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Biomedical subjects

C Q Chen

Publications and source records attributed to C Q Chen.

At least 19 recordsLinked to original sources
PubMed2006

Size dependence of Young's modulus in ZnO nanowires.

We report a size dependence of Young's modulus in [0001] oriented ZnO nanowires (NWs) with diameters ranging from 17 to 550 nm for the first time. The measured modulus for NWs with diameters smaller than about 120 nm is increasing dramatically with the decreasing diameters, and is significantly higher than that of the larger ones whose modulus tends to that of bulk ZnO. A core-shell composite NW model in terms of the surface stiffening effect correlated with significant bond length contractions occurred near the {1010} free surfaces (which extend several layers deep into the bulk and fade off slowly) is proposed to explore the origin of the size dependence, and present experimental result is well explained. Furthermore, it is possible to estimate the size-related elastic properties of GaN nanotubes and relative nanostructures by using this model.

Journal Article↗
PubMed2001

TNF receptor-associated factor-2 binding site is involved in TNFR75-dependent enhancement of TNFR55-induced cell death.

TNF recepter-55 is the main mediator of TNF-induced apoptosis. TNF receptor-75-dependent induction or enhancement of cytotoxicity has been explained by intracellular signaling, "ligand passing", or induction of endogenous TNF. To study the function of human TNF receptor-75 (hTR75) and the interaction between human TNF receptor-55 (hTR55) and hTR75 in hTNFalpha-induced cytotoxicity, HEp-2 cells were transfected with bicistronic expression vector of hTR75 and its deletion mutants genes. hTNFalpha-induced cytotoxicity was determined by crystal violet colorimetric method. The expression of hTR75 and its deletion mutants in HEp-2 cells was demonstrated by RT-PCR and indirect ELISA. We found that the overexpressed hTR75 could significantly increase the susceptibility of HEp-2 cells to hTNFalpha which especially required TRAF2 binding site. hTR75 could not only mediate partial hTNFalpha-induced cytotoxicity independently but also fulfill an accessory role in enhancing or synergizing hTR55-mediated cytotoxicity.

Antigens, CD↗
PubMed2001

Dual function of human necrosis factor receptor 75 in cytotoxicity induced by human tumor necrosis factor alpha.

AIM: To study the function of human TNF receptor-75 (hTR75) and the interaction between human TNF receptor-55 (hTR55) and hTR75 in hTNFalpha-induced cytotoxicity. METHODS: HEp-2 cells were transfected with bicistronic expression vector of hTR75 gene, and HEp-2-A75 cells with intrinsic hTR55 and overexpressed hTR75 were obtained. Two hTNFalpha muteins with exclusive specificity for hTR55 or hTR75 were constructed, expressed in high-levels in E coli, and then purified. hTNFalpha-induced cytotoxicity was determined by crystal violet colorimetric method. RESULTS: The expression of hTR75 in HEp-2 cells was demonstrated by RT-PCR and indirect ELISA, and was quantified by binding of [125I]hTNFalpha and Scatchard analysis. The overexpressed hTR75 could markedly increase the susceptibility of HEp-2 cells to hTNFalpha. CONCLUSION: hTR75 could not only partially mediate hTNFalpha-induced cytotoxicity independently but also fulfill an accessory role in enhancing or synergizing hTR55-mediated cytotoxicity. It played a dual function in hTNFalpha-induced cytotoxicity in HEp-2 cells.

Antigens, CD↗
PubMed2001

A novel human tumor necrosis factor alpha mutant showed potent antitumor activity and reduced toxicity in vivo.

