Biomedical subjects

J Chen

Publications and source records attributed to J Chen.

At least 253 records · Page 14Linked to original sources

PubMed2002

The barley stem rust-resistance gene Rpg1 is a novel disease-resistance gene with homology to receptor kinases.

Stem rust caused by Puccinia graminis f. sp. tritici was among the most devastating diseases of barley in the northern Great Plains of the U.S. and Canada before the deployment of the stem rust-resistance gene Rpg1 in 1942. Since then, Rpg1 has provided durable protection against stem rust losses in widely grown barley cultivars (cvs.). Extensive efforts to clone Rpg1 by synteny with rice provided excellent flanking markers but failed to yield the gene because it does not seem to exist in rice. Here we report the map-based cloning and characterization of Rpg1. A high-resolution genetic map constructed with 8,518 gametes and a 330-kb bacterial artificial chromosome contig physical map positioned the gene between two crossovers approximately 0.21 centimorgan and 110 kb apart. The region including Rpg1 was searched for potential candidate genes by sequencing low-copy probes. Two receptor kinase-like genes were identified. The candidate gene alleles were sequenced from resistant and susceptible cvs. Only one of the candidate genes showed a pattern of apparently functional gene structure in the resistant cvs. and defective gene structure in the susceptible cvs. identifying it as the Rpg1 gene. Rpg1 encodes a receptor kinase-like protein with two tandem protein kinase domains, a novel structure for a plant disease-resistance gene. Thus, it may represent a new class of plant resistance genes.

Alleles↗

PubMed2002

Hypoxia enhances the expression of autocrine motility factor and the motility of human pancreatic cancer cells.

The incidence of distant metastases is higher in the tumours with low oxygen pressure than in those with high oxygen pressure. It is well known that hypoxia induces the transcription of various genes involved in angiogenesis and anaerobic metabolism necessary for the growth of tumour cells in vivo, suggesting that hypoxia may also induce the transcription of metastasis-associated genes. We sought to identify the metastasis-associated genes differentially expressed in tumour cells under hypoxic conditions with the use of a DNA microarray system. We found that hypoxia enhanced the expression of autocrine motility factor mRNA in various cancer cells and also enhanced the random motility of pancreatic cancer cells. Autocrine motility factor inhibitors abrogated the increase of motility under hypoxic conditions. In order to explore the roles of hypoxia-inducible factor-1alpha, we established hypoxia-inducible factor-1alpha-transfectants and dominant negative hypoxia-inducible factor-1alpha-transfectants. Transfection with hypoxia-inducible factor-1alpha and dominant-negative hypoxia-inducible factor-1alpha enhanced and suppressed the expression of autocrine motility factor/phosphohexase isomerase/neuroleukin mRNA and the random motility, respectively. These results suggest that hypoxia may promote the metastatic potential of cancer cells through the enhanced autocrine motility factor/phosphohexase isomerase/neuroleukin mRNA expression and that the disruption of the hypoxia-inducible factor-1 pathway may be an effective treatment for metastasis.

Blotting, Northern↗

PubMed2002

Retroperitoneoscopic nephropexy for symptomatic nephroptosis.

BACKGROUND: Open nephropexy for nephroptosis creates significant morbidity. We describe our technique for retroperitoneoscopic nephropexy and evaluate its efficacy. METHODS: Twenty-five renal units in 23 patients with symptomatic nephroptosis underwent retroperitoneoscopic nephropexy by suturing the posterior renal capsules and transfixing them to the back muscles. The diagnosis and postoperative assessment were made by typical symptoms (via patient questionnaire) and findings of intravenous urography (IVU) when the position was changed from supine to erect. RESULTS: Mean operative time was 188 min (range, 90-330). Mean narcotic use was 15.6 mg morphine. Complete resolution of symptoms occurred in 84% (21/25) renal units; 12% (three of 25) achieved partial improvement (>75% decrease of preoperative symptoms). Follow-up IVU showed that 88% of patients had a renal descent of <2 cm on standing; the others had a descent of 2-4 cm. All of the five renal units with hydronephrosis resolved completely after the operation. CONCLUSIONS: This modified technique of retroperitoneoscopic nephropexy is a minimally invasive, feasible, and highly successful option for treating patients with symptomatic nephroptosis.

