Biomedical subjects

Z Liu

Publications and source records attributed to Z Liu.

At least 559 records · Page 31Linked to original sources

PubMed1999

Molecular basis for Rh(null) syndrome: identification of three new missense mutations in the Rh50 glycoprotein gene.

Rh(null) is a rare autosomal recessive disorder characterized by an absence of Rh antigens and a varying degree of hemolytic anemia and spherostomatocytosis. We report studies of two Japanese Rh(null) cases and describe three new missense mutations of RHAG, the locus that encodes Rh50 glycoprotein and modulates Rh antigen expression. In Rh(null)(HT), RHAG harbored in exon 6 two G-->A transitions, GTT-->ATT and GGA-->AGA, which cause Val(270)-->Ile and Gly(280)-->Arg substitutions, respectively. These missense mutations were cotransmitted from the propositus to the children and were predicted to reside in endoloop 5 and transmembrane (TM) segment 9, respectively. In Rh(null)(WO), RHAG contained in exon 9 a single G-->T transversion, GGT-->GTT, which caused a Gly(380)-->Val missense change in TM12 segment. The G-->T transversion, which is located at the +1 position of exon 9, had also affected pre-mRNA splicing and caused partial exon skipping. Although both Rh(null) cases had a structurally normal RH antigen locus, hemagglutination and immunoblotting showed no expression of Rh antigens or proteins. These results correlate each mutation with a structural defect in the respective TM domain of Rh50 glycoprotein.

Amino Acid Sequence↗

PubMed1999

Electrospray ionization multiple-stage tandem mass spectrometric analysis of diglycosyldiacylglycerol glycolipids from the bacteria Bacillus pumilus.

Electrospray ionization (ESI) combined with multiple-stage tandem mass spectrometry (MS(n)) was used to directly analyze the glycolipid mixture from bacteria Bacillus pumilus without preliminary separation. Full scan ESI-MS revealed the composition of picomole quantities of glycerolglycolipid species containing C(14)-C(19) fatty acids, some of which were monounsaturated. Two main components were identified from their molecular masses and fragmentation pathways. The fragmentation pathway of the known compound compared with the investigated compound verified the proposed structure as 1(3)-acyl-2-pentadecanoyl-3(1)-O-[beta-D-glucopyranosyl-(1-->6)-O-beta-D-glucopyranosyl]-sn-glycerols. A comparison of the multiple tandem mass spectra of the different alkali-metal cation adducts indicates that the intensity of fragments and the dissociation pathways are dependent on the alkali-metal type. The basic structures of glycerolglycolipids were reflected clearly from the fragmentation patterns of the sodium cations. The intense fragments of the sugar residue from the precursor ions were obtained from the lithiated adduct ions. ESI-MS(n) spectra of [M + K](+) ions did not provide as much fragmentation as [M + Na](+) and [M + Li](+) adducts, but their spectra allow the position of glycerol acylation to be determined. On the basis of MS(2) spectra of [M + K](+) ions, it was established that all components have a C(15:0) fatty acid at the sn-2 position of the glycerol backbone and C(14)-C(19) acids at the sn-1 position of the glycerol backbone. Copyright 1999 John Wiley & Sons, Ltd.

Journal Article↗

PubMed1999

Protein loops on structurally similar scaffolds: database and conformational analysis.

A general problem in comparative modeling and protein design is the conformational evaluation of loops with a certain sequence in specific environmental protein frameworks. Loops of different sequences and structures on similar scaffolds are common in the Protein Data Bank (PDB). In order to explore both structural and sequential diversity of them, a data base of loops connecting similar secondary structure fragments is constructed by searching the data base of families of structurally similar proteins and PDB. A total of 84 loop families having 2-13 residues are found among the well-determined structures of resolution better than 2.5 A. Eight alpha-alpha, 20 alpha-beta, 19 beta-alpha, and 37 beta-beta families are identified. Every family contains more than 5 loop motifs. In each family, no loops share same sequence and all the frameworks are well superimposed. Forty-three new loop classes are distinguished in the data base. The structural variability of loops in homologous proteins are examined and shown in 44 families. Motif families are characterized with geometric parameters and sequence patterns. The conformations of loops in each family are clustered into subfamilies using average linkage cluster analysis method. Information such as geometric properties, sequence profile, sequential and structural variability in loop, structural alignment parameters, sequence similarities, and clustering results are provided. Correlations between the conformation of loops and loop sequence, motif sequence, and global sequence of PDB chain are examined in order to find how loop structures depend on their sequences and how they are affected by the local and global environment. Strong correlations (R > 0.75) are only found in 24 families. The best R value is 0.98. The data base is available through the Internet.

