Protein loaded biodegradable microspheres based on PLGA-protein bioconjugates

The application of chitosan as a carrier for fertilizer: A review

The smart combination of agriculture and other sciences can greatly reduce the limits of fertilizer use. Chitosan is a linear amino polysaccharide with a rigid structure which has hydrophilic and crystal properties. The formation of intermolecular hydrogen bonds the presence of reactive groups and cross-linking, the formation of salts with organic and inorganic acids with complexing and chelating properties ionic conductivity, film formation are the characteristics of chitosan. With the presence of amino groups, chitosan can form a complex with other compounds and also enter the vascular system of plants and lead to the activation of metabolic-physiological pathways of plants. This polymeric compound can bond with other natural polymers and in combination with fertilizers and nutritional elements, on the one hand, it can provide the nutritional needs of the plant and on the other hand, it also helps to improve the soil texture. Chitosan nanomaterials as a Next-generation fertilizers act as plant immune system enhancers through slow, controlled, and targeted delivery of nutrients to plants. Chitosan can assist agricultural researchers and has become an ideal and effective option with its many applications in various fields.

Conjugation-Free Multilamellar Protein-Lipid Hybrid Vesicles for Multifaceted Immune Responses

Various lipid-based nanocarriers have been developed for the co-delivery of protein antigens with immunological adjuvants. However, their in vivo potency in vaccine delivery is limited by structural instability, which causes off-target delivery and low cross-presentation efficacies. Recent works employ covalent cross-linking to stabilize the lipid nanostructures, though the immunogenicity and side effects of chemically modified protein antigens and lipids can cause a long-lasting safety issue. Here robust "conjugation-free" multilamellar protein antigen-lipid hybrid nanovesicles (MPLVs) are introduced through the antigen-mediated self-assembly of unilamellar lipid vesicles for the co-delivery of protein antigens and immunologic adjuvants. The nanocarriers coated with monophosphoryl lipid A and hyaluronic acids elicit highly increase antigen-specific immune responses in vitro and in vivo. The MPLVs increase the generation of immunological surface markers and cytokines in mouse-derived bone-marrow dendritic cells compared to soluble antigens with adjuvants. Besides, the vaccination of mice with the MPLVs significantly increase the production of anti-antigen antibody and interferon-gamma via the activation of CD4⁺ and CD8⁺ T cells, respectively. These findings suggest that MPLVs can serve as a promising nanovaccine delivery platform for efficient antigen cross-presentation through the efficient co-delivery of protein antigens with adjuvants.

Nitrilotriacetic acid-end-functionalized polycaprolactone as a template for polymer–protein nanocarriers

Doxorubicin loaded Nickel-complexed nitrilotriacetic acid-end-functionalized polycaprolactone based biocompatible polymer–protein hybrid nanocarriers were developed in a one-pot process.

L-Valine appended PLGA nanoparticles for oral insulin delivery

AIMS

Oral insulin delivery has been the major research issue, since many decades, due to several obvious advantages over other routes. However, this route poses several constraints for the delivery of peptides and proteins which are to be worked upon. The small intestine has been shown to be able to transport the L-forms of amino acids against a concentration gradient and that they compete for the mechanism concerned. So, L-valine was used as a ligand for carrier-mediated transport of insulin-loaded polylactic-co-glycolic acid (PLGA) nanoparticles (NPs).

METHODS

L-Valine-conjugated PLGA nanoparticles were prepared using double emulsion solvent evaporation method. The NPs and conjugated NPs were characterized for their size, drug entrapment efficiency, zeta potential, polydispersity index and in vitro insulin release.

RESULTS

Ex vivo studies on intestine revealed that conjugated nanoparticles showed greater insulin uptake as compared to non-conjugated nanoparticles. In vivo studies were performed on streptozotocin-induced diabetic rabbits. Oral suspension of insulin-loaded PLGA nanoparticles reduced blood glucose level from 265.4 ± 8.5 to 246.6 ± 2.4 mg/dL within 4 h which further decreased to 198.7 ± 7.1 mg/dL value after 8 h. The ligand-conjugated formulation on oral administration produced hypoglycaemic effect (216.9 ± 1.9 mg/dL) within 4 h of administration, and the hypoglycaemic effect prolonged till 12 h of oral administration. Simultaneously, the insulin concentration in withdrawn samples was also assessed and found that profile of insulin level is in compliance with the blood glucose reduction profile.

CONCLUSIONS

Hence, it is concluded that the L-valine-conjugated NPs bearing insulin are the promising carrier for the transportation of insulin across the intestine on oral administration.

