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Biomedical subjects

J Chen

Publications and source records attributed to J Chen.

At least 379 records · Page 21Linked to original sources
PubMed2001

Observation of cation reordering during the olivine-spinel transition in fayalite by in situ synchrotron X-ray diffraction at high pressure and temperature.

The olivine-spinel phase transition in fayalite at high pressure and temperature has been studied using time-resolved x-ray diffraction. Structure refinements show a delay of cation reordering relative to anions during the phase transformation and an increase in the cell volume while the cations reorder into their sites. A significant stress drop in the sample is observed. This experiment, for the first time, quantitatively demonstrates a pseudomartensitic transformation: a diffusionless anion sublattice transition coupled with short-range diffusional cation reordering.

Journal Article↗
PubMed2001

[A comparative study of serum sFas in patients with hepatocellular cancer and chronic hepatitis].

OBJECTIVE: To study the effects of sFas in hepatocellular cancer (HCC) and chronic hepatitis (CH). METHODS: The serum sFas was detected in 18 patients with HCC, 12 patients with CH and 6 cases of normal control by ELISA. RESULTS: The serum sFas in HCC was obviously increased and had significant difference with the patients of CH and normal control (P < 0.01). The serum sFas had positive correlation with the serum TBIL(P < 0.01), but negative correlation with the ALB, PTA and the ratio of ALT/AST(P < 0.01). CONCLUSIONS: sFas may resist the occurrence of HCC apoptosis. In CH, sFas has correlation with the severity of CH. The role of sFas in viral hepatitis is uncertain.

Adolescent↗
PubMed2001

Cytochrome P450 CYP2J9, a new mouse arachidonic acid omega-1 hydroxylase predominantly expressed in brain.

A cDNA encoding a new cytochrome P450 was isolated from a mouse brain library. Sequence analysis reveals that this 1,958-base pair cDNA encodes a 57-58-kDa 502-amino acid polypeptide that is 70-91% identical to CYP2J subfamily P450s and is designated CYP2J9. Recombinant CYP2J9 was co-expressed with NADPH-cytochrome P450 oxidoreductase (CYPOR) in Sf9 cells using a baculovirus system. Microsomes of CYP2J9/CYPOR-transfected cells metabolize arachidonic acid to 19-hydroxyeicosatetraenoic acid (HETE) thus CYP2J9 is enzymologically distinct from other P450s. Northern analysis reveals that CYP2J9 transcripts are present at high levels in mouse brain. Mouse brain microsomes biosynthesize 19-HETE. RNA polymerase chain reaction analysis demonstrates that CYP2J9 mRNAs are widely distributed in brain and most abundant in the cerebellum. Immunoblotting using an antibody raised against human CYP2J2 that cross-reacts with CYP2J9 detects a 56-kDa protein band that is expressed in cerebellum and other brain segments and is regulated during postnatal development. In situ hybridization of mouse brain sections with a CYP2J9-specific riboprobe and immunohistochemical staining with the anti-human CYP2J2 IgG reveals abundant CYP2J9 mRNA and protein in cerebellar Purkinje cells. Importantly, 19-HETE inhibits the activity of recombinant P/Q-type Ca(2+) channels that are known to be expressed preferentially in cerebellar Purkinje cells and are involved in triggering neurotransmitter release. Based on these data, we conclude that CYP2J9 is a developmentally regulated P450 that is abundant in brain, localized to cerebellar Purkinje cells, and active in the biosynthesis of 19-HETE, an eicosanoid that inhibits activity of P/Q-type Ca(2+) channels. We postulate that CYP2J9 arachidonic acid products play important functional roles in the brain.

Amino Acid Sequence↗
PubMed2001

Effect of van der Waals interactions on the Raman modes in single walled carbon nanotubes.

We have measured the Raman spectrum of individual single walled carbon nanotubes in solution and compare it to that obtained from the same starting material where the tubes are present in ordered bundles or ropes. Interestingly, the radial mode frequencies for the tubes in solution are found to be approximately 10 cm (-1) higher than those observed for tubes in a rope, in apparent contradiction to lattice dynamics predictions. We suggest that there is no such contradiction, and propose that the upshift is due rather to a decreased energy spacing of the Van Hove singularities in isolated tubes over the spacings in a rope, thereby allowing the same laser excitation to excite different diameter tubes in these two samples.

Journal Article↗
PubMed2001

FTIR study of horseradish peroxidase in reverse micelles.

