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Biomedical subjects

Yu Zhang

Publications and source records attributed to Yu Zhang.

At least 217 records · Page 12Linked to original sources
PubMed2004

Effect of sandblasting on the long-term performance of dental ceramics.

A study has been made of the effects of sandblasting on the strength of Y-TZP and alumina ceramic layers joined to polymeric substrates and loaded at the top surfaces by a spherical indenter, in simulation of occlusal contact in ceramic crowns on tooth dentin. The sandblast treatment is applied to the ceramic bottom surface before bonding to the substrate, as in common dental practice. Specimens with polished surfaces are used as a control. Tests are conducted with monotonically increasing (dynamic) and sinusoidal (cyclic) loading on the spherical indenter, up to the point of initiation of a radial fracture at the ceramic bottom surface immediately below the contact. For the polished specimens, data from the dynamic and cyclic tests overlap, consistent with a dominant slow crack growth mode of fatigue. Strengths of sandblasted specimens show significant reductions in both dynamic and cyclic tests, indicative of larger starting flaws. However, the shift is considerably greater in the cyclic data, suggesting some mechanically assisted growth of the sandblast flaws. These results have implications in the context of lifetimes of dental crowns.

Algorithms↗
PubMed2004

Pur alpha and Sp8 as opposing regulators of neural gata2 expression.

Gata2 is an essential hematopoietic transcriptional factor that is also expressed prominently in the nervous system. The early lethality of knockout mice due to severe anemia has largely precluded studies of gata2 neural regulation and function. In this report, we describe the identification of zebrafish Pur alpha and Sp8 orthologs as two factors that function to regulate neuronal expression of gata2. During embryogenesis, Pur alpha is expressed widely, whereas Sp8 has an overlapping pattern of expression with gata2 in the nervous system. Knockdown and ectopic expressions of Pur alpha and Sp8 indicate that these factors function, respectively, as a repressor and an activator of gata2 gene expression in the nervous system. With consideration given to the previously established roles for these factors, we propose a model for how the transcriptional regulation of neural gata2 expression may be involved in controlling cellular proliferation in the nervous system.

Animals↗
PubMed2004

Fatigue and damage tolerance of Y-TZP ceramics in layered biomechanical systems.

The fatigue properties of fine-grain Y-TZP in cyclic flexural testing are studied. Comparative tests on a coarser-grain alumina provide a baseline control. A bilayer configuration with ceramic plates bonded to a compliant polymeric substrate and loaded with concentrated forces at the top surfaces, simulating basic layer structures in dental crowns and hip replacement prostheses, is used as a basic test specimen. Critical times to initiate radial crack failure at the ceramic undersurfaces at prescribed maximum surface loads are measured for Y-TZP with as-polished surfaces, mechanically predamaged undersurfaces, and after a thermal aging treatment. No differences in critical failure conditions are observed between monotonic and cyclic loading on as-polished surfaces, or between as-polished and mechanically damaged surfaces in monotonic loading, consistent with fatigue controlled by slow crack growth. However, the data for mechanically damaged and aged specimens show substantial declines in sustainable stresses and times to failure in cyclic loading, indicating an augmenting role of mechanical and thermal processes in certain instances. In all cases, however, the sustainable stresses in the Y-TZP remain higher than that of the alumina, suggesting that with proper measures to avoid inherent structural instabilities, Y-TZP could provide superior performance in biomechanical applications.

Biocompatible Materials↗
PubMed2004

Zebrafish Dpr2 inhibits mesoderm induction by promoting degradation of nodal receptors.

Nodal proteins, members of the transforming growth factor-beta (TGFbeta) superfamily, have been identified as key endogenous mesoderm inducers in vertebrates. Precise control of Nodal signaling is essential for normal development of embryos. Here, we report that zebrafish dapper2 (dpr2) is expressed in mesoderm precursors during early embryogenesis and is positively regulated by Nodal signals. In vivo functional studies in zebrafish suggest that Dpr2 suppresses mesoderm induction activities of Nodal signaling. Dpr2 is localized in late endosomes, binds to the TGFbeta receptors ALK5 and ALK4, and accelerates lysosomal degradation of these receptors.

Activin Receptors, Type I↗
PubMed2004

Molecular cytogenetic characterization of the Antirrhinum majus genome.

