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W Liu

Publications and source records attributed to W Liu.

At least 901 records · Page 50Linked to original sources
PubMed1994

Peptide synthesis catalyzed by the Glu/Asp-specific endopeptidase. Influence of the ester leaving group of the acyl donor on yield and catalytic efficiency.

We recently described a two-step enzymatic semisynthesis of the superpotent analog of human growth hormone releasing factor, [desNH2Tyr1,D-Ala2,Ala15]-GRF(1-29)-NH2 (4), from the precursor, [Ala15,29]-GRF(4-29)-OH (1). C-Terminal amidation of 1 to form [Ala15]-GRF(4-29)-NH2 (2) was achieved by carboxypeptidase-Y-catalyzed exchange of Ala29-OH for Arg-NH2. The target analog 4 was then obtained by acylation of segment 2 with desNH2Tyr-D-Ala-Asp(OH)-OR (3) (R = CH3CH2- or 4-NO2C6H4CH2-) catalyzed by the V8 protease. In this paper we report on the use of the recently isolated Glu/Asp-specific endopeptidase (GSE) from Bacillus licheniformis, which is shown to be an efficient catalyst for the segment condensation of 2 and 3. GSE is more stable than the V8 protease under the conditions employed (20% DMF, pH 8.2, 37 degrees C). The extent of conversion of 2 into 4 is limited by proteolyses at Asp3-Ala4 and Asp25-Ile26. However, this proteolysis is virtually eliminated by use of the appropriate ester leaving group, R. A systematic study of the kinetics of the GSE-catalyzed segment condensations of 2 and a series of tripeptide esters, desNH2Tyr-D-Ala-Asp(OH)-OR (3) [R = CH3CH2- (3a), CH3- (3b), ClCH2CH2- (3c), C6H5CH2- (3d), 4-NO2C6H4CH2- (3e)] revealed that rate of aminolysis versus proteolysis, and hence the conversion of 2 into 4, increase with increasing specificity (Vmax/Km) of GSE for the tripeptide ester.(ABSTRACT TRUNCATED AT 250 WORDS)

Acylation↗
PubMed1994

[Effects of compatible using of fructurs Evodiae on the main chemical components of rhizoma Coptidis].

The results of experimental studies on the compatible using of Fructus Evodiae with Rhizoma Coptidis show that in the decoction of the two drugs there is an additive property for the chemical constituents and no new chemical substances were found. But the decocting rate of berberine, the main constituent of Rhizoma Coptidis, decreases by 37.0% after decocting with Fructus Evodiae.

Berberine↗
PubMed1994

Macrophage colony-stimulating factor mediates astrocyte-induced microglial ramification in human fetal central nervous system culture.

Colony-stimulating factors are important mediators of microglial growth and function. Microglia, derived from ameboid precursor cells, undergo a series of morphological changes in the central nervous system to become ramified, a morphological hallmark of differentiated microglia. The cellular mechanisms and environmental factors involved in microglial ramification in the developing brain are not known. In the present study, we examined the role of macrophage colony-stimulating factor (M-CSF) in the induction of ramification of microglia in human fetal glial cultures. Human fetal microglia underwent spontaneous conversion from ameboid to ramified shape when co-cultured with human fetal astrocytes. Concurrently, high levels of M-CSF also accumulated in cultures of unstimulated human fetal astrocytes. That the M-CSF was essential in inducing microglial ramification was demonstrated by almost complete inhibition of ramification by an antibody to human M-CSF receptor, c-fms. Furthermore, profound inhibition of microglial ramification was exerted by herbimycin A, a specific inhibitor of tyrosine kinase (a component of the signal cascade of c-fms), supporting the role of M-CSF/c-fms in the induction of microglial ramification. Our results suggest a pivotal role played by astrocytes and astrocyte-produced M-CSF in the induction of microglial maturation and differentiation in the developing human brain.

Antibody Specificity↗
PubMed1994

[Malignant lymphomas in childhood in Sichuan province--a clinicopathological analysis of 304 cases].

