Search PubMed⌕ Search

Biomedical subjects

X Yu

Publications and source records attributed to X Yu.

At least 217 records · Page 12Linked to original sources
PubMed1999

[Recombination and cloning of MSP1(19) and PfCMR of Plasmodium falciparum].

AIM: To construct a recombinant plasmid DNA encoding multiantigens of Plasmodium falciparum and to provide the requirements for DNA immunization. METHODS: Two oligonucleotide primers were designed to amplify MSP1(19), the purified PCR products were digested by Sal I + Xba I, and the recombinant plasmid pWR450-1/PfCMR was digested by EcoR I + Sal I to recover PfCMR gene. PfCMR and MSP1(19) gene fragments were linked and recombined with mammalian expression vector pcDNA3. RESULTS: The MSP1(19) gene fragment with about 363 base pairs were specifically amplified by using PCR technique. The positive recombinant pcDNA3-PfCMR-MSP1(19) (named pcDNA3-Pf8) was screened and identified by agarose gel electrophoresis, endonulease digestion and PCR technique, the whole length of Pf8 is 618 bp. CONCLUSION: By specifically amplifying MSP1(19) gene at the C-terminal of MSP1, a recombinant plasmid pcDNA3-Pf8 encoding multiantigens of Plasmodium falciparum was successfully constructed.

Animals↗
PubMed1999

[Preliminary study on the levels of natural antibodies against Schistosoma japonicum in Microtus fortis in Dongting lake area].

AIM: To explore the detection rate and the levels of natural antibodies to cercarial antigen(CA), juvenile antigen(JA), adult worm antigen (AWA) and soluble egg antigen (SEA), respectively, derived from Schistosoma japoncum in Microtus fortis distributed in Dongting Lake area. METHODS: The antibodies in wild Microtus fortis(WMF), laboratory-bred Microtus fortis (BMF) and laboratory-bred Microtus fortis 15 days after S. japonicum infection (BMFi15) were detected by indirect ELISA and a comparison of the antibody levels between Microtus fortis including WMF, BMF, BMFi15 and albino mice without infection (AM), 15 days after infection(AMi15) and 42 days after infection (AMi42) was made. RESULTS: The positive rates of detection for anti-JA-Ab in WMF and BMF were 94.6% and 94.4%, respectively, followed by 85.5% and 83.3% for anti-AWA-Ab, 58.1% and 59.4% for anti-SEA-Ab, and 14.3% and 13.9% for anti-CA-Ab. The levels of antibodies to the above four antigens in BMFi15 increased significantly, the detection rates being 100% for anti-JA-Ab and anti-AWA-Ab, 84.4% for anti-SEA-Ab and 65.6% for anti-CA-Ab. The levels of antibodies in WME, BMF and BMFi15 had the similar trend(JA > AWA > SEA > CA), and those in BMFi15 to CA, JA, AWA and SEA increased by 1.9, 2.2, 2.1 and 1.5 folds, respectively, when compared with BMF. CONCLUSION: Natural antibodies to Schistosoma japonicum were found in wild and labortorybred Microtus fortis. The levels of antibodies in BMFi15 to four above antigens were apparently higher than those in AMi15.

Animals↗
PubMed1999

[Taxonomic studies on Echinochasmus fujienensis and its related species by random amplified polymorphic DNA analysis and experimental infection].

AIM: To explore the identification and differentiation of Echinochasmus fujianensis, Echinochasmus japonicus(Jiangxi strain and Fujian strain), Echinochasmus liliputanus Anhui and Echinochasmus per foliatus Hubei. METHODS: Random amplified polymorphic DNA analysis (RAPD) and experimental animal infection were performed. RESULTS: 469 polymorphic DNA fragments were obtained by 28 primers from 4 Echinochasmus species and strains in Fujian, Anhui and Jiangxi. 20.8% and 97.6% of the fragments in Echinochasmus fujianensis were the same as those in Echinochasmus japonicus Fujian strain and in Echinochasmus liliputanus Anhui, respectively, 99.7% of the fragments were the same between Echinochasmus japonicus Jiangxi strain and Fujian strain. CONCLUSION: Echinochasmus fujianensis and Echinochasmus liliputanus Anhui are the same species. Echinochasmus fujienensis is an independent species different from Echinochasmus japonicus. Polyinfection of Echinochasmus fujianensis, Echinochasmus japonicus and Echinochasmus perfoliatus exist in all the 3 provinces, Hubei, Anbui and Fujian, of which Echinochasmus fujienensis is a dominant species.