Amino Acid Sequence↗

PubMed1999

Determination of unbound drug concentration and protein-drug binding fraction in plasma.

The aim of this work was to provide a short overview of existing methods for the determination of free drug concentration and protein-drug binding fraction in plasma. Various methods have been described in terms of principles, evaluation of methods, and applications in recent years, with an emphasis on the chromatographic method, i.e. high-performance frontal analysis (HPFA).

Animals↗

PubMed1999

Study of physically absorbed stationary phases for open tubullar capillary electrochromatography.

A novel method based on the adsorption of positively charged compounds on the wall of a fused-silica capillary was applied to prepare stationary phases for open tubular capillary electrochromatography (OTCEC). The positively charged substances including cationic surfactant such as cetyltrimethylammonium bromide (CTAB) and basic chiral selectors such as protein, peptide and amino acid were physically adsorbed onto the capillary wall under specially selected conditions. The adsorbed stationary phase of CTAB was used to separate neutral compounds, while the others were used for chiral separations. The run-to-run reproducibility of retention time was rather good with relative standard deviation (RSD) values of less than 2.3%. The separation efficiency was excellent with the highest theoretical plate number of up to 590000/m and the average one above 250000/m. Stored at 2-8 degrees C in the refrigerator, the adsorbed stationary phase can last at least one month. It was observed that the UV spectra for the enantiomers are significantly different due to the diastereomeric interactions of enantiomers with the chiral stationary phase in the detection window. With the use of the same capillary, the same instrument, and the same mobile phase, the superiority of OTCEC over open tubular liquid chromatography (OTLC) and capillary zone electrophoresis (CZE) was illustrated.

Animals↗

PubMed1999

Effects of organic modifiers on solute retention and electrokinetic migrations in micellar electrokinetic capillary chromatography.

Influences of seven organic modifiers, including urea, methanol (MeOH), dioxane (DIO), tetrahydrofuran (THF), acetonitrile (ACN), 1-propanol (1-PrOH) and 2-propanol (2-PrOH), on the solute retention and the electrokinetic migrations in micellar electrokinetic capillary chromatography (MEKC) are investigated with sodium dodecyl sulfate (SDS) micelle as pseudostationary phase. It is observed that in the limited concentration ranges used in the MEKC systems the effect of organic modifier concentration on the retention can be described by the equation logk1=logk1w-SC for most binary aqueous-organic buffer, but deviations from this retention equation are observed at ACN and particularly THF as organic modifiers. With parameter S as a measure of the elutropic strength, the elutropic strength of the organic modifiers is found to follow a general order urea <MeOH<ACN<2-PrOH<DIO, while THF is found to be the most abundant modifier in selectivity among the organic modifiers studied. The electroosmotic mobility decreases linearly with increasing modifier concentrations. The strength of modifiers to suppress the electroosmotic mobility follows the order urea < MeOH, ACN < DIO, THF, 1-PrOH, 2-PrOH. The addition of ACN affects the electrophoretic mobility of the SDS micelle in different patterns depending on the buffer composition used, while the addition of the other modifiers leads to a rough linear decrease of the electrophoretic mobility of the SDS micelle. The suppressing strength of THF on the electrophoretic mobility of the SDS micelle is strongly related to the buffer composition, whereas the suppressing strength for the other modifiers follows the sequence urea < MeOH < DIO, 1-PrOH, 2-PrOH. The migration time window is expanded by the use of organic modifiers. Urea and MeOH have the least expanding strength while ACN, DIO, THF, 1-PrOH and 2-PrOH have the highest expanding strength on the migration time window.

Chromatography, Micellar Electrokinetic Capillary↗

PubMed1999

Mitosis and apoptosis in the liver of interleukin-6-deficient mice after partial hepatectomy.

