Biomedical subjects

L Yang

Publications and source records attributed to L Yang.

At least 397 records · Page 22Linked to original sources

PubMed1999

[Determination of zinc in vegetable oils by FAAS with trace injection method].

A method for the determination of zinc in the soybean, cottonseed and sesame oils by FAAS with trace injection technique was discribed in this paper. The injection volume was 30 microL. The characteristic concentration and the detection limit were 0.098 and 0.00368 microg/g, respectively. The relative standard deviation was 2.6% and the recoveries were in the range of 92.9%-107.8%. The contents of zinc in the samples were 9.67, 1.42 and 1.77 microg/g, respectively.

Limit of Detection↗

PubMed1998

[The use of microsatellite DNA markers for distinguishing metastatic tumor cells].

OBJECTIVE: To study the genetic stability and to establish a method for detection of micrometastasis using microsatellite DNA in human breast cancer xenograft in nude mice. METHODS: Fresh tissue of human breast cancer was xenotransplanted in nude mice or thotopically. Genomic DNA extracted from tissues of human breast cancer, xenotransplanted tumors and metastatic foci in nude mice were PCR amplified at three microsatellite loci (D14S68, D18S69, D20S199) and were analysed by electrophoresis and silver stain on PAGE. RESULTS Microsatellite DNA in genome of the xenotransplanted tumors and metastatic foci in nude mice were identical with that of the human breast cancer. CONCLUSION: This study has demonstrated in nude mice the xenotransplanted tumors and metastatic foci that originated from human breast cancer. The genetic stability in human breast cancer is evident in the processes of xenotransplantation, serial passages in nude mice, metastasis and in vitro culture. This method is sensitive and specific for the discrimination of metastatic tumor cells.

Animals↗

PubMed1998

Characterization of microdialysis acidification for capillary isoelectric focusing-microelectrospray ionization mass spectrometry.

A microdialysis junction, based on a microdialysis membrane connecting a separation capillary and a short, sharply tapered microelectrospray emitter capillary, is demonstrated for on-line combination of capillary isoelectric focusing (CIEF) with electrospray ionization mass spectrometry (ESI-MS). The microdialysis junction provides the necessary electrical connection across the dialysis membrane for defining the electric fields needed for the CIEF separation and the electrospray process. Additionally, postseparation acidification of focused protein zones eluted from the CIEF capillary is achieved using the microdialysis junction while separation efficiency and resolution is maintained. A microelectrospray emitter produces a stable electrospray of protein analytes without the need for a makeup liquid flow and eliminates any subsequent sample dilution and reduction in MS sensitivity. The microdialysis junction is advantageous over the coaxial liquid sheath interface as evidenced by the simplicity in operation procedures, the enhancement in detection sensitivity, and the linear correlation between protein migration time and isoelectric point in CIEF-ESI-MS.

Buffers↗

PubMed1998

Removal of superficial inhibition releases hyperexcitability in middle and deep horizontal slices from rat somatosensory neocortex.

Synaptic physiology was studied in horizontal slices of rat somatosensory neocortex. Intrinsic properties of pyramidal neurons from horizontal slices resembled those recorded in cells from coronal slices, but cells in superficial horizontal slices displayed more prominent fast and slow inhibition, while cells from deeper slices showed disinhibition. This disinhibition in deeper horizontal slices resulted in epileptogenesis in 81% of middle and 35% of deep layer horizontal slices. Brief exposure to glutamate antagonists and dantrolene was ineffective in preventing epileptic activity, but limited pentobarbital exposure reduced the proportion of deep slices manifesting epileptiform activity by 75%. Thus, within cortex inhibition dominates superficially and excitation predominates in deeper layers. While the cortex is vulnerable to hyperexcitability when superficial cortex is compromised, enhancing fast inhibition can reset the excitation-inhibition balance, and prevent epileptogenesis.

6-Cyano-7-nitroquinoxaline-2,3-dione↗

PubMed1998

Retrograde cerebral perfusion results in flow distribution abnormalities and neuronal damage. A magnetic resonance imaging and histopathological study in pigs.

