Biomedical subjects

J W Liu

Publications and source records attributed to J W Liu.

At least 91 records · Page 5Linked to original sources

PubMed1994

Prolactin-releasing activity of neurohypophysial hormones: structure-function relationship.

Oxytocin (OT) and arginine vasopressin (AVP) have been reported to release PRL both in vivo and in vitro. The objectives of this study were 1) to compare the potencies of the PRL-releasing activities of OT and TRH using cultured anterior pituitary (AP) cells, and 2) to assess the PRL-releasing activity of naturally occurring neurohypophysial hormones and selected analogs. AP cells were incubated with peptides for 15 min, and medium PRL concentrations were determined by enzyme-linked immunosorbent assay. OT at 25, 100, and 400 nM increased PRL release by 110%, 175%, and 270%, respectively; higher concentrations (1600 and 6400 nM) did not cause a further increase in PRL release. TRH was 5-10 times more potent than OT on a molar basis. GH3 cells, a somatommamotroph tumor cell line, did not respond to OT and related compounds, but showed a similar responsiveness to TRH as AP cells. Twelve neurohypophysial peptides and selected analogs were incubated with AP cells, and their relative PRL-releasing activities were compared. OT and arginine vasotocin (AVT) showed the highest PRL-releasing activity. T4-G7-oxytocin, mesotocin, isotocin, lysine vasotocin, and AVP showed a moderate PRL-releasing activity, whereas, lysine vasopressin, desmopressin, tocinoic acid, pressinoic acid, and oxytocin free acid showed very low or no PRL-releasing activity. Coincubation of OT, AVT, or AVP with a specific OT receptor antagonist abolished their PRL-releasing activity. We conclude that 1) OT and related peptides are capable of stimulating PRL release in vitro, but their potencies are significantly lower than that of TRH; 2) unlike primary AP cells, GH3 cells are unresponsive to OT and related peptides; 3) AVT and AVP probably stimulate PRL release by acting via an OT receptor; and 4) the amino acid residues in positions 3 and 8 in the peptide chain and an amidated C-terminus are critical for the PRL-releasing activity of the neurohypophysial peptides.

Amino Acid Sequence↗

PubMed1994

Peptide V: a VGF-derived neuropeptide purified from bovine posterior pituitary.

The objective of this study was to purify PRL-releasing factor (PRF) from the bovine posterior pituitary (PP) and determine its structure. Five hundred bovine PPs were acid extracted and fractionated using gel filtration chromatography followed by semipreparative and analytical HPLC. PRF activity was determined by an in vitro bioassay. After six chromatographic steps, a single peak with PRF activity was resolved. As determined by mass spectrometry and microsequencing, this peak contained a major peptide composed of 30 amino acids with a mol wt of 3708K. A synthetic peptide was then produced by solid-phase synthesis. When tested both in vivo and in vitro, the synthetic peptide lacked PRF activity. Further HPLC fractionation under different conditions resolved the synthetic peptide from a highly purified PRF activity. This indicated that the isolated peptide was coincidentally eluted with PRF during the purification. The major isolated peptide has 94% identity with a sequence at the C-terminus of a rat protein named VGF. VGF is a nerve growth factor-inducible protein that has been identified in PC12 cells and is localized in selected sites throughout the central nervous system. The isolated peptide has an Arg-Arg cleavage site at its junction within the VGF protein. Based on this information, we named this substance Peptide V (VGF-derived peptide). We postulate that Peptide V is: 1) a natural cleavage product of the VGF protein; 2) produced and processed either in the hypothalamus or within the pituitary proper, and 3) a releasable peptide that fulfills one or more endocrine functions.

Animals↗

PubMed1994

[The effect of trichosanthin on immunoregulatory T lymphocytes].

The effect of trichosanthin (TCS) on immune system has drawn attentions of the investigators both at home and abroad. The purpose of this study is to evaluate the prospects of TCS on autoimmune diseases and immunodeficiency diseases by detecting the immunoregulatory T lymphocytes (T8, 2H4, 4B4) count and cellular DNA content under the influence of TCS with flow cytometer using indirect immunofluorescence technique and lymphocyte culture in normal subjects and systemic lupus erythematosus patients. The results showed that the percentage of T8+ cells decreased, 4B4+ cells increased, 2H4+ cells did not markedly change after adding TCS. The raise of DNA content in S stage was dose-dependent to TCS, especially in large doses. It is concluded that TCS could selectively inhibit T8+ cells and could obviously increase the number of 4B4+ cells. It is suggested that TCS could enhance humoral immunity through the ratio of immunoregulatory T cells. So TCS might help immunodeficiency patients such as AIDS to reestablish their immune system.