Adult↗

PubMed2002

Antisense epidermal growth factor receptor RNA transfection in human glioblastoma cells down-regulates telomerase activity and telomere length.

Epidermal growth factor receptor is overexpressed and/or amplified in up to 50% of glioblastomas, suggesting an important role of this gene in glial tumorigenesis and progression. In the present study we demonstrated that epidermal growth factor receptor is involved in regulation of telomerase activity in glioblastoma. Antisense-epidermal growth factor receptor approach was used to inhibit epidermal growth factor receptor expression of glioblastoma U87MG cells. Telomerase activity in antisense-epidermal growth factor receptor cells decreased by up to 54 folds compared with control cells. Moreover, the telomere lengths of antisense-epidermal growth factor receptor cells were shortened. In addition, the tumorigenicity of antisense-epidermal growth factor receptor cells was significantly inhibited. Taken together, there were strong correlations between tumorigenicity and epidermal growth factor receptor expression levels, and between tumorigenicity and telomerase activity. These results provide evidence that epidermal growth factor receptor plays an important role in the regulation of telomerase activity of glioma cells. Our findings provide new insights into both the biological functions of epidermal growth factor receptor and the regulation of telomerase activity. The inhibition of telomerase activity triggered by antisense-epidermal growth factor receptor treatment may reflect yet another mechanism of antisense-epidermal growth factor receptor approach in tumour suppression.

Animals↗

PubMed2002

Platelets promote the adhesion of human hepatoma cells with a highly metastatic potential to extracellular matrix protein: involvement of platelet P-selectin and GP IIb-IIIa.

PURPOSE: To investigate the role and possible mechanisms of platelets in liver cancer metastasis. METHODS: The optimum conditions of hepatoma cell adhesion to the extracellular matrix (ECM) were determined. The ability of cells to adhere to the ECM was compared between human hepatoma cell lines with a highly metastatic potential (MHCC97) and human hepatoma cell lines with a lower metastatic potential (SMMC7721). By using adhesion assays and inhibition studies in vitro, the effects of platelets and their specific adhesive molecules were compared via the ability of MHCC97 and SMMC7721 to adhere to ECM protein. RESULTS: The SMMC7721 cell adhesion rate to vitronectin, fibronectin, and fibrinogen, respectively, was significantly lower than that of MHCC97 cells (44.9% vs 73.6%, 47.4% vs 76.4%, and 59.3% vs 80.6%, P<0.05). Both hepatoma cell adhesion to the ECM-bound platelets was unchanged whether the platelets were activated or not. SMMC7721 cell adhesion to the ECM was not affected by platelets, but MHCC97 cell adhesion to the ECM was significantly enhanced by platelets ( P<0.01). In addition, this effect was significantly reduced when either P-selectin or GP IIb-IIIa was blocked by monoclonal antibodies ( P<0.05, P<0.01). In the inhibition studies, the ability of SMMC7721 to adhere to the ECM-bound activated platelets was also lower than that of MHCC97 ( P<0.05). However, when GP IIb was blocked by antibody, the adhesion ability of both cells was similar ( P >0.05). CONCLUSIONS: Human hepatoma cells with a highly metastatic potential proved to have a highly adhesive ability. MHCC97 cell adhesion to the ECM was significantly enhanced by platelets. The interaction of MHCC97 cells with the ECM-bound activated platelets may be mediated by platelet P-selectin and GP IIb-IIIa.

Blood Platelets↗

PubMed2002

X-ray photoelectron spectroscopy study of disordering in Gd2(Ti1-xZrx)2O7 pyrochlores.

The dramatic increases in ionic conductivity in Gd2(Ti1-xZrx)2O7 solid solution are related to disordering on the cation and anion lattices. Disordering in Gd2(Ti1-xZrx)2O7 was characterized using x-ray photoelectron spectroscopy (XPS). As Zr substitutes for Ti in Gd2Ti2O7 to form Gd2(Ti1-xZrx)2O7 (0.25 < x < or =0.75), the corresponding O 1s XPS spectrum merges into a single symmetric peak. This confirms that the cation antisite disorder occurs simultaneously with anion disorder. Furthermore, the O 1s XPS spectrum of Gd2Zr2O7 experimentally suggests the formation of a split vacancy.

