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Biomedical subjects

P Tran

Publications and source records attributed to P Tran.

At least 37 records · Page 2Linked to original sources
PubMed1997

Identification of DNA methylation markers for human breast carcinomas using the methylation-sensitive restriction fingerprinting technique.

We have developed a PCR-based method, called methylation-sensitive restriction fingerprinting (MSRF), to screen changes in DNA methylation in breast carcinomas. Two hypermethylation-containing fragments, HBC-1 (for "hypermethylation in breast cancer") and HBC-2, were identified in the amplified breast tumor DNA relative to the amplified normal breast DNA of a patient. Nucleotide sequence analysis revealed no significant matches between the sequence of HBC-1 and the known sequences in the GenBank database, whereas the sequence of HBC-2 matched the upstream region of an antisense WT1 (Wilms' tumor suppressor gene) promoter. The methylation status in the breast tumor DNA from this patient was confirmed by Southern hybridization using HBC-1 and HBC-2 as probes, respectively. Further analysis showed that HBC-1 was methylated aberrantly in 90% (17 of 19 patients) of the primary breast carcinomas examined. This study demonstrates that MSRF provides a useful means for screening aberrant changes in DNA methylation during tumorigenesis. The commonly methylated fragments identified by MSRF could potentially supplement pathological markers currently used for cancers and additionally lead to the discovery of novel methylated tumor suppressor genes.

Base Sequence↗
PubMed1997

Polarized light microscopy and digital image processing identify a multilaminar structure of the hamster zona pellucida.

The zona pellucida (zona) is a glycoprotein coat that envelopes the oocyte and embryo, binds sperm during fertilization and facilitates transfer of the embryo through the Fallopian tube. Before implantation can occur, the blastocyst must hatch from the zona. Several lines of evidence suggest that the zona is multilaminar. We hypothesized that the multilaminar structure of the zona filaments could be imaged non-destructively with the polarized light microscope. A recent modification of the polarized light microscope (pol-scope), which combines innovations in polarization optics with novel image processing software, allows measurement of birefringence at all points of the image. Hamster metaphase II oocytes were placed on glass coverslips which replaced the bottom of culture dishes, imaged under differential interference contrast (DIC) and pol-scope optics, then digitized and processed to measure birefringence magnitude and orientation. The pol-scope revealed the zona to be divided into outer and inner layers separated by a zone of low retardance. This finding is consistent with filaments in the outer layer oriented tangentially and in the inner layer oriented radially. The multilaminar structure of the mammalian zona suggested by differential lectin binding and by scanning electron microscopy could be imaged non-destructively with the pol-scope. Because the pol-scope provides a non-destructive method to identify macro-molecular organization of the zona, it may prove useful in developmental studies of hatching and to direct resection of the zona.

Animals↗
PubMed1997

Standard olanzapine versus placebo and ineffective-dose olanzapine in the maintenance treatment of schizophrenia.

OBJECTIVE: Two studies compared the efficacy of standard-dose oral olanzapine (5 to 15 mg a day) with placebo and with ineffective-dose olanzapine (1 mg a day) in maintenance therapy of schizophrenia. METHODS: The studies were 46-week double-blind extensions of multicenter studies that assessed the efficacy of olanzapine in the acute treatment of schizophrenia. Subjects were 120 adults who met DSM-III-R criteria for schizophrenia with an acute exacerbation and who had a minimum score of 24 on the Brief Psychiatric Rating Scale, who had responded to acute therapy (defined as at least a 40 percent reduction in the BPRS score from baseline or a score of 18 or less during up to six weeks of treatment), and who were outpatients at their last acute-phase visit. Relapse was defined as hospitalization for psychopathology. Relapse risk was analyzed using Kaplan-Meier survival analysis and life table analysis. Patients who relapsed were discontinued from the studies. RESULTS: In the first study (N = 58), patients in the standard-dose olanzapine group experienced a significantly lower relapse risk (p = .002) over one year than patients treated with placebo. The estimated one-year risk of relapse with olanzapine was 28.6 percent, compared with 69.9 percent with placebo. Results were similar in the second study (N = 62); patients treated with standard-dose olanzapine had a significantly reduced risk of relapse (p = .018) over one year compared with patients treated with ineffective-dose olanzapine. The estimated one-year risks of relapse were 19.6 percent for standard-dose olanzapine and 45.5 percent for ineffective-dose olanzapine. CONCLUSIONS: Olanzapine is superior to placebo and ineffective-dose olanzapine in the maintenance therapy of schizophrenia.

