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PubMed1986

Distribution and processing of the polymeric immunoglobulin receptor in the rat hepatocyte: morphological and biochemical characterization of subcellular fractions.

The transepithelial transport of polymeric immunoglobulins is an essential process in the mucosal immune system. Transport across the epithelial cells of mucous or exocrine glands is affected by an integral membrane glycoprotein receptor known as membrane secretory component (SCm) or as polymeric immunoglobulin receptor (pIgR). This receptor binds polymeric immunoglobulins at the basolateral cell surface and mediates their transcellular translocation and their release from the apical plasma membrane into external secretions. Release depends on cleavage of the membrane-anchoring domain of the receptor, resulting in liberation of polymeric immunoglobulin bound to the ectoplasmic domain of the receptor (secreted SC or SCs) into extracellular secretions. Using a monoclonal antibody directed against the cytoplasmic tail of the receptor and a polyclonal antibody directed against the secreted ectoplasmic domain, we have combined cell fractionation and Western blotting techniques to examine the fate of these receptor domains in the hepatocyte. In this study, we characterize biochemically and morphologically the various subcellular components separated by our fractionation scheme, and correlate this with biochemical analysis of the receptor in each fraction.

Animals↗
PubMed2005

HIV-1 Tat protein enhances microtubule polymerization.

BACKGROUND: HIV infection and progression to AIDS is characterized by the depletion of T cells, which could be due, in part, to apoptosis mediated by the extra-cellular HIV-encoded Tat protein as a consequence of Tat binding to tubulin. Microtubules are tubulin polymers that are essential for cell structure and division. Molecules that target microtubules induce apoptosis and are potent anti-cancer drugs. We studied the effect on tubulin polymerization of three Tat variants: Tat HxB2 and Tat Eli from patients who are rapid progressors (RP) and Tat Oyi from highly exposed but persistently seronegative (HEPS) patients. We compared the effect on tubulin polymerization of these Tat variants and peptides corresponding to different parts of the Tat sequence, with paclitaxel, an anti-cancer drug that targets microtubules. RESULTS: We show that Tat, and specifically, residues 38-72, directly enhance tubulin polymerization. We demonstrate that Tat could also directly trigger the mitochondrial pathway to induce T cell apoptosis, as shown in vitro by the release of cytochrome c from isolated mitochondria. CONCLUSIONS: These results show that Tat directly acts on microtubule polymerization and provide insights into the mechanism of T cell apoptosis mediated by extra-cellular Tat.

Animals↗
PubMed1993

Diminished actin polymerization by neutrophils from newborn infants.

During the newborn period, abnormalities of neutrophil (PMN) function predispose infants to serious bacterial disease. Actin is a major contributor to PMN shape change and motile behavior. To determine the mechanism underlying defects in newborn granulocyte polarity and chemotaxis, we investigated actin polymerization by cord blood PMN from healthy term infants and adult controls. F-actin (filamentous) content was quantified in the resting state and after stimulation by fluorescence-activated cell-sorter analysis of nitrobenzoxadiazole-phallacidin-stained cells. PMN from newborn infants demonstrated similar basal F-actin levels when compared with adults. N-formyl methionyl leucyl phenylalanine induced a marked increase in actin polymerization that was maximal at 30 s in both neonates and adults and that then declined slowly (depolymerization) over the following 10 min. However, the F-actin content of PMN from newborn infants was significantly diminished when compared with adults at 30 and 60 s after N-formyl methionyl leucyl phenylalanine stimulation (p < 0.05). Both the rate and dose response of N-formyl methionyl leucyl phenylalanine-induced actin polymerization were similar for adult and neonatal PMN. PMN from newborn infants also demonstrated significantly diminished actin polymerization when compared with adults 60 s after stimulation with platelet-activating factor (p < 0.05). Decreased concentrations of F-actin may help explain the observed abnormalities of PMN polarity and chemotaxis in healthy newborn infants.

