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Biomedical subjects

L Chen

Publications and source records attributed to L Chen.

At least 667 records · Page 37Linked to original sources
PubMed1998

Regulation of fat synthesis and adipose differentiation.

Adipocytes have highly specialized function of accumulating fat as stored energy that can be used during periods of food deprivation. The process of fat synthesis and development of adipose tissue are under hormonal and nutritional control. This review first describes transcription of the two critical enzymes involved in fat synthesis, fatty acid synthase and mitochondrial glycerol-3-phosphate acyltransferase, is decreased to an undetectable level during fasting. Food intake, especially a high carbohydrate, fat-free diet, subsequent to fasting causes dramatic increase in transcription of these genes. Insulin secretion is increased during feeding, having a positive effect, whereas cAMP, which mediates the effect of glucagon which increases during fasting, has a negative effect on transcription of these genes. Using adipocytes in culture and in transgenic mice that express liciferase driven by the fatty acid synthase promoter, cis-acting and trans-acting factors that may mediate the transcriptional regulation were examined. Upstream stimulatory factors (USFs) that bind to -65 E-box are required for insulin-mediated transcriptional activation of the fatty acid synthase gene. This review next describes how pref-1 is a novel inhibitor of adipose differentiation and is a plasma membrane protein containing six EGF-repeats in the extracellular domain. Pref-1 is highly expressed in 3T3-L1 preadipocytes, but is not detectable in mature fat cells. Down regulation of pref-1 is required for adipose differentiation, and constitutive expression of pref-1 inhibits adipogenesis. Moreover, the ectodomain of pref-1 is cleaved to generate a biologically active 50 kDa soluble form. There are four major forms of membrane pref-1 resulting from alternate splicing, but two of the forms with a larger deletion do not produce biologically active soluble form, indicating that alternate splicing determines the range of action, juxtacrine or paracrine, of the pref-1.

Adipose Tissue↗
PubMed1998

Inhibition of caspase activity prevents anti-IgM induced apoptosis but not ceramide generation in WEHI 231 B cells.

In apoptosis induced by Reaper in Drosophila, as well as in a number of other systems, it has been suggested that the increased synthesis of ceramide might be a consequence of the activation of the caspase/ICE (Interleukin-1beta converting enzyme) protease pathway involved in cell death, implying that ceramide generation might often be the result rather than the cause of apoptosis. WEHI 231 B cells have previously been shown to undergo apoptosis following exposure to exogenous ceramide and to produce increased amounts of ceramide in response to anti-IgM crosslinking. We show here that in WEHI 231 cells a peptide inhibitor of caspase activity blocks cell death in response to both anti-IgM and exogenous ceramide. However, the induction of ceramide synthesis by WEHI 231 cells in response to anti-IgM crosslinking is not blocked by this peptide. These results indicate that antigen receptor induced ceramide generation in WEHI 231 cells does not require caspase activation, and support the view that ceramide generation in immature B cells may be the cause rather than the consequence of activation of the caspase dependent death pathway.

Amino Acid Chloromethyl Ketones↗
PubMed1998

Treatment of implanted liver tumors with focused ultrasound.

This article reports treatment of implanted liver tumors (HSN fibrosarcoma) with focused ultrasound (FUS). Experiments were carried out on implanted liver tumors in vivo. In order to determine the optimum treatment conditions, various combinations of exposure parameters were investigated. The results showed that it is possible to achieve total destruction of tumor cells in the treatment volume using an FUS system with a frequency of 1.7 MHz, with in situ ISAL of 261 W/cm2, 5-s exposure duration, and 1.5-mm exposure separation, with an in situ ISAL of 266 W/cm2, 10-s duration, and 2-mm separation, or with in situ ISAL of 213 W/cm2, 8-s duration, and 1.5-mm separation. Fifteen selected tumors were treated with these experimentally determined "optimum" exposure conditions. All the tumors were destroyed completely. Assessment of tumor viability in the treated volume was performed using both histologic and tissue culture methods. The mechanism of tumor damage, the limitations of the tumor model, and the effect of exposure parameters and liver blood flow on the treatment are discussed.

