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Biomedical subjects

T Zhang

Publications and source records attributed to T Zhang.

At least 217 records · Page 12Linked to original sources
PubMed1998

Application of analytical and preparative high-speed counter-current chromatography for separation of alkaloids from Coptis chinensis Franch.

Analytical high-speed counter-current chromatography (HSCCC) was used for the systematic selection and optimization of the two-phase solvent system to separate alkaloids from Coptis chinensis Franch. The optimum solvent system thus obtained led to the successful separation of alkaloids from C. chinensis Franch by preparative HSCCC. One batch separation yielded four pure alkaloids, including palmatine, berberine, epiberberine and coptisine from the crude alkaloid extract.

Alkaloids↗
PubMed1998

Repression of Stat3 activity by activation of mitogen-activated protein kinase (MAPK).

STAT proteins are activated by phosphorylation at specific tyrosine residue at the carboxy-terminus which is required for dimer-formation, nuclear translocation, DNA binding and transcriptional activity in cells treated with cytokines and growth factors. Recent studies have indicated that STATs are also phosphorylated by MAPK, or extracellular signal-regulated kinase (ERK) on serine. We investigated the role of ERK on the regulation of STAT activity. Here, we report that ERK2 activated by its upstream kinase, MEK1, represses Stat3 transcriptional activity induced by Src or Jak-2. To unravel the mechanism of repression, we further showed that Stat3 DNA binding activity and its tyrosine phosphorylation are also inhibited under the same conditions. ERK2 phosphorylates Stat3 on three serine-containing peptides and decreases its tyrosine phosphorylation induced by EGF treatment. We also detected an association of ERK2 and Stat3 in vivo which is modulated positively by activation of ERK2, but negatively by Jak2. We propose that MAP kinase cascade may negatively regulate Stat3 activities by decreasing its tyrosine phosphorylation and also possibly by association.

3T3 Cells↗
PubMed1998

[A rapid method for subtractive screening of hepatoma apoptotic cells cDNA library].

OBJECTIVE: To expedite the subtractive screening of human hepatoma apoptotic cells cDNA library. METHODS: The method of subtractive hybridization combined with dot blot hybridization was adopted. First, minus cDNA probe was used to screen the cDNA library, the minus clones that did not hybridize with the minus cDNA probe were picked up as the source of the second grade dot blot hybridization. Secondly, two probes of the plus and minus cDNA were used to screen the clones;the clones that only hybridize with the plus cDNA probe were picked up as the source of the third grade dot blot hybridization. RESULTS: Four clones were obtained and the lengths of the inserted cDNA fragments were about 1.5kb long. CONCLUSION: The results demonstrate this is a feasible, simple and quick method for subtractive screening of the cDNA library.

Apoptosis↗
PubMed1998

[Study on the changes of the levels of SOD and MDA in lung and MN in bone marrow exposed to cooking fume in rats].

In order to investigate the mechanism of the activities of superoxide dismutase (SOD) and the concentration of malondialdehyde (MDA) in lung and rate of micro-nucleus (MN) in bone marrow by which rape oil fume condensate(RC) exert their effect in rat lung, pouring into traches SD rat was performed with RC. Results showed that the SOD activities in RC and B(a)P groups were significantly higher than those in DMSO and control groups(P < 0.05). The concentrations of MDA were significantly lower than that in DMSO and control groups (P < 0.05). In experimental groups SOD/MDA decreased. MN rate significantly increased. It is concluded that lung tissue may be a target of RC.

Air Pollutants↗
PubMed1998

Preparative separation of alkaloids from the root of Sophora flavescens Ait by pH-zone-refining counter-current chromatography.

pH-Zone-refining counter-current chromatography was applied to the separation of alkaloids from a crude extract of the root of Sophora flavescens Ait using a multilayer coil planet centrifuge. After methyl tert.-butyl ether and water were equilibrated, triethylamine (10 mM) was added to the organic phase as a retainer and hydrochloric acid (5-10 mM) to the aqueous phase as an eluter. The separation was performed by eluting the aqueous phase while the organic phase was used as the stationary phase. From 1.0 g of the crude extract, sophocarpine (170 mg) and matrine (600 mg) were separated within 4.5 h at high purity of over 98%.

