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H Q Mao

Publications and source records attributed to H Q Mao.

14 recordsLinked to original sources
PubMed2002

Multi-layered microcapsules for cell encapsulation.

Mechanical stability, complete encapsulation, selective permeability, and suitable extra-cellular microenvironment, are the major considerations in designing microcapsules for cell encapsulation. We have developed four types of multi-layered microcapsules that allow selective optimization of these parameters. Primary hepatocytes were used as model cells to test these different microcapsule configurations. Type-1 microcapsules with an average diameter of 400 microm were formed by complexing modified collagen with a ter-polymer shell of 2-hydroxyethyl methylacrylate (HEMA), methacrylic acid (MAA) and methyl methacrylate (MMA), resulting in a capsule thickness of 2-5 microm. Cells in these microcapsules exhibited improved cellular functions over those cultured on collagen monolayers. Type-II microcapsules were formed by encapsulating the Type-I microcapsules in another 2-5 microm ter-polymer shell and a approximately 5 microm collagen layer between the two ter-polymer shells to ensure complete cell encapsulation. Type-II microcapsules comprised of a macro-porous exoskeleton with materials such as alumina sol-gel coated on the Type-I microcapsules. Nano-indendation assay indicated an improved mechanical stability over the Type-I microcapsules. Type-IV microcapsules were created by encapsulating Type-III microcapsules in another 2-5 microm ter-polymer shell, with the aim of imparting a negatively charged smooth surface to minimize plasma protein absorption and ensure complete cell encapsulation. The permeability for nutrient exchange, cellular functions in terms of urea production and mechanical stability of the microcapsules were characterized. The advantages and limitations of these microcapsules for tissue engineering are discussed.

Animals↗
PubMed2001

Chitosan-DNA nanoparticles as gene carriers: synthesis, characterization and transfection efficiency.

Chitosan-DNA nanoparticles were prepared using a complex coacervation process. The important parameters for the nanoparticle synthesis were investigated, including the concentrations of DNA, chitosan and sodium sulfate, temperature of the solutions, pH of the buffer, and molecular weights of chitosan and DNA. At an amino group to phosphate group ratio (N/P ratio) between 3 and 8 and a chitosan concentration of 100 microg/ml, the size of particles was optimized to approximately 100--250 nm with a narrow distribution, with a composition of 35.6 and 64.4% by weight for DNA and chitosan, respectively. The surface charge of these particles was slightly positive with a zeta potential of +12 to +18 mV at pH lower than 6.0, and became nearly neutral at pH 7.2. The chitosan-DNA nanoparticles could partially protect the encapsulated plasmid DNA from nuclease degradation as shown by electrophoretic mobility analysis. The transfection efficiency of chitosan-DNA nanoparticles was cell-type dependent. Typically, it was three to four orders of magnitude, in relative light units, higher than background level in HEK293 cells, and two to ten times lower than that achieved by LipofectAMINE-DNA complexes. The presence of 10% fetal bovine serum did not interfere with their transfection ability. Chloroquine could be co-encapsulated in the nanoparticles at 5.2%, but with negligible enhancement effect despite the fact that chitosan only showed limited buffering capacity compared with PEI. The present study also developed three different schemes to conjugate transferrin or KNOB protein to the nanoparticle surface. The transferrin conjugation only yielded a maximum of four-fold increase in their transfection efficiency in HEK293 cells and HeLa cells, whereas KNOB conjugated nanoparticles could improve gene expression level in HeLa cells by 130-fold. Conjugation of PEG on the nanoparticles allowed lyophilization without aggregation, and without loss of bioactivity for at least 1 month in storage. The clearance of the PEGylated nanoparticles in mice following intravenous administration was slower than unmodified nanoparticles at 15 min, and with higher depositions in kidney and liver. However, no difference was observed at the 1-h time point.

Animals↗
PubMed2001

Fabrication of poly(phosphoester) nerve guides by immersion precipitation and the control of porosity.

