohydrate electrophoresis. The major glycans were identified as biantennary oligosaccharides (including sialylated and non-core fucosylated glycans). The linkages of sialic acid and the branched fucose were analysed by digestion with linkage-specific enzymes and subsequent separation by electrophoresis. All data were consistent with the presence of sLe(x) moieties on the N-linked oligosaccharides of sCR1sLe(x). sCR1sLe(x) is a prime example of a recombinant protein expressed with oligosaccharides engineered for a specific biological function, and produced using a commercially viable method.

Carbohydrate Conformation↗
PubMed2000

Safety of intra-amniotic digoxin administration before late second-trimester abortion by dilation and evacuation.

OBJECTIVE: The purpose of this study was to determine the safety of intra-amniotic digoxin injection before late second-trimester pregnancy termination by dilation and evacuation through an assessment of maternal systemic digoxin absorption, cardiac rhythm, and coagulation parameters. STUDY DESIGN: Pregnant women at between 19 and 23 weeks' gestation received 1.0 mg digoxin through intra-amniotic injection and then had serum digoxin levels determined for 48 hours and Holter cardiac monitoring performed for 24 hours. Clotting parameters were assessed before digoxin injection and 24 hours later, at the time of the dilation and evacuation procedure. RESULTS: Eight patients completed the study. The mean (+/-SD) serum digoxin peak concentration was 0.81 +/- 0.22 microg/L (range, 0.5-1.1 microg/L). The mean (+/-SD) time to peak digoxin concentration was 11.0 +/- 5.55 hours (range, 4-20 hours). Ambulatory cardiac monitoring showed no rhythm or conduction abnormalities associated with digoxin. Prothrombin time, partial thromboplastin time, and fibrinogen levels did not change significantly between determinations before and after the dilation and evacuation procedure (11.5 to 11.4 seconds, 24.1 to 24.4 seconds, and 441 to 475 mg/dL, respectively). CONCLUSION: The maximum digoxin concentration peak achieved after intra-amniotic injection was in the low therapeutic range. No rhythm or conduction abnormalities associated with digoxin were noted by Holter monitoring. Coagulation parameters did not change significantly. On the basis of the limited systemic absorption and the absence of clinically significant cardiac or clotting effects, intra-amniotically administered digoxin may be considered safe for use before late second-trimester pregnancy terminations.

Abortion, Induced↗
PubMed2000

Vaccine-induced antibodies inhibit CETP activity in vivo and reduce aortic lesions in a rabbit model of atherosclerosis.

Using a vaccine approach, we immunized New Zealand White rabbits with a peptide containing a region of cholesteryl ester transfer protein (CETP) known to be required for neutral lipid transfer function. These rabbits had significantly reduced plasma CETP activity and an altered lipoprotein profile. In a cholesterol-fed rabbit model of atherosclerosis, the fraction of plasma cholesterol in HDL was 42% higher and the fraction of plasma cholesterol in LDL was 24% lower in the CETP-vaccinated group than in the control-vaccinated group. Moreover, the percentage of the aorta surface exhibiting atherosclerotic lesion was 39.6% smaller in the CETP-vaccinated rabbits than in controls. The data reported here demonstrate that CETP activity can be reduced in vivo by vaccination with a peptide derived from CETP and support the concept that inhibition of CETP activity in vivo can be antiatherogenic. In addition, these studies suggest that vaccination against a self-antigen is a viable therapeutic strategy for disease management.

Animals↗
PubMed1999

Recombinant glycoproteins that inhibit complement activation and also bind the selectin adhesion molecules.

Soluble human complement receptor type 1 (sCR1, TP10) has been expressed in Chinese hamster ovary (CHO) DUKX-B11 cells and shown to inhibit the classical and alternative complement pathways in vitro and in vivo. A truncated version of sCR1 lacking the long homologous repeat-A domain (LHR-A) containing the C4b binding site has similarly been expressed and designated sCR1[desLHR-A]. sCR1[desLHR-A] was shown to be a selective inhibitor of the alternative complement pathway in vitro and to function in vivo. In this study, sCR1 and sCR1[desLHR-A] were expressed in CHO LEC11 cells with an active alpha(1,3)-fucosyltransferase, which makes possible the biosynthesis of the sialyl-Lewisx (sLex) tetrasaccharide (NeuNAcalpha2-3Galbeta1-4(Fucalpha1-3)GlcNAc) during post-translational glycosylation. The resulting glycoproteins, designated sCR1sLex and sCR1[desLHR-A]sLex, respectively, retained the complement regulatory activities of their DUKX B11 counterparts, which lack alpha(1-3)-fucose. Carbohydrate analysis of purified sCR1sLex and sCR1[desLHR-A]sLex indicated an average incorporation of 10 and 8 mol of sLex/mol of glycoprotein, respectively. sLex is a carbohydrate ligand for the selectin adhesion molecules. sCR1sLex was shown to specifically bind CHO cells expressing cell surface E-selectin. sCR1[desLHR-A]sLex inhibited the binding of the monocytic cell line U937 to human aortic endothelial cells, which had been activated with tumor necrosis factor-alpha to up-regulate the expression of E-selectin. sCR1sLex inhibited the binding of U937 cells to surface-adsorbed P-selectin-IgG. sCR1sLex and sCR1[desLHR-A]sLex have thus demonstrated both complement regulatory activity and the capacity to bind selectins and to inhibit selectin-mediated cell adhesion in vitro.