Animals↗
PubMed1999

[Cloning and sequencing of the genes coding for the histidine-rich protein II of Plasmodium falciparum].

AIM: To compare and analyze the homology of genes encoding histidine-rich proteinII (HRPII) of different Plasmodium falciparum isolates. METHODS: Using PCR technique, the complete genes coding for HRPII of P. falciparum isolates FCC1/HN and VN isolates were amplified. PCR products were digested by HindIII/BamHI and cloned into plasmid pUC19. The recombinant plasmid HRPII/pUC19 was screened and identified by PCR and restriction analysis. The cloned HRPII genes were sequenced by Sanger's method. RESULTS: HRPII genes of FCC1/HN and VN isolates were successfully amplified and cloned into pUC19. DNA sequencing showed that the coding length of HRPII gene was 1,020 bp without introns in FCC1/HN and VN isolates, however, there were ten points mutations between them. FCC1/HN isolate exhibited 98.8%, 92.2% and 98.7% homology in amino acids with isolates VN, IMTM22, and Itg2, respectively. Though the numbers of repeat sequences were different in four isolates, they had the same hydrophobic leader sequence and a single putative glycosylation site. The secondary structure analysis showed that the main antigenic determinants of four isolates were located on 5' end non-repeat region (amino acids 1-60). CONCLUSION: FCC1/HN isolate was highly homologous in the coding region of HRPII with VN, IMTM22, and Itg2 isolate. Four isolates exhibited similar structural characteristics and antigenic determinants in HRPII.

Amino Acid Sequence↗
PubMed1999

[Aspirin inhibited the adhesion of platelets to neutrophil in patients with acute myocardiac infarction].

OBJECTIVE: To investigate the effect and mechanism of aspirin(ASA) on platelet-neutrophil adhesion. METHODS: Using rosette forming assay to observe the effect of ASA on the binding of platelets to neutrophil and radioimmunoassay to observe the effect of ASA on the thrombin-induced expression of GMP-140 on the surface of human platelets. RESULTS: Patients with acute myocardial infarction showed a significant increase in neutrophil-platelet adhesion (63.3 +/- 7.8)%, (n = 20, P < 0.001) as compared with normal subjects(16.5 +/- 2.6)% (n = 20). Thrombin promoted adhesion by increasing the expression of GMP-140 on the surface of human platelets. When the concentration of thrombin was 0.5 U/ml, the rate of neutrophil-platelet adhesion and the number of molecular of GMP-140 on the surface of platelet was (64.2 +/- 4.2)%, and (1.80 +/- 0.20) x 10(3) per platelet respectively. At high concentration, ASA significantly inhibited thrombin (0.5 U/ml) stimulated platelets binding to neutrophils and expressing GMP-140 on their surface. When the final concentration of ASA was 500,5000 micrograms/ml, the ratio of thrombin-stimulated platelets binding neutrophils was (34.7 +/- 3.8)%, (21.2 +/- 3.6)% respectively (n = 20, P < 0.01); the number of molecular of GMP-140 expressing on the surface of platelet was (1.02 +/- 0.24) x 10(3), (0.68 +/- 0.18) x 10(3) per platelet respectively (n = 9, P < 0.001). CONCLUSIONS: It contributes to the antithrombosis of ASA that inhibiting platelet-neutrophil adhesion by down expression of GMP-140 on the surface of human platelets.

