Biomedical subjects

Yan Zhang

Publications and source records attributed to Yan Zhang.

At least 325 records · Page 18Linked to original sources

PubMed2005

[Induction of immune tolerance for allogenic recipient mice by non-myeloablative bone marrow transplantation].

This study was aimed to explore the effects and mechanisms of transplantation tolerance induced by "TBI + cyclophosphamide (CTX)" regimen combined with intra-bone marrow injection of allogenic BMCs. On day 0 C57BL/6 (H-2(b), B6) mice received sublethal dose of total body irradiation (TBI) ((60)Co gamma-ray) followed by intrabone marrow-bone marrow transplantation (IBM-BMT) of 3 x 10(7) cells/30 microl BMCs from BALB/c (H-2(d)) mice. The recipient mice were given CTX intraperitoneally 2 days after IBM-BMT. On day 7 skin grafting was performed and the skin survival was observed. The tolerance mechanism was investigated by mixed lymphocyte reaction (MLR), IL-2 reverse test, adoptive transfer assay in vitro. The results showed that the mean survival time (MST) of skin allografts in group treated with TBI + CTX + BMT was significantly longer, compared with that of other groups (P < 0.01). On day 90 after IBM-BMT, the phenotypic character of the recipient mice (black color) began to convert to that of the donor mice (white color). The MLR demonstrated that the immune responses of recipient mice were donor-specific tolerance. Suppressive activity in the spleen cells of tolerant B6 mice was observed in adoptive transfer assay in vitro. IL-2 reversal and the phenotypic conversion showed that the tolerance mechanisms were involved in clonal anergy and the development of chimerism. It is concluded that the nonmyeloablative regimen combined with IBM-BMT can induce a long-term tolerance, and the multiple mechanisms including clonal anergy, suppressor cells and chimerism were involved in transplantation immune tolerance.

Animals↗

PubMed2005

[Effects of extremely low frequency electromagnetic fields on DNA of testicular cells and sperm chromatin structure in mice].

OBJECTIVE: To study the effects of 50 Hz electromagnetic fields (EMFs) on DNA of testicular cells and sperm chromatin structure in mice. METHODS: Mice were exposed to 50 Hz, 0.2 mT or 6.4 mT electromagnetic fields for 4 weeks. DNA strand breakage in testicular cells was detected by single-cell gel electrophoresis assay. Sperm chromatin structure was analyzed by sperm chromatin structure assay with flow cytometry. RESULTS: After 50 Hz, 0.2 mT or 6.4 mT EMFs exposure, the percentage of cells with DNA migration in total testicular cells increased from the control level of 25.64% to 37.83% and 39.38% respectively. The relative length of comet tail and the percentage of DNA in comet tail respectively increased from the control levels of 13.06% +/- 12.38% and 1.52% +/- 3.25% to 17.86% +/- 14.60% and 2.32% +/- 4.26% after 0.2 mT exposure and to 17.88% +/- 13.71% and 2.35% +/- 3.87% after 6.4 mT exposure (P < 0.05). Exposure to EMFs had not induced significant changes in S.D.alphaT and XalphaT, but COMPalphaT (cells outside the main population of alpha t), the percentage of sperms with abnormal chromatin structure, increased in the two exposed groups. CONCLUSION: 50 Hz EMFs may have the potential to induce DNA strand breakage in testicular cells and sperm chromatin condensation in mice.

Animals↗

PubMed2005

[Chemical constituents from the mangrove plant Ceriops tagal].

AIM: To investigate the secondary metabolites of the mangrove plant Ceriops tagal. METHODS: Column chromatography techniques including HPLC were used for the separation and purification, and extensive spectral analysis including various 2D NMR spectra were employed for structure elucidation. RESULTS: Nine compounds, namely, tagalsins A (1), ent-5alpha-dolabr-4 (18) -ene-15S,16-diol (2), squalene (3), betulinic acid (4), lup-20 (29) -en-3-on-28-oic acid (5), betulin (6), lup-20 (29) -en-3-on-28-ol (7), beta-sitosterol (8), n-hexacosanylferulate (9) were obtained. Of which 1 and 2 belong to dolabrane diterpene. CONCLUSION: Compound 1 is a new compound, and 2 to 9 are isolated from this species for the first time.