As a model system in classical plant genetics, the genus Antirrhinum has been well studied, especially in gametophytic self-incompatibility, flower development biology, and transposon-induced mutation. In contrast to the advances in genetic and molecular studies, little is known about Antirrhinum cytogenetics. In this study, we isolated two tandem repetitive sequences, CentA1 and CentA2, from the centromeric regions of Antirrhinum chromosomes. A standard karyotype has been established by anchoring these centromeric repeats on meiotic pachytene chromosome using FISH. An ideogram based on the DAPI-staining pattern of pachytene chromosomes was developed to depict the distribution of heterochromatin in the Antirrhinum majus genome. To integrate the genetic and chromosomal maps, we selected one or two molecular markers from each linkage group to screen an Antirrhinum transformation-competent artificial chromosome (TAC) library. These genetically anchored TAC clones were labeled as FISH probes to hybridize to pachytene chromosomes of A. majus. As a result, the relationship between chromosomes and the linkage groups (LGs) in Antirrhinum has been established.

Antirrhinum↗
PubMed2004

[Detection of alpha-fetoproteins mRNA and melanoma antigen-1 mRNA in peripheral blood of patients with hepatocellular carcinoma and its clinical significance].

OBJECTIVE: To explore the feasibility of alpha-fetoproteins (alpha-FP) mRNA and melanoma antigen-1 (MAGE-1) mRNA as 2 markers of micrometastasis in hepatocellular carcinoma (HCC) patients' peripheral blood. METHODS: Subjects were divided into five groups: patients with HCC (n=65); patients with hepatitisB and liver cirrhosis (n=22); patients with metastatic liver cancer (n=12); patients with hepatic hemangioma (n=12); and healthy volunteers (n=20). alpha-FP mRNA and MAGE-1 mRNA in peripheral blood were tested by nested reverse transcription polymerase chain reaction (RT-PCR). RESULTS: MAGE-1 mRNA and alpha-FP mRNA were detected in 27 (42%) and 35 (54%) of 65 HCC patients respectively, while 42 (65%) HCC patients were positive for at least 1 marker. The frequency of alpha-FP mRNA and MAGE-1 mRNA positivity strongly correlated with portal thrombosis, intrahepatic metastatic nodules, tumor diameter and TNM stage (P <0.05). With regard to controls, 4 of 12 (33%) samples from patients with metastatic liver cancer showed MAGE-1 mRNA in their peripheral blood, but groups of hepatitis and cirrhosis, hepatic hemangioma, healthy volunteers did not. And 3 of 22 samples (14%) from group hepatitis and cirrhosis showed alpha-FP mRNA, but none of samples from other control group showed alpha-FP mRNA. CONCLUSIONS: Nested RT-PCR is a sensitive and reliable method for detecting circulating HCC cells. Two-marker RT-PCR assay with a liver-specific alpha-FP marker in combination with a cancer-specific MAGE-1 marker may be a promising tool for detecting micrometastases with better sensitivity and specificity than one marker RT-PCR.

Adult↗
PubMed2004

Differential proteomic analysis of human hepatocellular carcinoma cell line metastasis-associated proteins.

PURPOSE: The comparative study of differentially expression of protein profiles of hepatocellular carcinoma cell lines with various metastasic potential and screening key molecules related to hepatocellular carcinoma metastasis and recurrence. METHODS: Using two-dimensional electrophoresis and liquid chromatography-electrospray ionization-tandem mass spectrometry (LC-ESI-MS/MS), we analyzed differentially displayed proteomics of human hepatocellular carcinoma cell lines Hep3B, MHCC97L, MHCC97H with different metastasic potential. RESULTS: Approximate 1,000 protein spots were detected on silver-stained gel by ImageMaster (977+/-113 spots in Hep3B, 1092+/-40 in MHCC97L, and 889+/-14 in MHCC97H). Fifty distinct different protein spots were analyzed with online LC-ESI-MS/MS. Only 26 protein spots had a positive result, including annexin1, S100A4, and so on. In comparison with nonmetastasis Hep3B cell lines, there were 16 proteins overexpressed in MHCC97H and MHCC97L, 10 proteins underexpressed in MHCC97H and MHCC97L. Applying cell immunohistochemistry and RT-PCR, we further validated two interesting and different proteins, annexin1 and S100A4. CONCLUSION: The protein profile of metastatic hepatocellular carcinoma cell lines displayed obvious differences compared with non-metastatic liver cancer cell lines. The results imply that various different proteins may lead to HCC metastasis together.