Animals↗
PubMed1998

Alkyl hydroperoxide reductase subunit C (AhpC) protects bacterial and human cells against reactive nitrogen intermediates.

In Salmonella typhimurium, ahpC encodes subunit C of alkyl hydroperoxide reductase, an enzyme that reduces organic peroxides. Here, we asked if ahpC could protect cells from reactive nitrogen intermediates (RNI). Salmonella disrupted in ahpC became hypersusceptible to RNI. ahpC from either Mycobacterium tuberculosis or S. typhimurium fully complemented the defect. Unlike protection against cumene hydroperoxide, protection afforded by ahpC against RNI was independent of the reducing flavoprotein, AhpF. Mycobacterial ahpC protected human cells from necrosis and apoptosis caused by RNI delivered exogenously or produced endogenously by transfected nitric oxide synthase. Resistance to RNI appears to be a physiologic function of ahpC. ahpC is the most widely distributed gene known that protects cells directly from RNI, and provides an enzymatic defense against an element of antitubercular immunity.

Apoptosis↗
PubMed1998

Physical characterization of nedocromil sodium hydrates.

Nedocromil sodium, which is used in the treatment of reversible obstructive airway diseases, such as asthma, is found to exist in the following hydrate phases: the heptahemihydrate, the trihydrate, a monohydrate, and an amorphous phase which contains variable amounts of water (1.5-3.0 mol). An anhydrate phase is formed from the trihydrate at zero humidity at >/= 150 degrees C, but is rapidly hydrated under ambient conditions. The physical and thermodynamic properties of the four hydrate phases were characterized using differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), powder X-ray diffraction (PXRD) at ambient and elevated temperatures, hot-stage microscopy (HSM), solid phase interconversion at various relative humidities (RH), intrinsic dissolution rate (IDR), equilibrium solubility measurements, and critical RH measurements. Below 100 degrees C in open pan TGA, the heptahemihydrate and the amorphous forms lose virtually all their water, the monohydrate loses negligible amounts of water, whereas the trihydrate loses the first two moles of water. From 130 degrees C to 200 degrees C in open pan TGA the trihydrate and the monohydrate lose their last mole of water to form the anhydrate. In crimped pan DSC, the thermal events observed are analogous to those observed in open pan TGA, but the temperatures are increased by about 75 degreesC for all except the heptahemihydrate, for which the thermal events are more complex. When the heptahemihydrate is heated in a crimped pan, a melting endotherm is observed at about 75 degrees C followed by three dehydration endotherms. For the crystalline hydrate phases at 22 degrees C, the ranges of stability are as follows: the monohydrate from 0 to 6.4% RH; the trihydrate from 6.4 to 79.5% RH; the heptahemihydrate above 80% RH. A microbalance study showed that the heptahemihydrate is kinetically stable over the range 11 to 79.5% RH. The IDR in water at 25 degrees C under constant hydrodynamic conditions decreases in the rank order: monohydrate > trihydrate > heptahemihydrate, corresponding to the rank order of free energy with respect to the aqueous solution. The equilibrium aqueous solubility of the heptahemihydrate at 25.0 +/- 0.2 degrees C is 0.956 +/- 0.010 M.

Anti-Asthmatic Agents↗
PubMed1998

Three cis-elements required for rice alpha-amylase Amy3D expression during sugar starvation.

Expression of alpha-amylase genes during seedling development plays a key role in production of sugar from the starch stored in the cereal seed. Rice alpha-amylase Amy3D promoter/GUS constructs in transgenic rice cell lines were studied to identify cis elements in the promoter of this metabolite-regulated gene. Three sequences having the greatest effects on Amy3D gene expression included the amylase element (TATCCAT), the CGACG element, and a G box-related element (CTACGTGGCCA). These promoter cis elements are needed for high-level expression of Amy3D under conditions of sugar starvation. The involvement of G box cis-elements in environmental stress responses suggest a link between the nutrient stress and the environmental stress responses of the plant.

