Biomedical subjects

A Li

Publications and source records attributed to A Li.

At least 19 recordsLinked to original sources

PubMed1999

Synthesis, SAR and in vivo activity of novel thienopyridine sulfonamide pyrrolidinones as factor Xa inhibitors.

Thienopyridine sulfonamide pyrrolidinones were found to be potent and selective inhibitors of the coagulation cascade enzyme factor Xa. SAR studies led to several compounds that were selected for further in vivo investigation. These novel aryl binding pocket moieties represent a structural modification to a series of fXa inhibitors. Several compounds proved to be efficacious i.v. antithrombotic agents.

Animals↗

PubMed1999

Neutral sequence variants and haplotypes at the 150 Kb ataxia-telangiectasia locus.

Sequence variants occur every few hundred bases in the human genome. We evaluated the relationship between disease-causing mutations and neutral sequence variants at the 150 Kb ataxia-telangiectasia (A-T) locus. Mutations at this locus cause a distinct autosomal recessive syndrome in homozygotes and predispose heterozygotes to cancer and coronary heart disease. Nine common neutral sequence variants were observed in the coding and splice junction regions of 132 chromosomes from Caucasian individuals of European origin. Each of these variants appeared frequently in both A-T and non-A-T chromosomes. However, there was remarkable linkage disequilibrium between the polymorphic loci, resulting in only 7 haplotypes in analyzed chromosomes. These 7 haplotypes fell into 3 major ancestral groups. No individual polymorphic variant or haplotype correlated reliably with the presence of an A-T mutation. Thus, comparing the frequency of neutral variants at the A-T locus in diseased and non-diseased populations is unlikely to uncover the relationship of mutations at this locus to common diseases. These data reflect general limitations on using single nucleotide polymorphisms (SNPs) to identify loci for many common diseases.

Alleles↗

PubMed1999

Relationship of the C242T p22phox gene polymorphism to angiographic coronary artery disease and endothelial function.

Patients with coronary artery disease (CAD) have impaired endothelial function in part due to an increase in vascular oxidant stress. p22phox, an essential component of the NADPH oxidase, is thought to play a critical role in the generation of superoxide anions in the vessel wall. The C242T polymorphism, located in the potential heme-binding site of the p22phox gene, has recently been reported to confer a protective effect on CAD risk in a Japanese study population. In a U.S. population of 252 patients (83% Caucasian) undergoing angiography for diagnosis of CAD, we investigated whether the C242T polymorphism was associated with the presence of CAD. In a subset of 142 patients, we studied whether the polymorphism manifests its potential protective effects through alteration of vascular endothelial function by measuring coronary epicardial and microvascular responses to intracoronary acetylcholine and sodium nitroprusside. Prevalence of the C242T allele was not different in 149 patients with CAD compared to 103 patients with angiographically normal coronary arteries (65.1% vs. 54.4%, P = 0.11). The C242T allele frequency in our population was nearly fourfold higher than reported previously in a Japanese population. There were also no significant differences in coronary epicardial or microvascular responses to acetylcholine or sodium nitroprusside between groups of patients with or without the C242T allele. In a U.S. population, the C242T polymorphism does not appear to confer protection from endothelial dysfunction or CAD. Am. J. Med. Genet. 86:57-61, 1999. Published 1999 Wiley-Liss, Inc.

Acetylcholine↗

PubMed1999

Regulation of endothelial cell adherens junctions by a Ras-dependent signal transduction pathway.

Adherens junctions, consisting of transmembrane cadherin molecules and their associated cytoplasmic alpha-, beta-, and gamma-catenin proteins, are thought to be critical for the development of stable cell adhesion and subsequent 3-dimensional tissue organization. In human endothelial cells there is a marked induction of gamma-catenin levels when cells reach confluence. We demonstrate that expression of a dominant negative ras gene product (N17ras) via adenoviral mediated gene transfer inhibits the confluent-dependent rise in gamma-catenin mRNA and protein levels. Consistent with its effects on overall gamma-catenin levels, expression of N17ras also reduces the amount of gamma-catenin associated with the adherens junction. Finally, although expression of N17ras under normal culture conditions produces no clear morphological phenotype, endothelial cells expressing a dominant negative ras gene product fail to form 3-dimensional, vascular-like structures when plated on reconstituted extracellular matrix.

