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Biomedical subjects

X Yu

Publications and source records attributed to X Yu.

At least 145 records · Page 8Linked to original sources
PubMed2000

Preparation of anti-idiotypic antibodies specific for anti-HEL and analysis of their functional mimicry.

OBJECTIVE: This study is to investigate the functional mimicry by using anti-idiotypic antibodies of enzymes. METHODS: Monoclonal anti-idiotypic antibodies against anti-HEL (hen egg-white lysozyme, HEL) antibodies were obtained by fusion of Sp2/0 myeloma cells with spleen cells of syngeneic mice immunized with monoclonal anti-HEL antibodies against HEL's different antigenic epitopes. Then bacteriolysis of the anti-idiotypic antibodies were observed. RESULTS: Eight hybridomas strains secreting anti-idiotypic antibodies were selected and characterized. It was shown that two of eight anti-idiotypic antibodies secreted by two hybridomas (1A10C9 and 2A11C1B3) could mimic HEL catalytic activity to lyse Micrococcus lysodeikticus and that the catalytic effect of mixed anti-idiotypic antibodies of 1A10C9 and 2A11C1B3 was stronger than that of one of them, but less than HEL. CONCLUSION: The results demonstrated that the anti-idiotypic antibodies that could mimic enzyme activity existed in the idiotype network during anti-enzymatic immune response.

Animals↗
PubMed2000

[Study on neodymium complexes by broad wavelength range photoacoustic spectroscopy].

Neodymium complexes were studied by photoacoustic(PA) spectroscopy from UV-Vis to mid-IR. According to the PA spectra, low excited energy levels, relaxation processes and fluorescence properties were discussed. Then the influence of interaction between Nd(III) and ligands in solid complexes was investigated on the basis of band shifts and intensity change.

Chelating Agents↗
PubMed2000

[The synthesis and spectral study of multicomponent heteropoly compounds with Keggin structure].

The Multicomponent heteropoly compounds [Me4N]3 + x[PVxMoyW12-x-yO40]. n(H2O) with Keggin structure have been synthesized, and have been characterized by FTIR and NIR FT-Raman. The vibrational regularity of oxygen-containing bonds (P-Oa, M = Od, M-Ob-M and M-Oc-M) in these heteropoly compounds have been studied. The vibrational frequencies nu as (M = Od) and nu as (M-Ob-M) was shown to prove the reason why the acidity of the heteropoly compounds descended and the oxidization increased by the substitution of V atoms.

English Abstract↗
PubMed2000

[Study on the photoacoustic phase of rare earth complexes].

The theory of the photoacoustic (PA) phase has been studied. The PA phase spectra of rare earth complexes with dibenzoylmethide have been explained basing on the theory. The phase shifts of Tb complexes at the ligand absorption peak have been calculated. The phase shifts and their intramolecular relaxation processes have been studied also.

Acoustics↗
PubMed1999

Alternative splicing patterns of CYP2D genes in human brain and neurodegenerative disorders.

The expression patterns of alternatively spliced forms of the CYP2D (6, 7, 7A, 7B) gene were analyzed in the brains of individuals with Lewy body disease (LBD) and correlated with CYP2D6 polymorphisms. Five different alternatively spliced transcripts were identified. The most common was the deletion of exon 6 (87.3% of cases), followed by a 91-base pair fragment deletion at the 3' end of the gene (63.9% of cases). There was no correlation between the polymorphisms in the CYP2D6B gene or presence of LBD and these five alternatively spliced transcripts. Susceptibility to LBD may occur through mechanisms other than altered mRNA splicing of the CYP2D6 gene.

Aged↗
PubMed1999

A loss of function mutation of presenilin-2 interferes with amyloid beta-peptide production and notch signaling.

