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Biomedical subjects

F Liu

Publications and source records attributed to F Liu.

At least 487 records · Page 27Linked to original sources
PubMed1996

A human Mad protein acting as a BMP-regulated transcriptional activator.

The TGF-beta/activin/BMP cytokine family signals through serine/threonine kinase receptors, but how the receptors transduce the signal is unknown. The Mad (Mothers against decapentaplegic) gene from Drosophila and the related Sma genes from Caenorhabditis elegans have been genetically implicated in signalling by members of the bone-morphogenetic-protein (BMP) subfamily. We have cloned Smad1, a human homologue of Mad and Sma. Microinjection of Smad1 messenger RNA into Xenopus embryo animal caps mimics the mesoderm-ventralizing effects of BMP4. Smad1 moves into the nucleus in response to BMP4. Smad1 has transcriptional activity when fused to a heterologous DNA-binding domain, and this activity is increased by BMP4 acting through BMP-receptor types I and II. The transactivating activity resides in the conserved carboxy-terminal domain of Smad1 and is disrupted by a nonsense mutation that corresponds to null mutations found in Mad and in the related gene DPC4, a candidate tumour-suppressor gene in human pancreatic cancer. Additionally, we show that DPC4 contains a transcriptional activation domain. The results suggests that the Smad proteins are a new class of transcription factors that mediate responses to the TGF-beta family.

Amino Acid Sequence↗
PubMed1996

Determination of dihydroetorphine in biological fluids by gas chromatography-mass spectrometry using selected-ion monitoring.

A method for the determination of dihydroetorphine hydrochloride, a powerful anaesthetic and analgesic drug, in biological fluids by GC-MS with selected-ion monitoring using etorphine as internal standard was established. Dihydroetorphine was extracted from human blood and urine with dichloromethane and then derivatized with N-heptafluorobutyrylimidazole after concentration to dryness. A dihydroetorphine monoheptafluorobutyl derivative was formed which showed good behavior on GC-MS with electronic-impact ionization. The main fragment, m/z 522, which is the base peak, was selected as the ion for quantitation and the corresponding ion, m/z 520, was selected for monitoring the internal standard, etorphine. The recoveries and coefficients of variation of the whole procedure were determined with five controlled dihydroetorphine-free urine and plasma samples spiked with different concentrations of dihydroetorphine. The concentration of dihydroetorphine for quantitation was in the range 1-20 ng/ml for urine and 2.5-250 ng/ml for plasma. The correlation coefficients of the standard curves are sufficient to determine the dihydroetorphine. The accuracy for quantitation of dihydroetorphine in urine and plasma is less than 10.6%.

Analgesics, Opioid↗
PubMed1996

Signal transduction pathways induced by heregulin in MDA-MB-453 breast cancer cells.

Heregulins (HRGs) induce tyrosine phosphorylation of several members of the erb-B family of receptors. Although originally isolated as the ligands for p185c-erb-2, recent evidence suggests that other receptors of the erbB family, including p180erbB-3 and p180erbB-4, are their true cognate receptors. Stimulation of MDA MB-453 cells with HRG beta 2 resulted in the tyrosine phosphorylation of p185c-erbB-2 and p180erbB-4 in a time- and dose-dependent fashion. This event was accompanied by the formation of multimeric complexes between the activated receptors and SH2-containing proteins. Ligand caused p120-rasGTPase activating protein (GAP), SHC and the p85 subunit of phosphatidylinositol-3'-kinase (PI3K) to be associated with both p185c-erbB-2 and p180erbB-4. In addition, tyrosine phosphorylation of p85-PI3K and SHC, but not of GAP or of its associated p62 and p190 proteins, was also detected. HRG also induced the association of GRB2 with tyrosine phosphorylated p185c-erbB-2, p180erbB-4 and SHC. Activation of mitogen-activated protein kinase (MAPK) ( > 30-fold over untreated controls) was observed upon receptor(s) activation, as it was the induction of the immediate early gene c-fos ( > 200-fold). These observations suggest that p21ras activation plays a role in the HRG pathway. Furthermore, comparative analysis of the binding of p85-PI3K to 185c-erbB-2 and p180erbB-4, revealed a preferential association with activated p180erbB-4. These findings might suggest a model of HRG action in which the relative expression of the various erb-B family members and the partitioning of signal transduction molecules between each type of receptor might determine the nature of the signal elicited by the ligand and the biological response attained.

