Biomedical subjects

X Tian

Publications and source records attributed to X Tian.

At least 37 records · Page 2Linked to original sources

PubMed2001

Vascular endothelial growth factor: acting as an autocrine growth factor for human gastric adenocarcinoma cell MGC803.

Vascular endothelial growth factor (VEGF) is known to be a highly specific mitogen for endothelial cells through two high-affinity tyrosine kinase receptors, VEGFR-1 and VEGFR-2, which are almost specifically expressed in endothelial cells. However, recent findings showed that VEGF receptors may also expressed by nonendothelial cells, especially by tumor cells. To further understand the functional expression of VEGF receptors by nonendothelial cells, our preliminary screening detected the expression of VEGFR-2 in 115 different paraffin-embedded cancer specimens including 35 cases of bladder tumor, 30 cases of breast cancer, 25 cases of intestinal cancer, and 25 cases of lung cancer with immunohistochemistry. The results showed that VEGFR-2 was widely expressed in different tumor tissues. By reverse transcription PCR, NCI-H23, NCI-H460, MGC803, MDA-MB-231, 293, and MCF7 cells were evaluated for the mRNA expression of both VEGF and VEGFR-2. The data indicated that all these tumor cell lines expressed detectable amounts of VEGF mRNA, but only 293, MCF7, and MGC803 cells coexpressed VEGFR-2. Immunoblot analysis also demonstrated the expression of VEGFR-2 at protein level. We further demonstrate that exogenous rhVEGF(165) could stimulate cell growth in MGC803, a tumor cell line derived from gastric adenocarcinoma, in a dose- and time-dependent manner. Furthermore, the antibodies against rhVEGF(165) and VEGFR-2 could block rhVEGF(165)-mediated proliferation of MGC803 cells. These unexpected results provided direct evidence that VEGF may act as an autocrine growth factor to induce the proliferation of gastric adenocarcinoma cells as well as tumor angiogenic cells, thus suggesting a promising tumor therapeutic application based upon the VEGF system.

Adenocarcinoma↗

PubMed2001

Prenylation of target GTPases contributes to signaling specificity of Ras-guanine nucleotide exchange factors.

Ras-GRF1 and Ras-GRF2 constitute a family of calmodulin-regulated guanine-nucleotide exchange factors (GEFs) that activate Ras proteins. Here we show that whereas Ras-GRF1 activated both Ha-Ras and R-Ras in cells, Ras-GRF2 activated only Ha-Ras. The inability of Ras-GRF2 to activate R-Ras was the consequence of the GTPase being post-translationally modified, since Ras-GRF2 activated unprocessed R-Ras as effectively as unprocessed Ha-Ras when assays were performed either in vivo or in vitro. Moreover, Ras-GRF2 failed to activate fully processed R-Ras in vitro. The particular C-terminal lipid attached to the GTPases played an important role in determining signaling specificity, since R-Ras became more responsive to Ras-GRF2 when it was farnesylated instead of geranylgeranylated. Similarly, Ha-Ras became less responsive to Ras-GRF2 when it was geranylgeranylated instead of farnesylated. Analysis of chimeras between Ras-GRF1 and Ras-GRF2 demonstrated that a 30-amino acid segment embedded with their catalytic domains was responsible for recognizing the presence of different lipids on Ras proteins. These results indicate that the specific lipid moiety attached to GTPases can contribute to signaling specificity of Ras-GEFs.

Amino Acid Sequence↗

PubMed2001

The development of a potential single photon emission computed tomography (SPECT) imaging agent for the corticotropin-releasing hormone receptor type.

A high-affinity radioligand for CRHR1 has been prepared that can serve as a template for the development of SPECT imaging agents. The 5-chloro-N-cyclopropylmethyl-N-(2,6-dichloro-4-iodophenyl)-2-methyl-N-propylpyrimidine-4,6-diamine (6b, Ki = 14 nM), and the corresponding 4-bromophenyl analogue (6a, Ki = 21 nM), were synthesized in four steps from compound 3.

Animals↗

PubMed2001

Enmein type diterpenoids from Isodon japonica.

Two enmein type diterpenoids, taibaijaponicains A and B, were isolated from the ethanol extract of the leaves and branches of Isodon japonica. Their structures are designated as 6beta,11alpha-dihydroxy-16alpha-methoxymethyl-6,20-epoxy-6,7-seco-ent-kaur-15-one-1,7-olide and 3beta-acetoxy-6beta,11alpha-dihydroxy-16alpha-methoxymethyl-6,20-epoxy-6,7-seco-ent-kaur-15-one-1,7-olide, respectively, on the basis of detailed spectroscopic analyses.

