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Biomedical subjects

L Sun

Publications and source records attributed to L Sun.

At least 451 records · Page 25Linked to original sources
PubMed1994

Effects of phenamiphos on muscarinic acetylcholine receptor in the brain synaptosome in rats and its mechanism.

The studies were performed to investigate the mechanism of phenamiphos affecting muscarinic acetylcholine receptor (M-AchR) of the brain synaptosome in rats. The results showed that phenamiphos inhibited the binding of 3H-quinuclidinyl benzilate (3H-QNB) to the brain synaptosome in rats, and this effect was dose and time-dependent. This suggests that phenamiphos might directly affect M-AchR. The KD and Bmax of phenamiphos to M-AchR were measured and found to be 1.3 x 10(-7) mol/L and 4.57 pmol/mg protein, respectively. It belongs to non-specific inhibition of phenamiphos on the binding of 3H-QNB to M-AchR. It was also found that phenamiphos decreased the level of protein sulfhydryl group in brain synaptosome membrane. Dithiothreitol (DTT) and the reduced glutathion (GSH) prevented the decrease of protein sulfhydryl group and the inhibition of phenamiphos on the binding of 3H-QNB to M-AchR. These showed that phenamiphos could affect the sulfhydryl group of M-AchR surface.

Animals↗
PubMed1994

Transfer of shuttle vectors containing Bacillus thuringiensis toxin gene into wild-type B. cereus, B. brevis and B. subtilis by electroporation.

Gram positive and negative bacterial shuttle vectors carrying Bacillus thuringiensis (B.t.) toxin gene were introduced by electroporation into wild-type Bacillus cereus, B. brevis and B. subtilis. The transformation efficiencies for these bacteria were around 10(1)-10(4) transformants per micrograms DNA based on the numbers of neomycin- and ampicillin-resistant colonies produced. The structure of the transferred plasmids proved identical with the original ones both in size and restriction pattern. Toxicity assays showed that the transformants gave a mortality of 90-100% against caterpillar of Heliothis assulta, indicating that the gene function was not changed by electroporation.

Bacillus↗
PubMed1994

Basic fibroblast growth factor stimulates proliferation and suppresses melanogenesis in cell cultures derived from early zebrafish embryos.

We are attempting to develop methods for in vitro culture of zebrafish embryonal stem cells. Primary cultures were initiated from wild-type zebrafish early embryos in basal nutrient medium supplemented with insulin, selenite, leukemia inhibitory factor, trout serum, fetal bovine serum, and trout embryo extract. In this medium, melanocytes appeared on the second day of culture. Basic fibroblast growth factor (bFGF) was mitogenic when cells were plated at low densities. bFGF suppressed melanogenesis is a dose-dependent fashion, with maximal effect at 20 ng/mL. Cultures initiated and maintained with bFGF for 24 hours and then incubated without bFGF for as long as 8 days did not contain pigmented cells. Experiments in which bFGF was added or removed at various times after initiation of cultures indicated that maximum sensitivity to bFGF occurred during the first 12 hours of culture. When wild-type cells from cultures without bFGF were injected into albino blastula-stage embryos, melanocytes subsequently developed in host embryos: no melanocytes appeared when cells from cultures with bFGF were injected into albino hosts.

Animals↗
PubMed1993

Activation of phospholipase A2 and stimulation of prostaglandin E2 production by transforming growth factor-alpha in rat thymic epithelial cells requires influx of calcium.

The stimulation of both phospholipase A2 (PLA2) enzymic activity and the production of prostaglandin E2 (PGE2) by transforming growth factor-alpha (TGF-alpha) and Ca2+ ionophore A23187 in TEA3A1 rat thymic epithelial cells were studied. TGF-alpha by itself at various concentrations (5-200 ng/ml) had no effect on the stimulation of PGE2 production. A23187 (1 microgram/ml) by itself stimulated PGE2 production on average by 18-fold over the control. When TGF-alpha (50 ng/ml) was added to the cells in the presence of A23187, a synergistic stimulation (on average 45-fold) of PGE2 production was observed. Synergistic stimulation was also observed at the level of arachidonic acid released from phospholipid pools, suggesting the activation of PLA2 enzymic activity. We have found that this synergistic activation of PLA2 enzymic activity and subsequent stimulation of PGE2 production required the activation of epidermal growth factor (EGF) receptor tyrosine kinase and Ca2+ influx. This was shown by the fact that genistein, an inhibitor of tyrosine kinase, blocks the synergistic stimulation by TGF-alpha and A23187 and by the fact that the stimulation of PGE2 production by TGF-alpha and A23187 is dependent on the culture-medium Ca2+ concentrations. The requirement for Ca2+ influx instead of intracellular mobilization of Ca2+ was shown by the fact that PGE2 production was not stimulated when cells were treated with TGF-alpha and thapsigargin. Moreover, the synergistic stimulation of PGE2 production by TGF-alpha and A23187 was not affected in protein kinase C down-modulated cells. In addition, the synergistic stimulation was not observed in cells treated with either phorbol 12-myristate 13-acetate (PMA) and TGF-alpha or PMA and A23187, and in cells treated with TGF-alpha and thapsigargin. The requirement for the activation of receptor tyrosine kinase seems to be specific to the EGF receptor, since a synergistic stimulation of PGE2 production was not observed when cells are treated with either insulin-like growth factor-I or fibroblast growth factor-I in the presence of A23187.

