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Biomedical subjects

Li Deng

Publications and source records attributed to Li Deng.

67 records · Page 4Linked to original sources
PubMed2003

[Isolating and culturing rat marrow mesenchymal stem cells and studying their phenotypical and functional properties].

OBJECTIVE: To establish a method for isolating and cultivating mesenchymal stem cells (MSCs) from SD rat bone marrow and to study their phenotypical and functional properties. METHODS: MSCs from rat bone marrow were separated and purified by gradient centrifugation and adherence to the culture plastic; then the cells were expanded by subculture successively. The growth curves were drawn, and the morphology was observed. In an attempt to analyze immuno- and adhesive-phenotype and differentiation properties, the MSCs were evaluated with cytochemical and immunocytochemical methods. RESULTS: MSCs belonged to the mononuclear cells of marrow, they could be isolated and purified by gradient centrifugation and adherence to the culture plastic; their living behavior was quite stable in Dulbecco's Modified Eagle's Medium with low glucose (L-DMEM) containing 100 ml/L newborn bovine serum; the growth curves of passage 1, 3 and 5 were much similar, exhibiting a 2.2-fold increase in cell number after each passage. The cells were noted to have a large expansive potential and a typical fibroblast-like morphology, and they uniformly expressed CD44, CD54, fibronectin and collagen I. When incubated in medium supplemented with dexamethasone, beta-glycerophosphate and ascorbic acid, the MSCs underwent differentiation into osteoblasts, showing positive stain of alkaline phosphatase activity and mineralized nodules. CONCLUSION: The cells obtained in this experiment possess phenotypical and functional properties of mesenchymal stem cells, and the method for isolating and culturing rat marrow-derived MSCs has been established.

Animals↗
PubMed2003

[Studies of enzymatic synthesis of biodiesel].

Biodiesel, an alternative diesel fuel, fatty acid alkyl ester, is made from renewable biological sources such as vegetable oils and animal fats. Two processes for biodiesel synthesis, enzymatic lipase catalytic esterification from fatty acid and transesterification from oils and fats, was investigated. The effects of various lipases, enzyme amount and purity, solvent, water absorbent, inhibition of short chains alcohol, specificity of substrate, molar ratio of substrate on esterification were studied in detail. The esterification degree with the optimal parameter and process can reach up to 92%. The purity of biodiesel obtained by separation and purification is up to 98%, and the half-life of the immobilized lipase for the esterification process can be up to 360hr, Moreover, the preliminary studies of the transesterification including the amount of methanol and mode of adding methanol into reaction system were made. The transesterification degree with adding methanol stepwise can reach 83%.

Biofuels↗
PubMed2002

Development of a rapid, room-temperature dynamic kinetic resolution for efficient asymmetric synthesis of alpha-aryl amino acids.

[reaction: see text] A rapid, highly efficient and general dynamic kinetic resolution (DKR) of racemic alpha-aryl UNCAs with the dual-function catalysis of modified cinchona alkaloid was accomplished at room temperature. This DKR led to the development of a highly enantioselective catalytic method for the practical synthesis of a wide range of alpha-aryl and alpha-heteroaryl amino acids in 89-92% ee and 86-95% yield from racemic UNCAs.

Amino Acids↗
PubMed2002

Radiation-induced genetic instability in vivo depends on p53 status.

In response to ionizing radiation and other agents that damage DNA, the p53 tumor suppressor protein activates multiple cellular processes including cell cycle checkpoints and programmed cell death. Although loss of p53 function is associated with radiation-induced genetic instability in cell lines, it is not clear if this relationship exists in vivo. To study the role of p53 in maintenance of genetic stability in normal tissues following irradiation, we have measured mutant frequencies at the adenine phosphoribosyltransferase (Aprt) and hypothanine-guanine phosphoribosyltransferase (Hprt) loci and examined mechanisms of loss of heterozygosity (LOH) in normal T cells of p53-deficient, Aprt heterozygous mice that were subjected to whole-body irradiation with a single dose of 4Gy X-rays. The radiation-induced mutant frequency at both the Aprt and Hprt loci was elevated in cells from mice with different p53 genotypes. The radiation-induced elevation of p53-/- mice was significantly greater than that of p53+/- or p53+/+ mice and was caused by several different kinds of mutational events at the both chromosomal and intragenic levels. Most significantly, interstitial deletion, which occurs rarely in unirradiated mice, became the most common mechanism leading to LOH in irradiated p53 null mice. These observations support the idea that absence or reduction of p53 expression enhances radiation-induced tumorigenesis by increasing genetic instability at various loci, such as those for tumor suppressor genes.