BACKGROUND: In the past few years, although significant efforts have been made to assess flow distribution during retrograde cerebral perfusion with microspheres, dye, or hydrogen clearance, flow distribution in real time is still undefined. We used MR perfusion imaging to monitor flow distribution in the brain during and after deep hypothermic circulatory arrest (DHCA) with antegrade or retrograde cerebral perfusion (ACP or RCP). METHODS AND RESULTS: Thirteen pigs were divided into 2 groups and exposed to 120 minutes of either RCP (n = 7) or ACP (n = 6) at 15 degrees C, followed by 60 minutes of cardiopulmonary bypass (CPB) at 37 degrees C. During DHCA, the brain was perfused antegradely through the common carotid artery or retrogradely through the superior vena cava at pressures of 60 to 70 mm Hg and 20 to 25 mm Hg in the ACP and RCP groups, respectively. Esophageal temperature was monitored continuously. MR perfusion images were acquired every 30 minutes before, during, and after DHCA. The brain was perfusion-fixed with formaldehyde solution for histopathology at the completion of each experiment. During initial normothermic CPB, MR perfusion imaging showed a nearly uniform distribution of flow in the brain. The same pattern was maintained with a significant increase in regional cerebral blood volume during ACP and reperfusion in the ACP group. RCP provided little or no detectable blood distribution to the brain, resulting in poor reperfusion of many areas of the brain on reflow with CPB at 37 degrees C. The total area suffering poor reperfusion was significantly higher in the RCP group than the ACP group. Histopathology showed no morphological changes in any area of the brain in the ACP group, whereas varying severity of neuronal damage was observed in different regions of the brain in the RCP group. CONCLUSIONS: ACP preserves uniform blood distribution and normal morphology of brain tissue after prolonged DHCA. RCP provides very little blood to the tissue of the brain. A 120-minute period of RCP results in abnormal flow distribution and neuronal damage during reperfusion. The damage resulting from shorter periods of RCP remains to be assessed.

Animals↗

PubMed1998

Essential role of nuclear factor kappaB in the induction of eosinophilia in allergic airway inflammation.

The molecular mechanisms that contribute to an eosinophil-rich airway inflammation in asthma are unclear. A predominantly T helper 2 (Th2)-type cell response has been documented in allergic asthma. Here we show that mice deficient in the p50 subunit of nuclear factor (NF)- kappaB are incapable of mounting eosinophilic airway inflammation compared with wild-type mice. This deficiency was not due to a block in T cell priming or proliferation in the p50(-/-) mice, nor was it due to a defect in the expression of the cell adhesion molecules VCAM-1 and ICAM-1 that are required for the extravasation of eosinophils into the airways. The major defects in the p50(-/-) mice were the lack of production of the Th2 cytokine interleukin 5 and the chemokine eotaxin, which are crucial for proliferation and for differentiation and recruitment, respectively, of eosinophils into the asthmatic airway. Additionally, the p50(-/-) mice were deficient in the production of the chemokines macrophage inflammatory protein (MIP)-1alpha and MIP-1beta that have been implicated in T cell recruitment to sites of inflammation. These results demonstrate a crucial role for NF-kappaB in vivo in the expression of important molecules that have been implicated in the pathogenesis of asthma.

Animals↗

PubMed1998

Oncoprotein TLS interacts with serine-arginine proteins involved in RNA splicing.

The gene encoding the human TLS protein, also termed FUS, is located at the site of chromosomal translocations in human leukemias and sarcomas where it forms a chimeric fusion gene with one of several different genes. To identify interacting partners of TLS, we screened a yeast two-hybrid cDNA library constructed from mouse hematopoietic cells using the C-terminal region of TLS in the bait plasmid. Two cDNAs encoding members of the serine-arginine (SR) family of proteins were isolated. The first SR protein is the mouse homolog of human splicing factor SC35, and the second SR member is a novel 183-amino acid protein that we term TASR (TLS-associated serine-arginine protein). cDNA cloning of human TASR indicated that mouse and human TASR have identical amino acid sequences. The interactions between TLS and these two SR proteins were confirmed by co-transfection and immunoprecipitation studies. In vivo splicing assays indicated that SC35 and TASR influence splice site selection of adenovirus E1A pre-mRNA. TLS may recruit SR splicing factors to specific target genes through interaction with its C-terminal region, and chromosomal translocations that truncate the C-terminal region of TLS may prevent this interaction. Thus TLS translocations may alter RNA processing and play a role in malignant transformation.

Amino Acid Sequence↗

PubMed1998

Rapid identification of subtype-selective agonists of the somatostatin receptor through combinatorial chemistry.