Recently, it was shown that hepatocyte DNA synthesis after partial hepatectomy (PH) is impaired in interleukin-6-deficient (IL-6(-/-)) mice, which results in significantly delayed, but eventual, recovery of normal liver weight, compared with the IL-6(+/+) controls. Four possible compensatory mechanisms might explain this phenomenon: 1) hepatocyte hypertrophy; 2) activation of the oval cell compartment and subsequent maturation to hepatocytes; 3) non-oval biliary epithelial cell (BEC) proliferation; and/or 4) differential rates of apoptotic cell death in the regenerating liver. These hypotheses were tested by subjecting IL-6(-/-) and IL-6(+/+) mice to PH and determining sequential liver weight, histology, hepatocyte and BEC 5'-bromo-2'-deoxyuridine (BrdU) labeling, liver DNA content, alpha-fetoprotein (AFP) mRNA production, and apoptosis at several time points after PH. Consistent with previous studies, we show that the absence of IL-6 significantly impairs hepatocyte DNA synthesis and delays liver weight recovery after PH, but the defect observed in this study is less severe than that previously reported, and no excess mortality, massive necrosis on histology, nor differences in liver injury test are seen. Interestingly, the IL-6(-/-) mice show more hepatocyte BrdU pulse labeling than the IL-6(+/+) controls at 24 hours, but less at 36, 48, and 60 hours. Continuous BrdU infusion up to 60 hours after PH showed a cumulative hepatocyte labeling index of 79.5% in IL-6(+/+) mice and 70.8% in IL-6(-/-) mice, respectively (P <.03). However, despite a lower labeling index and significantly delayed weight recovery, hepatic mass was equally restored in the two groups by 96 hours. There was no evidence of oval cell proliferation in the IL-6(-/-) mice, as determined by routine histology and AFP mRNA analysis, and non-oval BEC proliferation was also slightly impaired in the IL-6(-/-) mice compared with the IL-6(+/+) mice. In addition, liver DNA content per gram of liver showed an increase compared with normal at 60 hours in both groups, but by 96 hours, there was no difference between the two groups. Thus, neither oval cell nor BEC proliferation, nor hepatocyte hypertrophy, could account for the eventual equivalent weight recovery. There was, however, a difference between the two groups in the rate of apoptosis. In normal livers of both IL-6(-/-) and IL-6(+/+) mice, apoptotic cells were uncommon, and even fewer such cells were detected at 24, 36, and 48 hours after PH. Between 60 and 96 hours after PH, a wave of apoptosis spread through the livers of both groups. The number of apoptotic cells was directly proportional to the magnitude of hepatocyte BrdU labeling and liver DNA content after PH, and the difference between the nadir of apoptosis at 24 hours and the peak at 96 hours was greater for the IL-6(+/+) mice. In addition, a direct comparison between the two groups at 96 hours showed that hepatocyte apoptosis was significantly lower in the IL-6(-/-) versus the IL-6(+/+) mice (P <. 02). Treatment of the IL-6(-/-) mice with rIL-6 completely reversed the hepatocyte proliferation defect and increased the subsequent level of total apoptotic bodies. The fine control of liver weight recovery during regeneration after PH is a complex process that involves both mitosis and apoptosis. IL-6 affects this process by recruiting, and possibly synchronizing, the entry of hepatocytes into cell cycling, which quickly restores liver mass. However, this robust response generates superfluous hepatocytes, which are eliminated via apoptosis, similar to many other processes involving organ growth.

Animals↗

PubMed1999

Proliferative and regenerative capacities of CD4(+) T cells upon TCR stimulation.