Fourier transform infrared (FTIR) method was used to study the secondary structures of horseradish peroxidase (HRP) in aqueous solution and in reverse micelles for the first time. Results indicated that the structure of HRP in sodium bis(2-ethylhexy)sulfosuccinate (AOT) reverse micelles was close to that in aqueous solution. In cetyltrimethylammonium bromide (CTAB) and sodium dodecylfate (SDS) reverse micelles the position of some bands changed. Results indicated that the secondary structure had a close relationship with the surfactant species of the reverse micelles. Among the three types of reverse micelles, the system of AOT reverse micelles was probably the most beneficial reaction media to HRP.

Deuterium Oxide↗
PubMed2001

Sialomucin production in aberrant crypt foci relates to degree of dysplasia and rate of cell proliferation.

Aberrant crypt foci (ACF) are putative early preneoplastic lesions of colon cancer. To date, many different ACF parameters have been measured as indicators of degree of colon cancer risk. It has been suggested that ACF producing sialomucins (SIM) may be more advanced types of ACF than those producing sulphomucins (SUM), but little data are available to support this. The objective of this experiment was to see if SIM ACF, as observed in whole mount colons, are different from other ACF and surrounding normal colonic crypts in terms of their rate of cell proliferation and degree of dysplasia. Results showed that all ACF had a higher rate of cell proliferation than normal crypts and that SIM ACF had higher cell proliferation in the top regions of the crypt, higher phih index of cell proliferation, higher degree of dysplasia, greater size and increased degree of luminal alterations than SUM ACF. We conclude that SIM ACF, as observed in whole mount colons, have more alterations and are more advanced towards tumorigenesis than SUM ACF and may be a better predictor of colon cancer risk than other measures of ACF.

Animals↗
PubMed2001

[The biological function of platelet-derived growth factor-BB in the osteoblast-osteoclast co-culture system].

OBJECTIVE: To investigate the biological effects of platelet-derived growth factor (PDGF)-BB on the osteoclasts in the osteoblast-osteoclast co-culture system. METHODS: The human osteoblasts and osteoclasts were isolated from the iliac crest of patients and co-cultured in the same system. The PDGF-BB or PDGF-BB + NO synthase inhibitor, N(G)-monomethyl-L-arginine (L-NMMA) was administered to the co-culture system. The tartrate-resistant acid phosphatase (TRAP) activities in the medium were measured by enzyme kinetics. The resorption pits were stained by toludine blue. The area and number of the resorption pits were determined with the Leica Quantimet 500 system. RESULTS: Under the stimuli of PDGF-BB in the co-culture system, TRAP activities changed from 1.40 U/L +/- 0.12 U/L to 1.46 U/L +/- 0.08 U/L (P > 0.05) in the medium, and the area and number of resorption pits was changed from (427 +/- 149) micrometer(2) and (13.3 +/- 0.9) per slice to (436 +/- 147) micrometer(2) and (14.1 +/- 1.2) per slice respectively (P > 0.05). After the L-NMMA was applied to the system, the TRAP activities rose significantly from 1.46 U/L +/- 0.10 U/L to 2.47 U/L +/- 0.38 U/L along with the increase of dose of PDGF-BB, and the number and area of the resorption pits increased significantly from 436 micrometer(2) +/- 147 micrometer(2) and (14.1 +/- 1.2) per slice to 592 micrometer(2) +/- 171 micrometer(2) and (22.5 +/- 1.7) per slice. Both the TRAP activities and resorption pits rose significantly after the L-NMMA was administered. Comparisons of different treatment groups were made using analysis of variance (ANOVA) with multiple comparisons and a Student-Newman-Keuls test. CONCLUSIONS: The nitric oxide (NO) was produced by osteoblasts stimulated by PDGF-BB in the osteoblast-osteoclast co-culture system. Therefore, the direct promotion effects of PDGF-BB on the osteoclasts were inhibited.

Acid Phosphatase↗
PubMed2001

Rethinking the role of phosducin: light-regulated binding of phosducin to 14-3-3 in rod inner segments.

