Search PubMed⌕ Search

Biomedical subjects

G Liu

Publications and source records attributed to G Liu.

At least 397 records · Page 22Linked to original sources
PubMed1998

[Effects of daurisoline and its three optical isomers on ischemic injury in cultured pheochromocytoma (PC12) cells].

In this study, the protective effects of (-)-R.R-daurisoline and its three optical isomers on ischemic injury in cultured PC12 cells induced by treating cells with NaCN in glucose-free medium were investigated. Cell viability was measured using MTT assay. The results indicated that these compounds, especially (-)-S.R and (+)-R.S isomers were found substantially to attenuate ischemic injury in PC12 cells in a dose-dependent manner. The IC50 values of (-)-R.R, (-)-S.R, (+)-R.S and (+)-S.S isomers were shown to be 18.6 x 10(-6), 2.4 x 10(-6), 5.9 x 10(-6) and 90 x 10(-6) mol.L-1, respectively. Intracellular free Ca2+ concentration in PC12 cells was measured using AR-CM-MIC cation measurement system with Fura-2/AM as Ca2+ fluorescent indicator. (-)-R.R-daurisoline and its three optical isomers: (-)-S.R, (+)-R.S and (-)-S.S were found to markedly inhibit the increase of cytosolic free Ca2+ concentration induced by NaCN (20 mmol.L-1) in a dose-dependent manner. Their IC50 were found to be 3.55 x 10(-6), 0.59 x 10(-6), 1.29 x 10(-6) and 24.3 x 10(-6) mol.L-1 respectively. It is suggested that the cytoprotective effects of daurisoline and its isomers were mediated by blocking Ca2+ influx into cells.

Alkaloids↗
PubMed1998

[Protective effects of (-)-S.R-daurisoline on neuronal injury in rat primary cortical cultures].

The neuroprotective effects of (-)-S.R-daurisoline on glutamate-induced neurotoxicity were studied in rat primary cortical cultures. The inhibitory effects of (-)-S.R-daurisoline on glutamate-elicited free intracellular Ca2+ increase were also studied in freshly dissociated single brain cells isolated from new born rat using AR-CM-MIC Cation Measurement System. Our experimental results demonstrated that (-)-S.R-daurisoline could obviously inhibit the neurotoxicity induced by glutamate and significantly increased cell viability in dose-dependent manner. In inhibiting glutamate-induced neurotoxicity, the IC50 value of (-)-S.R-daurisoline was found to be 3.4 mumol.L-1. (-)-S.R-daurisoline was also shown to markedly inhibit glutamate-elicited increase of cytosolic free Ca2+ concentration in dose-dependent manner with IC50 value of 2.0 mumol.L-1. Our results showed that (-)-S.R-daurisoline has an obvious protective effect on glutamate-induced neurotoxicity in primary cortical cultures. The protective mechanism of (-)-S.R-daurisoline may be relevant to inhibit Ca2+ influx into cells via glutamate-mediated ligand-gated ion channels.

Alkaloids↗
PubMed1998

[The anti-ischemic effect of O, O-acetyldaurisoline].

O, O-acetyldaurisoline(Adau) is a derivative of daurisoline (Dau). In cultured PC12 cells, Adau was found to inhibit K+, Bay K8644 and norepinephrine induced intracellular free calcium concentration increase. Adau was also shown to protect PC12 cells from hypoxia-reoxygenation injury with EC50 of 64.3 +/- 12.5 mumol.L-1 by MTT assay. Adau (2.5, 5 and 10 mg.kg-1, i.v.) administrated 30 min before ischemia in bilateral carotid artery occlusion and four-vessel occlusion rats, attenuated the increase of lipid peroxide content and the decrease of SOD activity. These results show that Adau have significant protective effects against ischemic injury.

Alkaloids↗
PubMed1998

[Structure and function of saw1--a gene related to differentiation of Streptomyces ansochromogenes].

