Biomedical subjects

T T Nguyen

Publications and source records attributed to T T Nguyen.

At least 19 recordsLinked to original sources

PubMed2002

Model of inversion of DNA charge by a positive polymer: fractionalization of the polymer charge.

We model one strand of DNA by a one-dimensional lattice (ODL) of negative charges and consider the problem of inversion of its charge by a positive polyelectrolyte (PE). In the neutral state of the ODL-PE complex, each of the ODL charges is locally compensated by a PE charge. When an additional PE molecule is adsorbed by ODL, its charge gets fractionalized into monomer charges of defects (tails and arches) on the background of the perfectly neutralized ODL. Defects spread all over the ODL, eliminating the self-energy of PE. For DNA this fractionalization mechanism leads to a substantial inversion of charge, a phenomenon which is widely used for gene delivery.

DNA↗

PubMed2002

Kinetics of macroion coagulation induced by multivalent counterions.

Due to the strong correlations between multivalent counterions condensed on a macroion, the net macroion charge changes sign at some critical counterion concentration. This effect is known as the charge inversion. Near this critical concentration the macroion net charge is small. Therefore, short range attractive forces between macroions dominate Coulomb repulsion and lead to their coagulation. The kinetics of macroion coagulation in this range of counterion concentrations is studied. We calculate the Coulomb barrier between two approaching like charged macroions at a given counterion concentration. Two different macroion shapes (spherical and rodlike) are considered. A new "self-regulated" regime of coagulation is found. As the size of aggregates increases, their charge and Coulomb barrier also grow and diminish the sticking probability of aggregates. This leads to a slow, logarithmic increase of the aggregate size with time.

Journal Article↗

PubMed2002

Chronic caffeine treatment causes changes in cardiac adenosine receptor function in rats.

Caffeine exerts a number of cardiovascular effects via antagonism of adenosine A1 and A2a receptors, and chronic caffeine intake has been suggested to be a preventable risk factor for cardiovascular disease. We attempted, therefore, to determine the effects of chronic caffeine treatment on adenosine receptor function and the heart rate and blood pressure of anaesthetized rats. Rats were given two weeks of drinking water containing either caffeine (0.2%) or tap water alone. Rats were then anaesthetized and blood pressure and heart rate was assessed, as well as cardiovascular responses to adenosine receptor agonists and antagonists. Following 2 weeks caffeine treatment, both the resting blood pressure and heart rate of the treated rats were significantly increased compared to the non-caffeine treated (147 +/- 5 compared to 161 +/- 3 mm Hg). Negative chronotropic responses to A1 receptor agonist N6 cyclopentyladenosine occurred at lower concentrations in caffeine-treated rats than control (2.5-fold decrease in the ED50 of bradycardic responses to N6 cyclopentyladenosine), whilst vasodilator and reflex tachycardic responses to A2a receptor agonist CGS 21680 were unchanged. A shorter duration of caffeine- treatment resulted in moderate increases in heart rate and bradycardic responses to N6 cyclopentyladenosine. In summary, we found changes in resting heart rate and blood pressure in caffeine-treated rats which were concurrent with changes in adenosine receptor function.

Adenosine↗

PubMed2001

Absence of rapid selection for acyclovir or penciclovir resistance following suboptimal oral prodrug therapy of HSV-infected mice.

