Biomedical subjects

X Chen

Publications and source records attributed to X Chen.

At least 685 records · Page 38Linked to original sources

PubMed1999

Expanding the TRANSFAC database towards an expert system of regulatory molecular mechanisms.

TRANSFAC is a database on transcription factors, their genomic binding sites and DNA-binding profiles. In addition to being updated and extended by new features, it has been complemented now by a series of additional database modules. Among them, modules which provide data about signal transduction pathways (TRANSPATH) or about cell types/organs/developmental stages (CYTOMER) are available as well as an updated version of the previously described COMPEL database. The databases are available on the WWW at http://transfac.gbf.de/

Animals↗

PubMed1999

Collision-induced dissociation of protonated MK-0991: novel ring opening of a cyclic hexapeptide in the gas phase.

Electrospray ionization tandem mass spectrometry was applied to probe the collision-induced dissociation (CID) of protonated MK-0991 {(4R,5S)-5-[(2-aminoethyl)amino]-N(2)-(10, 12-dimethyl-1-oxotetradecyl)-4-hydroxy-L-ornithyl-L-threonyl-trans -4- hydroxy-L-prolyl-(S)-4-hydroxy-(4-hydroxyphenyl)-L-threonyl-threo-3-h ydroxy-L-or-nithyl-trans-3-hydroxy-L-proline cyclic (6-1)-peptide} in the gas phase; MK-0991 is a newly developed, broad-spectrum pneumocandin antifungal drug. The study showed that protonated MK-0991 (m/z 1094) undergoes specific ring opening under the CID conditions to form two protonated linear peptides at m/z 1076 and 1034. This is different from the commonly observed ring opening of a cyclic peptide that occurs by the cleavage of the N-acyl bonds in many places on the peptide backbone. The structures of the two linear peptides were elucidated on the basis of their tandem mass spectra. The results strongly indicate that the specific ring opening of MK-0991 is affected by the ethylenediamine side-chain formed from the modification of one of the ornithine amino acids in this cyclic hexapeptide.

Anti-Bacterial Agents↗

PubMed1999

Evaluation of the enantiomeric composition of amino acids in tobacco.

Despite the fact that several studies have reported the concentrations of various free amino acids in tobacco, their enantiomeric composition is unknown. Both the absolute and enantiomeric compositions of proline, alanine, asparagine, aspartic acid, valine, methionine, leucine,and phenylalanine were determined for three strains of tobacco leaf, three types of smokeless tobacco, and six different blended filtered and nonfiltered reference cigarettes. Some of the highest levels of D-amino acids ever found in agricultural products were observed. Possible mechanisms for the production of these D-amino acids are considered. The relevance of D-amino acids in tobacco is discussed.

Amino Acids↗

PubMed1999

Microplate array diagonal gel electrophoresis for mutation research in DNA banks.

Molecular genetic epidemiology, association and linkage studies in populations, human or other species, is now yielding powerful new insights into disease and susceptibility genes. Inter alia, the subject requires laboratory analytical methodologies focused on achieving high throughput. Here we review one suite of methodology suitable for such laboratories. Microplate array diagonal gel electrophoresis (MADGE) was invented for molecular genetic epidemiological studies. It combines direct compatibility with microplates, convenient polyacrylamide gel electrophoresis and economy of time and reagents, at minimal capital cost, and enables one user to run up to several thousand gel lanes per day for direct assay of single-base variations. Melt-MADGE combines temporal thermal ramp apparatus to achieve similar throughput for de novo mutation scanning.

Animals↗

PubMed1999

Isolation of oncogenes from rat mammary tumors by a highly efficient retrovirus expression cloning system.

