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PubMed1981

Interactions between polymerized human albumin, hepatitis B surface antigen, and complement: I. Binding of polyalbumin to Clq.

There is considerable evidence that substances other than immunoglobulins can bind human Clq. Utilizing purified human Clq immobilized on polystyrene beads, we have demonstrated that polymerized human albumin (PHALB-125I) binds to human Clq in a direct binding assay. This interaction required a high degree of albumin polymerization as the percentage of binding was proportional to the polymer size and monomeric albumin was unreactive. Binding was species specific in the human Clq bound only human, and not xenogeneic, polyalbumins. Similarly, polymers of various other human plasma proteins were unreactive. To demonstrate that this interaction was not unique to immobilized Clq, soluble Clq was shown to inhibit PHALB-125I binding to solid phase Clq. Because aggregated IgG, poly(I):poly(C), dextran sulfate, polyglutamic acid, and polylysine have been previously shown to bind Clq, we used them in further blocking experiments and found them also to inhibit the interaction between Clq and PHALB. Anti-human Clq and, to a lesser extent, anti-PHALB antibodies inhibited the interaction. The Clq-PHALB binding was pH, ionic strength, and temperature dependent. In addition, human Clq was not observed to bind hepatitis B surface antigen (HBsAg) directly; however, in the presence of sufficiently polymerized human albumin a Clq-PHALB-HBsAg complex was formed. These interactions may be implicated in hepatocyte-HBsAg receptor function as well as in the host defense mechanisms involved in hepatitis B virus infection.

Animals↗
PubMed2004

Release from polymeric prodrugs: linkages and their degradation.

Polymeric prodrugs have evolved into a very useful class of drug delivery agents. Numerous polymeric prodrugs have been prepared for applications ranging from passive drug targeting to controlled release. The mechanistic aspects of the release processes, however, have not been clearly delineated. This review highlights the salient features of the chemical reactions that are responsible for drug release from these systems. The mechanisms of release from polymeric prodrugs employing various chemical linkages, esters, carbonates, carbamates, C=N linkage and amides, are discussed.

Hydrolysis↗
PubMed2004

A novel method for determination of drug solubility in polymeric matrices.

Crystallization of drugs in metastable, supersaturated adhesive polymeric matrices in transdermal drug delivery devices can be avoided by determination of the solubility of the drug in the adhesive polymer. A novel method is described to determine the solubility of the drug in polymeric matrices. Unlike existing methods, this method does not require a long and uncertain experimental time, and is accurate. In this study, an easy and accurate method is presented for the determination of solubility of drugs in polymers based on the relationship between thermodynamic activity of drugs and steady-state flux. In particular, the steady-state flux from a reference saturated solution across a test membrane was compared to an experimentally determined relationship between the polymeric loading concentration and the observed steady-state fluxes. The validity of this method was demonstrated by comparing the results to microscopic observation of crystallization and the study of aged drug-loaded adhesives for lidocaine as a model drug and an acrylate pressure-sensitive adhesive as a model polymer. The solubility of lidocaine was 20.8 +/- 0.5% (w/w) in the acrylate polymer.

Adhesives↗
PubMed1979

Drug entrapment for controlled release in radiation-polymerized beads.

The preparation of beads including polymer, vinyl monomer, and drug was carried out by low temperature, radiation-induced polymerization. Complete spherical particles were obtained when ethanol was the precipitation medium Polymers such as polymethyl methacrylate and polystyrene were dissolved in various glass-forming monomers, and the drug was dispersed in the mixture. The mixture was dropped into cold precipitation media. The formed monomeric particle was irradiated at low temperatures to produce polymerization. The drug release profiles from polymerized particles were changed by varying the glass-forming monomer and the precipitation medium.

Delayed-Action Preparations↗
PubMed1986

Polymerized phospholipid vesicles containing amphotericin B: evaluation of toxic and antifungal activities in vitro.

