Biomedical subjects

H Liu

Publications and source records attributed to H Liu.

At least 559 records · Page 31Linked to original sources

PubMed1999

Molecular cloning and functional expression of two members of mouse NeuAcalpha2,3Galbeta1,3GalNAc GalNAcalpha2,6-sialyltransferase family, ST6GalNAc III and IV.

Two cDNA clones encoding NeuAcalpha2,3Galbeta1,3GalNAc GalNAcalpha2, 6-sialyltransferase have been isolated from mouse brain cDNA libraries. One of the cDNA clones is a homologue of previously reported rat ST6GalNAc III according to the amino acid sequence identity (94.4%) and the substrate specificity of the expressed recombinant enzyme, while the other cDNA clone includes an open reading frame coding for 302 amino acids. The deduced amino acid sequence is not identical to those of other cloned mouse sialyltransferases, although it shows the highest sequence similarity with mouse ST6GalNAc III (43.0%). The expressed soluble recombinant enzyme exhibited activity toward NeuAcalpha2, 3Galbeta1, 3GalNAc, fetuin, and GM1b, while no significant activity was detected toward Galbeta1,3GalNAc or asialofetuin, or the other glycoprotein substrates tested. The sialidase sensitivity of the 14C-sialylated residue of fetuin, which was sialylated by this enzyme with CMP-[14C]NeuAc, was the same as that of ST6GalNAc III. These results indicate that the expressed enzyme is a new type of GalNAcalpha2,6-sialyltransferase, which requires sialic acid residues linked to Galbeta1,3GalNAc residues for its activity; therefore, we designated it mouse ST6GalNAc IV. Although the substrate specificity of this enzyme is similar to that of ST6GalNAc III, ST6GalNAc IV prefers O-glycans to glycolipids. Glycolipids, however, are better substrates for ST6GalNAc III.

Amino Acid Sequence↗

PubMed1999

Surface densities of ephrin-B1 determine EphB1-coupled activation of cell attachment through alphavbeta3 and alpha5beta1 integrins.

Receptors of the Eph family and their ligands (ephrins) mediate developmental vascular assembly and direct axonal guidance. Migrating cell processes identify appropriate targets within migratory fields based on topographically displayed ephrin gradients. Here, EphB1 regulated cell attachment by discriminating the density at which ephrin-B1 was displayed on a reconstituted surface. EphB1-ephrin-B1 engagement did not promote cell attachment through mechanical tethering, but did activate integrin-mediated attachment. In endothelial cells, attachment to RGD peptides or fibrinogen was mediated through alphavbeta3 integrin. EphB1 transfection conferred ephrin-B1-responsive activation of alpha5beta1 integrin-mediated cell attachment in human embryonic kidney cells. Activation-competent but signaling-defective EphB1 point mutants failed to stimulate ephrin-B1 dependent attachment. These findings lead us to propose that EphB1 functions as a 'ligand density sensor' to signal integrin-mediated cell-matrix attachment.

Cell Adhesion↗

PubMed1999

The United States liver donor population in the 1990s: a descriptive, population-based comparative study.

BACKGROUND: Orthotopic liver transplantation in the United States is primarily limited by a shortage of donor organs. METHODS: To better understand the low rates of organ donation in the United States and identify areas for potential improvement, we analyzed detailed demographic and mortality-specific data from 10,689 adult cadaveric liver donors obtained from the United Network for Organ Sharing from April 1, 1994 to March 31, 1997. Comparative U.S. population demographic and economic data were obtained from the U.S. census. RESULTS: As compared with the U.S. population, we found there to be significantly fewer nonwhite (P=0.001) and foreign-born donors (P=0.001); 58.9% of liver donors were male (P=0.001). The mean age was 40.6 years; yet during the 3-year period analyzed, there was a significant trend toward increasing age of donors. Median household income was 18% to 32% lower in the donor population than in the general U.S. population. In 91.2% of cases, the donor cause of death was listed as cerebrovascular stroke or head trauma. Numerous significant interracial differences were found in both the donor mechanism and circumstance of death. These included black donors being more likely to have gunshot wound as the listed mechanism of death (P=0.001) and to have homicide as the listed circumstance of death (P=0.001). CONCLUSIONS: Nonwhites and foreign-born individuals are significantly underrepresented in the U.S. liver donor population. Furthermore, donors seem to be poorer than the general U.S. population. Increasing the liver donor pool, especially among minorities, will require creative and thoughtful public initiatives.

