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Biomedical subjects

W Wang

Publications and source records attributed to W Wang.

At least 1,099 records · Page 61Linked to original sources
PubMed1996

Depressed baroreflex in heart failure is not due to structural change in carotid sinus nerve fibers.

It is well known that the baroreceptor reflex is blunted in the heart failure state. However, the mechanisms for this depression are not well understood. The aim of the present study was to determine if carotid sinus nerve fiber density is decreased in the heart failure state. Experiments were carried out in pacing-induced heart failure and normal dogs. The carotid sinus nerve (CSN) was dissected and the CSN discharge responses to changes in arterial pressure with nitroglycerin (25 micrograms/kg, i.v.) or phenylephrine (10 micrograms/kg, i.v.) were recorded. Thereafter, the carotid sinus area was isolated and perfused with oxygenated Krebs-Henseleit solution. Carotid sinus baroreceptor single-unit activity was recorded and a carotid sinus pressure-discharge curve was constructed using either static or pulsatile pressure. Finally, the carotid sinus nerve was removed and fixed at its in situ length in 3% glutaraldehyde. The fixed carotid sinus nerve was cut transversely in 0.5-1.0-micron sections and prepared for electron microscopy. A photographic collage of the CSN was then analyzed at 4000 x magnification. The total number, diameter and area of myelinated and non-myelinated fibers were measured with a digitizer and the density and diameter distribution were calculated. Carotid sinus nerve discharge responses to change in arterial pressure were significantly blunted in dogs with pacing-induced heart failure. Furthermore, single-unit baroreceptor responses to both static and pulsatile pressurization were markedly depressed in dogs with heart failure. However, there was no change in either fiber density or the ratio of myelinated fibers to unmyelinated fibers in the carotid sinus nerve in heart failure. In addition, there was no change in the distribution of either fiber diameter or cross-sectional area in the carotid sinus nerve in dogs with heart failure. These data indicate that there is no significant change in the number or type of fibers in the CSN of dogs with heart failure. Therefore, the depressed baroreceptor reflex in heart failure is not due to structural changes in fibers of the CSN. The depressed baroreflex is most likely due to desensitization of individual baroreceptors.

Animals↗
PubMed1996

Acylfulvenes, a new class of potent antitumor agents.

Acylfulvene, derived from the sesquiterpene illudin S by treatment with acid (reverse Prins reaction), is far less reactive to thiols than illudin S. However, it is reduced readily to an aromatic product, in the same way as illudin S. This may explain its greatly improved therapeutic index compared to that of the parent compound.

Animals↗
PubMed1996

Inactivation of inosine 5'-monophosphate dehydrogenase by the antiviral agent 5-ethynyl-1-beta-D-ribofuranosylimidazole-4-carboxamide 5'-monophosphate.

Inosine 5'-monophosphate dehydrogenase (IMPDH) is the rate-limiting enzyme in de novo guanine nucleotide biosynthesis. IMPDH converts inosine 5'-monophosphate (IMP) to xanthosine 5'-monophosphate (XMP) with concomitant conversion of NAD+ to NADH. The antiviral agent 5-ethynyl-1-beta-D-ribofuranosylimidazole-4-carboxamide (EICAR) is believed to inhibit IMPDH by forming an active metabolite, the 5'-monophosphate EICARMP. The experiments reported here demonstrate that EICARMP irreversibly inactivates both human type II and Escherichia coli IMPDH. IMPDH is protected from EICARMP inactivation by IMP, but not by NAD+. Further, denaturation/renaturation of the EICARMP-inactivated enzyme did not restore enzyme activity, which indicates that EICARMP forms a covalent adduct with IMPDH. EICARMP was successfully used to titrate the active sites of IMPDH; these experiments demonstrate that four active sites are present in an IMPDH tetramer. Matrix-assisted laser desorption ionization time-of-flight (MALDI-TOF) mass spectrometry of native E. coli IMPDH established that protein translation initiates at the third ATG of the DNA sequence. Thus, the E. coli IMPDH monomer is only 488 amino acids long and contains five instead of six cysteines. In addition, MALDI-TOF mass spectrometry showed that EICARMP is covalently bound to Cys-305 (Cys-331 in human type II IMPDH numbering), suggesting that Cys-305 functions as a nucleophile in the IMPDH reaction. The inactivation of the E. coli enzyme is a single-step reaction with kon = 1.94 x 10(4) M-1 s-1. In contrast, the inactivation of human type II IMPDH involves a two-step mechanism where Ki = 16 microM, k2 = 2.7 x 10(-2) s-1 and kon = 1.7 x 10(3) M-1 s-1. These results demonstrate that significant differences exist between bacterial and human IMPDH and suggest that this enzyme may be a target for antibiotic drugs.