AIM: To study the antitumor activity and systemic toxicity of human tumor necrosis factor alpha (hTNFalpha) mutant M2 (R2K-N30S-R32W-L157F-hTNFalpha). METHODS: Mouse sarcoma S180 tumors and hepatoma HAC tumors were implanted into mice, and human urocyst carcinoma CP-3 tumors were implanted into nude mice. The xenografted mice were injected with wild-type hTNFalpha and its mutant M2 at different doses. After 7 d (mice) or 10 d (nude mice) of injection, the tumor weight was measured to calculate the inhibition rate of hTNFalpha and M2. Systemic toxicity experiments were done on Rhesus monkeys by injecting them with wild-type hTNFalpha and mutant M2 respectively for 10 consecutive d. Observations were made on the monkeys both before and after the injection. RESULTS: For mice implanted with sarcoma S180 and hepatoma HAC tumors, the inhibition rate of M2 was similar to that of wild-type hTNFalpha at the dose of 0.025 mg/kg, while for nude mice implanted with human urocyst carcinoma CP-3, the inhibition rate of M2 (45.5 %) was much higher than that of wild-type hTNFalpha (15.5 %). When the dose came to 0.25 and 2.5 mg/kg respectively, however, the inhibition rate of M2 greatly increased (the highest was 75.9 %). The tests of systemic toxicity of hTNFalpha and its mutant M2 in monkeys proved that M2 presented lower toxicity than wild-type hTNFalpha did. CONCLUSION: hTNFalpha mutant M2 not only presented higher antitumor activity than wild-type hTNFalpha did on mouse tumor (S180 and HAC)- and human tumor (CP-3)-implanted mice, but also showed lower systemic toxicity in the Rhesus monkey.

Animals↗
PubMed2001

[Determination of Pb, Zn, Fe and Cd in the crude zinc produced from the imperial smelting furnace by XRF].

This paper covers the determination of Pb, Zn Fe and Cd in the crude zinc produced from the imperial smelting furnace by XRF. Samples of crude zinc are taken on site and cast into ingots of definite shape. The analysed surface of the sample is polished and analysed directly without chemical treatment. The experience coefficient method is used to calibrate the matrix effect. Standard samples are prepared by artificial simulation. The linear relation coefficient between the concentration and the strength of X-ray is above 0.98. The standard deviation is less than 0.0056. The relative standard deviation is less than 2.41%. The results by XRF are the same as that by chemical analysis method.

Cadmium↗
PubMed2000

[Computer modeling and experimental research of interactions between two anti-hTNF alpha monoclonal antibody variable regions and hTNF alpha].

On SGI workstation, we constructed two anti-hTNF alpha McAbs by means of homologous protein-structure-prediction method. And then, on the basis of relative experimental results and the surface properties of hTNF alpha and two McAbs, we performed the docking of hTNF alpha into two anti-hTNF alpha McAbs. In order to confirm the models, we prepared two hTNF alpha mutants designed according to the binding models, analysed and predicted the possible changes in complexes resulted from hTNF alpha mutations. The experimental analysis results proved these complex models. This will make the base of our next antibody humanization and/or reshape work.

Antibodies, Monoclonal↗
PubMed2000

[Cultivation optimization of prolyl endopeptidase and high cell density fermentation].

Engineered E. coli BL21/pGEM-PEP could constitutively express recombinant prolyl endopeptidase from Aeromonas punctata, which was extremely effected by culture conditions, so fermentation conditions were optimized to obtain it's high expression level. Firstly, the stability of BL21/pGEM-PEP was investigated, then, culture temperature, pH, time, medium were optimized in shake flaskd. The L9(3(4)) orthogonal experiment confirmed that shaker speed, pH, culture temperature, culture time had high degree statistical meaning. Based on these data, high cell density fermentation of E. coli BL21/pGEM-PEP on NBS BioFlo 3000 5 L fermentor was achieved, after 20 h cultivation, the final density(dwt) was 60OD600(22.5 g/L), the expressed PEP was about 28% of total cellular protein, the yield was 3.15 g per litter broth.

Culture Media↗
PubMed2000

[Purification and characterization of recombinant Aeromonas punctata prolyl endopeptidase].

