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Biomedical subjects

M Yuan

Publications and source records attributed to M Yuan.

At least 55 records · Page 3Linked to original sources
PubMed1998

[Regulating function of enzymization and deenzymization of the lactate dehydrogenase isozymes in the mouse tissues during hypoxia].

OBJECTIVE: Study the characteristics of changes of LDH enzyme map of mouse under slight hypoxia. METHODS: Treated mouse with artificial hypoxia, various tissue biopsies were made for the test of LDH enzymatic activity by specific staining technical LDH(1-5)relative percent enzymatic activity were measured with CS-910 dual-wavelength thin-layer chromatography scanner. RESULTS: The relative percent enzymatic activity of LDH isozymes of various tissues after slight hypoxia shift to the isozymes LDH1 and LDH2, whose principal subunits are H subunits, and the relative percent enzymatic activity of LDH1 (H4), LDH2-(H3M) increased (the relative percent enzymatic activity of LDH2 increased markedly, P < 0.05), while LDH (M4) in various tissues decreased prominently except the cardiac muscle, and that of LDH4 (HM3) decreased as well. After the PAGE of the hypoxia treated cardiac muscle specimen was made, activity subbands originated regularly in the isozyme pattern of LDH, with the regularity of LDH1 (0 subband), LDH2 (0-1 subbands), LDH3 (0-2 subbands), LDH4 (1-3 subbands), LDH5 (2-4 subbands). After adding appropriate amount of NAD+ to mouse cardiac muscle specimen with hypoxia, PAGE showed the numbers of subbands of four kinds of isozymes (LDH2-LDH5) decreased even totally disappeared in the isozyme pattern. CONCLUSIONS: The negative feedback regulation of enzymization and deenzymization of LDH isozymes is one of mouse stress responses to slight hypoxia.

Animals↗
PubMed1998

[Determination of naftopidil and its main metabolite in plasma by high-performance liquid chromatography].

A method was developed for the determination of naftopidil (NAF) and its main metabolite desmethyl-naftopidil (DMN) in plasma by HPLC. A mixture of methanol, acetonitrile and 0.02 mol.L-1 K2HPO4 solution was used as mobile phase. Stationary phase was RP-C18. Propranolol was chosen as internal standard (IS), and the detector wavelength was 240 nm. Under these conditions, the retention times of IS, DMN and NAF were 6.2, 7.6 and 10.5 min respectively. Absolute recoveries from plasma were up to 93.4% (IS), 76.8% (DMN) and 80.2% (NAF). The assay was linear for DMN and NAF in the range of 10-800 ng.ml-1 plasma concentration, gamma = 0.9998. The lowest detection limits were 8 ng.ml-1 (DMN) and 5 ng.ml-1 (NAF), and the precisions within-day and day-to-day were no more than 6.3% for MDN and 11.6% for NAF. The drug concentration-time pattern of these two substances was also studied with this method. Result showed that naftopidil was quickly absorbed after p.o. and the concentration-time data were fitted to two compartment model, with half life (T1/2 beta) of 8.13 h.

Adrenergic alpha-Antagonists↗
PubMed1997

Bases of variation in resistance to beta-lactams in Klebsiella oxytoca isolates hyperproducing K1 beta-lactamase.

Nineteen isolates of Klebsiella oxytoca were examined, representing 18 distinct strains. All were from a 1994 survey of resistance amongst klebsiellae in intensive care units in Europe, and all had reduced susceptibility, or were resistant, to cefuroxime, ceftriaxone and aztreonam, suggesting hyperproduction of the chromosomal K1 beta-lactamase. We sought to confirm this mechanism and to identify why the levels of resistance varied between isolates. Possible reasons for variation were differences in the quantity or subtype of the K1 enzyme or differences in this enzyme's interplay with permeability. Spectrophotometric assays showed that all 19 isolates had K1-like beta-lactamases and that these were present at > or = 15-fold higher levels than in beta-lactam-sensitive K. oxytoca isolates. Fourteen of the 19 isolates had the OXY-2 form of K1 enzyme, while the remaining five had the OXY-1 form, as determined by isoelectric focusing and PCR amplification. Most isolates with the OXY-2 enzyme were more resistant than those with the OXY-1 subtype, but this difference partly reflected enzyme quantity rather than subtype. More generally, and irrespective of enzyme subtype, levels of resistance were broadly related to beta-lactamase specific activity, and the degree of hyperproduction was a major determinant of the level of resistance. Nevertheless, other factors had a role too: several isolates had reduced susceptibility or were resistant to cefoxitin, which is not a substrate for K1 enzyme, and examination of outer membrane protein profiles revealed considerable strain-to-strain diversity in the molecular weight range typical of the major enterobacterial porins (40-48 kDa).