Carcinoma, Hepatocellular↗
PubMed2004

[Expression and significance of Toll-like receptor 4 of splenic macrophage in patients with hypersplenism due to portal hypertension].

OBJECTIVE: To observe the change in expression of Toll-like receptor 4 (TLR4) of splenic macrophage in patients with hypersplenism due to portal hypertension (PH), and investigate the role of TLR4 of splenic macrophage in hypersplenism. METHODS: Splenectomy was performed on 20 patients with hypersplenism due to PH (hypersplenism group) and 6 patients with rupture of spleen by trauma (control group) and the specimens of spleen were collected. The splenic macrophages were isolated by adhibit wall method. The expression of TLR4 of splenic macrophage was detected by immunohistochemical method (SABC), and the result was analyzed by the image analysis system. The phagocytosis of splenic macrophage was measured by chicken red blood cell (CRBC) phagocytosis assay. The level of serum endotoxin was detected before the operation by limulus assay. The results of these 2 groups were compared, and correlation analysis was made among different results of the hypersplenism group. RESULTS: The expression of TLR4 of splenic macrophage was 109 +/- 32 in the hypersplenism group, significantly higher than that of the control group (62 +/- 5, P < 0.01). The rate of phagocytosis and index of phagocytosis of splenic macrophage in the hypersplenism group were 12.6% +/- 3.0% and 0.146 +/- 0.035 respectively, both significantly higher than those of the control group (6.9% +/- 0.5% and 0.076 +/- 0.008 respectively, both P < 0.01) The level of endotoxin of the hypersplenism group was 0.28 EU/ml +/- 0.21 EU/ml, significantly higher than that of the control group (0.054 EU/ml +/- 0.014 EU/ml, P < 0.05). The rate of phagocytosis and the index of phagocytosis of splenic macrophage were notably positively correlated with the expression of TLR4 (r = 0.601, P < 0.01 and r = 0.553, P < 0.05), and the level of endotoxin (r = 0.724 P < 0.01 and r = 0.506, P < 0.05). The expression of TLR4 of splenic macrophage was positively correlated with the level of endotoxin (r = 0.525, P < 0.05). CONCLUSION: The expression of TLR4 of splenic macrophage in patients with hypersplenism due to PH was increased significantly. It may be one of the important factors of hypersplenism due to PH that "endotoxemia-->increase of expression of TLR4 of splenic macrophage (activation of TLR of splenic macrophage)-->increased destruction of red blood cells by macrophage".

Adult↗
PubMed2004

[Quantitative analysis of Epstein-Barr virus DNA in plasma and peripheral blood cells in patients with nasopharyngeal carcinoma].

OBJECTIVE: To quantitative analysis of Epstein-Barr virus (EBV) DNA levels in plasma, peripheral blood cells (PBCs) and tumor tissue in nasopharyngeal carcinoma (NPC), to investigate the relationship between EBV-DNA levels and clinical parameters. METHODS: Blood of 150 primary NPC and 49 corresponding tumor tissues, 47 nasopharyngitis tissues and blood of 75 controls were entered this investigation. Plasma and PBCs were isolated for quantitative detection of EBV-DNA by using real-time quantitative PCR (RQ-PCR). The paraffin-embedded tissue sections were conducted to quantitative detection of EBV-DNA, and EBER1 in situ hybridization (ISH) for calculating the percentage of positive cells on the tissue section. RESULTS: Plasma EBV-DNA levels and detecting rate in NPC before treatment (median 82 500 copies/ml, 92%) were significantly higher than that in NPC after treatment (median 0 copy/ml, 19%) and in controls (median 0 copy/ml, 12%) (P < 0.05), whereas there was no significant difference between NPC after treatment and controls (P > 0.05). There was no significant difference of PBCs EBV-DNA load and detecting rate in NPC before (0 copy/actin, 24%) and after treatment (0 copy/actin, 14%), as well as in controls (0 copy/actin, 16%) (P > 0.05). Plasma EBV-DNA level was not correlated to PBCs EBV-DNA load in NPC before (P = 0.92) and after treatment (P = 0.27), and controls (P = 0.74). EBV-DNA level (27.8 copies/actin) in NPC tumor tissues was significantly higher than that in nasopharyngitis (0 copy/actin) (P < 0.05), and was positively correlated to the ratio of EBER1 positive cells to total cells on the NPC section. In NPC patients, plasma EBV-DNA level was significantly increased in TNM stage I (2500 copies/ml), II (32 590 copies/ml), III (86 000 copies/ml) and IV (166 200 copies/ml), whereas there was no significantly difference of PBCs EBV-DNA loads in difference stages of NPC. CONCLUSION: Plasma EBV-DNA level is a more sensitive and reliable biomarker than PBCs EBV-DNA loads for reflection the tumor volumes in NPC patients. Plasma EBV-DNA detection will improve TNM staging in NPC clinical practice on molecular level.

