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T Shen

Publications and source records attributed to T Shen.

At least 91 records · Page 5Linked to original sources
PubMed1994

Pancreatic receptors: initial feasibility studies with a targeted contrast agent for MR imaging.

PURPOSE: To evaluate cholecystokinin (CCK) as a target-specific vector for magnetic resonance (MR) receptor imaging of rat pancreas. MATERIALS AND METHODS: Monocrystalline iron oxide (MION) was labeled with CCK by noncovalent attachment. Receptor specificity of the conjugate was determined with competitive binding studies. Pharmacologic determinations were blood half-lives, biodistribution, time responses, dose responses, and limited toxicity. RESULTS: Specific cell binding of MION-20-CCK was saturable and inhibitable by a CCK antagonist. Blood half-life of MION-20-CCK was 20 minutes, which was shorter than that of unlabeled MION. Biodistribution studies showed a statistically significant decrease in relaxation times in pancreatic tissues from 42.7 msec +/- 2.0 to 33.8 msec +/- 1.4 (P < or = .05) but not in tumor after administration of MION-20-CCK. The half-life of MION-20-CCK in the pancreas was 3 weeks; no signs of toxicity were shown at the level tested. CONCLUSION: Target-specific MR imaging of pancreatic receptors is feasible. Additional studies are necessary to perfect binding strategies, optimize preparations, and scale up synthesis for imaging in other species.

Acute Disease↗
PubMed1994

Effect of pilocarpine on propranolol-induced bronchoconstriction in asthma.

To investigate whether increased release of acetylcholine may be involved in propranolol-induced bronchoconstriction (PIB), the inhibitory effect of pilocarpine (Pilo), an agonist of M2-muscarinic receptors that in 11 stable asthmatic subjects. The bronchial responsiveness to Pilo was also measured in terms of Dmin, defined as the cumulative dose at the point where respiratory resistance (Rrs) began to increase. In PIB, the maximum increase in Rrs (Rrs max) after stopping inhalation for 1 min was measured. Atropine reversed PIB. After pilocarpine pretreatment at a dose equal to Dmin, Rrs max divided by baseline Rrs decreased significantly from 206.6 +/- 61.1 to 163.0 +/- 42.6% (mean +/- SD) (p = 0.001). The ratio of PIB (Rrs max/baseline Rrs) with Pilo to PIB without Pilo correlated inversely according to the pretreatment dose (Dmin) of Pilo (p < 0.05). These results suggest increased release of acetylcholine in PIB and that M2-muscarinic receptors are at least in part functioning in stable asthmatic airways.

Acetylcholine↗
PubMed1994

Studies on the plasmid instability in Corynebacteria.

Recombinant plasmid pNAR4, which can be used as a shuttle vector between E. coli and Coryneform bacteria, was constructed by ligating the DNA fragments of pNAT65 and pACYC184. Plasmid instability was found when pNAR4 was transformed to other Corynebacterium strains, segregational instability in C. crenatum B9 and structural instability in C. glutamicum 10147 and C. crenatum T6-13. When pNAT65 was transformed into C. glutamicum 10147, the plasmids in the transformants were found different from pNAT65. The size and main restriction sites in these plasmids were identical to those of pXZ10145. DNA hybridization indicated that in C. glutamicum 10147 a superhelix DNA was showed higher homology with that in pXZ10145. We assume that the existence of this supercoil DNA is related to the phenomena of various plasmid instability. Inter- or/and intra-molecular recombination may be the reason to explain the related phenomena found in our work.

Corynebacterium↗
PubMed1993

Monocrystalline iron oxide nanocompounds (MION): physicochemical properties.

We have previously described a novel monocrystalline iron oxide nanocompound (MION), a stable colloid that enables target specific MR imaging. In this study, the physicochemical properties of MION are reported using a variety of analytical techniques. High resolution electron microscopy indicates that a MION consists of hexagonal shaped electron-dense cores of 4.6 +/- 1.2 nm in diameter. This iron oxide core has an inverse spinel crystal structure which was confirmed by x-ray powder diffraction. Chemical analysis showed that each core has 25 +/- 6 dextran molecules (10 kD) attached, resulting in a unimodal hydrodynamic radius of 20 nm by laser light scattering. Because of the flexibility of the dextran layer, the radius is only 8 nm in nonaqueous reverse micelles. At room temperature, MION exhibit superparamagnetic behavior with an induced magnetization of 68 emu/g Fe at 1.5 T. Mössbauer studies show that the saturation internal magnetic field is 505 KOe, and blocking temperature is at 100 K. The R1 relaxivity of MION is 16.5 (mM.sec)-1 and the R2 relaxivity is 34.8 (mM.sec)-1 in aqueous solution at 37 degrees C and 0.47 T. In vitro phantom studies show that the detectability of MION in liver tissue is less than 50 nmol Fe/g tissue using gradient echo imaging techniques.