The study of down-stream techniques of recombinant Aeromonas punctata prolyl endopeptidase (apPEP) was presented here. High cell-density fermentation of E. coli BL21/pKKH-PEP in NBS BioFlo 3000 5 L fermentor was achieved, the final cell density was 22.5 g (DCW)/L after 14 h cultivation, the yield of apPEP expressed in soluble protein was 3.0 g per litter broth. After sonication, the supernatant of free cell extract was purified by ammonium sulfate fractionation, High performance Q sepharose FF, Phenyl sepharose 6 FF, the purity of apPEP reached 96%, enzyme specific activity was 65.5 u/mg, apPEP yield reached 0.86 g/L broth. Total recovery of enzyme protein was 8.2%, actviity recovery was 24.4%. The molecular weight of apPEP was 76,464 +/- 30 Da measured by MS, N terminus amino acids sequence consistent with that deduced from DNA sequence. pI 6.0, which was similar with PEP from Aeromonas hydrophila.

Aeromonas↗
PubMed1999

Effect of metal surface topography on mechanical bonding at simulated total hip stem-cement interfaces.

Bonding and loosening mechanisms between bone cement and joint prostheses have not been well identified. In this study, the effects of simulated hip stem surface topography on the interfacial shear strength were examined. Six different surface topographies were used. They were described by several surface characterization parameters that may directly relate to the interfacial bonding strength: average surface roughness R(a), root mean square slope R(Deltaq), correlation length beta, and fluid retention index R(ri). The shear strengths between Palacos E bone cement and stainless steel rods were measured using an Instron materials testing machine. We found that cement can "flow" into the surface microtopography and establish good contact with the metal surface. The results show that the interfacial strength increases monotonically with the increase of R(Deltaq) instead of with R(a). The relationship between interfacial strength and surface parameters shows that a metal stem with an isotropic surface texture, higher R(Deltaq), and greater R(ri) gives a higher interfacial strength.

Biocompatible Materials↗
PubMed1995

Evidence for A+(anti)-G(syn) mismatched base-pairing in d-GGTAAGCGTACC.

Two-dimensional NMR spectroscopy has been used to study the structure and hydrogen bonding scheme of A:G mismatched base pairing in d-GGTAAGCGTACC at pH 5.8. Under the conditions of our study, the molecule forms a B-DNA helix, with the mismatched bases in the A+ anti)-G(syn) conformation. The adenosine exists in the protonated form. The NOESY spectrum in 90% H2O + 10% 2H2O has been used to assign all observable imino and amino protons including those involved in the A+(anti)-G(syn) base pair. Both the proton donors in the A:G mismatched inter-base hydrogen bonding are situated on adenosine.

Base Composition↗
PubMed1992

Chemical synthesis, molecular cloning, and expression of the gene coding for the Trichosanthes trypsin inhibitor--a squash family inhibitor.

The gene coding for a Trichosanthes trypsin inhibitor analog (Ala-6-TTI) in which methionine at position 6 was replaced by alanine was synthesized chemically. The synthetic gene was cloned into plasmid pWR590-1 and expressed in Escherichia coli as a fusion protein composed of beta-galactosidase fragment of 590 amino acid residues and (Ala-6)-TTI, with methionine as a connecting residue. After cyanogen bromide cleavage and reduction of the fusion protein, followed by refolding with trypsin-Sepharose 4B as a matrix and affinity chromatography on the immobilized enzyme, the fully active (Ala-6)-TTI was obtained. The trypsin inhibitory activity and amino acid composition of the recombinant (Ala-6)-TTI were consistent with those of the natural one. The (Ala-6)-TTI gene was also cloned into the secretion expression vector, pVT102U/alpha, in Saccharomyces cerevisiae. In order to make the reading frame of the gene compatible with the vector, a nucleotide was inserted into the (Ala-6)-TTI gene via site-directed mutagenesis. The secreted (Ala-6)-TTI was purified and found to be correctly processed at the junction between the alpha-factor leader peptide and (Ala-6)-TTI downstream. Of the two expression systems, the latter is more advantageous in the high yield (greater than 2 mg/liter), easy purification and needlessness of disulfide refolding.