Immersion precipitation was employed as a method for the fabrication of polymeric conduits from P(BHET-EOP/TC), a poly(phosphoester) with an ethylene terephthalate backbone, to be applied as guidance channels for nerve regeneration. Coatings of various porosities could be obtained by immersing mandrels coated with a solution of the polymer in chloroform into non-solvent immersion baths, followed by freeze or vacuum-drying. The porosity of the coatings decreased with an increase in polymer molecular weight, drying time before precipitation and concentration of polymer solution. The effects of these parameters can be rationalized by employing ternary phase diagrams, where porosity is directly related to the degree of phase separation available to the system before gelation occurs. To afford improved porosity control, a new system was developed which employed the contrasting phase-separation behavior of P(BHET-EOP/TC)/chloroform solution in methanol and water. As water is essentially a non-solvent for the polymer, the demixing boundary of the P(BHET-EOP/TC)-CHCl3-H2O system is located close to the polymer-solvent edge of the phase diagram, while that of the P(BHET-EOP/TC)-CHCl3-MeOH system is located further away. A mixture of methanol and water allows the demixing boundary to be shifted to intermediate coordinates. By immersing P(BHET-EOP/TC) coatings in immersion baths containing different ratios of water and methanol, then gradually titrating the bath with methanol to a concentration of 70% (v/v) methanol, surface porosities ranging from 2 to 58% could be achieved.

Biocompatible Materials↗
PubMed2001

A new nerve guide conduit material composed of a biodegradable poly(phosphoester).

There is a resurgence of interest in the development of degradable and biocompatible polymers for fabrication of nerve guide conduits (NGCs) in recent years. Poly(phosphoester) (PPE) polymers are among the attractive candidates in this context, in view of their high biocompatibility, adjustable biodegradability, flexibility in coupling fragile biomolecules under physiological conditions and a wide variety of physicochemical properties. The feasibility of using a biodegradable PPE, P(BHET-EOP/TC), as a novel NGC material was investigated. Two types of conduits were fabricated by using two batches of P(BHET-EOP/TC) with different weight-average molecular weights (Mw) and polydispersity indexes (PI). The polymers as well as conduits were non-toxic to all six types of cells tested, including primary neurones and neuronally differentiated PC12 cells. After in situ implantation in the sciatic nerve of the rat, two types of conduits triggered a similar tissue response, inducing the formation of a thin tissue capsule composed of approximately eight layers of fibroblasts surrounding the conduits at 3 months. Biological performances of the conduits were examined in the rat sciatic nerve model with a 10 mm gap. Although tube fragmentation, even tube breakage, was observed within less than 5 days post-implantation, successful regeneration through the gap occurred in both types of conduits, with four out of 10 in the Type I conduits (Mw 14,900 and PI 2.57) and 11 out of 12 in the Type II conduits (Mw 18,900 and PI 1.72). The degradation of conduits was further evidenced by increased roughness on the tube surface in vivo under scanning electron microscope and a mass decrease in a time-dependent manner in vitro. The Mw of the polymers dropped 33 and 24% in the Type I and II conduits, respectively, in vitro within 3 months. Among their advantages over other biodegradable NGCs, the PPE conduits showed negligible swelling and no crystallisation after implantation. Thus, these PPE conduits can be effective aids for nerve regeneration with potential to be further developed into more sophisticated NGCs that have better control of the conduit micro-environment for improved nerve regeneration.

Animals↗
PubMed2001

Interactions of phospholipid bilayer with chitosan: effect of molecular weight and pH.

Chitosan has demonstrated its potentials as a gene carrier and a membrane perturbant for subsequent drug delivery to cells. However, there is currently a lack of experimental correlation between the physiochemical properties of chitosan and the resulting degree of lipid bilayer destabilization. In this study, the effect of pH and chitosan molecular weight on the interaction between chitosan and dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) bilayer was examined with cross-polarization microscopy, differential scanning calorimetry (DSC), and Fourier transform- (FT-) Raman spectroscopy. Cross-polarized images showed that the direct hydration of the DPPC/chitosan mixture led to the formation of larger DPPC multilamellar vesicles (MLV), and pure chitosan also induced fusions of individual MLV. Under the influence of chitosan, the calorimetric enthalpy of DPPC was reduced in a concentration-dependent manner, and a new phase appeared at 28 degrees C during sample cooling. Even the lowest chitosan mole fraction of 0.04% reduced the cooperative unit of the DPPC bilayer by more than 70%. In addition, the electrostatic effect between chitosan and DPPC tuned the degree of membrane bilayer perturbation. Reduction of pH increased the number of protonated amines on the chitosan backbone and caused further disruption on the membrane organization. Mixing DPPC with chitosan in an organic medium before hydration enhanced the hydrophobic interactions between the two molecules and greatly reduced the cooperative unit among individual lipids during the main phase transition. The increase of chitosan molecular weight also affected the cooperativity in the thermotropic transition of DPPC bilayer. FT-Raman spectroscopy provided additional evidence that chitosan directly perturbed the organizations of the hydrophobic inner core of the DPPC bilayer.

