Preparation and characterization of magnetically responsive bacterial polyester based nanospheres for cancer therapy

Polyhydroxyalkanoates (PHA) are natural, thermoplastic polyesters and due to their biocompatible and biodegradable properties they are good alternatives for the production of scaffolds for engineered tissues or nanoparticles for drug delivery. As a member of polyhydroxyalkanoate family, polyhydroxybutyrates (PHB) have been widely used as a biomaterial for in vitro and in vivo studies since their mechanical properties are very similar to conventional plastics. By using multi-emulsion technique, iron oxide particles were coated with polyhydroxybutyrate (PHB) polymer synthesized from Alcaligenes eutrophus bacteria and the magnetic carrier system was prepared accordingly. The bare nanoparticles and magnetic nanoparticles were morphologically, structurally and magnetically characterized by using Scanning electron microscope (SEM) and Atomic force microscope (AFM); Fourier Transform Infrared Spectrometry (FTIR), and Electron Spin Resonance (ESR) and Vibrating Sample Magnetometer (VSM) techniques, respectively. Particle size of PHB nanoparticles was determined by Zeta Sizer. It was found that the smallest particles were in the range of 239.43 +/- 5.25 nm in diameter. Concanavalin-A (Con-A) was used for targeting the cancer cells while etoposide was used as drug. Con-A and etoposide were loaded onto the particles. Release studies of etoposide were evaluated and the system was optimized for the further in vivo applications. Finally different formulation magnetic PHB nanoparticles cytotoxicity were evaluated in cell culture studies and used HeLa cell line (cervical cancer cells) as a cancer cells and L929 cells (mouse fibroblast cells) as a non-cancer cell line.

Investigation via ion pore transplantation of the putative relationship between glutamate receptors and K+ channels

The pore domains of ionotropic glutamate receptors (iGluRs) and potassium channels (K(+) channels) show several structural similarities. To test for functional compatibility, we transferred pore regions from prokaryotic, invertebrate, and vertebrate K(+) channels into pharmacologically representative iGluRs and vice versa. Although the chimeric proteins were expressed on the cell surface, only one of 45 pore chimeras showed ion channel function: The kainate receptor subunit GluR6, carrying the pore loop plus adjacent transmembrane domains of the prokaryotic, glutamate-gated, K(+)-selective GluR0, adopted several electrophysiological properties of the donor pore upon pore transplantation. This suggests that, despite structural similarities between iGluR and K(+) channel pores, there is a lack of functional compatibility so that K(+) channel pores cannot be gated by the iGluR gating machinery, and vice versa. However, K(+)-selective pores can be gated in an iGluR sequence environment, given a similar signal transduction mechanism as appears to be present in GluR0.

Fluorescence resonance energy transfer imaging via fluorescence polarization measurement

Fluorescence resonance energy transfer (FRET) has become a widely used spectroscopic tool for detecting molecular interactions and molecular proximity in solution, as well as in membranes. On the other hand, fluorescence polarization (FP) is a convenient measure: ratiometric and simple to execute. This work presents a novel methodology for determining energy transfer efficiency (E) via FP measurement. The methodology is based on the fact that a donor's fluorescence lifetime is shortened due to FRET and, consequently, its FP increases. As a model, the present work evaluates the E between fluorescein and rhodamine conjugated ConA attached to the receptors in the lymphocyte membrane. It shows not only that FRET imaging via FP is possible, but also that it is inexpensive, simple to perform, conveniently adaptable to the commonly used fluorescent microscopy, and readily interpretable.

