Biomedical subjects

W Shi

Publications and source records attributed to W Shi.

At least 217 records · Page 12Linked to original sources

PubMed1995

Cardiopulmonary effects of positive pressure ventilation during acute lung injury.

STUDY OBJECTIVES: To assess the gas exchange and hemodynamic effects of pressure-limited ventilation (PLV) strategies in acute lung injury (ALI). We hypothesized that in ALI, the reduction of plateau airway pressure (Paw) would be associated with less alveolar overdistention and thus have better hemodynamic and gas exchange characteristics than larger tidal volume (Vr) ventilation. SETTING: Laboratory. DESIGN: Prospective time-controlled sequential animal study. MEASUREMENTS: Right atrial, pulmonary artery, left atrial, arterial, lateral pleural (Ppl), and pericardial (Ppc) pressures, Paw, ventricular stroke volume, mean expired CO2, and arterial and mixed venous oxygen contents. Airway resistance and static lung compliance were also measured. INTERVENTIONS: Intermittent positive pressure ventilation (IPPV) given before (control) and after induction of ALI by oleic acid infusion (0.1 mL/kg). IPPV at FIO2 of 1, VT of 12 mL/kg, and frequency adjusted to maintain normocarbia. ALI PLV was given during ALI and defined as that VT which gave a similar plateau Paw to that of control IPPV. High-frequency jet ventilation (HFJV) and ALI HFJV were also given and defined as frequency within 10% of heart rate and mean Paw similar to that during control IPPV. RESULTS: After ALI, static lung compliance, PaO2, and pH decreased, whereas airway resistance and PaCO2 increased. For a constant lung volume, Ppl and Ppc were not different between control and ALI. Both absolute dead space (VD) and intrapulmonary shunt fraction increased after ALI, but absolute VD was lower with ALI PLV and ALI HFJV when compared with ALI IPPV. Ventilation did not alter hemodynamics during ALI. CONCLUSIONS: Changes in lung volume determine Ppc and Ppl. PLV strategies do not alter hemodynamics but result in less of an increase in VD/VT than would be predicted from the obligatory decrease in VT.

Animals↗

PubMed1995

[Treatment of non-small-cell lung cancer by dual (bronchial and pulmonary) arterial drug infusion].

Since the lung receives blood supply from both the bronchial and pulmonary arteries, chemotherapeutic agents given through both channels would give higher local drug concentration and better therapeutic results in the treatment of lung cancer. In this study, 10 patients with advanced NSCLC were treated by dual arterial infusion (DAI) of carboplatin (300mg/m2) and VP-16 (200-300mg/m2) twice at 3-week interval. From DAI treatment, a response rate of 80% (CR 2, PR 6) was achieved. In 5 patients DAI treatment had made surgical resection of the lung cancer possible. The 1-, 2- and 3-year survivors were 8, 6 and 5 respectively, with a median survival time of 11.5 months.

Adult↗

PubMed1995

A rapid test for endotoxin in whole blood.

A rapid whole blood agglutination test has been developed for the detection of endotoxin. The test reagent consists of polymyxin B (PmB) conjugated to the Fab fragment of the anti-glycophorin antibody 1C3/86. After addition of reagent to whole blood, red cell agglutination occurs within two minutes in samples from endotoxaemic patients or with the addition of either whole Gram negative bacteria, supernatants from Gram negative bacterial cultures or purified endotoxin. In clinical samples there was a strong correlation (r = 0.83) between the strength of agglutination and the level of endotoxin measured by the Limulus amaebolysate test (LAL). The prospect of a rapid and accurate test for endotoxin may enable better clinical management of Gram negative sepsis.

Adult↗

PubMed1994

Identification of a putative metal binding site in a new family of metalloregulatory proteins.

The transcription of the ars operon is negatively controlled by the ArsR repressor and induced by arsenite and antimonite. Using hydroxylamine mutagenesis, four arsR mutants were isolated; three were selected for inability to respond to inducers: C32Y, C32F, and C34Y. Each of the three altered proteins still bound specifically to the ars operator, but inducers were less effective in effecting the release of the altered proteins from the DNA. Each of the mutant arsR genes in trans with a reporter gene controlled by the ars promoter repressed expression of the reporter gene, and addition of inducer did not relieve repression. These results suggest that the altered ArsR proteins are defective in the inducer binding site. The fourth arsR mutation, resulting in a H50Y alteration, produced constitutive expression. His-50 is located within a putative helix-turn-helix region of the ArsR protein. We propose that cysteines Cys-32 and Cys-34 in the ArsR protein comprise part of a metal binding motif found in members of the ArsR family of metalloregulatory proteins.