Diterpenes↗

PubMed2005

[Immunohistochemical study of RET protein in Hirschsprung's disease and allied Hirschsprung's disorder].

OBJECTIVE: Hirschsprung's Disease (HD) and allied Hirschsprung's disorder (HAD) have very similar clinical manifestations, but there are many different theories about the two diseases. The present study was designed to understand the expression of Ret protein in HD and HAD, and to explore the role of Ret protein in the pathogenesis of HD and HAD. METHODS: Colon specimens from patients with confirmed HD and HAD, including 15 cases of HD (male 12, female 3) and 11 cases of HAD (male 8, female 3) were collected for this study. At the same time normal colon specimens from 10 individuals with other diseases were used as control. The expression of Ret protein in the intestinal tissue was detected by using immunohistochemical SABC technique with mouse anti-Ret monoclonal antibody. RESULTS: In the colon specimens from normal controls and the dilated segments of colon from HD and HAD patients, moderate to large number of Ret-positive cells were observed among the ganglion cells of myenteric plexuses and submucosal plexuses (P > 0.05). On the contrary, Ret-positive cells were not seen in the stenotic segment of colon from HD patients. But there was positive staining in the stenotic segment of the colon from HAD. Moreover, giant ganglion cells showing strongly positive staining could be seen. There were also displastic cells, small cells, and cells with irregular shape. Statistical analysis showed significant differences in Ret cells positivity between the stenotic segment of colon of HD and the normal control (P < 0.001) as well as between HD and HAD (P < 0.001). CONCLUSION: Ret protein may play an important role in the pathogenesis of HD and could not have definite relationship with HAD.

Case-Control Studies↗

PubMed2005

[Correlation between blood flow velocity of feeding arteries and microvessel density of hepatocellular carcinoma].

OBJECTIVE: To evaluate the correlation between the mean of time blood flow velocity (TVmean) of feeding artery around hepatocellular carcinoma (HCC) and the microvessel density (MVD) in relation to tumor cell differentiation, and to evaluate the usefulness of TVmean as a noninvasive preoperative marker of biologic characteristic of HCC. METHODS: To measure TVmean of feeding arteries around the HCC in 45 patients before operation and TVmean of minute arteries in hepatic tissue in 45 normal subjects by ultrasonographic examination. Tumor cell differentiation grade was determined by routine histopathological staining. Tumor MVD was measured by immunohistochemical staining with monoclonal antibodies against F VIII RAg of excised HCC. Correlationship between TVmean of feeding arteries and MVD of HCC was studied. RESULTS: A linear correlation between TVmean of feeding arteries around the tumors of HCC and MVD of HCC tissue (r = 0.794, y = 18.2764 + 1.5544x) was obtained. With TVmean > or = 21.3 cm/s, the positive and negative predictive values of poorly differentiated HCC were 97.4% and 87.5%, respectively. With TVmean < 21.3 cm/s, those of well differentiated HCC were 88.5% and 97.3%, respectively. The degree of reliability of calculating HCC cell differentiation according to TVmean was 89.5%. CONCLUSION: Tumor growth and cellular differentiation, the two major factors affecting prognosis of HCC, may be evaluated by TVmean of feeding arteries around the tumor. It offers a useful preoperative information for predicting prognosis of HCC patients.

Adult↗

PubMed2005

[Cloning and expressing of cellulase gene (cbh2) from thermophilic fungi Chaetomium thermophilum CT2].