Functional nanostructures for effective delivery of small interfering RNA therapeutics

Small interfering RNA (siRNA) has proved to be a powerful tool for target-specific gene silencing via RNA interference (RNAi). Its ability to control targeted gene expression gives new hope to gene therapy as a treatment for cancers and genetic diseases. However, siRNA shows poor pharmacological properties, such as low serum stability, off-targeting, and innate immune responses, which present a significant challenge for clinical applications. In addition, siRNA cannot cross the cell membrane for RNAi activity because of its anionic property and stiff structure. Therefore, the development of a safe, stable, and efficient system for the delivery of siRNA therapeutics into the cytoplasm of targeted cells is crucial. Several nanoparticle platforms for siRNA delivery have been developed to overcome the major hurdles facing the therapeutic uses of siRNA. This review covers a broad spectrum of non-viral siRNA delivery systems developed for enhanced cellular uptake and targeted gene silencing in vitro and in vivo and discusses their characteristics and opportunities for clinical applications of therapeutic siRNA.

Prolonged gene silencing by siRNA/chitosan-g-deoxycholic acid polyplexes loaded within biodegradable polymer nanoparticles

Recently, small interfering RNA (siRNA) has received much attention for therapeutic applications; however, low transfection efficiency and intrinsic instability limit effective gene silencing. Here we show a new approach based on the incorporation of siRNA/polyelectrolyte complexes into biodegradable poly(d,l-lactic-co-glycolic acid) (PLGA) nanoparticles to stabilize siRNA within a hydrophobic solid matrix for prolonged gene silencing. To solubilize siRNA in organic media, chitosan oligosaccharides grafted with deoxycholic acids are synthesized and complexed with siRNA, generating a self-assembled polyelectrolyte complex of 123.9 ± 56.8 nm in diameter. The complex is mixed with PLGA solution and emulsified in water to prepare siRNA-loaded PLGA nanoparticles having a diameter of about 230 nm. The excellent structural stability of the prepared nanoparticles leads to efficient cellular uptake followed by effective gene silencing even in the presence of serum proteins. These results suggest that the encapsulation of siRNA into biodegradable polymer matrix can be an effective means of improving the structural stability of siRNA for prolonged therapeutic efficacy.

Chitosan microspheres in novel drug delivery systems

The main aim in the drug therapy of any disease is to attain the desired therapeutic concentration of the drug in plasma or at the site of action and maintain it for the entire duration of treatment. A drug on being used in conventional dosage forms leads to unavoidable fluctuations in the drug concentration leading to under medication or overmedication and increased frequency of dose administration as well as poor patient compliance. To minimize drug degradation and loss, to prevent harmful side effects and to increase drug bioavailability various drug delivery and drug targeting systems are currently under development. Handling the treatment of severe disease conditions has necessitated the development of innovative ideas to modify drug delivery techniques. Drug targeting means delivery of the drug-loaded system to the site of interest. Drug carrier systems include polymers, micelles, microcapsules, liposomes and lipoproteins to name some. Different polymer carriers exert different effects on drug delivery. Synthetic polymers are usually non-biocompatible, non-biodegradable and expensive. Natural polymers such as chitin and chitosan are devoid of such problems. Chitosan comes from the deacetylation of chitin, a natural biopolymer originating from crustacean shells. Chitosan is a biocompatible, biodegradable, and nontoxic natural polymer with excellent film-forming ability. Being of cationic character, chitosan is able to react with polyanions giving rise to polyelectrolyte complexes. Hence chitosan has become a promising natural polymer for the preparation of microspheres/nanospheres and microcapsules. The techniques employed to microencapsulate with chitosan include ionotropic gelation, spray drying, emulsion phase separation, simple and complex coacervation. This review focuses on the preparation, characterization of chitosan microspheres and their role in novel drug delivery systems.

Targeted lung cancer therapy using ephrinA1-loaded albumin microspheres

OBJECTIVES

EphrinA1, the ligand of EphA2 receptor tyrosine kinase, has been proven to suppress the growth of tumours. The aim of this study was to conjugate ephrinA1 on the surface of albumin microspheres and investigate the non-small cell lung carcinoma growth and migration in vitro.

METHODS

Bovine serum albumin microspheres were designed and synthesized using a natural polymer albumin by emulsification chemical cross-linking. EphrinA1 was then conjugated on the surface of microspheres by imine formation. The microspheres conjugated with ephrinA1 (ephrinA1-MS) were characterized for particle size, surface morphology, loading efficiency and stability in vitro. The ephrinA1-MS were labelled with fluorescein isothiocyanate to determine phagocytosis. In addition, the effects of ephrinA1-MS on A549 cell growth and migration were determined.

