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T N Nguyen

Publications and source records attributed to T N Nguyen.

At least 73 records · Page 4Linked to original sources
PubMed1997

Surface display of the cholera toxin B subunit on Staphylococcus xylosus and Staphylococcus carnosus.

The heterologous surface expression of the cholera toxin B subunit (CTB) from Vibro cholerae in two staphylococcal species, Staphylococcus xylosus and Staphylococcus carnosus, has been investigated. The gene encoding native CTB (103 amino acids) was introduced into gene constructs encoding chimeric receptors designed to be translocated and anchored on the outer cell surface of the staphylococci. Since functionality of CTB is correlated with its ability to form pentamers and the capacity of the pentameric CTB to bind the GM1 ganglioside, both the surface accessibility and the functionality of the surface-displayed CTB receptors were evaluated. It could be concluded that the chimeric receptors were targeted to the cell wall of the staphylococci, since they could be released by lysostaphin treatment and, after subsequent affinity purification, identified as full-length products by immunoblotting. Surface accessibility of the chimeric receptors was demonstrated by a colorimetric assay and by immunofluorescence staining with a CTB-reactive rabbit antiserum. Pentamerization was investigated by using a monoclonal antibody described to be specific for pentameric CTB, and the functionality of the receptors was tested in a binding assay with digoxigenin-labelled GM1. It was concluded that functional CTB was present on both types of staphylococci, and for S. carnosus, the reactivity to the pentamer-specific monoclonal antibody and in the GM1 binding assay was indeed significant. The implications of the results for the design of live bacterial vaccine delivery systems intended for administration by the mucosal route are discussed.

Antibodies, Bacterial↗
PubMed1997

Flow cytometric quantification of surface-displayed recombinant receptors on staphylococci.

Surface display of recombinant proteins on bacteria and phages has become an important tool in bioscience. To evaluate the various host systems, a great need exists for quantitative methods to determine the densities of displayed proteins and peptides on the bacteria and phage surfaces. Here we describe how a method previously applied for quantification of surface proteins on mammalian cells has been adapted for quantification of chimeric receptors surface-displayed on bacteria; in this study, the bacteria being recombinant staphylococci. The presented method takes advantage of fluorescence-activated cell sorting (FACS) technology and a new type of nonfluorescent plastic beads, similar in size (2 microns in diameter) to bacterial cells, and thus suitable for generation of calibration curves from which the number of chimeric receptors can be obtained. The method was used to estimate the number of antigenic sites on two types of recombinant staphylococci, both carrying heterologous chimeric receptors, and it was found that the recombinant Staphylococcus carnosus cells carried approximately 10(4) surface-displayed antigenic sites, while recombinant Staphylococcus xylosus exposed approximately 3 x 10(3) sites per cell. The use of the deviced method for different applications is discussed.

Animals↗
PubMed1996

Surface display on staphylococci: a comparative study.

Two different host-vector expression systems, designed for cell surface display of heterologous receptors on Staphylococcus xylosus and Staphylococcus carnosus, respectively, were compared for the surface display of four variants of a 101 amino acid region derived from the G glycoprotein of human respiratory syncytial virus (RSV). Surface localization of the different chimeric receptors was evaluated by a colorimetric assay and by fluorescence-activated cell sorting. It was concluded that the S. carnosus system was better both in the ability to translocate inefficiently secreted peptides and in the number of exposed hybrid receptors. The potential use of the described staphylococci as live bacterial vaccine vehicles or alternatives to filamentous phages for surface display of protein libraries is discussed.

Flow Cytometry↗
PubMed1996

Effects of majonoside-R2 on pentobarbital sleep and gastric lesion in psychologically stressed mice.