Journal Article↗

PubMed2002

Estrogenic effects from household stoves.

With the application of a genetically modified yeast, estrogen receptor-activating compounds were detected in the soot and emission gas of a wood-burning household stove. The EC50 value of 17beta-estradiol was divided by the EC50 value of soot, and the obtained relative estrogenic value for raw soot was 2.37E-5, indicating that soot was about 100,000 times less estrogenic than 17beta-estradiol. Chemical analysis revealed that alkyl phenol, benzonic acid, and PAHs represented the major constituents in the most potent fractions of the soot. Along with PAHs, other constituents might also contribute to the estrogenicity of soot.

Benzoic Acid↗

PubMed2002

Functionally rodless mice: transgenic models for the investigation of cone function in retinal disease and therapy.

Two genetically engineered strains of mice were used to characterize murine cone function electroretinographically, without interference of rod-driven responses: (1) mice with a deletion of the gene for the rod transducin alpha-subunit (transducin alpha-/-), and (2) mice with rod arrestin deleted (arrestin -/-). In the first three months of age, both strains have a normal complement of rods and normal rod structure, but transducin alpha-/- mice have no rod-driven responses to light, while rod-driven activity of arrestin -/- mice can be suppressed by a single intense flash for hours. In response to intense flashes the electroretinograms of these strains of mice showed a readily identifiable, pure-cone a-wave of approximately 10 microV saturating amplitude. A 530 nm background that saturates rod responses of wild type mice was found to desensitize the b-wave responses of mice of both transgenic lines, whether the b-waves were driven by photons captured by M- or UV-cone pigments. The desensitizing effect of the 530 nm background on UV-pigment driven responses provides new evidence in support of the hypothesis of functional co-expression of the M-pigment in cones expressing primarily the UV-pigment.

Animals↗

PubMed2002

Nociceptin inhibits excitatory but not inhibitory transmission to substantia gelatinosa neurones of adult rat spinal cord.

Although intrathecal administration of nociceptin, an endogenous ligand of the opioid receptor-like1 receptor, exhibits an antinociceptive effect in various pain models, cellular mechanisms underlying this action are still unknown. Here, we investigated the effects of nociceptin on excitatory and inhibitory synaptic transmission to substantia gelatinosa neurones of an adult rat spinal cord slice with an attached dorsal root by use of the blind whole-cell patch-clamp technique; this was done under the condition of a blockade of a hyperpolarising effect of nociceptin. In about 70% of the neurones examined, nociceptin (1 microM) reduced the amplitude of glutamatergic excitatory postsynaptic currents (EPSCs) which were monosynaptically evoked by stimulating Adelta- or C-afferent fibres; the inhibition of C-fibre EPSCs (50+/-6%, n=11) was larger than that of Adelta-fibre EPSCs (30+/-5%, n=23; P<0.05). Each of the nociceptin actions was dose-dependent in a concentration range of 0.1 to 1 microM, and was largely suppressed by a selective opioid receptor-like1 receptor antagonist, 1-[(3R,4R)-1-cyclooctylmethyl-3-hydroxymethyl-4-piperidyl]-3-ethyl-1,3-dihydro-2H-benzimidazol-2-one (3 microM). Nociceptin (1 microM) also decreased miniature EPSCs frequency by 22+/-6% (n=7) while not affecting their amplitude. Responses of substantia gelatinosa neurones to bath-applied alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionate (10 microM) were not changed by nociceptin. Both electrically evoked and miniature inhibitory postsynaptic currents, mediated by either the GABA(A) or glycine receptor, were unaffected by nociceptin. These results indicate that nociceptin suppresses excitatory but not inhibitory synaptic transmission to substantia gelatinosa neurones through the activation of the opioid receptor-like1 receptor; this action is pre-synaptic in origin. Considering that the substantia gelatinosa is the main part of termination of Adelta- and C-fibres transmitting nociceptive information, the present finding would account for at least a part of the inhibitory action of nociceptin on pain transmission. Nociceptin could inhibit more potently slow-conducting than fast-conducting pain transmission.

