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W Li

Publications and source records attributed to W Li.

At least 37 records · Page 2Linked to original sources
PubMed2004

Fibre reinforced composite dental bridge. Part I: Experimental investigation.

This experimental investigation aims at revealing the mechanical behaviour and failure pattern of direct fibre-reinforced resin-bonded dental bridge with various designs. To evaluate the overall effects of some newly developed dental materials, in the experiment, genuine composite dental bridge specimens are prepared and tested. The ultimate load, stiffness and mode at the failure of the bridges are measured and compared with the design variations. A good agreement between test and some clinical observations is demonstrated. It is verified that the weakest region appears across the pontic-abutment interface in the composite bridges. This study suggests that the composite bridges reinforced by fibres and supported by adjacent teeth could be of a higher structural strength and stiffness; therefore would provide better clinical performances.

Composite Resins↗
PubMed2004

Fibre reinforced composite dental bridge. Part II: Numerical investigation.

Motivated by the clinical success and limitations on experimental investigation of the fibre-reinforced composite dental bridge, this paper aims at providing a numerical investigation into the bridge structure. The finite element (FE) model adopted here is constructed from computer tomography images of a physical bridge specimen. The stress and strain distributions in the bridge structure especially in the bonding interfaces are analyzed in detail. The peak stresses and their variations with the different bridge designs are evaluated. Due to the lower bond strengths of adhesives and the high stress concentration in the pontic-abutment interface, the likelihood of failure in the interface is predicted by finite element analysis. The validity of the numerical results is established by a good agreement between the FE prediction and the tests in the load-deflection responses, the structural stiffness as well as the failure location of the composite dental bridge.

Composite Resins↗
PubMed2004

Intrasplenic transplantation of allogeneic hepatocytes modified by BCL-2 gene protects rats from acute liver failure.

BACKGROUND: Apoptosis of donor hepatocytes may be induced by recipient cytotoxic T lymphocytes (CTLs) during acute rejection, representing a major impediment for these cell transplants. Because the mechanisms of transplanted hepatocyte loss involve Fas-mediated pathways, BCL-2 genetic modification may protect liver cells. In the present study, we further investigated whether BCL-2 transfer into transplanted liver cells rendered them resistant to Fas ligand-induced apoptosis, and protected rats from acute liver failure. MATERIALS AND METHODS: Hepatocytes isolated from Sprague-Dawley rats were infected with an adenovirus vector encoding human BCL-2 gene (AdCMVBCL-2) or a control AdCMVLacZ vector. Forty-eight hours later, cells challenged with recombinant Fas ligand (rhsFasL) were assayed for apoptosis using TUNEL staining and caspase 3 activity. Other cells were transplanted into the spleens of Wistar rats with a 90% hepatectomy 12 hours later. RESULTS: Western blot analysis and RT-PCR confirmed the expression of hBcl-2 in AdCMVhBcl-2-infected hepatocytes. Recombinant FasL produced a dose-dependent increase in TUNEL-positive percentage and caspase-3 activity in uninfected hepatocytes, but did not influence these features in AdCMVhBcl-2-infected cells. On challenge with 90% hepatectomy, the survival of Wistar rats receiving transplantation of AdCMVhBCL-2-infected hepatocytes was significantly prolonged compared with the controls. CONCLUSION: Adenovirus-mediated BCL-2 gene transfer protects transplanted hepatocytes from Fas-mediated cytolysis, thus holding promise for a new avenue of acute liver failure treatment.

Adenoviridae↗
PubMed2004

Dioxin-like components in human breast milk collected from Hong Kong and Guangzhou.

