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Biomedical subjects

Tao Pan

Publications and source records attributed to Tao Pan.

50 records · Page 3Linked to original sources
PubMed2004

[Non-steroidal anti-inflammatory agents for chemoprevention of colorectal polyps: a meta-analysis].

OBJECTIVE: To assess whether or not non-steroidal anti-inflammatory agents (NSAIDs) might prevent colorectal polyps. METHODS: A systematic review of all relevant randomized controlled trials was performed. We searched all randomized controlled trials of chemoprevention of colorectal polyps. Abstracts was included. RESULTS: 8 trials were assessed in the final systematic analysis. We found a sufficient evidence to support that aspirin might prevent the development of colorectal adenomas in comparing with placebo group in two trails of high quality and large sample (P = 0.003). However, there is no evidence to support that sulindac and celecoxib might cure or prevent colorectal adenomas or familial adenomatous polyposis (P > 0.05) and also no evidence to support that dosage of NSAIDs is related with the result of prevention of colorectal adenomas. It was shown that regular aspirin use for 30-60 months cannot reduce the risk of colorectal cancer (P = 0.8). No significant difference in the number of adverse events was found between patients taking NSAIDs and those given placebo (P = 0.9). CONCLUSIONS: Aspirin might prevent the development of colorectal adenomas, but there is no evidence to support that sulindac and celecoxib might cure or prevent colorectal adenomas or familial adenomatous polyposis and that regular aspirin use might reduce the risk of colorectal cancer.

Anti-Inflammatory Agents, Non-Steroidal↗
PubMed2003

On the same cell type GPI-anchored normal cellular prion and DAF protein exhibit different biological properties.

Normal cellular prion protein (PrP(C)) and decay-accelerating factor (DAF) are glycoproteins linked to the cell surface by glycosylphosphatidylinositol (GPI) anchors. Both PrP(C) and DAF reside in detergent insoluble complex that can be isolated from human peripheral blood mononuclear cells. However, these two GPI-anchored proteins possess different cell biological properties. The GPI anchor of DAF is markedly more sensitive to cleavage by phosphatidylinositol-specific phospholipase C (PI-PLC) than that of PrP(C). Conversely, PrP(C) has a shorter cell surface half-life than DAF, possibly due to the fact that PrP(C) but not DAF is shed from the cell surface. This is the first demonstration that on the surface of the same cell type two GPI-anchored proteins differ in their cell biological properties.

CD55 Antigens↗
PubMed2003

Crystal structure of the specificity domain of ribonuclease P.

RNase P is the only endonuclease responsible for processing the 5' end of transfer RNA by cleaving a precursor and leading to tRNA maturation. It contains an RNA component and a protein component and has been identified in all organisms. It was one of the first catalytic RNAs identified and the first that acts as a multiple-turnover enzyme in vivo. RNase P and the ribosome are so far the only two ribozymes known to be conserved in all kingdoms of life. The RNA component of bacterial RNase P can catalyse pre-tRNA cleavage in the absence of the RNase P protein in vitro and consists of two domains: a specificity domain and a catalytic domain. Here we report a 3.15-A resolution crystal structure of the 154-nucleotide specificity domain of Bacillus subtilis RNase P. The structure reveals the architecture of this domain, the interactions that maintain the overall fold of the molecule, a large non-helical but well-structured module that is conserved in all RNase P RNA, and the regions that are involved in interactions with the substrate.

Bacillus subtilis↗
PubMed2003

Guanidine hydrochloride extraction and detection of prion proteins in mouse and hamster prion diseases by ELISA.

