Preparation and characterization of lectin-latex conjugates for specific bioadhesion

Nanoparticles for oral delivery: targeted nanoparticles with peptidic ligands for oral protein delivery

As the field of biotechnology has advanced, oral protein delivery has also made significant progress. Oral delivery is the most common method of drug administration with high levels of patient acceptance. Despite the preference of oral delivery, administration of therapeutic proteins has been extremely difficult. Increasing the bioavailability of oral protein drugs to the therapeutically acceptable level is still a challenging goal. Poor membrane permeability, high molecular weight, and enzymatic degradation of protein drugs have remained unsolved issues. Among diverse strategies, nanotechnology has provided a glimpse of hope in oral delivery of protein drugs. Nanoparticles have advantages, such as small size, high surface area, and modification using functional groups for high capacity or selectivity. Nanoparticles with peptidic ligands are especially worthy of notice because they can be used for specific targeting in the gastrointestinal (GI) tract. This article reviews the transport mechanism of the GI tract, barriers to protein absorption, current status and limitations of nanotechnology for oral protein delivery system.

Polymeric particulate technologies for oral drug delivery and targeting: a pathophysiological perspective

The oral route for delivery of pharmaceuticals is the most widely used and accepted. Nanoparticles and microparticles are increasingly being applied within this arena to optimize drug targeting and bioavailability. Frequently the carrier systems used are either constructed from or contain polymeric materials. Examples of these nanocarriers include polymeric nanoparticles, solid lipid nanocarriers, self-nanoemulsifying drug delivery systems and nanocrystals. It is the purpose of this review to describe these cutting edge technologies and specifically focus on the interaction and fate of these polymers within the gastrointestinal system.

Oral drug delivery with polymeric nanoparticles: the gastrointestinal mucus barriers

Oral delivery is the most common method for drug administration. However, poor solubility, stability, and bioavailability of many drugs make achieving therapeutic levels via the gastrointestinal (GI) tract challenging. Drug delivery must overcome numerous hurdles, including the acidic gastric environment and the continuous secretion of mucus that protects the GI tract. Nanoparticle drug carriers that can shield drugs from degradation and deliver them to intended sites within the GI tract may enable more efficient and sustained drug delivery. However, the rapid secretion and shedding of GI tract mucus can significantly limit the effectiveness of nanoparticle drug delivery systems. Many types of nanoparticles are efficiently trapped in and rapidly removed by mucus, making controlled release in the GI tract difficult. This review addresses the protective barrier properties of mucus secretions, how mucus affects the fate of orally administered nanoparticles, and recent developments in nanoparticles engineered to penetrate the mucus barrier.

Preparation and investigation of Ulex europaeus agglutinin I-conjugated liposomes as potential oral vaccine carriers

We prepared and optimized Ulex europaeus agglutinin I (UEAI)-modified Bovine serum albumin (BSA)-encapsulating liposomes (UEAI-LIP) as oral vaccine carriers and examined the feasibility of inducing systemic and mucosal immune responses by oral administration of UEAILIP. The prepared systems were characterized in vitro for their average size, zeta potential, encapsulation efficiency (EE%) and conjugation efficiency (CE%). In vitro release studies indicated that the presence of UEAI around the optimized liposomes was able to prevent a burst release of loaded BSA and provide sustained release of the encapsulated protein. In vivo immune-stimulating results in KM mice showed that BSA given intramuscularly generated systemic response only but both systemic and mucosal immune responses could be induced simultaneously in the groups in which BSA-loaded liposomes (LIP) and UEAI-LIP were administered intragastrically. Furthermore, the modification of UEAI on the surface of liposomes could further enhance the IgA and IgG levels obviously. In conclusion, this study demonstrated the high potential of lectin-modified liposomes containing the antigen as carriers for oral vaccine.

Mucus-penetrating nanoparticles for drug and gene delivery to mucosal tissues

Mucus is a viscoelastic and adhesive gel that protects the lung airways, gastrointestinal (GI) tract, vagina, eye and other mucosal surfaces. Most foreign particulates, including conventional particle-based drug delivery systems, are efficiently trapped in human mucus layers by steric obstruction and/or adhesion. Trapped particles are typically removed from the mucosal tissue within seconds to a few hours depending on anatomical location, thereby strongly limiting the duration of sustained drug delivery locally. A number of debilitating diseases could be treated more effectively and with fewer side effects if drugs and genes could be more efficiently delivered to the underlying mucosal tissues in a controlled manner. This review first describes the tenacious mucus barrier properties that have precluded the efficient penetration of therapeutic particles. It then reviews the design and development of new mucus-penetrating particles that may avoid rapid mucus clearance mechanisms, and thereby provide targeted or sustained drug delivery for localized therapies in mucosal tissues.