Afferent Pathways↗

PubMed2002

Early chronic aluminium exposure impairs long-term potentiation and depression to the rat dentate gyrus in vivo.

As an important neurotoxin, aluminium can cause cognitive dysfunctions and mental diseases. Previous studies have reported that aluminium impaired long-term potentiation (LTP) in vivo and in vitro. Here, we utilise two models of synaptic plasticity, LTP and long-term depression (LTD) to study the effects of aluminium on synaptic plasticity in vivo. Neonatal Wistar rats were chronically exposed to aluminium from birth to weaning via the milk of dams fed with 0.3% aluminium chloride solution. Excitatory postsynaptic potential (EPSP) and population spikes (PS) were recorded from the dentate gyrus (DG) of adult rats by electrically stimulating the perforant path. THE FOLLOWING RESULTS WERE OBTAINED: (1) The input/output function indicated that, as compared to controls, aluminium increased the baseline amplitude of the PS, but decreased the baseline slope of EPSP. (2) Aluminium significantly prevented LTD in PS (controls: 77.36+/-6.7%, n=7; aluminium-exposed: 102.01+/-9.1%, n=7; P<0.05) and decreased the LTD amplitude in EPSP (controls: 76.61+/-4.1%, n=7; aluminium-exposed: 94.31+/-7.9% n=7, P<0.05). (3) Aluminium reduced the amplitude of LTP in both PS (controls: 190+/-16.1%, n=7; aluminium-exposed: 135+/-9.7%, n=7; P<0.05) and EPSP (control: 132+/-9.3%, n=7; aluminium-exposed: 115+/-10.6%, n=7; P<0.05). As for LTD and LTP, PS was impaired more seriously than EPSP in aluminium-exposed rats. (4) Aluminium exposure decreased the paired-pulse facilitation (PPF) of PS at 30-150 ms interpulse interval (IPI), and reduced 93.5% of PPF at 80 ms IPI in PS (controls: 243.4+/-39.8%, n=7; aluminium-exposed: 149.9+/-12.3%, n=7). There was no significant difference in EPSP of PPF. From these results we conclude that aluminium exposure in neonatal rats thus reduces the amplitude of LTP and PPF and blocks the induction of LTD in the DG. We suggest that aluminium affects both presynaptic and postsynaptic mechanisms of synaptic transmission.

Aluminum↗

PubMed2002

Preparation of metallized GaN/sapphire cross sections for TEM analysis using wedge polishing.

The tripod polisher has been used successfully in the past, in the preparation of difficult Si-based TEM cross-section specimens. Good TEM specimens, with large electron transparent areas, can be prepared in a relatively short time. In addition, wedge polishing considerably reduces the ion milling time because of the thinness of the final specimen. For metallized GaN on sapphire substrates, there are problems not inherent to Si-based materials: (1) sapphire is a difficult material to thin due to its high hardness and its mechanical instability when thinned below 20 m; (2) delamination of metal layers from the GaN can occur during polishing and/or ion milling; (3) markedly different ion milling rates for the metals and semiconductors. In this paper, wedge polishing has been modified to make it suitable for preparation of metallized GaN/sapphire samples or other metallized semiconductors and ceramics for TEM analysis. Using this method, TEM cross section specimens can be prepared with reasonably large thin areas.

Journal Article↗

PubMed2002

Biomechanical aspects of Peyronie's disease in development stages and following reconstructive surgeries.

Peyronie's disease is a disorder of the penile connective tissues that leads to development of dense fibrous or ossified plaques in the tunica albuginea, causing penile deformity and painful erection. A biomechanical model of the penis was utilized for analyzing the mechanical stresses that develop within its soft tissues during erection in the presence of Peyronie's plaques. The model's simulations demonstrated stress concentrations around nerve roots and blood vessels due to the plaques. These stresses may irritate nerve endings or compress the vascular bed, and thus cause penile deformity and/or painful erection. The model was further used to elaborate the effects of different biological or artificial materials for reconstruction of the penis following plaque removal. Clinical applications of the present model can range from analysis of the etiology of the disease to assisting in the determination of optimal timing for therapeutic interventions and in the selection of patch material for penile reconstructions.