Actins↗
PubMed2003

Investigation of processing parameters of spray freezing into liquid to prepare polyethylene glycol polymeric particles for drug delivery.

The objective of this study was to investigate the influence of processing parameters on the morphology, porosity, and crystallinity of polymeric polyethylene glycol (PEG) microparticles by spray freezing into liquid (SFL), a new particle engineering technology. Processing parameters investigated were the viscosity and flow rate of the polymer solution, nozzle diameter, spray time, pressure, temperature, and flow rate of the cryogenic liquid. By varying the processing parameters and feed composition, atomization and heat transfer mechanisms were modified resulting in particles of different size distribution, shape, morphology, density, porosity, and crystallinity. Median particle diameter (M50) varied from 25 microm to 600 microm. Particle shape was spherical or elongated with highly irregular surfaces. Granule density was between 0.5 and 1.5 g/mL. In addition to producing particles of pure polymer, drug particles were encapsulated in polymeric microparticles. The encapsulation efficiency of albuterol sulfate was 96.0% with a drug loading of 2.4%, indicating that SFL is useful for producing polymeric microparticles for drug delivery applications. It was determined that the physicochemical characteristics of model polymeric microparticles composed of PEG could be modified for use as a drug delivery carrier.

Chemistry, Pharmaceutical↗
PubMed2003

Mechanical constraint imposed on plasma membrane through transverse phospholipid imbalance induces reversible actin polymerization via phosphoinositide 3-kinase activation.

Platelets were used to explore the effect of membrane curvature induced by phospholipid excess on cell shape and on organization of the actin cytoskeleton. We showed that the addition of short chain analogues of phospholipids to the outer leaflet of plasma membrane of resting platelets immediately induced a shape change with long filopodia formation containing newly polymerized actin. Cells recovered rapidly their discoid shape and their initial F-actin content only with the phosphatidylserine analogue, which was transported to the inner leaflet by aminophospholipid translocase. Filopodia formation and actin polymerization were inhibited in platelets pre-incubated with cytochalasin D. Both wortmannin and LY294002, two unrelated inhibitors of phosphoinositide 3-kinase, considerably reduced actin polymerization and filopodia formation. Phospholipid imbalance was accompanied by a reversible translocation of phosphoinositide 3-kinase from cytoplasm to plasma membrane. In agreement with a role for PI 3-kinase, when phospholipids were added to platelets, PtdIns(3,4)P2 increased two-fold and Akt protein was partly phosphorylated. A similar shape change was also observed in nocodazole-treated L929 fibroblasts which were incubated with the similar phospholipid analogues. In those nucleated cells, where the microtubule cytoskeleton was disrupted, a major actin-dependent membrane extension was induced by addition of short chain phospholipids that required the functional integrity of PI 3-kinase. We conclude that any physical constraint acting on plasma membrane and resulting on local changes in membrane curvature is sufficient to initiate transient actin polymerization via phosphoinositide 3-kinase activation.

Actin Cytoskeleton↗
PubMed1996

Polymerization degree of oligomethionine to determine its bioavailability when added to a low-protein diets.

Oligo-L-methionine ethylester (OMOEt) prepared by the papain-catalyzed oligomerization of L-methionine ethylester (MetOEt) is a mixture of pentamer to dodecamer and has nearly the same supplementary effect as free methionine (Met) for the growth of rats when added to a low casein diet, but its supplementary effect to a low-soy protein isolate (SPI) diet is not consistent and depends on the degree of polymerization. Rats were fed for 2 wk with an 8% casein or 10% SPI diet supplemented with 0.3% L-Met, each chemically synthesized MetnOEt with a polymerization degree (n) of 6, 7, 8, or 9, or with OMOEt prepared by papain-catalyzed polymerization of MetOEt. Met6OEt, Met7OEt, and Met8OEt had nearly the same supplementary effect on the growth of rats, as did free Met, both with the 8% casein and 10% SPI diets. The supplementary effect of Met9OEt was not significantly lower than that of Met when added to the 8% casein diet, but was significantly lower when added to the 10% SPI diet. The digestibility of Met9OEt supplemented to the 8% casein and 10% SPI diets was 50.5% and 35.6%, respectively. It appears likely that there is a gap in the bioavailability of oligomethionine between the octamer and nonamer when added to a low-protein diet, probably due to the rigidity of the structure increasing with the polymerization degree by alpha-helix formation. Although the differences in absorption rate of Met from OMOEt for a short time after feeding has been related to the different effects of supplemented OMOEt, the absorption rate of OMOEt for 30 min after feeding was not considered to be the main cause of the differential effects of OMOEt in this experiment.

