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Biomedical subjects

X Y Li

Publications and source records attributed to X Y Li.

At least 37 records · Page 2Linked to original sources
PubMed2001

The design of new molecular "light switches" for DNA.

Two novel ruthenium(II) complexes, [Ru(pztp)2(phen)](ClO4)2 and [Ru(pztp)2(bpy)] (ClO4)2, have been synthesized and characterized by UV/Vis and 1H NMR spectroscopies and mass spectrometry. The MeCN solutions of both complexes display fluorescence that was found to be highly sensitive to the presence and concentration of water. The complexes behave like a "light switch" for DNA in that they do not luminesce in water but were "turned on" in the presence of DNA and show emission enhancement with the increase of DNA concentration. Their DNA binding behavior was also studied by absorption spectroscopy and viscosity measurements, which suggest that the DNA-complex interaction involves intercalation of the metal-bound pztp ligand into the base pairs of duplex DNA.

Animals↗
PubMed2001

Permeability of fractal aggregates.

It is well known that the permeability and density of an aggregate decreases with its size, affecting its settling velocity and coagulation rate (rate of particle capture) with other particles. This change in aggregate density with size can be described by fractal scaling relationships. Two distinctly different fractal scaling approaches, however, have been used to describe aggregate permeability. In one approach (single-particle-fractal model), the permeability is calculated by assuming primary particles are uniformly distributed in the aggregate. In the other approach (cluster-fractal model), it is assumed that aggregates are composed of primary particles separated into individual clusters that are less permeable than the aggregate. The overall permeability of the aggregate is dependent on the number and sizes of these clusters. Using three different permeability correlations (Brinkman, Happel and Carmen-Kozeny), it is demonstrated through comparison with aggregate settling velocity data that the single-particle-fractal model does not provide realistic predictions of settling velocity as a function of aggregate size. In addition, it is shown that the Carmen-Kozeny permeability equation does not produce realistic settling velocity relationships. The transport settling velocity and capture rate of sinking aggregates in natural and engineered environments should therefore only be calculated using the Happel or Brinkman equations and a cluster-fractal model.

Chemical Precipitation↗
PubMed2001

Effect of several organic acids on phosphate adsorption by variable charge soils of central China.

The effect of several organic acids on phosphate adsorption by acidic soils in subtropical zone of central China was studied. Results showed: (1) citrate and oxalate remarkably reduced the amount of phosphate adsorption, but tartrate, benzoate and acetate had only a very slight influence on phosphate adsorption; (2) the ability of citrate in reducing phosphate adsorption was greater than that of oxalate, moreover, the reduction percentage was dependent on the concentration of organic ligands in the solution; (3) the effect of organic acids on phosphate adsorption was related to the pH value of organic acid solution. The minimum reduction in adsorption of phosphate was present at a specific pH value of organic acid solution which ranged from 2 to 10; (4) a minimum reduction of phosphate adsorption occurred when phosphate was added to the soils before organic acid, whereas a maximum occurred when organic acid was introduced before the addition of phosphate. Meanwhile, the treatment for the mixture of two organic acids resulted in more reduction in phosphate adsorption than each of the organic acids and less than the total of them. Based on these observations, we suggested that the competition between phosphate and organic acids relied on their relatively affinity to soil mineral surface at different conditions.

Adsorption↗
PubMed2001

Thermostable (SULT1A1) and thermolabile (SULT1A3) phenol sulfotransferases in human osteosarcoma and osteoblast cells.

