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Biomedical subjects

D Xiao

Publications and source records attributed to D Xiao.

At least 37 records · Page 2Linked to original sources
PubMed2001

[Analysis on landscape ecology literatures in China during recent ten years].

Landscape ecology has achieved great progress since its introduction to China in early 1980s. Based on 619 collections of literatures and 14 collections of books, this paper has all the literatures and books classified, arranged in order and counted on different special subject. According to the results of classified statistics, the authors discuss and analyze how landscape ecology research was going in China during 1990s. Moreover, this paper can also provide scientific basis for those who want to grasp and keep abreast of current focus and trend of landscape ecology in China.

China↗
PubMed2000

Identification of the interferon-inducible double-stranded RNA-dependent protein kinase as a regulator of cellular response to bulky adducts.

The double-stranded RNA-dependent protein kinase PKR plays a central role in IFN-mediated antiviral response. The ability of PKR mutants to transform rodent fibroblasts led to the hypothesis that PKR acts as a tumor suppressor. Recent studies have identified an expanding network of PKR signaling partners, including signal transducers and activators of transcription 1 (STAT1), p53, and IkappaB-kinase. Here we demonstrate that PKR is involved in the cellular response to genotoxic stress. PKR-deficient mouse-embryonic fibroblasts (PKR-/-) are hypersensitive to bulky adduct DNA damage caused by cisplatin, melphalan, and UV radiation but not to other DNA-damaging agents such as Adriamycin. PKR-deficient cells are highly susceptible to cisplatin-induced apoptosis. They demonstrate retarded cisplatin adduct removal kinetics. Most strikingly, PKR localizes to the nucleus rapidly upon cisplatin treatment. Restoration of PKR in PKR-/- cells results in resistance to cisplatin and enhanced cell capacity to remove cisplatin DNA adducts. We conclude that PKR has a function in the regulation of cellular response to bulky adduct-inducing agents, possibly by modulating DNA repair mechanisms.

Animals↗
PubMed2000

Multichannel mode-filtered light detection based on an optical fiber for small-volume chemical analysis

A novel mode-filtered light detection method is described in which an unjacketed optical fiber is inserted into a transparent capillary tube and three or more detection channels are set on the capillary side for different distances from the port of the fiber. This new method is the basis of synchronization of separation and analysis, with which a modern multidimensional analysis apparatus will be constructed. For samples of different concentration, the more close to the laser incidence port of the fiber the detector has been set up, the greater the change of the intensity profile of mode-filtered light (deltaI(F)) that is obtained. Vice versa, if a parameter alpha = I0/In is established and, instead of a mode-filtered light signal, the reversed alteration trend of deltaalpha is found in comparison with the alteration trend of deltaI(F), the reason is that the background rapidly lowers with the increasing distance to the laser incidence port of the fiber; moreover, the mode-filtered light signal decreases slowly with it. With the present method and apparatus, glucose and glycerol have been determined, with good reproducibility and stability and a small sample volume. Furthermore, a real sample of glucose injection is measured for a detection volume of 5 microL, and an acceptable result is observed.

Journal Article↗
PubMed2000

4-[3-(5,6,7,8-Tetrahydro-5,5,8,8-tetramethyl-2-naphthalenyl)phenyl]benzoic acid and heterocyclic-bridged analogues are novel retinoic acid receptor subtype and retinoid X receptor alpha agonists.

Aromatic retinoids having a meta-substituted aromatic ring bridge, such as 4-[3-(5,6,7,8-tetrahydro-5,5,8,8-tetramethyl-2-naphthalenyl)phenyl]benzo ic acid and its 3,5-diaryl-substituted 4,5-dihydroisoxazole analogue, function as retinoid receptor panagonists by activating both retinoic acid and retinoid X receptors to induce gene transcription, and thereby provide novel scaffolds for retinoid drug development. Both classes of these ligand-inducible transcription factors are involved in mediating the inhibitory effects of retinoids on cancer cell growth.

Benzoates↗
PubMed2000

Unique anti-activator protein-1 activity of retinoic acid receptor beta.