Adenoviridae↗

PubMed1999

Analysis methods for comparison of multiple molecular dynamics trajectories: applications to protein unfolding pathways and denatured ensembles.

In molecular dynamics simulations of protein unfolding, the pathway of one protein molecule is studied at a time. In contrast, experimental denaturation studies sample from large ensembles of molecules passing from the native to unfolded state. If reasonable comparisons with experiment are to be made, then the generality of the simulations needs to be confirmed by performing multiple unfolding simulations. Given that protein unfolding trajectories are very complicated functions of the proteins and the environment, comparing different trajectories, even under the same conditions, is not straightforward. Several methods are presented here that attempt to accomplish this task at different levels of complexity. The simpler methods are geometry based and make use of the root-mean-squared deviations between structures, while the more complicated methods are based on the time variation of the various properties of the system during the unfolding process. These methods are applied to multiple simulations of three different proteins, bovine pancreatic trypsin inhibitor, chymotrypsin inhibitor 2, and barnase. In general, for these three proteins protein unfolding proceeded via expansion of the core and fraying of secondary structure to yield the major transition state. Once past the transition state, the trajectories for a given protein diverged as the protein lost further secondary and tertiary structure by a variety of mechanisms. Although the unfolding pathways diverged, similar conformations were populated in the denatured state even when the unfolding occurred via different pathways. The multitude of different pathways leading to the denatured state agrees with the funnel description of protein folding. Although the pathways differed in conformational space, the physical properties of the conformations were often similar, highlighting the danger of assuming that similar observed properties imply similar conformations. In fact, there may be many different "conformational pathways" of unfolding that fit within a preferred "property space pathway".

Aprotinin↗

PubMed1999

Value of direct smears of synovial fluid in the diagnosis of canine joint disease.

Assessments of direct smears of synovial fluid by four clinicians were compared with the results obtained with a Coulter counter. Estimates of total white cell counts by the clinicians were inaccurate and generally higher than the Coulter counter results. The method had a low sensitivity and specificity for the identification of degenerative joint disease and normal joints in comparison with the identification of inflammatory joint disease. There were marked variations in the results obtained by the four clinicians for all the analyses in the study.

Animals↗

PubMed1999

A dominant-negative strategy for studying roles of G proteins in vivo.

G proteins play a critical role in transducing a large variety of signals into intracellular responses. Increasingly, there is evidence that G proteins may play other roles as well. Dominant-negative constructs of the alpha subunit of G proteins would be useful in studying the roles of G proteins in a variety of processes, but the currently available dominant-negative constructs, which target Mg2+-binding sites, are rather leaky. A variety of studies have implicated the carboxyl terminus of G protein alpha subunits in both mediating receptor-G protein interaction and in receptor selectivity. Thus we have made minigene plasmid constructs that encode oligonucleotide sequences corresponding to the carboxyl-terminal undecapeptide of Galphai, Galphaq, or Galphas. To determine whether overexpression of the carboxyl-terminal peptide would block cellular responses, we used as a test system the activation of the M2 muscarinic receptor activated K+ channels in HEK 293 cells. The minigenes were transiently transfected along with G protein-regulated inwardly rectifying K+ channels (GIRK) into HEK 293 cells that stably express the M2 muscarinic receptor. The presence of the Galphai carboxyl-terminal peptide results in specific inhibition of GIRK activity in response to agonist stimulation of the M2 muscarinic receptor. The Galphai minigene construct completely blocks agonist-mediated M2 mAChR K+ channel response whereas the control minigene constructs (empty vector, pcDNA3.1, and the Galpha carboxyl peptide in random order, pcDNA-GalphaiR) had no effect on agonist-mediated M2 muscarinic receptor GIRK response. The inhibitory effects of the Galphai minigene construct were specific because overexpression of peptides corresponding to the carboxyl terminus of Galphaq or Galphas had no effect on M2 muscarinic receptor stimulation of the K+ channel.