A majority of mammary tumors induced with N-methyl-N-nitrosourea in rats contain G to A transitional mutation of c-Ha-ras at the 12th codon. Additional oncogene activation is known to be necessary for further tumor progression. To isolate novel oncogenes, we used an expression cloning system utilizing the pMX retroviral vector in combination with BOSC23 packaging cells. First, we elucidated the sensitivity of this system in the NIH 3T3 focus assay; foci were detectable even after 10(-6) dilution using v-Ha-ras, neuT, and beta-galactosidase constructs in pMX vector. This system is sensitive enough to detect low copy number cDNAs. We used the pMX/BOSC23 expression cloning system to clone novel oncogenes from rat mammary tumors harboring an activated c-Ha-ras and isolated several candidate oncogenes that caused transformation of NIH 3T3 cells and/or generated tumors when transplanted to nude mice.

3T3 Cells↗

PubMed1999

Gender difference in dopamine concentration and postischemic neuronal damage in neostriatum after unilateral dopamine depletion.

Most neurons in the dorsal neostriatum die 1 day after 30 min of cerebral ischemia. Dopamine may play a role in the pathogenesis of neuronal injury in neostriatum following ischemia. It has been shown that the number of surviving neurons in the right neostriatum dramatically increased following ischemia after lesions were made in the right substantia nigra (SN), whereas no such protective effect was observed in the left neostriatum after left SN lesion. Using a voltammetric technique, the present study measured the dopamine concentration in neostriatum during ischemia after unilateral dopamine depletion and correlated it with the postischemic neuronal damage in neostriatum of male and female rats. In both genders, dopamine concentrations in the neostriatum of the intact side increased to 50-60 microM during ischemia while those of the lesion side were 15-30 microM. No difference in dopamine concentration was detected between animals with lesions in the left SN and those with lesions in right SN. In male rats, the number of surviving neurons in the right neostriatum (approximately 80% as control) was significantly greater than that in the left neostriatum (approximately 20%) after ipsilateral dopamine depletion, whereas in female animals, the number of surviving neurons in the right neostriatum (approximately 40%) was about the same as that in the left neostriatum (approximately 35%) after dopamine depletion. These results indicate that the asymmetry in ischemic outcome after unilateral dopamine depletion in male rats is not due to the difference in residual dopamine in neostriatum. The lateralization of D2 receptors in male rats may be responsible for the asymmetry of survivability of striatal neurons after transient forebrain ischemia.

Animals↗

PubMed1999

Hazards of smoking initiation among Asian American and non-Asian adolescents in California: a survival model analysis.

BACKGROUND: Information about the risk of smoking initiation among whites, African Americans, and Latino Americans has provided an important information base for smoking prevention programs among adolescents from these ethnic backgrounds. Unfortunately, there is a lack of such information for Asian Americans, a fast-growing ethnic minority group with much internal diversity. METHOD: This study used cross-sectional data from 20,482 subjects 12-17 years of age, randomly sampled in California, to describe and compare the risk of smoking initiation for adolescents by age among Asian American and other non-Asian ethnic groups, using survival analysis. Computer-aided telephone interview techniques were used in data collection. RESULT: The risk of early smoking initiation among Asian American adolescents is about a third of that of Caucasians. However, the risk among Asian Americans continues to increase throughout adolescence, while the same risk among Caucasians and African Americans plateaus around 14-15 years of age. Significant differences in the levels and patterns of smoking initiation among Asian American subgroups were observed, with Chinese Americans showing the lowest risk of smoking initiation and Filipino Americans the highest, Japanese and Korean Americans being in-between. CONCLUSION: Asian American adolescents may be especially at risk of smoking initiation later in adolescence, even though they are at lower risk early in adolescence. Smoking prevention programs for Asian Americans should continue throughout adolescence and early adulthood.

Adolescent↗

PubMed1999

HLA-DM and the MHC class II antigen presentation pathway.

The MHC class II antigen processing pathway provides a mechanism to selectively present peptides generated in the endosomal compartments of antigen presenting cells to CD4+ T cells. Transport of newly synthesized class II molecules to the endosomal pathway requires the function of an accessory protein, invariant chain, which contains a region that interacts directly with the class II peptide binding site. Release of invariant chain and peptide loading by class II molecules are facilitated by a second accessory protein, HLA-DM. This MHC-encoded membrane protein catalyzes peptide exchange reactions, influencing the repertoire of peptides that are available for recognition by T cells.