Helical disposition of proteins and lipopolysaccharide in the outer membrane of Escherichia coli

In bacteria, several physiological processes once thought to be the products of uniformly dispersed reactions are now known to be highly asymmetric, with some exhibiting interesting geometric localizations. In particular, the cell envelope of Escherichia coli displays a form of subcellular differentiation in which peptidoglycan and outer membrane proteins at the cell poles remain stable for generations while material in the lateral walls is diluted by growth and turnover. To determine if material in the side walls was organized in any way, we labeled outer membrane proteins with succinimidyl ester-linked fluorescent dyes and then grew the stained cells in the absence of dye. Labeled proteins were not evenly dispersed in the envelope but instead appeared as helical ribbons that wrapped around the outside of the cell. By staining the O8 surface antigen of E. coli 2443 with a fluorescent derivative of concanavalin A, we observed a similar helical organization for the lipopolysaccharide (LPS) component of the outer membrane. Fluorescence recovery after photobleaching indicated that some of the outer membrane proteins remained freely diffusible in the side walls and could also diffuse into polar domains. On the other hand, the LPS O antigen was virtually immobile. Thus, the outer membrane of E. coli has a defined in vivo organization in which a subfraction of proteins and LPS are embedded in stable domains at the poles and along one or more helical ribbons that span the length of this gram-negative rod.

Difference in Ulex europaeus agglutinin I–binding activity of decay-accelerating factor detected in the stools of patients with colorectal cancer and ulcerative colitis

Expression of decay-accelerating factor (DAF, CD55), a complement-regulatory glycoprotein, is enhanced in colorectal-cancer (CC) cells and colonic epithelium in ulcerative colitis (UC), and stools from these patients contain increased amounts of DAF. Carbohydrate chains of glycoproteins are often altered during malignant transformation or inflammation. In this study, we investigated whether DAF molecules in patients with CC and those with UC differ with respect to oligosaccharide side chains. We analyzed DAF in stools and homogenates of colonic-tissue specimens obtained from patients with CC or UC using solid-phase enzyme-linked assay and Western blotting for reactivity with the lectins Ulex europaeus agglutinin I (UEA-I), wheat-germ agglutinin, peanut agglutinin, and concanavalin A. UEA-I bound to DAF in stools from patients with UC but not in that from the stools of CC patients, as demonstrated on the solid-phase enzyme-linked assay (P <.05, Mann-Whitney U test) and Western blotting. Binding of UEA-I was specifically inhibited by the addition of fucose. The difference in UEA-I reactivity with DAF was observed also in colonic-tissue homogenates from patients with UC and those with CC. DAF expressed in the mucosa and excreted into the stools of UC patients is different from that expressed in CC with regard to UEA-I reactivity. Future studies should be directed toward determining whether a qualitatively unique isoform of DAF is present, of which sugar chains are specific to CC in UC patients.

Impact of operating variables on the expanded bed adsorption of Saccharomyces cerevisiae cells using a concanavalin A derivatized perfluorocarbon

The use of fluidizable affinity adsorbents for the adsorption of cells in expanded mode is investigated. Affinity adsorbents have been synthesized by immobilizing the lectin Concanavalin A onto the surface of triazine-activated perfluorocarbon-solids. The adsorbents were found to adsorb Saccharomyces cerevisiae cells from solution with adsorption capacities of up to 6.8 x 10(9) cells mL(-1). Adsorption kinetics were rapid with a time constant of </=8 min. The adsorbed cells could be eluted using 500 mM methyl alpha,D-mannopyranoside, although the kinetics of release were slowed by the multipoint nature of the interaction. The dynamic capacity of the Con A PVA FEP in expanded mode was up to 4.5 x 10(9) cells mL(-1). The operating parameters of bed height, application flow rate, and adsorbent size distribution were investigated for any potential improvements in throughput, which may improve utility for more fragile cells. A decrease in settled-bed height from 20 to 5 cm resulted in a decrease in dynamic capacity of 27% from 4.5 to 3.3 x 10(9) cells mL(-1). An increase in application flow rate from 0.7 to 2.0 mL/min(-1) (resulting in an expansion increase from two- to fourfold) resulted in a 40% decrease in dynamic capacity from 4.0 to 2.4 x 10(9) cells mL(-1). An increase in the mean size distribution of the perfluorocarbon from 42 to 69 microm and therefore the flow rate needed for twofold expansion of 0.7 to 1.5 mL/min(-1) resulted in a 56% decrease in dynamic capacity from 4.0 to 1.8 x 10(9) cells mL(-1). The expanded bed, using certain combinations of the operating parameters, therefore shows significant potential for the robust, high efficiency and high capacity capture and separation of cells.