BACKGROUND: Acyclovir (ACV) resistant herpes simplex virus (HSV) isolates can be readily selected in animal infection models receiving suboptimal ACV treatment, however no comparative studies of the emergence of resistance following suboptimal treatment with valacyclovir (VCV) or famciclovir (FCV), the prodrugs of acyclovir and penciclovir, respectively, have been reported. METHODS: Mice (n = 30) were infected with HSV type 1 or 2 in the ear pinnae and administered oral prodrugs at one fifth a dose previously shown to be effective. To select and amplify drug-resistant HSV, a total of seven consecutive in vivo passages with suboptimal treatment were performed for each virus sample and progeny virus from each passage was characterized by the plaque reduction (PRA) and plating efficiency assays (PEA). RESULTS: No drug-resistant HSV-2 and only a single drug-resistant HSV-1 variant were identified. Virus recovered from the first three sequential passages of this HSV-1 sample was susceptible by PRA, although the proportion of resistant virus recovered gradually increased upon passage. The resistant HSV-1 phenotype was confirmed by PRA after four sequential passages in mice. Unexpectedly, this in vivo-selected drug-resistant HSV-1 failed to yield an infection completely refractory to treatment in subsequent passages. CONCLUSIONS: Sub-optimal therapy of immunocompetent mice with either VCV or FCV did not readily select for HSV-mutants resistant to either ACV or PCV, suggesting that selection of resistance with either prodrug remains difficult using this system. Futhermore, this study suggests that the PEA may represent a useful adjunct to the PRA for monitoring alterations in the proportion of drug-resistant virus even when no change in IC50 is apparent.

Acyclovir↗

PubMed2001

Biochemical characterization of a virus isolate, recovered from a patient with herpes keratitis, that was clinically resistant to acyclovir.

In vitro susceptibility assays of herpes simplex virus (HSV) do not necessarily correlate with treatment outcome. An HSV type 1 (HSV-1) isolate, N4, recovered from a patient who presented with herpes keratitis with localized immunosuppression, was characterized for susceptibility. Although the 50% inhibitory concentration (IC(50)) for this isolate was less than the accepted breakpoint for defining resistance to acyclovir (>2.0 microg/mL), the following lines of evidence suggest that the isolate was acyclovir resistant: (1) the clinical history confirmed that the infection was nonresponsive to acyclovir; (2) the in vitro susceptibility was similar to that of a thymidine kinase (TK)-negative, acyclovir-resistant virus SLU360; (3) the IC(50) of acyclovir was more than 10 times the IC(50) for an acyclovir-susceptible control strain; (4) plaque-purified clonal isolates were resistant to acyclovir (IC(50)s, >2.0 microg/mL); and (5) biochemical studies indicated that the HSV-1 N4 TK was partially impaired for acyclovir phosphorylation. Although residue changes were found in both the viral tk and pol coding regions of HSV-1 N4, characterization of a recombinant virus expressing the HSV-1 N4 polymerase suggested that the TK and Pol together conferred the acyclovir-resistance phenotype.

Acyclovir↗

PubMed2001

Susceptibility of nonpromoter CpG islands to de novo methylation in normal and neoplastic cells.

BACKGROUND: Many cancers display alterations in methylation patterns of CpG islands--stretches of DNA rich in CpG dinucleotides often associated with gene promoters that are involved in initiation of gene transcription. This methylation may perturb expression of genes critical to the regulation of cell proliferation. Aberrant methylation is not limited to a few genes or to promoter regions but has been found on a genome-wide scale in a variety of neoplasias, including colorectal cancer and acute myelogenous leukemia. Our goal was to characterize, in a quantitative manner, the profiles of abnormally methylated genes that may be specific for different cancers. METHODS: Using a quantitative assay, methylation-sensitive single nucleotide primer extension (MS-SNuPE), we have analyzed the methylation levels of promoter and exonic (coding region) CpG islands of two cyclin-dependent kinase inhibitors [p15(INK4B) and p16(INK4A)] and the PAX6 gene, which encodes a transcriptional factor involved in neuronal proliferation, in DNA samples taken from patients with chronic myelogenous leukemia, acute myelogenous leukemia, myelodysplastic syndrome, and colorectal cancer. RESULTS: De novo methylation of all three exonic loci in tumors--relative to baseline levels found in nontumor tissue or blood--was observed in hematologic neoplasias and in solid tumors as well as in normal colonic tissue. However, methylation of promoter regions was more limited. Moreover, two different patterns of promoter methylation distinguished the leukemias from colorectal cancer: p15 promoter hypermethylation was found only in the leukemias, and p16 promoter hypermethylation occurred only in colon tumors. However, we did not address this issue prospectively; therefore, such an observation is only hypothesis generating. CONCLUSIONS: The methylation patterns that we observed suggest that exonic CpG islands are more susceptible to de novo methylation than promoter islands and that methylation may be seeded in exonic regions, from which it can spread to other islands, including promoter regions. Subsequent selection of cells with a growth advantage conferred by spread of methylation into and inactivation of a particular promoter might then contribute to the genesis of a specific type of cancer.