Biomechanical Phenomena↗

PubMed2002

Massive pseudotumour resection with recombinant factor VIIa (NovoSeven) cover.

Surgical resection is the only definitive treatment for haemophilic pseudotumour. For patients with high- responding factor (F)VIII inhibitors, the lack of reliable by-passing agents in the past has meant that surgery has been avoided in favour of conservative measures. The development of recombinant factor VIIa (rFVIIa) has revolutionized the management of surgery in these patients. We document the first successful report of the surgical resection of a massive pseudotumour in a patient with high responding FVIII inhibitors using rFVIIa to achieve haemostasis. Serial post-operative measurements indicated that FVII coagulation activity (FVII:C) levels were more sensitive to rFVIIa dose changes than the prothrombin time.

Adult↗

PubMed2002

Middle ear instillation of gentamicin and streptomycin in chinchillas: electrophysiological appraisal of selective ototoxicity.

The purpose of this study was to investigate selective vestibular ototoxicity of gentamicin and streptomycin in the chinchilla model. In total, 10 chinchillas underwent left middle ear instillation of one of three agents: gentamicin, streptomycin and saline. Electrophysiological data (otoacoustic emissions (OAEs), auditory brainstem evoked response (ABRs), and ice-water electronystagmography were recorded before and after instillation. Animals were sacrificed for temporal bone studies using scanning electron microscopy. Morphological changes in the cochlear and vestibular neuroepithelia were correlated with electrophysiological changes. Widespread ipsilateral cochlear and vestibular neuroepithelial injuries were observed and correlated with loss of OAEs, ABRs and ice-water caloric response. This study provides no evidence of selective vestibular ototoxicity of gentamicin or streptomycin. Morphological damage correlates with, but precedes loss of electrophysiological parameters. Chinchillas, like other small mammals, may not be an ideal model for the study of human ototoxicity.

Animals↗

PubMed2002

Mild heat treatment of lettuce enhances growth of Listeria monocytogenes during subsequent storage at 5 degrees C or 15 degrees C.

AIMS: The objective of this study was to determine the influence of mild heat treatment, storage temperature and storage time on the survival and growth of Listeria monocytogenes inoculated onto cut iceberg lettuce leaves. METHODS AND RESULTS: Before or after inoculation with L. monocytogenes, cut iceberg lettuce leaves were dipped in water (20 or 50 degrees C) containing or not 20 mg l(-1) chlorine, for 90 s, then stored at 5 degrees C for up to 18 days or 15 degrees C for up to 7 days. The presence of 20 mg l(-1) chlorine in the treatment water did not significantly (alpha=0.05) affect populations of the pathogen, regardless of other test parameters. The population of L. monocytogenes on lettuce treated at 50 degrees C steadily increased throughout storage at 5 degrees C for up to 18 days. At day 10 and thereafter, populations were 1.7-2.3 log10 cfu g(-1) higher on lettuce treated at 50 degrees C after inoculation compared with untreated lettuce or lettuce treated at 20 degrees C, regardless of chlorine treatment. The population of L. monocytogenes increased rapidly on lettuce stored at 15 degrees C. At 2 and 4 days, significantly higher populations were detected on lettuce that had been treated at 50 degrees C, compared with respective samples that had been treated at 20 degrees C, regardless of inoculation before or after treatment, or the presence of 20 mg l(-1) chlorine in the treatment water. CONCLUSIONS: The results clearly demonstrated that mild heat treatment of cut lettuce leaves enhances the growth of L. monocytogenes during subsequent storage at 5 or 15 degrees C. SIGNIFICANCE AND IMPACT OF THE STUDY: Mild heat treatment of cut lettuce may result in a prolonged shelf life as a result of delaying the development of brown discoloration. However, heat treatment also facilitates the growth of L. monocytogenes during storage at refrigeration temperature, thereby increasing the potential risk of causing listeriosis.