Biomarkers, Tumor↗
PubMed2004

Oncogenic role of eIF-5A2 in the development of ovarian cancer.

Amplification of 3q26 is one of the most frequent chromosomal alterations in many solid tumors, including ovarian, lung, esophageal, prostate, breast, and nasopharyngeal cancers. A candidate oncogene to eukaryotic initiation factor 5A2 (eIF-5A2), a member of eukaryotic initiation factor 5A subfamily, has been isolated from a frequently amplified region at 3q26.2. In this work, the tumorigenic ability of eIF-5A2 was demonstrated by anchorage-independent growth in soft agar and tumor formation in nude mice. Furthermore, antisense DNA against eIF-5A2 could inhibit cell growth in ovarian cancer cell line UACC-1598 with amplification of eIF-5A2 in form of double minutes. Cell growth rate in UACC-1598 was also inhibited when the expression level of EIF-5A2 was decreased by the reduction of the copy number of double minutes. The correlation of EIF-5A2 overexpression and clinical features of ovarian cancer was investigated using tissue microarray, and the result showed that eIF-5A2 overexpression was significantly associated with the advanced stage of ovarian cancer. These findings suggest that eIF-5A2 plays important roles in ovarian pathogenesis.

Animals↗
PubMed2004

Quantitative detection of common deletion of mitochondrial DNA in hepatocellular carcinoma and hepatocellular nodular hyperplasia.

AIM: To study the deletion of mitochondiral DNA in hepatocellular carcinoma and hepatocellular nodular hyperplasia and its significance in the development of cancer. METHODS: Deleted mtDNA (CD-mtDNA) and wild type mtDNA (WT-mtDNA) were quantitatively analyzed by using real-time PCR in 27 hepatocellular carcinomas (HCC) and corresponding noncancerous liver tissues and 27 hepatocellular nodular hyperplasiae (HNH). RESULTS: A novel CD (4 981 bp) was detected in 85% (23/27) and 83%(22/27) of HCC and HNH tumor tissues, respectively, which were significantly higher than that in paired noncancerous liver tissues (57%, 15/27) (P<0.05). The CD/WT-mtDNA ratio in HCC tumors was 0.00092 (median, interquartile range, 0.0001202-0.00105), which was significantly higher than that in paired noncancerous liver tissues (median, 0.000, quartile range, 0-0) (P=0.002, Mann-Whitney Test), and was 25 of times of that in HNH tissues (median, 0.0000374, quartile range, 0-0.0004225) (P=0.002, Mann-Whitney test). CONCLUSION: CD-mtDNA mutation plays an important role in the development and progression of HCC.

Base Sequence↗
PubMed2004

Long-term strength of ceramics for biomedical applications.

The influence of slow crack growth on the initiation of radial cracks at the lower surfaces of ceramic layers bonded to polymeric substrates is studied, with particular relevance to biomechanical systems, e.g., dental crowns and hip replacement prostheses. Critical loads are measured as a function of loading rate (dynamic fatigue) for model bilayers fabricated by epoxy-bonding selected clinical ceramics to polycarbonate bases. Radial crack initiation is observed in situ by viewing from below the transparent base during loading. Declines in the critical loads with diminishing load rate are consistent with slow crack growth of intrinsic flaws prior to radial crack pop in. A simple fracture mechanics relation incorporating a crack velocity function is used to analyze the data. Extrapolation beyond the data range enables long-lifetime (10 yr) estimates of sustainable loads. The procedure provides a basis for ranking ceramic types, and in particular for eliminating vulnerable candidate materials, for use in biomechanical systems. While slow crack growth is an important factor in failure, other mechanisms could operate in concert and even dominate under severe testing conditions, especially under cyclic loading.

Biocompatible Materials↗
PubMed2004

Structural features of the rice chromosome 4 centromere.

