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Biomedical subjects

M Cheng

Publications and source records attributed to M Cheng.

At least 55 records · Page 3Linked to original sources
PubMed1997

Secondary structure dependent on metal ions of copper,zinc superoxide dismutase investigated by Fourier transform IR spectroscopy.

Copper, zinc superoxide dismutase (Cu2Zn2-SOD) from bovine erythrocyte and its metal ion free derivatives, E2Zn2-SOD, Cu2E2-SOD, and E2E2-SOD (E: empty) were prepared and their secondary structures were investigated by Fourier transform ir spectroscopy. In 20 mM deuterated phosphate buffer (pD 7.5) solution at room temperature, the native Cu2Zn2-SOD contains about 34% beta-strand, 17% beta-turn, and 49% unordered structures, which is similar to the content determined by x-ray crystal structural analysis. The metal ion free derivatives decrease the component of beta-strand and increase the unordered structure component in trend. Especially in the cases of zinc-free derivatives, Cu2E2-SOD and E2E2-SOD, about 24% beta-strand, 20% beta-turn, and 57% unordered structures are obtained. The result indicates that the zinc ion plays an important role in determining the secondary structure of copper,zinc superoxide dismutase.

Animals↗
PubMed1997

Leishmania major: molecular modeling of cysteine proteases and prediction of new nonpeptide inhibitors.

The crystal structures of papain, cruzain, and human liver cathepsin B were used to build homology-based enzyme models of a cathepsin L-like cysteine protease (cpL) and a cathepsin B-like cysteine protease (cpB) from the protozoan parasite Leishmania major. Although structurally a member of the cathepsin B subfamily, the L. major cpB is not able to cleave synthetic substrates having an arginine in position P2. This biochemical property correlates with the prediction of a glycine instead of a glutamic acid at position 205 (papain numbering). The modeled active sites of the L. major cpB and cpL were used to screen the Available Chemicals Directory (a database of about 150,000 commercially available compounds) for potential cysteine protease inhibitors, using DOCK3.5. Based on both steric and force field considerations, 69 compounds were selected. Of these, 18 showed IC50's between 50 and 100 microM and 3 had IC50's below 50 microM. A secondary library of compounds, originally derived from a structural screen against the homologous protease of Plasmodium falciparum (falcipain), and subsequently expanded by combinatorial chemistry, was also screened. Three inhibitors were identified which were not only effective against the L. major protease but also inhibited parasite growth at 5-50 microM.

Animals↗
PubMed1997

Effect of 2-cyclohexene-1-one-induced glutathione diminution on ischemia/reperfusion-induced alterations in the physical state of brain synaptosomal membrane proteins and lipids.

Glutathione is able to protect membrane proteins from oxidative stress. In ischemia/reperfusion injury, free radicals cause synaptosomal membrane protein and lipid oxidation that is prevented by the free radical scavenger N-tert-butyl-alpha-phenylnitrone (Hall N. C. et al. (1995) Neuroscience 64, 81-89; 69, 591-600). We wondered if diminution of glutathione would lead to further membrane alterations. Accordingly, the effects of glutathione depletion, by intraperitoneal administration of 2-cyclohexene-1-one, on the physical state of cortical synaptosomal membrane proteins and lipids, with and without global ischemia/reperfusion, were studied in vivo and in vitro in adult and aged gerbils utilizing electron paramagnetic resonance spectrometry. 2-Cyclohexene-1-one (100 mg/kg, i.p.) was administered 30 min prior to 10-min ischemia followed by 1 or 14 h reperfusion. This glutathione reduction agent was also administered to gerbils under the same temporal schedule in the absence of ischemia and compared to untreated controls. Synaptosomal membranes were labeled with a protein-specific spin label, 2,2,6,6-tetramethyl-4-maleimidopiperidine-1-oxyl, or a lipid-specific spin probe, 5-doxylstearic acid. There were no significant changes in the physical state of the lipid portion of synaptosomal membranes when comparing ischemia reperfusion and 2-cyclohexene-1-one-treated ischemia reperfusion in either the adult or aged gerbils. However, glutathione depletion without ischemia/reperfusion caused significant changes in the physical state of the protein portion of cortical synaptosomal membranes in both the adult and aged models. Glutathione depletion, without ischemia/reperfusion, in the adult model showed a maximum change at 3 h that returned to control values by 14 h. In contrast, the aged model showed significant changes at 1 h reperfusion, which did not return to control values by 14 h reperfusion. Glutathione depletion combined with ischemia/reperfusion caused initial protein change in both adult and aged models at 1 h reperfusion, which did not return toward control values by 14 h reperfusion. The results of this study suggest that glutathione depletion increases the severity of membrane protein damage associated with ischemia/reperfusion injury.