Acute Disease↗

PubMed2001

Adsorption of charged particles on an oppositely charged surface: oscillating inversion of charge.

Adsorption of multivalent counterions on the charged surface of a macroion is known to lead to inversion of the macroion charge due to the strong lateral correlations of counterions. We consider a nontrivial role of the excluded volume of counterions on this effect. It is shown analytically that when the bare charge of the macroion increases, its net charge including the adsorbed counterions oscillates with the number of their layers. Charge inversion vanishes every time the top layer of counterions is completely full and becomes incompressible. These oscillations of charge inversion are confirmed by Monte Carlo simulations. Another version of this phenomenon is studied for a metallic electrode screened by multivalent counterions when the potential of the electrode is controlled instead of its charge. In this case, oscillations of the compressibility and charge inversion lead to oscillations of capacitance of this electrode with the number of adsorbed layers of multivalent counterions.

Journal Article↗

PubMed2001

A novel glucocorticoid regulatory unit mediates the hormone responsiveness of the beta1-adrenergic receptor gene.

The effects of glucocorticoids on expression of the beta1-adrenergic receptor (beta1AR) gene have been varied. To study the mechanism underling hormonal regulation of the beta1AR, transient transfection of progressively deleted ovine beta1AR promoter fragments was used to identify a 43-bp region (-1274 to -1232 from the translation start site) that contains a novel glucocorticoid regulatory unit (GRU) and confers glucocorticoid responsiveness. Using DNase I footprinting and electrophoretic mobility shift assays (EMSA), we demonstrated the GRU was composed of a palindrome, 5'-TAATTA-3', which is a core binding motif for the homeodomain proteins, an E-box (5'-CACGTG-3'), binding site for the Myc/Max family proteins, and an overlapping glucocorticoid response element (GRE) half-site (5'-TGTTCT-3'). EMSA demonstrated that the GRE half-site is critical for GRU-protein interactions, which also require binding of proteins to the E-box and the homeodomain region. Co-transfection of a plasmid expressing a c-myc antisense construct significantly reduced glucocorticoid responsiveness of the ovine beta1AR promoter. Furthermore, expression of proteins binding to the GRU was shown to be developmentally regulated, being high in embryonic, reduced in newborn and not detectable in adult heart. We conclude that the ovine beta1AR promoter contains a novel, functional GRU and that glucocorticoid receptor (GR) and the Myc/Max family proteins are involved in the cell-specific nuclear factor binding and transactivation via this element. The results suggest an alternative pathway through which glucocorticoids may exert their effects on genes lacking a full consensus GRE.

Animals↗

PubMed2001

The TprK protein of Treponema pallidum is periplasmic and is not a target of opsonic antibody or protective immunity.

The finding that Treponema pallidum, the syphilis spirochete, contains 12 orthologs of the Treponema denticola outer membrane major sheath protein has engendered speculation that members of this T. pallidum repeat (Tpr) family may be similarly surface exposed. In this regard, the TprK protein was reported to be a target of opsonic antibody and protective immunity and subject to immunologically driven sequence variation. Despite these findings, results from our previous analyses of treponemal outer membranes in concert with computer-based predictions for TprK prompted us to examine the cellular location of this protein. TprK-alkaline phosphatase fusions expressed in Escherichia coli demonstrate that TprK contains a signal peptide. However, opsonophagocytosis assays failed to indicate surface exposure of TprK. Moreover, results from three independent methodologies, i.e., (a) indirect immunofluorescence analysis of agarose-encapsulated organisms, (b) proteinase K treatment of intact spirochetes, and (c) Triton X-114 phase partitioning of T. pallidum conclusively demonstrated that native TprK is entirely periplasmic. Consistent with this location, immunization with the recombinant protein failed to induce either protective immunity or select for TprK variants in the rabbit model of experimental syphilis. These findings challenge the notion that TprK will be a component of an efficacious syphilis vaccine.