Current detection of transmissible spongiform encephalopathy (TSE) relies on the proteolytic generation of a protease-resistant core from the scrapie isoform of prion protein (PrP(Sc)) followed by immunoblotting. This process is non-quantitative, time-consuming, and technically demanding. Recently, an alternative in vitro test for TSE based on the differential extraction of brain homogenates using guanidine hydrochloride followed by DELFIA (Dissociation Enhanced Lanthanide FluoroImmunoAssay) has been developed. In the present study, this approach was adopted using a panel of anti-PrP monoclonal antibodies (MAbs) in conventional sandwich enzyme-linked immunosorbent assay (ELISA) to investigate hamster and two distinct strains of mouse prion diseases. Although PrP species were present in both soluble and insoluble fractions from normal as well as TSE samples, only the PrP species in the insoluble fractions from the latter samples were protease-resistant. In addition, certain anti-PrP MAb pairs could distinguish the PrP species in infected brains from those in the normal samples. The ability to differentiate disease-associated PrP isoforms without proteinase K digestion could serve as a panacea for developing a reliable and rapid diagnostic test for prion diseases.

Animals↗
PubMed2003

RNA folding: models and perspectives.

Intrinsic events during RNA folding include conformational search and metal ion binding. Several experimentally testable models have been proposed to explain how large ribozymes accomplish folding. Future challenges include the validation of these models, and the correlation of experimental results and theoretical simulations.

Kinetics↗
PubMed2003

Mid-infrared spectroscopic measurement of ionic dissociative materials in the metabolic pathway.

We determine the pH dependency of the mid-infrared spectra in aqueous solution of the organic dissociative materials in the metabolic pathway: saccharide phosphates (G6P, F6P), adenosine, and its phosphates (ATP, ADP, AMP). The series of molar absorbance spectra for these reagents were obtained in a pH range of about 2 to 11 with a Fourier transform infrared (FT-IR) spectrometer equipped with a horizontal diamond attenuated total reflection (ATR) sampling accessory. We also provide a method of infrared spectral extraction of ionic dissociative materials by performing a linear least-square fitting utilizing the formulas of ionic dissociation equilibrium shift, and we obtain the infrared spectrum of each ionic species of the dissociative materials: G6P-, G6P2-; F6P-, F6P2-; ATP2-, ATP3-, ATP4-; ADP-, ADP2-, ADP3-; AMP, AMP-, AMP2-; and adenosine+, adenosine0. The infrared spectral structure of each ionic species of the dissociative materials in the metabolic pathway are discussed. Additionally, the possibility for a quantification system of the concentrations of the organic dissociative materials in varying pH is suggested.

Adenosine Diphosphate↗
PubMed2003

[The surgical treatment of cancer in the base of tongue].

OBJECTIVE: To seek for a better approach for the resection of carcinoma of the base of tongue. METHOD: From 1991 to 2000, all 21 cases of tongue base carcinoma had been removed by transhyoid pharyngotomy(11 cases), mandibulectomy(7 cases) and step-liked mandibulotomy (3 cases). RESULT: Three patients with step-liked mandibulotomy had speech disorder and dysphagy. The rest had satisfactory speech and swallowing functions. During followed-up of 2-5 years, 2 cases lost follow-up, 18 cases were alive at 2 years, 13 cases were alive at 3 years, 5 cases 5 years. CONCLUSION: Transhyoid pharyngotomy provides good exposure to resect those tumors that involve the base of tongue, epiglottis, hypopharynx and larynx.

Adult↗
PubMed2002

Cell-surface prion protein interacts with glycosaminoglycans.

We used ELISA and flow cytometry to study the binding of prion protein PrP to glycosaminoglycans (GAGs). We found that recombinant human PrP (rPrP) binds GAGs including chondroitin sulphate A, chondroitin sulphate B, hyaluronic acid, and heparin. rPrP binding to GAGs occurs via the N-terminus, a region known to bind divalent cations. Additionally, rPrP binding to GAGs is enhanced in the presence of Cu2+ and Zn2+, but not Ca2+ and Mn2+. rPrP binds heparin strongest, and the binding is inhibited by certain heparin analogues, including heparin disaccharide and sulphate-containing monosaccharides, but not by acetylated heparin. Full-length normal cellular prion protein (PrPC), but not N-terminally truncated PrPC species, from human brain bind GAGs in a similar Cu2+/Zn2+-enhanced fashion. We found that GAGs specifically bind to a synthetic peptide corresponding to amino acid residues 23-35 in the N-terminus of rPrP. We further demonstrated that while both wild-type PrPC and an octapeptide-repeat-deleted mutant PrP produced by transfected cells bound heparin at the cell surface, the PrP N-terminal deletion mutant and non-transfectant control failed to bind heparin. Binding of heparin to wild-type PrPC on the cell surface results in a reduction of the level of cell-surface PrPC. These results provide strong evidence that PrPC is a surface receptor for GAGs.

