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Biomedical subjects

W Li

Publications and source records attributed to W Li.

At least 253 records · Page 14Linked to original sources
PubMed2001

Genomic organization of BmTXKbeta and BmTXKS2, two scorpion venom peptides from Buthus martensii Karsch.

To elucidate genomic organization of BmTXKbeta and BmTXKS2, two scorpion venom peptides from Chinese scorpion Buthus martensii Karsch(BmK) were first isolated and their genomic regions characterized using the PCR method. Analysis of nucleotide sequence shows that there exists different intron location in the venom genes. The region encoding mature peptide of BmTXKbeta is disrupted by an intron with 886 bp, whereas the intron of BmTXKS2 is located within its propeptide coding region, which is different from other scorpion toxin genes with their introns within the signal peptide coding region.

Amino Acid Sequence↗
PubMed2001

Clustering of highly homologous sequences to reduce the size of large protein databases.

We present a fast and flexible program for clustering large protein databases at different sequence identity levels. It takes less than 2 h for the all-against-all sequence comparison and clustering of the non-redundant protein database of over 560,000 sequences on a high-end PC. The output database, including only the representative sequences, can be used for more efficient and sensitive database searches.

Algorithms↗
PubMed2001

Altered interneuron development in the cerebral cortex of the flathead mutant.

One approach to defining mechanisms essential to neocortical development is to analyze the phenotype of novel spontaneous mutations that dramatically affect the generation and differentiation of different neocortical neurons. Previously we have shown that there is a large decrease in the total number of cortical neurons in the flathead mutant rat, and in this paper we show that the flathead (fh/fh) mutation causes an even larger decrease in the number of interneurons. The decrease in relative interneuron number is different in different cortical lamina and for different interneuron subtypes. Specifically, the percentage of GABA and calretinin- positive cells in upper layers of somatosensory cortex is not appreciably decreased in homozygous mutants, while other interneuron subtypes in somatosensory cortex and all GABA-positive interneuron types in entorhinal cortex are decreased. In addition, the soma and dendritic arbors of interneurons in flathead are greatly hypertrophied, while those of pyramidal neurons are not. Furthermore, we found that at embryonic day 14, flathead mutants display high levels of cell death throughout both the neocortical and ganglionic eminence (GE) proliferative zones with a larger increase in cell death in the GE than in the neocortical VZ. In addition, we provide evidence that there is widespread cytokinesis failure resulting in binucleate pyramidal cells and interneurons, and the number of binucleate interneurons is greater than the number of binucleate pyramidal neurons. Together, these results demonstrate that the fh mutation causes dramatic alterations in interneuron development, and suggest that the flathead mutation causes differential cytokinesis failure and cell death in different types of neocortical progenitors.

Animals↗
PubMed2001

Determination of astragaloside IV in Radix astragali (Astragalus membranaceus var. monghulicus) using high-performance liquid chromatography with evaporative light-scattering detection.

A reverse-phase high-performance liquid chromatographic method is developed for the determination of astragaloside IV, a characteristic constituent in Radix Astragali. Samples are analyzed by means of a reverse-phase column (Zorbax Eclipse XDB C18) using acetonitrile and water under gradient conditions as the mobile phase for 30 min. An evaporative light-scattering detector is used and set at an evaporating temperature of 43 degrees C with a nebulizing gas (compressed air) pressure of 3.4 bar. The detection limit (signal-to-noise ratio > 5) of astragaloside IV is 40 ng on-column.

Astragalus Plant↗
PubMed2001

Ectopic expression of alpha1,6 fucosyltransferase in mice causes steatosis in the liver and kidney accompanied by a modification of lysosomal acid lipase.

The alpha1,6 fucosyltransferase (alpha1,6 FucT) catalyzes the transfer of a fucose from GDP-fucose to the innermost GlcNAc residue of N-linked glycans via an alpha1,6 linkage. alpha1,6 FucT was overexpressed in transgenic mice under the control of a combined cytomegalovirus and chicken beta-actin promoter. Histologically numerous small vacuoles, in which lipid droplets had accumulated, were observed in hepatocytes and proximal renal tubular cells. Electron microscopic studies showed that the lipid droplets were membrane-bound and apparently localized within the lysosomes. Cholesterol esters and triglycerides were significantly increased in liver and kidney of the transgenic mice. Liver lysosomal acid lipase (LAL) activity was significantly lower in the transgenic mice compared to the wild mice, whereas LAL protein level, which was detected immunochemically, was increased, indicating that the specific activity of LAL was much lower in the transgenic mice. In all of the transgenic and nontransgenic mice examined, the activity of liver LAL was negatively correlated with the level of alpha1,6 FucT activity. As evidenced by lectin and immunoblot analysis, LAL was found to be more fucosylated in the transgenic mice, suggesting that the aberrant fucosylation of LAL causes an accumulation of inactive LAL in the lysosomes. Such an accumulation of inactive LAL could be a likely cause for a steatosis in the lysosomes of the liver and kidney in the case of the alpha1,6 FucT transgenic mice.