The effects of Vietnamese ginseng (VG) and its major constituent majonoside-R2 on pentobarbital-induced sleep and gastric lesion in psychologically stressed mice were examined. Psychological stress exposure for 30 min significantly decreased the duration of pentobarbital (50 mg/kg, IP)-induced sleep in mice. VG extract (50 mg/kg, PO), VG saponin (25 mg/kg, PO), and majonoside-R2 (3.1-12.5 mg/kg, PO and IP) had no effect on pentobarbital sleep in unstressed control mice, but these drugs significantly recovered pentobarbital sleep decreased by psychological stress to the level of unstressed control animals. On the other hand, Panax ginseng (PG) extract (50-100 mg/kg, PO) failed to affect pentobarbital sleep in psychologically stressed mice. The effect of majonoside-R2 on psychological stress-induced decrease in the hypnotic activity of pentobarbital was significantly blocked by flumazenil (1 mg/kg, IV), a selective benzodiazepine antagonist. Diazepam (0.1 mg/kg, IP) significantly prolonged pentobarbital sleep in unstressed and psychologically stressed groups, and the effect of diazepam was significantly attenuated by the same dose of flumazenil. Naloxone (0.5-5 mg/kg, IP), an opioid antagonist, had no effect on pentobarbital sleep in unstressed or psychologically stressed animals. Psychological stress exposure for 16 h caused gastric lesion in mice. VG extract (25-50 mg/kg, PO) and majonoside-R2 (6.2-12.5 mg/kg, PO), as well as diazepam and naloxone, produced the protective action on gastric lesion in psychologically stressed mice. These results suggest that VG and its major constituent majonoside-R2 have the protective effects on the psychological stress-induced pathophysiological changes and that benzodiazepine receptors are partly implicated in the effects of majonoside-R2.

Animals↗
PubMed1996

Flux measurements across Caco-2 monolayers may predict transport in human large intestinal tissue.

Confluent monolayers of Caco-2 cells, a human colonic carcinoma cell line, have been used extensively to predict intestinal absorption. A direct comparison of uptake characteristics, however, between cell monolayers and human tissue is missing in the literature. We have determined the flux for a series of small organic molecules, peptide and protein therapeutics, across Caco-2 monolayers and normal human colonic and rectal tissue in vitro to assess whether or not a predictive correlation of transport exists. Caco-2 cells were grown to confluency of Snapwells, and human tissue was obtained from patients undergoing surgery for localized tumors. Mucosa-serosa fluxes were measured by HPLC for small molecules and peptides, and proteins were analyzed by ELISA or RIA. Permeability coefficients were calculated from flux data and compared with previously published coefficients where possible. The permeability coefficients for the examined molecules were of a similar magnitude across Caco-2 cell monolayers and human tissues, ranging from 10(-7) to 10(-5) cm/s. A best-fit analysis of a log-log plot of transport measurements obtained in these two systems gave a good correlation (R2 = 0.991). From this limited data set it appears that uptake characteristics for human colon and rectum are similar to those of Caco-2 cell monolayers. Thus, flux measurements across Caco-2 monolayers may be predictive for permeabilities of human colon and rectum for different classes of therapeutics.

Atenolol↗
PubMed1996

The possible involvement of GABAA systems in the antinarcotic effect of majonoside-R2, a major constituent of Vietnamese ginseng, in mice.

The effect of majonoside-R2 on morphine- and U-50,488H-induced antinociception was examined by the tail-pinch test in mice and compared with that of diazepam. Majonoside-R2 and diazepam inhibited the morphine- and U-50,488H-induced antinociception, and the actions were antagonized by the benzodiazepine receptor antagonist flumazenil and the GABA-gated CI- channel blocker picrotoxin. Diazepam but not majonoside-R2 exhibited a protective activity against convulsion caused by the GABAA antagonists bicuculline and picrotoxin. These results indicate that GABAA systems are involved in the effect of majonoside-R2 on the opioid-induced antinociception and suggest that the mechanisms of action of majonoside-R2 may differ from those of diazepam.

3,4-Dichloro-N-methyl-N-(2-(1-pyrrolidinyl)-cycloh↗
PubMed1995

Hydrophobicity engineering to facilitate surface display of heterologous gene products on Staphylococcus xylosus.

Protein engineering has been employed to investigate the effect of specific amino acid changes on the targeting of heterologous proteins to the outer cell surface of the Gram-positive bacterium Staphylococcus xylosus. Three different variants, corresponding to a 101 amino acid region of the major glycoprotein (G protein) of human respiratory syncytial virus (RSV), were generated in which multiple hydrophobic phenylalanine residues were either substituted or deleted. The different G protein fragments were expressed as one part of recombinant receptors designed for surface display on S. xylosus cells. The engineered variants of the RSV G protein hybrid receptors were, in contrast to a non-engineered fragment, efficiently targeted to the outer cell surface of recombinant S. xylosus cells as determined by different methods, including fluorescence-activated cell sorting. In addition, immunization of mice with live recombinant S. xylosus demonstrated that surface exposure was required to generate receptor-specific antibodies. The present strategy of hydrophobic engineering should be of general interest in surface-display applications and for secretion of proteins otherwise difficult to translocate through host cell membranes.

