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Biomedical subjects

Y Q Zhu

Publications and source records attributed to Y Q Zhu.

At least 19 recordsLinked to original sources
PubMed2004

Novel nanoscale architectures: coated nanotubes and other nanowires.

Research has demonstrated that the structure and properties of a nanoscale system are inextricably linked. The advent of nanoscale research in 1991 relied upon nanoscale material production through random formation techniques, such as arc discharge, and the inherent properties and morphology of the system were therefore difficult to control. This article reviews some of the methods and ideas that have developed since the inception of nanotechnology, leading to fine control over the morphology of nanoscale systems and highlighting some interesting nanoscale architecture.

Coated Materials, Biocompatible↗
PubMed2001

[Establishing a FEM of mandibular first molar and stress analysis].

OBJECTIVE: Establishing a finite element model of mandibular first molar with analysis of the stress distribution to each of the tooth parts on the model. METHODS: The right mandibular first molar in vitro was scanned and the image was processed. The three dimensional finite-element model was established by the special software and loaded on it. RESULTS: Stress distribution on each part of the tooth was obtained. The maximum values of compressive stress, tensile stress and mises stress were calculated. CONCLUSION: In the research and analysis of the tooth stress, the finite element method is simple, effective, safe and reliable.

English Abstract↗
PubMed2001

[Experimental study on apical sealing ability of Sankin hydroxyapatite root canal sealer].

OBJECTIVE: To compare the apical sealing ability of Sankin hydroxyapatite root canal sealer with traditional root canal sealers. METHODS: Determination of the length of apical dye leakage by methylene leakage test. RESULTS: The length of apical dye leakge of Sankin hydroxyapatite root canal sealer was 2.40 mm, that of iodoform paste and zinc oxide eugenol paste was 4.37 mm and 5.80 mm,respectively. There was no significant difference between iodoform paste and zinc oxide-eugenol paste (P>0.05);whereas there was significant difference between Sankin hydroxyapatite root canal sealer and iodoform paste or zinc oxide eugenol paste(P<0.01). CONCLUSION: Sankin hydroxyapatite root canal sealer has better apical sealing ability than traditional root canal sealers.

English Abstract↗
PubMed1999

Characterization of a Pseudomonas aeruginosa efflux pump contributing to aminoglycoside impermeability.

Pseudomonas aeruginosa can employ many distinct mechanisms of resistance to aminoglycoside antibiotics; however, in cystic fibrosis patients, more than 90% of aminoglycoside-resistant P. aeruginosa isolates are of the impermeability phenotype. The precise molecular mechanisms that produce aminoglycoside impermeability-type resistance are yet to be elucidated. A subtractive hybridization technique was used to reveal gene expression differences between PAO1 and isogenic, spontaneous aminoglycoside-resistant mutants of the impermeability phenotype. Among the many genes found to be up-regulated in these laboratory mutants were the amrAB genes encoding a recently discovered efflux system. The amrAB genes appear to be the same as the recently described mexXY genes; however, the resistance profile that we see in P. aeruginosa is very different from that described for Escherichia coli with mexXY. Direct evidence for AmrAB involvement in aminoglycoside resistance was provided by the deletion of amrB in the PAO1-derived laboratory mutant, which resulted in the restoration of aminoglycoside sensitivity to a level nearly identical to that of the parent strain. Furthermore, transcription of the amrAB genes was shown to be up-regulated in P. aeruginosa clinical isolates displaying the impermeability phenotype compared to a genotypically matched sensitive clinical isolate from the same patient. This suggests the possibility that AmrAB-mediated efflux is a clinically relevant mechanism of aminoglycoside resistance. Although it is unlikely that hyperexpression of AmrAB is the sole mechanism conferring the impermeability phenotype, we believe that the Amr efflux system can contribute to a complex interaction of molecular events resulting in the aminoglycoside impermeability-type resistance phenotype.

Anti-Bacterial Agents↗
PubMed1999

Seven novel methylation guide small nucleolar RNAs are processed from a common polycistronic transcript by Rat1p and RNase III in yeast.

Through a computer search of the genome of the yeast Saccharomyces cerevisiae, the coding sequences of seven different box C/D antisense small nucleolar RNAs (snoRNAs) with the structural hallmarks of guides for rRNA ribose methylation have been detected clustered over a 1.4-kb tract in an inter-open reading frame region of chromosome XIII. The corresponding snoRNAs have been positively identified in yeast cells. Disruption of the nonessential snoRNA gene cluster specifically suppressed the seven cognate rRNA ribose methylations but did not result in any growth delay under the conditions of yeast culture tested. The seven snoRNAs are processed from a common polycistronic transcript synthesized from an independent promoter, similar to some plant snoRNAs but in marked contrast with their vertebrate functional homologues processed from pre-mRNA introns containing a single snoRNA. Processing of the polycistronic precursor requires nucleases also involved in rRNA processing, i.e., Rnt1p and Rat1p. After disruption of the RNT1 gene, the yeast ortholog of bacterial RNase III, production of the seven mature snoRNAs was abolished, while the polycistronic snoRNA precursor accumulated. In cells lacking functional Rat1p, an exonuclease involved in the processing of both pre-rRNA and intron-encoded snoRNAs, several processing intermediates of the polycistronic precursor accumulated. This allowed for the mapping in the precursor of the presumptive Rnt1p endonucleolytic cuts which provide entry sites for subsequent exonucleolytic trimming of the pre-snoRNAs. In line with known properties of double-stranded RNA-specific RNase III, pairs of Rnt1p cuts map next to each other on opposite strands of long double-helical stems in the secondary structure predicted for the polycistronic snoRNA precursor.