Chlorine↗

PubMed2002

Acute resumption of conduction in the cavotricuspid isthmus after catheter ablation in patients with common atrial flutter. Real-time evaluation and long-term follow-up.

AIMS: Cavotricuspid isthmus conduction (CIC) is closely associated with the maintenance and recurrence of common atrial flutter (AFL). This study systematically sought to assess the prevalence and characteristics of acute CIC recovery during AFL ablation and to define its predictors and its relationship with the results of long-term follow-up. METHODS AND RESULTS: A total of 124 consecutive patients (105 men, 19 women, mean age 58 +/- 11 years) who underwent successful AFL ablation were included. The procedure endpoint was defined as complete bi-directional CIC block. During an observation period of 30 min, the incidence of CIC restoration was 34.% in patients and 39.8% in applications. It increased with increasing block time and decreased over time during the observation period. Block time in successful burns followed by persistent block was shorter than in those followed by CIC resumption (12 +/- 6 vs 33 +/- 12 s, P<0.0001). A negative correlation between block time and resumption time was found (r = - 0.57, P<0.001). Patients with permanent pacemakers had a higher incidence of acute CIC resumption than those without pacemakers (5/7 vs 29/117, P = 0.007). The AFL recurrence rate was 4.8% during a mean follow-up period of 21 +/- 8 months. Our results suggest that acute CIC resumption may be a potential risk for clinical AFL recurrence during long-term follow-up. CONCLUSIONS: Acute CIC resumption in common AFL ablation varies in terms of incidence and time course. Block time has a predictive value for acute CIC recovery. Observation time can be shortened if block time is short. With longer block time, it is essential to observe for a longer period in order to minimize CIC resumption.

Atrial Flutter↗

PubMed2002

Linear free energy relationships on rate constants for dechlorination by zero-valent iron.

By correlation analysis, molecular structural factors governing surface area-normalized rate constants (k) for dechlorination by zero-valent iron, were identified. Twenty-nine quantum chemical descriptors computed by MNDO, AM1 and PM3 Hamiltonians for gas-phase and the conductor-like screening model (COSMO) for incorporating solvent (H2O) effects were studied. Besides the energy of the lowest unoccupied molecular orbital (E(LUMO)), the character of carbon-chlorine bonds (C-Cl bonds) and especially the strength of C-Cl bonds was found significant in governing the magnitude of log k. By PLS analysis, six two-parameter linear free energy relationships (LFER) were obtained. The best two-parameter LFER model was the one using E(LUMO) and C (the Coulombic interaction energy of the two-center term for the C-Cl bonds) computed by PM3/H2O method as molecular structural descriptors. Chlorinated compounds with high E(LUMO) and C values tend to have low dechlorination rate constants.

Carbon↗

PubMed2002

Determination of the pH of the Cryptococcus neoformans vacuole.

We have previously demonstrated the antifungal activity of the weak bases chloroquine and quinacrine against Cryptococcus neoformans. Quinacrine, being fluorescent, was seen to be concentrated within a complex vacuolar structure within the cryptococcal cell. Here we determined the pH of this compartment using the pH-sensitive fluorescent dye, 5-(and 6-) carboxy-2',7'-dichlorofluorescein diacetate (carboxy-DCFDA). Carboxy-DCFDA was concentrated within the cryptococcal vacuole, giving a pattern of fluorescence similar to that previously observed with quinacrine. For each experiment, a standard curve of fluorescence ratio against pH was generated using buffers of defined pH containing a mixture of ionophores and inhibitors to equilibrate vacuolar pH with that of the medium. The pH of the cryptococcal vacuole of five strains was calculated to range from 5.3 to 5.9 with a mean of 5.6. This acidic pH is consistent with a model in which weak bases such as chloroquine and quinacrine are accumulated, by ion trapping within the fungal vacuole. Antifungal activity may result from the consequent disruption of pH-dependent processes as well as effects on other as yet undefined fungal targets.

Cryptococcus neoformans↗