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Biomedical subjects

X Zheng

Publications and source records attributed to X Zheng.

At least 109 records · Page 6Linked to original sources
PubMed2000

A whole-genome assembly of Drosophila.

We report on the quality of a whole-genome assembly of Drosophila melanogaster and the nature of the computer algorithms that accomplished it. Three independent external data sources essentially agree with and support the assembly's sequence and ordering of contigs across the euchromatic portion of the genome. In addition, there are isolated contigs that we believe represent nonrepetitive pockets within the heterochromatin of the centromeres. Comparison with a previously sequenced 2.9- megabase region indicates that sequencing accuracy within nonrepetitive segments is greater than 99. 99% without manual curation. As such, this initial reconstruction of the Drosophila sequence should be of substantial value to the scientific community.

Algorithms↗
PubMed2000

Simplified purification of human basophils.

Studies of human basophils have been limited by the low number present in peripheral blood and the difficulties of purification to homogeneity with reasonable yield and functional status. Reproducible purification of human basophils to 96.5+/-0.5% with a yield of 40.8+/-5.3% was obtained by negative selection using immunomagnetic beads following initial separation by density gradient centrifugation. Isolated cells demonstrated complete viability by vital dye exclusion and spontaneous histamine release following incubation of <5%. Stimulation with anti-IgE or calcium ionophore A23187 caused histamine release and leukotriene C(4) production. Basophils demonstrated dose-dependent chemotaxis to monocyte chemotactic protein-3. This simplified methodology results in fully functional basophils in very high purity and good yield.

Antibodies, Anti-Idiotypic↗
PubMed2000

Unprecedented crystallization and X-ray crystal structure of racemic N(alpha)-(t-butyloxycarbonyl)-L-L-phenylalanine N-methoxy-N-methylamide.

Weinreb amide 3 was synthesized using isobutyl chloroformate, carbonyldiimidazole, or ethylcarbodiimide as the coupling agent in the reaction of Boc-phenylalanine with O,N-dimethylhydroxylamine hydrochloride. An optically active oil was isolated along with an optically inactive solid irrespective of the type of coupling agent used. Single crystal X-ray analysis of the solid revealed that it is a racemate. The molecular packing of the crystals reflect the stability of the racemate as opposed to an enantiomerically pure solid.

Calpain↗
PubMed2000

Effect of c-myc antisense oligodeoxynucleotides on hypoxia-induced proliferation of pulmonary vascular pericytes.

To study the effect of c-myc antisense oligodeoxynucleotides (ODNs) on proliferation of pulmonary vascular pericytes (PC) induced by hypoxia, cell culture, dot hybridization using probe of digoxigenin-11-dUTP-labeled cDNA, 3H-thymidine incorporation, immunocytochemical technique and image analysis methods were used to observe the effect of c-myc antisense ODNs on expression of c-myc gene and proliferating cell nuclear antigen (PCNA), and 3H-thymidine incorporation of PC induced by hypoxia. The results showed that hypoxia could significantly enhance the expression of c-myc and PCNA (P < 0.01), and elevate 3H-thymidine incorporation of PC (P < 0.01), but antisense ODNs could significantly inhibit the expression of c-myc and PCNA (P < 0.05), and 3H-thymidine incorporation of PC (P < 0.01). It was suggested that hypoxia could promote the proliferation of PC by up-regulating the expression of c-myc gene, but c-myc antisense ODNs could inhibit hypoxia-induced proliferation of PC by downregulating the expression of c-myc gene.

Animals↗
PubMed2000

The effect of hypoxia on expression of basic fibroblast growth factor in pulmonary vascular pericytes.

To examine whether hypoxia exerts effect on the expression of basic fibroblast growth factor (bFGF) in pulmonary vascular pericytes (PC), cell culture, in situ hybridization with probe of digoxigenin-11-dUTP-labled cDNA, immunocytochemistry and image analysis were employed in this study. The results showed that the expression amount of bFGF mRNA and protein in PC of hypoxia (H) group was 1.31 times (P < 0.01) and 1.17 times (P < 0.01) that of normoxia (N) group respectively. It suggests that hypoxia can directly enhance the expression of bFGF mRNA and protein in PC. Increased expression of bFGF may play an important role in the process of PC proliferation and differentiation of PC into smooth muscle-like cells.

Animals↗
PubMed2000

Bond strength of plasma-sprayed hydroxyapatite/Ti composite coatings.