Cell Line↗

PubMed1999

Modulation of hypoxic depressions of ventilatory activity in the newborn piglet by mesencephalic mechanisms.

In neonates, ventilatory responses to hypoxia are 'biphasic,' with an augmentation followed by a decline. The hypoxia-induced augmentations in ventilation are attenuated and the depressions are accentuated following denervation of the peripheral chemoreceptors. Piglets that were decerebrated at a rostral mesencephalic level exhibited these hypoxia-induced depressions. These depressions were lessened following transection through the caudal mesencephalon. Mesencephalic mechanisms play a fundamental role in the brainstem regulation of ventilatory responses to hypoxia.

Animals↗

PubMed1999

Effects of early eschar excision en masse at one operation for prevention and treatment of organ dysfunction in severely burned patients.

We sought to determine whether early eschar excision en masse (EEE) at one operation would be effective in the prevention and treatment of postburn organ dysfunction (OD) and multiple organ dysfunction syndrome (MODS). A total of 60 patients, with total body surface burned area over 35% and a third degree burn area over 20% were studied and divided into two groups, the EEE group (35 cases) and the group treated with repeated escharectomies by stages (repeated escharectomy group, 25 cases). Other than the different operations undertaken, the patients in both groups received identical conventional treatment. Before, during, and after operation the hemodynamic and blood gas indices, plasma levels of endotoxin and tumor necrosis factor (TNF), and the injurious effects of burn patients' sera on endothelial cells in vitro were determined in patients of the EEE group. The incidence of OD and MODS was decreased significantly (11.4%) in patients of the EEE group, and the cure rate increased greatly (85.7%). The cardiac output dropped to 77.8% of its preoperative level at the end of escharectomy but began to rise at 2 hours and returned to its baseline levels at 24 hours after operation. Plasma levels of endotoxin and TNF and levels of lactic dehydrogenase and 6-keto-prostaglandin F(1|ga) in the endothelial cell culture media were all reduced profoundly. The cultured endothelial cells maintained their original morphology. The findings substantiate the hypothesis that eschar excision en masse at one operation is feasible and effective in preventing and treating early postburn OD and MODS, mainly by alleviating systemic inflammatory response syndrome and endothelial cell injury.

Adult↗

PubMed1999

Characterization of the baboon responses to Shiga-like toxin: descriptive study of a new primate model of toxic responses to Stx-1.

The baboon response to intravenous infusion of Shiga toxin 1 (Stx-1) varied from acute renal failure, proteinuria, hyperkalemia, and melena with minimal perturbation of host inflammatory and hemostatic systems (high-dose group, 2.0 microg/kg; n = 5) to renal failure with hematuria, proteinuria, thrombocytopenia, schistocytosis, anemia, and melena (low-dose group, 0.05 to 0.2 microg/kg; n = 8). Both groups exhibited renal shutdown and died in 57 hours or less. Both groups produced urine that was positive for tumor necrosis factor and interleukin-6 although neither of these cytokines was detectable (</=5 ng/ml) in the general circulation. Light and electron microscopy showed organelle disintegration and necrosis of the renal proximal tubular epithelium and of the intestinal mucosal epithelium at the tips of the microvilli, both of which were previously shown to bear Gb3 receptors. The renal distal tubular epithelium was spared. The renal proximal tubular epithelial changes were accompanied by swelling of visceral epithelial cells (podocytes) and by swelling and detachment of endothelial cells of the glomerular capillaries. In addition, all of the animals receiving low-dose Stx-1 showed microvascular fibrin deposition and thrombosis in renal glomerular and peritubular capillaries in association with a fall in hematocrit and platelet count and a rise in schistocyte count. The gastrointestinal villous tip lesions were accompanied by varying degrees of mucosal and submucosal congestion, hemorrhage, or necrosis. Electron microscopic images of cerebral cortex and cerebellum showed diffuse unraveling of myelin sheaths with occasional disintegration of neuronal cell bodies. In contrast to the gastrointestinal mucosal and renal proximal tubular epithelium, the Gb3 receptor glycolipid of the renal glomerular and neuronal tissues as determined using toxin overlay thin-layer chromatography plates was below the limit of detection (<13 pM/g wet tissue). We conclude that, depending on the status of the host and amount of toxin infused, Stx-1 can produce a variety of responses ranging from damage to cells carrying the Gb3 receptor (renal proximal tubular epithelial cells and gastrointestinal mucosa) to damage to renal glomerular tissues with microvascular thrombosis as a result of the host's inflammatory response localized to the kidney. We conclude that this thrombotic coagulopathy arises from local changes in the kidney because the appearance of host inflammatory mediators was limited to the urine. This suggests that the initial host response is localized in the kidney, and that the systemic thrombocytopenia, anemia, and schistocytosis may arise secondarily.

