Search PubMed⌕ Search

Biomedical subjects

B Liu

Publications and source records attributed to B Liu.

At least 235 records · Page 13Linked to original sources
PubMed2000

An amperometric biosensor based on the coimmobilization of horseradish peroxidase and methylene blue on a beta-type zeolite modified electrode.

A new biosensor for the amperometric detection of hydrogen peroxide was developed based on the coimmobilization of horseradish peroxidase (HRP) and methylene blue on a beta-type zeolite modified glassy carbon electrode without the commonly used bovine serum albumin-glutaraldehyde. The intermolecular interaction between enzyme and zeolite matrix was investigated using FT-IR. The cyclic voltammetry and amperometric measurement demonstrated that methylene blue co-immobilized with HRP in this way displayed good stability and could efficiently transfer electrons between immobilized HRP and the electrode. The sensor responded rapidly to H2O2 in the linear range from 2.5 x 10(-6) to 4.0 x 10(-3) M with a detection limit of 0.3 microM. The sensor was stable in continuous operation.

Biosensing Techniques↗
PubMed2000

A spindle pole body-associated protein, SNAD, affects septation and conidiation in Aspergillus nidulans.

The nudA1 mutation in the cytoplasmic dynein heavy chain gene inhibits nuclear migration, colony growth and asexual sporulation (conidiation) in the filamentous fungus Aspergillus nidulans. It also alters the location of the first cell division event (septation) and prevents nucleation of tip cells. We showed previously that a suppressor of nudA1, snaD290, partially reversed the nuclear migration defect and partially restored colony growth. We have now demonstrated that the snaD290 mutation also delays septation and restores the septum to its normal position, allowing tip cells to be nucleated. Although snaD290 does not affect nuclear migration or vegetative hyphal growth, it almost completely inhibits conidiation. We propose that the SNAD protein participates in septation, and is essential for asexual spore formation. SnaD encodes a novel 76-kDa coiled-coil protein (SNAD) that is located at the spindle pole body throughout the cell cycle. Therefore, our results suggest that proteins at the spindle pole body are likely to be involved in temporal regulation of septation in A. nidulans.

Actins↗
PubMed2000

Chemiluminescent reporter gene assays with 1,2-dioxetane enzyme substrates.

1,2-Dioxetane chemiluminescent substrates provide highly sensitive, quantitative detection with simple, rapid assay formats for the detection of reporter enzymes that are widely used in gene expression studies. Chemiluminescent detection methodologies typically provide up to 100-1000x higher sensitivities than can be achieved with the corresponding fluorescent or colorimetric enzyme substrates. The varieties of 1,2-dioxetane substrates available provides assay versatility, allowing optimization of assay formats with the available instrumentation, and are ideal for use in gene expression assays performed in both biomedical and pharmaceutical research. These assays are amenable to automation with a broad range of instrumentation for high throughput compound screening.

Alkaline Phosphatase↗
PubMed2000

Novel methods for chemiluminescent detection of reporter enzymes.

Chemiluminescent reporter gene assays provide highly sensitive, quantitative detection in simple, rapid assay formats for detection of reporter enzymes that are widely employed in gene expression studies. Chemiluminescent detection methodologies typically provide up to 100-1000x higher sensitivities than may be achieved with fluorescent or colorimetric enzyme substrates. The variety of chemiluminescent 1,2-dioxetane substrates available enable assay versatility, allowing optimization of assay formats with the available instrumentation, and are ideal for use in gene expression assays performed in both biomedical and pharmaceutical research. In addition, 1,2,-dioxetane chemistries can be multiplexed with luciferase detection reagents for dual detection of multiple enzymes in a single sample. These assays are amenable to automation with a broad range of instrumentation for high throughput compound screening.

3T3 Cells↗
PubMed2000

Episomal expression of a hammerhead ribozyme directed against plum pox virus.