Ferric Compounds↗
PubMed1993

Determination of nucleotide sequence of Corynebacterium plasmid pXZ10145.

With ABI370A Autosequencer, the total nucleotide sequence of plasmid pXZ10145 from Corynebacterium glutamicum 1014-6T has been determined using the dideoxy chain termination method. The plasmid contain 4887 base pairs (bp). Computer-aided-analysis of the sequence showed the location and number of restriction enzyme cutting sites and revealed eight open reading frames (ORF) on the plasmid. The two sites on the plasmid pXZ10145, where deletion occurred to result in plasmid pNAT65 were confirmed. At these two sites a seven-base pairs sequence "ATCTAGC" was found.

Base Sequence↗
PubMed1993

[Cloning of beta-amylase gene from B. substitute and its expression in E. coli].

The gene coding for beta-amylase with raw starch-digestion ability was isolated from B. substitute R2 which was selected in this lab. The procedure used in this screening was developed in this work by the method named nutrition-restriction. The DNA fragment containing the beta-amylase gene was 5.25 kb in length. There was no difference in enzymological properties between the beta-amylase produced by the gene-donor strain and the expression product of E. coli. The yield of the cloned beta-amylase was over 500 IU/ml in our laboratory culture condition, the RDA value was 57%, and all of this enzyme were found to be secreted into medium.

Bacillus subtilis↗
PubMed1992

Identification and characterization of a cardiac-specific transcriptional regulatory element in the slow/cardiac troponin C gene.

The slow/cardiac troponin C (cTnC) gene has been used as a model system for defining the molecular mechanisms that regulate cardiac and skeletal muscle-specific gene expression during mammalian development. cTnC is expressed continuously in both embryonic and adult cardiac myocytes but is expressed only transiently in embryonic fast skeletal myotubes. We have reported previously that cTnC gene expression in skeletal myotubes is controlled by a developmentally regulated, skeletal muscle-specific transcriptional enhancer located within the first intron of the gene (bp 997 to 1141). In this report, we show that cTnC gene expression in cardiac myocytes both in vitro and in vivo is regulated by a distinct and independent transcriptional promoter and enhancer located within the immediate 5' flanking region of the gene (bp -124 to +32). DNase I footprint and electrophoretic mobility shift assay analyses demonstrated that this cardiac-specific promoter/enhancer contains five nuclear protein binding sites (designated CEF1, CEF-2, and CPF1-3), four of which bind novel cardiac-specific nuclear protein complexes. Functional analysis of the cardiac-specific cTnC enhancer revealed that mutation of either the CEF-1 or CEF-2 nuclear protein binding site abolished the activity of the cTnC enhancer in cardiac myocytes. Taken together, these results define a novel mechanism for developmentally regulating a single gene in multiple muscle cell lineages. In addition, they identify previously undefined cardiac-specific transcriptional regulatory motifs and trans-acting factors. Finally, they demonstrate distinct transcriptional regulatory pathways in cardiac and skeletal muscle.

3T3 Cells↗
PubMed1992

Antimyosin-labeled monocrystalline iron oxide allows detection of myocardial infarct: MR antibody imaging.

The synthesis and in vivo antigen targeting of a novel iron oxide compound were studied. A monocrystalline iron oxide nanoparticle (MION) was synthesized that contains a small (mean diameter, 2.9 nm +/- 0.9) single crystal core, passes through capillary membranes, and exhibits superparamagnetism. The MION was attached to antimyosin Fab (R11D10) and used for immunospecific magnetic resonance (MR) imaging of cardiac infarcts One hour after intravenous administration of MION-R11D10 in rats (100 mumol/kg), a marked decrease in the signal intensity of infarcted myocardium was observed. Immunohistochemical correlation confirmed the specific binding of the immunoconjugate to infarcted, but not to normal, myocardium. No decrease in cardiac signal intensity was observed when unconjugated MION was administered intravenously. The results indicate the feasibility of immunospecific MR imaging in living organisms.

Animals↗
PubMed1991

Prebiotic chemistry in clouds.