Amino Acid Sequence↗
PubMed1995

Hydrophobicity engineering to increase solubility and stability of a recombinant protein from respiratory syncytial virus.

Site-directed mutagenesis has been employed to engineer the hydrophobic properties of a 101-amino-acid fragment from the human respiratory syncytial virus (RSV) major glycoprotein (G protein). When this protein was produced in Escherichia coli, more than 70% of the gene product was found as inclusion bodies, and the product recovered from the soluble fraction was severely degraded. Substitution of two cysteine residues for serine residues, did not significantly change the solubility or stability of the gene product. In contrast, a dramatic increase in both solubility and stability was achieved by multiple engineering of hydrophobic phenylalanine residues. As compared to the non-engineered protein, the fraction of soluble protein in vivo could be increased from 27% to 75%. Surprisingly, this effect was accompanied by a remarkable increase in stability. The in vitro solubility of the purified gene products was similarly increased approximately fivefold. Structural studies using circular dichroism suggest that the two engineered fragments have a distribution of secondary-structure elements similar to the non-engineered fragment. In addition, the two engineered G-protein variants were demonstrated to be at least in part antigenically authentic to the non-engineered gene product. These results demonstrate that engineering of hydrophobic residues can be used as a tool to increase the solubility and proteolytic stability of poorly soluble and labile proteins.

Amino Acid Sequence↗
PubMed1995

Chromosomal locations of major tRNA gene clusters of Xenopus laevis.

In Xenopus laevis eight tRNA genes are located in a 3.18 kb tandemly repeated unit. There are 150 copies of the unit at a single locus near the long arm telomere of one of the acrocentric chromosomes in the 14-17 group. Two additional classes of tRNA gene-containing repeats have been isolated (defined by clones p3.1 and p3.2) that have structures related to that of the 3.18 kb unit. Using in situ hybridization at the electron microscopic level, the p3.2 repeats are found clustered at a single locus in the subtelomeric region on one of the submetacentric chromosomes, whereas the p3.1 repeats are clustered at a locus indistinguishable from that containing the 3.18 kb repeats. This suggests that these tDNA tandem repeats can diverge in sequence from each other without being at distantly separated loci.

Animals↗
PubMed1995

Role of nitric oxide in the relationship of pancreatic blood flow and exocrine secretion in cats.

BACKGROUND/AIMS: Recent studies have suggested that, in the gastrointestinal tract, nitric oxide is an important mediator of alterations in blood flow and, in some organs, a second messenger involved in secretion. This study examined the role of NO in changes in pancreatic blood flow associated with basal and stimulated pancreatic exocrine secretion. METHODS: In anesthetized cats, we determined the effects of the NO synthase inhibitor NG-monomethyl-L-arginine (10 mg/kg) and the NO donor sodium nitroprusside (10 micrograms.kg-1.min-1) on pancreatic secretion and blood flow (hydrogen gas clearance). RESULTS: NG-monomethyl-L-arginine had no effect on the increase in blood flow associated with secretin stimulation (271 +/- 52 vs. 290 +/- 50 mL.min-1.100 g-1) but reduced that associated with cholecystokinin stimulation (189 +/- 17 vs. 53 +/- 15 mL.min-1.100 g-1; P < 0.001). In contrast, NG-monomethyl-L-arginine significantly reduced both secretin- and cholecystokinin-stimulated secretion. Sodium nitroprusside had no effect on basal blood flow but significantly increased secretion. CONCLUSIONS: NO has a selective role in mediating changes in pancreatic perfusion and secretion. It seems to be important in stimulus-secretion coupling with both secretin and cholecystokinin but is only responsible for the accompanying increase in pancreatic blood flow with cholecystokinin.

