Biomedical subjects

J Xiong

Publications and source records attributed to J Xiong.

At least 91 records · Page 5Linked to original sources

PubMed1995

Diminished expression of insulin-like growth factor (IGF) binding protein-5 and activation of IGF-I-mediated autocrine growth in simian virus 40-transformed human fibroblasts.

The reduced growth factor requirements of murine fibroblasts transformed by simian virus 40 (SV 40) have been attributed to insulin-like growth factor (IGF)-I induction by T antigen and consequent activation of IGF-I receptor signaling. The present study shows that the autonomous growth of SV 40-transformed human fibroblasts also requires type-I IGF-I receptor activation but that this is not due to de novo induction of IGF-I gene expression since untransformed human fibroblasts, which fail to proliferate in the absence of serum, also showed IGF-I gene expression under serum-free conditions. DNA synthesis assays confirmed that untransformed cells were responsive to exogenous IGF and indicated that transformed cells were already maximally stimulated. In untransformed fibroblasts, IGF binding was principally to abundant membrane-associated IG-FBP-5, whereas in transformed fibroblasts this protein was minimally expressed, and IGF binding was to IGF receptors. Loss of detectable membrane-associated IG-FBP-5 in transformed cells was associated with diminished IGFBP-5 gene expression and with loss of IGF-II gene expression. Exogenous IGFBP-5 associated with the membranes of transformed cells and inhibited the autocrine growth of these cells. These findings suggest that loss of IGFBP-5 in SV 40-transformed fibroblasts facilitates interaction of endogenously produced IGF-I with the IGF-I receptor and increases their sensitivity to autocrine stimulation.

Base Sequence↗

PubMed1995

Solution nonideality related to solute molecular characteristics of amino acids.

By measuring the freezing-point depression for dilute, aqueous solutions of all water-soluble amino acids, we test the hypothesis that nonideality in aqueous solutions is due to solute-induced water structuring near hydrophobic surfaces and solute-induced water destructuring in the dipolar electric fields generated by the solute. Nonideality is expressed with a single solute/solvent interaction parameter I, calculated from experimental measure of delta T. A related parameter, I(n), gives a method of directly relating solute characteristics to solute-induced water structuring or destructuring. I(n)-values correlate directly with hydrophobic surface area and inversely with dipolar strength. By comparing the nonideality of amino acids with progressively larger hydrophobic side chains, structuring is shown to increase with hydrophobic surface area at a rate of one perturbed water molecule per 8.8 square angstroms, implying monolayer coverage. Destructuring is attributed to dielectric realignment as described by the Debye-Hückel theory, but with a constant separation of charges in the amino-carboxyl dipole. By using dimers and trimers of glycine and alanine, this destructuring is shown to increase with increasing dipole strength using increased separation of fixed dipolar charges. The capacity to predict nonideal solution behavior on the basis of amino acid characteristics will permit prediction of free energy of transfer to water, which may help predict the energetics of folding and unfolding of proteins based on the characteristics of constituent amino acids.

Amino Acids↗

PubMed1995

Manipulating rat lens glucose metabolism with exogenous substrates.

Diabetic lens glucose metabolism in vivo can be altered by a number of exogenous substrates. We have chosen two, one a glucose epimer (mannose) and the other a glycolytic intermediate (pyruvate), to demonstrate the possibility of this approach. D(+)-Mannose is a D(+)-glucose epimer but in lenses incubated in 35.5 mM mannose, no mannitol (the sorbitol equivalent) was detected, while both lactate production and 31P profile appeared normal. Mannose therefore is a good glucose substitute causing no polyol formation. Mannose metabolism in the rat lens in vivo was then examined. Diabetic rats fed mannose-enriched diet over a period of 14 days showed retardation of changes in 31P metabolites, specifically the levels of phosphorylcholine and glycerophosphorylcholine, suggesting a protective effect. Rat lenses incubated in 35.5 mM glucose in the presence of 5 mM pyruvate (pyr) showed 50% lower sorbitol than without pyr. With 5 mM pyr in the drinking water, i.e. pretreatment in vivo during a 3-day diabetes induction period, the diabetic rat lens accumulated acetate and alanine when incubated in the presence of pyr. The decrease in sorbitol was most likely due to a lower glucose flux rather than an increased polyol dehydrogenase activity. Increasing glucose concentration from 5.5 to 35.5 mM or provision of exogenous pyr both caused an intermediate increase in O2 consumption in the normal lens; a maximal activity was reached with both 35.5 mM glucose and 5 mM pyruvate in the incubating medium. In the diabetic lens, O2 consumption could reach the intermediate but not the maximal level. Dietary pyr pre-treatment also prevented normal and diabetic lenses from maximal pyr-stimulated O2 consumption. The NMR and O2 consumption data together indicated activation of alanine dehydrogenase and saturation of Krebs cycle. It appears that dietary supplement of mannose can preserve 31P membrane metabolites in the diabetic lens. Mannose can be used in conjunction with hypoglycemic therapy for the management of diabetic cataract. In addition, pyruvate may be effective in enhancing lens energy metabolism and lower sorbitol production.