Sulfate conjugation is an important pathway in the metabolism of many drugs, xenobiotic compounds, and hormones. Sulfotransferases (SULTs) catalyze these reactions and have been detected and characterized in various human tissues including the liver and small intestine. Substrates for SULTs that include estrogen and thyroid hormones have well-established roles affecting skeletal integrity and disease processes. We performed the following studies to determine the presence of SULTs in human osteoblast-like cells, and to compare their characteristics to SULTs expressed in other human tissues. Four osteosarcoma cell lines (SaOS-2, U2-OS, PR, and HOS-TE85) were screened for the presence of four different SULT activities. Predominant activities were found for SULT1A1 in SaOS-2 cells, and SULT-1A3 in HOS-TE85 cells. Several biochemical properties of each enzyme that included apparent K(m) values, thermal stabilities, and responses to the inhibitors 2,6-dichloro-4-nitrophenol and NaCl were used to further characterize the SULT activities. High-performance liquid chromatography (HPLC) of the reaction products confirmed the known products of SULT1A1 and SULT1A3. When the mature human osteoblast HOB-03-CE6 cell line was tested for activity alone, the predominant activity was SULT1A3, with minimal SULT1A1. The results indicate that SULT1A1 and SULT1A3 are present in human osteosarcoma and mature osteoblast cell lines, and that the characteristics of the osteosarcoma cell SULTs are similar to those expressed in other human tissues. SULTs may have regulatory roles in the deactivation of thyroid hormones or estrogenic compounds in bone, and thus may affect hormone action and bone responses in the human skeleton.

Arylsulfotransferase↗
PubMed2001

Sphingomyelin-enriched microdomains at the Golgi complex.

Sphingomyelin- and cholesterol-enriched microdomains can be isolated as detergent-resistant membranes from total cell extracts (total-DRM). It is generally believed that this total-DRM represents microdomains of the plasma membrane. Here we describe the purification and detailed characterization of microdomains from Golgi membranes. These Golgi-derived detergent-insoluble complexes (GICs) have a low buoyant density and are highly enriched in lipids, containing 25% of total Golgi phospholipids including 67% of Golgi-derived sphingomyelin, and 43% of Golgi-derived cholesterol. In contrast to total-DRM, GICs contain only 10 major proteins, present in nearly stoichiometric amounts, including the alpha- and beta-subunits of heterotrimeric G proteins, flotillin-1, caveolin, and subunits of the vacuolar ATPase. Morphological data show a brefeldin A-sensitive and temperature-sensitive localization to the Golgi complex. Strikingly, the stability of GICs does not depend on its membrane environment, because, after addition of brefeldin A to cells, GICs can be isolated from a fused Golgi-endoplasmic reticulum organelle. This indicates that GIC microdomains are not in a dynamic equilibrium with neighboring membrane proteins and lipids. After disruption of the microdomains by cholesterol extraction with cyclodextrin, a subcomplex of several GIC proteins including the B-subunit of the vacuolar ATPase, flotillin-1, caveolin, and p17 could still be isolated by immunoprecipitation. This indicates that several of the identified GIC proteins localize to the same microdomains and that the microdomain scaffold is not required for protein interactions between these GIC proteins but instead might modulate their affinity.

Adenosine Triphosphatases↗
PubMed2001

Relationship between ABO blood groups and carcinoma of esophagus and cardia in Chaoshan inhabitants of China.

AIM: To study the relationship between ABO blood groups and carcinoma of esophagus and cardia in Chaoshan inhabitants of China, which is a unique Littoral high-risk area of esophageal carcinoma in China. The poor communication and transportation in the past has made Chaoshan a relatively closed area and kept its culture and custure of old China thousand years ago. METHODS: Data on age, sex, ABO blood type and X-ray or pathological diagnose of the patients with carcinoma of esophagus or cardia were collected from the Tumor Hospital. First Affiliated Hospital, Second Affiliated Hospital of Shantou University Medical College; and the Central Hospital of Shantou and the Central Hospital of Jieyang. A total of 6685 patients with esophageal carcinoma (EC) and 2955 patients with cardiac cancer (CC) in Chaoshan district were retrospectively assessed for their association with ABO blood groups. RESULTS: The distribution of ABO blood groups in patients with EC or CC was similar to the normal local population in Chaoshan. However, blood group B in male patients with CC and in the patients with carcinoma in the upper third esophagus was 2.3% and 4.7% higher than the corresponding controls. The relative risk B O was 1.1415 (P<0.05) and 1.2696 (P<0.05), respectively. No relationship was found between ABO blood groups and tumor differentiation. CONCLUSION: ABO blood group B is associated with the incidence of CC in male individuals and carcinoma in the upper third esophagus. The distribution of ABO blood groups varies in the different geographical and ethnic groups. As a result, proper controls are very important for such studies.

