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Biomedical subjects

X Tan

Publications and source records attributed to X Tan.

At least 127 records · Page 7Linked to original sources
PubMed1997

[Molecular mechanism of mutagenesis induced by aflatoxin B1 using a shuttle vector pSP189/mammalian cell system].

AFB1 is one of the most potent carcinogenic mycotoxins, naturally occurred in foods. We applied a new SV40-based shuttle vector pSP189 and African Green kidney cells (VeroE6 cell line), which constitute shuttle vector/mammalian cell system to detect mutagenesis induced by AFB1 and to study the effects of AFB1 on the mutation site, type and sequence specificity of DNA molecular level through sequence analysis of pSP189 target gene SupF TRNA. The results indicated that through various time treatment of AFB1 and rat liver microsome, the mutants were obtained by transformation of E. Coli MBM 7070 with progeny of pSP189 generated during replication in veroE6 cells, which increased gradually with the lapse of time, and this experiment showed a significant dose-response relationship. Most detected mutants were point mutations evidenced by agarose gel electrophoresis analysis. The results of direct sequencing SupF TRNA of 53 independent mutants showed that most mutations (about 84.9%) were single base substitutions, among which 95.2% of base substitutions happened on the site of G:C base pair, the predominant mutation was G:C-->T:A transversion, accounting for 53.3%, followed by G:C-->A:T transition, accounting for 35.6%. AFB1-induced mutations did not distributed randomly, and had mutation hot spots and sequence specificity, which contained 5 base pair sequence 5'-NNTTC-3'. The mutations on the SupF shuttle vector were consistent with the results from studies of oncogene tumor suppressor genes and DNA adduct.

Aflatoxin B1↗
PubMed1997

[Mutiple factors analysis of the effects of excimer laser photorefractive keratectomy].

PURPOSE: To observe the effect of excimer laser photorefractive keratectomy (PRK) correcting myopia and astigmatism, and to study the related factors. METHOD: PRK was performed with the aim to correct myopia errors from 1.00 to 16.00 diopters on 529 myopia eyes (306 patients). All eyes were divided into two groups: Group I: -1.00-6.00 D(294 eyes); group II: -6.25-16.00 D(235 eyes). All the patients were followed up for 3 to 12 months. RESULTS: At postoperative 12 months the rates of uncorrected visual acuity more than or equal to 10/20 or 20/20 were 97.5%, 77.5% in group I, and 80.3%, 32.8% in group II respectively; 92.5% of eyes were within +/- 1.00 diopter of the desired emmetropia in group I, but 42.6% in group II; The influential factors of changes of postoperative diopters was the severity of corneal haze, methods of removing corneal epithelium, intraocular pressure, the central corneal thickness. CONCLUSION: The excimer laser PRK is regarded to be a very predictable, safe, stable, and effective method to correct myopia up to -6.00 D. Prior to operation, the plan would be disigned according to diopters, ages, corneal thickness intraocular pressure. During operation, the corneal epithelium bad better to be removed by laser.

Astigmatism↗
PubMed1997

[Technological study on the supercritical-CO2 fluid extraction of Curcuma longa oils].

This paper first reports technological study on the extraction of Curcuma longa oils by supercritical-CO2 fluid, mainly studies the influence of pressure, temperature, flow rate of CO2 and time on the yield of the oils, determines optimum technology of extracting the oils, analyzes chemical constituents extracted, compares the oils from SFE-CO2 and SD technology, studies industrial test on the SF-CO2 extraction. The results shows pressure and temperature are more important factors of influence; the optimum technological condition is the extracted pressure 25 MPa and temperature 45 degrees C, isolated pressure I 12.5 MPa and temperature I 60 degrees C, isolated pressure II 6MPa and temperature II 38 degrees C, CO2 flow rate 9 Kg/Kg.h, and extracted time 2 h; the constituents from SFE-CO2 and SD methods are identical, but their content has some difference; SFE-CO2 technology is better than that of SD, which is high yield shorter time, etc.; the industrial production of the oils with SFE-CO2 method is available.

Carbon Dioxide↗
PubMed1997

[Activation of L-Arg: no pathway in canine brain by the damage from complete cerebral ischemia-reperfusion].

To ascertain whether complete cerebral ischemia-reperfusion activate L-Arg: NO pathway in canine brain, we anestherized nine adult dogs with ketamine and fentayle and randomly divided into two groups. Four dogs were nonischemic control group. Five dogs were complete cerebral ischemia-reperfusion group, they underwent a 18-minute cardiac arrest, and were resusciatation by standard CPR, supported by intensive care for 8 hours. At the end of each experiment, the parietal cortex was assayed for content of Nitrite and NADPH-positive neurons. Compared with the control group, the contents of Nitrite and NADPH-positive neurons of coxtex in complete cerebral ischemia-reperfusion group increased significantly (P < 0.01). The results suggest that complete cerebral ischemia-reperfusion activate the L-Arg: NO pathway in canine brain, and NO may play an important role in cerebral ischemia-reperfusion injury.