Base Sequence↗
PubMed1998

Classical eyeblink conditioning in two strains of mice: conditioned responses, sensitization, and spontaneous eyeblinks.

Conditioned eyeblink responses (CRs), sensitization, and spontaneous eyeblinks were studied in C57BL/6J and BALB/c mice. Both strains of mice acquired CRs during 10 days of classical delay eyeblink conditioning. The BALB/c mice reached a higher asymptotic CR level than the C57BL/6J mice. The CRs were extinguished and recovered in both strains following conditioned stimulus-alone and paired conditioned stimulus-unconditioned stimulus training. During 10 days of explicitly unpaired training, the control groups showed no signs of sensitization and low incidence of spontaneous eyeblinks. When switched to paired training, the unpaired groups exhibited significant conditioned inhibition. These results suggest that strain differences must be considered in experimental design and data interpretation for these basic aspects of associative learning and memory.

Analysis of Variance↗
PubMed1998

Expression and inheritance of multiple transgenes in rice plants.

The ability to control integration, inheritance, and expression of multiple transgenes is a prerequisite for manipulating biosynthetic pathways and complex agronomic characteristics in plants. One hundred and twenty-five independent transgenic rice plants were regenerated after cobombarding embryogenic tissues with a mixture of 14 different pUC-based plasmids. Eighty-five percent of the R0 plants contained more than two, and 17% more than nine, of the target genes. Plants containing multiple transgenes displayed normal morphologies and 63% set viable seed. Multigene cotransformation efficiency was correlated with the ratio in which the plasmids were mixed with respect to the selectable marker. All target genes had an equal chance of integration, indicating that the nature of the coding region had no effect on the efficiency of integration. Three plant lines containing 11, 10, and 9 transgenes, respectively, were analyzed for patterns of integration and inheritance until the R3 generation. Integration of multiple transgenes occurred at either one or two genetic loci, with inheritance conforming to a 3:1 Mendelian ratio. Coexpression of four marker genes was investigated until the R2 generation.

Acetyltransferases↗
PubMed1998

Effect of subcutaneous recombinant human erythropoietin in cancer patients receiving radiotherapy: final report of a randomized, open-labelled, phase II trial.

The purpose of this study was to determine the safety, efficacy and impact on quality of life of recombinant human erythropoietin (r-HuEPO) for cancer patients undergoing radiotherapy (RT). An open-labelled randomized design was used, with patients randomized to either treatment or control arms. Patients in the treatment arm received r-HuEPO given by subcutaneous injection at a dose of 200 units kg(-1) day(-1) plus oral iron supplements (ferrous sulphate 325 mg p.o. t.i.d.). Entry was restricted to patients with carcinoma of the lung, uterine cervix, prostate or breast who presented for RT with anaemia parameters reflective of 'the anaemia of chronic disease'. Radiotherapy policies (portals, doses, fraction size, etc.) were determined by the site and stage of disease. Complete blood counts (CBCs) were obtained weekly. The target level of haemoglobin was 15 g dl(-1) for men and 14 g dl(-1) for women. Quality of life (QOL) was assessed weekly by using an analogue scale to judge energy, activities of daily living and overall quality of life. Forty-eight patients were entered in the study, 24 in the treatment arm and 24 in the control arm. The prerandomization demographic characteristics and mean laboratory values were comparable in both arms. The mean haemoglobin at completion was 13.6 g dl(-1) for r-HuEPO-treated patients compared with 11.0 g dl(-1) for control subjects (P = 0.0012). Patients who received r-HuEPO demonstrated a mean weekly haemoglobin increase of 0.41 g dl(-1) compared with a decrease in mean haemoglobin level in controls for 6 of the 7 weeks of the study (mean weekly decrease of 0.073 g dl(-1)). Target levels of haemoglobin were achieved by 41.6% of r-HuEPO-treated patients compared with none of the control subjects. The mean platelet count declined in both arms of the study with RT but the decline from pretreatment was less rapid in r-HuEPO-treated patients (11.2% decrease) compared with controls (26.3% decrease) and was statistically significant during weeks 4-6. Toxicity was minor with only mild irritation at the injection site. Mean quality of life end points were superior in the treatment arm but not statistically significant. r-HuEPO had a beneficial effect on weekly haemoglobin levels in patients undergoing RT with response rates similar to other studies. There was also a less rapid decline in weekly platelet counts in r-HuEPO-treated patients compared with control subjects. Further studies are needed to address the optimum dose and scheduling as well as the impact of r-HuEPO on clinical outcomes.

