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Qian Liu

Publications and source records attributed to Qian Liu.

At least 55 records · Page 3Linked to original sources
PubMed2005

Optimisation of the fluorescein diacetate antibacterial assay.

The fluorescein diacetate (FDA) antibacterial assay relies on the cleavage of fluorescein diacetate by metabolically active bacteria. The recent finding that microbiological media can lead to significant levels of cleavage has reduced the reliability of the assay. Using the nucleophilic scavengers N-ethylmaleimide and maleic anhydride, we have demonstrated that this abiotic cleavage is most likely due to nucleophiles such as cysteine and histidine commonly present in the media. To increase the reliability of the assay we have modified the original assay conditions to include use of dilute medium (peptone 0.2% w/v, yeast extract 0.1% w/v and NaCl 0.1% w/v) in a non-nucleophilic buffer and overnight incubation of the medium after addition of antibacterial agents. The optimised fluorescein diacetate assay has been used to determine the MIC of gentamicin, tetracycline and chloramphenicol for Escherichia coli, Staphyloccocus aureus and Pseudomonas aeruginosa and gave quantitative results that were reproducible and consistent with published data.

Amino Acids↗
PubMed2005

Candidate PET radioligands for cannabinoid CB1 receptors: [18F]AM5144 and related pyrazole compounds.

INTRODUCTION: The mammalian brain contains abundant G protein-coupled cannabinoid CB(1) receptors that respond to Delta(9)-tetrahydrocannabinol, the active ingredient of cannabis. The availability of a positron emission tomography (PET) radioligand would facilitate studies of the addictive and medicinal properties of compounds that bind to this receptor. Among the known classes of ligands for CB(1) receptors, the pyrazoles are attractive targets for radiopharmaceutical development because they are antagonists and are generally less lipophilic than the other classes. METHODS: A convenient high-yield synthesis of N-(4-[(18)F]fluorophenyl)-5-(4-bromophenyl)-1-(2,4-dichlorophenyl)-1H-pyrazole-3-carboxamide (AM5144) was devised by coupling the appropriate pyrazole-3-carboxyl chloride compound with 4-[(18)F]fluoroaniline. The labeled precursor was synthesized from 1-[(18)F]fluoro-4-nitrobenzene in 60% radiochemical yield for 10 min using an improved procedure involving sodium borohydride reduction with cobalt chloride catalysis. The product was purified by HPLC to give a specific activity >400 mCi/micromol and a radiochemical purity >95%, and a PET study was conducted in a baboon. RESULTS: Although the regional uptake of AM5144 in baboon brain was consistent with binding to cannabinoid CB(1) receptors, absolute uptake at <0.003% injected radioactivity per cubic centimeter was lower than the previously reported uptake of the radioiodinated pyrazole AM281. CONCLUSIONS: The relatively poor brain uptake of AM5144 and other pyrazole CB(1) receptor ligands is not surprising because of their high lipophilicity as compared with most brain PET radiotracers. However, for nine pyrazole compounds for which rodent data are available, brain uptake and calculated logP values are not correlated. Thus, high logP values should not preclude evaluation of radiotracers for targets such as the CB(1) receptor that may require very lipophilic ligands.

Aniline Compounds↗
PubMed2005

Total synthesis of scutellarin-7-O-glucuronide.

Scutellarin-7-O-glucuronide (1) has been synthesized from 2-hydroxyl-4,5,6-trimethoxyacetophenone through eight steps, including Michael addition, cyclization, hydrogenation, hydroxyl protection, deprotection, etc. The overall yield of 13% is much higher than that reported (0.6%) by L. Farkas, G. Mezey-Vàndor et al. in 1974.

Acetophenones↗
PubMed2005

Determination of the molecular weight distribution of the PEGylated bovine hemoglobin (PEG-bHb).

The method to determine the average molecular weight and distribution of molecular weight of the PEGylated hemoglobin (PEG-bHb) and their molecular weight of polypeptides in PEG-bHb with UV absorbance (UV), light scattering (LS) and refractive index (RI) detectors is described in this paper. The results indicate that when molar ratio of PEG to hemoglobin is 7:1, the average molecular weight of PEG-bHb (M(CP) is 95 kDa, the average molecular weigh of protein moiety in PEG-bHb (M(P)) is 68 kDa, and their distribution is from 48-157 kDa and 44-121 kDa, respectively; when the molar ratio is 10:1, the M(CP) is 106 kDa, the M(P) is 70kDa, and their distribution is from 56-216kDa, 49-135kDa, respectively; when the molar ratio is 13:1, the M(CP) is 73kDa, and their distribution is from 81-272 kDa and 41-144 kDa, respectively. It has been proved that this method is a simple and reliable way for the determination of average molecular weight and distribution of molecular weight of PEGlyted hemoglobin. This experiment also suggests that there exists not only aggregation in the frontal of elution peak of PEG-bHb, but dissociation of tetramer of hemoglobin into dimmer in the tail of elution peak, and the degree of aggregation is depended on the molar ratio of PEG to hemoglobin due to the present of diol PEG and the dissociation is dependant on the concentration of hemoglobin.