Two related antisense RNAs directed against plum pox virus (PPV) were expressed episomally in Nicotiana clevelandii by infection with recombinant potato virus X (PVX). One recombinant PVX expressed an ordinary PPV antisense RNA of about 400 nucleotides, while the other expressed a related antisense RNA that carried the catalytic domain of a hammerhead ribozyme. Inoculation with the latter recombinant PVX resulted in the accumulation of ribozyme RNA that was catalytically active when tested in vitro with a PPV substrate RNA. Plants that had been inoculated with recombinant PVX viruses, expressing either PPV-directed antisense or ribozyme sequences or GUS RNA as a control, were challenged with PPV by a sequential second inoculation. In plants that expressed PPV antisense sequences, the appearance of PPV disease symptoms was delayed for 3-5 days. Quantification of PPV 1 week after inoculation showed that the protective effect by the episomally expressed catalytic antisense RNA was stronger than that of the ordinary antisense RNA. However, eventually all plants tested accumulated comparable titers of PPV.

Genetic Vectors↗
PubMed2000

Reduction by naloxone of lipopolysaccharide-induced neurotoxicity in mouse cortical neuron-glia co-cultures.

An inflammatory response in the CNS mediated by activation of microglia is a key event in the early stages of the development of neurodegenerative diseases. Using mouse cortical mixed glia cultures, we have previously demonstrated that the bacterial endotoxin lipopolysaccharide induces the activation of microglia and the production of proinflammatory factors. Naloxone, an opioid receptor antagonist, inhibits the lipopolysaccharide-induced activation of microglia and the production of proinflammatory factors. Using neuron-glia co-cultures, we extended our study to determine if naloxone has a neuroprotective effect against lipopolysaccharide-induced neuronal damage and analysed the underlying mechanism of action for its potential neuroprotective effect. Pretreatment of cultures with naloxone (1 microM) followed by treatment with lipopolysaccharide significantly inhibited the lipopolysaccharide-induced production of nitric oxide and the release of tumor necrosis factor-alpha, and significantly reduced the lipopolysaccharide-induced damage to neurons. More importantly, both naloxone and its opioid-receptor ineffective enantiomer (+)-naloxone were equally effective in inhibiting the lipopolysaccharide-induced generation of proinflammatory factors and the activation of microglia, as well as in the protection of neurons. These results indicate that the neuroprotective effect of naloxone is mediated by its inhibition of microglial activity and may be unrelated to its binding to the classical opioid receptors.

Animals↗
PubMed2000

High concentrations of extracellular potassium enhance bacterial endotoxin lipopolysaccharide-induced neurotoxicity in glia-neuron mixed cultures.

A sudden increase in extracellular potassium ions (K(+)) often occurs in cerebral ischemia and after brain trauma. This increase of extracellular K(+) constitutes the basis for spreading depression across the cerebral cortex, resulting in the expansion of neuronal death after ischemic and traumatic brain injuries. Besides spreading depression, it has become clear that cerebral inflammation also is a key factor contributing to secondary brain injury in acute neurological disorders. Experiments to validate the relationship between elevated levels of extracellular K(+) and inflammation have not been studied. This study aims to elucidate the roles of high concentrations of extracellular K(+) in bacterial endotoxin lipopolysaccharide-induced production of inflammatory factors. Increased concentration of KCl in the medium (20mM) significantly enhanced neurotoxicity by lipopolysaccharide in glia-neuron mixed cultures. To delineate the underlying mechanisms of increased neurotoxicity, the effects of high extracellular K(+) were examined by using mixed glial cultures. KCl at 20mM significantly enhanced nitrite, an index for nitric oxide, production by about twofold, and was pronounced from 24 to 48h, depending on the concentration of KCl. Besides nitric oxide production of tumor necrosis factor-alpha was also enhanced. The augmentative effects of high KCl on the production of inflammatory factors were probably due to the further activation of microglia, since high KCl also enhanced the production of tumor necrosis factor-alpha in microglia-enriched cultures. The increased production of nitrite by high K(+) was eliminated through use of a K(+)-blocker. Taken together, the results show that increases of extracellular K(+) concentrations in spreading depression augment lipopolysaccharide-elicited neurotoxicity, because production of inflammatory factors such as nitric oxide and tumor necrosis factor-alpha are potentiated. Since spreading depression and cerebral inflammation are important in acute neurological disorders, the present results suggest a biochemical mechanism: elevated extracellular K(+) concentrations augment glial inflammatory responses, and thus the neurotoxicity.