Animals↗
PubMed2001

Aged garlic extract, a modulator of cardiovascular risk factors: a dose-finding study on the effects of AGE on platelet functions.

Aged garlic extract (AGE) has been shown previously to have moderate cholesterol-lowering and blood pressure-reducing effects. We have now investigated whether platelet function, a potential risk factor for cardiovascular disease, can be inhibited by AGE administration. In a randomized, double-blind study of normal healthy individuals (n = 34), both men and women, the effect of AGE was evaluated in doses between 2.4 and 7.2 g/d vs. equal amounts of placebo. Platelet aggregation and adhesion were measured at 2-wk intervals throughout the study. Threshold concentrations for epinephrine and collagen increased moderately during AGE administration compared with the placebo and baseline periods. Only at the highest supplementation level did AGE show a slight increase in the threshold level of ADP-induced aggregation. Platelet adhesion to collagen, fibrinogen and von Willebrand factor was investigated by perfusing whole blood through a laminar flow chamber under controlled flow conditions. Adherence of platelets was inhibited by AGE in a dose-dependent manner when collagen was the adhesive surface perfused at low shear rates ( approximately 30 s(-1)). At high shear rates (1200 s(-1)), AGE also inhibited platelet adhesion to collagen but only at higher intake levels. Adhesion to von Willebrand factor was reduced only at 7.2 g/d AGE, but adherence to fibrinogen was potently inhibited at all levels of supplementation. Thus, AGE exerts selective inhibition on platelet aggregation and adhesion, platelet functions that may be important for the development of cardiovascular events such as myocardial infarction and ischemic stroke. We briefly review the effect of garlic preparations in general on cardiovascular risk factors and point out differences between AGE and other garlic preparations that we feel are important to explain the efficacy of AGE.

Cardiovascular Diseases↗
PubMed2001

Structure and dynamics of translation initiation factor aIF-1A from the archaeon Methanococcus jannaschii determined by NMR spectroscopy.

Translation initiation factor 1A (aIF-1A) from the archaeon Methanococcus jannaschii was expressed in Escherichia coli, purified, and characterized in terms of its structure and dynamics using multidimensional NMR methods. The protein was found to be a member of the OB-fold family of RNA-associated proteins, containing a barrel of five beta-strands, a feature that is shared with the homologous eukaryotic translation initiation factor 1A (eIF-1A), as well as the prokaryotic translation initiation factor IF1. External to the beta barrel, aIF-1A contains an alpha-helix at its C-terminal and a flexible loop at its N-terminal, features that are qualitatively similar to those found in eIF-1A, but not present in prokaryotic IF1. The structural model of aIF-1A, when used in combination with primary sequence information for aIF-1A in divergent species, permitted the most-conserved residues on the protein surface to be identified, including the most likely candidates for direct interaction with the 16S ribosomal RNA and other components of the translational apparatus. Several of the conserved surface residues appear to be unique to the archaea. Nitrogen-15 relaxation and amide exchange rate data were used to characterize the internal motions within aIF-1A, providing evidence that the protein surfaces that are most likely to participate in intermolecular interactions are relatively flexible. A model is proposed, suggesting some specific interactions that may occur between aIF-1A and the small subunit of the archaeal ribosome.

Amino Acid Sequence↗
PubMed2001

Protection of xenogeneic cells from human complement-mediated lysis by the expression of human DAF, CD59 and MCP.