Animals↗
PubMed2005

Solution structure of the carbon storage regulator protein CsrA from Escherichia coli.

The carbon storage regulator A (CsrA) is a protein responsible for the repression of a variety of stationary-phase genes in bacteria. In this work, we describe the nuclear magnetic resonance (NMR)-based structure of the CsrA dimer and its RNA-binding properties. CsrA is a dimer of two identical subunits, each composed of five strands, a small alpha-helix and a flexible C terminus. NMR titration experiments suggest that the beta1-beta2 and beta3-beta4 loops and the C-terminal helix are important elements in RNA binding. Even though the beta3-beta4 loop contains a highly conserved RNA-binding motif, GxxG, typical of KH domains, our structure excludes CsrA from being a member of this protein family, as previously suggested. A mechanism for the recognition of mRNAs downregulated by CsrA is proposed.

Amino Acid Sequence↗
PubMed2005

Diverse gene expression pattern during 5-fluorouridine-induced apoptosis.

The purpose of this study was to establish experimental conditions to produce apoptosis by the fluorinated pyrimidine 5-fluorouridine and to examine the changes in gene expression that occurred during cell death. HCT-116 colorectal carcinoma cells were exposed to 10 microM 5-fluorouridine alone or in the presence of 1 mM uridine, 30 microM thymidine or both uridine and thymidine. A time-dependent increase in the percentage of apoptotic cells and a decrease in the percentage of viable cells were observed when the cells were treated with 5-fluorouridine in the absence of uridine (p < 0.001) but not in the presence of uridine. cDNA microarray analysis was used to study the expression of 1,200 different genes during apoptosis by 5-flurouridine. The expression of 33 genes was upregulated by 5-fold or greater at 16 and 24 h of 5-fluorouridine exposure. The largest cluster of upregulated genes included a group of genes classified as growth factors, cytokines and chemokines (e.g. interleukin-3, interleukin-4, B-cell growth factor 1 and stem cell growth factor). The expression of MIC-1 increased up to 100-fold during 5-flurouridine exposure. One hundred and twenty-four genes were downregulated by 5-fold or greater following exposure to 5-fluorouridine. The downregulated genes were distributed throughout the six different classifications on the array. Our data demonstrate a diverse pattern of gene expression during the fluorouridine-induced apoptosis and suggest that mechanisms besides a global inhibition of RNA synthesis/ processing contribute to the RNA-directed cytotoxicity of fluoropyrimidines.

Analysis of Variance↗
PubMed2005

Isolation of low-molecular-weight glutenin subunit genes from wild emmer wheat (Triticum dicoccoides).

Three low-molecular-weight glutenin subunit (LMW-GS) genes, designated LMW-Td1, LMW-Td2 and LMW-Td3, were isolated from wild emmer wheat (Triticum dicoccoides), which is the tetraploid progenitor of common wheat (T. aestivum). The complete nucleotide sequence lengths of LMW-Td1, LMW-Td2 and LMW-Td3 are 858, 900 and 1062 bp, respectively. LMW-Td1 and LMW-Td3 can encode proteins with 284 and 352 amino acid residues, respectively, whereas LMW-Td2 is a putative pseudogene due to the presence of 3 inframe stop codons in its C-terminal domain. The deduced protein sequences of the 3 genes share the same typical polypeptide structures with known LMW-GS genes containing 8 cysteines in the mature protein domains. LMW-Td1 was clearly distinguished from all known LMW-GS genes, and considered as a novel LMW-GS gene. Two hydrophobic motifs (i.e. PIIIL and PVIIL) were observed in the repetitive domain of LMW-Td3. Sequence comparison indicates that sequences of the 3 LMW-GS genes from this study are strongly similar to known LMW-GS genes. Our phylogenetic analysis suggests that LMW-Td1 and LMW-Td2 are homologous with genes on chromosome 1A, and LMW-Td3 is closely related to genes on chromosome 1B.