Animals↗
PubMed1996

Cell-mediated infection of cervix derived epithelial cells with primary isolates of human immunodeficiency virus.

We have previously demonstrated that HIV-infected transformed T-cells or monocytes adhere to monolayers of CD4-negative epithelial cells. Adhesion is soon followed by budding of HIV from infected mononuclear cells onto the surface of epithelial cells. Epithelial cells subsequently take up virus and become productively infected. Based on these findings, we proposed that sexual transmission of HIV may involve cell-mediated infection of intact mucosal epithelia of the urogenital tract. However, it has become increasingly clear that primary cells and HIV strains isolated from patients are more appropriate models for HIV infection than established cell lines and lab strains of virus. In the studies described here, we infected cervix-derived epithelial monolayers with primary monocytes infected with patient isolates of non-syncytial inducing (NSI) macrophage-tropic strains of HIV. Under the culture conditions employed, HIV-infected primary monocytes do not remain adherent to the apical surface of the epithelium, as did HIV-infected transformed cells. Instead, following adherence, the primary cells migrate between epithelial cells. Virus is secreted from a pseudopod as HIV-infected primary monocytes pass between cells of the epithelium. Productive infection of the epithelium was detected by p24 ELISA and PCR Southern blot analysis. Infection can be blocked by sera from HIV-seropositive individuals or by certain sulfated polysaccharides. These findings support the supposition that transmission of HIV may occur via cell-mediated infection of intact epithelia. The observations also hint at the possibility that-HIV-infected monocyte/macrophages in semen or cervical-vaginal secretions could cross intact epithelia by passing between epithelial cells. Blocking studies suggest that it may be possible to inhibit sexual transmission of HIV either by antibodies in genital tract secretions or by a topical formulation containing certain sulfated polysaccharides.

Acquired Immunodeficiency Syndrome↗
PubMed1996

Flunitrazepam effects on human sleep EEG spectra. II: Sigma and beta alterations during NREM sleep.

Flunitrazepam (FNZ) is known to enhance the higher EEG frequencies, including sigma (10-15 Hz) and beta (20-28 Hz). Both sigma and beta frequency bands show an inverse relationship with delta (0.3-3 Hz) during NREM periods, as we have previously reported. It is not known whether generation of these two EEG frequencies is mediated by the same or different neuronal mechanisms. In this report, we compare alterations of delta, sigma and beta EEG induced by FNZ (4 mg) orally administered to five healthy male subjects for seven consecutive nights. Sleep EEG on the baseline night (BLN), and the fourth and seventh drug nights (4DN, 7DN) was subjected to fast Fourier transform (FFT) analysis. On drug nights, sigma was enhanced without regard to delta amount, but beta was enhanced only during epochs containing low delta. Thus, sigma and beta EEG were altered differently by the same pharmacological agent. These results suggest that sigma and beta EEG are mediated by different neuronal mechanisms.

Adult↗
PubMed1996

Directional budding of human immunodeficiency virus from monocytes.

Time-lapse cinematography revealed that activated human immunodeficiency virus (HIV)-infected monocytes crawl along surfaces, putting forward a leading pseudopod. Scanning electron micrographs showed monocyte pseudopods associated with spherical structures the size of HIV virions, and transmission electron micrographs revealed HIV virions budding from pseudopods. Filamentous actin (F-actin) was localized by electron microscopy in the pseudopod by heavy meromyosin decoration. Colocalization of F-actin and p24 viral antigen by light microscopy immunofluorescence indicated that F-actin and virus were present on the same pseudopod. These observations indicate that monocytes produce virus from a leading pseudopod. We suggest that HIV secretion at the leading edges of donor monocytes/macrophages may be an efficient way for HIV to infect target cells.

Actins↗
PubMed1996

[Effect of ginger-processing on l-ephedrine contents in rhizoma Pinelliae].

The contents of l-ephedrine in Rhizoma Pinelliae have been determined to be approximately 3.44 x 10(-3). The contents vary with the five different processing methods in the following order, Pinellia boiled with ginger juice and alum > raw Pinellia > Pinellia dipped in ginger juice > Pinellia boiled only with ginger juice > Pinellia dipped in alum solution. The alum solution and the Pinellia boiled only with ginger juice bear most strongly on the l-ephedrine contents of Pinellia.

Drugs, Chinese Herbal↗
PubMed1996

[The immunologic influence of clinical implantation of the machinable bioactive glass ceramics (MBGC)].