Animals↗
PubMed2002

Loss of heterozygosity and point mutation at Aprt locus in T cells and fibroblasts of Pms2-/- mice.

Mice null for the Pms2 mismatch repair (MMR) gene exhibit a predisposition to lymphoma, microsatellite repeat instability, and failure of spermatogenesis. To study the role of Pms2 in the maintenance of in vivo genomic integrity in somatic cells, we characterized Aprt mutations in T cells and fibroblasts of 129 x C3H Pms2-/-Aprt+/- mice. The spontaneous frequency of DAP-resistant T lymphocytes, as a consequence of APRT-deficiency, was increased threefold. Point mutation, which accounted for less than 20% of the DAP(r) mutant clones in Pms2+/+ mice, was predominant in the mutant T cell clones from Pms2-/- mice. These point mutations were predominantly TA to CG transitions. Fibroblasts of Pms2-/- mice exhibited only a modest increase in the frequency of clones with point mutations, such that mitotic recombination was still the primary cause of APRT deficiency. Thus, the mutator phenotype as a consequence of PMS2 deficiency is tissue-dependent, which may be related to the tissue-specific tumor proneness of Pms2-/- mice.

Adenine Phosphoribosyltransferase↗
PubMed2002

Dynamic kinetic resolution via dual-function catalysis of modified cinchona alkaloids: asymmetric synthesis of alpha-hydroxy carboxylic acids.

A highly enantioselective catalytic transformation of racemic alpha-hydroxy acids to optically active alpha-hydroxy acids is reported. A new procedure was developed for the condensation of racemic alpha-hydroxy acids with trichloromethyl chloroformate (diphosgene) at room temperature in the presence of activated charcoal to form 5-substituted-1,3-dioxolane-2,4-diones in 90-100% yield. An efficient dynamic kinetic resolution of 5-aryl dioxolanediones was realized via a modified cinchona alkaloid-catalyzed alcoholytic opening of the dioxolanedione ring, generating a variety of optically active alpha-hydroxy esters in 91-96% ee and 61-85% chemical yield. In this dynamic kinetic resolution, the modified cinchona alkaloid was found to serve dual catalytic roles, mediating both the rapid racemization of the 5-aryl dioxolanediones and the enantioselective alcoholytic ring opening of the 5-aryl dioxolanediones. Consequently, both enantiomers of the 5-aryl dioxolanediones were converted to highly enantiomerically enriched aromatic alpha-hydroxy esters in yields (61-85%), far exceeding the maximum of 50% for a normal kinetic resolution. This development not only represents an expansion of the scope of asymmetric acyl-transfer catalysis of synthetic catalysts but also provides a new approach for the development of efficient chemical dynamic kinetic resolutions promoted by a single catalyst. 5-Alkyl dioxolanediones were resolved by a conventional but highly enantioselective kinetic resolution to provide alpha-hydroxy acids and esters in high optical purity and good yields.

Carboxylic Acids↗
PubMed2002

Morphological behavior of osteoblast-like cells on surface-modified titanium in vitro.

In recent papers, we reported the results of a study on the graded porous titanium coatings on titanium by plasma spraying and amino-group ion implantation. The paper is to preliminarily evaluate the biocompatibility of surface-modified titanium through 2, 5 and 7 days cell culture in vitro. Cell morphology was observed by a scanning electron microscope. Cell proliferation and type I collagen synthesis were measured by 3(4.5-dimethyl-thiazole-2-yl)2,5-diphenyl tetrazolium bromide (MTT) and enzyme-linked immunosorbent assay (ELISA), respectively. Our experimental results showed that osteoblast-like cells attached and spread well on surface-modified titanium. Cells were observed to grow into the pores and form extracellular matrix. MTT and ELISA results showed no detrimental effect on the development of cell. These studies support the biocompatibility of surface-modified titanium.