Animals↗
PubMed2000

Activation of integrin receptors is required for growth factor-induced smooth muscle cell dysfunction.

PURPOSE: Growth factors and cytokines such as platelet-derived growth factor (PDGF), epidermal growth factor (EGF), basic fibroblast growth factor (bFGF), and transforming growth factor beta (TGF-beta) stimulate smooth muscle cell (SMC) proliferation and extracellular matrix (ECM) protein production by binding and activating their respective receptors. Recent investigations suggest that simultaneous activation of integrins, which are heterodimeric receptors for ECM, may also be required for growth factor and cytokine function. In this study, we tested the hypothesis that activation of two integrins, alpha v beta 3 and alpha 2 beta 1, both previously identified in vascular SMCs, is necessary for growth factor- and cytokine-induced vascular SMC dysfunction. METHODS: DNA synthesis was measured after stimulation of SMCs derived from human saphenous vein with the growth factors PDGF-BB, EGF, and bFGF. SMC fibronectin (Fn) production was measured (by means of Western blotting) in SMCs stimulated for 72 hours with TGF-beta1 or EGF. Both endpoints were measured in the presence and absence of antibodies that block the function of the alpha v beta 3 and alpha 2 beta 1 integrins as well as the alpha2 and beta1 subunits. RESULTS: The alpha v beta 3 integrin blocking antibody significantly inhibited PDGF-BB-, EGF-, and bFGF-induced SMC proliferation. The alpha v beta 3 integrin antibody also markedly inhibited TGF-1- and EGF-induced SMC Fn production. Neither the alpha 2 beta 1 integrin nor the alpha2 or the beta1 subunits inhibited either proliferation or matrix protein production in response to any of these agonists. CONCLUSION: The alpha v beta 3 integrin is required for growth factor- and cytokine-induced SMC proliferation and FN production, whereas alpha 2 beta 1 is not. Since activation of alpha v beta 3 is required for the activity of at least four distinct growth factors and cytokines, inhibition of this integrin might be used as a therapeutic tool for the prevention of intimal hyperplasia.

Antibodies, Blocking↗
PubMed2000

Structural basis of the recognition of the dishevelled DEP domain in the Wnt signaling pathway.

The DEP domain of Dishevelled (Dvl) proteins transduces signals to effector proteins downstream of Dvl in the Wnt pathway. Here we report that DEP-containing mutants inhibit Wnt-induced, but not Dvl-induced, activation of the transcription factor Lef-1. This inhibitory effect is weakened by a K434M mutation. Nuclear magnetic resonance spectroscopy revealed that the DEP domain of mouse Dvl1 comprises a three-helix bundle, a beta-hairpin 'arm' and two short beta-strands at the C-terminal region. Lys 434 is located at the tip of the beta-hairpin 'arm'. Based on our findings, we conclude that DEP interacts with regulators upstream of Dvl via a strong electric dipole on the molecule's surface created by Lys 434, Asp 445 and Asp 448; the electric dipole and the putative membrane binding site are at two different locations.

3T3 Cells↗
PubMed2000

Umbilical cord blood transplantation from unrelated HLA-matched donor in an adult with severe aplastic anemia.

A 23-year-old male suffering from severe aplastic anemia (SAA) weighing 60 kg was successfully treated by unrelated allo-CBSCT (cord blood stem cell transplantation). A six-loci HLA-identical umbilical cord blood (UCB) was infused after conditioning with low-dose cyclophosphamide (CTX) and antilymphocyte globulin (ALG). The prophylaxis of GVHD consisted of CsA and MTX. The infused cord blood provided 1.89 x 10(7) nucleated cells per kg, CD34-positive cells: 0.89%. Neutrophils >0.5 x 10(9)/l were reached 10 days after transplant, and platelets greater than 50.0 x 10(9)/l at day 26. RBC and platelet transfusion independence were reached on days 15 and 18. The patient developed grade 1 skin GVHD 10 months after engraftment of the donor cells. Microsatellite DNA fingerprinting indicated a stable and persistent donor-recipient mixed chimerism, whilst the circulating red cells remain of host origin.