We have prepared lipid vesicles (liposomes) composed of polymerized bis[12-(methacryloyloxy)dodecanoyl]-L-alpha-phosphatidylcholine (DPL) which contain the antifungal polyene antibiotic amphotericin B (AMB). It was necessary to devise a novel method for incorporating AMB into the liposomes subsequent to polymerization. The polymer liposome AMB was as effective as AMB in "conventional" liposomes in terms of inhibiting fungal growth in vitro. However, in contrast to "conventional" liposomes, the polymerized DPL vesicles did not protect mammalian cells against AMB induced toxicity.

Amphotericin B↗
PubMed1987

In vivo behavior of polymerized lipid vesicles.

We have investigated the blood clearance kinetics and tissue distribution of large multilamellar liposomes (MLVs) and small unilamellar liposomes (SUVs) composed of the photopolymerizable lipid bis[12-(methacryloyloxy)dodecanoyl]-L-alpha-phosphatidylcholine. Polymerized MLVs or SUVs are cleared from the bloodstream more rapidly than nonpolymerized vesicles with similar size profiles. Both polymerized and nonpolymerized vesicles primarily accumulate in liver and spleen. However, the polymerized vesicles display an enhanced biostability as revealed by an elevated level of radioactive lipid marker remaining in the tissues.

Animals↗
PubMed1991

Post polymerization strength values of an argon laser cured resin.

A hybrid composite resin, Prisma APH, and a microfilled composite resin, Silux Plus, were compared regarding diametral tensile strength values following conventional visible light polymerization and argon lasing. The time interval between resin polymerization and physical property testing ranged from 1 hour to 20 days. Results demonstrated considerable mean tensile strength value variation in the earlier phases of the study with a lessening of the differences between the tensile strengths achieved by each method of polymerization as the 20 day interval was approached. It was concluded that composite resin testing protocols should be lengthened to be able to fully assess the effects of the widely variant, time dependent mean test results.

Argon↗
PubMed2004

Peroxidase-catalyzed oxidative polymerization of phenol with a nonionic polymer surfactant template in water.

Peroxidase-catalyzed oxidative polymerization of phenol has been examined using the template, poly(ethylene glycol) monododecyl ether (PEGMDE), in water. The role of this template, which forms a complex with phenol in the polymerization, was verified by UV measurements. During the reaction, a complex of the resulting polymer and PEGMDE was precipitated in high yields. The amount and the PEG chain length of PEGMDE strongly affected the polyphenol yield. The unit molar ratio of polyphenol and PEG of the template was about 1:0.9. The presence of the PEGMDE template in the aqueous medium greatly improved the regioselectivity of the polymerization, yielding polyphenol with a phenylene unit content close to 90%. FT-IR, DSC, and XRD analyses confirmed the formation of the miscible complex of polyphenol and PEGMDE by hydrogen-bonding interactions.

Flavonoids↗
PubMed2004

Ring-opening polymerization of L-lactide and preparation of its microsphere in supercritical fluids.

The ring-opening polymerization of L-lactide initiated by stannous octoate was carried out in supercritical chlorodifluoromethane (scR22) at various reaction conditions (time and temperature) and reactant concentrations (initiator, monomer, and solvent). The monomer conversion increased to ca. 70% on increasing the reaction time to 1 h. The molecular weight of the poly(L-lactide) (PLLA) product also increased to ca. 160,000 g x mol(-1) over the same period. Increasing reaction temperature from 90 to 130 degrees C resulted in increased monomer conversion and PLLA molecular weight. A series of polymerizations conducted at various 1-dodecanol and stannous octoate concentrations suggested that stannous octoate does not act as an initiator by itself, and that the tin-alkoxide formed from 1-dodecanol and stannous octoate serves as the initiating species in scR22. While enhancements of the monomer conversion and PLLA molecular weight were observed with increasing monomer concentration, the chlorodifluoromethane concentration had the opposite on both. After the polymerization, PLLA microspheres were prepared in situ by using a continuous supercritical antisolvent process without residual organic solvent and monomer to yield highly purified microspheres for environmental and biomedical applications.