ABO Blood-Group System↗
PubMed2001

[Cloning and characterization of pathogenesis-related protein 1 from wheat-H. villosa translocation lines].

A Triticum aestivum-Haynaldia villosa 6VS/6AL translocation line contained powdery mildew resistance gene Pm21 which is effective against all the current biotypes of Erygsiphe gramins. Cloning of the related genes for powdery mildew resistance is significance for understanding its resistance mechanism and disease resistance breeding. Using RT-PCR and RACE technology, a wheat pathogenesis related protein 1 cDNA clone (TaPr-1) corresponding to a mRNA differentially induced in resistant 6VS/6AL translocation line compared to susceptible wheat cultivar "Yangmai 5" by powdery mildew infection was isolated and characterized. This sequence contained 823 bp and had an open reading frame (ORF) containing 164 amino acids with 24 amino acids in the putative signal peptide and 140 amino acids comprising the mature peptide (15.1 kD). The deduced amino acid sequence showed close homology to PR-1 like proteins, which have been isolated from many plants. Northern blot analysis revealed the most abundantly accumulation of the corresponding mRNA 12 h after infection in translocation line (6VS/6AL). The obviously difference in the expression of the PRw-1 was also observed between resistant translocation line (6VS/6AL) and susceptible parent "Yangmai 5", it showed the TaPr-1 gene is related to powdery mildew resistance. Southern blot indicated that the wheat genome contains more than one copies of TaPr-1 genes, and there are polymorphism between translocation lines and "Yanmai 5", the result shows that 6VS may contain TaPr-1 genes.

Amino Acid Sequence↗
PubMed2001

Naloxone increases vascular responsiveness in chronic morphine treated rats and facilitates intracellular signaling in cultured vascular cells.

AIM: To probe the changes of vascular responsiveness and intracellular signaling during opiate withdrawal syndrome. METHODS: Morphine withdrawal syndrome in rats was precipitated by iv naloxone following daily injection of increasing dose of morphine for 2 weeks, the changes in mean arterial blood pressure (MBP) caused by acetylcholine (ACh) were recorded. Isolated mesenteric vascular beds were perfused with Kreb's solution containing different concentration of drugs. The cytoplasmic Ca2+ ([Ca2+]i) in Fura 2-loaded cultured bovine aortic endothelial cells (aec) and smooth muscle cells (smc) were assayed. The positive immunoreaction to the phosphorylated cyclic AMP responsive element-binding protein (phospho-CREB) in cultured smc was calculated. RESULTS: Naloxone 2 mg/kg iv following chronic morphine treatment precipitated severe opiate withdrawal signs in company with blunted hypotensive effect of Ach that was the same as chronic morphine treated rats before withdrawal. In the mesenteric vascular beds from chronic morphine treated rats, the EC50 of pressor effect of norepinephrine (NE) was decreased from (2.06 +/- 0.38) to (1.14 +/- 0.21) micromol/L (n = 8, P < 0.01) after the perfusion solution containing morphine 20 micromol/L was replaced by Kreb's containing naloxone 25 micromol/L. Furthermore, NE-induced perfusion pressure increases were completely prevented by Kreb's contained morphine 40 micromol/L. Morphine acutely applied to control smc produced some variable and naloxone-reversible [Ca2+]i changes, but naloxone did not. However, naloxone increased [Ca2+]i in two thirds of smc preincubated with morphine 0.1 or 0.5 mmol/L for 48 h from (97 +/- 20) to (167 +/- 29) nmol/L (n = 9, P < 0.01) and from (106 +/- 19) to (225 +/- 48) nmol/L (n = 10, P < 0.01), respectively, and it also increased the ratio of positive immunoreaction to phospho-CREB from (7.7 +/- 3.2) % to (19.6 +/- 4.7) % (n = 6, P < 0.01) in smc preincubated with morphine 0.5 mmol/L. In addition, naloxone decreased [Ca2+]i from (146 +/- 34) to (78 +/- 24) nmol/L in one third morphine-preincubated aec (n = 10, P < 0.01). CONCLUSION: That naloxone enhances vascular responsiveness to NE in chronic morphine treatment rats may be relevant to [Ca2+]i transient facilitation in company with cAMP-dependent phosphorylation enhancement.