Adjuvants, Immunologic↗

PubMed1993

New high-toxicity mosquitocidal strains of Bacillus sphaericus lacking a 100-kilodalton-toxin gene.

Five new high-toxicity mosquitocidal strains of Bacillus sphaericus were isolated in Singapore. They all belong to phage group 8 and have binary toxin (51.4- plus 41.9-kDa) genes located on the chromosome but lack a 100-kDa-toxin gene. These strains of B. sphaericus constitute a new subgroup, as only two weakly toxic strains in phage group 8 have previously been described and all the known high-toxicity strains have both binary toxin and 100-kDa-toxin genes.

Animals↗

PubMed1993

Mosquitocidal toxins of bacilli and their genetic manipulation for effective biological control of mosquitoes.

The identification, cloning, and characterization of protein toxins from various species of bacilli have demonstrated the existence of mosquitocidal toxins with different structures, mechanisms of action, and host ranges. A start has been made in understanding the polypeptide determinants of toxicity and insecticidal activity, and the purification of toxins from recombinant organisms may lead to the elucidation of their X-ray crystal structures and the cloning of brush border membrane receptors. The results of cloning mosquitocidal toxins in heterologous microorganisms show the potential of expanding the range of susceptible mosquito species by combining several toxins of different host specificity in one cell. Toxins have been expressed in new microorganisms with the potential for increasing potency by persisting at the larval feeding zone. The powerful tools of bacterial genetics are being applied to engineer genetically stable, persistent toxin expression and expand the insecticidal host ranges of Bacillus sphaericus and Bacillus thuringiensis strains. These techniques, together with modern formulation technology, should eventually lead to the construction of mosquitocidal microorganisms which are effective enough to have a real impact on mosquito-borne diseases.

Animals↗

PubMed1993

Coculturing posterior pituitary and GH3 cells: dramatic stimulation of prolactin gene expression.

UNLABELLED: Recent evidence suggests that the posterior pituitary (PP), also called the neurointermediate lobe, regulates PRL release. We previously reported that cocultures of anterior pituitary and PP cells resulted in a 2- to 3-fold increase in PRL content and release. For this study we chose GH3 cells (a somatomammotroph tumor cell line) to determine whether coculturing GH3 with PP cells: 1) stimulates the release and cell content of PRL as compared with GH; 2) increases GH3 cell proliferation; and 3) affects PRL messenger RNA (mRNA) levels. Exp 1. GH3 cells (25,000 cells per well; 25K) were cocultured with PP cells (0K, 12.5K, or 25K) from male rats in serum-free media for 1, 2, 4, and 7 days; hormones were measured by RIA. Coculturing resulted in 5- to 10-fold increases in both media and cell PRL that were linear with time and dependent on the number of PP cells. In contrast, media GH increased only 1.5- to 2-fold, and GH cell content reduced by 75%. Exp 2. GH3, PP, and GH3 + PP cells were cultured for 1, 2, and 4 days and then incubated with [3H]thymidine for 5 h. The incorporation of [3H]thymidine in GH3 cells remained constant over time and showed a small, early increase in cocultures. In contrast, incubation of PP cells alone resulted in a 50- to 60-fold rise in [3H]thymidine incorporation from days 1-4 in culture. Exp 3. Cytoplasmic mRNA was determined by slot blot hybridization with 32P-labeled complementary DNA probes for PRL and GH. After coculturing 25K GH3 cells with 12.5K and 25K PP cells for 4 days, PRL mRNA levels increased 15- and 30-fold, respectively, whereas GH mRNA levels rose less than 2-fold. Neither PRL nor GH mRNA were detected in PP cells. CONCLUSIONS: 1) coculturing GH3 with PP cells dramatically stimulates PRL gene expression, synthesis, and release; 2) this response is specific for PRL, has little effect on GH, and is not due to increased GH3 cell proliferation; and 3) we speculate that a subpopulation of intermediate lobe cells, possibly with a proliferative capacity, is responsible for inducing these effects.