Engineering strategies to enhance nanoparticle-mediated oral delivery

Oral delivery is the most preferred route of drug administration due to convenience, patient compliance and cost-effectiveness. Despite these advantages it remains difficult to achieve satisfactory bioavailability levels via oral administration due to the harsh environment of the gastrointestinal (GI) tract, particularly for biomacromolecules. One promising method to increase the bioavailability of macromolecular drugs such as proteins and nucleic acids is to encapsulate them in nanoparticles before oral administration. This review describes innovative strategies for increasing the efficacy of nanoparticle-mediated delivery to the GI tract. Approaches to optimize nanoparticle formulation by exploiting mucoadhesion, environmental responsiveness and external delivery control mechanisms are discussed. The application of recent advances in nanoparticle synthesis using supercritical fluids, microfluidics and imprint lithography to oral delivery are also presented, as well as possible strategies for incorporating nanoparticles into micro- and macroscale oral delivery devices.

Nanoparticles as potential oral delivery systems of proteins and vaccines: a mechanistic approach

Peptides and proteins remain poorly bioavailable upon oral administration. One of the most promising strategies to improve their oral delivery relies on their association with colloidal carriers, e.g. polymeric nanoparticles, stable in gastrointestinal tract, protective for encapsulated substances and able to modulate physicochemical characteristics, drug release and biological behavior. The mechanisms of transport of these nanoparticles across intestinal mucosa are reviewed. In particular, the influence of size and surface properties on their non-specific uptake or their targeted uptake by enterocytes and/or M cells is discussed. Enhancement of their uptake by appropriate cells, i.e. M cells by (i) modeling surface properties to optimize access to and transport by M cells (ii) identifying surface markers specific to human M cell allowing targeting to M cells and nanoparticles transcytosis is illustrated. Encouraging results upon in vivo testing are reported but low bioavailability and lack of control on absorbed dose slow down products development. Vaccines are certainly the most promising applications for orally delivered nanoparticles.

Lectin anchored stabilized biodegradable nanoparticles for oral immunization 1. Development and in vitro evaluation

The investigation comprises development of a stable and targeted formulation of HBsAg for the oral immunization against Hepatitis B. PLGA nanoparticles bearing HBsAg was prepared by double emulsion method. The antigen was protected from organic/aqueous interface by using protein stabilizer, trehalose. The acidic environment generated within PLGA nanoparticles was neutralized by co-encapsulation of a basic additive, Mg(OH)(2) which provides an additional stabilization to the antigen especially against acid induced antigen inactivation. Furthermore, lectin from Arachis hypogaea (PNA) was anchored on to the surface of the HBsAg loaded nanoparticles in order to enhance their affinity towards the antigen presenting cells of the Peyer's patches. The developed system was characterized for shape, size and loading efficiency. The antigen integrity was assessed by using SDS-PAGE followed by isoelectric focusing analysis. Bovine submaxillary mucin (BSM) was used as a biological model for in vitro ligand affinity determination and activity studies. The lectin anchored nanoparticles exhibited 52.18+/-4.73% loading while ligand density was estimated to be of 17.90+/-1.14 microg/mg. The results suggest that HBsAg can be successfully stabilized by co-encapsulation of an appropriate protein stabilizer, i.e. trehalose and a basic additive, Mg(OH)(2). The ligand-coupled nanoparticles demonstrated approximately four folds increase in degree interaction with the BSM as compared to plain nanoparticles. Additionally, the nanoparticles maintained their intrinsic sugar specificity as associated due to lectin (PNA).

Gastroretentive dosage forms: Overview and special case of Helicobacter pylori

The challenge to develop efficient gastroretentive dosage forms began about 20 years ago, following the discovery of Helicobacter pylori by Warren and Marshall. In order to understand the real difficulty of increasing the gastric residence time of a dosage form, we have first summarized the important physiologic parameters, which act upon the gastric residence time. Afterwards, we have reviewed the different drug delivery systems designed until now, i.e. high-density, intragastric floating, expandable, superporous hydrogel, mucoadhesive and magnetic systems. Finally, we have focused on gastroretentive dosage forms especially designed against H. pylori, including specific targeting systems against this bacterium.