Amino Acid Oxidoreductases↗
PubMed1995

Pancreatic interstitial pH in human and feline chronic pancreatitis.

BACKGROUND & AIMS: Advanced chronic pancreatitis is associated with a reduction in pancreatic blood flow. To determine the physiological significance of this decrease, pancreatic interstitial pH was measured in a model of obstructive chronic pancreatitis in cats and in patients with chronic pancreatitis. METHODS: In cats, pancreatic interstitial pH and blood flow were measured serially under basal conditions and after secretory stimulation as chronic pancreatitis evolved. Basal pancreatic interstitial pH was also measured in patients undergoing an operation for chronic pancreatitis or periampullary cancer (controls). RESULTS: In normal cats, pancreatic interstitial pH was 7.41 +/- 0.01 and blood flow was 124 mL.min-1.(100 g pancreas-1). With the evolution of chronic pancreatitis, interstitial pH and blood flow progressively decreased to 7.21 +/- 0.04 (P < 0.007) and 75 +/- 11 (P < 0.007), respectively. From 1 to 2 weeks, secretory stimulation reduced pancreatic interstitial pH and blood flow further, but as secretory function was lost, this effect disappeared. In patients with chronic pancreatitis, the interstitial pH was lower (7.02 +/- 0.06) than in controls (7.25 +/- 0.04; P < 0.05). CONCLUSIONS: These observations are consistent with the hypothesis that, in chronic pancreatitis, acidic metabolites associated with pancreatic secretion accumulate within the pancreas, probably because of impaired blood flow.

Adult↗
PubMed1995

Crude saponin extracted from Vietnamese ginseng and its major constituent majonoside-R2 attenuate the psychological stress- and foot-shock stress-induced antinociception in mice.

Effects of Vietnamese ginseng (VG) crude saponin and majonoside-R2, a major saponin constituent, on the psychological stress- and foot shock stress-induced antinociception in the tail pinch test were examined in mice. VG crude saponin (6.2, 12.5, and 25 mg/kg, P.O.) attenuated psychological stress- but not foot shock stress-induced antinociceptive response, whereas majonoside-R2 (3, 6.2, and 12.5 mg/kg, P.O. and i.p.), as well as naloxone (2 mg/kg, i.p.), suppressed both psychological stress- and foot shock stress-induced antinociception. Pretreatment with the crude saponin (12.5 mg/kg, P.O.) or majonoside-R2 (6.2 mg/kg, P.O.) for 5 days followed by the treatment in combination with stress for next 5 days did not affect the development of adaptation to foot shock stress, but they significantly suppressed the antinociceptive action of the stress measured on the first, second, and third day during the stress exposure period. Majonoside-R2 (6.2 mg/kg, P.O.) but not the crude saponin (12.5 mg/kg, P.O.) significantly blocked the development of adaptation to psychological stress. These results suggest that VG crude saponin has the suppressing effect on psychological stress- and foot shock stress-induced antinociception and that majonoside-R2 is important for the action of the saponin.

Adaptation, Psychological↗
PubMed1995

Cell surface display of recombinant proteins on Staphylococcus carnosus.

A novel expression system for surface display of heterologous proteins on Staphylococcus carnosus cells has been developed. Taking advantage of the promoter and secretion signals, including a propeptide region, from the lipase gene of Staphylococcus hyicus and the cell wall-spanning and membrane-binding region of protein A from Staphylococcus aureus, efficient surface display of an 80-amino-acid peptide from a malaria blood stage antigen could be achieved. A serum albumin binding protein from streptococcal protein G was used both as a general reporter molecule and to increase the accessibility of the surface-displayed proteins. Immunoblotting, immunogold staining, and immunofluorescence on intact recombinant S. carnosus cells verified the presence of the propeptide, the malaria antigen, and the albumin-binding reporter protein on the bacterial surface. For the first time, fluorescence-activated cell sorting was used to analyze the presence of surface-displayed hybrid receptors on gram-positive bacteria.

Antigens, Protozoan↗
PubMed1995

[Vietnam: appropriate management of a pediatric hospital in the context of limited resources].

