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Biomedical subjects

L Huang

Publications and source records attributed to L Huang.

At least 469 records · Page 26Linked to original sources
PubMed1995

Liposome-mediated in vivo E1A gene transfer suppressed dissemination of ovarian cancer cells that overexpress HER-2/neu.

The HER-2/neu proto-oncogene is frequently amplified or overexpressed in many different types of human cancers, a phenomenon that has been shown to correlate with shorter survival time and lower survival rate in ovarian cancer patients. We previously reported that increased HER-2/neu expression led to more severe malignancy and increased metastatic potential in animal models and that the adenovirus 5 E1A gene repressed HER-2/neu gene expression at transcriptional level and was able to suppress tumor growth when stably transfected into human ovarian cancer SKOV-3 cells which overexpress HER-2/neu. To investigate whether the E1A gene may be used as a therapeutic agent for HER-2/neu-overexpressing human cancers in living hosts, we first developed tumor-bearing mice by injecting SKOV-3 cells that overexpress HER-2/neu intraperitonealy into female nu/nu mice. Five days later, we used cationic liposomes to directly deliver the E1A gene into adenocarcinomas that developed in the peritoneal cavity and on the mesentery of the mice that received the SKOV-3 cell injection. We found that liposome-mediated E1A gene transfer significantly inhibited growth and dissemination of ovarian cancer cells that overexpress HER-2/neu in the treated mice; about 70% of these mice survived at least 365 days, whereas all the control mice that did not receive the gene therapy developed severe tumor symptoms and died within 160 days. The results suggest that liposome-mediated E1A gene transfer may serve as an effective therapy for human ovarian cancers that overexpress HER-2/neu by directly targeting the HER-2/neu oncogene.

Adenovirus E1A Proteins↗
PubMed1995

Prototropic control of intramolecular electron transfer in trimethylamine dehydrogenase.

The pH dependence of static optical/EPR spectra of trimethylamine dehydrogenase reduced to the level of two equivalents (TMADH2eq) has been examined and indicates the existence of three different states for this iron-sulfur flavoprotein. At pH 6, TMADH2eq exists principally in a form possessing flavin mononucleotide hydroquinone, with its iron-sulfur center oxidized. At pH 8, the enzyme principally contains flavin mononucleotide semiquinone and reduced iron-sulfur, but despite the proximity of the two centers to one another, their magnetic moments do not interact. At pH 10, TMADH2eq exhibits the EPR spectrum that is diagnostic of a previously characterized spin-interacting state in which the magnetic moments of the flavin semiquinone and reduced iron-sulfur center are strongly ferromagnetically coupled. The kinetics of the interconversion of these three states have been investigated using a pH jump technique in both H2O and D2O. The observed kinetics are consistent with a reaction mechanism involving sequential protonation/deprotonation and intramolecular electron transfer events. All reactions studied show a normal solvent kinetic isotope effect. Proton inventory analysis indicates that at least one proton is involved in the reaction between pH 6 and 8, which principally controls intramolecular electron transfer, whereas at least two protons are involved between pH 8 and 10, which principally control formation of the spin-interacting state. The results of these and previous studies indicate that for TMADH2eq, between pH 10 and 6, at least three protonation/deprotonation events are associated with intramolecular electron transfer and formation of the spin-interacting state, with estimated pK alpha values of 6.0, 8.0, and approximately 9.5. These pK alpha values are attributed to the flavin hydroquinone, flavin semiquinone, and an undesignated basic group on the protein, respectively.

Bacterial Proteins↗
PubMed1995

Interaction of the cobalt complex of a bleomycin functional model with d(CGCAATTGCG)2: evidence of minor groove binding by 2D NMR methods.

