Biomedical subjects

X M Yang

Publications and source records attributed to X M Yang.

At least 73 records · Page 4Linked to original sources

PubMed1993

NAD-dependent methylenetetrahydrofolate dehydrogenase-methenyltetrahydrofolate cyclohydrolase is the mammalian homolog of the mitochondrial enzyme encoded by the yeast MIS1 gene.

The recombinant human bifunctional NAD-dependent methylenetetrahydrofolate dehydrogenase-methenyltetrahydrofolate cyclohydrolase is unique in its absolute requirement for Mg2+ and inorganic phosphate. Both ions affect the affinity of the enzyme for NAD and have no effect on the binding of methylenetetrahydrofolate. The NAD cofactor can be replaced by NADP with a much higher KM and lower VMAX. Kinetic investigation using NADP supports the role of Mg2+ in dinucleotide binding and illustrates that the 2'-phosphate can substitute for phosphate in this process. The human NAD-dependent bifunctional enzyme has a 44% amino acid sequence identity with the dehydrogenase-cyclohydrolase domain of the yeast mitochondrial NADP-dependent trifunctional enzyme encoded by the MIS1 gene, compared to 37% identity with the corresponding domain of the cytosolic trifunctional enzyme. The sequence comparison and the kinetic properties suggest that the NAD bifunctional enzyme is the mammalian homolog of the yeast mitochondrial trifunctional enzyme, which has evolved a unique use of inorganic phosphate to change its dinucleotide specificity from NADP to NAD. Its role is proposed to be in providing formyltetrahydrofolate for the synthesis of formylmethionyl transfer RNA required for the initiation of protein synthesis in mitochondria.

Aminohydrolases↗

PubMed1993

Expression of the met/hepatocyte growth factor/scatter factor receptor and its ligand during differentiation of murine P19 embryonal carcinoma cells.

The met proto-oncogene is a member of the family of tyrosine kinase growth factor receptors and was recently identified as a receptor for hepatocyte growth factor and scatter factor (HGF/SF). From Northern hybridization studies the met/HGF/SF receptor (R) is expressed in many adult and embryonic mouse tissues. To identify which specific differentiated cell types express the met/HGF/SFR and to investigate the biological function of this receptor and its ligand during early murine development, we chose to study the expression of the met/HGF/SFR and HGF/SF during differentiation of the pluripotent P19 murine embryonal carcinoma cell line in culture. In this paper we demonstrate that met/HGF/SFR mRNA, protein, and its ligand are expressed at a low level in undifferentiated P19 cells and that their expression is increased as P19 cells are induced to differentiate into neuroectodermal derivatives following treatment with retinoic acid (RA) and into mesodermal derivatives following treatment with dimethyl sulfoxide (DMSO). From in situ hybridization analyses, only a subpopulation of differentiating P19 cells treated with RA or DMSO expresses high levels of the met/HGF/SFR RNA. In cultures treated with RA and cytosine arabinoside, both met/HGF/SFR mRNA and protein can be localized specifically to nondividing neuronal cells. Expression of the met/HGF/SFR and its ligand, HGF/SF, in undifferentiated P19 cells and differentiated derivatives suggests that stimulation of this signal transduction pathway may be an important event for the control of cell differentiation, proliferation, or positioning during embryogenesis.

Animals↗

PubMed1993

The protection of ischaemic preconditioning can be reinstated in the rabbit heart after the initial protection has waned.