Acute Disease↗
PubMed1996

Methylthioadenosine phosphorylase cDNA transfection alters sensitivity to depletion of purine and methionine in A549 lung cancer cells.

Methylthioadenosine phosphorylase (MTAP), an enzyme involved in purine and methionine metabolism, is present in all normal tissues but is frequently deficient in a variety of cancers. It has been suggested that this metabolic difference between normal and cancer cells may be exploited to selectively treat MTAP-negative cancers by inhibiting de novo purine synthesis and by depleting L-methionine. However, these therapeutic strategies have only been tested in naturally occurring MTAP-positive and -negative cell lines, which might have additional genetic alterations that affect chemotherapeutic sensitivity. Therefore, it is of importance to examine the feasibility of enzyme-selective treatment using paired cell lines that have an identical genotype except for MTAP status. MTAP-negative A549 lung cancer cells were transfected with eukaryotic expression vectors encoding MTAP cDNA in sense and antisense orientations. The resultant stable transfectomas were treated with inhibitors of de novo purine synthesis such as methotrexate, 5,10-dideazatetrahydrofolate, and L-alanosine and by methionine depletion. The A549 cells transfected with an antisense construct (antisense transfectoma) expressed no MTAP protein and were more sensitive to both purine and methionine depletion than were cells expressing MTAP protein (sense transfectoma). Methylthioadenosine was able to completely rescue the sense transfectoma but not the antisense transfectoma from growth inhibition by depletion of purine and methionine. These results prove that MTAP deficiency contributes directly to the sensitivity of cancer cells to purine or methionine depletion. Inhibition of de novo purine synthesis, combined with methionine depletion in the presence of methylthioadenosine, is a highly selective treatment for MTAP-negative cancers.

Alanine↗
PubMed1996

Genomic cloning of methylthioadenosine phosphorylase: a purine metabolic enzyme deficient in multiple different cancers.

5'-Deoxy-5'-methylthioadenosine phosphorylase (methylthioadeno-sine: ortho-phosphate methylthioribosyltransferase, EC 24.2.28; MTAP) plays a role in purine and polyamine metabolism and in the regulation of transmethylation reactions. MTAP is abundant in normal cells but is deficient in many cancers. Recently, the genes for the cyclin-dependent kinase inhibitors p16 and p15 have been localized to the short arm of human chromosome 9 at band p21, where MTAP and interferon alpha genes (IFNA) also map. Homozygous deletions of p16 and p15 are frequent malignant cell lines. However, the order of the MTAP, p16, p15, and IFNA genes on chromosome 9p is uncertain, and the molecular basis for MTAP deficiency in cancer is unknown. We have cloned the MTAP gene, and have constructed a topologic map of the 9p21 region using yeast artificial chromosome clones, pulse-field gel electrophoresis, and sequence-tagged-site PCR. The MTAP gene consists of eight exons and seven introns. Of 23 malignant cell lines deficient in MTAP protein, all but one had complete or partial deletions. Partial or total deletions of the MTAP gene were found in primary T-cell acute lymphoblastic leukemias (T-ALL). A deletion breakpoint of partial deletions found in cell lines and primary T-ALL was in intron 4. Starting from the centromeric end, the gene order on chromosome 9p2l is p15, p16, MTAP, IFNA, and interferon beta gene (IFNB). These results indicate that MTAP deficiency in cancer is primarily due to codeletion of the MTAP and p16 genes.

