Biomedical subjects

H Chen

Publications and source records attributed to H Chen.

At least 307 records · Page 17Linked to original sources

PubMed2001

[Manufacture and study of porous poly(l-lactic acid) (PLLA)/beta-tricalcium phosphate (beta-TCP) composite].

A promising alternative to supply bone substitutes is to develop living tissue substitutes based on biodegradable materials, which is called bone tissue engineering. One of the research high-lights of bone tissue engineering is to design and manufacture scaffolds for cell attaching, migrating, and proliferating. A process which consists of a solvent casting stage, a compression molding stage and a leaching stage has been used to fabricate macroporous composites of poly(l-lactic acid) (PLLA) and beta-tricalcium phosphate (beta-TCP). The effects of the weight fraction of porogen--NaCl, of the weight ratio of PLLA to beta-TCP and of the diameters of beta-TCP on the porosities, the average pore diameters and the compressive yield strength and compressive modulus have been studied. The results showed that the porosities and the average pore diameters increased and the compressive yield strength and modulus decreased when the weight fraction went from 50% to 90%. The compressive yield strength and compressive modulus could be improved by changing the weight ratio of PLLA to beta-TCP and the diameters of beta-TCP in low-porosity composites (lower than 70%). But high-porosity composites (90%) were not reinforced by changing the weight ratio.

Biocompatible Materials↗

PubMed2001

[Effect of different cultured conditions on endothelial cell and its resistance to the fluid imposed shear stress--a comparative study].

This study was intended to enhance the resistance of cultured endothelial cells (EC) to fluid shear stress and clarify the possible mechanism. A modified parallel plate flow apparatus was used to compare the strength between the grafts and the endothelial cells under shear stress condition and static condition. The dynamic change of cytoskeletal actin filaments and the effects of different adhesive proteins coated on the strength of EC adhesion to the glass were studied. The results showed that the number of cells retention of the shear stress-conditioned group was significantly larger than that of the static group. Precoated fibronectin and laminin significantly promoted the adherence of the EC cultured in a steady environment but seemed to have no effect on the EC cultured under flow condition. The results suggest that the vascular endothelial cell cytoskeleton, stress fiber and the shape of EC reorganize in response to long term fluid-imposed shear stress, and the endothelial cells become tightly adherent to the grafts.

Actins↗

PubMed2001

[Effect of flow shear stress on the expression of adhesion molecules of endothelial cells].

Adherence of various leukocytes, including monocyte, to vascular endothelial cells may play an important role in the development of atherosclerosis. In vivo, the hemodynamic shear forces have a critical effect on the surface expression of adhesion proteins. In order to elucidate the effect of flow shear stress on the expression of adhesion molecules of endothelial cells, we investigated the effect of flow shear stress (2.23-6.08 dyne/cm2) on the expression of adhesive molecules, intercellular adhesion molecule(ICAM-1), vascular cell adhesion molecule (VCAM-1), and E-selectin on cultured human umbilical vein endothelial cells(HUVECs). The expression of adhesion molecules on the surface of HUVECs induced by shear stress was analyzed using flow cytometry. The results showed that compared with stationary control, the surface expression of ICAM-1 was significantly increased (P < 0.05) on HUVECs after exposure to different shear stress (2.23, 4.20, 6.08 dyne/cm2), and it was found to be in close relationship with the shearing time (r = 0.992, 0.997, 0.997; P < 0.05). After exposure to shear(2.23 dyne/cm2), VCAM-1 expression was significant increased(P < 0.05), and it was positively correlated with the shearing time(r = 0.930; P < 0.05), while VCAM-1 expression dropped down to basal level(P < 0.05) after it was sheared at 4.20 or 6.08 dyne/cm2, and the magnitude of the reduction of VCAM-1 expression was negatively correlated with the shearing time (r = -0.975, -0.989; P < 0.05). E-selectin expression was less sensitive to shear stress, especially at the lower magnitudes of shear. These results indicate that the increase of ICAM-1 and VCAM-1 expression in endothelial cells induced by low shear stress may play a prominent role in the development of both inflammation and atherosclerosis.

Cells, Cultured↗

PubMed2001

[Design and improvement of stenosis model in cylindrical tubal flow via pulsed Doppler ultrasound in vitro].

A model of disturbed flow downstream of a severe stenosis has been established and improved in vitro, and the relevant method and feasibility for the detection of flow indices are discussed via commercially available Pulsed Doppler Ultrasound (PDU). Detection is done temporally and spatially, upstream and downstream. The methodology is proved to be feasible and has good prosperity of clinical use.