Chaetomium thermophilum CT2 can produce extracellular cellulase with industrial value. We designed two degenerate primers to amplify catalytic domain sequence of cellobiohydrolase II ( CBH II). Full length of cDNA was obtained by rapid amplification of cDNA ends technologies. DNA sequencing revealed that cbh2 has an open reading frame of 1428bp, which encodes a putative polypeptide of 476 amino acids. The deduced amino acid sequence shows that the predicted molecular mass is 53 kD and the cbh2 consists of a fungal-type carbohydrate binding domain (CBD) separated from a catalytic domain by a linker region rich in proline/serine/threonine. PCR product consisting of the entire CBH II coding region without its signal sequences was cloned into the yeast secretive plasmid pPIC9K, which was then transformed into Pichia pastoris GS115. Highly efficient production of the cellobiohydrolase II was achieved in P. pastoris under the control of the AOX1 promoter, and the expressing level was 1.2 mg/mL by small-scale culturing. The recombinant cellobiohydrolase II was purified by using ammonium sulfate fraction, DEAE-Sepharose Fast flow chromatography. A molecular mass of the purified enzyme is 67 kD determined by SDS-PAGE and this is similar to the native cellobiohydrolase II purified from C. thermophilum CT2. The recombinant enzyme exhibited optimum catalytic activity at pH 4.0 and 50 degrees C respectively. It was thermostable at 50 degrees C and retained 50% of its original activity after 30 min at 70 d degrees C . The high level of fully active recombinant cellobiohydrolase II got from P. pastoris makes this expression system attractive for fermentor and industrial applications.

Amino Acid Sequence↗

PubMed2005

[Polyethylene glycol-accompanied ion-exchange chromatography to purify recombinant hepatitis B virus surface antigen].

The dissociation of virus-like particles of Hepatitis B surface antigen (HBsAg) during the adsorption-desorption on the solid-phase of chromatography is a main challenge for its purification. Herein, poly (ethylene glycol) (PEG) was applied as an additive during the purification of HBsAg from recombinant Chinese hamster ovary (CHO) cell culture to improve the HBsAg recovery and protect its structural assembly. The presence of 1% of PEG10000 in the mobile phase of ion-exchange chromatography (IEC) of DEAE-Sepharose FF column could increase the recovery of HBsAg from about 55% to 80%, with a similar purification (-fold) (about 12) compared with the absence of PEG. Importantly, glycosylated protein forms of HBsAg were reserved well by PEG-accompanied chromatography. Furthermore, size exclusion chromatography-multiangle laser light scattering (SEC-MALLS) analysis was performed on line to monitor the aggregates, particle size and molecular weight distribution of HBsAg. The results demonstrated that the HBsAg particle size and assembly are more homogenous after adding PEG in the mobile phase of IEC than no PEG added in the mobile phase.

Animals↗

PubMed2005

[Determination of residual sulfonamides in meat by high performance liquid chromatography with solid-phase extraction].

A method was developed for determining residual sulfonamides (SAs) such as sulfamethazine (SM2), sulfamonomethoxine (SMM), sulfamethiazole (SMZ), sulfadimethoxine (SDM) and sulfaquinoxaline (SQ) in pork and chicken using solid-phase extraction (SPE) and high performance liquid chromatography (HPLC) with a photodiode array detector. The samples were extracted with ethyl acetate. An NH2 column was used for clean up. For the HPLC determination, an Intersil ODS-2 column was used with a mixture of methanol-acetonitrile-water-acetic acid (2: 2: 9: 0.2, v/v) as the mobile phase. The detection limits (S/N = 3) were 3 microg/kg for SM2, SMM and SMZ, and 7 microg/kg for SDM and SQ. The quantitation limits (S/N = 10) were 10 microg/kg for SM2, SMM and SMZ, and 25 microg/kg for SDM and SQ. The linear ranges were 30 - 5 000 microg/L for SM2, SMM and SMZ, and 60 - 5 000 microg/L for SDM and SQ. The recoveries were between 73.2% and 97.3% with the relative standard deviations between 2.5% and 11.6% originated from the spiked level of 50 microg/kg.

Animals↗

PubMed2004

Yeast frataxin solution structure, iron binding, and ferrochelatase interaction.