Micromachined devices: the impact of controlled geometry from cell-targeting to bioavailability

Advances in microelectomechanical systems (MEMS) have allowed the microfabrication of polymeric substrates and the development of a novel class of controlled delivery devices. These vehicles have specifically tailored three-dimensional physical and chemical features which, together, provide the capacity to target cells, promote unidirectional controlled release, and enhance permeation across the intestinal epithelial barrier. Examining the biological response at the microdevice biointerface may provide insight into the benefits of customized surface chemistry and structure in terms of complex drug delivery vehicle design. Therefore, the aim of this work was to determine the interfacial effects of selective surface chemistry and architecture of tomato lectin (TL)-modified poly(methyl methacrylate) (PMMA) drug delivery microdevices on the Caco-2 cell line, a model of the gastrointestinal tract.

Design, synthesis, physical and chemical characterisation, and biological interactions of lectin-targeted latex nanoparticles bearing Gd–DTPA chelates: an exploration of magnetic resonance molecular imaging (MRMI)

The physical and chemical parameters involved in the design and synthesis of biospecifically targeted nanoparticulate contrast media for magnetic resonance molecular imaging (MRMI) were explored in this pilot investigation. Latex nanoparticles 100, 400 and 900 nm in diameter were doubly derivatised, first with tomato lectin and then with gadolinium(III)-diethylenetriamine pentaacetic acid (Gd-chelates) to target them to epithelial and endothelial glycocalyceal N-glycans and to generate contrast enhancement in magnetic resonance imaging (MRI). After intravenous injection into mice, human placental cotyledons or human Vena saphena magna, contrasty images of the vascular structures were obtained in 1.5 T MRI with spatial resolution 0.1 mm in the imaging plane and 0.6 mm in the z axis, persisting >60 min and resistant to washing out by buffer rinses. Ultrastructural analysis of the nanoparticles revealed the targeting groups at the nanoparticle surfaces and the distribution of the Gd-chelates within the nanoparticles and enabled counts for use in determining relaxivity. The relaxivity values revealed were extremely high, accounting for the strong MR signals observed. Occasionally, nanoparticles larger than 100 nm were seen in close spatial association with disrupted regions of cell membrane or of collagen fibrils in the extracellular matrix. The data suggest that 100-nm nanoparticles generate adequate contrast for MRMI and cause least disruption to endothelial cell surfaces.

Investigation of lectin-modified insulin liposomes as carriers for oral administration

The aim of this study was to design and characterize lectin-modified liposomes containing insulin and to evaluate the potential of these modified colloidal carriers for oral administration of peptide and protein drugs. Wheat germ agglutinin (WGA), tomato lectin (TL), or Ulex europaeus agglutinin 1 (UEA1) were conjugated by coupling their amino groups to carbodiimide-activated carboxylic groups of N-glutaryl-phosphatidylethanolamine (N-glut-PE). Insulin liposomes dispersions were prepared by the reverse-phase evaporation technique and modified with the lectin-N-glut-PE conjugates. Lectin-modified liposomes were characterized according to particles size, zeta potential and entrapment efficiency. The hypoglycemic effect indicated by pharmacological bioavailability of insulin liposomes modified with WGA, TL and UEA1 were 21.40, 16.71 and 8.38% in diabetic mice as comparison with abdominal cavity injection of insulin, respectively. After oral administration of the insulin liposomes modified with WGA, TL and UEA1 to rats, the relative pharmacological bioavailabilities were 8.47, 7.29 and 4.85%, the relative bioavailability were 9.12, 7.89 and 5.37% in comparison with subcutaneous injection of insulin, respectively. In the two cases, no remarkable hypoglycemic effects were observed with the conventional insulin liposomes. These results confirmed that lectin-modified liposomes promote the oral absorption of insulin due to the specific-site combination on GI cell membrane.