The H4IIE rat hepatoma cell line was employed as a cell model to screen 7-ethoxyresorufin O-deethylase (EROD)-TCDD equivalents (EROD-TEQ) of human breast milk samples collected from Hong Kong and Guangzhou, China. The screening methods employed a 96-well plate spectrofluorometer-EROD assay. For cell-line validation, our results demonstrated a dose-dependent increase in the Ah receptor-mediated response (i.e., CYP1A1 mRNA and EROD) of the cells upon exposure to a number of known Ah receptor agonists, including 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), 2,3,7,8-tetrachlorodibenzothiophene, benzo[a]pyrene, and beta-naphthaflavone. TCDD induced CYP1A1 mRNA and EROD was in a close positive correlation (r=0.98). For the screening of dioxin-like compounds, breast milk samples collected during lactation weeks 3-5 were used. One hundred (from Hong Kong) and 48 (from Guangzhou) breast milk samples were assayed, of which 65% and 68% of the samples, respectively, showed detectable dioxin-like activities using the H4IIE cell EROD screening method. For sixty-five samples from Hong Kong the mean EROD-TEQ values ranged from 58.1 to 96.5 pg/g of milk fat for those aged 21-36 years while 32 samples from Guangzhou had mean values of 98.8-202.1 pg/g of milk fat. In comparisons of the EROD-TEQ values for different age groups from both cities, there were no significant differences (P<0.05). However, the mean and median EROD-TEQ values of the Guangzhou population were in general higher than those of the Hong Kong population. The results of the present study indicate that it is feasible to use the H4IIE cell-line as a model for screening dioxin-like compounds in human breast milk. In addition, the method is rapid and cost-effective, particularly for a routine and high-throughput sample screening analysis, compared to the costly and time-intensive chemical analytical techniques.

Animals↗
PubMed2004

Improved transduction of primary murine hepatocytes by recombinant adeno-associated virus 2 vectors in vivo.

Adeno-associated virus 2 (AAV) vectors are currently in use in Phase I/II clinical trials for gene therapy of cystic fibrosis and hemophilia B. Although 100% of murine hepatocytes can be targeted by AAV vectors, the transgene expression is limited to approximately 5% of hepatocytes. Since the viral genome is a single-stranded DNA, and single strands of both polarities are encapsidated with equal frequency, it has been suggested that failure to undergo DNA strand-annealing accounts for the lack of efficient transgene expression. We and others, on the other hand, have proposed that failure to undergo viral second-strand DNA synthesis attributes to the observed low efficiency of transgene expression. We have previously documented that a cellular protein, designated FKBP52, when present in phosphorylated forms, inhibits the viral second-strand DNA synthesis, and consequently, limits transgene expression in nonhepatic cells, whereas unphosphorylated forms of FKBP52 have no effect. To further evaluate whether phosphorylated FKBP52 is also involved in regulating AAV-mediated transgene expression in murine hepatocytes, we generated transgenic mice overexpressing the cellular T-cell protein tyrosine phosphatase (TC-PTP) protein, known to catalyze dephosphorylation of FKBP52, as well as mice deficient in FKBP52. We demonstrate here that dephosphorylation of FKBP52 in TC-PTP transgenic (TC-PTP-TG) mice, and removal of FKBP52 in FKBP52-knockout (FKBP52-KO) mice results in efficient transduction of murine hepatocytes following tail-vein injection of recombinant AAV vectors. We also document efficient viral second-strand DNA synthesis in hepatocytes from both TC-PTP-TG and FKBP52-KO mice. Thus, our data strongly support the contention that the viral second-strand DNA synthesis, rather than DNA strand-annealing, is the rate-limiting step in the efficient transduction of hepatocytes, which should have implications in the optimal use of recombinant AAV vectors in human gene therapy.

Animals↗
PubMed2004

Ablation of canine prostate using two-stage intraprostatic hot agarose solution and enzyme injection.