Animals↗
PubMed1993

Antitumor agents. 141. Synthesis and biological evaluation of novel thiocolchicine analogs: N-acyl-, N-aroyl-, and N-(substituted benzyl)deacetylthiocolchicines as potent cytotoxic and antimitotic compounds.

Three series of novel thiocolchicine analogs, N-acyl-, N-aroyl-, and N-(substituted benzyl)-deacetylthiocolchicinoids, have been synthesized and evaluated for their cytotoxicity against various tumor cell lines, especially solid tumor cell lines, and for their inhibitory effects on tubulin polymerization in vitro. Most of these compounds showed strong inhibitory effects on tubulin polymerization comparable to that obtained with thiocolchicine and greater than that obtained with colchicine. Only compounds with a long side chain at the C(7) position, such as 22-24, did not inhibit tubulin polymerization. Several of the active N-aroyldeacetylthiocolchicine analogs had positive optical rotations, in contrast to the negative optical rotation observed with most colchicinoids. This property might be attributed to a reversal of biaryl configuration from the normal aS to aR. Therefore, the N-aroyl analogs were further evaluated by circular dichroism, which readily distinguishes between the aS and aR biaryl configurations. This latter technique demonstrated that the active N-aroyl analogs do have an aS configuration despite their positive optical rotations. However, comparison of 1H NMR and UV spectral data of N-(substituted benzyl)-deacetylthiocolchicines with those of corresponding N-aroyldeacetylthiocolchicines suggested a different biaryl dihedral angle [even though these compounds have the same aS biaryl configuration]. The similar tubulin binding properties of these compounds suggest that a biaryl dihedral angle of 53 degrees is not essential for colchicinoid-tubulin interaction. The increased cytotoxicity of N-(substituted benzyl)deacetylthiocolchicines compared to the N-aroyldeacetylthiocolchicines may be attributed to different lipophilicity, drug uptake, or drug metabolism in the tumor cells. The side chain at the C(7) position affects inhibition of tubulin polymerization and the cytotoxic activity of colchicinoids as a function of its size and its contribution to lipophilicity.

Antineoplastic Agents↗
PubMed1993

Antitumor agents. 139. Synthesis and biological evaluation of thiocolchicine analogs 5,6-dihydro-6(S)-(acyloxy)- and 5,6-dihydro-6(S)-[(aroyloxy)methyl]-1,2,3-trimethoxy-9-(methylthio)-8H- cyclohepta[a]naphthalen-8-ones as novel cytotoxic and antimitotic agents.

A series of novel thiocolchicine analogs, 5,6-dihydro-6(S)-(acyloxy)-and 5,6-dihydro-6(S)-[(aroyloxy)-methyl]-1,2,3-trimethoxy-9-(methylthi o)-8H- cyclohepta[a]naphthalen-8-ones, possessing a six-membered ring B, have been synthesized and evaluated for their cytotoxicity against various tumor cell lines, including solid tumor cell lines, and for their interaction with tubulin. The configuration of the parent alcohol (compound 5) was established unequivocally as (aR,6S) by X-ray crystallographic analysis. The side chain at the C(6) position is in a pseudoaxial orientation. The optical properties and 1H NMR data indicated that these compounds have the same conformations in solution as in the solid state. Biological results showed that compounds (5, 6, 14, 15, 17, and 18) bearing a small side chain at C(6) demonstrate high potency in inhibiting tubulin polymerization and binding of radiolabeled colchicine to tubulin. The most cytotoxic compounds were 14, 15, 17, and 18, with good activity against several solid tumor cell lines. To explain the strong antitubulin activity of compound 5 (with an aR configured biaryl system in contrast to the aS configuration previously described for colchicinoids, allocolchicinoids, and steganacin) we speculate that a rapid atropisomerism equilibrium must exist for 5 and its active derivatives. This equilibrium would yield adequate amounts of aS-configured conformers that interact, strongly with tubulin. Since the optically inactive 18 is also a potent inhibitor of tubulin, the configuration of the side chain of these six-membered ring B analogs cannot be essential for their binding to tubulin. Instead we propose that the size of ring B and of its side chain play important roles in tubulin binding activity by affecting the rotation of the rings A and C along their linking C-C bond axis.