Animals↗

PubMed1992

The spinach chloroplast chromosome is bound to the thylakoid membrane in the region of the inverted repeat.

By using a novel fractionation procedure we show that the chloroplast chromosome is specifically bound to the spinach thylakoid in the region of the inverted repeat, near the 16S and 23S rRNA genes. Central to the method is the use of restriction endonucleases, followed by ethylenediaminetetraacetic acid (EDTA) treatment to loosen or uncoil the nucleoid by the removal of specific proteins. The data we present provide a basis for understanding the molecular mechanism of membrane-bound cpDNA function.

Chloroplasts↗

PubMed1991

Regulation of IL-6 expression by oncostatin M.

Endothelial cells produce immunomodulatory cytokines in response to soluble mediators of inflammatory/immune reactions. We have previously demonstrated that the leukocyte-derived cytokine, oncostatin M (Onco M) can alter endothelial cell morphology, regeneration, and fibrinolytic activity in vitro. Here we demonstrate that Onco M stimulates the production of the pleiotropic cytokine, IL-6, in cultured human endothelial cells (HEC) in a time- and dose-dependent manner. Specific antibodies to IL-6 neutralize the growth-inhibitory activity for human breast carcinoma cells that is secreted by HEC in response to Onco M treatment. Specific immunoassays indicate greater than 10-fold increases in the IL-6 content of culture supernatants as early as 6 h post-treatment with Onco M (ED50 = 17 pM). This stimulation of IL-6 production by Onco M is associated with a sevenfold increase in intracellular levels of IL-6 mRNA. IL-1 alpha and TNF-alpha are also potent inducers of IL-6 production in these cells, the order of potency being IL-1 alpha greater than Onco M greater than TNF-alpha. TNF-alpha, but not IL-1 alpha, synergizes with Onco M to augment IL-6 production in HEC. HEC are 10 to 20 times more responsive to Onco M than are other nonendothelial cell types. In addition, HEC express 10 to 20 times greater numbers of high affinity cell-surface receptors for Onco M than do other nonendothelial cell types. Based on these findings, we propose that Onco M may represent a new immunomodulator regulating cytokine-induced gene products in endothelial cells.

Antineoplastic Agents↗

PubMed1991

Granulocyte-macrophage colony-stimulating factor induces transcriptional activation of Egr-1 in murine peritoneal macrophages.

Granulocyte-macrophage colony-stimulating factor (GM-CSF) is a pleiotropic hematopoietic growth factor that induces both growth and differentiation of tissue macrophages. The subcellular mechanism of action of GM-CSF is unknown. We have examined the effect of GM-CSF on the immediate early response gene, Egr-1, in murine peritoneal macrophages. Our data demonstrate that recombinant GM-CSF (25 units/ml) produces a 12-fold increase in Egr-1 mRNA within 30 min. Pretreatment with cycloheximide (10 micrograms/ml) had no effect on the ability of GM-CSF to increase Egr-1 mRNA. In nuclear runoff studies, GM-CSF increased the transcription rate of Egr-1 by 10-fold at 10 min. The maximal effect on Egr-1 transcription occurred at 25 min (13-fold) and decreased by 45 min. The half-life of Egr-1 mRNA in GM-CSF-treated macrophages is 13-21 min. We were unable to calculate the half-life in control cells, however, because of the short half-life and low level of constitutive expression of Egr-1 mRNA. Endogenous protein kinase C activity in macrophages was depleted by treatment with 12-O-tetradecanoylphorbol-13-acetate for 24 h. GM-CSF increased Egr-1 mRNA in protein kinase C-depleted macrophages, whereas the stimulatory effect of 12-O-tetradecanoylphorbol-13-acetate on Egr-1 was blocked. These data show that GM-CSF rapidly increases transcription of Egr-1 mRNA. The effect of GM-CSF on Egr-1 mRNA does not require de novo protein synthesis or protein kinase C. These findings provide a basis for investigating the molecular mechanism of action of GM-CSF in tissue macrophages.

Animals↗

PubMed1991

Purification and characterization of the apically secreted 80 KDa glycoprotein from Madin-Darby canine kidney (MDCK) cells.