The mitochondrial protein frataxin is essential for cellular regulation of iron homeostasis. Although the exact function of frataxin is not yet clear, recent reports indicate the protein binds iron and can act as a mitochondrial iron chaperone to transport Fe(II) to ferrochelatase and ISU proteins within the heme and iron-sulfur cluster biosynthetic pathways, respectively. We have determined the solution structure of apo yeast frataxin to provide a structural basis of how frataxin binds and donates iron to the ferrochelatase. While the protein's alpha-beta-sandwich structural motif is similar to that observed for human and bacterial frataxins, the yeast structure presented in this report includes the full N-terminus observed for the mature processed protein found within the mitochondrion. In addition, NMR spectroscopy was used to identify frataxin amino acids that are perturbed by the presence of iron. Conserved acidic residues in the helix 1-strand 1 protein region undergo amide chemical shift changes in the presence of Fe(II), indicating a possible iron-binding site on frataxin. NMR spectroscopy was further used to identify the intermolecular binding interface between ferrochelatase and frataxin. Ferrochelatase appears to bind to frataxin's helical plane in a manner that includes its iron-binding interface.

Binding Sites↗

PubMed2004

Photoinduced [4 + 4] cycloadditions of o-quinones with oxazoles.

[reaction: see text] Photocycloadditions of 9,10-phenanthraquinone (PQ) with oxazoles (1a and 1b) gave [4 + 4] products 2 with the O=C-C=O functionality in PQ and the 2-azadiene moiety in oxazole as 4pi addends. Photoreactions of 1-acetylisatin (IS) with 1a, 1c, and 1d gave [4 + 4] product A, which underwent further [2 + 2] reactions with another (3)IS to furnish 5. These regioselective and diastereoselective [4 + 4] photocycloadditions are rationalized by the intervening of the key conformers for ISC and bond formation of the most stable 1,6-diradical intermediates.

Journal Article↗

PubMed2004

Evaluation of multiple genomic targets for identification and confirmation of Mycobacterium avium subsp. paratuberculosis isolates using real-time PCR.

Specificity of six previously published Mycobacterium avium subsp. paratuberculosis (MAP) genomic loci, including 10, 38, 56, 93, 251, and 252 were evaluated in this study. Target 251 which was identified as MAP-specific was further evaluated in 210 MAP isolates, 14 non-MAP mycobacterial species, 7 atypical mycobacterial isolates, and 9 other bacterial species using real-time PCR. A previously published IS900 primer and probe combination was used as a positive control along with a universal ribosomal DNA gene sequence (UVA) as an internal control to evaluate PCR inhibition. All MAP isolates were positive with IS900, 251, and UVA by real-time PCR. All non-MAP mycobacterial species except one atypical mycobacterial isolate and other bacterial species used in this study were negative for IS900. All of these species were negative for 251. The atypical mycobacterial isolate, positive for IS900 and UVA, was negative for 251. A combination of IS900 and 251 PCR is ideal for sensitive and specific confirmation of MAP isolates from conventional fecal cultures. This study also evaluated the specificity of 251 real-time PCR, on broth cultures from 50 known bovine fecal samples. Acid fast staining followed by IS900 and 251 real-time PCR can be used for accurate identification and confirmation of MAP from broth cultures.

Animals↗

PubMed2004

Molecular recognition remolds the self-assembly of hydrogelators and increases the elasticity of the hydrogel by 10(6)-fold.

Addition of vancomycin (1, the receptor) to the supramolecular hydrogel of self-assembled pyrene-d-Ala-d-Ala (2, the ligand) increases the storage modulus of the hydrogel of 2 by about 106-fold. Rheology, microscopy, and spectroscopy investigations suggest that the two-dimensional polymers, formed by the ligand-receptor interaction between 1 and 2, and the self-dimerization of 1, are mainly responsible for the observed dramatic increase in elasticity.

Biomimetic Materials↗

PubMed2004

Transformation of vascular endothelial cells by a point mutation in the Tie2 gene from human intramuscular haemangioma.