Alkaloids↗
PubMed1998

[Studies on molecular teratogenic mechanism of methylmercury in early developing rat embryos].

The present study further revealed the teratogenic mechanism of methylmercury chloride (MMC) during rat neurulation by means of nonradioactive in situ hybridization (ISH), semiquantitative analysis of immunohistochemical staining and in vivo teratogenic test. The main aim was to teat the hypothesis that iNOS, HSP70, NT, TGF-beta and Bcl-2 genes contribute to MMC-induced day 9.5 embryonic damages. Results showed there were no obvious poisoning signs and death of pregnant female rats injected intraperitoncally with 0, 0.2, 0.4, 0.8, 1.6 and 3.2 mg/kg MMC. While the doses increased, the total morphological scores decreased gradually, and the rates of embryo deformity and development delay increased step by step to 34% and 76% respectively. The levels of iNOS mRNA and protein and HSP70 mRNA increased, and NT mRNA with its protein became down, all these changes were concentration dependent. In addition, MMC could inhibit the level of TGF-beta mRNA, but no obvious influence on the levels of Bcl-2 mRNA and Bcl-2 protein. On the basis of parallel findings from embryos, genes and proteins, abnormal expression of genes in transcriptional level might be related to MMC-induced teratogenic insult.

Animals↗
PubMed1998

A 29-kilodalton Golgi soluble N-ethylmaleimide-sensitive factor attachment protein receptor (Vti1-rp2) implicated in protein trafficking in the secretory pathway.

Expressed sequence tags coding for a potential SNARE (soluble N-ethylmaleimide-sensitive factor attachment protein receptor) were revealed during data base searches. The deduced amino acid sequence of the complete coding region predicts a 217-residue protein with a COOH-terminal hydrophobic membrane anchor. Affinity-purified antibodies raised against the cytoplasmic region of this protein specifically detect a 29-kilodalton integral membrane protein enriched in the Golgi membrane. Indirect immunofluorescence microscopy reveals that this protein is mainly associated with the Golgi apparatus. When detergent extracts of the Golgi membrane are incubated with immobilized glutathione S-transferase alpha soluble N-ethylmaleimide-sensitive factor attachment protein (GST-alpha-SNAP), this protein was specifically retained. This protein has been independently identified and termed Vti1-rp2, and it is homologous to Vti1p, a yeast Golgi SNARE. We further show that Vti1-rp2 can be qualitatively coimmunoprecipitated with Golgi syntaxin 5 and syntaxin 6, suggesting that Vti1-rp2 exists in at least two distinct Golgi SNARE complexes. In cells microinjected with antibodies against Vti1-rp2, transport of the envelope protein (G-protein) of vesicular stomatitis virus from the endoplasmic reticulum to the plasma membrane was specifically arrested at the Golgi apparatus, providing further evidence for functional importance of Vti1-rp2 in protein trafficking in the secretory pathway.

Amino Acid Sequence↗
PubMed1998

The influence of huntingtin protein size on nuclear localization and cellular toxicity.

Huntington disease is an autosomal dominant neurodegenerative disorder caused by the pathological expansion of a polyglutamine tract. In this study we directly assess the influence of protein size on the formation and subcellular localization of huntingtin aggregates. We have created numerous deletion constructs expressing successively smaller fragments of huntingtin and show that these smaller proteins containing 128 glutamines form both intranuclear and perinuclear aggregates. In contrast, larger NH2-terminal fragments of huntingtin proteins with 128 glutamines form exclusively perinuclear aggregates. These aggregates can form in the absence of endogenous huntingtin. Furthermore, expression of mutant huntingtin results in increased susceptibility to apoptotic stress that is greater with decreasing protein length and increasing polyglutamine size. As both intranuclear and perinuclear aggregates are clearly associated with increased cellular toxicity, this supports an important role for toxic polyglutamine-containing fragments forming aggregates and playing a key role in the pathogenesis of Huntington disease.