Animals↗
PubMed1997

Complementation of growth factor receptor-dependent mitogenic signaling by a truncated type I phosphatidylinositol 4-phosphate 5-kinase.

Substitution of phenylalanine for tyrosine at codon 809 (Y809F) of the human colony-stimulating factor 1 (CSF-1) receptor (CSF-1R) impairs ligand-stimulated tyrosine kinase activity, prevents induction of c-MYC and cyclin D1 genes, and blocks CSF-1-dependent progression through the G1 phase of the cell cycle. We devised an unbiased genetic screen to isolate genes that restore the ability of CSF-1 to stimulate growth in cells that express mutant CSF-1R (Y809F). This screen led us to identify a truncated form of the murine type Ibeta phosphatidylinositol 4-phosphate 5-kinase (mPIP5K-Ibeta). This truncated protein lacks residues 1 to 238 of mPIP5K-Ibeta and is catalytically inactive. When we transfected cells expressing CSF-1R (Y809F) with mPIP5K-Ibeta (delta1-238), CSF-1-dependent induction of c-MYC and cyclin D1 was restored and ligand-dependent cell proliferation was sustained. CSF-1 normally triggers the rapid disappearance of CSF-1R (Y809F) from the cell surface; however, transfection of cells with mPIP5K-Ibeta (delta1-238) stabilized CSF-1R (Y809F) expression on the cell surface, resulting in elevated levels of ligand-activated CSF-1R (Y809F). These results suggest a role for PIP5K-Ibeta in receptor endocytosis and that the truncated enzyme compensated for a mitogenically defective CSF-1R by interfering with this process.

Amino Acid Sequence↗
PubMed1997

[Determination of human urinary pseudouridine by high performance capillary electrophoresis].

Pseudouridine, mainly as a degradation product of transfer ribonucleic acid, has been shown to be excreted in abnormal amounts in the urine of patients with cancer and can be used as one of the potentially valuable tumor markers. In this paper, a method for the rapid determination of human urinary pseudouridine by HPCE is reported. We used a 24 cm x 25 microm i.d. coated capillary and a borate buffer solution (0.1 mol/L, pH 8.6), and set the UV detection wavelength at 200 nm. In this experiment, pseudouridine can be separated completely with uridine and anti-tumor drugs (5-fluouridine and methetrexation) and other endogenous substances in urine within 4 minutes. Assay precision was determined for concentrations of 50 micromol/L and 200 micromol/L as 2.38% and 1.92% for within-day CV, 3.7% and 2.4% for between-day CV respectively. Sulfosalicylic acid was used as internal standard. Linearity, between the concentrations of pseudouridine and the corresponding peak height or area ratios of pseudouridine and the internal standard, was demonstrated in the 6.25-200 micromol/L range (r>0.9990). The detection limit of concentration for pseudouridine was 4 micromol/L. This method, with simple sample preparation, good assay precision, lower cost and full-automation, is an effective means for the assessment of pseudouridine in clinical application.

Electrophoresis, Capillary↗
PubMed1997

[A case of systemic lupus erythematosus associated with minimal change nephrotic syndrome].

