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Biomedical subjects

X Chen

Publications and source records attributed to X Chen.

At least 847 records · Page 47Linked to original sources
PubMed1999

[Intraobserver reproducibility study of parameters for measurement of position and height of ciliary process by ultrasound biomicroscopy].

OBJECTIVE: To search for suitable measurement parameters for the study of the position and height of cilliary process by ultrasound biomicroscopy (UBM), to test the intraobserver measurement reproducibility of the new parameters we designed as well as the old ones. METHODS: Five parameters: TCPD, A angle, B angle, theta 4 angle and T value, are measured in 21 pieces of UBM image by one observer on five separate occasions. The intraobserver reproducibility is assessed by calculating the coefficient of variation (CV) and the difference among the parameters is tested by grouped T-test. RESULTS: Among 21 images, parameter A angle and T value have no image with CV > 10%, TCPD and B angle have 2 respectively and theta 4 angle has 5. As to average variation level, A angle is lower than TCPD, theta 4 angle is higher than TCPD, both differences of which are significant, and B angle and TCPD are about the same level, the difference between them is not significant. CONCLUSION: Among all the parameters reflecting the position of ciliary process in UBM image, A angle has the best intraobserver reliability, TCPD and B angle are less reliable, theta 4 angle has the worst reliability. The parameter reflecting the height of ciliary process, T value has very good intraobserver reliability.

Adolescent↗
PubMed1999

Phase-1 studies of malariotherapy for HIV infecton.

OBJECTIVE: To determine whether malariotherapy (an old therapy for treatment of neurosyphilis) improves some clinical and laboratory parameters of HIV-positive patients without iatrogenic complications. METHODS: Total 8 asymptomatic HIV-1 positive subjects whose CD4 cell counts were over 250 x 10(6) cells/L were selected for the phase-1 studies of malariotherapy and were intravenously injected Plasmodia vivax to induce artificial malaria. Malaria was terminated with chloroquine after 10 to approximately 20 malarial fever episodes. Cell-bound CD4 levels were measured by APAAP (a solid-phase enzyme essay) and levels of neopterin (NPT), beta-2-microglobulin (B2M), soluble tumor necrosis factor receptor-2 (sTNF-RII), interleukin-2 (IL-2) and HIV P24 antigen were measured by ELISA. Patients were followed up to 24 to approximately 30 months. RESULTS: CD4 levels increased in 5, NPT decreased in 7 of 8 patients; IL-2 increased in 5 of 6 patients after malariotherapy. The total trends of B2M and sTNF-RII basically remained stable. HIV P24 antigen remained undetectable in 6, remained detectably low level in 1 and experienced increase in 1 of 8 patients after malariotherapy. No any severe complications occurred in all 8 patients. CONCLUSIONS: The results indicate that malariotherapy basically is safe for HIV infection and it seems that the therapy improves some immunological parameters of HIV patients.

Adult↗
PubMed1999

Inhibition of farnesyl protein transferase and P21ras memebrane association by d-limonene in human pancreas tumor cells in vitro.

The monoterpene d-limonene inhibit the plasma-membrane associated P21ras expression and the post-translational isoprenylation of P21ras, a mechanism that may contribute to its efficacy in the chemoprevention and therapy of chemically induced rodent cancers and some human solid tumor cells. In the present study, the relative abilities of d-limonene to inhibit membrane associated P21ras expression in pancreas tumor cell (PaCa) was carried out with Western blotting, and the inhibition of farnesyl protein transferase (FTPase) activity during the Ras protein isoprenylation and cell proliferation were determined. Concomitantly, the effects of d-limonene on P21ras localization by immunohistochemistry and H-ras oncogene expression in PaCa tumor cell line by Northern blotting were observed. The results showed that d-limonene inhibited FPTase activity, thus to reduce P21H-ras isoprenylation. d-limonene could decrease P21ras membrane association and increase cytosolic accumulation of P21ras. This phenomenon was also noted when d-limonene-treated PaCa cells were stained immunohistochemically with anti-P21ras antibody. It is suggested that the inhibition of FPTase activity was closely related with the inhibiton of P21ras membrane association and the alteration of P21ras localization. Inhibition of farnesylation of P21ras altered their intracellular localization and, hence, disrupted their biological activity, but no relationship with H-ras oncogene expression was found.