The interaction between the cobalt complex of a bleomycin functional model and d(CGCAATTGCG)2 was determined by 2D NMR methods. The intermolecular NOE cross peaks between ligand protons and the DNA minor groove protons suggest that the cobalt complex of AMPHIS-NET binds in the minor groove of DNA at the central AATT site. Also, the NOEs interactions of H8 pyridine proton and H2 imidazole proton in the metal-binding domain with H4' sugar proton of C9 and H4' sugar proton of A15 demonstrate that the sixth ligand site of cobalt complex, which is occupied by a solvent molecule, faces towards the minor groove of DNA. This binding model is in accord with the observed non-diffusion DNA cleavage by the metal-complexes of the bleomycin functional model compounds.

Base Sequence↗
PubMed1995

HER-2/neu-targeting gene therapy--a review.

The HER-2/neu (also named c-erbB-2) oncogene is known to be overexpressed in many human cancers, including breast, ovarian, lung, gastric and oral cancers. In animal models, HER-2/neu overexpression was shown to enhance malignancy and metastasis phenotypes. Repression of HER-2/neu overexpression suppresses the malignant phenotypes of HER-2/neu-overexpressing cancer cells, suggesting that HER-2/neu may serve as an excellent target for developing anti-cancer agents. We have previously shown that the adenovirus-5 (Ad5) E1a gene products and the SV40 large T antigen (large T) inhibit transcription of the HER-2/neu promoter and accordingly suppresses transformation induced by HER-2/neu. In this review, we summarize our recent findings on using cationic liposomes or an Ad vector to deliver E1a or large T into tumor-bearing mice. Our results indicate that both cationic liposomes or an Ad vector can efficiently deliver E1a or large T into tumor cells in mice, and this results in suppression of tumor growth and longer survival of the mice.

Adenoviridae↗
PubMed1995

The role of dioleoyl phosphatidylethanolamine in cationic liposome mediated gene transfer.

In a reported gene assay, cationic liposomes containing the cationic lipid 3 beta-(N-(N',N'-dimethylaminoethane)carbamoyl)cholesterol (DC-Chol) and a neural phospholipid dioleoylphosphatidylethanolamine (DOPE) showed high transfection activity. DNA/liposome complex which contained low amount of liposomes could bind to the cell surface but failed to transfect the cells. We have designed a two-step protocol to examine this phenomenon in more detail. A431 human cells were incubated on ice (pulse) with DNA complexed to a low level of cationic liposomes. The cells were washed and incubated at 37 degrees C (chase) with or without free cationic liposomes of various composition (helper liposomes). Only liposomes enriched with DOPE showed helper activity; liposomes containing dioleoylphosphatidylcholine (DOPC), a structural analog of DOPE, had no helper activity. The delivery was inhibited by the lysosomotropic agent chloroquine and was optimal if the helper liposome chase was initiated immediately after the pulse. An endocytosis model of DNA delivery by cationic liposomes is proposed in which the principal function of the chase liposomes is to destabilize the endosome membrane and allow the release of DNA into the cytosol. This model is consistent with the known activity of DOPE to assume non-bilayer structures, hence destabilizing the endosome membrane.

Cations↗
PubMed1995

Targetability of novel immunoliposomes modified with amphipathic poly(ethylene glycol)s conjugated at their distal terminals to monoclonal antibodies.