1,2-Dipalmitoylphosphatidylcholine↗
PubMed1999

Stereoselective determination of fenfluramine enantiomers in rat liver microsomal incubates.

An enantioselective assay for l- and d-fenfluramine in rat liver microsomal incubates was developed. The method involves extraction of fenfluramine from the microsomal incubates, and formation of fenfluramine diastereomeric derivatives with the chiral reagent S-(-)-N-trifluoroacetyl prolyl chloride. Separation and quantitation of the diastereomeric fenfluramine derivatives are carried out by a capillary gas chromatographic system with flame ionization detection. The assay is linear from 1 to 50 microg/ml for each enantiomer. The analytical method affords average recoveries of 92.28 and 96.44% for l- and d-fenfluramine, respectively. The limits of detection and quantitation for the method are 0.1 and 1.0 microg/ml for the l- and d-fenfluramine isomers, respectively. The reproducibility of the assay was <10% (RSD). The method allowed study of the depletion of l- and d-fenfluramine in rat liver microsomal incubates. The stereoselectivity of fenfluramine phase I metabolism was observed.

Animals↗
PubMed1999

Gene transfer by DNA-gelatin nanospheres.

A DNA and gelatin nanoparticle coacervate containing chloroquine and calcium, and with the cell ligand transferrin covalently bound to the gelatin, has been developed as a gene delivery vehicle. In this study, the coacervation conditions which resulted in the formation of distinct nanoparticles are defined. Nanospheres formed within a narrow range of DNA concentrations and achieved incorporation of more than 98% of the DNA in the reaction. Crosslinking of gelatin to stabilize the particles does not effect the electrophoretic mobility of the DNA. DNA in the nanosphere is partially resistant to digestion with concentrations of DNase I that result in extensive degradation of free DNA but is completely degraded by high concentrations of DNase. Optimum cell transfection by nanosphere DNA required the presence of calcium and nanospheres containing transferrin. The biological integrity of the nanosphere DNA was demonstrated with a model system utilizing DNA encoding the cystic fibrosis transport regulator (CFTR). Transfection of cultured human tracheal epithelial cells (9HTEo) with nanospheres containing this plasmid resulted in CFTR expression in over 50% of the cells. Moreover, human bronchial epithelial cells (IB-3-1) defective in CFTR-mediated chloride transport were complemented with effective transport activity when transfected with nanospheres containing the CFTR transgene.

Calcium↗
PubMed1999

Oral gene delivery with chitosan--DNA nanoparticles generates immunologic protection in a murine model of peanut allergy.

Food allergy is a common and often fatal disease with no effective treatment. We describe here a new immunoprophylactic strategy using oral allergen-gene immunization to modulate peanut antigen-induced murine anaphylactic responses. Oral administration of DNA nanoparticles synthesized by complexing plasmid DNA with chitosan, a natural biocompatible polysaccharide, resulted in transduced gene expression in the intestinal epithelium. Mice receiving nanoparticles containing a dominant peanut allergen gene (pCMVArah2) produced secretory IgA and serum IgG2a. Compared with non-immunized mice or mice treated with 'naked' DNA, mice immunized with nanoparticles showed a substantial reduction in allergen-induced anaphylaxis associated with reduced levels of IgE, plasma histamine and vascular leakage. These results demonstrate that oral allergen-gene immunization with chitosan-DNA nanoparticles is effective in modulating murine anaphylactic responses, and indicate its prophylactic utility in treating food allergy.

2S Albumins, Plant↗
PubMed1998

DNA-polycation nanospheres as non-viral gene delivery vehicles.

Nanospheres synthesized by salt-induced complex coacervation of cDNA and polycations such as gelatin and chitosan were evaluated as gene delivery vehicles. DNA-nanospheres in the size range of 200-750 nm could transfect a variety of cell lines. Although the transfection efficiency of the nanospheres was typically lower than that of lipofectamine and calcium phosphate controls in cell culture, the beta-gal expression in muscle of BALB/c mice was higher and more sustained than that achieved by naked DNA and lipofectamine complexes. This gene delivery system has several attractive features: (1) ligands can be conjugated to the nanosphere for targeting or stimulating receptor-mediated endocytosis; (2) lysosomolytic agents can be incorporated to reduce degradation of the DNA in the endosomal and lysosomal compartments; (3) other bioactive agents or multiple plasmids can be co-encapsulated; (4) bioavailability of the DNA can be improved because of protection from serum nuclease degradation by the polymeric matrix; (5) the nanosphere can be lyophilized for storage without loss of bioactivity.