Constriction, Pathologic↗

PubMed2001

[Apoptosis in pressure overload-induced heart hypertrophy].

Pressure overload can result in heart hypertrophy, and induce apoptosis, but the phenomenon of apoptosis during the forepart of cardiomyocyte hypertrophy remains unclear. The aim of this study was to inquire into the process of cardiomyocyte apoptosis during the forepart of cardiomyocyte hypertrophy. We constructed the hypertrophy model by transverse aortic constriction of male SD rat. The apoptosis ratio was detected by TUNEL method and FCM. The result demonstrated that hypertrophy indexes increased with the time of constriction, reached the highest level at day 7, maintained that level, and then decreased at day 91. The apoptosis ratio of cardiomyocyte at day 4 was higher than that at day 0 detected by FCM method, and the ratio at day 7 was markedly lower than that at day 4. After day 28, the apoptosis ratio of cardiomyocyte went up again with the time of constriction after surgery. TUNEL method revealed that positive nuclei were observed in cardiomyocytes exclusively in the left ventricle; the apoptosis ratio increased when constriction continued. TUNEL method confirmed the result of FCM. These data indicate that cardiac hypertrophy is initiated by apoptosis of cardiomyocyte, these two factors(hypertrophy and apoptosis) maintain the balance between growth and death during the early short period of aortic constriction, and when aortic constriction goes on they are involved in the pathogenesis of heart remodeling.

Adaptation, Physiological↗

PubMed2001

[RGD peptides and endothelialization of biomaterials].

Endothelialization can remarkably improve blood compatibility of biomaterials and promote their clinical application, especially the uses of cardiovascular grafts. The attachment and growth of endothelial cells on artificial surfaces is the critical factor affecting the process of endothelialization. Many adhesive proteins contain the Arg-Gly-Asp(RGD) sequence which plays an important role in cell adhesion, migration and growth. In this review, the interaction of RGD peptides sequence and integrins, the influential factors of RGD peptides bioactivity and its application in endothelialization of biomaterials were discussed.

Biocompatible Materials↗

PubMed2001

Abrogation of tumor necrosis factor-alpha converting enzyme inhibits embryonic lung morphogenesis in culture.

TNF-alpha converting enzyme (TACE)-mediated cell surface protein ectodomain cleavage constitutes an important cellular regulatory mechanism during mammalian lung development. Herein, we have found that TAPI, a synthetic inhibitor of TACE, inhibits embryonic mouse lung branching morphogenesis in culture. To further investigate the biological significance of TACE as a shedding enzyme during early lung organogenesis, we have devised an antisense oligonucleotide to specifically block endogenous TACE gene expression at both transcriptional and translational levels in embryonic mouse lung explant culture. Addition of TACE antisense oligonucleotide resulted in a concentration-dependent reduction in lung branching morphogenesis in culture, whereas both scrambled and sense control oligonucleotides showed no adverse effects on lung growth. Furthermore, both aquaporin-5 (Aqp5) and surfactant protein-C (SP-C) mRNA expression and protein immunoreactivity were significantly inhibited in cultured mouse lungs treated with TACE antisense oligonucleotide, indicating defective epithelial cell differentiation in embryonic lungs with decreased TACE expression. TACE is known to be involved in the proteolytic release of TGF-alpha, an EGF family stimuli critical for lung growth and maturation. We therefore tested the possibility that a lack of diffusable TGF-alpha, due to TACE deficiency, contributes to the inhibitory lung morphogenesis in the presence of TACE antisense oligonucleotide in lung culture. Soluble TGF-alpha, when included in the lung culture, rescued the TACE antisense oligonucleotide-treated lungs from inhibition of both lung branching morphogenesis and lung epithelial cell differentiation, suggesting an impaired release of circulating regulators necessary for lung development in the absence of TACE gene expression. Our findings provide evidence that TACE-mediated membrane protein shedding is indispensable for normal lung branching morphogenesis and cytodifferentiation, probably through regulating the availability of positive cytokines/growth factors essential for lung organogenesis such as TGF-alpha.

ADAM Proteins↗

PubMed2001

Characterization and mechanisms of chromosomal alterations induced by benzene in mice and humans.