Animals↗

PubMed1999

Quantitative study on expression of p16 multiple tumor suppressor gene in salivary gland neoplasm.

The expression of p16 gene in normal salivary acini, benign tumors and carcinomas were microscopically and quantitatively observed by using immunohistochemical method LSAB and CMIASWIN methods. The expression of p16 gene were found in all 3 groups. The positive unit (PU) was higher in tumor group and cancer group than that in normal group (P < 0.01). Furthermore, the PU of p16 was stronger in cytoplasm than in nucleus. Malignant tumors and acini surrounding the tumor revealed strong positives and weak positives respectively. The PU of p16 gene was higher in deep lobe of recurrent parotid neoplasm with incomplete capsule than that in shallow lobe of primary parotid neoplasm with complete capsule. The findings suggests that p16 gene plays an equally important role in the salivary gland tumors and tumors in other part of the body.

Adenoma, Pleomorphic↗

PubMed1999

Concordant evolution of a symbiont with its host insect species: molecular phylogeny of genus Glossina and its bacteriome-associated endosymbiont, Wigglesworthia glossinidia.

Many arthropods with restricted diets rely on symbiotic associations for full nutrition and fecundity. Tsetse flies (Diptera: Glossinidae) harbor three symbiotic organisms in addition to the parasitic African trypanosomes they transmit. Two of these microorganisms reside in different gut cells, while the third organism is harbored in reproductive tissues and belongs to the genus Wolbachia. The primary symbiont (genus Wigglesworthia glossinidia) lives in differentiated epithelial cells (bacteriocytes) which form an organ (bacteriome) in the anterior gut, while the secondary (S) symbionts are present in midgut cells. Here we have characterized the phylogeny of Wigglesworthia based on their 16S rDNA sequence analysis from eight species representing the three subgenera of Glossina: Austenina (=fusca group), Nemorhina (=palpalis group), and Glossina (=morsitans group). Independently, the ribosomal DNA internal transcribed spacer-2 (ITS-2) regions from these species were analyzed. The analysis of Wigglesworthia indicated that they form a distinct lineage in the gamma subdivision of Proteobacteria and display concordance with their host insect species. The trees generated by parsimony confirmed the monophyletic taxonomic placement of Glossina, where fusca group species formed the deepest branch followed by morsitans and palpalis groups, respectively. The placement of the species Glossina austeni by both the traditional morphological and biochemical criteria has been controversial. Results presented here, based on both the ITS-2 and the symbiont 16S rDNA sequence analysis, suggest that Glossina austeni should be placed into a separate fourth subgenus, Machadomyia, which forms a sister-group relationship with the morsitans group species.

Animals↗

PubMed1999

Hematopoietic donor chimerism and graft-versus-myeloma effect in relapse of multiple myeloma after allogeneic bone marrow transplantation.

A large group of patients relapsing after allogeneic bone marrow transplantation (BMT) have obtained remission after infusion of leukocytes from their original donor, suggesting a graft-versus-myeloma effect. However, side effects such as graft-versus-host disease and myelosuppression are severe, and sometimes fatal, complications of this therapeutic approach. Previously we demonstrated that patients with leukemia who lack donor hematopoiesis in relapse after BMT experience severe and lasting aplasia after infusion of donor leukocytes. In two patients - one with extramedullary and one with marrow relapse after a sex-mismatched transplantation - we analyzed hematopoietic chimerism by cell sorting and bone marrow cultures. CD34-positive cells, CD4-CD8-positive cells, committed progenitors, and LTC-IC were of donor origin, as demonstrated by two-color fluorescence in situ hybridization (FISH). Additionally, in relapse complete donor T-cell chimerism was seen. In contrast, plasma cells were of recipient origin in the patient who had a relapse in the bone marrow. Both patients were treated with infusions of donor leukocytes from their original donor. Neither patient suffered myelosuppression, and one achieved a stable complete remission.

Adult↗

PubMed1999

Effects of caffeine on fluoride, calcium and phosphorus metabolism and calcified tissues in the rat.