Amino Acid Sequence↗

PubMed1994

Effects of carboxyl-terminal truncation on the stability and G protein-coupling activity of bovine rhodopsin.

A number of studies have suggested that G protein-coupled receptors possess domains within the carboxyl terminus that are important for the catalytic activation of G proteins. To define these regions, truncation mutants were generated in the cDNA of bovine rhodopsin, the receptor responsible for visual signal transduction in the retinal rod cell. The mutants were expressed in HEK-293 cells and analyzed for their ability to bind the chromophore, 11-cis-retinal, and for activating Gt, the G protein of the rod cell regulated by rhodopsin. Removal of 38 carboxyl-terminal amino acids resulted in the production of a mutant (K311 stop) that does not bind 11-cis-retinal, has an abnormal pattern of glycosylation, and does not catalyze light-dependent binding of GTP gamma S to Gt, suggesting that it is unable to fold properly during biogenesis. However, a truncation mutant with only five additional amino acids (C316stop) coupled normally to Gt, using membranes from transfected cells, despite the fact that it lacked the "fourth cytoplasmic loop" formed by palmitoylation of cysteines-322 and -323. When C316stop is extracted from the membrane with detergent, only a fraction is able to bind 11-cis-retinal, but the fraction that binds retinal activates Gt normally. In contrast, detergent-solubilized wild-type rhodopsin and K325stop (a truncation mutant with the longest carboxyl terminus) both bind retinal and activate Gt normally. These data suggest that the proximal region of the carboxyl terminus is critical for the proper folding and stability of the rhodopsin molecule and that amino acids Cys316 to Ala348 are not necessary for the activation of Gt.

Amino Acid Sequence↗

PubMed1994

Isolation and phenotypic characterization of Myxococcus xanthus mutants which are defective in sensing negative stimuli.

Myxococcus xanthus is a gram-negative gliding bacterium that exhibits a complex life cycle. Exposure of M. xanthus to chemicals like dimethyl sulfoxide (DMSO) at nondeleterious concentrations or the depletion of nutrients caused several negative responses by the cells. DMSO (> 0.1 M) or nutrient depletion triggered a repellent response: cell swarming was inhibited and FrzCD (a methyl-accepting chemotaxis protein) was demethylated; higher concentrations of DMSO (> 0.3 M) or prolonged starvation induced an additional response which involved cellular morphogenesis: DMSO caused cells to convert from rod-shaped vegetative cells to spherical, environmentally resistant "DMSO spores," and starvation induced myxospore formation in the fruiting bodies. In order to investigate the nature of these responses, we isolated a number of mutants defective in negative chemotaxis and/or sporulation. Characterization of these mutants indicated that negative chemotaxis plays an important role in colony swarming and in developmental aggregation. In addition, the results revealed some of the major interrelationships between the signal transduction pathways which respond to negative stimuli: (i) DMSO exposure and starvation were initially sensed by different systems, the neg system for DMSO and the stv system for starvation; (ii) the repellent response signals triggered by DMSO or starvation were then relayed by the frz signal transduction system; mutants defective in these responses showed altered FrzCD methylation patterns; and (iii) the morphogenesis signals in response to DMSO or starvation utilize a group of genes involved in sporulation (spo).

Bacterial Proteins↗

PubMed1994

Sensory adaptation during negative chemotaxis in Myxococcus xanthus.

Myxococcus xanthus exhibits many tactic movements that require the frz signal transduction system, such as colony swarming and cellular aggregation during fruiting body formation. Previously we demonstrated that the Frz proteins control the chemotactic movements of M. xanthus (W. Shi, T. Köhler, and D. R. Zusman, Mol. Microbiol. 9:601-611, 1993). However it was unclear from that study how chemotaxis might be achieved at the cellular level. In this study, we showed that M. xanthus cells not only modulate the reversal frequency of cell movement in response to repellent stimuli but also exhibit sensory adaptation in response to the continuous presence of nonsaturating repellent stimuli. The sensory adaptation behavior requires FrzF (a putative methyltransferase) and is correlated with the methylation-demethylation of FrzCD, a methyl-accepting chemotaxis protein. These results indicate that negative chemotaxis in M. xanthus is achieved by chemokinesis plus sensory adaptation in a manner analogous to that of the free-swimming enteric bacteria.