Amino Acid Sequence↗
PubMed1996

Characterizations and comparisons of eupnoea and gasping in neonatal rats.

1. Our purpose was to characterize the ventilatory patterns of eupnoea and gasping in the neonatal rat. This study was precipitated by reports, using in vitro brainstem spinal cord preparations, that only a single pattern is present in neonatal rats. 2. In anaesthetized or decerebrate rat pups aged less than 13 days, eupnoea was characterized by a sudden onset of inspiratory activity and then a more gradual rise to peak levels. Following vagotomy, frequency fell and peak phrenic activity and tidal volume increased. The rate of rise of inspiratory activity also rose, but peak levels were still achieved during the latter half of inspiration. Vagal efferent activity exhibited bursts during both inspiration and the early expiration. This basic eupnoeic rhythm was not altered after sectioning of the carotid sinus nerves. 3. Upon exposure to hypoxia or anoxia, phrenic activity, tidal volume and frequency initially increased and then declined. In many animals, ventilatory activity then ceased, but later returned with a gasping pattern. 4. Gasping was characterized by a sudden onset of phrenic activity, which reached a peak intensity during the early portion of inspiration. The expiratory burst of vagal activity was eliminated. 5. Reductions of body temperature from 37 to 27 degrees C resulted in prolongations of inspiration and expiration and decreases of phrenic amplitude; phasic phrenic activity completely disappeared in some animals. Upon exposure to anoxia, gasping was observed, even in animals in which phrenic activity had disappeared in hyperoxia. 6. We conclude that, from the day of birth, rats can exhibit eupnoea and gasping patterns which are very similar to those of adult animals. 7. The rhythmic neural activities of the in vitro brainstem-spinal cord preparation, reported by others, differ markedly from eupnoea but are identical with gasping. We therefore conclude that this preparation is not suitable for investigation of the mechanisms that generate eupnoeic breathing.

Age Factors↗
PubMed1996

Segment inertial properties of primates: new techniques for laboratory and field studies of locomotion.

Studies of the dynamics of locomotor performances depend on knowledge of the distribution of body mass within and between limb segments. However, these data are difficult to derive. Segment mass properties have generally been estimated by modelling limbs as truncated cones, but this approach fails to take into account that some segments are of elliptical, not circular, cross section; and further, the profiles of real segments are generally curved. Thus, they are more appropriately modelled as solids of revolution, described by the rotation in space of convex or concave curves, and the possibility of an elliptical cross section needs to be taken into account. In this project we have set out to develop a general geometric model which can take these factors into account, and permit segment inertial properties to be derived from cadavers by segmentation, and from living individuals using linear external measurements. We present a model which may be described by up to four parameters, depending on the profile and serial cross section (circular or ellipsoidal) of the individual segments. The parameters are obtained from cadavers using a simplified complex-pendulum technique, and from intact specimens by calculation from measurements of segment diameters and lengths. From the parameters, the center of mass, moments of interia, and radii of gyration may be derived, using simultaneous equations. Inertial properties of the body segments of four Pan troglodytes and a single Pongo were determined, and contrasted to comparable findings for humans. Using our approach, the mass distribution characteristics of any individual or species may be represented by a rigid-link segment model or "android." If this is made to move according to motion functions derived from a real performance of the individual represented, we show that recordings of resulting ground reaction forces may be quite closely simulated by predictive dynamic modelling.