Anti-Bacterial Agents↗
PubMed1997

[Effects of calcium inhibitor on hydrogen peroxide-induced damage and calcium influx in bovine aortic endothelial cells in culture].

Hydrogen peroxide(H2O2)-induced cell damage and Ca2+ influx into bovine aortic endothelial cells (BAEC) were investigated. Our data suggested that H2O2 could dose- and time-dependently induce damage in cultured BAEC assessed by 3-(4, 5-dimethylthiazol-2-yl)-2, 5-diphenyltetrazolium bromide(MTT) assay and increase malondialdehyde (MDA) production, which reflects the level of lipid peroxidation. Exposure of BAEC to H2O2 (100 mumol.L-1) caused significant increase in intracellular free calcium ([Ca2+]i) within 6 min, suggesting that the increase of [Ca2+]i might implicate in H2O2-induced cell damage. The calcium inhibitor nifedipine was found to dose-dependently decrease the increase of [Ca2+]i caused by H2O2 and protect BAEC against H2O2-induced damage reflected by significant decrease of MDA production and increase of MTT value. These results indicate that overload of calcium might be responsible to some extent causing oxidative damage to cells.

Animals↗
PubMed1997

[Separation and determination of plant growth regulators by capillary micellar electrokinetic chromatography].

It is important for separation and determination of plant growth regulators in the research of plant physiology. A study of the separation of five plant growth regulators, such as abscisic acid (ABA), gibberellic acid (GA), indole-butyric acid (IBA), indole acetic acid (IAA) and naphthaleneacetic (NAA) by micellar electrokinetic chromatography (MEKC) is presented. The effects of pH, SDS concentration, applied voltage and organic additives on migration behavior were investigated. Results showed that satisfactory separation was achieved on optimization of electrophoretic condition: 80 mmol/L SDS, 10 mmol/L borate-phosphate, 5% isopropanol, 18 kV applied voltage, pH 8.0. The SDS concentration and organic additives played an important role in separating plant growth regulators, and the applied voltage and pH gave less effect. The detection limit of ABA, GA, IBA, IAA and NAA were 5.0 x 10(-3), 3.0 x 10(-3), 5.8 x 10(-4), 1.5 x 10(-4) and 1.4 x 10(-4) g/L respectively. Increasing of the SDS concentration or organic additives would change separation factor (alpha) and result an improvement of the resolution of difficult separation pairs ABA-GA and IAA-NAA.

Abscisic Acid↗
PubMed1997

[Hypoglycemic effects of peroxovanadate complexes on glucose transportor of diabetic rats].

OBJECTIVE: To demonstrate the hypoglycemic effects and translocation of glucose transport (Glut 1 and Glut 4) promoted by peroxovanadate and nicotinic acid complexes (POR) in streptozotozin-induced diabetic rats. METHODS: Peroxovanadate complexes nicotinic acid (POR) was prepared in laboratory. POR and vanadate were administered in drink water. The muscles from diabetic rats were subjected to sucrose density gradient centrifugation to prepare plasma membrane and microsome membrane. Antibodies to COOH-terminal of glucose transportor were used in Western Blot to evaluate the translocation. RESULTS: Peroxovanadate complexes of nicotinic acid (POR) showed marked hypoglycemic effects on STZ-induced diabetic rats. 1mg/kg oral pathway POR could significantly reduce the plasma glucose levels (from 18.95 +/- 2.61mmol/L to 6.36 +/- 2.23mmol/L, t = 12.233, P < 0.01) over four week's treatment, whereas, same dose of single sodium vanadate or nicotinic acid did not have hypoglycemic effects. The net vanadium intake was about 1/90 of single effectively vanadate treatment. When Western blot was used POR increased the translocation of Glut 4 and Glut 1 from intracellular site of plasma membrane. CONCLUSION: Peroxovanadate-nicotinic acid complexes (POR) are the novel vanadyl that markedly reduce plasma glucose in a lower dose comparing to vanadate in STZ-DM rats by oral administration. Translocation of glucose transportor may play a part in hypoglycemic mechanism.

