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Biomedical subjects

H Nguyen

Publications and source records attributed to H Nguyen.

At least 91 records · Page 5Linked to original sources
PubMed1999

Calcium influx through NMDA receptors, chronic receptor inhibition by ethanol and 2-amino-5-phosponopentanoic acid, and receptor protein expression.

Chronic treatment of neurons with either ethanol or competitive and noncompetitive antagonists of NMDA receptors leads to enhanced expression of NMDA receptor density and function in neurons. The signal transduction pathways for such receptor up-regulation are not known. The focus of the present study was on the role of Ca2+ entry into neurons, either through receptor or voltage-gated channels, in the expression of the NMDA receptor subunit NR1 and the 71-kDa glutamate-binding protein (GBP) of a glutamate/NMDA receptor-like complex. Chronic inhibition of NMDA receptors in cortical neurons in primary cultures by either 100 mM ethanol or 100 microM 2-amino-5-phosphonopentanoic acid (2-AP5) increased the expression of NR1 and GBP. The effect of 2-AP5 on the expression of the two proteins was not additive with that of ethanol when neuronal cultures were treated with both agents at the same time. However, the effects of ethanol on NR1 and GBP expression were blocked by the simultaneous treatment with NMDA (50 microM). Activation or inhibition of other glutamate ionotropic receptors had no effect on the expression of NR1 and GBP. The inhibition of L- or N-type voltage-sensitive Ca2+ channels and voltage-gated Na+ channels also had little effect on the expression of either protein; neither did exposure of neurons to elevated extracellular Ca2+ concentrations (3 or 5 mM). On the other hand, treatment of neurons for 48 h with the intracellular Ca2+ chelator BAPTA-AM as well as partial chelation of extracellular Ca2+ with EGTA caused an up-regulation in NR1 and GBP expression. The enhanced expression of NR1 in neurons treated for 48 h with either ethanol or EGTA was correlated with increases in the activity of NMDA receptors demonstrated as a doubling of the NMDA-stimulated rise in intracellular free Ca2+ concentration. The effects of chronic administration of EGTA on both NR1 expression as well as NMDA receptor function were probably related to an acute inhibition by EGTA of NMDA-induced Ca2+ influx into neurons. It appears that the expression of both the NR1 subunit of NMDA receptors and the GBP of a receptor-like complex is regulated by intracellular Ca2+, especially that entering through NMDA receptor ion channels.

2-Amino-5-phosphonovalerate↗
PubMed1999

Effects of nitric oxide on platelet activation during plateletpheresis and in vivo tracking of biotinylated platelets in humans.

BACKGROUND: The use of platelet transfusions has risen considerably over the last few years, which leads to the collection and transfusion of a greater number of donor plateletpheresis units. Plateletpheresis activates platelets in platelet concentrates, which determines the degree of the storage lesion subsequently observed. STUDY DESIGN AND METHODS: As nitric oxide (NO) is a potent inhibitor of platelet aggregation and activation, a placebo-controlled crossover trial was performed in healthy young male volunteers to determine whether the NO-donating compound, sodium nitroprusside (SNP), decreases platelet activation during apheresis and whether activated (p-selectin+) platelets circulate in vivo after transfusion. The study also investigated whether nonradioactive biotin labeling of apheresis platelets is feasible for the study of platelet recovery after transfusion in humans. RESULTS: Platelet activation increased after plateletpheresis in the platelet components, but SNP did not inhibit platelet activation during apheresis, as measured by the percentage of p-selectin expression and the secretion of soluble p-selectin and RANTES. Only a minor increase in p-selectin+ platelets was seen in peripheral blood at 60 minutes after transfusion of the platelets, a rise that was considerably less than that calculated in p-selectin+ platelets if they all were recovered as activated platelets after transfusion. Biotin-labeled platelets averaged 1.5 percent at 10 minutes after transfusion and increased slowly to 2.6 and 3.4 percent after 60 minutes and 24 hours, respectively (p<0.05). CONCLUSION: SNP does not decrease platelet activation during apheresis and subsequent storage, and only a minor proportion of activated (p-selectin+) platelets circulate after transfusion in men. Moreover, biotin labeling of PCs can safely be used in humans for the study of platelet recovery after transfusion, and measuring recovery at 1 hour may lead to an underestimation of the true recovery when activated platelets are transfused.

Biotinylation↗
PubMed1999

Late onset of tonsillar metastasis from breast cancer.