Animals↗
PubMed1996

Reproducibility of erythrocyte polyamine measurements and correlation with plasma micronutrients in an antioxidant vitamin intervention study.

Erythrocyte polyamine measurements have been previously investigated as candidate biomarkers for hyperproliferation and recently as a potential intermediate endpoint in clinical chemoprevention trials with difluoromethylornithine, an inhibitor of polyamine biosynthesis. This study was performed to determine the reproducibility of erythrocyte polyamine measurements and their possible correlation with plasma micronutrients in seven healthy adults in an antioxidant vitamin intervention study. As part of this cross-over intervention study, three subjects took beta-carotene (31.4 mg/day) plus D-alpha-tocopherol acetate (720 IU/day) supplements during the first 3 months and four subjects took the supplements during the second 3 months. Heparinized blood samples were collected at baseline and every month over total 6 months for simultaneous determination of erythrocyte polyamines and plasma micronutrients by the high-performance liquid chromatographic method. For all the measures of erythrocyte polyamines the intraindividual variation was smaller than that between subjects, and three or four measurements required to accurately characterize long-term erythrocyte polyamines for an individual. The intra-class correlations were moderately high for all erythrocyte polyamine measurements, indicating a good reproducibility for intra-individual erythrocyte polyamine measurements. Based on monthly values, significant inverse correlations were found between erythrocyte spermidine and the plasma levels of retinol (r = -0.50) and lutein (r = -0.52). There were also significant inverse associations between erythrocyte spermine and plasma levels of alpha-tocopherol (r = -0.29), lutein (r = -0.44), lycopene (r = -0.29), beta-cryptoxanthin (r = -0.30), and total carotenoids (r = -0.29). The effects of supplementation upon the associations between erythrocyte polyamines and plasma nutrient levels were additionally addressed. The results indicate an acceptable longitudinal reproducibility of erythrocyte polyamine measurements, support the hypothesis that erythrocyte polyamine measurements may be correlated with plasma levels of certain nutrients, and suggest a further biomarker application in cancer prevention trials involving dietary modifications or specific relevant micronutrients.

Adult↗
PubMed1996

Up-regulation of D3 dopamine receptor mRNA by neuroleptics.

The effects of 14 days neuroleptic treatment on the expression of the D3 dopamine receptor gene was investigated in rats using a sensitive polymerase chain reaction assay. In olfactory tubercle, D3 mRNA levels increased following haloperidol (40%), pimozide (56%), and sulpiride (63%) administration, and in nucleus accumbens, levels increased after haloperidol (50%) and sulpiride (50%). D3 expression in the motor striatum did not change with any antagonist tested. Clozapine did not affect D3 expression in any brain region. These data suggest that dopamine antagonists can regulate the expression of the D3 receptor in a brain region selective manner. The findings also suggest that the motor complications of chronic antipsychotic therapy are not due to D3 receptor up-regulation in the striatum.

Animals↗
PubMed1996

Modulation of B-cell immunoglobulin synthesis by retinoic acid.