The DNA sequence of double strands of saw1 gene was determined by the method of chaintermination inhibitors. The result indicated that the 1500 bp of DNA fragment displayed a complete open reading frame (ORF), the encoding regions were located in 419 to 1252 bp positions, saw1 product has 89% identity to amino acids of sigma whiG of Streptomyces coelicolor. When recombinant plasmid containing a 1500 bp saw1 DNA fragment insert in plasmid pIJ702 was introduced into Streptomyces coelicolor C71, the sporulation deficient mutant C71 could form spore and produce grey pigment. The gene function was studied by using the method of gene disruption and the result showed that the saw1 played an important role in developmental changes from aerial hypha to spore formation of Streptomyces ansochromogenes.

Amino Acid Sequence↗
PubMed1998

[Effects of artemisia capillaris on blood glucose and lipid in mice].

The effects of Artemisia capillaris Thunb (AC) on blood glucose and lipid in mice were studied and its effective mechanism was explained. The results showed that hyperglycemic effect in aloxan-induced mice was inhibited (P < 0.01); that hyperglycemica in DM mice was decreased (P < 0.05); but the change of fasting blood glucose (FBG) in normal and hyperlipidemia mice was not significant (P < 0.05); that the level of total cholesterol (TC) and/or atherosclerotic index (AI) was decreased (P < 0.01-0.05) and the content of high density lipoprotein cholesterol (HDL-C) was increased in the above different model mice (P < 0.01-0.05). These results indicated that the AC would have the similar hypoglycemic effect as biguanide-drugs, improve endogenous and exogenous metabolic derangement in blood lipid. These suggest that AC could be used to protect and treat DM and its chronic complication.

Alloxan↗
PubMed1998

[FTIR-PAS of rare earth coordinated compounds of Schiff base derived from vanillin and p-toluidine].

The Fourier transform infrared photoacoustic spectra (FTIR-PAS) of Schiff base derived from vanillin (3-methoxy-4-hydroxybenzaldehyde) and p-toluidine and its rare earth coordinated compounds in the 3800-200cm(-1) were measured and inverstigated. The coordinated compounds have two classes: [LnL2Cl x 3H2O]Cl2(Ln:La,Ce,Pr,Nd,Sm,Eu,Gd,Dy;L:Schiff base ligand) and [LnL2Cl2 x 2H2O] Cl x H2O(Ln:Ho,Er,Tm,Yb,Lu). In the coordinated compounds there is intermolecular hydrogen bond derived from phenolic hydroxy group. The bands at 400 and 300cm(-1) are respectively assigned to bonds M-O (water) and M-N.

Benzaldehydes↗
PubMed1998

[Experimental research on laser-induced single-molecule detection].

Single-molecule detection is a kind of ultra-high sensitive detection technique. It is widely used in biology, medicine, environment and so on. Here we report briefly the principle and device of our laser-induced single-molecule detection spectrum instrument. We also report the experimental results on the instrument by using C445 dye, including the affection of sample velocity, energy characteristic, consistence linearity and detection limit. We discuss the effect of photon bleach on experimental results. These results are the base of our future work.

Chemistry Techniques, Analytical↗
PubMed1998

[Ultrasensitive analysis of R6G and R110 in solution].

This paper describes the ultrasensitive detection of R6G and R110 in a flowing aqueous sample, based on laser-induced fluorescence (LIF) combined with mode-locked pulsed excitation and time-correlated single-photon counting. A high repetition rate mode-locked argon ion laser operated at 514.5 nm was used as the excitation source. The laser beam was found tightly into a thin wall capillary flow cell. The probe volume was about 12.6 x 10(-12)L. Fluorescence was collected at 90 degrees using a x 40 microscope objective, and was detected by a fast response PMT detector. A time-gate was used to discriminate Raman scattering light background. Using the criterion of 3 standard deviations above background, the detection limits obtained for R6G and R110 were 3.8 x 10(-14) mol/L and 1 x 10(-13) mol/L respectively, and the average probability was lower than 1 in the presence of a R6G or a R110 molecule in the detection volume.