Animals↗
PubMed1993

Cyclovergence: a comparison of objective and psychophysical measurements.

Several psychophysical procedures have been used to measure cyclovergence but none has been adequately validated with respect to an objective measure. Scleral search coils were used to measure cyclovergence induced by dichoptic textured patterns which cyclorotated in antiphase through 6 degrees at frequencies between 0.05 and 2 Hz. In one psychophysical procedure subjects nulled the apparent oscillatory motion of radial nonius lines superimposed on a small black disc at the center of a large cyclorotating display. In the second, subjects nulled the apparent inclination in depth of a vertical line displayed in the same way. The amplitude of cyclovergence measured objectively and the magnitude of oscillation of the nonius lines were similar at low stimulus frequencies. At higher frequencies of cyclorotation, both amplitudes declined but the nonius amplitude exceeded that of cyclovergence. The apparent inclination of the vertical test line, as indicated by the nulling procedure, also declined with increasing frequency of cyclorotation, but not at the same rate. At low frequencies, the apparent inclination of the test line was greater than that corresponding to the cyclodisparity induced into the line and almost as great as that corresponding to the relative disparity between the oscillating pattern and the line. The implications of these results for measuring cyclovergence and for an understanding of stimuli driving cyclovergence and perceived inclination in depth are discussed.

Eye Movements↗
PubMed1993

The role of growth regulatory aberrations in progression of human colon carcinoma.

Colon carcinoma is a multistage disease. Most malignancies arise from pre-existing benign tumors. Multiple chromosomal defects affecting oncogene and tumor suppressor gene function are associated with disease progression. These aberrations result in an imbalance between the normal positive and negative growth effectors, which contribute further to disease progression. We have studied how changes in the expression of TGF alpha and TGF beta affect colon carcinoma cell behavior. Overexpression of the stimulatory factor TGF alpha in a relatively benign cell line with weak TGF alpha autocrine activity converted the cell type to an aggressive, progressed phenotype in vivo and in vitro. In contrast, disruption of TGF alpha expression by constitutive expression of TGF alpha antisense RNA in a progressed cell line with a strong, internalized autocrine loop resulted in the development of clones with decreased tumorigenicity in vitro and in vivo. Suppression of the inhibitory effects of TGF beta by constitutive expression of TGF beta antisense RNA increased the tumorigenicity of the cell lines in vitro and in vivo. None of these alterations in TGF alpha or TGF beta expression affected the doubling time of the cells. The changes in tumorigenicity were due to effects on the lag phase of growth. We conclude that TGF beta functions to maintain the cells in a quiescent state while TGF alpha drives reentry into the cell cycle. We have identified a unique cis-element that mediates TGF alpha autoregulation. The transcription factor binding this element is also involved in the cell-cycle regulation of TGF alpha expression. We hypothesize that this factor may be a convergent point TGF alpha and TGF beta interact in controlling movement into and out of quiescence.

Animals↗
PubMed1993

The distorted alpha 2-adrenoceptor genotype distribution in F2 populations of Dahl salt sensitive and resistant rats cross.

To examine the role of the alpha 2-adrenoceptor gene in the development of genetic hypertensive rats, we tested Dahl salt sensitive (S) and resistant rats (R) for the presence of a restriction fragment length polymorphism (RFLP) in that gene. An RFLP was found between the S and R rats with a human kidney cDNA alpha 2-adrenoceptor probe (alpha 2-C4) and Msp I restriction endonuclease. The alpha 2-C4 probe detected two alleles, S and R, of 3.0 and 2.8 kb in size. The two strains of rats were each homozygous for their corresponding allele. The inheritance of the alleles was investigated by crossbreeding S and R rats and subsequent brother/sister mating of F1 rats. Two hundred and fifteen F2 rats were produced by breeding 14 pairs of F1 rats. An atypical distribution of alpha 2-adrenoceptor genotypes was observed. We found a reduced number of the SS genotype in both males and females of the F2 generation. To investigate the mechanism of this distorted alpha 2-adrenoceptor genotype distribution in the F2 rats of S and R cross, we backcrossed the F1 rats to their S and R parents. The litter size and gender distribution were counted for each breeding colony. Analysis by chi-square test showed that there was no sex difference among the backcrosses. Also, there was no significant decrease in litter size. This excludes the possibilities of fetal demise of S homozygotes and intrauterine selection. Therefore the deficiency of SS genotype may be due to gene recombination or may not be due to the alpha 2-adrenoceptor gene itself, but to the effect of other genes closely linked to the alpha 2-adrenoceptor.

