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Biomedical subjects

J G Liu

Publications and source records attributed to J G Liu.

At least 19 recordsLinked to original sources
PubMed2003

Correlations between cadmium and mineral nutrients in absorption and accumulation in various genotypes of rice under cadmium stress.

The absorption and accumulation of Cd2+, Fe3+, Zn2+, Mn2+, Cu2+ and Mg2+ in the roots and leaves of 20 rice cultivars (Oryza sativa L.) with different genotypes under cadmium (Cd) stress were investigated with pot experiments. The results showed that there existed significant differences among the rice cultivars in the contents of six mineral elements in both roots and leaves at both heading and ripening periods. The statistical analysis showed that, for their contents in roots, significant and positive correlations between Cd2+ and Fe3+, Cd2+ and Zn2+, Cd2+ and Mn2+, Cd2+ and Cu2+ existed, but no significant correlation between Cd2+ and Mg2+, at the two periods. In the leaves, Cd also showed significant and positive correlations with Fe3+, Zn2+ and Cu2+ at the both periods, but a significant and negative correlation with Mn2+ and no significant correlation with Mg2+ at heading, a significant and positive correlation with Mg2+ and no significant correlation with Mn2+ at ripening. These results suggested that there were cooperative absorption between Cd2+ and Fe3+, Mn2+, Cu2+, Mn2+ in rice plants. Genotypic differences in Cd uptake and translocation among the rice cultivars suggested that paddy field of some rice cultivars may be irrigated with partially treated sewage water.

Absorption↗
PubMed2001

Constitutively active mu-opioid receptors inhibit adenylyl cyclase activity in intact cells and activate G-proteins differently than the agonist [D-Ala2,N-MePhe4,Gly-ol5]enkephalin.

The most convincing evidence demonstrating constitutive activation of mu-opioid receptors is the observation that putative inverse agonists decrease basal G-protein activity in membrane preparations. However, it is not clear whether constitutively active receptors in isolated membranes have any physiological relevance in intact cells. GH3 cells expressing mu-opioid receptors (GH3MOR) exhibit higher basal G-protein activity and lower basal cAMP levels than wild-type GH3 cells, indicative of constitutively active receptors. This study determined whether alkylation of mu-opioid receptors by the irreversible antagonist beta-funaltrexamine would decrease spontaneous receptor activity in intact cells, revealing constitutive activity. GH3MOR cells were pretreated with increasing concentrations of beta-funaltrexamine followed by functional testing after removal of unbound drug. beta-Funaltrexamine pretreatment produced a concentration-dependent decrease in mu-opioid receptor binding with an IC50 of 0.98 nm and an Emax of 77%. Similar concentrations of beta-funaltrexamine pretreatment produced a half-maximal reduction in basal [35S]GTPgammaS binding, a decrease in basal photolabeling of G-proteins with azidoanilido-[alpha-32P]GTP, and an increase in basal adenylyl cyclase activity in intact cells. Therefore, mu-opioid receptors are constitutively active in intact cells, producing stimulation of G-proteins and inhibition of adenylyl cyclase. Importantly, photolabeling of Galpha-subunits with azidoanilido-[alpha-32P]GTP demonstrated that constitutively active mu-opioid receptors activate individual G-proteins differently than the agonist [d-Ala2,N-MePhe4,Gly-ol5]enkephalin.

Adenylate Cyclase Toxin↗
PubMed2001

DNA-binding and photocleavage studies of cobalt(III) polypyridyl complexes:.

Two complexes of [Co(phen)2IP]3+ (IP=imidazo[4,5-f][l,10]phenanthroline) and [Co(phen)2PIP]3+ (PIP=2-phenylimidazo[4,5-f][1,10]phenanthroline) have been synthesized and characterized by UV/VIS, IR, EA and mass spectra. The binding of the two complexes with calf thymus DNA has been investigated by absorption spectroscopy, cyclic voltammetry, viscosity measurements and DNA cleavage assay. The spectroscopic studies together with cyclic voltammetry and viscosity experiments support that both of the complexes bind to CT DNA by intercalation via IP or PIP into the base pairs of DNA. [Co(phen)2PIP]3+ binds more avidly to CT DNA than [Co(phen)2IP]3+, which is consistent with the extended planar and pi system of PIP. Noticeably, the two complexes have been found to be efficient photosensitisers for strand scissions in plasmid DNA.

Cobalt↗
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

DNA-binding and photocleavage studies of cobalt(III) mixed-polypyridyl complexes containing 2-(2-chloro-5-nitrophenyl)imidazo [4,5-f][1,10]phenanthroline.