Proliferation of activated CD4(+) T cells effectively amplifies the immune response. Based on a model of selective CD4(+) T cell proliferation using an anti-CD3:anti-CD8 bispecific monoclonal antibody that leads to selective proliferation of CD4(+) T cells, we demonstrated that the peripheral CD4(+) T cells of normal subjects can divide for 17 to 38 generations, expanding 1.7 x 10(5) to 3 x 10(11) fold, following a single short period of anti-TCR stimulation. The proliferating CD4(+) T cells maintained IL2R expression. A large subgroup from each subject maintained the CD45RA(hi)CD45RO(lo) phenotype, demonstrating that activation and proliferation do not automatically convert CD4(+) T cells into CD45RA(lo)CD45RO(hi) phenotype. The enormous number of cells generated demonstrated that the peripheral CD4(+) T cells have remarkable regenerative expansion capacity. The high, but substantially variable, proliferative capacities among subjects have important implications for diseases in which CD4(+) T cells play an important role, such as HIV-infection, graft rejection, and autoimmunity.

Adult↗

PubMed1999

The effects of Radix Ginseng rubra on cAMP of experimental ischemic myocardium in rats.

The model of SD rats ligated at the proximate left anterior descend (LAD) of coronary was used. The number and dissociation constant of beta receptor were studied by using receptor autoradiography to observe the changes in beta receptor and the effects of Radix Ginseng Rubra on cAMP in experimental ischemic myocardium. The result showed that the number of binding site in simple ligation group (Bmax = 0.279) was obviously higher than that in sham operation group (Bmax = 0.093) and the dissociation constant of simple ligation group (Kd = 12. 431) was higher than that of sham operation group (kd = 1.319). There was a significant difference between the two groups (P < 0.05). It proved that the number of beta receptor was increased and the activity was elevated in myocardial cell membranes after ligation of LAD. The myocardial cAMP level in simple ligation group [(1293.96 +/- 519.36) x 10(-3) nmol/g] was much higher than that in sham operation group [(774.44 +/- 210.55) x 10(-3) nmol/g]; but the level of cAMP in ligation group after receiving Radix Ginseng Rubra treatment (805.02 +/- 362.48 pm/g) was obviously lower than that in simple ligation group (P < 0.01), which was close to the result of sham operation. The results indicated that Radix Ginseng Rubra could decrease the cAMP level in ischemic myocardium.

Animals↗

PubMed1999

Multidrug resistance P-glycoprotein function of bone marrow hematopoietic cells and the reversal agent effect.

The multidrug resistance P-glycoprotein (P-gp) expression and function in hematopoietic stem/progenitor cells were studied to investigate whether the inhibition of hematopoietic cell P-gp function by multidrug resistance reversal agent increases the cytotoxicity of chemotherapy drugs on the hematopoietic cells. The expression of P-gp on the surface of CD34+ cells from healthy human marrow was examined by flow cytometry. The multidrug resistance reversal agent MS-209 was used to measure the effects of MS-209 on the Rhodamin-123 uptaking of CD34+ hematopoietic cells. By using methylcellulose semi-solid culture, normal human granulocyte-macrophage clonal formation unit (CFU-GM) was cultured. The changes in CFU-GM inhibitory rate caused by daunorubicin were determined in the presence or absence of MS-209. The results showed that the P-gp expression rate of bone marrow CD34+ cells was 13.3%. MS-209 obviously increased the Rhodamin-123 uptake of CD34+ positive cells. The mean inhibitory rate of daunorubicin for CFU-GM was 29.6%, but it was increased to 43.3% in the presence of MS-209 with the difference being significant (P < 0.05). It was concluded that hematopoietic cells expressed P-gp protein and possessed active function. MS-209 could inhibit the membrane efflux pump and increase the cytotoxicity of chemotherapy drugs to the clonal growth of hematopoetic stem cells, suggesting the side effects of these drugs on the hematopoietic system should be taken into consideration in the clinical use.

ATP Binding Cassette Transporter, Subfamily B↗

PubMed1999

Measurement of the activation of IL-2 on bone marrow by flow cytometry.

The changes of cell surface markers before and after activation by IL-2 were detected by flow cytometry (FCM) to establish a more convenient and precise criterion for the judgment of the activation of bone marrow. By using the measurement of the release of lactate dehydrogenase (LDH) the cytotoxicity of mononuclear cells (MNCs) from bone marrow, activated or inactivated, on tumor cell line K562 was evaluated, and at the same time the changes of surface markers on MNCs before and after activation were examined by using FCM. The results showed that the cytotoxicity of MNCs from bone marrow activated by IL-2 on tumor cell line K562 was increased obviously and the number of CD25+ and CD70+ positive cells in bone marrow MNCs was higher than before activation. The enhanced cytotoxicity of MNCs on tumor cell line K562 was synchronous with the increase of the number of CD25+ and CD70+ positive cells in 48 to 72 h. It is more direct, simple and precise to demonstrate the activation of IL-2 on bone marrow by detecting the changes of the amount of the CD25+ and CD70+ positive cells in bone marrow by FCM.