Animals↗
PubMed2003

Recording performance of holographic diffraction gratings in dry films containing hyperbranched polyisophthalesters as polymeric binders.

By use of a photopolymerization-diffusion model, the diffraction efficiency of photopolymerizable recording dry films prepared from hyperbranched polyisophthalesters as polymeric binders was investigated. The recording characteristics of these films, i.e., spatial frequency, polymeric binder structure, exposure intensity, and modulation depth, are discussed in detail. For a given total exposure dose the diffraction efficiency first increases and then decreases with increasing exposure intensity, and this effect becomes more remarkable as the unsaturated concentration of polymeric binder increases. An optimum total exposure dose of 36 mJ cm(-2) and an exposure intensity of 0.4 mW cm(-2) were determined. A modulation depth of 1 was found to produce the highest diffraction efficiency. Longer-lasting gratings could be obtained by use of polymeric binders with higher cross-linking densities.

Journal Article↗
PubMed2002

A comparison of polymerization by light-emitting diode and halogen-based light-curing units.

BACKGROUND: Light-emitting diode, or LED, technology provides certain advantages over halogen-based light polymerization of resin-based composites. The authors investigated the adequacy of cure of LED light-curing units, or LCUs. METHODS: The authors used two halogen-based light-curing units (Optilux 400 and 501, Demetron Research Corp., Danbury, Conn.) and two commercially available LED LCUs (LumaCure, LumaLite, Spring Valley, Calif., and VersaLux, Centrix, Shelton, Conn.) to polymerize top surfaces of hybrid (Filtek Z-250, 3M, St. Paul, Minn.) and microfilled (Renamel, Cosmedent, Chicago) resin-based composite specimens. Specimens were indented on their top and bottom surfaces with a Knoop hardness tester and measured for hardness. Bottom:top hardness ratios determined the percentage of cure. The authors separated the data into eight groups (two composites cured with four different lights) with 15 observations per group, for a total sample size of 120. RESULTS: The authors compared composites and curing lights by a two-way analysis of variance, and results indicated significant main effects. The main effect of composite was statistically significant (P < .0001) when microfilled composite was compared with hybrid composite, regardless of curing light, for all top and bottom hardness measurements, with the hybrid producing much higher hardness measurements overall. The main effect of light was significant as well (P < .0001), regardless of composite type, with the two halogen-based lights producing harder top and bottom composite surfaces than the two LED LCUs. CONCLUSIONS: The light output of commercially available diodes for resin-based composite polymerization still requires improvement to rival the adequacy of cure of halogen-based LCUs. Additional studies are necessary. CLINICAL IMPLICATIONS: Commercially available LED LCUs were introduced just in the past year. However, they may not adequately polymerize resin-based composites, which can lead to restoration failures and adverse pulpal responses to unpolymerized monomers.

Analysis of Variance↗
PubMed2006

The kinetics of nucleated polymerizations at high concentrations: amyloid fibril formation near and above the "supercritical concentration".