Distearoyl-N-(3-carboxypropionoyl poly(ethylene glycol) succinyl)phosphatidylethanolamine (DSPE-PEG-COOH) was newly synthesized and used to prepare novel immunoliposomes carrying monoclonal antibodies at the distal ends of the PEG chains (Type C). Liposomes were prepared from egg phosphatidylcholine (ePC) and cholesterol (CH) (2;1, m/m) containing 6 mol% of DSPE-PEG-COOH, and a monoclonal IgG antibody, 34A, which is highly specific to pulmonary endothelial cells, was conjugated to the carboxyl groups of DSPE-PEG-COOH to give various amounts of antibody molecules per liposome. Other immunoliposomes with PEG coating (Type B) or without PEG coating (an earlier type of immunoliposome, Type A) were prepared for comparison. The average molecular weight of PEG in Type B or C immunoliposomes was 2000. Type B and Type C liposomes without antibodies showed prolonged circulation time and reduced reticulo-endothelial system (RES) uptake owing to the presence of PEG. These three different types of 34A-immunoliposomes with 30-35 antibody molecules per vesicle were injected into mice to test the immunotargetability to the lung. The efficiency of lung binding of 34A-Type B was one-half of that of 34A-Type A, though a large amount of 34A-Type B remained in the blood circulation for a long time, suggesting that the steric hindrance of PEG chains reduced not only the immunospecific antibody-antigen binding, but also the RES uptake. The degree of lung binding of 34A-Type C was about 1.3-fold higher than that of 34A-Type A, indicating that recognition by the antibodies attached to the PEG terminal was not sterically hindered and that the free PEG (i.e., that not carrying antibody) was effective in increasing the blood concentration of immunoliposomes by enabling them to evade RES uptake. The latter phenomenon was confirmed by using nonspecific antibody-Type C immunoliposomes (14-Type C), which showed a high blood level for a long time. Our approach provides a simple means of conjugating antibodies directly to the distal end of PEG which is already bound to the liposome membrane, and should contribute to the development of superior targetable drug delivery vehicles for use in diagnostics and therapy.

Animals↗
PubMed1995

Capillary electrophoresis-based immunoassay to determine insulin content and insulin secretion from single islets of Langerhans.

The development of a competitive immunoassay for insulin that is based on capillary zone electrophoresis with laser-induced fluorescence detection (CZE-LIF) is described. The assay uses fluorescein isothiocyanate-derivatized insulin (FITC-insulin) as a tracer and the Fab fragment of an anti-insulin monoclonal antibody as the immunoreagent. Reproducibility and reliability of the assay are improved when CZE capillaries are coated with a neutral hydrophilic polymer. The assay has an average relative standard deviation of 3.4% and a detection limit of 3 nM or about 6 fg injected. Using the assay, insulin content of single islets of Langerhans was determined to be 35 +/- 4 ng, which is in good agreement with literature values. The assay was also used to determine insulin secretion from single islets. During 5-min static incubations, 3 mM glucose elicited 0.8 +/- 0.2 ng of insulin release while 16 mM glucose elicited 3.2 +/- 0.5 ng of insulin release. These values are also in good agreement with previously reported results. These applications demonstrate the capability of rapidly determining a low level of protein in a complex biological microenvironment.

Animals↗
PubMed1995

Inhibition of human ovarian carcinoma cell proliferation by liposome-plasmid DNA complex.

Anti-cancer gene therapy should ultimately lead to specific growth inhibition and loss of tumorigenicity of the tumor cells. Therefore, when using cationic liposomes as DNA delivery systems, it is essential to know how the liposome-plasmid DNA complex itself influences the cell growth. This paper reports on the finding that liposome-plasmid DNA complexes specifically inhibited proliferation of human ovarian carcinoma cells, in vitro and in vivo. This inhibiting activity is likely to be sequence independent, since it was observed using several different plasmids. The degree of growth inhibition appeared dependent on both the lipid to DNA ratio and the total dose of liposome-plasmid DNA complex given to the cells.

Animals↗
PubMed1995

Codelivery to mammalian cells of a transcriptional factor with cis-acting element using cationic liposomes.

The human immunodeficiency virus-1 transactivator protein (tat) was codelivered efficiently with a reporter gene under the control of a tat-responsive DNA element using different formulations of cationic liposomes. Expression of a tat-responsive reporter gene was induced by incubating cells with a mixture of purified recombinant tat protein, reporter DNA, and liposomes. Different cell lines were tested successfully as targets for the codelivery. Tat was shown to trans-activate the codelivered virus promoter specifically in the cells tested. Codelivery of tat with DNA is a useful model for studying the function of trans-acting factors and their cis-acting DNA elements. The currently available methods such as foot-printing only reveal the binding, but not the functional consequence of the binding, of the factor with the element. In addition, this system may prove useful as a model for high level and regulated transgene expression in target cells.