The levels of the immunoglobulins (IgG, IgA, IgM), complements (C3, C4) and circulating immune complex (CIC) of the patients were measured before and after implantation of the machinable bioactive glass ceramics in maxillofacial surgery. No significant changes were detected. The results indicate that the patients' immunologic function and status were not affected by the material and machinable bioactive glass ceramics is good bloodcompatibility.

Adolescent↗
PubMed1995

PER3, a gene required for peroxisome biogenesis in Pichia pastoris, encodes a peroxisomal membrane protein involved in protein import.

PER genes are essential for the biogenesis of peroxisomes in the yeast Pichia pastoris. Here we describe the cloning of PER3 and functional characterization of its product Per3p. The PER3 sequence predicts that Per3p is a 713-amino acid (81-kDa) hydrophobic protein with at least three potential membrane-spanning domains. We show that Per3p is a membrane protein of the peroxisome. Methanol- or oleate-induced cells of per3-1, a mutant strain generated by chemical mutagenesis, lack normal peroxisomes but contain numerous abnormal vesicular structures. The vesicles contain thiolase, a PTS2 protein, but only a small portion of several other peroxisomal enzymes, including heterologously expressed luciferase, a PTS1 protein. These results suggest that the vesicles in per3-1 cells are peroxisomal remnants similar to those observed in cells of patients with the peroxisomal disorder Zellweger syndrome, and that the mutant is deficient in PTS1 but not PTS2 import. In a strain in which most of PER3 was deleted, peroxisomes as well as peroxisomal remnants appeared to be completely absent, and both PTS1- and PTS2-containing enzymes were located in the cytosol. We propose that Per3p is an essential component of the machinery required for import of all peroxisomal matrix proteins and is composed of independent domains involved in the import of specific PTS groups.

Acetyl-CoA C-Acetyltransferase↗
PubMed1995

Active site mapping of the catalytic mouse primase subunit by alanine scanning mutagenesis.

In the eukaryotic cell, DNA synthesis is initiated by DNA primase associated with DNA polymerase alpha. The eukaryotic primase is composed of two subunits, p49 and p58, where the p49 subunit contains the catalytic active site. Mutagenesis of the cDNA for the p49 subunit was initiated to demonstrate a functional correlation of conserved residues among the eukaryotic primases and DNA polymerases. Fourteen invariant charged residues in the smaller catalytic mouse primase subunit, p49, were changed to alanine. These mutant proteins were expressed, purified, and enzymatically characterized for primer synthesis. Analyses of the mutant proteins indicate that residues 104-111 are most critical for primer synthesis and form part of the active site. Alanine substitution in residues Glu105, Asp109, and Asp111 produced protein with no detectable activity in direct primase assays, indicating that these residues may form part of a conserved carboxylic triad also observed in the active sites of DNA polymerases and reverse transcriptases. All other mutant proteins showed a dramatic decrease in catalysis, while mutation of two residues, Arg162 and Arg163, caused an increase in Km(NTP). Analysis of these mutant proteins in specific assays designed to separately investigate dinucleotide formation (initiation) and elongation of primer indicates that these two activities utilize the same active site within the p49 subunit. Finally, mutations in three active site codons produced protein with reduced affinity with the p58 subunit, suggesting that p58 may interact directly with active site residues.

Alanine↗
PubMed1995

Characterization of peroxisome-deficient mutants of Hansenula polymorpha.

In the methylotrophic yeast Hansenula polymorpha, approximately 25% of all methanol-utilization-defective (Mut-) mutants are affected in genes required for peroxisome biogenesis (PER genes). Previously, we reported that one group of per mutants, termed Pim-, are characterized by the presence of a few small peroxisomes with the bulk of peroxisomal enzymes located in the cytosol. Here, we describe a second major group of per mutants that were observed to be devoid of any peroxisome-like structure (Per-). In each Per- mutant, the peroxisomal methanol-pathway enzymes alcohol oxidase, catalase and dihydroxyacetone synthase were present and active but located in the cytosol. Together, the Pim- and Per- mutant collections involved mutations in 14 different PER genes. Two of the genes, PER5 and PER7, were represented by both dominant-negative and recessive alleles. Diploids resulting from crosses of dominant per strains and wild-type H. polymorpha were Mut- and harbored peroxisomes with abnormal morphology. This is the first report of dominant-negative mutations affecting peroxisome biogenesis.

Alcohol Oxidoreductases↗
PubMed1995

An assay for HIV infection of cultured human cervix-derived cells.

There is a critical need to develop new strategies to prevent sexual transmission of HIV. Condoms have limited acceptance, and a vaccine may not be available for many years. A vaginal formulation could provide an alternative method if a compound that inhibits sexual transmission of HIV can be identified or synthesized, and if this agent can be formulated for vaginal use. In this report we describe an infection assay for testing compounds that may be useful in a vaginal formulation. This assay system utilizes a cell line (ME-180) derived from the human cervix which, on the basis of morphological features, is an appropriate model of female and male genital and urinary tract epithelia. These cells can be productively infected with HIV upon exposure to HIV-infected T-cell lines. Blocking experiments can be readily carried out in this model because in this p24 ELISA assay system the quantity of virus released by the infected epithelium over a 24-h period is 40 times background.