Chromatography, Supercritical Fluid↗
PubMed1998

Effect of replacement of the tightly bound Ca2+ by Ba2+ on actin polymerization.

G-actin has a single tight-binding (high-affinity) site for divalent cations per mole of protein, whose occupancy is important for the stability of the molecule. Different tightly bound divalent cations differently influence the polymerization properties of actin. The tightly bound metal ion easily exchanges for free exogenous cations. Moreover, biochemical and structural evidence demonstrates that actin, in both the G- and F-forms, assumes different conformations depending on the metal ion bound with high affinity in the cleft between two main domains of the molecule. In this work, we used proteolytic susceptibility to detect possible local conformational alterations of the actin molecule following a brief incubation of Ca-G-actin with barium chloride and ethylene glycol-bis(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid. We found that substitution of Ba2+ for the tightly bound Ca2+ affects the regions around Arg-62 and Lys-68 in subdomain 2 of G-actin, as judged from inhibition of tryptic cleavage at these residues. Using the fluorescent chelator Quin-2, we observed that about 0.95 mol of Ba2+ is released per 1 mol of actin. We also examined the effect of replacement of the tightly bound Ca2+ by Ba2+ on actin polymerization. With respect to Ca-actin, Ba-actin shows an increased polymerization rate, mainly due to its enhanced nucleation and a higher critical concentration.

Actins↗
PubMed1995

A fluorescence quench and dequench assay of fibrinogen polymerization, fibrinogenolysis, or fibrinolysis.

We present a kinetic assay based on the use of fluorescein isothiocyanate (FITC)-labeled fibrinogen as a fluoroactive substrate. The multiple FITCs bound to fibrinogen experienced quenching due to their close proximity. The thrombin-induced polymerization of FITC-fibrinogen led to additional fluorescence quenching due to enhanced neighbor-neighbor interactions in protofibrils and protofibril aggregates. The initial rate of quenching was directly dependent on the thrombin concentration at either low or high ionic strength. The final extent of quenching during polymerization with thrombin could be modulated by prevailing ionic strength and thrombin concentration suggesting that the quenching was due to fibril extension as well as aggregation. The full extent of quenching was greatly reduced by addition to the reaction of unlabeled fibrinogen or Gly-Pro-Arg-Pro, as expected for quenching due to neighbor-neighbor interactions. In contrast to polymerization, cleavage of fibrinogen by plasmin released FITC-labeled fragments free of proximity-based quenching that resulted in a large intensity increase as lysis proceeded--a process termed dequenching. The majority of the dequenching signal during fibrinogenolysis occurred during the generation of fragment X which proceeded as a first-order process with respect to fibrinogen-bound plasmin with kcat = 0.479 s-1. The Kd of active plasmin to fibrinogen was calculated to be 0.42 microM. Addition of epsilon-aminocaproic acid (epsilon ACA)-plasmin complex to FITC-fibrinogen produced little dequenching, demonstrating a requirement for binding in order to initiate lysis.(ABSTRACT TRUNCATED AT 250 WORDS)

Fibrinogen↗
PubMed1995

High-performance liquid chromatographic analysis of biological and chemical heme polymerization.

Free hematin can be converted to a stable polymer both chemically, by heating hematin in acid suspensions, or biologically, in the food vacuoles of malaria. A high-performance liquid chromatographic assay has been developed which can separate and quantitate both free hematin and the polymer (beta-hematin), based on the differential solubility of the two compounds. Ion-pair reverse-phase chromatography, utilizing tetramethylammonium chloride and heptane sulfonate as the ion-pair agents in the presence of 40% acetonitrile, was performed on a polymeric-resin-based column with a phenyl bonded phase. Initiating the runs at pH 2.5 led to elution only of the free hematin, and a subsequent shift to pH 12.0 converted the beta-hematin back to hematin which then eluted separately. The method was found to have a linear range of detection from 78 pmol to 20 nmol injected hematin and intra- and interday variations of 9.71 and 12.46%, respectively. The assay was used to study several basic aspects of heme polymerization in vitro, including effects of hematin and beta-hematin concentration on the rate of polymerization.