Animals↗
PubMed1993

Vasoactive intestinal peptide downregulates the expression of IL-2 but not of IFN gamma from stimulated murine T lymphocytes.

The neuropeptide vasoactive intestinal peptide (VIP) has been previously reported to inhibit T cell proliferation. Here we report on the effect of VIP on IL-2 and on IFN gamma production by murine T lymphocytes stimulated with mitogens (ConA), or activated through the antigen-specific T cell receptor. VIP inhibited IL-2 production by either unfractionated spleen cells, or by purified CD4+ T cells in a dose-dependent manner. The effect was specific, since structurally related peptides such as secretin and glucagon had little or no inhibitory effect. VIP induced a rapid increase in intracellular cAMP in CD4+ T cells, suggesting that the inhibitory effect of VIP could be mediated through the induction of cAMP. Northern blots showed that VIP downregulated IL-2 mRNA, indicating the occurrence of a transcriptional regulatory event. In contrast with its effect on IL-2, VIP did not affect IFN gamma production by either mitogen-stimulated normal T lymphocytes, or by the L12R4 murine T cell line which produces IFN gamma in response to PMA stimulation.

Animals↗
PubMed1993

Vasoactive intestinal peptide inhibits interleukin (IL)-2 and IL-4 production through different molecular mechanisms in T cells activated via the T cell receptor/CD3 complex.

The neuropeptide vasoactive intestinal peptide (VIP) has been reported previously to inhibit cell proliferation and interleukin (IL)-2 production in mitogen-stimulated T lymphocytes. In physiological conditions, T lymphocytes are specifically activated by antigen-binding through the T cell receptor (TCR). Here we report on the effect of VIP and related peptides on IL-2 and IL-4 production of murine T lymphocytes stimulated through the TCR. VIP inhibited IL-2 and IL-4 production (both at the level of protein concentration and biological activity) by unfractionated spleen cells or purified CD4+ T cells stimulated with either anti-CD3 monoclonal antibodies (mAbs) or with anti-CD3 mAbs plus phorbol esters. The inhibition was dose-dependent, and specific, since structurally related peptides such as secretin and glucagon had little or no inhibitory activity. VIP inhibited IL-2 and IL-4 production through different molecular mechanisms. IL-2 production was regulated at a transcriptional level through the downregulation of IL-2 mRNA, whereas the production of IL-4 was modulated at a posttranscriptional level.

Animals↗
PubMed1993

Design and optimization of a breast coil for magnetic resonance imaging.

Mathematical methods were implemented to optimize the configuration of specially designed breast coils leading to substantial improvements in magnetic field homogeneity. Multiple-turn shaped coils were constructed according to mathematically determined parameters derived from B1 field optimization calculations. Significant improvements in coil homogeneity were obtained without overcompromising quality factors and signal-to-noise ratios (S/N). Coil performance was verified using both phantom and breast images, revealing improved coil performance particularly in the region adjacent to the chest wall. These new coils are easily constructed and can be designed to accommodate various breast sizes. They can be utilized in the transmit/receive or receive only mode and can be doubly tuned for multinuclear spectroscopic studies. Moreover, nothing precludes their use to image both breasts simultaneously. The results demonstrate the ease of our approach and suggests that these methods can be feasibly applied to other surface coil designs.

Breast↗
PubMed1993

Synthesis and biological evaluation of tetrademethyl isocolchicine derivatives as inhibitors of DNA topoisomerase action in vitro.

Four tetrademethyl isocolchicine analogs were prepared and evaluated as inhibitors of mammalian DNA topoisomerase in vitro. All compounds inhibited topoisomerase II-dependent DNA unknotting by a mechanism which did not involve "cleavable-complex" formation. N-Deacetylation as well as N-substitution with the (3',4',5'-trihydroxybenzoyl)-group afforded compounds which were less selective, based on their added ability to inhibit topoisomerase I-mediated DNA relaxation.