Amino Acid Motifs↗
PubMed2002

Dimeric and monomeric Bacillus subtilis RNase P holoenzyme in the absence and presence of pre-tRNA substrates.

Ribonuclease P (RNase P) is a ribonucleoprotein enzyme that catalyzes the 5' maturation of tRNA precursors. The bacterial RNase P holoenzyme is composed of a large, catalytic RNA and a small protein. Our previous work showed that Bacillus subtilis RNase P forms a specific "dimer" that contains two RNase P RNA and two RNase P protein subunits in the absence of substrate. We investigated the equilibrium and the structure of the dimeric and the monomeric holoenzyme in the absence and presence of substrates by synchrotron small-angle X-ray scattering, 3' autolytic processing, and hydroxyl radical protection. In the absence of substrate, the dimer-monomer equilibrium is sensitive to monovalent ions and the total holoenzyme concentration. At 0.1 M NH4Cl, formation of the dimer is strongly favored, whereas at 0.8 M NH4Cl, the holoenzyme is a monomer. Primary hydroxyl radical protection in the dimer is located in the specificity domain, or domain I, of the RNase P RNA. The ES complex with a substrate containing a single tRNA is always monomeric. In contrast, the dominant ES complex with a substrate containing two tRNAs is dimeric at 0.1 M NH4Cl and monomeric at 0.8 M NH4Cl. Our results show that the B. subtilis holoenzyme can be a dimer and a monomer, and the fraction of the dimer is very sensitive to the environment. Under a variety of conditions, both the holoenzyme dimer and monomer can be present in significant amounts. Because the majority of tRNA genes are organized in large operons and because of the lack of RNase E in B. subtilis, a dimeric holoenzyme may be necessary to facilitate the processing of large precursor tRNA transcripts. Alternatively, the presence of two forms of the RNase P holoenzyme may be required for other yet unknown functions.

Bacillus subtilis↗
PubMed2002

Intercellular transfer of the cellular prion protein.

The cellular prion protein (PrP(C)) is a glycosylphosphatidylinositol (GPI)-anchored protein. We investigated whether PrP(C) can move from one cell to another cell in a cell model. Little PrP(C) transfer was detected when a PrP(C) expressing human neuroblastoma cell line was cultured with the human erythroleukemia cells IA lacking PrP(C). Efficient transfer of PrP(C) was detected with the presence of phorbol 12-myristate 13-acetate, an activator of protein kinase C. Maximum PrP(C) transfer was observed when both donor and recipient cells were activated. Furthermore, PrP(C) transfer required the GPI anchor and direct cell to cell contact. However, intercellular protein transfer is not limited to PrP(C), another GPI-anchored protein, CD90, also transfers from the donor cells to acceptor cells after cellular activation. Therefore, this transfer process is GPI-anchor and cellular activation dependent. These findings suggest that the intercellular transfer of GPI-anchored proteins is a regulated process, and may have implications for the pathogenesis of prion disease.

Blotting, Western↗
PubMed2002

Heterogeneity of normal prion protein in two- dimensional immunoblot: presence of various glycosylated and truncated forms.