Lasers↗
PubMed1998

[Study on a new method for spectrophotometry].

In this paper, the relation between absorbance difference and concentration was measured by the ultraviolet spectrophotometer and computer made P-E company of U.S.A. The basic goal is to prove that the standard absorption curve method can be replaced by the new method, in which the sample was put in standard room and the standard material in sample room. Utilizing this method can minimize the error, most importantly, can measure the higher concentration sample, which can not be measured by the standard curve method. The new method does not require a Linear deltaA-c linear relationship.

English Abstract↗
PubMed1997

Cytoskeletal protein ABP-280 directs the intracellular trafficking of furin and modulates proprotein processing in the endocytic pathway.

Furin catalyzes the proteolytic maturation of many proproteins within the trans-Golgi network (TGN)/endosomal system. Furin's cytosolic domain (cd) directs both the compartmentalization to and transit between its manifold processing compartments (i.e., TGN/biosynthetic pathway, cell surface, and endosomes). Here we report the identification of the first furin cd sorting protein, ABP-280 (nonmuscle filamin), an actin gelation protein. The furin cd was used as bait in a yeast two-hybrid screen to identify ABP-280 as a furin-binding protein. Binding analyses in vitro and coimmunoprecipitation studies in vivo showed that furin and ABP-280 interact directly and that ABP-280 tethers furin molecules to the cell surface. Quantitative analysis of both ABP-280-deficient and genetically replete cells showed that ABP-280 modulates the rate of internalization of furin but not of the transferrin receptor, a cycling receptor. However, although ABP-280 directs the rate of furin internalization, the efficiency of sorting of the endoprotease from the cell surface to early endosomes is independent of expression of ABP-280. By contrast, efficient sorting of furin from early endosomes to the TGN requires expression of ABP-280. In addition, ABP-280 is also required for the correct localization of late endosomes (dextran bead uptake) and lysosomes (LAMP-1 staining), demonstrating a pleiotropic role for this actin binding protein in the organization of cellular compartments and directing protein traffic. Finally, and consistent with the trafficking studies on furin, we showed that ABP-280 modulates the processing of furin substrates in the endocytic but not the biosynthetic pathways. The novel roles of ABP-280 and the cytoskeleton in the sorting of furin in the TGN/ endosomal system and the formation of proprotein processing compartments are discussed.

Amino Acid Sequence↗
PubMed1997

Irreversible inhibition of lysyl oxidase by homocysteine thiolactone and its selenium and oxygen analogues. Implications for homocystinuria.

Homocysteine thiolactone, selenohomocysteine lactone, and homoserine lactone were found to be competitive, irreversible inhibitors of lysyl oxidase, with KI values of 21 +/- 3 microM, 8.3 +/- 2.2 microM, and 420 +/- 56 microM, respectively. The first order rate constants for inactivation (k2) of the enzyme varied over a much smaller range, ranging from 0.12 to 0.18 to 0.28 min-1 for the Se-, thio-, and O-lactones, respectively. Mutually exclusive labeling of the enzyme by [1-14C]beta-aminopropionitrile, [U-14C]phenylhydrazine, or [35S]homocysteine thiolactone was observed. These labeling results, together with the closely similar perturbations of the near UV-visible spectra of lysyl oxidase and of a model of its lysine tyrosylquinone cofactor by the thiolactone, indicate that the lactones likely derivatize and reduce the active site carbonyl cofactor. Substitution with deuterium at the alpha-carbon of the thiolactone caused a deuterium kinetic isotope effect on k2 of 3.2 +/- 0.2, consistent with the involvement of rate-limiting alpha-proton abstraction during lactone-induced inactivation of the enzyme. The activities of plasma amine oxidase and diamine oxidase were only minimally reduced at concentrations of the sulfur or selenium lactones that fully inhibited lysyl oxidase. Thus, these lactones constitute a new category of mechanism-based inactivators selective for lysyl oxidase. Further, these results may relate to the development of connective tissue defects seen in homocystinuria.