Animals↗
PubMed2001

Regulation of growth-regulated oncogene alpha expression by estrogen in human endothelial cells.

AIM: To study the effect of estrogen on expression of growth-regulated oncogene alpha (GROalpha) in human umbilical vein endothelial cells (HUVEC) in vitro. METHODS: Expressions of CXC chemokine GROalpha mRNA and protein were measured by Northern blotting assay and ELISA, respectively. The physiological significance of GROalpha expression was tested by static cell adhesion assay. RESULTS: Both the GROalpha mRNA and protein levels decreased markedly after HUVEC were exposured to 17beta-estradiol (2 0.05 micromol/L. Moreover, the inhibition of the protein was depended on the concentration of 17beta-estradiol. Tamoxifen (0.1 micromol/L), an estrogen receptor alpha antagonist, alone did not affect GROalpha protein expression, but can reverse the E2 -induced inhibition of GROalpha protein expression (by up to 50 %) and the binding of U937 cells to E2-treated HUVEC (by up to 40 %). CONCLUSION: Estrogen might functionally down-regulates GROalpha expression through estrogen receptor alpha on endothelial cells.

Cells, Cultured↗
PubMed2001

Rapid activation of p38 mitogen-activated protein kinase by corticosterone in PC12 cells.

The present study using immunoblot showed that corticosterone (B) could induce a rapid activation of p38 in PC12 cells. The dose and time response curves w ere bell shaped with a maximal activation at 10-9 mol/L and 15 min respectively. The activation was not affected by steroid nuclear receptor antagonist RU38486. Bovine serum albumin coupled B (B-BSA) could induce phosphorylation of p38. Tyrosine kinase inhibitor genistein failed to block the phosphorylation, a fact suggesting that the tyrosine kinase activity is not involved in the pathway. On the other hand, phorbol 12-myristate 13-acetate (PMA), a protein kinase C (PKC) activator, could mimic the actions of B, while G 6976, a PKC inhibitor, could completely abolish the phosphorylation induced by B. These results clearly demonstrate that B activates p38 MAPK readily via a putative membrane receptor through a PKC-dependent pathway.

Animals↗
PubMed2001

New biflavanones and bioactive compounds from Stellera chamaejasme L.

AIM: To study the chemical constituents of the root of Stellera chamaejasme L. METHODS: Various column chromatographies on silica gel and RP-18 were employed for isolation and purification. Structures of compounds were elucidated by spectral analysis. RESULTS: Eight lignans and three biflavonoids possessing a C-3/C-3" linkage were isolated. They are ruixianglangdusu A (1) and B (2), 4',4'",5,5",7,7"-hexahydroxy-3,3"-biflavone (3), (+)-kusunokinin (4), lirioresinol-B (5), magnolenin C (6), (-)-pinoresinol monomethyl ether (7), (-)-pinoresinol (8), (+)-matairesinol (9), isohinokinin (10) and (-)-eudesmin (11). CONCLUSION: Compounds 1 and 2 are new biflavanones, 1 is enantiomeric to known chamaejasmenin C, 4, 6, 8, 9, 10 and 11 were isolated from this plant for the first time, and 7 was isolated from natural resources for the first time. In vitro bioassays showed that 3 and 8 exhibited antibacterial activity, and 1, 2, 9 and 11 exhibited immunomodulatory activity.

Adjuvants, Immunologic↗
PubMed2000

Chain length determination of prenyltransferases: both heteromeric subunits of medium-chain (E)-prenyl diphosphate synthase are involved in the product chain length determination.