Adult↗
PubMed2000

A randomized controlled trial of kurorinone versus interferon-alpha2a treatment in patients with chronic hepatitis B.

It has recently been shown that a Chinese traditional medicine, kurorinone, extracted from Sophora Flavescens Ait, possesses antiviral properties. We evaluated the efficacy and safety of kurorinone treatment in patients with chronic hepatitis B. Ninety-four patients with abnormal alanine transaminase (ALT) levels and hepatitis B e antigen (HBeAg) and/or hepatitis B virus (HBV) DNA-positivity were randomly assigned to receive either kurorinone 400 mg daily (45 patients) or 3 million units (MU) of interferon-alpha (IFN-alpha) (49 patients, daily for 1 month, every other day for 2 months) for 3 months. Patients were followed-up for 12 months. At baseline, both groups were comparable regarding age, gender and serological parameters. At the end of treatment, complete response (defined as ALT normalization and HBeAg and/or HBV DNA loss) occurred in 50% of the kurorinone group and in 61.3% of the IFN-alpha-treated group (P > NS). At the end of the 12-month follow-up period, a complete response (sustained response) occurred in 26.7-36.7% of kurorinone-treated patients with moderate or mild liver damage and in 44.4-46.7% of IFN-alpha-treated patients with similar liver injury. In kurorinone- as well as in IFN-alpha-treated patients, there was no statistical significant difference with respect to complete response rates between HBeAg-positive and hepatitis B e antibody-positive subgroups. Kurorinone had no untoward side-effects except for local pain at injection sites. The results of this trial suggest that kurorinone is able to inhibit HBV replication and improve disease remission in patients with chronic hepatitis B.

Adolescent↗
PubMed2000

Fatty acid transport regulatory proteins in the developing rat placenta and in trophoblast cell culture models.

The placenta forms a selective barrier that is able to transport nutrients that are of critical use to the fetus. Delivery of essential fatty acids to the fetus is dependent upon transplacental transport and provides the backbone for the biosynthesis of biological membranes, myelin and various signalling molecules. The primary objective of this research was to elucidate the expression patterns of genes that regulate fatty acid transport across the placenta. Several fatty acid transport regulatory genes have been identified in the rat including; cytoplasmic heart fatty acid binding protein (hFABP), plasma membrane fatty acid binding protein (FABPpm), fatty acid translocase (FAT) and fatty acid transport protein (FATP). In this study, we have elucidated temporal and spatial expression patterns for these genes in the rat placenta and in cell culture models of the rat placenta by Northern blot, RT-PCR, Western blot and/or by in situ hybridization analyses. Expression of hFABP was specific to the labyrinth zone, the main barrier and site of transplacental transport in the rat placenta. In addition, the levels of hFABP expression increased with gestational age, suggesting a growing requirement for fatty acid transport with advancing stages of pregnancy. FABPpm, FAT and FATP are expressed in both the junctional and labyrinth zones of the rat placenta. FAT was predominantly localized to the labyrinth zone by in situ hybridization analysis. The placental cell expression patterns of the genes involved in fatty acid transport were supported by our observations of HRP-1 (labyrinth zone) and Rcho-1 (junctional zone) trophoblast cell culture models. Given their cell surface location, we predict that FABPpm, FAT and FATP potentially participate in placental fatty acid uptake. The predominant expression of hFABP and FAT in the labyrinth zone of the chorioallantoic placenta implicates hFABP and FAT in the transplacental movement of fatty acids from maternal to fetal compartments.

Animals↗
PubMed2000

Induction of apoptosis and activation of the caspase cascade by anti-EGF receptor monoclonal antibodies in DiFi human colon cancer cells do not involve the c-jun N-terminal kinase activity.