Amino Acid Sequence↗
PubMed1991

Hairpin formation in the self-complementary dodecamer d-GGTACGCGTACC and derivatives containing GA and IA mispairs.

The dodecamer d-GGTACGCGTACC and four derivatives with GA and IA mispairs in the 6,7 and 5,8 positions have been examined in dilute solution and 0.01-0.1 M sodium chloride. Concentration dependence of Tm, gel electrophoresis, and equilibrium centrifugation indicate that these self-complementary oligomers can form hairpins under the present conditions. Thermal transitions measured in the ultraviolet primarily represent melting of hairpin to coil [cf. Scheffler et al. (1968, 1970)]. The Tm values show little or no depression for 6,7 substitution but rather large depression for 5,8 replacement. We interpret the results to indicate that the 6,7 sequences have two-base loops and five base pair stems and that the 5,8 sequences have four-base loops and four base pair stems. A concurrent theoretical modeling study [Raghunathan et al. (1991) Biochemistry (following paper in this issue)] provides support for this interpretation.

Base Composition↗
PubMed1991

An efficient site-directed mutagenesis using polymerase chain reaction.

We report here a simple and efficient method for site-directed mutagenesis using polymerase chain reaction (PCR). In constructing a new expression plasmid for the EcoRI restriction gene, we made two point mutations. While one created a new SalI site prior to the SD sequence, the other replaced Glu144 with Lys. A 1.5 kb SalI-PstI fragment isolated from pER101 was used as the template. Two 25 mer oligonucleotide primers containing the desired mutations were synthesized and used to direct PCR amplification with Taq DNA polymerase. About 0.5 microgram of the 0.49 kb fragment was obtained from 0.05 microgram of the 1.5 kb fragment by carrying out polymerase chain reaction for 30 cycles. As calculated theoretically, 99% of the product contained the desired mutations. The product was cloned into pUC19 using SalI and PstI, two of the transformed colonies were randomly chosen for sequence analysis, and both of them were shown to contain the desired mutations. Finally, the amplified fragment was cloned into pER304 to place the EcoRI (Lys144) gene directly under the control of the lambda PL promoter.

Base Sequence↗
PubMed1989

Quantification of DNA structure from NMR data: conformation of d-ACATCGATGT.

Resonance assignments of nonexchangeable base and sugar protons have been obtained in double-helical d-ACATCGATGT by using two-dimensional correlated spectroscopy (COSY) and nuclear Overhauser enhancement spectroscopy (NOESY). The exchangeable imino protons have been assigned on the basis of their chemical shifts. The characteristic phase-sensitive multiplet patterns of the intrasugar cross-peaks in the omega 1-scaled COSY spectrum have been used to estimate several scalar coupling constants (J). The information on the J values combined with the intranucleotide COSY cross-peak intensities has been used to identify sugar puckers of individual nucleotide units. In most cases, the deoxyribofuranose rings are found to adopt a conformation close to O4'-endo. Spin diffusion has been monitored from the buildup of the normalized volumes of NOE cross-peaks in NOESY spectra as a function of mixing time. A set of 52 intranucleotide and internucleotide proton-proton distances have been estimated by using low mixing time NOESY spectra (tau m = 40 and 80 ms). The estimated intrasugar proton-proton distances rule out possibilities of existence of a fast equilibrium between C2'-endo and C3'-endo conformations. Intranucleotide proton-proton distances combined with the knowledge of sugar puckers have been used to fix the glycosidic bond torsion angle (chi). For this purpose, simulated distance contours depicting the dependence of intranucleotide proton-proton distances on pseudorotational phase angle (P) and glycosidic bond torsion angle (chi) have been used. Further, the proton homonuclear (J, delta) spectrum has been used to monitor the 31P-1H heteronuclear couplings, which are preserved in the omega 2 projection.(ABSTRACT TRUNCATED AT 250 WORDS)

Base Composition↗
PubMed1989

10-year survival rate for patient with nasopharyngeal carcinoma after radiation therapy. Clinical analysis of 367 cases.