Current methods for attaching targeting ligands to liposomes and nanoparticles

Liposomes and nanoparticles have emerged as versatile carrier systems for delivering active molecules in the organism. These colloidal particles have demonstrated enhanced efficacy compared to conventional drugs. However, the design of liposomes and nanoparticles with a prolonged circulation time and ability to deliver active compounds specifically to target sites remains an ongoing research goal. One interesting way to achieve active targeting is to attach ligands, such as monoclonal antibodies or peptides, to the carrier. These surface-bound ligands recognize and bind specifically to target cells. To this end, various techniques have been described, including covalent and noncovalent approaches. Both in vitro and in vivo studies have proved the efficacy of the concept of active targeting. The present review summarizes the most common coupling techniques developed for binding homing moieties to the surface of liposomes and nanoparticles. Various coupling methods, covalent and noncovalent, will be reviewed, with emphasis on the major differences between the coupling reactions, on their advantages and drawbacks, on the coupling efficiency obtained, and on the importance of combining active targeting with long-circulating particles.

Bioadhesive interaction and hypoglycemic effect of insulin-loaded lectin–microparticle conjugates in oral insulin delivery system

Biodegradable microparticles were prepared with alginate by the piezoelectric ejection process, and lectin (wheat germ agglutinin, WGA) was conjugated to alginate microparticles to take advantage of the protective effects of alginate microparticles and the mucoadhesive properties of WGA for improved oral delivery of insulin. Their specific interaction with model mucin was determined by pig mucin (PM) immobilized surface plasmon resonance (SPR) biosensor and in vitro adsorption studies. The hypoglycemic effects of alginate and WGA-conjugated alginate microparticles were examined after oral administration in streptozotocin-induced diabetic rats. The alginate microparticles were fabricated by ejecting alginate/insulin solution into 0.1 M CaCl2 solution through a nozzle actuated by the piezoelectric transducer. The WGA was conjugated to alginate microparticles by activating hydroxyl groups with carbonyldiimidazole (CDI). The affinity constant (K(A)) of alginate-WGA microparticles from the SPR data (K(A)=5.455 g(-1) L) was about nine times greater than alginate microparticles (K(A)=0.628 g(-1) L). In vitro experiments in the mucin solution showed that the conjugated WGA enhanced the interaction about three times. In vivo studies with diabetic rats showed that the blood glucose level of SPF rats was lowest when alginate-WGA microparticles were orally administered. Larger K(A) of alginate-WGA microparticles resulted in larger glucose change (%) from base level. Still, it is not clear whether the transport of insulin through the intestinal mucous membrane was influenced by the increase of residence time at intestinal membrane through the specific adsorption of WGA-conjugated microparticles. However, it is concluded that alginate-WGA microparticles enhance the intestinal absorption of insulin sufficient to drop the glucose level of blood.

Lectin-mediated drug targeting: history and applications

The purpose of this paper is to review the history of using lectins to target and deliver drugs to their site of action. The hour of birth of "lectinology" may be defined as the description of the agglutinating properties of ricin, by Herrmann Stillmark in 1888, however, the modern era of lectinology began almost 100 years later in 1972 with the purification of different plant lectins by Sharon and Lis. The idea to use lectins for drug delivery came in 1988 from Woodley and Naisbett, who proposed the use of tomato lectin (TL) to target the luminal surface of the small intestine. Besides the targeting to specific cells, the lectin-sugar interaction can also been used to trigger vesicular transport into or across epithelial cells. The concept of bioadhesion via lectins may be applied not only for the GI tract but also for other biological barriers like the nasal mucosa, the lung, the buccal cavity, the eye and the blood-brain barrier.

The lectin-cell interaction and its implications to intestinal lectin-mediated drug delivery

Based on the fact that oligosaccharides encode biological information, the biorecognition between lectinised drug delivery systems and glycosylated structures in the intestine can be exploited for improved peroral therapy. Basic research revealed that some lectins can mediate mucoadhesion, cytoadhesion, and cytoinvasion of drugs. Entering the vesicular pathway by receptor mediated endocytosis, part of the conjugated drug is accumulated within the lysosomes. Additionally, part of the drug is supposed to be transported across the epithelium. Moreover, factors probably adversely influencing feasibility of the concept such as toxicity, immunogenicity, and intestinal stability of plant lectins are discussed. As exemplified by lectin-grafted prodrug and carrier systems, this strategy is expected to improve absorption and probably bioavailability of poorly absorbable drugs, peptides and proteins as well as therapeutic DNA.