KEY FINDINGS

Albumin microspheres exhibited low toxicity for A549 cells (above 90% cell viability). More than 80% of microspheres were phagocytosed within 2 h of incubation. EphrinA1-MS decreased the expression of focal adhesion kinase more effectively than recombinant ephrinA1 alone. Furthermore, ephrinA1-MS showed significant inhibition of non-small cell lung cancer migration when compared with resting cells. EphrinA1-MS attenuated the growth of tumour colonies in matrigels.

CONCLUSIONS

The developed ephrinA1-MS may serve as potential carriers for targeted delivery of the tumour suppressive protein ephrinA1, with minimal cytotoxic effects and greater antitumour therapeutic efficacy against non-small cell lung cancer.

Synthesis and evaluation of novel polyester-ibuprofen conjugates for modified drug release

Ibuprofen was conjugated at different levels to a novel polyester, poly(glycerol-adipate-co-omega-pentadecalactone) (PGA-co-PL), via an ester linkage to form a prodrug. The conjugates were characterized by differential scanning calorimetry (DSC), nuclear magnetic resonance (NMR), infrared (IR), gel permeation chromatography (GPC), ultraviolet (UV), and high-performance liquid chromatography (HPLC). The conjugates had a molecular weight between 18 and 24 kDa, and there was a suppression of the free hydroxyl groups within the conjugated polymer. DSC scans showed a lowering of the melting point (T(m)) when compared with the polyester alone and a difference in the number and area of T(m) peaks. Drug release studies showed an initial burst release (13-18%) followed thereafter by very slow release (maximum 35% after 18 days). Continuous work may produce ester-linked conjugates that are sufficiently labile to allow for complete release of ibuprofen over the time period studied.

Two-stage optimization process for formulation of chitosan microspheres

The objective of the present study was to optimize the concentration of a chitosan solution, stirring speed, and concentration of drugs having different aqueous solubility for the formulation of chitosan microspheres. Chitosan microspheres (unloaded and drug loaded) were prepared by the chemical denaturation method and were subjected to measurement of morphology, mean particle size, particle size distribution, percentage drug entrapment (PDE), drug loading, and drug release (in vitro). Morphology of the microspheres was dependent on the level of independent process parameters. While mean particle size of unloaded microspheres was found to undergo significant change with each increase in concentration of chitosan solution, the stirring rate was found to have a significant effect only at the lower level (ie, 2000 to 3000 rpm). Of importance, spherical unloaded microspheres were also obtained with a chitosan solution of concentration less than 1 mg/mL. Segregated unloaded microspheres with particle size in the range of 7 to 15 microm and mean particle size of 12.68 microm were obtained in the batch prepared by using a chitosan solution of 2 mg/mL concentration and stirring speed of 3000 rpm. The highest drug load ( microg drug/mg microspheres) was 50.63 and 13.84 for microspheres containing 5-fluorouracil and methotrexate, respectively. While the release of 5-fluorouracil followed Higuchi's square-root model, methotrexate released more slowly with a combination of first-order kinetics and Higuchi's square-root model. The formation of chitosan microspheres is helped by the use of differential stirring. While an increase in the concentration of water-soluble drug may help to increase PDE and drug load over a large concentration range, the effect is limited in case of water-insoluble drugs.

Preservation of lysozyme structure and function upon encapsulation and release from poly(lactic-co-glycolic) acid microspheres prepared by the water-in-oil-in-water method

When proteins are encapsulated in bioerodible polymers by water-in-oil-in-water (w/o/w) encapsulation techniques, inactivation and aggregation are serious drawbacks hampering their sustained delivery. Hen egg-white lysozyme was employed to investigate whether stabilizing it towards the major stress factors in the w/o/w encapsulation procedure would allow for the encapsulation and release of structurally unperturbed, non-aggregated, and active protein. When it was encapsulated in poly(lactic-co-glycolic) acid (PLGA) microspheres without stabilizing additives, lysozyme showed substantial loss in activity and aggregation. It has been shown that by co-dissolving various sugars and polyhydric alcohols with lysozyme in the first aqueous buffer, interface-induced lysozyme aggregation and inactivation can be minimized in the first emulsification step [J. Pharm. Pharmacol. 53 (2001) 1217]. Herein, it was found that those excipients, which were efficient in preventing interface-induced structural perturbations, were also efficient in minimizing lyophilization-induced structural perturbations (e.g. lactulose). The efficient excipients identified also reduced structural perturbations upon lysozyme encapsulation in PLGA microspheres and this led to reduced lysozyme inactivation and aggregation. However, the data obtained also show that later steps in the encapsulation procedure are detrimental to lysozyme activity. Lysozyme inactivation was completely prevented only by employing the efficient excipients in the second aqueous phase also. In summary, protein aggregation and inactivation were minimized by rationally selecting excipients efficient in stabilizing lysozyme against the major stress factors of w/o/w encapsulation.