A clinicopathological study of 304 cases of malignant lymphomas (ML) in children in Sichuan province is reported. One hundred and sixty of them were Hodgkin's disease (HD). The ratio between males and females was 5.7 to 1. The disease was more prevalent in children aged from 5 to 9. Cervical lymph nodes were more easily involved. Extra-nodal HD wasn't found in these cases. When subtypes of HD were concerned 62.5% of cases belonged to mixed-cellularity HD. The prognosis of HD was better than that of non-Hodgkin's lymphoma (NHL). The remaining 144 cases were NHL. The ratio between males and females was 3.4 to 1. The disease was more prevalent in children aged from 4 to 14. Eighty four percent of NHL primarily originated from superficial lymph nodes and the other 16.0% of NHL was of extranodal involvement. Seventy two point nine percent of cases in this group was of high grade malignancy. Among them the lymphoblastic type of NHL occupied 44.5%. On the other hand, the follicular type of NHL was rare (0.7%). The specialities of malignant lymphomas in childhood in China are also discussed in the present report.

Adolescent↗
PubMed1994

Clinical observation on osteoporosis treated with traditional kidney-tonifying medicaments.

The method of scoring kidney deficiency symptoms and bone density was used to judge therapeutic efficacy on osteoporosis of traditional kidney-tonifying drugs. It was proved that the drugs not only improved clinical symptoms but also delayed the developmental process of this disorder. It also verified the correctness of the traditional theory that the kidney dominates the bone and generates the marrow.

Adult↗
PubMed1993

The time trend and age-period-cohort effects on incidence of adenocarcinoma of the stomach in Connecticut from 1955-1989.

BACKGROUND: Adenocarcinoma of the gastric cardia has been be increasing in Connecticut, and the risk factors responsible for the increasing incidence are unknown. This study examined the incidence pattern of adenocarcinoma of the gastric cardia and distal stomach in Connecticut during the past decades and identified components of birth cohort, period, and age as determinants of the observed time trends by regression modeling. METHODS: This study was based on all histologically confirmed incident cases of gastric adenocarcinoma reported to the Connecticut Tumor Registry between 1955 and 1989. Stomach cancers were grouped into cancers of the gastric cardia, distal stomach, or unknown/unspecified subsite. Age-adjusted incidence rates were calculated by the direct method standardized to the 1970 United States population. A regression model was used to identify birth cohort, period, and age as determinants of the observed time trends. RESULTS: The results indicated that the incidence rate of adenocarcinoma of the cardia is increasing, particularly in white males, whereas adenocarcinoma of the distal stomach is now decreasing in both sexes in Connecticut. Regression modeling suggests that the increase of adenocarcinoma of the cardia may be explained partly by a birth cohort phenomenon. CONCLUSION: There is little information regarding the risk factors that might be responsible for the observed increasing trend for adenocarcinoma of the cardia, although smoking, alcohol intake, retinol intake, and hiatal hernia have been associated with an increased risk of adenocarcinoma of the cardia or gastric cancer. Considering the different epidemiologic features of adenocarcinoma of the cardia and distal stomach, future analytic studies should separate cancer of the gastric cardia and cancer of the distal stomach in searching for etiologic factors.

Adenocarcinoma↗
PubMed1993

Cytokine production by human fetal microglia and astrocytes. Differential induction by lipopolysaccharide and IL-1 beta.