The common use of one-dimensional (1-D) immunoblot with a single monoclonal antibody (Mab) engenders the notion that the normal or cellular prion protein (PrP(C) ) comprises few and simple forms. In this study we used two-dimensional (2-D) immunoblot with a panel Mabs to various regions of the prion protein to demonstrate the complexity of the PrP(C) present in human brain. We distinguished over 50 immunoblot spots, each representing a distinct PrP(C) species based on combinations of different molecular weights and isoelectric points (pIs). The PrP(C) heterogeneity is due to the presence of a full-length and two major truncated forms as well as to the diversity of the glycans linked to most of these forms. The two major truncated forms result from distinct cleavage sites located at the N-terminus. In addition, enzymatic removal of sialic acid and lectin binding studies indicate that the glycans linked to the full-length and truncated PrP(C) forms differ in their structure and ratios of the glycoforms. The truncation of PrP(C) and the heterogeneity of the linked glycans may play a role in regulating PrP(C) function. Furthermore, the presence of relatively large quantities of different PrP(C) species may provide additional mechanisms by which the diversity of prion strains could be generated.

Antibodies, Monoclonal↗
PubMed2002

[Electrically evoked auditory nerve compound action potentials in Nucleus CI24M cochlear implant users].

OBJECTIVE: To study the feasibility and clinical applicability of electrically evoked auditory nerve compound action potentials (ECAP) in young patients with Nucleus CI24M cochlear implants. METHOD: ECAPs have been recorded from 37 Nucleus CI24M cochlear implant users in response to monopolar electrical stimulation of the cochlea by using the neural response telemetry(NRT) software and the hardware. Behavioral thresholds and maximum comfortable levels were measured in 12 of those patients. RESULT: ECAPs could be recorded in 87.6% of all patients. Good relations were observed between ECAP threshold and behavioral threshold, but poor relations between ECAP threshold and the impedance of different electrodes. We also observed growth functions and threshold variations of ECAP across subjects for a given place as well as across electrodes within a subject. These findings might be that these particular physiological measures are related to the number of living neural fibers and the excitability of the auditory nerve to electrical stimulation. CONCLUSION: ECAPs were proved to be useful in adjusting the stimulation parameters of the cochlear implant speech processor in order to maximize an individual's performance with the device, especially in young children.

Action Potentials↗
PubMed2002

[The extensibility and retractility of surgical margins in digestive tract cancer].

OBJECTIVE: To study the extensibility and retractility of the surgical margins in digestive system neoplasms. METHODS: The length difference of the digestive tract was measured in vivo and in vitro under different conditions. Five cm of the stomach, small intestine and large bowel and 2 cm of the esophagus were measured as standard control length in vivo just before resection. The length was measured with a ruler under pull of 500 g and 1 000 g in vivo, in fresh status in vitro, and 10% formaldehyde fixed for 6 - 8 h, 12 - 24 h and 48 - 72 h. The extension or retraction ratio was calculated. The length difference was divided by the natural length in vivo. RESULTS: Seventeen cases of the esophagus, 18 cases of the stomach, 15 cases of the small intestine and 25 cases of the large bowel were measured under pull of 500 g and 1 000 g. The esophagus extended 16.5% and 30.5%, stomach 15.0% and 22.6%, small intestine 66.4% and 120.0%, large bowel 36.0% and 56.0% respectively. In natural status ex vivo, the esophagus retracted 44.5%, stomach 13.6%, small intestine 11.4% and large bowel 15.6% respectively; they continue to retract after 10% formaldehyde fixation until 12 - 24 h later. If the length of surgical margin of the fresh specimen ex vivo was x, the natural length of margin in vivo of the esophagus would be 1.80 x, stomach 1.16 x, small intestine 1.13 x, and large bowel 1.18 x. If formaldehyde fixation for 6 - 8 h, the natural length of surgical margin in vivo of the esophagus would be 1.82 x, stomach 1.41 x, small intestine 1.22 x, large bowel 1.55 x. If formaldehyde fixation for 12 - 24 h, the surgical margin length in vivo of the esophagus would be 2.22 x, stomach 1.43 x, small intestine 1.28 x, and large bowel 1.57 x. CONCLUSION: The length of surgical margin of digestive system cancers varied under different conditions, and the evaluation of surgical margin during surgery should be performed under natural status in vivo.

Adult↗