1-Phosphatidylinositol 4-Kinase↗
PubMed1996

Serum independent liposome uptake by mouse liver.

The rate of liposome clearance from blood by the reticuloendothelial system (RES), primarily the Kupffer cells of the liver, depends largely on liposome composition. Inclusion of phosphatidylserine or dicetyl phosphate into liposomes with a simple composition of phosphatidylcholine and cholesterol increases liposome clearance, while inclusion of GM1 or amphipathic poly(ethylene glycol) decreases the rate of liposome clearance. To understand the underlying mechanism by which liposome clearance is regulated by the RES, we have developed a simple liver perfusion system. Using mouse liver as a model, we demonstrated that hepatic uptake of neutral or negatively charged liposomes does not involve serum components. Liver uptake of liposomes is directly related to the surface characteristics of liposomes. Liposomes with a neutral composition of phosphatidylcholine and cholesterol exhibit relatively low liver uptake. Inclusion of PS or DCP into these liposome dramatically enhances liposome uptake by the perfused liver. Conversely, inclusion of GM1 or PEG derivatives into liposomes greatly reduces the liposome uptake by the mouse liver. In contrast to the neutral or negatively charged liposomes, serum enhances the liver uptake of positively charged liposomes. Such serum effect on liver uptake of the positively charged liposomes is likely due to liposome aggregations caused by serum proteins. Inhibition of the liver uptake for PS-containing liposomes using liposomes with different compositions suggests that liver uptake of liposomes may involve different receptors.

Animals↗
PubMed1996

p53 alterations in chemically induced hamster cheek-pouch lesions.

To confirm that the hamster cheek-pouch carcinogenesis model reflects development of human squamous cell carcinoma (SCC), we determined if and when p53 mutations occur in the development of SCC in this model by using immunohistochemical staining and polymerase chain reaction (PCR)-single-strand conformation polymorphism (SSCP) analysis plus direct DNA sequencing. Twenty-four hamster cheek-pouches were treated with a solution of 0.5% 7,12-dimethylbenz[a]anthracene in mineral oil three times a week for 16 wk. The malignant endophytic and exophytic tumors induced with this protocol are preceded by a sequence of premalignant lesions such as hyperplasia with or without dysplasia and carcinoma in situ, similar to the development of this cancer in humans. For this study, p53 protein accumulation was evaluated by immunostaining of various hamster cheek-pouch exophytic and endophytic SCCs as well as flat dysplastic hyperplasia and carcinomas in situ. A moderate percentage (33.3%) of exophytic lesions and most endophytic carcinomas (90%) showed positive p53 staining. In addition we also found p53-positive staining in a number of preneoplastic lesions, including areas of focal hyperplasia, dysplastic hyperplasia, and carcinomas in situ. To determine whether the alterations in p53 staining were due to p53 gene mutation, we used PCR-SSCP analysis and direct sequencing. PCR products corresponding to exons 5a, 6, 7, and 8 from 40 tumors with the highest percentage of p53-stained cells were analyzed. We detected shifted bands in 17 lesions. Direct sequencing of eight selected shifted bands revealed four mutations, including two G-->T transversions in codons 216 (tumor #1) and 252 (tumor #2) and one G-->C transversion in codon 282 (tumor #3). Tumor #4 contained a frameshift mutation in codon 251. These mutations are consistent with those reported in many human cancers. Therefore, we concluded that in the hamster cheek-pouch model, p53 protein accumulation occurs frequently and early in carcinogenesis, as it does in human SCCs, and some of these p53 alterations are due to p53 gene mutations. These findings may help us better define the mechanisms of carcinogenesis in the hamster cheek-pouch model, and p53 alterations may be an early biomarker of progression for chemoprevention studies.

9,10-Dimethyl-1,2-benzanthracene↗
PubMed1996

Insulin-like growth factor binding proteins as growth inhibitors in children with chronic renal failure.