OBJECTIVE: Preconditioning the heart with 5 min of ischaemia followed by reperfusion renders the myocardium resistant to infarction from subsequent ischaemia. This protection lasts for about 1 h. The aim of this study was to test whether the protection could be reinstated with a second episode of preconditioning after protection from an initial episode had worn off. METHODS: To induce infarction animals experienced 30 min of coronary artery occlusion and then 3 h reperfusion. Ischaemic preconditioning was accomplished with 5 min of coronary branch occlusion. In one group of rabbits the subsequent reperfusion period was prolonged to 2 h to permit protection to wear off before the 30 min coronary occlusion was initiated. In another group a second 5 min coronary occlusion was performed at the end of the 2 h reperfusion. After 10 min of reperfusion the 30 min ischaemic period began. Control animals experienced only the 30 min ischaemia and 3 h reperfusion. Infarct volume was measured with tetrazolium and expressed as a percentage of the ischaemic zone volume. RESULTS: Average infarct size in seven control rabbits [36.0 (SEM 2.0)% of the ischaemic zone] was not significantly different from that in eight rabbits with the prolonged coronary occlusion occurring 2 h after the preconditioning stimulus [28.6 (2.9)% infarction]. In contrast infarcts were significantly smaller in the re-preconditioned group of seven rabbits [8.3 (4.2)%] and comparable to those previously seen with a single preconditioning stimulus followed 10 min later by the 30 min occlusion [6.1 (1.8)%]. CONCLUSIONS: The rabbit heart can be protected with a second preconditioning stimulus after protection from an initial period of preconditioning has subsided.

Animals↗

PubMed1993

Catecholamines can induce adenosine receptor-mediated protection of the myocardium but do not participate in ischemic preconditioning in the rabbit.

The role of catecholamines in ischemic preconditioning is unclear. Accordingly, the effects of tyramine-induced norepinephrine release and alpha 1-receptor blockade were examined. Ischemic preconditioning with a 5-minute coronary occlusion 10 minutes before a 30-minute ischemic interval resulted in only 7.7 +/- 3.1% infarction of the risk area, significantly less than that in control rabbits with isolated 30-minute coronary occlusions (34.4 +/- 3.2%, P < .01). Intravenous infusion of tyramine 10 minutes before 30 minutes of ischemia also protected the heart from infarction to an extent similar to that seen with ischemic preconditioning (6.9 +/- 2.4% infarction). This protection observed with tyramine infusion was eliminated by alpha 1-receptor blockade with BE 2254 (36.8 +/- 2.6% infarction) but was unaffected by beta-blockade with propranolol (10.5 +/- 2.4% infarction). Furthermore, the protection was unaffected when the tyramine-induced hypertension was attenuated by allowing blood to flow into a volume reservoir (3.9 +/- 0.8% infarction, P < .01 vs control value). The nonselective adenosine-receptor blocker PD 115,199 also eliminated tyramine-induced protection (40.2 +/- 5.6% infarction), indicating that adenosine is involved in adrenergic-mediated protection. BE 2254 could not block ischemic preconditioning (3.9 +/- 1.1% infarction, P < .01 vs control value). Therefore, catecholamine release before prolonged ischemia can protect the heart from infarction via the alpha 1-receptor, but adenosine receptor stimulation is also involved. alpha-Adrenergic stimulation does not appear to be critical to the protection observed after ischemic preconditioning.

Adenosine↗

PubMed1993

[Suppurative mediastinitis as a complication of deep neck infection (report of 15 cases)].

Fifteen cases of suppurative mediastinitis secondary to perforation of pharynx or esophagus are reported. The cervical fascial spaces are the main route of spread of infection from the neck to the mediastinum. The infection is caused by both aerobic and anaerobic bacteria. Major treatments for suppurative mediastinitis are early surgical drainage and proper use of antibiotics; Irrigation of the mediastinum with povidone-iodine is a safe and effective treatment. Of these 15 patients, 11 survived and 4 died. One case complicated by common carotid artery rupture was cured by surgical repair.

Adolescent↗

PubMed1993

Detrimental effects of interrupting warm blood cardioplegia during coronary revascularization.