Diterpenes↗

PubMed2001

Triterpenoid saponins from Clematis tangutica.

Two new triterpenoid saponins, tanguticoside A and B along with seven known saponins vitalboside B, alpha-hederin, saponin PK, beta-hederin, saponin PJ3, saponin PE, and ciwujianoside A were isolated from aerial part of Clematis tangutica. By chemical and spectral evidences methods, the structures of tanguticoside A and B were elucidated as 3-O-beta-D-glucopyranosylhederagenin 28-O-alpha-L-rhamnopyranosyl-(1-->4)-beta-D-glucopyranosyl-(1-->6)-beta-D-glucopyranoside and 3-O-beta-D-glucopyranosyl-(1-->2)-beta-D-glucopyranosylhederagenin 28-O-alpha-D-rhamnopyranosyl-(1-->4)-beta-D-glucopyranosyl-(1-->6)-beta-D-glucopyranoside, respectively.

Drugs, Chinese Herbal↗

PubMed2001

Regulation of Ras signaling specificity by protein kinase C.

Ras proteins have the capacity to bind to and activate at least three families of downstream target proteins: Raf kinases, phosphatidylinositol 3 (PI 3)-kinase, and Ral-specific guanine nucleotide exchange factors (Ral-GEFs). We have previously shown that the Ras/Ral-GEF and Ras/Raf pathways oppose each other upon nerve growth factor stimulation, with the former promoting proliferation and the latter promoting cell cycle arrest. Moreover, the pathways are not activated equally. While the Ras/Raf/Erk signaling pathway is induced for hours, the Ras/Ral-GEF/Ral signaling pathway is induced for only minutes. Here we show that this preferential down-regulation of Ral signaling is mediated, at least in part, by protein kinase C (PKC). In particular, we show that PKC activation by phorbol ester treatment of cells blocks growth factor-induced Ral activation while it enhances Erk activation. Moreover, suppression of growth factor-induced PKC activation enhances and prolongs Ral activation. PKC does not influence the basal activity of the Ral-GEF designated Ral-GDS but suppresses its activation by Ras. Interestingly, Ras binding to the C-terminal Ras binding domain of Ral-GDS is not affected by PKC activity. Instead, suppression of Ral-GDS activation occurs through the region N terminal to the catalytic domain, which becomes phosphorylated in response to phorbol ester treatment of cells. These findings identify a role for PKC in determining the specificity of Ras signaling by its ability to differentially modulate Ras effector protein activation.

Animals↗

PubMed2001

Magnetic tracker calibration for an augmented reality system for therapy.

Magnetic trackers are widely used position/orientation measurement devices in interactive computer systems. These trackers output six-degree-of-freedom position and orientation of their receiver coordinates with respect to their transmitter coordinates. It is a potential solution for real-time position/orientation measurement in an augmented reality system for therapy (ART). However, an obstruction to be overcome is that a magnetic tracker is vulnerable to measurement inaccuracy caused by magnetic field distortions (including ferric and non-ferric distortions) when it is used in metallic environments. The purpose of this paper is to discuss calibration methods used to compensate distortions produced by metallic objects which are moving during the measurement procedure, but fixed with a receiver. Past work on the calibration of magnetic trackers has concentrated on static distortions, which are produced by stationary metallic objects in the environment. Compared with static distortions, in this paper a relatively dynamic situation is considered where the distortion is not constant with time. However, the location of the metallic objects is reflected in the outputs of the receiver so that the distortion can be compensated. This type of distortions, which is called 'quasi-static distortion' in this paper, is common in an ART. Compensation of quasi-static distortion is more complicated than that of static distortion and has not been mentioned in past publications. Some new compensation methods for quasi-static distortion will be introduced here. The results demonstrate that the methods are capable of significantly reducing quasi-static distortions.

Calibration↗

PubMed2001

Variations in cardiac diastolic function in hypertensive patients with different left ventricular geometric patterns.