One of the most important clinical applications of hydroxyapatite (HA) is as a coating on metal implants, especially plasma-sprayed HA coating applied on Ti alloy substrate. However, the poor bonding strength between HA and Ti alloy has been of concern to orthopedists. In this paper, an attempt has been made to enhance the bonding strength of HA coating by forming a composite coating with Ti. The bioactivity of the coating has also been studied. HA/Ti composite coatings were prepared via atmospheric plasma spraying on Ti-6Al-4V alloy substrates. The bond strength evaluation of HA/Ti composite coatings was performed according to ASTM C-633 test method. X-ray diffractometer and scanning electron microscopy were applied to identify the phases and the morphologies of the coatings. The bioactivity of HA/Ti composite coating was qualified by immersion of coating in simulated body fluid (SBF). The obtained results revealed that the addition of Ti to HA improved the bonding strength of coating significantly. In the SBF test, the coating surface was covered by carbonate-apatite, which was testified by X-ray photoelectron spectroscope, indicating good bioactivity for HA/Ti composite coating. The bioactivity of the coating has not been reduced by the addition of Ti.

Alloys↗
PubMed2000

New carbamoylpiperidines as human platelet aggregation inhibitors.

A series of 3-carbamoylpiperidines (nipecotamides) are designed, synthesized and tested for their inhibitory action against adenosine diphosphate (ADP)-induced aggregation of human platelets. A structure-activity analysis of the bis(nipecotamido)aralkane type showed that a substituent on the piperidine ring should preferably be an amide and that the electronegativity of the carbonyl oxygen and the orientation of the amide group affected activities. Based on the knowledge of factors influencing platelet activation and aggregation, a nitric ester moiety which could release nitric oxide (NO) in situ, is incorporated into the nipecotamide structure. These compounds exhibit increased activity compared to those having no -ONO2 function. They also show stereoselectivity, with the meso isomer being approximately twice as potent as the synthetic diastereomeric mixture. Replacement of the -ONO2 function with hydroxyl, ester or alkyl groups considerably diminishes aggregation-inhibitory potential. Nipecotamides are shown here to inhibit the basal and collagen-induced rise in platelet inositol trisphosphate (IP3) levels, as well as phosphoinositide turnover. A comprehensive mechanism of action is proposed taking earlier results into consideration.

Adult↗
PubMed2000

Electrode impedance: an indicator of electrode-tissue contact and lesion dimensions during linear ablation.

Pre-ablation impedance was evaluated for its ability to detect electrode-tissue contact and allow creation of long uniform linear lesions with a multi-electrode ablation catheter. The study consisted of 2 parts, both of which used the in vivopig thigh muscle model. In part 1, a 7 Fr. multi-electrode catheter was held in 3 electrode-tissue contact conditions: (1) non-contact; (2) light contact with a 30g downward force; and (3) tight contact with a 90g downward force. Impedances were measured in unipolar, modified unipolar and bipolar configurations using a source with frequencies from 100Hz to 500kHz. Compared with non-contact, the impedance increased 35 +/- 22 % with 30g contact pressure and 68 +/- 40% when the contact pressure was increased to 90g across the range of frequencies studied. In part 2, the same catheter was held against the tissue with different forces. Pre-ablation impedance was measured using a 10kHz current. Phased radiofrequency energy was applied to the 5 electrodes simultaneously using 10W power at each electrode for 120s. A total of 32 linear lesions were created. The lesion dimensions correlated with pre-ablation impedance. A unipolar impedance > or = 190 Omega indicates 95% possibility to create a uniform linear lesion of at least 3mm depth with our ablation system. We conclude that pre-ablation impedance may be a useful indicator for predicting electrode-tissue contact and the ability to create a continuous and transmural linear lesion with a multi-electrode catheter.

Analysis of Variance↗
PubMed2000

Experimental corneal endotheliitis in rabbit.