Elevated frequencies of chromosomal aberrations have been observed in the lymphocytes of benzene-exposed workers. Similar changes occurring in the bone marrow may play an important role in the development of leukemia. The objective of this research has been to characterize chromosomal alterations induced by benzene in mice and humans and to investigate the potential role of inhibition of topoisomerase II in the myelotoxic effects of benzene. The research is presented in three sections corresponding to the specific aims of the project: genotoxicity studies in the mouse, topoisomerase II studies, and initial studies using a new fluorescence in situ hybridization (FISH) approach to detect chromosome alterations in benzene-exposed workers. The results of the mouse experiments indicate that both chromosome breakage and aneuploidy are induced in the bone marrow of B6C3F1 mice following benzene administration. Chromosome breakage is the predominant effect, and this occurs primarily in the mouse euchromatin. Significant breakage within the mouse heterochromatin was also observed, as was aneuploidy. Breakage in the mouse bone marrow erythrocytes increased as a function of both dose and duration of benzene administration. The aneuploidy resulting from benzene exposure in mice was a relatively infrequent event, with increases of both chromosome loss and hyperdiploidy being observed. In the topoisomerase studies, benzene or its metabolites were shown to inhibit topoisomerase II enzyme activity in an isolated enzyme system, in a human bone marrow-derived leukemia cell line, and in vivo in the bone marrow of treated mice. The decreased activity was probably due to the rapid degradation of the topoisomerase II protein in the treated cells. In the human biomonitoring studies, the feasibility of using FISH with tandem DNA probes to detect chromosome alterations in interphase granulocytes and lymphocytes of benzene-exposed workers was demonstrated. The results from the two worker studies were somewhat inconsistent, however. In the study of Estonian workers, characterized by lower exposures and a smaller sample size, the benzene-exposed workers exhibited elevated frequencies of breakage in the lq12 region as compared with those seen in controls. A suggestive trend toward increased hyperdiploidy was also seen, although the frequencies in the exposed workers were low and within the range of our laboratory's historical control frequencies. In the larger study of more highly exposed Chinese workers, no increase in breakage affecting the 1q12 region was seen among the exposed workers. A trend toward increased hyperdiploidy of chromosome 1 was seen in the exposed workers when the concentration of urinary benzene metabolites was used in conjunction with the frequency of hyperdiploidy observed in the lymphocytes of the individual workers. The results of these studies indicate that benzene exposure is characterized by chromosome breakage, primarily within the euchromatin, and modest increases in aneuploidy. These findings also provide the first direct evidence that benzene is capable of inhibiting the enzymatic activity of topoisomerase II in vivo, providing additional support for the hypothesis that inhibition of topoisomerase II contributes to benzene-induced toxicity and leukemogenesis.

Adult↗

PubMed2001

[Cloning, sequence analysis of deacetoxycephalosporin C synthetase/hydroxylase gene cefEF].

Chromosomal DNA preparations were made form the fungi C. acremonium and A. chrysogenum respectively by a method using 1-Chloro methyl benzene solution. Then the cefEF gene of deacetoxycephalosporin C synthetase/hydroxylase was amplified by polymerase chain reaction. The cefEF gene could only be amplified from the chromosomal DNA of A. chrysogenum. This fragment about 1.0 kb was cloned into pGME-T vector and then sequenced. The sequence indicates that the cloned cefEF gene contains 999 nucleotides encoding for 333 amino acids and there are three bases and two amino acids different from those that have been reported. Both of the two amino acids are not in active site. The result also indicates that the reported C. acremonium or A. chrysogenum generating deacetoxycephalosporin C synthetase/hydroxylase corresponds with A. chrysogenum but not C. acremonium in China.

Base Sequence↗

PubMed2001

Toward understanding the role of insulin alpha-helix II in the growth-promoting activity of insulin.

For further understanding the contribution of the alpha-helix II (alphaII) in the growth-promoting activity of insulin, the residues A2Ile, A5Gln, and A8Thr located in alphaII were mutated to Leu, Glu, and Tyr, respectively. Three mutant insulins, [A2Leu]human insulin, [A5Glu]human insulin, and [A8Tyr]human insulin, were prepared by means of site-directed mutagenesis. The in vitro growth-promoting activities of the three mutant insulins, measured using GR2H6 cells, were 7.5%, 291%, and 250% of that of native insulin, respectively. Their receptor-binding activities to the insulin receptor were 2.3%, 46.7%, and 138.7%, respectively, compared with native insulin. Both the growth-promoting and receptor-binding activities of [A2Leu]human insulin and [A3Leu]insulin (Shi et al., 1997) were parallel and greatly decreased compared with native insulin. The results demonstrate that the residues A2Ile and A3Val in the alphaII are essential for the growth-promoting activity of insulin, and the growth-promoting function of insulin might be performed through, or mainly through, binding to the insulin receptor. The growth-promoting activities of [A5Glu]human insulin and [A8Tyr]human insulin were increased 6-fold and 2-fold, respectively, compared with native insulin, indicating that their growth-promoting activities might be expressed by, or mainly by, binding to the IGF-1 receptor.