Anemia↗
PubMed1998

Sequence elements that contribute to the degradation of yeast G alpha.

BACKGROUND: Gpa1 is the alpha subunit of the yeast G-protein that regulates signal transduction during mating. The stability of Galpha/Gpa1 is influenced by the ubiquitin-dependent N-end rule pathway, suggesting that the regulation of G alpha levels may be important for effective mating response and recovery. RESULTS: The G alpha sequences that confer sensitivity to degradation by the N-end rule pathway were identified. The insertion of this degradation signal (G1-Deg) into the ordinarily stable Gpa2 protein conferred proteolytic targeting. We examined G alpha degradation under different conditions and found that it was efficiently degraded in haploid and diploid cells, but was stable if it was synthesized prior to expression of the N-end rule pathway. Interestingly, a specific mutation in G alpha that is believed to promote the GTP-bound form (N388K) caused accelerated degradation. CONCLUSION: A region encompassing a putative effector-binding domain (G1-Deg) is required for G alpha degradation via the N-end rule pathway. Our studies have shown that G alpha is susceptible to proteolysis soon after synthesis. These results are in agreement with the idea that G alpha is more unstable in the GTP-bound form, which is the predominant state of monomeric/free G alpha soon after synthesis. It is likely that the signal transduced by Gbetagamma can be regulated by adjusting the levels of G alpha through proteolysis.

Amino Acid Sequence↗
PubMed1998

Apoptosis is associated with atypical or malignant change in meningiomas. An in situ labelling and immunohistochemical study.

AIMS: Although necrosis is an important phenomenon with implications for grading and prognostication in meningiomas, the alternate form of cell death, apoptosis, has not been extensively studied. In this series, we aimed to determine whether apoptosis in meningiomas correlated with histological types and grading. We also looked for a relationship between expression of apoptosis-related genes bcl-2, p53, c-myc and apoptosis meningiomas. METHODS AND RESULTS: Fifty-one meningiomas of diverse histological subtypes and grades were investigated with in situ end-labelling of DNA fragments as well as immunohistochemical analysis of three apoptosis-related genes: p53, bcl-2 and c-myc. Our results showed that the apoptosis index was significantly higher in high-grade meningiomas (0.12%, n = 12) in than the benign meningiomas (0.023%, n = 39) P = 0.001) but there was no difference among the different histological subtypes of the benign meningiomas (P = 0.125). There is no obvious relationship between p53, bcl-2 and c-myc staining and apoptosis index in this group of meningiomas. CONCLUSION: We conclude that apoptosis is an important phenomenon in meningiomas and that it is associated with atypical or malignant changes in meningiomas. Apoptosis in meningiomas has no clearcut relationship with expression of p53, bcl-2 and c-myc.

Adult↗
PubMed1998

A rapid method to screen for cell-wall mutants using discriminant analysis of Fourier transform infrared spectra.