A 71-year-old woman non-smoker referred for repeated haemoptysis showed a tumoral lesion of the left tonsil. Pathological analysis of the biopsy showed characteristics compatible with a breast carcinoma metastasis, in which oestrogen and progesterone receptors were present. The patient had undergone mastectomy and had received adjuvant radiotherapy 24 years previously for a breast cancer with no complaints or signs of recurrence since. Investigations showed disseminated bone metastases but no other soft-tissue deposits. Anti-oestrogen therapy was applied. Only seven similar cases of tonsillar metastasis from breast cancer have been reported.

Adenocarcinoma↗
PubMed1999

Triggering the interferon response: the role of IRF-3 transcription factor.

The interferon (IFN) regulatory factors (IRF) consist of a growing family of related transcription proteins first identified as regulators of the IFN-alpha/beta gene promoters, as well as the IFN-stimulated response element (ISRE) of some IFN-stimulated genes. IRF-3 was originally identified as a member of the IRF family based on homology with other IRF family members and on binding to the ISRE of the IFN-stimulated gene 15 (ISG15) promoter. Several recent studies have focused attention on the unique molecular properties of IRF-3 and its role in the regulation of IFN gene expression. IRF-3 is expressed constitutively in a variety of tissues, and the relative levels of IRF-3 mRNA do not change in virus-infected or IFN-treated cells. Following virus infection, IRF-3 is posttranslationally modified by protein phosphorylation at multiple serine and threonine residues, located in the carboxy-terminus of IRF-3. Phosphorylation causes the cytoplasmic to nuclear translocation of IRF-3, stimulation of DNA binding, and increased transcriptional activation, mediated through the association of IRF-3 with the CBP/p300 coactivator. The purpose of this review is to summarize recent investigations demonstrating the important role of IRF-3 in cytokine gene transcription. These studies provide the framework for a model in which virus-dependent phosphorylation of IRF-3 alters protein conformation to permit nuclear translocation, association with transcriptional partners, and primary activation of IFN and IFN-responsive genes.

Amino Acid Sequence↗
PubMed1999

Human genome anatomy: BACs integrating the genetic and cytogenetic maps for bridging genome and biomedicine.

Human genome sequencing is accelerating rapidly. Multiple genome maps link this sequence to problems in biology and clinical medicine. Because each map represents a different aspect of the structure, content, and behavior of human chromosomes, these fundamental properties must be integrated with the genome to understand disease genes, cancer instability, and human evolution. Cytogenetic maps use 400-850 visible band landmarks and are the primary means for defining prenatal defects and novel cancer breakpoints, thereby providing simultaneous examination of the entire genome. Recent genetic, physical, and transcript maps use PCR-based landmarks called sequence-tagged sites (STSs). We have integrated these genome maps by anchoring the human cytogenetic to the STS-based genetic and physical maps with 1021 STS-BAC pairs at an average spacing of approximately 1 per 3 Mb. These integration points are represented by 872 unique STSs, including 642 polymorphic markers and 957 bacterial artificial chromosomes (BACs), each of which was localized on high resolution fluorescent banded chromosomes. These BACs constitute a resource that bridges map levels and provides the tools to seamlessly translate questions raised by genomic change seen at the chromosomal level into answers based at the molecular level. We show how the BACs provide molecular links for understanding human genomic duplications, meiosis, and evolution, as well as reagents for conducting genome-wide prenatal diagnosis at the molecular level and for detecting gene candidates associated with novel cancer breakpoints.

Chromosome Mapping↗
PubMed1999

Mycobacterium species identification and rifampin resistance testing with high-density DNA probe arrays.

Species identification within the genus Mycobacterium and subsequent antibiotic susceptibility testing still rely on time-consuming, culture-based methods. Despite the recent development of DNA probes, which greatly reduce assay time, there is a need for a single platform assay capable of answering the multitude of diagnostic questions associated with this genus. We describe the use of a DNA probe array based on two sequence databases: one for the species identification of mycobacteria (82 unique 16S rRNA sequences corresponding to 54 phenotypical species) and the other for detecting Mycobacterium tuberculosis rifampin resistance (rpoB alleles). Species identification or rifampin resistance was determined by hybridizing fluorescently labeled, amplified genetic material generated from bacterial colonies to the array. Seventy mycobacterial isolates from 27 different species and 15 rifampin-resistant M. tuberculosis strains were tested. A total of 26 of 27 species were correctly identified as well as all of the rpoB mutants. This parallel testing format opens new perspectives in terms of patient management for bacterial diseases by allowing a number of genetic tests to be simultaneously run.