In the traditional concept for the origin of life as proposed by Oparin and Haldane in the 1920s, prebiotic reactants became slowly concentrated in the primordial oceans and life evolved slowly from a series of highly protracted chemical reactions during the first billion years of Earth's history. However, chemical evolution may not have occurred continuously because planetesimals and asteroids impacted the Earth many times during the first billion years, may have sterilized the Earth, and required the process to start over. A rapid process of chemical evolution may have been required in order that life appeared at or before 3.5 billion years ago. Thus, a setting favoring rapid chemical evolution may be required. A chemical evolution hypothesis set forth by Woese in 1979 accomplished prebiotic reactions rapidly in droplets in giant atmospheric reflux columns. However, in 1985 Scherer raised a number of objections to Woese's hypothesis and concluded that it was not valid. We propose a mechanism for prebiotic chemistry in clouds that satisfies Scherer's concerns regarding the Woese hypothesis and includes advantageous droplet chemistry. Prebiotic reactants were supplied to the atmosphere by comets, meteorites, and interplanetary dust or synthesized in the atmosphere from simple compounds using energy sources such as ultraviolet light, corona discharge, or lightning. These prebiotic monomers would have first encountered moisture in cloud drops and precipitation. We propose that rapid prebiotic chemical evolution was facilitated on the primordial Earth by cycles of condensation and evaporation of cloud drops containing clay condensation nuclei and nonvolatile monomers. For example, amino acids supplied by , or synthesized during entry of, meteorites, comets, and interplanetary dust would have been scavenged by cloud drops containing clay condensation nuclei. Polymerization would have occurred within cloud systems during cycles of condensation, freezing, melting, and evaporation of cloud drops. We suggest that polymerization reactions occurred in the atmosphere as in the Woese hypothesis, but life originated in the ocean as in the Oparin-Haldane hypothesis. The rapidity with which chemical evolution could have occurred within clouds accommodates the time constraints suggested by recent astrophysical theories.

Aluminum Silicates↗
PubMed1991

Polyclonal human immunoglobulin G labeled with polymeric iron oxide: antibody MR imaging.

Human polyclonal immunoglobulin (Ig) G was attached to a monocrystalline iron oxide nanocompound (MION), a small superparamagnetic probe developed for receptor and antibody magnetic resonance (MR) imaging. The resulting complex, MION-IgG, had a slightly negative surface charge, a molecular weight of 150-180 kDa, and 0.36 microgram of IgG attached per milligram of iron. After intravenous administration of MION-IgG to normal rats, most of the compound localized in liver, spleen, and bone marrow. In an animal model of myositis, MION-IgG caused reduced signal intensity (most apparent on T2-weighted spin-echo and gradient-echo images) at the site of inflammation. No change in signal intensity existed after an injection of unlabeled MION. Site-specific localization of MION-IgG was corroborated with scintigraphic imaging with indium-111 IgG and MION-In-111-IgG and was confirmed histologically with iron staining. These results indicate that antibody MR imaging is feasible in vivo. Target-specific and antibody MR imaging could be easily extended to other applications, including detection of cancer, infarction, and degenerative diseases.

Animals↗
PubMed1991

[Construction of phage vector for Bacillus subtilis].

Recombinant phages phi 105S35 and phi 105S36, derived from phage phi 105DI:1t, remain the ability to infect and be lysogenized in the host cell. In the their genome there is a 1 kb inset fragment which occurs between the DNA fragments D and E resulted from SmaI degested DNA of phi 105DI:1t. But the orientation of this insert fragment is opposite in two recombinant phages, respectively. The cat gene on this fragment makes the host cell resistant to chloramphenaical. The unique BamHI and XbaI sites which were introduced into the genome of the recombinant phages provide inserting sites of foreign DNA fragment. DNA from these two recombinant phages can transfect protoplast of Bacillus subtilis at high frequency. Therefore, phi 105S35 and phi 105S36 are suitable as phage vectors in the molecular cloning of Bacillus subtilis.

Bacillus subtilis↗
PubMed1991

Characterization of the natural deletion mutant of plasmid pXZ10145 in Corynebacterium glutamicum and construction of a recombinant plasmid.

Plasmid pNAT65, carrying the chloramphenicol resistance marker, was chosen from a number of natural deletion mutants of pXZ10145 when pXZ10145 DNA, originally isolated from Corynebacterium glutamicum 1014-6T, was used to transform the protoplast of Corynebacterium crenatum T6-13. The size of pNAT65 was 2.4 kb, determined by electrophoresis on 0.7% agarose gel. The physical map of plasmid pNAT65 was determined. One recombinant plasmid, pNAR67, was constructed with the DNA fragments of pNAT65 and pBR322 digested respectively with EcoRI. This plasmid was capable of replication in E. coli, expressing ampicillin and tetracycline resistance; but with lower chloramphenicol, the resistance was only about 2 micrograms/ml.

Chromosome Deletion↗
PubMed1990

Early diagnosis of tuberculous meningitis by detection of anti-BCG secreting cells in cerebrospinal fluid.