Recent trends in stabilizing protein structure upon encapsulation and release from bioerodible polymers

Sustained release of pharmaceutical proteins from biocompatible polymers offers new opportunities in the treatment and prevention of disease. The manufacturing of such sustained-release dosage forms, and also the release from them, can impose substantial stresses on the chemical integrity and native, three-dimensional structure of proteins. Recently, novel strategies have been developed towards elucidation and amelioration of these stresses. Non-invasive technologies have been implemented to investigate the complex destabilization pathways that can occur. Such insights allow for rational approaches to protect proteins upon encapsulation and release from bioerodible systems. Stabilization of proteins when utilizing the most commonly employed procedure, the water-in-oil-in-water (w/o/w) double emulsion technique, requires approaches that are based mainly on either increasing the thermodynamic stability of the protein or preventing contact of the protein with the destabilizing agent (e.g. the water/oil interface) by use of various additives. However, protein stability is still often problematic when using the w/o/w technique, and thus alternative methods have become increasingly popular. These methods, such as the solid-in-oil-in-oil (s/o/o) and solid-in-oil-in-water (s/o/w) techniques, are based on the suspension of dry protein powders in an anhydrous organic solvent. It has become apparent that protein structure in the organic phase is stabilized because the protein is "rigidified" and therefore unfolding and large protein structural perturbations are kinetically prohibited. This review focuses on strategies leading to the stabilization of protein structure when employing these different encapsulation procedures.

Preparation and characterization of a composite PLGA and poly(acryloyl hydroxyethyl starch) microsphere system for protein delivery

PURPOSE

To prepare and characterize a novel composite microsphere system based on poly(D,L-lactide-co-glycolide) (PLGA) and poly(acryloyl hydroxyethyl starch) (acHES) hydrogel for controlled protein delivery.

METHODS

Model proteins, bovine serum albumin, and horseradish peroxidase were encapsulated in the acHES hydrogel, and then the protein-containing acHES hydrogel particles were fabricated in the PLGA matrix by a solvent extraction or evaporation method. The protein-loaded PLGA-acHES composite microspheres were characterized for protein loading efficiency, particle size, and in vitro protein release. Protein stability was examined by size-exclusion chromatography, sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE), and monitoring the enzymatic activity.

RESULTS

Scanning electron microscopy showed discrete PLGA microspheres containing many acHES particles. The composite microspheres were spherical and smooth in size range of 39-93 microm. The drug loading efficiency ranged from 51 to 101%. The composite microspheres showed more favorable in vitro release than conventional PLGA microspheres. The composite microspheres showed 20% less initial with a gradual sustained release compared to high burst (approximately 60%) followed by a very slow release with the conventional PLGA microspheres. The composite microspheres also stabilized encapsulated proteins from the loss of activity during the microsphere preparation and release. Proteins extracted from the composite microspheres showed good stability without protein degradation products and structural integrity changes in the size-exclusion chromatography and SDS-PAGE analyses. Horseradish peroxidase extracted from microspheres retained more than 81% enzymatic activity.

CONCLUSION

The PLGA-acHES composite microsphere system could be useful for the controlled delivery of protein drugs.

Lysozyme microencapsulation within biodegradable PLGA microspheres: urea effect on protein release and stability

Lysozyme was encapsulated within biodegradable poly(D, L-lactide-co-glycolide) microspheres by a double emulsion solvent evaporation method for studying its release mechanism associated with protein stability problems. When urea, a protein unfolding agent, was added into the incubation medium lysozyme release rate from the microspheres increased with the increase in urea concentration. The enhanced lysozyme release was attributed to the suppression of protein aggregation, to the facilitated diffusion of unfolded lysozyme by an efficient reptile motion of unfolded protein molecules through porous channels in microspheres, and to the largely decreased extent of nonspecific protein adsorption onto the enlarged surface area of degrading polymer microspheres in the presence of urea. Encapsulating lysozyme in an unfolded form within PLGA microspheres was attempted by using urea as an excipient. This new urea-based formulation exhibited a more sustained lysozyme release profile than the control formulation, and released lysozyme from the microspheres showed a much less amount of lysozyme dimer population while maintaining a correct conformation after refolding in the incubation medium. This study provides new insights for the formulation of protein encapsulated PLGA microspheres.