Adolescent↗

PubMed1999

Polymorphism in RANTES chemokine promoter affects HIV-1 disease progression.

RANTES (regulated on activation normal T cell expressed and secreted) is one of the natural ligands for the chemokine receptor CCR5 and potently suppresses in vitro replication of the R5 strains of HIV-1, which use CCR5 as a coreceptor. Previous studies showed that peripheral blood mononuclear cells or CD4(+) lymphocytes obtained from different individuals had wide variations in their ability to secrete RANTES. These findings prompted us to analyze the upstream noncoding region of the RANTES gene, which contains cis-acting elements involved in RANTES promoter activity, in 272 HIV-1-infected and 193 non-HIV-1-infected individuals in Japan. Our results showed that there were two polymorphic positions, one of which was associated with reduced CD4(+) lymphocyte depletion rates during untreated periods in HIV-1-infected individuals. This mutation, RANTES-28G, occurred at an allele frequency of approximately 17% in the non-HIV-1-infected Japanese population and exerted no influence on the incidence of HIV-1 infection. Functional analyses of RANTES promoter activity indicated that the RANTES-28G mutation increases transcription of the RANTES gene. Taken together, these data suggest that the RANTES-28G mutation increases RANTES expression in HIV-1-infected individuals and thus delays the progression of the HIV-1 disease.

Base Sequence↗

PubMed1999

Phosphorylation-mediated activation and translocation of the cyclic AMP-specific phosphodiesterase PDE4D3 by cyclic AMP-dependent protein kinase and mitogen-activated protein kinases. A potential mechanism allowing for the coordinated regulation of PDE4D activity and targeting.

In this study, we describe a novel mechanism by which a protein kinase C (PKC)-mediated activation of the Raf-extracellular signal-regulated kinase kinase (MEK)-extracellular signal-regulated kinase (ERK) cascade regulates the activity and membrane targeting of members of the cyclic AMP-specific phosphodiesterase D family (PDE4D). Using a combination of pharmacological and biochemical approaches, we show that increases in intracellular cAMP cause a protein kinase A-mediated phosphorylation and activation of the two PDE4D variants expressed in vascular smooth muscle cells, namely PDE4D3 and PDE4D5. In addition, we show that stimulation of PKC via the associated activation of the Raf-MEK-ERK cascade results in the phosphorylation and activation of PDE4D3 in these cells. Furthermore, our studies demonstrate that simultaneous activation of both the protein kinase A and PKC-Raf-MEK-ERK pathways allows for a coordinated activation of PDE4D3 and for the translocation of the particulate PDE4D3 to the cytosolic fraction of these cells. These data are presented and discussed in the context of the activation of the Raf-MEK-ERK cascade acting to modulate the activation and subcellular targeting of PDE4D gene products mediated by cAMP.

3',5'-Cyclic-AMP Phosphodiesterases↗

PubMed1999

In vivo glutamate neurotoxicity is associated with reductions in calcium/calmodulin-dependent protein kinase II immunoreactivity.