Children with chronic renal failure (CRF) often fail to attain an adult height consistent with their genetic potential. The growth hormone (GH)/insulin-like growth factor (IGF)/growth plate chondrocyte axis has been intensively studied in these children to determine the basis for this growth failure. Evidence suggests that hepatic GH resistance results in deficient expression of IGF-I. However, serum IGF-I levels are usually normal and it is IGF-I action on target tissues which is inhibited, possibly by the presence of excess high-affinity IGF binding proteins (IGFBPs) in CRF serum. In this paper we evaluate the roles of IGFBP-1, -2, and -3 as growth inhibitors in CRF children. The data support a role for each of these IGFBPs as growth inhibitors. Currently, IGFBP-1 meets most criteria expected of a growth inhibitor, but IGFBP-2 and -3 will likely also meet these criteria and may well be important contributors to the growth failure of CRF. Ultimately, many or all of the six IGFBPs may be found to contribute to the excess high-affinity IGF binding sites which are a hallmark of CRF serum and are possible contributors to the growth failure of CRF children.

Adult↗
PubMed1996

Magnetoenterography (MENG): noninvasive measurement of bioelectric activity in human small intestine.

The basic electrical rhythm (BER) of the gastrointestinal tract creates minute magnetic fields that have been measured in animals using a Superconducting QUantum Interference Device (SQUID) gradiometer. The aim of this study was to measure noninvasively the biomagnetic fields of human stomach and small intestine. Twenty-one human volunteers were studied using a 37-channel SQUID gradiometer positioned over the epigastrium and umbilicus. In one volunteer additional biomagnetic recordings were performed in order to map the spatial variation of the biomagnetic fields. Cyclical waveforms consistent with gastric BER [3.0+/-0.5 cycles per minute (cpm)] and small intestine BER (10.26+/-1.74 cpm) were seen in the epigastrium and umbilicus, respectively. The mapping study identified the expected frequency gradient (12.0 cpm in duodenum, 11.3 cpm in jejunum, to 9.7 cpm in ileum) within the small intestine. Noninvasive recordings of human gastric and small intestinal BER can be obtained using a SQUID gradiometer.

Adult↗
PubMed1996

Characterization of insulin-like growth factors and their binding proteins in peritoneal dialysate.

Serum insulin-like growth factors (IGFs), which circulate bound to specific IGF binding proteins (IGFBPs), must exit the intravascular space before acting on target tissues. Little is known about the nature of IGF/IGFBPs in extravascular fluids of patients with chronic renal failure (CRF). Peritoneal dialysate (PD) was studied since, after a short incubation, PD contains proteins which have entered an extravascular space; thus, IGF/IGFBP forms in PD are more likely than serum forms to interact with target tissues. IGF-I and IGF-II, and IGFBPs 1-4, were readily identified by specific immunoassays and/or 125iodine-IGF ligand blotting of simultaneously obtained PD and serum samples from seven CRF children; IGFBP-3 was a major IGFBP in PD as in serum. Where quantitated, IGF and IGFBP levels in PD were approximately 10% of serum concentrations. After separation of PD and serum by size-exclusion chromatography, serum had more IGFBP-3 in 150-kilodalton (kDa) than 35-kDa fractions, while PD had far less IGFBP-3 in 150-kDa than 35-kDa fractions. Immunoblot studies revealed a major 29-kDa IGFBP-3 fragment, in addition to intact 41- and 38-kDa IGFBP-3 forms, in PD and CRF serum; the 29-kDa form predominated in the 35-kDa PD fractions. These data suggest that the 29-kDa fragment is the IGFBP-3 form most likely to modulate IGF effects on target tissues of CRF individuals.

Adolescent↗
PubMed1996

Induction in the mouse of gene expression of immunomodulating cytokines by mushroom polysaccharide-protein complexes.

Two antitumor polysaccharide-protein complexes, PSPC and PSK from mushrooms, were compared for their modulating effect on cytokine and cytokine receptor gene expression. RNA samples were isolated from the splenocytes and peritoneal exudate cells of the untreated or treated mice. Reverse transcription-polymerase chain reaction (RT-PCR) was used to analyze the cytokine gene expression. Nine out of 17 cytokine mRNAs and 5 out of 6 cytokine receptor mRNAs were detected in the splenocytes and peritoneal exudate cells from both untreated and treated mice. However, IL-4 was only detected in the splenocytes while IL-7 and IL-1R(typeI) were only detected in the peritoneal exudate cells. Among the 9 cytokine genes, the expression level of M-CSF was up-regulated in splenocytes and peritoneal exudate cells of the mice by PSPC and PSK. The expression level of TNF-alpha was only up-regulated in the peritoneal exudate cells by PSK, but not by PSPC.