Animals↗
PubMed1997

Risk and predictors for pregnancy-related complications in women with heart disease.

BACKGROUND: The physiological changes of pregnancy can result in cardiovascular complications in the mother, which in turn may have fetal implications. Prior studies have focused on specific cardiac lesions or identified univariate predictors. There is a need to refine the risk stratification of women with heart disease so they can receive appropriate obstetrical counseling and care. METHODS AND RESULTS: We examined the outcomes of 221 women with heart disease who underwent 276 pregnancies and received their obstetrical care at three Toronto hospitals from 1986 through 1994. Those who underwent therapeutic abortions were excluded. Among the study participants, there were 24 miscarriages and 252 completed pregnancies (pregnancies not ending in miscarriage). Maternal heart failure, arrhythmia, or stroke occurred in 45 completed pregnancies (18%). There were no maternal deaths. Poor maternal functional class or cyanosis, myocardial dysfunction, left heart obstruction, prior arrhythmia, and prior cardiac events were predictive of maternal cardiac complications. These predictors were incorporated into a point score that can be used to estimate the probability of a cardiac complication in the mother. The rate of cardiac complications for a patient with 0, 1, and >1 of the above factors was 3%, 30%, and 66%, respectively. Neonatal complications occurred in 42 completed pregnancies (17%). Neonatal events included death (2), respiratory distress syndrome (16), intraventricular hemorrhage (2), premature birth (35), and small-for-gestational-age birth weight (14). Poor maternal functional class or cyanosis was predictive of neonatal events. CONCLUSIONS: Despite low maternal and neonatal mortality, pregnancy in women with heart disease is associated with significant cardiac and neonatal morbidity. The probability of maternal cardiac or neonatal events can be predicted from baseline characteristics of the mother.

Adolescent↗
PubMed1997

Detection and characterization of Sp1 binding activity in human chondrocytes and its alterations during chondrocyte dedifferentiation.

We have detected DNA binding activity for a synthetic oligonucleotide containing an Sp1 consensus sequence in nuclear extracts from human chondrocytes. Changes in the levels of Sp1 oligonucleotide binding activity were examined in nuclear extracts from freshly isolated human chondrocytes, from chondrocytes that had been cultured under conditions that allowed the maintenance of a chondrocyte-specific phenotype on plastic dishes coated with the hydrogel poly(2-hydroxyethyl methacrylate), and from chondrocytes induced to dedifferentiate into fibroblast-like cells by passage in monolayer culture on plastic substrata. It was observed that Sp1 binding was 2-3-fold greater in nuclear extracts from dedifferentiated chondrocytes than in nuclear extracts from either freshly isolated chondrocytes or from cells cultured in suspension. The Sp1 binding activity was specific, since it was competed by unlabeled Sp1 but not by AP1 or AP2. The addition of a polyclonal antibody against Sp1 to nuclear extracts from freshly isolated chondrocytes or to extracts isolated from chondrocytes cultured in monolayer decreased the binding of Sp1 by approximately 85%. However, when the same experiment was carried out with nuclear extracts prepared from cells cultured on poly(2-hydroxyethyl methacrylate)-coated plates, only a very slight inhibition of Sp1 binding was observed. When fragments of the COL2A1 promoter containing putative Sp1 binding sites amplified by polymerase chain reaction were examined, it was found that the amounts of DNA-protein complex formed with nuclear extracts from dedifferentiated chondrocytes were 2-3-fold greater than the amounts formed with nuclear extracts from freshly isolated chondrocytes or from cells cultured in suspension. Quantitation of DNA binding activity by titration experiments demonstrated that nuclear extracts from fibroblast-like cells contained approximately 2-fold greater Sp-1 specific binding activity than nuclear extracts from chondrocytes. The direct role of Sp1 in type II collagen gene transcription was demonstrated by co-transfection experiments of COL2A1 promoter-CAT constructs in Drosophila Schneider line L2 cells that lack Sp1 homologs. This is the first demonstration of Sp1 binding activity in human chondrocytes and of differences in Sp1 DNA binding activity between differentiated and dedifferentiated chondrocytes.