This 6-week study was designed to determine the effects of graded doses of caffeine intake (3, 25 or 100 mg/kg per day) on the metabolic balance and tissue concentrations of fluoride, calcium and phosphorus in Sprague-Dawley rats. Caffeine intake did not affect the absorption, urinary excretion or balance of fluoride, the plasma, bone or enamel concentrations of fluoride, nor the occurrence of incisor enamel fluorosis. Neither did it affect the metabolism of calcium or phosphorus except that the urinary excretion of calcium was increased. This effect, however, was not sufficient to influence significantly calcium balance. The ash content of the femur epiphysis and bone mineral content of the tibia were significantly reduced only in the group exposed to the highest dose of caffeine. These effects on bone were not significantly related to the balance of calcium or phosphorus. It was concluded that caffeine, even at an extremely high level of intake, has no detectable effect on the balance or tissue concentrations of fluoride, calcium or phosphorus in the rat.

Animals↗

PubMed1999

Growth inhibition of capsaicin on HeLa cells is not mediated by intracellular calcium mobilization.

The effects of capsaicin on cellular growth and intracellular calcium mobilization were examined in human cervical carcinoma derivation, HeLa cells. Capsaicin inhibited cellular growth and increased intracellular calcium level in HeLa cells. This capsaicin-induced intracellular calcium concentration rise was blocked by capsazepin, vanilloid (capsaicin) receptor antagonist. But, an intracellular calcium chelator BAPTA/AM did not block the inhibitory effect of capsaicin on cellular growth. These observations suggest that intracellular calcium mobilization is not required for the capsaicin-induced inhibition of cellular growth.

Calcium↗

PubMed1999

Studies on the heme and H2-uptake reaction from Azotobacter vinelandii bacterial ferritin.

Bacterial ferritin of Azotobacter vinelandii (AvBF) is directly able to pick electrons up for iron release from or transfer them for storage to a platinum electrode in the absence of mediator or other reducer. The ferritin containing the structure of heme-Co2+ in part shows weakened activity to electrode and decreases the rate of iron release greatly. A reversible reduction process of the ferritin is observed by the spectral change regularly ranging from 310 to 260 nm under mixed gases containing 98% H2 and 2% to O2. The activity of nitrogen fixation from the whole cell of A. vinelandii increases greatly by H2 reduction with potentials ranging from -397 to -425 mV vs. NHE, indicating two important roles of H2-uptake reaction of the ferritin in increasing activity of nitrogen fixation and in supplying iron to synthesize nitrogenase.

Azotobacter vinelandii↗

PubMed1999

Dopamine depresses glutamatergic synaptic transmission in the rat parabrachial nucleus in vitro.

Nystatin-perforated patch recordings were made from rat parabrachial neurons in an in vitro slice preparation to examine the effect of dopamine on parabrachial cells and on excitatory synaptic transmission in this nucleus. In current clamp mode, dopamine reduced the amplitude of the evoked excitatory postsynaptic potential without significant change in membrane potential. In cells voltage-clamped at -65 mV, dopamine dose dependently and reversibly decreased evoked, pharmacologically isolated, excitatory postsynaptic currents with an EC50 of 31 microM. The reduction in excitatory postsynaptic current was accompanied by an increase in paired pulse ratio (a protocol used to detect presynaptic site of action) with no change in the holding current or in the decay of the evoked excitatory postsynaptic currents. In addition, dopamine altered neither postsynaptic (+/-)-alpha-amino-3-hydroxy-5-methylisoxazole-4-propionate-induced currents, nor steady-state current voltage curves. Miniature excitatory postsynaptic current analysis revealed that dopamine caused a rightward shift of the frequency-distribution curve with no change in the amplitude-distribution curve, which is consistent with a presynaptic mechanism. The dopamine-induced attenuation of the excitatory postsynaptic current was almost completely blocked by the D1-like receptor antagonist SCH23390 (10 microM), although the D2-like antagonist sulpiride (10 microM) also partially blocked it. Combined application of both antagonists blocked all dopamine-induced synaptic effects. The synaptic effect of dopamine was mimicked by the D1-like agonist SKF38393 (50 microM), but the D2-1ike agonist quinpirole (50 microM) also had a small effect. Combined application of both agonists did not produce potentiated responses. Dopamine's effect on the excitatory postsynaptic current was independent of serotonin, GABA and adenosine receptors, but may have some interactions with adrenergic receptors. These results suggest that dopamine directly modulates excitatory synaptic events in the parabrachial nucleus predominantly via presynaptic D1-like receptors.