Warm blood cardioplegia has emerged as a substitute for cold blood cardioplegia as a method of myocardial protection. However, the continuous infusion of blood in this technique may obscure the operative field and necessitate interruption of warm blood cardioplegia. This experimental study was therefore undertaken to determine whether interrupting warm blood cardioplegia during coronary revascularization would increase myocardial damage. In 30 adult pigs, the second and third diagonal vessels were occluded with snares for 90 minutes. All animals underwent cardiopulmonary bypass and 45 minutes of cardioplegic arrest. During the period of cardioplegic arrest, 10 pigs received intermittent antegrade/retrograde infusion of cold blood cardioplegic solution (4 degrees C) 10 pigs received continuous retrograde infusion of warm blood cardioplegic solution (37 degrees C) at 100 ml/min, and 10 pigs received retrograde infusion of warm blood cardioplegic solution that was interrupted for three 7-minute periods. After aortic unclamping, the coronary snares were released and all hearts were reperfused for 180 minutes. Interrupting retrograde warm blood cardioplegia resulted in more tissue acidosis during cardioplegic arrest (6.20 +/- 0.16 interrupted retrograde warm blood cardioplegia and 6.45 +/- 0.12 continuous retrograde warm blood cardioplegia, both p < 0.05 compared with 6.98 +/- 0.17 intermittent antegrade and retrograde cold blood cardioplegia), decreased echocardiographic wall-motion scores (4 [normal] to -1 [dyskinesis]; 2.06 +/- 0.30 interrupted retrograde warm blood cardioplegia, p < 0.05 compared with 3.30 +/- 0.40 intermittent antegrade and retrograde cold blood cardioplegia, 2.80 +/- 0.40 continuous retrograde warm blood cardioplegia), and increased tissue necrosis as measured by the area of necrosis/area at risk (38% +/- 5% interrupted retrograde warm blood cardioplegia, p < 0.05 compared with 21% +/- 2% intermittent antegrade and retrograde cold blood cardioplegia; 25% +/- 2% continuous retrograde warm blood cardioplegia). We concluded that interrupting warm blood cardioplegia during coronary revascularization diminishes the effectiveness of warm blood cardioplegia and results in increased ischemic damage.

Animals↗

PubMed1992

Anxiogenic effects of acute and chronic cocaine administration: neurochemical and behavioral studies.

The effects of cocaine on defensive withdrawal behavior in rats and elevated plus-maze behavior in mice were investigated. Cocaine (20 mg/kg IP) injected daily for 7 or 14 days induced defensive withdrawal; that is, the latency to emerge from a small chamber in an open field and the mean time in the chamber were both significantly increased. Acute cocaine administration also induced defensive withdrawal, and this effect was prevented by prior treatment with chlordiazepoxide (5 mg/kg IP). Both acute and chronic cocaine treatments significantly increased plasma concentrations of corticosterone and reduced the ratios of 3,4-dihydroxyphenylacetic acid to dopamine and 5-hydroxyindoleacetic acid to serotonin in several brain regions. Further evidence for an acute anxiogenic effect of cocaine was obtained from mice studied in the elevated plus-maze. Acute cocaine administration decreased both the number of entries into and the time spent in the open arms of the maze. These results taken together strongly support an anxiogenic action of acute and chronic cocaine administration.

Animals↗

PubMed1992

Optimization of a cultivation process for recombinant protein production by Escherichia coli.

A single-stage fed-batch bioprocess for the production of a recombinant protein beta-galactosidase, by E. coli has been developed. The XL1-blue strain of E. coli which harbors a multi-number foreign plasmid PT was cultured in a reformulated medium. Critical medium components were selected and their respective concentrations were optimized with the Orthogonal Table method. An exponential substrate feeding schedule was used to maintain optimum conditions. Inhibition of growth and protein expression caused by excessive concentrations of glucose and acetate was investigated and subsequently minimized with an incremental nutrient feeding schedule which limited the specific growth rate of a culture. The program necessary to facilitate the control of substrate addition is fully described. This program has been used with a 2.5 l bioreactor and a commercially available software package for optimization without on-line or off-line measurement of optical density (OD), CO2, glucose or acetate. The optimized fed-batch process limited the acetate concentration to less than 20 mM; maintained an exponential growth phase for 50 h; and produced a cell density of 51 g l-1 dry cell weight (DCW) or 154 OD600 with a beta-galactosidase activity of 990 U ml-1.

Acetates↗

PubMed1992

Production of recombinant human interferon-alpha 1 by Escherichia coli using a computer-controlled cultivation process.