3T3 Cells↗
PubMed2002

An overlapping-feature-based phonological model incorporating linguistic constraints: applications to speech recognition.

Modeling phonological units of speech is a critical issue in speech recognition. In this paper, our recent development of an overlapping-feature-based phonological model that represents long-span contextual dependency in speech acoustics is reported. In this model, high-level linguistic constraints are incorporated in automatic construction of the patterns of feature-overlapping and of the hidden Markov model (HMM) states induced by such patterns. The main linguistic information explored includes word and phrase boundaries, morpheme, syllable, syllable constituent categories, and word stress. A consistent computational framework developed for the construction of the feature-based model and the major components of the model are described. Experimental results on the use of the overlapping-feature model in an HMM-based system for speech recognition show improvements over the conventional triphone-based phonological model.

Humans↗
PubMed2002

Induction of alpha-catenin, integrin alpha3, integrin beta6, and PDGF-B by 2,8-dihydroxyadenine crystals in cultured kidney epithelial cells.

BACKGROUND: Homozygous adenine phosphoribosyltransferase (APRT) deficiency is associated with 2,8-dihydroxyadenine (DHA) nephrolithiasis. Using whole kidney RNA from Aprt knockout mice, we previously showed that the renal deposition of DHA leads to changes in the expression of genes involved in tissue injury. To determine the cellular basis for these changes, we investigated gene expression in cultured human kidney (NHK-C) and African green monkey (BSC-1) epithelial cells exposed to DHA or calcium oxalate monohydrate (COM) crystals. METHODS: First-strand cDNAs, synthesized from mRNA isolated from treated and untreated cells, were hybridized to membrane-bound cDNA arrays containing 588 genes associated with various physiological and pathological processes. Changes in gene expression were confirmed by reverse transcription PCR. RESULTS: Twenty-seven percent of the array cDNAs were expressed in untreated NHK-C cells at varying levels relative to a housekeeping gene. The expression of three adhesion molecules (alpha-catenin, integrin alpha3, and integrin beta6) and platelet-derived growth factor B (PDGF-B) was elevated following exposure of NHK-C cells to DHA. Increased expression of the adhesion molecules was also observed in BSC-1 cells, but PDGF-B expression could not be detected. COM crystals also stimulated the expression of these four genes in NHK-C cells, but the expression profile was quantitatively different compared with DHA. CONCLUSIONS: These findings suggest that DHA crystals stimulate the expression of specific genes in kidney epithelial cells and that the pathways for DHA-induced cell injury may be similar to those for COM crystals. The induction of adhesion molecules and PDGF-B may affect cell-cell or cell-matrix interactions and/or alter the actin cytoskeleton. These alterations may ultimately contribute to crystal-induced renal injury.

Adenine↗
PubMed2002

[A multi-team case-control study on the effects of psychosocial stress to overall health].

OBJECTIVE: To explore the quantitative relationship between the intensity of psychosocial stress and the degree of overall health damages. METHODS: A multi-group case-control study was designed and implemented. The cases included two groups of out-patients (177) and in-patients (214) in a hospital in Jianyang city, and controls (587) were from the follow-up cohort in the same city. Three groups were studied on the following contents: general demographic characteristics, psychosocial factors and the degree of health damages including mental, physical, and social status. Major statistical analyses were as follows: ranks test, ANOVA, cluster analysis, multinomial logistic regression and ordered-logit regression. RESULTS: Ordered-logit regression model showed that the odds ratio of negative life-events on degree of health damages was 1.335 (P < 0.01). This result showed that there was a positive dose-effect relationship between the negative life-events score and overall health damages. The utility of social support to overall health had protective effect (OR = 0.513). CONCLUSION: Negative life-events were the major risk factors to overall health, and there was a dose-effect relationship between negative events and health damages. Function of social support played a protective factor for health.