Synthesis of cytoadhesive poly(methylmethacrylate) for applications in targeted drug delivery

The objective of this work was to incorporate cytoadhesive properties into poly(methylmethacrylate) (PMMA) for potential applications in highly localized tissue-specific drug delivery. First, the PMMA was chemically modified by aminolysis to yield amine-terminated surfaces. X-ray photoelectron microscopy confirmed the presence of surface nitrogen entities, and the distribution of amine groups was found to be relatively uniform, as characterized by atomic force microscopy. The availability of these groups for attachment of biologically active molecules was characterized by fluorescence microscopy after immobilization of avidin-FITC. To render the PMMA cytoadhesive, avidin molecules were conjugated to the amine-terminated surfaces with a hydroxy-succinimide-catalyzed carbodiimide reagent and biotin-labeled lectins (tomato, which binds selectively to Caco-2 cells, and peanut, an unrelated lectin) subsequently were attached utilizing avidin-biotin chemistry. Cytoadhesive activity was evaluated by characterizing the interactions between microfabricated PMMA particles and Caco-2 monolayers. After 15-, 30-, 60-, and 120-min incubation periods, the tomato lectin-conjugated PMMA showed a two to sixfold increase in Caco-2 cell recognition over control particles. Furthermore, the stability of the cytoadhesive PMMA interactions appeared to be three to seven times greater than that of the control surfaces. These findings demonstrate that cytoadhesive properties of modified PMMA, making this novel bioactive polymer very promising for applications in targeted drug delivery.

Surface modification of poly(lactic acid) nanoparticles by covalent attachment of thiol groups by means of three methods

The aim of the present work was to find a suitable method for the introduction of thiol functions on the surface of poly(DL-lactic acid) (PLA) nanoparticles. Three different approaches were investigated. The modification of the surface involves the activation of PLA carboxylic acid groups followed by the attack of a nucleophile such as cysteine (method #1) or cystamine (method #2 and #3) that provide thiol functions via an amide bond. For the conjugation with cystamine, a second reaction step is required to expose the sulfhydryl function of cystamine that is otherwise protected in a disulfide bond. 1,4-Dithio-DL-threitol (DTT) (method #2) or Tris(2-carboxyethyl)-phosphine hydrochloride (method #3) were evaluated for their ability to reduce this linkage. Method #1 allowed a maximum of 8.5+/-2.8 mmol of thiol functions per mol of PLA to be attached on the surface of the nanoparticles. Method #2 allowed the introduction of a greater number of thiol functions (up to 190+/-15 mmol per mol of PLA). However, this latter method has a major drawback: DTT interacts strongly with the nanoparticle matrix during the reduction step. Method #3 has the advantage over method #2 in that it allowed a significant number of thiol functions to be covalently bound to the particles (up to 107.6+/-0.6 mmol per mol of PLA) without the problem of undesired interaction between DTT and the nanoparticle matrix. The introduction of thiol groups onto the surface of PLA nanoparticles is possible with all three suggested methods. The method #3 provides a straight forward approach for the substitution of carboxylic acid groups with a high number of activated sulfhydryl at the surface of PLA nanoparticles.

Gantrez AN as a new polymer for the preparation of ligand-nanoparticle conjugates

The aim of this study was to evaluate the feasibility and in vitro activity of ligand-conjugates based on the use of poly(methyl vinyl ether-co-maleic anhydride) (PVM/MA or Gantrez AN). Fluorescently labelled PVM/MA nanoparticles were prepared by desolvation and cross-linkage with 1,3-diaminopropane (DP). Conjugates were obtained by incubation between the carriers and Sambucus nigra agglutinin (SNA) for 1 h in an aqueous medium. The lectin binding to the surface of nanoparticles was increased by both increasing the bulk ligand concentration and decreasing the amount of cross-linker. However, a concentration of about 0.3-0.4 mg DP per mg polymer was necessary to obtain maximum agglutination activity. Under optimal conditions, the amount of fixed ligand was 46 microg/mg nanoparticle (binding efficiency of 86%); although the activity of SNA conjugates was 13.3 microg/mg particle. The activity of nanoparticles, measured by the association to Caco-2 monolayers, was higher when SNA was covalently bound onto their surface. The lectin-conjugate interaction was 6-fold higher than conventional nanoparticles. Moreover, energy-dependent mechanisms were only observed in SNA-PVM/MA particles. Finally, the decrease in association in the presence of lactose demonstrates that both SNA- and SNA-conjugate-binding was due to a true lectin-sugar interaction.