The anticancer effects of retinoids are mainly mediated by two classes of nuclear receptors, the retinoic acid receptors (RARs) and retinoid X receptors (RXRs), which are encoded by three distinct genes (alpha, beta, and gamma). Recent studies have demonstrated that RARbeta plays a critical role in mediating anticancer effects of retinoids. However, how RARbeta exerts its potent anticancer effects remains largely unknown. In this study, we investigated anti-Activator Protein-1 (AP-1) activity of RARbeta. In a transient transfection assay, all three RAR subtypes, RARalpha, RARbeta, and RARgamma, could effectively inhibit phorbol ester 12-O-tetradecanoylphorbol-13-acetate-induced AP-1 activity and the activity of oncogenes c-Jun and c-Fos on AP-1 containing reporter genes in the presence of retinoic acid (RA). However, RARbeta showed a strong RA-independent inhibition of AP-1 activity, whereas inhibition of AP-1 activity by RARalpha and RARgamma was RA dependent. By using several hybrid receptors that contain either the COOH-terminal portion or the NH2-terminal portion of RARbeta, we demonstrated that the NH2-terminal portion of RARbeta, the A/B domain, was mainly responsible for the RA-independent inhibition of AP-1 activity. This activity was not attributable to constitutive AF-1 activity of RARbeta, because it did not activate several RA response element-containing reporter genes. In addition, inhibition of histone deacetylase activity by trichostatin A did not overcome the inhibitory effect of RARbeta. In cancer cells, stable transfection of RARbeta exhibited strong inhibition of AP-1 activity, even in the absence of RA. Moreover, expression of endogenous AP-1-responsive gene collagenase I was strongly repressed in cancer cells stably transfected with RARbeta. In studying the antitransforming activity of RARbeta, we observed that the growth of breast cancer MDA-MB231 cells in soft agar was significantly repressed in a RA-independent manner when cells were stably transfected with RARbeta but not RARalpha. Together, our results demonstrate that RARbeta may exert its potent anticancer effect in part through its unique anti-AP-1 activity.

Breast Neoplasms↗
PubMed2000

Synthesis of chiral hydroxyl phospholanes from D-mannitol and their use in asymmetric catalytic reactions.

Chiral hydroxyl monophosphane 3 [(2S,3S,4S,5S)-3,4-dihydroxy-2, 5-dimethyl-1-phenylphospholane] and bisphospholanes 5a [1,2-bis[(2S, 3S,4S,5S)-3,4-dihydroxy-2,5-dimethylphospholanyl]benzene] and 5b [1, 2-bis[(2S,3S,4S,5S)-2,5-diethyl-3,4-dihydroxyphospholanyl]benzene] were synthesized from readily available D-mannitol in high yields. Strategies for protection and deprotection of OH-groups in the presence of phosphines have been explored. Rate acceleration in the Baylis-Hillman reaction was observed when a hydroxyl phosphine was used as the catalyst. Rhodium complexes with chiral bisphospholanes are highly enantioselective catalysts for the asymmetric hydrogenation of various kinds of functionalized olefins such as dehydroamino acid derivatives, itaconic acid derivatives, and enamides. An interesting feature of the hydroxyl phospholane system is that hydrogenation of some substrates can be carried out in water with >99% ee and 100% conversion (e.g., itaconic acid).

Catalysis↗
PubMed2000

Determination of low-level mercury based on a renewable-drops sensing technique.

The design and characteristics of a novel drop-based fluorescence-detection technique for the determination of mercury(II) are described. The method, using a flow injection technique, is based on the renewable-drops of 3,3',5,5'-tetramethylbenzidine(TMB), which are formed at the bottom tip of a silica capillary tube connected to the end of the flow system. An excitation beam from a high-pressure Hg lamp directly illuminates the drops, the fluorescence emission is conducted to a photodiode (PD) to convert the photocurrent into a voltage signal (mV). Optimum analytical conditions for Hg(II) assays have been established. In NaAc/HAc buffer at pH 3.09 this assay has a wide linear range for Hg(II) from 8.0 x 10(-8) to 2.0 x 10(-5) mol/L with a detection limit of 2.0 x 10(-8) mol/L. The use of renewable drops allowing a fresh reaction surface for each sample is of particular value to solving the problems of irreversible reactions. Besides its high sensitivity, the method permits a simple, fast, and inexpensive measurement with only micro-quantities of reagent consumption. The technique described provides a simple and sensitive way to fabricate sensors of feasible prospects and commercial advantages.