Aspirin↗
PubMed1999

[Study on chitosan-Zn (II) complex by IR spectroscopy].

A series of chitosan-Zn (II) complexes were synthesized by reaction of chitosan and ZnSO4 in different ratios(chitosan : Zn (II) = 1 : 0.05-1 : 1) in dilute formic acid aqueous solution. The results showed that -NH2, -OH and -NHCO- of chitosan molecule were coordinated to Zn (II) based on the analyse of the IR spectra of chitosan, chitosan-H2SO4 and chitosan-ZnSO4. SO4(2-) of chitosan-ZnSO4 may be crosslinking of chitosan molecule, but Cl-, CH3COO- and NO3- were not crosslinked to chitosan molecule in the chitosan-ZnCl2, chitosan-Zn (CH3COO)2 and chitosan-Zn (NO3)2 complexes.

Chitosan↗
PubMed1998

Nitric oxide and N-acetylcysteine inhibit the activation of mitogen-activated protein kinases by angiotensin II in rat cardiac fibroblasts.

Angiotensin II acts on the cardiac fibroblast to produce a mitogenic response. Nitric oxide and N-acetylcysteine have been used to determine if oxidative stress influenced the effects of angiotensin II on the cardiac fibroblast. Angiotensin II activated the mitogen-activated protein kinases designated extracellular signal-regulated kinases within 5 min by interacting with the AT1 receptor. This activation was completely independent of protein kinase C and was inhibited when farnesylation was blocked, implicating Ras involvement. Pretreatment of cardiac fibroblasts with either N-acetylcysteine for 8 h or nitric oxide for 10 min suppressed this activation by angiotensin II in a dose-dependent manner. However, when both agents were added, inhibition was essentially complete. This combined effect of N-acetylcysteine and nitric oxide to block ERKs activation also was found if the activity was stimulated by either another growth factor (platelet-derived growth factor) or by the addition of phorbol ester, suggesting the effect was not limited to the receptor site alone. The results are consistent with the hypothesis that hormonal activation of mitogenic steps such as ERKs is influenced by increased oxidative stress, which is reduced by the combined effects of N-acetylcysteine and nitric oxide.

Acetylcysteine↗
PubMed1998

Transcriptional repression due to high levels of Wingless signalling.

Extracellular signals can act at different threshold levels to elicit distinct transcriptional and cellular responses. Here, we examine the transcriptional regulation of the Wingless target gene Ultrabithorax (Ubx) in the embryonic midgut of Drosophila. Our previous work showed that Ubx transcription is stimulated in this tissue by Dpp and by low levels of Wingless signalling. We now find that high levels of Wingless signalling can repress Ubx transcription. The response sequence within the Ubx midgut enhancer required for this repression coincides with a motif required for transcriptional stimulation of Dpp, namely a tandem of binding sites for the Dpp-transducing protein, Mad. Indeed, Wingless-mediated repression depends on low levels of Dpp, although apparently not on Mad itself. In contrast, high levels of Dpp signalling antagonize Wingless-mediated repression. This suggests that transcriptional activation of Ubx is subject to competition between Dpp-activated Mad and another Smad whose function as a transcriptional repressor depends on high Wg signalling. Finally, we show that Wingless can repress its own expression via an autorepressive feedback loop that results in a change of the Wingless signalling profile during development.

Armadillo Domain Proteins↗
PubMed1998

Identification of a defined epitope on the surface of the active RecA-DNA filament using a monoclonal antibody and three-dimensional reconstruction.