UNLABELLED: Enzyme ablation of the hyperplastic prostate may be an ideal method of management of BPH. However, the unsatisfactory ablation affects in vivo contrast with successful in vitro results limiting the enthusiasm for further research. In this study, we make efforts to solve the problems in the use of enzyme ablation of BPH in vivo and to measure satisfactory effect. MATERIAL AND METHODS: A total of 18 hybrid dogs between the ages of 7 and 11 y underwent this experiment. Eight dogs were divided into four groups according to the injection formula: enzyme solution, hot D-Hanks' plus enzyme solution, hot agarose plus enzyme solution, and hot agarose solution alone. After selecting the agarose plus enzyme solution group in the first month, the remainder 10 dogs were treated with this two-stage method. Intravenous or oral antibiotics were administered perioperatively. All operations were performed directly by way of laparotomy. The prostates were observed and harvested with surrounding tissue at 24 hrs, 7 days, 14 days, 1 month and 3-5 months after treatment. Gross and microscopic examinations were performed. RESULTS: Only agarose plus enzyme group shows obvious cavity formation with concomitant size reduction and softening of the prostate ablation effect in the four groups. At 24 h after injection, the prostates demonstrated cavity formation containing liquefied necrotic tissue. The liquefied tissue was absorbed in 7-14 days. At 1 month, the size of most prostates decreased with a corresponding decrease in the size of the cavities. The cavities nearly disappeared within 3-5 months, and the size of prostates decreased to between 1/2 and 1/4 of the pretreatment sizes. All prostates had intact urethral mucosa and capsule. No complications directly related to enzyme ablation were identified. In the control groups there were no significant cavities or decrease in prostate size. CONCLUSIONS: This two-stage thermal and enzyme ablative method can significantly ablate prostate tissue without identifiable complications, and would be possibly applied to treating human BPH in the future.

Administration, Oral↗
PubMed2004

Field and storage testing Bt potatoes for resistance to potato tuberworm (Lepidoptera: Gelichiidae).

Potato tuberworm, Phthorimaea operculella (Zeller), is the most serious insect pest of potatoes worldwide. The introduction of the Bacillus thuringiensis (Bt) toxin gene through genetic engineering offers host plant resistance for the management of potato tuberworm. We report on the field and storage studies to evaluate Bt-cry5 potato lines for resistance to potato tuberworm in Egypt under natural infestations and their agronomic performance in both Egypt and Michigan. From 1997 to 2001, field experiments were conducted at the International Potato Center (CIP) Research Station, Kafr El-Zyat, Egypt, and/or Agricultural Genetic Engineering Institute (AGERI), Giza, Egypt, to evaluate resistance to tuberworm. A total of 27 Bt-transgenic potato lines from six different Bt constructs were evaluated over a 5-yr period. After harvest and evaluation of the agronomic trials, storage evaluation of potato tuberworm damage was done at the CIP Research Station. The 1997 field trial was the first field test of genetically engineered crops in Egypt. Field tests to assess potato tuberworm resistance in Egypt were able to differentiate between the Bt-transgenic lines and the nontransgenic lines/cultivars in 1999, 2000, and 2001. The Bt-cry5-Spunta lines (Spunta-G2, Spunta-G3, and Spunta-6a3) were the most resistant lines in field with 99-100% of tubers free of damage. In the 2001 storage study, these lines were also over 90% free of tuberworm damage after 3 mo. NYL235-4.13, which combines glandular trichomes with the Bt-cry5/gus fusion construct, also had a high percentage of clean tubers in the field studies. In agronomic field trials in Michigan from 1997 to 2001, the Bt-transgenic lines in most instances performed similar to the nontransgenic line in the agronomic trials; however, in Egypt (1998-1999), the yields were less than one-half of those in Michigan. Expression of the Bt-cry5 gene in the potato tuber and foliage will provide the seed producer and grower a tool in which to reduce potato tuberworm damage to the tuber crop in the field and storage.

Animals↗
PubMed2004

Baculovirus and dsRNA induce Hemolin, but no antibacterial activity, in Antheraea pernyi.

