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Biomedical subjects

L Chen

Publications and source records attributed to L Chen.

At least 901 records · Page 50Linked to original sources
PubMed1997

[Effects of progesterone on proliferation and differentiation of fetal rat calvarial osteoblasts in vitro].

OBJECTIVES: To investigate the influence of progesterone on proliferation and differentiation of osteoblast at the levels of gene expression and cell functions. METHODS: Fetal rat calvarial osteoblasts were cultured in vitro in the presence of (10(-9) mol/L-10(-6) mol/L) progesterone. Cell proliferation, alkaline phosphalase (ALP) activity, osteocalcin mRNA expression and osteocalcin secretion in the medium and bone nodule formation were analyzed. RESULTS: Progesterone did not influence cell proliferation; Progesterone enhanced the ALP activity in rat osteoblasts; Progesterone stimulated osteocalcin mRNA expression in a dose-dependent manner and increased the amount of osteocalcin in the culture medium; Progesterone increased both number and area of bone nodule formation. CONCLUSION: Progesterone has a multi-stimulating effect on the differentiation of fetal rat calvarial osteoblast, hut no effect on cell proliferation.

Animals↗
PubMed1997

[Simultaneous detecting of C3 phenotypes and C3 cleavage by immunofixation].

The C3 phenotypes and C3 cleavage were simultaneously detected using cellulose acetate electrophoris followed by immunofixation and desitometry. Compared to crossed-immunoelectro-phoresis, this method has some advantages in resolution between different bands and was much more rapid, less expensive and more sensitive.

Complement C3↗
PubMed1997

Clinical, pathologic and genetic studies on mitochondrial myopathy, encephalopathy, lactic acidosis and stroke-like episodes.

OBJECTIVE: To study the clinical, pathological and genetic characteristics of mitochondrial myopathy, encephalopathy, lactic acidosis and stroke-like episodes (MELAS). METHODS: Eight cases of MELAS (6 of them were from 2 families) underwent clinical study, muscle biopsy, autopsy on one patient, brain biopsy on one patient and genetic research. RESULTS: In clinical report the average age of onset was 10-22 years old. Four cases from one family were 3 brothers and their nephew (sister's son). The death age of the three brothers was 16-20 years. Two cases from another family were a brother and a sister. The six patients of the two families showed the typical inherited characters of MELAS. The symptoms were myoclonic epilepsy, stroke-like episodes, paralysis of limbs, progressive mental retardation and neurological deaf. CT showed calcification in globus pallidus and MRI demonstrated clearly the abnormal prolongation of T2-weighed signals that distributed in frontal, parietal, occipital and temporal cortex as multiple focal, cystic and laminar necrotic areas. Pathological studies on brain showed multi-focal, cystic, and laminar or spongy necrotic abnormality primarily in gray matter of frontal, parental, temporal and occipital cortex. Decrease and loss of nerve fibers of the sub-cortical white matters of the lesion areas of cortex and calcification of globus pallidus were also observed. Red ragged fibers (RRF) and abnormal mitochondron were found by muscle biopsies. A point mutation (A-G transition) at nt 4243 in the mitochondrial tRNA Leu (UUR) was confirmed by using PCR and Southern Blot. CONCLUSION: Although great progress has been made in the clinical, pathological and genetic research of MELAS, the pathogenesis of the disease remains further research.

Adolescent↗
PubMed1997

[cDNA library construction from compacted eight-cell mouse embryos and differential screening for specific-expressed cDNA clones].

A large and representative cDNA library containing 6.9 x 10(5) independent clones was constructed from about 2 x 10(3) mouse embryos at the compacted 8-cell stage to identify and characterize gene products which play crucial roles in the first differentiation process of mouse embryogenesis. The cDNA library was differentially screened with labelled cDNA probes synthesized on poly (A)+ RNA isolated from the compacted 8-cell morula or late 2-cell mouse embryos. The results showed that difference in gene expression existed between these two developmental stages. Two clones which appeared only at the 8-cell stage were selected. This study provides a valuable tool for further detailed analysis of specific proteins associated with developmental events.