Amino Acid Sequence↗
PubMed2005

[The effect of double-balloon and triple-channel transurethral perfusion and drainage catheter on patient's sperm quality in the therapy of chronic prostatitis].

OBJECTIVE: To investigate the clinical improvement of patient's sperm quality after the therapy on chronic prostatitis (CP) with double-balloon and triple-channel transurethral perfusion and drainage catheter. METHODS: Double-balloon and triple-channel transurethral perfusion and drainage catheter along with millimeter wave physical therapy and intravenous infusion with antibiotics were adopted to treat 58 CP patients. The patient's sperm quality was analyzed pre- and post- therapy by Computer-assisted Sperm Analysis Instrument. RESULTS: The comparison of patient's sperm quality parameters between pre- and post-therapy: percentage of motile sperm (42.66 +/- 17.12)% vs (55.23 +/- 14.79)%, grade a sperm (12.63 +/- 12.50)% vs (29.84 +/- 14.86)%, grade a + b sperm (29.14 +/-15.04)% vs (42.28 +/- 12.67)%, amplitude of the lateral head displacement (ALH) (3.04 +/- 1.55) microm vs (2.69 +/- 1.67) microm. The differences between pre- and post-therapy in above mentioned sperm parameters were all statistically significant (P < 0.01). While the differences among other sperm parameters were not statistically significant (P > 0.05). CONCLUSION: Timely and effective therapy with transurethral perfusion and drainage catheter can improve the patient's sperm quality significantly, but sperm movement function cannot resume completely in a short time.

Adult↗
PubMed2005

[Spatial orientation interaction mechanism of three component complex of protein--BSA/SDS/Azur a system].

The interaction of bovine serum albumin (BSA), sodium dodecyl sulphate (SDS) and Azur A(AA) was studied by spectral probe. The influence of the molar ratio of SDS/BSA on the absorption spectra of BSA-SDS-AA complex was investigated. It was found that the new absorption peak and color changes generated by BSA-SDS-AA complex arose from the difference in the spatial orientation aggregative degree of AA binding on BSA-SDS-AA complex.

Animals↗
PubMed2004

A mixed epigenetic/genetic model for oligogenic inheritance of autism with a limited role for UBE3A.

The genetic contribution to autism is often attributed to the combined effects of many loci (ten or more). This conclusion is based in part on the much lower concordance for dizygotic (DZ) than for monozygotic (MZ) twins, and is consistent with the failure to find strong evidence for linkage in genome-wide studies. We propose that the twin data are compatible with oligogenic inheritance combined with a major, genetic or epigenetic, de novo component to the etiology. Based on evidence that maternal but not paternal duplications of chromosome 15q cause autism, we attempted to test the hypothesis that autism involves oligogenic inheritance (two or more loci) and that the Angelman gene (UBE3A), which encodes the E6-AP ubiquitin ligase, is one of the contributing genes. A search for epigenetic abnormalities led to the discovery of a tissue-specific differentially methylated region (DMR) downstream of the UBE3A coding exons, but the region was not abnormal in autism lymphoblasts or brain samples. Based on evidence for allele sharing in 15q among sib-pairs, abnormal DNA methylation at the 5'-CpG island of UBE3A in one of 17 autism brains, and decreased E6-AP protein in some autism brains, we propose a mixed epigenetic and genetic model for autism with both de novo and inherited contributions. The role of UBE3A may be quantitatively modest, but interacting proteins such as those ubiquitinated by UBE3A may be candidates for a larger role in an oligogenic model. A mixed epigenetic and genetic and mixed de novo and inherited (MEGDI) model could be relevant to other "complex disease traits".

Alleles↗
PubMed2004

Metabolic imaging of tumors using intrinsic and extrinsic fluorescent markers.

One of the biochemical "hallmarks" of malignancy is enhanced tumor glycolysis, which is primary due to the overexpression of glucose transporters (GLUTs) and the increased activity of mitochondria-bound hexokinase in tumors. Easy methods for assessing glucose utilization in vitro and in vivo should find widespread application in biological and biomedical studies, as illustrated by the adoption of FDG PET imaging in medicine. We have recently synthesized a new NIR fluorescent pyropheophorbide conjugate of 2-deoxyglucose (2DG), Pyro-2DG, as a GLUT-targeted photosensitizer. In this study, we have evaluated the in vivo uptake of Pyro-2DG and found that Pyro-2DG selectively accumulated in two tumor models, 9L glioma in the rat and c-MYC-induced mammary tumor in the mouse, compared to surrounding normal muscle tissues at a ratio of about 10:1. By simultaneously performing redox ratio and fluorescence imaging, a high degree of correlation between the PN/(Fp+PN) redox ratio, where PN denotes reduced pyridine nucleotides (NADH) and Fp denotes oxidized flavoproteins, and the Pyro-2DG uptake was found in both murine tumor models, indicating that Pyro-2DG could serve as an extrinsic NIR fluorescent metabolic index for the tumors. The fact that only a low level of correlation was observed between the redox ratio and the uptake of Pyro-acid (the free fluorophore without the 2-deoxyglucose moiety) supports the hypothesis that Pyro-2DG is an index of the mitochondrial status (extent of PN reduction) of a tumor.