Amino Acid Sequence↗

PubMed2001

Acute management of dengue shock syndrome: a randomized double-blind comparison of 4 intravenous fluid regimens in the first hour.

Dengue hemorrhagic fever is an important cause of morbidity among Asian children, and the more severe dengue shock syndrome (DSS) causes a significant number of childhood deaths. DSS is characterized by a massive increase in systemic capillary permeability with consequent hypovolemia. Fluid resuscitation is critical, but as yet there have been no large trials to determine the optimal fluid regimen. We undertook a randomized blinded comparison of 4 fluids (dextran, gelatin, lactated Ringer's, and "normal" saline) for initial resuscitation of 230 Vietnamese children with DSS. All the children survived, and there was no clear advantage to using any of the 4 fluids, but the longest recovery times occurred in the lactated Ringer's group. The most significant factor determining clinical response was the pulse pressure at presentation. A comparison of the colloid and crystalloid groups suggested benefits in children presenting with lower pulse pressures who received one of the colloids. Further large-scale studies, stratified for admission pulse pressure, are indicated.

Adolescent↗

PubMed2001

Immunocytochemical characterization of viruses and antigenic macromolecules in viral vaccines.

Gold immunolabeling combined with negative staining (GINS) provides a valuable immunocytochemical approach that allows a direct ultrastructural definition of all viral vaccine constituents that share common antigenic features with pathogenic viral particles. These results have implications for the development of viral vaccines since it has been demonstrated that incomplete viral particles such as natural empty capsides and Rotavirus-like particles lacking the infective genome are potential candidates for the production of neutralizing antibodies. Furthermore comparative results of the application of GINS to either inactivated vaccines or unfixed samples provide direct evidence that even after inactivation specific antigenic sites are still available for gold immunolabeling.

Animals↗

PubMed2001

A new application for the sympathetic skin response: the evaluation of auditory thresholds in cochlear implant patients.

OBJECTIVES: Cochlear implants (CI) are now widely used in patients with profound sensorineural deafness. Determining threshold levels for each CI electrode is required during the initial postoperative tuning session. While behavioral testing is appropriate in post-lingually deafened patients, it may be really tricky in pre-lingually deafened children. CI stimulation is responsible for auditory perception and logically induces brainstem reticular formation arousal which can be studied by sympathetic skin response (SSR). METHODS: Thirteen patients (aged 3-70 years) implanted with an MXM Digisonic((R)) were postoperatively studied. SSR as well as behavioral thresholds were recorded after electrical stimulation of CI electrodes at various intensities. RESULTS: SSR could be recorded in all patients including the 6 studied children. There was a strong correlation between SSR threshold and subjective auditory threshold (r=0.93). CONCLUSIONS: The present data indicate that SSR could have a clinical application as a routine test in postoperative fitting procedures of CIs especially in pre-lingually deafened children.

Adult↗

PubMed2001

Induction of apoptosis in mammary gland by a pure anti-estrogen ICI 182780.