Animals↗
PubMed1997

Effects of peroxovanadate complexes on reducing glycemia in diabetic rats and translocation of glucose transporter.

OBJECTIVE: To demonstrate the hypoglycemic effects and translocation of glucose transporter (Glut 1 and Glut 4) promoted by peroxovanadate and nicotinic acid complexes (nicotinic chelated bitriperoxovanadate, POR; N-O nicotinic chelated peroxovanadate, POV) in streptozotozin-induced diabetic rats. METHODS: Peroxovanadate complexes of nicotinic acid (POR and POV) were prepared and characterized in laboratory. POR, POV and vanadate were administrated in drink water. The muscles from diabetic rats were subjected to prepare plasma membrane and microsome membrane. Antibodies to COOH-terminal of glucose transporter were used in Western Blot to evaluate the translocation. RESULTS: POR and POV showed markedly hypoglycemic effects in streptozotocin (STZ)-induced diabetic rats. POV, which may be a N-oxide compound of peroxovanadate, have high potency of acute effects comparing to carboxylate-complexes of peroxovanadate (POR). In chronic tests, 1 mg/kg oral pathway POR could significantly reduce the plasma glucose levels over four week's treatment, whereas the same dose of single sodium vanadate or nicotinic acid did not have hypoglycemic effects. The net vanadium intake is about 1/90 of single effectively vanadate treatment. The Western Blot showed that POR increased the translocation of Glut 4 and Glut 1 from intracellular site of membrane. CONCLUSIONS: Peroxovanadate-nicotinic acid complexes (POR and POV) are the novel vanadyl that acutely and markedly reduce plasma glucose in a lower dose comparing to vanadate in STZ-DM rats by oral administration. Translocation of glucose transportor may take a part in their hypoglycemic effects.

Animals↗
PubMed1996

Antibiotic resistance and production of extended-spectrum beta-lactamases amongst Klebsiella spp. from intensive care units in Europe.

Consecutive klebsiellae were collected from ICU patients at 35 centres in Western and Southern Europe. Of 966 isolates obtained, 716 were Klebsiella pneumoniae, 248 were Klebsiella oxytoca and two were Klebsiella ozaenae. Most were from Belgium, France, Germany, Holland, Italy, Portugal, Spain, Turkey and a few from Greece and the UK. Production of extended-spectrum beta-lactamases (ESBLs) was inferred in 220 isolates on the basis of synergy between ceftazidime and clavulanate. Putative ESBL producers were received from 23 centres, including 20 of the 27 that contributed more than 10 klebsiellae. Over 88% of putative ESBL producers were resistant to ceftazidime 2 mg/L, ceftriaxone 1 mg/L and aztreonam 1 mg/L, whereas, amongst ESBL-negative isolates, more than 98% of K. pneumoniae and 87% of K. oxytoca were susceptible to these concentrations. Putative ESBL producers wre also more resistant to cefuroxime and cefoxitin than non-producers, but not to biapenem. MIC distributions of ciprofloxacin, piperacillin/tazobactam and aminoglycosides were bimodal for ESBL producers, with some isolates highly sensitive and others very resistant. For example, 70% of putative ESBL producers were susceptible to piperacillin/tazobactam 16 + 4 mg/L, but 30% were resistant, some highly so. Resistance to this combination, and to ciprofloxacin, was clustered in certain centres. Two other groups of cephalosporin-resistant isolates were identified besides ESBL producers, viz. (i) nine isolates, from three centres, with AmpC beta-lactamases and (ii) 20 K. oxytoca, from 15 centres, that hyperproduced K1 enzyme. Examination of the hospitals' own susceptibility data indicated that up to 33% of putative ESBL producers had been reported susceptible to third-generation cephalosporins or monobactams. This is disturbing, since ESBLs have been associated with clinical failure even when only low-level resistance was apparent in vitro.

Ampicillin↗
PubMed1996

[Anti-tumor activity and immune responses induced by human cancer-associated mucin core peptide].