Animals↗

PubMed1999

Circulating basic fibroblast growth factor declines during Cy/TBI bone marrow transplantation.

Basic fibroblast growth factor (bFGF) inhibits radiation-induced apoptosis, and radioprotects haematopoietic, cartilage growth plate, pulmonary and gastrointestinal tissues. Conversely, chronic overexpression of bFGF may promote fibrosis. We measured the endogenous circulating bFGF in blood of patients undergoing conditioning TBI. Twenty-six patients with haematopoietic malignancies were conditioned with cyclophosphamide/TBI for allogeneic BMT. Daily blood samples were collected each morning prior to, during, and for several days after TBI. bFGF levels in plasma of normal volunteers are 0.8-26 pg/ml. bFGF was below detectability in 22%, 30% and 45% of patients pre-TBI, during TBI or post-TBI respectively. Mean circulating plasma levels of bFGF decreased from a median of 52 pg/ml pre-TBI to 26 pg/ml during TBI, and to 5 pg/ml post-TBI. Among the 26 patients, 13 had more than one non-detectable plasma bFGF level, an additional five had at least one non-detectable level, and only eight patients had detectable levels in all daily samples. Naturally high levels of bFGF were observed in some patients undergoing fractionated TBI. In contrast, as many as 79% of patients had low bFGF levels in one or more samples. The impact of endogenous bFGF on the tolerance of normal tissues to irradiation is unknown, and warrants further study.

Adult↗

PubMed1999

Immunohistochemical analysis of pericryptal fibroblast sheath and proliferating epithelial cells in human colorectal adenomas and carcinomas with adenoma components.

In order to examine stromal-epithelial interaction during the oncogenic progression of large bowel tumors, the association between pericryptal fibroblast sheath (PCFS) and expression of Ki-67 antigen was evaluated in 87 cases of colorectal adenoma and 95 cases of carcinoma with an adenoma component (CWA). For the immunohistochemistry, anti-alpha-smooth muscle actin antibody (alpha-SMA) and anti-Ki-67 antigen antibody (MIB-1) were used. In adenomas and adenoma components of CWA, the quantity of neoplastic glands with PCFS was reduced relative to the progression of histological atypia. Pericryptal fibroblast sheath was virtually absent from invasive carcinoma areas of CWA. Increased expression of Ki-67 correlated with the degree of histological atypia of adenomas. A significant reverse correlation was also seen between Ki-67 expression and PCFS-positive glands in adenoma components of CWA. These findings suggest that the prevalence of PCFS and Ki-67 expression are important indicators of colorectal neoplasia progression. The significant reduction of PCFS in colorectal epithelial neoplasms reflects progression in the adenoma-carcinoma sequence.

Actins↗

PubMed1999

Espin contains an additional actin-binding site in its N terminus and is a major actin-bundling protein of the Sertoli cell-spermatid ectoplasmic specialization junctional plaque.