PURPOSE: Corneal endotheliitis may cause permanent visual loss due to endothelial decompensation. The pathogenesis underlying this distinct clinical entity is not known. In the current study, a rabbit herpetic corneal endotheliitis model was made of induced anterior chamber-associated immune deviation (ACAID). METHODS: One group of rabbits received left-eye intracameral inoculation of UV-inactivated herpes simplex virus (HSV)-1 (strain McKrae). The second group received cell medium in the same manner as the first group. The third group subcutaneously received the same inoculum as the first group. Seven days later, all right eyes were intracamerally infected with 2.5 x 10(4) plaque-forming units of infectious HSV-1. Eyes were evaluated by slit lamp examination. Two weeks after infection, rabbits were killed, and right eyes were examined by immunohistochemical staining and electron microscopy. Aqueous humor was detected for HSV-1 DNA and antibody. RESULTS: Nonspecific inflammation occurred in the anterior segments of the eyes from the second and third groups. In contrast, at 14 days after infection, the first group of rabbits showed a specific pattern of inflammation that greatly resembled clinical features of corneal endotheliitis. Viral antigen was detected only in the endothelial layer. Electron microscopy revealed enlarged intercellular gaps and infiltration of inflammatory cells that are characteristic of endothelial defects. HSV-1 DNA was detected at a significantly higher number in the aqueous humor aspirates from endotheliitis rabbits. In addition, ACAID was shown to be induced in the rabbits with corneal endotheliitis. CONCLUSIONS: HSV-1 infection can induce corneal endotheliitis and ACAID may play the pivotal role in this entity.

Animals↗
PubMed2000

Asymmetric synthesis of 2,3-methanoleucine stereoisomers from common intermediates.

2,3-Methanoamino acids are useful probes for studying the bioactive conformation of peptides and for investigating the effect of local conformational constraints on the activity of peptidomimetics. We synthesized all four stereoisomers of Cbz-protected 2, 3-methanoleucine for incorporation into peptidomimetic inhibitors of calpain. While the synthesis of 2,3-methanoamino acids has been previously reported, our procedure offers a versatile route in which the pair of diastereomers of each geometric isomer was synthesized from a common intermediate.

Amino Acids↗
PubMed2000

[The modification of combined subperiosteal facelift].

OBJECTIVE: To reposit all the elements of the aging midface more adequately. METHODS: We have performed combined facelift on 100 patients using extended subperiosteal dissection or sub-SMAS and subcutaneous dissection. In particular, the zygomatic arch subperiosteal dissect releases the attachment of the zygomatic ligament. RESULTS: In this group of 100 patients, postoperative follow-up showed that this technique can restore the initiate anatomical relationship of multiple tissue layers of the face, provides the patient with both an excellent nasolabial fold and jawline contour without damage of the frontal branch of the facial nerve. CONCLUSION: This technique is most suitable for the patients about 40 years old.

Adult↗
PubMed2000

Fusion of low-fusing porcelain to Ti-75 alloy: an experimental study.

OBJECTIVE: To study the stomatological feasibility of low-fusing porcelain fused to Ti-75 alloy. METHODS: Electroprobemicroanalysis (EPMA) and shear test were used to observe interface state and bonding strength of porcelaintitanium. RESULTS: Shear bond strengths of low-fusing porcelain with Ti-75 alloy and conventional porcelain each fused to metal (NC-VMK68) were 47.38 +/- 7.95 MPa and 48.50 +/- 7.60 MPa, respectively. There was no significant difference between the shear bonding strength of low-fusing porcelain with Ti-75 and that of conventional porcelain fused to metal (PFM) (P > 0.05). EPMA showed that Ti-75 alloy and low-fusing porcelain bound tightly, had no fissure, and that low-fusing porcelain had good infiltration to Ti-75. It was shown that Ti spread from Ti-75 basal body into porcelain, and elements such as Si-Sn spread from porcelain to Ti-75. CONCLUSION: Ti-75 alloy can be used stomatologically, as a porcelain alloy.

Biocompatible Materials↗
PubMed2000

[Diagnosis and management of Mycoplasma pneumonia with cold agglutinin disease].

OBJECTIVE: To study the Mycoplasma pneumonia (MP) with cold agglutinin disease (CAD) and inquire into its diagnosis and treatment. METHODS: 3 report of cases and literature were reviewed. RESULTS: Accompanying with hemolysis and microcirculatory retardation, 3 patients with acute respiratory infection were finally diagnosed MP with CAD. Antimicrobial therapy and plasmapheresis showed favorable effect. CONCLUSIONS: MP patients would be highly suspected to be associated with CAD, if accompanying with hemolysis and microcirculatory retardation. Laboratory examinations are helpful for diagnosis. On the basis of combined therapy, plasmapheresis is effective.

Adult↗
PubMed2000

Synergistic effects of clinically achievable concentrations of 12-O-tetradecanoylphorbol-13-acetate in combination with all-trans retinoic acid, 1alpha,25-dihydroxyvitamin D3, and sodium butyrate on differentiation in HL-60 cells.