2,3,4,5-Tetrahydro-7,8-dihydroxy-1-phenyl-1H-3-ben↗

PubMed1999

Potentiometric sensor for methylene blue based on methylene blue-silicotungstate ion association and its pharmaceutical applications.

A methylene blue (MB) poly(vinyl chloride) membrane sensor based on MB-silicotungstate (SLT) ion association as electroactive material was described. The linear response covered the range 1 x 10(-3)-1 x 10(-6) mol x dm(-3) MB solution, with a slope 52.0+/-0.8 mV decade(-1) (pH range 3.0-10.0). The detection limit was 7.65 x 10(-7) mol x dm(-3). The electrode showed stability, good reproducibility and fast response. Interferences from common inorganic cations, some organic base were negligible. These characteristics of the electrode enabled it to be used successfully for the determination of MB in injection. There was a good agreement for the results of MB content in injection between potentiometric method and USP standard procedure.

Calibration↗

PubMed1999

A phosphate binding assay for sevelamer hydrochloride by ion chromatography.

Sevelamer hydrochloride is a cross-linked polymeric amine; it is the active ingredient of Renagel capsules. Renagel is indicated for the control of hyperphosphatemia in patients with end-stage renal disease. An in vitro phosphate-binding assay is required to measure the drug's efficacy. The assay developed for this purpose involves mixing the drug (polymer) with a solution of known phosphate concentration, filtering off the polymer-phosphate complex, and quantitating the unbound phosphate concentration by ion chromatography. The binding capacity, reported as mmol of phosphate bound g of polymer(-1), is calculated from the calculated amount of bound phosphate and the weight of polymer used. The method has been validated for accuracy, precision, linearity, range, and ruggedness.

Chromatography, Ion Exchange↗

PubMed1999

Identification of oxidative degradates of the thrombin inhibitor, 3-(2-phenethylamino)-6-methyl-1-(2-amino-6-methyl-5-methyleneca rboxamidomethylpyridinyl)pyrazinone, using liquid chromatography/mass spectrometry and liquid chromatography/tandem mass spectrometry.

Liquid chromatography/mass spectrometry was used to identify reaction products from a solution of 3-(2-phenethylamino)-6-methyl-1-(2-amino-6-methyl-5-methyleneca rboxamidomethylpyridinyl)pyrazinone (L-375,378) and hydrogen peroxide, a system that generates high levels of the oxidative degradates which form in the tablets and intravenous (i.v.) solutions of L-375,378. Two major hydrogen peroxide reaction products of L-375,378 (m/z 407) with m/z values of 369 and 370 were separated and identified. Both compounds were products of ring opening with elimination of three carbon atoms from the center pyrazinone ring. The structural assignments for these two products were alpha-amidinoamide and alpha-diamide compounds, respectively. In addition, five products (m/z 423) with a molecular weight 16 Da greater than that for L-375,378 were separated. Further liquid chromatography/tandem mass spectrometry experiments indicated that three of these M + 16 products were phenolic derivatives of L-375,378. Among them, the para-hydroxy compound has been verified using an authentic standard. The other two phenolic compounds were believed to be the meta- and ortho-hydroxy derivatives of L-375,378. The fourth M + 16 product was derived from hydroxylation of the methyl group on the center pyrazinone ring. The fifth M + 16 product was derived from oxidation on the aminopyridine moiety, most likely N-oxide of the pyridine ring. Other minor hydrogen peroxide reaction products were not studied in detail because they did not appear in tablets or i.v. formulations.

Amides↗