Mucin molecules are displayed on most human cancer cell surface, and are different from that expressed on normal epithelial cells. The molecular structure of mucin core peptide (apomucin) was identified recently. However, the function of apomucin is only poorly understood. To further elucidate the role of apomucin in the modulation of cancers, this study was to investigate the immune responses induced by mucin core peptide in mice. The mucin core peptide was isolated from pancreatic cancer cell line SW1990. When mice immunized with this apomucin (10 micrograms/time x 6) plus DETOX, all mice developed delayed-type hypersensitivity (DTH) after challanged with apomucin or synthetic mucin core peptide MUC-2 or MUC-3, while the mice immunized with only apomucin did not develop DTH. No antibodies were detected by ELISA after immunization. When the splenic cells of vaccinated mice were cocultured with this apomucin (10-50 micrograms/ml) and rhIL-2 (50 U/ml) in vitro, the proliferated lymphocytes showed cytotoxicity against human cancer cells, including colon cancer, gastric cancer, pancreatic cancer and leukemia as measured by Cr-51 release assay. The cytotoxicity could be blocked by antibodies against MUC-2 and MUC-3. These results provide a rational basis for the use of apomucin as a vaccine to stimulate anti-tumor immunity.

Animals↗
PubMed1995

Oxidatively modified very low density lipoprotein enhances monocyte adhesion to endothelial cells.

Very los density lipoprotein (VLDL) was incubated with CuCl2(10 mumol/L) at room temperature for 24 hours. The thiobarbituric acid reactive substance (TBARS) was much higher and the electrophoretic mobility was much faster in VLDL after incubation with CuCl2 than that in VLDL without incubation with CuCl2. It demonstrated that VLDL was oxidatively modified by Cu2+. Endothelial cells were pretreated with normal VLDL (N-VLDL) and oxidatively modified VLDL (O-VLDL) and then the adhesion of monocyte to endothelial cells was assayed. We observed that O-VLDL at all the concentrations used enhanced monocyte adhesion to endothelial cells significantly. The results suggest that oxidative modification of VLDL may play a role in the early stage of atherogenesis by increasing monocyte adhesion to endothelial cells.

Cell Adhesion↗
PubMed1995

Dynamic microtubules under the radial and outer tangential walls of microinjected pea epidermal cells observed by computer reconstruction.

By microinjecting rhodamine-conjugated pig brain tubulin into living pea stem epidermal cells it has been possible to follow cortical microtubules beneath the outer tangential wall (OTW) as they re-orientate from a transverse to a longitudinal alignment. Earlier immunofluorescence studies on fixed material have shown that parallel cortical microtubules circumnavigate the cell forming apparently continuous arrays which are transverse, oblique or longitudinal to the cell's long axis. If the array re-orientates as a whole then microtubules along the radial walls would be expected to share the alignment of those on the tangential walls. There are, however, reports that microtubules beneath the outer tangential wall have a different orientation from microtubules at the radial cell walls, raising important questions about the construction and behaviour of the array. Using computer-rotated stacks of optical sections collected by confocal scanning laser microscopy it has been possible to display the microtubules along radial as well as tangential walls of the same microinjected cells. These observations demonstrate for living epidermal cells that when microtubules are aligned longitudinally at the outer epidermal wall they remain oblique or transverse at the radial walls. The array may not therefore re-orientate as a whole but seems to undergo re-organization on only one cell face. However, despite the differing angles between the OTW and radial walls microtubules still form patterns which at the level of the confocal microscope are continuous from one cell face to another, around the cell.(ABSTRACT TRUNCATED AT 250 WORDS)

Computer Simulation↗
PubMed1995

National survey of susceptibility to antimicrobials amongst clinical isolates of Pseudomonas aeruginosa.