We have developed a rapid method to screen large numbers of mutant plants for a broad range of cell wall phenotypes using Fourier transform infrared (FTIR) microspectroscopy of leaves. We established and validated a model that can discriminate between the leaves of wild-type and a previously defined set of cell-wall mutants of Arabidopsis. Exploratory principal component analysis indicated that mutants deficient in different cell-wall sugars can be distinguished from each other. Discrimination of cell-wall mutants from wild-type was independent of variability in starch content or additional unrelated mutations that might be present in a heavily mutagenised population. We then developed an analysis of FTIR spectra of leaves obtained from over 1000 mutagenised flax plants, and selected 59 plants whose spectral variation from wild-type was significantly out of the range of a wild-type population, determined by Mahalanobis distance. Cell wall sugars from the leaves of selected putative mutants were assayed by gas chromatography-mass spectrometry and 42 showed significant differences in neutral sugar composition. The FTIR spectra indicated that six of the remaining 17 plants have altered ester or protein content. We conclude that linear discriminant analysis of FTIR spectra is a robust method to identify a broad range of structural and architectural alterations in cell walls, appearing as a consequence of developmental regulation, environmental adaptation or genetic modification.

Arabidopsis↗
PubMed1998

Low Na+ diet inhibits Na+ and water transport response to vasopressin in rat cortical collecting duct.

BACKGROUND: We previously demonstrated that vasopressin (AVP) produces a sustained increase in Na+ reabsorption by the isolated perfused cortical collecting duct (CCD) from rats on a normal diet, and that this effect is synergistic with that of pharmacological doses of deoxycorticosterone (DOC) or physiological levels of aldosterone. The present experiments examined the effect of AVP under the more physiological circumstances when plasma aldosterone was elevated by prior volume depletion. METHODS: Rats were volume depleted by a single dose of furosemide followed by a low-salt diet (0.3% NaCl) for four to nine days. Some of these rats were also implanted with a pellet containing 2.5 mg DOC. Rats in a third group were not injected with furosemide but were implanted with the DOC pellet and maintained on a standard (approximately 1% NaCl) diet. CCD were perfused and the lumen-to-bath Na+ flux (JNA), transepithelial voltage (VT), and osmotic water permeability (Pf) were measured in the presence and absence of 200 pm AVP. RESULTS: Although Na+ depletion by a single injection of furosemide and the low salt diet elevated plasma aldosterone and Vt, JNA remained low and there was a decreased response to AVP in comparison with DOC-treated rats on a standard diet. In CCD from rats on the low salt-diet with DOC, JNa was less than observed in CCD from DOC-treated rats on a standard diet. AVP-dependent Pf in CCD from rats on the low salt-diet, with or without DOC treatment, was also markedly lower. CONCLUSIONS: We interpret the results to demonstrate that maximal rates of Na+ reabsorption in the CCD depend not only on the synergistic stimulatory effects of aldosterone and AVP, but also require normal to high rates of salt delivery in vivo for the effects of the hormones on Na+ transport to be maximized in vitro.

Animals↗
PubMed1998

Long-term functional results of contralateral C7 transfer.

From 1986 to 1994, 82 patients with brachial plexus root avulsion were operated on using a contralateral C7 nerve-root transfer. Forty-four patients underwent a one-stage procedure in which the distal end of the ulnar nerve was anastomosed to the contralateral C7 root, and the other 38 underwent a two-stage procedure (first phase: C7 root --> ulnar nerve; second phase: ulnar nerve --> recipient nerve). Twenty postoperative cases were followed-up for 2 years. Of them, the ulnar nerve was transferred to the musculocutaneous nerve in six cases, with recovery of the biceps up to M3 in four and S3 in five cases; the ulnar nerve was transferred to the median nerve in eight cases, with recovery of the wrist and finger flexors up to M3 in five and S3 in six cases; the ulnar nerve was transferred to the radial nerve in four cases, with recovery of the triceps up to M4 in two and S3 in three cases; and the ulnar nerve was transferred to the thoracodorsal nerve in two cases, with recovery of the latissimus dorsi to M4 in one case. The total muscle recovery rate (up to M3) of the series was 60 percent, and the sensory recovery rate (S3) was 78 percent. Outcomes were related to patient age, operative delay, and whether or not the ulnar nerve was used as a bridge for transfer.