Animals↗
PubMed2004

Discriminative stimulus effects in rats of SR-141716 (rimonabant), a cannabinoid CB1 receptor antagonist.

OBJECTIVE: To examine the discriminative stimulus effects of (i) the cannabinoid CB(1) receptor antagonist SR-141716 (SR, 5.6 mg/kg) and vehicle, and (ii) the cannabinoid receptor agonist Delta(9)-THC (THC, 1.8 mg/kg) and vehicle using a discriminated taste aversion (DTA) procedure. METHODS: Two groups of rats ( n=6) were trained to discriminate between these drugs and vehicle in DTA ( t'=20 min). The 30-min drinking bout of tap water following drug (SR or THC) treatment was followed by an injection of lithium chloride (LiCl, 120 mg/kg) in the experimental animals. When offered water after vehicle pretreatment, experimental animals subsequently were given IP saline (NaCl, 10 ml/kg). Post-drinking treatment for controls ( n=6) was NaCl, irrespective of the pretreatment condition (SR, THC or vehicle). Additional water was provided during the afternoon (30 min) with no other manipulations. Food was available ad lib at all times. When the discriminations were established other doses and drugs were examined ( t'=20 min). In testing there were no post-drinking treatments. RESULTS: The SR-related analog AM-251 (dose range: 1-5.6 mg/kg) substituted for SR, whereas other drugs such as the cannabinoid CB(2) receptor antagonist SR-144528 (3 and 10 mg/kg), THC (1-10 mg/kg), flumazenil (1-10 mg/kg), naloxone (1-10 mg/kg), morphine (10 and 18 mg/kg) and d-amphetamine (1 and 3 mg/kg) did not. There was a dose-related attenuation of SR-induced suppression of drinking when THC (1.8-10 mg/kg) was given together with SR (5.6 mg/kg). In the THC trained rats, SR (1-10 mg/kg), morphine (10 and 18 mg/kg) and d-amphetamine (1 and 3 mg/kg) did not substitute for THC. SR (1 mg/kg) attenuated the THC (1.8 mg/kg) induced suppression of drinking. Together with 3 mg/kg SR and 1.8 mg/kg THC, drinking was roughly equally suppressed in both the experimental group and the controls. CONCLUSION: SR-141716 induces a discriminative stimulus complex in DTA that shows potential for further examination of cannabinoid receptor antagonism.

Animals↗
PubMed2004

Laser speckle imaging of blood flow in microcirculation.

Monitoring the spatio-temporal characteristics of microcirculation is crucial for studying the functional activities of biotissue and the mechanism of disease. However, conventional methods used to measure blood flow suffer from limited spatial resolution or the injection of exogenous substances or the need of scanning to obtain the dynamic of regional blood flow. Laser speckle imaging (LSI) technique makes up these disadvantages by obtaining the regional blood flow distribution with high spatio-temporal resolution without the need to scan. In this paper, LSI was introduced to investigate the dynamic responses of the rat mesenteric microcirculation to an incremental dose of phentolamine. The results showed that when the dose of phentolamine was less than 4 microg ml(-1), local application of phentolamine on the mesentery would increase the blood perfusion as the concentration increased. When the dose increased further, the improvement decreased. At a dose of 200 microg ml(-1), a microcirculation impediment was caused. At the same time, different responses between veinules and arterioles were manifested. These suggested that LSI is promising to be a useful contribution to drug development and testing.