Bone Marrow Cells↗

PubMed1999

Detection of the level of urinary FPA in chronic nephritis with renal failure and its clinical implication.

The level of urinary FPA was assayed by high performance liquid chromatography (HPLC) in 42 normal controls, 57 cases of chronic glomerulonephritis, including 24 with normal renal function, 12 with renal insufficiency and 21 with uremia. Their levels were 24.40 +/- 10.30 micrograms/L, 26.99 +/- 5.77 micrograms/L, 38.81 +/- 6.28 micrograms/L, 79.74 +/- 18.76 micrograms/L, respectively. The level of urinary FPA in renal insufficiency function group was significantly higher than those of the control group and normal renal function group (P < 0.01). The patients with uremia presented dramatically higher level of urinary FPA than those in the renal insufficiency group (P < 0.01). A positive correlation was found between the level of urinary FPA and the blood creatine (r = 0.9120, P < 0.01). It was suggested that a hypercoagulable state existed in the patients with chronic nephritis with renal failure, in which the severity was closely related with the occurrence and development of the disease. The urinary FPA could serve as a good indicator for renal function.

Biomarkers↗

PubMed1999

Clonal growth of human acute leukemia cells in serum-free methylcellulose medium.

The clonal growth of human acute leukemia cell line (K562) and acute myeloid leukemia cells in the serum-free culture (SFC) was studied in order to establish a SFC system which could replace the effects of serum by using semi-solid methylcellulose culture technique. Our results showed that the clonal growth of K562 cells in semi-solid culture was dependent on exogenous serum. The K562 could be grown in SFC supplemented with 4 major replacing substances. The multifactor and multilevel orthogonal experiment demonstrated that the colony formation was statistically influenced by the 4 replacing substances at various concentrations (P < 0.01). Among them, bovine serum albumin had greatest effect on clonal growth of K562 cells with the optimal concentration being 15 mg/L, followed by transferring, cholesterol and insulin with their optimal concentrations being of 150 mg/L, 7.8 mg/L and 7.0 mg/L respectively. SFC system was formed with the 4 substances at their optimal concentrations. Colony formation of the blast cells in 10 patients with acute myeloid leukemia was observed in this SFC system. There was a heterogeneity of acute myeloid leukemia cells among the 10 patients in response to the growth substances. In SFC system, there was a linear relationship between the number of the clonal formation and the count of the added cells, indicating the colony growth of the cells. Primary acute leukemia cells maintained in SFC system in 10 cases could completely form clones. The colony formation number in some cases in SFC system was more than that of the serum-containing culture. The SFC system could partially replace the serum for study of the clonal formation of human leukemia cells.

Cell Division↗

PubMed1999

Development of Polymorphic EST Markers Suitable for Genetic Linkage Mapping of Catfish.

: Expressed sequence tag (EST) markers are important for gene mapping and for marker-assisted selection (MAS). To develop EST markers for use in catfish gene mapping, 100 randomly picked complementary DNAs from the channel catfish (Ictalurus punctatus) pituitary library were sequenced. The EST sequences were used to design primers to amplify channel catfish and blue catfish (I. furcatus) genomic DNAs. Polymerase chain reaction products of the ESTs were analyzed to determine length polymorphism between the channel catfish and blue catfish. Eleven polymorphic EST markers were identified. Five of the 11 EST markers were from known genes and the other six were from unidentified ESTs. Seven ESTs were found to be associated with microsatellite sequences. Analysis of channel catfish gene sequences indicated highly biased codon usage, with 16 codons being preferably used. These codons were more preferably used in highly expressed ribosomal protein genes and in highly expressed pituitary hormone genes. G/C-rich codons are less used in channel catfish than those in other vertebrates suggesting AT-richness of the channel catfish genome.