Animals↗
PubMed1997

[The effect of root canal irrigation and variance of apical foramen pressure by use of casing aspiration needle system in vitro].

The authors introduced casing aspiration needle system (CANS) to irrigating root canal. The effect of root irrigation on removing canal debris and the variance of apical foramen pressure on extracted teeth were compared between the conventional irrigation and CANS irrigation. The results indicated that the effect of root canal irrigation by CANS was much better than the conventional method (P < 0.01). CANS irrigation didn't produce pressure to apical foramen during root canal irrigation. However, in the conventional method, with irrigation needle inserted deeper and deeper in root cancal the pressure of apical foramen gets higher and higher.

Humans↗
PubMed1996

Control of apolipoprotein B mRNA editing: implication of mRNA dynamics at various maturation stages.

Apolipoprotein (apo) B mRNA editing is a genetic regulatory mechanism whereby nucleotide 6666 in apo-B-100 mRNA is converted from a C to a U. The end result of this change is the creation of a premature stop codon so that the translation product of the edited (apoB-48) mRNA contains 2152 amino acids residues instead of 4536 residues in the product (apoB-100) encoded by the unedited mRNA. ApoB mRNA editing is a post-transcriptional process that is expressed in a tissue-specific manner. Here we present a model for the control of apoB mRNA editing. The three variables in the model include editing activity, apoB mRNA transcription rate and mRNA degradation rate at various maturation stages for the mRNA, and a simple formula can be used to quantify the degree of apoB mRNA editing with respect to these variables at different apoB mRNA maturation stages. Time-dependent equations were solved numerically. Using this model, it can be shown that, in addition to editing activity, the degradation kinetics of apoB mRNA can also serve as an efficient modulator of the degree of editing. The rate of apoB mRNA transcription has a transient effect on the degree of editing; varying the apoB mRNA degradation constant tends to change the degree of editing only at the specific maturation stage. This model can render some previously proposed hypothesis (e.g. coupling of mRNA editing to splicing/polyadenylation) unnecessary and provides a rational basis for the design of experiments on specific aspects of apoB mRNA editing in the future; it may also be applicable to other types of RNA editing.

Animals↗
PubMed1996

Small molecule interactions with protein-tyrosine phosphatase PTP1B and their use in inhibitor design.

We have previously shown that a small peptide bearing the hydrolytically stable phosphotyrosyl (pTyr) mimetic, (difluorophosphonomethyl) phenylalanine (F2Pmp), is an extremely potent inhibitor of PTP1B, with an IC50 value of 100 nM [Burke, T. R., Kole, H. K., & Roller, P. P. (1994) Biochem. Biophys. Res. Commun. 204, 129-134]. We further demonstrated that removal of the peptide portion and incorporation of the difluorophosphonomethyl moiety onto a naphthalene ring system, but not a phenyl ring system, resulted in good inhibitory potency [Kole, H. K., Smyth, M. S., Russ, P. L., & Burke, T. R., Jr. (1995) Biochem, J. 311, 1025-1031]. In order to understand the structural basis for this inhibition, and to aid in the design of further analogs, we solved the X-ray structure of [1, 1-difluoro-1-(2-naphthalenyl)-methyl]phosphonic acid (6) complexed within the catalytic site of PTP1B, solved to 2.3 A resolution. In addition to showing the manner in which the phosphonate group is held within the catalytic site, the X-ray structure also revealed extensive hydrophobic interactions with the naphthalene ring system, beyond that possible with an analog bearing a single phenyl ring. It is further evident that, of the two fluorine atoms, the pro-R alpha-fluorine interacts with the enzyme to a significantly greater degree than the pro-S alpha-fluorine, forming a hydrogen bond to Phe 182. On the basis of a computer-assisted molecular modeling analysis, it was determined that addition of a hydroxyl to the naphthyl 4-position, giving [1, 1-difluoro-1-[2-(4-hydroxynaphthalenyl)] methyl]phosphonic acid (8), could potentially replace a water molecule situated in the PTP1B-6 complex, thereby allowing new hydrogen-bonding interactions with Lys 120 and Tyr 46. Compound 8 was therefore prepared and found to exhibit a doubling of affinity (Ki = 94 microM) relative to parent unsubstituted 6 (Ki = 179 microM), supporting, in principle, the development of high-affinity ligands based on molecular modeling analysis of the enzyme-bound parent.