Animals↗
PubMed1999

Actin polymerization induces shedding of FcgammaRIIIb (CD16) from human neutrophils.

FcgammaRIIIb (CD16) is a glycosyl phosphatidylinositol (GPI)-anchored low-affinity IgG receptor, exclusively expressed on human neutrophils. FcgammaRIIIb associates with complement receptor 3 (CR3, Mac-1, CD11b/CD18), which may indirectly link FcgammaRIIIb to the actin cytoskeleton. Upon neutrophil activation, apoptosis, or chemotaxis, FcgammaRIIIb is shed from the cell surface. In all of these events, actin rearrangements play an important role. To establish a role for the actin cytoskeleton in the control of FcgammaRIIIb shedding, we treated human neutrophils with jasplakinolide, an actin-polymerizing peptide. We show that enhanced actin polymerization induces time- and dose-dependent shedding of FcgammaRIIIb. This effect was not restricted to FcgammaRIIIb, because the cell surface expression of CD43, CD44, and L-selectin was also downregulated after induction of actin polymerization. This actin-dependent pathway is staurosporine sensitive but does not appear to involve activation of PKC or CR3. These data show that the actin cytoskeleton can regulate protein ectodomain shedding from human neutrophils.

Actins↗
PubMed2002

Examination of actin polymerization and viscosity induced by cations and ionic strength when cross-linked by alpha-actinin.

Increasing potassium chloride concentration from 0 to 100 mM and magnesium chloride from 0 to 2 mM show a parallel rate increase in polymerizing actin, whereas increasing calcium chloride concentration from 0 to 0.2 mM decreases the rate of polymerizing actin. The presence of alpha-actinin has little influence on the polymerization kinetics of actin under these conditions. Viscometric measurements indicate that the presence of various mono- and divalent cations, ionic strength, and alpha-actinin in combination are responsible for changes in the mechanical properties of solutions containing actin. The actin filament dynamic behavior is drastically reduced under these conditions as confirmed by quasi-elastic light scattering.

Actinin↗
PubMed1999

The receptor for the globular "heads" of C1q, gC1q-R, binds to fibrinogen/fibrin and impairs its polymerization.

The 33-kDa cellular C1q binding protein, designated gC1q-R was previously shown to bind a number of plasma proteins involved in the coagulation and kinin systems. This study demonstrates the interaction between recombinant gC1q-R and fibrinogen. Using enzyme-linked immunosorbent assays, biotinylated gC1q-R was found to bind to microplate-immobilized fibrinogen in a manner which was specific and inhibited by excess soluble fibrinogen or polyclonal antibodies directed against either gC1q-R or fibrinogen. Moreover, gC1q-R inhibited fibrin polymerization in a dose-dependent manner. Reptilase induced fibrin clot formation was completely inhibited by gC1q-R at a 2:1 molar ratio (gC1q-R:fibrinogen), and repolymerization of thrombin induced fibrin monomers was similarly abrogated. At equivalent molar concentrations, gC1q-R appeared to be a more potent inhibitor of fibrin polymerization than fibrinogen, a well-known inhibitor. Moreover, in the presence of both gC1q-R and soluble fibrinogen, the effect of each inhibitor on fibrin polymerization was additive. When plasmin derived fibrinogen degradation products, including the C-terminal D domain (D-100) or the N-terminal E domain, were immobilized on microtiter plates, gC1q-R bound to fibrinogen fragment D-100, but not to fragment E. Further digestion of fibrinogen fragment D-100 by plasmin to fragment D-60 resulted in loss of gC1q-R binding. Thus, gC1q-R binds to the D domain of fibrinogen/fibrin, and the carboxyterminal segment of at least the fibrinogen/fibrin gamma chain appears important for this interaction. These observations may suggest a potential role for gC1q-R in modulating fibrin formation particularly at local sites of immune injury or inflammation.