Studies of the Escherichia coli RecA protein are expected to illuminate mechanisms of DNA recombination and repair in bacteria, and in all higher organisms as well, due to the functional and structural homology with the eukaryotic Rad51 protein. The active form of the RecA protein is a helical filament formed on DNA in the presence of ATP or ATP analogs, and this has been studied at low-resolution by electron microscopy. An atomic model of the protein comes from an X-ray crystallographic study of a filament formed in the absence of DNA and ATP. This filament is believed to be an inactive, storage form of the protein. A key step in generating an atomic model of the active filament, and a detailed model for function, is to understand the large conformational changes that occur between these two states. Towards this end, we have decorated active RecA-DNA filaments with monoclonal antibodies (ARM191) against a known epitope (residues 285 to 320) to determine the position of this epitope in the low-resolution structure. Electron microscopy and three-dimensional reconstruction of the RecA-antibody complex reveal that the lobe containing the epitope is very disordered on the surface of the filament, but in a position similar to that in the inactive crystal filament. The antibody binding also induces a significant conformational change in the RecA filament. This study shows that the basic orientation of the subunit is likely to be similar within the inactive and active filaments, and that the large movement of mass that occurs between these two states must involve other residues than the 285-320 region.

Animals↗
PubMed1998

The C-terminal (BRCT) domains of BRCA1 interact in vivo with CtIP, a protein implicated in the CtBP pathway of transcriptional repression.

The BRCA1 tumor suppressor encodes a polypeptide with two recognizable protein motifs: a RING domain near the N terminus and two tandem BRCT domains at the C terminus. Studies of tumor-associated mutations indicate that the RING and BRCT sequences are required for BRCA1-mediated tumor suppression. In addition, recent work has shown that BRCA1 is a potent regulator of RNA transcription and that the BRCT domains are also essential for this activity. Therefore, we used the Sos recruitment system to screen for proteins that bind this critical region of BRCA1. Our results show that the BRCT domains interact in vivo with CtIP, a protein originally identified on the basis of its association with the CtBP transcriptional co-repressor. This finding suggests that BRCA1 regulates gene expression, at least in part, by modulating CtBP-mediated transcriptional repression. Moreover, the in vivo interaction between BRCA1 and CtIP is completely ablated by each of three independent tumor-associated mutations affecting the BRCT motifs of BRCA1. These results indicate that the BRCA1-CtIP interaction may be required for tumor suppression by BRCA1.

Alcohol Oxidoreductases↗
PubMed1998

Linear and cyclic peptides as substrates and modulators of P-glycoprotein: peptide binding and effects on drug transport and accumulation.

One cause of multidrug resistance (MDR) in human cancers is the overexpression of the P-glycoprotein multidrug transporter, a member of the ABC superfamily of membrane proteins. Natural products and chemotherapeutic drugs are pumped out of the cell by P-glycoprotein in an ATP-dependent fashion. There is growing evidence that many hydrophobic peptides are also P-glycoprotein substrates. With the use of a fluorescence-quenching assay, we have shown that some linear and cyclic hydrophobic peptides interact with P-glycoprotein, whereas others do not. The measured values of the quenching constant, Kq, for interaction of peptides with P-glycoprotein ranged from 200 nM for cyclosporine A to 138 microM for the tripeptide N-acetyl-leucyl-leucyl-norleucinal. Peptides that interacted with P-glycoprotein in the fluorescence assay also blocked colchicine transport into plasma membrane vesicles from MDR cells. The values of Dm, the peptide concentration causing 50% inhibition of drug uptake, were highly correlated with the values of Kq, over three orders of magnitude. The P-glycoprotein ATPase stimulation/inhibition profile of the peptides was not helpful in making a quantitative assessment of the ability of a peptide to interact with P-glycoprotein or to block drug transport. Some hydrophobic peptides were able to restore accumulation in MDR cells of the chemotherapeutic drug daunorubicin and the fluorescent dye rhodamine 123 to the levels observed in the drug-sensitive parent. Peptides that interacted with P-glycoprotein also displayed a relatively low overall toxicity to intact MDR cells, and inhibited drug transport at concentrations below the toxic range. Hydrophobic peptides should be given serious consideration for development as clinical chemosensitizing agents.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed1998

Identification of drug metabolites in biological matrices by intelligent automated liquid chromatography/tandem mass spectrometry.