Acclimatization↗

PubMed1994

[The sensitivity of the CA125 immunoradiometric assay for patients with epithelial ovarian cancer and its correlation with complex treatment].

From 1988 to 1993, 141 patients with epithelial ovarian cancer were treated in our hospital. Histologically, tumors were: 69 serous, 16 mucinous, 6 clear cell, 24 endometrioid, and 26 undifferentiated. Serial serum specimens were obtained from 50 patients at least 2 times in posttreatment 1 to 3 months to observe the correlation between CA125 levels and disease progression or regression. The result showed that CA125 levels were elevated (> 33kU/L) in 65/69 of serous, 0/16 of mucinous, 6/6 of clear cell, 19/24 of endometrioid, 10/26 of undifferentiated tumors. The CA125 determinants was associated with the 80% of cases of nonmucinous epithelial ovarian cancer. Moreover, increases or decreases in CA125 levels have been found to correlate well with disease progression or regression in more than 96% of instances. The determination of CA125 levels may aid in monitoring the response to treatment in patients with epithelial ovarian cancer.

Adenocarcinoma, Mucinous↗

PubMed1994

Induction of cyclin D1 overexpression by activated ras.

Activated ras genes are known to alter control of cell proliferation. This is consistent with the fact that ras proteins are a key component of the biochemical pathway triggered by ligand-bound cell surface receptors that are tyrosine kinases. Although an important part of the ras signaling pathway has been recently uncovered, the molecular target(s) that mediates the effects of ras on cell cycle control remains unknown. Cyclins and cyclin-dependent kinases are key molecules in the control of cell cycle. Cyclin D1, in particular, is a critical target for proliferative signals in G1 and it has been shown that ectopic overexpression of this cyclin can significantly alter cell cycle regulation. Here we report that activated ras induces significant overexpression of cyclin D1 in epithelial cells derived from normal rat intestine and mouse mammary gland. A definitive causal role for activated ras in this overexpression is demonstrated by using intestinal cells transfected with an inducible ras expression vector. Treatment of the ras-transformed intestinal clones with anti-sense cyclin D1 oligonucleotides reduces their rate of cell proliferation indicating that the increment in cyclin D1 expression induced by activated ras is instrumental in the higher rate of cell proliferation conferred by the ras oncogene to the IEC cells. Based on these results we propose that, at least in certain cell types, cyclin D1 can be one of the mediators of the transforming action of activated ras.

Animals↗

PubMed1993

Crystallization and preliminary X-ray studies of L-aspartase from Escherichia coli.

Single crystals of L-aspartate ammonia-lyase (L-aspartase) from Escherichia coli have been obtained by microdialysis at room temperature using polyethylene glycol 3350 and sodium acetate as co-precipitants. The crystals exhibit the symmetry of space group P2(1)2(1)2 with a = 156.5 A, b = 147.6 A, c = 102.5 A and diffract at least to 2.8 A.

Aspartate Ammonia-Lyase↗

PubMed1993

Fatal attraction.

Explore the source record for details and available documents.

Bacterial Proteins↗

PubMed1993

Anticardiolipin antibodies block the inhibition by beta 2-glycoprotein I of the factor Xa generating activity of platelets.

Antiphospholipid antibodies, defined either by lupus anticoagulant (LA) activity or positive anticardiolipin immunoabsorbent assay (ACA) are associated with a predisposition to thromboses, recurrent fetal loss or thrombocytopenia. The mechanisms for these predispositions remain undefined. We have enriched immunoglobulin fractions from two patient plasmas to obtain antibodies with LA activity but no ACA, or conversely, with ACA positivity but no LA, in order to investigate in vitro characteristics which might explain a thrombotic propensity. beta 2-glycoprotein I (beta 2-GPI), the plasma cofactor required for ACA binding to negatively charged phospholipid, has previously been shown to inhibit prothrombinase generation in the presence of activated platelets (8). We now report that beta 2-GPI, at physiological concentrations, inhibits the generation of factor Xa in the presence of activated gel-filtered platelets. Further, ACA interferes with this inhibition, resulting in protracted, unopposed factor Xa generation. This interference with beta 2-GPI, a natural anticoagulant component of plasma, is potentially prothrombotic. LA immunoglobulins behave differently and inhibit factor Xa generation in a manner similar to beta 2-GPI. These findings provide the basis for a previously unsuspected mechanism for thrombosis in patients with aPL.