Calcium/calmodulin-dependent protein kinase II (CaM kinase) activity is inhibited in cultured hippocampal cells following direct application of glutamate. The goal of the present study was to determine if hippocampal regions that undergo delayed cell death following glutamate microinfusion would exhibit changes in CaM kinase immunoreactivity. Gerbils received bilateral intra-hippocampal infusions of L-glutamate (34 microg/microl), or control treatments of D-glutamate or saline. Animals were sacrificed at 12 or 24 hr to assess cell loss and determine changes in CaM kinase-like immunoreactivity. Hippocampi of gerbils euthanized 12 hr following L-glutamate, or 24 hr following D-glutamate, did not exhibit cell death in the hippocampal CA1 region. Animals injected with L-glutamate and sacrificed 24 hr after infusion had extensive cell damage that was restricted to the hippocampal CA1 region. CaM kinase-like immunoreactivity was absent in the hippocampal CA1 region of all L-glutamate treated animals sacrificed at 12 hr. In these same sections, CaM kinase immunoreactivity was evident in the subiculum, CA2 and CA3 regions. Reduction in CaM kinase immunoreactivity following L-glutamate were also observed using Western analysis. The results confirm and extend the findings of earlier cell culture studies by demonstrating a reduction in CaM kinase immunoreactivity that occurred prior to cell death.

Animals↗

PubMed1999

Preparation of Polymer-Stabilized Noble Metal Colloids.

A series of polymer-stabilized platinum and palladium colloids were prepared via methanol reduction for the investigation of the preparation conditions. Through TEM observation and catalytic hydrogenation of olefins, it was found that adding a suitable amount of NaOH was good for small-sized colloidal particles and higher catalytic hydrogenation activity. Copyright 1999 Academic Press.

Journal Article↗

PubMed1999

A Drosophila TNF-receptor-associated factor (TRAF) binds the ste20 kinase Misshapen and activates Jun kinase.

Two families of protein kinases that are closely related to Ste20 in their kinase domain have been identified - the p21-activated protein kinase (Pak) and SPS1 families [1-3]. In contrast to Pak family members, SPS1 family members do not bind and are not activated by GTP-bound p21Rac and Cdc42. We recently placed a member of the SPS1 family, called Misshapen (Msn), genetically upstream of the c-Jun amino-terminal (JNK) mitogen-activated protein (MAP) kinase module in Drosophila [4]. The failure to activate JNK in Drosophila leads to embryonic lethality due to the failure of these embryos to stimulate dorsal closure [5-8]. Msn probably functions as a MAP kinase kinase kinase kinase in Drosophila, activating the JNK pathway via an, as yet, undefined MAP kinase kinase kinase. We have identified a Drosophila TNF-receptor-associated factor, DTRAF1, by screening for Msn-interacting proteins using the yeast two-hybrid system. In contrast to the mammalian TRAFs that have been shown to activate JNK, DTRAF1 lacks an amino-terminal 'Ring-finger' domain, and overexpression of a truncated DTRAF1, consisting of only its TRAF domain, activates JNK. We also identified another DTRAF, DTRAF2, that contains an amino-terminal Ring-finger domain. Msn specifically binds the TRAF domain of DTRAF1 but not that of DTRAF2. In Drosophila, DTRAF1 is thus a good candidate for an upstream molecule that regulates the JNK pathway by interacting with, and activating, Msn. Consistent with this idea, expression of a dominant-negative Msn mutant protein blocks the activation of JNK by DTRAF1. Furthermore, coexpression of Msn with DTRAF1 leads to the synergistic activation of JNK. We have extended some of these observations to the mammalian homolog of Msn, Nck-interacting kinase (NIK), suggesting that TRAFs also play a critical role in regulating Ste20 kinases in mammals.

Amino Acid Sequence↗

PubMed1999

A controlled trial of exercise rehabilitation after heart transplantation.