Nonpeptide agonists of each of the five somatostatin receptors were identified in combinatorial libraries constructed on the basis of molecular modeling of known peptide agonists. In vitro experiments using these selective compounds demonstrated the role of the somatostatin subtype-2 receptor in inhibition of glucagon release from mouse pancreatic alpha cells and the somatostatin subtype-5 receptor as a mediator of insulin secretion from pancreatic beta cells. Both receptors regulated growth hormone release from the rat anterior pituitary gland. The availability of high-affinity, subtype-selective agonists for each of the somatostatin receptors provides a direct approach to defining their physiological functions.

Amides↗

PubMed1998

Cripto is required for correct orientation of the anterior-posterior axis in the mouse embryo.

The anterior-posterior axis of the mouse embryo is established by two distinct organizing centres in the anterior visceral endoderm and the distal primitive streak. These organizers induce and pattern the head and trunk respectively, and have been proposed to be localized through coordinate cell movements that rotate a pre-existing proximal-distal axis. Here we show that correct localization of both head- and trunk-organizing centres requires Cripto, a putative signalling molecule that is a member of the EGF-CFC gene family. Before gastrulation, Cripto is asymmetrically expressed in a proximal-distal gradient in the epiblast, and subsequently is expressed in the primitive streak and newly formed embryonic mesoderm. A Cripto null mutation generated by targeted gene disruption results in homozygous Cripto-/- embryos that mostly consist of anterior neuroectoderm and lack posterior structures, thus resembling a head without a trunk. Notably, markers of the head organizer are located at the distal end of the embryo, whereas markers of the primitive streak are absent or localized to the proximal side. Our results indicate that Cripto signalling is essential for the conversion of a proximal-distal asymmetry into an orthogonal anterior-posterior axis.

Animals↗

PubMed1998

1-Methyl-4-phenyl-1,2,3,6-tetrahydropyride neurotoxicity is attenuated in mice overexpressing Bcl-2.

The proto-oncogene Bcl-2 rescues cells from a wide variety of insults. Recent evidence suggests that Bcl-2 protects against free radicals and that it increases mitochondrial calcium-buffering capacity. The neurotoxicity of 1-methyl-4-phenyl-1,2,3, 6-tetrahydropyride (MPTP) is thought to involve both mitochondrial dysfunction and free radical generation. We therefore investigated MPTP neurotoxicity in both Bcl-2 overexpressing mice and littermate controls. MPTP-induced depletion of dopamine and loss of [3H]mazindol binding were significantly attenuated in Bcl-2 overexpressing mice. Protection was more profound with an acute dosing regimen than with daily MPTP administration over 5 d. 1-Methyl-4-phenylpyridinium (MPP+) levels after MPTP administration were similar in Bcl-2 overexpressing mice and littermates. Bcl-2 blocked MPP+-induced activation of caspases. MPTP-induced increases in free 3-nitrotyrosine levels were blocked in Bcl-2 overexpressing mice. These results indicate that Bcl-2 overexpression protects against MPTP neurotoxicity by mechanisms that may involve both antioxidant activity and inhibition of apoptotic pathways.

1-Methyl-4-phenylpyridinium↗

PubMed1998

An early phase of embryonic Dlx5 expression defines the rostral boundary of the neural plate.

Relatively little is known about the molecular events that specify the rostrocaudal axis of the neural plate. Here we show that a member of the Distal-less (Dlx) homeobox gene family, Dlx5, is one of the earliest known markers for the most rostral ectoderm, before the formation of an overt neural plate. During late gastrulation Dlx5 expression becomes localized to the anterior neural ridge, which defines the rostral boundary of the neural plate, and also extends caudolaterally, marking the region of the presumptive neural crest. Subsequently, Dlx5 is expressed in tissues (olfactory epithelium, ventral cephalic epithelium) that are believed to derive from the anterior neural ridge, based on the avian fate map. The early phase of Dlx5 expression in the anterior neural ridge and its derivatives is distinct from a later phase of expression in the ventral telencephalon and diencephalon and also appears to be unique for Dlx5 among members of the Dlx family. Another distinctive feature of Dlx5 expression is the occurrence of an alternative transcript (deltaDlx5), which encodes a truncated protein lacking the homeodomain, and represents a significant fraction of total Dlx5 transcripts at all embryonic stages that were examined. In contrast with full-length DLX5, the deltaDLX5 truncated protein is deficient in DNA-binding activity and does not interact with the homeoprotein partner MSX1. Taken together, our findings suggest that Dlx5 activity may be regulated via the expression of an alternative transcript and demonstrate that Dlx5 marks the anterior boundary of the neural plate.