Hemolin is one of the haemolymph proteins most strongly induced upon bacterial infection in Lepidoptera. When we applied RNA interference (RNAi) to suppress Hemolin expression in the Chinese oak silk moth Antheraea pernyi, we discovered that Hemolin is induced by double-stranded RNA (dsRNA) per se. As dsRNA is recognized as a virus pattern molecule, we then investigated the effect of a baculovirus (ApNPV) infection. We found that Hemolin is induced and expressed with similar kinetics as upon dsRNA injection. Notably, no Attacin gene expression or antibacterial activity was recorded. When baculovirus and high amounts of dsRNA were coinjected, the viral symptoms appeared earlier with Hemolin dsRNA than with GFP dsRNA. This indicates that silencing of hemolin affected the progress of the viral infection.

Animals↗
PubMed2004

Characterization and evolution of furanocoumarin-inducible cytochrome P450s in the parsnip webworm, Depressaria pastinacella.

Depressaria pastinacella, the parsnip webworm, a specialist on two genera in the Apiaceae, routinely consumes plant tissues high in furanocoumarin content and is capable of rapid cytochrome P450-mediated detoxification of these compounds. In this study, four cDNAs were cloned from the larval midgut of this insect: two full-length CYP6AB3 and CYP6AE1 cDNAs are closely related to members of the furanocoumarin-metabolizing CYP6B subfamily and two partial CYP9A6 and CYP9A7 cDNAs are related to members of the CYP9A subfamily that have also been linked to the detoxification of xenobiotics. At least one of these P450s (CYP6AB3) is inducible by dietary furanocoumarins, indicating its potential involvement in furanocoumarin metabolism. A homology model of CYP6AB3 was constructed and compared to models of CYP6B1 from the specialist species, Papilio polyxenes, and CYP6B4 from the generalist species, P. glaucus. Structural superpositioning of these models has revealed very high spatial similarity of elements, including the B helix, B'-C loop, I helix and C-terminal domain, within the catalytic sites of these proteins. Most importantly, key amino acid residues that can potentially come into contact with furanocoumarin substrates display conservation in their spatial positioning and side chain polarities. Three of these residues, Val103, Leu113 and Phe118 (numbered according to CYP6AB3), are conserved in all three of these proteins, further implicating CYP6AB3 in furanocoumarin metabolism by parsnip webworms. Characterization of these P450 cDNAs will allow for functional analyses aimed at elucidating the molecular mechanisms underlying the coevolutionary interactions between this herbivore and its principal host plant.

Amino Acid Sequence↗
PubMed2004

In vitro and in vivo investigation of a novel monoclonal antibody to plasma cells (W5 mAb).

Natural antibodies (Abs), predominantly anti-Gal alpha 1-3Gal (Gal) Abs, in non-human primates and human beings present a major hurdle to successful pig-to-primate xenotransplantation. Attempts to inhibit anti-Gal Ab production in naïve baboons using non-specific immunosuppressive or B cell-specific reagents have failed. A new rat monoclonal antibody (W5 mAb) has been generated, which binds to all B cells, including memory cells, and to the majority of plasma cells, but not to T cells. It has been tested in vitro and in vivo. By immunoprecipitation, W5 mAb bound a human leukocyte antigen class II (HLA-DR) determinant. Sorting splenic or bone marrow W5+ cells resulted in a highly enriched anti-Gal Ab and total immunoglobulin (Ig)-secretory population. In vivo studies in baboons demonstrated that W5 mAb was safe but, despite the concomitant administration of an anti-CD154 mAb to inhibit sensitization, anti-rat Abs were detected within 10 days and inhibited the effect of the W5 mAb. High levels of W5 mAb were able to completely deplete B cells in the blood, but not in lymphoid tissues. Enzyme-linked spot-forming assay (ELISPOT) demonstrated that only 50 to 60% of secreting cells (SC) were depleted in the bone marrow. No reduction in the serum levels of anti-Gal Ab was observed. W5 mAb did not cause complete inhibition of anti-Gal Ab production, probably as a result of its inability to completely deplete B and plasma cells from all lymphoid compartments.

Animals↗
PubMed2004

Using child reported respiratory symptoms to diagnose asthma in the community.