Alkyl and Aryl Transferases↗
PubMed1999

[The manufacture and clinical use of the auto-sialographic instrument by remote controlling]

OBJECTIVE:The purpose of this article is to realize the auto-control of the injection of radiographic drugs in terms of the principle in remote controlling.METHODS:30 cases of sialaden diseases was studied using the auto sialographic instrument by remote controlling,compared to 67 cases studied using sialography by hand-controlling.RESULTS:The auto-sialographic instrument by remote controlling realize the telecontrol of the injection of the sialographic drugs and auto-injection,simplify the working procedure,and prevent medical staffs from X-ray radiation at work.CONCLUSION:The auto sialographic instrument by remote controlling can not only bring much convenience to medical staffs,but also improve the conformation to clinical diagnosis.

Journal Article↗
PubMed1999

[Multi-channel probing for emission spectra of metals stimulated by LD pumping laser].

Emission spectra of several metals stimulated at a tiny spot by an YAG laser pumped by a LD were obtained analyzed by means of a CCD optical multi-channel analyzer. The emission spectra collected and analyzed by multi-channel with high signal to noise ratio and high dynamic range were obtained, and the wavelengths accord well with the standard spectra of these metals. Application of this method was discussed.

English Abstract↗
PubMed1999

[The 1. 54 microm laser and upconversion luminescence of YELPP noncrystalline induced by 969 nm LD laser].

In this paper, the absorption of Er3+, Yb3+ penta-phosphate noncrystalline (YELPP) was measured and the basic spectral parameters were calculated. Adopting the longitudinal-pump method with a domestic diode laser (LD), we achieved CW 1.5 microm chipped laser in China for the first time. The power of 1.5 microm laser was quite stable. The target of 1.5 microm laser reached the international level of early 1990s' in this field. In addition, the up-conversion luminescence was measured under the condition that 1.5 microm laser was either oscillating or not. The relationship between 1.5 microm chipped laser and up-conversion luminescence was analyzed initially.

English Abstract↗
PubMed1999

[Ultra trace determination of platinum, palladium, gold and rhodium in minerals].

Our work studied the minerals dissolved in aqua regia. The trace Pt(II), Pd(II) Au (III) and Rh(I) complexes were loaded by the mixed carbon powder which carried diphenyl thiourea when aqua regia or hydrochloric acid media as well as stannous chloride were present. We added some carbon powder in ashen loader and determined the elements with atomic emission spectrometry. The determination sensitivity counted with 10 grams of samples is 1 x 10(-9). The RSD for 0.05 x 10(-6) standard Pt, Pd, Au and Rh solutions are 6.0%, 5.1%, 8.5% and 11.4%, respectively. The method is simple and operation is easy. The results satisfy our requirement.

English Abstract↗
PubMed1999

[Direct upconversion sensitization luminescence of Tm(0.1) Yb (10.9) oxyfluoride vitroceramincs].

This paper studied the direct upconversion sensitization luminescence of Tm (0.1) Yb (10.9) oxyfluoride vitroceramics pumped by 966 nm diode laser for the first time. We found that there are both strong 477 nm three-photon upconversion fluorescence of 1G4 --> 3H6 transition and 799.5 nm two-photon upconversion fluorescence of 3H4 --> 3H6 transition as well as weak upconversion fluorescence of 1D2 --> 3H6, 1Dz --> 3F4,1G4 --> 3F4 and 3F3 --> 3H6 transitions at 361 nm, 449.5 nm, 647.0 nm and (679.5, 698.5 nm), respectively.

English Abstract↗
PubMed1999

[Transmission grating spectrograph for soft X-ray spectrum measurements with a pre-optics].

A novel diffraction spectroscopic instrument consisting of a large area transmission grating and a grazing-incidence pre-optics comprising of a toroidal mirror, a slit and a cylindrical mirror has been implemented. A nearly perfect stigmatism and a medium spectral resolution are due to the separation of the focusing and dispersing function. The experimental results show that it is possible to construct large area transmission grating spectrograph with high collecting efficiency and good spatial resolution.