An 80 KDa glycoprotein (gp 80), known to be released predominantly from the apical surface by filter-grown Madin-Darby canine kidney cells, was purified to electrophoretic homogeneity. Purified gp 80 was found to have a disulfide-bonded dimeric structure, and appeared to exist in two molecular forms, a major (high-molecular weight) form consisting of a 46 KDa subunit and a 39 KDa subunit and a minor (low-molecular weight) form consisting of a 46 KDa subunit and a 33 KDa subunit. Upon de-glycosylation by N-glycanase treatment, the 46 KDa subunit was converted to a 25.6 KDa form, whereas both the 39 KDa and the 33 KDa subunit gave rise to a 21.1 KDa form. V8 protease mapping of deglycosylated polypeptides revealed the 39 KDa and the 33 KDa subunit to have nearly identical band patterns, which also exhibited a high degree of homology to that derived from the 46 KDa subunit. Radioimmunoassays revealed that the binding of the purified gp 80 to fibrinogen (or heparin) was dependent on both pH and divalent cations. Furthermore, binding of gp 80 to immobilized fibrinogen (or heparin) was inhibited in the presence of free fibrinogen (or heparin) added in the assay mixture.

Amidohydrolases↗

PubMed1991

Effect of a traditional Chinese medicine, yin zhi huang, on bilirubin clearance and conjugation.

Oral administration of Yin Zhi Huang (YZH) daily for 3 days in rabbits accelerated plasma clearance of infused unconjugated bilirubin. A similar but less dramatic effect resulted from 3 days pretreatment with phenobarbital, 70 mg/kg/day orally. Similar doses were injected intraperitoneally in rats for 3 days, following which the bile ducts were ligated and bilirubin infused intravenously. Plasma clearance of unconjugated bilirubin and plasma appearance of conjugated bilirubin were faster, and hepatic bilirubin content was higher in both YZH- and phenobarbital-treated rats than in control animals. These observations indicate that YZH is as effective as phenobarbital in stimulating bilirubin metabolic pathways and suggest that the drugs may share common mechanisms of action.

Administration, Oral↗

PubMed1990

Bean pathogenesis-related (PR) proteins deduced from elicitor-induced transcripts are members of a ubiquitous new class of conserved PR proteins including pollen allergens.

We have searched for induced transcripts in a cDNA library derived from bean cell supension cultures treated with an elicitor from Colletotrichum lindemuthianum. Six independently isolated cDNAs corresponding to rapidly induced small mRNAs have been classified by their DNA sequence and slightly different induction behaviour into two groups. 5'- and 3'-untranslated regions exhibit little similarity, but the deduced small acidic proteins designated PvPR1 and PvPR2 are 89% identical. No relationship was found with the well-characterized PR1 proteins from tobacco. However, the PvPR proteins are closely related to pI49 in pea (64% identity), pSTH2 in potato (41% identity) and PcPR1-1 in parsley (39% identity), which are also induced in response to elicitor or microbial attack. Moreover, a major pollen allergen in birch (BetvI) has a 44% identity with PvPR1 proteins. These similarities establish a ubiquitous class of conserved defense-related proteins and suggest a common yet still unknown function. Southern blot analysis indicates that PvPR protein gene organization is highly complex with an estimated copy number of more than 12 genes.

Amino Acid Sequence↗

PubMed1989

Electron microscopic study of platelet agglutination induced by thrombotic thrombocytopenic purpura plasma containing 37-KDa platelet agglutinating protein.

It has been demonstrated that plasma from a patient with thrombotic thrombocytopenic purpura (TTP) and 37-KDa platelet-agglutinating protein (PAP p37) purified from the same plasma caused the agglutination of platelets from normal subjects as well as from the same patient after recovery without the requirement of extracellular Ca++ and fibrinogen. Experiments were designed to study the morphologic changes of platelets as a result of agglutination and the distribution of platelet receptors for PAP p37 under transmission electron microscope. Following incubation with TTP plasma or PAP p37 with stirring, platelets showed shape change, pseudopod formation, variable degrees of degranulation, dilatation of open canalicular systems and formation of agglutinates composed of a few to several hundred platelets. After platelets were incubated with TTP plasma or PAP p37 they were washed and further incubated with rabbit anti-PAP p37 serum without stirring followed by immuno-staining. Abundant electron dense reaction products were bound directly and randomly to the outer surface of the membrane of solitary platelets. When the reaction mixture was stirred, electron dense particles were also present between the platelet membranes in the agglutinates. No staining was observed in control experiments using normal plasma or non-immune rabbit serum. These results indicate that the TTP plasma containing PAP p37 causes agglutination, shape change, and variable degrees degranulation in platelets and that PAP p37 binds randomly to the outer surface of platelet membrane.