Benzidines↗
PubMed2000

Orphan receptor COUP-TF is required for induction of retinoic acid receptor beta, growth inhibition, and apoptosis by retinoic acid in cancer cells.

Retinoic acid receptor beta (RARbeta) plays a critical role in mediating the anticancer effects of retinoids. Expression of RARbeta is highly induced by retinoic acid (RA) through a RA response element (betaRARE) that is activated by heterodimers of RARs and retinoid X receptors (RXRs). However, RARbeta induction is often lost in cancer cells despite expression of RARs and RXRs. In this study, we provide evidence that orphan receptor COUP-TF is required for induction of RARbeta expression, growth inhibition, and apoptosis by RA in cancer cells. Expression of COUP-TF correlates with RARbeta induction in a variety of cancer cell lines. In addition, stable expression of COUP-TF in COUP-TF-negative cancer cells restores induction of RARbeta expression, growth inhibition, and apoptosis by RA, whereas inhibition of COUP-TF by expression of COUP-TF antisense RNA represses the RA effects. In a transient transfection assay, COUP-TF strongly induced transcriptional activity of the RARbeta promoter in a RA- and RARalpha-dependent manner. By mutation analysis, we demonstrate that the effect of COUP-TF requires its binding to a DR-8 element present in the RARbeta promoter. The binding of COUP-TF to the DR-8 element synergistically increases the RA-dependent RARalpha transactivation function by enhancing the interaction of RARalpha with its coactivator CREB binding protein. These results demonstrate that COUP-TF, by serving as an accessory protein for RARalpha to induce RARbeta expression, plays a critical role in regulating the anticancer activities of retinoids.

Animals↗
PubMed2000

Processing of kinetically defined boundaries in areas V1 and V2 of the macaque monkey.

We recorded responses in 107 cells in the primary visual area V1 and 113 cells in the extrastriate visual area V2 while presenting a kinetically defined edge or a luminance contrast edge. Cells meeting statistical criteria for responsiveness and orientation selectivity were classified as selective for the orientation of the kinetic edge if the preferred orientation for a kinetic boundary stimulus remained essentially the same even when the directions of the two motion components defining that boundary were changed by 90 degrees. In area V2, 13 of the 113 cells met all three requirements, whereas in V1, only 4 cells met the criteria of 107 that were tested, and even these demonstrated relatively weak selectivity. Correlation analysis showed that V1 and V2 populations differed greatly (P < 1.0 x 10(-6), Student's t-test) in their selectively for specific orientations of kinetic edge stimuli. Neurons in V2 that were selective for the orientation of a kinetic boundary were further distinguished from their counterparts in V1 in displaying a strong, sharply tuned response to a luminance edge of the same orientation. We concluded that selectivity for the orientation of kinetically defined boundaries first emerges in area V2 rather than in primary visual cortex. An analysis of response onset latencies in V2 revealed that cells selective for the orientation of the motion-defined boundary responded about 40 ms more slowly, on average, to the kinetic edge stimulus than to a luminance edge. In nonselective cells, that is, those presumably responding only to the local motion in the stimulus, this difference was only about 20 ms. Response latencies for the luminance edge were indistinguishable in KE-selective and -nonselective neurons. We infer that while responses to luminance edges or local motion are indigenous to V2, KE-selective responses may involve feedback entering the ventral stream at a point downstream with respect to V2.

Analysis of Variance↗
PubMed2000

Subtalar pronation--relationship to the medial longitudinal arch loading in the normal foot.

A three-dimensional biomechanical model was used to calculate the mechanical response of the foot to a load of 683 Newtons with the subtalar joint in the neutral position, at five degrees of pronation, and at five degrees of supination. Pronation causes the forefoot to evert, increasing the load borne by the first metatarsal. This results in a 47% increase in the moment about the talonavicular joint and a 58% increase in the moment about the navicular-medial cuneiform joint. Subtalar joint supination causes the forefoot to invert and results in a 55% increase in the moment about the calcaneal-cuboid joint.