A complete sequence of a chromosome centromere is necessary for fully understanding centromere function. We reported the sequence structures of the first complete rice chromosome centromere through sequencing a large insert bacterial artificial chromosome clone-based contig, which covered the rice chromosome 4 centromere. Complete sequencing of the 124-kb rice chromosome 4 centromere revealed that it consisted of 18 tracts of 379 tandemly arrayed repeats known as CentO and a total of 19 centromeric retroelements (CRs) but no unique sequences were detected. Four tracts, composed of 65 CentO repeats, were located in the opposite orientation, and 18 CentO tracts were flanked by 19 retroelements. The CRs were classified into four types, and the type I retroelements appeared to be more specific to rice centromeres. The preferential insert of the CRs among CentO repeats indicated that the centromere-specific retroelements may contribute to centromere expansion during evolution. The presence of three intact retrotransposons in the centromere suggests that they may be responsible for functional centromere initiation through a transcription-mediated mechanism.

Base Sequence↗
PubMed2004

Estimating model parameters by chaos synchronization.

Using chaos synchronization and a proposed iterative method of parameter adaptation, we precisely estimate the model parameters of chaotic systems and synchronize two chaotic systems with originally mismatching model parameters. This parameter adaptation method can be applied to a spatiotemporal chaotic system with a one-way-coupled map lattice. As a biomedical application, this method is capable of estimating the asymmetric tension parameter of a vocal fold model.

Biophysical Phenomena↗
PubMed2004

Comparison between a submerged membrane bioreactor and a conventional activated sludge system on treating ammonia-bearing inorganic wastewater.

A submerged membrane bioreactor (SMBR) and a conventional activated sludge system (CAS) were compared in parallel over a period of 210 days on treating synthetic ammonia-bearing inorganic wastewater under similar conditions. Except for a short period of pH control failure, almost complete conversion of NH(4)(+)?N to NO(3)(-)?N was constantly achieved over an NH(4)(+)?N concentration range from 180 to 1300mgl(-1) at a hydraulic retention time (HRT) of 24h in the SMBR, compared to an average conversion ratio of 95.0% in the CAS. Scanning electron micrographs (SEMs) demonstrated the accumulation of extracellular polymeric substances (EPSs) in the SMBR. Ubiquinone-8 (UQ-8), followed by UQ-10, UQ-7 and UQ-9, was the dominant ubiquinone in both the systems. The dominant menaquinone in the SMBR was menaquinone-6 (MK-6), while that in the CAS was MK-7, indicating that some differences existed between the two systems in terms of microbial community structure. Soluble microbial products (SMPs) tended to accumulate, and then biodegrade in SMBR.

Ammonia↗
PubMed2004

Formulation and characterization of spray-dried powders containing nanoparticles for aerosol delivery to the lung.

Spray-drying is a common practice of powder preparation for a wide range of drugs. Spray-dried powders can be used to deliver particles to the lungs via a dry powder inhaler (DPI). The present study investigated the feasibility of developing a platform for aerosol delivery of nanoparticles. Lactose was used as the excipient and spray-dried with two different types of nanoparticles: gelatin and polybutylcyanoacrylate nanoparticles. Results showed that some carrier particles were hollow while others had a continuous matrix. Gelatin nanoparticles were incorporated throughout the matrix and sometimes accumulated at one end of the lactose. Polycyanoacrylate nanoparticles mostly clustered in different spots within the lactose carriers. The mean sizes of both nanoparticle types were characterized at two different times: before they were spray-dried and after they were redissolved from the spray-dried powders. Both nanoparticle types remained in the nano-range size after spray-drying. The mean nanoparticle sizes were increased by approximately 30% after spray-drying, though this increase was statistically significant only for the gelatin nanoparticles. Dispersion of the powder with an in-house passive dry powder inhaler and subsequent cascade impaction measurements showed that incorporation of the nanoparticles did not affect the fine particle fraction (FPF) or mass median aerodynamic diameter (MMAD) of the powders. FPF was approximately 40% while MMAD was 3.0+/-0.2 microm, indicating the present formulations yield aerosols of a suitable particle size for efficient lung delivery of nanoparticles. The present work demonstrates that nanoparticles can be delivered to the lungs via carrier particles that dissolve after coming in contact with the aqueous environment of the lung epithelium. This opens the way for new drug-targeting strategies using nanoparticles for pulmonary delivery of drugs and diagnostics.

Aerosols↗