Amino Acid Sequence↗
PubMed1996

Factors affecting neuronal birth and death in the mammalian olfactory epithelium.

To identify factors regulating neurogenesis and neuronal death in mammals and to determine the mechanisms by which these factors act, we have studied mouse olfactory epithelium using two different experimental paradigms: tissue culture of olfactory epithelium purified from mouse embryos; and ablation of the olfactory bulb in adult mice, a procedure that induces olfactory receptor neuron (ORN) death and neurogenesis in vivo. Studies of olfactory epithelium cultures have allowed us to characterize the cellular stages in olfactory neurogenesis and to identify factors regulating proliferation and differentiation of precursor cells in the ORN lineage. Studies of adult olfactory epithelium have enabled us to determine that all cell types in this lineage-proliferating neuronal precursors, immature ORNs and mature ORNs-undergo cell death following olfactory bulb ablation and that this death has characteristics of programmed cell death or apoptosis. In vitro studies have confirmed that neuronal cells of the olfactory epithelium undergo apoptotic death and have permitted identification of several polypeptide growth factors that promote survival of a fraction of ORNs. Using this information, we have begun to explore whether these factors, as well as genes known to play crucial roles in cell death in other systems, function to regulate apoptosis and neuronal regeneration in the adult olfactory epithelium following lesion-induced ORN death.

Animals↗
PubMed1996

Olanzapine versus placebo: results of a double-blind, fixed-dose olanzapine trial.

Olanzapine is a potential new "atypical" antipsychotic agent. This double-blind, acute phase study compared two doses of olanzapine [1 mg/day (Olz1.0); 10 mg/day (Olz10.0)] with placebo in the treatment of 152 patients who met the DSM-III-R criteria for schizophrenia and had a Brief Psychiatric Rating Scale (BPRS)-total score (items scored 0-6) > or = 24. In overall symptomatology improvement [BPRS-total score and Positive and Negative Syndrome Scale (PANSS)-total score], Olz10.0 was statistically significantly superior to placebo. In positive symptom improvement (PANSS-positive score, BPRS-positive score), Olz10.0 was statistically significantly superior to placebo. In negative symptom improvement (PANSS-negative score), Olz10.0 was statistically superior to placebo. Olz 1.0 was clinically comparable to placebo in all efficacy comparisons. The only adverse event to show an overall statistically significant incidence difference was anorexia (reported for 10% of placebo-treated and 0% of Olz10.0-treated patients). The Olz10.0-treated patients improved over baseline with respect to parkinsonian and akathisia symptoms, and these changes were comparable with those observed with placebo. There were no dystonias associated with Olz10.0 treatment. At endpoint, the incidence of patients with elevated prolactin values did not differ statistically significantly between placebo-treated and Olz10.0-treated patients. Olanzapine appears to be not only safe and effective, but a promising atypical antipsychotic candidate.

Adult↗
PubMed1996

Olanzapine versus placebo and haloperidol: acute phase results of the North American double-blind olanzapine trial.

Olanzapine is a potential new "atypical" antipsychotic agent. The double-blind acute phase of this study compared three dosage ranges of olanzapine (5 +/- 2.5 mg/day [Olz-L], 10 +/- 2.5 mg/day [Olz-M], 15 +/- 2.5 mg/day [Olz-H]) to a dosage range of haloperidol (15 +/- 5 mg/day [Hal]) and to placebo in the treatment of 335 patients who met the DSM-III-R criteria for schizophrenia. In overall symptomatology improvement (Brief Psychiatric Rating Scale [BPRS]-total), Olz-M, Olz-H, and Hal were significantly superior to placebo. In positive symptom improvement (BPRS-positive), Olz-M, Olz-H, and Hal were comparable and significantly superior to placebo. In negative symptom improvement (Scale for the Assessment of Negative Symptoms [SANS]-composite), Olz-L and Olz-H were significantly superior to placebo and Olz-H was also significantly superior to Hal. The most common treatment-emergent adverse events included somnolence, agitation, asthenia, and nervousness. No acute dystonia was observed with olanzapine. Treatment-emergent parkinsonism occurred with Olz-H at approximately one-third the rate of Hal, and akathisia occurred with Olz-H at approximately one-half the rate of Hal. Prolactin elevations associated with olanzapine were not significantly greater than those observed with placebo and were also significantly less than those seen with haloperidol.