The ligand 2-(2-chloro-5-nitrophenyl)imidazo[4,5-f][1,10]phenanthroline(CNOIP) and its complexes [Co(bpy)(2)(CNOIP)](3+) (1) and [Co(phen)(2)(CNOIP)](3+) (2) (bpy=2,2'-bipyridine; phen=1,10-phenanthroline) have been synthesized and characterized. Binding of the two complexes with calf thymus DNA has been investigated by spectroscopic methods, cyclic voltammetry, viscosity, and electrophoresis measurements. The experimental results indicate that both complexes bind to DNA through an intercalative mode. In comparison with their parent complexes containing PIP ligand (PIP=2-phenylimidazo[4,5-f][1,10]phenanthroline), the introduction of NO(2) and Cl groups to the PIP ligand decreased the binding affinity of complexes 1 and 2 to CT DNA. Both complexes have also been found to promote the photocleavage of plasmid pBR 322 DNA, the hydroxyl radical (OH*) is suggested to be the reactive species responsible for the cleavage.

Cobalt↗
PubMed2001

Protein kinases modulate the cellular adaptations associated with opioid tolerance and dependence.

Prolonged opioid exposure occurs frequently as a result of clinical use or drug abuse. Research using different ligands, cell lines, and animal models in the past three decades has elucidated some correlation between the biochemical events and behavioral changes resulting from opioid tolerance, dependence and addiction. For the most part, opioid tolerance and dependence are associated with up-regulation of the cAMP pathway, mediated by the supersensitization of adenylyl cyclase and by the altered coupling of opioid receptors to stimulatory G proteins. Neuroadaptive changes in signal transduction following prolonged opioid exposure are mediated by protein kinase systems, such as protein kinase C (PKC), cyclic AMP-dependent protein kinase (PKA), Ca2+/camodulin-dependent protein kinase II (CaMKII), G protein-coupled receptor kinases (GRKs) and mitogen-activated protein kinases (MAPKs). Intermediate steps between opioid receptor activation and the second- or third-messenger cascades include GRK-mediated receptor endocytosis and intracellular trafficking, as well as interactions with excitatory amino acid receptors and regulation of nitric oxide synthesis. Thus, prolonged occupancy by opioid receptor agonists can have differential effects on opioid receptor internalization, down-regulation and desensitization, and in the supersensitization of adenylyl cyclase, which contribute to the development of opioid tolerance and dependence. We discuss the role of various protein kinases in the signaling mechanisms underlying these differences. Clearer understanding of the molecular mechanisms of opioid tolerance and dependence will help in the treatment of patients suffering from acute and chronic pain, or drug dependence and addiction.

Adaptation, Physiological↗
PubMed2001

Dichloro(2,2'-diamino-4,4'-bi-1,3-thiazole-N3,N3')copper(II).

The title complex, [CuCl(2)(C(6)H(6)N(4)S(2))], has a flattened tetrahedral coordination. The Cu(II) atom is located on a twofold rotation axis and is coordinated by two N atoms from a chelating 2,2'-diamino-4,4'-bi-1,3-thiazole ligand and by two Cl atoms. Intramolecular hydrogen bonding exists between the amino groups of the 2,2'-diamino-4,4'-bi-1,3-thiazole ligand and the Cl atoms. The intermolecular separation of 3.425 (1) A between parallel bithiazole rings suggests there is a pi-pi interaction between them.

Journal Article↗
PubMed2001

Chronic exposure to mu-opioid agonists produces constitutive activation of mu-opioid receptors in direct proportion to the efficacy of the agonist used for pretreatment.

Chronic morphine treatment has been shown to produce constitutive activation of mu-opioid receptors, and this transition might contribute to the development of tolerance and dependence. The apparent ability of chronic morphine to increase the spontaneous, agonist-independent activation of mu-opioid receptors may be unique, due to its distinct partial agonist properties of possessing a relatively high intrinsic activity coupled with a poor ability to produce desensitization and down-regulation. Therefore, the present study tested the hypothesis that prolonged exposure to morphine would produce greater constitutive activity of mu-opioid receptors than exposure to the full agonist [D-Ala(2),N-MePhe(4),Gly-ol(5)]enkephalin (DAMGO). GH(3) cells expressing mu-opioid receptors were exposed to chronic morphine, DAMGO, or no opioid under conditions determined to produce maximal desensitization, down-regulation, and cAMP rebound. After chronic treatment, the mu-opioid antagonists naloxone and beta-chlornaltrexamine (beta-CNA) were evaluated in two assays predictive of inverse agonist activity. Both antagonists produced a concentration-dependent inhibition of [(35)S]GTP gamma S binding only in membranes prepared from cells chronically exposed to opioids. This effect was reversed by the neutral mu-opioid antagonist CTAP. Additionally, conditions known to uncouple G protein-coupled receptors from G proteins produced a leftward shift in the competition curve of beta-CNA for [(3)H]DAMGO binding only in membranes prepared from chronically treated cells. In contrast, these conditions produced no shift in the competition curve by the neutral antagonist CTAP in cells exposed to chronic DAMGO. Therefore, prolonged exposure of GH(3)MOR cells to opioids produced constitutive activation of mu-opioid receptors. Surprisingly, chronic treatment with the more efficacious agonist DAMGO produced greater increases in both measures of inverse agonist activity than did morphine. These observations may lend novel insight into the mechanisms of opioid tolerance and dependence.