AIMS: To study how respiratory symptoms reported by children, with or without spirometry, could help to discriminate those with asthma from those without. METHODS: Respiratory symptoms (frequent cough, frequent phlegm, and wheezing) reported by 1646 schoolchildren (aged 8-12 years) in a respiratory questionnaire and the FEV1:FVC ratio measured with spirometry (at three different cut-off values of 0.70, 0.75, and 0.80) were compared against the criterion standard of a physician diagnosis of asthma reported by the parents. RESULTS: The overall prevalence of asthma was 6%; more boys had asthma. Wheezing had the best discriminating ability among the three symptoms and a cut-off point at 75% was best for the FEV1:FVC ratio. Combining wheezing with an FEV1:FVC ratio <75% gave the highest discriminating ability of 83%. If the tests were applied to hypothetical populations with higher prevalence ratios of asthma, the added value of the FEV1:FVC ratio became less apparent. CONCLUSION: Respiratory symptoms, especially wheezing, reported by children had good discriminating ability for asthma and could be adopted for opportunistic screening in the primary care settings.

Asthma↗
PubMed2004

Racial segregation and county level intentional injury in Pennsylvania: analysis of hospital discharge data for 1997-1999.

STUDY OBJECTIVE: This study examined whether high levels of racial segregation are associated with high county level intentional injury rates. DESIGN: Multiple linear regression was used to assess the association between county racial segregation (measured by the Gini coefficient) and intentional injury rates. Multicollinearity was assessed with Eigenvalues and condition indices. SETTING: State of Pennsylvania. PATIENTS: County level intentional injury rates for 1995 to 1997 were calculated from hospital discharge data. MAIN RESULTS: After controlling for other known county level risk factors, higher levels of racial segregation in a county were significantly related to higher intentional injury rates. Multicollinearity was not a problem. Population size and density, family stability and median income, together with the percentage male, unemployed, in poverty, divorced men, and high school graduates of the county were controlled. CONCLUSIONS: Racial segregation is an important factor in the rate of intentional injury in a community. These results may be important for municipal and state agencies when developing public policies to prevent violence and promote racial integration.

Adult↗
PubMed2004

The status of structural genomics defined through the analysis of current targets and structures.

Structural genomics--large-scale macromolecular 3-dimenional structure determination--is unique in that major participants report scientific progress on a weekly basis. The target database (TargetDB) maintained by the Protein Data Bank (http://targetdb.pdb.org) reports this progress through the status of each protein sequence (target) under consideration by the major structural genomics centers worldwide. Hence, TargetDB provides a unique opportunity to analyze the potential impact that this major initiative provides to scientists interested in the sequence-structure-function-disease paradigm. Here we report such an analysis with a focus on: (i) temporal characteristics--how is the project doing and what can we expect in the future? (ii) target characteristics--what are the predicted functions of the proteins targeted by structural genomics and how biased is the target set when compared to the PDB and to predictions across complete genomes? (iii) structures solved--what are the characteristics of structures solved thus far and what do they contribute? The analysis required a more extensive database of structure predictions using different methods integrated with data from other sources. This database, associated tools and related data sources are available from http://spam.sdsc.edu.

Computational Biology↗
PubMed2004

Dentonin, a fragment of MEPE, enhanced dental pulp stem cell proliferation.

Matrix extracellular phosphoglycoprotein (MEPE) is a SIBLING protein, found in bone and dental tissues. The purpose of this study was to determine whether a 23-amino-acid peptide derived from MEPE (Dentonin or AC-100) could stimulate dental pulp stem cell (DPSC) proliferation and/or differentiation. DPSCs were isolated from erupted human molars, and the mitogenic potential of Dentonin in DPSCs was measured by BrdU immunoassay and cell-cycle gene SuperArray. Differentiation of DPSCs with Dentonin was characterized by Western blot and by osteogenesis gene SuperArray. Dentonin enhanced DPSC proliferation by down-regulating P16, accompanied by up-regulation of ubiquitin protein ligase E3A and human ubiquitin-related protein SUMO-1. Enhanced cell proliferation required intact RGD and SGDG motifs in the peptide. This study shows that Dentonin can promote DPSC proliferation, with a potential role in pulp repair. Further studies are required to determine the usefulness of this material in vivo.