Presenilin-1 (PS1) facilitates gamma-secretase cleavage of the beta-amyloid precursor protein and the intramembraneous cleavage of Notch1. Although Alzheimer's disease-associated mutations in the homologous presenilin (PS2) gene elevate amyloid beta-peptide (Abeta42) production like PS1 mutations, here we demonstrate that a gene ablation of PS2 (unlike that of PS1) in mice does not result in a severe phenotype resembling that of Notch-ablated animals. To investigate the amyloidogenic function of PS2 more directly, we mutagenized a conserved aspartate at position 366 to alanine, because the corresponding residue of PS1 is known to be required for its amyloidogenic function. Cells expressing the PS2 D366A mutation exhibit significant deficits in proteolytic processing of beta-amyloid precursor protein indicating a defect in gamma-secretase activity. The reduced gamma-secretase activity results in the almost complete inhibition of Abeta and p3 production in cells stably expressing PS2 D366A, whereas cells overexpressing the wild-type PS2 cDNA produce robust levels of Abeta and p3. Using highly sensitive in vivo assays, we demonstrate that the PS2 D366A mutation not only blocks gamma-secretase activity but also inactivates PS2 activity in Notch signaling by inhibiting the proteolytic release of the cytoplasmic Notch1 domain. These data suggest that PS2 is functionally involved in Abeta production and Notch signaling by facilitating similar proteolytic cleavages.

Amyloid beta-Peptides↗
PubMed1999

2-Bromopropane causes ovarian dysfunction by damaging primordial follicles and their oocytes in female rats.

Ovarian dysfunction induced by 2-bromopropane (2-BP) has been described in female factory workers and experimental animals. However, the underlying mechanism is still unclear. To establish the reproductive target site and define mechanisms of 2-BP toxicity in adult female rats, we examined the effects of different doses and duration of exposure to 2-BP in female rats. In the dose-dependent experiments, female rats were exposed to 2-BP at 100, 300, or 1000 ppm or fresh air (n = 9 each) in exposure chambers for 8 h/day for 9 weeks. In the time-course experiments, female rats were exposed to 2-BP at 3000 ppm for 8 h (n = 7 each). The rats were then euthanized 1, 3, 5, and 17 days after exposure. Differential follicle counts and in situ terminal deoxynucleotidyl transferase assay were used to evaluate 2-BP effect on primordial, growing, and antral follicles. Exposure to 2-BP at 300 and 1000 ppm produced a significant reduction in the percentage of primordial, growing, and antral follicles in a dose-dependent manner. Significant reduction in the percentage of primordial follicles at 17 days after exposure was observed in time-course experiments. Exposure to 2-BP at 3000 ppm for 8 h resulted in histological changes in primordial follicles complex at 5 and 17 days after exposure. These changes consisted of distortion of the symmetry of oocytes and their nuclei at Day 5 after exposure and appearance of eccentric pyknotic cells and shrinkage of oocyte nuclei at Day 17 after exposure. In situ end labeling showed increased numbers of apoptotic oocytes and granulosa cells in primordial follicles at Days 5 and 17 after exposure. Our results suggested that ovarian dysfunction induced by 2-BP was caused by the destruction of primordial follicle and its oocyte due to the induction of apoptosis. Our studies also show that the follicle differential count is a more sensitive method than the vaginal smear in monitoring the female reproductive disorders induced by 2-BP.

Animals↗
PubMed1999

Human Dmc1 protein binds DNA as an octameric ring.

The bacterial RecA protein has been the most intensively studied enzyme in homologous genetic recombination. The core of RecA is structurally homologous to that of the F1-ATPase and helicases. Like the F1-ATPase and ring helicases, RecA forms a hexameric ring. The human Dmc1 (hDmc1) protein, a meiosis-specific recombinase, is homologous to RecA. We show that hDmc1 forms octameric rings. Unlike RecA and Rad51, however, hDmc1 protein does not form helical filaments. The hDmc1 ring binds DNA in the central channel, as do the ring helicases, which is likely to represent the active form of the protein. These observations indicate that the conservation of the RecA-like ring structure extends from bacteria to humans, and that some RecA homologs may form both rings and filaments, whereas others may function only as rings.

Bacteriophages↗
PubMed1999

Nitric oxide inhibits angiotensin II-induced activation of the calcium-sensitive tyrosine kinase proline-rich tyrosine kinase 2 without affecting epidermal growth factor receptor transactivation.