Amino Acid Motifs↗

PubMed2001

Parents' attitudes and expectations regarding science education: comparisons among American, Chinese-American, and Chinese families.

This study examined the differences in attitudes toward science education among American, Chinese-American, and Chinese parents and students. Parents' expectations for their high school children's science performance were also compared among the three cultural groups. It was found that both Chinese parents and students had more positive attitudes toward science education than did their American counterparts. Chinese parents placed greater emphasis on self-improvement, set higher standards, and more often helped their children to learn science than did American parents. The attitudes of the Chinese-Americans appeared to show the influences of both their Chinese heritage and American culture. Overall, a high positive correlation was found between parents' and students' attitudes toward science education.

Adolescent↗

PubMed2001

[The study on the shear stress responsive element in endothelial cells].

Vascular endothelial cells, by virtue of their unique anatomical position, are constantly exposed to the fluid mechanical forces generated by flowing blood. The fluid forces could influence endothelial cell's gene expression. At a molecular level, fluid shear stress is known to increase or decrease the expression of a wide variety of genes. The shear stress responsive element (SSRE) was proposed after the identification of the first SSRE, the GAGACC sequence identified in the platelet-derived growth factor (PDGF) B chain promoter and subsequently identified in other genes whose promoters respond to shear stress. In addition, there are the existence of other positive shear responsive regulatory elements. There is a report on the activation of these promoters in vitro and in vivo and propose an application of these mechanically inducible promoters in the treatment of vascular diseases.

Animals↗

PubMed2001

[Protective effect of tanshinone IIA on acute hepatic injury in mice].

OBJECTIVE: To study the effect of tanshinone IIA on two models of acute hepatic injury in mice. METHODS: Two acute hepatic injury models induced by carbon tetrachloride (CCl4) and D-galactosamine (D-GalN) in mice were used. ALT, AST in serum and MDA in liver homogenate were used as indexes. RESULTS: Tanshinone IIA (10 mg.kg-1, 20 mg.kg-1, 30 mg.kg-1), similar to biophenyldicarboxylate, could decrease ALT, AST in serum and MDA in hepatic homogenate on acute hepatic injury induced by CCl4 and D-GalN. CONCLUSION: Tanshinone IIA possessed obvious protective effect against liver injury induced by CCl4 or D-GalN.

Abietanes↗

PubMed2001

[Preliminary study of HLA haplotype matched and T-cell undepleted allogeneic bone marrow transplantation for treatment of leukemia].

OBJECTIVE: To explore the feasibility of allogeneic bone marrow transplantation (Allo-BMT) with graft from HLA haplotype matched related donor without T-cell depleted for the treatment of leukemia. METHODS: Fifteen patients with leukemia received allo-BMT with grafts from HLA 2 or 3 antigen mismatched related donors. All patients were treated with standardized conditioning regimen consisting of high dose Ara-C, cyclophosphamide (CY) and total body irradiation (TBI). Donors were given G-CSF at 3 to 4 micrograms.kg-1.d-1 for seven days prior to marrow harvest. GVHD prophylaxis programme consisted of CsA, MTX, ATG and mycophenolate mofetial. RESULTS: All patients established successful engraftment. The median days of granulocyte > 0.5 x 10(9)/L and platelet > 20 x 10(9)/L were 19(range 13-23) and 21 (range 16-32) days, respectively. Acute grade II-IV GVHD occurred in 5 of 15 patients (33.3%). Two of them were grade II gut aGVHD, 2 grade III gut aGVHD, and 1 grade IV gut and liver aGVHD. Chronic GVHDs were seen in 8 of 9 evaluable patients (88.9%) and none developed extensive cGVHD. The median follow-up duration was 395 (110-690) days. Six of fifteen patients died. Five of them died from transplantation related mortality and 1 from relapse. Nine patients were alive in a disease-free situation. Six of them survived more than one year. CONCLUSION: The major histoincompatibility barriers in the haplotype matched related donor/recipient allo-BMT might be crossed by donor stimulated with G-CSF and combined GVHD prophylaxis program.

Adolescent↗

PubMed2001

[Analysis of short tandem repeats with fluorescence labeling polymerase chain reaction to document engraftment following allogeneic bone marrow transplantation].