Analysis of Variance↗
PubMed2002

[The difference in proliferation and differentiation ability of cultured marrow stromal cells between 3-month-old and 12-month-old rats in vitro].

OBJECTIVE: To compare the difference in proliferation and differentiation (to osteoblast or adipocyte) ability of cultured rat marrow stromal cells (rMSCs) between 3-month-old and 12-month-old rats in vitro. METHODS: The rMSCs of 3-month-old and 12-month-old were cultured in vitro. The growth curves were depicted to compare their proliferation ability. Both 3-month-old and 12-month-old rMSCs were induced to osteoblasts or adipocytes by osteogenic inducer or adipogenic inducer. At different times, these cells were observed by histochemistry staining. RESULTS: The growing ability of both passage 4 (P4) and passage 9 (P9) of 12-month-old rMSCs decreased in comparison with that of 3-month-old rMSCs. The growing ability of P9 was less than that of P4 of 12-month-old rMSCs. The expression of alkaline phosphatase (ALP) of the control group and induced group of 12-month-old rMSCs was less than that of 3-month-old rMSCs after 1-week osteogenic induction. 12 days later, calcification was observed in 3-months-old group. Lipid droplets occurred in the cells of 12-month-old group after 2-day adipogenic induction, whereas the droplets occurred after 3-day or 4-day induction in the 3-month-old group. CONCLUSION: The ability of proliferation and osteogenesis of 12-month-old group is weaker than that of 3-month-old group, but the ability of adipogenesis of 12-month-old group is stronger.

Alkaline Phosphatase↗
PubMed1997

Enantiospecific Formation of Trans 1,3-Disubstituted Tetrahydro-beta-carbolines by the Pictet-Spengler Reaction and Conversion of Cis Diastereomers into Their Trans Counterparts by Scission of the C-1/N-2 Bond.

The factors which effect the stereoselective formation of trans-1-alkyl-2-benzyl-3-(alkoxycarbonyl)-1,2,3,4-tetrahydro-beta-carbolines and trans-3-(alkoxycarbonyl)-1-alkyl-2-(diphenylmethyl)-1,2,3,4-tetrahydro-beta-carbolines by the Pictet-Spengler cyclization were examined by heating tryptophan derivatives with aldehydes of varied steric bulk under aprotic and acidic conditions, followed by determination of the ratio of cis to trans diastereomers so formed. The presence of a benzyl group at the N(b)-nitrogen atom alters the diastereochemical outcome of this condensation to provide 100% trans stereoselectivity when the cyclization is carried out with cyclohexanecarboxaldehyde. Furthermore, when N(b)-(diphenylmethyl)tryptophan isopropyl ester was condensed with aldehydes of any size, trans diastereomers are formed with 100% stereoselectively. The trans N(b)-substituted diastereomers are thermodynamically more stable than their cis congeners as shown by equilibration experiments in TFA. Conversion of the cis diastereomers into the more stable trans diastereomers is believed to occur under acidic conditions by cleavage of the carbon (C-1)-nitrogen (N-2) bond with complete retention of configuration at the C-3 stereocenter. Evidence from deuterium exchange experiments as well as optical rotations support this model for epimerization. In addition, when cis diastereomer 66a was allowed to stir in CF(3)COOD, the trans isomer 66b was isolated in 90% yield, while treatment of cis 66a with CF(3)COOH/NaBH(4) provided a mixture of the ring cleaved [scission across C(1)-N(2) bond] product 67 and the trans isomer 66b. Treatment of 66b (control experiment) with NaBH(4)/CF(3)COOH under the same conditions returned only starting trans 66b in excellent yield. The Pictet-Spengler reaction of substrates with sufficiently large substituents, followed by treatment with acid, permits the 100% enantiospecific formation of trans-1,3-disubstituted-1,2,3,4-tetrahydro-beta-carbolines for alkaloid total synthesis.

Journal Article↗