Genetically engineered E. coli K12 BMH-71-18 with plasmid PBV-867 was used for constitutive expression of human interferon-alpha 1 (IFN) with a defined medium. A manual, time-based, fed-batch cultivation process produced a cell density of 26.3 g l-1 (OD550 89), an IFN activity of 1.55 x 10(8) IU l-1 and a specific IFN productivity of 0.65 x 10(6) IU g-1. An analysis was conducted to characterize the problems involved in the high density microbial processes of recombinant protein production. The strategy suggested by the analysis is to establish a nutrient feeding profile that improves both the plasmid stability and the overall productivity of IFN. The nutrient feeding procedure developed here was based on the growth dynamics and a glucose consumption model. By using this procedure to continuously supply nutrients during cultivations, cell density reached 58 to 80 g l-1 and the specific IFN productivities of these runs were increased over that of the manual process. Nutrient feeding rates were found to affect the specific IFN productivity substantially. The optimized process achieved an IFN activity of 1.26 x 10(9) IU l-1, a cell density of 58 g l-1 and a specific IFN productivity of 2.2 x 10(7) IU g-1. More significantly, the overall productivity IU l-1 h-1 of the optimized, computer-controlled cultivation process was increased 12.9-fold over that of the manual cultivation process.

Cloning, Molecular↗

PubMed1992

Expression of human NAD-dependent methylenetetrahydrofolate dehydrogenase-methenyltetrahydrofolate cyclohydrolase in Escherichia coli: purification and partial characterization.

NAD-dependent methylenetetrahydrofolate dehydrogenase-methenyltetrahydrofolate cyclohydrolase is a bifunctional enzyme synthesized as a 37-kDa precursor that is imported into the mitochondria of embryonic and transformed mammalian cells. The cDNA encoding the human bifunctional enzyme was modified to remove nucleotides corresponding to the mitochondrial targeting sequence and was subcloned into a procaryotic expression vector under the control of the T7 RNA polymerase promoter. The soluble dehydrogenase-cyclohydrolase was expressed in Escherichia coli at levels up to 150-fold higher than those found in transformed mammalian cells. Forms of the recombinant enzyme with one, three, or seven additional amino-terminal residues were purified to homogeneity and shown to have similar kinetic properties. Investigation of the absolute requirement of the enzyme for Mg2+ using fluorescence quenching indicates that this ion binds in the absence of substrates.

Amino Acid Sequence↗

PubMed1992

Impaired relaxation of the human mammary artery after temporary clamping.

Internal mammary artery specimens from 17 patients were each divided into three separate rings. One ring (control) remained in Krebs solution and the other two were clamped for 30 minutes with either a soft or hard jaw clamp. Isometric tensions were measured in an organ chamber by contracting the rings twice with a thromboxane A2 mimetic, U46619, and relaxing the rings first with the endothelium-dependent agent acetylcholine followed by the endothelium-independent agent sodium nitroprusside. Endothelium-dependent maximal relaxation of the rings was impaired from control after both soft (20% versus 91%; p < 0.01) and hard (1% versus 91%; p < 0.01) jaw clamps were used. However, relaxation after use of hard jaw clamps was significantly less than after use of soft jaw clamps (1% versus 20%; p < 0.05). Endothelium-independent maximal relaxation was not impaired from control after soft jaw clamps (89% versus 97%) were applied but was significantly impaired after use of the hard jaw clamps compared with control (73% versus 97%; p < 0.01) and compared with soft jaw clamps (73% versus 89%; p < 0.05). Rings of internal mammary artery specimens from 10 patients from each experimental group were silver stained. The percentage of intact endothelial cells was significantly greater after soft jaw clamping than after hard jaw clamping (39% versus 15%; p < 0.02). These data suggest that soft jaw clamps significantly reduce the degree of vasoactive dysfunction compared with hard jaw clamps. In addition, soft jaw clamps produce fewer morphologic changes in the human mammary artery after temporary occlusion.

Acetylcholine↗

PubMed1991

Abnormalities of neural tube formation in pre-spina bifida splotch-delayed mouse embryos.