To evaluate the alteration of cardiac function in hypertensive patients with different left ventricular geometric patterns. Echocardiography was used to study left ventricular geometry and cardiac diastolic function in 117 cases of essential hypertension, with 45 normal cases as controls. Echocardiographic date were used to calculated the left ventricular mass index (LVMI) and relative wall thickness (RWT), which values in turn were used to divide the subjects into four groups. The left atrial dimension of the group, with the exception of these hypertensives who showed normal geometry, was larger than that of the control group. The damage of peak of E velocity, peak of A velocity, E/A and the slope between the E and F points (E to F slope) were greater than in hypertension than in the control group. The concentric hypertrophy group and eccentric hypertrophy group suffered more serious damage of left ventricular diastolic function than the concentric remodeling group, and damage of left ventricular diastolic function in the concentric remodeling group was greater than that in the normal geometry group. The degree of cardiac diastolic function damage differed among patients with different left ventricular geometric patterns, when the cardiac structure was changed, the degree of cardiac diastolic function damage increased.

Diastole↗

PubMed2001

Resistant potato selections contain leptine and inhibit development of the Colorado potato beetle (Coleoptera: Chrysomelidae).

We recently described a new source of host-plant resistance to the Colorado potato beetle, Leptinotarsa decemlineata (Say), in a tetraploid potato (Solanum tuberosum L.) selection, ND2858-1. This genotype, and selected backcross progeny, had little damage while check cultivars were defoliated in open-choice field assays. To further characterize the observed deterrence, we determined foliar glycoalkaloids and conducted no-choice assays with ND2858-1 backcross progeny genotypes (ND4382-n). Development of neonate L. decemlineata in detached leaf assays on resistant progeny genotypes was delayed and larval weight gain after 4 d was inhibited by 75% relative to larval development and weight gain on susceptible genotypes. Inhibition of larval development in detached leaf assays with the selected progeny genotypes was equivalent to that of high-leptine genotypes of S. chacoense Bitter. Foliar glycoalkaloids of resistant genotypes included low levels of leptines I and II. The unlikely nature of this cross and the presence of leptine in this and resistant progeny selections cast doubt on the recorded pedigree. Molecular analyses were conducted by restriction fragment-length polymorphism and amplified fragment-length polymorphisms. Both methods established a high degree of relatedness to S. tuberososum and S. chacoense but not to S. fendleri. We conclude that ND2858-1 did not originate from a cross with S. fendleri, but is likely derived from S. chacoense. Oviposition and larval survival were reduced when adult L. decemlineata were placed in cages with resistant genotypes; an effect that was enhanced by inclusion of Perillus bioculatus F. Therefore, the nonpreference previously observed in open-choice field defoliation assays is also associated with antibiotic effects on L. decemlineata. The resistance may be caused by leptines, but is greater than would be expected by the leptine content. This source of host plant resistance could be a cost-effective management strategy, especially if combined with other resistance mechanisms or compatible control measures to delay development of resistance in the target insects.

Animals↗

PubMed2001

[Magnetic stimulation: theory and advance].

Magnetic stimulation is a noninvasive diagnostic and therapeutic technique. The basic theory of magnetic stimulation is presented briefly. Its advances are elaborated in three aspects of mechanism, instrumentation and applications. The problems in focality, location, safety and its trend are discussed.

Humans↗

PubMed2001

Disposable 1-day Acuvue contact lenses for the delivery of lomefloxacin to rabbits' eyes.

PURPOSE: To investigate the ability of a disposable soft contact lens (1-Day Acuvue) to deliver lomefloxacin, a fluoroquinolones antibiotic, into the cornea and aqueous humor of rabbits. METHODS: Experiments were conducted on adult albino rabbits. 1-Day Acuvue lenses were immersed for 1 hour in commercially-available lomefloxacin eye solution and then placed on the cornea. After 0.5, 2, 4,6, and 8 hours, the animals were killed and the lenses were removed and placed into a 20 mL saline bath. Corneal tissue and aqueous humor samples were also obtained at these times. The release of lomefloxacin from the lenses was calculated by measuring the amount of drug remaining in the lenses after removal from the rabbit eyes. The concentration of lomefloxacin in the cornea and anterior chamber following the wearing of lomefloxacin-loaded lenses was compared with the concentrations following frequent-drop therapy (one drop of lomefloxacin hourly for 8 hours). RESULTS: In vivo, lomefloxacin was released from 1-Day Acuvue lenses gradually over 8 hours. The cornea and aqueous humor levels in the eyes following the wear of lomefloxacin-loaded lenses were significantly higher than those achieved by frequent-drop therapy. The drug levels in the cornea and aqueous humor generally remained above the 90% minimal inhibitory concentration for 8 hours in the 1-Day Acuvue lens group. CONCLUSIONS: 1-Day Acuvue contact lenses soaked in 0.3% lomefloxacin can release sufficient amounts of lomefloxacin and in this study produced higher levels in both the cornea and aqueous humor than that achieved by frequent-drop therapy for up to 8 hours. We conclude that 1-Day Acuvue contact lens can be used as a drug delivery system for lomefloxacin.