Animals↗
PubMed1999

Endothelial targeting and enhanced antiinflammatory effects of complement inhibitors possessing sialyl Lewisx moieties.

The complement inhibitor soluble complement receptor type 1 (sCR1) and a truncated form of sCR1, sCR1[desLHR-A], have been generated with expression of the selectin-reactive oligosaccharide moiety, sialyl Lewisx (sLex), as N-linked oligosaccharide adducts. These modified proteins, sCR1sLex and sCR1[desLHR-A]sLex, were assessed in the L-selectin- and P-selectin-dependent rat model of lung injury following systemic activation of complement by cobra venom factor and in the L-selectin-, P-selectin-, and E-selectin-dependent model of lung injury following intrapulmonary deposition of IgG immune complexes. In the cobra venom factor model, sCR1sLex and sCR1[desLHR-A]sLex caused substantially greater reductions in neutrophil accumulation and in albumin extravasation in lung when compared with the non-sLex-decorated forms. In this model, increased lung vascular binding of sCR1sLex and sCR1[desLHR-A]sLex occurred in a P-selectin-dependent manner, in contrast to the absence of any increased binding of sCR1 or sCR1[desLHR-A]. In the IgG immune complex model, sCR1[desLHR-A]sLex possessed greater protective effects relative to sCR1[desLHR-A], based on albumin extravasation and neutrophil accumulation. Enhanced protective effects correlated with greater lung vascular binding of sCR1[desLHR-A]sLex as compared with the non-sLex-decorated form. In TNF-alpha-activated HUVEC, substantial in vitro binding occurred with sCR1[desLHR-A]sLex (but not with sCR1[desLHR-A]). This endothelial cell binding was blocked by anti-E-selectin but not by anti-P-selectin. These data suggest that sLex-decorated complement inhibitors have enhanced antiinflammatory effects and appear to have enhanced ability to localize to the activated vascular endothelium.

Anti-Inflammatory Agents, Non-Steroidal↗
PubMed1998

Filter matrix estimation in automated DNA sequencing.

In four-color fluourescence-based automated DNA sequencing, a 4 x 4 filter matrix parameterizes the relationship between the dye-intensity signals of interest and the data collected by an optical imaging system. The filter matrix is important because the estimated DNA sequence is based on the dye intensities that can only be recovered via inversion of the matrix. In this paper, we present a calibration method for the estimation of the columns of this matrix, using data generated through a special experiment in which DNA samples are labeled with only one fluorescent dye at a time. Simulations and applications of the method to real data are provided, with promising results.

Algorithms↗
PubMed1997

A method to determine the filter matrix in four-dye fluorescence-based DNA sequencing.

In a previous paper (Yin et al., Electrophoresis 1996, 17, 1143-1150), an automated method for matrix determination in four-dye fluorescence-based DNA sequencing was presented. As a continuation of that work, we have developed an alternative method to estimate the matrix from raw sequence data. The method uses an iterative clustering technique to associate each 4 x 1 data vector with one column of the desired filter matrix, using Kullback's I-divergence as a distance measure. The method requires less preprocessing of the data and less computation than the approach described by Yin et al. (Electrophoresis 1996, 17, 1143-1150). An example demonstrating applicability of the proposed method to Applied Biosystems sequencer data is given.

Algorithms↗
PubMed1994

Artifacts in computational optical-sectioning microscopy.