Animals↗

PubMed1995

Desflurane reduces the gain of thermoregulatory arteriovenous shunt vasoconstriction in humans.

BACKGROUND: Thermoregulatory responses, such as arteriovenous shunt vasoconstriction, provide substantial protection against core hypothermia. A response can be characterized by its threshold (core temperature triggering response), gain (rate at which response intensity increases, once triggered), and maximum response intensity. Reduced gain decreases the efficacy of a thermoregulatory response at a given threshold because response intensity will increase more slowly than usual. The effects of general anesthesia on the gain of arteriovenous shunt vasoconstriction have not been reported. Accordingly, we tested the hypothesis that desflurane decreases the gain of centrally mediated vasoconstriction. METHODS: We studied seven healthy male volunteers. Each was studied twice: (1) desflurane (end-tidal concentration 0.4 minimum alveolar concentration); and (2) control (no anesthesia). Mean skin and fingertip temperatures were controlled at 35.5 degrees C throughout the study. Core temperature was reduced at a rate of 1.5 degrees C/h by central venous infusion of cold fluid. Fingertip arteriovenous shunt flow was measured using venous occlusion volume plethysmography at 1-min intervals. Flow was also evaluated using the perfusion index and laser Doppler flowmetry. Vasoconstriction thresholds were calculated as the core temperatures triggering fingertip flows of 1.0 ml/min (beginning of vasoconstriction) and 0.25 ml/min (intense vasoconstriction). The gain of vasoconstriction was considered to be the slope of the fingertip flow versus core temperature regression within the linear range from 1.0 ml/min to 0.15 ml/min. The minimum observed flow was considered maximum vasoconstriction intensity. Data are presented as means +/- SD; P < 0.01 was considered statistically significant. RESULTS: The vasoconstriction threshold (when defined using a flow of 1.0 ml/min) was reduced from 36.8 +/- 0.3 degrees C to 35.6 +/- 0.3 degrees C by desflurane anesthesia (P < 0.01). Desflurane reduced the gain of vasoconstriction by a factor of three, from 2.4 to 0.8 ml.min-1.degrees C-1 (P < 0.01). Gains, as determined by the perfusion index and laser Doppler flowmetry, were likewise reduced (P < 0.01). The threshold on the control day was only 0.2 +/- 0.1 degrees C less when significant vasoconstriction was defined as a flow of 0.25 ml/min rather than 1.0 ml/min. Because gain was reduced, however, the threshold during desflurane administration was 0.8 +/- 0.2 degrees C less when significant vasoconstriction was defined by a flow of 0.25 ml/min. Minimum flows were comparable and near zero with and without anesthesia. CONCLUSIONS: The threshold reduction (1.2 degrees C/0.4 minimum alveolar concentration) was similar to that observed previously during isoflurane anesthesia. Similarly, it is established already that maximum vasoconstriction intensity is comparable with and without isoflurane anesthesia. However, the data also indicate that even relatively low desflurane concentrations markedly reduce the gain of vasoconstriction. It is likely that reduced gain (i.e., slow onset of vasoconstriction) contributes to core hypothermia in some surgical patients.

Adult↗

PubMed1995

[Cardial myxoma: analysis of cardiopulmonary bypass perfusion in 95 cases].

From 1980 to 1993, 95 patients with cardial myxoma (male 32 and female 63) were treated surgically. The myxoma located on left-atrium in 88 patients, right-atrium in 5, left-ventricle in 1, and pulmonary in 1. All the operations were carried out under cardiopulmonary bypass. After operations, 12 patients had dyspnea and 8 died of pulmonary infection and heart or respiratory failure. The hemoglobin level was 118.02 +/- 16.7 g/L, 72.33 +/- 8.82 g/L, and 105.75 +/- 5.91 g/L respectively for pre-dilution, post-dilution, and post-operation. The patients with cardial myxoma often complicated with anemia (56), hepatic enlargement (36), and history of heart failure (64), and embolism (12). Combined with clinical characteristics mentioned above, the preparation of prime solution and the management of perfusion were discussed.

Adolescent↗

PubMed1994

A cysteine in the C-terminal region of alanyl-tRNA synthetase is important for aminoacylation activity.