Developments in the area of bioadhesive drug delivery systems

This paper aims to review the current progress in bioadhesion for drug delivery applications as well as new techniques related to this field. Research started with mucoadhesive polymers that had already been in use as excipients and were rapidly used in new formulations. Their major drawback was found in their unspecific binding, as they adhere to almost any mucosal surface. As some of the polymers showed additional properties such as enzyme inhibition and permeation enhancement, however, they remain interesting as multifunctional excipients. In contrast to mucoadhesion, the concept of specific bioadhesion by use of lectins and other adhesion molecules is now gaining increasing attention as these substances bind directly to receptors on the cell surface rather than to the mucus gel layer. Since specific binding to the cell surface is often followed by uptake and intracellular transport, new chances for drug delivery evolved. Bioadhesion may, thus, enable researchers to deliver macromolecular drugs directly to specific target cells and has implications also relevant to other fields of science, such as tissue engineering, gene delivery and nanotechnology.

Gastrointestinal transit and mucoadhesion of colloidal suspensions of Lycopersicon esculentum L. and Lotus tetragonolobus lectin-PLA microsphere conjugates in rats

PURPOSE

To investigate in vivo the fate and the behavior of lectin-particle conjugates after oral administration.

METHODS

Two plant lectins were selected, namely Lycopersicon esculentum L. and Lotus tetragonolobus lectins, which have been reported to be specific for oligomers of N-acetyl-D-glucosamine and L-fucose, respectively, and conjugated to small poly(lactide) microspheres. Their intestinal transit was investigated in detail using radiolabeled particles. The transport and the distribution of the particles along the intestine, as well as their interactions with the intestinal mucosa, were determined after oral administration in rat.

RESULTS

The overall transit of the particles was shown to be strongly delayed when the microspheres were conjugated to the lectins, mainly due to the gastric retention of the particles. A significant fraction of the conjugates adhered to the gastric and intestinal mucosae. No significant differences were observed after a preliminary incubation of lectin-microsphere conjugates with specific sugars.

CONCLUSION

Although specific interactions could not be excluded, especially in the stomach, it was likely that adhesion was predominantly due to nonspecific interactions. These results could be attributed both to unfavorable physicochemical characteristics of the conjugates and to premature adsorption of soluble mucin glycoproteins, preventing any further specific adhesion.

Covalent coupling of asparagus pea and tomato lectins to poly(lactide) microspheres

Lectin-poly(lactide) microsphere conjugates specifically designed for oral administration were prepared and their activity and specificity in presence of mucus were characterized. The presence of hydroxyl or amino groups suitable for covalent coupling of lectins by the glutaraldehyde method at the surface of the microspheres have been ensured by preparing the particles in presence either of poly(vinyl alcohol) (PVA) or bovine serum albumin (BSA). Tomato and asparagus pea lectins could be covalently attached to these particles (1.0-1.3 mg/m(2) of particles). The conjugates demonstrated a 4-10 fold increase in their interactions with mucus compared to control particles. Moreover, the sugar specificity of the lectins was maintained.

Preparation of surface modified protein nanoparticles by introduction of sulfhydryl groups

The objective of the present study was to establish several methods for the introduction of thiol groups onto the surface of human serum albumin (HSA) nanoparticles. Besides the epsilon-amino groups of lysine, the carboxyl groups of asparaginic and glutaminic acid, and the carbonyl groups of the cross-linker glutaraldehyde, sulfhydryl groups are possible targets for the covalent linkage of drugs to particle surfaces. In principle, the thiol groups were introduced by the reaction with dithiotreitol (DDT) or 2-iminothiolane, by quenching reactive aldehyde residues with cystaminiumdichloride or by coupling L-cysteine and cystaminiumdichloride by the aqueous carbodiimide reaction. The resulting nanoparticulate systems were characterised concerning the number of available sulfhydryl groups, particle size and particle density. It was shown, that by variation of the reaction conditions, e.g., the concentration of the coupling reagent or the sulfhydryl containing component as well as the reaction time, the proposed methods enabled the preparation of HSA nanoparticles with a well defined surface characteristic. Stability studies showed that the introduced thiol groups were relatively stable and lost their reactivity with a half-life of 28.2 days independently of the method used for the sulfhydryl group introduction. Besides the quantification of free sulfhydryl groups the covalent attachment of cystaminiumdichloride by the carbodiimide reaction was used to calculate the amount of free carboxyl groups on the surface of the nanoparticles. The toxicity of the modified nanoparticles was evaluated in cell culture experiments.