The espins are actin-binding and -bundling proteins localized to parallel actin bundles. The 837-amino-acid "espin" of Sertoli cell-spermatid junctions (ectoplasmic specializations) and the 253-amino-acid "small espin" of brush border microvilli are splice isoforms that share a C-terminal 116-amino-acid actin-bundling module but contain different N termini. To investigate the roles of espin and its extended N terminus, we examined the actin-binding and -bundling properties of espin constructs and the stoichiometry and developmental accumulation of espin within the ectoplasmic specialization. An espin construct bound to F-actin with an approximately threefold higher affinity (K(d) = approximately 70 nM) than small espin and was approximately 2.5 times more efficient at forming bundles. The increased affinity appeared to be due to an additional actin-binding site in the N terminus of espin. This additional actin-binding site bound to F-actin with a K(d) of approximately 1 microM, decorated actin stress fiber-like structures in transfected cells, and was mapped to a peptide between the two proline-rich peptides in the N terminus of espin. Espin was detected at approximately 4-5 x 10(6) copies per ectoplasmic specialization, or approximately 1 espin per 20 actin monomers and accumulated there coincident with the formation of parallel actin bundles during spermiogenesis. These results suggest that espin is a major actin-bundling protein of the Sertoli cell-spermatid ectoplasmic specialization.

Actins↗

PubMed1999

Inclusion of black Americans in oncology clinical trials: the Louisiana State University Medical Center experience.

Recruitment of patients from diverse ethnic, racial, and socioeconomic backgrounds for clinical trials is desirable for both scientific and ethical reasons. Participation rates in clinical trials are low for minorities and especially for black Americans. This report summarizes the experience at Louisiana State University Medical Center in Shreveport, Louisiana, in enrolling black Americans in oncology treatment and prevention trials. Barriers to enrollment are identified and discussed. Although major strides must still be made in the area of cancer prevention, the university's experience demonstrates that black Americans can be encouraged to participate in and can be enrolled in cancer clinical trials.

Black or African American↗

PubMed1999

Pathogenesis of early cardiac myocyte damage after severe burns.

BACKGROUND: The importance of early cardiac myocyte damage during postburn trauma has been emphasized in recent years. However, its pathogenesis, prevention, and treatment have not been fully clarified. The aim of this study is to define its pathogenesis. METHODS: Rats with 30% third-degree burns were used. Cardiac biochemical markers reflecting cardiac myocyte damage including troponin T, cardiac myosin light chain 1, creatinine kinase and its cardiac-specific isoenzyme compound, as well as inflammatory mediators such as tumor necrosis factor, endothelin/nitric oxide ratio, malondialdehyde, and superoxide dismutase, were determined. RESULTS: Cardiac biochemical markers reflecting cardiac myocyte damage, including troponin T, cardiac myosin light chain 1, cardiac-specific isoenzyme compound, were all significantly elevated between 3 hours and 24 hours after burn. Changes in tumor necrosis factor, endothelin/nitric oxide ratio, and malondialdehyde were similar to those of cardiac biochemical markers. In contrast, levels of superoxide dismutase declined markedly after burn. CONCLUSION: The findings of this study showed that considerable amounts of myocardial constructive protein degradation and release due to destruction of cardiac myocytes occurred early after severe burns. The inflammatory mediators released after burn injury may be involved in the pathogenesis of myocardial destruction.

Animals↗

PubMed1999

Effects of salicylic acid derivatives on red blood cell membranes.