Alanyl-tRNA synthetase (AlaRS) from Escherichia coli is a multimeric enzyme that catalyzes the esterification of alanine to tRNA(Ala) in the ATP-dependent aminoacylation reaction. The functional binding of all three substrates follows Michaelis-Menten kinetics. The role of cysteines in this enzyme has been evaluated via modification of these residues with p-(hydroxymercuri)phenylsulfonic acid, monobromobimane, and 5,5'-dithiobis(2-nitrobenzoic acid) (DTNB). The former two reagents induce nearly complete inactivation of AlaRS aminoacylation activity and the release of all tightly bound zinc. In the case of mild DTNB treatment, only two of the six cysteines in AlaRS are modified, with release of all zinc and partial loss of aminoacylation activity. These experiments indicate the importance of one or more cysteines, other than those thought to be coordinated with zinc, in the aminoacylation reaction. Substitution of each of the cysteine residues outside the zinc-binding motif with serine does not disrupt zinc binding. However, the cysteine most removed in primary sequence from the active site (Cys665) is identified as important in the aminoacylation step. Mutation of Cys665 to serine induces a 120-fold decrease in the catalytic efficiency of this enzyme, primarily through a kcat effect, and introduces sigmoidal kinetics (nH = 1.8) with respect to the RNA substrate. The results demonstrate that a simple manipulation in the C-terminal region can introduce positive cooperativity in this otherwise noncooperative enzyme.

Acylation↗

PubMed1994

Intrinsic ligand binding properties of the human and bovine alpha-interferon receptors.

The Type I interferon receptor (IFN-alpha R) interacts with all IFN-alpha s, IFN-beta and IFN-omega, and seems to be a multisubunit receptor. To investigate the role of a cloned receptor subunit (IFN-alpha R1), we have examined the intrinsic ligand binding properties of the bovine and human IFN-alpha R1 polypeptides expressed in Xenopus laevis oocytes. Albeit with different efficiencies, Xenopus oocytes expressing either the human or bovine IFN-alpha R1 polypeptide exhibit significant binding and formation of crosslinked complexes with human IFN-alpha A and IFN-alpha B. Thus, the IFN-alpha R1 polypeptide most likely plays a direct role in ligand binding.

Animals↗

PubMed1994

Production of mouse V/human C chimeric kappa genes by homologous recombination in hybridoma cells. Analysis of vector design and recombinant gene expression.

Homologous recombination between transferred and chromosomal Ig genes in mouse hybridoma cells offers a general method of altering the chromosomal Ig genes in predetermined ways. Recombination is infrequent in hybridoma cells, and we have been interested in improving the methods for identifying and recovering the rare recombinants. We have used vectors that are designed to replace the mouse chromosomal C kappa segment with the human equivalent, so that recombinants produce mouse V/human C chimeric kappa-chains. We describe an enhancerless, replacement type vector that can be used with the herpes thymidine kinase counterselection to provide such enrichment that homologous recombinants constitute 15% of the selected G418-resistant, FIAU-resistant cells. We have also measured the level of chimeric kappa gene expression and found surprisingly that (1) it is very variable among transformants with the same recombinant gene structure, (2) there is no systematic difference in the level of production by recombinants that retain or have lost the J-C kappa intron enhancer, and (3) the amount of chimeric kappa mRNA in even the highest producing transformants is much less than the amount of the corresponding mouse kappa mRNA.

Animals↗

PubMed1994

Prospective evaluation of a prostacyclin-sparing aspirin formulation and heparin/warfarin in aspirin users with unstable angina or non-Q wave myocardial infarction at rest. The Antithrombotic Therapy in Acute Coronary Syndromes Research Group.

The aim of this trial was to compare the efficacy of combination antithrombotic therapy with a prostacyclin-sparing aspirin plus anticoagulation versus conventional aspirin plus anticoagulation, when added to antianginal therapy, in patients with unstable angina or non-Q wave myocardial infarction already being treated with aspirin. In a double-blind (for the aspirin) study, 144 prior aspirin users were randomized; 72 patients received controlled-release, prostacyclin-sparing aspirin 75 mg daily plus anticoagulation (intravenous heparin followed by warfarin to maintain the international normalized ratio at 2-3), and 72 patients received conventional aspirin 75 mg daily plus the same anticoagulation. Controlled-release aspirin was formulated to preserve endothelial cell prostacyclin synthesis. Trial therapy was begun by 13.2 +/- 12.3 h of qualifying pain, and continued for 12 weeks. The frequency of recurrent angina with electrocardiographic changes, myocardial infarction, or death, was analysed by intention to treat. At 12 weeks, events were: [table: see text] Twenty-six of the 42 (62%) recurrent ischaemic events occurred within 7 days of presentation. Four of the 144 patients (3%) experienced a major bleeding complication. It is concluded that in spite of maximal antithrombotic therapy, there is a significant failure rate of medical therapy in aspirin users presenting with unstable angina or non-Q wave myocardial infarction while at rest. Prostacyclin-sparing aspirin offers no clinical benefit over conventional aspirin.