Our recent studies demonstrated that 12-O-tetradecanoylphorbol-13-acetate (TPA) has pharmacological activity for the treatment of acute myelocytic leukemia patients. In the present study, we investigated the potential synergistic effect of all-trans retinoic acid (RA), 1alpha,25-dihydroxyvitamin D3 (VD3), and sodium butyrate (NaB) on TPA-induced differentiation in HL-60 human promyelocytic leukemia cells. The cells were treated once with these agents for 48 h or treated every 24 h for 96 h. Treatment of HL-60 cells once with TPA, RA, VD3, or NaB for 48 h resulted in concentration-dependent growth inhibition and cell differentiation. At clinically achievable concentrations, TPA (0.16 nM) increased the number of adherent cells and RA (0.1-1 microM) increased the number of nitroblue tetrazolium (NBT)-positive cells. The combinations of TPA (0.16 nM) with RA (0.1-1 microM), VD3 (1 nM), or NaB (100 microM) for 48 h synergistically increased differentiation as measured by the formation of adherent cells (P < or = 0.01). Moreover, cells treated with various combinations of low concentrations of TPA, RA, VD3, and NaB every 24 h for 96 h resulted in a further decrease in cell growth and an increase in differentiation. At clinically achievable concentrations, the strongest stimulation of differentiation was achieved in cells treated with a "cocktail" that combined TPA, RA, VD3, and NaB. The synergistic effect of combinations of TPA with RA or NaB at clinically effective concentrations on HL-60 cell differentiation suggests that the combination of these agents may improve the therapeutic efficacy of TPA for the treatment of acute promyelocytic leukemia (APL) patients. A differentiation "cocktail" that combines TPA, RA, VD3, and NaB may provide an even more effective strategy for improving the therapeutic efficacy of TPA and RA.

Anesthetics, Intravenous↗
PubMed2000

[Tolerance of various geographic populations of brown planthopper to adverse environmental stresses].

The populations of brown planthopper(BPH), Nilaparvata lugens, were collected from Zhejiang, Guangxi and Yunnan provinces to study their tolerance to various adverse environmental stresses. The results indicated that all of these three populations could adapt to the rice variety IR26 bearing resistant gene 1 (Bph1), and Guangxi and Yunnan populations could successfully infest rice varieties ASD7 bearing bph2 and Rathu Heenati bearing Bph3, implying that these two populations had a higher adaptability to resistant rice varieties. The significantly negative relationship between female brachypterous rate and nymphal density in Zhejiang population showed a lower tolerance to high nymphal density of Zhejiang population than that of Guangxi and Yunnan populations. A higher resistance to high temperature and a lower tolerance to starvation were obviously found in Guangxi and Yunnan populations. The resistance to insecticide (Omethoate) of Zhejiang population was little higher than that of Guangxi population. It was suggested that the tolerance of different geographic populations of BPH to various adverse environmental stresses be closely related to their habitat characteristics.

Animals↗
PubMed2000

[NO emission from winter wheat fields of rice-wheat rotation ecosystem in southeast China].

Measurements of NO emission from the winter wheat field of rice-wheat rotation ecosystem in southeast China during the whole period of wheat growth show that a higher NO emission was observed in spring than in autumn, and almost no emission in winter could be detected. Temperature was the most important factor determining the seasonal variation pattern of NO emission. Although the N fertilization might enlarge NO emission by a factor of 5-7, it could not modify the seasonal variation pattern. During the period of relatively weak plant activity, the diurnal variation pattern, with the maximum emission at 9:00-14:00, was determined by temperature. When plants luxuriated, however, the competition of NH4+ by plant uptake and by microbial nitrification led to a night-peak variation pattern, in which, the maximum diurnal emission usually occurred during 18:00 and 4:00 of next day, and the minimum at 8:00-16:00.

China↗
PubMed2000

[Hunger tolerance of Microvelia horvathi hibernating generation].

The experimental results showed that the hunger tolerance (HT) of different wing forms Microvelia horvathi adults had significant difference at 14-32 degrees C, and decreased with increasing temperature, which was 32.10 and 29.58 days at 14 degrees C, and 9.46 and 7.82 days at 32 degrees C, respectively for apterous and pterygote adults. The HT of apterous adults was higher than that of pterygote ones, and females was higher than males with the same wing form. The lower the temperature, the bigger the difference. The HT of M. horvathi adults differed obviously with densities. 1 female 1 male per bottle had a higher HT than 5 females 5 males per bottle and 10 females 10 males per bottle, while no difference was found between two latter densities. The HT of the 1st instar nymphs of M. horvathi had an obvious difference at different temperatures, which was significantly higher at 14 and 20 degrees C than at 26 and 32 degrees C.

Animals↗