A case of systemic lupus erythematosus (SLE) associated with minimal change nephrotic syndrome (MCNS) in a 25-year-old female is described. The patient suddenly manifested butterfly rash and proteinuria was first pointed out on March, 1994. On admission, her skin biopsy indicated SLE. Subsequently, she developed nephrotic syndrome. Urinalysis showed heavy proteinuria (4.1 g/day), with no other abnormalities in the urinary sediment. Immunological examination revealed positive antinuclear antibody at a titer of 1:80 with a speckled pattern. Anti-ssDNA and anti-SS-A antibodies were positive, but other antibodies were negative. Serum complement (CH50) was within the normal range (30.5 U/ml). The renal biopsy showed no apparent cellular proliferation or increase of extracellular matrices in glomeruli by light microscopy. Slight deposition of IgG, IgM, C3 and C1q was focally seen in the mesangium and capillary wall by immunofluorescence. Electron microscopic examination revealed small and scattered dense deposits in the mesangium, subepithelium and subendothelium, associated with diffuse fusion of the foot processes of epithelial cells along the glomerular basement membrane. According to the WHO classification, the histological features were compatible with those of lupus nephritis (LN), class Ib. The patient was treated with PREDNISOLONE, Mizorbine and Dilazep, resulting in the disappearance of proteinuria and a normal serum level of total protein. The association of LN and MCNS is very rare. We also investigated the relationship between the intensity of proteinuria and histological types of 53 cases with LN examined in our laboratory. The cases with heavy proteinuria were mostly classified as WHO-Class IV and Class V. We report here a case of LN associated with MCNS and also review the literatures.

Adult↗
PubMed1997

[Comparison of mechanical properties between human aortic valve and pulmonary arterial valve].

We have investigated the mechanical properties of Chinese aortic and pulmonary valves by means of uniaxial tension. The parameters include the stress-strain curve, the maximum tangent modulus E (the slope of linear segment) in the curve, the tensile strength delta b, and the ultimate strain epsilon b. The results have shown that E, delta b, and epsilon b values between aortic valve and pulmonary valve exist significant differences (significant level = 0.01), but the mechanical property differences between circumferential direction and radial direction in the pulmonary arterial valve are not significant, that means, the valve appears small anisotropic behaviour.

Adult↗
PubMed1996

Contributions of the mitogen-activated protein (MAP) kinase backbone and phosphorylation loop to MEK specificity.

To examine the specificity of MEKs for MAP kinase family members, we determined the abilities of several MEK isoforms to phosphorylate mutants of the MAP kinase ERK2 and the related kinase ERK3 which are modified in the phosphorylation loop. The ERK2 mutants included mutations of the two phosphorylation sites, mutations of the acidic residue between these two sites, and mutations that shorten the length of this loop. All mutants were tested for phosphorylation by six mammalian MEKs and compared with several wild type MAP kinases. MEK1 and MEK2 phosphorylate a majority of the ERK2 mutants. MEK2 but not MEK1 will phosphorylate ERK3. Alteration of the residue between the two phosphorylation sites neither dramatically affected the activity of MEK1 and MEK2 toward ERK2 nor conferred recognition by other MEKs. Likewise, reduction of the length of the phosphorylation loop only partially reduces recognition by MEK1 and MEK2 but does not promote recognition by other MEKs. Thus other yet to be identified factors must contribute to the specificity of MEK recognition of MAP kinases.

Amino Acid Sequence↗
PubMed1996

Characterization of a protein kinase that phosphorylates serine 189 of the mitogen-activated protein kinase homolog ERK3.

A novel protein kinase activity present in nuclear and cytosolic extracts has been identified and partially purified as a consequence of its tight binding to and phosphorylation of the extracellular signal-regulated protein kinase (ERK) 3. This novel protein kinase is inactivated by treatment with phosphoprotein phosphatase 2A. The ERK3 protein kinase was immunologically distinct from mitogen-activated protein (MAP) kinase/ERK kinases (MEK) 1 and 2 which phosphorylate the ERK3-related MAP kinases ERK1 and ERK2. This ERK3 kinase phosphorylated a single site on ERK3, Ser189, comparable to Thr183, one of the two activating phosphorylation sites of ERK2. To test the specificity of the ERK3 kinase, mutants of ERK3 and ERK2 were made in which the phosphorylated residues were exchanged. The double mutant S189T,G191Y ERK3, in which the phosphorylated residues from ERK2 replaced the comparable residues in ERK3, was phosphorylated by the ERK3 kinase but only on threonine. The ERK3 kinase did not phosphorylate ERK2 or ERK2 mutants. These findings indicate that although the ERK3 kinase is highly specific for ERK3, it does not recognize tyrosine, a feature that distinguishes it from MEKs that phosphorylate other ERK/MAP kinase family members.