We tested the most complete optical model available for computational optical-sectioning microscopy and obtained four main results. First, we observed good agreement between experimental and theoretical point-spread functions (PSF's) under a variety of imaging conditions. Second, using these PSF's, we found that a linear restoration method yielded reconstructed images of a well-defined phantom object (a 10-microns-diameter fluorescent bead) that closely resembled the theoretically determined, best-possible linear reconstruction of the object. Third, this best linear reconstruction suffered from a (to our knowledge) previously undescribed artifactual axial elongation whose principal cause was not increased axial blur but rather the conical shape of the null space intrinsic to nonconfocal three-dimensional (3D) microscopy. Fourth, when 10-microns phantom beads were embedded at different depths in a transparent medium, reconstructed bead images were progressively degraded with depth unless they were reconstructed with use of a PSF determined at the bead's depth. We conclude that (1) the optical model for optical sectioning is reasonably accurate; (2) if PSF shift variance cannot be avoided by adjustment of the optics, then reconstruction methods must be modified to account for this effect; and (3) alternative microscopical or nonlinear algorithmic approaches are required for overcoming artifacts imposed by the missing cone of frequencies that is intrinsic to nonconfocal 3D microscopy.

Artifacts↗
PubMed1993

Shoulder dystocia: an analysis of risks and obstetric maneuvers.

OBJECTIVE: The purpose of this study was to determine whether there is a risk profile for predicting or preventing shoulder dystocia and whether any of the obstetric maneuvers to disimpact a shoulder reduce the likelihood of permanent injury. STUDY DESIGN: A retrospective analysis of 14,297 parturients with 12,532 vaginal deliveries and 1765 cesarean sections (12.4%) from January 1986 through June 1990 was performed. A total of 204 maternal and infant charts, related to shoulder dystocia or neonatal injury, were reviewed in depth for age, parity, episiotomy, type of delivery, hemorrhage, maternal obesity, diabetes, weight gain, fetal weight, sex, and Apgar scores. In addition, the type of maneuver or combination thereof used to relieve the dystocia, type of injury to the infant, and follow-up of the injury were reviewed. RESULTS: The 185 coded episodes of shoulder dystocia represent 1.4% of all vaginal deliveries (12,532). There were 42 injuries recorded: 14 fractured clavicles and 28 brachial plexus injuries. An additional 19 patients, not coded for shoulder dystocia, sustained 14 fractured clavicles and five brachial plexus injuries. All but one of the brachial plexus injuries resolved by 6 months. The occurrence of shoulder dystocia increased in direct relationship to the birth weight and becomes significant in newborns over 4000 gm (p < 0.01). The occurrence of a previous large infant was also a significant risk factor (p < 0.01). Diabetes and midforceps delivery become significant factors only in the presence of a large fetus. Obesity, multiparity, postdate pregnancy, use of oxytocin, low forceps delivery, episiotomy, and type of anesthesia were unrelated to shoulder dystocia. No delivery method was without injury. CONCLUSIONS: This study clearly indicates that most of the traditional risk factors for shoulder dystocia have no predictive value, shoulder dystocia itself is an unpredictable event, and infants at risk for permanent injury are virtually impossible to predict. In addition, no delivery method in shoulder dystocia was superior to another with respect to injury. Thus no protocol should serve to substitute for clinical judgment.

Delivery, Obstetric↗
PubMed1992

Biosynthesis of phosphatidylinositol-glycan (PI-G)-anchored membrane proteins in cell-free systems: PI-G is an obligatory cosubstrate for COOH-terminal processing of nascent proteins.

It is generally recognized that nascent proteins destined to be processed to a phosphatidylinositol-glycan (PI-G)-anchored membrane form contain a hydrophobic signal peptide at both their NH2 and COOH termini. In previous studies we showed that rough microsomal membranes (RM) prepared from CHO cells can carry out COOH-terminal processing. We have now investigated RM prepared from many additional cell types, including frog oocytes, B cells, and T cells, and found that all are competent with respect to COOH-terminal processing. Exceptions were certain mutant T cells that had been shown to be defective at various steps of PI-G anchor biosynthesis [Sugiyama, E., De Gasperi, R., Urakaze, M., Chang, H.-M., Thomas, L. J., Hyman, R., Warren, C. D. & Yeh, E. T. H. (1991) J. Biol. Chem. 266, 12119-12122]. In one such defective mutant, COOH-terminal processing activity of RM could be restored either by transfecting the intact cells with the gene for the deficient step in PI-G synthesis or by adding PI-G extracts to the RM in vitro. Cleavage of the COOH-terminal signal peptide in the RM is therefore dependent on the presence of intact PI-G incorporated into the mature protein.

Acyltransferases↗
PubMed1992

A personal computer based implementation of the maximum-likelihood method of analysis of electron microscope autoradiographs.