As part of a study on the role of cytokines in central nervous system development and dysfunction, we determined the pattern of cytokine production in highly purified cultures of microglia and astrocytes isolated from second-trimester human fetal brains. Levels of TNF-alpha, IL-1 beta, and IL-6 mRNA and protein were determined by Northern blot analysis and ELISA before and after stimulation with LPS, TNF-alpha, or IL-1 beta. In microglia, LPS induced mRNA for all three cytokines. High protein levels of IL-6 and TNF-alpha were also found in the medium, whereas IL-1 beta protein was mostly cell associated. IL-1 beta also induced message for all three cytokines, in the rank order of IL-1 beta > IL-6 > TNF-alpha. TNF-alpha induced mRNA and protein for IL-1 beta but not for TNF-alpha or IL-6. In contrast, LPS failed to stimulate either mRNA or protein expression for any of the three cytokines in astrocytes. On the other hand, IL-1 beta provided a strong stimulus for astrocytes. IL-1 beta induced mRNA and protein for both TNF-alpha and IL-6, but the kinetics of the response differed for the two cytokines. TNF-alpha mRNA and protein levels peaked early (at 4 h and 16 h, respectively) and were undetectable by 72 h, whereas IL-6 mRNA peaked later (at 16 h) and protein levels continued to accumulate in the medium through 72 h. IL-1 beta did not induce IL-1 beta mRNA or protein in astrocytes. TNF-alpha did not induce expression of any of the cytokines in astrocytes. In conclusion, our results demonstrate that cytokine production can be induced in human fetal microglia and astrocytes but that the stimuli for induction differed significantly for the two cell types. Whereas LPS was a potent stimulus for microglia, astrocytes primarily responded to IL-1 beta. The data further suggest that microglia may be key regulators of astrocyte response, working primarily through the expression of cell-associated IL-1 beta.

Astrocytes↗
PubMed1993

Macrophage colony-stimulating factor in human fetal astrocytes and microglia. Differential regulation by cytokines and lipopolysaccharide, and modulation of class II MHC on microglia.

CSF-1 is a growth factor that selectively promotes the proliferation, survival, and differentiation of cells of the mononuclear phagocyte series. As part of a study on the role of cytokine and hematopoietic growth factors in central nervous system (CNS) development and inflammation, we examined the expression of CSF-1 in dissociated glial cells cultured from human fetal CNS tissue. CSF-1 mRNA and protein were constitutively expressed by astrocytes. The steady state level of CSF-1 mRNA was markedly up-regulated by both IL-1 beta and TNF-alpha in a time- and dose-dependent manner, whereas only a minimal increase was detected after stimulation with LPS. In unstimulated astrocyte cultures, CSF-1 protein levels gradually increased to 3.5-fold base-line values by 96 h and were significantly increased by all three stimulants in the order of IL-1 > or = TNF > LPS. Low levels of CSF-1 mRNA and protein were also detected in unstimulated microglia cultures. In contrast to astrocyte cultures, CSF-1 mRNA and protein increased significantly after stimulation with LPS, but changed only minimally after exposure to TNF-alpha or IL-1 beta. The effect of CSF-1 on cell proliferation, morphology, and class II MHC Ag expression was determined in highly enriched cultures of microglia and astrocytes. Microglia treated with CSF-1 showed a modest level of proliferation and differentiation into rod-shaped cells, whereas neither cell number nor shape was changed in astrocyte cultures. Interestingly, marked inhibition of both basal and IFN gamma-induced class II MHC Ag expression was observed in microglial cells cultured in the presence of CSF-1, whereas no effect was detected in astrocytes. These results suggest the possibility that in situ production of CSF-1 in the CNS may regulate normal glial cell development and contribute to the immunologic status of the CNS through the down-regulation of class II MHC expression.

Astrocytes↗
PubMed1993

Molecular cloning, sequencing, and analysis of the cDNA for rabbit muscle glycogen debranching enzyme.