English Abstract↗
PubMed1999

[Study on properties of fluorescence and room temperature phosphorescence of 2-bromomethyl naphthalene].

The properties of fluorescence and room temperature phosphorescense (RTP) of 2-Bromomethyl naphthalene (2-BrMN)were studied. The results show that the wavelength for maximum fluorescence of 2-BrMN is lambda(ex/lambda(em) = 274/334 nm. The fluorescence intersity is proportional to the concentration of 2BrMN in the range of 1.0 x 10(-6) - 1.2 x 10(-4) mol x L(-1), and the detection limit is 4.7 x 10(-8) mol x L(-1). The RTP signal of 2-BrMN was induced by beta-cyclodextrin (beta-(CD) in the presence of dibromopropane (DBP) acting as a heavy atom perturbation. The RTP intensity is linear for 2-BrMN/beta-CD/DBP systems of 2-BrMN concentration in the range of 1.0 x 10(-5) - 1.2 x 10(-4) mol x L(-1) (lambda(ex)/lambda(em) = 271/493,521 nm), and the detection limit is 2.7 x 10(-6) mol x L(-1).

English Abstract↗
PubMed1998

Cloning of a brain N-methyl-D-aspartate- and D, L-epsilon-2-amino-4-propyl-5-phosphono-3-pentanoic acid (CGP 39653)-binding protein.

A complex of four proteins isolated from neuronal membranes has ligand binding sites for N-methyl-d-aspartate (NMDA) receptor agonists and antagonists and forms NMDA-activated ion channels upon reconstitution into lipid membranes. In this study, the cDNA of a subunit of this complex containing binding sites for the competitive antagonists of NMDA receptors was cloned. The cDNA clone coded for a protein of 719 amino acids (78.9 kDa). The expressed protein had binding activity for the agonists l-[3H]glutamate and [3H]glycine, the antagonist (+/-)-[3H]-(E)-2-amino-4-propyl-5-phosphonopentanoic acid ([3H]CGP 39653), but not the ion channel inhibitors. The cloned cDNA had no homology to other cloned cDNAs. Northern blot analyses indicated high expression of an 3.8 kb poly(A+) RNA in brain, but not in other tissues. These findings indicate that proteins that have recognition sites for NMDA receptor activators and inhibitors and that differ from the well-characterized NMDA receptor proteins NR1-3 are expressed in mammalian brain.

2-Amino-5-phosphonovalerate↗
PubMed1998

Potent piperazine hydroxyethylamine HIV protease inhibitors containing novel P3 ligands.

The 2-isopropyl thiazolyl group is a highly optimized P3 ligand for C2 symmetry-based HIV protease inhibitors, as exemplified in the drug ritonavir. Here we report that incorporation of this P3 ligand into a piperazine hydroxyethylamine series also yielded novel, highly potent inhibitors. In tissue culture assays, the presence of human serum was less deleterious to the activity of these inhibitors than to that of ritonavir. Furthermore, potent activity against ritonavir resistant HIV was observed.

Animals↗
PubMed1998

A novel end-to-end binding of two netropsins to the DNA decamers d(CCCCCIIIII)2, d(CCCBr5CCIIIII)2and d(CBr5CCCCIIIII)2.

Netropsin is bound to the DNA decamer d(CCCCCIIIII)2, the C-4 bromo derivative d(CCCBr5CCIIIII)2and the C-2 bromo derivative d(CBr5CCCCIIIII)2in a novel 2:1 mode. Complexes of the native decamer and the C-4 bromo derivative are isomorphous, space group P1, unit cell dimensions a = 32.56 A (32.66), b = 32.59 A (32.77), c = 37.64 A (37.71), alpha = 86.30 degrees (86.01 degrees), beta = 84.50 degrees (84.37 degrees), gamma = 68.58 degrees (68.90 degrees) with two independent molecules (A and B) in the asymmetric unit (values in parentheses are for the derivative). The C-2 bromo derivative is hexagonal P61, unit cell dimensions a = b = 32.13 A, c = 143.92, gamma = 120 degrees with one molecule in the asymmetric unit. The structures were solved by the molecular replacement method. The novelty of the structures is that there are two netropsins bound end-to-end in the minor groove of each B-DNA decamer which has nearly a complete turn. The netropsins are held by hydrogen bonding interactions to the base atoms and by sandwiching van der Waal's interactions from the sugar-phosphate backbones of the double helix similar to every other drug.DNA complex. Each netropsin molecule spans approximately 5 bp. The netropsins refined with their guanidinium heads facing each other at the center, although an orientational disorder for the netropsins cannot be excluded. The amidinium ends stretch out toward the junctions and bind to the adjacent duplexes in the columns of stacked symmetry-related complexes. Both cationic ends of netropsin are bridged by water molecules in one of the independent molecules (molecule A) of the triclinic structures and also the hexagonal structure to form pseudo-continuous drug.decamer helices.