Animals↗
PubMed1998

Caspase cleavage of gene products associated with triplet expansion disorders generates truncated fragments containing the polyglutamine tract.

The neurodegenerative diseases Huntington disease, dentatorubropallidoluysian atrophy, spinocerebellar atrophy type 3, and spinal bulbar muscular atrophy are caused by expansion of a polyglutamine tract within their respective gene products. There is increasing evidence that generation of truncated proteins containing an expanded polyglutamine tract may be a key step in the pathogenesis of these disorders. We now report that, similar to huntingtin, atrophin-1, ataxin-3, and the androgen receptor are cleaved in apoptotic extracts. Furthermore, each of these proteins is cleaved by one or more purified caspases, cysteine proteases involved in apoptotic death. The CAG length does not modulate susceptibility to cleavage of any of the full-length proteins. Our results suggest that by generation of truncated polyglutamine-containing proteins, caspase cleavage may represent a common step in the pathogenesis of each of these neurodegenerative diseases.

Amino Acid Sequence↗
PubMed1998

Syntaxin 7, a novel syntaxin member associated with the early endosomal compartment.

Members of the syntaxin family are key molecules involved in diverse vesicle docking/fusion events. We report here the molecular, biochemical, and cell biological characterizations of a novel member (syntaxin 7) of the syntaxin family. Syntaxin 7 is structurally related to all known syntaxins. Within a 79-residue region preceding the C-terminal hydrophobic tail, syntaxin 7 is 35, 34, 34, 34, 25, and 19% identical to syntaxins 1, 2, 3, 4, 5, and 6, respectively. Northern blot analysis showed that syntaxin 7 is widely expressed. Indirect immunofluorescence microscopy revealed that syntaxin 7 is primarily associated with the early endosome. In vitro binding assays established that syntaxin 7 in membrane extracts interacts with immobilized recombinant alpha-soluble N-ethylmaleimide-sensitive factor attachment proteins fused to glutathione S-transferase. Our results highlight the general importance of members of the syntaxin family in protein trafficking and provide new avenues for future functional and mechanistic studies of this first endosomal syntaxin as well as the endocytotic pathway.

Amino Acid Sequence↗
PubMed1998

Permeability of dechorionated one-cell and six-somite stage zebrafish (Brachydanio rerio) embryos to water and methanol.

The permeability of dechorionated one-cell and six-somite stage zebrafish (Brachydanio rerio) embryos to water and the cryoprotectant methanol at 22 degreesC was studied, using real-time video microscopy to determine the volumetric changes of the embryos during cryoprotectant exposure. The equilibrium volumetric behavior of the embryos and the Boyle-van't Hoff relationships were determined using sucrose as a nonpermeating compound. These showed the embryos to behave as nearly ideal osmometers over the range of 253-1724 mOsm, with osmotically inactive volumes of 72.9 and 82.6% for one-cell and six-somite stage embryos, respectively. The Boyle-van't Hoff relationship of the ovary eggs was also determined for comparison and their osmotically inactive volume was 63.9%. The Kedem-Katchalsky parameters of water permeability (Lp), cryoprotectant permeability (Ps), and reflection coefficient (sigma) were determined using DIFFCHAM software. The parameters reported in this study are phenomenological parameters referring to the overall embryo response. The mean values of these parameters were Lp = 0.34 and 0.35 (micrometer/min*atm), Ps = 0.45 and 0.04 (micrometer/s), and sigma = 0.88 and 0.93 for one-cell and six-somite stage embryos, respectively. While the water permeability of the dechorionated zebrafish embryos at different developmental stages remained relatively stable, the permeability to the cryoprotectant methanol (Ps) appeared to decrease during embryo development. The Ps and sigma values for methanol are the first reported for dechorionated fish embryos at these stages.

Animals↗
PubMed1998

A new method for the automated detection of spontaneous otoacoustic emissions embedded in noisy data.