The maximum-likelihood (ML) method for the quantitative analysis of electron-microscopic autoradiographs has been shown to be substantially superior to the conventional crossfire (CF) method. It can generate reliable and accurate tracer concentration estimates with far fewer micrographs and produce valid estimates even at counts low enough to preclude the use of the crossfire method while eliminating the need for special ad hoc treatment of narrow membranous structures as well as the secondary verification of the tracer concentration estimates. Despite these significant advantages, the large computational requirements of the ML method has to date hampered its widespread use. In this paper, we present a new line-integration method that allows us to reduce the computational requirements of the ML method to a point where it becomes feasible to implement it on a small computer system of the type typically available to a laboratory user of EM autoradiography. We present the complete line-integration method for the particular case of EM autoradiography with tritium, and show how it can be adapted to other isotopes. We have constructed a software package that implements the complete maximum-likelihood method on the IBM PC class of machines using our line-integration method. Features of this software package which are of particular importance to the research community are device independence, which makes it usable with a large variety of currently available laboratory equipment, and easy portability of the software and data between different computer systems.

Algorithms↗
PubMed1992

Differential expression of glycosylphosphatidylinositol-anchored proteins in a murine T cell hybridoma mutant producing limiting amounts of the glycolipid core. Implications for paroxysmal nocturnal hemoglobinuria.

A T cell hybridoma mutant, which expressed a markedly reduced level of glycosylphosphatidylinositol (GPI)-anchored proteins on the cell surface, was characterized. The surface expression level of Thy-1 was approximately 17% of the wild-type level, whereas the surface expression of Ly-6A was approximately 2.4% of the wild-type level. We show here that these cells synthesized limiting amounts of the GPI core and that the underlying defect in these cells was an inability to synthesize dolichyl phosphate mannose (Dol-P-Man) at the normal level. The defect in Ly-6A expression could be partially corrected by tunicamycin, which blocked the biosynthesis of N-linked oligosaccharide precursors and shunted Dol-P-Man to the GPI pathway. Full restoration of Thy-1 and Ly-6A expression, however, required the stable transfection of a yeast Dol-P-Man synthase gene into the mutants. These results revealed that when the GPI core is limiting, there is a differential transfer of the available GPI core to proteins that contain GPI-anchor attachment sequences. Our findings also have implications for the elucidation of the defects in paroxysmal nocturnal hemoglobinuria.

Animals↗
PubMed1992

Regularized linear method for reconstruction of three-dimensional microscopic objects from optical sections.

The inverse problem involving the determination of a three-dimensional biological structure from images obtained by means of optical-sectioning microscopy is ill posed. Although the linear least-squares solution can be obtained rapidly by inverse filtering, we show here that it is unstable because of the inversion of small eigenvalues of the microscope's point-spread-function operator. We have regularized the problem by application of the linear-precision-gauge formalism of Joyce and Root [J. Opt. Soc. Am. A 1, 149 (1984)]. In our method the solution is regularized by being constrained to lie in a subspace spanned by the eigenvectors corresponding to a selected number of large eigenvalues. The trade-off between the variance and the regularization error determines the number of eigenvalues inverted in the estimation. The resulting linear method is a one-step algorithm that yields, in a few seconds, solutions that are optimal in the mean-square sense when the correct number of eigenvalues are inverted. Results from sensitivity studies show that the proposed method is robust to noise and to underestimation of the width of the point-spread function. The method proposed here is particularly useful for applications in which processing speed is critical, such as studies of living specimens and time-lapse analyses. For these applications existing iterative methods are impractical without expensive and/or specially designed hardware.

Computer Simulation↗
PubMed1992

A graphical user interface for quantitative imaging and analysis of electrophoretic gels and autoradiograms.

DNA/GUI (DNA Graphical User Interface) is an interactive software system for rapid and efficient analysis of images of the types used in genome mapping, such as autoradiograms and electrophoretic gels. Images are digitized using a commercially available charge-coupled-device (CCD) camera system and analyzed on a graphics workstation using a menu-driven user interface. DNA/GUI features automatic lane and band detection, simultaneous display of multiple images and a unique spatial-normalization algorithm. Images and their associated data are archived and easily available for later recall. Preliminary results indicate that DNA/GUI is a useful tool in the analysis and comparison of images used in a variety of applications such as genetic-linkage analysis and DNA restriction mapping. The interactive display software is based on the X Window System and is therefore readily portable to a variety of graphics workstations.

Autoradiography↗