BACKGROUND: In patients who have received a cardiac transplant, the denervated donor heart responds abnormally to exercise and exercise tolerance is reduced. The role of physical exercise in the treatment of patients who have undergone cardiac transplantation has not been determined. We assessed the effects of training on the capacity for exercise early after cardiac transplantation. METHODS: Twenty-seven patients who were discharged within two weeks after receiving a heart transplant were randomly assigned to participate in a six-month structured cardiac-rehabilitation program (exercise group, 14 patients) or to undergo unstructured therapy at home (control group, 13 patients). Each patient in the exercise group underwent an individualized program of muscular-strength and aerobic training under the guidance of a physical therapist, whereas control patients received no formal exercise training. Cardiopulmonary stress testing was performed at base line (within one month after heart transplantation) and six months later. RESULTS: As compared with the control group, the exercise group had significantly greater increases in peak oxygen consumption (mean increase, 4.4 ml per kilogram of body weight per minute [49 percent] vs. 1.9 ml per kilogram per minute [18 percent]; P=0.01) and workload (mean increase, 35 W [59 percent] vs. 12 W [18 percent]; P=0.01) and a greater reduction in the ventilatory equivalent for carbon dioxide (mean decrease, 13 [20 percent] vs. 6 [11 percent]; P=0.02). The mean dose of prednisone, the number of patients taking antihypertensive medications, the average number of episodes of rejection and of infection during the study period, and weight gain did not differ significantly between the groups. CONCLUSIONS: When initiated early after cardiac transplantation, exercise training increases the capacity for physical work.

Blood Pressure↗

PubMed1999

Conformational Structure of Triblock Copolymers by FT-Raman and FTIR Spectroscopy.

Fourier transform Raman (FT-Raman) and Fourier transform infrared (FTIR) spectra of poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) (PEO-PPO-PEO) triblock copolymers as pure solids or liquids and in aqueous solutions have been examined. The qualitative features in Raman and FTIR spectra of these copolymers have been presented. The Raman and FTIR spectra of PEO-PPO-PEO triblock copolymers are very sensitive to the structural and conformational changes. It shows that the relative intensities of several peaks in Raman spectra are dependent on the PPO/PEO ratios and the conformation of the copolymers. From Raman and FTIR spectra, Pluronic F68 and F88 assume helical structures with a few trans conformers. Other block copolymers exhibit that the disordered structure increases with increasing PPO/PEO ratio. Comparison of Raman spectra of PEO-PPO-PEO triblock copolymers as pure solids or liquids with those in aqueous solutions has been presented. Copyright 1999 Academic Press.

Journal Article↗

PubMed1999

TFAR19, a novel apoptosis-related gene cloned from human leukemia cell line TF-1, could enhance apoptosis of some tumor cells induced by growth factor withdrawal.

Using the cDNA-representative differences analysis (cDNA-RDA) approach, we identified a novel gene, TFAR19 (TF-1 cell apoptosis related gene-19), from TF-1 cells undergoing apoptosis. The human TFAR19 encodes a protein which shares significant homology to the corresponding proteins of species ranging from yeast to mice. TFAR19 exhibits a ubiquitous expression pattern and its expression is upregulated in the tumor cells undergoing apoptosis. Overexpression of TFAR19 in tumor cells enhances apoptosis triggered by growth factor or serum deprivation. We propose that TFAR19 may play a general role in the apoptotic process.

Amino Acid Sequence↗

PubMed1999

Comparison of ephrin-A ligand and EphA receptor distribution in the developing inner ear.

Members of the recently discovered Eph family appear to play important roles in a variety of developmental processes including tissue segmentation, cell migration and axonal guidance. To begin to understand the functions of the EphA subclass of receptors and their corresponding GPI-linked (ephrin-A) ligands in the inner ear, a developmental immunohistochemical analysis was completed. The results indicated that the ligands ephrin-A1 and ephrin-A2 were localized mainly at cellular boundaries in the inner ear. Ephrin-A1 was detected mainly in the epithelial cells lining the fluid filled ducts of the inner ear, whereas ephrin-A2 was prominently expressed in connective tissue regions. The receptor EphA4 was detected in vestibular hair cells. EphA5 and EphA7 were detected mainly in cochlear and vestibular supporting cells. These results suggest that these Eph molecules play a role in establishing the formation and cellular organization of the complex inner ear labyrinth. Additionally, all of the ligands and receptors evaluated were expressed in vestibular and cochlear neurons at various developmental stages, suggesting they may play a role in establishing or maintaining innervation to the inner ear.