Base Sequence↗
PubMed1998

The 16-kDa alpha-crystallin (Acr) protein of Mycobacterium tuberculosis is required for growth in macrophages.

Although the 16-kDa alpha-crystallin homologue of Mycobacterium tuberculosis (MTB) is the dominant protein produced by stationary phase cultures in vitro, it is undetectable in logarithmically growing cultures. By growing bacilli at defined oxygen concentrations, acr transcription was shown to be strongly induced by mildly hypoxic conditions. Acr expression also was found to be induced during the course of in vitro infection of macrophages. The acr gene was replaced with a hygromycin resistance cassette by allelic exchange in MTB H37Rv. The resulting Deltaacr::hpt strain was shown to be equivalent to wild-type H37Rv in in vitro growth rate and infectivity but was significantly impaired for growth in both mouse bone marrow derived macrophages and THP-1 cells. In addition to its proposed role in maintenance of long-term viability during latent, asymptomatic infections, these results establish a role for the Acr protein in replication during initial MTB infection.

Animals↗
PubMed1998

[Effect on preparing curved artificial root cancals with five handle endodonic instruments I.comparison of cutting ability]

OBJECTIVE: To compare the cutting ability of five handle endodontic instruments. METHODS: The speciments weight loss following serial preparation of artificial root canal were measured with electronic analysis balance. RESULTS: The greatest cutting ability occurred with H file,then with K-flex file,Unifile,K file and K reamer. CONCLUSION: The cutting ability of endodontic instrument is influenced by several factors,such as metallurgical properties,cross-sectional configuration of shaft,flute design and tip design.

Journal Article↗
PubMed1998

[Effect on preparing curved artificial root canal with five handle endodontic instruments II comparision of shaping ability]

OBJECTIVE:To compared the shaping ability of five handle endodontic instruments. METHODS: The canal shape of prepared artificial root canals with five handle endodontic instruments were observed by light-microscope. RESULTS: Apical zips,elbows and perforations were not found. Ledges occurred in speciments of K-Flex group and they were relating to resinous plugs.The apical transportatins were relating to resinous plugs.The apical transportations of K-Flex group and H file group are much greater than other groups. CONCLUSION: Unifile or K file is first choice to prepare curved artificial root canals with routine preparation technique by comprehensive evaluaion of the cutting ability and shaping ability of five handle endodontic instruments.

Journal Article↗
PubMed1998

[A study of the shape of prepared canal of commonly used hand endodontic instruments]

OBJECTIVE:Straight or slightly curved single root canals of teeth (<20 degree) were instrumentated with three commonly the hand endodontic instruments,which included K reamer,K file and H filel.The shape of prepared canal and root canal deviation at three levels were measured by computerized digital image processing program.The results demostrated that any significant differences were not found on root canal deviation in either labio-lingual or mesiodistal direction at each level,and that the shape of prepared canal was not different significantly.Apical transportation of the severely curved artificial root canals(25-30 degree) showed that H file was the most severe,K reamer was the least.It is suggested in this article how we select endodontic instruments rationally and effectively.

Journal Article↗
PubMed1997

Pharmacokinetics of bendazac lysine in 10 Chinese young men.

AIM: To compare the pharmacokinetics of domestic and imported tablets of bendazao lysine (BL). METHODS: A single oral dose of 500 mg BL of this 2 kinds of tablets was given to 10 Chinese volunteers of Han nationality in a randomized crossover study. Plasma levels were determined with HPLC-UV method. Data were analyzed automatically by using a CAPP program on microcomputer. RESULTS: The plasma concentration-time curve was fitted to 2-compartment open model, and the major pharmacokinetic parameters of domestic and imported BL tablets were shown respectively as following: Cmax 66 +/- 16 and 65 +/- 8 mg.L-1; Tmax 0.98 +/- 0.22 and 0.98 +/- 0.21 h; T1/2 beta 6.2 +/- 1.8 and 6.2 +/- 1.7 h; AUC 335 +/- 47 and 337 +/- 58 mg.h.L-1. There was no significant difference between domestic and imported tablets. The bioavailability of the domestic vs that of the imported tablet was 99 +/- 12%. The unchanged BL in urine were about 5.4% and 5.6% respectively of the dosage in 24 h after a single oral dose. CONCLUSION: The two kinds of tablets had the same biological effects.

Adult↗
PubMed1996

Inhibitory RNA ligand to reverse transcriptase from feline immunodeficiency virus.