Adult↗

PubMed1993

The two motility systems of Myxococcus xanthus show different selective advantages on various surfaces.

Myxococcus xanthus, a bacterium that forms fruiting bodies, moves by gliding motility utilizing dual motility systems that differ both genetically and morphologically [system A, having at least 21 genetic loci and moving mainly single cells, and system S, having at least 10 genetic loci and moving groups (rafts) of cells] [Hodgkin, J. & Kaiser, D. (1979) Mol. Gen. Genet. 172, 177-191]. In this study, we found that A- and S-gliding-motility systems have different selective advantages on surfaces containing different concentrations of agar. We observed that colonies of A+S- cells (A-motile cells) swarmed better than A-S+ cells (S-motile cells) on relatively firm and dry surfaces (e.g., 1.5% agar). In contrast, colonies of A-S+ cells swarmed much better than A+S- cells on soft and wet surfaces (e.g., 0.3% agar). Individual A-motile cells moved at a rate of 2-4 microns/min on 1.5% agar but they barely moved on 0.3% agar (< 0.5 microns/min); in contrast S-motile cells moved 3-5 times faster on 0.3% agar than on 1.5% agar. Wild-type cells with both A- and S-motility systems were able to move well over a wide range of surfaces. These results suggest that dual motility systems enable the myxobacteria to adapt to a variety of physiological and ecological environments and show similarities in function to the dual motility systems of flagellated bacteria such as Vibrio spp.

Agar↗

PubMed1993

Beta 2-glycoprotein I is a requirement for anticardiolipin antibodies binding to activated platelets: differences with lupus anticoagulants.

Antiphospholipid (aPL) antibodies are of major interest not only because the lupus anticoagulant (LA) causes an inhibition of in vitro blood coagulation, but also because the presence of aPL antibodies confers a risk of thrombosis. The inhibition of in vitro phospholipid-dependent coagulation (LA) is thought to be caused by the binding of LA to procoagulant phospholipid surfaces, thus impeding the clotting process. Another class of aPL antibodies are those originally described to be directed against negatively charged phospholipids, in particular cardiolipin (ACA). ACA are usually directed against a complex antigen consisting of negatively charged phospholipid and a plasma protein, beta 2-glycoprotein I (beta 2-GPI). Further, there is antibody heterogeneity even within individual patients so that ACA and LA are separable using physicochemical techniques such as ion exchange chromatography and chromatofocusing. Using such techniques we have enriched Ig fractions for LA and ACA from two patient plasmas. The majority of Ig with LA activity had a pI of 7.2 to 7.3 whereas ACA had a pI of 5.0 to 5.2. Using these enriched fractions labeled with [125I]-iodine we have shown that LA binds to platelets in a specific and saturable manner. Binding is dependent on thrombin activation. [125I]-ACA behaves differently. Like LA, binding is specific and dependent on thrombin activation but in this case requires the presence of beta 2-GPI. ACA, in the presence of beta 2-GPI, competes for binding with LA suggesting the same or contiguous site. There is no cross-reactivity of these antibodies with GPIIb/IIIa and the most likely binding site is phospholipid. In neither case does LA nor ACA have an effect on thrombin-induced release of serotonin or beta-thromboglobulin nor do they affect platelet aggregation induced by a number of agonists. This antibody binding may play an etiological role in thrombocytopenia associated with aPL, but does not explain thrombosis on the basis of hyperaggregability or increased platelet release.

Adult↗

PubMed1993

Effect of varying laser parameters on pulsed Ho:YAG ablation of bovine knee joint tissues.