Actins↗

PubMed1999

An efficient MR phosphorous spectroscopic localization technique for studying ischemic heart.

To obtain the spatially resolved (31)P spectroscopic image from myocardium during an acute myocardium ischemia at a high signal-to-noise ratio (SNR) in a very limited time window, we have exploited the spatial variation of the radiofrequency (RF) field produced by a single loop transmit/receive (TR) RF coil along its axis for spatial discrimination. By incrementally lengthening the duration of a square RF excitation pulse, the positional information can be systematically encoded as harmonics of various orders in MR signal. In the in vivo open-chest animal experiment, this RF coil was surgically sutured onto the epicardial surface of the left ventricular (LV) wall over the region perfused by the left anterior descending coronary artery. Using only 17 encoding steps, we have obtained one-dimensional (31)P spectroscopic images from both a multiple-layer phosphor phantom and an in vivo LV myocardium. In the animal study, the cardiac gating is used with respiratory synchronization. The MR data were only collected during the end diastole phase of the cardiac cycle (cardiac and respiratory synchronized) with an effective sequence repetition time (TR) of 6 seconds (to ensure the complete relaxation of the phosphorous magnetization). The total acquisition time for a complete experiment is about 10 minutes. Prior to the CSI reconstruction process, the raw data matrix was zero-filled in the spatial dimension. The spatially resolved metabolite map exhibited all the metabolite peaks including creatine phosphate and adenosine triphosphate. At the layer of endocardium, two peaks corresponding to 2, 3-diphosphoglycerate, which is contained in the erythrocytes, were clearly seen in the LV wall. Also, the method allows compensation in both volume and coil sensitivity variations for the resulting spectra. All results have demonstrated that it is an efficient nuclear magnetic resonance method capable of obtaining high-quality (31)P spectroscopic images with both excellent spatial localization and SNR in the research of cardiac ischemia. J. Magn. Reson. Imaging 1999;10:892-898.

Animals↗

PubMed1999

g-matrix based on configuration interaction and Stone's perturbation theory

Stone's formula, which has usually been applied to the calculation of the g-matrix, is based on a single-configuration treatment. Here a limited configuration interaction is included to obtain the expressions of the principal g values for an orbitally nondegenerate molecule with spin S = 12. Copyright 1999 Academic Press.

Journal Article↗

PubMed1999

The g values of some halomolybdenyl, -vanadyl, and -chromyl complexes.

The principal g values of a series of [MOXn]m- (M = VIV, CrV, MoV; X = F-, Cl-, Br-; n = 4, 5; m = 1, 2, 3) complexes are calculated by the INDO-CI-Stone method. The results agree well with the experimental data and reveal that the traditional models have some limitations in calculating g values for some complexes of this type.

Chromates↗

PubMed1999

A comparative study on neurochemistry of cerebrospinal fluid in advanced Parkinson's disease.

This study addresses two issues: (1) the comparative neurochemistry of classic tremor type of Parkinson's disease or PD-A and akinetic type of Parkinson's disease or PD-B; and (2) the neurochemistry of levodopa failure syndrome (LDFS). Cerebrospinal fluid from the lateral ventricle was collected from 50 patients with idiopathic Parkinson's disease of PD-A and PD-B. Levels of monoamine neurotransmitters and metabolites were determined using high performance liquid chromatography. We have found that (1) 5-hydroxylindoleacetic acid (5-HIAA) level is significantly lower in PD-B than in PD-A; (2) 5-HIAA level is inversely associated with score of part one of United Parkinson's Disease Rating Score (UPDRS); (3) 5-HIAA level is inversely associated with score of part four of UPDRS; (4) 3-O-methyldopa (3-OMD) level is positively associated with levodopa failure syndrome (LDFS) assessed by part four of UPDRS and inversely associates with 5-HIAA. From these data, it can be inferred that serotonergic activity is decreased in PD-B to a greater extent than in PD-A and that decreased serotonergic activity plays a role in LDFS.