Alternative Splicing↗

PubMed1998

Differential responsiveness of the IL-5 and IL-4 genes to transcription factor GATA-3.

The cytokines IL-4 and IL-5 are often coordinately produced by Th2 cells as in asthma. However, it is unclear whether similar molecular mechanisms underlie transcription of the two genes. We have previously shown that the transcription factor GATA-3 is expressed in Th2 but not Th1 cells and is crucial for activation of the IL-5 promoter by different stimuli. In a different study, GATA-3 was shown to be sufficient for the expression of IL-4 and other Th2 cytokine genes. Here, we show that ectopic expression of GATA-3 is sufficient to drive IL-5 but not IL-4 gene expression. Also, in Th2 cells, antisense GATA-3 RNA inhibits IL-5 but not IL-4 promoter activation. The induction of IL-5 gene expression by GATA-3 involves high affinity binding of GATA-3 to an inverted GATA repeat in the IL-5 promoter.

Animals↗

PubMed1998

Sequence motifs in adenoviral DNA block immune activation by stimulatory CpG motifs.

Unmethylated CpG dinucleotides in particular base contexts (CpG-S motifs) are relatively common in bacterial DNA but are rare in vertebrate DNA. B cells and monocytes have the ability to detect such CpG-S motifs that trigger innate immune defenses with production of Th1-like cytokines. Despite comparable levels of unmethylated CpG dinucleotides, DNA from serotype 12 adenovirus is immune-stimulatory, but serotype 2 is nonstimulatory and can even inhibit activation by bacterial DNA. In type 12 genomes, the distribution of CpG-flanking bases is similar to that predicted by chance. However, in type 2 adenoviral DNA the immune stimulatory CpG-S motifs are outnumbered by a 15- to 30-fold excess of CpG dinucleotides in clusters of direct repeats or with a C on the 5' side or a G on the 3' side. Synthetic oligodeoxynucleotides containing these putative neutralizing (CpG-N) motifs block immune activation by CpG-S motifs in vitro and in vivo. Eliminating 52 of the 134 CpG-N motifs present in a DNA vaccine markedly enhanced its Th1-like function in vivo, which was increased further by the addition of CpG-S motifs. Thus, depending on the CpG motif, prokaryotic DNA can be either immune-stimulatory or neutralizing. These results have important implications for understanding microbial pathogenesis and molecular evolution and for the clinical development of DNA vaccines and gene therapy vectors.

Adenoviridae↗

PubMed1998

Astrocytes modulate nitric oxide production by microglial cells through secretion of serine and glycine.

We investigated lipopolysaccharide (LPS)-induced nitric oxide (NO) production by rat microglia in neuron-microglia and astrocyte-microglia cocultures to evaluate the influence of neurons and astrocytes on microglial activity. Microglial cells solely cultured in medium devoid of serine (Ser), glycine (Gly) hardly expressed inducible NO synthase (iNOS), while those cocultured with neurons and astrocytes expressed iNOS. When microglial cells and astrocytes were separately cultured by using tissue culture inserts, which allowed the microglial cells to be exposed to only diffusible factors arising from astrocytes, NO production was significantly enhanced. On the other hand, neurons, when separated from microglial cells by the inserts, could not activate microglial cells possibly due to lacking of direct contact between neurons and microglial cells. NO production in pure microglial cultures was significantly enhanced in the presence of Ser/Gly at concentrations higher than 25 microM. Conditioned media obtained from microglia culture and neuron-microglia coculture contained less than 10 microM of Ser and Gly, while media from astrocyte culture and astrocyte-microglia coculture contained 33-41 microM Ser and 20-26 microM Gly. Accordingly, astrocytes modulate the activity of microglial cells by secreting Ser and Gly. The present study proposes a novel metabolic coupling between astrocytes and microglial cells via amino acids.

Animals↗

PubMed1998

Synthesis and biological activities of potent peptidomimetics selective for somatostatin receptor subtype 2.