Retinoic acid (RA) and its parent compound retinol (ROH, vitamin A) have been recognized as important immunopotentiating agents since the early 1900s. We have focused our studies on the effects of retinoids on B-cell immune function in the newborn infant. The response of cord blood mononuclear cells (CBMC) to formalinized Cowan I strain Staphylococcus aureus (SAC), a T-cell-dependent factor for inducing the differentiation of B cells into immunoglobulin (Ig)-secreting cells, was used as a model system for studying whether RA could alter the immunoglobulin synthesis of newborn B lymphocytes. The addition of RA to SAC-stimulated CBMC cultures produced a 2- to 47-fold increase in IgM synthesis. An ELISA-spot assay showed that the RA-induced enhancement in Ig synthesis was due to the recruitment of more B cells to differentiate into Ig-secreting cells. Whereas RA enhanced IgM production of CBMC stimulated with SAC, RA augmented only IgG production of SAC-stimulated adult peripheral blood mononuclear cells (PBMC). To determine if the differences in dose-response characteristics between CBMC and adult PBMC resided within the target cell, i.e., the B cell, T-cell-enriched and T-cell-depleted (B-cell) fractions from CBMC and adult PBMC were cocultured in various combinations. The isotype, i.e., IgM vs IgG, and the dose-response curve characteristics were intrinsic to the responding B-cell source, i.e., newborn vs adult. Highly purified T cells from CBMC, when preincubated for 36 hr with RA, enhanced IgM synthesis of cord blood B cells. Supernatants from purified T cells generated a factor which could enhance B-cell synthesis. Although interleukin (IL)-2, IL-4, and IL-6 could not be detected by ELISA in the T-cell-derived supernatants, RA probably generates a cytokine/interleukin from T cells which modulates B-cell Ig secretion. RA can also act directly on B cells as evidenced by the augmentation in Ig synthesis of Epstein-Barr virus (EBV)-transformed B-cell lines. These data suggest that RA can have a direct effect on B cells. Since increased proliferation (numbers) of lymphoblastoid B cells was not responsible for the increased amounts of Ig in the supernatant fluids, we examined whether cytokines secreted by EBV-transformed B cells could be acting as an autocrine factor in increasing Ig synthesis. EBV-transformed B-cell clones incubated with RA for 6 days produced a 20- to 45-fold increase in IL-6. An understanding of the mechanisms by which RA enhances B-cell immune function may lead to the use of RA or its derivatives in patients with immune deficiencies and in preterm infants with immature immune systems.

Adjuvants, Immunologic↗
PubMed1996

A novel kinesin-like protein with a calmodulin-binding domain.

Calcium regulates diverse developmental processes in plants through the action of calmodulin. A cDNA expression library from developing anthers of tobacco was screened with 35S-labeled calmodulin to isolate cDNAs encoding calmodulin-binding proteins. Among several clones isolated, a kinesin-like gene (TCK1) that encodes a calmodulin-binding kinesin-like protein was obtained. The TCK1 cDNA encodes a protein with 1265 amino acid residues. Its structural features are very similar to those of known kinesin heavy chains and kinesin-like proteins from plants and animals, with one distinct exception. Unlike other known kinesin-like proteins, TCK1 contains a calmodulin-binding domain which distinguishes it from all other known kinesin genes. Escherichia coli-expressed TCK1 binds calmodulin in a Ca(2+)-dependent manner. In addition to the presence of a calmodulin-binding domain at the carboxyl terminal, it also has a leucine zipper motif in the stalk region. The amino acid sequence at the carboxyl terminal of TCK1 has striking homology with the mechanochemical motor domain of kinesins. The motor domain has ATPase activity that is stimulated by microtubules. Southern blot analysis revealed that TCK1 is coded by a single gene. Expression studies indicated that TCK1 is expressed in all of the tissues tested. Its expression is highest in the stigma and anther, especially during the early stages of anther development. Our results suggest that Ca2+/calmodulin may play an important role in the function of this microtubule-associated motor protein and may be involved in the regulation of microtubule-based intracellular transport.

Adenosine Triphosphatases↗
PubMed1996

A potato cDNA encoding a homologue of mammalian multidrug resistant P-glycoprotein.

A homologue of the multidrug resistance (MDR) gene was obtained while screening a potato stolon tip cDNA expression library with 35S-labeled calmodulin. The mammalian MDR gene codes for a membrane-bound P-glycoprotein (170-180 kDa) which imparts multidrug resistance to cancerous cells. The potato cDNA (PMDR1) codes for a polypeptide of 1313 amino acid residues (ca. 144 kDa) and its structural features are very similar to the MDR P-glycoprotein. The N-terminal half of the PMDR1-encoded protein shares striking homology with its C-terminal half, and each half contains a conserved ATP-binding site and six putative transmembrane domains. Southern blot analysis indicated that potato has one or two MDR-like genes. PMDR1 mRNA is constitutively expressed in all organs studied with higher expression in the stem and stolon tip. The PMDR1 expression was highest during tuber initiation and decreased during tuber development.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed1996

Efficacy of HMAF (MGI-114) in the MV522 metastatic lung carcinoma xenograft model nonresponsive to traditional anticancer agents.