The splotch-delayed homozygous mutant (Spd/Spd) develops spina bifida with or without exencephaly, has spinal ganglia abnormalities, and delays in posterior neuropore closure and neural crest cell emigration. The heterozygote (Spd/+) has a pigmentation defect, and occasionally neural tube defects. To investigate the underlying mechanisms, we compared the neuroepithelium in the posterior neuropore region of cytogenetically identified 15-18 somite pair Spd/Spd, Spd/+, and +/+ mouse embryos by transmission electron and light microscopy. The notochordal area and cell number in the non-fused neuroepithelium region of Spd/Spd and Spd/+ embryos were significantly reduced compared to those of normal (+/+) embryos, which suggests an abnormality in notochord elongation. In the mesoderm, the mean cell number and mean ratio of cell number to area in the non-fused region were significantly lower in the Spd/Spd compared with +/+ embryos. The distance of exposed neuroepithelium above the mesoderm in the just-fused region was significantly lower in the Spd/Spd versus +/+ embryos, which may indicate an insufficient force exerted by the mesoderm during neural tube closure. Within the neuroepithelium, significantly more intercellular space was found in Spd/Spd than in +/+ embryos indicating disorganization. The basal lamina was poorly organized and the formation delayed around the neural tube in Spd/Spd and Spd/+ embryos. All together, these results suggest an early abnormality in interactions among the neuroepithelium, mesoderm, and notochord, which may lead to the delay or inhibition of neural tube closure observed in Spd/Spd mutants.

Animals↗

PubMed1991

Role of percutaneous bypass in reducing infarct size after revascularization for acute coronary insufficiency.

This study compares the effectiveness of percutaneous bypass (PB) with that of the intra-aortic balloon pump (IABP) in reducing infarct size and ischemic damage after revascularization for acute coronary occlusion. In 30 adult pigs, the second and third diagonal vessels were occluded with snares for 1 1/2 hours, followed by 1/2 hour of cardioplegic arrest and 3 hours of reperfusion with the snares released. During the period of coronary occlusion before the institution of cardiopulmonary bypass, 10 pigs were placed on PB, 10 pigs received IABP, and 10 others received no intervention (unmodified). Ischemic damage in the area at risk was assessed by echo wall motion scores (ranging from 4 indicating normal to -1 indicating dyskinesia), changes in myocardial tissue pH (delta pH) from preischemia, and the area of necrosis/area of risk (AN/AR) ratio. Hearts treated with the IABP had the highest wall motion scores (1.27 +/- 0.33 for unmodified versus 1.40 +/- 0.30 for PB versus 2.04 +/- 0.30 for IABP), the least change in pH values from preischemia (delta pH: 0.41 +/- 0.13 for unmodified versus 0.60 +/- 0.10 for PB versus 0.25 +/- 0.09 for IABP, p less than 0.05 for IABP versus PB), and the least amount of myocardial necrosis (AN/AR ratio: 73 +/- 4% for unmodified versus 43 +/- 2 for PB versus 27 +/- 4 for IABP, p less than 0.05 for PB and IABP versus unmodified and for IABP versus PB). Although the PB group experienced less myocardial necrosis than did the unmodified group, the most optimal recovery occurred in the IABP group.

Angioplasty, Balloon, Coronary↗

PubMed1991

Laser ablation ability of different fiber tips on human arteries. The role of photothermal effect.

To compare laser ablation abilities of bare tip and metal probe as well as spectraprobe, specimens from human normal and atherosclerotic aorta were irradiated with Nd-YAG laser. To evaluate the influence of photothermal effect thermal energy productions of 3 tips were measured with a calorimeter. The results showed that the bare tip produced the most effective ablation in arterial atheroma, followed by the metal probe and the spectraprobe. Similarly, the ratio of the ablation area on atheroma to that on normal vessel was the best with the bare tip and the worst with the spectraprobe. However, the extent of surrounding tissue damage adjacent to the ablation crater was the largest with the bare tip and the smallest with the spectraprobe. These differences cannot be explained only by variations in the photothermal effect, since thermal energy production is proved to be almost equal among the 3 laser fiber tips.

Aged↗

PubMed1990

Carbon dioxide gas as a perfusion medium for the sapphire probe in laser ablation of human atheromatous plaques: comparison study with saline.