The formation of amyloid and other types of protein fibrils is thought to proceed by a nucleated polymerization mechanism. One of the most important features commonly associated with nucleated polymerizations is a strong dependence of the rate on the concentration. However, the dependence of fibril formation rates on concentration can weaken and nearly disappear as the concentration increases. Using numerical solutions to the rate equations for nucleated polymerization and analytical solutions to some limiting cases, we examine this phenomenon and show that it is caused by the concentration approaching and then exceeding the equilibrium constant for dissociation of monomers from species smaller than the nucleus, a quantity we have named the "supercritical concentration". When the concentration exceeds the supercritical concentration, the monomer, not the nucleus, is the highest-energy species on the fibril formation pathway, and the fibril formation reaction behaves initially like an irreversible polymerization. We also derive a relation that can be used in a straightforward method for determining the nucleus size and the supercritical concentration from experimental measurements of fibril formation rates.

Amyloid↗
PubMed2006

Actin polymerization upon processive capping by formin: a model for slowing and acceleration.

Formin family proteins act as processive cappers of actin filaments, and determine the dynamics of a number of intracellular processes that are based on actin polymerization. The rate of filament growth upon processive capping varies within a broad range depending on the formin type and presence of profilin. While FH2 domains of various formins slow down polymerization by different extents, the FH1-FH2 domains in conjunction with profilin accelerate the reaction. Study of the physical mechanism of processive capping is vital for understanding the intracellular actin dynamics. We propose a model predicting that variation of a single physical parameter-the effective elastic energy of the formin-capped barbed end-results in the observed diversity of the polymerization rates. The model accounts for the whole range of the experimental results including the drastic slowing down of polymerization by FH2 of Cdc12 formin and the 4.5-fold acceleration of the reaction by FH1-FH2 of mDai1 formin in the presence of profilin. Fitting the theoretical predictions to the experimental curves provides the values of the effective elastic energies of different formin-barbed end complexes.

Actin Cytoskeleton↗
PubMedDate not supplied

Effectiveness of composite resin polymerization using light-emitting diodes (LEDs) or halogen-based light-curing units.

The clinical performance of composite resins is greatly influenced by the quality of the light-curing unit used. The aim of this study was to compare the efficiency of a commercial light-emitting diode (LED) with that of a halogen-based light-curing unit by means of dye penetration of a micro hybrid composite resin. The composite resin evaluated was Filtek Z250 (3M Dental). The composite was filled into acrylic moulds that were randomly polymerized for 40 seconds by each of the light-emitting systems: light-emitting diode Ultraled (Dabi Atlante) or halogen light Degulux (Degussa Hülls) curing units. Immediately after polymerization, each specimen was individually immersed in 1 ml of 2% methylene blue solution at 37 degrees C +/- 2 degrees C. After 24 hours, the specimens were rinsed under running distilled water for 1 minute and stored at 37 degrees C +/- 2 degrees C at relative humidity for 24 hours. The composite resins were removed from the moulds and individually triturated before being immersed in new test tubes containing 1 ml of absolute alcohol for 24 hours. The solutions were filtered and centrifuged for 3 minutes at 4,000 rpm and the supernatant was used to determine absorbance in a spectrophotometer at 590 nm. To verify the differences between groups polymerized by LED or halogen light t-test was applied. No significant differences were found between composite resins light-cured by LED or halogen light-curing unit (p > 0.05). The commercially LED-based light-curing unit is as effective to polymerize hybrid composite resins as the halogen-based unit.

Composite Resins↗
PubMed2004

Amperometric glucose biosensor based on mediated electron transfer between immobilized glucose oxidase and plasma-polymerized thin film of dimethylaminomethylferrocene on sputtered gold electrode.

We propose an electron transfer-mediated amperometric enzyme biosensor based on plasma-polymerized thin film of dimethylaminomethylferrocene (DMAMF) on a sputtered gold electrode. The DMAMF plasma-polymerized film is deposited directly onto the surface of the electrode under dry conditions. The resulting thin film not only has redox sites but also is extremely thin (approximately 20 nm), adheres well onto the substrate (electrode), has a flat surface and a highly-crosslinked network structure, and is hydrophilic in nature. Glucose oxidase is densely immobilized onto the surface of DMAMF plasma-polymerized film on the gold electrode. From the electrochemical measurement, the biosensor can cover the wide range of glucose concentration (1.3 - 81 mM) at +350 mV of applied potential. The current response of the glucose biosensor was decreased by less than 5% in an aerobic solution as compared to that in an anaerobic solution. These show that the DMAMF plasma-polymerized films play a role as the electron transfer mediators between the reaction center of enzyme and the electrode.