Blood Platelets↗

PubMed1989

The use of Chinese herb medicine in experimental radiotherapy.

Extracts from a group of destagnative herbs, 764-1, and the effective chemical, 764-3, were tested by an in vitro experiment using a HeLa-S3 cell line. Under aerobic conditions, the shoulder of the cell survival curve diminished or disappeared according to the different doses of 764-1 used, but no change in slope was observed. In nitrogen, when the dose of 764-1 increased to 20 mg/ml (ID20), besides the disappearance of the shoulder, the slope of the curve also showed changes at lower doses (4-8 Gy); up to 10-25 Gy the curve became more flattened. 764-3 showed almost a similar effect by mainly affecting the shoulder of the survival curve. At low drug doses a SER as high as 1.87 might be obtained under hypoxic condition. At the same time 764-1 was used in testing the effect on radiation lung damage. It was found that 764-1 could markedly inhibit the change of alveolar surfactant at 1 and 3 weeks after radiation. A wide field of investigation is thus spread out in front of us on radiosensitization and protection. Further studies on 764-3 are carried out.

Animals↗

PubMed1989

The effect of transposition of pedicled omentum to spinal cord ischemia segments. An animal experiment.

This animal experiment was in succession to the research on paraplegia caused by spinal cord local ischemia in an animal model. Immediately after the operative production of local spinal cord ischemia, pedicled omentum spinal transposition onto the ischemic segments of spinal cord was performed. The animals recovered from paraplegia around two months afterwards. Spinal cord specimens showed adhesion of omentum to the spinal cord without compression. Omental vessels grew into the cord. Gross sections of specimen stained with Nissl method revealed that normal structure of nerve cells were preserved but number of nerve cell decreased.

Animals↗

PubMed1989

Paraplegia caused by local spinal cord ischemia. An animal spinal cord ischemia model.

Local spinal cord ischemia model was established in 11 adult dogs. The anterior spinal artery, posterior spinal artery and radicular artery were cauterized with bipolar cautery. Ischemia of this segment of spinal cord was thus produced followed by paraplegia. The pathological findings of this spinal cord segment were softening and necrosis. The establishment of this animal model of segmental spinal cord ischemia is beneficial to scientific research in basic medicine and clinical practice.

Animals↗

PubMed1989

Anti-arrhythmic action of cycloprotobuxine-A.

Cycloprotobuxine-A (CPB-A) 1-4 mg/kg (1/100-1/25 LD50) produced therapeutic and prophylactic effects which were found to be dose-dependent on experimental arrhythmias induced by BaCl2, aconitine and chloroform. Given at equitoxic doses, the anti-arrhythmic action of CPB-A was as potent as cyclovirobuxine-D (CVB-D) and amiodarone (Amio). However, its therapeutic index (LD50/ED50) was 1.8 times that of CVB-D and 1.2 times that of Amio. The most pronounced effects of CPB-A (0.3-30 mumol/L) on the electrophysiology of ventricular muscle of guinea pig were the lengthening of APD50, APD90 and ERP. This may contribute to its anti-arrhythmic action and suggests that CPB-A most likely belongs to class III anti-arrhythmic drugs (prolongation of APD). Perfused with the same concentration (3 mumol/L), CPB-A brought about more significant increases in APD50, APD90 and ERP than CVB-D and Amio did.

Action Potentials↗

PubMed1989

Positive inotropic effect of cycloprotobuxine-A on isolated guinea pig myocardium.

Cycloprotobuxine-A (CPB-A) 0.1-100 mumoles/L produced positive inotropic effects in left and right atria in a concentration-dependent manner. CPB-A 30 mumoles/L enhanced post-rest contraction, augmented the response of left atrium to increase in stimulating frequency, and increased the developing tension evoked by paired pulse stimulation. By taking simultaneous recordings of action potentials and contractile force of papillary muscles, it was found that CPB-A 30 mumoles/L increased the contractile force and prolonged the action potential duration at 50% of depolarization. It is concluded that the positive inotropic effect of CPB-A on myocardium may be associated with an increase in transsarcolemmal influx of calcium as well as an augmentation of the amount of calcium released from intracellular stores.

Action Potentials↗