Binding Sites↗
PubMed1996

Electrically Conductive Crust in Southern Tibet from INDEPTH Magnetotelluric Surveying

The crust north of the Himalaya is generally electrically conductive below depths of 10 to 20 km. This conductive zone approaches the surface beneath the Kangmar dome (dipping north) and extends beneath the Zangbo suture. A profile crossing the northern Yadong-Gulu rift shows that the high conductivity region extends outside the rift, and its top within the rift coincides with a bright spot horizon imaged on the INDEPTH CMP (common midpoint) profiles. The high conductivity of the middle crust is atypical of stable continental regions and suggests that there is a regionally interconnected fluid phase in the crust of the region.

Journal Article↗
PubMed1996

Selective transgene expression for detection and elimination of contaminating carcinoma cells in hematopoietic stem cell sources.

Tumor contamination of bone marrow (BM) and peripheral blood (PB) may affect the outcome of patients receiving high dose chemotherapy with autologous transplantation of hematopoietic stem cell products. In this report, we demonstrate that replication defective adenoviral vectors containing the cytomegalovirus (CMV) or DF3/MUC1 carcinoma-selective promoter can be used to selectively transduce contaminating carcinoma cells. Adenoviral-mediated reporter gene expression in breast cancer cells was five orders of magnitude higher than that found in BM, PB, and CD34+ cells. Our results demonstrate that CD34+ cells have low to undetectable levels of integrins responsible for adenoviral internalization. We show that adenoviral-mediated transduction of a reporter gene can detect one breast cancer cell in 5 x 10(5) BM or PB cells with a vector containing the DF3/MUC1 promoter. We also show that transduction of the HSV-tk gene for selective killing by ganciclovir can be exploited for purging cancer cells from hematopoietic stem cell populations. The selective expression of TK followed by ganciclovir treatment resulted in the elimination of 6-logs of contaminating cancer cells. By contrast, there was little effect on CFU-GM and BFU-E formulation or on long term culture initiating cells. These results indicate that adenoviral vectors with a tumor-selective promoter provide a highly efficient and effective approach for the detection and purging of carcinoma cells in hematopoietic stem cell preparations.

Adenoviruses, Human↗
PubMed1996

A helper-dependent adenovirus vector system: removal of helper virus by Cre-mediated excision of the viral packaging signal.

Adenoviruses are attractive vectors for the delivery of foreign genes into mammalian cells for gene therapy. However, current vectors retain many viral genes that, when expressed at low levels, contribute to the induction of a host immune response against transduced cells. We have developed a helper-dependent packaging system for production of vectors that have large regions of the genome deleted. Helper viruses were constructed with packaging signals flanked by loxP sites so that in 293 cells that stably express the Cre recombinase (293Cre), the packaging signal was efficiently excised, rendering the helper virus genome unpackageable. However, the helper virus DNA was replicated at normal levels and could thus express all of the functions necessary in trans for replication and packaging of a vector genome containing the appropriate cis-acting elements. Serial passage of the vector in helper virus-infected 293Cre cells resulted in an approximately 10-fold increase in vector titer per passage. The vector could be partially separated from residual helper virus by cesium chloride buoyant density centrifugation. Large scale preparations of vector yielded semi-purified stocks of approximately 10(10) transducing virions/ml, with < 0.01% contamination by the E1-deleted helper virus. This system should have great utility for the generation of adenovirus-based vectors with increased cloning capacity, increased safety and reduced immunogenicity.