Of 1,344 patients with nasopharyngeal carcinoma treated during 1961-1965 at the Shanghai Cancer Hospital, 367 who survived over 10 years after radiation therapy, were analysed. The results showed that the patients with stage I, II nasopharyngeal carcinoma and those with stage III, IV, the 10-year survival rates were 41.5% and 22.8% respectively, the overall 10-year survival rate being 27.3%. The 10-year survival rate was higher for female patients than for males, and was not related to the age of the patients and the pathological type of this carcinoma. The optimal tumor dosage was thought to be 60-70 Gy 350(95.4%) out of the 367 patients received radiotherapy only once. The rest received repeated irradiation for recurrence. For the reirradiated patients, the 10-year survival rate was 13.5%. Most recurrences occurred 5 years after radiotherapy (12/17), and only 5 within 3 years.

Adolescent↗
PubMed1988

Atypical abasic sites generated by neocarzinostatin at sequence-specific cytidylate residues in oligodeoxynucleotides.

Neocarzinostatin chromophore produces alkali-labile, abasic sites at cytidylate residues in AGC sequences in oligonucleotides in their duplex form. Glutathione is the preferred thiol activator of the drug in the formation of these lesions. The phosphodiester linkages on each side of the abasic site are intact, but when treated with alkali, breaks are formed with phosphate moieties at each end. Similar properties are exhibited by the abasic lesions produced at the purine residue to which the C in AGC is base-paired on the complementary strand. The abasic sites at C residues differ from those produced by acid-induced depurination in the much greater lability of the phosphodiester linkages on both sides of the deoxyribose, in the inability of NaBH4 to prevent alkali-induced cleavage, and in the relative resistance to apurinic/apyrimidinic endonucleases. The importance of DNA microstructure in determining attack site specificity in abasic site formation at C residues is shown not only by the requirement for the sequence AGC but also by the findings that substitution of G by I 5' to the C decreases the attack at C, whereas placement of an I opposite the C markedly enhances the reaction. Quantitation of the abstraction of 3H into the drug from C residues in AGC specifically labeled in the deoxyribose at C-5' or C-1',2' suggests that, in contrast to the attack at C-5' in the induction of direct strand breaks at T residues, abasic site formation at C residues may involve attack at C-1'. Each type of lesion may exist on the complementary strands of the same DNA molecule, forming a double-stranded lesion.

Antibiotics, Antineoplastic↗
PubMed1988

Sequence-specific solution structure of d-GGTACGCGTACC.

Complete resonance assignments of nonexchangeable base protons and sugar protons in d-GGTACGCGTACC at 500 MHz have been obtained by two-dimensional correlated spectroscopy (COSY) and nuclear Overhauser enhancement spectroscopy (NOESY). The characteristic phase-sensitive multiplet patterns of the ntrasugar cross peaks in the omega 1-scaled COSY spectrum have been used to estimate several scalar coupling constants (J). These coupling constants combined with the intranucleotide COSY cross peak intensities have been used to identify the sugar pucker of individual nucleotide units. In most cases, the deoxyribose rings adopt a conformation close to O4'-endo. Spin-diffusion has been monitored from the buildup of the normalized volumes of NOE cross peaks in NOESY spectra as a function of mixing time. A set of 55 intranucleotide and internucleotide interproton distances have been estimated from the low mixing time NOESY spectrum (tau m = 75 ms). The estimated intranucleotide proton-proton distances have been used to determine the individual glycosidic dihedral angles of the nucleotide units which lie in the anti domain. It is observed that the molecule adopts an overall conformation close to that of the B-form although there are differences in the intricate details.

Base Sequence↗