Phosducin (Pd), a small protein found abundantly in photoreceptors, is widely assumed to regulate light sensitivity in the rod outer segment through interaction with the heterotrimeric G protein transducin. But, based on histochemistry and Western blot analysis, Pd is found almost entirely in the inner segment in both light and dark, most abundantly near the rod synapse. We report a second small protein, 14-3-3, in the rod with a similar distribution. By immunoprecipitation, phospho-Pd is found to interact with 14-3-3 in material from dark-adapted retina, and this interaction is markedly diminished by light, which dephosphorylates Pd. Conversely, unphosphorylated Pd binds to inner segment G protein(s) in the light. From these results and reported functions of 14-3-3, we have constructed a hypothesis for the regulation of light sensitivity at the level of rod synapse. By dissociating the Pd/14-3-3 complex, light enables both proteins to function in this role.

14-3-3 Proteins↗
PubMed2001

Search for quadrupole strength in the electroexcitation of the delta+(1232).

High-precision 1H(e,e'p)pi(0) measurements at Q2 = 0.126 (GeV/c)2 are reported, which allow the determination of quadrupole amplitudes in the gamma*N-->Delta transition; they simultaneously test the reliability of electroproduction models. The derived quadrupole-to-dipole ( I = 3/2) amplitude ratios, R(SM) = (-6.5+/-0.2(stat+sys)+/-2.5(mod))% and R(EM) = (-2.1+/-0.2(stat+sys)+/-2.0(mod))%, are dominated by model error. Previous R(SM) and R(EM) results should be reconsidered after the model uncertainties associated with the method of their extraction are taken into account.

Journal Article↗
PubMed2001

Hybrid characteristics of oligonucleotides consisting of isonucleoside 2',5'-anhydro-3'-deoxy-3'-(thymin-1-yl)-D-mannitol with different linkage modes.

Oligonucleotides consisting of the isonucleoside repeating unit 2',5'-anhydro-3'-deoxy-3'-(thymin-1-yl)-D-mannitol (4) were synthesized with the monomeric unit 4 incorporated into oligonucleotides as 1'-->4' linkage 4a (oligomer I) or 6'-->4' linkage 4b (oligomer II). The hybrid properties of the two oligonucleotides I and II with their complementary strands were investigated by thermal denaturation and CD spectra. Oligonucleotide I (4a) formed a stable duplex with d(A)(14) with a slightly reduced T(m) value of 36.6 degrees C, relative to 38.2 degrees C for the control duplex d(T)(14)/d(A)(14), but oligomer II (4b) failed to hybridize with a DNA complementary single strand. The spectrum of the duplex oligomer I/d(A)(14) showed a positive CD band at 217 nm and a negative CD band at 248 nm attributable to a B-like conformation. Molecular modeling showed that in the case of oligomer I: the C6' hydroxy group of each unit could be located in the groove area when hybridized to the DNA single strand, which might contribute additional hydrogen bonding to the stability of duplex formation.

Circular Dichroism↗
PubMed2001

Changes in HIV-1 incidence in heroin users in Guangxi Province, China.

Guangxi Province, China recently experienced an outbreak of HIV-1 infection among heroin users. We studied HIV-1 incidence rates and associated risk factors for HIV-1 infection among heroin users residing in Pingxiang City. A total of 318 heroin users were followed from February 1998 through January 1999 (median follow-up: 8.1 months). Of these, 130 were prospectively followed from January through September 1999 (median follow-up: 8.3 months). HIV-1 and hepatitis C virus (HCV) incidence rates for each period were calculated. A generalized estimating equation approach was implemented to identify independent risk factors associated with HIV-1 infection across both periods. Among 318 study participants, 97.2% were men. The median age was 22 years. Approximately 60% reported sharing needles. HIV-1 prevalence at baseline was 15.4%. During the first follow-up period, HIV-1 incidence was 2.38 per 100 person years (py), and HCV incidence was 26.8 per 100 py. During the second follow-up period, HIV-1 incidence was 6.86 per 100 py, and HCV incidence was 28.9 per 100 py. After controlling for age and other factors, HCV seropositivity, history of sexually transmitted diseases, and sharing needles were independently associated with HIV-1 infection. These data suggest that HIV-1 incidence was rising over time in Pingxiang City, Guangxi Province. The high incidence of HCV heightens the importance of enhanced prevention programs to reduce injection and needle sharing among heroin users.

Adult↗
PubMed2001

Packaging cell line DNA contamination of vector supernatants: implication for laboratory and clinical research.