Animals↗

PubMed2001

Studies on the uptake and release of fluoroquinolones by disposable contact lenses.

PURPOSE: To evaluate the ability of three types of disposable contact lenses to take up and release three kinds of fluoroquinolones in vitro. METHODS: We evaluated three FDA-approved disposable soft contact lenses (1-Day Acuvue, Medalist, and 14UV) for their ability to absorb and release three kinds of fluoroquinolones. Contact lenses were presoaked in fluoroquinolones for 1, 4, and 24 hours, and the uptake was determined by measuring the concentration of fluoroquinolones in the three types of disposable soft contact lenses by high pressure liquid chromatography (HPLC). After uptake, the lenses were placed in fresh saline baths, and release rates from the lenses were determined by measuring the concentration of fluoroquinolones in the saline baths by HPLC. RESULTS: The disposable soft contact lens with the highest uptake of fluoroquinolones was the 1-Day Acuvue. After presoaking, drug concentrations in the 1-Day Acuvue and Medalist were higher than their theoretical saturation concentrations (i.e., the concentration of the fluoroquinolone eye drops [0.3%]). The release rates from the 1-Day Acuvue and Medalist lenses were slower than for the 14 UV lens. CONCLUSIONS: These results indicate that among the lenses tested, the most practical drug delivery system is the 1-Day Acuvue disposable soft contact lens.

Anti-Infective Agents↗

PubMed2001

Anti-inflammatory effect and mechanism of proanthocyanidins from grape seeds.

AIM: To investigate the anti-inflammatory effect and mechanism of proanthocyanidins (PA) from grape seeds. METHODS: Croton oil-induced ear swelling in mice and carrageenan-induced hind paw edema in rats were prepared. The nitric oxide synthase (NOS) activity was measured by NADPH-diaphoras stain assay, nitric oxide (NO) content by Griess diazotization assay, N-acetyl-beta- D-glucosaminidase (beta-NAG) activity by spectrophotography, malondialdehyde (MDA) content by thiobarbituric acid (TBA) fluorescence technique, and IL-1beta, TNFalpha, and PGE2 content by radioimmunoassay (RIA). RESULTS: PA 10-40 mg/kg ip inhibited carrageenan-induced paw edema in rats and croton oil-induced ear swelling in mice in a dose-dependent manner. PA 10 mg/kg reduced MDA content in inflamed paws, inhibited beta-NAG and NOS activity, and lowered the content of NO, IL-1beta, TNFalpha, and PGE2 in exudate from edema paws of rats induced by carrageenan. The inhibitory effect of PA on all above indices was more evident than that of dexamethasone 2 mg/kg. CONCLUSION: PA has anti-inflammatory effect on experimental inflammation in rats and mice. Its mechanisms of anti-inflammatory action are relevant to oxygen free radical scavenging, anti-lipid peroxidation, and inhibition of the formation of inflammatory cytokines.

Animals↗

PubMed2001

[Water quality of closed polyculture of penaeid shrimp with tilapia and constricted tagelus].

A variety of water quality parameters were monitored in enclosures for the polyculture of penaeid shrimp with tilapia and constricted tagelus. The result showed that the environment of the polyculture systems was better than that of monoculture one. The fluctuation of DO in the water of polyculture enclosures was less violent, and their lowest values were obviously higher than those in monoculture ones. The value of COD and the number of bacteria in the water of polyculture enclosures were significantly lower than those in monoculture ones(t-test, alpha < 0.05), showing that the amount of organic matter in the water of polyculture systems was less than that in monoculture one. The biomass of plankton and the concentration of chlorophyll-a in the polyculture enclosures were also lower, showing that the suppression of the filtering animals to the plankton was obvious. The accumulation of N and P in the sediment of polyculture enclosures was 39.76% and 51.26%, lower than those of monoculture ones, respectively; and the number of bacteria in the sediment was 7.63% lower. Therefore, it is obvious that closed culture system can greatly decrease the effluent to the coastal waters caused by the pond culture industry, and decrease the pollution to the coastal waters.