Animals↗
PubMed1995

Molecular mass and carbohydrate structure of prostate specific antigen: studies for establishment of an international PSA standard.

Despite the widely accepted use of prostate specific antigen (PSA) as a marker of prostate cancer, this molecule has not yet been completely characterized. Past studies have well established, however, using both amino acid and cDNA sequencing techniques, that PSA contains 237 amino acids, with a molecular mass of 26,079 Da for the peptide moiety of the molecule. The present study reports analysis of this protein by ion spray mass spectrometry (ISMS) and analysis of its carbohydrate moiety by NMR spectroscopy. The predominant PSA molecular species detected by ISMS was at relative molecular mass (M(r)) of 28,430, indicating that PSA contains a carbohydrate residue of M(r) 2,351, for a total percentage of carbohydrate of 8.3%. Analysis of PSA by SDS-PAGE, however, showed a M(r) of 32,000 to 33,000, suggesting an overestimation of the molecular weight by the latter technique. The complete primary structure of the PSA carbohydrate chain was determined by NMR spectroscopy in combination with carbohydrate composition analysis. The experimentally determined carbohydrate content of PSA confirms that only one N-glycosylation site is occupied in the protein. The proposed carbohydrate structure is a diantennary N-linked oligosaccharide of the N-acetyllactosamine type, with a sialic acid group at the end of each of the two branches. In addition, our data indicate that approximately 70% of the PSA molecules contain a fucose group in the core chitobiose moiety. The calculated molecular weight of this carbohydrate structure (M(r) 2,351.8) is in excellent agreement with the predicted molecular weight of the carbohydrate group, based on the M(r) 28,430 for PSA measured by ion spray mass spectrometry and M(r) 26,079 calculated from the consensus sequence for the peptide portion of the molecule. ISMS of PSA is thus proposed as a convenient and reliable method of quality control, an indispensible step towards international standardization of this very important tumor marker for detection and monitoring of prostatic diseases, especially prostate cancer.

Amino Acid Sequence↗
PubMed1995

Characterization of organ-specific immunoliposomes for delivery of 3',5'-O-dipalmitoyl-5-fluoro-2'-deoxyuridine in a mouse lung-metastasis model.

A previous study has shown that lipophilic prodrugs can be delivered efficiently to normal lung endothelium by incorporation into liposomes covalently conjugated to monoclonal antibody (mAb) 34A against the lung endothelial anticoagulant protein thrombomodulin. In the present study, the potential use of these lung-targeted immunoliposomes (34A-liposomes) for delivery of a lipophilic prodrug, 3',5'-O-dipalmitoyl-5-fluoro-2'-deoxyuridine (dpFUdR), to the tumor-bearing lung was examined using BALB/c mice bearing experimental lung metastasis induced by i.v. injection of EMT-6 mouse mammary tumor cells. Immunohistochemical examination of the tumor-bearing lung showed specificity of mAb 34A to lung endothelium. Tumor cells appeared to localize just outside of the normal blood vessels and were within a small diffusion distance from the mAb 34A-binding sites. 111In-labeled 34A-liposomes containing monosialoganglioside (GM1) were prepared that included [3H]-dpFUdR at 3.0 mol% in the lipid mixture. In vitro cell binding studies further demonstrated that 34A-liposomes bound specifically to normal mouse lung cells that expressed thrombomodulin but not to EMT-6 cells. Biodistribution study showed efficient and immunospecific accumulation of [3H]-dpFUdR incorporated into 34A-liposomes in the lung at a level parallel with that of 111In-labeled 34A-liposomes, indicating that the drug is delivered to the target organ in intact liposomes. Liposomal dpFUdR appeared to be metabolized in the lung to the parent drug FUdR at a rate slower than in the liver and spleen. Furthermore, treatment of lung-metastasis-bearing mice with dpFUdR incorporated into 34A-liposomes on days 1 and 3 after tumor cell injection resulted in a significant increase in the median survival time of treated mice as compared with control mice (%T/C value, 165%). dpFUdR either dispersed in emulsion or incorporated into antibody-free liposomes was ineffective in prolonging the survival of mice. These results indicate the potential effectiveness of organ-specific immunoliposomes containing a lipophilic prodrug for the targeted therapy of metastatic tumors.