Among prenyltransferases, medium-chain (E)-prenyl diphosphate synthases are unusual because of their heterodimeric structures. The larger subunit has highly conserved regions typical of (E)-prenyltransferases. The smaller one has recently been shown to be involved in the binding of allylic substrate as well as determining the chain length of the reaction product [Zhang, Y.-W., et al. (1999) Biochemistry 38, 14638-14643]. To better understand the product chain length determination mechanism of these enzymes, several amino acid residues in the larger subunits of Micrococcus luteus B-P 26 hexaprenyl diphosphate synthase and Bacillus subtilis heptaprenyl diphosphate synthase were selected for substitutions by site-directed mutagenesis and examined by combination with the corresponding wild-type or mutated smaller subunits. Replacement of the Ala at the fifth position upstream to the first Asp-rich motif with bulky amino acids in both larger subunits resulted in shortening the chain lengths of the major products, and a double combination of mutant subunits of the heptaprenyl diphosphate synthase, I-D97A/II-A79F, yielded exclusively geranylgeranyl diphosphate. However, the combination of a mutant subunit and the wild-type, I-Y103S/II-WT or I-WT/II-I76G, produced a C(40) prenyl diphosphate, and the double combination of the mutants, I-Y103S/II-I76G, gave a reaction product with longer prenyl chain up to C(50). These results suggest that medium-chain (E)-prenyl diphosphate synthases take a novel mode for the product chain length determination, in which both subunits cooperatively participate in maintaining and determining the product specificity of each enzyme.

Alkyl and Aryl Transferases↗
PubMed2000

Distinct classes of yeast promoters revealed by differential TAF recruitment.

The transcription factor TFIID contains the TATA box binding protein (TBP) and multiple TBP-associated factors (TAFs). Here, the association of TFIID components with promoters that either are dependent on multiple TAFs (TAFdep) or have no apparent TAF requirement (TAFind) is analyzed in yeast. At TAFdep promoters, TAFs are present at levels comparable to that of TBP, whereas at TAFind promoters, TAFs are present at levels that approximate background. After inactivation of several general transcription factors, including TBP, TAFs are still recruited by activators to TAFdep promoters. The results reveal two classes of promoters: at TAFind promoters, TBP is recruited in the apparent absence of TAFs, whereas at TAFdep promoters, TAFs are co-recruited with TBP in a manner consistent with direct activator-TAF interactions.

Cross-Linking Reagents↗
PubMed2000

Constitutive expression of stromal derived factor-1 by mucosal epithelia and its role in HIV transmission and propagation.

HIV particles that use the chemokine receptor CXCR4 as a coreceptor for entry into cells (X4-HIV) inefficiently transmit infection across mucosal surfaces [1], despite their presence in seminal fluid and mucosal secretions from infected individuals [2] [3] [4]. In addition, although intestinal lymphocytes are susceptible to infection with either X4-HIV particles or particles that use the chemokine receptor CCR5 for viral entry (R5-HIV) during ex vivo culture [5], only systemic inoculation of R5-chimeric simian-HIV (S-HIV) results in a rapid loss of CD4(+) intestinal lymphocytes in macaques [6]. The mechanisms underlying the inefficient capacity of X4-HIV to transmit infection across mucosal surfaces and to infect intestinal lymphocytes in vivo have remained elusive. The CCR5 ligands RANTES, MIP-1alpha and MIP-1beta suppress infection by R5-HIV-1 particles via induction of CCR5 internalization, and individuals whose peripheral blood lymphocytes produce high levels of these chemokines are relatively resistant to infection [7] [8] [9]. Here, we show that the CXCR4 ligand stromal derived factor-1 (SDF-1) is constitutively expressed by mucosal epithelial cells at sites of HIV transmission and propagation. Furthermore, CXCR4 is selectively downmodulated on intestinal lymphocytes within the setting of prominent SDF-1 expression. We postulate that mucosally derived SDF-1 continuously downmodulates CXCR4 on resident HIV target cells, thereby reducing the transmission and propagation of X4-HIV at mucosal sites. Moreover, such a mechanism could contribute to the delayed emergence of X4 isolates, which predominantly occurs during the later stages of the HIV infection.

Chemokine CXCL12↗
PubMed2000

Oxidative modification of neurogranin by nitric oxide: an amperometric study.