In a previous study, we showed that nitric oxide donors and N-acetylcysteine, either alone or in combination, inhibited the activation of several mitogen-activated protein kinases by angiotensin II in rat cardiac fibroblasts (Wang, D., Yu, X., and Brecher, P. (1998) J. Biol. Chem. 273, 33027-33034). In the present study, we have focused on the mechanism by which nitric oxide exerts this effect on the activation of extracellular signal-regulated kinase (ERK). We contrasted the effects of nitric oxide on ERK activation by angiotensin II and epidermal growth factor (EGF), since the transactivation of the EGF receptor has been implicated as a response to angiotensin II. We found that nitric oxide inhibited ERK activation by angiotensin II but did not inhibit the relatively slight but significant transactivation of the EGF receptor by angiotensin II. The tyrphostin AG1478, known to inhibit EGF receptor phosphorylation, also inhibited the angiotensin II and EGF-induced activation of ERK, the phosphorylation of the EGF receptor, and the subsequent association of Shc and Grb2. Nitric oxide did not affect either EGF receptor phosphorylation or Shc-Grb2 activation induced by either Ang II or EGF. However, the activation of the calcium-sensitive tyrosine kinase PYK2, which occurred in response to angiotensin II, but not EGF, was inhibited by nitric oxide. The data suggested that PYK2 activation may be an important inhibitory site in signaling pathways affected by nitric oxide.

Adaptor Proteins, Signal Transducing↗
PubMed1999

Interaction of the P-glycoprotein multidrug transporter (MDR1) with high affinity peptide chemosensitizers in isolated membranes, reconstituted systems, and intact cells.

P-glycoprotein-mediated multidrug resistance can be reversed by the action of a group of compounds known as chemosensitizers. The interactions with P-glycoprotein of two novel hydrophobic peptide chemosensitizers (reversins 121 and 205) have been studied in model systems in vitro, and in a variety of MDR1-expressing intact tumor cells. The reversins bound to purified P-glycoprotein with high affinity (77-154 nM), as assessed by a quenching assay using fluorescently labeled purified protein. The peptides modulated P-glycoprotein ATPase activity in Sf9 insect cell membranes expressing human MDR1, plasma membrane vesicles from multidrug-resistant cells, and reconstituted proteoliposomes. Both peptides induced a large stimulation of ATPase activity; however, higher concentrations, especially of reversin 205, led to inhibition. This pattern was different from that of simple linear peptides, and resembled that of chemosensitizers such as verapamil. In both membrane vesicles and reconstituted proteoliposomes, 1-2 microM reversins were more effective than cyclosporin A at blocking colchicine transport. Reversin 121 and reversin 205 restored the uptake of [3H]daunorubicin and rhodamine 123 in MDR1-expressing cells to the level observed in the drug-sensitive parent cell lines, and also effectively inhibited the extrusion of calcein acetoxymethyl ester from intact cells. In cytotoxicity assays, reversin 121 and reversin 205 eliminated the resistance of MDR1-expressing tumor cells against MDR1-substrate anticancer drugs, and they had no toxic effects in MDR1-negative control cells. We suggest that peptides of the reversin type interact with the MDR1 protein with high affinity and specificity, and thus they may be good candidates for the development of MDR1-modulating agents to sensitize drug resistance in cancer.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed1999

Preparation of chitooligosaccharides from chitosan by a complex enzyme.

Chitosan of 24% degree of acetylation was depolymerized by a mixture of cellulase, alpha amylase, and proteinase to give the title oligosaccharides. The removal of products by membrane separation permitted yield maximization of products having degree of polymerization in the 3-10 range.

Chitin↗
PubMed1999

Determination of lead in blood and urine by SPME/GC.

Lead is the most frequently quantitated toxic metal in biological matrixes. In this paper, a method is described for lead determination in whole blood and urine using solid-phase microextraction (SPME) gas chromatography. Lead ion is first derivatized with sodium tetraethylborate to form tetraethyllead, which is then extracted from the headspace over the sample by SPME. The analytical procedure was optimized for coating selection, pH, extraction time, and effect of salt. The relative standard deviation was less then 10% for both urine and blood samples. The limit of detection was 3 and 4 ppb; the limit of quantification is 5 and 10 ppb for urine and blood samples, respectively. Good linearity was found for both urine and blood samples when PDMS coating was used. The standard addition method was used for quantitation. Certified urine and blood samples were analyzed, and good accuracy was obtained.

Borates↗
PubMed1999

Effect of inhalation exposure to 2-bromopropane on the nervous system in rats.