Animals↗
PubMed2004

A high-throughput method to monitor the expression of microRNA precursors.

microRNAs (miRNAs) are small, functional, non-coding RNAs. miRNAs are transcribed as long primary transcripts (primary precursors) that are processed to the approximately 75 nt precursors (pre-miRNAs) by the nuclear enzyme Drosha. The approximately 22 nt mature miRNA is processed from the pre-miRNA by the RNase III Dicer. The vast majority of published studies to date have used northern blotting to detect the expression of miRNAs. We describe here a sensitive, high throughput, real-time PCR assay to monitor the expression of miRNA precursors. Gene-specific primers and reverse transcriptase were used to convert the primary precursors and pre-miRNAs to cDNA. The expression of 23 miRNA precursors in six human cancer cell lines was assayed using the PCR assay. The miRNA precursors accumulated to different levels when compared with each other or when a single precursor is compared in the various cell lines. The precursor expression profile of three miRNAs determined by the PCR assay was identical to the mature miRNA expression profile determined by northern blotting. We propose that the PCR assay may be scaled up to include all of the 150+ known human miRNA genes and can easily be adaptable to other organisms such as plants, Caenorhabditis elegans and Drosophila.

Blotting, Northern↗
PubMed2004

Evaluation and application of multiple scoring functions for a virtual screening experiment.

In order to identify novel chemical classes of factor Xa inhibitors, five scoring functions (FlexX, DOCK, GOLD, ChemScore and PMF) were engaged to evaluate the multiple docking poses generated by FlexX. The compound collection was composed of confirmed potent factor Xa inhibitors and a subset of the LeadQuest screening compound library. Except for PMF the other four scoring functions succeeded in reproducing the crystal complex (PDB code: 1FAX). During virtual screening the highest hit rate (80%) was demonstrated by FlexX at an energy cutoff of -40 kJ/mol, which is about 40-fold over random screening (2.06%). Limited results suggest that presenting more poses of a single molecule to the scoring functions could deteriorate their enrichment factors. A series of promising scaffolds with favorable binding scores was retrieved from LeadQuest. Consensus scoring by pair-wise intersection failed to enrich the hit rate yielded by single scorings (i.e. FlexX). We note that reported successes of consensus scoring in hit rate enrichment could be artificial because their comparisons were based on a selected subset of single scoring and a markedly reduced subset of double or triple scoring. The findings presented in this report are based upon a single biological system and support further studies.

Animals↗
PubMed2004

Pharmacodynamic study of polyethylene glycol conjugated bovine hemoglobin (PEG-bHb) in rats.

The purpose of this study was to determine the pharmacodynamics of polyethylene glycol (PEG) conjugation on stroma-free bovine hemoglobin, hemorrhage shock, and exchange transfusion rat models were used. In both rat models, blood pressure increased in 6% PEG-bHb treated animals was significantly higher than dextran 70, even than whole blood (isovolume of hemorrhage) transfusion. Six percent PEG-BHb could ameliorate the micro-circulation of the experimental animals markedly, including reducing the blood viscosity and improving the blood flow. This effect of PEG-bHb was superior to autogenous blood which only recovered 50% blood flow, and there's no effect on blood flow when used isovolumic dextran 70. Tissue oxygenations of rats were evaluated by the oxygen dependent quenching of phosphorescence using an Oxyspot phosphorimeter, and the results showed that capability of oxygen-delivery of PEG-bHb was close to autogenous blood and superior to dextran 70. Based on these effects, the survival rates of animals treated with PEG-bHb were close to that of the whole blood transfusion. And data suggested that half of the hemorrhage transfusion is the reasonable therapeutic dosage. In conclusion, PEG-bHb is an effective blood substitute with powerful tissue oxygenation and blood volume expansion.

Animals↗
PubMed2004

Study of bovine hemoglobin dissociation by multiangle laser light-scattering method.

Hemoglobin (Hb) is an oligomeric protein, composed of four monomeric subunits. Hb molecule may undergo dissociation from a single native tetramer to two dimmers, which is called hemoglobin dissociation. In this article the dissociation of bovine Hb is studied by measurment of the average MW of the samples using the multiangle laser light-scattering method. Advanced multiangle laser light-scattering technique is a powerful method to determine the absolute molecular weights of the protein in solution. Two different methods, microbatch multiangle light-scattering (MALS) and on-line size-exclusion high-performance liquid chromatography light scattering with refractive index detector, are used to measure the average molecular weight of bovine Hb in different concentration respectively. The results of the two methods are agreed well. From the results, it can be concluded that the average molecular weigh of bovine Hb will be about 54 kDa when the bovine Hb concentration is more than 1.5 mg/mL, and will be about 36 kDa when the concentration is less than 0.03 mg/mL. The other conclusion, which can be derived from these results, is that the dissociation of bovine Hb is related with the pH and the tetramer appears to be more stable in the pH range of 6-9.

Animals↗