Adolescent↗
PubMed1994

[Tachycardia with wide QRS. Limitations of electrocardiographic criteria in patients treated with anti-arrhythmia agents].

The diagnosis of ventricular tachycardia is difficult, often requiring endocavitary investigation to obtain proof. Many authors have attempted to define criteria used to distinguish between ventricular tachycardia and supraventricular tachycardia with wide QRS in the surface electrocardiogram. These criteria have been determined in patients not taking antiarrhythmic drugs. The authors report the case of a patient treated with flecainide for atrial fibrillation and hospitalised because of faints and tachycardia with wide complexes. The diagnosis of ventricular tachycardia was justified by surface electrocardiogram but was eliminated by subsequent endocavitary electrophysiological studies. The use of anti-arrhythmic drugs thus limits the applicability of electrocardiographic criteria in cases of tachycardia with wide QRS.

Anti-Arrhythmia Agents↗
PubMed1993

Comparison of different perfluorocarbons as ultrasound contrast agents.

RATIONALE AND OBJECTIVES: The sonographic properties of Fluosol 20% (F20), which was recently approved for clinical use as an oxygen carrier for coronary angioplasty, were compared to those of perflubron emulsion, which is still in clinical testing. METHODS: Contrast agents were evaluated in 21 normal rabbits divided into three groups of seven rabbits each. All rabbits received 2.7 g/kg of perfluorocarbon (PFC). One group received 2.7 ml/kg of an experimental formulation of perflubron emulsion AF0102, which contains 1 g of PFC in 1 ml of emulsion (P100), the other received 13.5 ml/kg of F20 (1 ml has 0.2 g of PFC), and the third received 13.5 ml/kg of P100 diluted to a 20% concentration (P20). All rabbits were scanned by a blinded sonographer before, during, and immediately after infusion, and then again at 30 minutes and 48 hours. Doppler enhancement, echogenicity of inferior vena cava lumen, echogenic enhancement of perfused tissues, and reticuloendothelial organs were assessed. RESULTS: P100 and P20 had nearly identical sonographic properties at all points. During their vascular phase they enhanced Doppler signal, filled the lumen of the IVC and hepatic veins with flowing echogenic reflectors, and enhanced perfused tissues. F20 had no detectable sonographic effect during its vascular phase. All three emulsions enhanced the liver relative to kidney to a similar degree at 48 hours. CONCLUSIONS: Because RE enhancement was similar for F20, P100, and P20, and because P100 and P20 had similar properties during the vascular phase, the lack of vascular effect of F20 could not be due to the different PFCs used in these agents, or due to the difference in the dilution or volume. The most likely cause for the observed sonographic behavior of F20 and P100 is the difference in emulsion formulation.

Animals↗
PubMed1993

Retinoic acid receptors and retinoid X receptor-alpha down-regulate the transforming growth factor-beta 1 promoter by antagonizing AP-1 activity.