A rapid and systematic strategy for the identification of drug metabolites in biological matrices based on liquid chromatography-tandem mass spectrometry (LC/MS/MS) techniques was utilized for the identification of drug metabolites of the HIV protease inhibitor Indinavir. This strategy integrates intelligent realtime mass spectrometry with HPLC detection and a predictive strategy for detecting metabolites arising from common biotransformations, to rapidly elucidate structures of drug metabolites. Structures of metabolites generated from in vitro incubation mixtures of Indinavir were characterized from a single chromatographic analysis using the automated LC/MS/MS methodology, thus reducing data acquisition time and improving efficiency.

Animals↗
PubMed1998

Assessing the relative contribution of molecular and morphological characters in simultaneous analysis trees.

We examined the contribution of morphological and molecular character information for 15 systematics studies in which these two kinds of data were used in combined or simultaneous analyses. Assessment of the disagreement between these data sources, as measured by the incongruence length difference, reveals substantial conflict for the studies surveyed. In addition, the partitioned Bremer support was used to measure the degree of support provided by each data partition when analyzed together. Despite the significant incongruence found for nearly half the studies, the PBS indices suggest both types of data contribute positively to the combined analyses and that, when standardized by the number of phylogenetically informative characters, morphology data generally provide equal or greater support than do the molecular data. This result, combined with the fact that morphological characters generally exhibit higher consistency, indicates that this source of character information continues to be useful in systematics studies despite the increasing volume of available molecular data.

Animals↗
PubMed1998

Urinary 2,5-hexanedione increases with potentiation of neurotoxicity in chronic coexposure to n-hexane and methyl ethyl ketone.

OBJECTIVE: MEK (methyl ethyl ketone) is widely and frequently used as an ingredient of mixed solvents together with n-hexane. MEK is known to decrease urinary levels of 2,5-hexanedione dose-dependently in an acute or chronic coexposure with a constant level of n-hexane. This change in urinary 2,5-hexanedione appears to contradict the potentiation effect of MEK on n-hexane-induced neurotoxicity because it is believed that the toxicity of n-hexane is activated through n-hexane metabolism. We aimed to clarify how the urinary level of 2,5-hexanedione changes when MEK modifies the degree of n-hexane-induced neurotoxicity. METHOD: A total of 32 male Wistar rats were divided into 4 groups of 8 each and were then exposed to fresh air only, 2000 ppm n-hexane only, 2000 ppm n-hexane plus 200 ppm MEK, and 2000 ppm n-hexane plus 2000 ppm MEK, respectively. Inhalation exposures were performed 12 h/day, 6 days/week, for 20 weeks. Motornerve conduction velocity (MCV), distal latency (DL), and urinary 2,5-hexanedione were measured every 4 weeks. RESULTS: The MCV decreased, the DL increased, and urinary levels of 2,5-hexanedione increased in the 2000-ppm n-hexane plus 200 ppm MEK group in comparison with the 2000-ppm n-hexane only group following 4 weeks' exposure. On the 1st day of exposure, however, coexposure to MEK decreased urinary levels of 2,5-hexanedione dose-dependently. CONCLUSIONS: The present study showed that urinary concentrations of 2,5-hexanedione increased with potentiation of n-hexane neurotoxicity. Urinary 2,5-hexanedione concentration does not necessarily reflect the exposure concentration of n-hexane in coexposure to n-hexane along with MEK or other solvents, but it may be useful as a marker in the assessment of neurotoxicity in coexposure to n-hexane and other solvents.

Animals↗
PubMed1998

Accelerated Alzheimer-type phenotype in transgenic mice carrying both mutant amyloid precursor protein and presenilin 1 transgenes.