There is, as yet, no universally agreed upon method for the detection of spontaneous otoacoustic emissions (SOAEs). In this paper, we augment extant techniques by presenting a new automated approach. The new procedure reliably labels the spectral peaks as SOAEs, rejects noisy data such as that due to body movements or breathing, provides a subject-specific measure of the probability that a particular peak is erroneously identified as a SOAE, and can be accomplished on-line. Comparison of results with this new approach and with methods undertaken previously in this laboratory and elsewhere are made. The estimated prevalence of SOAEs for the new method is as large as that for any method previously proposed.

Acoustic Stimulation↗
PubMed1998

Inactivation and conformational changes of fatty acid synthase from chicken liver during unfolding by sodium dodecyl sulfate.

Fatty acid synthase is an important enzyme participating in energy metabolism in vivo. The inactivation and conformational changes of the multifunctional fatty acid synthase from chicken liver in SDS solutions have been studied. The results show that the denaturation of this multifunctional enzyme by SDS occurred in three stages. At low concentrations of SDS (less than 0.15 mM) the enzyme was completely inactivated with regard to the overall reaction. For each component of the enzyme, the loss of activity occurred at higher concentrations of SDS. Significant conformational changes (as indicated by the changes of the intrinsic fluorescence emission and the ultraviolet difference spectra) occurred at higher concentrations of SDS. Increasing the SDS concentration caused only slight changes of the CD spectra, indicating that SDS had no significant effect on the secondary structure of the enzyme. The results suggest that the active sites of the multifunctional fatty acid synthase display more conformational flexibility than the enzyme molecule as a whole.

Animals↗
PubMed1998

Effect of chronic duodenal ulceration and its treatment with lanzoprazole or sucralfate on gastroduodenal mucosal protein turnover and TGF-alpha, bFGF, and EGF receptor expression in humans.

In order to investigate whether chronic duodenal ulcer disease is a consequence of disturbed mucosal turnover and growth factor expression, we studied 16 patients with duodenal ulcers before, during, and after endoscopic healing with lansoprazole or sucralfate. Before treatment, gastric fundal and antral mucosal protein turnover rates were higher in patients than controls, without parallel increases in growth factors. Both forms of therapy produced similar changes, with overall increases in duodenal mucosal turnover and transforming growth factor-alpha (TGF-alpha) and epidermal growth factor receptor (EGF-r) levels. Measurements after healing showed persistent elevations of mucosal turnover in the antrum and duodenum and depressions of basic fibroblast growth factor (bFGF) in gastric fundal and duodenal mucosa. We conclude that mucosal turnover is abnormally high in patients with chronic duodenal ulcer disease and is not easily explained by growth factor changes. The failure of lansoprazole and sucralfate to normalize rates, despite endoscopic healing, may explain the high ulcer relapse rates in non-HP-eradicated patients.

2-Pyridinylmethylsulfinylbenzimidazoles↗
PubMed1998

Endobrevin, a novel synaptobrevin/VAMP-like protein preferentially associated with the early endosome.

Synaptobrevins/vesicle-associated membrane proteins (VAMPs) together with syntaxins and a synaptosome-associated protein of 25 kDa (SNAP-25) are the main components of a protein complex involved in the docking and/or fusion of synaptic vesicles with the presynaptic membrane. We report here the molecular, biochemical, and cell biological characterization of a novel member of the synaptobrevin/VAMP family. The amino acid sequence of endobrevin has 32, 33, and 31% identity to those of synaptobrevin/VAMP-1, synaptobrevin/VAMP-2, and cellubrevin, respectively. Membrane fractionation studies demonstrate that endobrevin is enriched in membrane fractions that are also enriched in the asialoglycoprotein receptor. Indirect immunofluorescence microscopy establishes that endobrevin is primarily associated with the perinuclear vesicular structures of the early endocytic compartment. The preferential association of endobrevin with the early endosome was further established by electron microscopy (EM) immunogold labeling. In vitro binding assays show that endobrevin interacts with immobilized recombinant alpha-SNAP fused to glutathione S-transferase (GST). Our results highlight the general importance of members of the synaptobrevin/VAMP protein family in membrane traffic and provide new avenues for future functional and mechanistic studies of this protein as well as the endocytotic pathway.