High-affinity, high-specificity RNA ligands for reverse transcriptase from feline immunodeficiency virus (FIV) were isolated from an RNA library by the SELEX (Systematic Evolution of Ligands by EXponential enrichment) procedure. The selected RNA ligands bound to FIV reverse transcriptase with dissociation constants in the nanomolar range. One of the ligands was a potent inhibitor of the RNA-dependent DNA polymerase activity of both the recombinant and the virion-derived FIV reverse transcriptase. It also inhibited the reverse transcriptase from an FIV mutant that is resistant to 3'-azido-3'-deoxythymidine (AZT). The inhibition of FIV reverse transcriptase was competitive with respect to template-primer and noncompetitive with respect to deoxyribonucleoside 5'-triphosphates. This ligand was specific for the FIV enzyme and did not inhibit other reverse transcriptases tested (avian myeloblastosis virus, Moloney murine leukemia virus, and human immunodeficiency virus type 1).

Animals↗
PubMed1996

Selection and characterization of a mutant of feline immunodeficiency virus resistant to 2',3'-dideoxycytidine.

We have selected and plaque purified a mutant of feline immunodeficiency virus (FIV) that is resistant to 2',3'-dideoxycytidine (ddC). This mutant was selected in cultured cells in the continuous presence of 25 microM ddC. The mutant, designated DCR-5c, was fourfold resistant to ddC, threefold resistant to 2',3'-dideoxyinosine, and more than fourfold resistant to phosphonoformic acid. DCR-5c displayed little or no resistance to (-)-beta-2',3'-dideoxy-3'-thiacytidine, 3'-azido-3'-deoxythymidine, or 9-(2-phosphonylmethoxyethyl) adenine. Reverse transcriptase purified from DCR-5c was less susceptible to inhibition by ddCTP, phosphonoformic acid, ddATP, or azido-dTTP than the wild-type FIV reverse transcriptase. Sequence analysis of DCR-5c revealed a single base change (G to C at nucleotide 2342) in the reverse transcriptase-encoding region of FIV. This mutation results in substitution of His for Asp at codon 3 of FIV reverse transcriptase. The role of this mutation in ddC resistance was confirmed by site-directed mutagenesis.

Amino Acid Sequence↗
PubMed1996

Mutants of feline immunodeficiency virus resistant to 2',3'-dideoxy-2',3'-didehydrothymidine.

We selected mutants of feline immunodeficiency virus (FIV) that are resistant to 2',3'-dideoxy-2',3'-didehydrothymidine (d4T). Two mutants were selected in cultured cells with a stepwise increase in d4T concentration, resulting in mutants able to replicate in 100 microM d4T. These mutants were three- to sixfold more resistant to d4T than wild-type FIV. They were also cross-resistant to 3'-azido-3'-deoxythymidine (AZT), 3'-fluoro-2',3'-dideoxythymidine, 2',3'-dideoxycytidine, 2',3'-dideoxyinosine, and 9-(2-phosphonylmethoxyethyl)adenine, and they were highly resistant to phosphonoformic acid (PFA). Plaque-purified mutants were isolated from each of the mutant populations. The mutant phenotype was stable, because both of the plaque-purified mutants remained d4T resistant even after three passages in the absence of d4T. One of the plaque-purified mutants, designated D4R-3c, was further characterized. Compared with wild-type reverse transcriptase (RT), RT purified from D4R-3c was 3-fold resistant to inhibition by the 5'-triphosphate of d4T, 10-fold resistant to inhibition by the 5'-triphosphate of AZT, and 6-fold resistant to PFA. D4R-3c had a single point mutation in the RT-encoding region of the pol gene at position 2474, resulting in a Val to Ile mutation at codon 47 of the FIV RT. The role of this mutation in d4T resistance was confirmed by site-directed mutagenesis.

Animals↗
PubMed1994

Multiple-drug-resistant mutants of feline immunodeficiency virus selected with 2',3'-dideoxyinosine alone and in combination with 3'-azido-3'-deoxythymidine.

Mutants of feline immunodeficiency virus (FIV) were selected in cell culture in the continuous presence of 10 microM (each) 3'-azido-3'-deoxythymidine (AZT) and 2',3'-dideoxyinosine (ddI). These mutants (AIR-1 and AIR-3) displayed a 13-fold resistance to AZT but had less than a 2-fold decrease in susceptibility to ddI. Interestingly, the AIR mutants were cross-resistant to phosphonoformate (PFA) and were hypersensitive to 2',3'-dideoxycytidine (ddC). Mutants of FIV were also selected in the presence of 10 microM ddI alone (DIS-1, DIS-2c), and these displayed a two- to fourfold decrease in susceptibility to ddI. Like the mutants selected with the combination of AZT plus ddI, DIS-1 and DIS-2c were cross-resistant to PFA and were hypersensitive to ddC. However, they remained as susceptible as wild-type FIV to AZT. Thus, the mutants selected with the combination of AZT plus ddI have phenotypes which reflect those obtained by selection with these drugs individually.

Animals↗