Lectin-mediated bioadhesion: preparation, stability and caco-2 binding of wheat germ agglutinin-functionalized Poly(D,L-lactic-co-glycolic acid)-microspheres

To take advantage of the cytoadhesive characteristics of Wheat germ agglutinin (WGA) for improved particulate drug delivery, the interaction between WGA-grafted poly(D,L-lactic-co-glycolic acid)-microspheres and Caco-2 monolayers was investigated using bovine serum albumin (BSA) or glycine coated microspheres as a control. Covalent immobilization of WGA by the carbodiimide/N-hydroxysuccinimide-method on 4 microm microspheres yielded a surface density of 9.67+/-1.21x10(6) molecules/particle, whereas 0.22+/-0.04x10(6) WGA-molecules were bound by physical adsorption. After storage for 21 days in HEPES-buffer and treatment of the particles with 5 M urea, 86% of covalently linked lectin was still attached to the particles. At 4 degrees C the Caco-2 binding rate of both, WGA- and BSA-modified particles increased with addition of increasing numbers of particles until saturation was reached at 38150+/-1740 (WGA) or 12066+/-1195 (BSA) microspheres bound/mm(2) Caco-2 monolayer. Inhibition of Caco-2 binding of WGA-functionalized microspheres by chitotriose indicated for specificity of the interaction. As observed by confocal laser scanning microscopy, the fluorescein-loading of the particles was accumulated intracellularly after incubation of Caco-2 monolayers with WGA-modified microspheres contrary to glycine-grafted microspheres. Additionally, in case of WGA-functionalized microspheres the amount of cell associated fluorescein was 200-fold higher than that of the free solution. In conclusion, WGA-modified microspheres are expected to enhance intestinal transport of incorporated drugs due to cytoadhesion provided by the lectin coating.

Preparation of Ulex europaeus lectin-gliadin nanoparticle conjugates and their interaction with gastrointestinal mucus

One approach to improve the bioavailability and efficiency of drugs consists of the association of a ligand (i.e. lectins), showing affinity for biological structures located on the mucosa surfaces, to nanoparticulate drug delivery systems. In this context, Ulex europaeus lectin-gliadin nanoparticle conjugates (UE-GNP) were prepared with the aim of evaluating their in vitro bioadhesive properties. The lectin was fixed by a covalent procedure to gliadin nanoparticles by a two-stage carbodiimide method. Typically, the amount of bound lectin was calculated to be approximately 15 microg lectin/mg nanoparticle, which represented a coupling efficiency of approximately 16% of the initial lectin concentration. In addition, the activity of these conjugates was tested with bovine submaxillary gland mucin (BSM) and the level of binding to this mucin was always much greater with UE-GNP than with controls (gliadin nanoparticles). However, the presence of 50 micromol fucose, which is the reported specific sugar for U. europaeus lectin, specifically inhibited the activity of these conjugates and, therefore, the UE-GNP binding to BSM was attenuated by 70%. These results clearly showed that the activity and specificity of U. europaeus lectin was preserved after covalent coupling to these biodegradable carriers.

Lectin-mediated drug targeting: quantification of binding and internalization of Wheat germ agglutinin and Solanum tuberosum lectin using Caco-2 and HT-29 cells

For the potential use of Wheat germ agglutinin (WGA) and Solanum tuberosum lectin (STL) as auxiliary excipients for targeting drugs to colonocytes, the number of Caco-2 and HT-29-bound lectins was determined by fluorimetry using fluorescein-labelled derivatives of the N-acetylglucosamine-specific lectins. After 1 h of incubation, the WGA-binding capacity of 5 x 10(4) Caco-2 cells was 26.9 +/- 0.5 pmol at 4 degrees C and 27.2 +/- 1.0 pmol at 37 degrees C respectively. In comparison, 19.5 +/- 2.9 pmol (37 degrees C) and 16.7 +/- 0.9 pmol (4 degrees C) WGA were bound within 1 h to 5 x 10(4) HT-29 cells referring to about 80% of the total amount of WGA bound within 4 h of incubation. In contrast, binding of STL to the colon carcinoma cell lines was independent of incubation times and temperatures tested exhibiting a binding rate of 8.4 +/- 0.6 pmol (HT-29) and 9.9 +/- 0.8 pmol (Caco-2) STL/5 x 10(4) cells. As determined by flow cytometry, non-specific binding is lower than 1.0% (WGA) and 3.4% (STL). Uptake and intracellular accumulation of the lectins were investigated by confocal laser scanning microscopy at 4 degrees C and 37 degrees C respectively. A decrease of initially membrane-bound lectins concurrent with increasing cytoplasmic enrichment by time was observed by digital cell image analysis. Due to specific and numerically sufficient adhesion as well as internalization, WGA and STL are anticipated as targeting tools in lectin-mediated drug delivery systems.