Adenylyl Cyclase Inhibitors↗
PubMed2001

A meiotic chromosomal core consisting of cohesin complex proteins recruits DNA recombination proteins and promotes synapsis in the absence of an axial element in mammalian meiotic cells.

The behavior of meiotic chromosomes differs in several respects from that of their mitotic counterparts, resulting in the generation of genetically distinct haploid cells. This has been attributed in part to a meiosis-specific chromatin-associated protein structure, the synaptonemal complex. This complex consist of two parallel axial elements, each one associated with a pair of sister chromatids, and a transverse filament located between the synapsed homologous chromosomes. Recently, a different protein structure, the cohesin complex, was shown to be associated with meiotic chromosomes and to be required for chromosome segregation. To explore the functions of the two different protein structures, the synaptonemal complex and the cohesin complex, in mammalian male meiotic cells, we have analyzed how absence of the axial element affects early meiotic chromosome behavior. We find that the synaptonemal complex protein 3 (SCP3) is a main determinant of axial-element assembly and is required for attachment of this structure to meiotic chromosomes, whereas SCP2 helps shape the in vivo structure of the axial element. We also show that formation of a cohesin-containing chromosomal core in meiotic nuclei does not require SCP3 or SCP2. Our results also suggest that the cohesin core recruits recombination proteins and promotes synapsis between homologous chromosomes in the absence of an axial element. A model for early meiotic chromosome pairing and synapsis is proposed.

Animals↗
PubMed2001

[Cloning and expression of urate oxidase and its application in serum uric acid analysis].

Anurate oxidase (uricase, EC 1.7.3.3) gene from Candida utilis AS2.117 was cloned by PCR amplification with primers derived from conserved regions of published uicase DNA sequence. The DNA sequence of cloned uricase gene was determined and a high homology compared to the reported gene was found. The cloned gene was inserted into Bam H I and Nde I sites of pET21a to create the recombinant plasmid pURO. In Escherichia coli BL21(DE3) host, the expression lever of uricase reached to about 40% of total soluble proteins of the cell. The western blot analysis confirmed the result of expression. Properties of the enzyme protein produced by E. coli BL21(DE3)/pURO were determined and similar with those of original protein from Candida utilis AS2.117. Furthermore, the thermostability of the expressed protein was enhanced. The purified recombinant uricase was used in serum uric acid analysis.

Cloning, Molecular↗
PubMed2001

[Experimental study in rabbit on repair of radial bone defect by bioactive degradable polymer].

OBJECTIVE: To investigate the availability of bone defect repair by degradable porous polycaprolactam (PCL) as the carrier of bone morphogenetic protein (BMP). METHODS: Three different kinds of bone substitutes, including decalcified bone matrix, PCL-BMP compounds and simple PCL, were implanted into the radial bone defects in 36 rabbits, and in the other 12 rabbits the bone defects were left untreated as control. X-ray examination, X-ray morphometry, histological and electron microscopic observation were performed at different time after operation. RESULTS: The quantity of new bone formation in PCL-BMP group was prior to that in simple PCL group. The pattern and speed of bone defect repair in PCL-BMP group were similar to those in decalcified bone matrix. Electron microscopic observation showed that the PCL-BMP group degraded faster than simple PCL group, which was more suitable for bone repair. CONCLUSION: PCL is a good carrier of BMP with potential for clinical use.

Animals↗
PubMed2001

Fractal scaling of effective diffusion coefficient of solute in porous media.

Fractal approach is used to derive a power law relation between effective diffusion coefficient of solute in porous media and the geometry parameter characterizing the media. The results are consistent with the empirical equations analogous to Archie's law and are expected to be applied to prediction of effective diffusion coefficient.

Algorithms↗
PubMed2001

[Cloning and expression of MGMT cDNA and analysis of the DNA repair activity of the recombinant protein].

A cDNA encoding human O6-methylguanine-DNA methyltranferase (MGMT) was cloned from Hela S3 cells and the sequence is identical with the published data. The MGMT cDNA was inserted into the expression vector pET-21a and transformed into E. coli BL21 (DE3). A 24 kD protein was expressed after IPTG induction. Essays using lethal dose of alkylating agents indicate that expression of MGMT protein can repair the DNA mutations of the recombinant bacteria produced by alkylating agents.

Cloning, Molecular↗
PubMed2000

Enantiomeric ruthenium(II) complexes binding to DNA: binding modes and enantioselectivity.