Illudin analogs are cytotoxic to a variety of multidrug resistant cell lines, and display an unusual toxicity towards DNA helicase-deficient cell lines. Earlier illudin analogs demonstrated efficacy in several xenograft models, including a metastatic MV522 lung cancer model, resistant to conventional anticancer agents. These illudin analogs prolonged life span as compared to conventional agents, but did not induce complete remission of primary tumors. In vitro screening studies identified a semisynthetic derivative, hydroxymethylacylfulvene (HMAF, MGI-114), with increased selective cytotoxicity towards carcinoma cells. The HMAF analog was markedly effective in the experimental MV 522 metastasizing lung carcinoma xenograft system, a model refractory to treatment with existing anticancer agents. Treatment with paclitaxel, doxorubicin, or cisplatin failed to significantly inhibit primary tumor growth or prolong life span of MV522 tumor-bearing animals. Treatment with mitomycin C at the LD20 increased life span in surviving animals up to 61% (p = 0.04). Treatment with HMAF induced primary tumor regression in all animals and increased life span greater than 150% (p < 0.001). Thus, administration of HMAF inhibited development of lung metastasis in a model refractory to treatment with conventional anticancer agents. These results support further evaluation of HMAF as a therapeutic agent for treatment of solid tumors such as adenocarcinoma of the lung.

Adenocarcinoma↗
PubMed1996

The Y-27H39 polymorphism in a Japanese population.

We studied 184 Japanese males for the tetranucleotide TAGA repeat polymorphism at the Y-27H39 locus on the Y chromosome, and discovered a new allele, tentatively named F. Direct sequencing of Y-27H39 alleles revealed that the new allele (206 nt) is larger than allele E (202 nt) by 1 repeat unit. The six alleles differ only in the number of repeats, the flanking sequences being constant. The allele frequencies are different in Japanese and Caucasians.

Alleles↗
PubMed1996

The effects of retinoic acid on immunoglobulin synthesis: role of interleukin 6.

Retinoic acid (RA) and its parent compound, retinol (ROH, vitamin A), have been recognized as important immunopotentiating agents. Previous studies from our laboratory have demonstrated that RA can augment formalin-treated Staphylococcus aureus (SAC)-stimulated immunoglobulin (Ig) synthesis of cord blood mononuclear cells (CBMC). To determine the mechanism(s) by which RA modulates Ig synthesis, we studied the effects of RA on B cells and cytokine production. The addition of RA (10(-5) to 10(-10) M) to Epstein-Barr virus (EBV)-transformed B-cell clones derived from either adult or cord blood B cells augmented Ig secretion twofold. In contrast, cell proliferation was inhibited as measured by 3H-thymidine incorporation. We evaluated two cytokines known to be constitutively produced by EBV cell lines, IL-1 and IL-6. While RA had no effect on IL-1 production, IL-6 synthesis was greatly enhanced (20- to 45-fold), which was also reflected by an increase in steady-state mRNA levels for IL-6 but not TNF-alpha or TGF-beta on Northern blot analysis. Polyclonal rabbit anti-IL-6 antibodies were used to block the augmenting effects of RA on Ig synthesis of adenoidal B cells. RA-induced augmentation in IgG and IgA synthesis was blocked 58 and 29%, respectively, by anti-IL-6 antibodies. These studies suggest that the enhancing effects of RA on Ig synthesis are mediated, at least in part, by the autocrine or paracrine effects of IL-6 on B-cell differentiation.