Bromine↗
PubMed1998

[Homocysteine-induced neural tube defects in chick embryos and protection of folic acid].

To reveal whether homocysteine(HCY) will be able to induce neural tube defects (NTDs) and possible teratogenic mechanisms, and identify the interventional effects of folic acid and vitamin B12 on HCY-induced NTDs, 1274 chick embryos treated with L. D-HCY (0-16 mumol/embryo) were detected by the methods of teratogenic trial, scanning electron microscopy(SEM), Nile blue sulfate vital staining, TdT-mediated dUTP nick end labeling(TUNEL) methylgreen-pyronine special staining for showing nucleic acid, and interventional assay of folic acid and VB12 in different developmental stage. Results showed that HCY could induce teratogenesis in chick neurulation and organogenetic period, in dose-response relationship (P < 0.0001). The main forms of NTDs were exencephaly, cranioschisis and spina bifida. It has been first found that HCY could target excessive apoptosis of cells of embryonic nervous system, which consists with the sites of embryos developing NTDs. HCY could inhibit chick yolk sac vessel formation and blood circulation, and damage amniotic membrane. Under SEM it was observed that HCY resulted in abnormal ultrastructures, for example cavernous damages, atrophied microvilli and so on. After the injection of 5 micrograms/embryo folic acid, the teratogenicity of HCY (8 mumol/embryo) was significantly antagonized, the occurrence rate of NTDs was down from 43.5% to 0(P < 0.05). However, vitamin B12 (1 microgram/embryo) did not obviously attenuate the teratogenicity of HCY in day 6 chick embryos. These data prove that HCY per se causes dymorphogenesis of the neural tube. Apoptosis may play an important role in the etiopathology of NTDs. Folic acid can effectively prevent from the homocysteine-induced NTDS. Causes of homocysteine-induced NTDs may result from interaction or combination of different mechanisms.

Animals↗
PubMed1998

Tsetse thrombin inhibitor: bloodmeal-induced expression of an anticoagulant in salivary glands and gut tissue of Glossina morsitans morsitans.

The tsetse thrombin inhibitor, a potent and specific low molecular mass (3,530 Da) anticoagulant peptide, was purified previously from salivary gland extracts of Glossina morsitans morsitans (Diptera: Glossinidae). A 303-bp coding sequence corresponding to the inhibitor has now been isolated from a tsetse salivary gland cDNA library by using degenerate oligonucleotide probes. The full-length cDNA contains a 26-bp untranslated segment at its 5' end, followed by a 63-bp sequence corresponding to a putative secretory signal peptide. A 96-bp segment codes for the mature tsetse thrombin inhibitor, whose predicted molecular weight matches that of the purified native protein. Based on its lack of homology to any previously described family of molecules, the tsetse thrombin inhibitor appears to represent a unique class of naturally occurring protease inhibitors. Recombinant tsetse thrombin inhibitor expressed in Escherichia coli and the chemically synthesized peptide are both substantially less active than the purified native protein, suggesting that posttranslational modification(s) may be necessary for optimal inhibitory activity. The tsetse thrombin inhibitor gene, which is present as a single copy in the tsetse genome, is expressed at high levels in salivary glands and midguts of adult tsetse flies, suggesting a possible role for the anticoagulant in both feeding and processing of the bloodmeal.

Amino Acid Sequence↗