Neurogranin (Ng) is a neuron-specific protein kinase C (PKC) substrate, which contains four cysteine (Cys) residues. Recently, it has been shown that Ng is a redox-sensitive protein and is a likely target of nitric oxide (NO) and other oxidants [F.-S. Sheu, C.W. Mahoney, K. Seki, K.-P. Huang, Nitric oxide modification of rat brain neurogranin affects its phosphorylation by protein kinase C and affinity for calmodulin, J. Biol. Chem. 271 (1996) 22407-22413: J. Li, J.H. Pak, F.L. Huang, K.-P. Huang, N-methyl-D-aspartate induces neurogranin/RC3 oxidation in rat brain slices, J. Biol. Chem. 274 (1999) 1294-1300]. In this study, we directly examine the redox reactions between dissolved NO and Cys as well as between NO and bacterial expressed Ng in its reduced form, at concentrations approximate to the physiological levels in phosphate buffer solution (PBS) under aerobic conditions. The reaction kinetics are measured directly by our newly developed electrochemical sensor. Our sensor is based on the chemical modification of electrode with immobilized nanoparticles of transition metal palladium (Pd) which serves as catalytic centers for the electrochemical oxidation of thiol and NO selectively and quantitatively at different potentials. It detects Cys and Ng in a linear range from nano to micromolar concentration at + 450 mV, vs. a saturated calomel reference electrode (SCE), while the detection of NO at the sensor can be optimally achieved at + 700 mV (vs. SCE) with a linear current-to-concentration range of nM to microM. It thus provides a selective control to monitor two reactants independently. With this sensor as a detector, we found that (1) the oxidation of either Cys or Ng by NO is a fast reaction which reaches a near completion within 1-2 min at its physiological concentration; and (2) after the completion of reaction, NO is mostly, if not all, regenerated, an observation consistent with the reaction mechanism involving the formation of S-nitrosothiol as an intermediate. The reaction kinetics of both NO to Cys and NO to Ng implies that NO can achieve local action on cellular proteins in addition to its effect on targets located in neighboring cells via concentration-gradient-dependent diffusion.

Animals↗
PubMed2000

Characterization of the antiviral effect of 2',3'-dideoxy-2', 3'-didehydro-beta-L-5-fluorocytidine in the duck hepatitis B virus infection model.

A novel L-nucleoside analog of deoxycytidine, 2',3'-dideoxy-2', 3'-didehydro-beta-L-5-fluorocytidine (beta-L-Fd4C), was recently shown to strongly inhibit hepatitis B virus (HBV) replication in the 2.2.15 cell line. Therefore, its antiviral activity was evaluated in the duck HBV (DHBV) infection model. Using a cell-free system for the expression of the DHBV polymerase, beta-L-Fd4C-TP exhibited a concentration-dependent inhibition of dCTP incorporation into viral minus-strand DNA with a 50% inhibitory concentration of 0.2 microM which was lower than that of other tested deoxycytidine analogs, i.e. , lamivudine-TP, ddC-TP, and beta-L-FddC-TP. Further analysis showed that beta-L-Fd4C-TP is likely to be a competitive inhibitor of dCTP incorporation and to cause premature DNA chain termination. In primary duck hepatocyte cultures infected in vitro, beta-L-Fd4C administration exhibited a long-lasting inhibitory effect on viral DNA synthesis but could not clear viral covalently closed circular DNA (CCC DNA). Results of short-term antiviral treatment in experimentally infected ducklings showed that beta-L-Fd4C exhibited the most potent antiviral effect, followed by beta-L-FddC, lamivudine, and ddC. Longer administration of beta-L-Fd4C induced a sustained suppression of viremia (>95% of controls) and of viral DNA synthesis within the liver. However, the persistence of trace amounts of viral CCC DNA detected only by PCR was associated with a recurrence of viral replication after drug withdrawal. In parallel, beta-L-Fd4C treatment suppressed viral antigen expression within the liver and decreased intrahepatic inflammation and was not associated with any sign of toxicity. Our data, therefore, demonstrate that in the duck model of HBV infection, beta-L-Fd4C is a potent inhibitor of DHBV reverse transcriptase activity in vitro and suppresses viral replication in the liver in vivo.

Animals↗