Amino Acid Sequence↗
PubMed1996

ERK3 is a constitutively nuclear protein kinase.

The ERK3 cDNA predicts a protein of 62,000 in size with a C-terminal domain that extends 180 amino acids beyond the conserved core of ERK family protein kinases. Immunoblotting with antibodies raised to recombinant protein and to peptides from the catalytic core and three regions of the C-terminal tail revealed that ERK3 is the expected size and is ubiquitously expressed in a variety of cell lines and tissues. ERK3, unlike the MAP kinases ERK1 and ERK2, is localized in the nucleus in exponentially growing, quiescent, and growth factor-stimulated cells. If the 180 amino acids at its C terminus are deleted, the resulting ERK3 fragment of 45 kDa is still found primarily in the nucleus, indicating that the C terminus is not required for its localization. Recombinant ERK3 expressed in mammalian cells or in bacteria is a protein kinase, as deduced from its capacity to autophosphorylate. Mutation of a conserved residue (Asp171) expected to be involved in catalysis eliminated autophosphorylation. Ser189 of ERK3, which corresponds to Thr183, one of the activating phosphorylation sites of ERK2, is autophosphorylated in vitro and phosphorylated in vivo. Despite marked similarities to ERK1 and ERK2, ERK3 does not phosphorylate typical MAP kinase substrates, indicating that it has distinct functions.

Amino Acid Sequence↗
PubMed1996

Trapidil modifies mesangial cell proliferation and collagen accumulation in anti-thymocyte serum (ATS)-induced glomerulonephritis.

This study was designed to assess whether the glomerular mesangial-cell proliferation and the increased extracellular matrix (ECM) accumulation that occur in anti-thymocyte serum (ATS)-induced glomerulonephritis (GN) are affected by Trapidil, a potent antagonist for platelet-derived growth factor (PDGF). Fifteen male Wistar rats were divided into three groups. In group I, GN was induced by injecting a single dose of ATS. In group II, rats were given a single dose of ATS followed by daily treatment with Trapidil. In group III, the rats (controls) were treated with a single dose of phosphate buffered saline. All the rats were killed on the 10th day of the experiment. ATS induced marked mesangial cell proliferation (P < 0.01) in group I rats and Trapidil treatment (group II) significantly suppressed such proliferation (P < 0.01). Increased type III and IV collagen immunolabelling was observed in the expanded mesangial matrix in group I rats. In group II, immunolabelling for type III and IV collagen was much less than in group I. The study suggests that Trapidil therapy is effective in suppressing both mesangial cell proliferation and mesangial matrix expansion by reducing collagen accumulation.

Animals↗
PubMed1996

The influence of the age of the rat on the neuromuscular response to mivacurium in vitro.

The effective concentrations of mivacurium induced neuromuscular block were studied in the phrenic nerve-hemidiaphragm preparations of forty male Sprague-Dawley rats in four groups according to body weight, 10 g, 25 g, 100 g, and 200 g. Mivacurium was added to the Krebs' solution to obtain an initial concentration of 0.275 microgram.ml-1 (2.5 x 10(-7) mole.litre-1). Thereafter, the concentration of mivacurium was increased in increments to obtain more than 90% neuromuscular twitch inhibition at 0.1 Hz. Data were analysed by probit and logistic models. The two statistical techniques yielded very similar results, almost identical values of EC50 and EC95. There were significant decreases in the effective concentrations of mivacurium needed to depress the twitch response in neonatal rats (10 g) compared to older rats. No significant differences were observed between 25, 100 and 200 g rats. We conclude that the neonatal neuromuscular junctions of rats show increased sensitivity to mivacurium related to pharmacodynamic factors.