Animals↗
PubMed1992

Reactivity of gamma delta T cells induced by the tumour cell line RPMI 8226: functional heterogeneity of clonal populations and role of GroEL heat shock proteins.

The human tumour cell lines RPMI 8226 and Daudi are potent inducers of V gamma 9-expressing T cells. The inducing element of RPMI 8226 has not been defined but evidence suggests that a member of the GroEL heat shock protein (HSP) family (HSP 58) may have a role in the induction by Daudi cells. The present study examined the reactivity patterns of gamma delta T-cell clones generated in response to RPMI 8226 and addressed the possible role of HSP 58 in this process. RPMI 8226 induced a population of V gamma 9 TCR+ cells which were heterogeneous in terms of their cell surface markers, patterns of proliferation and cytotoxic responses. All clones expressed CD3, CD2, CD18 and CD29. They demonstrated variability in expression of CD56, CD8 and HLA-DR. RPMI 8226 stimulated proliferation in purified bulk gamma delta cultures and clones. Daudi was also capable of inducing these cells to proliferate while mycobacterial products were not effective. The clones demonstrated a limited non-MHC-restricted cytotoxicity pattern with some evidence of clonal heterogeneity. Although both Daudi and RPMI 8226 were sensitive to lysis by the clones, cold inhibition experiments indicated differential activity towards these targets. Anti-HSP 58 was inhibitory to gamma delta T-cell induction by RPMI 8226, Daudi and mycobacterial products. However, the anti-HSP 58 antibody appears to bind to the surface of at least six different tumour cell lines with no correlation to their ability to induce gamma delta T cells and the anti-HSP 58 inhibited non-gamma delta responses.

Bacterial Proteins↗
PubMed1988

Pulmonary injury in laboratory animals induced by Huai-Nan coal mine respirable dust.

The BAL technique was used to assess the pulmonary injury of coal dust and rock dust in Huai-Nan coal mine in Anhui Province. Dust suspended in saline and dust-free supernatant were instilled intratracheally to Wistar rats and Syrian hamsters. Saline was used in treating controls. The animals were sacrificed 24 h after treatment, their lungs were lavaged, and pulmonary damage was evaluated by cellular and biochemical assays of lavage fluid. Pulmonary injury was expressed by the cell toxicity index (CTI). CTI is the product of the number of times of meaningful parameters for treated groups compared to controls (LDH, acid phosphatase, and polymorphonuclear neutrophils in this case). The CTI values were found to be 5.19, 2.28, and 5.15 for rock dust, coal dust, and Shanghai suspended particulates, respectively. The toxicity of rock dust is higher than that of coal dust, but is similar to that of Shanghai suspended particulates. The cell toxicity of dust suspension solution is higher than that of dust-free supernatant. CTI can be used as an indicator of the relative toxicity of respirable dusts in in vivo studies.

Acid Phosphatase↗
PubMedDate not supplied

Immobilization of galactose ligands on acrylic acid graft-copolymerized poly(ethylene terephthalate) film and its application to hepatocyte culture.

Surface modification of argon-plasma-pretreated poly(ethylene terephthalate) (PET) films via UV-induced graft copolymerization with acrylic acid (AAc) was carried out. Galactosylated surfaces were then obtained by coupling a galactose derivative (1-O-(6'-aminohexyl)-D-galactopyranoside) to the AAc graft chains with the aid of a water-soluble carbodiimide (WSC) and N-hydroxysulfosuccinimide (sulfo-NHS). The modified PET films were characterized by X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), and water contact-angle measurements. The galactosylated PET films were used as substrates for hepatocyte culture. The effects of surface carboxyl group concentration on the extent of galactose ligand immobilization, the extent of hepatocyte attachment, and the surface morphology were investigated. The amount of the galactose ligands immobilized on the PET surface increased with the AAc polymer graft concentration. AFM images revealed that the surface roughness of the PET film increased after graft copolymerization with AAc, but did not change appreciably with the subsequent immobilization of the galactose ligands. At the surface carboxyl group concentration of about 0.56 micromol/cm(2) or galactose ligand concentration of about 0.51 micromol/cm(2), the hepatocyte culture on the galactosylated surface exhibited the optimum concentration and physiological functions and formed aggregates or spheroids after just 1 day of culture. The albumin and urea synthesis functions of these hepatocytes were comparable to or higher than those of the hepatocytes cultured on the collagen-modified PET substrates.

Acrylates↗