Amino Acid Sequence↗
PubMed1998

Polymorphism of the apolipoprotein E and angiotensin I converting enzyme genes in Japanese patients with myocardial infarction.

OBJECTIVE: To investigate the genetic contribution for myocardial infarction. METHODS: We investigated common polymorphisms of apolipoprotein E gene and angiotensin converting enzyme (ACE) gene in Japanese population. Subjects were 422 healthy people and 254 patients with myocardial infarction. We evaluated the 287 base pair (bp) insertion (I)/deletion (D) polymorphism in intron 16 of the ACE gene and a polymorphism in the apolipoprotein E gene by using the polymerase chain reaction. RESULTS: The ACE genotype prevalences for II, ID, and DD were 36.2, 46.1, and 17.7%, respectively, among the myocardial infarction patients. The prevalence of the D allele of the ACE gene among the myocardial infarction patients (0.593) exceeded that among the healthy controls (0.407). The prevalences of the epsilon 2, epsilon 3, and epsilon 4 alleles of the apolipoprotein E genotype among healthy controls were 0.024, 0.882, and 0.094, and those among survivors of myocardial infarction were 0.024, 0.834, and 0.142, respectively. Myocardial infarction patients had an excessive prevalence of the apolipoprotein E epsilon 4 allele (P < 0.05). Multiple regression analysis demonstrated that the independent risk factors for developing myocardial infarction were age, DD genotype of ACE gene, and apolipoprotein E epsilon 4 allele. Stenotic coronary vessels in myocardial infarction patients did not differ significantly among the patients with various ACE and apolipoprotein E genotypes in the present study. CONCLUSIONS: Among the Japanese, apolipoprotein E epsilon 4 carriers and subjects with ACE DD genotype are at an increased risk of myocardial infarction.

Aged↗
PubMed1998

Chaotic characteristics of renal nerve peak interval sequence in normotensive and hypertensive rats.

1. The use of non-linear dynamic analysis for the measurement of control processes in low-dimensional signals, for example, blood pressure and heart rate variability, are well established and accepted. However, the application of these analytical techniques to a high-dimensional signal, such as renal sympathetic nerve activity (RSNA), has not been validated. 2. The present study set out to develop an approach whereby the high-dimensional signal of RSNA was reduced to a low-dimensional one by extracting the peak interval sequence (PIS), using Cluster analysis, in order to allow the use of non-linear dynamics analysis. Brachial nerves were electrically stimulated (1.6 Hz, 0.2 ms, 15 V) to elicit a sympatho-excitation in groups of anaesthetized normotensive Wistar and stroke-sprone spontaneously hypertensive rats (SHRSP). 3. It was found that, under basal conditions, the correlation dimension, D2, was stable over a range of embedding dimensions from 12 to 25. Moreover, the largest Lyapunov exponent had a small positive value that was also stable over these embedding dimensions. These values showed that the signal was of low dimensionality and that chaos was present. 4. In Wistar rats, brachial nerve stimulation significantly (P < 0.05-0.001) increased blood pressure (by 25%), heart rate (by 5%) and RSNA (by 200%), which was associated with significant (P < 0.05) reductions in the correlation dimension D2 and the largest Lyapunov exponent of the PIS generated from the renal nerve signal. In contrast, in SHRSP, there were similar increases in blood pressure, heart rate and RSNA in response to brachial nerve stimulation, but neither the correlation dimension nor largest Lyapunov exponent was altered. 5. These findings demonstrate that by extracting the PIS from the renal sympathetic nerve signal, the application of non-linear chaos analysis makes it possible to distinguish differences in the pattern of reflexly induced excitation in sympathetic traffic to the kidney in the pathophysiological state of hypertension. Whether this applies to sympathetic outflow to other organs and tissues remains to be investigated.

Animals↗