Between September and December 1993, each of 24 hospitals in the UK collected up to 100 consecutive clinical isolates of Pseudomonas aeruginosa and sent these to the London Hospital Medical College (LHMC). Of 2184 cultures received, 1991 contained viable P. aeruginosa. Minimum inhibitory concentrations (MICs) of antimicrobials were determined by agar dilution. The frequencies of resistance to low breakpoints were as follows: gentamicin, MIC > 2 mg/L, 11.7%; amikacin, MIC > 4 mg/L, 10.5%, carbenicillin, MIC > 128 mg/L, 11.7%; azlocillin, MIC> 16 mg/L, 10.9%; ceftazidime, MIC > 4 mg/L, 9.6%; ciprofloxacin, MIC > 1 mg/L, 8.1%; imipenem, MIC > 4 mg/L 2.5% and meropenem, MIC > 4 mg/L, 1.1%. Resistance to each antimicrobial except amikacin was commoner among the 134 isolates from patients in intensive care units (ICUs) than amongst the 1042 isolates from other in-patients (P < 0.01). Resistance to penicillins and ceftazidime, though not to other agents, was rarer among the 797 isolates from out-patients than amongst those from non-ICU in-patient (P < 0.01). Compared to a similar study in 1982, during which 1866 isolates had been examined, the frequency of resistance to the aminoglycosides increased (P < 0.05) as had those to the penicillins and ceftazidime (P < 0.01). Ciprofloxacin and the carbapenems were not tested in 1982. Cross-resistance patterns suggested that the increases in resistance to aminoglycosides and beta-lactams were largely a reflection of greater numbers of isolates with barrier or efflux mechanisms and were not due to an increase in isolates with antibiotic-degrading enzymes. The participating hospitals mostly employed Stokes' disc diffusion method and, when the results were compared to the MICs determined at the LHMC, fewer than 9% of the isolates reported as susceptible were found to be resistant. However, up to 72% of those reported by the hospitals as resistant were found to be susceptible.

Anti-Bacterial Agents↗
PubMed1995

Mechanisms of resistance to beta-lactam antibiotics amongst Pseudomonas aeruginosa isolates collected in the UK in 1993.

Antimicrobial resistance among 1991 Pseudomonas aeruginosa isolates collected at 24 UK hospitals during late 1993 was surveyed. Three-hundred and seventy-two of the isolates were resistant, or had reduced susceptibility, to some or all of azlocillin, carbenicillin, ceftazidime, imipenem and meropenem, and the mechanisms underlying their behaviour were examined. Only 13 isolates produced secondary beta-lactamases: six possessed PSE-1 or PSE-4 enzymes and seven had novel OXA enzyme types. Those with PSE types were highly resistant to azlocillin and carbenicillin whereas those with OXA enzymes were less resistant to these penicillins. Chromosomal beta-lactamase derepression was demonstrated in 54 isolates, most of which were resistant to ceftazidime and azlocillin although susceptible to carbenicillin and carbapenems. beta-Lactamase-independent "intrinsic" resistance occurred in 277 isolates and is believed to reflect some combination of impermeability and efflux. Two forms were seen: the classical type, present in 195 isolates, gave carbenicillin resistance (MIC > 128 mg/L) and reduced susceptibility to ciprofloxacin and to all beta-lactam agents except imipenem; a novel variant, seen in 82 isolates, affected only azlocillin, ceftazidime and, to a small extent, meropenem. Resistance to imipenem was largely dissociated from that to other beta-lactam agents, and probably reflected loss of D2 porin, whereas resistance to meropenem was mostly associated with intrinsic resistance to penicillins and cephalosporins. Comparison of the present results with those of a similar study in 1982 revealed significant increases in the proportions of isolates with intrinsic resistance or stable derepression (p < 0.01, chi 2 test).(ABSTRACT TRUNCATED AT 250 WORDS)

Carbapenems↗
PubMed1995

Cloning, expression and characterization of a single-chain antibody PS-9 targeted to pancreatic cancer.

Genes encoding single-chain antibodies have been first constructed, which consist of the heavy and light chain variable domains of antibody PS-9 joined together by a flexible peptide linker. The genes were cloned into coat protein g3p genes of pCANTAB5 phagemids, and expressed as fusion proteins on the phage tips. Immunological assay demonstrated that the engineered antibodies specifically bound to cancer cells LS-174-T as well as to pure bovine submaxillary gland mucin. Their specificity and affinity appeared the same as their parent antibodies. Our results supposed that the single-chain antibodies will be a target for the diagnosis and treatment of cancer.

Antibodies, Monoclonal↗
PubMed1994

Dynamic reorientation of cortical microtubules, from transverse to longitudinal, in living plant cells.