Aging↗
PubMed1996

[The prospect of prevention and treatment of Cor pulmonale on a 20-year follow-up of 40 middle to old aged cases of COPD and Cor pulmonale].

OBJECTIVE: To study the outcome of current therapy for COPD and Cor pulmonale by long-term follow-up of COPD patients. METHOD: Forty cases of middle to old aged COPD and Cor pulmonale patients were followed up for a period of 20 years. RESULTS: The pulmonary function of all the patients reduced significantly more than healthy elderly, while no difference was noted in blood gas analysis. 23 patients with advanced COPD developed cor pulmonale, so that the number of cases with cor pulmonale increased significantly from 7 to 30. By the end of follow-up 19 cases survived (48%), 21 cases (Cor pulmonale 19, COPD 2) died (53%). CONCLUSIONS: In view of the high mortality of cor pulmonale and the tremendous treatment cost, it was considered that the prospect for cor pulmonale management should be put on treating COPD to avoid development of Cor pulmonale. The keys of treating COPD are stop of smoking, protection from cold, early treatment of respiratory infection and further establishment of pulmonary rehabilitation work.

Aged↗
PubMed1995

Prevention of ischemia/reperfusion-induced alterations in synaptosomal membrane-associated proteins and lipids by N-tert-butyl-alpha-phenylnitrone and difluoromethylornithine.

Previous studies in our laboratory demonstrated the alteration in the physical state of synaptosomal membrane lipids and proteins in ischemia/reperfusion injury using selective spin labels and electron paramagnetic resonance spectroscopy [Hall et al. (1995) Neuroscience 61, 84-89]. Since many investigations have provided evidence for free radical generation during ischemia/reperfusion injury, we investigated whether a free radical scavenger would prevent the membrane damage, in gerbils. Further, experiments to determine if a secondary effect of polyamine generation at 14 h reperfusion could be blocked by this free radical scavenger or by an inhibitor of ornithine decarboxylase were also carried out. The alterations in synaptosomal membrane integrity observed during ischemia/reperfusion injury were selectively neutralized by treatment with the free radical spin trap N-tert-butyl-alpha-phenylnitrone or an inhibitor of ornithine decarboxylase, difluoromethylornithine. Administration of N-tert-butyl-alpha-phenylnitrone prior to ischemia totally abrogated both lipid and protein alterations observed at 1 and 14 h reperfusion. Pretreatment with difluoromethylornithine neutralized only the 14 h change in lipid label motion. Treatment with N-tert-butyl-alpha-phenylnitrone at 6 h post ischemia showed only a slight attenuation of the 14 h lipid effect and no change in the protein effect. Difluoromethylornithine treatment at 6 h post ischemia negated the 14 h ischemia/reperfusion injury-induced lipid effect and had no effect on the protein change. These data support previous suggestions that free radicals and polyamines play a critical role in neuronal damage and cell loss following ischemia/reperfusion injury and that the polyamine effect is dependent upon free radical generation during ischemia/reperfusion injury.

Analysis of Variance↗
PubMed1995

Quantitative trait loci that modify the severity of spotting in piebald mice.

Mice homozygous for the recessive mutation piebald (s) exhibit a white-spotted coat caused by the defective development of neural crest-derived melanocytes. The severity of white spotting varies greatly, depending on the genetic background on which s is expressed. A backcross between two inbred strains of s/s mice that exhibit large differences in the degree of spotting was used to identify six genetic modifiers of piebald spotting on chromosomes 2, 5, 7, 8, 10, and 13. The loci differed in their spatial contribution to spotting on the dorsal versus ventral surfaces of mice; nonadditive interactions were observed between loci on chromosomes 2 and 5. This study underscores the power of using genetic analyses to identify and analyze loci involved in modifying the severity of phenotypic traits in mice.

Animals↗