Animals↗

PubMed2001

Intrathecal injection with methotrexate plus dexamethasone in the treatment of central nervous system involvement in systemic lupus erythematosus.

OBJECTIVE: To investigate the effect of intrathecal injection (i.t.) with methotrexate (MTX) plus dexamethasone (DXM) in treating central nervous system involvement in systemic lupus erythematosus (CNS lupus). METHODS: Twenty-four CNS lupus patients that were refractory to conventional steroid therapy were selected for i.t. with MTX 10-20 mg plus DXM 10-20 mg. The effects and side effects of i.t. were closely observed. RESULTS: The symptoms and signs of 22/24 (91.7%) CNS lupus patients receiving i.t. improved considerably. Cerebrospinal fluid pressure, protein and WBC levels declined from 201.5 +/- 155.4 mm H2O, 145.2 +/- 87.6 mg/dl and 25.1 +/- 14.3/mm3 to 128.7 +/- 108.1 mm H2O, 60.8 +/- 38.3 mg/dl and 6.8 +/- 2.1/mm3 respectively. Transient side effects were observed in 4 patients: 1 with itching sensation of lower limbs, 2 with headache and 1 with incontinence. CONCLUSION: I.t. with MTX plus DXM is a promising method for treating CNS lupus and deserves further investigation.

Adolescent↗

PubMed2001

Sesquiterpene polyol esters from Euonymus phellomana Loes.

Three new (1-3) and six known (4-9) beta-dihydroagarofuran sesquiterpene polyol esters were isolated from a methanol extract of the seed oil of Euonymus phellomana Loes. and their structures were established on the basis of spectral analysis, including 2D-NMR spectroscopy.

China↗

PubMed2001

[Study on the construction of standard D1S549 allelic ladder via molecular cloning and its genetic polymorphism in Chinese three populations].

OBJECTIVE: To resolve the problem of the accuracy and standardization of STR-PCR typing in forensic practice, we have designed a new method to produce standard D1S549 allelic ladder. METHODS: Eight different PCR amplified D1S549 allelic fragments were isolated from the gel, eluted into the distilled water and re-amplified by PCR. The purified allelic fragments were then blunt-end subcloned individually into the pUC plasmid vectors and transfected into competent E. coli DH5 alpha cells. RESULTS: The sequencing results confirmed that the size and the construe of the inserts were correct. The recombinant plasmids DNA with 8 inserts were then used as templates for re-amplification to generate D1S549 standard ladder, with which the genetic polymorphisms of D1S549 locus in Chinese Han population in chengdu, Hui population in Gansu and Wei population in Xinjiang were studied. CONCLUSION: The results showed that the standard ladder made via this method is excellent, and D1S549 locus is robust for genetic research and forensic application.

Alleles↗

PubMed2001

[Measurement of microvessel density in laryngeal carcinoma and its clinical significance].

OBJECTIVE: To determine the microvessel density (MVD) in laryngeal carcinoma and its clinical significance. METHOD: Thirty-eight tumor specimens were selected from laryngeal cancer patients from January, 1994 to March, 1996. Histological sections of the tumors were stained immunohistochemically for factor VIII. Using light microscopy, we counted microvessels per 400 x field in the most active areas of tumor angiogenesis. RESULT: 1. The tumor blood vessels, composed of only one layer of endothelium were mainly distributed heterogeneously in the interstitial tissue of laryngeal carcinoma with irregular lumen, poorly developed structure. 2. The MVD in the cancer tissues were statistically higher than that in peritumoral tissues (P < 0.01). 3. The MVD in the cancer tissues in group of patients with metastasis to cervical lymphonodes were statistically higher than in group without metastasis (P < 0.01), the MVD in the cancer tissues in group of advanced cases (III, IV stages) were statistically higher than that in group of early cases (I, II stages, P < 0.01). 4. There was no statistically difference in MVD in the cancer tissue between supraglottic and glottic laryngeal carcinoma patients (P > 0.05). 5. There was no statistically difference in MVD in the cancer tissue among the G1, G2 and G3 group (P > 0.05). CONCLUSION: The laryngeal cancer blood vessels have some characteristics that don't appear in normal vessels. It is suggested that tumor angiogenesis can promote tumor growth and metastasis and MVD may be a new prognostic indicator of laryngeal carcinoma.

Adult↗