Six peptides were isolated from glycogen debranching enzyme purified from rabbit muscle, and their sequences were determined. A cDNA library made from rabbit muscle using random hexamer primers was screened with oligonucleotide probes constructed in accordance with these peptide sequences. Seven cDNA clones comprising the open reading frame were found, whereas oligo(dT) cDNA libraries yielded no positive clones because of the long 3'-nontranslated region of 2.3 kb. The open reading frame of 4665 bases codes for a 1555-amino-acid protein of M(r) 177,542. Compared to the sequence from human muscle, there are an additional 40 amino acid residues upstream from the N-terminus, and the next 10 residues show no homology. For the remaining 1505 residues, the two sequences exhibit an identity of 93%. The four consensus sequences commonly found at the carboxy termini of beta-strands in the alpha/beta barrel domains of amylases and glucanotransferases are also found in the N-terminal half of the debranching enzyme, suggesting that this structural domain may be present. This and other evidence suggests that the N-terminal half may encompass the transferase activity, leaving the glucosidase activity for the C-terminal half. The latter shows no significant homology to known proteins. An unusual feature of the sequence is the presence of three pairs of adjacent cysteines, which may explain inhibition of the enzyme by organic arsenites.

Amino Acid Sequence↗
PubMed1993

Isolation and characterization of cerebral resistance vessel endothelium in culture.

Organ-derived endothelia have been shown to exhibit distinct patterns of morphology and growth responsiveness in vitro. This report describes the development, cloning and establishment of long-term serial cultures of rat vascular endothelial cells derived from cerebrocortical resistance vessels (small arteries and arterioles). Modification of our previous published technique for establishing resistance vessel-derived smooth muscle cells (RV-SMC) resulted in enhanced levels of endothelial outgrowth from collagenase-treated microvessel fragments. Although primary culture growth consisted predominantly of SMC, subsequent subcultivation of these cultures revealed the presence of distinct endothelial cell clusters within the SMC monolayer. Serial cloning of these isolates resulted in a homogeneous population of cells with the characteristic endothelial cobblestone growth pattern and positive immunofluorescence for factor VIII-related antigen. Previously established RV-SMC frozen stocks provided an additional source for obtaining resistance vessel endothelial cells. This was made possible by the slow proliferation rate of early-passage RV-SMC and their inability to withstand freezing procedures. Endothelial cells from both preparations were identical and designated resistance vessel derived endothelial cells RV-EC. Upon long-term cultivation (> P15), confluent RV-EC cultures expressed spontaneous multicellular cord development that stained positive for factor VIII-related antigen. Cell growth studies demonstrated that RV-EC were capable of significant growth when maintained in serum-free conditions. Growth kinetics using serum-free conditioned medium demonstrated mitogenic activity indicating the presence of an autocrine growth factor. Increase growth responsiveness was also noted in RV-EC when treated with a variety of peptide growth factors. These results indicate that resistance vessel endothelium can be successfully isolated and maintained in long-term serial cultures. Furthermore, the availability of cultured EC and SMC from this unique microvascular site will enable examination of cerebrovascular endothelial-smooth muscle cell interactions in vitro and may help to elucidate the mechanisms of altered vascular function in disease states.

Animals↗
PubMed1993

An intermediate loading rate technique for the determination of mechanical properties of human femoral cortical bone.

An experimental method to evaluate the mechanical properties of human femoral cortical bone under an intermediate strain rate of 4 x 10(-2) s-1 is presented. The dynamic loading was developed by dropping weights from various heights; results were obtained for Young's modulus and Poisson's ratio when the specimens were loaded along the longitudinal axis of the femur. The results were compared with those under a slow strain rate of 2 x 10(-5) s-1 and a fast strain rate of 1 x 10(-2) s-1. It was found that Young's modulus for the intermediate strain rate is 10.5% higher than for the slow strain rate and 10% lower than for the fast strain rate. Poisson's ratio did not show any significant variation for the above three strain rates. The results were compared with those given previously by other investigators.

Biomechanical Phenomena↗
PubMed1993

Correlative light and electron microscopic study of boutons on neuronal somas isolated from fixed mammalian brain.

Procedures are described for isolating neuronal somas by ultrasonic disruption of fixed rat brain and for fashioning a device that facilitates studying the same single soma by light microscopy and scanning and transmission electron microscopy. The device enables one to carry and repeatedly locate individual cells as well as hold solutions used to bathe the cells. Sequential electron microscopic examination of individual somas was used to confirm the presence of axosomatic boutons at the surface of isolated neurons.

Animals↗