Antibiotics, Antitubercular↗
PubMed1999

IkappaB-mediated inhibition of virus-induced beta interferon transcription.

We have examined the consequences of overexpression of the IkappaBalpha and IkappaBbeta inhibitory proteins on the regulation of NF-kappaB-dependent beta interferon (IFN-beta) gene transcription in human cells after Sendai virus infection. In transient coexpression studies or in cell lines engineered to express different forms of IkappaB under tetracycline-inducible control, the IFN-beta promoter (-281 to +19) linked to the chloramphenicol acetyltransferase reporter gene was differentially inhibited in response to virus infection. IkappaBalpha exhibited a strong inhibitory effect on virus-induced IFN-beta expression, whereas IkappaBbeta exerted an inhibitory effect only at a high concentration. Despite activation of the IkappaB kinase complex by Sendai virus infection, overexpression of the double-point-mutated (S32A/S36A) dominant repressors of IkappaBalpha (TD-IkappaBalpha) completely blocked IFN-beta gene activation by Sendai virus. Endogenous IFN-beta RNA production was also inhibited in Tet-inducible TD-IkappaBalpha-expressing cells. Inhibition of IFN-beta expression directly correlated with a reduction in the binding of NF-kappaB (p50-RelA) complex to PRDII after Sendai virus infection in IkappaBalpha-expressing cells, whereas IFN-beta expression and NF-kappaB binding were only slightly reduced in IkappaBbeta-expressing cells. These experiments demonstrate a major role for IkappaBalpha in the regulation of NF-kappaB-induced IFN-beta gene activation and a minor role for IkappaBbeta in the activation process.

Amino Acid Sequence↗
PubMed1999

Cell-free degradation of p27(kip1), a G1 cyclin-dependent kinase inhibitor, is dependent on CDK2 activity and the proteasome.

Entry into S phase is dependent on the coordinated activation of CDK4,6 and CDK2 kinases. Once a cell commits to S phase, there must be a mechanism to ensure the irreversibility of this decision. The activity of these kinases is inhibited by their association with p27. In many cells, p27 plays a major role in the withdrawal from the cell cycle in response to environmental cues. Thus, it is likely that p27 is a target of the machinery required to ensure the irreversibility of S-phase entry. We have been interested in understanding the mechanisms regulating p27 at the G1/S transition. In this report, we define a cell-free degradation system which faithfully recapitulates the cell cycle phase-specific degradation of p27. We show that this reaction is dependent on active CDK2 activity, suggesting that CDK2 activity is directly required for p27 degradation. In addition to CDK2, other S-phase-specific factors are required for p27 degradation. At least some of these factors are ubiquitin and proteasome dependent. We discuss the relationships between CDK2 activity, ubiquitin-dependent, and possibly ubiquitin-independent proteasomal activities in S-phase extracts as related to p27.

Base Sequence↗
PubMed1999

Ethanol modulation of intestinal epithelial tight junction barrier.

Previous studies have shown that high concentrations of ethanol (>/=40%) cause functional damage of the gastrointestinal epithelial barrier by direct cytotoxic effect on the epithelial cells. The effects of lower noncytotoxic doses of ethanol on epithelial barrier function are unknown. A major function of gastrointestinal epithelial cells is to provide a barrier against the hostile substances in the gastrointestinal lumen. The apicolaterally located tight junctions (TJs) form a paracellular seal between the lateral membranes of adjacent cells and act as a paracellular barrier. In this study, we investigated the effects of lower doses of ethanol on intestinal epithelial TJ barrier function using filter-grown Caco-2 intestinal epithelial monolayers. The Caco-2 TJ barrier function was assessed by measuring epithelial resistance or paracellular permeability of the filter-grown monolayers. Ethanol (0, 1, 2.5, 5, 7.5, and 10%) produced a dose-related drop in Caco-2 epithelial resistance and increase in paracellular permeability. Ethanol also produced a progressive disruption of TJ protein (ZO-1) with separation of ZO-1 proteins from the cellular junctions and formation of large gaps between the adjacent cells. Ethanol, at the doses used (</=10%), did not cause cytotoxicity (lactate dehydrogenase release) to the Caco-2 cells. Ethanol produced a disassembly and displacement of perijunctional actin and myosin filaments from the perijunctional areas. On ethanol removal, actin and myosin filaments rapidly reassembled at the cellular borders. Ethanol stimulated the Caco-2 myosin light chain kinase (MLCK) activity but did not affect the MLCK protein levels. Specific MLCK inhibitor ML-7 inhibited both ethanol increases in MLCK activity and TJ permeability without affecting the MLCK protein levels. Consistent with these findings, metabolic inhibitors sodium azide and 2,4-dinitrophenol significantly prevented ethanol-induced increase in Caco-2 TJ permeability, whereas cycloheximide or actinomycin D had no effect. The results of this study indicate that ethanol at low noncytotoxic doses causes a functional and structural opening of the Caco-2 intestinal epithelial TJ barrier by activating MLCK.