Exposure to 2-bromopropane (2-BP) is suspected to have adverse effects on the nervous system. The aim of this study was to investigate whether the exposure of rats to 2-BP had neurotoxic effects using histological and electrophysiological studies. Wistar strain male rats were exposed daily to either 100 or 1000 ppm 2-BP or to fresh air for 8 h a day for 12 weeks. Body weight was measured before exposure and every 2 weeks. Motor nerve conduction velocity (MCV) and distal latency (DL) were measured before exposure and every 4 weeks during exposure. Histological examination of the nervous system was also performed. Exposure of rats (n = 9) to 1000 ppm resulted in suppression of body weight gain and a significant decrease in brain weight compared to the control (n = 9). Electrophysiological measurements showed a significant decrease in MCV in 1000 ppm exposed rats at 8 weeks and significant prolongation of DL at 8 and 12 weeks. Abnormalities of the myelin sheath were detected in the common peroneal nerves. In 100-ppm exposed rats (n = 9), no significant changes were noted in body weight and the peripheral nerve. In conclusions, long-term exposure to 1000 ppm of 2-BP may result in peripheral neuropathy in rats.

Administration, Inhalation↗
PubMed1999

Human follicular dendritic cells inhibit superantigen-induced T-cell proliferation by distinct mechanisms.

Follicular dendritic cells (FDCs) reside within germinal centers of secondary lymphoid tissue where they play a critical role in antigen-driven immune responses. FDCs express numerous adhesion molecules that facilitate cellular interactions with B and T cells within the germinal center microenvironment. Although human FDCs have been shown to influence B-cell development, very little is known about the ability of FDCs to regulate T-cell responses. To investigate this functional aspect of FDCs, highly enriched preparations were isolated by magnetic cell separation using the FDC-restricted monoclonal antibody HJ2. We found that isolated human FDCs inhibited proliferation of both autologous and allogeneic T cells, and were dependent on the number of FDCs present. Inhibition by FDCs was observed using two serologically distinct superantigens at multiple concentrations (Staphylococcus enterotoxin A and B). In contrast, B cells failed to inhibit, and often augmented superantigen-induced T-cell proliferation. Antibody-blocking studies showed that CD54 and CD106 were involved in the ability of FDC to inhibit T-cell proliferative responses. When FDCs and T cells were separated by a semipermeable membrane, the inhibitory effect was partially abrogated, demonstrating that in addition to cell-cell interactions, a soluble factor(s) was also involved in the process. The addition of indomethicin to cultures improved the proliferative response in the presence of FDCs, indicating that inhibition was mediated, in part, by prostaglandins. These results indicate that FDCs regulate T-cell proliferation by two molecular mechanisms and that FDC:T-cell interactions may play a pivotal role in germinal center development.

Antigen Presentation↗
PubMed1999

Sensory feedback can coordinate the swimming activity of the leech.

Previous studies showed that sensory feedback from the body wall is important and sometimes critical for generating normal, robust swimming activity in leeches. In this paper, we evaluate the role of sensory feedback in intersegmental coordination using both behavioral and physiological measurements. We severed the ventral nerve cord of leeches in midbody and then made video and in situ extracellular recordings from swimming animals. Our electrophysiological recordings unequivocally demonstrate that active intersegmental coordination occurs in leeches with severed nerve cords, refuting earlier conclusions that sensory feedback cannot coordinate swimming activity. Intersegmental coordination can in fact be achieved by sensory feedback alone, without the intersegmental interactions conveyed by the nerve cord.

Animals↗
PubMed1999

Rings and filaments of beta protein from bacteriophage lambda suggest a superfamily of recombination proteins.

The beta protein of bacteriophage lambda acts in homologous genetic recombination by catalyzing the annealing of complementary single-stranded DNA produced by the lambda exonuclease. It has been shown that the beta protein binds to the products of the annealing reaction more tightly than to the initial substrates. We find that beta protein exists in three structural states. In the absence of DNA, beta protein forms inactive rings with approximately 12 subunits. The active form of the beta protein in the presence of oligonucleotides or single-stranded DNA is a ring, composed of approximately 15-18 subunits. The double-stranded products of the annealing reaction catalyzed by the rings are bound by beta protein in a left-handed helical structure, which protects the products from nucleolytic degradation. These observations suggest structural homology for a family of proteins, including the phage P22 erf, the bacterial RecT, and the eukaryotic Rad52 proteins, all of which are involved in homologous recombination.

Bacteriophage lambda↗