Lectin-mediated bioadhesion: binding characteristics of plant lectins on the enterocyte-like cell lines Caco-2, HT-29 and HCT-8

In order to take advantage of the biorecognition between lectins and specific carbohydrates for targeted drug delivery, fluorescein-labelled lectins of different carbohydrate specificities were screened for binding to human colorectal carcinoma cell lines by flow cytometry and confocal microscopy. The lectin-binding rate increased as follows: Dolichos biflorus agglutinin, DBA<peanut agglutinin, PNA<Lens culinaris agglutinin, LCA<Solanum tuberosum lectin, STL<Ulex europaeus isoagglutinin I, UEA-I<wheat germ agglutinin, WGA (Caco-2); PNA<UEA-I<WGA (HT-29); DBA<UEA-I<WGA (HCT-8), thus reflecting the glycosylation pattern of the cells. Compared to the BSA-binding capacity of the cells, the extent of nonspecific binding was strongly dependent on the type of cell line and lectin under investigation being lower than 2% in the case of WGA, STL and UEA-I/Caco-2 and HT-29 cells. Whereas 50% of DBA was bound nonspecifically to Caco-2 cells, the interactions DBA/HCT-8 and PNA/HT-29 were due to nonspecific binding. By competitive inhibition of lectin-adhesion to the cells upon addition of the complementary carbohydrate, specificity of lectin-binding was confirmed except for the interaction of DBA/HCT-8 and PNA/HT-29. Following on from this work, we consider WGA-, STL- and UEA-I-mediated drug delivery to be a promising approach for peroral bioadhesive formulations adhering to absorptive enterocytes.

Enhanced oral uptake of tomato lectin-conjugated nanoparticles in the rat

PURPOSE

To investigate the usefulness of a surface-conjugated, bioadhesive molecule, tomato lectin, to augment intestinal uptake of orally administered inert nanoparticles.

METHODS

Fluorescent 500 nm polystyrene nanoparticles with tomato lectin covalently surface coupled using a carbodiimide reaction were administered to female Wistar rats by oral gavage daily for 5 days.

RESULTS

Analysis of tissue extracted polymer by gel permeation chromatography revealed a 23% systemic uptake of tomato lectin conjugated nanoparticles compared to < 0.5% of TL nanoparticles blocked with N-acetylchitotetraose thus representing an increase of almost 50 fold across the intestine. Intestinal uptake of tomato lectin-conjugated nanoparticles via the villous tissue was 15 times higher than uptake by the gut-associated lymphoid tissue.

CONCLUSIONS

The application of tomato lectin as a bioadhesive agent in vivo has been demonstrated to enhance subsequent intestinal transcytosis of colloidal particulates to which it is bound.

Bioadhesion of lectin-latex conjugates to rat intestinal mucosa

PURPOSE

The specific interactions between three lectin-latex conjugates and different structures of rat intestinal mucosa have been studied ex vivo.

METHODS

These systems were prepared by covalent coupling of different ligands, i.e., tomato lectin (TL), asparagus pea lectin (AL), mycoplasma gallisepticum lectin (ML), and bovine serum albumin (BSA) as control, to poly(styrene) latexes.

RESULTS

Using mucosa samples without Peyer's patches (PP), the extent of interaction of all three lectin-latex conjugates with the mucosa decreased from duodenum to ileum, probably due to progressive diminution of the mucin concentration along the gastrointestinal tract. The following order of interaction of the conjugates with the mucus gel layer was observed: TL > ML = AL (p < 0.05). For each lectin, these results corresponded well to the concentration of its specific sugar in the mucus. Using intestinal samples with PP, an important increase of interaction of the conjugates with the mucosa was found for ML (about 25%) and AL (about 50%), whereas the interaction of TL decreased about 25%.

CONCLUSIONS

Photomicrographs with fluorescent latexes have confirmed the specificity of the ML- and AL-latex conjugates for the PP region and of the TL-latex conjugates for the mucus gel.