Azepines↗
PubMed1999

NGF activates similar intracellular signaling pathways in vascular smooth muscle cells as PDGF-BB but elicits different biological responses.

The signaling pathways that regulate smooth muscle cell migration and proliferation are incompletely understood. Smooth muscle cells express at least 3 families of receptor tyrosine kinases that mediate cell migration: platelet-derived growth factor (PDGF) receptors, the trk family of neurotrophin receptors, and insulin-like growth factor 1 receptor. The neurotrophin, nerve growth factor (NGF), and insulin-like growth factor 1 induce the migration but not the proliferation of smooth muscle cells, whereas PDGF-BB stimulates both responses. To determine whether distinct signaling pathways downstream of receptor tyrosine kinases specifically mediate smooth muscle cell migration or proliferation, the ligand-induced activation of different signaling pathways in smooth muscle cells was examined. NGF induces prolonged activation of the Shc/MAP kinase pathway and phospholipase Cgamma compared with PDGF-BB. The activation of phosphatidylinositol-3 kinase, however, was 10-fold greater in response to PDGF-BB compared with NGF. Insulin-like growth factor 1 activates only phosphatidylinositol-3 kinase. Pharmacological inhibitors of phosphatidylinositol-3 kinase, Wortmannin and LY294002, inhibit PDGF-BB and NGF-induced migration, whereas an inhibitor of MAP kinase kinase, PD98059, has no effect. Our results suggest that (1) different receptor tyrosine kinases use similar patterns of activation of signaling pathways to mediate distinct biological outcomes of cell migration and proliferation, (2) NGF activates signaling proteins in smooth muscle cells similar to those activated during NGF-induced neuronal differentiation, and (3) the combinatorial effects of different signaling pathways are important for the regulation of smooth muscle cell migration and proliferation. Further studies using mutant trk receptors will help to define the signal transduction pathways mediating NGF-induced smooth muscle cell migration.

Animals↗
PubMed1999

Arterial baroreflex control of the sinus node during dobutamine exercise stress testing.

The contributions of increases in circulating catecholamines, changes in central command, and muscle afferents on baroreflex control of the sinus node during exercise are unclear. We used a dobutamine infusion to induce hemodynamic changes comparable to those of moderate physical exercise in the absence of changes in central command and muscle afferents in 13 healthy subjects. Dobutamine (up to 9 microg/kg body weight per minute) increased systolic blood pressure, shortened the RR interval, increased systolic blood pressure variability, but blunted RR interval variability (P<0.05 versus placebo). Consequently, dobutamine decreased the coherence between variations in systolic blood pressure and RR interval and decreased arterial baroreflex sensitivity from 12+/-2 to 3+/-1 ms/mm Hg (P<0.01). The largest increases in systolic blood pressure with dobutamine were paralleled by the greatest impairments in arterial baroreflex sensitivity (0. 50<r<0.56, P<0.01). The chronotropic effects of dobutamine prevented a reflex bradycardia in response to the blood pressure increase. However, less predominant low-frequency oscillations in systolic blood pressure (P<0.0001) suggested preserved sympathetic withdrawal in response to the blood pressure increase induced by dobutamine. In conclusion, this study revealed that a shift in the operating point of the arterial baroreceptors and the chronotropic effects of adrenergic stimulation impair baroreflex control of the sinus node during dobutamine exercise stress testing. Baroreflex control of the sinus node is not reset when hemodynamic characteristics of exercise are reproduced in the absence of modifications in central command and muscles afferents.

Adult↗
PubMed1999

A comparison of HIV/AIDS knowledge among high school freshmen and senior students.