We investigated the effect of varying laser parameters on ablation of fresh bovine knee joint tissues (fibrocartilage, hyaline cartilage, and bone) with a free-running Ho:YAG laser. Ablation rate was measured in saline for each tissue type as a function of laser fluence (160-950 J/cm2), pulse width (150-450 microseconds, full width at half maximum), and fiber core diameter (400 and 600 microns). A weight that was attached to the fiber end was used to exert a constant pressure of 40 g/mm2 to the tissue underneath to ensure a constant contact between the fiber tip and the tissue throughout the ablation process. All tissues could be efficiently ablated, and the ablation rate increased linearly with the fluence. Change in laser pulse width and fiber core diameter resulted in minor variations in the ablation rate for fibro- and hyaline cartilage. On the other hand, use of longer pulses and/or the larger fiber significantly accelerated bone ablation. Histology analysis revealed that zones of thermal damage in Ho:YAG irradiated bovine knee joint tissues differed by tissue types and ranged between 100 and 400 microns, but were independent of fluence, pulse width, and fiber size within the range tested.

Animals↗

PubMed1993

Chemotaxis plays a role in the social behaviour of Myxococcus xanthus.

Myxococcus xanthus is a Gram-negative bacterium that glides on a solid surface and displays a wide range of social behaviour including microbial development. The frz genes are homologues to the chemotaxis genes of Escherichia coli and Salmonella typhimurium and have been shown to be involved in microbial development. However, chemotaxis has never been clearly demonstrated in Myxococcus. In this study, we showed that M. xanthus exhibited tactic movements to many chemicals when they were subjected to steep and stable chemical gradients. M. xanthus was observed to spread into areas with abundant nutrients like yeast extract or Casitone and avoid areas with no nutrients or repellents (short-chain alcohols or DMSO). Responses to attractants and repellents were additive. Movement towards attractants or away from repellents required the frz genes and was correlated with methylation or demethylation of FrzCD, a methyl-accepting taxis protein. Furthermore, the frz genes were found to be required for both fruiting body formation during starvation and swarming in nutrient-rich medium. In wild-type strains, cells near the colony edge were observed to swarm towards the surrounding growth medium and to contain highly methylated FrzCD; cells near the colony centre contained mainly demethylated FrzCD and showed directed movement towards the colony edge. FrzCD was also found to be methylated during the aggregation stage of fruiting body formation on agar but largely demethylated in cells shaken in liquid starvation media. An frzE mutant failed to exhibit directed cell movements and no longer showed modification of FrzCD under these conditions. These observations suggest that M. xanthus does show chemotactic movements, that these movements require the frz genes, and that chemotaxis plays a very important role in the social behaviour of this organism.

Bacterial Proteins↗

PubMed1993

Behavioral responses of Escherichia coli to changes in temperature caused by electric shock.

The behavioral response of Escherichia coli to electric shock in 10(-2) M potassium phosphate plus 10(-4) M potassium EDTA was studied. When presented with a 150-V/cm electric shock that lasted 250 ms, the bacteria at first exclusively ran, then exclusively tumbled, and finally returned to their original running and tumbling. This response is due to increased temperature caused by the electric shock, i.e., to thermotaxis, and it is mediated by the chemotaxis machinery. A more severe electric shock, 150 V/cm for 550 ms, caused cells to tumble immediately, and then they went back to their original running and tumbling. The mechanism of that response is unknown since, unlike known thermotaxis, it does not require the chemotaxis machinery.

Chemotaxis↗

PubMed1993

The pss and psd genes are required for motility and chemotaxis in Escherichia coli.

Mutants of Escherichia coli defective in phosphatidylserine synthase (encoded by pss) and phosphatidylserine decarboxylase (encoded by psd) make cell membranes deficient in phosphatidylethanolamine. In this report we show that wild-type pss and psd genes are required for motility and chemotaxis. Null mutants or strains with temperature-sensitive pss or psd mutations grown at high temperature (35 degrees C) were nonmotile. They lacked flagella and showed reduced rates of transcription of the flhD master operon (encoding FlhD and FlhC), the fliA operon (encoding sigma F), and the fliC operon (encoding flagellin). At low temperature (25 degrees C), the temperature-sensitive mutant cells showed motility and chemotaxis but at reduced levels. The extent of the motility and chemotaxis defects in the mutants was correlated with the amount of phosphatidylethanolamine in the membranes, suggesting a link between membrane phospholipid composition and expression of the flagellum chemotaxis regulon.

Bacterial Proteins↗