Cell Line↗
PubMed1995

The Hansenula polymorpha PER8 gene encodes a novel peroxisomal integral membrane protein involved in proliferation.

We previously described the isolation of mutants of the methylotrophic yeast Hansenula polymorpha that are defective in peroxisome biogenesis. Here, we describe the characterization of one of these mutants, per8, and the cloning of the PER8 gene. In either methanol or methylamine medium, conditions that normally induce the organelles, per8 cells contain no peroxisome-like structures and peroxisomal enzymes are located in the cytosol. The sequence of PER8 predicts that its product (Per8p) is a novel polypeptide of 34 kD, and antibodies against Per8p recognize a protein of 31 kD. Analysis of the primary sequence of Per8p revealed a 39-amino-acid cysteine-rich segment with similarity to the C3HC4 family of zinc-finger motifs. Overexpression of PER8 results in a markedly enhanced increase in peroxisome numbers. We show that Per8p is an integral membrane protein of the peroxisome and that it is concentrated in the membranes of newly formed organelles. We propose that Per8p is a component of the molecular machinery that controls the proliferation of this organelle.

Amino Acid Sequence↗
PubMed1995

Multidrug resistance gene expression in childhood medulloblastoma: correlation with clinical outcome and DNA ploidy in 29 patients.

Twenty-nine children treated for medulloblastoma between 1987 and 1991 were reviewed. Thirteen patients with high-risk medulloblastoma characterized by incomplete resection, diploid tumor or subarachnoid dissemination received chemotherapy following radiation therapy. Three received postoperative chemotherapy. Eight patients who had been treated with postoperative radiation therapy also received chemotherapy for recurrent tumors. After a minimum 3-year follow-up period, 16 were alive but 13 had died from recurrent tumors. In order to evaluate the possible participation of P-glycoprotein (Pgp)-mediated multidrug resistance (MDR) in medulloblastoma therapy and its correlation with prognosis, archival specimens were examined by immuno-histochemistry utilizing 3 monoclonal antibodies against Pgp and 6 cases by reverse-transcriptase polymerase chain reaction (RT-PCR) using MDR1-specific primers. Sixteen patients (55%) had MDR expression detected either by 1 of the 3 antibodies or by RT-PCR. DNA ploidy study was also performed on 18 specimens. We correlated patients' outcome with variable factors (extent of surgical resection, chemotherapy, DNA ploidy) and MDR expression. Patients who were treated with radiation therapy and adjuvant chemotherapy had a significantly better (p = 0.036) survival than those with radiation therapy alone, despite the fact that the former group of patients was considered to be high-risk. The extent of surgical resection and DNA ploidy did not correlate with prognosis. However, a statistically significant association was found between MDR expression and outcome (p = 0.007). Among the patients who received chemotherapy, positive MDR expression significantly correlated with poor outcome (p = 0.036). Our results showed that Pgp-mediated intrinsic MDR in medulloblastomas seems to correlate with an adverse outcome. This information may be used in designing new therapeutic protocols for medulloblastoma.

Adolescent↗
PubMed1994

PAF and TNF increase the precursor of NF-kappa B p50 mRNA in mouse intestine: quantitative analysis by competitive PCR.

NF-kappa B, a nuclear transcription factor, is involved in the regulation of inflammatory cytokines. We have previously reported that PAF and TNF induce intestinal injury in rats and mice and the interaction of TNF and PAF probably plays a central role in its pathogenesis. In the present study, we developed a competitive PCR method to quantitate the transcripts of NF-kappa B p50/p105 gene, and investigated the effects of PAF and TNF on p50/p105 gene expression in the small intestine of C3H/HeN mice - p105 is the precursor of the p50 subunit of NF-kB. We found that NF-kappa B p50/p105 gene is constitutively expressed in the normal small intestine in small quantities (7.05 +/- 1.04 attomol/micrograms total RNA). PAF at a dose (1 microgram/kg) causing no systemic changes (e.g., hypotension, hemoconcentration), markedly increased intestinal p50/p105 transcripts within 30 min. TNF, at dose (1 mg/kg) also insufficient to induce systemic changes, increased intestinal p50/p105 gene expression, although its effect was much slower than PAF. The effect of TNF was not blocked by WEB 2086, a PAF antagonist. Our results indicate that both PAF and TNF stimulate the expression of NF-kappa B p50/p105 in vivo. However, the mechanisms of their respective actions are probably different.

Animals↗