Adenoviridae↗
PubMed1996

Angiographic features of vein grafts versus ungrafted coronary arteries in patients with unstable angina and previous bypass surgery.

OBJECTIVES: The aim of the study was to compare the angiographic features of culprit coronary lesions located in grafts with those in native coronary arteries in patients with unstable angina and previous coronary artery bypass graft surgery (CABG). BACKGROUND: Deterioration of angina in patients with previous CABG is usually due to progression of atherosclerosis in coronary arteries or in vein grafts, but the relative importance of graft versus native coronary artery disease as well as the morphologic features of the culprit lesions in unstable angina have not been systematically assessed. METHODS: Disease progression and angiographic features of vein grafts and ungrafted and grafted coronary arteries were assessed in 95 consecutive patients admitted with unstable angina or non-Q wave myocardial infarction with CABG > 6 months previously. All patients were receiving aspirin and heparin, and 46 had received streptokinase during the acute phase in a doubleblind, placebo-controlled study. Coronary and vein angiography was performed within 8 days after admission (mean [+/- SD] 5 +/- 2 days). The most recent angiogram served to assess disease progression by quantitative angiography. RESULTS: The culprit lesion was located in a vein graft in 51 patients, an ungrafted coronary artery in 17 and a grafted artery (proximal and distal to the site of graft insertion) in 9 and was of undetermined site in the remaining 18. The proportion of grafts accounting for acute disease increased to 85% with CABG > or = 5 years. Total occlusion occurred in 25 vein grafts and 4 ungrafted coronary arteries (49% vs. 24%, p = 0.02). Intravessel thrombus was found in 18 culprit vein grafts but in only 2 ungrafted coronary arteries (37% vs. 12%, p = 0.04). Both intravessel thrombus and total occlusion were demonstrated in six culprit vein grafts but in none of the ungrafted coronary arteries (12% vs. 0%, p = NS). The prevalence of total occlusion and thrombus was not influenced by trial medication, streptokinase or placebo. CONCLUSIONS: Unstable angina in patients with previous CABG is most often due to graft disease and is associated with more frequent thrombi that are more refractory to medical therapy.

Age Factors↗
PubMed1996

Organization of the gene encoding human prostacyclin synthase.

Prostacyclin is a potent vasodilator and inhibitor of platelet aggregation. Prostacyclin synthase (PGIS), which converts prostaglandin H2 to prostacyclin, is a member of the cytochrome P450 superfamily. We report here the characterization of the human PGIS gene. The gene is about 60 kb long and contains 10 exons. The PGIS gene was assigned to chromosome 20 by analysis of a human-hamster somatic hybrid DNA panel. The transcription start site was identified by primer extension, and approximately 3 kb of DNA upstream of this site was sequenced. The region surrounding the transcription start site presents features characteristic of a house-keeping gene promoter. It lacks a TATA box but is very rich in GC content. Several putative potential binding sites for transcription factors were identified.

Animals↗
PubMed1996

A lysozyme folding intermediate revealed by solution X-ray scattering.

Equilibrium unfolding of hen egg lysozyme as a function of urea concentration at pH 2.9 has been studied by solution X-ray scattering. Differences in the unfolding transition are observed as monitored by the radius of gyration Rg, and by far and near UV CD (circular dichroism) at 222 nm and 298 nm, respectively. This suggests the existence of a third unfolding species, in addition to the native and the unfolded states. A singular value decomposition (SVD) analysis was made of the scattering curves at different urea concentrations. This analysis shows clear evidence of a third basis component in the X-ray scattering curves, thus supporting the results of the Rg and CD measurements. The denaturant binding model was employed to estimate the thermodynamic parameters of denaturation for the intermediate and unfolded states. Use of these parameters to refine the SVD analysis allows us to reconstruct a scattering profile for the pure intermediate state. Simplified partially folded models, based on the crystal structure of hen lysozyme, support a working model for the intermediate, whose structure may be correlated with that of the kinetic intermediate found in the refolding pathway studied by Dobson and coworkers.

Circular Dichroism↗