Influence of mannan epitopes in glycoproteins–Concanavalin A interaction. Comparison of natural and synthetic glycosylated proteins

Two natural glycoproteins/glycoenzymes, invertase and glucoamylase, and two neoglycoconjugates, synthetized from Saccharomyces cerevisiae mannan, bovine serum albumin and penicillin G acylase were tested for interaction with lectin Concanavalin A (Con A). The interaction of natural and synthetic glycoproteins with Con A was studied using three different experimental methods: (i). quantitative precipitation in solution (ii). sorption to Con A immobilized on bead cellulose; and (iii). kinetic measurement of the interaction by surface plasmon resonance. Prepared neoglycoproteins were further characterized: saccharide content, molecular weight, polydispersion, kinetic and equilibrium association constants with Con A were determined. It can be concluded that the used conjugation method proved to be able to produce neoglycoproteins with similar properties like natural glycoproteins, i.e. enzymatic activity (protein part) and lectin binding activity (mannan part) were preserved and the neoglycoconjugates interact with Con A similarly as natural mannan-type glycoproteins.

Biochemical properties of platelet microparticle membranes formed during exocytosis resemble organelles more than plasma membrane

Studies of [3H]glycerol turnover in phosphatidylcholine (PC) in platelets revealed two metabolic pools, a 'low turnover PC' in collagen-induced microparticles with specific radioactivity only 10% of that found in the 'high turnover PC' of bulk platelet PC. Isolated organelle fractions of [3H]glycerol-labelled platelets contained [3H]PC with specific radioactivities about 20% of that in membrane fractions. These results together with studies on distribution of concanavalin A-FITC and GPlb, a plasma membrane receptor, indicate that microparticles formed during exocytosis are not simple vesiculations of plasma membrane, but they seem rather to originate from a relatively metabolically static membrane pool not accessible to extracellular reagents.

Role of kainate receptor activation and desensitization on the [Ca(2+)](i) changes in cultured rat hippocampal neurons

We investigated the role of kainate (KA) receptor activation and desensitization in inducing the increase in the intracellular free Ca(2+) concentration ([Ca(2+)](i)) in individual cultured rat hippocampal neurons. The rat hippocampal neurons in the cultures were shown to express kainate receptor subunits, KA2 and GluR6/7, either by immunocytochemistry or by immunoblot analysis. The effect of LY303070, an alpha-amino-3-hydroxy-5-methyl-isoxazole-4-propionate (AMPA) receptor antagonist, on the alterations in the [Ca(2+)](i) caused by kainate showed cell-to-cell variability. The [Ca(2+)](i) increase caused by kainate was mostly mediated by the activation of AMPA receptors because LY303070 inhibited the response to kainate in a high percentage of neurons. The response to kainate was potentiated by concanavalin A (Con A), which inhibits kainate receptor desensitization, in 82.1% of the neurons, and this potentiation was not reversed by LY303070 in about 38% of the neurons. Also, upon stimulation of the cells with 4-methylglutamate (MGA), a selective kainate receptor agonist, in the presence of Con A, it was possible to observe [Ca(2+)](i) changes induced by kainate receptor activation, because LY303070 did not inhibit the response in all neurons analyzed. In toxicity studies, cultured rat hippocampal neurons were exposed to the drugs for 30 min, and the cell viability was evaluated at 24 hr using the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay. The selective activation of kainate receptors with MGA, in the presence of Con A, induced a toxic effect, which was not prevented by LY303070, revealing a contribution of a small subpopulation of neurons expressing kainate receptors that independently mediate cytotoxicity. Taken together, these results indicate that cultured hippocampal neurons express not only AMPA receptors, but also kainate receptors, which can modulate the [Ca(2+)](i) and toxicity.