Adult↗

PubMed1994

Combination antithrombotic therapy in unstable rest angina and non-Q-wave infarction in nonprior aspirin users. Primary end points analysis from the ATACS trial. Antithrombotic Therapy in Acute Coronary Syndromes Research Group.

BACKGROUND: The purpose of this study was to compare combination antithrombotic therapy with aspirin plus anticoagulation versus aspirin alone, when added to conventional antianginal therapy in patients with unstable rest angina or non-Q-wave myocardial infarction who were nonprior aspirin users. METHODS AND RESULTS: Two hundred fourteen patients were randomized; 109 were randomized to receive aspirin alone (162.5 mg daily) and 105 to receive a combination of aspirin plus anticoagulation, ie, aspirin 162.5 mg daily plus heparin (activated partial thromboplastin time, two times control) followed by aspirin 162.5 mg daily plus warfarin (international normalized ratio, 2 to 3). Trial therapy was begun by 9.5 +/- 8.8 hours of qualifying pain and was continued for 12 weeks. Primary end points were recurrent angina with ECG changes, myocardial infarction, and/or death. Analysis by intention to treat of primary events at 12 weeks was performed. At 14 days, there was a significant reduction in total ischemic events in the combination group versus aspirin alone (10.5% versus 27%, P = .004). An efficacy analysis of primary events at 12 weeks also revealed a large reduction in total ischemic events in the combination group versus aspirin alone (13% versus 25%, P = .06). Bleeding complications were slightly more common with combination therapy. CONCLUSIONS: In nonprior aspirin users, combination antithrombotic therapy with aspirin plus anticoagulation significantly reduces recurrent ischemic events in the early phase of unstable angina.

Angina, Unstable↗

PubMed1994

[Bacteriological detection of anterior chamber aspirate after extracapsular cataract extraction with intraocular lens implantation].

We cultured the anterior chamber aspirates of 83 patients with extracapsular cataract extraction and IOL implantation. Of the 83 cases, 5 (6.1%) had positive aspirates including 3 cases of staphylococcus epidermidis and 2 cases of staphylococcus aureus. No eye in our study developed bacterial endophthalmitis. Our study suggests that the anterior chamber of human eyes is capable of clearing a low inoculum of bacteria after cataract surgery without the development of bacterial endophthalmitis.

Aged↗

PubMed1994

[Pathological study of secondary thymic atrophy caused by steroid hormone in mice].

According to the pathological observations on BALB/c mice after being given steroid hormone, the following results were obtained: secondary thymic atrophy could be observed 24 hours after steroid therapy. The degree of atrophy correlated with the amount of medication and duration of therapy; the weight and pathological changes under light and electron microscope examination almost returned to normal 7 days after the drug was stopped except in individual animals. Our study indicated that secondary atrophy of the thymus can be reversed after elimination of the pathogenic factor.

Animals↗

PubMed1993

Prospective comparison of unstable angina versus non-Q wave myocardial infarction during antithrombotic therapy. Antithrombotic Therapy in Acute Coronary Syndromes Research Group.

OBJECTIVES: This study was designed to compare the response of unstable angina and non-Q wave myocardial infarction during treatment with antithrombotic therapy. BACKGROUND: Antithrombotic therapy is beneficial in patients with these two coronary syndromes. METHODS: In a multicenter trial of antithrombotic therapy in unstable angina or non-Q wave myocardial infarction, 358 patients admitted within 48 h of chest pain were randomized to antithrombotic therapy with either 1) aspirin alone, or 2) aspirin plus heparin followed by aspirin plus warfarin, and were prospectively followed up for 12 weeks. Admission cardiac enzyme analyses revealed unstable angina in 268 patients and non-Q wave myocardial infarction in 62. Given an event rate of about 25%, this study has a power of 80% to detect a 50% difference between the two groups. RESULTS: Patients with unstable angina and non-Q wave myocardial infarction were similar with regard to age, gender, coronary risk factors and prior antianginal medication. Primary end points at 12 weeks were recurrent ischemia, infarction and death. [table: see text] In the non-Q wave group, all infarctions and death occurred within the 1st week. CONCLUSIONS: Patients with unstable angina or non-Q wave myocardial infarction on antithrombotic therapy have a similar total number of ischemic events by 12 weeks. However, despite maximal medical therapy with antianginal and antithrombotic medication, patients with non-Q wave infarction have a significantly higher rate of reinfarction and death.