Biosensing Techniques↗
PubMed2005

Pulsed NMR study of network formation in the course of bulk polymerization of methyl acrylate.

The proton spin-spin relaxation time (T2) during the bulk polymerization of methyl acrylate was measured as a function of the reaction time at various temperatures. Three kinds of T2 (T2L (long), T2S (short) and T2M (intermediate)) were obtained as the polymerization proceeded. The fraction of T2S (FS) increased sigmoidally at a certain reaction time, while that of T2L (FL) decreased reciprocally. The former corresponded to the amount of a polymer whose molecular weight was sufficiently high enough to cause a tight entanglement that produced a transient network structure; the latter reflected a decrease in the mixture of the monomer and the low molecular weight of the polymer. T2M is considered to arise from a relatively mobile region of the entanglement. The relationship between the fractions of T2S + T2M and the polymer yield was found to be linear, which led us to monitor the polymer yield in real time during the polymerization in a non-distractive manner. 13C DD (dipolar decoupling)/MAS (magic angle spinning) NMR spectra were also measured to monitor the polymerization process in terms of the molecular motions between the main chain and the side chain in the formation of a network structure. The 13C DD/MAS NMR spectra show that the side chain motion became restricted as well as the main chain when the "Trommosdorff effect" (gel effect) was observed, and a part of the monomers were trapped in the network structure.

Journal Article↗
PubMed2000

Pyrophosphorolysis-activated polymerization (PAP): application to allele-specific amplification.

To measure mutation load or to detect minimal residual disease, a robust method for identifying one mutant allele in the range of 10(6)-10(9) wild-type alleles would be advantageous. Herein, we present evidence that pyrophosphorolysis-activated polymerization (PAP) has the potential to provide a highly specific and robust method of allele-specific amplification if DNA polymerases with higher pyrophosphorolysis activity can be found or engineered. In PAP, pyrophosphorolysis and polymerization by DNA polymerase are coupled serially by utilizing a pyrophosphorolysis-activatable oligonucleotide (P*). P*, which is an allele-specific oligonucleotide with a dideoxynucleotide at the 3' terminus, can be activated by pyrophosphorolysis to remove the 3' terminal dideoxynucleotide in the presence of pyrophosphate (PPi) and the complementary strand of the allelic template; then the activated P* can be extended by DNA polymerization. Specificity results from both pyrophosphorolysis and polymerization because significant nonspecific amplification requires the combination of mismatch pyrophosphorolysis and misincorporation by the DNA polymerase, which is an extremely rare event. Proof of principle has been achieved with a polymorphic site within the human D1 dopamine receptor gene. The effects of the dideoxyoligonucleotide sequences, DNA polymerases, PPi concentrations, allele-specific templates, pH and dNTP concentrations were examined.

Alleles↗
PubMed2006

The effect of polymeric flocculants on floc strength and filter performance.

Polymeric flocculants are widely used throughout the water industry as flocculant aids, they are known to increase floc density and aid settlement in the clarification stage of the water treatment process. In this research, polymeric flocculants were used to improve floc strength prior to filtration on a dissolved air flotation (DAF) plant in an attempt to prevent filter breakthrough. A modified jar test procedure using a PDA (photometric dispersion analyser) optical flocculation monitor was developed in order to evaluate the system floc strength. Filtration trials were carried out on a pilot filter rig situated on a surface water treatment works in Yorkshire. The filter feed originated from the main plant filter channel. Filter performance was assessed by continuous online monitoring of effluent particle counts, turbidity and headloss over the period of the filter run. Results indicated that low doses of polymeric flocculants had a beneficial effect on filtered water quality, as measured by particle counts, turbidity, UV254 absorption and dissolved organic carbon (DOC). Polymeric flocculants also had the effect of extending filter run length. The modified jar test results indicated that the flocculants used improved the floc strength and enhanced reflocculation of the micro flocs present after the flotation process.