A series of enantiomerically pure polypyridyl ruthenium(II) complexes, delta- and lambda-[Ru(bpy)2 (HPIP)](PF6)2 (delta-1 and lambda-1; bpy=2,2'-bipyridine, HPIP = 2-(2-hydroxyphenyl)imidazo[4,5-f][1,10]phenanthroline), delta and lambda-[Ru(bpy)2(HNAIP)](PF6)2 (delta-2 and lambda-2; HNAIP = 2-(2-hydroxy-1-naphthyl)imidazo[4,5-f][1,10]phenanthroline), delta- and lambda-[Ru(bpy)2 (HNOIP)](PF6)2 (delta-3 and lambda-3; HNOIP = 2-(2-hydroxy-5-nitrophenyl)imidazo[4,5-f][1,10]phenanthroline), and delta- and lambda-[Ru(bpy)2(DPPZ)](PF6)2 (delta-4 and lambda-4; DPPZ= dipyridophenazine), have been synthesized. Binding behavior of these chiral complexes to calf thymus DNA (CT-DNA) has been investigated by electronic absorption, steady-state emission, and circular dichroism spectroscopies, as well as by viscosity measurements and equilibrium dialysis binding studies. Several points came from the results. (1) The DNA-binding properties were distinctly different for the [Ru(bpy)2L]2+ (L=HPIP, HNAIP, HNOIP) series of ruthenium(II) complexes, which indicates that the photophysical behavior of the complexes on binding to DNA can be modulated through ligand design. (2) Different binding rates of individual enantiomers of complexes 1 and 4 to DNA were observed through dialysis experiments. The lambda enantiomer bound more rapidly than the lambda enantiomer and their different intercalative binding geometries were suggested to be responsible. (3) Both delta-2 and lambda-2 bound weakly to CT-DNA; delta-2 may bind through a partial intercalation mode, whereas lambda-2 may bind in the DNA groove. (4) There was no noticeable enantioselectivity for complexes 1, 3, and 4 on binding to CT-DNA. Both of their enantiomers can intercalate into DNA base pairs. It is noted that delta-3 and lambda-3 exhibited almost identical spectral changes on addition of CT-DNA, and a similar binding manner of the isomers to the double helix was proposed.

Binding Sites↗
PubMed2000

Synthesis, characterization and DNA binding of ruthenium(II) complexes containing the atatp ligand.

Acenaphtheno[1,2-b]-1,4,8,9-tetraazatriphenylene (atatp) and its complexes [Ru(L)2atatp](ClO4)2 x nH2O (L = 2,2'-bipyridine (bpy), n=2 (1); 1,10-phenanthroline (phen), n=2 (2); and 2,9-dimethyl-1,10-phenanthroline (dmp), n=1 (3)) have been synthesized and characterized by elemental analyses and 1H NMR. The spectral and electrochemical properties of these complexes are also examined. Complexes 1 and 2 display bright luminescence in acetonitrile but very weak luminescence in water solution. However, complex 3 is not luminescent in either solvent. The interaction of the complexes with calf thymus DNA (CT-DNA) has been studied by absorption, emission and viscosity measurements. The intrinsic binding constants of complexes 1 and 2 are 7.6 x 10(4) and 8.8 x 10(4) M(-1) respectively. The relatively low affinities of complexes 1 and 2 with DNA may arise from the atatp ligand, indicating that the size and shape of the intercalated ligand have a marked effect on the strength of interaction. Complexes 1 and 2 bind with CT-DNA in an intercalative mode but complex 3 in a non-intercalative one, showing that changing the ancillary ligand affects not only the binding magnitude, but also the binding mode of the interaction.

Acenaphthenes↗
PubMed2000

Parathyroid hormone-related peptide is involved in protection against invasion of tooth germs by bone via promoting the differentiation of osteoclasts during tooth development.

In order to elucidate the role of parathyroid hormone-related peptide (PTHrP) in tooth development, we treated tooth germ explants of mouse molars with antisense phosphorothioate-oligodeoxynucleotide (ODN) against PTHrP. Antisense ODN-treatment of the explants resulted in the invasion of the tooth germs by bone. The number of tartrate-resistant acid phosphatase (TRAP)-positive cells around the tooth germs in antisense ODN-treated explants was much lower than that of the control explants. Electron microscopic examination suggested that the antisense ODN-treatment inhibited differentiation of osteoclasts. Treatment of the explants with bisphosphonate or vitamin K2, inhibitors of the differentiation of osteoclasts, induced the invasion by bone into the tooth germs as observed in the antisense ODN-treated explants. The results obtained suggest that PTHrP is involved in the mechanism protecting tooth germs from bone invasion by promoting the differentiation of osteoclasts around them.

Animals↗