Investigation of luminal surface structures of rod photoreceptor outer segments by lectin cytochemistry combined with freeze-etching

The luminal surface of the rod photoreceptor disk membrane was exposed by means of osmotic shock and labeled with ferritin- conjugated concanavalin A. The structural changes of the luminal surface were examined by a freeze-etching procedure with cryoprotectant (methanol). On replicas from freeze-etched membranes with concanavalin A labeling, 6- to 10-nm particles were codistributed with ferritin particles on the luminal surface of the disk membrane. By contrast, there were few ferritin particles or less numerous 6- to 10-nm particles on the corresponding surface without concanavalin A labeling. If 6- to 10-nm particles corresponded to the carbohydrate moiety of rhodopsin, concanavalin A binding might tend to preserve this carbohydrate moiety. These results suggest that the two-dimensional analysis of lectin-induced structural changes of the membrane surface glycoconjugates may become available by lectin cytochemistry combined with freeze-etching.

Polyethylene glycol-modified concanavalin A as an effective agent to stimulate anti-tumor cytotoxicity

The jack bean lectin, concanavalin A (Con A), was modified with 2,4-bis[O-methoxypoly(ethylene glycol)]-6-chloro-s-triazine, activated PEG2, to form PEG-Con A. The immunoreactivity of PEG-Con A towards anti-Con A antibodies was reduced by increasing the degree of modification of amino groups in the Con A molecule. PEG-Con A had a complete reduction of the immunogenicity in mice and prolonged the clearance-time in blood. Although the mitogenic activity of Con A towards murine spleen cells was reduced by the conjugation with activated PEG2, the administration of PEG-Con A to mice enhanced the anti-tumor cytotoxicity of peripheral lymphocytes against melanoma B16 cells.

Effects of Concanavalin A, fed as a constituent of Jack bean (Canavalia ensiformis L.) seeds, on the humoral immune response and performance of broiler chickens

An experiment was conducted to investigate the effects of the lectin, Concanavalin A (Con A), contained in raw Jack bean (JB) (Canavalia ensiformis, L.) seeds on the immunological response of broilers. A maize-soybean meal basal diet was prepared to which either 2.5, 5, or 10% of ground raw Jack bean (RJB) seeds was added. The RJB seeds contained 24 g Con A/kg on a dry matter basis, as measured by rocket immunoelectrophoresis. Similar diets were prepared by using the same levels of JB after toasting at 190 C for 16 min. In addition, the basal diet was pair-fed to groups of chicks at the level of feed intake of chicks fed the 10% RJB diet. Each diet was fed to six groups of six chicks for 6 wk. At 5 wk, 15 of chicks from each diet were immunized against Brucella abortus (BA) and the anti-BA antibody titers were determined 1 wk later by ELISA. Antibody production against Con A was also measured by the same method. Binding of Con A to intestinal villi and subsequent endocytosis were confirmed by microscopic examination using a specific peroxidase-antiperoxidase-staining technique. Performance was recorded weekly. Feed intake and weight gain were reduced (P < 0.05) only by the diet containing 10% RJB, indicating that broiler chicks can tolerate daily intakes of 100 mg of Con A over 6 wk without affecting growth. Toasted JB diets supported adequate chick performance. The antibody response to BA did not differ with dietary treatment. Serum from chicks fed raw JB also contained antibodies against Con A. The bursa of Fabricius, thymus, spleen, and pancreas dry weights, as a percentage of dry body weight, were not affected by the experimental diets. The data indicated that Con A binds to the cells of the gastrointestinal tract, passes into the general circulation and, eventually, elicits an immunological response without affecting the production of antibodies to BA.