The direction in which plant tissue cells expand is reflected in the alignment of microtubules in the cortical array. When microtubules and coaligned wall microfibrils are arranged transversely around the cell, turgor pressure is chaneled into cell elongation. However, various agents (such as wounding, ethylene, abscisic acid) can cause the microtubules to reorientate by 90 degrees so that they become aligned parallel to the cell's long axis, allowing lateral expansion instead of elongation. The mechanism by which microtubules undergo rapid shifts of alignment is crucial to understanding growth control in plants, but because current models are derived from studies on fixed cells, nothing is known about the dynamics of converting one microtubule alignment to another. Cells tend to have one predominant microtubule alignment--transverse, oblique, or longitudinal--but it is not established whether each represents a stable independent set that only changes by rounds of complete de- and repolymerization, or whether reorientation is a more continuous process involving movement of stable or dynamic microtubules. By microinjecting pea (Pisum sativum) epidermal cells with rhodamine-conjugated brain tubulin and optically sectioning them by confocal laser scanning microscopy, we could follow labeled microtubules for up to 2 hr as they reorientate. Reorientation does not occur by complete depolymerization of microtubules in one orientation followed by polymerization of a new array in another orientation. Instead, increased numbers of discordant microtubules in nontransverse alignment appear in particular locations. Neighboring microtubules then adopt the new alignment, so that there is a stage during which different alignments coexist before the array on the outer tangential cell face finally adopts a uniform steeply oblique/longitudinal configuration. Rapid fluorescence recovery after photobleaching confirms that bundles of cortical microtubules are not stable but exhibit properties consistent with dynamic instability. Dynamic microtubules offer a mechanism for rapid growth responses to a range of physiological stimuli.

Journal Article↗
PubMed1994

Microinjected profilin affects cytoplasmic streaming in plant cells by rapidly depolymerizing actin microfilaments.

BACKGROUND: Cytoplasmic streaming is a conspicuous feature of plant cell behaviour, in which organelles and vesicles shuttle along cytoplasmic strands that contain actin filaments. The mechanisms that regulate streaming and the formation of actin filament networks are largely unknown, but in all likelihood involve actin-binding proteins. The monomeric actin-binding protein, profilin, is a key regulator of actin-filament dynamics in animal cells and it has recently been identified in plants as a pollen allergen. We set out to determine whether plant profilin can act as a monomeric actin-binding protein and influence actin dynamics in plant cells in vivo. RESULTS: Recombinant birch-pollen profilin was purified by polyproline affinity chromatography and microinjected into Tradescantia blossfeldiana stamen hair cells. After profilin injection, a rapid and irreversible change in cellular organization and streaming was observed: within 1-3 minutes the transvacuolar cytoplasmic strands became thinner and snapped, and cytoplasmic streaming ceased. Fluorescein-labelled-phalloidin staining confirmed that this was due to depolymerization of actin filaments. To confirm that the effects observed were due to sequestration of monomeric actin, another monomeric actin-binding protein, DNase I, was injected and found to produce comparable results. CONCLUSIONS: Profilin can act as a potent regulator of actin organization in living plant cells. Its rapid effect on the integrity of cytoplasmic strands and cytoplasmic streaming supports a model in which organelle movements depend upon microfilaments that exist in dynamic equilibrium with the pool of monomeric actin.

Actin Cytoskeleton↗
PubMed1994

An evaluation of growth changes and treatment effects in Class II, Division 1 malocclusion with conventional roentgenographic cephalometry and finite element method analysis.

Conventional methods of roentgenographic cephalometry will yield differences in interpretation of growth or treatment changes depending on which methods of superimposition are used. The finite element method of analysis has been reported to have significant advantages since it does not require a reference frame to describe the changes that have taken place. This article describes the growth of a patient with a Class II, Division 1 malocclusion during approximately 2 years of orthodontic treatment with the use of conventional cephalometric growth and static analyses, as well as the finite element method. Thirty cephalometric points were digitized on the pretreatment and the posttreatment lateral cephalograms of a patient undergoing orthodontic treatment between the ages of 10 and 12 years. The finite element method provided a reference frame invariant description of the size, shape, change, and rotation of each of the 12 finite elements representing different anatomic structures.

Cephalometry↗