Adolescent↗
PubMed1998

On the relative salience of Euclidean, affine, and topological structure for 3-D form discrimination.

A match-to-sample task was performed, in which observers compared configurations of line segments presented stereoscopically in different three-dimensional orientations. Several different structural properties of these configurations were manipulated, including the relative orientations of line segments (a Euclidean property), their coplanarity (an affine property), and their patterns of cointersection (a topological property). Although the differences in these properties to be detected were all metrically equivalent, they varied dramatically in their relative perceptual salience, such that the error rates and reaction times in the three conditions varied by as much as 400%. Performance was highest in the topological condition, intermediate in the affine condition, and lowest in the Euclidean condition. These findings suggest that the relative perceptual salience of object properties may be systematically related to their structural stability under change, in a manner that is similar to the Klein hierarchy of geometries.

Depth Perception↗
PubMed1998

Environmental factors influence P. aeruginosa binding to the wounded mouse cornea.

PURPOSE: To determine whether environmental factors or bacterial viability affect the binding of two strains of P. aeruginosa to mouse cornea. METHODS: Scarified corneas were placed in organ culture and inoculated with P. aeruginosa cell suspensions containing either ATCC 19660 or PAO1 bacterial strains classed as cytotoxic or invasive, respectively. Eyes were incubated in vitro for 1 h after bacterial application at different pH or temperature conditions or in PBS containing various divalent cations. The adhesion of heat-killed or formalin-fixed bacteria was tested similarly. Scanning electron microscopy (scanning EM) was used to quantitate adherent bacteria. RESULTS: P. aeruginosa ATCC 19660 showed an increase in binding at pH 8.0, favored higher temperatures and required both calcium and magnesium for optimum binding. Adherence of PAO1 was enhanced at pH 6.5 and decreased at pH 8.0. This strain favored binding at lower temperatures and did not require either divalent cation for optimum binding. In addition, the presence of magnesium ions resulted in reduced binding for this strain. Both strains exhibited less binding ability after formalin fixation or heat killing. CONCLUSION: Environmental factors and bacterial viability are important factors which influence the ability of both cytotoxic and invasive strains of P. aeruginosa to bind to the scarified cornea.

Animals↗
PubMed1998

Thimerosal-induced Ca2+ mobilization in isolated guinea pig cochlear outer hair cells.

Intracellular calcium mobilization of isolated guinea pig cochlear outer hair cells (OHCs) was investigated using thimerosal, a -SH group oxidizing agent, and fura-2 fluorescence ratio imaging microscopy. In the presence of thimerosal, intracellular Ca2+ concentrations ([Ca2+]i) of OHCs were elevated in a dose-dependent manner. Even in Ca(2+)-free medium, Ca2+ response was still induced. The effects of thimerosal on [Ca2+]i were completely blocked and reversed by dithiothreiotol (DTT). Neither 1-100 microM ryanodine nor 5-20 mM caffeine altered the effects of thimerosal. Pretreatment with pertussis toxin (PTX) for 30 min did not affect the thimerosal-induced increase in [Ca2+]i. The increase in [Ca2+]i when Ca2+ was added during thimerosal application in Ca(2+)-free medium was almost completely blocked by 500 microM LaCl3, while nifedipine did not inhibit further increase in [Ca2+]i caused by thimerosal. Thus, oxidation of the -SH group of the OHC membrane can induce a Ca2+ release from intracellular Ca2+ stores, which are ryanodine- and caffeine-insensitive, and Ca2+ influx through non-specific Ca2+ channels, but not the nifedipine-sensitive Ca2+ channels. The possible oxidation of -SH group gated Ca2+ channels in OHCs is worthy of further study.

Animals↗