A series of nonpeptide somatostatin agonists which bind selectively and with high affinity to somatostatin receptor subtype 2 (sst2) have been synthesized. One of these compounds, L-054,522, binds to human sst2 with an apparent dissociation constant of 0.01 nM and at least 3,000-fold selectivity when evaluated against the other somatostatin receptors. L-054,522 is a full agonist based on its inhibition of forskolin-stimulated adenylate cyclase activity in Chinese hamster ovary-K1 cells stably expressing sst2. L-054,522 has a potent inhibitory effect on growth hormone release from rat primary pituitary cells and glucagon release from isolated mouse pancreatic islets. Intravenous infusion of L-054,522 to rats at 50 microgram/kg per hr causes a rapid and sustained reduction in growth hormone to basal levels. The high potency and selectivity of L-054, 522 for sst2 will make it a useful tool to further characterize the physiological functions of this receptor subtype.

Animals↗

PubMed1998

Microglial cells prevent nitric oxide-induced neuronal apoptosis in vitro.

Apoptotic neuronal death is known to occur in the developing brain and in the mature brain of patients with ischemic and degenerative disorders. Although microglial cells are known to become activated in specific conditions, it has not been elucidated whether they enhance or prevent neuronal apoptosis. The present study was intended to observe how microglial cells are involved in neuronal death. When rat primary cortical neurons were incubated with a nitric oxide (NO) donor sodium nitroprusside (SNP; 300 microM) for 10 min, neuronal death occurred 12-16 hr later. The NO-induced neuronal death was inhibited by cycloheximide, and the SNP-treated neurons were characterized by nuclear fragmentation and intact cell membrane under electron microscopy. Agarose gel electrophoresis demonstrated DNA fragmentation of the SNP-treated neurons. Thus, the NO-induced neuronal death appeared to be apoptosis. When neurons were cocultured with rat primary microglial cells, the SNP treatment failed to induce the neuronal death. Because microglia-conditioned medium also prevented apoptotic neuronal death, microglial cells were considered to secrete antiapoptotic factors. The microglia-conditioned medium rescued neurons even when they were added to neuronal cultures after the SNP treatment, implying that the factors acted on neurons in a manner other than scavenging NO. Interleukin-3, interleukin-6, macrophage colony-stimulating factor, and basic fibroblast growth factor, which are known to be secreted by microglial cells, were not effective in preventing NO-induced neuronal death. Among microglia-derived substances, tumor necrosis factor alpha and plasminogen, which are heat-labile proteins, inhibited neuronal apoptosis. The neuroprotective action of the microglia-conditioned medium, however, still remained, even after it was heated. These findings suggest that microglial cells protect neurons against NO-induced lethal damage by secreting heat-labile and heat-stable neuroprotective factors in vitro.

Animals↗

PubMed1998

Macrophage colony-stimulating factor augments beta-amyloid-induced interleukin-1, interleukin-6, and nitric oxide production by microglial cells.

In Alzheimer's disease (AD), a chronic cerebral inflammatory state is thought to lead to neuronal injury. Microglia, intrinsic cerebral immune effector cells, are likely to be key in the pathophysiology of this inflammatory state. We showed that macrophage colony-stimulating factor, a microglial activator found at increased levels in the central nervous system in AD, dramatically augments beta-amyloid peptide (betaAP)-induced microglial production of interleukin-1, interleukin-6, and nitric oxide. In contrast, granulocyte macrophage colony-stimulating factor, another hematopoietic cytokine found in the AD brain, did not augment betaAP-induced microglial secretory activity. These results indicate that increased macrophage colony-stimulating factor levels in AD could magnify betaAP-induced microglial inflammatory cytokine and nitric oxide production, which in turn could intensify the cerebral inflammatory state by activating astrocytes and additional microglia, as well as directly injuring neurons.

Alzheimer Disease↗

PubMed1998

Capillary isoelectric focusing-electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry for protein characterization.

On-line combination of capillary isoelectric focusing (CIEF) with electrospray ionization Fourier transform ion cyclotron resonance (ESI-FTICR) mass spectrometry is demonstrated for high-resolution analysis of model proteins, human hemoglobin variants, and Escherichia coli proteins. The acquisition of high-resolution mass spectra of hemoglobin beta chains allows direct identification of hemoglobin variants A and C, differing in molecular mass by 1 Da. Direct mass determination of cellular proteins separated in the CIEF capillary is achieved using their isotopic envelopes obtained from ESI-FTICR. The factors which dictate overall performance of CIEF-ESI-FTICR, including duty cycle, mass resolution, scan rate, and sensitivity, are discussed in the context of protein variants and cell lysates analyzed in this study.

Bacterial Proteins↗