Adult↗
PubMed1996

Molecular evolution of the 14-3-3 protein family.

Members of the highly conserved and ubiquitous 14-3-3 protein family modulate a wide variety of cellular processes. To determine the evolutionary relationships among specific 14-3-3 proteins in different plant, animal, and fungal species and to initiate a predictive analysis of isoform-specific differences in light of the latest functional and structural studies of 14-3-3, multiple alignments were constructed from forty-six 14-3-3 sequences retrieved from the GenBank and SwissProt databases and a newly identified second 14-3-3 gene from Caenorhabditis elegans. The alignment revealed five highly conserved sequence blocks. Blocks 2-5 correlate well with the alpha helices 3, 5, 7, and 9 which form the proposed internal binding domain in the three-dimensional structure model of the functioning dimer. Amino acid differences within the functional and structural domains of plant and animal 14-3-3 proteins were identified which may account for functional diversity amongst isoforms. Protein phylogenic trees were constructed using both the maximum parsimony and neighbor joining methods of the PHYLIP(3.5c) package; 14-3-3 proteins from Entamoeba histolytica, an amitochondrial protozoa, were employed as an outgroup in our analysis. Epsilon isoforms from the animal lineage form a distinct grouping in both trees, which suggests an early divergence from the other animal isoforms. Epsilons were found to be more similar to yeast and plant isoforms than other animal isoforms at numerous amino acid positions, and thus epsilon may have retained functional characteristics of the ancestral protein. The known invertebrate proteins group with the nonepsilon mammalian isoforms. Most of the current 14-3-3 isoform diversity probably arose through independent duplication events after the divergence of the major eukaryotic kingdoms. Divergence of the seven mammalian isoforms beta, zeta, gamma, eta, epsilon, tau, and sigma (stratifin/HME1) occurred before the divergence of mammalian and perhaps before the divergence of vertebrate species. A possible ancestral 14-3-3 sequence is proposed.

14-3-3 Proteins↗
PubMed1996

rTP: a candidate telomere protein that is associated with DNA replication.

In this paper we describe the isolation and characterization of rTP, the replication Telomere Protein, formerly known as the telomere protein homolog. The rTP was initially identified because of its homology to the gene for the Oxytricha telomere-binding protein alpha-subunit. The protein encoded by the rTP gene has extensive amino acid sequence identity to the DNA-binding domain of the telomere-binding proteins from both Euplotes crassus and Oxytricha nova. We have now identified the protein encoded by the rTP gene and have shown that it differs from the telomere-binding protein in its abundance, solubility and intracellular location. To learn more about the function of rTP, we determined when during the Euplotes life cycle the gene is transcribed. The transcript was detectable only in nonstarved vegetative cells and during the final stages of macronuclear development. Since the peak transcript level coincided with the rounds of replication that take place toward the end of macronuclear development, it appeared that rTP might be involved in DNA replication. Immunolocalization experiments provided support for this hypothesis as antibodies to rTP specifically stain the replication bands. Replication bands are the sites of DNA replication in Euplotes macronuclei. Our results suggest that rTP may be a new telomere replication factor.

Amino Acid Sequence↗
PubMed1996

Purification and some properties of a novel microbial lactate oxidase.

Geotrichum candidum was found to produce a lactate oxidase. The enzyme was purified by gel filtration and ion-exchange chromatography. The purified lactate oxidase showed a molecular mass of 50 kDa under denaturing and about 400 kDa under non-denaturing conditions. Transmission electron microscopy analysis confirmed an octameric structure. FMN was found to be a cofactor for this enzyme. Polarographic studies confirmed an oxygen uptake by the lactate oxidase. The enzyme showed specificity towards the L isomer of lactate and did not oxidise pyruvate, fumarate, succinate, maleate and ascorbate. It was stable at alkaline pH and also for 15 min at 45 degrees C. The addition of glycerol and dextran 500,000 to the enzyme sample enhanced storage stability.

Amino Acid Sequence↗