Filtration↗
PubMed2004

Polymeric radiotracers in nuclear imaging.

Water-soluble polymers have been used in the last two decades to modify the pharmacokinetics and physicochemical properties of targeted therapeutic agents. Non-invasive imaging techniques such as nuclear imaging can be used to assess the drug delivery efficiency of novel formulations in a cost-effective fashion and thereby facilitate their development process. Polymeric radiopharmaceuticals have also been investigated on their own right as potential nuclear imaging agents. Clinical applications of polymeric radiopharmaceuticals include blood-pool imaging and targeted molecular imaging. In the latter case, water-soluble polymers are often used to modify the pharmacokinetics and biodistribution pattern of ligands that target receptors or antigens at disease sites. As advances are continue to be made in the emerging field of molecular imaging, nuclear imaging will play an increasingly important role in the development of polymeric drug delivery systems. Similarly, polymer technology will also be integrated into the development of molecularly targeted radiopharmaceuticals. Here, we review various aspects of polymeric radiotracers and their applications in nuclear imaging.

Animals↗
PubMedDate not supplied

Comparison of composite curing parameters: effects of light source and curing mode on conversion, temperature rise and polymerization shrinkage.

This study analyzed the degree of conversion, temperature increase and polymerization shrinkage of two hybrid composite materials polymerized with a halogen lamp using three illumination modes and a photopolymerization device based on blue light emitting diodes. The degree of conversion of Tetric Ceram (TC) (Ivoclar Vivadent) and Filtek Z 250 (F) (3M/ESPE) was measured by Fourier transformation infrared spectroscopy at the surface and 2-mm depth; temperature rise was measured by digital multimeter, and linear polymerization shrinkage was measured during cure by digital laser interferometry. Composite samples were illuminated by quartz-tungsten-halogen curing unit (QTH) (Astralis 7, Ivoclar Vivadent) under the following modes: "high power" (HH) 40 seconds at 750 mW/cm2, "low power" (HL) 40 seconds at 400 mW/cm2 and "pulse/soft-start" (HP) increasing from 150 to 400 mW/cm2 during 15 seconds followed by 25 seconds pulsating between 400 and 750 mW/cm2 in 2-second intervals and by light emitting diodes (LED) (Lux-o-Max, Akeda Dental) with emitted intensity 10 seconds at 50 mW/cm2 and 30 seconds at 150 mW/cm2. A significantly higher temperature increase was obtained for both materials using the HH curing mode of halogen light compared to the HP and HL modes and the LED curing unit after 40 seconds. Significantly lower temperature values after 10-second illumination were obtained when LED was used compared to all halogen modes. For all curing modes, there was no significant difference in temperature rise between 20 and 40 seconds of illumination. Results for the degree of conversion measurements show that there is a significant difference in the case of illumination of resin composite samples with LED at the surface and 2 mm depth. For polymerization shrinkage, lower values after 40 seconds were obtained using LED compared to QTH.

Acrylic Resins↗
PubMedDate not supplied

Polymerization and fractionation of house dust mite allergen.

Glutaraldehyde polymerization and appropriate fractionation of allergens result in significantly decreased allergenicity with retained immunogenicity. In a manner similar to that employed with other allergens, we have prepared monomer dust mite (MDM) and polymerized dust mite (PDM). As with other polymerized allergens such as polymerized ragweed, PDM is more than 2 logs less allergenic than MDM as determined by cutaneous end point titration in sensitive patients. Moreover, PDM and MDM are similarly immunogenic in rabbits. As determined by inhibition studies (with rabbit antisera) PDM is antigenically complete and contains no new epitopes against which antibody was produced. In summary, we have prepared PDM which has the desired characteristics of reduced allergenicity, retained immunogenicity, antigenic completeness, and absence of new antigenic determinants.

Allergens↗