OBJECTIVE: In order to determine the status of engraftment following allogeneic bone marrow transplantation (allo-BMT) and predict the outcome, short tandem repeats (STR) were analysed by fluorescence labeling polymerase chain reaction (PCR). METHOD: Fluorescence labeling PCR detecting STR 9 loci was established. DNA was extracted by monoclonal magnetic beads from recipients peripheral blood nucleated cells and labeled with four color fluorescences before and from 7 days to six months after allogeneic bone marrow transplantation. RESULTS: 1. STR and clinical feature of 12 patients after allogeneic bone marrow transplantation were analysed. In the ten patients with full donor chimeras, 8 received marrow grafts from HLA identical sibling donors, 1 from HLA identical unrelated donor and 1 from HLA haploidentical mother. All of the 10 patients had durable engraftment and survived disease-freely for 3-25 months of follow-up. 2. One patient received a HLA-AB loci mismatched graft and his STR showed mixed chimeras at day 30, and converted into full donor chimeras at day 60 after transplantation. 3. One patient received HLA haploidentical sibling donor stem cells failed to be engrafted and died 4 months later. CONCLUSION: Analysis of multi-loci of STR after allo-BMT provided a real indication of engraftment. Mixed chimeras after transplantation suggested that donor lymphocytes or bone marrow cells be re-infused to enhance the conversion from mixed chimeras to full donor chimeras. For the documentation of engraftment, analysis of STR was better than any other available methods.

Adolescent↗

PubMed2001

Lovastatin increases nitric oxide synthesis in IL-1 beta-stimulated smooth muscle cells.

OBJECTIVE: Nitric oxide (NO) production by inducible NO synthase (iNOS) may play an important role in the pathogenesis of atherosclerosis. Although lovastatin has been shown to reduce the progression of atherosclerosis, it is not known whether it regulates NO production. We investigated the effects of lovastatin on NO synthesis and the mechanisms by which lovastatin exerts its effects in rat vascular smooth muscle cells. METHODS: Primary cultures of the vascular smooth muscle cells were obtained from the media of the thoracic aorta of Sprague Dawley rats (200-250 g). Nitrite levels in the culture medium of rat vascular smooth muscle cells were determined colorimetrically. RESULTS: Lovastatin (10(-5) mol/L) significantly increased interleukin-1 beta (IL-1 beta, 10 ng/mL)-induced nitrite accumulation in a time (0-24 hours)-dependent manner. Exogenous mevalonate and geranylgeranyl-pyrophosphate completely reversed the stimulatory effects of lovastatin on nitrite production. Furthermore, inhibition of Rho by C3 exoenzyme mimicked the increase in IL-1 beta-induced nitrite accumulation induced by lovastatin in the vascular smooth muscle cells. CONCLUSION: These results demonstrate that lovastatin up-regulates NO formation in rat vascular smooth muscle cells stimulated by IL-1 beta, and the effect may be associated with the inhibition of Rho activity.

Animals↗

PubMed2001

[Decomposition processes of Tilia amurensis leaves in the Changbai Mountain forest ecosystem].

A 4-year field experiment was carried out in the Changbai Mountain to study the decomposition process of Tilia amurensis leaf and its affecting environmental factors. The results reveal that the decomposition process of Tilia amurensis leaves could be expressed by an exponent equitation. With the increase of elevation and the change of vegetation types, the decomposition rate in 1-5 standard experimental fields was -0.391, -0.339, -0.257, -0.198 and -0.125, respectively, indicating that the decomposition rate was decreased with ascending elevation. The maximum decomposition took place when the environment was in the shadow of 60%-80%. The leaves were acceleratively decomposed when the tested moisture was increased. Moisture affected the decomposition process more strongly than light.

Biodegradation, Environmental↗

PubMed2001

[Effect of organic acids on soil chemical behavior of lead and cadmium and their toxicity to plants].

The interaction between organic acids (citric and oxalic acids) and heavy metals was examined in this paper. Equilibrium dialysis showed that the extent organic acids bound metals depended on the metal involved, and their binding properties affected the adsorption of Pb and Cd by soil, which was increased in the presence of oxalic acid, and decreased in the presence of citric acid. The effect of citric acid on the behavior and toxicity of Pb and Cd to plants was also studied. The presence of citric acid could reduce the toxicity of Pb, and inhibit the uptake of Cd in shoots and roots. However, there was no significant effect on the apparent toxicity of Cd. The interaction between Pb and Cd was found to be complicated. The Pb content in rice was higher in the presence of Cd, while the content of Cd is lower in the presence of Pb.

Aconitic Acid↗