Animals↗
PubMed1997

In vitro pancreatic ductal cell carcinogenesis.

Our experiments were designed to identify initial biochemical and biological changes that occur during pancreatic carcinogenesis. TAKA-1, an immortal hamster pancreatic ductal cell line, was treated in vitro for up to 11 weeks with the pancreatic carcinogen N-nitorosobis(2-oxopropyl)amine (BOP). These treated cells were designated TAKA-1 + BOP. The growth of TAKA-1 and TAKA-1 + BOP cell lines was investigated in soft agar and in hamsters intradermally. The resulting tumor from TAKA-1 + BOP was re-cultured in vitro and designated TAKA-1 + BOP-T. Mutation of c-K-ras and p53 oncogenes, chromosomal changes, expression of transforming growth factor alpha (TGF-alpha) and epidermal growth factor (EGF) receptor and several biochemical markers were examined in all cell lines. TAKA-1 + BOP but not TAKA-1 cells grew in soft agar and produced an invasive tumor in vivo. However, there were no differences in cell growth rate, DNA flow cytometry, or immunohistochemical findings between the non-transformed and transformed cells. TAKA-1, TAKA-1 + BOP and TAKA-1 + BOP-T cells all expressed mRNA of TGF-alpha and EGF receptor in a comparable pattern. DNA sequence analysis following polymerase chain reaction showed that neither TAKA-1 nor TAKA-1 + BOP cells has a mutation of c-K-ras or p53. Karyotype analysis demonstrated that TAKA-1 + BOP cells had more chromosomal abnormalities compared with TAKA-1 cells. Mutation of c-K-ras and p53 was not essential for carcinogenesis in hamster pancreatic ductal cells in vitro. In conclusion, immortality of the TAKA-1 cells caused expression of TGF-alpha to the same extent as in malignant cells. Chromosomal and ultrastructural patterns were the only differences detected between the non-transformed and BOP-transformed cells.

Amino Acid Sequence↗
PubMed1997

The effects of imidazole binding on the conformation of cytochrome c.

Many individual protons exhibit different chemical shifts in Im-cyt c and cyt c, reflecting diamagnetic shift effects as a result of structure change, and in addition contact and pseudocontact shifts that occur only in the paramagnetic oxidized form. To estimate the chemical shift differences caused by structure change, we removed the pseudocontact shift contribution. The anisotropy and direction of the magnetic susceptibility anisotropy tensor were determined. There was evidence for conformational changes induced by the breakage of Fe-S bond. It was concluded that the Im-cyt c had undergone a rearrangement of several regions forming the heme pocket of the protein. The hydrogen-bond network in the heme cavity was affected by the substitution.

Cytochrome c Group↗
PubMed1997

Biochemical and functional characterization of DNA complexes capable of targeting genes to hepatocytes via the asialoglycoprotein receptor.

Electrostatic binding of polycations or basic polypeptides to the DNA phosphate backbone has been previously described as a one-step process which results in uncontrolled aggregation and precipitation of the DNA in solution. We describe here a multistep process in which the condensation of DNA in the presence of poly-L-lysine can be controlled to produce particles of discrete size and shape suitable for receptor-mediated gene transfer in vivo and in vitro. The first step in this process involves the gradual accretion of poly-L-lysine onto the DNA phosphate backbone, until charges are neutralized. The addition of poly-L-lysine to a concentrated solution of DNA in this fashion prevents intermolecular aggregation of the DNA, presumably by promoting the formation of a nucleus of condensation along the length of each DNA molecule. The second stage of the process involves adjusting the ionic strength of the solvent to facilitate the solubilization of compact DNA.poly-L-lysine complexes. Several physical and biochemical parameters have been studied and correlated with the efficacy of DNA/ligand-poly-L-lysine particles in transferring genes to the liver of adult animals by receptor-mediated endocytosis.

Asialoglycoprotein Receptor↗