Tie2, an endothelial-cell-specific receptor tyrosine kinase, collaborates with vascular endothelial growth factor (VEGF) in regulating angiogenesis and vascular maturation. Here, we report a mutation of glycine to aspartic acid at the second glycine of the GXGXXG motif of Tie2 (G833DTie2) in human intramuscular haemangiomas (IMHs) of the capillary type. Murine endothelial cells (ECs) overexpressing this G833DTie2 receptor exhibited an increase in cell proliferation at low serum concentrations and angiosarcomas developed in nude mice, whereas cells overexpressing either wild-type Tie2 or Q837HTie2 failed to elicit these responses. Furthermore, the G833DTie2 receptor increased VEGF expression in ECs. These findings provide molecular mechanisms for pathogenesis of IMH

Amino Acid Sequence↗

PubMed2004

Valdecoxib: assessment of cyclooxygenase-2 potency and selectivity.

The discovery of a second isoform of cyclooxygenase (COX) led to the search for compounds that could selectively inhibit COX-2 in humans while sparing prostaglandin formation from COX-1. Celecoxib and rofecoxib were among the molecules developed from these efforts. We report here the pharmacological properties of a third selective COX-2 inhibitor, valdecoxib, which is the most potent and in vitro selective of the marketed COX-2 inhibitors that we have studied. Recombinant human COX-1 and COX-2 were used to screen for new highly potent and in vitro selective COX-2 inhibitors and compare kinetic mechanisms of binding and enzyme inhibition with other COX inhibitors. Valdecoxib potently inhibits recombinant COX-2, with an IC(50) of 0.005 microM; this compares with IC values of 0.05 microM for celecoxib, 0.5 microM for rofecoxib, and 5 microM for etoricoxib. Unique binding interactions of valdecoxib with COX-2 translate into a fast rate of inactivation of COX-2 (110,000 M/s compared with 7000 M/s for rofecoxib and 80 M/s for etoricoxib). The overall saturation binding affinity for COX-2 of valdecoxib is 2.6 nM (compared with 1.6 nM for celecoxib, 51 nM for rofecoxib, and 260 nM for etoricoxib), with a slow off-rate (t(1/2) approximately 98 min). Valdecoxib inhibits COX-1 in a competitive fashion only at very high concentrations (IC(50) = 150 microM). Collectively, these data provide a mechanistic basis for the potency and in vitro selectivity of valdecoxib for COX-2. Valdecoxib showed similar activity in the human whole-blood COX assay (COX-2 IC(50) = 0.24 microM; COX-1 IC(50) = 21.9 microM). We also determined whether this in vitro potency and selectivity translated to significant potency in vivo. In rats, valdecoxib demonstrated marked potency in acute and chronic models of inflammation (air pouch ED(50) = 0.06 mg/kg; paw edema ED(50) = 5.9 mg/kg; adjuvant arthritis ED(50) = 0.03 mg/kg). In these same animals, COX-1 was spared at doses greater than 200 mg/kg. These data provide a basis for the observed potent anti-inflammatory activity of valdecoxib in humans.

Animals↗

PubMed2004

p53 polymorphism in human papillomavirus-associated Kazakh's esophageal cancer in Xinjiang, China.

AIM: To investigate the relationship between p53 codon 72 polymorphism and human papillomavirus (HPV) type 16 infection in Kazakh's esophageal cancer (EC) in Xinjiang, China. METHODS: Encoding regions of p53 codon 72 and HPV-16 E6 were amplified by polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) and polymerase chain reaction (PCR) methods using pairs of primary esophageal squamous cell carcinoma (SCC) tissue and corresponding normal mucosa, which were collected from 104 patients of Kazakh in Xinjiang, China. RESULTS: Only arginine allele was detected in 70.1% (39/55) of HPV-16-E6- positive cases but only in 40.8% (20/49) of HPV-16-E6-negative cases (P<0.05; OR, 3.53; 95% CI, 1.57-7.98). In contrast, such a significant correlation between p53 polymorphism and HPV infection was not evident in corresponding normal mucosae. The allele frequency of Arg allele in cancer cases (0.68) was higher than that in normal mucosa samples (0.54) (P<0.05; OR, 1.80; 95% CI, 1.21-2.69). CONCLUSION: p53 codon 72 Arg homozygous genotype is one of the high-risk genetic factors for HPV-associated SCC of Kazakh. Individuals carrying Arg allele compared to those with Pro allele have an increased risk for esophageal SCC.