Overexpression of the multifunctional growth factor transforming growth factor-beta 1 (TGF beta 1) has been connected to numerous diseases in human. TGF beta 1 expression is largely governed by three AP-1 binding sites located in two different promoters of this gene. We have examined the ability of retinoid receptors to inhibit the activity of the two promoters (especially the promoter 1) by cotransfection assays in the hepatocellular carcinoma cell line HepG2. When the TGF beta 1 promoter activity is induced by 12-O-tetradecanoyl phorbol13-acetate (an activator of AP-1-controlled gene transcription), this activity can be strongly repressed by retinoic acid receptor-alpha (RAR alpha), RAR beta, or retinoid X receptor-alpha (RXR alpha) as well as other members of the nuclear receptor family. Repression was hormone dependent and a function of receptor concentration. Heterodimerization of RAR alpha or RAR beta with RXR alpha did not modify the inhibition activities of these receptors, indicating that heterodimer formation is not required for antagonizing of AP-1 activity. On further examining the anti-AP-1 activity of RXR alpha we observed that three different AP-1-controlled promoters (TGF beta 1, collagenase, and cFos) can be inhibited. Using gel shift assays, we demonstrated that RXR alpha inhibits Jun and Fos DNA binding and that 9-cis RA enhances this inhibition, suggesting that a mechanism involving direct protein-protein interaction between RXR and AP-1 components mediates the inhibitory effect observed in vivo. Transfection analyses with RXR alpha point mutations revealed that residues L422, C432, and, to a lesser extent, residues L418 and L430, are involved in ligand-induced anti-AP1 activity of RXR alpha in vivo. Thus both types of retinoid receptors can inhibit AP-1-activated promoters, including the TGF beta 1 gene promoter, via a mechanism that involves protein-protein interaction.

Amino Acid Sequence↗
PubMed1992

Homodimer formation of retinoid X receptor induced by 9-cis retinoic acid.

Retinoid response pathways are mediated by two classes of receptors, the retinoic acid receptors (RARs) and the retinoid X receptors (RXRs). A central question is whether distinct response pathways are regulated by these two classes of receptors. The observation that the stereoisomer 9-cis-retinoic acid binds with high affinity to RXRs suggested that this retinoid has a distinct role in controlling RXR activity, but it was almost simultaneously discovered that RXRs function as auxiliary receptors for RARs and related receptors, and are essential for DNA binding and function of those receptors. Hence, although RARs seem to operate effectively only as heterodimeric RAR/RXR complexes, RXRs themselves apparently function predominantly, if not exclusively, as auxiliary receptors. Here we report that 9-cis-retinoic acid induces RXR homodimer formation. Our results demonstrate a new mechanism for retinoid action by which a ligand-induced homodimer mediates a distinct retinoid response pathway.

Animals↗
PubMed1992

COUP orphan receptors are negative regulators of retinoic acid response pathways.

The vitamin hormone retinoic acid (RA) regulates many complex biological programs. The hormonal signals are mediated at the level of transcription by multiple nuclear receptors. These receptors belong to the steroid/thyroid hormone receptor superfamily that also includes a large number of orphan receptors whose biological roles have not yet been determined. Although much has been learned in recent years about RA receptor (RAR) functions, little is known about how specific RA response programs are restricted to certain tissues and cell types during development and in the adult. It has been recently shown that RAR activities are regulated by retinoid X receptors (RXR) through heterodimer formation. In an effort to isolate and further characterize nuclear receptors that modulate RAR and/or RXR activities, we have screened cDNA libraries by using a RXR alpha cDNA probe. Two clones, COUP alpha and COUP beta, identical and closely related to the orphan receptor COUP-TF, were obtained. We show that COUP proteins dramatically inhibit retinoid receptor activities on certain response elements that are activated by RAR/RXR heterodimers or RXR homodimers. COUP alpha and -beta bind strongly to these response elements, including a palindromic thyroid hormone response element and a direct repeat RA response element as well as an RXR-specific response element. In addition, we found that the previously identified COUP-TF binding site in the ovalbumin gene functions in vitro as an RA response element that is repressed in the presence of COUP. Our data suggest that the COUP receptors are a novel class of RAR and RXR regulators that can restrict RA signaling to certain elements. The COUP orphan receptors may thus play an important role in cell- or tissue-specific repression of subsets of RA-sensitive programs during development and in the adult.

Base Sequence↗