Anticoagulants↗
PubMed1996

Fate and biological effects of polymeric MDI (4,4'-diphenylmethane diisocyanate and homologs) in small artificial ponds.

The effects from a simulated accidental pollution event in a pond with polymeric MDI (4,4'-diphenylmethane diisocyanate and homologs) on different trophic levels of the aquatic ecosystem were investigated in small artificial ponds. Three 4.5-m3 volume ponds, interconnected with closable locks, were provided with natural lake sediment and ground water. Caged fish (rainbow trout, Oncorhynchus mykiss) were added to each pond, and the interconnecting locks were kept open to establish nearly identical physicochemical and biological conditions. At this stage, the ponds were isolated from one another and MDI was added at a dosage of 1 g/liter on top of the sediment of treated part of the first pond, 10 g/liter to the second pond, and 0 g/liter to the third pond (untreated control). Neither the applied monomer MDI nor its potential reaction product MDA (4,4'-diphenylmethanediamine) was detected in water or accumulated by fish. The MDI polymerized to inert polyurea on the sediment of the test ponds. This polymerization formed carbon dioxide, released as bubbles which floated to the water surface. Some carbon dioxide was solubilized in water and reduced the water pH of about 9 by 2.0 units as an average in the high-dosed pond and 0.7 in the low-dosed pond. This reduction caused some other minor changes in the physicochemical characteristics of the pond water. Neither application rate caused any direct effect on the pelagic community (phytoplankton, zooplankton, fish, macrophytes) of the test ponds. Some minor indirect effects caused by the production of carbon dioxide were observed in phyto- and zooplankton community structures. Also, an increase of macrophyte growth was noted. Organisms living in the untreated part of the sediment (macrobenthos) were affected as a result of physical obstructions in this habitat. These populations, however, regained densities equivalent to the control after some weeks, except for Bivalvia which have too long of a generation time for the test period of this study.

Allergens↗
PubMed1997

Does actin polymerization status modulate Ca2+ storage in human neutrophils? Release and coalescence of Ca2+ stores by cytochalasins.

The aim of this paper was to establish whether actin polymerization modulated cytosolic Ca2+ storage in human neutrophils. Over the concentration ranges which inhibit actin polymerization, cytochalasins A, B, and D liberated Ca2+ from membrane-bound stores within neutrophils. Two Ca2+ storage sites were identified in neutrophils by the accumulation of the Ca2+ binding probe, chlortetracycline: one at the center of the cell and the other at the cell periphery. Confocal imaging demonstrated that cytochalasins released Ca2+ from the neutrophil periphery, but not from the central Ca2+ store. Ca2+ store release was coupled to Ca2+ influx, suggesting that the peripheral site may be a physiological store containing a Ca2+ influx factor. 3,3'-Dihexyloxacarbocyanine iodide staining organelles, which correlate with Ca2+ release sites, coalesced in neutrophils after treatment with cytochalasins. We propose that peripheral Ca2+ storage sites are restricted from coalescence by cortical polymerized actin and that Ca2+ store coalescence and Ca2+ release are coupled events.

Actins↗
PubMed2001

alpha-, beta-, and gamma-Tubulin polymerization in response to DNA damage.

Microtubules provide structural support for a cell and play key roles in cell motility, mitosis, and meiosis. They are also the targets of several anticancer agents, indicating their importance in maintaining cell viability. We have investigated the possibility that alterations in microtubule structure and tubulin polymerization may be part of the cellular response to DNA damage. In this report, we find that gamma-radiation stimulates the production and polymerization of alpha-, beta-, and gamma- tubulin in hematopoeitic cell lines (Ramos, DP16), leading to visible changes in microtubule structures. We have found that this microtubule reorganization can be prevented by caffeine, a drug that concomitantly inhibits DNA damage-induced cell cycle arrest and apoptosis. Our results support the idea that microtubule polymerization is an important facet of the mammalian response to DNA damage.

Apoptosis↗