Low temperature reversibly inhibits transport from tubular endosomes to a perinuclear, acidic compartment in African trypanosomes

We have used electron microscopy and flow cytofluorimetry to study endocytosis and intracellular transport of fluid phase bovine serum albumen gold complexes and membrane bound concanavalin A through endosomal compartments of bloodstream forms of Trypanosoma brucei rhodesiense. Both markers were rapidly endocytosed from the flagellar pocket. Within 20 minutes at 37 degrees C the markers reached a large, vesicular, perinuclear compartment that stained heavily with the CB1 monoclonal antibody. Neither marker left the flagellar pocket and entered cells at 4 degrees C. When cells were incubated at 12 degrees C, both markers entered the cell and were transported to collecting tubules, a tubular endosomal compartment that receives endocytosed material from coated endocytic vesicles. However, no material was transported from collecting tubules to the late, perinuclear compartment at 12 degrees C. The morphology of collecting tubule membranes was specifically altered at 12 degrees C; tubules became shorter and were arrayed near the flagellar pocket. The morphological alteration and the block in transport of endocytic markers to the perinuclear compartment seen at 12 degrees C were reversed 10 minutes after cells were returned to 37 degrees C. We also used flow cytofluorimetric measurements of pH dependent fluorescence quenching to measure the pH of the terminal endocytic compartment. Fluoresceinated lectins accumulated in a terminal compartment with a pH of 6.0-6.1, a value considerably higher than that of mammalian lysosomes. Fluorescence from fluoresceinated lectins in this terminal endocytic compartment was dequenched when bloodstream forms were incubated in the presence of chloroquine.

Vascular permeability in a human tumor xenograft: molecular size dependence and cutoff size

Molecular size is one of the key determinants of transvascular transport of therapeutic agents in tumors. However, there are no data in the literature on the molecular size dependence of microvascular permeability in tumors. Therefore, we measured microvascular permeability to various macromolecules in the human colon adenocarcinoma LS174T transplanted in dorsal skin chambers in severe combined immunodeficient mice. These molecules were fluorescently labeled and injected i.v. into mice. The microvascular permeability was calculated from the fluorescence intensity measured by the intravital fluorescence microscopy technique. The value of permeability varied approximately 2-fold in the range of molecular weight from 25,000 to 160,000. These data indicate that tumor vessels are less permselective than normal vessels, presumably due to large pores in the vessel wall. The transport of macromolecules appears to be limited by diffusion through these pores. The cutoff size of the pores was estimated by observations of transvascular transport of sterically stabilized liposomes of 100-600 nm in diameter. We found that tumor vessels in our model were permeable to liposomes of up to 400 nm in diameter, suggesting that the cutoff size of the pores is between 400 and 600 nm in diameter.

Time-resolved delayed luminescence image microscopy using an europium ion chelate complex

Improvements and extended applications of time-resolved delayed luminescence imaging microscopy (TR-DLIM) in cell biology are described. The emission properties of europium ion complexed to a fluorescent chelating group capable of labeling proteins are exploited to provide high contrast images of biotin labeled ligands through detection of the delayed emission. The streptavidin-based macromolecular complex (SBMC) employs streptavidin cross-linked to thyroglobulin multiply labeled with the europium-fluorescent chelate. The fluorescent chelate is efficiently excited with 340-nm light, after which it sensitizes europium ion emission at 612 nm hundreds of microseconds later. The SBMC complex has a high quantum yield orders of magnitude higher than that of eosin, a commonly used delayed luminescent probe, and can be readily seen by the naked eye, even in specimens double-labeled with prompt fluorescent probes. Unlike triplet-state phosphorescent probes, sensitized europium ion emission is insensitive to photobleaching and quenching by molecular oxygen; these properties have been exploited to obtain delayed luminescence images of living cells in aerated medium thus complementing imaging studies using prompt fluorescent probes. Since TR-DLIM has the unique property of rejecting enormous signals that originate from scattered light, autofluorescence, and prompt fluorescence it has been possible to resolve double emission images of living amoeba cells containing an intensely stained lucifer yellow in pinocytosed vesicles and membrane surface-bound SBMC-labeled biotinylated concanavalin A. Images of fixed cells represented in terms of the time decay of the sensitized emission show the lifetime of the europium ion emission is sensitive to the environment in which it is found. Through the coupling of SBMC to streptavidin,a plethora of biotin-based tracer molecules are available for immunocytochemical studies.