We previously reported that exposure of DiFi human colon cancer cells to the anti-epidermal growth factor (EGF) receptor monoclonal antibody (mAb) 225 resulted in apoptosis, but the mechanisms remain to be elucidated. In the present study, we investigated the effects of a panel of four anti-EGF receptor mAbs, each of which binds to different epitopes of the EGF receptor in DiFi cells, on the induction of apoptosis. We found that each of these mAbs induced apoptosis in DiFi cells. Exposure of DiFi cells to mAb 225 activated the initiation caspase-8, which was detectable between 8 and 16 h after exposure of the cells to the antibody. There was also an activation of the initiation caspase-9, which lagged a few hours behind the activation of caspase-8. Exposure of DiFi cells to mAb 225 also activated the execution caspase-3, which was accompanied temporally by evidence of cleavage of a well-characterized caspase-3 substrate, poly(ADP)ribosepolymerase (PARP). Pre-exposure of the cells to the caspase-3-specific inhibitor DEVD-CHO partially reduced the mAb 225-induced PARP cleavage and apoptosis, whereas pre-exposure of the cells to the caspase pan-inhibitor z-VAD-fmk completely inhibited mAb 225-induced apoptosis. Caspases-3, -8 and -9 were not activated in the cell lines in which mAb 225 only induced G1 phase arrest of the cell cycle. In contrast to the apoptosis of DiFi cells induced by ultraviolet irradiation, which strongly activated the c-jun N-terminal kinase-1 (JNK1) and the caspase cascade, mAb 225-induced apoptosis and activation of the caspase cascade in DiFi cells were not associated with activation of JNK1.

Adenocarcinoma↗
PubMed2000

Vascular osteomuscular autograft prefabrication using coral, type I collagen and recombinant human bone morphogenetic protein-2.

In 20 male Sprague-Dawley rats, 10 pieces of L-shaped coral combined with type I collagen and recombinant human bone morphogenetic protein-2 (rhBMP-2) and 10 discs (diameter 5 mm) were wrapped in the gracilis muscle, and left pedicled on the femoral vessels. Untreated coral was buried in muscle at a distant control site in 4 animals. After 3 weeks, autografts were examined for the shape of new bone, vascular patency, and induction of bone. In all grafts in viable tissue, heterotopic bone was formed. The shape of the new bone was the same as that of the coral, and there was no significant inflammatory reaction. Part of the coral in the composite was absorbed. Bone was not formed in any of the control sites. Coral and type 1 collagen are effective as a carrier for BMP to prefabricate vascular osteomuscular autografts with designed shape. There is a potential clinical application for BMP to bioengineer microvascular free flaps with intrinsic skeletal muscle for maxillofacial reconstruction.

Animals↗
PubMed2000

The effect of protein kinase C and its alpha subtype on human vascular smooth muscle cell proliferation, migration and fibronectin production.

BACKGROUND: Vascular smooth muscle cell (SMC) migration, proliferation and extracellular matrix protein production are key steps in the formation of intimal hyperplasia, a process that leads to failure of vascular reconstructions. Protein kinase C (PKC) may be involved in all 3 cellular events. PKC consists of a family of 11 isotypes, 8 of which we have identified in human vascular SMCs. In this study we evaluate the role of PKCalpha as a second messenger for proliferation, migration and fibronectin production induced by human saphenous vein SMCs. METHODS: DNA synthesis was evaluated by using (3)H-thymidine incorporation. Mitogen-activated protein kinase (MAP-K) activation was quantified by Western blotting with an antibody to its phosphorylated substrate, Elk-1. Chemotaxis was evaluated by using a microchemotaxis chamber. SMC fibronectin was measured by Western blotting. For all experiments, PKCalpha was blocked with a selective inhibitor, Gö6976. RESULTS: Gö6976, at concentrations that allow selective inhibition of PKCalpha, inhibited platelet-derived growth factor-stimulated SMC proliferation and MAP-K activation by 30% to 40% and 30% to 60%, respectively. SMC chemotaxis was stimulated approximately 2-fold by the PKCalpha inhibitor. Neither basal nor transforming growth factor-betaI induced fibronectin production was affected by Gö6976. CONCLUSIONS: Our data suggest that PKCalpha is a positive mediator of SMC proliferation and MAP-K activity, a negative regulator of migration and has no effect on SMC fibronectin production. These data suggest that modulating activities of specific PKC isotypes might be useful in both the study and control of intimal hyperplasia.

Carbazoles↗