Salicylamide, sodium salicylate and acetylsalicylic acid are salicylic acid derivates. They differ in their substitution on the benzene ring and may have different effects on membranes. Red blood cells were used as a prototypical cellular system regarding drug mediated plasma bilayer effects. Established photometric methods sensing tiny changes of red blood cell morphology at rest (red blood cell shape) and at very low shear forces (red blood cell stiffness, red blood cell relaxation time) were applied. The derivative induced effects were detected in a time- and dose-dependent manner. Salicylamide induced a most pronounced echinocytic shape at 5 mM. The shape effect was smaller above as well as below 5 mM. Sodium salicylate induced echinocytes with increasing concentrations showing a saturation above 10 mM. In contrast, the shape was not affected by acetylsalicylic acid. All shape changes occurred within 2 min, and were reversible. The above tendencies were in parallel to a slight red blood cell stiffening. The relaxation time continuously increased with increasing concentrations in both salicylamide and sodium salicylate, with salicylamide always acting stronger. Acetylsalicylic acid again showed no effect. We hypothesize that the observed effects of sodium salicylate and salicylamide are due to their phenolic character mediating a molecular hydrophobicity. According to the bilayer couple hypothesis this would lead to an insertion into the red blood cells outer plasma bilayer leaflet. The extension induced here would cause a positive membrane bending leading to echinocytic shapes and the observed loss of red blood cell fluidity. In contrast, the hydrophilic aspirin would penetrate and thus not affect the red blood cell plasma membrane.

Aspirin↗

PubMed1999

rRNA gene internal transcribed spacer 1 and 2 sequences of asexual, anthropophilic dermatophytes related to Trichophyton rubrum.

The ribosomal region spanning the two internal transcribed spacer (ITS) regions and the 5.8S ribosomal DNA region was sequenced for asexual, anthropophilic dermatophyte species with morphological similarity to Trichophyton rubrum, as well as for members of the three previously delineated, related major clades in the T. mentagrophytes complex. Representative isolates of T. raubitschekii, T. fischeri, and T. kanei were found to have ITS sequences identical to that of T. rubrum. The ITS sequences of T. soudanense and T. megninii differed from that of T. rubrum by only a small number of base pairs. Their continued status as species, however, appears to meet criteria outlined in the population genetics-based cohesion species concept of A. R. Templeton. The ITS sequence of T. tonsurans differed from that of the biologically distinct T. equinum by only 1 bp, while the ITS sequence of the recently described species T. krajdenii had a sequence identical to that of T. mentagrophytes isolates related to the teleomorph Arthroderma vanbreuseghemii.

Arthrodermataceae↗

PubMed1999

TRH microdialysis into the RTN of the conscious rat increases breathing, metabolism, and temperature.

Thyrotropin-releasing hormone (TRH) injected into the retrotrapezoid nucleus (RTN) of anesthetized rats produces a large, prolonged stimulation of ventilatory output (C. L. Cream, A. Li, and E. E. Nattie. J. Appl. Physiol. 83: 792-799, 1997). Here we inject or dialyze TRH into the RTN of conscious rats. In 6 of 17 injections (200 nl, 3.1 +/- 1.7 mM), ventilation (VE) increased 31% by 10 min, with recovery by 60 min. With dialysis, each animal of one group (n = 5) received, in random order, 10 mM TRH, 10 mM TRHOH (a metabolite of TRH), and artificial cerebrospinal fluid (aCSF); each animal of a second group (n = 5) received aCSF and 1 mM TRH. TRHOH and aCSF had no sustained effects. TRH (1 mM) increased VE (32%, P < 0.02, by 10 min, with recovery by 60 min), O(2) consumption (VO(2); 19%, P < 0. 03), and body (rectal) temperature (T(re); 0.5 degrees C, P < 0.09). TRH (10 mM) increased VE (78%, P < 0.01, by 10 min, with no recovery at 60 min), VO(2) (48%, P < 0.01), and T(re) (1.0 degrees C, P < 0. 01). TRH also induced arousal. The tissue volume affected in dialysis, estimated by spread of dialyzed fluorescein (332.3 mol wt, mol wt of TRH = 362.4), was 1,580 +/- 256 nl for 10 mM (n = 5) and 590 +/- 128 nl for 1 mM (n = 5). We conclude that 1) the RTN is involved in the integration of VE, VO(2), T(re), and arousal and 2) TRH may establish the responsiveness of RTN neurons.

Animals↗