Statistical data show that heterosexual transmission of AIDS among teenagers is a significant problem. The purpose of this study was to assess and compare the level of knowledge concerning HIV/AIDS among high school freshmen- and senior-level students and to determine the association between certain demographic variables and the students' knowledge level. A convenience sample of 169 freshmen and 274 senior high school students were surveyed at a local area high school (N = 443). A 49-item knowledge questionnaire, used by the high school district HIV/Abstinence program, and a demographic questionnaire developed by the investigators were used to collect the data. The findings revealed that both the freshmen and senior students had several misconceptions about HIV/AIDS, including the modes of transmission, the sure way of preventing the sexual transmission, donating blood, and the usual causes of death for people with AIDS. A comparison of the mean knowledge scores among freshmen and senior students indicated there was no significant difference among the two groups. The mean knowledge score of the seniors was significantly affected by whether they had received HIV/AIDS education. However, this was not the case for the freshmen. African American students, especially the female students, had significantly lower knowledge scores than other ethnic groups.

Adolescent↗
PubMed1999

Lengthening of the Achilles tendon in diabetic patients who are at high risk for ulceration of the foot.

BACKGROUND: The purpose of this study was to determine the degree to which pressure on the plantar aspect of the forefoot is reduced following percutaneous lengthening of the Achilles tendon in diabetic patients who are at high risk for ulceration of the foot. METHODS: Ten diabetic patients who had a history of neuropathic plantar ulceration of the forefoot were enrolled in a laboratory gait trial. A repeated-measures design and a computer analysis of force-plate data were used to examine dynamic pressures on the forefoot, with the patient walking barefoot, immediately before percutaneous lengthening of the Achilles tendon and at eight weeks afterward. Although the wound in each patient had healed at least one month before the operation, we considered the patients to be at high risk for ulceration because they had had an ulcer previously. RESULTS: The mean peak pressure (and standard deviation) on the plantar aspect of the forefoot decreased significantly from 86+/-9.4 newtons per square centimeter preoperatively to 63+/-13.2 newtons per square centimeter at eight weeks postoperatively (p<0.001). Commensurately, the mean dorsiflexion of the ankle joint increased significantly from 0+/-3.1 degrees preoperatively to 9+/-2.3 degrees at eight weeks post-operatively (p<0.001). CONCLUSIONS: The results of this study suggest that peak pressures on the plantar aspect of the forefoot are significantly reduced following percutaneous lengthening of the Achilles tendon in diabetic patients who are at high risk for ulceration of the foot. We are unaware of any other reports in the medical literature that describe such findings. These data may lend support to studies that have indicated that this procedure should be used as an adjunctive therapeutic or prophylactic measure to reduce the risk of neuropathic ulceration.

Achilles Tendon↗
PubMed1999

Toxicology and pharmacokinetics of intravesical gemcitabine: a preclinical study in dogs.

More active and well-tolerated agents are needed for the treatment of superficial bladder cancer. This study investigated intravesical gemcitabine to establish the toxicology and pharmacokinetics necessary for clinical trials. Beagle dogs (in groups of 2; n = 6) received 100 mg, 350 mg, or 1 g of drug by intravesical administration on alternate days three times/week for 4 weeks. Animals were observed for clinical signs of toxicity; gemcitabine levels and peripheral blood counts were taken three times weekly. The dogs were euthanized, and a full necropsy was performed at days 1 and 14 after the last dose. Intravesical gemcitabine was given at 100 mg (n = 2), 350 mg (equivalent to the 1000 mg/m2 human dose; n = 3), and 3.5 g (n = 1). i.v. gemcitabine was given at 350 mg (n = 2). Plasma samples drawn at time points up to 8 h were analyzed for systemic absorption and clearance of drug. Doses of 100 and 350 mg were well tolerated with no clinical side effects. Necropsies revealed normal bone marrow cellularity and normal bladder histology. At 1 g, signs of severe clinical toxicity were evident, and after only three doses, necropsies demonstrated severe bone marrow hypoplasia, cystitis, and intestinal necrosis. At all intravesical doses, significant systemic absorption was seen. The T1/2 (+/- SD) for intravesical and i.v. administration of 350 mg was 328 (+/-6.8) min and 99.3 (+/-5.2) min, respectively (P<0.001). Intravesical gemcitabine is well tolerated and has no direct bladder toxicity at doses up to 1000 mg/m2. Higher doses result in gastrointestinal, bladder, and bone marrow toxicity.

Absorption↗