The antiestrogen, ICI 182780 (ICI) proves to be clinically useful for the treatment of estrogen receptor positive breast tumours. We report the assessment of the in vivo and in vitro effects of ICI on apoptosis of breast epithelial cells. In vivo, administration of rats with ICI for 3 weeks resulted in a reduction in the size of the lobular structures with the rate of mammary epithelial apoptosis equivalent to 10, 35 and 45% on treatment with 1, 1.5 and 2 mg ICI per kg body weight, respectively. Concomitantly, these treatment led to a 2.0-, 2.2- and 2.5-fold increase in Bax. Similar elevations were also observed in Bad levels which increased 1.7-, 2.6- and 2.7-fold respectively in the ICI treatment as compared to controls. This also resulted in a dose dependent decrease in Bcl-2 and Bcl-xL protein expressions. Growth inhibition and induction of apoptosis were also observed in the MCF-7 cells following in vitro treatment with ICI. This is closely associated with [1] the down-regulation of Bcl-2 and Bcl-xL proteins and [2] upregulation of Bax and Bad, whose gene products are known to be involved the regulation of apoptosis in mammalian cells. Stable over-expression of Bcl-2 resulted in protection of MCF-7 cells from apoptosis and growth inhibitory effects of ICI. Conversely, reduction of Bcl-2 by antisense transfection make MCF-7 cells more sensitive to ICI-induced growth inhibition and apoptosis. These findings suggest that modulation of Bax, Bcl-xL, Bcl-2 and Bad proteins by ICI may be, in part, responsible for the anti-proliferative and apoptotic effect of ICI seen clinically and in animal models.

Animals↗

PubMed2001

Consistency of care with national guidelines for children with asthma in managed care.

OBJECTIVE: To evaluate the consistency of pediatric asthma care with the National Asthma Education and Prevention Program Guidelines. DESIGN: Cross-sectional survey at 2 managed care organizations in the United States (winter 1997-1998). The participants were parents of children (n = 318) age 5 to 17 years with asthma. There were no interventions. The outcome measures were indicators of care in 4 domains: (1) periodic physiologic assessment, (2) proper use of medications, (3) patient education, and (4) control of factors contributing to asthma severity. RESULTS: Of 533 eligible patients with asthma, 318 (60%) parents responded; 59% of children were male, 76% were white, and 60% were aged 5 to 10 years. Deficiencies in care were identified in all care domains including, for patients with moderate and severe persistent symptoms, only 55% used long-term control medication daily, 49% had written instructions for handling asthma attacks, 44% had instructions for adjustment of medication before exposures, 56% had undergone allergy testing, and 54% had undergone pulmonary function testing. CONCLUSIONS: There are significant opportunities to improve the quality of care for children with asthma enrolled in managed care. A comprehensive approach to improving care may be necessary to address multiple aspects of care where opportunities exist.

Adolescent↗

PubMed2001

Relation of acanthosis nigricans to hyperinsulinemia and insulin sensitivity in overweight African American and white children.

OBJECTIVES: Acanthosis nigricans (AN) has been proposed as a reliable marker of hyperinsulinemia, but its utility for predicting hyperinsulinism has not been systematically evaluated in overweight children. We examined the relationship of AN to hyperinsulinemia and body adiposity. STUDY DESIGN: One hundred thirty-nine children underwent physical examination for AN, body composition studies, an oral glucose tolerance test, and a hyperglycemic clamp. RESULTS: Thirty-five children (25%) had AN. AN was more prevalent in African Americans (50.1%) than in white subjects (8.2%, P < .001). Independent of race, children with AN had greater body weight and body fat mass (P < .001); greater basal and glucose-stimulated insulin levels during oral glucose tolerance test (P < .001); greater first-phase, second-phase, and steady-state insulin levels (P < .001); and lower insulin sensitivity (P < .001) during the hyperglycemic clamp. After adjusting for body fat mass and age, none of these differences remained significant. When categorized by fasting insulin, 35% with fasting insulin levels > 20 microU/mL and 50% with fasting insulin levels > 15 microU/mL did not have AN. Eighty-eight percent of children with fasting insulin levels > or = 15 microU/mL had a body mass index SD score > or = 3.0. CONCLUSIONS: AN is not a reliable marker for hyperinsulinemia in overweight children. Children with a race-, sex-, and age-specific body mass index SD scores > or = 3.0 should be screened for hyperinsulinemia, whether or not they have AN.