Biomechanical Phenomena↗
PubMed2000

[The relationship of vasoactive intestinal peptide, other substances and the changes of nocturnal blood pressure in patients with obstructive sleep apnea syndrome].

OBJECTIVE: To determine the difference of plasma VIP, NO and ET concentrations in awake and in different sleep periods and the relationship between VIP, NO and ET values and the changes in nocturnal blood pressure in patients with obstructive sleep apnea syndrome(OSAS). METHODS: Retaining manometric tube in radial artery and polysomnography(PSG) were done synchronously in 12 patients with OSAS whom was diagnosed by whole-night PSG. Blood specimens were collected before sleep, during NREM sleep and REM sleep and the next morning to detect the concentrations of VIP and ET by radioimmunoassay(RIA) and NO by nitrate reductase method. RESULTS: (1) Plasma NO values were significantly decreased in the morning than those before sleep (P = 0.014). There was no remarkable changes of VIP and ET values in different testing periods. (2) Plasma NO and ET values in the morning were correlated with hypoxia at night, but not with AHI (P > 0.05). (3) Plasma VIP values were significantly correlated with the baseline of SBP (r = 0.654, P < 0.05) and DBP (r = 0.706, P < 0.01) in NREM sleep and that of DBP (r = 0.613, P < 0.05) in REM sleep. There was no significant correlation between BP and plasma NO and ET values in different times. CONCLUSIONS: Endothelial dysfunction associated with NO reduction might be present and VIP might be involved in regulating BP changes in patients with OSAS.

Adult↗
PubMed2000

[Study on the volatile oil of Nardostachys chinensis].

The volatile oil of Nardostachys chinensis Batal has been studied by GC-MS, and 21 compounds have been isolated and identified. The total content of the components are 88.51%. Major compounds have been identified as Calarene (29.44%). delta 1(10)-Aristolenone-2 (16.57%) and Jatamansinol (8.80%).

Gas Chromatography-Mass Spectrometry↗
PubMed2000

[Spectroscopic properties of 7-hydroxyquinoline in polymeric matrices].

In this paper, the absorption and fluorescence spectra of 7-Hydroxyquinoline (7HQ) in the copolymer of methyl methacrylate (MMA) and methacrylic acid (MAA) monomers were observed. The influence of different matrices on the species of 7HQ and the excited state proton transfer effect were investigated. The results showed that, as the number of carboxylic group in the matrix was increased, the relative contents of different species of 7HQ should be changed and the excited state proton transfer effect of 7HQ was enhanced.

Adsorption↗
PubMed1999

Synthesis of a novel chiral binaphthyl phospholane and its application in the highly enantioselective hydrogenation of enamides.

[formula: see text] A new chiral phosphine, (R,R)-1,2-bis[(R)-4,5-dihydro-3H-dinaphtho[2,1- c:1',2'-e]phosphepino]benzene [abbreviated as (R,R)-binaphane] was prepared on the basis of a practical route from a readily accessible enantiomerically pure binaphthanol. This ligand possesses both binaphthyl chirality and phospholane functionality. Excellent enantioselectivities (95-99.6% ee) have been observed in hydrogenation of an isomeric mixture of (E)- and (Z)-beta-substituted-alpha-arylenamides by using a Rh-binaphane catalyst. These enantioselectivities are the highest reported to date for this transformation.

Amides↗
PubMed1999

The first total synthesis of (-)-tamandarin A.

[formula: see text] Tamandarin A (1), a newly isolated natural product similar in structure to didemnin B (2), was shown to be somewhat more active in vitro than 2 against pancreatic carcinoma with an ED50 value 1.5 to 2 ng/mL. We report here the first total synthesis of 1. The key steps include a practical stereoselective synthesis of the Hiv-isostatine unit, high-yielding linear precursor formation, a successful macrocyclization, and coupling of the macrocycle with the side chain to afford tamandarin A (1).

Antineoplastic Agents↗