CD59 and membrane cofactor protein (MCP, CD46) are widely expressed cell surface glycoproteins that protect host cells from the effect of homologous complement attack. cDNAs encoding human CD59 and MCP cloned from Chinese human embryo were separately transfected into NIH/3T3 cells resulting in the expression of human CD59 and MCP protein on the cell surface. The functional properties of expressed proteins were studied. When the transfected cells were exposed to human serum as a source of complement and naturally occurring anti-mouse antibody, they were resistant to human complement-mediated cell killing. However, the cells remained sensitive to rabbit and guinea pig complement. Human CD59 and MCP can only protect NIH/3T3 cells from human complement-mediated lysis. These results demonstrated that complement inhibitory activity of these proteins is species-selective. The cDNAs of CD59 and MCP were also separately transfected into the endothelial cells (ECs) of the pigs transgenic for the human DAF gene to investigate a putative synergistic action. The ECs expressing both DAF and MCP proteins or both DAF and CD59 proteins exhibited more protection against cytolysis by human serum compared to the cells with only DAF expressed alone.

3T3 Cells↗
PubMed2001

The Hong Kong Bridge Protocol. Immediate loading of mandibular Brånemark fixtures using a fixed provisional prosthesis: preliminary results.

BACKGROUND: The Brånemark System Classic is well documented for its successful and predictable results in dental implant rehabilitation. However, the classic two-stage protocol is associated with problems, such as long treatment time and high treatment cost. To overcome these problems, new developments, including early functional loading protocol and Brånemark System Novum, have been introduced by various groups of researchers. In Hong Kong, a protocol has been developed to immediately load the Brånemark System fixtures with a fixed provisional prosthesis. PURPOSE: The goal of this prospective study was to present the Hong Kong Bridge protocol and report the short-term evaluation of this protocol in a group of patients who had undergone dental implant treatment for their edentulous mandibles. MATERIALS AND METHODS: Twenty-seven consecutive patients being treated at the Hong Kong Osseointegration Implant Centre between June 1998 and December 2000 were included in this study. A total of 123 Brånemark System fixtures were installed and regularly followed up for 3 to 30 months. The prosthesis stability and the marginal bone level were regularly evaluated clinically and radiographically, respectively, after the implant surgery. RESULTS: Fifteen of the 27 patients had been followed up for 1 year or longer. Two patients with eight fixtures were withdrawn from the study. Two of the 115 remaining fixtures failed, resulting in an overall implant survival rate of 98.3%. The mean marginal bone change was reported on 49 fixtures that had passed the 1-year review. The mean marginal bone loss was 0.60 mm (p < .05) after 1 year of functional loading. CONCLUSIONS: To load the mandibular Brånemark System fixtures immediately according to the Hong Kong Bridge protocol was a predictable and simple method with good results during this preliminary study period.

Adult↗
PubMed2001

[Effect of highly active antiretroviral therapy (HAART) on hypergammaglobulinemia in HIV infected patients].

To investigate the mechanism of hypergammaglobulinemia in HIV infected patients, the effect of highly active antiretroviral therapy (HAART) on the hypergammaglobulinemia was analyzed. Involved in this study were 34 untreated, 21 HAART-effective (complete response) and 14 HAART-non-effective (partial response) patients. Serum levels of HIV-RNA and gammaglobulin and immunoglobulin (Ig) isotypes were measured. Mean HIV-RNA levels of untreated and partial response patients were 1.6 x 10(4) copies/ml and 0.4 x 10(4) copies/ml, respectively. HIV-RNA levels of all complete response patients were below 4.0 x 10(2) copies/ml. Mean gammaglobulin percentages of untreated, partial response and complete response patients were 24.4%, 21.8% and 17.9%, respectively (p < 0.01 in untreated vs complete response patients). Mean IgG levels in the three groups were 2,489 mg/dl, 1,947 mg/dl and 1,618 mg/dl, respectively (p < 0.001 in untreated vs complete response patients). IgA levels were high in some untreated patients and lower in complete response patients. IgE levels were increased in some untreated and partial response patients, but there was no significant difference among the three groups. These results suggested that the hypergammaglobulinemia found in HIV infected patients was associated with HIV replication. The activation mechanism might differ by Ig isotypes.

Adult↗
PubMed2001

Development of a quantitative competitive PCR assay for detection and quantification of Escherichia coli O157:H7 cells.

A quantitative competitive PCR (QC-PCR) assay was developed to detect and quantify Escherichia coli O157:H7 cells. From 10(3) to 10(8) CFU of E. coli O157:H7 cells/ml was quantified in broth or skim milk, and cell densities predicted by QC-PCR were highly related to viable cell counts (r(2) = 0.99 and 0.93, respectively). QC-PCR has potential for quantitative detection of pathogenic bacteria in foods.