Animals↗
PubMed1996

Immunomodulation and antitumor activity of polysaccharide-protein complex from the culture filtrates of a local edible mushroom, Tricholoma lobayense.

1. The polysaccharide-protein complex (PSPC) isolated from the culture filtrate of Tricholoma lobayense showed antitumor activity in mice. 2. PSPC had the ability to restore the phagocytic function of peritoneal exudate cells (PEC) and T-cell mitogenic activity of tumor-bearing mice. 3. An increase in the production of reactive nitrogen intermediates and tumor necrosis factor (TNF) was determined in PEC of mice that had received PSPC. 4. The present study showed that PSPC both induced the various immune responses in vivo and exhibited cytotoxicity against tumor cell lines in the presence of PSPC at doses of 30 and 60 micrograms/ml in vitro.

Adjuvants, Immunologic↗
PubMed1996

Impaired production and increased apoptosis of neutrophils in granulocyte colony-stimulating factor receptor-deficient mice.

We have generated mice carrying a homozygous null mutation in the granulocyte colony-stimulating factor receptor (G-CSFR) gene. G-CSFR-deficient mice have decreased numbers of phenotypically normal circulating neutrophils. Hematopoietic progenitors are decreased in the bone marrow, and the expansion and terminal differentiation of these progenitors into granulocytes is impaired. Neutrophils isolated from G-CSFR-deficient mice have an increased susceptibility to apoptosis, suggesting that the G-CSFR may also regulate neutrophil survival. These data confirm a role for the G-CSFR as a major regulator of granulopoiesis in vivo and provide evidence that the G-CSFR may regulate granulopoiesis by several mechanisms. However, the data also suggest that G-CSFR-independent mechanisms of granulopoiesis must exist.

Animals↗
PubMed1996

New cationic lipid formulations for gene transfer.

PURPOSE: To develop appropriate dosage forms of DNA for gene delivery. METHODS: 3 beta [N-(N', N' dimethylaminoethane) carbamoyl] cholesterol (DC-Chol) was mixed either with Tween 80 alone, or with additional lipid components including castor oil and phosphatidylcholine (PC) or dioleoylphosphatidylethanolamine (DOPE) to make different lipid formulations. The particle size and the physical stability of the formulations upon mixing with plasmid DNA containing the luciferase cDNA were examined using laser light scattering measurement. The transfection activity of the DNA/lipid complexes was tested in presence or absence of serum using a cell culture system. RESULTS: We demonstrated that many favorable properties as a gene carrier could be achieved by formulating DNA into new dosage forms using Tween 80 as the major emulsifier. Compared to the cationic liposomes, these new formulations transfected different cell lines with an equivalent or higher efficiency. Not only are they resistant to serum, but also form stable DNA complexes which could be stored for longer periods of time without losing transfection activity. CONCLUSIONS: Cationic lipids formulated into different lipid formulations using Tween 80 as a surfactant appeared to have more favorable physical and biological activities than traditional cationic liposomes as a carrier for gene delivery.

Cell Line↗
PubMed1996

Effect of non-ionic surfactants on the formation of DNA/emulsion complexes and emulsion-mediated gene transfer.