Genetic causes of Alzheimer's disease (AD) include mutations in the amyloid precursor protein (APP), presenilin 1 (PS1), and presenilin 2 (PS2) genes. The mutant APP(K670N,M671L) transgenic line, Tg2576, shows markedly elevated amyloid beta-protein (A beta) levels at an early age and, by 9-12 months, develops extracellular AD-type A beta deposits in the cortex and hippocampus. Mutant PS1 transgenic mice do not show abnormal pathology, but do display subtly elevated levels of the highly amyloidogenic 42- or 43-amino acid peptide A beta42(43). Here we demonstrate that the doubly transgenic progeny from a cross between line Tg2576 and a mutant PS1M146L transgenic line develop large numbers of fibrillar A beta deposits in cerebral cortex and hippocampus far earlier than their singly transgenic Tg2576 littermates. In the period preceding overt A beta deposition, the doubly transgenic mice show a selective 41% increase in A beta42(43) in their brains. Thus, the development of AD-like pathology is substantially enhanced when a PS1 mutation, which causes a modest increase in A beta42(43), is introduced into Tg2576-derived mice. Remarkably, both doubly and singly transgenic mice showed reduced spontaneous alternation performance in a "Y" maze before substantial A beta deposition was apparent. This suggests that some aspects of the behavioral phenotype in these mice may be related to an event that precedes plaque formation.

Alzheimer Disease↗
PubMed1998

The role of B7-CD28 co-stimulation in tumor rejection.

The role of B7 co-stimulatory signaling in in vivo tumor rejection remains incompletely characterized. In particular, the relative competence of B7-1 (CD80) and B7-2 (CD86) to provide effective co-stimulus is not well defined, and the identification of the T cell co-stimulatory receptor that mediates B7 co-stimulation in tumor rejection has not been addressed. These issues were studied by assessing rejection of B7-negative or B7-transfected tumor cells in CD28-expressing or CD28-deficient hosts. B7-negative EL4 tumor cells grew progressively in normal syngeneic C57BUL6 (B6) mice. In contrast EL4 cells transfected with either full length B7-1 or full length B7-2 were rejected, indicating that both B7-1 and B7-2 are competent to mediate rejection of EL4 tumor cells. Expression of truncated B7-1 or B7-2 products, with complete deletion of cytoplasmic domains, was as effective as expression of full length B7-1 or B7-2 in mediating rejection. In contrast to the rejection of B7-transfected EL4 cells observed in CD28-expressing syngeneic hosts, B7-1- and B7-2-positive EL4 cells as well as control EL4 cells grew progressively in CD28-deficient mice, demonstrating the requirement for host expression of CD28 in B7-mediated tumor rejection. These results indicate that interaction of host CD28 with co-stimulatory extracellular B7-1 or B7-2 ligands expressed on tumor cells can play a necessary role in mediating tumor rejection.

Age Factors↗
PubMed1998

Expression of a defense-related 3-hydroxy-3-methylglutaryl CoA reductase gene in response to parasitization by Orobanche spp.

Orobanche spp. are angiosperms that live parasitically on the roots of other plants, and are capable of significantly reducing the yield and quality of their crop hosts. We have demonstrated that parasitization by Orobanche induces expression of hmg2, a defense-related isogene of 3-hydroxy-3-methylglutaryl CoA reductase (HMGR) in tobacco. Transgenic tobacco plants expressing a construct containing 2.3 kb of the tomato hmg2 gene promoter fused to the beta-glucuronidase (GUS) reporter gene were parasitized by O. aegyptiaca. Expression of the hmg2:GUS construct was detected within 1 day following penetration of the host root by the O. aegyptiaca radicle and was localized to the region immediately around the site of parasite invasion. This expression continued and intensified over the course of O. aegyptiaca development. In addition, the hmg2:GUS expression was induced by secondary parasitization, where secondary roots of O. aegyptiaca contacted the host root at a distance from the primary attachment site. This GUS expression was specific to plants containing the hmg2:GUS construct, and was not observed in control plants transformed with a construct of the cauliflower mosaic virus 35S promoter fused to the GUS gene. These results indicate that Orobanche parasitization initiates rapid and sustained induction of a defense-related gene in the host root.

Gene Expression Regulation, Enzymologic↗