Colchicine↗
PubMed1993

Anti-AIDS agents, 9. Suberosol, a new C31 lanostane-type triterpene and anti-HIV principle from Polyalthia suberosa.

A new C31 lanostane-type triterpene, assigned the trivial name suberosol [1], has been isolated from Polyalthia suberosa as an anti-HIV principle. The structure has been characterized as 24-methylenelanost-7,9(11)-diene-3 beta, 15 alpha-diol (suberosol) [1], based on spectroscopic evidence. Compound 1 was found to show anti-HIV replication activity in H9 lymphocyte cells with an EC50 of 3 micrograms/ml.

Antiviral Agents↗
PubMed1993

A prospective, randomized, blinded, and placebo-controlled trial of intraoperative intra-arterial urokinase infusion during lower extremity revascularization. Regional and systemic effects.

OBJECTIVE: This study was designed to evaluate the safety and regional and systemic effects of three doses of urokinase (UK) infused into the distal arterial circulation during routine operative lower extremity revascularization. METHODS: One hundred thirty-four patients were prospectively randomized to receive one of three bolus doses of UK (125,000, 250,000, or 500,000 U) or placebo (saline) infused into the distal circulation before lower extremity bypass for chronic limb ischemia. Regional (femoral vein) and systemic (arm) blood was sampled before drug infusion, prereperfusion, and postreperfusion, and systemic blood samples were obtained 2 hours postreperfusion. Assays evaluated plasma levels of fibrinogen, fibrin(ogen) degradation products (FDP), fibrin breakdown products (D-dimer and fragment B-beta 15-42), and plasminogen. Patients were monitored for clinically evident bleeding complications. The Wilcoxon rank-sum test was used to compare different drug doses with the placebo. RESULTS: Intraoperative bolus UK infusions produced no significant fibrinogen breakdown compared with placebo. There was a dose-related decline in plasminogen levels, which became significant at a dose of 500,000 U of UK (p < 0.001). There were dose-related increases in plasma FDP, which became significant at dose of 250,000 and 500,000 U (p < or = 0.005), and in plasma D-dimer, which were significant at all UK doses (p < 0.001). The changes in plasma fibrinogen and markers of fibrin breakdown were similar in the regional and systemic circulations. There was no increase in operative blood loss, blood replaced, or wound hematoma formation. There was an unexplained increased mortality in the placebo group (21.1% vs. 2.0%, p = 0.033). CONCLUSIONS: Intraoperative bolus UK infusion is safe, with no significant fibrinogen depletion or increased operative blood loss or wound hematoma formation. Dose-related plasminogen activation resulted in significant breakdown in cross-linked fibrin in the distal circulation. Intraoperative bolus UK infusion may be valuable as an adjunct in patients with chronic occlusive disease who are undergoing revascularization. Detailed randomized studies are indicated to establish clinical efficacy.

Aged↗
PubMed1993

CA-1, a novel phosphoprotein, interacts with the promoter of the cab140 gene in Arabidopsis and is undetectable in det1 mutant seedlings.

We have identified and partially purified a DNA binding protein from Arabidopsis that interacts specifically with the phytochrome-responsive promoter of the Arabidopsis cab140 gene. Promoter deletion analyses in transgenic tobacco showed that, if a region that includes the sequence interacting with this protein was deleted, both expression and phytochrome responsiveness were lost. The protein protected a cytosine- and adenine-rich region from DNase I digestion, and therefore it has been called Ca-1. CA-1 was shown to be a phosphoprotein, and dephosphorylation changed the migration of the protein-DNA complex in DNA mobility shift assays. The data suggested that the protein has an apparent molecular weight of 70,000. The CA-1-protected region of the cab140 promoter included an ACGT motif that has been found in the target sequences of a number of bZIP transcription factors, but the binding behavior of CA-1 differed from those factors. CA-1 binding activity was present in plants grown in either white light or darkness, and no differences in the binding activity were detected in the dark-grown plants after short red or white light treatments. However, the CA-1 binding activity was not detectable in extracts of seedlings bearing the det1 mutation grown in the dark and given the same illumination treatments as wild type. In contrast to wild type, the mutant seedlings express cab RNA at a high level when grown in complete darkness, and we found no further increase in cab140 mRNA in response to brief red illumination. The lack of CA-1 activity in the det1 mutant suggests that it may function as a transcriptional repressor regulating the expression of the cab140 gene in Arabidopsis.

Arabidopsis↗