Aged↗

PubMed1999

Microemulsion of seal oil markedly enhances the transfer of a hydrophobic radiopharmaceutical into acetylated low density lipoprotein.

Four different microemulsions differing in their core lipid component (triolein, canola oil, squalene, or seal oil) and containing 1,3-dihydroxypropan-2-one 1,3-diiopanoate (DPIP), a potential radioimaging probe, were prepared by means of ultrasonication. The DPIP microemulsions were incubated with acetylated human low density lipoprotein (AcLDL) and the amount of DPIP transferred into AcLDL was examined. The amount of DPIP in the microemulsions expressed as DPIP/oil (w/w) was dependent on the core lipid component of the microemulsion in the order of seal oil (0.19+/-0.04, mean +/- standard deviation) > squalene (0.15+/-0.02) > canola oil (0.12+/-0.02) > triolein (0.07+/-0.004). With the exception of canola oil, all microemulsions were effective in enhancing the transfer of DPIP into AcLDL in comparison with commonly used methods, i.e., direct diffusion and detergent solubilization. DPIP in seal oil resulted in the highest amount of DPIP transferred into AcLDL [309.16+/-34.82 vs. 203.19+/-64.51 using squalene and 151.31+/-28.54 using triolein (DPIP molecules per AcLDL particle)]. For the first time, oil from harp seals, was studied as a major core lipid component of formulating pharmaceutical microemulsions. DPIP in seal oil resulted in the highest transfer of DPIP into AcLDL which is likely due to the highest DPIP concentration found in this microemulsion as well as the high fluidity of seal oil.

Animals↗

PubMed1999

Attenuation of ischemia induced increases in sodium and calcium by the aldose reductase inhibitor zopolrestat.

OBJECTIVE: We have previously demonstrated that zopolrestat, an inhibitor of the enzyme aldose reductase, reduces ischemic injury in hearts from diabetic and non-diabetic rats. To further explore potential cardioprotective mechanisms of zopolrestat, we measured changes in intracellular sodium, calcium, and Na+,K(+)-ATPase activity in zopolrestat treated hearts during ischemia and reperfusion. METHODS: Hearts from acute diabetic (Type I) and age-matched control rats were isolated and retrogradely perfused. Hearts had either control perfusion or exposure to 1 microM zopolrestat for 10 min, followed by 20 min of global ischemia and 60 min of reperfusion. Changes in intracellular sodium and calcium were measured using 23Na and 19F magnetic resonance spectroscopy, respectively, while the activity of Na+,K(+)-ATPase was measured using biochemical assays. RESULTS: Zopolrestat blunted the rise in [Na]i during ischemia in both diabetic hearts and non-diabetic hearts. The end-ischemic [Na]i was 21.3 +/- 2.6 mM in the zopolrestat treated diabetics and 25.9 +/- 2.3 in zopolrestat treated non-diabetics, versus 31.6 +/- 2.6 mM and 32.9 +/- 2.8 mM in the untreated diabetics and untreated non-diabetics, respectively, (P = 0.002). Similarly, the rise in [Ca]i at the end of ischemia was significantly reduced in zopolrestat treated diabetic and non-diabetic hearts (P = 0.005). Zopolrestat increased the activity of Na-,K(+)-ATPase in diabetic hearts under baseline conditions (11.70 +/- 0.95 versus 7.28 +/- 0.98 mumol/h/mg protein, P = 0.005) as well as during ischemia and reperfusion. Similar changes in Na+,K(+)-ATPase activity were also observed in non-diabetic hearts. CONCLUSIONS: The data provide additional support to the protective effects of zopolrestat and suggest that a possible mechanism of action may be associated with the attenuation of the rise in [Na]i and [Ca]i during ischemia and reperfusion.

Aldehyde Reductase↗