Journal Article↗

PubMed1999

Developmental regulation of the gene for chimeric calcium/calmodulin-dependent protein kinase in anthers.

Chimeric Ca(2+)/calmodulin-dependent protein kinase (CCaMK) was cloned from developing anthers of lily (Lilium longiflorum Thumb. cv. Nellie White) and tobacco (Nicotiana tabacum L. cv. Xanthi). Previous biochemical characterization and structure/function studies had revealed that CCaMK has dual modes of regulation by Ca(2+) and Ca(2+)/calmodulin. The unique structural features of CCaMK include a catalytic domain, a calmodulin-binding domain, and a neural visinin-like Ca(2+)-binding domain. The existence of these three features in a single polypeptide distinguishes it from other kinases. Western analysis revealed that CCaMK is expressed in a stage-specific manner in developing anthers. Expression of CCaMK was first detected in pollen mother cells and continued to increase, reaching a peak around the tetrad stage of meiosis. Following microsporogenesis, CCaMK expression rapidly decreased and at later stages of microspore development, no expression was detected. A tobacco genomic clone of CCaMK was isolated and transgenic tobacco plants were produced carrying the CCaMK promoter fused to the beta-glucuronidase reporter gene. Both CCaMK mRNA and protein were detected in the pollen sac and their localizations were restricted to the pollen mother cells and tapetal cells. Consistent results showing a stage-specific expression pattern were obtained by beta-glucuronidase analysis, in-situ hybridization and immunolocalization. The stage- and tissue-specific appearance of CCaMK in anthers suggests that it could play a role in sensing transient changes in free Ca(2+) concentration in target cells, thereby controlling developmental events in the anther.

Amino Acid Sequence↗

PubMed1999

LD-IgG, IgA, IgM complex in a postburn patient.

A 4-year-old Chinese boy was admitted to our hospital with burns over 25% of his body. He had an extremely high LD activity (1743 U/l). LD isoenzyme analysis showed an abnormal band cathodic to LD-5. It was demonstrated by counter immunoelectrophoresis that the extra band was a complex of LD with IgG, IgA and IgM. Because LD-Ig complex is extremely rare in patients with burns, the clinical significance of this substance in blood remains unclarified.

Burns↗

PubMed1999

Dissociating stimulus information from internal representation--a case study in object recognition.

Human object recognition is a function of both internal memory representation(s) and stimulus input information. The role of the latter has been so far largely overlooked, and the nature of the representation is often directly equated with recognition performance. We quantify stimulus information for three classes of objects in order of decreasing object complexity: unconnected balls, balls connected with lines, and balls connected with cylinders. In an object discrimination task, subjects' performance improved with the decreasing object complexity. We show that input information also increases with decreasing object complexity. Therefore, the results could potentially be accounted for either by differences in the object representations learned for each class of objects, or by the increased information about the three-dimensional (3D) structure inherent in images of the less complex objects, or by both. We demonstrate that, when image information is taken into account, by computing efficiencies relative to a set of ideal observers, subjects were more efficient in recognizing the less complex objects. This suggests that differences in subjects' performance for different object classes is at least partly a function of the internal representations learned for the different object classes. We stress that this conclusion cannot be achieved without the quantitative analysis of stimulus input information.

Discrimination, Psychological↗

PubMed1999

Perceptual learning on orientation and direction discrimination.

Two experiments were conducted to determine the extent to which perceptual learning transfers between orientation and direction discrimination. Naive observers were trained to discriminate orientation differences between two single-line stimuli, and direction differences between two single-moving-dot stimuli. In the first experiment, observers practiced the orientation and direction tasks along orthogonal axes in the fronto-parallel plane. In the second experiment, a different group of observers practiced both tasks along a single axis. Perceptual learning was observed on both tasks in both experiments. Under the same-axis condition, the observers' orientation sensitivity was found to be significantly elevated after the direction training, indicating a transfer of learning from direction to orientation. There was no evidence of transfer in any other cases tested. In addition, the rate of learning on the orientation task was much higher than the rate on the direction task. The implications of these findings on the neural mechanisms subserving orientation and direction discrimination are discussed.

Discrimination, Psychological↗