Investigators conducting retroviral gene therapy trials are required to monitor for the presence of replication-competent retrovirus (RCR). The required testing utilizes a combination of biologic assays and molecular tests using PCR. In the course of a human clinical gene therapy trial, we detected 4070A viral envelope sequences in CD34(+) peripheral blood stem cells 2 days after transduction using a PCR-based assay, suggesting the presence of RCR. The supernatant and producer cells used for vector generation had been negative in extensive screening using the extended S(+)/L(-) assay. The presence of a replication-competent virus was subsequently excluded by a combination of biologic and PCR analyses. The source of the 4070A viral envelope sequences was determined to be packaging cell line DNA in the vector supernatant. The analysis of a variety of vector supernatants by quantitative real-time PCR revealed 4070A envelope DNA sequences from the packaging cell line in concentrations equivalent to approximately 50-500 focus-forming units per milliliter of wild-type 4070A virus. When PCR was performed after reverse transcriptase treatment of supernatant (i.e., assessing both RNA and DNA content), 4070A envelope sequence concentrations ranged from 10(2) to 3.5 x 10(3) focus-forming units per milliliter of wild-type 4070A virus. Our data indicate that PCR should not be used to analyze transduced cells for RCR within the first 2 weeks of vector exposure. Furthermore, investigators using PCR to analyze transduction efficiency shortly after vector exposure may experience false-positive findings.

Cell Line↗
PubMed2001

Activation of latent Kaposi's sarcoma-associated herpesvirus by demethylation of the promoter of the lytic transactivator.

Kaposi's sarcoma-associated herpesvirus (KSHV) is strongly linked to Kaposi's sarcoma, primary effusion lymphomas, and a subset of multicentric Castleman's disease. The mechanism by which this virus establishes latency and reactivation is unknown. KSHV Lyta (lytic transactivator, also named KSHV/Rta), mainly encoded by the ORF 50 gene, is a lytic switch gene for viral reactivation from latency, inasmuch as it is both essential and sufficient to drive the entire viral lytic cycle. Here we show that the Lyta promoter region was heavily methylated in latently infected cells. Treatment of primary effusion lymphoma-delivered cell lines with tetradecanoylphorbol acetate caused demethylation of the Lyta promoter and induced KSHV lytic phase in vitro. Methylation cassette assay shows demethylation of the Lyta promoter region was essential for the expression of Lyta. In vivo, biopsy samples obtained from patients with KSHV-related diseases show the most demethylation in the Lyta promoter region, whereas samples from a latently infected KSHV carrier remained in a methylated status. These results suggest a relationship among a demethylation status in the Lyta promoter, the reactivation of KSHV, and the development of KSHV-associated diseases.

DNA Methylation↗
PubMed2001

Quantitative structure-property relationships on photodegradation of PCDD/Fs in cuticular waxes of laurel cherry (Prunus laurocerasus).

By the use of the partial least squares (PLS) method and 13 fundamental quantum chemical descriptors computed by PM3 Hamiltonian, a OSPR model was developed for first order rate constants of photodegradation of 10 PCDD/Fs dissolved in cuticular wax from laurel cherry (Prunus laurocerasus) leaves and exposed to sunlight. The QSPR showed that photodegradation rates increase with the degree of chlorination of the homologues. PCDD/Fs with large values of Q(Cl) (the largest positive atomic charge on a chlorine atom in a molecule), Q(O)- (the most negative atomic charge on the oxygen atoms in a molecule), and mu (dipole moment) tend to photodegrade fastest. PCDD/Fs with large values of E(lumo) (the energy of the lowest unoccupied molecular orbital), E(homo) (the energy of the highest occupied molecular orbital), and E(lumo) - E(homo) tend to have the lowest photodegradation rates.

Benzofurans↗
PubMed2001

[Atrial flutter--diagnosis and therapeutic possibilities].

BACKGROUND: Atrial flutter and atrial fibrillation are among the most common heart rhythm disturbances in the population, with an assumed prevalence of 1-2%. About 40,000-60,000 Norwegians endure such rhythm disorders, with an increasing occurrence in the elderly population. MATERIAL AND METHODS: Surface ECG remains the corner-stone for the clinical diagnosis. We describe the various mechanisms, clinical presentation, and diagnosis based on modern invasive electrophysiological methods of atrial flutter. RESULTS: The available therapeutic modalities for conversion during episodes and prophylaxis with drugs, various pacing techniques, DC conversion and surgical therapy are discussed. INTERPRETATION: Radiofrequency catheter ablation is the only available method to cure the patient in a gentle manner.

Anti-Arrhythmia Agents↗