Adrenergic beta-Antagonists↗

PubMed1993

Solid-state NMR studies of 1H spin diffusion in adsorbed organic molecules.

1H spin diffusion times of toluene (MB) and tetrahydrofuran (THF) adsorbed on a series of porous solids (charcoal, SiO2 and Al2O3) were measured by a selective inversion technique. The experimental results show that they cover a wide range (from less than one millisecond to several hundreds of milliseconds). For all samples, a tri-exponential behavior was observed in the magnetization recovery processes of the negative peaks. This is attributed to the existence of the two different kinds of spin diffusion processes in addition to the T1 relaxation. One is assigned to the intermolecular spin diffusion between the surface acidic protons of the adsorbent and the organic molecules adsorbed on the solid surface, the other to the intramolecular spin diffusion of adsorbed molecules. Due to hydrogen bonding between the surface hydroxyl groups and the adsorbate, the intermolecular spin diffusion of THF adsorbed on various solids is more effective compared to that of adsorbed MB. In addition, the intermolecular 1H spin diffusion between charcoal and adsorbed THF molecules was confirmed by indirect measurement suggested by Tekely et al.

Charcoal↗

PubMed1992

Visualization of water movement in the living rabbit eye.

Water enriched with the stable isotope 17O (H2(17)O) shortens the transverse relaxation time (T2) of protons in water and can therefore be used as the contrast agent for proton magnetic resonance (MR) imaging. This agent can be given topically or intravenously to demonstrate water movement in the eye. Topical H2(17)O (0.05-0.1 ml/eye, 10% enrichment) entered the anterior chamber within 5 min and dissipated from the chamber in a single-exponential fashion (flow-rate constant k = 0.1 min-1), principally due to an exchange with the iridic circulation. No H2(17)O was detected in the vitreous. Intravenous administration of H2(17)O (1 ml/kg, 10% enrichment) resulted in rapid entry (less than 20 min) of the agent into the aqueous chamber. Again, no H2(17)O was detected in the vitreous. The lens region, on the other hand, showed an increase in image intensity with time that reached a plateau after 40 min. Although these findings are preliminary, acetazolamide (20 mg/kg injected intravenously) appeared to affect iridic circulation, possibly through vasoconstriction. Potential application of this H2(17)O-enhanced MR imaging technique is discussed.

Administration, Topical↗

PubMed1992

High-resolution MR imaging of water diffusion in the rabbit lens.

Movement of water in the lens, specifically water diffusion, was examined with diffusion imaging and H217O-enhanced proton imaging. Diffusion imaging showed restricted water self-diffusion in the cortex which was not concurrent with the change in proton density; nevertheless it was dependent on the gradient direction and might be related to lens fiber/protein organization. The difference in water diffusion patterns between control and galactosemic cataract was subtle but distinguishable. On the other hand, intracameral H217O injection allowed visualization of water movement across the lens. In galactosemic cataracts, water diffused from the anterior cortex towards posterior cortex and into the vitreous. This pattern was not seen in the normal lens.

Animals↗

PubMed1992

Shape of the myopic eye as seen with high-resolution magnetic resonance imaging.

We have obtained multislice magnetic resonance (MR) images of the eye and calculated ocular dimensions along the three cardinal axes: antero-posterior (A-P), equatorial, and vertical. We found no difference in the shape of hyperopic (average refractive error: +3.72 D) and emmetropic eyes, both of which had an equatorial diameter longer than the A-P and vertical diameters. Myopic eyes (average refractive error: -6.54 D) were larger than hyperopic eyes, and most had the same spheroelliptical shape as that of the emmetropic and hyperopic eyes. The results suggest that during myopic progression an overall enlargement or a radial volume expansion has occurred.

Adult↗

PubMed1992

Complete amino Acid sequence of soybean leaf p21 : similarity to the thaumatin-like polypeptides.

A polypeptide structurally related to the thaumatin family of proteins has been purified from soybean (Glycine max) leaves and the complete amino acid sequence has been determined. The mature protein, which we have termed P21, has a calculated molecular weight of 21,461 and an isoelectric point of 4.6. The soybean protein shows 64% amino acid identity with thaumatin, a sweet-tasting protein found in the West African shrub Thaumatococcus danielli, and as much as 71% identity with thaumatin-like polypeptides present in tobacco and maize.

Journal Article↗