Animals↗
PubMed2001

Rag-1 mutations associated with B-cell-negative scid dissociate the nicking and transesterification steps of V(D)J recombination.

Some patients with B-cell-negative severe combined immune deficiency (SCID) carry mutations in RAG-1 or RAG-2 that impair V(D)J recombination. Two recessive RAG-1 mutations responsible for B-cell-negative SCID, R621H and E719K, impair V(D)J recombination without affecting formation of single-site recombination signal sequence complexes, specific DNA contacts, or perturbation of DNA structure at the heptamer-coding junction. The E719K mutation impairs DNA cleavage by the RAG complex, with a greater effect on nicking than on transesterification; a conservative glutamine substitution exhibits a similar effect. When cysteine is substituted for E719, RAG-1 activity is enhanced in Mn(2+) but remains impaired in Mg(2+), suggesting an interaction between this residue and an essential metal ion. The R621H mutation partially impairs nicking, with little effect on transesterification. The residual nicking activity of the R621H mutant is reduced at least 10-fold upon a change from pH 7.0 to pH 8.4. Site-specific nicking is severely impaired by an alanine substitution at R621 but is spared by substitution with lysine. These observations are consistent with involvement of a positively charged residue at position 621 in the nicking step of the RAG-mediated cleavage reaction. Our data provide a mechanistic explanation for one form of hereditary SCID. Moreover, while RAG-1 is directly involved in catalysis of both nicking and transesterification, our observations indicate that these two steps have distinct catalytic requirements.

B-Lymphocytes↗
PubMed2001

Radiologist performance in the diagnosis of internal hernia by using specific CT findings with emphasis on transmesenteric hernia.

PURPOSE: To evaluate the performance of radiologists in the diagnosis of internal hernia with specific computed tomographic (CT) findings. MATERIALS AND METHODS: Abdominal CT scans obtained in 42 patients were retrospectively reviewed by three radiologists. The case group consisted of 18 patients with internal hernias (two paraduodenal, 16 transmesenteric); the comparison group was 24 patients with no internal hernia. Images were reviewed in a random and blinded fashion. Individual and group performance was evaluated with receiver operating characteristic (ROC) analysis, and interobserver agreement was measured with Cronbach coefficient alpha. Individual CT signs relevant as predictors of transmesenteric hernia were identified with logistic regression analysis and ranked by their odds ratio and P values. RESULTS: Both paraduodenal hernias were diagnosed by all readers on the basis of CT signs, including a retrogastric saclike mass of small-bowel loops. Diagnosis of transmesenteric hernia was more difficult and variable, with an average accuracy of area under the ROC curve (A(z)) of 77%, sensitivity of 63%, and specificity of 76%. CT signs of transmesenteric hernia were recognized consistently (Cronbach coefficient alpha >or= 0.80) and included a cluster of dilated small-bowel segments and stretching and displacement of mesenteric vessels. Coexisting volvulus and ischemia were diagnosed with low sensitivity (46% and 43%, respectively) but high specificity (96% and 98%, respectively). CONCLUSION: Diagnosis of internal hernia with CT remains difficult. Special attention should be given to the clustering of bowel loops, the mesenteric vessels, and signs of small-bowel obstruction.

Adolescent↗
PubMed2001

Integrin and FAK-mediated MAPK activation is required for cyclic strain mitogenic effects in Caco-2 cells.

Rhythmic strain stimulates Caco-2 proliferation. We asked whether mitogen-activated protein kinase (MAPK) activation mediates strain mitogenicity and characterized upstream signals regulating MAPK. Caco-2 cells were subjected to strain on collagen I-precoated membranes or antibodies to integrin subunits. Twenty-four hours of cyclic strain increased cell numbers compared with static conditions. MAPK-extracellular signal-regulated kinase (ERK) kinase inhibition (20 microM PD-98059) blocked strain mitogenicity. p38 Inhibition (10 microM SB-202190) did not. Strain rapidly and time-dependently activated focal adhesion kinase (FAK), paxillin, ERK1 and 2, and p38 on collagen. c-Jun NH(2)-terminal kinase (JNK)1 and 2 exhibited delayed activation. Similar activation occurred when Caco-2 cells were subjected to strain on a substrate of functional antibody to the alpha2-, alpha3-, alpha6-, or beta1-integrin subunits but not on a substrate of functional antibody to the alpha5-subunit. FAK inhibition by FAK397 transfection blocked ERK2 and JNK1 activation by in vitro kinase assays, but pharmacological protein kinase C inhibition did not block ERK1 or 2 activation by strain. Strain-induced ERK signals mediate strain's mitogenic effects and may require integrins and FAK activation.