Amino Acid Sequence↗
PubMed2004

Amelogenin-guided crystal growth on fluoroapatite glass-ceramics.

The formation of aligned fibrous apatite crystals in enamel is predominantly attributed to the involvement of amelogenin proteins. We developed a model to study interactions of matrix proteins with apatite mineral in vitro and tested the hypothesis that amelogenin solubility affects the ability to induce protein-guided mineralization. Crystal growth experiments were performed on fluoroapatite (FAP) glass-ceramics in mineralizing solutions containing recombinant full-length amelogenin (rH174) at different concentrations. Using atomic force microscopy, we observed that mineral precipitated randomly on the substrate, but also formed thin layers (height, 10 nm) on FAP within 24 hrs. This growth pattern was unaffected when 0.4 mg/mL of rH174 was added. In contrast, crystals grew on FAP at a rate up to 20 times higher, at 1.6 mg/mL protein. Furthermore, nanospheres and mineral bound specifically to FAP and aligned in strings approximately parallel to the c-axis of FAP, leading us to the conclusion that amelogenin proteins indeed control direction and rate of growth of apatite in enamel.

Amelogenin↗
PubMed2004

Mechanisms of human skin cell motility.

The extracellular matrix (ECM) in contact with the cells and the soluble growth factors (GFs) binding to their cell surface receptors are the two main signals that directly regulate cell motility. Human keratinocytes and dermal fibroblasts are two primary cell types in skin that must undergo migration for skin wounds to heal. In this cell migration, ECMs play an "active" role by providing the cells with both focal adhesions and a migration-initiating signal, even in the absence of GFs. In contrast, GFs cannot initiate cell migration in the absence of a pro-migratory ECM. Rather, GFs play a "passive" role by enhancing the ECM-initiated motility and giving the moving cells directionality. Inside the cells, the initiation signal of the ECM and the optimization signals of the GFs are propagated by both overlapping and discrete signaling networks. However, activation of no single signaling pathway by itself is sufficient to replace the role of ECMs or GFs. This review focuses on our current understanding of both the individual and the combined functions of ECMs and GFs in the control of skin cell motility. An abbreviation of the terminologies used in this article is provided.

Cell Movement↗
PubMed2003

Electrophysiological evidence for detection and discrimination of pheromonal bile acids by the olfactory epithelium of female sea lampreys ( Petromyzon marinus).

Electro-olfactograms were used to determine sensitivity and specificity of olfactory organs of female sea lampreys ( Petromyzon marinus) to four bile acids: 3-keto petromyzonol sulfate and 3-keto allocholic acid from spermiating males and petromyzonol sulfate and allocholic acid from larvae. Spermiating male bile acids are thought to function as a mating pheromone and larval bile acids as a migratory pheromone. The response threshold was 10(-12) mol l(-1) for 3-keto petromyzonol sulfate and 10(-10) mol l(-1) for the other bile acids. At concentrations above 10(-9) mol l(-1), the sulfated bile acids showed almost identical potency, as did the non-sulfated bile acids. The two sulfated bile acids were more potent than the two non-sulfated ones. In addition, 3-keto petromyzonol sulfate and water conditioned with spermiating males induced similar concentration-response curves and response thresholds. Cross-adaptation experiments demonstrated that the sulfated and non-sulfated bile acids represent different odors to the olfactory epithelium of females. Further exploration revealed that 3-keto petromyzonol sulfate represents a different odor than petromyzonol sulfate, while 3-keto allocholic acid and allocholic acid represent the same odor. Results indicate that male-specific bile acids are potent and specific stimulants to the female olfactory organ, supporting the previous hypothesis that these bile acids function as a pheromone.

Adaptation, Physiological↗