PURPOSE: To study the structure-function relationship of non-ionic surfactants in emulsion-mediated gene delivery. METHODS: Four different types of non-ionic surfactants including Tween, Span, Brij and pluronic copolymers were used as co-emulsifiers for preparation of emulsions composed of Castor oil, dioleoylphosphatidylethanolamine (DOPE) and 3 beta [N-(N', N'-dimethylaminoethane) carbamoyl] cholesterol (DC-Chol). The effect of different surfactants on the formation of DNA/emulsion complexes and transfection activity were analyzed using plasmid DNA containing luciferase cDNA as a reporter gene. RESULTS: Non-ionic surfactants containing branched polyoxyethylene chains as the hydrophilic head group were more effective in preventing the formation of large DNA/emulsion complexes than those containing one or no polyoxyethylene chain. All emulsion formulations except those containing Brij 700 exhibited high activity in transfecting mouse BL-6 cells in the absence of serum. In the presence of serum, however, transfection activity of each formulation varied significantly. Emulsions containing Tween, Brij 72, pluronic F68 and F127 demonstrated increased activity in transfecting cells in the presence of 20% serum. In contrast to emulsions containing Span, long chain polyoxyethylene of Brij showed decreased transfection activity. The particle size of the DNA/emulsion complexes and their ability to transfect cells are dependent on the concentration of non-ionic surfactant in the formulation. CONCLUSIONS: The structure of the hydrophilic head group of the non-ionic surfactants in the emulsion is important in determining how DNA molecules interact with emulsions and the extent to which DNA is transferred inside the cell.

Animals↗
PubMed1996

Pharmacokinetics of insulin-like growth factor-1 in advanced chronic renal failure.

Information regarding the impact of chronic renal failure (CRF) on IGF-1 serum clearance is limited. Thus we evaluated the pharmacokinetics of insulin-like growth factor-1 (IGF-1) in six normal adults and six adults with advanced CRF (serum creatinine 7 +/- 0.8 mg/dl). All subjects were given 80 micrograms/kg recombinant human IGF-1 s.c. and blood was sampled over 48 hours. Baseline total serum IGF-1 levels were similar in both groups, but peak levels were elevated significantly in CRF; this was apparently related to the reduced distribution volume in CRF subjects. CRF did not affect the metabolic clearance rate (MCR) of total serum IGF-1. Immunoreactive IGF binding protein-3 (IGFBP-3) levels were greater in CRF. Western immunoblots revealed that the apparent increase in IGFBP-3 was largely due to an increase in immunoreactive fragments. IGFBP-3 protease activity was not increased. Thus IGFBP fragment accumulation likely reflects reduced fragment clearance. Western ligand blots revealed elevated 30 and 34 kDa IGFBP levels and IGFBP products in CRF serum. Serum acid labile subunit levels were unchanged in CRF. Peak free IGF-1 levels and the MCR of free IGF-1 did not differ between groups. In both groups the MCR of free IGF-1 exceeded the MCR of total IGF-1 by approximately 30-fold. These data suggest that in CRF patients receiving s.c. IGF-1: (a) total serum IGF-1 levels are increased as a result of elevated circulating IGFBPs that may restrict the distribution of IGF-1 beyond plasma; (b) serum free IGF-1 levels are not altered; and (c) the IGF-1 MCR is unchanged in CRF. Thus, in advanced CRF, apart from a reduction in the total IGF-1 volume of distribution the pharmacokinetics of IGF-1 are largely unaltered.

Adult↗
PubMed1996

Neuroligand-evoked calcium-dependent release of excitatory amino acids from cultured astrocytes.

The release of excitatory amino acids (EAAs) from neuron-free cultures of neocortical astrocytes was monitored using HPLC. The neuroligand bradykinin caused a dose-dependent receptor-mediated increase in release of the EAAs glutamate and aspartate from type 1 astrocyte cell cultures obtained from rat cerebral cortex. Removal of calcium from the extracellular fluid prevented the bradykinin-induced release of EAAs from astrocytes. The addition of the calcium ionophore ionomycin caused a calcium-dependent release of EAAs. Inhibitors of the glutamate transporters p-chloromercuriphenylsulfonic acid, L-trans-pyrrolidine-2,4-dicarboxylate, and dihydrokainate failed to impair the ability of bradykinin to stimulate glutamate release from astrocytes. alpha-Latrotoxin, an active compound of black widow spider venom, caused a significant increase of the release of glutamate in calcium-containing saline. In calcium-depleted saline, alpha-latrotoxin produced an initial increase in the concentration of glutamate followed by a decline in the concentration of glutamate indicating stimulation of exocytosis coupled with low calcium-induced inhibition of endocytosis. Taken together, these data suggest that astrocytes may release neurotransmitter through a mechanism that is similar to the neuronal secretory process. Given the important role of glutamate in the induction of long-term potentiation, learning, memory, and excitotoxicity, it will be important to determine external signals that control both the uptake and release of glutamate by astrocytes.

Animals↗