Caco-2 Cells↗
PubMed2001

Moderate levels of ethanol induce expression of vascular endothelial growth factor and stimulate angiogenesis.

Alcohol abuse has a negative impact on human health; however, epidemiological studies show that moderate consumption of ethanol (EtOH) reduces the risk of coronary heart disease, sudden cardiac death, and ischemic stroke. The mechanisms for these reductions in cardiovascular disease are not well established. Using cultured coronary artery vascular smooth muscle cells, we found that moderate levels of EtOH (10 and 20 mM) caused dose-related increases in both vascular endothelial growth factor (VEGF) mRNA (Northern blot) expression (1.9- and 2.6-fold) and VEGF protein (ELISA) expression (19 and 68%) compared with control (P < 0.05). EtOH at 0.25 g. kg(-1). day(-1) (7 days) increased VEGF mRNA expression by 1.48-fold over control, and increased vessel length density from 3.9 +/- 0.7 (control) to 6.0 +/- 0.3 mm/mm(2) (P < 0.05) in chick chorioallantoic membrane (CAM). We conclude that moderate levels of ethanol can induce VEGF expression and stimulate angiogenesis in chick CAM. Therefore, the results provide a theoretical basis for speculating that the cardiovascular-protective effects of moderate alcohol consumption may be partly mediated through VEGF-induced angiogenesis.

Animals↗
PubMed2001

Calcium channels in Xenopus spinal neurons differ in somas and presynaptic terminals.

Calcium channels play dual roles in cell signaling by promoting membrane depolarization and allowing entry of calcium ions. Patch-clamp recordings of calcium and calcium-dependent currents from the soma of Xenopus spinal neurons indicate key functional differences from those of presynaptic terminals. Both terminals and somas exhibit prominent high-voltage-activated (HVA) calcium current, but only the soma expresses additional low-voltage-activated (LVA) T-type current. Further differences are reflected in the HVA current; N- and R-type channels are predominant in the soma while the terminal calcium current is composed principally of N type with smaller contribution by L- and R-type channels. Potential physiological significance for these different distributions of channel types may lie in the differential channel kinetics. Activation of somatic HVA calcium current occurs more slowly than HVA currents in terminals. Additionally, somatic LVA calcium current activates and deactivates much more slowly than any HVA calcium current. Fast-activating and -deactivating calcium current may be critical to processing the rapid exocytotic response in terminals, whereas slow LVA and HVA calcium currents may play a central role in shaping the somatic firing pattern. In support of different kinetic behavior between these two compartments, we find that somatic calcium current activates a prominent slow chloride current not observed in terminal recordings. This current activates in response to calcium entering through either LVA or HVA channels and likely functions as a modulator of excitability or synaptic input. The restriction of this channel type to the soma lends further support to the idea that differential expression of fast and slow channel types in these neurons is dictated by differences in signaling requirements for somatic and terminal compartments.

Animals↗
PubMed2001

Apoptotic death of inflammatory cells in human atheroma.

Although the accumulation of cholesterol and other lipidic material is unquestionably important in atherogenesis, the reasons why this material progressively accumulates, rather than being effectively cleared by phagocytic cells such as macrophages, are not completely understood. We hypothesize that atheromatous lesions may represent "death zones" that contain toxic materials such as oxysterols and in which monocytes/macrophages become dysfunctional and apoptotic. Indeed, cathepsins B and L, normally confined to the lysosomal compartment, are present in the cytoplasm and nuclei of apoptotic (caspase-3-positive) macrophages within human atheroma. The possible involvement of oxysterols is suggested by experiments in which cultured U937 and THP-1 cells exposed to 7-oxysterols similarly undergo marked lysosomal destabilization, caspase-3 activation, and apoptosis. Like macrophages within atheroma, intralysosomal cathepsins B and L are normally present in the cytoplasm and nuclei of these oxysterol-exposed cells. Lysosomal destabilization, cathepsin release, and apoptosis may be causally related, because inhibitors of cathepsins B and L suppress oxysterol-induced apoptosis. Thus, toxic materials such as 7-oxysterols in atheroma may impair the clearance of cholesterol and other lipidic material by fostering the apoptotic death of phagocytic cells, thereby contributing to further development of atherosclerotic lesions.

Apoptosis↗