A nitrocellulose immunospot assay to enumerate cells secreting anti-BCG antibodies was evaluated in the diagnosis of tuberculous meningitis. Among 25 Chinese patients with this disease diagnosed on clinical and cerebrospinal fluid (CSF) criteria, 24 had anti-BCG IgG antibody secreting cells in CSF, at a median value of 56 per 10(4) CSF cells. Among 6 patients examined within one week, 5 had antibody secreting cells in CSF, and all 19 patients examined 2-8 weeks after onset had such cells in CSF. Blood examined from 5 patients contained anti-BCG IgG or IgM antibody secreting cells, but usually at much lower numbers than in corresponding CSF, indicating that the specific antibody response is largely confined to CSF. Anti-BCG antibodies measured in parallel by ELISA were slightly raised in CSF in only 1 of the 6 patients examined within a week, whereas a good correspondence was seen between numbers of antibody secreting cells and antibody concentrations from the second week onwards. Detection of anti-BCG IgG antibody secreting cells has higher sensitivity and specificity than ELISA measurement of anti-BCG IgG antibodies, and represents a new, useful method for the early diagnosis of tuberculous meningitis.

Adolescent↗
PubMed1990

[Determination of traces of gallium in air by oscillographic polarography].

Gallium and its compounds in air collected by millipore filter membrane are leached by 10% HNO3 at room temperature. After being adjusted with ammonia solution to pH8-9, the leachate is filtered and the filtrate is evaporated to dryness on a water bath. The residue is dissolved with 2 ml of 10% HNO3 and then into the solution are added 0.5 ml of 5% hydroxylamine hydrochloride solution, 0.20 ml of 5% sulfosalicyclic acid solution, 0.5 ml of NaF solution (1mg F/ml) and 1 drop of methyl red solution. Let it stand for 5 min after the color of the solution turns orange by addition of 1:1 NH4OH solution. Add 0.20ml of 0.20% cupferron solution, 0.20ml of 0.5% diphenyl-guanidine solution (prepared in 95% ethanol) and 0.5ml of acetic acid-ammonium acetate buffer (pH 7.0). Then add water to make the final volume of the test solution to be 10ml and measure the height of the second derivative polarographic wave at -1.08V (vs.SCE). The sensitivity of the method is 0.005-0.10 microgram/ml, the coefficient of variation 6.8%, recovery 97.8%. Within 0.005-0.10 microgram/ml, the wave height is linear with the concentration of gallium.

Air↗
PubMed1989

Lack of drug-induced DNA cross-links in chlorambucil-resistant Chinese hamster ovary cells.

Chlorambucil (CLB) is an alkylating agent commonly used in the treatment of several neoplastic disorders. The mechanisms underlying resistance to this drug are not fully defined. We used the DNA alkaline elution technique to study cross-link formation in the wild type (K1) and a CLB-resistant (ChlR) Chinese hamster ovary cell line. [14C]CLB was used to measure drug uptake. The CLB-resistant cells were found to have negligible DNA cross-link formation compared to K1 cells at all time points tested. There was a correlation between the resistance to CLB and the decreased ability of resistant cells to form DNA cross-links. Results of drug uptake experiments excluded altered CLB accumulation as the basis for these findings. Assays of O6-alkylguanine transferase and topoisomerase. II provide evidence against a role of these enzymes in CLB resistance. These studies suggest that the mechanism of CLB cytotoxicity involves the formation of DNA cross-links. Reduced cross-link formation may confer resistance to CLB.

Animals↗
PubMed1987

A diet rich in (n-3) fatty acids increases peroxisomal beta-oxidation activity and lowers plasma triacylglycerols without inhibiting glutathione-dependent detoxication activities in the rat liver.

By using comparisons with a safflower oil diet (15% w/w) and a control, low-fat diet, the ability of a fish oil diet (15% MaxEPA) rich in the (n-3) fatty acids, eicosapentaenoic acid and docosahexaenoic acid, to alter hepatic activities has been determined in adult, male rats. Compared with the safflower diet, treatment for 2 weeks with the fish oil diet caused significant increases in the ratio of liver weight/body weight and the specific activities in liver homogenates of peroxisomal enzymes fatty acyl-CoA oxidase (263%) and catalase (149%) and caused a significant lowering of plasma triacylglycerol levels. Fish oil diets rich in (n-3) fatty acids should thus be placed in the category of hypotriglyceridemic agents which stimulate peroxisomal beta-oxidation activity. In contrast to the effects seen with the other hypotriglyceridemic, peroxisomal proliferating agents such as clofibrate, hepatic glutathione peroxidase and glutathione S-transferase activities are unchanged or are increased rather than inhibited with the fish oil diet.

Acyl-CoA Oxidase↗