The effectiveness of CO2 gas as a perfusion medium was compared to that of saline in laser ablation of human atheromatous plaque. In an experimental circulation-occlusion model using flowing whole blood, human cadaveric arterial samples were irradiated by a sapphire probe with the Nd-YAG laser. The following experiments were performed: 1) lasing without perfusion, 2) lasing with saline perfusion of the probe, and 3) lasing with CO2 perfusion. Different perfusion flow rates of saline and CO2 were used. Results showed that the mean ablation area was 1.6-fold larger with CO2 than with saline perfusion (P less than 0.05, Student's t test). The mean lateral injury at the site adjacent to the ablation crater and at the area directly facing the probe was not significantly different with either perfusion medium. The larger ablation area with CO2 was probably due to the fact that CO2 is a good insulator for maintaining a higher probe temperature and keeps the probe free of blood debris. In conclusion, our results show that CO2 perfusion facilitates more effective laser ablation of atheromatous plaque than saline perfusion by the sapphire probe with the continuous wave Nd-YAG laser.

Aged↗

PubMed1990

Superiority of substrate enhancement over oxygen free-radical scavengers during extended periods of cold storage for cardiac transplantation.

When cold storage techniques used in cardiac transplantation are extended beyond 3 hours, there is significant depression in ventricular function. This study was undertaken to determine whether the addition of the amino acid L-glutamate or the oxygen free-radical scavengers superoxide dismutase (SOD) and catalase (CAT) during extended periods of cold storage would improve ventricular function. Fifteen rabbit hearts were placed on a Langendorff apparatus, arrested with crystalloid potassium cardioplegia, stored in iced saline solution (3 degrees C) for 5 hours, and then reperfused at 37 degrees C for 1 hour. In five hearts L-glutamate (4 mmol/L) was added to the cardioplegic and reperfusate solutions, and five hearts received SOD (1500 units/kg/L) and CAT (3500 units/kg/L), whereas in five others the cardioplegic and reperfusate solutions were unmodified. Hearts treated with L-glutamate had the best recovery of positive dP/dt (79%* glutamate vs 49%* SOD and CAT vs 36% unmodified), negative dP/dt (76%* glutamate vs 53% SOD and CAT vs 45% unmodified), developed pressure (67%* glutamate vs 51% SOD and CAT vs 45% unmodified), and coronary flow (81%* glutamate vs 79%* SOD and CAT vs 62% unmodified). We conclude that substrate enhancement with L-glutamate provides superior myocardial protection than is possible with the oxygen free-radical scavengers SOD and CAT during extended periods of cold storage for cardiac transplantation.

Animals↗

PubMed1990

Central beta 1-adrenergic receptors are involved in CRF-induced defensive withdrawal.

Previous studies indicated that peripheral administration of propranolol, a nonselective beta-adrenergic antagonist, attenuated ICV CRF-induced suppression of a conditioned emotional response and defensive withdrawal behavior in rats, suggesting the involvement of a beta-adrenergic receptor in the CRF-induced behavioral changes. The present study was carried out to determine whether central or peripheral beta-adrenergic receptors are involved in CRF-induced defensive withdrawal behavior, and which subtype of beta-adrenergic receptor is involved. l-Propranolol (2.5 mg/kg IP) significantly reversed CRF-induced defensive withdrawal behavior. CGP-12177 (1 mg/kg IP), a beta-adrenergic antagonist with predominant effects on peripheral beta-adrenergic receptors, and ICI 118,551 (0.5 mg/kg IP), a selective beta 2-adrenergic antagonist, had no significant effects on CRF-induced defensive withdrawal. When administered ICV, two selective beta 1-adrenergic antagonists, CGP-20712A (10 micrograms) and atenolol (100 micrograms), significantly antagonized CRF-induced defensive withdrawal. Our results suggest that a central beta 1-adrenergic receptor is involved in CRF-induced defensive withdrawal in rats.

Animals↗

PubMed1990

Percutaneous transluminal laser angioplasty. Progress over the past two years.

The progress in percutaneous transluminal laser angioplasty (PTLA) over the past two years is presented. The technical development includes the application of new equipments to laser sources, delivery systems and monitors. We review new experimental research in rapidly establishing animal models and human postmortem specimens, as well as efforts to select adequate wave length and irradiation time for laser energy with suitable infusion media. A summary of clinical trials is given on expanding usage, complication rates and long-term patency of PTLA. The current trends in PTLA respecting guide wire assisted balloon angioplasty and other recanalization methods are described.

Angioplasty, Balloon↗