Amino Acid Substitution↗

PubMed2004

Human endostatin gene transfer, either naked or with liposome, has the same inhibitory effect on growth of mouse liver tumor cells in vivo.

AIM: To explore a safe and efficient strategy of tumor therapy using anti-angiogenetic agents. METHODS: Endostatin gene with a signal sequence of human IgGgamma chain was amplified by PCR and cloned into pVAX1 plasmid which was the only vector authorized by FDA in clinical trial to construct a recombinant plasmid named as pVAX-sEN. The recombinant plasmid was detected with EcoRI/KpnI and DNA sequencing. BALB/c mice bearing hepatocarcinoma cell line H22 were treated with naked pVAX-sEN or liposome-DNA complex in which the dose of DNA and the ratio of DNA and liposome were different from each other. To compare the efficiency of gene transfection, expression of endostatin at the treated tumor site was assayed with ELISA. To investigate the effect of pVAX1-sEN on hepatocellular carcinoma, pVAX-sEN either naked or in liposome-DNA complex was injected into BALB/c mice bearing H22, then the diameter of tumors was measured, microvessel density was detected by immunohistochemistry, endostatin expression in vivo was assayed at different time points. RESULTS: DNA sequencing showed the endostatin gene with the signal peptide was correctly cloned. In situ gene expression assay indicated that both the ratio of DNA and liposome and the dose of DNA could affect the gene transfection efficiency. Interestingly, naked pVAX-sEN had a similar in situ endostatin expression to pVAX-sEN with liposome. Animal experiments showed that pVAX-sEN together with pVAX-sEN-liposome complex could efficiently suppress the growth of mouse hepatoma cells. CONCLUSION: Naked endostatin plasmid intratumoral injection can get a similar gene transfection efficiency to liposome-DNA complex when used in situ.

Animals↗

PubMed2004

Squamous cell carcinoma cell aggregates escape suspension-induced, p53-mediated anoikis: fibronectin and integrin alphav mediate survival signals through focal adhesion kinase.

Resistance to anoikis, or apoptosis triggered by detachment from the extracellular matrix (ECM), lengthens the survival of malignant cells, facilitating reattachment and colonization of secondary sites. To examine the molecular mechanisms underlying resistance to anoikis in human oral squamous cell carcinoma (SCC) cells, we cultured human squamous carcinoma (HSC-3) cells in suspension on plates coated with poly-2-hydroxyethyl methacrylate, which blocks access to the ECM. Cells in suspension that formed multicellular aggregates had significantly lower levels of apoptosis than single cells. Aggregates, but not single cells, had high levels of fibronectin. Preincubation with a cyclic arginine-glycine-aspartic acid peptide or fibronectin-blocking antibody significantly increased anoikis. Single cells had markedly lower expression of the integrin alpha(v) receptor than aggregates. Blocking alpha(v) function with a blocking antibody or by transfection with an antisense oligonucleotide increased apoptosis and inhibited aggregation. In single cells but not aggregates, phosphorylation of the integrin-associated focal adhesion kinase (FAK) at tyrosine 397 was reduced, and p53 levels were increased. Apoptosis was increased by blocking FAK with an antisense oligonucleotide and reduced by blocking p53. These findings show that SCC cells escape suspension-induced anoikis by forming multicellular aggregates that avail themselves of fibronectin survival signals mediated by integrin alpha(v). Single cells in suspension that do not form aggregates undergo anoikis because of decreased FAK phosphorylation and increased p53 levels. Thus, SCC cells appear to use neighboring cells and the ECM molecule FN to promote the metastatic phenotype.

Animals↗

PubMed2004

Signal-processing algorithm for white-light optical fiber extrinsic Fabry-Perot interferometric sensors.

We present a novel signal-processing algorithm for single-mode optical fiber extrinsic Fabry-Perot interferometric sensors that can achieve both high-resolution, absolute measurement of the cavity length and a large dynamic measurement range simultaneously. The algorithm is based on an accurate model of the characteristics of a fiber-optic sensor that takes into account the phase shift that is due to the coupling of light reflected at the second surface to the lead-in fiber end.

Journal Article↗