To cope with problems arising from limited economic resources, the pediatric hospital of Ho Chi Minh City, Vietnam, integrated several primary health care concepts into its overall policy: designation of priority diseases, adaptation of therapeutic modalities, decentralisation, and community funding. These concepts have been in use since 1988. Five diseases were designated for priority, i.e. diarrhea, acute pulmonary infection, dengue fever (DF), malaria, and routine pediatric emergencies, malnutrition. Training courses focusing on these diseases have been organized for hospital staff and health care assistants and education programs have been offered to the families of patients. Outpatient treatment is encouraged to lower the number of unnecessary hospitalizations and use of simple, cost-effective therapies has been developed for priority diseases. Responsibility has been delegated to department heads. Treatment is provided at no cost to the poorest but a small fee is requested from others and funding is also obtained from local authorities and non-governmental organizations. In five years, these concepts have achieved a 40% reduction in overall mortality. Funding from non-governmental organizations has been allocated to training and research programs designed to respond to specific community needs. This experience shows that reducing mortality does not depend only on budgetary increases but also to a great extent on rational spending and managing available resources. These can be effective in any developing countries that cannot increase budgetary spending.

Ambulatory Care↗
PubMed1995

A clinical trial on diagnostic scoring system of choriocarcinoma and invasive mole in Vietnam.

OBJECTIVES: The aim was to discriminate preoperatively invasive mole (IM) and choriocarcinoma (CC) in patients with gestational trophoblastic neoplasm (GTN) for early and satisfactory treatment in Vietnam. METHODS: In 1990, 122 patients with GTN treated at TUDU Hospital were retrospectively analysed to make a differential diagnosis between CC and IM by using the JSOG scoring system and these results were later compared with postoperative histopathological findings. Furthermore, to raise the predictive diagnostic value for CC, the authors modified the JSOG system and devised a scoring system of TUDU hospital which results were compared with that of the JSOG ones. From the end of 1990 to March 1993, in 151 patients with GTN who underwent surgery, preoperative and postoperative diagnoses of CC and IM were prospectively compared using the JSOG and the modified scoring system. The comparative data were statistically analysed using the t-test, chi 2 test and Fisher test. The sensitivity, specificity, and the positive and negative predictive value, and false positive and false negative were calculated and compared. RESULTS RETROSPECTIVE STUDY: In making a predictive diagnosis of 122 patients with findings of trophoblastic tumors, the authors found some differences in possibility of CC of the following subfactors: latent period, primary lesion, pulmonary metastases, metastases except pulmonary metastases and hCG rerise. So, a modified scoring system of TUDU hospital was devised. PROSPECTIVE STUDY: Of 151 Vietnamese patients with GTN using the JSOG scoring system and the modified system, a diagnostic probability in 108 cases predicted choriocarcinoma by JSOG scoring system was 61%, while that of invasive mole in 43 cases was 62.8%. Accordingly, the false positive rate for invasive mole of 64 cases predicted choriocarcinoma was 38.9%. According to the modified scoring system, of 75 patients predicted choriocarcinoma, 69 patients were histologically confirmed choriocarcinoma. Therefore, the diagnostic specificity was high (94.20%) and the false positive rate was low (5.3%), while of 76 patients predicted invasive mole, 13 patients were histologically diagnosed as choriocarcinoma. Accordingly, the false negative rate was low (13.1%). CONCLUSION: The modified JSOG scoring system is of more diagnostic value in the preoperative differentiation between CC and IM in Vietnam.

Choriocarcinoma↗
PubMed1994

Oleanane and ursane glycosides from Schefflera octophylla.

Twelve triterpene glycosides were isolated from the bark of Schefflera octophylla of Vietnamese origin. Three of them were identified as asiaticoside, cauloside D and 3 alpha-hydroxyurs-12-ene-23,28-dioic acid 28-O-alpha-L-rhamnopyranosyl (1-->4)-beta-D-glucopyranosyl(1-->6)-beta-D-glucopyranoside. The structures of nine new glycosides were elucidated by chemical and spectroscopic evidence. Including the known compounds, the 12 glycosides consisted of six pairs of corresponding ursene and oleanene glycosides and all of them had the same triose moiety at the C-28 position. The names scheffurosides A-F and scheffoleosides B-F were proposed for corresponding pairs of ursene and oleanene glycosides, respectively.

Carbohydrate Sequence↗