Transport of low and high molecular peptides across rabbit Peyer's patches

The permeability of peptides across rabbit jejunal epithelium (JE) and Peyer's patches (PP) was compared. Kyotorphin (L-tyrosyl-L-arginine) was almost completely hydrolyzed during its membrane transport in both PP and JE, but [D-Arg2]Kyotorphin (L-tyrosyl-D-arginine) was less hydrolyzed in PP than in JE. Since the permeability of intact [D-Arg2]Kyotorphin was almost equal in PP and JE, no superiority of PP to JE was found for dipeptide transport. More intact fluorescein isothiocyanate (FITC)-labeled bovine serum albumin (FITC-BSA) and concanavalin A (FITC-Con A) were transported in PP than in JE. At both absorption sites, the transport of the intact FITC-Con A was superior to that of the intact FITC-BSA. Colchicine significantly reduced the total transport of the intact and degradation forms of both peptides and the reduction ratio was greater in PP than in JE. Accordingly, it was suggested that PP can be used as prominent absorption sites for polypeptides since they have lower peptidase activity and higher endocytosis activity than JE.

[Polysaccharides in fungi. XXV. Biological activities of two galactomannans from the insect-body portion of Chán hua (fungus: Cordyceps cicadae)]

Biological activities of two galactomannans (CI-P and CI-A) isolated from the insectbody portion of Chán hua (fungus: Cordyceps cicadae) were studied. CI-P having low affinity for concanavalin A (Con A) exhibited potent carbon-clearance activity in mouse, although both polysaccharides had little antitumor activity against sarcoma 180 in mice. Furthermore, CI-P and CI-A was found to have potent hypoglycemic activity in normal mice, and CI-A having high affinity for Con A showed slightly higher activity than CI-P.

Penetration and uptake of colloidal gold-labeled concanavalin A in the junctional epithelium of the rat

A complex of colloidal gold and concanavalin A (CG-Con A) with various biological properties and high ultrastructural resolution was applied into the sulcus of rat molar gingiva and traced with an electron microscope for three hours to examine the cytological changes occurring in the cells of the junctional epithelium (JE) during penetration of extrinsic irritants, and to determine the roles of JE cells in such a circumstance. While the penetration of CG-Con A was impeded on the surface of keratinized oral gingival/sulcular epithelium, CG-Con A penetrated swiftly through JE into the connective tissue. In the process of penetration, CG-Con A was taken up by lysosomal and vacuolar structures of JE cells in which degenerative changes were often provoked. Degeneration of JE cells was seen selectively in the second and/or third cell layers from the innermost cell layer of JE. It was assumed that JE cells by their phagocytic activity might participate in the first line of defense against extrinsic irritants. On the other hand, the phagocytic activity of JE cells seems also to be involved in tissue destruction, if the amount and/or toxicity of irritants exceed the dissimilating capacity of JE cells.

A differentiation-defective concanavalin-A-resistant variant of a pluripotent embryonal carcinoma cell line

A concanavalin-A(Con A)-resistant variant of the pluripotent mouse embryonal carcinoma cell line, PSA1-NG2, was isolated. This variant, designated NG2-2.16, fails to exhibit the extensive spontaneous differentiation displayed by PSA1-NG2 in colonies in vitro and in tumours in vivo. The molecular nature of the defect in NG2-2.16 cells was not revealed by quantitative studies of the binding, uptake and metabolism of tritiated Con A, or by Western blotting of membrane and whole cell homogenates, thus indicating the defect to be the result of a more subtle molecular alteration. Statistical evidence suggests that the same mutation is responsible for both the Con A resistance and the lack of spontaneous differentiation. NG2-2.16 cells were induced to differentiate by exposure to retinoic acid, suggesting that the mutation affects the regulation of differentiation rather than the potential for differentiation.