Acanthosis Nigricans↗

PubMed2001

Beta-adrenergic receptors (betaAR) regulate cardiomyocyte proliferation during early postnatal life.

Cardiomyocyte development switches from hyperplasmic to hypertrophic growth between postnatal days 3 and 4 in rats. The mechanisms responsible for this transition have been controversial. beta-Adrenergic receptor (betaAR) activation of mitogenic responses in vitro has been reported. We hypothesized that tonic activation of the betaAR signaling regulates cell division in neonatal cardiomyocytes via effects on signaling kinases known to be important in cell cycle regulation. The purpose of the current study was to elucidate the roles of betaAR in rat cardiomyocyte growth in vivo. We demonstrated that betaAR blockade induced a significant reduction in cardiomyocyte proliferation as measured by the BrdU labeling index. Blockade of betaAR did not affect p38 or p44/42 MAPK activities. We further demonstrated that betaAR blockade induced a prompt deactivation of the p70 ribosomal protein S6 kinase (p70 S6K). To confirm these results, we measured p70 S6K activity directly. Basal activity of p70 S6K in neonatal cardiomyocytes was fourfold higher than that of insulin-treated adult rat liver. The activity of p70 S6K was reduced by 60% within 1 min after betaAR blockade. We conclude that the betaAR are involved in regulation of neonatal cardiomyocyte proliferation and that this mitogenic control may be mediated via the p70 S6K pathway.

Adrenergic beta-Antagonists↗

PubMed2001

Tsukamurella strandjordae sp. nov., a proposed new species causing sepsis.

We have isolated a gram-positive, weakly acid-alcohol-fast, irregular rod-shaped bacterium from cultures of blood from a 5-year-old girl with acute myelogenous leukemia. This isolate was compared with 14 other strains including reference strains of Tsukamurella species by a polyphasic approach based on physiological and biochemical properties, whole-cell short-chain fatty acid and mycolic acid analyses, DNA-DNA hybridization, and sequencing of the 16S rRNA gene. This isolate represents a new taxon within the genus Tsukamurella for which we propose the name Tsukamurella strandjordae sp. nov. Our study also revealed that Tsukamurella paurometabola ATCC 25938 represents a misnamed Tsukamurella inchonensis isolate and confirms that Tsukamurella wratislaviensis belongs to the genus Rhodococcus.

Actinomycetales↗

PubMed2001

Characterization of herpes simplex viruses selected in culture for resistance to penciclovir or acyclovir.

Penciclovir (PCV), an antiherpesvirus agent in the same class as acyclovir (ACV), is phosphorylated in herpes simplex virus (HSV)-infected cells by the viral thymidine kinase (TK). Resistance to ACV has been mapped to mutations within either the TK or the DNA polymerase gene. An identical activation pathway, the similarity in mode of action, and the invariant cross-resistance of TK-negative mutants argue that the mechanisms of resistance to PCV and ACV are likely to be analogous. A total of 48 HSV type 1 (HSV-1) and HSV-2 isolates were selected after passage in the presence of increasing concentrations of PCV or ACV in MRC-5 cells. Phenotypic analysis suggested these isolates were deficient in TK activity. Moreover, sequencing of the TK genes from ACV-selected mutants identified two homopolymeric G-C nucleotide stretches as putative hot spots, thereby confirming previous reports examining Acv(r) clinical isolates. Surprisingly, mutations identified in PCV-selected mutants were generally not in these regions but distributed throughout the TK gene and at similar frequencies of occurrence within A-T or G-C nucleotides, regardless of virus type. Furthermore, HSV-1 isolates selected in the presence of ACV commonly included frameshift mutations, while PCV-selected HSV-1 mutants contained mostly nonconservative amino acid changes. Data from this panel of laboratory isolates show that Pcv(r) mutants share cross-resistance and only limited sequence similarity with HSV mutants identified following ACV selection. Subtle differences between PCV and ACV in the interaction with viral TK or polymerase may account for the different spectra of genotypes observed for the two sets of mutants.

Acyclovir↗