Animals↗
PubMed1995

Serum biochemical values and mineral element contents of tissues in yaks.

Serum biochemical values and the wet weight to dry weight ratios of tissues were determined in yaks in Shandan county of Gansu province. The liver, kidney, heart and muscle contents of seven elements in yaks were also analysed. Most serum biochemical values were similar to those of cattle, camels and sheep, but the calcium concentration was considerably above the normal range for other ruminants. The liver contained the highest concentrations of copper, manganese and cobalt and the kidney of selenium, iron and calcium.

Animals↗
PubMed1995

Data clustering and other archive retrieval strategies for teleradiology and picture archiving and communication systems.

A key advantage in the conversion from film-based to digital radiology is the possibility of a long-term on line electronic archival of patient studies. The popular approach based on optical disk jukeboxes for the long-term archive and magnetic disk storage for data caching is not economically attractive because of the cost of both the jukebox and the medium. Strategies for extending the archival system design with a tape jukebox have been studied. The proposed strategy calls for the use of high-ratio lossy compression together with low-cost tape storage to make long-term on line archiving more affordable. An intelligent prefetching algorithm based on hospital information system and radiologic information system triggers, which in turn are augmented by manual case preparation, can effectively overcome the longer latency of ad hoc retrievals. This longer latency is caused by both system-level bottlenecks and the sequential access constraint of the tape drive. Strategies for image clustering and tape allocation by patient classification also enhance retrieval efficiency. This archival design using image compression, prefetching, and clustering could be implemented in many of the existing teleradiology and picture archiving and communication systems.

Algorithms↗
PubMed1995

Qualitative analysis of Kolmogorov-type models of predator-prey systems.

The qualitative behaviors of Kolmogorov-type models are investigated under assumptions that are consistent with models of predator-prey systems and biologically realistic. The main purpose of this paper is to prove the boundedness of solutions and to give criteria for the existence of limit cycles for the system. In the case that the positive equilibrium is locally asymptotically stable, an example shows that there could be more limit cycles. This example serves as a counterexample to the global stability criterion of Huang.

Animals↗
PubMed1995

Biomechanics of snoring.

A large proportion of the population either snores or suffers the snoring of others. Recent advances with the use of fibre-optic endoscopes have enabled surgeons to observe the inside of the pharynx while a patient is asleep and snoring. In this article we look at the underlying structure of the upper airway and explain, with the use of simple mechanical models, the aerodynamic events occurring inside the upper airway during snoring.

Adult↗
PubMed1995

Design, synthesis and sequence selective DNA cleavage of functional models of bleomycin--II. 1,2-trans-disubstituted cyclopropane units as novel linkers.

The design and syntheses of functional models for bleomycin in which AMPHIS, a simplified model of the metal-chelating subunit of bleomycin is connected to distamycin analogs with a series of linkers, are described. Kinetic studies and DNA cleavage assay show that 1,2-trans-disubstituted cyclopropane units are the best linkers within this series. Study of selective DNA cleavage on high resolution polyacrylamide sequencing gels indicates that the linker modified hybrids generally cleave selectively at the 5' end of poly T sites and at the 3' end of poly A sites. Cleavage activity is enhanced for most of the compounds related to those with shorter linkers, previously reported, (Huang, L.; Quada, Jr J. C.; Lown, J. W. Bioconjugate Chem. 1995, 6, 21, Ref. 1) probably as a result of the linker allowing the active complex to approach the target deoxyribose more closely and efficiently. Certain of the compounds, ones containing a (S)-methyl in the linker and the (S,S)-cyclopropyl linker, exhibit unique cleavage sites, indicating that these linkers allow the hybrids to locate novel, individual DNA binding sites.

Antibiotics, Antineoplastic↗